SHRI SHIVAJI EDUCATION SOCITY’S COLLEGE OF ENGINEERING & TECHNOLOGY,

AKOLA.

CertificateThis is to certify that, following students of Final Year B.Tech. Chemical have submitted a Project

entitled.“ Modelling and Simulation of Osmotic

Dehydration of Onion. ” during the academic section 2005 – 2006 in a satisfactory manner in the partial fulfillment of the requirement for the Degree of “ Bachelor of Technology ” in Chemical Engineering Branch,

under affiliation of Sant Gagde Baba University, Amravati.

Submitted By1. Mr. Mohit Ulhaque 2. Mr. Rilesh Mehata

Prof. S. K. Navhale Prof. V. C. Renge( Guide ) ( H.O.D)

Department of chemical technology

2005 – 2006

ACKNOWLEDGEMENTIt is with great pleasure we express our sincere gratitude to all those who rendered us help selflessly carrying out educative project.

We have the privilege of working under Prof. S. K. Navhale ( Guide ) to whom we are indebted for his immenselly valuable guidance, suggestions and encouragement for the project.

We express our sincere gratitude to all Professors, advices and facilities imparted to us by them and also for giving us a good insight into this project.

Mr. Mohit Ul haque Mr. Rilesh Mehata

Final Year B. Tech. ChemicalCollege of Engg. & Tech. Akola.

ABSTRACT

India is largest producess of onion after China with production of 4.06 million tonnes. In the past few years the demand of dehydrated onions has increased tremendously.

In this study we tried to present different aspects of onion drying. A comparison based on various aspects of onion dehydration like size, onion quality was studied satisfactorily. We also tried to study the application of phenomena of Osmotic Dehydration and its effect on the Drying process.

We also studied the kinetics of onion dehydration by using models. The results were simulated successfully and gave satisfactory results. We also assumed an empirical equation for onion which was also tested with good results.

IndexSr. No. Topic Page

No.1. Introduction2. Literature Survey

2.1 Drying Principles2.2 Market Scenerio2.3 Raw Material2.4 Osmotic Dehydration

3. Experimentation3.1 Experimental set-up & Procedure3.2 Analysis3.3 Result & Discussions3.3.1 General Study3.3.2 Comparative Graphs

4. Cost Estimation4.1 Experimental Cost4.2 Scale-up Cost

5. Plant Layout6. Mathematical Modelling & Simulation

6.1 General Principles6.2 Drying Equations6.3 Mathematical Modelling

6.4 Simulation & Testing7. Conclusion8. References9. Appendix

1. INTRODUCTIONOnion (Allium cepa L.) is one of the major bulb crops of the

world and is most important commercial vegetable vis-a-vis spice crops grown in India. A large quantity of onion is used as fresh; however, some of the surplus quantities of onion available in the market are processed by dehydration and are meant for export and armed forces . The pungency in onion is due to volatile oil known as alkyl-propyl-disulphide. Nutritionally, fresh onions contain about 868 g/kg moisture, 116 g/kg carbohydrates, 12 g/kg proteins, 2-5 g/kg calcium, 0.5 g/kg phosphorus and traces of iron, thiamine, riboflavin and ascorbic acid. A distinctive characteristic of onion is due to presence of alliaceous odour which accounts for its use as food, salad, spice, condiment and medicine; because of which it has a paramount effect in preventing heart diseases and other ailments. Despite the fact that the world production of onion is steadily increasing due to improved production technology and expansion of area under cultivation; the postharvest losses due to sprouting, rotting, rooting and physiological loss in weight accounts for 40-60% of annual production in India.

Preservation of food by drying is one of the oldest methods and is used on large scale. The heart of the onion processing operation centers around the dehydration of the produce. "Dehydration" of onion is one of the economical and feasible methods of preservation of surplus produce for use in season of short fall. This method has advantages like greater concentration in dry form to save packaging cost; requires minimal labor, processing equipment and distribution cost. Dehydrated onions are becoming a product of considerable importance in international agricultural trade. Out of the total dehydrated vegetables export from the developing countries,

dehydrated onions have the largest share of 45 per cent6. Dried and processed vegetables constitute total export of processed product between 40-42 per cent both by volume and by value, prominent among them was dehydrated onion flakes and powder.India is the largest producer of onions in the world after China with a total production of 4.06 million tones in 1995-96. It is cultivated widely covering about 16% of the total area and its production is 10% among vegetables. Generally, it is available throughout the year and can be stored under ambient conditions on Improvised racks under a thatched roof with a free flow of air. But heavy losses can occur due to non-availability of sufficient storage, transport and proper processing facilities at the production point. The preservation of vegetables by dehydration offers a unique challenge and it may be considered as an alternate low cost preservation process. Dried & processed vegetables constitute between 40-42% of total exports of processed products both by volume and by value, prominent among them being dehydrated onion flakes and powder. Onions can be dehydrated and conveniently used by the consumer in the dry form. Large quantities of onions are dehydrated for export and use by armed forces.Objective

The objectives of this study are as follows :-1. Maharashtra region is the largest producer of onion in

India. The price of onion grown in these region varies from 50 ps/kg. to 15 Rs/kg. during each year. Thus this study was undertaken so as to store onion in dehydrated forms like flakes or powder during the low cost season utilizing it for exports.

2. To study the effect of pretreatment processes like osmotic dehydration & sulphianition on the manufacture of dehydrated onion.

3. To compare the different processes of onion dehydration and to verify the most economic and effective processes.

4. To propose a mathematical model for onion dehydration and further simulating it, which can be useful for designing and improving the performance of predrying and drying procedures.

2. LITERATURE SURVEY 2.1 Drying Fundamentals

Drying refers to an operation in which moisture of a substance is removed by thermal means (i.e. with the help of thermal energy).

It is an operation in which the solvent (usually water) is evaporated from the wet solid with the help of heat. In majority of drying operations, the heat is provided by hot air or any other gas in which the solvent evaporates.

During drying operation, mass and heat transfer occur simultaneously. Heat is transferred from the bulk of the gas phase (drying media) to the solid phase and mass is transferred from the solid phase to the gas phase in the form of liquid and vapour through various resistances. The material (liquid) that is transferred is the solute and transfer takes place as the gas phase is always unsaturated with respect to the solute material.

In case of drying, relatively small amounts of water or other liquid is removed from a solid or semi-solid material whereas in case of evaporation, relatively large amounts of water are removed from solutions. Drying involves the removal of water at a temperature below the boiling point while evaporation involves the removal of water as a vapour at its boiling point. Drying involves the circulation of hot air or other gas over the material for removal of water while in evaporation use of steam heat is done for removal of water (i.e. for evaporator). To obtain the products almost in dried form is the purpose of drying operation whereas concentration of solution is the main purpose of evaporation. In drying operation, the emphasis is usually on the solid product and in evaporation, the emphasis is on concentrated liquor.

As the removal of moisture by thermal means is more costly than mechanical means (e.g. filtration), the liquid content of solids must be reduced to the minimum possible level by latter means before the material is fed to drying equipments.

Drying is frequently the last operation in the manufacturing process and is usually carried after evaporation, filtration, or crystallisation.

Drying operations are mostly encountered in food, chemical, agricultural, pharmaceutical and textile industries.General Definitions 1. Moisture content on wet basis :It is expressed as the ratio of the weight of moisture to the weight of wet feed material. If X is the kg moisture associated with one kg of dry solids, thenMoisture content on wet basis : = X/(1 + X)Percent moisture on wet basis is the moisture associated with feed material expressed as the percentage of weight of feed material (i.e. wet solids).2. Moisture content on dry basis:It is expressed as the ratio of the weight of moisture to the weight of dry solids present in the wet feed material. If the feed material contains X kg moisture and 1 kg of dry solids, then

Moisture content on dry basis = = X/1 = X

Percentage moisture content on dry basis = 100 X 3. Equilibrium moisture content (X*):The moisture content of substance that is in thermodynamic equilibrium with its vapour (given partial pressure of vapour) in gas phase under specified humidity and temperature of gas is termed as equilibrium moisture content. It represents the

limiting moisture content to which a given material can be dried under constant drying conditions.

4. Bound moisture content:It is that moisture in the substance which exerts a vapour

pressure less than that of the pure liquid at the same temperature.5. Unbound moisture content:

It is the moisture held by a material in excess of equilibrium moisture content corresponding to saturation in the surrounding atmosphere. It is primarily held in the voids of solid.It is the moisture in the substance which exerts an equilibrium vapour pressure equal to that if pure liquid at the given temperature. 6. Free moisture content:

It is the moisture contained by a substance in excess of equilibrium moisture content (X-X*). At a given temperature and humidity, it is the moisture content of material that can be removed by drying.7. Critical moisture content (Xc):

The moisture content of a material at which the constant rate period ends and the falling rate period starts is called as critical moisture content. It is a function of constant drying rate, material properties and particle size. 8. Relative humidity (R.H.):

It is defined as the ratio of the partial pressure of water vapour in an air water-vapour mixture to the vapour pressure of pure water at the temperature of the mixture (at DB).% R.H. = (pA/p°) x 1009. Humidity (H):

It is the ratio of the mass of water vapour to the mass of dry air present in the air-water vapour mixture under any given set of conditions. 10. Dry bulb temperature (DB):

The temperature of vapour-gas mixture recorded by the thermometer whose bulb is kept dry, is called as dry bulb temperature.11. Wet bulb temperature (WB):

The temperature recorded by the thermometer whose bulb is kept wet by wrapping a wet cloth in the open air is called as wet bulb temperature.12. Saturation humidity :

It is the humidity of air when saturated with water vapour and is denoted by symbol — Hs.13. Percentage humidity (Ho):

It is the ratio of the actual absolute humidity of air (H) to the humidity of saturated airPercentage humidity, H0 = pA (P – p0A)/p0A (P - PA)14. Dew point (DP):

When the air-water vapour mixture is cooled at constant pressure, it becomes saturated and further cooling results in condensation of water vapour. The temperature at which the condensation will first occur is known as the dew point. For the saturated air, the dew point, wet bulb and dry bulb temperatures are identical.15. Equilibrium:

The moisture of wet solids exerts definite vapour pressure depending upon the temperature and the nature of solid and the moisture content. Consider that the wet solids containing water which exert the vapour pressure of p° are exposed to continuous supply of fresh gas (usually air) with fixed partial pressure of vapour (pA). If the p° is greater than pA, then the solids will lose moisture (reverse is true for p° < pA) by evaporation till the vapour pressure of moisture of the solids equals the partial pressure of vapour in gas. The solid and the gas are then said to

be in equilibrium with each other and corresponding moisture content is referred to as equilibrium moisture content. The equilibrium data in case of drying operations are given as the relationship between the moisture content of solid (expressed on dry basis) and relative humidity of gas (usually air) in contact with the solid.When the humidity of air is less as compared with the moisture content of solid, then solid will lose moisture by evaporation and dry to equilibrium and if the air is more humid than the solids, then solids will gain moisture until the equilibrium is attained. (fig. 2.1.a)

Fig. 2.1.a Equilibrium Moisture Curve

16. Rate of batch drying and drying test:A knowledge of time required for drying a substance from

one particular level of moisture content (initial) to another level (desired) under specified drying conditions is needed for determining the size of a dryer and also for setting up of drying schedules. In respect of time required to dry a substance using one particular type of dryer one is also interested to estimate the effect of different drying conditions upon the time. For the said purposes in many cases we have to run a drying test of material in question in a model dryer of the type that is desired. Conducting the test and measuring the rates of batch drying is

relatively simple and thus provides information useful for batch as well as continuous drying operation.

In drying test, for determining the rate of drying (needed for further calculations) we have to keep a sample of a wet material uniformly distributed over the tray (of uniform thickness) suspended from a weighing balance in the cabinet. The bottom and edges of the tray should be well insulated. Then we have to blow the air over the surface of the wet material. The air should be blown over the material at constant velocity and should of of constant temperature and humidity. Then, all that we have to do is to measure the weight of a sample as a function of time and also the dry weight of a sample. The test can be performed on samples of different thickness.17. Constant rate period:

It is that part of the drying process during which the rate of drying expressed as the moisture evaporated per unit time per unit area of drying surface, remains constant.

18. Falling rate period :It is that part of the drying process during which the rate of drying varies with time am instantaneous drying rate expressed as the amount of moisture evaporated per unit time, per unit area of drying surface continuously decreases.2.2 Osmotic Dehydration: 2.2.1. Principle and Applications

The osmotic process is a technique for the concentration of solid foods, which consists in placing pieces of fruit or vegetables in a hypertonic solution (sugars, sodium chloride, glycerol etc...), giving rise to at least two major simultaneous counter-current flows (Fig. 1)1) an important water flow out of the food into the solution .2) a simultaneous transfer of solute from the solution into the food . A third phenomenon has been described concerning leakage of natural solutes from the food into the solution (sugars, organic acids, mineral salts...). Though quantitatively neglectable, it may remains essential as far as the organoleptic or nutritional (vitamin, mineral) qualities are concerned.

Therefore, as opposed to mere drying processes, Osmotic Dehydration., achieves a twofold transformation of the food item, by both a decreasing water load, and a solute incorporation, which may result in a subsequent weight reduction.

Provided that further lowering of water activity by moderate air dry ing, or inhibition of microbial growth by heat and / or chemical treatment, is achieved alter the osmotic dipping, the “osmotically” dehydrated product can be stored up to several months or longer, at room temperature, depending upon the packaging material and the storage conditions. Air-drying following osmotic dipping is still commonly used,

especially in tropical countries, for the production of so called "Semi candied" dried fruit.

2.2.2. Advantages of an Osmotic StageAn actual revival of interest for the process has been

triggered off by an awareness of the advantages of Osmosis over traditional drying processes.A) Improved organoleptic qualities, thanks to minimized heat damages to colour and flavour, less volatile component drive, favorable effect of the incorporated solute upon the sugar to acid ratio , and the texture, less discoloration by enzymic oxydative browning thus limiting, in some cases, the use of sulphur dioxide.B) Considerable, potential energy-savings in comparison to conventional processes, though hardly ever evaluated. In fact, mass transport coefficient in liquid phase are generally good. Moreover, water is removed from the product without undergoing a phase change. Therefore, osmotic dehydration may be much quicker than air drying or freeze-drying. Recycling the syrup by reconcentration, which constitutes the second stage of the process, is not limiting, thanks to the present perfected techniques for the concentration of liquids.2.2.3. Technological Limitations

With regard to other drying processes, the osmotic dehydration has not been studied very much, in terms of engineering properties. Current technologies, somewhat empirical, result in detrimental erratic performances of processed items, and often excessive sugar entrance in the product, because of poor control of the main variables, Water Loss (WL) and Sugar Gain(SG).

Yet, WL and SG show different and sometimes opposing reactions to the influence of the process parameters (concentration and composition of the solution, temperature, nature of the product and chemical or physical pre-treatments)

and this intrinsic property of the process makes it theoretically possible to conceive, in particular, combinations which result in substantial water removal with only marginal sugar pickup or, more generally, to obtain different WL/SG ratios, depending on the desired organoleptic qualities of the end-product, and on further treatments to be involved. For instance, increasing the solute concentration will favour both WL, and SG, but a higher sugar concentration has a significant effect on WL, whereas SG shows little variation, which is reflected by an increasing Weight Reduction (WR) with the concentration of the solute. Increasing the specific surface area of the product (size and shape) may be favourable to both WL and SG, especially for short osmosis periods, but an over-reduced surface area will favour SG to the detriment of WL.

The first reason for the poor control of the main variables is that a full understanding of mechanisms involved with simultaneous interacting counter-current flows is still lacking. This is aggraved by the complex structure of natural tissues, and by the specific problem for liquid /solid contacting which is found in the osmotic process.2.2.4. Mass Transfer Considerations

There have been several studies on the diffusion of solutes in food items and gels.

But most of the diffusional mass transfer studies concern binary processes ( interpretation of Fick's law) or assume an independance of the movement of each species in multicomponent systems. The only literature lo date in food systems where interaction between components has been taken into account.

In osmotic dehydration, most available models are based on Fick's law of diffusion with simplifying assumtions and use the particular solution for unsteady one-dimensional transfers for instance between a plane sheet and a well-stirred solution, either with a constant surface concentration or with a limited volume of solution. The resulting apparent diffusivities are generally correlated with the concentration and temperature of the solution.The limits of such models are the following:A) In all cases, simultaneous mass transfer are reduced to a single transfer of water, or solute. So, the resulting diffusivities are in fact a combination of the respective water and solute diffusivities, and hence, cannot be used to predict the contribution of each transfer in the process.B) As a corollary, the probable interaction between the counter -current flows, which is strongly suggested by the opposing response of Water Loss and Sugar Gain rates to some of the process parameters, cannot be taken into account.C) No proof is given that resulting diffusivities do represent the internal transfers (transfers inside the particle) and not the internal and external phenomena together. And yet, external conditions prove to be a key- factor for the transfer rates. This suggests a frequent control of the process by external phenomena, related to specific circumstances involved in the osmotic process.D) Lastly, the possible specific action of natural cell membranes cannot be taken into account. The mass transfer phenomena that occuring plant tissue upon osmosis are likely to involve complex mechanisms, most ol them controlled by the plant cells. This greatly impairs the use of such models. This essential

influence of tissue structure will be discussed further on. (Fig. 2.2.a )

Fig. 2.2.a Schematic drawing of mass transfer in soaking processes

2.3 Market Survey

Onion is one of the most important horticultural products of India is World’s second largest exporters of onion with the market share of 13.6 percent in 1992-93. Since 1980 India’s onion export have been mainly confined to the neighboring South East Asian countries and a few Middle East Nations. The UAE, Bangladesh, Malaysia and Srilanka are the major importers of Indian Onion.

There is a considerable scope for increasing the exports of dehydrated onions from India, the demand for which is growing at the rate of 7% per annum in E.C.markets India should take advantage of this by strengthening its processing facilities.

The Gujarat Government has been permitted to export 50,000 tones of onions by the Union Government. The terms and conditions were similar to the case of Maharashtra Government for the export of 75,000 tonnes.

India happen to be the second largest produce of onions in the world amounting up to 4.08 million tones during the year 1995-96 .

Onion is one of the India’s major export commodity

The prices of onion ranged between Rs.135/- 100 Kg and Rs.1502/- 100 Kg during 1994-95. India exported fresh onions of 4.27 lakh tonnes worth Rs.265.21 crores during 1996-97 and 0.09 lakh tonne worth Rs.19.18 crores of preserved onions and 0.04 lakh tonnes worth Rs.17.82 crores of dehydrated onions flakes / power as onion.

Onion occupies approximately 7.41 percent area out of a total area of 5.33 million hectares of land under vegetable cultivation. Major states producing of onion are Haryana,

Maharastra, Karnataka, Punjab, Gujarat, Tamilnadu, Rajasthan, Madhya Pradesh, Uttar Pradesh, Andhra Pradesh, Bihar.

2.3.1. International Scenario On Dehydrated Products

The international scenario has been studied on the basis of the exhaustive data obtained through secondary research. The analysis of the international trade has been derived from the import and export data of the entire E.U. comprising of 15 member countries, U.S.A and Japan as these three regions constitute most of the global trade in dried fruit and vegetable products. While E.U and U.S.A have significant intra as well as extra import/export trade in these products, Japan is basically a net importer.

Amongst all these products the dehydrated green peas is the largest traded commodity of which India itself is a net importer to the extent of about 1.05 lac tonnes. India stands at a total disadvantage in terms of the quality of the green peas, the cost of the raw material and that of the energy requirements for dehydration due to which it is not able to compete. As regards the exports from India the dehydrated Onion flakes and powder has been the only product worth a mention. The total import of selected dehydrated fruits in three foremost regions as mentioned above has been about 562,000 MT valued at US$ 738 million in 1999 which in last three years has reduced to 268,000 MT valued at US$ 372 million in the year 2001. The India's share has been about 0.25% on the average. As regards the dehydrated vegetables, the import in these regions has been 2,289,000 MT valued at US$ 836 million in 1999 which has reduced to 87,200 MT valued at US$ 449 million in the year 2001 and the Indian share has been 0.68% on the average.

The E.U. has a negative trade balance in DHD/VFD fruit and vegetable products to the extent of 535,761 MT (year 2001) as the total import has been about 929,162 tonnes against the total export of about 393,401 tonnes. The major exporting countries to E.U have been Canada, Turkey, U.S.A and China. The largest importing commodity in DHD products has been green peas (73%) followed by grapes (10.61%), mixed and other vegetables (7.21%) and prunes (2.59%). The import of tropical fruit and vegetables has been very insignificant. The maximum export from E.U has been that of dehydrated peas (77.93%) followed by mixed and other vegetables (9.26%) and grapes (7.25%). Thus E.U has been mostly a net importer of fruits and vegetables in the world.

The opportunities of Indian products in E.U market lie mainly with Onion, Mushroom, some tropical vegetables and fruits etc. because of the enormous availability of the quality raw materials. It is interesting to note that dry tropical fruits have started attracting a good consumer market in E.U though until now dried banana has been the only popular product. Dried tropical fruit such as mango, papaya, banana and pineapple are now becoming more common items in health food stores and super markets where they are sold pre-packed in attractive polybags and cartons. The major customers of dried tropical fruits are the companies who cater to breakfast cereal industry, health foods and confectionery industry. The major departmental stores dealing in dried tropical fruit products in E.U include J. Sainsbury, Holland & Barrett and Marks & Spencer but none of these stores have been sourcing these products from India. The estimated import market size of dehydrated tropical fruits in Europe is estimated at about 11,500 MT of

which about 4,700 MT would be the demand for banana. U.K amongst the E.U members would be the largest buyer.

The market for dried tropical fruits in U.S.A is estimated at about 5,000 MT of which about 3,500 MT would be of banana chips. This is the major opportunity for Indian producers as the quality of Indian tropical fruits is any time better except for pineapple, the superior quality of which comes from Thailand and Philippines. Amongst the vegetables dried tomato and carrots are items of interest in E.U but it is almost impossible to compete against East European countries supplying to E.U. For DHD vegetables the largest consumption comes from the soup industry but the requirements of product quality are too high.

As regards the freeze dried products, the process is applicable only to high valued items such as mushrooms, herbs and ready-to-use delicacies in the form of pre-prepared meals. The products exported from India at present are freeze dried mushroom, herbs and to some extent onion flakes. .

As regards Japan, it is the net importer of most of the dehydrated products. The average import of dehydrated products in Japan is of the order of 62,000 MT valued at US$ 133 million in 1998 which is estimated to have gone up to 68,000 tonnes valued at US$ 145 million in the year 2001. The maximum commodity of import is dried grapes followed by vegetables, onion, radish and sweet corn. In the export to Japan India as such has no contribution except for small quantities of banana.

As regards the trade of DHD/VFD products of U.S.A, the country is the largest exporter of prunes, shelled peas, raisins and some dried fruits. U.S.A has a trade surplus of 413,000 MT in these products against the total export of 556,236 MT (based

on the figure of the year 2001). The major products of import have been onion (38%), mixed vegetables (12%), grapes (9%) and other dried fruits including tropicals (6.4%). The Indian share in the import of dried products in U.S.A is rather insignificant. India has the potential to meet the increasing demand for tropical fruit products and with assured determination it can even succeed in exporting to U.S.A the traditional DHD products like garlic and mushrooms etc.

The import of dehydrated products in U.S.A has been almost static between US$ 186 million and about US$ 225 million in last four years but the exports from U.S.A almost nose-dived in these four years from US$ 1078 million in 1998 to US$ 419 million in 2001. The major reasons could be:

i. Surplus stocks of the previous year's imports

ii. The fall in demand for these products in other countries vis-a-vis their indigenous production.

iii. The restructuring of the overall future business plans of E.U and

iv. The vagaries of weather which affected the production and supply from U.S.A.

Nevertheless this is not going to affect the potential of Indian exports to U.S.A particularly for the products in which India has the advantage. India has certainly the potential to achieve a breakthrough in the export of dehydrated products to E.U, Japan and U.S.A if the following aspects are carefully considered:

i. The products have to be innovative based on the exclusive and exotic fruit and vegetable products grown in the country.

ii. The quality of the products and their packaging has to conform to the Codex standards laid under WTO agreement.

iii. The growing, handling and processing of raw materials have to follow GMP with the incorporation of HACCP systems.

iv. The commitments on the delivery schedule have to be adhered to without pretext.

v. The market promotion has to be professional in all respects.

vi. The Indian producers/exporters would be required to participate in the international thematic fairs for food ingredients where the products can be displayed for the interested global buyers.

2.3.2. Status of Dehydration in India

The dehydration of vegetables was started in India on industrial scale in early sixties when Hindustan Levers Ltd. set up a plant at Ghaziabad in U.P. The dehydrated green peas produced in this unit was sold under the brand name 'HIMA'. The project however was not a success, mainly because the Indian consumers who are oriented to traditional use of fresh vegetables did not accept the product. The company had fixed a sale target of 1500 tpa but could never realise a total sale of more than 300 tpa. In the meanwhile India imported about seven mechanical dryers from Bulgaria under a bilateral agreement which were set up at various places in the country but all these units faced lot of problems on account of:

i. Technology obsolescence leading to inefficient operation of the dryers

ii. Locational disadvantage of some units which led to the difficulties in procurement of raw materials as well as the sale of products and

iii. The changing scenario of the food processing industry in India and

iv. Lack of consumer preference for dehydrated products.

However a lot many units were set up in the state of Gujarat for dehydration of onion and garlic as the primary product for export. Most of these units have been operating somewhat successfully but on low returns due to the fact that their cost of production is much higher than in the developed countries where the process operations are less energy intensive and the raw materials are far superior.

The Indian industry for dehydration of fruits and vegetables can therefore survive in the present scenario only on the strength of product quality and cost competitiveness, which can be possibly achieved in the following ways:

i. Growing raw materials through contract farming.

ii. Introducing technology upgradation in the manufacturing process.

iii Keeping close interaction with the market demand and producing products in concurrence with the market requirements.

iv. Promoting the products in a professional manner etc.

v. Imparting training to the personnel responsible for raw material procurement, plant operation and quality control.

The existing status of the industry is far from being satisfactory as most of the units in small and medium scale have already closed down as they could not sustain under the pressure of poor availability and high cost of the quality raw materials, high cost of production and higher rates of interest on long and short term loans. The other negative factor that put odds against the Indian industry has been their failure to meet the commitments on delivery schedules, the pretext for what is

usually not the concern of the buyer. Some successful units like Unique Dehydrates Ltd., Chhatariya Dehydrate Exports Ltd., Murtuza Foods Ltd., all from Gujarat attribute their success to mainly technical innovations that they have introduced in their plants to reduce the energy costs and their strong marketing efforts backed by the quality aspects of the products. The units successfully catering to the domestic market which is predominantly dependent on army supplies are:

i. Oceanic Foods Pvt. Ltd., Gujarat.

ii. Pan Foods Ltd., Haryana

iii. Markfed Canneries Ltd., Punjab

Their success in the domestic market can be attributed to their sound financial resources to manage the flow of working capital requirements even while the stock inventories pile up sometimes due to the lack of market demand. The comparative statement of the product sale of 13 units producing dehydrated food products both in domestic as well as in export market is projected in table 4.1 from which it can be construed that lower cost of production and better quality are the two basic aspects responsible for the market success.

The existing institutional demand for dehydrated products in India is of the order of about 2800 TPA while the sale of these products in the year 2001 was about 2358 MT. Thus another 450 MT can be conveniently absorbed by the Indian market.

The export of dehydrated vegetables from India is dominated by just five main products which are onion flakes and powder, tamarind powder, dehydrated vegetables, garlic powder/flakes and some small quantity of fruits. The main product of export is dehydrated onion flakes/powder which has

been of the order of about 7224 MT valued at Rs.32.95 crores approximately in the year 2000-01. It has slightly came down from the previous year because of the mounting competition from other countries. Germany was the largest importer of dehydrated onion followed by Netherlands. The dehydrated vegetables from India in the same year was just 848 MT valued at Rs.6.16 crores. Export of dried tamarind powder matched almost the volume of onions exported in the year 2000-01, to UAE, Saudi Arabia and Egypt etc. Likewise 598 MT of DHD garlic powder and flakes were exported in the same year valued at Rs.2.62 crores. The export volume of dehydrated tropical fruits from India continue to be dismal low which should be a matter of serious concern.

Most of the DHD banana chips and slices exported to Europe and U.S.A originate from Philippines, though India is the largest producer of the fruit. Similarly other tropical fruits like mango, papaya, guava etc. are sourced mainly from Thailand. This is an opportunity that India has not been able to encash. The estimated export demand forecast for dehydrated fruit and vegetable from India by the year 2007 is estimated at 19500 MT and the domestic demand at 3375 MT respectively.

As regards, the VFD industry in India, only two companies are in commercial production which include Flex Foods Ltd., Dehradun and Saraf Foods Ltd., Vadodara. The former is a 100% EOU and exporting mainly the freeze dried mushroom and culinary herbs. Their export of last couple of years is averaging around Rs.14 crores p.a. and the company is a regular winner of APEDA export performance awards. They have already incorporated the expansion of the plant capacity which was partly financed by a soft loan from NHB and a grant from APEDA.

Saraf Foods Ltd. have recently changed the product mix and are now producing ready-to-use pre-prepared Indian food recipes in VFD form. They are now reported to be doing well. The present export of VFD products from India are of the order of 150 MT which by 2007 is expected to touch 176 MT. The estimated domestic demand shall be around 6.5 MT.

The Indian dehydration and freeze drying industry have to go a long way in their development and transformation into one of the world standards.

The international scenario with respect to the trade in major products and the selected countries involved in import/export of these products has been studied in depth and detail. Based on the findings of the survey the action plan that needs to be undertaken to develop this industry has been accordingly chalked-out and described in the report. The summary of the report follows as under:

2.3.3. Raw material Availability

The dehydrated products which are presently of importance to India on the, basis of their acceptability in the dehydrated form in the world markets are onion and garlic, even though mushroom, dehydrated vegetable and tamarind powder also figure amongst the major products being exported. The raw material availability for the products proposed for processing into dehydrated products and for export are briefly described as under:

i. Onion

India with a production of 4.9 million tonnes of onion is the second largest producer of onion in the world after China, contributing almost 10% of the world production. The major

onion producing states are Maharashtra, Karnataka, Andhra Pradesh and Gujarat etc. The export variety of onion is mostly white in colour though the rose onion from Karnataka has started getting quite popular in the world markets.

India has the most suitable climate for production of onion and can be the world leader in its global trade. The peak availability lasts for about three months It's storage properties are quite good which can ensure a regular availability for a period of 9 months.

It is of interest to note that the raw onion variety in India particularly for the purpose of dehydration is normally not suitable because of it's relatively lower dry matter content. The problem therefore needs to be referred to the pioneer R&D institutions like IARI etc. with a time bound research programme to develop the variety of onion with higher solid content and other desired characterstics.

ii. Potato

India is the fourth largest producer of potato in the world with a production of 25.0 million tonnes contributing 8% of the total world production. U.P with 42% followed by West Bengal with 30% are the two leading potato producing states. A number of varieties of potato with high solid and low sugar content have been successfully developed. These can compete even with the world famous qualities that are specially grown for dehydrated products. The predominant variety of this kind is Kufri Chipsona I & II.

iii. Tomato

India produces 7.4 million tonnes of tomato which is equivalent to 8% of the total world production. The processing

varieties with low water content and with extended period of maturity are now available to ensure the raw material availablility for processing for most of the time around the year.

iv. Cabbage

With a production of 5.9 million tonnes India is the largest producer of cabbage in the world contributing almost 12% of the total world production. The quality of Indian cabbage is very good.

v. Cauliflower

The production of cauliflower in India is about 4.7 million tonnes which is equivalent to 34% of the total world production. The best qualities are available between the months of September to January.

vi. Okra

With a production of 3.4 million tonnes, India is the largest producer of okra in the world market. Though okra is a typical tropical vegetable, it's demand with the asian ethnic population abroad is on the rise. The peak season of its availability is April to September.

vii. Brinjal (Egg Plant/Aubergine)

India produces 8.1 million tonnes of brinjals which is 38% of the world production. In fact it is produced in different varieties such as spherical, cylindrical and so on.

viii. Garlic

Most of the garlic in India is produced in drought-prone areas due to which it's availability fluctuates from season to season. When the crop is hit by the drought the prices go up

almost about 7 times. Otherwise the availability of garlic in the country remains somewhat stable.

The size of the raw garlic available in India is much smaller than the variety grown in China. Besides the dry matter content of Indian garlic is much lower, which calls for addressing the problem to the Indian R&D Institutions like IARI for developing the variety similar to the one available in China so that Indian producers of dehydrated garlic are able to reduce the production cost and compete in the international market.

2.4.General Process of Dehydration

2.4.1.Predrying TreatmentsPredrying treatments prepare the raw fruits and

vegetables for the dehydration process, and include raw product preparation and color preservation. Most fruits and vegetables follow similar raw product preparation steps, although the peeling and the blanching steps may be specific to the type of fruit or vegetable that is being prepared. The color preservation method differs for fruits and vegetables, with most fruits using sulfur dioxide (SO2 ) gas and most vegetables using sulfite solutions.2.4.1.1.Raw Product Preparation.

Raw product preparation prepares the raw fruit or vegetable for the color preservation step. Preparation includes selection and sorting, washing, peeling (some fruits and vegetables), cutting into appropriate forms, and blanching for some fruits and vegetables. The initial step involved in the common predrying treatments for fruits and vegetables is selection and sorting for size, maturity, and soundness. The raw product is then washed to remove dust, dirt, insect matter, mold spores, plant parts, and other material that might contaminate

or affect the color, aroma, or flavor of the fruit or vegetable. Peeling or removal of any undesirable parts follows washing. Methods used for peeling fruits and vegetables for dehydrating include hand peeling (not generally used due to high labor cost), lye solution, dry caustic and mild abrasion, steam pressure, high pressure washers, or flame peelers. For fruits that are commonly dehydrated, only apples, pears, bananas, and pineapples are usually peeled prior to dehydration. Vegetables normally peeled include beets, carrots, parsnips, potatoes, onions, and garlic.

Except for potatoes, onions, and garlic, the specific method of peeling is not identified for individual fruits and vegetables. Potatoes are commonly peeled using dry caustic and mild abrasion. Onions and garlic are peeled by either high-pressure washers or flame peelers. Prunes and grapes are dipped in an alkali solution to remove the waxy surface coating which enhances the drying process. Next, the product is cut into the appropriate shape or form (i.e., halves, wedges, slices, cubes, nuggets, etc.), although some items, such as cherries and corn, may by-pass this operation. Some fruits and vegetables are blanched, which inactivates the enzymes by heating. Fruits and vegetables are blanched by immersion in hot water (95E to 100EC [203E to 212EF] for a few minutes or exposure to steam.2.4.1.2 Color Preservation.

The final step in the predehydration treatment is color preservation,also known as sulfuring. The majority of fruits are treated with SO2 for its antioxidant and preservative effects. The presence of SO2 is very effective in retarding the browning of fruits, which occurs when the enzymes are not inactivated by the sufficiently high heat normally used in drying. Sun-dried fruits (e.g.,

apricots, peaches, raisins, and pears) are usually exposed to the fumes of burning elemental sulfur before being put out in the sun to dry. In addition to preventing browning, SO2 treatment reduces the destruction of carotene and ascorbic acid, which are the important nutrients for fruits. Sulfuring dried fruits must be closely controlled so that enough sulfur is present to maintain the physical and nutritional properties of the product throughout its expected shelf life, but not be so large that it adversely affects flavor. Some fruits, such as apples, are treated with solutions of sulfite (sodium sulfite and sodium bisulfite in approximately equal proportions) before dehydration. Sulfite solutions are less suitable for fruits than burning sulfur (SO2 gas), however, because the solution penetrates the fruit poorly and can leach natural sugar, flavor, and other components from the fruit.

Although dried fruits commonly use SO2 gas to prevent browning, this treatment is not practical for vegetables. Instead, most vegetables (potatoes, cabbage, and carrots) are treated with sulfite solutions to retard enzymatic browning. In addition to color preservation, the presence of a small amount of sulfite in blanched, cut vegetables improves storage stability and makes it possible to increase the drying temperature during dehydration, thus decreasing drying time and increasing the drier capacity without exceeding the tolerance for heat damage.

2-4 Sulfur (as SO2 or sulfite) is the most widely used compound to prevent browning of fruits and vegetables, but it can cause equipment corrosion, induce off-flavors, destroy some important nutrients, such as vitamin B1 , and is not approved in some countries. Therefore, several alternative methods of color preservation have been investigated. These include lowering pH by using citric or other organic acids, rapid dehydration to very

low water contents, use of other antioxidants (e.g., ascorbic acid, tocopherols, cysteine, and glutathione), heat inactivation or individual quick blanching, reduction of the water activity (osmotic treatment), and the centrifugal fluidized bed (CFB) process.

The most commonly used sulfur-alternative treatments for fruits are osmotic treatment and the CFB process. In osmotic treatment, fruit pieces, slices, and chunks are exposed to concentrated sugar syrup (dry syrup) or to salt to remove the water from the fruit by osmosis. The partially dehydrated fruit piece is then further dried using conventional dehydration techniques (most commonly in a vacuum shelf drier). Fruits that have successfully used the osmotic treatment are apples, peaches, bananas, mangos, and plantains. Advantages of osmotic treatment are reduced exposure time to high temperature, minimized heat damage to color and flavor, reduced loss of fresh fruit flavor, and removal of some fruit acid by the osmosis process. However, the removal of fruit acid and addition of sugar may be disadvantages in certain products. In the CFB process, blanching and an approximate 50 percent reduction in water can be achieved in less than 6 minutes. This treatment can then be followed by any conventional dehydration process. This process eliminates the disadvantages associated with the addition of sugar or salt to the product during osmotic treatment and been successfully use in diced apples. Advantages of the CFB treatment include simplicity of design and an intimate gas-to-particle conduction that provides uniformparticle exposure without mechanical agitation. However, the CFB process is limited to small (one-half inch or smaller) cubes.2.4.2.Drying or Dehydration

Drying or dehydration is the removal of the majority of water contained in the fruit or vegetable and is the primary stage in the production of dehydrated fruits and vegetables. Several drying methods are commercially available and the selection of the optimal method is determined by quality requirements, raw material characteristics, and economic factors. There are three types of drying processes: sun and solar drying; atmospheric dehydration including stationary or batch processes (kiln, tower, and cabinet driers) and continuous processes (tunnel, continuous belt, belt-trough, fluidized-bed, explosion puffing, foam-mat, spray, drum, and microwave-heated driers); and subatmospheric dehydration (vacuum shelf, vacuum belt, vacuum drum, and freeze driers). 2.4.2.1 Sun and Solar Drying.

Sun drying (used almost exclusively for fruit) and solar drying (used for fruit and vegetables) of foods use the power of the sun to remove the moisture from the product. Sun drying of fruit crops has remained largely unchanged from ancient times in many parts of the world, including the United States. It is limited to climates with hot sun and dry atmosphere, and to certain fruits such as prunes, grapes, dates, figs, apricots, and pears. These crops are processed in substantial quantities without much technical aid by simply spreading the fruit on the ground, racks, trays, or roofs and exposing them to the sun until dry. Advantages of this process are its simplicity and its small capital investment. Disadvantages include complete dependence on the elements and moisture levels no lower than 15 to 20 percent (corresponding to a limited shelf life). Solar drying utilizes black-painted trays, solar troughs, and mirrors to increase solar energy and accelerate drying. Indirect solar driers collect solar energy in collectors that, in turn, heats the air as it

blows over the collection unit before being channeled into the dehydration chamber. In commercial applications, solar energy is used alone or may be supplemented by an auxiliary energy source, such as geothermal energy.

2.4.2.2 Atmospheric Dehydration. Atmospheric forced-air driers artificially dry fruits and

vegetables by passing heated air with controlled relative humidity over the food to be dried, or by passing the food to be dried through the heated air. Various devices are used to control air circulation and recirculation. Stationary or batch processes include kiln, tower (or stack), and cabinet driers. Kiln driers utilize the natural draft from rising heated air to dry the product and are the oldest and simplest type of dehydration equipment still in commercial use. Tower or stack driers consist of a furnace room containing a furnace, heating pipes, and cabinets in which trays of fruits or vegetables are dried. In a typical design, each tower or stack holds approximately 12 trays and a furnace room holds about 6 stacks. Heated air from the furnace rises through the trays holding the product. As the trays of food at the bottom are dried, they are removed. All trays are then shifted downward and freshly loaded trays are inverted at the top. Cabinet driers are similar in operation to a tower drier, except that the heat for drying is supplied by steam coils located between the trays. This design provides some temperature control and uniformity, and thus represents an improvement over the tower drier. However, cabinet driers are suitable only for establishing the drying characteristics of a new product or for high-valued raw materials, such as bananas or mushrooms, due to small capacity and high operating costs.

Continuous processes include tunnel, continuous belt, belt-trough, fluidized-bed, explosion puffing, foam-mat, spray, drum, and microwave-heated driers. Tunnel driers are the most flexible and efficient dehydration system used commercially, and is widely used in drying fruits and vegetables. The equipment is similar to a cabinet drier, except that it allows a continuous operation along a rectangular tunnel throughwhich tray-loaded trucks move. The tunnel is supplied with a current of heated air that is introduced at one end. Fruits and vegetables of almost any size and shape can (so long as they are solids) be successfully dried in a truck-and-tray tunnel drier. Continuous belt or conveyor driers are similar to tunnel driers, except that the food is conveyed through a hot air system on a continuous moving belt without the use of trays. This difference eliminates the costly handling of the product on trays before and after drying and allows continuous operation and automatic feeding and collection of the dried material. Belt-trough driers have a continuous stainless steel wire mesh belt that forms a trough about 10 feet (ft) in length and 4 ft wide. The raw material is fed onto one end of the trough and is dehydrated by forcing hot air upward across the belt and the product. Fluidized-bed driers, a modification of the belt-trough drier, uses heated airflow from beneath the bed to lift the food particles and at the same time convey them toward the outlet. However, if the air velocity becomes too great, channeling will occur and most of the air will escapewithout performing its function; therefore, fluidized-bed driers are limited to the preparation of foodpowders. In explosion puffing, fruit pieces (e.g., blueberries) are partially dehydrated in a conventional manner and then heated in a closed vessel, known as a gun because of its quick-opening

lid. Pressure is built-up in the vessel to a specific level and the closure is then released, causing the pieces to expand by sudden volatilization of internal mositure. The fruit particles are then dried to 4 to 5 percent moisture content by conventional drying methods. Foam-mat drying involves drying liquid or pureed materials as a thin layer of stabilized foam by heating air at atmospheric pressure. The prepared foam is spread on perforated trays and dried by hot air, followed by crushing into powder. Spray driers involve the dispersion of liquid or slurry in a stream of heated air, followed by collection of the dried particles after their separation from the air. This process is widely used to dehydrate fruit juices. In drum driers, a thin layer of product is applied to the surface of a slowly revolving heated drum. In the course of approximately 300E of a full revolution, the moisture is flashed off, and the dried material is scraped off the drum by a stationary or reciprocating blade. Drum driers are generally heated from within by steam and are suitable for a wide range of liquid, slurried, and pureed products. Microwave driers have been tried experimentallyfor the dehydration of fruits, but no commercial installations are in place. 2.4.2.3 Subatmospheric Dehydration.

Subatmospheric (or vacuum) dehydration occurs at low air pressures and includes vacuum shelf, vacuum drum, vacuum belt, and freeze driers. The main purpose of vacuum drying is to enable the removal of moisture at less than the boiling point under ambient conditions.

Because of the high installation and operating costs of vacuum driers, this process is used for drying raw material that may deteriorate as a result of oxidation or may be modified chemically as a result of exposure to air at elevated

temperatures. All vacuum-drying systems have the following essential components: vacuum chamber, heat supply, vacuum-producing unit, and a device to collect water vapor as it evaporates from the food. All vacuum driers must also have an efficient means of heat transfer to the product in order to provide the necessary latent heat of evaporation and means for removal of vapor evolved from the product during drying.

There are two categories of vacuum driers. In the first category, moisture in the food is evaporated from the liquid to the vapor stage and includes vacuum shelf, vacuum drum, and vacuum belt driers.Vacuum shelf driers and drum driers are batch-type driers and are suitable for a wide range of fruits and vegetables (e.g., liquids, powders, chunks, slices, wedges, etc.). Vacuum belt driers are continuous-type driers suitable for food pieces, granules, and discrete particles. It operates at a relatively high vacuum and has a capital cost much higher than a batch-type unit of similar operating capacity. In the second category of vacuum driers, the moisture of the food is removed from the product by sublimination, which is converting ice directly into water vapor. The advantages of freeze drying are high flavor retention, maximum retention of nutritional value, minimal damage to the product texture and structure, little change in product shape and color, and a finished product with an open structure that allows fast and complete rehydration. Disadvantages include high capital investment, high processing costs, and the need for special packing to avoid oxidation and moisture gain in the finished product.2.4.3 Postdehydration Treatments.

Treatments of the dehydrated product vary according to the type of fruit or vegetable and the intended use of the

product. These treatments may include sweating, screening, inspection, instantization treatments, and packaging. Sweating involves holding the dehydrated product in bins or boxes to equalize the moisture content. Screening removes dehydrated pieces of unwanted size, usually called "fines." The dried product is inspected to remove foreign materials, discolored pieces, or other imperfections such as skin, carpel, or stem particles. Instantization treatments are used to improve the rehydration rate of the low-moisture product and include compressing the product after dehydration (flaking) and/or perforating the product after it is partially dehydrated and then dehydrating the perforated segments to the desired moisture level (used primarily for apples).

Packaging is common to most all dehydrated products and has a great deal of influence on the shelf life of the dried product. Packaging of dehydrated fruits and vegetables must protect the product against moisture, light, air, dust, microflora, foreign odor, insects, and rodents; provide strength and stability to maintain original product size, shape, and appearance throughout storage, handling, and marketing; and consist of materials that are approved for contact with food. Cost is also an important factor in packaging. Package types include cans, plastic bags, drums, bins, and cartons, depending on the end-use of the product.

3. Experimentation3.1 Experimental set up & Procedures

The experimental set up for onion dehydration consist of number of steps as shown in the fig. It consist of Following steps : 3.1.1. Predrying Treatments : 3.1.1.1 Raw Product Preparation

Medium & large sized red & white onion were chosen for this drying experiment. Peeling & trimming were done manually by sharp steel knifes.

After cutting the onion samples were meshed with aluminium meshers manually with 4 mm mesh size.3.1.1.2 Sulphination & pH lowering.

A combined sulphination & citric acid treatment was given by steeping the onion slices successively in 0.2 % potassium metabi-sulphite ( KM5 ) & 0.2 % citric acid for 5 min.3.1.1.3. Osmotic Dehydration

After sulphination the weights of samples were noted down. Then they were dipped in 5 %, 10% & 15% brine solutions respectively both red & white onion. The volume was brine solution was taken as double the volume of samples. A intermediate agitation was provided during this period.

After 1 hr. the samples were removed from brine & dried with using filter papers. The respective weights of each sample was noted down.3.1.2 Drying3.1.2.1 Atmospheric Drying :

Atmospheric forced air dries artificially dry vegetables by blowing hot air. For our experiment a commercial tray drier was used. About 3 samples each of red & white onion species were

selected for this step of 5%, 10% & 15 % of brine in osmotic dehydration.

The onions were spread uniformly in the aluminium trays. The trays were stocked in dryer at 700C. The drying was started & weights of samples were noted down after each ½ hr. intervals till the samples attained a weight corresponding to a moisture content of 5 – 6 %. The samples were collected carefully used for further process.3.1.2.2 Solar Drying :

Six samples with similar specifications of the samples used in atmospheric drying were used. The initial was were noted. The samples were spread uniformly on aluminium trays. The trays were placed in sun. The loss in weights by samples were measured at hourly intervals till the weights reach to moisture content of 5 – 6 %. The samples were properly collected & weighted finally.3.1.3 Post Dehydration Steps :

These techniques were used for powder forms.3.1.3.1 Grinding :

The product or samples collected from the trays were grinded in a ball mill for ½ hr.

The grinded product was then collected for further steps.3.1.3.2. Sieving :

The product was the sieved to remove fines & the oversize. The powder on 30 mesh size was collected for packing.3.1.3.3 Packing & Storage :

Onion powder was packed in 200 & 400 gauge low density pollyethylene ( LDPE ) & 200 gauge high density polyethylene ( HDPE ) pouches of 8 X 6 cm & stored at room temperature ( 18

– 35 0C) 50 – 60 % RH & low temperature ( 7 0C, 85 % RH ) respectively.

Fig. 3.a Onion dehydration process

3.2 Analysis3.2.1 Physical characteristicsAverage weight, average volume, average bulb size [length and diameter] as measured by a vernier caliper, nature of bulb neck as observed visually, per cent yield of edible bulb after peeling and trimming were determined. (Table 3.2.a)3.2.2 Chemical analysis

Moisture content was determined by drying the sample in a vacuum oven at 700C to constant weight. Total soluble solids (TSS) content of pressed juice was determined by a hand refractometer. Acidity in terms of total titratable acids was estimated by titrating a known weight of the sample with standard NaOH solution using phenolphthalein as indicator and the results were expressed as per cent malic acid. Ascorbic acid content was estimated by titrating a known weight of the sample with 2, 6-dichlorophenolido-phenol dye using 3% metaphosphoric acid as stabilizing agent. Water insoluble matter was determined by washing onion paste free from soluble matter with water on a weighted filter paper and drying it along with the residue at 60 0C to constant weight. To estimate reducing sugars, a known weight of the prepared sample was mixed with water for extraction of sugar. Following clarification with lead acetate and deleading with potassium oxalate, reducing sugars were estimated. Total sugars were estimated by the same method in an aliquot of the clarified extract following hydrolysis with hydrochloric acid and neutralisation of the excess acid with sodium hydroxide. Browning in dehydrated onion was measured in terms of optical density at 420 nm of an aliquot of 10% NaCl solution with which the dehydrated product was drenched thoroughly. The residual sulphur dioxide in dehydrated onion was determined.

3.2.3 Drying studiesThe ratio of the dried weight of the product to the weight

before drying was recorded as drying ratio. The dried was recorded as drying ratio. The dried product was rehydrated by dipping in distilled water and the rehydration ratio was computed in terms of the ratio of the weight of the rehydrated sample to that of the dried product. Moisture content, browning, total sugars, reducing sugars, ascorbic acid and residual sulphur dioxide were estimated in the dried products.3.2.4 Sensory evaluation

Sensory evaluation of the dried onion takes in terms of colours, flavour, texture and overall acceptability was performed by a panel of 8 judges on a 9-point hedonic scale varying from ‘like extremely’ [rating 9] to ‘dislike extremely’ [rating 1].

Sr. No Properties Red Onion White Onion1 Average weigth(gm) 78 74.22 Average volume(ml) 81 79.63 Average Length (cm) 4.26 4.064 Average Diameter

(cm) 5.02 5.41

5 Shape Index (L/D) 0.849 0.756 Bulb neck Disposition Closed Open7 Moisture Content 88.531 % 88.899%8 Rehydration Ratio 1 : 4.62 1 : 4.549 Dehydration

ratio(5%moisture)6.07 : 1 5.85 :1

Table 3.2.a Physical characteristics of onion

3.3 Result & Discussion 3.3.1 General DiscussionBatch A] Tray Drying Of White Onions Sample 1 = Osmotic treated in 5% brine.Sample 2 = Osmotic treated in 10% brine.Sample 3 = Osmotic treated in 15% brine.Initial solid content (Ss) Area of Drying. (A)Sample 1 = Ss1 = 0.059462 kg. A1 = 0.0629 m2

Sample 2 = Ss2 = 0.053027 kg. A2 = 0.0565 m2 Sample 3 = Ss3 = 0.064297 kg. A3 = 0.0680m2 Initial moisture content (W.B.) = 88.53%

Sr.

No.

Time(Sec

)

Sample 1 Sample 2 Sample 3 Type of dryingW1 X1 N1 W2 X2 N2 W3 X3 N3

1 0 518.4 88.53 - 462.3 88.53 - 560.6 88.53 -

Osmotic2 ½ - - - - - - - - -3 1 307.9 47.94 - 299.6 53.35 - 370.9 54.70 -4 1 ½ 191.9 25.54 42.33 187 28.98 45.72 245.8 32.38 42.22

Forced drying

5 2 141.8 15.88 18.27 138.7 18.53 19.61 184.5 21.44 20.676 2 ½ 107.3 9.22 12.58 99.5 10.05 15.91 140.6 13.61 14.817 3 85 4.95 8.13 79.8 5.79 7.99 108.2 7.831 10.938 3 ½ 70 2.03 5.56 68 3.24 4.79 83.8 3.48 8.239 4 66.2 1.33 1.33 64.5 2.48 1.42 79.4 2.69 1.4810 4 ½ 64.4 0.95 0.72 62.6 2.07 0.77 77.6 2.37 0.6115 5 63.8 0.84 0.22 61.6 1.85 0.41 76 2.08 0.54

From the above graph it is clearly seen that the moisture remove in 5% concentration osmotic dehydration is maximum & minimum in 15% concentration brine. The above figure represents the drying of white onion in tray drying.

Batch B] Solar Drying Of White OnionsSample 1 = Osmotic treated in 5% brine.Sample 2 = Osmotic treated in 10% brine.Sample 3 = Osmotic treated in 15% brine.Initial solid content (Ss) Area of Drying. (A)Sample 1 = Ss1 = 0.00286kg. A1 = 0.00312 m2

Sample 2 = Ss2 = 0.00286 kg. A2 = 0.00312 m2 Sample 3 = Ss3 = 0.00286 kg. A3 = 0.00312 m2 Initial moisture content (W.B.) = 88.53%

Sr. No.

Time(Hr.)

Sample 1 Sample 2 Sample 3 Type of dryingW1 X1 N1 W2 X2 N2 W3 X3 N3

1 0 25 88.53 - 25 88.53 - 25 88.53 -Osmotic2 1 14.84 47.94 - 16.19 53.33 - 16.92 56.24 -

3 2 9.05 24.76 21.24 10.67 31.24 20.25 11.71 35.40 19.10 Forced drying4 3 5.41 10.20 13.34 6.96 16.40 13.61 8.23 21.48 12.76

5 4 3.68 3.28 6.34 4.60 6.96 8.65 5.85 11.92 8.766 5 3.14 1.12 1.98 3.44 2.32 4.25 4.52 6.64 4.847 6 3.06 0.8 0.29 3.24 1.52 0.73 4.24 5.52 1.03

From the above graph it is clearly seen that the moisture remove in 5% concentration osmotic dehydration is maximum & minimum in 15% concentration brine. The above figure represents the drying of white onion in solar drying.

Batch C] Tray Drying Of Red Onions Sample 1 = Osmotic treated in 5% brine.Sample 2 = Osmotic treated in 10% brine.Sample 3 = Osmotic treated in 15% brine.Initial solid content (Ss) Area of Drying. (A)Sample 1 = Ss1 = 0.00277 kg. A1 = 0.00503 m2

Sample 2 = Ss2 = 0.00277 kg. A2 = 0.00503 m2 Sample 3 = Ss3 = 0.00277 kg. A3 = 0.00503 m2 Initial moisture content (W.B.) = 88.89%

Sr. No.

Time(Hr.)

Sample 1 Sample 2 Sample 3 Type of dryingW1 X1 N1 W2 X2 N2 W3 X3 N3

1 0 25 88.89 - 25 88.89 - 25 88.89 -

Osmotic2 ½ - - - - - - - - -3 1 13.86 44.36 - 14.62 47.4 - 14.82 48.20 -4 1 ½ 8.45 22.72 23.83 8.91 24.56 25.15 9.03 25.04 25.51

Forced drying

5 2 5.05 9.12 14.97 5.33 10.24 9.87 5.50 10.92 15.556 2 ½ 3.44 2.68 7.09 3.63 3.44 7.48 3.78 4.08 7.537 3 2.93 0.6 2.29 3.09 1.28 2.38 3.25 1.92 2.388 3 ½ 2.86 0.36 0.264 3.02 1.0 0.31 3.18 1.64 0.31

From the above graph it is clearly seen that the moisture remove in 5% concentration osmotic dehydration is maximum & minimum in 15% concentration brine. The above figure represents the drying of red onion in tray drying.

Batch D] Solar Drying Of Red Onions Sample 1 = Osmotic treated in 5% brine.Sample 2 = Osmotic treated in 10% brine.Sample 3 = Osmotic treated in 15% brine.Initial solid content (Ss) Area of Drying. (A)Sample 1 = Ss1 = 0.00277kg. A1 = 0.00503 m2

Sample 2 = Ss2 = 0.00277 kg. A2 = 0.00503 m2 Sample 3 = Ss3 = 0.00277 kg. A3 = 0.00503 m2 Initial moisture content (W.B.) = 88.89%

Sr. No.

Time(Hr.)

Sample 1 Sample 2 Sample 3 Type of dryingW1 X1 N1 W2 X2 N2 W3 X3 N3

1 0 25 88.89 - 25 88.89 - 25 88.89 -Osmotic2 1 13.86 44.36 - 14.62 47.4 - 14.82 48.2 -

3 2 8.86 24.36 11.01 9.35 26.32 11.61 9.48 26.84 11.76 Forced drying4 3 5.09 9.28 8.31 5.37 10.4 8.77 5.44 10.68 8.90

5 4 3.07 1.20 4.44 3.24 1.88 4.69 3.28 2.04 4.966 5 2.91 0.56 0.35 3.07 1.20 0.36 3.12 1.40 0.357 6 2.81 0.16 0.22 2.96 0.76 0.24 3.02 1.00 0.22

From the above graph it is clearly seen that the moisture remove in 5% concentration osmotic dehydration is maximum & minimum in 15% concentration brine. The above figure represents the drying of red onion in solar drying.

3.3.2 Comparative GraphsComparison A) Moisture removed versus concentration of brine.Sr. No. Concentration of brine

(%)Moisture removed

(%)1 2 40.562 5 45.853 10 39.754 15 38.21

From the above graph it is clearly seen that the moisture removed in 5% concentration osmotic dehydration is maximum & minimum in 15% concentration brine. From the above figure it is clearly seen that the optimum brine concentration for osmotic dehydration is 5%.

Comparison B) Comparison between osmotic dehydrated white onion dried in tray & solar drier & without osmotic effect.Sample 1 = 5% osmotic treated white onion (tray dried).Sample 2 = 5% osmotic treated white onion (solar dried).Sample 3 = white onion without osmotic treatment (tray dried).

Sr. No. Time(Hr.)

Sample 1% X1 (W.B.)

Sample 2% X2 (W.B.)

Sample 3% X3 (W.B.)

1 0 88.53 88.53 88.532 1 47.94 47.94 53.543 2 15.88 24.76 28.854 3 4.93 10.20 12.25 4 1.33 3.28 4.686 5 0.84 1.12 1.827 6 - 0.80 1.4

From the above graph represents the drying of white onion with and without osmotic dehydration in tray & solar drying. It is seen that maximum moisture is removed in osmotic dehydrated tray drying & less moisture is removed in without osmotic treatment.

Comparison C) Comparison on basis of size of onion (white onion, tray dried).Sample 1 = 5% osmotic dehydrated meshed white onion.Sample 2 = 5% osmotic dehydrated sliced white onion.

Sr. No. Time(Hr.)

Sample 1(moisture %)

Sample 2(moisture %)

1 0 88.53 88.532 1 47.94 80.923 2 15.88 40.404 3 4.93 24.815 4 1.33 14.316 5 0.83 9.947 6 - 6.758 7 - 4.71

The above graph gives comparison of white onion dehydration on the basis of size. As by general rule the drying in smaller size in onion is more as compare to bigger sized one. From above it is seen that the drying of meshed onion is with faster rate then of the slice one.

Comparison D) Comparison between RED & WHITE onions (tray dried).Sample 1 = 5% osmotic dehydrated meshed white onion.Sample 2 = 5% osmotic dehydrated meshed red onion.

Sr. No. Time(Hr.)

Sample 1(moisture %)

Sample 2(moisture %)

1 0 88.53 88.892 1 47.94 44.363 2 15.88 9.124 3 4.93 0.665 4 1.33 -6 5 0.84 -

From above figure shows comparison between white and red onion. By the above figure we can consider the drying rate of red onion is more than white onion because of its high moisture contain and low quality.

4.COST ESTIMATION4.1.Experimental costBASIS:- 24 Kgs of onion (5%osmotically dehydrated onion)Sr. No.

Operation Tray Drying Solar DryingWhite (Rs.)

Red (Rs.)

White (Rs.)

Red (Rs.)

1 Raw material 3x24=72

2.25x24= 54

3x24=72

2.25x24= 54

2 Man powerPeeling & Meshing)

24 24 24 24

3 Chemical required (salt & KMS)

8 8 8 8

4 Power consumption (3.37 Kw x (Hr.)x 4Rs.)

27 29 - -

5 Utilities (Water) 2 2 2 2

6 2 2 2 2

7 Total 135 119 108 90

Yield / batch (5% M.C.) :-Losses in (cutting + peeling) = 5%

= 0.05 x 24= 1.2 kgs.

Wt. after peeling = 24 – 1.2 = 22.8 kgs.Considering 5% moisture in products we get yield as :-For red onion = 22.8 (1-0.8353)

= 3.755 kgs.

For white onion = 22.8 (1-0.8290) = 3.899 kgs.

Cost/Kg.of the product:-For White onionTray Drying , Cost Price=135/3.899= 34.628 Rs./Kg. Solar Drying , Cost Price = 119/3.899= 30.521 Rs./Kg.

For Red onion Tray Drying , Cost Price = 108/3.755 = 28.762 Rs./Kg.

Solar Drying , Cost Price = 90/3.755 = 23.968 Rs./Kg.

4.2.Scale-up cost consideration

Basis:

a. 1500 kgs. of onion . b. Working hours - Three shifts each of 8 hours duration c. Working days in a year - 300 days d. Annual production capacity - 112.5 M.T. of dehydrated vegetables and 37.5 M.T. of dehydrated onion .e. Capacity utilisation - 100% f. Annual output envisaged - 150 M.T.

Plant and Machinery The equipment required for the unit are:

SL. Description Nos Amount (Rs.)

i Pre cooling facility at + 10 degrees centigrade as raw material store

85000.00

ii Stacking trays for vegetables with each tray holding 10 kilograms of the vegetable

500 75000.00

iii Preparatory section comprising washing tank, slicers, cubers, dicers etc

220000.00

iv Blanching tank with thermostat control solenoid valves, circulation pump to keep

155000.00

blanching solution in circulation

v Stainless steel vibratory shaker to remove excess water after blanching

50000.00

vi Fluidized bed driers for dehydrating vegetables at a capacity of 1000 kgs. in a span of 8 to 10 hours, complete with heat changers, blower fans and accessories.

440000.00

vii Form fill and seal packing machine with augur weighers and fillers

236000.00

viii How water boiler and accessories 165000.00

ix Pin mill with accessories at a capacity of 50 kgs. per hour

500000.00

x Laboratory testing equipment comprising Precision weighing scales; Hot air oven; Ashing oven; Soxhlet apparatus; PH meter; Kjeldhal apparatus; Glassware; Chemicals

75000.00

xi Total 2136000.00

Infrastructural Facilities a. Land 15000 square feet

b. Shed 8000 square feet c. Power 50 HP connected load d. Water 500 kilo litres per month e. Fuel Furnace oil for boiler

Total Capital Requirement a. The total capital requirement is Rs. 96.38 lakhs. b. Fixed capital is Rs. 66.36 lakhs as follows. c. Working capital is Rs. 30.02 lakhs as follows. d. Project cost comprising fixed capital and margin money for working capital is Rs. 77.80 lakhs.

A. FIXED CAPITAL

Rs. in lakhs

a. Land and building 25.00

b. Plant and machinery 21.36

c. Delivery vehicle - LCV 4.00

d. Erection and commissioning 3.50

e. Cost of power connection and electrification 3.00

f. Moulds, fixtures and office equipment 2.50

g. Preoperative expenses 3.00

h. Contingencies 2.00

i. Know how fees 2.00

Total (A) 66.36

B. WORKING CAPITAL

Period (days) Rs. in lakhs

a. Raw material 30 5.76

b. Packing material 30 0.51

c. Finished goods 7 3.50

d. Debtors 30 15.00

e. Salaries and wages 30 1.64

f. Utilities 30 0.61

g. Contingencies 30 3.00

Total (B) 30.02

Total (A) + (B) 96.38

Working Capital to be Finances As: Margin money Rs. 11.44 lakhs Bank Finance Rs. 18.58 lakhs

Means of Finance a. Promoters contribution Rs. 28.03 lakhs b. Term loan Rs. 49.77 lakhs c. Subsidy nil

d. Total Rs. 77.80 lakhs

Requirement of Raw and Packing Materials Per Month

sl Description Unit Qty Price (Rs.)

a. Onions kgs 40000 160000.00

b. Total raw material 54000 482000.00

c. Primary packing material metallized polyester-poly film

kgs 50 12500.00

d. Secondary packing material cartons and straps

nos 2500 30000.00

e. Total packing material 42500.00

Salaries and Wages of Employees Per Month

sl. Designation No Salary per head

Total salary

i Factory Manager 1 8000.00 8000.00

ii Maintenance Engineer 1 6000.00 6000.00

iii Production Supervisor 3 4000.00 12000.00

iv Skilled labour 4 3000.00 12000.00

v Packing labour 3 3000.00 9000.00

vi Unskilled labour 15 2000.00 30000.00

vii Van driver 1 3000.00 3000.00

viii Administrative staff 1 3000.00 3000.00

ix Marketing Manager 1 8000.00 8000.00

x Sales officers 3 6000.00 18000.00

xi Marketing salesmen 6 5000.00 30000.00

xii Security staff 2 2000.00 4000.00

xiii Total 38 143000.00

xiv Perquisites @ 15% 21450.00

xv Total 164450.00

Operating Expenses The annual operating expenses at full capacity utilisation are estimated at Rs. lakhs as follows:

sl Description Total value (Rs. lakhs)

i Raw materials 57.84

ii Packing materials 5.10

iii Utilities 7.32

iv Salaries and wages 19.73

v Contingencies 36.00

vi Depreciation on land and civil works @ 10%

2.50

vii Depreciation on machinery @ 10% 2.15

viii Depreciation on moulds and fixtures @ 10%

0.25

ix Depreciation on office equipment @ 20%

0.20

x Depreciation on vehicle @ 10% 0.40

xi Interest on term loan @ 14% 6.98

xii Interest on short term borrowings @ 14%

3.34

xiii Total production cost 141.81

Sales Realisation

sl Item Qty in kgs.

Rate/kg (Rs.)

Total Value (Rs. lakhs)

ii Dehydrated onion 285000 60.00 171.00

iii Total 285000 171.00

Profitability

a. Pre tax profit Rs. 29.19 lakhs

b. Break even point 72 percent

c. Rate of return 33 percent

d. Profit as percent of sales 18 percent

6. Mathematical Modelling & simulation 6.1 Modelling Fundamentals6.1.1 Chemical Engineering Modelling The use of models in chemical engineering is well established, but the use of dynamic models, as opposed to the more traditional use of steady-state models for chemical plant analysis, is much more recent. This is reflected in the development of new powerful commercial software packages for dynamic simulation, which has arisen owing to the increasing pressure for design, process integrity and operation studies for which a dynamic simulator is an essential tool. Indeed it is possible to envisage dynamic simulation becoming a mandatory condition in the safety assessment of plant,, with consideration of such factors as start up, shutdown abnormal operation, and relief situations. Dynamic simulation can thus be an essential part of any hazard or operability study, both in assessing the consequences of plant failure and in the mitigation of possible effects. Dynamic simulation is thus of equal importance in large scale continuous process operations as in other inherently dynamic operations such as batch, semi-batch and cyclic. Manufacturing processes. Dynamic simulation also aids in a very positive sense in gaining a better understanding of process performance and is a powerful tool for plant optimisation, both ai the operational and at the design stage. Furthermore steady-state operation is then seen in its rightful place the end result a dynamic process for which rates of change have become eventually zero.The approach in this book is to concentrate on a simplified approach to dynamic modelling and simulation. Large scale commercial software packages for chemical engineering dynamic simulation are now very powerful and contain highly

sophisticated mathematical procedures which can solve both for the initial steady-stat: condition as well as for the following dynamic changes. They also contain extensive standard model libraries and the means of synthesising a complete process model by combining standard library models. Other important aspects are the provision for external data interfaces and built-in model identification and optimisation routines, together with access to a physical property data package. The complexity of the software, however, is Basic Conceptssuch that the packages are often non-user friendly and the simplicity of .the basic modelling approach can be lost in the detail of the solution procedures. The correct use of such design software requires a basic understanding of the sub-model blocks modeling. Our simplified approach to dynamic modelling and simulation incorporates no large model library, no attached database and no relevant physical property package. Nevertheless quite realistic process phenomena can be demonstrated, using a very simple approach. Often a simplified approach can also be very useful in clarifying preliminary ideas before going to the large scale commercial package, as we have found several times in fir research. Again this follows our general philosophy of starting simple and building in complications as the work and as a full understanding of the process model progresses.Kapur (1988) thus listed thirty-six characteristics or principles of mathematical modelling. These are very much a matter of common sense, but it is very important to have them restated, as it is often very easy :o lore sight of the principles during the active involvement of modelling. Thev can he summarised as follows:

1)The mathematical model can only he an approximation of real-life. processes, which are often extremely complex and often only partially understood. Thus models are themselves neither good nor bad but, as pointed out by Kapur, will either give a good fit or a bad fit to actual process behaviour. Similarly, it is possible to develop several different models for the same process, and these will all differ in some respect in the nature of predictions. Indeed it is often desirable to try to approach the solution of a given problem from as many different directions as possible, in order to obtain an overall improved description. The purpose of the model also needs lo be very clearly defined,I. Of course, whilst the aim of the modelling exercise is

always to obtain as realistic a description of (h^ process phenomena as possible, additional realism often involves adJ'tionat numerical complexity and \vi!J demand additional data, which may be difficult or impossible to obtain. A marginal additional decree of realism can thus become rapidly outv/eighed by the large amount of extra time and efiort ncjr"ed.

?. Modelling is a process of continuous development, in which it is generally advisable to slart off witii i!ic simplest conceptual lepiesentafion of (he process and to build in more and more complexities, as the model develops Starting off with the process in its most complex form, often Icadn to confusion. A process of continuous validation is necessary, in which the model theory, data, equation formulation and model predictions must all be examined repeatedly. In formulating any moUcl. it is therefore important to include the potential for change. The final form of the model will lie somewhere between the initial highly-simplified and unrealistic model and a possible final

overcomplicated and over-ambitious model, but should provide a reasonable description of the process :;nd must be capable of being used.Often it is possible to consider the process or plant, as a system of independent sub-sets or modules, which are then modelled individually and combined to form a description of the complete system. This technique is also used in the large scale commercial simulation software, in which various library sub-routines or modules for the differing plant elements, arc combined into a composite simulation program.3. Modelling i.% an art but also a very important learning process. In addition to a mastery c! the relevant theory, considerable insigh' ! '^ the actual functioning of the process is required. One of the most important factors in modelling is to understand the basic cause and effect sequence of individual processes. Often the model itself, by generating unexpected behaviour, will assist in gaining the additional process Insight, since ;hc basic cause for the anomalous behaviour must be thought out and a plausible explanation found. The modelling process will often also uggest the need fur new data or for experimentation needed to elucidate various aspects of process beha\ iour that arc no: well undersiood.4. Modclr must be both realis'i; and also robust. A model which predicts effects which are quite contrary to common sense or to normal experience is unlikely tv: be met with confidence. To accord with this, some use of empirical adjustment factors in the model may be needed, in order to represent combinations of relatively unknown unknown factors.The basic stages in the above modelling methodology are indicated in Fig. I.I.

Compared to purely empirical methods of describing chemical process phenomena, the modelling approach attempts to describe performance, by the use of well-established thcc.y, which when described !n mathematical termj. represents a working 'model for the process. In carrying out a modelling exercise, the modeller is forced to consider the nature of all the important parameters of the process, their effect on the proce.- s and how each parameter can be defined in quantitative terms, i.e., the modeller must identify the important variables and their separate effects, which in practice may have a very highly interactive effect on the overall process. Thus the very act of modelling is one that forces a better understanding of the process, since all the relevant theorv must be critically assessed. Jn addition, the task of formulating theory into terms of mathematical equations is also a very positive factor that forces a clear formulation of basic concepts.Once formulated, the model can be solved and the behaviour predicted by the model compared wlih experimental data. Any differences in performance may then bo used to further redefine or refine rhe model until good agreement is obtained. Once the model is established it can then be used, with reasonable confidence, to predict "pjru>rmarice under differing process conditions, and used for process design, optimisation end control. Input of-plant or experimental data is, of course, required in order to establish or validate the model, but the quantity of data required, as compared to the empirical approach is considerably reduced.A comparison of the modelling and empirical approaches are given below.Empirical Approach: Measure productivity for all combinations of plant operating conditions, and make correlations.

- Advantage: Little thought is necessary.- Disadvantage: Many experiments are required.Modelling Approach: Establish a model and design experiments to determine the model parameters. Compare the mode! behaviour with the experimental measurements. Use the model for rational design, control and optimisation.- Advantages: Fewer experiments are required and greater understanding is obtained.

- Disadvantage: Time is required for developing models. 1.1.2 General Aspects of the Modelling ApproachAn essential stage in the development of any model, is the formulation of the appropriate mass and energy balance equations (Russell and Denn, 1972). To these must be added appropriate kinetic equations for rates of chemical reaction, rates of heat and mass transfer and equations representing system property changes, phase equilibrium, and applied control. The combination of these relationships provides a basis for the quantitative description of the process and comprises the basic mathematical model. The resulting model can range from a simple case of relatively few equations to models of great complexity. The greater the complexity of the model, however, the greater is then the difficulty in identifying the increased number of parameter values. One of the skills of modelling is thus to derive the simplest possible model, capable of a realistic representation of the process.A basic use.of a process model is to analyse experimental data and ro use this to characterise the process, by assigning numerical values to the important process variable.?. The model can then also be solved with appropriate numerical data values and the model predictions compared with actual practical results. This procedure is known as simulation and may be used

to confirm that the mode' and the appropriate parameter values are "correct''. Simulations, however, can also be used in a predictive manner to test probable behaviour under varying conditions, leading to process optimisation and advanced control strategies. The application of a combined modelling and simulation approach leads to the following advantages:1. Modelling improves understanding. In formulating a mathematical model, the modeller is forced to consider the complex cause-and-effect sequences of the process in detail, together with all the complex inter-relationships ilrit may be involved in the process. The comparison of a model prediction with actual behaviour usually leads to an increased understanding of the process, simply by having to consider the v/ays in which the mods! might be in error.2. Models help in experimental design. It is important that experiments be designed in such a way mat the model can be properly tested. Often the model itself will suggest the need for data for certain parameters, which might otherwise be neglected. Conversely, sensitivity tests on the model may indicate that certain parameters may be negligible and her.ce can be neglected in the model. ..3. Models may be used predictively for design and control. Once the model has been established, it should be capable of predicting performanc- under differing process conditions, that may be difficult to achieve experimentally Models can aiso be used for the design of relatively sophisticated control , systems and can often form an integral par! of the control algon'thm. Both mathematical and know/edge based models can be used in designing and optimising new processes.4. Models may be used in training and education. Many important aspects of reactor operation can be simulafed by the

use of simple models. These include process start-up and shut down, feeding strategies, measurement dynamics, heat effects and control. Such effects are easily uemonstrated by computer, as shown in the accompanying simulation examples, but are often difficult and expensive to demonstrate in practice5. Models may be used for process optimisation. Optimisation usually involves the influence of two or more variables, with one often directly related to profits and the other related to costs.1.1.3 General Modelling ProcedureOne of the more important, features of modelling is the frequent reed to . reassess both the basic theory (physical model), and fhe mathematical equations, representing the physical model, (mathematical model), in order to achieve agreement, between the mode) prediction and actual plant performance (experimental data)..As shown in Fig. 1.2, the following stages in the modelling procedure can be identified:(i) The first involves tit" proper "Pliniu'on of the problem and hence the gonls and objectives of the study. All the relevant theory must be assessed in combination with any prac.icr.J experience, and perhaps alternative physical models need to be developed and examined.(ii) The available theory must then be formulated in mathematical terms. Most reac'or operations involve many different variables (reactar.t ana product concentrations, temperature, rates cf rcactan; consumption, product formation and heat production) ?nd many vary as a function of time (batch, semi-batch operation). For these reasons the -nathematical model w'.'A often consist of many differentia' ecjirUions.

(Hi) Having developed a model, the equation., must then be solved. Mathematical models of chemical engineering systems, are usually quite complex and highly non-linear and are such thai an analytical means of solution is not possible. Numerical methods of solution must therefore be employed, wiih the method preferred in this iexi being that of digital simulation. With this method, the solution of even very complex models i accomplished with relative ease. Digital simulation languages are designed specially for the solution of sets of simultaneous differentia! equations, based on the use of numerical integration. Many fas! and efficient numerical integration routines are now available, such that many digi'a! simulation languages are able to offer a choice of integration routine. Sorting algorithms within the structure of the language enable very simple programs to be written, having an almost cne-to-one conespondencc.-with the way in which the basic model'equations are originally formula'ed. Tne resulting simulation programs ape therefore very easy to understand and airo to write. A further major advantage is a convenient output of results, in both tabulated and graphical form, obtained via very simple program commands.(iv) The validity of the computer prediction must be checked and steps (i) to (iii) will often need to be revised at frequent intervals. The validity of uie solution depends on the correct choice of theory (piiysicnl and mathematical model), the ability to identify model parameters correctly and accuracy in the numerical solution method. In iiian> cases, the system will not be fully understood, thus leaving large areas of uncertainty. The relevant theory may also be very difficult to apply. In such cases, it is then often necessary to make simplifying assumptions, which may subsequently be eliminated or

improved as a better understanding is obtained. Care and judgement must be taken such that the model does not become over complex and'that it is not defined in terms of immeasurable parameters. Often a lack of agreement can be caused by an incorrect choice of parameter values, which can even lead to quite contrary trends being observed dui-'ng the course of the simulation. It is evident that these parameters to which the model response is very sensitive have to be chosen or determined with greatest care.It should be noted that often the model does not have to give an exact fit to data as sometimes it iuuj be sufficient to s ;mply have a qualitative agreement with the process.1.1.4 Simulation ToolsMar.y different digital simulation software packages are available on the market. Fortunately many, but not 'til, conform tc the standard strucfre of a Continuous System Simulation Language (CSSL). The programming structures for aii CSSL languages are very similar. In addition, all CSSL languages are adjuncts to other high level languages such as FORTRAN, PASCAL or BASIC and tin s provide the programmer with ail the facilities and all the power of the host language.()ther interesting features of simulation tools concern user interfacing, compu.mg power, portability to various computer systems, optimisation and parameter estimation. Some tools allow a graphical set-up of a mode! Some languages, for example ACSL and ESL, a development by the ISIM-group as advertised in the back of this book, run on PC's and larger machines, and include more powerful numerical algorithms and supply many predefined building blocks, which facilitate such tasks as the modelling of control systems.

Mathematical software, such as MATLAB and MATHEMATICA have great computing power and may be portable to almost any available computer system. One useful application of modelling and simulation is optimisation of a process. MATLAB and SIMUSOLV include powerful algorithms for nonlinear optimisation, which can also be applied for parameter estimation. For this latter purpose SIMUSOLV is an excellent tool especially for practical work owing to its flexibility in handling experimental data (Heinzle and Saner, 1991). Some eharacteristics of the differing simulation programs are given in Table 1.1. Optimisation and parameter estimation are also discussed in greater detail in Sees. 2.4.1 and 2.4.2. Recent surveys of the differing packages now available include Matko et al. (1992) arid Wo/.ny and Lut?. (1991).1SIM and HSL, 1SIM International Simulation Ltd., Technology House. Salford University Business Park. Lissadd Street, Salford M6 6AP. UK; STELLA, High-performance Systems Inc.. 13 Dartmouth College Highway, Lyme, New Hampshire, 03768. USA; MATLAB, The Math Works, Inc., 21 Eliot Street. South Nntick, MA 01760, USA; MATHEMATICA, Wolfiam Res. Inc., P.O. Box 6059, Champaign. Illinois 61821, USA; ACSL, SIMUSOLV, Mitchcll & Gautllier Associates, 73 Junction Square Dr., Concord, MA 01742-3096, USA: MODEL WORKS, A. Fischlin, Inst. Terrestr. Ecology, ETH, Grabcnstr. 11, CH-8952 ScUieren, Switzerland; SIMNON, Oepartment of Automatic Control, Lund Institute of Technology, Sweden; SPEEDUP, Aspen Technology. Inc. Ten Canal Park. Cambridge, Mass. 02141, USA.

The drying characteristics of wet solids are general described by the drying rate curves. Such curve with moisture contain verses time and drying rate verses moisture contain are

shown below. Generally, experimental evaluation of this curve is done before performing design calculation.

Consider that the wet solids with initial moisture content (Xi) are exposed to air of constant temperature and humidity. If we then measure the moisture content with time (i.e. moisture content of material is measured at various values of time), then curve as shown in Fig. (a) is obtained from the collected data. The curve relates the moisture content on dry basis with time. It is clear from the curve that the moisture content of solids decreases with time and after some time it remains constant at X , which is the equilibrium moisture content.

From this curve, we can draw another type of curve which is known as rate of drying curve. This curve is much more descriptive of drying process. The rate of drying gives relationship between rate of drying, expressed as, the moisture evaporated per unit time per unit area of drying surface and moisture content on dry basis. This curve can be constructed by measuring the slopes of tangents drawn to the curve of X v/s at various values of moisture content and then calculating rate as N = -Ss dX/d x 1/A, where Sg is the weight of dry solids and A is the area of drying surface.

Fig. C shows the rate of drying curve. The section AB of the curve represents the warming up period during which the temperature of the solid is becoming equal to the temperature of drying air. From B to C, the curve is straight line parallel to x-axis representing the constant rate of drying, thus the section BC is called constant rate period during which the layer of water on the surface of solid is being evaporated. The rate of drying is constant from B to C as the drying takes place from a saturated surface. The section (CE) of the curve represents the falling rate period composed of first falling rate period (CD) and second

falling rate period (DE). From point 'C1 onwards some dry patches have started forming on the surface of the solid. The rate of drying decreases for the unsaturated portion and hence rate for total surface decreases. The section CD of the curve represents the period corresponding to the zone of unsaturated surface drying. The moisture content at which constant rate period ends i.e. at which unsaturated surface drying starts is known as critical moisture content. After point D, (die surface of the solid is completely dry and now internal moment of moisture starts coming to the surface and this is continued up to the point E, where the equilibrium is attained. The rate of drying over section DE is governed by the rate of internal moisture movement. The second falling rate period (DE) represents zone where internal moisture movement controls.

5.3 Mathematical Modelling 5.3.1 For Mechanical dryimg of onion5.3.1.1 By using falling rate equation(model 1): As we know that drying of onion is falling rate phenomena. We consider equation of falling rate period. -S/A X dX/dt = m (x-x0) - --1Where S = Solid content of material (kg)A = Area of Drying (m2)m = Slope of drying curve for falling rate.X1 = Initial moisture contentX = Moisture content at any time t.X0 = Equilllibrium moisture content.Solving equation 1 we get-S/A X dX/x-x0 = mdtIntegrating both side

When x = x1 t = 0x = x t = t

Considering m as constant

Let mA/S = KWe get

ln = kt

= e-kt

x-x0 = (x1-x0) e-kt

x = (x1-x0) e-kt + x0 --2Equation 2 represents the model equation i.e. model I.5.3.1.2 By using equation of diffusion mechanism. The drying equation based on diffusion mechanism as reported by McCabe and Smith is as follows :-

MR = ….1

Where M = moisture content (db) at time t (h). subscripts o and e = initial and final values. A = the shape factor and k = the drying constant. The value of A and k were graphically determined from fig. And presented in table. It was found that both the shape factor and drying constant were temperature dependent and the relationships between A and t and k and t were determined graphically.K = 0.0244 exp 0.0556t

A = 22.477T-0.7241

Where, T = the drying air temperature in 0C. Thus the drying equation derived from experimental observations becomes

(22.477T0.7241) exp (0.244 exp0.0556T) t …….2

5.3.2 For osmotic dehydration we know that curve for osmotic dehydration has equation

x = a0e a1t …1by solving the above equation by linear least square method we obtain value of a0 and a1. Hence getting the values the equation ..1 cane also be assumed as

x = x1edct/10 …2Where X = moisture content at time td = ratio of osmotic solution volume to onionC = concentration of NaCl in the brine.Here equation …2 is the model equation for the osmotic dehydration of onion. i.e (model 2)

4.4 Simulation and Testing result. 5.4.1 For model I and IISample A) Here we consider moisture content during forced drying only.

Here , m = 0.8941 X 0 = 0.837 % A = 0.0629m2 X1 = 47.936% S = 0.05946 kg T = 70 C K= 0.9458 A = 1.0466 , K = 1.357

We get equations Model I as -0.9458t X = 47.099 e + 0.837

Model II as -1.357t X= 49.2938 e + 0.837

S.NO Time {Hr} Actual M.C% Simulated Readings

Model I Model II1 0.0 47.936 47.941 50.13082 0.5 25.545 30.001 25.853 1.0 15.881 18.96 13.534 1.5 9.227 12.08 7.275 2.0 4.926 7.81 4.106 2.5 2.033 5.16 2.497 3.0 1.33 3.52 1.678 3.5 0.952 2.50 1.269 4.0 0.837 1.87 1.05

Sample B ]

Here we consider moisture content of onion during forced( Tray drying)

Here the values of constants determined experimentally are:-

M = 0.880 X 0= 1.854 % A = 0.0565m2 X1= 53.335 % S = 0.053027 kg T = 70 C K= 0.9376 A = 1.0466 , K = 1.357

We get equations Model I as -0.9376t X = 51.481 e + 1.854

Model II as -1.357t X= 53.880 e + 1.854

S.NO Time Actual Simulated Reading

M.C% Model I Model II1 0 53.33 53.33 55.732 0.5 28.98 34.07 29.183 1.0 18.53 22.01 15.724 1.5 10.05 14.46 8.885 2.0 5.79 9.75 5.426 2.5 3.24 6.79 3.667 3.0 2.48 4.94 2.778 3.5 2.07 3.79 2.329 4.0 1.85 3.064 2.09

5.4.2] For Osmotic dehydration

Sample A ] Here values of constants are determined by experimental readings as

X1 = 88.531% d = 2:1=2 C = 5 % = 0.05

the equation becomes

-0.01 t X = 88.531 e

S.NO Time (Min) Actual

M.C %Simulated Reading

M.C%1 0 88.53 88.532 12 80.35 78.523 24 72.17 69.644 36 64.0 61.765 48 55.82 54.786 60 47.94 48.59

Sample B] Here the values of constant are determined by experimental reading as

X1 = 88.899 d = 2:1=2 C = 10 % = 0.1

The equation becomes -0.02 t X = 88.899 e

S.No Time { min } Actual M.C % Simulated

ReadingM.C %

1 0 88.90 88.902 12 76.69 69.933 24 62.47 55.014 36 54.27 43.275 48 46.05 34.0

CONCLUSION

Onion (Allium Cepium) the most utilized vegetable in the world after potato was successfully used for drying study.

Through experiments we tried to study different aspects of Dehydration by using comparative graphs based on size, onion type, brine concentration and type of drying.

We also studied the phenomena of Osmotic Dehydration was also applied for onion dehydration and its effect on cost and quality were studied successfully.The technological consequences of our study are therefold:-

1) Dehydration of white onion renders good quality product.2) As the size decreases rate of drying increases.3) Osmotic dehydration reduces 20% of time required for

drying.4) The drying of onion takes place in falling rate period and is

governed by moisture dehydration.5) Solar dried onion gives better quality than mechanical

one.We also tried to study the drying process by creating model

equations for mechanical drying as well as osmotic dehydration. This models were simulated and gave satisfactory results.

This data would be useful in design and development of dryer and improvement in processing techniques of onions.

REFERENCES

1. Arun Muzumdar, “Drying of Solids.”a. Kalyani Pubs, Varanasi (P.P. 226-

248)2. K. A. Gavhane, “ Mass Transfer – II”

a. Nirali Pubs, Pune (P.P. 6.1-6.20)3. John Ingham “chemical Engineering Dynamics.”

a. V.C.H. Pubs, New York (P.P. 1-10)4. Mc Cabe Smith “ M. T. & its Applications.”

a. John uliley Pubs (P.P. 767 – 789)5. V. N. Pawar “ Solar Drying of White onion flakes”

a. Indian Food Packer, Jan-Feb (1998) (P.P. 15-21)

6. Arun Mujumdar “Drying (89)”.a. Oxford Pubs Washington D. C. (P.P 21-51)

7. Hardeep Singh “Dehydration Kinetics of Onion”.a. J. Food. Sci. Technol, 2000 (Vol 37) (P.P.520-526)

8. Report No. 85394www.epa.gov.

9. V. R. Sagar “Preparation of Onion Powder”.a. J. Food. Sci. Technol, 2000 (Vol 38) (P.P.525-528)