Deodorisation

Sadanand PatelHBTI-K

Layout of Presentation

Refining (Physical/Chemical) What is Deodorization? Effect of Deodorization Chemistry of Odour Sources of Odour Principles Laws Process Variables Process Steps Operation(Batch, Semi-continuous and Continuous) Equipment Effect of Deodorization on Oil Quality Losses Newer Developments Utilities Consumption Deodoriser safety

Crude Oïl

Water degumming

Alkali Neutralisation

Deodorization

Refined Oil

Soapstock

Spent bleaching earth

Deodorizer Distillate

Mechanical Pressing

OILSEEDS

Oil ExtractionSolvent Extraction

WDG Oil

Acid degumming

Bleaching

Physical deacidificationDeodorization

Acid Gums

Deoiled Meal

Gums LECITHIN

Chemical Physical

Refining(Physical/Chemical)

Bleaching

This is usually the last stage of the refining process of edible oils

Today, the process is still commonly named ‘deodorisation’, but the objectives have become much broader than just the removal of off-flavours.

Quality defining process in the refining of oils to eliminate the FFA and odoriferous substances.

What is Deodorization?

High Temperature, High Vacuum, Live Steam Distillation Process

Distillation is a physical and not a chemical process and does not change the molecular structure of the components

Stripping of volatile components such as: FFA (in the case of physical

refining), contaminants (pesticides, light

PAH etc.)

Actual deodorisation by removal ofdifferent off-flavours

Thermal destruction of pigments (so-called heat bleaching)

Its Effects

Desirable

Some unwanted side-reactions cis-trans-isomerization, polymerization, conjugation, and so on

Removal of valuable minor components tocopherols, sterols etc.

Undesirable

If the oil is not properly pretreated,the oil can become darker duringdeodorization. This phenomenon isalso known as ‘‘color fixation’’

Chemistry of Odour

Fats & OilsPrimary Oxidation Products

Secondary Oxidation Products

Tertiary Oxidation Products

Factors DecompositionOxidation

Hydroperoxides

Aldehydes, Ketones, Diene and triene

Acids, Epoxides,Dimers, Oxirane rings

Most vegetable oil retains characteristicsundesirable flavors & odors that obtain duringprocessing.

Peroxides (primary oxidation products),Hydrocarbons, Aldehydes, Ketones (secondaryoxidation products), Tocopherols, Sterols, FFAare the main odoriferous and volatilecompounds need to remove.

As a total, odoriferous components generally addup to not more than 200 ppm.

Bleaching imparts “Earthy” flavors whereashydrogenation adds on odor and flavors that canbe described as undesirable.

Sources of Odour

Underlying Principle

Difference in volatilitiesAldehyde/Ketone > FFAs > Squalene > Tocopherols > Sterols > Sterols esters > TAGs

The degree of separation of a simple binary mixture is expressed in terms of the relative volatility of the two components. The theoretical separation ratio,α, is defined as

The vapour pressure for a given constituent is a function of the temperature and increases with increasing temperature (Clausius-

Clapeyron's equation)

Dalton's Law describes the vapour pressure of a mixture as the sum of the partial pressures of its single components

The partial pressure of the single components can be calculated following Raoult's law:

Whitman’s two film theory:

At any instant the rate of transfer of volatile components from the oil into the steam bubble is proportional to the difference in pressure inside the bubble and actual pressure in the vessel and interfacial area of the steam bubble.

Laws

Process Variables

Tem

per

atu

re

Pre

ssu

re

Tim

e

Stri

pp

ing

Stea

m

• Temperature has its influence on deodorization because the vapour pressure is directly proportional to it.

• T α Rate of removal of Volatile Substances

• An increase of nx17K decreases deodorization time by the factor 2n

• Increase in temperature also means that stripping steam can be reduced. This is important in reducing entrainment losses

• Short chain fatty acid deodorized at low temp and hydrogenated oil deodorized at higher temp because of higher FFA content and distinctive odor it imparts.

• Heat Bleach Effect is higher at higher temperature:

Deodorization Temperature

Higher Temperature is avoided because: Insufficient thermal stability of oils Economy of the process (high energy

consumption)

• If the pressure is decreased, the temperature required also decreases because a lower vapour pressure is then sufficient to ensure evaporation.

• Reduced pressure helps to protect the oil from oxidation because oxygen from the air is reduced almost to zero.

• The amount of distillation steam required is also directly proportional to the pressure. If the pressure is halved steam consumption also halves.

Deodorization Pressure

Higher P means more steam. More steammeans more possibility for entrainment.And more stripping steam will increasehydrolysis. This will increase oil lossesand lower quality

• The time necessary to separate a certain amount of undesired components from the oil depends mainly on the speed with which the necessary amount of stripping steam can be introduced

• Deodorization time also increases with the height of the oil in thedeodorizer, i.e., with the thickness of the oil layer that the stripping stream has to penetrate.

• Because all side reactions are also time dependent, deodorization time is kept as low as possible. In Europe, longer deodorization time and lower temperatures are preferred. In the U.S., the reverse is true

Deodorization Time

• External pressure of the gas adds to the Vapour pressure of volatiles in deodorizer and speed up their removal.

• Stripping agents with the lowest possible molecular weights are selected. In most cases, steam is the best solution, but sometimes nitrogen is preferred.

• Since the surface area of the oil is increased by bubble formation, the mass transferand consequently the distillation rate is increased.

• The height of the oil in the vessel also influences the consumption of steam because the steam has to work against the hydrostatic pressure to be able to penetrate the oilbefore being sucked off or distilling off from its surface.

Stripping Gas

A Carrier to the Undesired Components

where S is the total moles of steam, V, is the initial molar concentration of the volatilecomponent in the oil, and V, is the final molar concentration of the volatile component in theoil. When the initial FFA content is low, as in the case of a classical deodorization, (Va- Vo)becomes so small that the equation can be simplified as follows:

The amount of gas required for deodorization is directly proportional to the amount of oiland the absolute pressure in the deodorizer and inversely proportional to the vapourpressure of the pure volatile component at the process temperature and the overallvaporization efficiency E.

On the surface of the steam bubbles, the oil/steam contact must be maximized; there thesparge gas has its lowest specific volume, equivalent to the highest relative surface area.Athanassiadis (1991) postulated that 300,000 m3 was a minimum contact area of oil/steamfor every kilogram of gas injected to ensure good deodorization efficiency.

Process Optimization

To achieve a proper deodorization, an optimal deodorizing temperature, operating pressure,and amount of stripping gas are required. These are determined not only by the type and state

of the oil (chemically or physically refined), but also by the deodorizer design.

Today, most deodorizers used in the refining of soft oils operate at temperatures between230 and 26OoC, a pressure of 3 mbar or even lower, with a stripping steam consumption of~10 kg/ton of processed oil.

Refining chemical physical

Temperature 230 – 250 °C 240 – 265 °C

Pressure 3 mbar 2 mbar

Sparge steam 5 – 15 kg/t 7 – 20 kg/t

Time 45 – 90 min 45 – 90 min

Final FFA 0.03 % 0.05 %

Trans-increase 0.5 – 1.5 % 0.7 – 2 %

Tocopherol retention 70 – 90 % 60 – 80 %

Source@alfalaval

Unit operations of deodorization & Processing Steps

Degassing

Heating Up

Deodorization

Cooling

Polishing

Bleached Oil

Deodorized Oil

Deaeration

Heating

Stripping

Thermal action

Cooling

Polishing

To avoid excessive oxidation and hence risk of polymerization. Soft oils dissolve readily between 4 and 10% of their own volume of air and other

gases at ordinary temperature. Solubility increase with increasing in temperature. The relation between solubility

(S) and temperature (t) can be expressed as:

De-aeration

with S (%, v/v), at normalpressure and t in °Celsius

The bleached oil is sprayed into a tank under reduced pressure. The lower the pressure applied,the lower the residual oxygen in the oil. Usually the oil is heated to at least 80°C and sprayedinto a tank, which is kept at a pressure of 40 mbar. Some refiners even use the low pressure ofthe deodorizer or add some sparge steam in the spraying tank to improve deaeration.

Heating of the oil is usually accomplished in two stages. First stage,Oil is heated counter-currently in an oil-oil heat exchanger (economizer), with the finishedoil leaving the deodorizer. Second stage,Oil is heated under reduced pressure to deodorizing temperature with a high temperaturesource such as high pressure steam, heat transfer fluids. Saturated steam of -50 bar isrequired to heat the oil to 240-260°C.

Heating

(Heating energy required for a deodorizing system)

where O is the amount of oil (kg), T1 and T2 are the incomingand final temperature of the oil (°C), C is the average specific

heat capacity of vegetable oils [typically 2.2-2.4 kJ/(kg. °C)], fL is

the heat loss factor from radiation typically 1.05-1.15) and fR, is

the heat recovery factor [ 1 - (%heat recovery/100)].

Stripping

It is Conducted at a temperature between 230 and 260 oC, at a pressure between 2 and 4mbar and under injection of 0.5-2% sparging steam. From a thermodynamic point of view,the stripping agent takes over the part of the total pressure equal to its partial pressure. Asa consequence, the vapour-liquid equilibrium is reached at a lower molar fraction, xi,resulting in the removal of significantly more volatile substances only. Nitrogen

- inert and non-condensable gas- lower losses (no hydrolysis) and higher distillate quality- more powerful vacuum system required- profitability is very uncertain

Steam (Superheated)- most ‘evident’ choice- Boost up the vacuum when condensed- But support hydrolysis

The sparge gas is introduced into the oil through special steam distributors. These can besparge coils with very fine holes (between 0.5 and 2.5 mm) or even sintered metal pipes

The oil is then held in a retention sectionfor a certain amount of time for thermaltreatment – known as heat bleaching –that deals with undesirable pigments andensures the stability of the final product.The length of time the oil is kept in theretention section depends heavily on thedesired product specifications

Thermal action

Finally the oil is cooled in two stages.First in the economizer, and then to thespecified final temperature. It thenundergoes polish filtration and istransferred to subsequent processes,storage or packaging

Cooling

Oil polishing is done to remove any fineparticles of soaps , metallic salts rusts , filleraids, polymerized oil or other solidimpurities. Horizontal plate filters have longbeen used as polishing filters of choice fordeodorization.

Oil Polishing

Batch Processing

Processing Options

Semi-Continuous Processing

Continuous Processing

- Vertical Deodorizer

- Horizontal Deodorizer

• Thin Film Technology

• Packed Column Technology

• Dual Temperature Technology

Batch Process Batch deodorization is especially suitable for small

capacities (<50 ton /day) . Batch deodorizers mainly consist of welded

vertical cylindrical vessel with dished or conicalhead and made up of 304 stainless steel to avoiddeleterious catalytic activity of Cu & Fe

Vessel diameter are chosen to the depth of 8 to 10feet of oil and a similar amount of word space aboveto avoid entrainment loss.

Steam is injected into the bottom of the vessel Include a device to measure temperature and a

pressure gauge to indicate low pressure withindeodorizer.

In principle, semi-continuous deodorizationis an automaticallycontrolled batch-wiseprocess.

Used when frequentfeedstock changes of oilsensitive to crosscontamination.

Steam produced in thebottom deodorized oil-cooling section is sent in aclosed thermo siphon loopto the top bleached oilheating section to heat theincoming oil.

Main advantage is shorterhold up time , anddisadvantage is less heatrecovery than thecontinuous process.

Semi-Continuous Processing

Horizontal deodorizer

Continuous Processing

Vertical deodorizer

Continuous Processing

Vacuum system

Steam

Cooling water

To hot well

Demister

ScrubberSteam

VHE Final

Heater

Deaerator

Steam

Acid oil

Coolingwater

Citric acid

Steam

Steam

Steam

Polishing

filters

Economizer

Heater

Inlet filters

Cooler

CoolingwaterHigh pressure

steam boiler

Oil in Oil out

SoftColumn

columnPacked column technology

(Alfalaval Soft column)

Packed column technology

(Crown Works, MaxEfficiency

Deodorizing System)

Continuous Processing

Equipment

Scrubber• Single Scrubber• Double Scrubber

Stripping Column• Horizontal Column• Vertical Column

Vacuum System• Ejector Booster • Ice Condensation

This highly efficient, structured packed column isdesigned to condense and recover free fatty acids(FFA) and other volatiles from the deodorizationprocess and to prevent carryover of thesematerials to the vacuum system

Scrubber

• Composition of vapor phase Volatile components (FFA, odor components) Stripping steam Non condensable gases (air….)

• The volatile substances are condensed by creating an intimate contact between the vapor and fatty acid distillate circulating in the scrubber.

• The distillate which is circulated is at its lower possible temperature (just above its melting point).

StrippingColumn

The pre-treated and heated oil flows either by gravity or under pressure from the finalheater to the distributor on the top of the column. The distributor spreads the oil evenlyover the cross-section of the column. This oil then trickles down the structured packing,flowing as a thin layer on this extended surface until it reaches the bottom of the column.It then continues to the next process step. The counter current flow of the steam isachieved via a steam distributor installed in the bottom of the column or from anothersource. The oil in the column meets the stripping steam in a counter current flow.The column is under vacuum, so exposing the oil to the vacuum at a high temperatureremoves volatile substances and the steam carries them out to the vacuum outlet at thetop of the column. The height of the column is a function of the number of desireddistillation steps.

Horizontal Column

Vertical Column

Effect of Deodorization on Quality of Oil

Losses by evaporation

FFA are among the most easilyevaporated materials in fats and oils.Normally reduced to below 0.03%by deodorization.

Sterols, tocopherols and otherunsaponifiable matter may make upa large portion of the fatty matterare distilled from the oil.

Mono- and diglycerides which havebeen produced during refining, asthey have a lower molecular weight.

Losses by entrainment

Deodoriser distillate always containsa certain amount of ‘neutral oil’which has been mechanicallyentrained from the oil.

Mechanical entrainment (carryover)of oil by stripping steam is the mainunwanted loss in deodorization.

Losses in Deodorization

Newer Developments

Thin Film Technology

The first plant for large scale (250 MT/d) thin film seed oil deodorization wasstarted in 1996.

It had been known for some time that thin-film stripping theoretically hadconsiderable advantages over tray stripping. Because the steam passes over a verythin oil film in a true counter-current operation, the contact between steam and oilis optimized.

The surface area of the oil can be further increased by a special design of thepacked column. Other means to enhance mass transfer are eddy currents causedby wall heat transfer in the falling film design or centrifugal action if rotating disksare used.

However, there are still some major drawbacks,• Increased trans fatty acid level.• Removal of antioxidants and vitamins as a result of the very high effectiveness

of the operation.• Heat bleaching effect may be reduced

These deodorisers operate at two different temperatures in order toreach the best compromise between-• required residence time for actual deodorisation (longer time

at lower temperature) and• heat bleaching and stripping of volatile components (shorter

time at higher temperature).

The dual-temperature concept has been successfully introduced onan industrial scale. Both the low/high temperature and thehigh/low temperature concept can be applied.

Dual Temperature Technology

With such systems, the stripping steamis condensed on surface condensersoperating alternately at very lowtemperature (−30 ◦C).

The efficient sublimation of steam andother volatile matter will give a very lowpressure in the deodoriser (<1.5 mbar)and will strongly reduce odour emission.

Dry–ice condensing systems stronglyreduce the motive steam consumptionbut require extra electrical energy.

Commercially available systems consistof two or more freeze condensers withhorizontally or vertically orientatedstraight tubes, a refrigeration plant forthe generation of the cold refrigerantevaporated in the tubes and a vessel forthe defrosting and cleaning of the tubesafter a certain period of freezing.

Ice Condensation Vacuum System

Deodoriser distillate contains neutral oil. This refiningloss can be reduced by integration of a so-called ‘neutraloil recovery system’ (NORES) in the first part of thescrubber section. The purpose of this system is to recoverthe mechanical entrained neutral oil from the vapourphase before the volatile matter (FFA, tocopherols, sterols,

The vapour phase leaving the deodoriser is firstpartially condensed at a higher temperature, giving a socalled ‘hot distillate’ in which the least volatilecomponents (e.g. tocopherols and sterols) areconcentrated.

Complete condensation of the remaining, more volatilesubstances (mainly FFA) is then achieved in the secondso-called ‘cold scrubber’, giving an FFA-rich ‘colddistillate’.

Provided that the condensation temperatures of the hotand cold scrubbers are properly set, this concept gives avery good separation between the FFA and tocopherols.Combining NORES with a double scrubber in thephysical refining of soybean oil (for which processorsseem to have a growing preference) gives a ‘hotdistillate’ with 21.2% tocopherols

Dual Scrubbing System

Electric Power:

2 - 4 kWh depending on plant size

Add about 2.5 kWh for ice condensation

Steam(4 bar)

Steam (10 bar)

10-15kg Stripping Purpose

60 kg (with surface condensers)

20 kg with ice condensation

Heating Energy 105,000 kJ + 3,500 kJ/% FFA

Cooling Water (30⁰C)

9 m3 at ΔT 6⁰C

4 m3 at ΔT 6 T⁰C with ice condensation

Citric Acid: 0.05 kg (optional as synergist)

Utilities Consumption

Deodoriser safety

The deodoriser is operated at the highest temperature of the refining plant. The oil iskept under non-combustible conditions, due to the absence of air in the deodoriser. Afire hazard is possible when air is entrained in the deodoriser at high temperature.The following preventative measures should be used to avoid this situation:

Properly maintained equipment, to avoid air leaks. Trained personnel, to identifyair leaks and react to starting fires.

Well-established procedures for start-up, shutdown and maintenance.

The high-pressure boiler develops up to 90 bar pressure. Its condition and safetysystem integrity must be periodically checked.