drum dryers
TRANSCRIPT
Presented by: AMNINDER SINGH SEKHON
(Batch-2014)Registration No. L2014DT03Bachelor in Dairy Technology
Presented to:ER . NARENDER KUMAR
ASSTT. PROF. (DAIRY ENGINEERING)
Department of Dairy Engineering , CODST, Guru Angad Dev Veterinary and Animal Science University
(GADVASU), Ludhiana, Punjab, India -141001
6 May, 2016
Drum dryers
The removal of nearly all the water present through vaporization is known as drying or dehydration.
Removal of moisture to a very low moisture content nearly to a bone dry condition
Bone dry material is the material from which all the moisture has been removed
INTRODUCTION
• Drying is carried out for one or more of the following reasons:
To eliminate moisture which may lead to corrosion and decrease the product or drug stability.
To improve the good properties of a material, e.g. flowability, compressibility.
To reduce the cost of transportation
To make the material easy to handle
to increase the shelf life
PURPOSES OF DRYING
Minimal chemical and biochemical degradation reactions
Selective removal of water over other salts and volatile flavor and aroma substances
Maintenance of product structure (for a structured food)
Control of density
Lack of contamination or adulteration
Minimal product loss
GOALS OF DRYING
Rapid rate of water removal
Inexpensive energy source (if phase change is involved)
Facility of continuous operation
Noncomplex apparatus (reliable and minimal labor requirement)
Minimal environmental impact
DRYING SHOULD ACHIEVE THESE GOALS (CONTD…)
In drying processes, the main operation usually
carried out on solid materials, e.g. powders, or products
Drying in most of the cases means the removal of relatively small amounts of water from solids .
Evaporation include the removal of large amounts of water from solutions.
DIFFERENCE BETWEEN DRYING AND EVAPORATION
In most cases, drying involves the removal of water at
temperatures below its boiling point, whereas evaporation means the removal of water by boiling a solution.
In drying , water is usually removed by circulating air over the material in order to carry away the water vapour , while in evaporation , water is removed from the material as pure water vapour mixed with other gases.
The drum dryer is an indirect type dryer in which the
milk to be dried is maintained in a thin film on a rotating steam heated drum.
The milk being dried is spread over the outside surface of the dryer. Clinging to it and drying continues as the hot drum rotates.
DRUM DRYING
At the end of a revolution, the drum comes to a
‘doctor blade’ which scrapes the dried film from the drum, when the product has made about three-quarter of a complete rotation on the drum surface
The process is also known as roller drying
Drum drying requires less space and is more economical than spray dryers for small volumes. The ratio of steam consumption to water evaporation is from 1.2 to 1.6:1
Drum Drying(contd..)
Diameter of typical drums ranges from 0.5m to 6m and the
length from 1m to 6m.
In operation , steam at temperature up to 200 degree Celsius heats the inner surface of the drum.
The moist material is uniformly applied in a thin layer(0.5mmñ2mm)on to the outer drum surface.
SYSTEM DESCRIPTION
The energy consumption in a drum dryer may range between
1.1 kg steam per kg of evaporated water and 1.6kg steam per kg of evaporated water , corresponding to energy efficiencies of about 60%-90%.
Under ideal conditions ,the maximum evaporation capacity of a drum dryer is 80 kg H2O/hour m2
Number of drums (a) single drum, (b) double drum, or (c) twin
drum.
Pressure surrounding the product (a) atmospheric, and (b) vacuum.
Feeding arrangement: (a) nip feed, (b) splash feed, (c) dip feed or (d) roller feed.
Material of construction: (a) alloy steel, (b) stainless steel, or (c) chrome, or nickel plate steel
CLASSIFICATION
a)Roller feed b) Nip feed.
Freeze drying is a process used to dry extremely heat –
sensitive materials. It allows the drying , without excessive damage
In this process the initial liquid solution or suspension is frozen, the pressure above the frozen state is reduced and the water removed by sublimation.
Thus a liquid –to-vapour transition takes place, but here three states of matter involved: liquid to solid, then solid to vapour
FREEZE DRYING
large
production capacity
continuous operation
simple structure
easy to operate less failure
low maintenance
costs
ADVANTAGES OF DRUM DRYING
The equipment
is large, one-time
investment are high;
installation and removal are
difficult;
The heat loss is large, thermal
efficiency is low
material in the dryer stay for a
long time
DISADVANTAGES OF DRUM DRYING
Not able to process salty or other corrosive materials due to potential pitting of drum surface
High cost of changing drum surface because of the precision machining that is required
Some products ,especially those with high sugar content , may not be easily scrapped off from the drum
Continued…