Presentation on basic introduction of equipments used in dairy technology

By:- AMRITA RANA(2113920)

GAYATRI BHATIA(2113910)

DOON VALLEY INSTITUTE OF ENGINEERING AND TECHNOLOGY, KARNAL

Dairy Technology•Dairy technology is a part of food engineering which deals with the processing of milk & its product

•It is one of the main part of F.E which provides so many products with good nutritive value to us

•E.g. cheese, paneer, yogurt, curd, milk (varieties), khoya, lassi, ice-cream, butter, ghee, milk powder, cream etc

•Indian diary technology has made a rapid progress with 2nd position of milk production

•As there are so many products which are made by milk, thus different equipments are used for processing of milk and formation of different milk products.

Equipments Mainly used •Homogenizers

•Pasteurizers

•Evaporators

•Dryers

•Freezers

HomogenizerIntroduction

* A homogenizer is a machine that takes a substance and makes it a uniform consistency and helps reduce separation.

*It reduces the big fat globules into smaller one.

*Provides uniform consistency and give a smooth, rich flavor.

*One of the oldest applications of homogenizer is in milk processing.

*Homogenizer mainly works by agitating the liquid that is to be homogenized

Types of homogenizers• Single stage homogenizer

• Two stage homogenizer

Two stage Homogenizer

Difference between single stage and two stage HomogenizerSINGLE STAGE

Pressure used= 2500psi

Mean size= 0.5um

Range = 0.2 to 2um

Clustering takes place

TWO STAGE

Pressure used

1. 1st stage= 2000psi

2. 2nd stage=500psi

No clustering takes place

More efficient than 1st stage

Commonly used in industrial scale

Pasteurizer A pasteurizer is a device which pasteurizes, treating a food product to kill disease-causing organisms such as bacteria.

Milk is one of the most widely pasteurized foods, but pasteurizers can also be used with a variety of other liquids, and some other foods can be pasteurized as well.

Pasteurization is used to make food safer, so that it can be sold commercially without concerns that people will get sick when they consume it.

People can also pasteurize foods at home when processing foods they have made.

Methods of Pasteurization1. Batch pasteurization

2. Continuous pasteurization

3. Flash pasteurization (HTST)

1.Batch pasteurization:•Batch (or "vat") pasteurization is the simplest and oldest method for pasteurizing milk. Milk is heated to 63 degrees Celsius in a large container and held at that temperature for 30 minutes.

•This process can be carried out at home on the stovetop using a large pot or, for small-scale dairies, with steam-heated kettles and fancy temperature control equipment.

•In batch processing, the milk has to be stirred constantly to make sure that each particle of milk is heated

Batch pasteurizer

2.Continuous pasteurization: Continuous processing, a high temperature short time (HTST) pasteurizer is used. The milk is heated to a temperature of 72 C and held for 15 seconds and then cooled rapidly. The heat treatment is accomplished using a plate heat exchanger.

Continuous pasteurizer

3)High-temperature short-time (HTST) pasteurization, or flash pasteurization, is the most common method these days, especially for higher volume processing. This method is faster and more energy efficient than batch pasteurization

Flash pasteurizer (HTST)

EVAPORATORS An evaporator is a device used to turn the liquid form of a chemical into its gaseous form. The liquid is evaporated, or vaporized, into a gas.

Or

Evaporation is an important unit operation commonly employed to remove water from dilute liquid foods to obtain concentrated liquid products.

Removal of water from foods provides microbiological stability and assists in reducing transportation and storage cost

Examples :-

Concentration of milk to produce condensed milk

The manufacture of tomato paste, usually around 35-37% total solids, obtained by evaporating water from tomato juice, which has an initial conc. Of 5-6% total solids.

EvaporatorVapor out

Feed inSteam in (Saturated vapor)

Product out

Condensate out (Saturated Liquid)

Vapor Separator

Heat Exchanger

Vaccum for non condensable

Condensor unit

Coolant In

Coolant out

The basic factors that affect the rate of evaporation are the:

• rate at which heat can be transferred to the liquid,

• quantity of heat required to evaporate each kg of water,

• maximum allowable temperature of the liquid,

• pressure at which the evaporation takes place,

• changes that may occur in the foodstuff during the course of the evaporation process.

Types of Evaporators 1. Open kettle or pan

2. Horizontal-tube natural circulation evaporator

3. Vertical-type natural circulation evaporator

4. Long-tube vertical-type evaporator

5. Falling-film-type evaporator

6. Forced-circulation-type evaporator

7. Agitated-film evaporator

8. Open-pan solar evaporator

FIGURE 8.2-1. Different types of evaporators: (a) horizontal-tube type, (b) vertical-tube type,

FIGURE 8.2-1. Different types of evaporators: (c) long-tube vertical type, (d) forced-circulation type.

Methods of Operation of Evaporators

1. Single-effect evaporators

2. Multiple effect evaporators

• Forward-feed multiple-effect evaporators

• Backward-feed multiple-effect evaporators

• Parallel-feed multiple-effect evaporators

1. Single-effect evaporators:

FIGURE 8.2(2). Simplified diagram of single-effect evaporator

•The feed enters at TF •Saturated steam at TS enters the heat- exchange section.•Condensed steam leaves as condensate or drips. •The solution in the evaporator is assumed to be completely mixed•Hence, the concentrated product and the solution in the evaporator have the same composition.•Temperature T1 is the boiling point of the solution.•The temperature of the vapor is also T1, since it is in equilibrium with the boiling solution. •The pressure is P1, which is the vapor pressure of the solution at T1.

If the solution to be evaporated is assumed to be dilute and like water, then 1 kg of steam condensing will evaporate approximately 1 kg of vapor (if the feed entering has TF near the boiling point)

The concept of an overall heat-transfer coefficient is used in the calculation of the rate of heat transfer in an evaporator

The general equation can be written as:

Where-q is the rate of heat transfer in W (btu/h), U is the overall heat-transfer coefficient in W/m2. K (btu/h ft. °F),A is the heat-transfer area in m2 (ft2),TS is the temperature of the condensing steam in K (°F), T1 is the boiling point of the liquid in K (°F).

Single-effect evaporators are often used when the required capacity of operation is relatively small and/or the cost of steam is relatively cheap compared to the evaporator cost.

However, for large-capacity operation, using more than one effect will markedly reduce steam costs.

Multiple effect evaporator •A multiple-effect evaporator, as defined in chemical engineering, is an apparatus for efficiently using the heat from steam to evaporate water.

• In a multiple-effect evaporator, water is boiled in a sequence of vessels, each held at a lower pressure than the last.

• Because the boiling temperature of water decreases as pressure decreases, the vapor boiled off in one vessel can be used to heat the next, and only the first vessel (at the highest pressure) requires an external source of heat.

• Originally designed for concentrating sugar in sugar cane juice, it has since become widely used in all industrial applications where large volumes of water must be evaporated, such as salt production and water desalination

Multiple effect evaporator

2. Forward-feed multiple-effect evaporators:

•A single-effect evaporator is wasteful of energy.

•The latent heat of the vapor leaving is not used but is discarded.

•Much of this latent heat, however, can be recovered and reused by employing a multiple - effect evaporator.

•A simplified diagram of a forward-feed triple-effect evaporation system

FIGURE 8.2-3. Simplified diagram of forward -feed triple-effect evaporator.

•If the feed to the first effect is near the boiling point at the pressure in the first effect, 1kg of steam will evaporate almost 1 kg of water.•The first effect operates at a temperature that is high enough that the evaporated water serves as the heating medium to the second effect.•Here, again, almost another kg of water is evaporated, which can then be used as the heating medium to the third effect•As a very rough approximation, almost 3 kg of water will be evaporated for 1 kg of steam in a three-effect evaporator. •Hence, the steam economy, which is kg vapor evaporated/kg steam used, is increased. •This also holds approximately for more than three effects. •However, the increased steam economy of a multiple-effect evaporator is gained at the expense of the original first cost of these evaporators. In forward-feed operation as shown in Fig. 8.2-3, the fresh feed is added to the first effect and flows to the next in the same direction as the vapor flow. •This method of operation is used when the feed is hot or when the final concentrated product might be damaged at high temperatures. •The boiling temperatures decrease from effect to effect. This means that if the first effect is at P1 = 1 atm abs pressure, the last effect will be under vacuum at a pressure P3.

3. Backward-feed multiple-effect evaporators: In the backward-feed operation shown in Fig. 8.2-4 for a triple-effect evaporator, the fresh feed enters the last and coldest effect and continues on until the concentrated product leaves the first effect.

FIGURE 8.2-4. Simplified diagram at backward-feed triple-effect evaporator.

•This method of reverse feed is advantageous when the fresh feed is cold, since a smaller amount of liquid must be heated to the higher temperatures in the second and first effects. •However, liquid pumps must be used in each effect, since the flow is from low to high pressure.•This reverse-feed method is also used when the concentrated product is highly viscous. •The high temperatures in the early effects reduce the viscosity and give reasonable heat-transfer coefficients.

4. Parallel-feed multiple-effect evaporators:

• Parallel-feed in multiple-effect evaporators involves the adding of fresh feed and withdrawal of concentrated product from each effect.

•The vapor from each effect is still used to heat the next effect.

•This method of operation is mainly used when the feed is almost saturated and solid crystals are the product, as in the evaporation of brine to make salt.

Uses of evaporators•An evaporator is used in an air-conditioning system to allow a compressed cooling chemical• It can also be used to remove water or other liquids from mixtures. The process of evaporation is widely used to concentrate foods and chemicals as well as salvage solvents. In the concentration process, the goal of evaporation is to vaporize most of the water from a solution which contains the desired product. In the case of desalination of sea water or in Zero Liquid Discharge plants, the reverse purpose applies; evaporation removes the desirable drinking water from the undesired product, salt.•One of the most important applications of evaporation is in the food and beverage industry. Foods or beverages that need to last for a considerable amount of time or need to have certain consistency, like coffee, go through an evaporation step during processing.•In the pharmaceutical industry, the evaporation process is used to eliminate excess moisture, providing an easily handled product and improving product stability. Preservation of long-term activity or stabilization of enzymes in laboratories are greatly assisted by the evaporation process.•Another example of evaporation is in the recovery of sodium hydroxide in kraft pulping. Cutting down waste-handling cost is another major reason for large companies to use evaporation applications. Legally, all producers of waste must dispose of waste using methods compatible with environmental guidelines; these methods are costly. By removing moisture through vaporization, industry can greatly reduce the amount of waste product that must be processed.

DryersINTRODUCTION

The term drying refers generally to the removal of moisture from a substance. It is one of the oldest, most commonly used and most energy consuming unit operation in the process industries.

Drying is often necessary in various industrial operations particularly in chemical process industries to remove moisture from a wet solid, a solution or a gas to make it dry and choice of drying medium is depends on the chemical nature of the materials.

Three basic methods of drying are used today

1) sun drying, a traditional method in which materials dry naturally in the sun,

2) hot air drying in which matrials are exposed to a blast of hot air and

3) freeze drying, in which frozen materials are placed in a vacuum chamber to draw out the water.

Types of dryers1. Drum dryers

2. Flash dryer

3. Fluidized bed dryer

4. Screen conveyor dryer

5. Spray dryer

6. Vacuum dryer

7. Tray dryer

8. Rotary dryer

9. Freeze dryer

10. Tower dryer

11. Screw conveyor dryer

12. Thin film dryer etc

Spray drying It is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals

Spray dryer

Drum drying It is a method used for drying out liquids from raw materials with drying drum. In the drum-drying process, pureed raw ingredients are dried at relatively low temperatures over rotating, high-capacity drums that produce sheets of drum-dried product. This product is milled to a finished flake or powder form. Modern drum drying techniques results in dried ingredients which reconstitute immediately and retain much of their original flavor, color and nutritional value.

Some advantages of drum drying include the ability of drum dryers to dry viscous foods which cannot be easily dried with other methods. Drum dryers can be clean and hygienic and easy to operate and maintain.

Other products where drum drying can be used are for example starches, breakfast cereals, baby food, instant mashed potatoes to make them cold water soluble.

Drum dryer

Fluidized bed dryer

In fluid bed drying

heat is supplied by the fluidization gas, but the gas flow need not be the only source. Heat may be effectively introduced by heating surfaces (panels or tubes) immersed in the fluidized layer.

Freezers•Those equipments which help in the freezing process so as to maintain the shelf life of a product and

•Prevents the growth of mo’s

•Slow down the self decomposition of food products and enzymatic activity of product and chemical changes within the product.

Ice cream freezer•Batch freezers

•Continuous freezers

A batch freezerIt is a piece of equipment used in the commercial production of ice cream and frozen desserts, like gelato and sorbet. As the name suggests, this freezer makes frozen desserts in batches that can vary in size, with the size of each being controllable by the operator. Many small ice cream stores and gourmet shops make their ice cream in this way:

Definite quantity of the mix is frozen at a time

Batch freezer

Continious freezer Continuous freezing, which uses a steady flow of mix,

The principle of operation is very similar to that of a batch freezer, except that the freezing is done under pressure(which increases the heat transfer rate) and the air is forced in or drawn into the freezing chamber continuously at a metered rate.

Continuous freezer

Any queries?

Thank you