Epp

a) 7888.32

b) 2955.12

Finishing and clarification a) 12621.31

Dewatering a) 7099.49

a) 1577.66

b) 1083.56

a) 8677.15

b) 3743.16

a) 11043.7

Wet pomace

Blending a) 338.41

Slush-freezing Filling and seaming Blast-freezing Storage

a) 7099.49

a) 1577.66

b) 1083.56

a) 11043.7

Blending

Slush-freezing Filling and seaming Blast-freezing Storage

a) 8677.15

b) 3743.16

Water evaporated a) 6985.1

b) 2872.88

a) 1533.32

a) 1353.64

Concentrated citrus juice

Figure 3. Flow diagram and material balance flow sheet for a concentrated citrus juice production plant with working capacity of 20,000 kg of raw oranges per hour and 10,000 kg of raw lemons per hour. The data reported here are expressed as kgh-1; symbol (a) refers to orange, while symbol (b) to lemons. Stream identification symbols: COWE, citrus oils and water emulsion; EPP excess pulp and peel; PPS, peel, pulp, and seeds; WCW, water and citrus waste; WW, washing water. Source: Reprinted with permission from Ref. 11.

Raw citrus oils

Water evaporated a) 6985.1

b) 2872.88

a) 1533.32

a) 1353.64

Frozen concentrated citrus juice

Concentrated citrus juice

Figure 3. Flow diagram and material balance flow sheet for a concentrated citrus juice production plant with working capacity of 20,000 kg of raw oranges per hour and 10,000 kg of raw lemons per hour. The data reported here are expressed as kgh-1; symbol (a) refers to orange, while symbol (b) to lemons. Stream identification symbols: COWE, citrus oils and water emulsion; EPP excess pulp and peel; PPS, peel, pulp, and seeds; WCW, water and citrus waste; WW, washing water. Source: Reprinted with permission from Ref. 11.

2. Degree of concentration required (percentage dry solids in the product).

3. Heat sensitivity of product in relation to the residence time and temperature of evaporation.

4. The requirement for volatile recovery facilities.

5. Ease of cleaning.

6. Reliability and simplicity of operation.

7. Size of evaporator.

8. Capital and operating costs.

9. Product quality.

Evaporators are classified as natural circulation evaporators and forced circulation evaporators.

Natural Circulation Evaporators

These may be open or closed pan evaporators, short-tube evaporators (also known as calandria vacuum pans in the food industry) (Fig. 5), or long-tube evaporators. Natural circulation evaporators operate by the thermo-syphon principle. The density difference between the boiling liquor and the circulation leg produces the driving force for liquid circulation. Typical applications include beet sugar, low to moderately viscous liquors, and nonsalting materials.

Pan evaporators are heated directly by gas or electrical resistance wires or indirectly by steam. They have relatively low rates of heat transfer, low energy efficiencies, and cause damage to heat-sensitive foods. However, they have low capital costs and are easy to construct and maintain. They have found wide applications in the preparation of sauces, gravies, and jam or other preserves (12).

Short-tube evaporators consist of a vessel or shell that contains a bundle of tubes. The feed solution is heated by steam condensing on the outside of the tubes. Liquor rises through the tubes, boils, and recirculates by flowing back down through a wide central bore. The vertical arrangement of tubes promotes natural convection currents and, therefore, higher heat transfer rates. The flow velocity is typically 0.3-1 m/s (15). These evaporators have low capital costs and are flexible, although generally unsuited to high-viscosity solutions. They are widely used for concentrating syrups, salt, and fruit juices.

The long-tube evaporators consist of a vertical bundle of tubes, each up to 50 mm in diameter and 5-15 m high. The length-to-diameter ratio is 70:130 (15). Liquid is preheated almost to boiling point (evaporation temperature) before entering the evaporator. For low-viscosity (less than 0.1 N • s/m2) foods such as milk, the thin film of liquor is forced up the evaporator tubes and this arrangement is known as the climbing-film evaporator (Fig. 6). A great deal of foaming does not matter, but they are susceptible to caking (15). As steam is admitted to the chest of the evaporator, the liquid reaches the boiling point and evaporation starts; a lot of small vapor bubbles appears in the liquid and starts the two-phase flow. The bubbles expand and push the mixture of liquid and vapor upward, further heat is applied resulting in more vapor formed (plug flow). Farther upward the remaining liquid is maintained as a film on the tube wall with vapor flowing as a core (annular flow). In the final part of the tube, the film is bursting and the liquid appears as droplets in a flow of vapor (mist flow).

Table 2. Material and Energy Balance for the Evaporation Unit of the Concentrated Citrus Process

Parameter

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