Further studies

Another case study analysing a sugar plant by heat integration methodology in a developing country has been recently published by Raghu Ram and Banerjee (2003). In this particular case pinch analysis was used to determine the hot utility requirement, which was found to be 9% less than the amount that was actually being consumed. Modifications to the

X

r

L r

—c

S

L r

j

L

ld ol

ld ol

Existing network Modified network

(a) Internal changes comprising rearrangement of the existing heat exchangers ld ol

First

effect

Condensate Vapour

Second effect

Condensate Vapour

Third effect

Vapour Condensate

Flash drum-1

Fourth effect

Vapour Condensate

Flash drum-2

Condensate

Flash drum-3

Existing condensates gathering system

Flash drum-1

Flash drum-2

Flash drum-3

Existing condensates gathering system

Modified condensates gathering system (b) Tuning of condensates gathering system into a pressure sequenced system

Fig. 4.16 Retrofit modifications.

Modified condensates gathering system (b) Tuning of condensates gathering system into a pressure sequenced system

Fig. 4.16 Retrofit modifications.

evaporator system were proposed that would reduce the steam consumption by 9 t/h, in line with the results provided by the pinch study. Additionally, the analysis was extended to include elements of total site targeting and analysis. The findings lead to proposals for a cogeneration system producing 26.8 MW of power.

Further case studies related to energy efficiency in the sugar industry have been presented; for example, Klemes et al. (1999c) and Grabowski et al. (2001, 2002a,b). Heat integration analysis of a brewery with resultant considerable energy savings were presented by Hufendiek and Klemes (1997). Klemes et al. (1998) presented a comprehensive study covering a sugar plant, a raw sunflower oil plant and a corn crystal glucose plant.

Thin juice

Sugar

Green syrup

White syrup

Second. condensate

Thin juice

Second. condensate

Exhausted slices

Water Beet

Sugar

White syrup

Fig. 4.17 Modified heat exchanger network and overall process.

Exhausted slices

Water Beet o o a

Fig. 4.17 Modified heat exchanger network and overall process.

Fig. 4.18 Modified heat exchanger network.

Enthalpy (kW)

Fig. 4.19 Composite curves for the modified network. Hot utility, 14 850 kW; cold utility 7 015 kW.

Enthalpy (kW)

Fig. 4.19 Composite curves for the modified network. Hot utility, 14 850 kW; cold utility 7 015 kW.

Several case studies have been documented by the Department of the Environment, Transport and the Regions (DETR, 1996, 1997). They developed a waste heat recovery potential for the United Kingdom alone of 8.3 PJ/year which at that time represented around £14 million, more than £20 million in today's energy prices. They concluded that, in the dairy industry, the pasteurisation process is already highly efficient in terms of heat recovery (up to 95%), but that this was not the case for sterilisation, which is more energy intensive with bottle sterilisation consuming 300500 MJ/t. They mentioned several energy saving measures implemented by Associated Dairies.

00 2000.00 4000.00 6000.00 8000.00 10000.00 0.12E+05 0.14E+05 0.16E+05 Enthalpy (kW)

Fig. 4.20 Grand composite curve for modified network. Table 4.4 Overview of the sugar plant retrofit results

Network

Steam consumption

Cooling water consumption

Total area (m2)

Available Used

Energy cost (£/campaign)

Existing 26.4 42.2

Retrofitted 24.0 38.3

(absolute)

250 250 0

5.601 5.601

4.317 5.091 774

647670 591540 56 129

The other food and drink processes reviewed by DETR (1996, 1997) were bakeries, breweries, drying in the production of flavourings and ingredients, and a developed example of a breadcrumb dryer plant where an energy saving potential of about 30% was identified.

A number of case studies have been completed by Linnhoff March-KBC Advanced Technologies (see Section 4.7.2). The details are mostly confidential, but publicity information can be obtained from the company (Table 4.5). This table demonstrates the variety of potential applications of heat integration and energy efficiency improvement in food processing industries.

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