Case study in Dairy Processing

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1. Case study or built example

Case study

2. Industry Sector


3. Industrial application

Cleaner production assessment was carried out in a dairy in the Netherlands as a part of the PRISMA project (Dutch University of Economic Affairs, 1991). 105 million litres of milk are processed every year, 92 million litres for market milk and 13 million litres for other dairy products.

4. Process description

After delivering in milk tanks to the plant the milk is separated. Depending on the required end product milk may be mixed with non-separated milk to obtain a correct fat content. Afterwards it is pasteurized and homogenized and packed into card boarder or glass packaging. A certain proportion is further processed into yogurt, custard and buttermilk. During the production process the product comes in contact to internal surfaces of pipes and equipment. This can lead to a reduction of products quality. To avoid it entire process and also specific pieces of equipment are cleaned and sanitised after each production day. Cleaning agents containing sodium hydroxide, hydrogen peroxide and peracetic acid are commonly used.

5. Assessment of Cleaner Production

At the beginning areas where large amounts of waste and emissions are produced were identified. It includes product losses to the effluent stream, the use of the detergents and the need for frequent cleaning and the high consumption for heating and cooling. In these areas different strategies of CP were developed.

1. Better emptying of production tanks

The filling of packaging containers with products is a batch process and at its end residual product remains in the processing vessel. Previous the CP project the rest was discharged to sewer with the effluent stream. Now it is collected and returned to the production process or is used as cattle feed.

This measure has reduced the product loss of the wastewater stream by 11.500 l which is 1.6% of the total product loss.

2. Elimination of rinsing between yogurt batches

Rinsing takes place between different batches of yogurt. The product losses are 110 litres per rinse or an amounted product loss of 22.800 litres per year. The total amount of rinse water is 2.500m3 per year. So a new procedure for product changeover was developed. The processing vessel drain of yogurt was let and then the next batch of yogurt was allowed into the system. The mixed zone is collected and used as animal feed. The rinse between two batches is avoided in this way.

As following consequence the product loss has been reduced by 60 litres per batch which is a total of 12.500 litres per year. Also the consumption of water is decreased by 25.00 m3 per year. Moreover the new concept took one hour less of work than the old procedure.

3. Reduced rinsing at product changeover

Rinsing between batches of sweet/sour and light/dark products was undertaken eight times with a total water consumption of 2000 litres. It was specified that six times are sufficient enough so that reduction of water consumption and furthermore costs savings are secured.

4. Optimisation of cleaning operations

An analysis showed that cleaning of pipes and equipment is an area of product losses. Furthermore it was found out by installing a trial in the cleaning procedure that there is potential to optimize cleaning operations.

Different changes to the cleaning cycle were taken:

  • Level controllers were installed on mixing vessel to control the required volume of cleaning water.
  • The output temperature of the heat exchanger was lowered to reduce the temperature of cleaning water.
  • A software program for better control of the cleaning cycle was installed.
  • The cleaning time was reduced by 20 minutes.

As a result of the changes the consumption of detergents was reduced by 23% and also the organic load of the wastewater was lowered.

5. Recovery of low grade heat

One step in processing procedure requires heating up the product to 90°C. Heat recovered from the return leg of the cooling water system is used to heat product up to 30°C. Steam is used to heat it up the rest of the way. This measure has reduced the consumption natural gas by 54.000 m3.

Checklist cp diary.JPG

Figure 1: List of identified Cleaner Production strategies

6. Results and Savings

Economic savings

' Savings per year in US$ Savings in certain areas in US$ Investment costs? Payback time
Total 94.000 Effluent discharge: 26.000 US$32.000
Others: 68.000
Better emptying of production tanks 6.000 Product recovery: 4.850 no
Effluent discharge: 1.150
Elimination of rinsing between yogurt batches 14.100 Product costs: 4.600 no
Effluent discharge: 2.100
Water consumption: 7.400
Reduced rinsing at product changeover 2.450 no
Optimisation of cleaning operations 40.100 Detergents: 28.500 US$3.150 One month
Effluent discharge: 4.200
Water consumption: 7.400
Recovery of low grade heat 7.900 Natural gas US$15.800 Two years

Reference: Cleaner Production Assessment in Dairy Processing; prepared by COWI, Denmark for UNEP and Danish Environmental Protection Agency

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