ONE-DAY SYMPOSIUM

10 February 1982 at the Scientific Societies Lecture Theatre, Savile Row, London WI

Subject: Energy - use and conservation in the dairy industry

Energy usage in the milk processing industry P. S. HARRIS Energy Conservation Branch, Energy Technology Support Unit, AERE Hanvell, Oxon OX11 ORA

Lord Kelvin once said, ‘When you can measure what you are talking about and express it in numbers you know something about it-when you cannot express it in numbers your knowledge is o fa meagre and unsatisfactory kind‘. In providing a background to the more specia- lized papers in this symposium, therefore, I have set about to quantify energy use in the areas under discussion.

OVERALL ENERGY CONSUMPTION

The Department ofEnergy published a report on the use of energy in the dairy industry in its Energy Audit Series in 1978. Estimates were made of energy consumption in 1974175 and 1968; total energy con- sumption was estimated to be about 1 million tonnes coal equivalent. The estimates were very crude because they were based on small samples ofdata. Comparison ofthe estimates with the 1968 Census of Production seemed to indicate that the industry had held its energy consumption constant between 1968 and 1974/75 despitea substantial increase in production. Because the estimates were so crude it was felt at the time that it might be reading too much into the figures to make this claim.

Since then the results of the 1974/75 Census of Production have been published. As shown in Table I, the total energy consumption for the two years was roughly the same at around 0.6 million tonnes coal equivalent heat supplied or 0.75 million tonnes coal equivalent on a primary fuel basis. There is a shift from coal to liquid fuels and a slight increase in electricity consumption.

TABLE I Energy consumption in the dairy industry (million GJ)

1968 1974175

Heat supplied basis: Solid fuel 4.4 1.6 Liquid fuels 10.6 13.4 Gas 0.1 0.2 Electricity 1.7 2.0 Total 16.8 17.2

Primary fuel basis: Total 23. I 24.7

Source: Censuses of Production

It is important to be aware ofhow the census is compiled in order to appreciate how to interpret these figures. The census is based on ques- tionnaires returned by factories which are classified to the milk and milk products industry for the purpose ofthe census and so it includes ice-cream manufacture but excludes retail distribution depots. (Tran-

sport fuels have also been excluded in this Table.) It is not actually a census of production at all since it does not ask how much factories produce; it asks what they sell and purchase. This means that, for some industries, relating fuel consumption to production is difficult and can mislead.

Fortunately, the UK Federation of Milk Marketing Boards pro- vides exceptionally good production statistics,and we can use these as an aid to interpretation of the census results. Table 2 shows the pro- duction and coverage ofthe census for 1968 and 1974/75. We find that the coverage oftotal production in the two censuses is roughly similar and so they can be compared. Total production has increased by 13 per cent but underlying thisisonlya4percent increase in liquidmilkpro- duction and 29 per cent in manufactured milk, which we know to be the energy-intensive part ofthe industry, yet energy consumption has increased by only 7 per cent.

TABLE 2 (‘overage of the Census of Production and milk

utilization in 1974/75 and 1968

1968169 1974175

Utilization (million litres) Liquid sales 7,486 Manuhctured 4,189 Total 11,658

Census coverage VO Liquid sales 79 Manufactured 97 Total 85

7,761 5,407

13.167

74 97 83

Ofcourse the real reasonwhyanyonein the industryisinterestedin saving energy is the cost involved. The total spent on fuels and elec- tricity (Table 1) wasf7.19 million in 1968 andf17.6 million in 1974/75. If the industry has continued to hold down consumption since then this means a total fuel bill this year of €59.1 million. Even modest savings on that would be very worthwhile.

LIQUID MILK PROCESSING

In 1978 the National Dairyman’s Association carried out a survey of the use of energy in liquid processing. The results were published by Elsy (1980). The survey was particularly successful, covering the pro- duction of 4,500 million litres, 69 per cent of the total industry liquid production, so it covers almost the sameamountas theCensusofPro- duction. The total consumption was4.55 million GJ or 120,000 tonnes coal equivalent on a heat-supplied basis. Therefore this part of the industry consumes about one-quarter of the total energy (excluding transport); at that time this was estimated to be costing the industry around €13 million a year.

Journal of the Society of Dairy Technology, Vol. 35, No. 3. July 1982 81

The survey also covered the use ofwater which, at the then prevail- ing supply and eflluent charges, was costing the industry around €4 million a year.

This survey was analysed in much greater detail than is possible for official statistics. I t was analysed for dairy size and pattern of produc- tion. Average fuel usecameoutat0.89MJ/litreandaverageelectricity use at 0.10 MJ/litre, making a total of ofO.99 MJ/litre. Water use was 2.77 litres/litre milk processed. In general, energy and water to milk ratios tended to decrease with increasing size and to increase with moves away from glass and when other products additional to liquid milk were processed. Broadly, this was as expected, but what was sur- prising, alarming almost, was the extraordinarily wide variation in these ratios. The authors of the survey ventured to put forward a fi- gure for what might be a reasonable target reduction in the use of energy from the survey. I f those dairies with more than the current median consumption (i.e., the level below which halfofall dairies al- ready operate) were to reduce consumption to that level there would beasavingof20percentoffuel use,3 percentofelectricityuse,and 11 per cent of water use - a total of €2.8 million a year.

EVAPORATION AND DRYING O F MILK We have recently estimated in ETSU that some 21.5 million tonnes of water are extracted by evaporation plant and 9.4 million tonnes bydri- ers each year in industry. This involves a total expenditure of 48 million GJ (1.76 million tonnes coal equivalent) for evaporation and 127 million GJ (4.6 million tonnes coal equivalent) for drying.

Milk products feature prominently in these; 3.2 million tonnes of waterwereevaporatedfrommilkand wheyinl978ata totalenergyex- penditure of 2.4 million GJ,and 0.24 million tonnes ofwater were ex- tracted in driers at a total energy consumption of 2.1 million GJ. This total of4.5 millionGJ (150,000tonnes coalequivalent primary energy) accounts fora major part ofthe totalenergyin themilkmanufacturing industry.

REFRIGERATION Refrigeration is a different kind of energy use from most in the dairy industry and needs to be thought about in a different way, but it is not in fact any more difficult. The rewards can be potentially enormous. The figures we have at ETSU indicate that the food industry, not inc- luding retail and wholesale distribution, consumes about 1,500 GWh a year ofelectricity for refrigeration. It costs the industryf50 milliona year, and 20 to 30 per cent ofthat is simply wasted. The dairy industry, again not including the retail storage of milk, spends about €2.25 millionorabout75 million kwhayearon refrigeration. The retail dis- tribution probably adds about 24 million kWh (€0.5 million) for milk storage.

TRANSPORT Transport is an important area for the dairy industry. The bulk tanker fleet travels 200,000 miles a day- 73 million miles a year. The dairy in- dustry as a whole transports 18 million tonnes of perishables a year from farm to dairy and out again to depots, shops, and export. In 1968 it consumed 11.5 million gallons offuel and in 1974/75 8.2 milliongal- Ions for transport. These figures exclude doorstep delivery.

A massive change like the shift from churn to bulk collection, which significantly reduced transport fuel usage, is not likely to hap- pen again for a long time. Though we may look to the long term for large energy savings I am sure that we shall find the route a long series of short steps.

REFERENCES Department of Energy (1978) Energy Audir Series No. 3, The Da1r.v Industry. Census of Production (1968 and 1974175). HMSO. Elsy, W. F. (1980) Milk Industy82 (lo), 18-23 Federation of Milk Marketing Boards (1981) Daiy Facrs and Figures. Department OfTransport (1979) TransporlSraristics in Brirain 1968-78. HMSO.

Energy use and conservation in concentrated and dried milk production R. DARLINGTON Leatherhead Food Research Association

The importance ofproviding energv supplies in the most efficient way possible is stressed. Reductions in spect$cenergy consumption for the concentration step can be achieved by using multiple-effect evaporation and thermal and mechanical vapour recompression or by the use of reverse osmosis followed by evaporation. Significant reductions in spectjk energv consumption for the dryingprocess can be achieved by recovering the heat from the hot exhaust gases using suitable heat exchangers, by using afluidized bed for thefinal water removal step, and by altering the process conditions. Freeze concentration, freeze dying, dielectric dying, and roller dying are also discussed.

Dairy technologists are concerned principally with food preservation and the production of high-quality products. In order to accomplish this they use plant especially designed to preserve the wholesomeness of the product by minimizing adverse biological, chemical, physio- chemical, and physical changes during production and subsequent storage. Since most of these changes occur in an aqueous environ- ment removal of water from dairy products is the main process used

for food preservation. The plants available to the dairy industry for concentration and drying purposes are listed in Fig. 1 together with the energy sources that are needed to accomplish the water removal operation.

The main criterion when choosing a suitable plant must always be the production of a product that is of a good consistent quality and is readily marketable. Once these aims have been met, consideration

82 Journal of rhe Society af Dairy Technology, Vol. 35, No. 3, July 1982