Chapter 4 SERVICES

The consumption of services at full utilization of machine capacities and the effective operating time including pre-running and post-running periods are the major factors affecting the quantities of services required. In addition, the number of cleaning periods per working day and the relation between processing and dispatch times also have an impact on services consumption.

In order to arrive at comparable estimates a simplified model was adopted, according to which the requirements of services except refrigeration (steam, air, water, electricity) are presented by the equations:

	… (1)
tf =	… (2)
Qsp =	… (3)

where Q is the total daily quantity of the service concerned

Q_n is the service capacity (consumption per hour) required for full machine throughput (manufacturer's data)

C_d is the daily quantity of liquid milk packaged in thousand litres

C_m is the capacity of installed machinery in thousand litres per hour

t_f is the theoretically required full working time of the machines

Q_sp is the specific quantity of a particular service per thousand litres of milk

In equation (1) two hours of full services requirements has been added to the value of t_f for cleaning and sanitation. The second component of this equation covers the assumption that during the period equivalent to the difference between two full shifts (16 hours) and the value of (t_f + 2), the rate of consumption of services is reduced to 50%.*

* In plants where the value of t_f is short, i.e. about five hours, equation (3) takes the form

Water requirements for steam generation and air supplies have not been included in the estimate since they are negligible. For the refrigeration plant water requirement has been estimated at 250 litres per 1 000 kcal. The term ‘water requirement’ is used in this study as the amount needed to operate the machines, regardless of whether it is recirculated or not. In this respect ‘water requirement’ is different from ‘water consumption’, the latter meaning basically the amount extracted from wells or other sources of supply.

Refrigeration requirements have been estimated as equivalent to 1 200 kcal/m² day of the total cold stores and air-locks area. This calculation is based on the assumption that the temperature of the product should be maintained during storage, but that the product does not require to be chilled during the short time is normally remains in the store. For refrigeration, the value of Q was obtained by multiplying the cold store and air-lock areas by the coefficient 1 200 kcal/m². day, Q_n being one twenty-fourth of Q.

The electricity consumption has been estimated separately for (a) machines installed for liquid milk packaging, (b) steam raising plant, (c) air supply, (d) refrigeration and (e) water supply. For packaging the installed power was taken as the Q_n value; for the steam raising plant the electricity consumption was estimated at 0.5 kWh/100 kg of steam produced, and for the air supply a constant coefficient of 4 kWh/100 m³ free air has been used. The electric power requirements for refrigeration and water supply change according to the installed capacities on which the respective Q_n values depend. To take this into account the Q_n values of electric power requirements have been calculated using the load/capacity curves given in Fig. 37 and 38. (For the purpose of this study it was also assumed that water is supplied from a well by a pump of suitable capacity and 35 m total head).

The services consumption for the automatic bulk vending system (see Chapter 7) for filling and in-place cleaning (CIP) of tankers is negligible and has not been included in this calculation. Table 9 gives the nominal capacity of services required (Q_n) for the various packaging systems and plant throughputs analysed. Table 10 gives the corresponding figures for the quantity of each service per 1 000 litres of milk. The data estimated should be considered as approximations, particularly because with the method of calculation used the services requirements for CIP become proportional to the throughput of milk packaged. This would not be the case in practice where the services required per 1 000 litres of milk diminish with increasing plant throughput. The data given in Tables 9 and 10 are plotted graphically in Figs 39–44.

Fig. 37 Nominal power requirement for water supply

Fig. 38 Nominal power requirement for refrigeration

Table 9 Capacity of services required (Q_n)

Table 10 Specific consumption of services per 1000 litres of milk packages (Q_sp)

•   Pasteurized milk in glass bottles
o   Sterilized milk in glass bottles
×   Pasteurized milk in cans
  Pasteurized milk in tetrahedral cartons in returnable crates
  UHT - aseptic milk in rectagular cartons in non-returnable wraps
+   Pasteurized milk in plastic sachets in returnable crates

Fig. 39 Specific steam requirements

Fig. 40 Specific refrigeration requirements

•   Pasteurized milk in glass bottles
o   Sterilized milk in glass bottles
×   Pasteurized milk in cans
  Pasteurized milk in tetrahedral cartons in returnable crates
  UHT - aseptic milk in rectagular cartons in non-returnable wraps
+   Pasteurized milk in plastic sachets in returnable crates

Fig. 41 Specific water requirements

Fig. 42 Specific air requirements

•   Pasteurized milk in glass bottles
o   Sterilized milk in glass bottles
×   Pasteurized milk in cans
  Pasteurized milk in tetrahedral cartons in returnable crates
  UHT - aseptic milk in rectagular cartons in non-returnable wraps
+   Pasteurized milk in plastic sachets in returnable crates

Fig. 43 Specific power requirements - all components

Fig. 44 Specific power requirements - excluding refrigeration