DAIRY PLANT DESIGN AND LAYOUT

Module 1. Introduction of dairy plant design and layout

Lesson 4
MILK RECEPTION

4.1 Introduction

The objective of handling the milk as quickly as possible continues even at the milk reception, as the milk is still vulnerable to the spoilage, till it is chilled and taken into milk storage tank, and processed. The crucial stage of milk reception also involves the responsibility of checking the quantity, quality for acceptance, and the time management of handling many vehicles.

As mentioned earlier the timing is an important parameter while deciding about the mode of reception and transport. The load, distance to be covered and relative merits are given below in Table 4.1 and 4.2.

Table 4.1 Various modes of transportation of milk to the dairy plant

Table 4.2 Mode of transport and their corresponding advantage

4.2 Reception at the Dock

The milk as soon as it is received at plant, is weighed, dumped into the dump tank (weigh tank) and has to be chilled before it is stored for processing. This has to be done in quick succession through equipment well planned and installed at milk reception dock and receiving room.

The reception of milk at the Raw Milk Reception Dock (RMRD) is done in three ways i.e., in cans, in milk tankers and combination of both. The type, size and number of vehicles can be determined by factors such as distance or nature of the roads and condition of milk production. In the chilling centres or BMCs, the milk is received only in cans (may be 40 lit or 20 lit capacity cans). In case of Marketing Dairies, the milk is received only in milk tankers where as in feeder dairies the milk is received in both cans as well as in tankers. The trend of establishing BMCs at village clusters has changed the mode of reception and monitoring of quality and quantity at Dairies.

There are some products that depend on the type of milk like cow and buffalo milk. Therefore, the reception dock may consists of two separate systems for cow milk reception and buffalo milk reception at chilling centres as well as in feeder dairy plants. In most of the dairy plants however, the milk is received as mixed milk.

If the milk is received in bulk through tankers, the arrangement has to be made for quick transfer of milk through milk pumps installed at milk reception dock to milk storage tanks. The milk received in the evening may be chilled and the stored for processing next day. All this will need careful planning of layout of equipment at milk reception dock and milk receiving room. Roads leading to milk reception dock and dispatch dock have to be planned in such a manner so as to avoid traffic congestion inside the factory or road blockage.

4.2.1 Essential features of RMRD

The RMRD dock should be of height suitable (usually 1.5 m) to receive milk from whatever mode of transport without spillage during unloading. For Milk tankers, the Tanker Bay must be spacious, suitable for washing and unloading atleast two tankers at a time. The pump should be of 20,000 l/h capacity to unload faster. If the milk quantity is to be measured by weigh bridge, it should be properly calibrated and inspected periodically by local weights and measure authorities. If the quantity is to be measured by dip stick alone, then the tanker by must be suitably levelled to avoid errors in measurement.

4.3 The Important Equipments for Reception of Milk Processing Plant on the RMRD are

• Can conveyor: It should be of suitable type and length to transport easily the cans from the edge of the dock to the can tilting bar at the dump tank. The rate of reception and capacity of the dairy plant are also important in deciding about the type of can conveyor, like whether a Roller type or motorized chain conveyor.

• Milk weighing tank: The equipment involves a weigh bowl and dump tank. The capacity of weigh bowl should be able to weigh at least 4 cans, which may be an average quantity received from each village. Weigh bowl may be linked to indicate on a dial type of scale or through load cells in digital form of indication and recording

• Weighing scale: The weigh scale must at least be of 300 kg, so that the normal range of quantity of milk received from village is between 40 to 60% of the scale. The trend of digital indication through load cells are catching up, which has the advantage of recording as well as print out simultaneously, for easy monitoring and documentation. This is improving the confidence level between milk collection centres and dairy that is receiving the milk.

• Dump tank with cover: The capacity of Dump tank is at least twice the capacity of weigh bowl, so that while the milk quantity of one village is being weighed, the other quantity is being pumped out from dump tank to the milk chiller. Recent trend is to link the level sensors and milk pump to get started and stopped when the milk level is high and low respectively.

• Drip saver: The drip saver must be of SS and should have drain leading to the dump tank, or to a separate can, which is emptied to dump tank from time to time.

• Can washer: The capacity of can washer should meet the rate of reception and dumping. Mostly Straight through can washers are chosen, and the empty can conveyor leads the washed cans to the dock or to the edge of RMRD to be loaded into vehicles.

• Milk pump: The milk pump used for pumping milk from dump tank to the plate chiller through in-line filter, should match the rate of reception. It is installed at a level lower than the dump tank and has flow control valve at the discharge side, The filter is sometimes located on the suction side to avoid threads, tags, etc connected with cans getting jammed into the pump impeller. The pump, in recent times is linked with control system to operate as per the level in the dump tank, to prevent overflow of dump tank or pump running dry by oversight of the operator.

• Plate chiller: The Plate chiller is usually of PHE type and used for chilling milk to 4^oC. The Plate chiller is sized to meet the reception rate, and may sometimes be two in number, one each to receive milk by cans or road tankers. If the chiller is to receive milk from road tankers, the capacity is usually much larger, to meet the higher rate of reception to unload tanker rapidly.

• Raw milk silo: This is a vertical storage tank or a battery of storage tanks, that are specifically identified to store raw milk only. The silos can be located outside the processing hall, but connected to the hall through an opening called ‘Alcove’. The operation of opening, closing of inlet and outlet valves, measuring the temperature, controlling the agitator etc are done from inside of the processing hall itself, though the silo is located outside. The tank overflow line will be positioned to inside of hall, so that the operator can know if the tank is full and overflowing.

• Milk testing laboratory: This is a preliminary testing laboratory, to perform so called Platform tests, like COB, acidity, turbidity, etc.

The Reception dock is essentially separated from the processing hall by partition doors, or walls, with fly proof devices like air curtains, or mesh doors. The trend now is to provide even the RMRD dock with provisions to prevent entry of flies and insects.

The crucial design calculations of the rate of dumping is illustrated by following example :

1. Milk to be received by Dairy Plant : 10,000 lpd

2. Milk to be received by AM and PM in the ratio of : 60 :40

3. Milk to be recived in the AM : 10,000 x 0.60 = 6,000 lts

4. Milk to be received in two hours

5. Milk reception per hour : 6,000 / 2 = 3000 lph

Hence the design of all the reception dock equipment will be to meet the above requirement of 3,000 lph.