We have studied the importance of pasteurization process and the important components of a pasteurization plant. Now let us see the operations involved in running of a pasteurization plant and how to cope with operational problems.
The following steps should be followed to start the plant:
a) Start the air compressor;
b) Switch on the control panel mains;
c) Fill the hot water tank, start the hot water pump;
d) Open the air vents
e) Start flow of the milk to the float controlled balance tank
f) Start the milk pump
g) Close the air vents when the milk coming out from them indicates that all air has been displaced.
h) Set the temperature controller to maintain the milk at 72°C.
i) Turn on cold water and chilled water and hot water set.
For shutting down the plant, at the end of the milk run:
a) Make available in the storage tank a sufficient quantity of water (approx. equal
to the capacity of the plant).
b) As the last milk is leaving the float balance tank, tip in the water from the tank.
c) When the last of the water is leaving the float balance, turn the three-way cock
at the finished milk outlet so that the flow is diverted to the floor.
d) Place a hose in the float balance tank and flush the plant thoroughly with water
until the discharge from the finished milk outlet becomes clear.
e) Turn off the cold water, brine or chilled water in the cooling sections.
f) Shut off the steam supply to the hot water set.
g) Admit cold water to the hot water tank and run until the plant is cold.
h) Stop the milk and hot water pumps.
i) If brine is used, flush out with running water.
j) Turn off the air supply and the main electric switch at the panel.
Thereafter, the plant must be thoroughly cleaned.
The operation of plant with the milk is called running of the plant. The plant is started. It is sterilized. The plant is run on water. The standardization is done to check the flow, operation of flow diversion valve, heating temperature and cooling temperature. The homogenizer pressure is also set in according to requirements.The flow of milk from raw milk tank to pasteurized milk tank is monitored.
Pasteurizing problems may occur during start up procedures or during the run.When a problem occurs it is important to be able to identify the problems from the symptoms, identify the cause of the problem and take the appropriate action towards solving the problem. If the problem causes a delay in processing it is advisable to turn off essential services such as steam and heating and cooling system to prevent burn on in the heating section and a freeze up in the cooling system. The common problems and their remedial measures are given in practical exercises. These could be grouped in three broad areas: (i) inadequacy in achieving temperature, (ii)chocking of plates and (iii) leaking plant assembly. The broad reasons for these are given here.
(i)Inadequacy in achieving temperature : The possible reasons are: inadequate steam supply, faulty temperature controllers, air in milk and improper assembly of plates.
(ii) Chocking of plates : Fouling, high milk temperature, high milk acidity and inadequate filtering of milk could be the reasons for chocking of the plant.
(iii) Leaking plant assembly : The reasons are: damaged and worn gaskets,damaged plates and wrongly fitted plates.
Preventive maintenance will help to control damage, excessive wear and tear and occurrence of accidents. Preventive maintenance can be divided into two areas, (i)avoiding damage to the plant and equipment and (ii) observations and inspection of plant and equipment. Avoiding damage consists of basically the careful handling of machinery and equipment. The regular inspection of the plant and equipment is important as a part of preventive maintenance, and may include:
a) Periodical tests may be made to check the flow rates of heating medium,cooling medium and milk.
b) The recording instruments such as thermometers, etc must be periodically checked for accuracy.
c) Air operated instruments should be supplied with clean air.
d) The plate surfaces and gaskets must be checked during the manual cleaning of plants.
e) Filter cloth/filters must be changed at regular intervals.
f) The faces of the plate bar and tightening spindle should be lightly coated with grease.
i. Starting the Plant
The following steps should be followed to start the plant:
a) Start the air compressor;
b) Switch on the control panel mains;
c) Fill the hot water tank, start the hot water pump;
d) Open the air vents
e) Start flow of the milk to the float controlled balance tank
f) Start the milk pump
g) Close the air vents when the milk coming out from them indicates that all air has been displaced.
h) Set the temperature controller to maintain the milk at 72°C.
i) Turn on cold water and chilled water and hot water set.
ii. Shut down of the Plant
For shutting down the plant, at the end of the milk run:
a) Make available in the storage tank a sufficient quantity of water (approx. equal
to the capacity of the plant).
b) As the last milk is leaving the float balance tank, tip in the water from the tank.
c) When the last of the water is leaving the float balance, turn the three-way cock
at the finished milk outlet so that the flow is diverted to the floor.
d) Place a hose in the float balance tank and flush the plant thoroughly with water
until the discharge from the finished milk outlet becomes clear.
e) Turn off the cold water, brine or chilled water in the cooling sections.
f) Shut off the steam supply to the hot water set.
g) Admit cold water to the hot water tank and run until the plant is cold.
h) Stop the milk and hot water pumps.
i) If brine is used, flush out with running water.
j) Turn off the air supply and the main electric switch at the panel.
Thereafter, the plant must be thoroughly cleaned.
iii. Cleaning and Sterilization of the Plant
- Cleaning the plant: Cleaning is done after completion of pasteurization process.The milk supply is stopped to constant head tank by turning off the valve of Raw Milk Storage Tank. Clarifier and homogenizer are stopped. The water is added to the constant head tank. Hot water temperature is set at 70°C. Primary detergent solution is circulated for 20-30 minutes. Flush the system with lukewarm water. Secondary detergent solution is circulated for 20-30 minutes. Flush the plant with water.
- Sterilization: The plant can be sterilized by hot water or sodium hypochlorite solution. The raw milk tank and pasteurized milk tank are bypassed and hot water (87-90°C) is circulated for 10 minutes. The sterilization is done before running the plant with milk for pasteurization.
iv. Pasteurization of milk
The operation of plant with the milk is called running of the plant. The plant is started. It is sterilized. The plant is run on water. The standardization is done to check the flow, operation of flow diversion valve, heating temperature and cooling temperature. The homogenizer pressure is also set in according to requirements.The flow of milk from raw milk tank to pasteurized milk tank is monitored.
v. Trouble shooting
Pasteurizing problems may occur during start up procedures or during the run.When a problem occurs it is important to be able to identify the problems from the symptoms, identify the cause of the problem and take the appropriate action towards solving the problem. If the problem causes a delay in processing it is advisable to turn off essential services such as steam and heating and cooling system to prevent burn on in the heating section and a freeze up in the cooling system. The common problems and their remedial measures are given in practical exercises. These could be grouped in three broad areas: (i) inadequacy in achieving temperature, (ii)chocking of plates and (iii) leaking plant assembly. The broad reasons for these are given here.
(i)Inadequacy in achieving temperature : The possible reasons are: inadequate steam supply, faulty temperature controllers, air in milk and improper assembly of plates.
(ii) Chocking of plates : Fouling, high milk temperature, high milk acidity and inadequate filtering of milk could be the reasons for chocking of the plant.
(iii) Leaking plant assembly : The reasons are: damaged and worn gaskets,damaged plates and wrongly fitted plates.
vi. Preventive maintenance
Preventive maintenance will help to control damage, excessive wear and tear and occurrence of accidents. Preventive maintenance can be divided into two areas, (i)avoiding damage to the plant and equipment and (ii) observations and inspection of plant and equipment. Avoiding damage consists of basically the careful handling of machinery and equipment. The regular inspection of the plant and equipment is important as a part of preventive maintenance, and may include:
a) Periodical tests may be made to check the flow rates of heating medium,cooling medium and milk.
b) The recording instruments such as thermometers, etc must be periodically checked for accuracy.
c) Air operated instruments should be supplied with clean air.
d) The plate surfaces and gaskets must be checked during the manual cleaning of plants.
e) Filter cloth/filters must be changed at regular intervals.
f) The faces of the plate bar and tightening spindle should be lightly coated with grease.
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