Petroleum Conservation Research Association
Ministry of Petroleum & Natural Gas, Government of India
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Energy Audit at Dairy plant at Mehsana,Gujarat.Print
A comprehensive energy conservation study of the Dairy plant at Mehsana,Gujarat was carried out by PCRA.This Dairy is engaged in the manufacture of various qualities of milk & also other milk products like butter, ghee, as well as milk powder in their plant. The milk processing capacity of the plant is 18 lakh litres per day. There are 6 nos. boilers of various capacities using natural gas as fuel for generating steam for use in the plant. The boilers use both furnace oil & natural gas as fuel. Natural gas is also used as fuel in powder plant air heater .There are 4 powder plants with air heaters of various capacities Natural gas is generally used as fuel in the air heaters. Annual natural gas consumption is 123.25 Lakh NM3. Annual furnace oil consumption is 3329 MT.The unit takes its electricity supply from the GEB .The contract demand is 2400KVA.The unit has also installed 8 nos. GG sets of capacities 125, 380 & 750 KVA operating on natural gas which generates electricity in the plant. Electricity is consumed in a variety of equipment in the refrigeration plant compressors & auxiliary equipment like cooling & chilled water pumps, powder plant blowers, air compressors, water & milk pumps & lighting.
A comprehensive energy conservation study of the plant was carried out by PCRA, The identified total annual energy saving potential is around Rs. 148.76 Lakhs on a recurring basis. The energy audit has identified several areas for energy conservation in thermal & electrical energy. The steps identified for energy conservation are given below:
- The excess air percentage on all the boilers on natural gas firing is quite high. This is due to the fact that the natural gas pressure varies. Due to this the air – gas ratio also varies resulting in high excess air levels & low combustion efficiencies. By installing an online oxygen monitoring & control system, the efficiency of the boiler will improve on both natural gas & furnace oil firing. The savings on furnace oil are to the tune of 3% at least.
- Furnace in the main storage tank is heated by steam coils. This results in churning of the furnace oil & does not allow the moisture present in the furnace oil to settle down. It is recommended that steam heating in the main storage tank be stopped. It is also recommended that the furnace oil storage & service tanks should be drained at least once a week. This will ensure that all the water is removed from furnace oil & prevent sludge formation.
- Furnace oil main storage tanks should be cleaned at least once a year to remove the sludge accumulated at the bottom of the tanks.
- Steam line insulation is not in good shape in the plant. All the valves & flanges are not insulated in the plant. Also some bare steam lines were observed. By insulating with 2" thick mineral wool with aluminium cladding, 90% of the heat loss can be minimised.
- A steam trap survey was conducted in the plant. Steam traps identified as leaking /blocked should be rectified immediately.
- It is recommended that the steam pressure powered pumps be installed from the two sections identified. This will enable the condensate to be pumped to the boiler house as soon as it is formed. This will raise the boiler feed water temperature by at least 20 deg c.
- It is recommended that the air heater be tuned to reduce the excess air levels. Also the flue gas temperature observed in both the air heaters is on the higher side. It is recommended that the air heaters be checked for leakages & cleaned. This will reduce the flue gas temperature to at least 230 deg c.
- Even after cleaning/servicing of air heaters, the flue gas temperature will be in the range of 230 deg c. It is recommended that airpreheaters be installed on the hot air generators to preheat combustion air. The flue gas temperature after the air preheater can be brought down to 110 deg c. The savings due to this will be 5%. The air preheaters have to be installed on all the hot air generators.
- It is observed that the hot air flow to both the dryers seems to be on the higher side.It is recommended that the hot air flow be reduced on a trial basis for both the plants & the hot air generation temperature be increased to 185 deg c. This will result in appreciable natural gas savings & power savings.
- It is recommended that for N2 plant Supply air fan & milk pump, soft starters should be installed before reducing the size of the motor. This is due to the fact that the starting torque is quite high & soft starter is essential to take up the initial high torque. SAF fan motor size is presently 125 HP. It can be reduced to 75 HP after installation of a soft starter.
- Chilled water is sent to the plant at 1- 2 deg c & comes back to the refrigeration section at 7 -8 deg c. It is sent to the ice bank tank directly in the main plant. In the glycol plant , the chilled glycol is sent to the instant chiller . The chilled glycol evaporator temperature is – 10 deg c. The main refrigeration plant has a single - 10 deg c ammonia refrigeration system. It is recommended that the load be handled by a 2 stage system. Ammonia from the -2 deg c accumulator be used in the instant chillers & ammonia from the -5 deg c accumulator be used in the IBT & for other loads. The glycol plant should be operated at 0 deg c suction saturation temperature.
- It is observed that the in cream pasteurizers , cream chilling is done from 57 deg c to 7 deg c by chilled water. It is recommended that an intermediate cooling water section be included in the cream pasteurizers. This will bring down the milk temperature to 35 deg c. The milk can then be chilled to 7 deg c from 35 deg c. This will drastically reduce the chilling load on the chilled water system.
- It is recommended that the 100 TR PHE condenser pump impeller be trimmed by 10%. This will reduce the power consumption in the pump.
- It is to be noted that the 200 TR condenser pumps have a rated head of 22 metres as against that of 10 metres for the 100 TR condenser pump. It is recommended that this pump be replaced by a pump with similar capacity but lower head around 10 metres. This will reduce the power consumption in the pumps by 30-40%.
- It is observed that milk is underchilled in the plant. During the audit study, we observed pasteurized milk temperatures ranging from as low as 1 deg c to 12 deg c. This is a direct loss in terms of steam as well as of refrigeration capacity. It is recommended that the plant personnel be more vigilant & throttle the chilled water valves incase the milk flow in the pasteurizers is not as per the rated capacity of the unit.
- It is observed that the milk temperature rises quite appreciably in the pasteurized milk silos in the plant.There is a rise in the milk temperature of at least 5 -6 deg c in an 8 hour period as per the plant personnel. This was also confirmed by the moisture condensation observed on the surface of the milk silos. This increases the refrigeration load unnecessarily.
- It is observed that the insulation of chilled water supply & return lines to N3/N4 is quite poor as seen from the moisture condensation on the surface of the lines. It is recommended that the insulation be upgraded at the earliest.
- It is recommended that the compressed air requirement for N1/N2 plant should be met by the central plant screw compressors. The central compressor room is very close to the N1/N2 plant & hence minimum length of new line will need to be put up. Savings due to utilization of screw compressors over reciprocating compressors will be at least 10% due to the fact that the reciprocating m/cs are belt driven & the screw m/cs are direct driven.
- Present lighting single phase voltage is 250 to 260 volts. Nowadays lighting transformers are available, which reduce the voltage to around 220 volts. The reduction in voltage also reduces power consumption with little reduction in lumens emitted by the light source. The savings due to installation of lighting transformer is 30% of the power consumption.
- It is recommended to replace the existing 4 feet fluorescent tubes with Asian “E+” energy efficient tubelights. Power consumption of these tubelights is 28 Watts.
For further information, please write to:
Sanrakshan Bhawan, 10,
Bhikaji Cama Place,|
Web site: www.pcra.org