FINDINGS OF A DETAILED ENERGY AUDIT AT A CHEMICAL PLANT IN SINGAPORE

FINDINGS OF A DETAILED ENERGY AUDIT AT A CHEMICAL PLANT IN SINGAPORE

Main Energy Consuming Systems Process chiller system Brine chiller system Process cooling tower water system Air Compressors Boilers

Breakdown of Electrical Energy Consumption

Breakdown of Energy Consumption by Source of Energy

Process Chiller System Schematic 2 x 400 RT water cooled chillers Operating at 6.5oC

Typical Chiller Efficiency for Process Chiller Chiller Efficiency: 0.8 to 1.65 kw/rt Achievable Efficiency Range

Typical System Efficiency for Process Chiller System Efficiency: 1.5 to 5.2 kw/rt

Main Findings & Recommendations Main Findings Chillers operate at an average part load of 200 to 250 RT (50 to 60% loading) Primary pumps are fixed speed Secondary pumps are also fixed speed Chilled water is pumped to all the plants even if a plant is not in operation Recommendations Install a new high efficiency chiller with a variable speed compressor to better match capacity to cooling load Size primary pumps to match chiller requirements Install variable speed drives for secondary pumps and control pump capacity based on demand Install motorized valves to isolate plants not in operation

Comparison of Chiller Efficiency

Optimising Pumping System Proposed Installation of valves

Brine Chiller System 2 x 33 RT brine chillers Operating at -11oC

Typical Efficiency for Brine Chillers Chiller Efficiency: 2.5 to 8 kw/rt

Estimated System Efficiency Profile for Brine Chillers System Efficiency: 4 to 17 kw/rt

Main Findings & Recommendations Main Findings Two chillers operate at part-load (since the load is higher than the capacity of one chiller and poor chiller efficiency) All pumps are fixed speed Brine is pumped to all the plants (even those not in operation) Recommendations Recommended to replace the existing chillers with more efficient 50 RT capacity chillers Size primary pumps to match chiller requirements Install variable speed drives for secondary pumps and control pump capacity based on demand Install motorized valves to isolate plants not in operation

Comparison of Chiller Efficiency

Optimizing Pumping System Proposed Installation of valves

Process Cooling System Consists of two cooling towers with constant speed fans Cooling towers also serve the water cooled chillers Water supply temperature about 27.5oC Low temperature difference between the return and supply water streams at the cooling tower Valves on the return pipes at the cooling towers are throttled to create the necessary back pressure for the process cooling applications Process cooling water flows through all the plants (including those not in operation)

Recommendations for Process Cooling System Separate the process cooling and chiller cooling systems Open the throttled valves at the return header pipe Install variable speed drives (VSDs) for fans and control fan speed to supply water at the desired temperature Install motorized valves to stop water flow through systems not in operation Install VSDs for pumps and vary speed based on demand

Compressed Air System Two big air compressors and one small air compressor are installed in the facility During normal plant operations, one of the big compressors is in operation On Sundays when there are no production activities, the small compressor is in operation

Pressure and Power consumption on Sundays Pressure: 6.25 to 6.75 bar Power Consumption: 15 to 35 kw

Recommendations for Compressed Air System Repair leaks Replace one of the big compressors with a new more efficient machine

Boiler System Boiler rated at 15 tons/hours used to generate the steam (smaller boiler rated at 1 ton/hr is used when the steam demand is low) Steam set point at 13.5 bar All condensate in the plant is discarded (due to possible contamination) Blowdown is performed intermittently to maintain the TDS level Many steam traps are leaking

Condensate Not Recovered

Recommendations for Boiler System Recommended to install a condensate recovery system to collect most of the condensate Use a heat exchanger to recover heat from the condensate and pre-heat the make-up water Install a blowdown heat recovery unit with suitable controls and change intermittent blowdown to continuous blowdown Repair / replace leaking steam traps

Proposed Condensate and Blowdown Heat Recovery System

Conclusions Overall electrical energy savings identified is about 2.3 million kwh/year Savings account for about 30% of the annual electricity consumption Overall fuel energy savings is estimated to be about 1.4 million kwh/year Overall energy savings is about 14% The overall simple payback period is less than 5 years

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