Best practices to reduce the Auxiliary power consumption (APC) in Sugar based Cogeneration plants.

Auxiliary power consumption is directly related with power plant profit. Lesser the APC more will be the power export & hence more profit. So it becomes duty of every power plant professions to strive to reduce APC wherever possible.

Below table gives the area wise APC in Bagasse/coal based power plants

Sl No.	Area	APC in %
1	Boiler fans	35-38%
2	Boiler feed water pumps	35-36%
3	Turbo generator & its auxiliaries	10-12%
4	Bagasse feeding system	2-2.5%
5	Coal feeding system	1%
6	Bagasse handling system	4-4.5%
7	Coal handling system	1.5- 2%
8	Ventilation, AC & Air Compressors	4-5%
9	Water treatment plant	2-3%

Note: Bagasse based Cogeneration plant have incorporated coal handling system as supporting system & also run the power plant in non-season days. So APC for bagasse handling/feeding & coal handling/feeding has been considered separately.

Now a day there is huge scope for reduction of plant APC. Here scope of APC reduction at various areas of plant has been discussed.

A-Boiler:

1-Improve the combustion efficiency:

Combustion efficiency improvement will directly relate to the air consumption. Improved combustion will reduce load on FD, SA & ID fans, hence power consumption will reduce. In cogeneration plants or ion any power plants Boiler fans consume around 35-38% of total auxiliary power consumption.

In order to reduce the air requirement & to improve the combustion efficiency need to concentrate on bellow areas

• Select good quality of fuel, if using bagasse the moisture should be 49 to 50%, as the moisture increases excess air required will also increases. This loads the FD, SA & ID fans more than requirement.
• Arrest all leakages in air & flue gas paths
• Modify combustion air ducts to reduce resistance to air flow

16-Perfect reasons for increasing the fuel consumption of Boilers

Opportunities for energy conservation in power plant...

2-Boiler fans:

As discussed above Boiler fans consume 35-38% of total APC, so need to concentrate on Boiler fans efficient operation.

• Operate boiler fans in VFD mode at optimum speed
• Incorporate inlet guide vanes to the system
• For high speed fans, ensure the silence fitted at suction size has sufficient opening & at lesser height
• Ensure all inspection & man way doors are sealed properly
• Ensure clearance between inlet cone & impeller suction neck is minimum
• Monitor draught losses in flue gas duct, air ducting, APH, Economiser & ESP regularly
•  Follow lubrication schedule, replace damaged bearings to reduce vibrations & bearing temperature. High vibration bearings consume more power

3-Boiler feed water pumps (BFP)

Boiler feed water consume around 35% of total APC of the plant. Hence it is utmost important to reduce the BFP power consumption. Attention must be given on following points to reduce BFP power consumption.

• Select optimum capacity BFPs, Under load running pumps have low efficiency
• Better to install HT drives for BFP
• Incorporate VFD to BFPs
• Operate BFP in Auto mode based on discharge header pressure & drum pressure
• Do not operate the pump with discharge valve throttled
• Ensure BFP ARC valve has no leakage
• Ensure BFP has sufficient suction pressure
• Maintain Deaerator level on higher set point side.
• Replace worn out balance & counter balance discs
• Schedule pumps servicing as per OEM guidelines. And replace impeller wear rings or impellers if clearance found more. More clearance between wear ring & impeller will lead to higher power consumption
• Follow lubrication schedule, replace damaged bearings to reduce vibrations & bearing temperature.
• Do not uses BFP discharge water for de-super heating of LP process steam, instead use CEP discharge water
• Clean suction strainers regularly

4-ESP

• Implement hopper heater automation by thermostat
• Optimize the charge ratio of Transformer

Questions & Answers on ESP troubleshooting

B-Fuel feeding system:

Fuel feeding system consumes around 2-4% of total APC. Hence it need to give attention to reduce APC in this area. Following are the some listed action points to reduce APC.

• Incorporate VFDs to all fuel feeding systems, as fuel feeding system never run on 100% load.
• Select planetary type gear boxes to fuel feeding system, as planetary gear boxes found of higher efficiency
• Follow regular preventive maintenance to reduce wear, tear & friction of rotating parts, which ultimately lead to more power consumption
• Replace all loose V belts. Loose V belts lead to increased power consumption

C-Turbo generator & Auxiliary:

Turbine auxiliary consume around 10-12% of total APC of the plant. Following are the areas where we can monitor the APC

• Maintain lube & control oil filters clean
• Maintain optimum lube oil temperature
• Maintain cooling tower fills & drift eliminators clean to get required cooling water temperature
• Incorporate VFDs to all cooling water pumps
• Set CT blade angle at 11-14 degree.
• Replace CT fan aluminium blades by FRP
• Ensure cooling tower surrounding area is free of trees & structures for free flow of air
• Incorporate VFDs to Condensate extraction pumps (CEP)
• Ensure hot well make up is going on from gravity water from feed tank or surge tank
• Schedule regular cleaning of heat exchangers like steam condenser, oil cooler, ejectors & Generator air cooler & gland steam condensers
• Replace TG building exhaust fans by turbo ventilators

D-Fuel handling (Coal & Bagasse handling):

• Ensure motors selected for all Bagasse belt conveyors are of optimum rating
• Incorporate planetary gear boxes to belt & chain conveyors
• Replace all damaged idlers regularly. Damaged idlers lead to more friction in the system
• Ensure Vertical gravity take up height is optimum (1 to 1.5% of conveyor length)
• Ensure belt scrapers (cleaners) & skirt boards are not over rubbing the belt to avoid friction & wear/tear
• Follow regular preventive maintenance & lubrication schedule for conveyor pulleys bearings & idlers
• Remove saturated bagasse/coal from deck plates of conveyors regularly to avoid friction

It's all about HP heaters

E-Compressors/blowers & Ventilation/air conditioning system

For air compressors optimise discharge air pressure & set loading & unloading times as per requirement

• Clean air filters regularly
• Replace all globe valves by gate valves or ball valves
• Ensure compressor discharge air line is of correct size to avoid pressure drop in the line
• For pneumatic ash handling system operate ash handling plant in probe mode or else optimize cycle time & conveying time
• Incorporate VFDs to ventilation system
• Optimize the usage of Air conditioning system in offices, meeting halls etc
• Avoid compressed air for cleaning applications

F-Water treatment plant

Thumb rules water treatment plant

• Ensure enough capacity of tanks for DM water storage, so that the operation time of the plant can be reduced
• Plan to get more quantity of return condensate from process
• Optimize boiler & CT blow down to reduce pumping power
• Incorporate drain condensate recovery system to reduce pumping power as well as to conserve thermal energy
• Operate DM plant at its full capacity & carryout regeneration as per out put OBR given by OEM to reduce pumping power as well as water consumption
• Use treated N-pit water as  service water

Other:

1-Motor

• Provide proper ventilation to the motors. For every 10 °C increase in motor operating temperatures over recommended peak, the motor life is estimated to be halved.
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• Synchronous motors are more suitable to improve power factor.
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• Balance the three phase power supply, an unbalanced voltage can increase motor input power by 3–5%.
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• Ensure the motor proper rewinding, an improper rewinding could lead to efficiency reduction.
• Ensure proper alignment between motor and load ends (fans, pump, gear box, blower etc.) to avoid more power consumption and failures.

2-Lighting

Incorporate timers for plant lighting systems like conveyors, street, bagasse & coal yards etc

Replace all CFL & incandescent bulbs by LED bulbs

Read POWER PLANT CALCULATIOS