Thumb rules for power plant

BOILER:

• Boiler heating surface (M2) = Boiler capacity in kg/hr/(17–18)..Ex: 115 TPH boiler will have heating surface = (115 X 1000/17 or 18) = 6390 to 6750 M2 (Appx.)......

• Boiler flue gas ducting size (M2) = Boiler capacity in TPH/15.

• No. of open tubes in steam drum for water recirculation = 30–31% of total no. of tubes present.

• Deaerator steam venting capacity = Deaeration capacity X 0.1%.

• Super heater safety valve relieving capacity at full open condition in TPH = Boiler MCR X 36–38%.......Ex: 125 TPH Boiler has SH safety valve of relieving capacity = (125 X 36/100) = 45 TPH.

• Drum safety valve (1 no.) relieving capacity at full open condition in TPH = Boiler MCR X 46–48%.

• All boiler safety valves (super heater and drum safety valves) relieving capacity at full open condition= Boiler MCR X 125–130%.

• Safety valves pop up pressure = Operating pressure X 106–107%.Ex: A boiler operating pressure of 110 kg/cm2 has safety valve set at 110 X 106/100 =116.6 kg/cm2.

• Boiler start up vent steam blow capacity 30–35% of boiler MCR on full open condition.

• Boiler CBD water flow is 0.8 to 2% of steam generating capacity of the boiler.

• Drum man hole door size 410 mm X 310 mm (Elliptical).

• Boiler drum hold up capacity is 2–4 minutes at MCR operation.

• Feed water velocity in Economiser coils 0.6 to 1 meter/sec.

• Pressure drop in Economiser coils 0.5 to 1 kg/cm2.

• Flue gas Pressure drop in ESP 25 to 30 mmwc.

• A travelling grate Boiler ID fans motor rated capacity in KW = Boiler capacity TPH X 200%.....Ex: A boiler of capacity 75 TPH requires ID fan motor of rated KW = 75 X 200/100 = 150 KW each

• A travelling grate Boiler ID fans (2 Nos) capacity (m3/sec.) with 25% extra margin = Boiler Capacity(TPH) X 95%.....Ex: A 100 TPH boiler has two ID fans of each capacity =100 X 95/(100 X 2) = 47.5 m3/sec.

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• Mass of flue gas generated = Mass of air per kg of fuel to be burned + 1.

• Boiler fans power consumption = Total plant auxiliary consumption X 35–38%.

• Boiler feed pumps power consumption = Total plant auxiliary consumption X 35–38%.

• Turbine auxiliary power consumption = Total plant auxiliary consumption X 10–12%.

• Fuel handling power consumption = Total plant auxiliary consumption X 4%.

• For every 1% increase in bagasse moisture, boiler efficiency reduces by 0.27% and vice versa.

• For every 5% increase in excess air for bagasse, boiler efficiency decreases by 0.18% and vice versa.

• For every 100 kcal/kg increase in bagasse GCV, boiler efficiency increases by 1.2% and vice versa.

• For every 0.5% increase of Hydrogen in bagasse, boiler efficiency decreases by 0.8–1% and vice versa.

• For every 10 °C increase in flue gas temperature, boiler efficiency decreases by 0.45% and vice versa.

• For every 100 kcal/kg increase in GCV of coal, boiler (TG) efficiency increases by 0.36% and vice versa.

• Boiler peak load = Boiler MCR X 110%.

• Minimum possible duration of boiler peak load is 30 minutes/shift.

• Minimum stable operating load on the boiler is around 30% of boiler MCR.

• Total dissolved solids = Conductivity X 06.

It's all about HP HEATERS

TURBINE AND AUXILIARIES:

• Control oil pump capacity = AOP/MOP capacity X 10%.

• Emergency oil pump capacity = AOP/MOP capacity X 25%.

• Lube oil required for gear box = Total lube oil circulating X 60–65%.

• Lube oil required for generator = Total lube oil circulating X 8–10%.

• Lube oil required for turbine = Total lube oil circulating X 20–25%.

• Lube oil outlet temperature = Lube oil inlet temperature + 15–20 °C.

• Cooling tower evaporation loss = Turbine exhaust steam to condenser X 80–90%.

Also read:RULES OF THUMB IN WATER TREATMENT PLANT

MAINTENANCE:

• Minimum allowable bearing clearance in mm = 0.00185 X bearing ID

• Maximum allowable bearing clearance in mm = 0.00254 X bearing ID.

• Bearing grease top up quantity = 0.05 X b X d, b = bearing width in mm, d = bearing OD in mm.

• Hub size = 2 X Shaft diameter.

• Shaft Key size, width = (d/4) + 2, thickness = d/6, (d = diameter of shaft).

• Minimum span for pipe line supporting in meter = (7√d)/3, where d = pipe OD in inches.

• Threading length of half threaded bolt = 2d + 6 mm (if bolt length l <150 mm) and 2d + 12 mm (if bolt length l >150 mm).

• Spanner size = Bolt major diameter (mm) X 1.5.

• Nut thickness = 0.9 X d, d = nut size.

• Bolt head thickness = 0.8 X d, d = major diameter of bolt.

• Washer Internal diameter = D + 1…mm.

• Washer outer diameter = 2D + 3……mm.

• Washer thickness = D/8, where D is OD of washer.

• Diameter of bolt head across the flat ends = 1.5 X d + 3 mm.

• Welding current required for welding (Amps) = Welding rod size (mm) X 40 +/- 20.

• Pipe weight/foot = (dt − t2) X 4.85...kg/foot, (pipe OD in inches & t is thickness of pipe in inch).

• Pipe line spacing = Flange size of maximum diameter pipe + Smallest pipe size + Insulation thickness + 25 mm.

• Preheating of steel is done if %C + %Mn/4 is >0.58.

• Boiler platform loading capacity 500 kg/m2.

• Boiler fire man floor platform loading capacity 1000 kg/m2.

• Brinnel hardness number (BHN) = Rockwell hardness number X 10.8.

• Bearing, grease or lip seals have a design life of less than 2000 hours. In a constantly running pump this would be only 83 days.

FUEL HANDLING:

• Tail pulley, bend pulley and take up pulley Outer diameter = Head pulley OD X 80%.

• Snub pulley OD = Head pulley OD X 60%.

• PCS (Pull Chord Switch) are placed at every 15 meters along the length of conveyor.

• BSS (Belt Sway Switch) are placed at every 30 meter along the length of conveyor.

• Carrying and return self aligning transoms are placed at every 20 meters along the length of the belt.
• Horizontal chain conveyor motor capacity = Chain span X Fuel handling capacity / 80

Example: A chain conveyor of capacity 100 TPH & having centre to center distance 30 meters requires motor of capacity 100 X 30 / 80 =37.5 KW to drive the conveyor safely

PUMPS:

• Pump shutoff head = Design head X 1.07.

• Pump efficiency with cold water is less than pump efficiency with hot water

• Safe operating speed of boiler feed pumps is 55–60% of rated speed.

• Boiler feed pumps suction strainer pressure drop should be 0.04 to 0.06 kg/cm2.

• The pumps best efficiency point (B.E.P.) is between 80% and 85% of the shut off head.

• A double suction pump can run with less N.P.S.H. or at faster speed without cavitating.

• Multistage pumps reduce efficiency 2% to 4%.

• 1% capacity of pump will reduce on every 0.025 mm increase in wear ring clearance.

• Suction piping should be at least one size larger than the suction flange of the pump.

• Pumps piped in series must have the same capacity (impeller width and speed).

• Pumps piped in parallel must have the same head (impeller diameter and speed). 

• A centrifugal pump can handle 0.5% air by volume. At 6% it will probably become air bound and stop pumping. Cavitation can occur with any amount of air.

• A Vortex pump is 10% to 15% less efficient than a comparable size end suction centrifugal pump.

• There should be at least 10 diameters of pipe between the suction of the pump and the first elbow.

ELECTRICAL:

• Rating current of motor = 1.36 X hp or 1.79 3 KW.

• Starting current of a single phase motor (1 to 10 HP) = 3 X Motor full load current.

• Starting current of a three phase motor (up to 15 HP) = 2 X Motor full load current.

• Starting current of a three phase motor (>15 HP) = 1.5 X Motor full load current.

• Current carrying capacity of copper cable: 2 amps/mm2.

• Earthling resistance for single pit is <2 ohm.

• Voltage between neutral and earth <2 V.

• Resistance between neutral and earth <1 ohm.

Motor body earthing strip size:

• 85 SWG GI Wire for motors <5.5 KW.

• 25 X 6 mm GI Strip for motors 5.5 to 22 KW and Lighting and control panels.

• 40 X 6 mm GI Strip for motors 5.5 to 22 KW.

• 50 X 6 mm GI Strip for motors >55 KW and D.G and Exciter Panel.

• Motor insulation resistance = (20 X voltage)/(1000 + 2 X motor KW).

• Single phase motor draws 7 amps current per HP.

• Three phase motor draws 1.25 to 1.36 amps current per HP.

• No load current of three phase motor is 30 to 40% of full load current of motor.

• Submersible pump takes 0.4 KWH of extra energy at 1 meter drop of Water.

• Creepage Distance 5 18 to 22 mm/KV for moderate polluted air and 25 to 30 mm/KV for highly polluted air.

• Minimum Bending Radius for LT Power Cable is 12 X diameter of Cable.

• Minimum Bending Radius for HT Power Cable is 20 X diameter of Cable.

• Minimum Bending Radius for Control Cable is 10 X diameter of Cable.

• Insulation Resistance Value for Panel = 2 X KV rating of the panel.

• Test Voltage (AC for Meggering = (2 X Name Plate Voltage) + 1000.

• Test Voltage (DC for Meggering = (2 X Name Plate Voltage).

• Current Rating of Transformer = KVA X 1.4.

• No load current of Transformer = <2% of Transformer rated current.

• There are 4 Nos. of earth pits per transformer (2 No. for body and 2 No. for neutral earthing).

• Diesel generator set produces 3 to 3.5 KWH/liter of diesel.

• DG less than or equal to 1000 KVA must be in a canopy.

• DG greater than 1000 KVA can either be in a canopy or skid mounted in an acoustically treated room.

• DG fuel storage tanks should be a maximum of 990 Litter. Storage tanks above this level will trigger more stringent explosion protection provision.

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Opportunities for energy conservation in power plant

Opportunities for energy conservation in power plants

   

Energy conservation in Boilers:

• Control excess air in combustion which can lead to huge dry flue gas loss. Install online O2 analyzer for better controlling of excess air.

• Control Air pre-heater (APH) out let flue gas temperature, it is said that on every 22 °C rise in boiler outlet flue gas temperature leads to decrease in boiler efficiency by 1%.

• Optimize fuel moisture, which can lead to loss due to moisture.

• Installation of fuel (bagasse) driers for recovering potential heat from chimney inlet flue gas.

• Control unburnt in bed ash and fly ash, which can lead heat and fuel loss.

• Maintain maximum possible feed water inlet temperature at economizer inlet. On 6–7 °C rise in temperature of feed water at economizer inlet leads to 1% fuel saving. And 15 °C rise can lead to increase in overall thermal efficiency by 3%.

• Utilize unburnt from Economiser, bank zones by incorporating Cinder reinjection (CR) system

• Optimize boiler continuous blow down to reduce heat loss with hot water

• Create the ideas for utilizing blow down water for heating of combustion air, or feed water and even boiler blow down water can be used for cooling tower make up by reducing its temperature

• Utilize blow down flash steam for heating feed water in deaerator. Continuous blow down (CBD) from steam drum operating at 115 kg/cm2 releases 42–45% flash steam.

• Reduce boiler pressure if permissible, for process, boiler pressure can be maintained as per process requirement. This is the most effective way of fuel saving.

• Incorporate VFD to all boiler auxiliaries like fans and fuel feeding systems.

• Instead of throttling discharge air dampers ,provide inlet guide vanes to fans to control the air flow.

• Arrest all boiler steam, flue gas and water leakages.

• Operate boiler on optimum loads, boilers give more efficiency at 65–85% of full load.

• Inspect air distribution nozzles, dampers regularly.

• Try to get maximum temperature of combustion air by incorporating Steam coil air preheaters (SCAPH).It is said that on every 20 °C rise in combustion air temperature leads to increase in boiler efficiency by 1%.

• 10–12% of hot air recirculation into FD fan suction can maintain rated APH inlet air temperature, which can lead to elimination of SCPAH thereby reducing LP steam consumption.

• Utilize DG exhaust flue gas temperatures for heating systems like combustion air, feed water etc.

• Operate the soot blowers regularly to remove soot formed on heating surfaces. It is estimated that 2.5% of fuel consumption will increase on deposition of 3 mm soot on heating surfaces of pressure parts.

• Operate boiler feed pumps at rated or maximum possible suction pressure to reduce auxiliary power consumption.

• Incorporate VFD to boiler feed pumps and reduce speed whenever possible

• Operate feed water control valve at maximum opening i.e. control valves should open 70–80% for normal operation. It will reduce the pressure drop in control valves and hence load on boiler feed pumps.

• Attend the the leakage of Boiler feed pumps ARC valves.

• Use Neutra pit water or ETP treated water for ash quenching and other services.

• Use Neutra pit water or ETP treated water for ash quenching and other services.

• Operate the pneumatic ash handling system in probe mode instead of timer mode to save the compressor power.If run in timer mode optimise ash conveying time & cycle time.

• Use high temperature coatings for valves, lines etc. o reduce heat loss.

• Optimize deaerator steam vent line and orifice size to avoid excess steam vent or utlise this vent out steam for heating combustion air.Deaerator steam vent loss is around 0.1 % of Boiler steam generation.

• Remove air from indirect steam using equipments, as 0.25 mm thick air offers the same resistance to heat transfer as a 330 mm thick copper wall.

• Maintain water quality to avoid boiler scaling. A 1 mm thick scale deposit in the water side could increase fuel consumption by 5–8%.

• Insulate all hot water storage tanks.

Energy conservation in Fuel handling & storage system:

• Always store fuel in fuel shed to avoid wetting and excess drying of fuel in rainy and summer seasons respectively.

• Store fuel on PCC (Plain cement concrete) bed to avoid carpet loss of fuel.

• Cover fuel yard and storage shed by trees (bamboo) to reduce handling and feeding loss of fuels during high wind speed.

• Conveyors should have seal proof hood covers to avoid flying/escaping of fuel during high wind speed.

Energy conservation in Turbine and its auxiliary system:

• Maintain maximum rated pressure at Turbine inlet to achieve less SSC.

• Maintain maximum possible vacuum to reduce SSC.

• Maintain optimum cooling water inlet and outlet temperatures for all heat exchangers like steam condensers, oil coolers and Generator air coolers

• Optimize cooling tower blade angles, more the angle more the power consumption.

• Reduce the clearance between CT fan blade and concrete hood or fiber hood; generally it should be up to 25–30 mm.

• Provide VFDs to cooling tower fans and Main cooling water pumps to control speed as per requirement.

• Replace all aluminum blades by energy efficient FRP blades.

• Clean cooling tower water spray nozzles regularly.

• Arrange drift eliminators and fills properly for uniform spreading of air and water.

• Clean condenser and ejector tubes yearly to achieve proper heat transfer

• Keep cooling tower surrounding free from structures, building, trees to enable free air movement.

• Ensure cooling water pump top casing crub level is below the normal operating level of cooling tower toavoid carrying of air in water or it may lead to cavitation.

• Make a provision for online backwash systems for surface condenser and oil coolers to improve heat transfer.

• Clean oil pumps filters regularly.

• Incorporate VFD to Condensate extraction pumps (CEPs).

• Install condensate recovery system from all process line drains and traps.

• Use CEP discharge water instead of BFP discharge water for desuperheating of low pressure process steam.

• Select optimum head condensate extraction pumps. If Deaerator working pressure is 2.75 kg/cm2A CEP of 80 meter discharge head considering all losses is sufficient.

• Try to get maximum percentage of condensate from processes.

Energy conservation in other balance of plant (BOP) areas:

• Replace all globe valves by ball valves of instrument pressurized air.

• Clean suction air filters of compressors regularly as 250 mmwc pressure drop in suction filter will lead to the reduction of compressor efficiency by 2%.

• Opening of air filters should be sufficient to suck enough air.

• Locate compressors at lower level as at higher elevation compressors consume more power.

• Install compressors in well ventilated areas.

• Ensure cool water and air for compressors air cooling system. At every 4 °C rise in inlet cooling water temperature will increase power consumption by 1%.

• Clean after and inter coolers regularly to get better heat transfer.

• Install auto moisture drains for air lines.

• Avoid unnecessary use of compressed air for applications like cleaning, washing, pneumatic tools etc.

• Optimize discharge air pressure of compressor, on reduction of 1 kg/cm2 discharge air pressure leads to input power saving by 6–10% And on reduction of discharge air pressure by 1 kg/cm2 will reduce air leakage by 10%.

• Carryout periodic air leakages test.

• Prefer two stage reciprocating air compressors over single stage for same FAD and pressure as single stage compressors consume much power than multi stage.

• In centrifugal fans (ID, FD and SA fans) Maintain optimum cone clearance and overlap gap to reduce power consumption.

• Provide optimum height  silencers for high speed centrifugal fans and take care the silencer is free from all obstacles.

• Modify ducting system by removing all obstacles to avoid pressure drop.

• Incorporate VFDs to ventilation blowers to control speed during low temperature season (Winter and rainy seasons).

• Provide VFDs to all possible pumps.

• Replace all loose V belts as loose and damaged V belts conribute in more power consumption

• Timely checking of equipment vibrations and alignment to avoid unnecessary power consumption and machine failure.

• Avoid over greasing of bearings to reduce churning effect and energy consumption.

• Replace higher rated capacity pumps with rated to avoid running of higher capacity pumps under load.

• Replace all worn out wear rings of impellers and casing, as more clearance between wear ring and pump suction will contribute in more power consumption to maintain required flow.

• Instead of controlling discharge valve, impeller trimming is the best way to control flow and power consumption.

• Use booster pumps for small loads requiring higher pressure.

• Provide all measuring instruments like flow, pressures for pumps to monitor their performance regularly.

• Avoid bends and U seal pattern for suction line of pumps.

• Use mechanical seals over gland packings.

• Avoid connecting small size pump discharge line to higher size header, the ratio of header and discharge line should be in the range of 1.3 to 1.6 only. For higher size ratio power consumption will be more.

• Replace all conventional gear boxes like worm-worm wheel and helical by more efficient planetary gear box.

• Replace DOL starter motors of heavy equipments like chain conveyors with soft starters.

• Modify the chain conveyor system to reduce unwanted dead loads like slat weights, link size etc.

• Incorporate timers of street and plant lighting system.

• Replace all the plant lighting bulbs by high efficient LED bulbs.

• Maintain higher power factor at all the load ends by installing capacitor banks to reduce excess reactive power.

• Provide forced cooling system for higher capacity power transformers to reduce losses.

• 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.

• Synchronous motors are more suitable to improve power factor.

• Balance the three phase power supply, an unbalanced voltage can increase motor input power by 3–5%.

• 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.

• Optimize the quantity of lubricants in bearings and gearboxes to reduce unwanted load due to excessive lubricants.

• Provide an alternate arrangement for connecting river water directly into clarifier; it will save power consumption for lifting water from reservoir to clarifier.

• Prefer gravity make up system for condenser hot well make up, it will save pump power for hot well

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