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