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1001 Boiler Feed Pump Selection   Ahr Expo 1001 Boiler Feed Pump Selection Ahr Expo Presentation Transcript

  • Boiler Feed Pump Selection 25 January 2010 Greg Towsley Grundfos Pumps Corporation Olathe, Kansas 913-227-3400 gtowsley@grundfos.com www.grundfos.com/cbs/us
  • 2006 Commercial Energy End-Use (Quadrillion Btu) Other Cooking 20% 2% Lighting Computers 25% 4% Refrigeration 4% Space Cooling 13% Water Heating 6% Space Heating Ventilation 12% 7% Electronics 7% Source: U.S. Department of Energy 25 January 2010 Boiler Feed Pump Selection 2
  • Presentation Objective The objective of this presentation is to help gain an understanding of how the proper sizing, selection, and operation of boiler feed water pumps will help reduce energy consumption, making the commercial building more efficient. 25 January 2010 Boiler Feed Pump Selection 3
  • Typical boiler system Return condensate Deaerator Level sensor Level sensor From water treatment Steam boiler Condensate tank Condensate pumps Feed pumps 25 January 2010 Boiler Feed Pump Selection 4
  • Boiler feed methods • On/off control • Via feed control valve • Via feed control valve and variable speed pumps • Variable speed pumps only 25 January 2010 Boiler Feed Pump Selection 5
  • Boiler feed, on/off control Level sensor Deaerator Steam boiler Feed pumps 25 January 2010 Boiler Feed Pump Selection 6
  • Boiler feed, on/off control System type Benefits Level Boiler feed, on/off control. > Inexpensive and simple to sensor install Function > No bypass Deaerator Steam boiler In on/off control the feed pump is switched on/off via a level Important Feed pumps sensor or a differential pressure Requirements vary from one sensor. When the water level municipal jurisdiction to falls to the “Pump on” level, the another as to the sizing of pump starts pumping a large boiler feed pumps (two pumps quantity of relatively cold water must always back up each into the boiler. This will reduce other 100%, requirements as the quantity of steam and cause to over-sizing, etc.) the steam pressure to fall. Poor inlet pressure could be a problem – NPSH available This is the reason why on/off control causes variations in steam production. It may also cause over-boiling in the boiler, which may cause water to enter the system. 25 January 2010 Boiler Feed Pump Selection 7
  • Boiler feed via feed control valve Bypass Level sensor Deaerator Steam boiler Feed pumps 25 January 2010 Boiler Feed Pump Selection 8
  • Boiler feed via feed valve Bypass System type Drawbacks Boiler feed via feed control valve. > The pump must be set to Level continuous operation (energy sensor Function consumption) In this type of system the water level > Bypass Deaerator in the boiler is controlled by means of > Feed valve is expensive Steam boiler a feed control valve, which is > Pressure loss across feed valve controlled by a level sensor or a Feed pumps differential pressure transmitter Important positioned on the boiler. Requirements vary from one municipal jurisdiction to another as The feed valve controls the water to the sizing of boiler feed pumps intake, which is adjusted according to (two pumps must always back up steam consumption. This, however, each other 100%, requirements as requires that the feed pump is set to to over-sizing, etc.) continuous operation. Remember to size bypass according This system operates smoothly and is to the pump manufacturer’s data as ideal for all types of steam boilers, to min. flow. It may be an idea to both small and large, and will stop the pump at closed valve. This minimize the risk of over-boiling. requires, however, a signal from the valve. Benefits > Boiler feed adjusted according to Poor inlet pressure could be a steam consumption, as described. problem – NPSH available 25 January 2010 Boiler Feed Pump Selection 9
  • Boiler feed via feed valve with variable speed pumps Bypass Level sensor Deaerator Steam boiler Feed pumps 25 January 2010 Boiler Feed Pump Selection 10
  • Boiler feed via feed valve with variable speed pumps Bypass System type Drawbacks Boiler feed via feed valve with variable > Bypass speed pumps. > Feed valve is expensive Level Level sensor sensor > Pressure loss across feed valve Function In this system, the water level in the Important Deaerator boiler is controlled by means of a feed Requirements vary from one Steam boiler valve, which is controlled by a level municipal jurisdiction to another as sensor or a differential pressure to the sizing of boiler feed pumps. Feed pumps transmitter positioned on the boiler. The feed valve controls the water Remember to size bypass according intake, which is adjusted according to to the manufacturer’s data as to steam consumption. This, however, min. flow. It may be an idea to stop requires that the feed pump is set to the pump at closed valve. This continuous operation. This system requires, however, a signal from the operates smoothly and is ideal for all valve. Find out whether variable types of steam boilers, both small and speed controlling of both pumps is large, and will minimize the risk of required, as this increases expenses, over-boiling but does not provide the same flexibility as to alternating pump Benefits operation. > Boiler feed adjusted according to steam consumption. Poor inlet pressure could be a > Energy savings on pump operation. problem – NPSH available > Constant differential pressure across feed valve Accessories required Possibly custom controls, pressure transmitter. 25 January 2010 Boiler Feed Pump Selection 11
  • Boiler feed with variable speed pumps without feed valve Level sensor Deaerator Steam boiler Feed pumps 25 January 2010 Boiler Feed Pump Selection 12
  • Boiler feed with variable speed pumps without feed valve System type Drawback Boiler feed with variable speed pumps > Requires precise and qualified Level without feed valve. start-up. sensor Function Important Deaerator In this system, the water level in the Requirements vary from one Steam boiler boiler is controlled directly by means of municipal jurisdiction to another as the variable speed pumps without the to the sizing of boiler feed pumps Feed pumps use of a feed valve. The pumps are (two pumps must always back up controlled by means of a level sensor or each other 100%, requirements as a differential pressure transmitter to over-sizing, etc.). A non-return positioned on the boiler. This way the valve must be installed on the water intake is controlled according to suction pipe of the boiler. steam consumption. This system operates smoothly and is ideal for all A minimum frequency must be types of steam boilers, both small and defined ensuring that the pump can large, and will minimize the risk of over- always overcome the pressure in boiling. the boiler. It must be ensured that the pump stops when steam Benefits consumption is zero. > As described, boiler feed adjusted according to steam consumption. Poor inlet pressure could be a > Energy-savings on pump operation problem – NPSH available. > No pressure loss across feed valve > Money earned equal to the price of Accessories required an expensive feed valve Possibly custom controls. 25 January 2010 Boiler Feed Pump Selection 13
  • Pump sizing Example for calculating flow and head. From the boiler nameplate, we have the following information: •Boiler HP = 600 (20,700 lb/hr @ 212°F) Never use the steam temperature - it is the •Max. Steam supply press. = 200 psig deaerator temperature •Min. Steam supply press. = 150 psig you must use when •Temperature = 350 °F sizing the pump From the vapor table we have following data on water with a temp. of 212°F Bypass Steam •Specific Gravity = 0.96 20,700 lb/hr •Vapor pressure = 14.7 psia 350°F 212°F Deareator Condensate Boiler Feed pumps 25 January 2010 Boiler Feed Pump Selection 14
  • Pump sizing QBoiler = QBoiler × 0.069 = 600 × 0.069 = 43.13gpm For a continuously operated boiler - 15% S.F. may be applied: Q PumpContinuous = 1.15 × QBoiler = 1.15 × 43.13 = 49.60 gpm For min. flow –> refer to manufacturer: Q Min = Q PumpCont ×15% = 49.60 × 15% = 7.44 gpm Q =Q +Q = 49.60 + 7.44 = 57.0 gpm Pump PumpCont Min 25 January 2010 Boiler Feed Pump Selection 15
  • Throttling H No Load Partial Load HN Full Load Q QN Allowable Operating Range 25 January 2010 Boiler Feed Pump Selection 16
  • Total Dynamic Head The Total Dynamic Head (H) is determined after the system is designed! static 0 static dynamic. p a −p e v 2 −v 2 H= + + z a − z e + Hv a e ρg 2g pa Closed System pe z Hv 25 January 2010 Boiler Feed Pump Selection 17
  • System Characteristics HN = Hstat + Hdyn H Hstat QN Q 25 January 2010 Boiler Feed Pump Selection 18
  • System Head HN = Hstat + Hdyn H HN Hdyn Hstat QN Q 25 January 2010 Boiler Feed Pump Selection 19
  • Friction Loss Each pipe, each shaped part, each fitting and each filter has friction loss Q = HV The resistance of many fittings change over time in a piping system! (filters, etc..) Don’t forget regular cleaning! 25 January 2010 Boiler Feed Pump Selection 20
  • Boiler scale Image source: http://www.aalborg-industries.com/marine_solutions/documents/6ScalinginblrwtrMAR04.pdf 25 January 2010 Boiler Feed Pump Selection 21
  • Steam Pressure and Specific Gravity of Water Vapor Vapor Vapor Pressure Vapor Pressure S.G. @ 60 F Pressue Feet Abs. S.G. @ 60 F Pressue Feet Abs. Temp. F Temp. C Reference PSI Abs. (@ Temp.) Temp. F Temp. C Reference PSI Abs. (@ Temp.) 32 0 1.002 0.089 0.204 120 48.9 0.990 1.692 3.943 40 4.4 1.001 0.122 0.281 130 54.5 0.987 2.223 5.196 45 7.2 1.001 0.148 0.340 140 60.0 0.985 2.889 6.766 50 10.0 1.001 0.178 0.411 150 65.6 0.982 3.718 8.735 55 12.8 1.000 0.214 0.494 160 71.2 0.979 4.741 11.172 60 15.6 1.000 0.256 0.591 170 76.7 0.975 5.992 14.178 65 18.3 0.999 0.306 0.706 180 82.3 0.978 7.510 17.825 70 21.1 0.999 0.363 0.839 190 87.8 0.968 9.339 22.257 75 23.9 0.998 0.430 0.994 200 93.4 0.964 11.526 27.584 80 26.7 0.998 0.507 1.172 212 100.1 0.959 14.696 35.353 85 29.5 0.997 0.596 1.379 220 104.5 0.956 17.186 41.343 90 32.2 0.996 0.698 1.617 240 115.6 0.948 24.970 60.770 95 35.0 0.995 0.815 1.890 260 126.8 0.939 35.430 87.050 100 37.8 0.994 0.949 2.203 280 137.9 0.929 49.200 122.180 110 43.4 0.992 1.275 2.965 300 149.0 0.919 67.010 168.220 25 January 2010 Boiler Feed Pump Selection 22
  • Total Dynamic Head Given: •Maximum boiler pressure = 200 psig •Water temperature = 212°F •Friction loss = 5 psig •Static head = 0 feet •Velocity head = 0 psig H= Pressure (psi) × 2.31 = (200 psi + 5 psi )× 2.31 Specific Gravity (S.G.) 0.959 H = 494 ft. Pump Design Size: Q = 57 gpm H = 494 ft. 25 January 2010 Boiler Feed Pump Selection 23
  • Pump Selection 59 gpm @ 541 ft. (+10%) 57 gpm @ 494 ft. η = 68.2% P2 = 11.9 hp NPSHr = 10 ft. 25 January 2010 Boiler Feed Pump Selection 24
  • Energy Saving Pump Selection 57 gpm @ 494 ft. η = 68.1% P2 = 10.0 hp NPSHr = 9.2 ft. 25 January 2010 Boiler Feed Pump Selection 25
  • Energy Saving Pump Selection 35 gpm @ 494 ft. η = 65.4% P2 = 6.4 hp 25 January 2010 Boiler Feed Pump Selection 26
  • Energy Conservation: Energy Conservation - Pump operates only at the speed that is required. No pressure loss across a pinched valve. 600 H (ft.) Constant Pressure 450 Max. Speed Operating Point 300 Reduced Speed Operating Point at Reduced Speed 150 0 0 5 10 15 20 25 30 35 40 Q (gpm) 25 January 2010 Boiler Feed Pump Selection 27
  • Advantages ... • ...with the installation of the variable speed pump as a boiler feed pump •Even steam production. •Faster reaction with changed steam consumption. •Fewer losses by variable level. •Smaller loss of water. Less energy consumption Energy Cost Savings A smaller pump can be used, since the pressure loss of the regulating valve is eliminated. 25 January 2010 Boiler Feed Pump Selection 28
  • Regulation: Constant Level Max. • The level sensor gives a signal to 4-20 mA to the control box. 10 inches Set point P-band • The P-Band relates to 1.5 inches. • The variable speed pump receives 0-10 V Min. Level sensor output a signal for speed adjustment. 4 mA 20 mA • If the sensor signals 5 mA, corresponding Speed P-band to 9.375 inches of the desired value, the 100% pump is switched off. • The pump is restarted when if the sensor 55% falls within the P-Band. Control box Stop 5 mA output 25 January 2010 Boiler Feed Pump Selection 29
  • Cavitation • Cavitation involves a bubble that is formed in the impeller. • Cavitation occurs due to a local pressure drop in the eye of the impeller, and because of the increase of the flow rate. The bubbles follow along the impeller vane and if they come into range of a higher pressure - they implode. • The imploded bubbles forms a micro jet against the impeller or impeller vane. At this point, this high speed micro jet hits the impeller and it can hit pressure peaks to 1450 psi. 25 January 2010 Boiler Feed Pump Selection 30
  • Net Positive Suction Head (NPSH) To avoid cavitation: NPSHsystem > NPSHPump NPSHsystem= hb – hf – hv ± hgeo – hs NPSHsystem = The pressure available on the inlet of the pump hb = Atmospheric pressure at the pump site hf = Friction loss in the suction pipe hv = Vapor pressure of the liquid. hgeo = The water level above or under the pump inlet hs = Safety factor. Normally 1.5 to 2.0 feet minimum Example: With the value from earlier and the tank placed 15 feet above the pumps. hsystem = hb − h f − hv ± hgeo − hs = 35.4 ft. − 1 ft. − 35.4 ft. + 13 ft. − 2 ft. = 10 ft. In boiler systems, the atmospheric pressure and the vapor pressure always cancel each other. In this closed system, pressure of the water in the deaerator is required to be high enough to prevent the water from boiling. 25 January 2010 Boiler Feed Pump Selection 31
  • Steam Pressure and Specific Gravity of Water Vapor Vapor Vapor Pressure Vapor Pressure S.G. @ 60 F Pressue Feet Abs. S.G. @ 60 F Pressue Feet Abs. Temp. F Temp. C Reference PSI Abs. (@ Temp.) Temp. F Temp. C Reference PSI Abs. (@ Temp.) 32 0 1.002 0.089 0.204 120 48.9 0.990 1.692 3.943 40 4.4 1.001 0.122 0.281 130 54.5 0.987 2.223 5.196 45 7.2 1.001 0.148 0.340 140 60.0 0.985 2.889 6.766 50 10.0 1.001 0.178 0.411 150 65.6 0.982 3.718 8.735 55 12.8 1.000 0.214 0.494 160 71.2 0.979 4.741 11.172 60 15.6 1.000 0.256 0.591 170 76.7 0.975 5.992 14.178 65 18.3 0.999 0.306 0.706 180 82.3 0.978 7.510 17.825 70 21.1 0.999 0.363 0.839 190 87.8 0.968 9.339 22.257 75 23.9 0.998 0.430 0.994 200 93.4 0.964 11.526 27.584 80 26.7 0.998 0.507 1.172 212 100.1 0.959 14.696 35.353 85 29.5 0.997 0.596 1.379 220 104.5 0.956 17.186 41.343 90 32.2 0.996 0.698 1.617 240 115.6 0.948 24.970 60.770 95 35.0 0.995 0.815 1.890 260 126.8 0.939 35.430 87.050 100 37.8 0.994 0.949 2.203 280 137.9 0.929 49.200 122.180 110 43.4 0.992 1.275 2.965 300 149.0 0.919 67.010 168.220 25 January 2010 Boiler Feed Pump Selection 32
  • Pump sizing 3.7 25 January 2010 Boiler Feed Pump Selection 33
  • Considerations • Caution when providing fresh make-up water in a closed feed water tank! 1. Condensate t = 240°F p = 24.97 psia 2. Cold water make-up t = 50° Mixed Temperature 195°F p = 10.43 psia The pressure pad in the tank sinks at 10.43 psia, and concurrently at the pump inlet. The pressure at the intake of the pump sinks under the minimum inlet pressure...... Cavitation 25 January 2010 Boiler Feed Pump Selection 34
  • Considerations A strainer ... …increases the friction loss on the pump suction side! The existing NPSH Available drops. A drop of NPSH Available in the system below the level of the NPSH Required of the pump ...... Cavitation 25 January 2010 Boiler Feed Pump Selection 35
  • Considerations Minimum Water Level! When falling below the minimum water level in the deaerator due to insufficient fresh water refilling and without dry-run operation protection! Dry-run Operation / Cavitation 25 January 2010 Boiler Feed Pump Selection 36
  • Considerations Leaking discharge check valve! Steam in the pump! Overheating/Dry-run operation 25 January 2010 Boiler Feed Pump Selection 37
  • References • Cleaver-Brooks, Inc. 2006. The Boiler Book. Milwaukee, WI: Cleaver- Brooks, Inc. • D&R International, Ltd., 2009. 2009 Buildings Energy Data Book. Buildings Technologies Program, Energy Efficiency and Renewable Energy, U.S. Department of Energy, Washington, D.C. • Grundfos Pumps Corporation, 2008. Grundfos Pump Handbook. Olathe, Kansas: Grundfos Pumps Corporation • Hydraulic Institute, 2007 Draft. ANSI/HI 9.6.3 - American National Standard for Centrifugal and Vertical Pumps For Guideline for Allowable Operating Region, New Jersey: Hydraulic Institute 25 January 2010 Boiler Feed Pump Selection 38
  • Questions? Greg Towsley – gtowsley@grundfos.com 25 January 2010 Boiler Feed Pump Selection 39