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Compressed Air

Compressed Air. Walter Bright MAE406 – Energy Conservation in Industry wabright@ncsu.edu 10/29/2013. C.A. Basics. C.A. Basics. Why Compressed Air?. Compressed air is simply a medium to transmit power, similar to electricity or steam to transmit heat

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Compressed Air

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  1. Compressed Air Walter Bright MAE406 – Energy Conservation in Industry wabright@ncsu.edu 10/29/2013

  2. C.A. Basics

  3. C.A. Basics Why Compressed Air? • Compressed air is simply a medium to transmit power, similar to electricity or steam to transmit heat • Often referred to as the ‘fourth utility’ • Compressed air can be used for a multitude of applications • Simple: Pumping up tires and blow-off nozzles • More Complex: Instrumentation, Vacuum generation, Pneumatic tools, cylinders and valves • Ex: flow controllers, pumps, impact wrenches, nail guns, etc • End-use equipment is cheap, lightweight, compact & powerful • Explosive environments • Easy to control (solenoid valves, pressureproportional to force)

  4. C.A. Basics Basic Compressor Specialized Bicycles/Popular Mechanics

  5. C.A. Basics Why NOT Compressed Air? $$$ Typically the most expensive utility at a plant Rule of Thumb: It takes 7 units of compressor horsepower to provide one horsepower of useful work! Why is compressed air so expensive??? Ex: Cost of operating a 10hp motor for 1 year (8,760hrs) 10hp Electric Motor 10hp Pneumatic Motor $5,388 $32,818

  6. C.A. Basics Why Manage Compressed Air? Compressed Air Challenge, www.compressedairchallenge.org • Surely if it’s the most expensive utility at a plant it’s being continuously managed… • Example: • Foundry Sand Transport System • 350 hp of compressor power • Energy consumption reduced by 36% • $16,300 in annual savings • 1.3 year simple payback • Substantial opportunity throughout industry to reduce compressed air usage and cost • Plant personnel often think compressed air is free

  7. C.A. Basics Compression Thermodynamics Greg Harrell, Energy Management Services (EMS) 100 kW of electrical energy input MOTOR COMP

  8. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 100 kW of electrical energy input MOTOR COMP 5-8 kW of thermal energy loss

  9. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 100 kW of electrical energy input MOTOR COMP 5-8 kW of thermal energy loss # kW of loss??

  10. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 100 kW of electrical energy input MOTOR COMP 5-8 kW of thermal energy loss 98-99% Efficient

  11. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 100 kW of electrical energy input MOTOR COMP We want high-pressure air from the compressor… 5-8 kW of thermal energy loss 98-99% Efficient

  12. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 100 kW of electrical energy input MOTOR COMP We want high-pressure air from the compressor… 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient

  13. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 100 kW of electrical energy input MOTOR COMP We want high-pressure air from the compressor… 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient*

  14. C.A. Basics Greg Harrell, EMS Compression Thermodynamics # kW of thermal energy loss?? 100 kW of electrical energy input MOTOR COMP We want high-pressure air from the compressor… 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient*

  15. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 90 kW of thermal energy loss 100 kW of electrical energy input MOTOR COMP We want high-pressure air from the compressor… 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient*

  16. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 90 kW of thermal energy loss 100 kW of electrical energy input # kW of shaft energy from comp. air motor?? MOTOR COMP C.A.MTR We want high-pressure air from the compressor… 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient*

  17. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 90 kW of thermal energy loss 100 kW of electrical energy input 10 to 20 kW of shaft energy from comp. air motor MOTOR COMP C.A.MTR We want high-pressure air from the compressor… 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient*

  18. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 90 kW of thermal energy loss 100 kW of electrical energy input 10 to 20 kW of shaft energy from comp. air motor MOTOR COMP C.A.MTR We want high-pressure air from the compressor… What about the 1stLaw of Thermo?? 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient*

  19. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 90 kW of thermal energy loss 100 kW of electrical energy input 10 to 20 kW of shaft energy from comp. air motor MOTOR COMP C.A.MTR We want high-pressure air from the compressor… The 1stLaw of Thermo is not violated because the air discharged is very cold 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient*

  20. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 90 kW of thermal energy loss 100 kW of electrical energy input 10 to 20 kW of shaft energy from comp. air motor MOTOR COMP C.A.MTR We want high-pressure air from the compressor… The 1stLaw of Thermo is not violated because the air discharged is very cold 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient* COMPRESSION EFF: 10-20%

  21. C.A. Basics Greg Harrell, EMS Compression Thermodynamics 90 kW of thermal energy loss 100 kW of electrical energy input 10 to 20 kW of shaft energy from comp. air motor PROVE IT MOTOR COMP C.A.MTR We want high-pressure air from the compressor… The 1stLaw of Thermo is not violated because the air discharged is very cold 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient* COMPRESSION EFF: 10-20%

  22. The C.A. System

  23. The C.A. System Typical System Compressed Air Challenge Supply Side Demand Side

  24. The C.A. System Supply Side Types of Compressors Compressed Air Challenge

  25. The C.A. System Supply Side Reciprocating Compressed Air Challenge(pg. 129) • Analogy: Car IC Engine • How it works: • Oil and Oil-free • Single-acting and double-acting • Single or multi-stage, depending on pressure/size • Typically smaller units (less than 30hp*)

  26. The C.A. System Supply Side Reciprocating Belliss and Morcom • Originally THE compressor technology • Many vintage reciprocating compressors operating today, some in excess of 1,000 hp • THE most efficient compressor technology (double-acting) • Not used much today in industry • 22-24 kW/100 cfm (single-acting), 15-16 kW/100 cfm (double-acting)

  27. The C.A. System Supply Side Centrifugal • Analogy: Car turbocharger • How it works: • Impeller spinning at 10,000+ rpm • Typically larger units (300 hp to >4,500 hp) • All Oil Free • Multi-stage, typically 2-4 depending on size/pressure • Centrifugal Compressor Animation

  28. The C.A. System Supply Side Centrifugal • Low vibration, don’t need a heavy concrete pad like reciprocating • Still very efficient • Favored by industry today for large applications • Operating range limited • 16-20 kW/100 cfm

  29. The C.A. System Supply Side Rotary Screw • Analogy: Car supercharger • How it works: • Two screws meshed together which squeeze air • Typically medium sized units (20 hp to 300 hp) but can be as large as 600 hp • Oil and Oil Free • Typically single stage, some larger units 2 stage

  30. The C.A. System Supply Side Rotary Screw Ingersoll Rand • By far, most common industrial air compressor today • Low first cost, good efficiency, large operating range • Variety of control techniques and manufacturers • 17-22 kW/100 cfm (single stage)

  31. The C.A. System Supply Side Rotary Screw(Lubricant-Injected) Credit: Ponna Pneumatic Compressed Air/Oil Mixture Oil (Lubricant) “Oil-Free” Compressed Air (2-3 ppm)

  32. The C.A. System Supply Side Dryers Compressed Air Challenge • Air dryers condense water out of compressed air • Air at 80°F and 50% = 60°F dewpoint and 0.01092 lbw/lba • Compressed to 100 psig and 185°F, how much water in air? • Same! 0.01092 lbw/lba Squeeze water into space 8 times smaller (114.7/14.7=7.8) • What is new dewpoint? • 125°F (Rule of Thumb: Double pressure, increase dewpoint by 20°F • What happens if we send that air into a industrial plant that is 80°F ambient? • Rain inside compressed air pipes

  33. The C.A. System Supply Side Refrigerated Dryers • Refrigerated dryers utilize a refrigerant circuit to condense moisture from the air stream • Typical leaving dewpoint of 40°F • Cycling, non-cycling and head-unloading designs • 0.80 kW/100 cfm

  34. The C.A. System Supply Side Desiccant Regenerative Dryers • Desiccant dryers use a desiccant to dry the air (via adsorption) • Typical leaving dewpoint of -40°F to -100°F, depending on desiccant type • Heatless, heat-assisted and blower-heat assisted designs • 2-3 kW/100 cfm

  35. The C.A. System Supply Side Additional Components • Storage (Air Receivers, piping, etc) • Pressure/Flow Controllers • After-coolers • Air/Lubricant Separators • Filters • Particulate: Removes dirt/debris • Coalescing: Removes vapors (typically oil/lubricant vapors) • Adsorption: Additional hydrocarbons and other impurities • Traps and Drains • Level operated • Timer operated • Zero-air loss

  36. The C.A. System Demand Side Usage Breakdown Compressed Air Challenge • In a typical compressed air system, how much air is used “appropriately” by production? • Leaks: Compressed air which leaks from distribution • Inappropriate Uses: Anything that compressed air is used for which could be replaced via a more efficient process • Increased Demand from Excessive System Pressure: Better known as artificial demand

  37. The C.A. System Demand Side End-Users (Normal Production) • Pneumatic tools, cylinders, valves • Automation equipment • Instrumentation Air • Baghouses • Blow-off (special cases) • Motors/Pumps (where appropriate) • Etc.

  38. The C.A. System Demand Side Leaks Compressed Air Challenge • Higher the system pressure, higher the leak rate • <2 cfm leak: can’t feel, can’t hear • 3-4 cfm leak: can feel, can’t hear • >5 cfm leak: can feel, can hear • Leaks do more than waste energy • Shortens life of supply equipment because of increased runtime • Buy/add new compressor capacity that is not needed • Leak Table for a ‘perfect’ orifice (values are cfm)

  39. The C.A. System Demand Side Inappropriate Uses DOE Tip Sheets • An inappropriate use is anything that compressed air is currently used for, but has a more efficient alternative

  40. The C.A. System Demand Side Artificial Demand • If the pressure of the system is too high, uncontrolled uses consume more air • For example, a system that is at 100 psig has a leak load of 100 cfm. If the pressure is decreased, the leak rate is also decreased. • An unregulated air cylinder • Reducing the pressure not only saves energy because the compressor doesn’t have to work as hard, it also reduces the amount of air it has to generate

  41. The C.A. System Measurements and Baselining • Compressed air systems are dynamic, meaning that a spot check is not sufficient to determine how well it is operating • Determining how a compressor is operating requires logging equipment

  42. C.A. Control Strategies

  43. C.A. Control Strategies On/Off Control • The simplest and most efficient control method • Turn compressor on and low pressure setpoint and turn off at high pressure setpoint • Only practical for small motors

  44. C.A. Control Strategies Load/Unload Control • Compressor operates in a pressure dead-band, similar to on/off • At upper band, instead of shutting off, compressor “unloads” • Bleed off air/oil separator (~40 seconds) • Only bleed down to ~40 psi • Why does it take 40 second to bleed sump? • Wait for pressure to reach lower setpoint • Compress air/oil separator back to operating pressure (~6 seconds) • Resume operation

  45. C.A. Control Strategies Lubricant-Injected Rotary Screw Load/Unload Control Credit: Ponna Pneumatic Loaded Unloading Unloaded Compressed Air/Oil Mixture Oil (Lubricant) “Oil-Free” Compressed Air (2-3 ppm)

  46. C.A. Control Strategies Lubricant-Injected Rotary Screw Load/Unload Control Credit: Ponna Pneumatic Loaded Loading Unloaded Compressed Air/Oil Mixture Oil (Lubricant) “Oil-Free” Compressed Air (2-3 ppm)

  47. C.A. Control Strategies Lubricant-Injected Rotary Screw Load/Unload Control • Storage plays a huge role in load/unload power consumption

  48. C.A. Control Strategies Load/Unload Control Compressed Air Challenge Capacity of TRIM compressor!

  49. C.A. Control Strategies Modulating Control • A low and high pressure limit as with load/unload • Inlet valve modulates flow rate into compressor • System pressure increases, inlet valve closes • System pressure decreases, inlet valve opens • No blowdown valve, sump always pressurized • Pressure drop across inlet valve • inlet pressure at screws decreases • increases pressure ratio, increases work • Results in competition between savings and costs

  50. C.A. Control Strategies Modulating Control Compressed Air Challenge

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