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Compressed Air Walter Bright MAE406 – Energy Conservation in Industry 10/29/2013.

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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 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, pressure proportional to force) Why Compressed Air?

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

5 C.A. Basics Why NOT Compressed Air? $5,388 $32,818

6 C.A. Basics 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 Why Manage Compressed Air? Compressed Air Challenge, www.compressedairchallenge.org

7 C.A. THERMODYNAMICS

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

23 C.A. Thermo An isothermal process is ideal – That way, every portion of power goes into pressure energy instead of thermal and pressure energy Compression is essentially adiabatic (no heat transfer) Ideally, it would be reversible also, or isentropic Equations

24 THE C.A. SYSTEM

25 The C.A. System Typical System Compressed Air Challenge

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

27 The C.A. System 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*) Typically smaller units (less than 30hp*) Supply Side Reciprocating Compressed Air Challenge (pg. 129)

28 The C.A. System 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) Supply Side Reciprocating Belliss and Morcom

29 The C.A. System 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 Centrifugal Compressor Animation Supply Side Centrifugal

30 The C.A. System 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 Supply Side Centrifugal

31 The C.A. System Supply Side Rotary Screw Analogy: Car supercharger How it works: – Two screws meshed together which squeeze air 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

32 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)

33 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)

34 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 lb w /lb a Compressed to 100 psig and 185°F, how much water in air? – Same! 0.01092 lb w /lb a 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

35 The C.A. System 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 Supply Side Refrigerated Dryers

36 The C.A. System 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 Supply Side Desiccant Regenerative Dryers

37 The C.A. System 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 Supply Side Additional Components

38 The C.A. System In a typical compressed air system, how much air is used “appropriately” by production? Demand Side Usage Breakdown Compressed Air Challenge 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

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

40 The C.A. System 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) Demand Side Leaks Compressed Air Challenge 1/64”1/32”1/16”1/8”1/4”3/8” 70 psig 0.3001.204.7919.276.7173 80 psig 0.3351.345.3621.485.7193 90 psig 0.3701.485.9223.894.8213 100 psig 0.4061.626.4926.0104234 125 psig 0.4941.987.9031.6126284

41 The C.A. System An inappropriate use is anything that compressed air is currently used for, but has a more efficient alternative Demand Side Inappropriate Uses DOE Tip Sheets Potentially Inappropriate UsesSuggested Alternatives/Actions Clean-up, Drying, Process CoolingLow-pressure blowers, electric fans, brooms, nozzles SpargingLow-pressure blowers and mixers Aspirating, AtomizingLow-pressure blowers PaddingLow to medium-pressure blowers Vacuum generatorDedicated vacuum pump or central vacuum system Personnel coolingElectric fans Open-tube, compressed air-operated vortex coolers without thermostats Air-to-air heat exchanger or air conditioner, add thermostats to vortex cooler Air motor-driven mixerElectric motor-driven mixer Air-operated diaphragm pumpsProper regulator and speed control; electric pump Idle equipmentPut an air-stop valve at the compressed air inlet Abandoned equipmentDisconnect air supply to equipment

42 The C.A. System 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 Demand Side Artificial Demand

43 The C.A. System 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 Measurements and Baselining

44 C.A. CONTROL STRATEGIES

45 C.A. Control Strategies 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 On/Off Control

46 C.A. Control Strategies 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 Load/Unload Control

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

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

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

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

51 C.A. Control Strategies 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 Modulating Control

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

53 C.A. Control Strategies Add variable speed drive to motor Speed is proportional to capacity – So at 80% speed, you produce roughly 80% of the rated capacity Less efficient than other types at 100% capacity – VFD drive consumes some power – Screws on constant speed machines can be designed for a single speed. Screws on variable speed machines must pick a design point, typically about 80% of full speed. Variable Speed Control Compressed Air Challenge

54 C.A. Control Strategies Variable Speed Control Compressed Air Challenge

55 C.A. ENERGY SAVINGS 55

56 C.A. Energy Savings Compressed air leaks can be between 5 and 30% of system energy usage – Typically 20-30% for ‘unmanaged’ systems – Poorly maintained plants can be even more! Savings depend on type of compressor and control type, but applicable for all compressed air systems Fix Compressed Air Leaks

57 C.A. Energy Savings At $0.10/kWh, 8,760 hrs/yr For a variable speed compressor: Fix Compressed Air Leaks LeakVolumetricPower LossDemandEnergyCost Diameter, DFlow Rate, VfLReduction, DRSavings (in)(cfm)(hp)(kW)(kWh/yr)($/yr) 1/32 1.00.220.16727$72 1/16 4.00.880.662,908$291 1/8 16.13.532.6311,634$1,163 1/4 64.614.1110.5346,535$4,654 For a modulating compressor: LeakVolumetricPower LossDemandEnergyCost Diameter, DFlow Rate, VfLReduction, DRSavings (in)(cfm)(hp)(kW)(kWh/yr)($/yr) 1/32 1.00.22 0.048218$22 1/16 4.00.88 0.198872$87 1/8 16.13.53 0.7893,490$349 1/4 64.614.113.1613,961$1,396 Ex: Reduce air leaks by 160 cfm, save $3,458/yr

58 C.A. Energy Savings Pressure typically set at whatever compressor is rated Plant rarely needs that high of a pressure Pressure should be set based on highest pressure need – If the highest pressure need is 65 psig for a process line, then the compressor should be set at a pressure to provide that 65 psig – <100 psi is a typical header pressure Rule of Thumb: 1% for every 2 psi reduction Recall discussion about artificial demand Example: Can we decrease pressure with system “as-is?” – No, already below critical pressure at high demand! – Then modify the system Reduce Compressor Pressure

59 C.A. Energy Savings Screw compressors can switch from modulating to load/unload very easily* – *Many compressors can do it at the flip of a switch, not all – Storage is important (next slide) Difficult to retrofit from single speed to variable speed – Typically have to buy new compressor, even more pricy Interlink multiple compressors with network controls – Typically only useful for many compressor systems – Not as helpful in our example Overlapping control bands – With pressure fixed, control bands can be separated Change Control Type/Setpoint

60 C.A. Energy Savings Only for load/unload Adding storage allows for compressor to run unloaded for longer periods of time, resulting in lower overall energy usage Storage is expensive – $20,000 or more for 7,000 gal of storage What does 7,000 gallons look like? What does 20,000 gallons look like? Add 4,000 gal of storage to system – Switch to Load/Unload – Lower control bands to appropriate points (18 psi improvement) – Savings of $22,226/yr (this includes load/unload savings, pressure reduction savings and overlapping control band savings) Add Storage

61 C.A. Energy Savings Cooling the air at the compressor inlet reduces energy consumption Doesn’t work for flooded-oil screw compressors Works well for reciprocating, centrifugal and oil-free rotary screw compressors Cool Compressor Inlet

62 C.A. Energy Savings Baghouse pulse causes severe pressure drops in system 6 cubic foot pulse for 0.25 seconds every 1 minute Instantaneous Flow: – (6 ft3)/(.25 sec)x(60 sec/min) = 1,440 cfm Average Flow – (6 ft3)/(2 minutes)=6 cfm Add secondary storage Savings are hard to figure, likely from productivity increase High Volume, Intermittent Needs

63 C.A. Energy Savings Air Knifes can be replaced with low pressure blowers Think about an industrial-strength hair blower without the heat High flow, low pressure Low Pressure Blowers

64 C.A. Energy Savings Use the 80-85% of energy wasted as heat – If air cooled, use to heat areas during winter – If water cooled, might be able to utilize for boiler makeup water or other sources Piping can get very expensive Low-grade heat, makes it difficult to capture Utilize Compressor Waste Heat

65 C.A. Energy Savings Facility not operating, still need compressed air Typically a result of a “dry” sprinkler system Compressed air pressurizes and fills pipes, if a sprinkler head bursts the compressed air escapes and the water follows behind Typically need <5 hp to keep system pressurized Many companies run one compressor off-shift to pressurize system Savings for our example are $14,400/yr! Off-Hours Compressed Air Use

66 C.A. Energy Savings Savings are intertwined; cannot add savings from other slides all together because effects are cumulative Summary – Eliminate Compressed Air Leaks – Reduce Pressure and Fix Control Bands – Add storage and switch to Load/Unload – Add low pressure blower for air knifes – Add new 5 hp compressor for sprinkler system Total savings: $66,331 or 65%! Implementation cost likely below $30,000 Doesn’t include Productivity Increase! Total Savings from Example

67 QUESTIONS??? 67

68 Notes Required Materials – Road Bike Tire – Hand Pump/Compressor – Pancake compressor – Air hose – Extension cord – Blow-off nozzle – Open connector – Compressed air tools Nail gun – Two boards – Ammo Air Wrench – Gatorade Bottle w/ soap & water – Loggers HOBO logger with CT HOBO logger with power meter Fluke Pressure transducer – Plastic model of screw compressor – Data log of air compressor


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