MAE406 – Energy Conservation in Industry Compressed Air What is compressed air? Anyone w/ compressed air experience? 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 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)

C.A. Basics Basic Compressor Specialized Bicycles/Popular Mechanics http://www.popularmechanics.com/home/improvement/energy-efficient/1275131 Talk about basic compressor Specialized Bicycles/Popular Mechanics

Why is compressed air so expensive??? 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

C.A. Basics Why Manage Compressed Air? 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 DOE offers 6 days worth of compressed air training! Compressed Air Challenge, www.compressedairchallenge.org

C.A. Thermodynamics

100 kW of electrical energy input C.A. Basics Compression Thermodynamics 100 kW of electrical energy input MOTOR COMP Demonstrate how much heat is created via a bike pump and road bike tire Greg Harrell, Energy Management Services (EMS)

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

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

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

C.A. Basics 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 Greg Harrell, EMS

C.A. Basics 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 Greg Harrell, EMS

C.A. Basics 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* Greg Harrell, EMS

C.A. Basics Compression Thermodynamics 100 kW of electrical energy input # kW of thermal energy loss?? 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* Greg Harrell, EMS

C.A. Basics Compression Thermodynamics 100 kW of electrical energy input 90 kW of thermal energy loss 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* Greg Harrell, EMS

C.A. Basics Compression Thermodynamics 100 kW of electrical energy input 90 kW of thermal energy loss # 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* Greg Harrell, EMS

C.A. Basics Compression Thermodynamics 100 kW of electrical energy input 90 kW of thermal energy loss 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* Greg Harrell, EMS

C.A. Basics Compression Thermodynamics 100 kW of electrical energy input 90 kW of thermal energy loss 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 1st Law of Thermo?? 5-8 kW of thermal energy loss What we get is high-pressure, high-temperature air 98-99% Efficient* Greg Harrell, EMS

C.A. Basics Compression Thermodynamics 100 kW of electrical energy input 90 kW of thermal energy loss 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 1st Law 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* Greg Harrell, EMS

COMPRESSION EFF: 10-20% C.A. Basics Compression Thermodynamics 100 kW of electrical energy input 90 kW of thermal energy loss 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 1st Law 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% Greg Harrell, EMS

PROVE IT COMPRESSION EFF: 10-20% C.A. Basics Compression Thermodynamics 100 kW of electrical energy input 90 kW of thermal energy loss 10 to 20 kW of shaft energy from comp. air motor MOTOR PROVE IT COMP C.A. MTR We want high-pressure air from the compressor… The 1st Law 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 Demonstration with air nozzle or just a open connector 7 units of compressor work for 1 useful unit of mechanical work = 14.3% compression efficiency 98-99% Efficient* COMPRESSION EFF: 10-20% Greg Harrell, EMS

C.A. Thermo An isothermal process is ideal Equations 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

The C.A. System

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

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

The C.A. System Analogy: Car IC Engine How it works: Oil and Oil-free Supply Side Reciprocating 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*) http://www.youtube.com/watch?v=ITCu7gNMicc Compressed Air Challenge (pg. 129)

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

The C.A. System Analogy: Car turbocharger How it works: 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 http://www.youtube.com/watch?v=DnpLlOMha5M Important content starts @54sec

The C.A. System Supply Side Centrifugal Low vibration, don’t need a heavy concrete pad like reciprocating Favored by industry today for large applications Operating range limited Still very efficient 16-20 kW/100 cfm Saint Gobain in Wilson, NC. Picture of four 1000hp, 3 stage Centac units. Three more two stage units @ 1000hp behind photographer to right. Also a ~250hp screw

The C.A. System Analogy: Car supercharger How it works: 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 http://www.youtube.com/watch?v=stjvbAO_6JQ How do I know the front of the picture is the intake and back is discharge? Answer: Size of hole, density of air is much greater at exit, need less space

The C.A. System By far, most common industrial air compressor today Supply Side Rotary Screw 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) Ingersoll Rand

The C.A. System Supply Side Rotary Screw (Lubricant-Injected) Compressed Air/Oil Mixture Oil (Lubricant) “Oil-Free” Compressed Air (2-3 ppm) http://www.poonapneumatic.com/rotary-compressors.html Credit: Ponna Pneumatic

The C.A. System Supply Side Dryers 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 Compressed Air Challenge

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 http://catalog.wlimg.com/1/392427/other-images/table1-753375.jpg

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

The C.A. System Storage (Air Receivers, piping, etc) 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

The C.A. System Demand Side Usage Breakdown 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 Compressed Air Challenge

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

The C.A. System Demand Side Leaks 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) 1/64” 1/32” 1/16” 1/8” 1/4” 3/8” 70 psig 0.300 1.20 4.79 19.2 76.7 173 80 psig 0.335 1.34 5.36 21.4 85.7 193 90 psig 0.370 1.48 5.92 23.8 94.8 213 100 psig 0.406 1.62 6.49 26.0 104 234 125 psig 0.494 1.98 7.90 31.6 126 284 Compressed Air Challenge

Potentially Inappropriate Uses Suggested Alternatives/Actions The C.A. System Demand Side Inappropriate Uses An inappropriate use is anything that compressed air is currently used for, but has a more efficient alternative Potentially Inappropriate Uses Suggested Alternatives/Actions Clean-up, Drying, Process Cooling Low-pressure blowers, electric fans, brooms, nozzles Sparging Low-pressure blowers and mixers Aspirating, Atomizing Low-pressure blowers Padding Low to medium-pressure blowers Vacuum generator Dedicated vacuum pump or central vacuum system Personnel cooling Electric 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 mixer Electric motor-driven mixer Air-operated diaphragm pumps Proper regulator and speed control; electric pump Idle equipment Put an air-stop valve at the compressed air inlet Abandoned equipment Disconnect air supply to equipment http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/compressed_air2.pdf DOE Tip Sheets

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

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

C.A. Control Strategies

C.A. Control Strategies The simplest and most efficient control method 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 http://www.firstelectricmotor.com/motor%20failure.htm

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

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

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

Storage plays a huge role in load/unload power consumption C.A. Control Strategies Lubricant-Injected Rotary Screw Load/Unload Control Storage plays a huge role in load/unload power consumption Graph of “ideal” unload curve, 50% on and 50% unloaded. Then draw actual with various amounts of storage

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

A low and high pressure limit as with load/unload 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

C.A. Control Strategies Modulating Control Compressed Air Challenge

Add variable speed drive to motor Speed is proportional to capacity C.A. Control Strategies Variable Speed Control 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. Compressed Air Challenge

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

C.A. Energy Savings

C.A. Energy Savings Fix Compressed Air Leaks 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

C.A. Energy Savings At $0.10/kWh, 8,760 hrs/yr Fix Compressed Air Leaks At $0.10/kWh, 8,760 hrs/yr For a variable speed compressor: Leak Volumetric Power Loss Demand Energy Cost Diameter, D Flow Rate, Vf L Reduction, DR Savings (in) (cfm) (hp) (kW) (kWh/yr) ($/yr) 1/32 1.0 0.22 0.16 727 $72 1/16 4.0 0.88 0.66 2,908 $291 1/8 16.1 3.53 2.63 11,634 $1,163 1/4 64.6 14.11 10.53 46,535 $4,654 For a modulating compressor: Leak Volumetric Power Loss Demand Energy Cost Diameter, D Flow Rate, Vf L Reduction, DR Savings (in) (cfm) (hp) (kW) (kWh/yr) ($/yr) 1/32 1.0 0.22 0.048 218 $22 1/16 4.0 0.88 0.198 872 $87 1/8 16.1 3.53 0.789 3,490 $349 1/4 64.6 14.11 3.16 13,961 $1,396 Ex: Reduce air leaks by 160 cfm, save $3,458/yr

C.A. Energy Savings Reduce Compressor Pressure 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

C.A. Energy Savings Change Control Type/Setpoint 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

C.A. Energy Savings Add Storage 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)

C.A. Energy Savings Cool Compressor Inlet 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

C.A. Energy Savings High Volume, Intermittent Needs 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

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

C.A. Energy Savings Use the 80-85% of energy wasted as heat Utilize Compressor Waste Heat 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

C.A. Energy Savings Facility not operating, still need compressed air Off-Hours Compressed Air Use 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!

C.A. Energy Savings Total Savings from Example 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!

QUESTIONS???

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