CompAir_SolenoidValves

7/29/2019 CompAir_SolenoidValves

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Compressed Air Systems: Solenoid Valves

OverviewCompressed air is useful, but expensive. A highly cost-effective method to reduce thecost of compressed air is to reduce the quantity of compressed air required by plantprocesses.

Solenoid ValvesCompressed air should be to shut off whenever it is not needed. Sometimes this meansshutting off compressed air for a few seconds at a time, such as between stamping cyclesor between parts moving down a conveyor. Other times this means eliminating air lossthrough leaks or open valves by shutting off the supply of compressed air to a machine,group of machines or entire section of the plant when it is not in use.

Simple, reliable and inexpensive solenoid valves can be installed to automatically shutoff the flow of compressed air when it is not needed. Three-way two-position solenoidvalves are sufficient for shutting off the supply of compressed air. Solenoid valves openor close when an electric current energizes the solenoid. Typically, the return position isactuated by a spring (solenoid/spring), or a second solenoid (solenoid/solenoid).Solenoid valves for compressed air are typically designed to operate up to 600 cycles perminute and at air pressures from 50 psig to 150 psig. Solenoid valves can be controlledby connection to process machines, photo sensors or other input mechanisms.

Approximate costs of solenoid valves are shown below:

1/8-inch NPT (solenoid/spring) $301/4-inch NPT (solenoid/spring) $403/8-inch NPT (solenoid/spring) $703/8-inch NPT (solenoid/solenoid) $1001/2-inch NPT (solenoid/spring) $2001/2-inch NPT (solenoid/solenoid) $2503/4-inch NPT (solenoid/spring) $2903/4-inch NPT (solenoid/solenoid) $360Source: Grainger Catalog 2001, pgs 2886-2895

Calculating Energy Savings From Reducing Compressed Air UseTo calculate the compressor power required to generate a given quantity of compressed

air, use the published compressor performance specifications for scfm of compressed airgenerated per brake horsepower from the motor. If the performance specifications areunavailable, it is reasonable to assume that most compressors generate about 4.2 scfm perbrake horsepower from the motor (or inversely, require about 0.25 hp/scfm ofcompressed air).

Using this number it is easy to estimate how much power is required to generatecompressed air. However, the energy savings from reducing compressed air demand can


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be much less than the power required to generate the air demand depending on the type ofcompressor control. For example, if the compressor runs unloaded at 60% of full loadpower when not generating compressed air, then the energy savings will be only 40% ofthe power required to supply the demand. The savings from modulating compressors areeven less. Only when the compressor completely turns off when not compressing air will

the electricity savings equal the power required to generate the compressed air.

ExampleA leak consumes about 4 scfm of compressed air. The annual electricity cost ofgenerating this much compressed air if a 90% efficient compressor motor runs 8,000hours per year and electricity costs $0.06 /kWh would be about:

4 scfm x 0.25 hp/scfm x 0.75 kW/hp / 90% x 8,000 hr/yr x $0.06 /kWh = $400 /yr

If the compressor shuts off when not generating compressed air (such as would be the

case for reciprocating compressors with on/off control or lag compressors withautomatic shut-off control, then the savings from shutting off this demand would equalthe cost to feed the leak of $400 /yr. If the compressor runs unloaded at 60% of full-load power when not generating compressed air, the savings would be about:

$400 /yr x 40% = $160 /yr


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AR X: Reconnect Compressed Air Supply to Presses Through

Automation Valves

Annual Savings Project Simple Investment

Resource CO2 (lb) Dollars Cost Payback IRR

Electricity 103,000 kWh 30,000 $6,900 $1,740 3 months 400%

Analysis

Each of the six press machines, plus the Kurimoto press, employ continuous streams ofcompressed air through two 3/8-inch open pipes to blow parts from the dies. In AR #X,we estimate the savings from installing ITW Vortec Model #1205 high-thrust nozzles onthe open pipes.

Additional savings are possible if the compressed air supply to each press were connectedthrough automation valves in the presses. The automation valves open only during thepart of each stroke when compressed air is needed. Management estimates that

reconnecting the compressed air supply through the automation valves would reduce thetime that compressed air is required by one half.

Recommendation

We recommend reconnecting the compressed air supply through the automation valves inthe seven major presses to reduce the time that compressed air is required.

In addition, to maximize electricity savings, we recommend staging the compressors toactivate at sequentially lower pressures and enabling the control that turns thecompressors off if they run unloaded for 10 minutes (See AR#X).

Estimated Savings

In this section, we estimate the savings from reconnecting the compressed air supplythrough the automation valves after the Model #1205 high-thrust nozzles have beeninstalled. The savings from reconnecting the compressed air supply through theautomation valves if the nozzles were not installed would be about five times greater.

According to the ITW Vortec Air Nozzles and Jets Product Catalog, the quantity of 100psig compressed air consumed by a 3/8-inch Exair Model 1003 nozzle is about 31 scfm.Thus, the quantity of compressed air required after installing 3/8-inch nozzles on all 14open blow-off pipes would be about:

14 pipes x 31 scfm/pipe = 434 scfm

The electricity savings resulting from reducing compressed air demand is highlydependent on the control mode of the compressors. Staging the compressors to activateat sequentially lower pressures and enabling the control that turns the compressors off ifthey run unloaded for 10 minutes, as recommended in AR # X, will result in themaximum electricity savings. In the analysis that follows, we assume that these measures


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will be implemented. If not, the savings from reconnecting the automation valves wouldbe about 60% less than the estimate below since the compressors will continue to rununloaded even with reduced compressed air demand.

According to management, the presses operate about eight hours per day, six days per

week, for 50 weeks per year. Management estimates that one half requires reconnectingthe compressed air supply through the automation valves would reduce the time thatcompressed air. Most compressors generate about 4.2 scfm per brake horsepower.Assuming the compressor motors are 90% efficient and the measures recommendedabove are activated, the savings from reconnecting the automation valves would beabout:

434 scfm / 4.2 scfm/hp x 0.75 kW/hp / 90% = 86 kW86 kW x 8 hrs/dy x 6 dy/wk x 50 weeks/year x 50% = 103,000 kWh/year103,000 kWh/year x $0.067 /kWh = $6,900 /year

This would reduce CO2 emissions by the electric utility by about:

103,000 kWh/year x 2.3 lb CO2/kWh = 30,000 lb CO2 /yr

Estimated Implementation Cost

Management estimates that reconnecting the automation valves would require five valvesat about $300 per valve and eight hours of labor. At a labor rate of $30 per hour, the totalimplementation cost would be about:

(5 valves x $300 /valve) + (8 hours x $30 /hr) = $1,740

Estimated Simple Payback($1,740 / $6,900 /year) x 12 months/year = 3 months


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AR 5: Install Optical Sensor and Fix Leaks to Reduce Compressed Air

Use

Present Recommended Annual Savings

Electric Demand 17.73 kW 0 kW 17.73 kW; $2,993

Electric Usage 44,325 kWh 0 kWh 44,325 kWh; $1,152Net $4,145

Implementation Cost $1,000Simple Payback: 3 months

Analysis

During our visit we found numerous leaks in the compressed air system. In addition, theblow bar used for dust removal on the finishing machine for the hot pressed doors rancontinuously.

Recommendation

We recommend fixing all major holes and leaks in the compressed air system andinstalling an optical sensor on the blow bar to spray compressed air only when there is adoor in need of dust removal.

Estimated Savings

Fixing LeaksThe table below shows the leaks we observed, the approximate amount of air lost throughthe leaks, and the approximate air-compressor horse power required to supply air to theleaks. The estimates of air lost through the leaks are from Compressed Air Systems:DOE/CS/40520-T2. We assume that the compressor uses about 0.25 hp per scfm ofcompressed air.

Size of Hole # holes scfm/hole scfm lost hp lost1/8 3 15.86 47.49 121/16 6 3.96 23.76 6

Total* 9 71.25 18

*There were numerous other holes either too small to find with my hand, or inside ofmachines

Equivalent Hole Diameter Leakage Rate scfm

1/64 " 0.25

1/32 " 0.991/16 " 3.96

1/8 " 15.86

1/4 " 63.44

3/8 " 12.74

From Compressed Air Systems: DOE/CS/40520-T2.


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Assuming the 50-hp compressor motor is 90.2% efficient, the power required to supplyair to these leaks is about:

18 hp x 0.746 kW/hp / 90.2% = 14.9 kW14.9 kW x $14.07 /kW-month x 12 month/year = $2,515 /year

14.9 kW x 2,500 hour/year = 37,250 kWh/year37,250 kWh/year x $0.026 /kWh = $968 /year

Install optic sensor on blow barThere are 23 1/16 holes in the blow bar used for dust removal from the hot pressed doorsafter finishing. This blow bar runs continuously. A simple optical sensor and solenoidvalve would enable the blow bar to be turned off in between doors and during breaks.We estimate that this would reduce the blowing time by about 15%. The savings wouldbe about:

Size of Hole # holes scfm/hole scfm lost hp lost1/16 23 3.96 x 0.15 13.66 3.42

Total* 23 13.66 3.42

The electricity savings would be about:

3.42 hp x 0.746 kW/hp / 90.2% = 2.83 kW2.83 kW x $14.07 / kW/ month x 12 month/year = $478 /year

2.83 kW x 2,500 hour/year = 7,075 kWh/year7,075 kWh/year x $0.026 /kWh = $184 /year

The total savings would be about:Hole fixing savings: $2,515 /year + $968 /year = $3,483 /yearChange blow bar operation: $478 /year + $184 /year = $662 /yearTotal Savings: $4,145 /year

Estimated Implementation Cost

Cost of fixing holes: $600Cost of changing blow bar operation: $400Total cost of implementation: $1,000

Estimated Simple Payback$1,000 / $4,145 /yr x 12 months/yr = 3 months


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AR x: Install Optical Sensor to Reduce Compressed Air Used in Ball

Inflation Process

Present Recommended Annual Savings

Elec. Usage 5,022 kWh/yr None 5,022 kWh; $116

Elec. Demand 11.16 kW None 11.16 kW; $3,134Net $3,250

Implementation Cost $5,600Simple Payback 21 months

Analysis

The ball inflation system inflates balls prior to packing and shipping. The system worksas follows, balls are produced on the rotocast machines and moved to a position in frontof the handler. The handler places balls on filling needles. Inflated balls are thrown itinto a bin. Compressed air continues to be exhausted even when no balls are beinginflated.

Recommendation

We recommend installing an electric-eye system that would activate the supply ofcompressed air only when a ball is being inflated. This type of system is currently beingtried out on a different ball inflation process. This would save both air compressorelectricity and wear and tear.

Estimated Savings

Each fill hole is about 1/16 inch in diameter. If the compressed air discharge pressure isabout 100 psig, about 4 scfm of air is lost through each hole (Compressed Air Systems:DOE/CS/40520-T2). There are 2 inflation needles on each of the 14 rotocast machines,

but only about half of the needles are open at the same time. Thus, the total supply ofcompressed air to the inflation machines is about:

14 holes x 4 scfm/hole = 56 scfm

According to management, the rotocast machines run 4 hours per shift, 3 shifts per day.Based on our observations, we estimate that compressed air is being wasted about 1/8 ofthe time, for a total of about 1.5 hours per day. Installing an electric eye on each machinewould essentially eliminate this waste. Rotary air compressors generally require about0.25 brake-hp to compress one cfm of free air (Compressed Air Systems:DOE/CS/40520-T2). Assuming that the efficiency of the 200-hp air compressor motor is

93.6 %, the power and energy required for the excess air flow are about:56 scfm x 0.25 hp/scfm x 0.746 kW/hp / 0.936 = 11.16 kW11.16 kW x 1.5 hr/dy x 6 dy/wk x 50 wk/yr = 5,022 kWh/yr

Electricity savings from eliminating excess compressed air would be about:

11.16 kW x $23.40 /kW-mo x 12 mo/yr = $3,134 /yr


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5,022 kWh/yr x $0.023 /kWh = $116 /yr$3,134 /yr + $116 /yr = $3,250 /yr

Estimated Implementation CostAccording to management, the material and labor cost of adding electric eye controls

would be about $400 per machine. The total implementation cost for 14 machines wouldbe about:

$400 /machine x 14 machines = $5,600

Estimated Simple Payback

The simple payback would be about:SP = $5,600 / $3,250 /yr x 12 mo/yr = 21 monthsROR = $3,250/yr /$5,600 = 58% per year

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CompAir_SolenoidValves