Trinity Structural Towers, Inc Tulsa, OK

Compressed air system recommendations

Written By: Shane Egner

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Executive Summary

Egnergy was contracted by Blast One to investigate the compressed air system at the Tulsa, OK Trinitity

Structural Towers, Inc facility. The investigation was to determine the current supply and distribution

compressed air system capacity with a special focus on increasing production capacity in the media blasting

booths to reduce the overall cycle time of the tower sections. The current compressed air supply system is

inadequate to supply the future demand of the facility, but the distribution piping should be able to maintain the

flow and pressure requirements .

The table below shows the date and time of some interesting flow and pressure events.

Date%

Flow%(SCFM)%

Pressure%(PSI)%

From%

To%

Peak%

Average%

Peak%

Average%

Minimum%

8/30%

2534%

1981%

128%

124%

117%

20:13%

20:20%

8/30%-%8/31%

2194%

1305%

131%

129%

125%

20:23%

1:10%

8/31%

2610%

1863%

130%

118%

93%

1:24%

3:02%

9/1%

2355%

1915%

125%

116%

106%

2:42%

3:46%

9/1%

553%

452%

131%

130%

129%

6:06%

6:40%

9/2%

3295%

2189%

129%

125%

117%

12:39%

13:33%

9/4%

477%

361%

133%

131%

128%

10:16%

13:48%

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Compressor Room

Equipment list:

• Three air compressors with a flow rating of 1504 SCFM @ 125 PSI

•

Three air dryers rated at 1600 SCFM

• Three inline filters rated at 2119 SCFM Particle removal down to 1 micron, including water and oil

aerosols.

•

Two horizontal compressed air receivers with a capacity of 3000 gallons (one installed)

• Ten pneumatically actuated no loss condensate drain valves

Current configuration of compressed air system:

The piping and equipment have been reorganized to better show the equipment set up.

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Air compressors:

The QSI1500 air compressors were installed approximately 10 years ago. They use a method of control called

“variable capacity”. This control method uses a valve at the inlet of the air compressor and lift valves installed

along the air end (pump) to efficiently vary output flow of the machine. While the variable capacity method offers

a high level of efficiency it also provides potential for equipment malfunction resulting in diminished output

capacity. The air compressors do not have the capability to monitor whether or not the control system is

functioning properly which can result in system pressure loss without increased compressed air demand. One

way to determine if the compressor control system is functioning properly is to measure incoming current to each

air compressor while the compressor controller shows it is 100% loaded. The current draw of the compressors

shows that Compressor 2 and Compressor 3 are running at a diminished output capacity.

The table below shows the incoming current for each air compressor when the controller shows 100% load.

Trinity%Structural%Towers%Air%Compressor%Maximum%Current%

Compressor%Number%

S/N%

Max%Current%

Compressor%1%

UN100594%

380%Amps%

Compressor%2%

UN100595%

331%Amps%

Compressor%3%

UN100593%

288%Amps%

Maintenance was advised about the issue and repaired the equipment the next day.

Dryers:

There is moisture in the compressed air system. One operator stated that he has to purge an air hose every morning

for 15 – 30 minutes to remove the moisture from the line. This moisture can be due to the dryer being under sized or

malfunctioning or a drain valve not opening to allow the condensed moisture to exit the system.

The 1600NCF compressed air dryers have a rated capacity of 1600 SCFM with inlet conditions of 100 F, 100 PSI and

ambient air temperature of 100 F. The flow of the dryers needs to be rerated based on the conditions in which they

are installed. The table below shows the factors used for rerating compressed air dryers.

𝑪𝒐𝒓𝒓𝒆𝒄𝒕𝒆𝒅(𝑭𝒍𝒐𝒘 = (

𝑹𝒂𝒕𝒆𝒅(𝑭𝒍𝒐𝒘

𝒊𝒏𝒍𝒆𝒕(𝒕𝒆𝒎𝒑 (𝒇𝒂𝒄𝒕𝒐𝒓(×(𝒊𝒏𝒍𝒆𝒕( 𝒑𝒓𝒆𝒔𝒔𝒖𝒓𝒆(𝒇𝒂𝒄𝒕𝒐𝒓(×(𝒂𝒎𝒃𝒊𝒆𝒏𝒕(𝒂𝒊𝒓(𝒕𝒆𝒎𝒑(𝒇𝒂𝒄𝒕𝒐𝒓

𝑪𝒐𝒓𝒓𝒆𝒄𝒕𝒆𝒅(𝑭𝒍𝒐𝒘 = (

𝟏𝟔𝟎𝟎(𝑪𝑭𝑴

𝟏. 𝟓𝟏(×(. 𝟗𝟐(×(𝟏. 𝟎𝟎

= 𝟏, 𝟏𝟓𝟏(𝑺𝑪𝑭𝑴

Using an ambient temperature of 100 F, inlet compressed air temperature of 120 F (normal CTD of compressor

aftercooler) and inlet compressed air pressure of 125 PSI each dryer’s rerated flow is 1,151 SCFM.

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Filters:

The compressed air filters installed inline between the air compressor and dryer are adequate for the flow of the

system and should provide clean mostly oil free compressed air to production.

Tanks:

There is one 3000 gallon receiver tank installed between the compressed air supply and distribution system and one

3000 gallon receiver tank onsite that is to be installed at a later date.

Note: tanks should be installed to minimize the effect on pressure of intermittent system demand spikes, but do not

generate compressed air. Long periods of compressed air demand above the output of the air compressors will result

in reduced pressure in production areas.

Condensate Drains:

There are 10 pneumatically operated no loss condensate drains installed in the system. One for each of the

compressors, dryers, filters, and tank. These valves are installed to remove the condensed moisture from the system

and only open when there is condensate present. The effect of these valves malfunctioning is that moisture that is

supposed to be removed in the cleanup equipment will pass into the distribution system.

Distribution Piping

The compressed air distribution piping installed throughout the facility is more than adequate to handle current

and future production demands. The pipe installed between the distribution loop and blast pots in both blast

booths is 4” black iron. The table below shows the pressure loss per 100 feet for 4” schedule 40 black iron pipe.

It shows that there should be minimal pressure drop between the loop and the and the blast pot.

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Graph of pressure and flow

The graph below shows compressed air pressure and flow in the main header between the receiver tank and

production.

The first period of high flow (from ~12:00 PM to ~12:40 PM) has an average flow of approximately 1600 SCFM. During

this period there were two size 10 blast nozzles operating in one blast booth and a tower section was being painted

along with regular production.

The flow during the time when the employees were at lunch and there was no production was approximately 450

SCFM. This flow is due to paint recirculation pumps and leaks in the plant.

Blast booth 3 started using the ID Blaster at around 3:00 PM and the portable diesel was started around 3:30 to

provide air so repairs could be performed on the air compressors.

The flow and pressure sensor and data logger will remain installed until Tuesday September 6

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Recommendations:

1. Install new tank in the compressed air supply system using drawing below. This configuration will allow the

compressed air to flow through all 3 dryers from 1, 2, or 3 running air compressors and will allow more

equipment to be installed in the future. This configuration also allows for more redundancy with the

compressed air clean up equipment.

2. Review the operation of the no loss drain valves. The chiller temperatures on all 3 dryers was between 36 F

and 41 F, but there is still water in the compressed air lines. The drain valves could be the reason for the

moisture.

3. Remove or perform maintenance on the moisture trap installed in the 4” line between the main loop and the

blast pot for blast cabinet 3. If the moisture trap is dirty or clogged it will cause a pressure drop when

compressed air flow increases. If the air is dry leaving the compressor room the moisture trap will no longer be

necessary.

4. Review plan for the unexpected loss of an air compressor. Paint rework on a tower section can have a cost of

up to $10K and pressure loss can cause the paint process to fail.

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Conclusion:

Based on the inspection of the compressed air supply and generation systems and the data recorded the compressed

air supply system capacity will need to be increased to meet the demands caused by the planned increase in

production. The increase in supply capacity cannot be specified until the new equipment to be installed is identified.

The compressed air distribution piping installed throughout the plant is large enough to handle double installed

compressed air generation capacity with no problem.

All Data:

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8/30/2016

8/31/2016

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9/1/2016

9/2/2016

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9/3/2016

9/4/2016