Air compressor optimization 3

[sergeyzhan]

I'm currently working on the air compressor optimization project.
We have max.750cfm air consumption 7 hrs/day, and 350 cfm consumption 17 hrs of cyclical load/no-load regime (15 sec. load and 45 sec. unload). Type of compressor in use is piston. We are planning to develop new utility area and install new compressors. We have another 1200cfm Denver-Gardner Electro-Saver compressor, which is currently not in use. The problem is that I believe that 1200cfm compressor is too big and cost ineffective to run in terms of motor HP utilization and energy consumption. However, Denver-Gardner Electro-Saver has an option of automatic adjustment to air load, which they believe can save a lot on energy consumption by constant pumping air 24 hrs/day at different motor utilization depending on air load (no load/no-load regime). According to my calculations it is more expensive to run electro-saver rather than regular load/no-load regime.
I would appreciate any ideas for sizing compressor and the most efficient way to run it: load/no-load regime or 24 hrs constant run with automatic adjustment for a current load.

 

[sbi]

what is the size of your storage tanks around the plant

we are a small foundry getting by with 150cfm screw, by means
of two ways, we installed large lines, 3" loop all over the shop, and back in the molding are we have a 1200 gal. tank

the tank takes awhile to pump up but even with or automatic running full bore we never have a problem
# we run a B&P 2016 at 120 mph + 3 jolt squeesers with 14 to 18 inch squeeze cyl. plus the air opp. grinders in cleanup.

we learned to get rid of the small leaks and the smaller screw
has been very efficiant

 

[automatic2]

Is your Denver plumbed?. Fire it up at the start of your 750cfm period. Set your piston pressure range slightly lower than the screw so that it will come on only when you shut down the Denver after your 750cfm period.

I like to run a water cooled wet screw at about 80% duty. An air cooled unit would be at 70-75% duty. As Sbi posted, an inplant reciever will smooth out your duty.

 

[quark]

If you are using 1200 cfm air compressor even the power consumption in unload condition is going to be quite high.

Ingersoll Rand has variable speed arrangement to take care of fluctuating loads.

If your compressor is loading and unloading frequently, check for the leakages in the system. Close all the terminal valves and drain valves in the system.At the point of no consumption check the loading and unloading times.

%leak = loading time *100/(unloading time - loading time)

Generally accepted leakage rates are 5 to 10%.

Check this link

http://www.conservair.com/

(if you are not aware of already)They have very good systems (add ons) for compressed air management.

Finally, compressed air pressure requirement for any equipment reduces when you supply constant pressure air. By reducing pressure you can save compressor power as well as leakage in the system.

 

[DanTheMan]

load/unload operation is always less expensive to run than part load, or "modulating" service. The motors run at near full load even when you back off the ammount of air that you push with the compressor. Most of the time all that hapens in a modulating situation is that the inlet will throttle shut forcing the compressor to run less efficiently. This can be confirmed by vendor data. Even variable frequency drives are less efficient than load/unload.

 

[evelrod]

Here is my two cents worth. Not having installed compressors much over the 250 to 500cfm range. I really can't address your power demands but an educated guess is that it will be high no matter what.
The 1200cfm Gardner-Denver is a screw machine that CAN operate without a receiver but it's not a good idea. A lot of money tied up in the machine so why not opt for a decent sized receiver, at least 1000 gal. capacity is a guess. It will smooth out the peaks in pressure and ease compressor loading during short term, temporary spikes in demand. Keep in mind that during normal maintenance service the machine will be down for 4 or more hours and you may need a backup. Why not cycle more than one machine to moderate the load during off demand?

As to leaks---leaks will kill ANY compressor and contrary to the above, IMHO, 10% is TOTALLY unacceptable. I am not happy with 1 o 2%, but sometimes I just can't seem to find them all. You cannot put in words the calls that are made saying my compressor will not keep up anymore---when a service rep goes out, invariably the problem can be traced to leaks. Leaks and lack of maintenance is the biggest killers of industrial air units (most often they go hand in hand).

Rod

 

[automatic2]

I agree that 10% leakage is horrendous. Air audit is a must. Unfortunately I've been through many plants where it occurs, much to the distaste of management.

 

[quark]

Guys!

What could be an ideal leakage? Isn't it 0%? And who is that Alchemist who could try for it?

Length of piping, type of end use and the interest of engineer or the variables which decide the leakage. Controlling between 5 to 10% will also give you good savings for I saw worst plants (with leakages upto 30% and the engineers were pretty sure about the tightness of their system before doing the audit, because they said they never observed any noise.lol)

And as far as our type of plant was concerned (Pharmaceutical) I could never acheive below 5% on a real basis. If you guys did then Bravo! (Once you do the tightening job how long will it hold?)

If you are patient enough to search the internet with 'compressed air leakage' the rough values given are below 10%. But as far as my practical experience is concerned it is upto 5%.

 

[evelrod]

quark, I retired after 38 years in 1998 and took a part time job with an industrial air company. A couple of days a week for four years (I am still on an 'on call' basis). In that capacity I designed and installed several systems as well as maintenance on others (Jonathan Mfg. , McDonald-Douglas, now Boeing, etc.) and I would never sign off on 10%, never! I don't know every circumstance and, obvioulsy there are plants around that have 30% leaks. I know, I've had to go in and repair them. It's hard to hear small leaks and LOTS of small leaks make BIG air loss! It is seldom one big leak that is the offender. We signed many companies to a PM agreement and when you maintain a system on a regular basis it is not so difficult to stay at less than 10% (my personal shop's admittadly small scale air system will hold pressure indefinately after the system is shut down) . I always try for perfection but rarely attain it. I still keep trying, though.
Keep after it, quark. I know it can drive you nuts but the end result can be worth it.

Rod

 

[sergeyzhan]

First of all, thank you everybody for great replies. Everybody helped me a lot.
As for leakages, I can give you my opinion only based on my own experience. It is pretty much impossible to define exact percentage of leakages in my plant- we have a continuous process with constant usage of compressed air. But anyway, leakages more than 5% are unavoidable for large scale production. At least in cost effective manner. I tried to estimate the costs for line enspections and fixing all the leaks (moreover, you can not identify them all) and cost savings for 2-3%. I can say that it does not worth it. You'll get a little payback with relatively distant break-even. If you have leakages within 5% you are good. Again, it is only on the large scale production with hundreds feet pipe lines.
Thank you again, you all great!

 

[automatic2]

Interesting comments in regards to acceptable leakages. I guess it varies according to type of industry. My background in manufacturing, with plants that can/do shutdown for maintenance or holidays. A small leak is easily identified in a static plant. My experience has been that actuators and valving are the largest culprits. Piping is way low on the list. I don't agree with the comments on cost, as leakage will in many cases have secondary effect, such as control swing, enviroment contamination (process dependant), as well as physcological implications (operator perception). What wasn't mentioned is the loss attributed to effeciencies of the actuators, or processes that consume. Dry cylinders, motors, bypassing pistons, incorrecting aligned nozzles, etc. 1-2% leakage is useless as a static target, if the motor has a couple of siezed vanes and outputs 30% of input.

 

[quark]

Great Evelrod!

I still couldn't imagine Why you didn't eat me out for my arrogance. Obviously your experience outweighed me in all aspects.(even in balancing mind)

In my plant the main culprits were 3/5 way valves, quick exhaust valves and pneumatic pistons. I really vexed up finding the leakage shoot up every week. Till this time I thought restricting leakage below 5% was practically impossible (may be because I never used ultrasonic detectors or any other hitech gizmo)

I will be much delighted to know what procedures you follow in determining leakage or reducing the wastage?

Note: I assure I will take more care in my future posts.

Cheers

 

[evelrod]

I certainly don't mean to be patronizing when I say that the smaller the shop and/or the more dedicated the company is toward air management, the easier it is to control leaks. 5% is probably acceptable in just about any industry accept perhaps medical or dental (Delta Dental is able to operate a 20 station lab using only a 10hp Champion with an 80gal receiver) The problem is not so much in getting a NEW system below 10% but in KEEPING it there! The older the system, the more difficult it becomes and, the more effort ($$$) needed to maintain it at acceptable levels.

Quark, I have no magic to give you. I did it 'the old fashioned way', a stethascope and a bottle of soapy water(actually it was "Leak Detector&quot. As to arrogance, compared to me, you are just a beginner. My hat size has incresased TWO sizes since we started this thread!!! LOL

Rod

 

[quark]

Though I fully agree I am just a beginner when compared to you God forbid me from further posting for we all have to live on earth until some other planet is being discovered and I am apprehensive about the Hat Size in future otherwise

Cheers!

 

[evelrod]

Well, I guess I had it coming. I disjointed my arm patting myself on the back---
Went out to my shop this morning. My air system was down! First time in a long while, perhaps one day I'll stop bragging as it allways seems to come back and bite me in the arse! LOL LOL LOL

Rod