Conquer Compressed Air Challenges

Nov. 2, 2020
Carefully consider what’s contributing to capacity issues

This Month’s Puzzler

We shoot sulfuric acid into our yeast fermenters as a nutrient. When we bought the facility three years ago, it had two fermenters. Since then, we’ve added another fermenter as well as expanded our packaging lines and other parts of the plant (see figure). We now are seeing delays in the injection time that are affecting our yields. We must inject the right amount of acid during a precise ¼-hr window to maximize yield and product quality.

I think the culprit is compressed air, which we ignored in the expansion. I generated a diagram of the users of the compressed air system.

The technology expert at corporate instead blames corrosion in the valves in the top of the acid egg. “I’ve seen it a dozen times,” he declares. He also says the actuator may be fouled. The air for the valves used to come from the compressor but a new instrument air system was installed to eliminate oil that was fouling control valves.

I talked to the boiler-house operators who manage the compressor. They note the compressor tripped several times in the last three months and the dryer is having trouble keeping the air wet bulb down to -20°F — in fact, they say it sometimes runs at 32°F. This brought a “See, I told you” from the corporate engineer, who claims the water in the air was causing corrosion in the acid egg valves. The operators also mention a drop reported in pressure whenever the new packaging line is running. The foreman there tells me that half the lines frequently are down. The fermentation operator says blowing down the egg line after shots leaves acid in the lines.

Do you think corporate is right? Is there anything we can do about the problems with the compressor?

Check Current Constraints

The puzzler presents a number of plausible scenarios that merit consideration. However, some additional quantitative information will be helpful. Consider the following before adding a new compressor to boost air capacity:

1. In addition to Fermenter No. 3, some 8–10 intermittent new periodic high or periodic low users were added. In the absence of quantitative information, it’s hard to compare the consumption with the compressor capacity. You can do a number of tests that involve keeping selected new users on to see if the compressor can keep up with the demand. Of course, you must check with Operations to ensure such tests don’t disrupt its fermentation and packaging requirements. These tests may show whether the compressor is adequate for the new configuration.
2. Check compressor operation — seemingly minor items such as “unloaders,” if not set properly, could cause the compressor to deliver inadequate pressure; or an inlet air filter, if partially clogged, adversely could affect compressor capacity. Similarly, air inlet/outlet valves or packing leaks merit checks. Trace discharge piping to the fermenters to make sure all valves, including block valves, are completely open while other valves on equipment not in service are closed.
3. Perform an air leak survey. Plug in all leaks.
4. Explore ways in which you can stagger fermenter air addition with the other big users such as packaging. This will minimize peak demand.
5. If the problem of “bad batches” is from the new fermenter only, then check the piping and sparger layout for potential flow restriction to that fermenter.
6. Check the air dryer to determine if change of air-dryer charge is required. Of course, you must make sure charge regenerations are carried out properly and in time.
7. Confirm the new instrument air system provides dry air at the required pressure to the valves on the “acid egg” container. Check actuators on these valves. Inspect internals of these valves and replace if necessary.
Wood, Houston

Build Slowly

Obviously, you’re up against politics: you need to convince corporate and your managers to let you explore bottlenecks in the compressed air. Start small. When Governor Clinton of New York built the Erie Canal, he did the opposite of what others tried: he started with the easy part of the canal so he could learn as he went.

The best way to convince people is to identify some high air demands from the packaging equipment lines and create loops to allow the pressure to balance, thereby reducing downtime on the lines. That will be a big money-maker.

The truth is that water interacting with the acid really is causing the corrosion in the eggs. So, tackle the dryer next. A cheap fix is a series of water/oil traps in the system — if you can chill the traps, even better. This should win some support at corporate. If space or available money won’t allow a larger dryer, consider a smaller dryer where it counts, like for air to the acid eggs. You even may want to think about breaking up the air system and connecting the separated section to another compressor system.

Acid in the lines, as reported by the operators, is common. It doesn’t matter what the pipe material is: acid will eat it. Change the procedure to include flushing with water briefly and then blowing with air; do this a couple of times, perhaps. You could recover the acid and use it.
Dirk Willard, consultant
Wooster, Ohio

January’s Puzzler

We meter corrosion inhibitor (an aqueous mixture of sodium benzoate and sodium nitrite) into tanker trucks containing our product, ethylene glycol radiator fluid. Previously, we metered the inhibitor into lines to the product tanks. Corporate and our customers can’t seem to decide if they want to continue the current approach or revert to the original system. Complicating this further, corporate is grappling with whether to increase the injection rate by 25%. Now, it’s October in Indiana and winter is coming. “What are we going to do when winter comes?,” an operator complained. Money is tight, I told him.

We use 275-gal totes of inhibitor, and go through 8 or even 12 on some days. Storage space limitations restrict us to only six totes near unloading; the others are stored way across the plant, taking a fork truck about 30 minutes to deliver.

Safety already is upset by the lack of containment around the totes. Because the whole system is “temporary,” we’re using a ½-in. air-diaphragm pump and a ¾-in. garden hose strung 75 ft from the totes outside the dike wall to the loading arm 18 ft above ground level.

Sales is thrilled because the chemical in the totes includes new additives the customer wants. Production is concerned about the additional inventory filling its warehouse and yard — and also displeased with the slow filling rate that adds 20 minutes to the operation and requires an operator on standby because the measurement is by tote level. I’m not happy that we’re wasting ingredients due to all the leaks. I’m not sure how quality control feels about this.

How can we prepare for winter at this late date? Should containment of a water solution worry us?

Send us your comments, suggestions or solutions for this question by December 11, 2020. We’ll include as many of them as possible in the January 2021 issue and all on ChemicalProcessing.com. Send visuals — a sketch is fine. E-mail us at [email protected] or mail to Process Puzzler, Chemical Processing, 1501 E. Woodfield Rd., Suite 400N, Schaumburg, IL 60173. Fax: (630) 467-1120. Please include your name, title, location and company affiliation in the response.

And, of course, if you have a process problem you’d like to pose to our readers, send it along and we’ll be pleased to consider it for publication.