Air Compressors for Pharmaceutical Manufacturing

What fermentation shop process engineers dread hearing most is "oil detected in compressed air." One 1,300 gallon fermenter, media cost alone is tens of thousands of dollars. Add upfront strain activation, equipment cleaning and sterilization, one batch from charging to fermentation end runs over ten days. Compressed air has problems, this whole batch is gone.

Anyone who's done pharmaceutical projects knows compressor station investment as share of whole plant utilities isn't that high. The trouble is validation and daily management afterward. Equipment selection wrong, next few years you're paying off that debt.

Pharmaceutical

Compressed Air System

Air Use Classification Isn't That Complicated

Many textbooks divide pharmaceutical air use into four or five categories. Process air, equipment drive, instrument air, and so on. Classification itself is fine. Problem is dividing too fine actually confuses people.

Simple way to put it is two categories: does air touch product or not.

Touches product, highest requirements. Fermentation aeration, fluid bed, spray drying, air and drug directly mixed together. Particles, moisture, oil, microorganisms, any metric exceeding limit is big deal.

Doesn't touch product, requirements can be appropriately relaxed. Pneumatic valves, instruments, cleanroom pressure makeup, these applications have much lower probability of causing problems. Valve leaks, leak point area releases a little compressed air. Very small amount. Cleanroom HVAC system circulates few times and it's diluted.

Purpose of classification is tiered management. Fermenter aeration line, sterilizing filter gets integrity tested weekly, microbial testing every batch. Packaging shop pneumatic equipment, filters changed every six months, nobody does weekly testing. Resources are limited. Money needs to be spent where it matters.

Some companies don't understand this logic. Whole plant all use points configured to highest standard. Investment goes up. Daily maintenance can't keep up at all. Filters due but not changed. Online monitoring instruments broken but nobody repairs. End result, system configuration is luxurious, operating condition is a mess.

Oil-Free Machines Have No Controversy Anymore

Ten years ago people still asked, can oil-flooded machine with good oil removal equipment substitute for oil-free machine. Now this question basically doesn't exist.

Oil-free screw machines are more expensive. One 700 CFM machine, price difference roughly $15,000 to $25,000. Spread over ten year use cycle, $1,500-2,500 more per year. Saves oil removal equipment maintenance cost, element replacement cost, validation cost. Worth it.

Dry oil-free screw versus water-lubricated oil-free screw, how to choose, this one can be discussed. Dry type rotors have Teflon coating. Life affected by discharge temperature. High temperature ages coating faster. Water-lubricated rotors soak in water. Temperature can't go up. Rotor life long. Trade-off is water treatment system needs maintenance. Bad water quality, machine easily has problems. Southern regions with soft water, water-lubricated models have good reliability control. Northern water is hard. More use dry type.

Centrifugal machines have advantage at large flow applications. Systems over 1,750 CFM can consider. Maintenance simple. No wear parts. Energy efficiency ratio also looks good. Startup current is big. Grid capacity needs to be sufficient.

Dryer Selection Pitfalls

Pharmaceutical air dew point requirement is typically -40°F. This metric only desiccant dryers can stably achieve. Refrigerated dryer limit is around 37°F. That's pressure dew point, not atmospheric dew point. Converting to atmospheric roughly around -4°F. This value is on the high side for pharmaceutical systems.

Some will say, refrigerated dryer is cheap, can't you use refrigerated dryer to remove most of the water first, then desiccant dryer for final treatment. Yes. This scheme is called combination drying. Refrigerated dryer outlet dew point 37°F. Desiccant dryer inlet water load reduced by more than half. Adsorbent life extended. Regeneration energy consumption reduced. Investment increases by one refrigerated dryer. Operating cost can be saved back. Large volume systems are worth configuring this way.

Desiccant dryer regeneration method, heatless versus heated, this choice often gets overlooked. Heatless regeneration uses dried compressed air to purge adsorbent. Consumes about 15% of product air. Heated regeneration uses electric heating or steam heating. Compressed air consumption drops to 2-3%. Electricity or steam cost increases.

Do the math. A dryer with 350 CFM per minute processing capacity. Heatless regeneration loses 53 CFM compressed air per minute. Compressed air cost at $0.005 per cubic foot (electricity plus equipment depreciation), one hour loss cost is $19, one year at 8,000 hours operation is $152,000. Heated regeneration compressed air loss drops to 10 CFM per minute. This portion of cost becomes $30,000. Saves $122,000. Heating electricity annually roughly $15,000-20,000. Net save $100,000 or so. Three years can earn back equipment price difference.

Small volume systems don't need to calculate this finely. Processing capacity under 70 CFM, heatless regeneration is simple and reliable. Maintenance also convenient.

Adsorbent choosing molecular sieve or activated alumina. Molecular sieve has larger adsorption capacity. Regeneration temperature requirement also lower. Overall molecular sieve is more economical. Years ago molecular sieve was expensive. Now price difference isn't much.

Drying

Desiccant System

Filtration

Multi-Stage Filters

Filters This Thing Is Simple When You Think About It

Four-stage filtration is standard configuration. Coarse filter blocks large particles and liquid water, protects downstream equipment. Precision filter catches aerosol oil mist and fine particles. Filtration precision 0.01 micron. Activated carbon filter adsorbs gaseous oil molecules. That stuff that smells oily but you can't see oil mist. Sterilizing filter uses 0.2 micron membrane element. Intercepts bacteria and fungi.

How to determine element replacement cycle. Look at differential pressure. New element has low differential. As contaminants accumulate, differential gradually rises. Differential reaches critical value, time to change. Continue using, either filtration efficiency drops, or element gets burst. Each stage filter housing should have differential gauge installed. Operating records should have differential data.

Sterilizing filter integrity testing is another matter. Normal differential doesn't mean membrane is intact. Membrane might have pinhole. Might have seal ring not pressed tight during installation. Bubble point test is most commonly used method: first wet the element, then slowly pressurize from upstream, observe when downstream starts bubbling. Bubble pressure lower than supplier's specified value means there's a problem. Do this test weekly, or by batch. Records must be filed.

Fermentation shop process engineers are very familiar with integrity testing. It's part of daily work. Some companies got automated integrity testers. Machine automatically pressurizes, automatically records. Results print out and go directly to file. Saves labor.

About filter location, terminal filter should be as close to use point as possible. Filter on main pipe can't handle secondary contamination in branch pipes. Pipe welding residual slag, rust accumulated from long-term operation, these things can all mix into compressed air before terminal filter. Large volume critical equipment, separate set of terminal filters is standard practice.

Validation Is Pure Paperwork

IQ, OQ, PQ three phases. What gets done isn't complicated. Documents are the focus.

Installation qualification is checking boxes against list. Equipment model right? Installation location right? Piping routing right? Electrical wiring right? Verify item by item. Sign after verification. Sounds simple. Actually doing it, you'll find supplier documents are often missing stuff. Piping material certificate can't be found. Welding records incomplete. Pressure gauge missing calibration certificate. These all need to be collected during installation phase.

Operational qualification needs to test various conditions. Full load running, does air quality meet spec. 50% load running, can desiccant dryer stably maintain dew point. During two compressor switchover moment, how much does pressure drop, does downstream equipment get affected. All these scenarios need to be covered. All data needs to be recorded.

Some companies rushing schedule, operational qualification done hastily. Pick few normal conditions, test a bit and call it done. Years later problem occurs, trace back the cause. Find that condition was never tested back then. Validation report has a blank.

Performance qualification needs to run for a period under actual production conditions. Usually two to four weeks. Cover several complete production cycles. Prove system can stably output qualified compressed air under real usage conditions.

After validation passes, change control begins. Any change: changed a filter element brand, adjusted an alarm setpoint, replaced a compressor, all need to go through change process. Fill change request form, assess impact, approve, execute, verify, archive. One process through, fast is two to three weeks. Involving equipment replacement might take months.

Some people think change control is too cumbersome. Casually changing a parameter needs to go through process. Indeed cumbersome. Pharmaceutical industry logic is any change might bring unknown risk. Rather have slow process, can't let uncontrolled changes sneak in.

Piping Layout Isn't Complicated But Has Many Details

Main pipe from compressor station out, heading to production shops. This distance might be tens to hundreds of feet. Air flowing in pipe gradually cools. Winter temperature difference is more noticeable. Condensate from cooling, if there's no exit, accumulates at low points. Over time pipe inner wall rusts. Rust gets carried downstream by airflow.

Pipe needs slope, sloped toward drain point. 1/4 inch per 10 feet slope is minimum requirement. Can do 3/8 inch per 10 feet is more reliable. Low points install automatic drains. Condensate accumulates to certain amount, automatically drains. Many old factory pipes have insufficient slope, or even reverse slope. Drains are useless. Pipe inner wall severely corroded.

Branch pipe connects from top of main pipe. This principle has been emphasized for years. On site still often see connecting from side or even bottom. Bottom-connected branch pipe is like a straw. Sucks accumulated water from main pipe directly to air-using equipment.

Material-wise, 304 stainless steel is mainstream choice. Easy to process. Corrosion resistance is also sufficient. 316L used in sterile areas. Extra layer of insurance. Carbon steel pipe is rarely seen in pharmaceutical systems now. Galvanized pipe occasionally still exists. Long-term use, galvanizing layer will peel off. Not recommended. Aluminum alloy piping is new choice in recent years. Inner wall smooth. Low pressure drop. Light weight. Installation more convenient than stainless steel. Price not expensive either. Downside is strength not as good as stainless steel. Can't withstand too high pressure. Also can't be welded, only compression fittings.

Pipe inner wall needs passivation treatment. Stainless steel surface has oxide film layer. Passivation treatment makes this film denser and more stable. Better corrosion resistance. Stainless steel pipe without passivation will still rust in high humidity environment. Seen plenty of cases. Passivation isn't complicated. Soak or circulate with passivation solution. Cost not high either. No reason to skip this step.

Redundancy

Backup System

Station

Compressor Room

Backup plan design depends on production continuity requirements. Fermentation shop most afraid of losing air. Once it stops, fermentation is ruined. Two compressors in parallel, one running one backup, either one is sufficient, is standard configuration. Air receiver capacity sized for three to five minutes of air usage. Compressor faults can hold for a bit. Enough for operators to react and switch to backup machine.

Filling and packaging, these intermittent production processes have lower continuity requirements. Losing air for ten to twenty minutes doesn't matter much. Backup configuration can be simplified. Budget saved can be spent elsewhere.