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Quotes - Engineering - SalesRefrigerated Air Dryers for Food Packaging
A packaging hall is a pneumatic plant with food in it. Form-fill-seal machines close their jaws with air cylinders, tray sealers clamp and cut with air, case erectors, labelers and palletizer grippers run on valve islands, checkweighers reject with an air blast, and vacuum pick-and-place heads run on venturi generators. Water in that air sticks a sealing jaw for a fraction of a second and the pack leaks; it corrodes cylinders in a washdown environment; and in the air that reaches open product, a reject blast, a blow-off into an open tray, a pneumatically conveyed ingredient, it carries whatever grew in the wet pipe onto the food.
The food-grade codes of practice split the specification in two. Non-contact air, the cylinders and valve islands, is ISO 8573-1 class 2.4.2: a 38°F pressure dew point from a refrigerated dryer, with coalescing filtration. Contact air is class 2.2.1: a –40°F dew point, oil to 0.01 mg per cubic meter and a sterile filter at the point of use, which means a desiccant stage on that branch, fed by the refrigerated dryer.
A packaging hall with six lines runs on a 50 to 100 hp screw, 220 to 450 SCFM, and a large plant with pneumatic ingredient conveying on 150 hp and more. A 75 hp screw at 320 to 340 SCFM is the 400 SCFM dryer in a normal compressor room and the 450 or 500 size in a hot one. The dryer sits in the compressor room; the packaging hall gets stainless drops, filters at the machines and the desiccant branch where product is touched.
Halls that run two shifts with changeovers between products spend hours at low flow, and there a cycling dryer stops its refrigeration compressor while the thermal mass carries the load. A three-shift hall with a loaded compressor is the non-cycling case.
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ISO class for air that touches the foodClass 2.2.1 means a -40°F dew point and oil to 0.01 mg per cubic meter, so only the contact branch carries a desiccant stage while the rest of the hall stays refrigerated.
What water does on a packaging line
Seals, cylinders and the product itself
- Sealing jaws hesitating as condensate washes the lubricant from the cylinder, leaving leaking packs
- Reject blasts and blow-off nozzles carrying organisms from a wet pipe onto open product
- Cylinders and valve islands corroding where washdown humidity meets wet internal air
- Vacuum pick-and-place heads losing grip as rust dust from the header blocks the venturi
The two specifications a food plant writes
Non-contact and contact air
- Non-contact, class 2.4.2: 38°F pressure dew point from a refrigerated dryer, coalescing filter, oil to 0.1 mg per cubic meter
- Contact, class 2.2.1: –40°F from a desiccant stage fed by the refrigerated dryer, oil to 0.01 mg, sterile filter at the point of use
- Activated carbon after the coalescer on a lubricated compressor, so oil vapor never reaches the hall
- Dew point logged at the dryer outlet, because an auditor wants a reading, not a rating
Dryers that fit a packaging hall
Capacities at the 100 psig, 100°F inlet rating point. A hall on a 50 to 100 hp screw uses the 250 to 500 SCFM sizes; larger plants use 600 to 1,250 SCFM, where the FLXA and AES series follow the swing between changeovers and full production.
| SERIES | TYPE | FLOW RANGE | MAX INLET | MAX PRESSURE |
| DXR Series | Non-Cycling | 10 to 4,200 SCFM | 131°F | 203 psig |
| FLXA Series | Cycling | 75 to 2,000 SCFM | 120°F | — |
| NXC Series | Cycling | 20 to 2,000 SCFM | 158°F | 232 psig |
| AES Series | Digital Scroll Cycling | 600 to 10,000 SCFM | 120°F | 232 psig |
| HF Series Filters | Compressed Air Filter | 20 to 21,250 SCFM | — | 300 psig |
| GFN Series Filters | Compressed Air Filter | 6 to 1,500 SCFM | — | 232 psig |
| ND Series Zero-Loss Drains | Condensate Drain | Call for sizing | — | 290 psig |
| PDM Dew Point Monitor | Dew Point Monitor | Call for sizing | — | 145 psig |
The packing hall air plan comes down to this.
- Dryer in the compressor room, never inside the washdown zone
- Stainless header into the hall with drops taken off the top
- Desiccant branch and sterile filter wherever air reaches open product
A reading beats a rating at audit time
A dryer's data sheet says 38°F at 100 psig, 100°F inlet and 100°F ambient. The auditor's question is what the dew point was last Tuesday at 3 pm, when the compressor room was 108°F and the aftercooler needed cleaning. The only good answer is a logged reading from a dew point monitor at the dryer outlet, checked against the ISO 8573-1 class the plant's food-safety plan claims.
A portable monitor that reads –148 to +68°F covers both the refrigerated plant air and the desiccant contact branch, and a quarterly reading with a note of the compressor room temperature is the record most audit schemes accept.
- Dew point logged at the dryer outlet, not assumed from the rating
- Quarterly readings and after any change to the compressor or dryer
- One monitor for the refrigerated header and the desiccant branch
Where the dryer and filters go
Compressor, aftercooler, receiver, 1 micron prefilter, refrigerated dryer, 0.01 micron coalescer, activated carbon filter, header. The dryer stays in the compressor room, never in the washdown zone, and the header enters the hall in stainless with drops taken off the top and a filter-regulator at each machine. Where a branch touches product it leaves the header through a desiccant dryer sized for that branch and ends in a sterile filter at the nozzle. The filter placement page shows the order of the stages and the drains between them.
Chilled halls and cold stores
A refrigerated dryer holds about 38°F, and a fresh-food packaging hall at 45°F leaves only a few degrees of margin; a cold store at 36°F leaves none, and the air line along its ceiling condenses. Where a line enters space at or below 40°F, feed it from the desiccant branch rather than the plant header, or route it through warm space and drop into the cold room from above. The refrigerated versus desiccant page draws that line in detail.
Cycling or non-cycling for packaging
Packaging demand follows the schedule. A hall that runs two shifts, stops for changeovers and washdown, and holds pressure overnight spends most of its hours well below the compressor's output, and a cycling dryer such as the FLXA or NXC saves 50 to 80 percent of dryer power there. A three-shift hall with a loaded compressor gets little from cycling and does better with the simpler non-cycling DXR. Above 600 SCFM the AES digital-scroll dryers modulate refrigeration to the load continuously, which suits a plant whose demand never settles.
Oil-free compressors
Many food plants run oil-free compressors so that oil class 1 is met at the source. Oil-free air is still saturated with water at the aftercooler outlet, so the dryer, the separator and the drains are unchanged; only the carbon filter becomes optional. The 0.01 micron coalescer stays, because an oil-free machine still passes dust and the water aerosol the dryer's separator does not catch. The dew point and ISO classes page lists what each class number means.
Contact air and machine air in a packing hall
Usually not for the hall itself, but the margin is thin. Air at a 38°F pressure dew point leaves only a few degrees between the dew point and the coldest pipe, so any line that passes near an evaporator coil or the door of a cold store can condense. Route the header high, in the warmest part of the room, and send anything that enters space at or below 40°F through the desiccant branch instead of the plant header.
As product contact, since the air carries the ingredient itself. It falls under class 2.2.1, so the branch is dried by the desiccant stage to -40°F, kept to 0.01 mg of oil per cubic meter and finished with a sterile element where the air meets the product. Conveying draws far more air than reject blasts or blow-offs, so that branch can be the largest share of the desiccant duty and has to be sized on its own flow, not lumped in with the small contact points.
A logged reading at the dryer outlet, not the figure on the data sheet. Take one each quarter and after any change to the compressor, dryer or piping, and note the compressor room temperature beside it so a high reading can be explained. A portable monitor reading -148 to +68°F serves both the refrigerated header and the desiccant branch with one instrument, and each reading is compared with the ISO 8573-1 class the food-safety plan claims.
The coalescer stops oil droplets but not oil vapor, and vapor carried through a warm header can condense again on cooler surfaces and inside machine valves close to open product. A carbon stage after the 0.01 micron coalescer adsorbs that vapor, provided the air reaching it is already dry and free of aerosol. Its element gives no pressure-drop warning when saturated, so change it on running hours and file the change log with the audit records.
More on packaging hall air
Dew point and ISO 8573-1 classes
What the class numbers for particles, water and oil mean, and which dryer and filter combination delivers each one.
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