The paper producer established a new air system specification of -40ºF dew points. After thorough cost efficiency studies, older refrigerated compressed air dryers were replaced with sophisticated Van Air HB-6000 blower purge dryers. According to the plant’s instrumentation engineer, the Van Air heated blower purge units were the most cost effective in terms of annual energy consumption and simplicity of operation over other competitive units.

Van Air blower purge compressed air dryers process large volumes of compressed air economically since no compressed air is required during regeneration of the desiccant bed. Instead, atmospheric air is used to purge accumulated moisture.

In HB Series compressed air dryers, wet compressed air enters through an inlet transfer valve and flows through the drying desiccant bed where moisture is adsorbed. Dry process air with a -40ºF pressure dew point exits through an outlet valve.

In the tower that is regenerating, moisture is stripped from the desiccant by hot atmospheric air drawn in by an external blower and passed over a heater. It flows through the bed, collects moisture, and is discharged through a purge valve.

Van Air’s patented valve and control design, known as Interlock Logic, assures reliable drying operation and prevents accidental blow down and loss of flow and pressure.

Interlock Logic pneumatically links the inlet transfer and purge valves so that each phase of the dryer cycle is complete before the next cycle begins. Thus, compressed air blow down and system blockages are avoided. Interlock Logic is self-adjusting to variable operating conditions; manual adjustment is not required.

In addition to many standard features, the paper producer ordered its HB-6000 compressed air dryers with many optional features. To name a few, these included: dew point demand switching, which reduces operating costs by lengthening the drying cycle and reducing the number of regeneration cycles; a failure-to-switch alarm and indicators that directly measure moisture content; digital dew point readouts; and cycle sequence lights. The HB-6000 compressed air dryers also has alarms for excessive heater temperatures, low regeneration temperatures, and blower failure.

The two dryers were built onto a structural steel base. F101 Series pre-filters and after-filters were installed on-site. Also included were filter pressure differential gauges and motorized, automatic drain valves for use with each pre-filter.

Since the installation of the compressed air dryers, “We’ve seen better air quality in places where there were problems before,” according to a plant supervisor. “The HB-6000 dryers are easy to maintain and the service we received from Van Air and its distributor, the Al Xander Company, is highly responsive.”

Compressed air is vital to the lumber industry. However, when compressors take in atmospheric air, they also take in the moisture contained within that air. This moisture can freeze when it condenses, causing frozen valves and broken lines, lost production and unnecessary downtime. Freeze-ups are therefore a particular concern for sawmills with outdoor air lines exposed to freezing temperatures. Although methanol injection into the airlines is a common solution for some industries, it is not a good answer for sawmills due to the flammability and toxicity of methanol. Methanol also damages seals and valves.

The Boise Cascade facility used three rotary screw compressors (750 scfm, 1250 scfm, and 410 SCFM), all operating at 100 PSIG, to supply compressed air for its automated system, which covers all manufacturing phases from debarking to finishing. Ambient air temperatures in the vicinity of the saw mill during January average between 20°F and 25°F, but can drop as low as -25°F. Summer temperatures can reach 90°F with an average of 75°F to 80°F.

When manufacturing pine lumber at a rate of 150,000 board feet per shift, it is vital that the saw mills have clean, dry compressed air. Although a refrigerated air dryer was being used to dry all of the air, freeze-ups were being experienced during the winter months at the debarker and green lumber stacker. When downtime and slow production became a problem, Boise Cascade turned to Van Air Systems.

Set Point Control, a Van Air distributor in Portland, Oregon, helped Boise Cascade personnel identify the moisture problem and select two Van Air compressed air dryers with filters. According to a Boise Cascade maintenance supervisor, a Van Air Freedom Dryer model D36 with an MDV automatic drain valve was installed near the outdoor debarker, approximately 100 yards from the compressors. The Freedom Dryer model D12 was installed near the outdoor green lumber stacker, approximately 500 yards from the compressors. Unlike in most applications, after-coolers were not required because the long pipe runs between the compressors and the dryers. This allowed the compressed air to sufficiently cool to within a few degrees of the ambient air temperature before entering the Freedom Dryer vessel.

Operation of the Freedom Dryer is automatic from start to finish. The dryers compensate for variable operating temperatures, flows, and pressures. Cool, dry, and clean outlet air is assured. The dryers lower the outlet pressure dew point 20ºF below the inlet temperature. Thus, no moisture can condense because the dew point temperature of the compressed air is always lower than the ambient temperature.

The Freedom Dryers operate without an outside power source and have no moving parts. Moisture is absorbed from the air using Dry-O-Lite, a special drying agent (deliquescent desiccant) in tablet form. Dry-O-Lite tablets gradually dissolve. Condensate drops into a claim area at the bottom of the dryer vessel for automatic draining. Final processing of the air is achieved by the filters that trap any oil aerosols with high efficiency microfiber elements that are changed periodically.

Since the Van Air dryers were installed, Boise Cascade has not experienced any downtime due to freeze-ups in their air lines or equipment. Sawmill operators report an increase in production efficiency. The Van Air dryers are particularly critical when the ambient air temperature is below 35ºF, which is beyond the dew point range of the refrigerated dryer.