Analyzing the Torrance facility’s compressed air system, ExxonMobil engineers, in consultation with Van Air personnel, identified the source of the problem: three outdated and improperly sized internally heated regenerative desiccant air dryers.

These compressed air dryers could not supply the refinery's normal requirement for approximately 13,000 scfm of compressed air dried to a pressure dew point of -40°F. Moisture-laden air was a serious and costly problem. For example, 1 ½" drive impact wrenches required frequent replacement at a cost of about $4,200 each. Smaller wrenches were similarly affected.

In addition, normal operation of the dryers was causing a periodic pressure loss of 10-12 psig. The pressure drops affected downstream equipment, as well as operating costs. With compressed air costing roughly 30 cents per 1,000 cubic feet, ExxonMobil estimated that lost air power was costing the refinery more than $75,000 per year. (See Van Air's online "Cost of Pressure Drop" calculator.)

Following Van Air’s recommendations, two new Van Air HB-5000 externally heated blower purge regenerative compressed air dryers with particulate and coalescing filters were specified.

Two Van Air F101-5000-C coalescing filters installed upstream of the HB-5000 dryers remove oil aerosols from the air system. Downstream of the dryers, two F101-5000-HT high temperature filters remove particulates.

The air system installed at the Torrance refinery also includes four reciprocating air compressors. Integrated compressor after-coolers deliver compressed air at 90ºF. At this temperature, the capacity of each HB-5000 dryer is 6,650 scfm or a combined total of 13,300 scfm at 100 PSIG.

This is more than sufficient for ExxonMobil’s requirements, said company engineers, especially since the advanced design of Van Air dryers eliminates purge loss and reduces pressure drop.

Each dual tower Van Air blower purge dryer processes large volumes of compressed air economically, since no compressed air is required for desiccant bed regeneration. Instead, heated atmospheric air is used to purge accumulated moisture from the desiccant in the tower being regenerated. The 8-hour drying cycle includes three hours of desiccant regeneration (heater on), one hour of cooling, and four hours of drying in each tower.

During operation, wet air enters the drying tower through an inlet transfer valve and flows through the drying desiccant bed where moisture is adsorbed. Dry process air with a -40°F pressure dew point exists through either of two outlet valves.

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. That flows through the bed, collecting 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.

“Since installation of the new air system, there has been no moisture-related downtime,” ExxonMobil reports.  “Moisture, rust and pipe scale are no longer a problem. Productivity is up and we are realizing substantial savings.”