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Taking Pressure Off Blower Selection With Regenerative Technology

Wed, 03/05/2008 - 6:35am
Among the many advantages of regenerative blowers are energy efficiency, low maintenance, and high reliability. They also supply clean air and eliminate the need for expensive outlet filters and dryers or special water and oil traps
By Jay Jarboe

Blowers provide critical enabling technology for chemical processing plants and refineries to handle or separate hazardous and corrosive gases, whether in vent header off-gassing, spot source, centrifuge venting, or scrubber applications. But changes are in the wind concerning the equipment used to perform these jobs, largely due to mounting industry pressures to reduce energy and maintenance costs, simplify processes, and improve productivity.

Most such blower applications can be satisfied by multi-stage or positive air-displacement blowers and compressors, but at a relatively high price when factoring in their levels of energy consumption and demanding maintenance requirements. In contrast, regenerative blower technology can serve as a practical, efficient, and industry-friendly alternative to help keep costs down and output high.

Here’s how these blowers work and compare favorably with conventional counterparts.

How They Work
Regenerative blowers draw air or other gases into the blower unit by impeller blades passing an inlet port. The impeller blades then accelerate the air in an outward and forward direction using centrifugal action. The air is turned back, or “regenerated,” by the blower’s annular-shaped housing to the base of following blades, where it is again projected outward. Every “regeneration” imparts more pressure to the air.

When the air reaches a “stripper section” at the outlet, it is “stripped” from the impeller and diverted out the blower. (The stripper section is located between the inlet and the outlet where the annulus is reduced in size to fit closely to the sides and tips of the impeller blades.)

The outcome: Pressures generated by the one or two spinning, non-contacting, oil-free impellers are equal to those obtained by many larger multi-stage or positive displacement blowers.

Among the notable advantages, compared with other traditional blower types, are the following:

1. Energy Efficiency
Developing pressures higher than required for applications wastes energy. Regenerative blowers have been engineered to deliver the ideal pressure and flow for properly sized pneumatics at point-of-use.

2. Low Maintenance and High Reliability
Fewer moving parts reduce wear, tear, maintenance, and downtime to promote sustained blower reliability. Unlike competing technologies incorporating necessary sliding vanes, valves, and pistons, the only contacting moving parts inside a regenerative blower are two permanently sealed ball bearing assemblies.

3. Green Performance
Regeneratives supply clean air, free of oil, excess moisture, and other compressor-induced contaminants. They further eliminate any need for expensive, high-maintenance outlet filters and dryers or special water and oil traps.

Making the Grade
Regenerative blower technology can help keep costs down and output high.
In general, when selecting a regenerative blower for a system, the blower’s pressure-flow curve initially should be evaluated and compared. Regenerative blowers for chemical processing applications typically can achieve flows up to 1,000 SCFM (standard cubic feet per minute) for single-stage units and up to 1,900 SCFM for double-stage units. Pressures up to 230 IWG (inches of water gauge) can be achieved. Once flow and pressure requirements are satisfied, other factors can be considered to help develop a properly engineered blower for an application.

Criteria guiding basic blower selection will include size (compact units suit ever-smaller system design envelopes); noise levels (“the lower the better” consistent with OSHA standards for plants); construction (rugged blower housings can best survive industrial conditions); and desirable long service life (motor bearings hold the key to documented longevity).

Applications encountered in chemical processing often add more selection criteria, especially when blowers must perform in unfriendly and demanding environments. In these cases, users may want to specify the following:

1. Specialized Surface Treatment
The capability to withstand extremely corrosive, hazardous, and harsh conditions is essential for all equipment in the chemical processing industry, and regenerative blowers are no exception. This has led to development of an innovative surface-conversion process that literally changes the molecular structure of a blower’s surface and combines the advantages of anodizing, hardcoat plating, low-friction polymers, and dry lubricants. The resulting plastic/ceramic surface has been shown to be harder than steel. It exhibits higher wear resistance than either case-hardened steel or hard-chrome plate and provides for continuous inherent lubrication. It also resists moisture and corrosion from chemicals.

2. Gas-Leakage Seals
Lip seals offer a moderate gas-leakage option (typical leakage containment to 5cc/min or less), while a pair of face carbon seals can provide even greater containment protection (leakage less than 0.06cc/min). Lip seals in a stainless steel case will reduce gas leakage at the motor shaft; a sealing compound then can be applied to cut off all leakage paths at the blower’s metal-to-metal surfaces. Double face seals will work against each other on opposite sides of a common mating ring to effectively reduce gas leakage at the motor shaft.

3. Explosion Proofing
Maximum safety can be achieved with specific safeguards. These can include spark-resistant housing and integrally mounted, direct-drive NEMA frame motors meeting the “Explosion Proof” requirements of a Division 1 & 2, Class I, Group D hazardous atmosphere. Motors should be UL and CSA approved.

Other Considerations
Regenerative blowers draw air or other gases into the blower unit by impeller blades passing an inlet port.
Depending on needs and preferences, additional options for regenerative blowers may become appropriate. For example, it may be critical to measure correct air flow to help fine-tune a system for optimized efficiency. An air flow meter will allow for direct readings in SCFM. (Basic models can yield accuracy within 2 percent at standard conditions.) Meters can even help in troubleshooting. For systems in which channeling or plugging can occur, a noted diversion in measured CFM may signal an otherwise unseen system change likely requiring attention.

Air flow meters additionally can play a role in balancing multi-piping systems. When evacuating CFM from more than one pipe, differently run lengths or end system impedance may cause one pipe to handle more CFM that the others. With an accurate and timely CFM reading, piping can then be balanced by bleeding air in/out or by creating extra impedance.

Users may further want to investigate inlet/outlet mufflers and/or filter silencers in areas where reduced sound levels may be required; an inlet filter (normally used in pressure systems) to protect the blower and the air distribution system from dust, other airborne particles, and contaminants; or gauges dedicated for measuring pressure, vacuum, and temperature in various ranges. All can contribute to ideal system performance and reliability.

Footnote: When evaluating regenerative blower technology for any chemical processing application, a recommended first step is to partner with an experienced manufacturer. Such an expert resource can deliver input and insights that can make all the difference in realizing the full potential and all the benefits.

Jay Jarboe is sales manager-industrial products for Ametek Technical & Industrial Products, 627 Lake St., Kent, OH 44240. The company (a unit of Ametek Inc.) is a leading designer and manufacturer of blower, motor, and pump products for a wide variety of industry applications. More information is available at 815-877-5404, jay.jarboe@ametek.com or www.ametektechnicalproducts.com.

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