Case study - Paint mixing

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Courtesy of Anguil Environmental Systems, Inc.

Overview

A company involved in the automotive aftermarket had a paint batch mixing and filling operation that used primers and fillers. They were faced with installing air pollution control equipment to handle the volatile organic compounds (VOCs) emitted by the solvents used in their processes. An independent consultant had determined that total exhaust volume from the facility was 28,000 SCFM of air. The high volume of air resulted in a low concentration of solvent vapor. This combination of high exhaust volume and low vapor concentration posed an operating cost problem. In addition, powdered material dumped into the batch mixers generated dust, causing potential OSHA violations and hazards to the operators.

Action

After thorough technical evaluation, Anguil Environmental Systems, Inc. was selected and contracted to solve the VOC problem and satisfy EPA requirements.

Solution

Anguil analyzed the operation and focused on the composition of the solvents and the high air volume. Of the solvents used, a small portion was methylene chloride. Chlorinated compounds are a potential poison to most catalytic systems and the company's consultant recommended a thermal incinerator. Anguil recognized that a less expensive alternative to a thermal unit would be an Anguil Chloro-Cat capable of processing the chlorinated compounds. However, Anguil recommended evaluation of alternate compounds to replace the chlorinated organics. Upon investigation, the company chemist determined that all of the chlorinated compounds could be replaced with regular organic solvents.

The high air volume was then addressed. One of Anguil's strengths is their knowledge in capture hooding and air flow reduction techniques. The 28,000 SCFM (44,159 Nm3/Hr) of exhaust was originally recommended based on the assumption that all thirteen (13) batch mixing devices could potentially be at their peak mixing and vapor loading capacity simultaneously. Interviewing the facility manager, it was determined that not all thirteen mixers were ever loaded simultaneously.

With this information, Anguil developed an air reduction strategy that greatly reduced capital cost. Anguil designed an air reduction system after mapping the fugitive VOC's with a portable FID (Flame Ionizing Detector). This research allowed Anguil engineers to determine the areas of high VOC concentration and to subsequently design the innovative capture system.

The company had been using floor sweeps as part of their capture system that were up to ten (10) feet away from the mixing devices. The mixing containers had covers that were poor fitting and extremely heavy. The distance between the floor sweeps and the mixing devices was the primary cause of floating dust and escaping vapors. The Anguil solution was to replace the floor sweeps and mixing tank covers with a close capture hooding system. Anguil designed a series of aluminum custom fabricated mixing covers with integral flexible duct connectors to draw the vapors and dust directly from the mixers. The added benefit of the close capture hooding was the decrease in air volume necessary to capture the vapors from the VOC source.

Anguil determined that all of the VOC's from the mixing room could be adequately captured with 9,000 SCFM (14,194 Nm3/Hr) of air and that future plans for expansion would not take the exhaust air volume above 12,000 SCFM (18,925 Nm3/Hr). Rather than focusing on costly outside make-up air to replace this 9,000 SCFM (14,194 Nm3/Hr) of exhaust, Anguil supplied close capture pick-up hoods in the mixing room immediately adjacent to the room containing the fill devices. This air was then transferred or 'cascaded' into the adjacent mixing room, creating makeup air. The VOC concentration of this makeup air was well below the Threshold Limit Values (TLVs) but the state of Michigan determined that these VOC's were fugitives and should be destroyed. The air supply was introduced on the far side of the mixing room which helped sweep the vapors across the 120 by 60 foot room towards the pick-up points.

Outside of the building, an Anguil 12,000 SCFM catalytic oxidizer was supplied and installed on a concrete pad. Prior to entering the catalytic oxidizer, the entire airstream was fed through a two chamber dust collector to prevent the particulate and dust from masking the catalyst or blocking the plate type heat exchanger. A precious metal platinum catalyst was supplied to destroy the hexane and toluene organics. Adequate catalyst was supplied to process 9,000 SCFM (14,194 Nm3/Hr) and as the facility capacity increased, more catalyst would be added. Due to the well designed air reduction strategy, Anguil saved the customer tens of thousands of dollars on their pollution control system while achieving compliance.

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