Case study - Engine cell exhaust: Catalytic oxidizer

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Courtesy of Anguil Environmental Systems, Inc.

Overview

Endurance testing of outboard motors for boats has typically been done in lakes and sometimes on barges. This testing was time consuming, presented logistic problems and removed the testing from the R & D department and the factory. When a company in Oklahoma decided to build their own endurance test cell area, the Environmental Protection Agency required them to control the emissions from the test engines. Four test cells were considered for pollution abatement. The initial design exhaust volume was in excess of 4,400 SCFM (6,940 Nm3/Hr) per test cell. This high exhaust volume per cell posed a significant capital and operating cost problem when the company considered pollution control equipment.

Action

The customer believed a thermal incinerator would be the preferred solution because of the low cost of natural gas in Oklahoma. After looking at equipment capital cost and operating costs the company recognized the benefit of considering a catalytic oxidizer. After thorough technical evaluation, Anguil Environmental Systems, INC. was selected and contracted to solve their VOC problem and insure that the new test cells were in EPA compliance.

Solution

Automotive catalysts have proven effective in handling exhaust gases from internal combustion engines, where both unburned hydrocarbons and carbon monoxide are destroyed. Anguil analyzed the operation and concluded that the enclosed engine test cells needed significantly less exhaust volume than the 4,400 SCFM (6,940 Nm3/Hr) proposed. Anguil determined that the exhaust from even the largest stern drive engine was under 800 SCFM (1,262 Nm3/Hr) of air. Exhausting 800 SCFM (1,262 Nm3/Hr) from each test cell would place each tank under negative pressure, therefore no carbon monoxide would leak into the test facility. Using 850 SCFM (1,341 Nm3/Hr) as a design criteria, it was determined that a 6,800 SCFM (10,725 Nm3/Hr) catalytic oxidizer could handle the initial four test cells with the additional capacity for four future test cells.

Anguil supplied and installed the catalytic oxidizer inside the building on a mezzanine adjacent to the test area. Only enough catalyst to handle the initial loading from four test cells was supplied which reduced the initial capital cost. An exhaust stack test analysis was performed to determine what concentration of carbon monoxide and hydrocarbons could be anticipated. The presence of carbon monoxide dictated a total enclosure around the catalytic oxidizer. An exhaust fan was placed in the enclosure creating negative pressure and eliminating the possibility of carbon monoxide leaking into the facility. The oxidizer was equipped with a variable speed/variable frequency drive to provide a high degree of turndown if only one test cell was being run. A stainless steel plate and frame type heat exchanger was used to accommodate high exotherm across the catalyst.

Some of the engines in the facility were diesel engines and some endurance runs were lengthy. Since these engines potentially could go out of tune, a ceramic particulate filter was installed within the catalytic oxidizer down-stream of the gas burner to protect the catalyst from unburned carbonaceous materials. The periodic cycling and high fire of the gas burner eventually vaporizes these carbonaceous materials and allows them to be oxidized by the catalyst.

After approximately eight months of successful operation, the company decided to expand and add the four additional test cells. The new exhaust fans and ductwork were completed by Anguil's installation crew and additional catalyst was added to meet the company's increased capacity. The result is a state of the art engine test facility in compliance with EPA requirements.

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