Like many electrical power plants built in pre-emissions times, the VMEA Generation Plant in Manassas, Va., was originally built in a remote area, literally "out in the country." Built in 1990, the 24 MW plant has 16 Caterpillar 3516A-powered generator sets providing peak electrical power for the city of Manassas and the other VMEA members, all nearby municipalities. The 12,600 sq.ft. plant is owned by the Virginia Municipal Electric Association (VMEA), a seven-member purchase power group.
Over time, the area around the plant has been developed, said Jamie Hester, generation supervisor for the power plant. An industrial park is now close by, and more recently a highway bypass routes thousands of people past the plant daily.
With environmental concerns becoming increasingly important for such facilities and a top priority for the City of Manassas Utility Dept., a two-year study was conducted by Aegis Environmental, Richmond, Va., to reduce visible smoke from the VMEA Generation Plant.he result was a $1.1 million project to install 16 regenerative exhaust filter/silencer systems at the plant. Manufactured by CleanAIR Systems, Santa Fe, N.M., the first filter/silencer was installed as a pilot project in late 2005. Results from the pilot installation showed a 90% reduction in visible emissions. The remaining 15 filter/ silencers were due to be installed by the end of April.
Founded in 1993, CleanAIR is an integrated manufacturer of complete emission control systems for almost all types of engines for both mobile and stationary applications.
For the VMEA installation, the CleanAIR filters are a custom-designed regenerative exhaust filter and silencer package specifically designed to fit into the same installation envelope as the exhaust silencers they are replacing. CleanAIR took a flat "race track"-type silencer design and redesigned and repackaged it to fit the vertical installation required at VMEA.
The regenerative exhaust filters at the VMEA plant are part of CleanAIR's Permit Filter system. A catalyzed diesel particulate filter verified by CARB for Level 3 (greater than 85%) particulate matter reduction on emergency standby generators, the Permit Filter system also reduces emissions of carbon monoxide, hydrocarbons and odor by greater than 90%, said CleanAIR's Daniel Serrano.
He said the design of the Permit Filter controls PM by removing particulates of carbon from the engine's exhaust. The filter is made of a cordierite ceramic honeycomb with thousands of parallel channels. To control the flow of exhaust gas, 0.5 in. long plugs are placed in the end of half of the channels, forming a checkerboard pattern.
Plugs are also placed in the other end of the filter to form the same checkerboard pattern, offset by one. This checkerboard arrangement of plugs forces the exhaust gases through the porous, thin ceramic honeycomb walls. When the gases carrying the carbon particles flow through the fine pores of the walls, the carbon particles are filtered out of the exhaust gases.
Serrano said the process of particulate matter collection begins as soon as an engine is started and continues while the engine is operating. As the carbon particles are collected on the ceramic walls, the backpressure of the system increases. The filter substrate has a catalyst coating that allows the filter to regenerate by oxidizing the trapped particulate into gases, mostly C[O.sub.2], that can pass through the filter.
Regeneration occurs when the exhaust gas temperature increases enough to initiate the oxidation of trapped particulate in the filter, with those temperatures varying depending on the sulfur content of the fuel.
CleanAIR also said that the catalyst coating reduces CO and HC. As the exhaust gases come in contact with the catalyst, a chemical reaction takes place that oxidizes the gases. The oxidation process turns carbon monoxide into carbon dioxide and hydrocarbons into water and carbon dioxide.
The Permit Filter catalyzed diesel particulate filter is packaged with the race track-type silencer that CleanAIR redesigned for the vertical installation required at VMEA. The filter/ silencer package is housed in a 304 L stainless-steel shell and achieves a sound attenuation of 27 to 35 dB(A), the company said.
Serrano said typically the filter package can be incorporated into a variety of configurations depending upon the specific application requirements.
The most basic configuration is a packaged filter with cones on both inlet and outlet ends. Typical sound attenuation for this design is 12 to 20 dB(A). Replacement muffler designs are used for applications where space is too tight to add the filter separate from the existing muffler. Special inlet or outlet configurations, or brackets can be used that will allow the filter to replace an existing muffler
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