October 8, 2009
by James Stone
Energy efficiency in the automotive industry extends beyond making cars that will travel farther on a tank of gas. Central Motor Wheel of America Inc. (CMWA), a manufacturer of steel and aluminum wheels for the automotive industry, focused on its paint line to not only reduce emissions, but save on the consumption of power fuelled by natural gas.
To do so, the aluminum division of CMWA approached the Environmental and Energy Systems group of Dürr Systems Inc. to help with a company wide initiative to reduce energy at both the aluminum and steel wheel divisions.
CMWA is a joint venture of Central Motor Wheel of Japan Ltd. (CMW) and Toyota Tsusho of America (TAI) located on 22.5 hectares in Paris, Ky.
Dürr, a supplier of abatement systems for volatile organic compounds (VOC) based in Plymouth, Mich., targeted the company’s two paint lines and their respective emission control devices at the aluminum division as a basis for an initial evaluation. Each paint line consists of primer and topcoat booths that recirculate a significant amount of air back to the spray booth while a portion of the air is exhausted to a thermal oxidizer emission control system. Air that’s exhausted to abatement is then replaced by fresh air source to the spray booths. Each line is also equipped with primer and topcoat ovens that exhaust to the oxidizers.
One of the paint lines was equipped with a Dürr Ecopure RL15, a 15,000 standard cubic feet per minute (scfm), high-efficiency regenerative thermal oxidizer with a thermal energy recovery rating of 95 per cent. The average temperature increase across the unit was 37.7 degrees C.
The other line treated its emissions with a 13,000 Scfm recuperative thermal oxidizer with a thermal energy recovery rating of about 55% and a temperature increase across the unit of about 304 degrees C.
Since both oxidizers treated relatively the same air volume and emission concentration (average 11,675 scfm and 21 lb./hr.), the recuperative oxidizer became a likely energy saving opportunity.
“The recuperative oxidizer probably offered a lower capital cost and improved the bottom line of the initial paint line package investment. However, the inefficiency of the recuperative oxidizer resulted in long term fuel consumption approaching $500,000 a year based upon today’s natural gas prices,” said Dürr’s Karl Walby, a member of the EES aftermarket sales team.
The comparative fuel consumption costs of the other aluminum line with the Ecopure RL were closer to $65,000 per year.
Since the capacity utilization of both aluminum paint line oxidizers was upwards of 84%, either the inefficient recuperative unit would have to be replaced by a new high-efficiency RTO to recover exhaust heat that could supplement the paint process oven, or a creative alternative would have to be found.
It turned out the most beneficial solution existed at the end of the steel division’s paint line about 183 metres from the aluminum division.
The steel division was equipped with a high-efficiency 40,000 scfm Ecopure RL40 regenerative thermal oxidizer to treat emissions from a similar paint process. The capacity utilization of the steel line RTO was only about 35% requiring a nominal 14,000 scfm of the available 40,000 scfm. The plant originally expected its utilization level to be greater, but various changes to process formulations, plus environmental and air balance initiatives have kept the emission control volume of the steel line comparable to the aluminum lines. And it was determined the overall emission control scheme for both the aluminum and steel divisions would be optimized.
The project was one of both reconditioning and relocation. The RL40 from the steel line was relocated to treat the combined emissions from both aluminum paint lines and the inefficient recuperative oxidizer was removed from service while the RL15 was relocated from the aluminum division to the steel paint line and operated at about 93% of its capacity.
During the relocation, both units were reconditioned. The reconditioning was further simplified and expedited while the units were dismantled for relocation. And CMWA handled infrastructure changes that were mitigated by the similarity in orientation between the two RTOs.
Once the RLs were relocated the recuperative oxidizer was removed from service and the ductwork from the corresponding paint line was re-routed a nominal 55 metres to the newly relocated RL40 along with the first paint line.
Even with the combined emissions from both of the aluminum lines the unit has 40% spare capacity if future sources require controls.
The project was completed in six weeks with an 80% reduction in natural gas fuel consumption amounting to 7.25 million btu per hour and a projected $427,000 per year savings based upon current fuel costs and production hours of operation. And return on investment was less than 12 months.
By targeting its paint lines, CMWA saved energy and money, but it has also shortened its environmental footprint, which is especially important as governments place greater emphasis on manufacturers taking responsibility for their carbon emissions.