Tech Briefs

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Dürr controls NOx and VOCs

Choosing an environmental control technology for destroying oxides of nitrogen (NOx) became essential when Engelhard, an automotive catalyst manufacturer, included inorganic nitrate compounds in its formulations. Heat treating catalysts inside a high-temperature oven causes these compounds to decompose, producing NOx and other gaseous byproducts, including volatile organic compounds (VOC). Because the NOx continuously emitted from the oven reached concentrations of more than 20,000 ppm with VOC levels reaching 500 ppm, an emissions-control strategy needed to be implemented.

Dürr Environmental's selective catalytic-reduction (SCR) system was chosen for Engelhard's Huntsville, AL, plant due to the conversions of NOx required. A scrubber was considered; however, the company required a 99.9% NOx reduction and a scrubber was limited to about a 90-95% reduction. A selective non-catalytic-reduction (SNCR) process was another option considered briefly, but the reductions would be limited to about 75% and the equipment would be a bit more expensive.

"We really didn't look at other technologies," said Richard Rodenhausen, Senior Project Engineer for Engelhard. "The SCR was the best application in terms of reducing NOx for this situation."

The exhaust temperature of the mixed gas stream in Engelhard's oven operates at an average of 230°C (446°F). The composition of the different oxidation states of NOx stays relatively constant at 30% nitrogen dioxide (NO₂) and 70% nitric oxide (NO). Previous experience with a packed tower scrubber used a scrubber column with high surface-area packing to affect intimate contact between the gas and absorbing liquid in a countercurrent flow pattern, which resulted in a 60% maximum NOx destruction efficiency. The absorbing liquid was a dilute solution of sodium hydroxide. Since NO is insoluble, it must be oxidized to NO₂ before being diffused across the mass transfer interface into the liquid phase to react with caustic soda and form sodium nitrate.

The combination NOx and VOC control technology implemented by Dürr used a single skid-mounted system, combining SCR for the reduction of NOx and an oxidation catalyst for VOC removal. Most SCR systems used in the industry today reduce NOx from stationary power-generating sources in constant operation, though with relatively low NOx concentrations. However, SCR technology has recently become a more popular option to reduce NOx from more complex chemical manufacturing processes, mainly because of its ability to reduce NOx to extremely low levels in the presence of other compounds, but also because of its process flexibility in handling varying concentrations of NOx.

In a Dürr combination system, the gas stream first passes through an oxidation catalyst to convert VOCs to carbon dioxide and water. Then it passes through a control system that modulates the ammonia flow added to the polluted gas stream. Ammonia regulated through a control valve mixes with ambient air pumped through a distribution manifold for uniform mixing with the NOx-containing gas before entering the SCR catalyst bed. This process ensures an even distribution of ammonia to aid in achieving optimal NOx reduction.

"This is the first time I know of that both VOC and NOx were treated in the same system to the high degree that this required," said Jim Griffin, Regional Sales Manager, Dürr Environmental. "Prior systems sometimes treated the VOC or CO to about 50% reduction. Here we went over a 99% reduction."

Two SCR/VOC systems have now been installed at Engelhard to combat the NOx generated during the high-temperature treatment of automotive catalysts. These abatement systems have allowed Engelhard to stay within VOC and NOx emissions limits while proving to be easy to maintain and operate. They do not produce a secondary waste stream (low ammonia slip) and have lower capital costs compared to other available technologies considered.

"Any system will have some maintenance," said Rodenhausen. "Overall, the SCR system requires less maintenance because its operation is a lot simpler than other technologies."

- Jean L. Broge

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SLP Engineering for GM and Ford

SLP Engineering's airbox system.

In the 2002 model year, SLP Engineering marks its eleventh year of working with General Motors. In that time span, SLP has done performance enhancements to more than 35,000 new F-cars (Chevrolet Camaros and Pontiac Firebirds) as well as provided content to the sports cars.

"What really differentiates SLP from our competitors is the fact that we work closely, on a day-to-day basis, with the Camaro- and Firebird-brand teams as well as the F-car engineering platform," said Ed Hamburger, President and founder of SLP Engineering. "Operating at essentially no cost to GM, we're involved in the engineering, validation, parts manufacturing, assembly, sales, and warranty support of our high-performance F-cars."

New for 2002 is SLP's high-flow induction system and an air cleaner lid, which together add 15 kW (20 hp) to the Camaro SS. Performance enhancements raise power from 242 to 257 kW (325 to 345 hp). The induction system mates to either a center-mounted performance exhaust or a dual-dual performance exhaust. The air cleaner lid is made of 15% glass-filled polypropylene.

"The inside of the part is designed so that the airflow is smoother into the engine vs. the production part, which has sharp edges," said Jeff Yachnin, Chief Engineer for SLP Engineering. SLP also provides select content on every Camaro SS, including the production/painting/installation of its scoop hood and rear deck spoiler.

SLP Engineering provides its expertise for the 2002 Chevrolet Camaro SS and Ford Thunderbolt.

New on the Firehawk for 2002 is a high-flow induction system as well as an optional rear deck spoiler with a wide, center, high-mounted signal lamp (available only on the Trans Am coupe). The Firehawk has a composite resin-transfer-molding hood.

Vehicles are shipped from GM's Ste. Thérèse Canadian facility to SLP Engineering in LaSalle, Quebec, Canada, for final assembly, and then back to GM for shipment to dealers. (In late September, GM announced that 2002 will be the last model year for the Camaro and Firebird, and that therefore the Ste. Thérèse plant will close in September 2002.)

SLP Engineering also is providing content on the Ford Ranger-based 2002 Thunderbolt, which marks the first time a niche vehicle company is simultaneously producing and marketing second-sticker, factory-approved programs for both GM and Ford Motor Co. The base Thunderbolt package includes a front fascia, full body cladding, and a revised exhaust outlet. The Thunderbolt gains 11 kW (15 hp) compared to the Ranger.

"On the 4.0-L SOHC V6, power goes from 154 to 166 kW (207 to 222 hp). This (increase) is a result of the cold-air induction system, which allows better airflow through a high-flow air filter and box," said Yachnin. "The exhaust system is also a high-flow design. Together, (those modifications) yield the power increase."

Officials at SLP Engineering expect Thunderbolt-packaged Rangers to account for 1-2% of the Ranger's annual 325,000 units. In 2001, SLP provided content to about 6400 Camaro SS cars and 600 Firehawks, as well as about 500 Camaro RS and Firebird GT cars.

- Kami Buchholz

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