Selective catalytic reduction (SCR) technology configured with a diesel oxidation catalyst (DOC) have combined to reduce nitrous oxide (NOX) emissions by more than 73 percent and carbon monoxide (CO) emissions more than 90 percent on diesel generators.
Combustion Components Associates Inc. (CCA) designed and installed an SCR system to reduce NOX emissions from four 2,100 kW diesel generators at RC Cape May Holdings’ B.L. England Generating Station in Beesley’s Point, N.J. The NOX reduction system was done as a turnkey project by CCA. It was installed and commissioned in 2007 to comply with New Jersey’s new NOX reduction regulations.
Figure 1 Non air-assisted urea injector
In 2008, the plant was required to reduce CO emissions as well. CCA re-engineered and configured the internals of the SCR reactor box to accept a diesel oxidation catalyst (DOC).
B.L. England is owned by RC Cape May Holdings, LLC, an affiliate of Rockland Capital Energy Investments LLC, which bought the generating station (including the four diesel engines) in 2007. Rockland has made investments to improve the plant’s overall environmental signature, whereas the previous owner had planned to shut it down.
At B.L. England, three boilerstwo burning coal and another using #6 fuel oilprovide around 450 MW of power. The plant is located on the Great Egg Harbor Bay in New Jersey. The 4 x 2,100 kW diesel gen-sets provide power to the grid during peak demand. Prior to March 2007, New Jersey regulations stipulated that lean-burn reciprocating engines fueled by liquid fuels and capable of producing an output of 500 bhp or more were subject to a maximum NOX emission rate of 8.0 grams per brake horsepower hour (g/bhp-hr).
After that date, liquid-fueled lean-burn stationary engines capable of producing an output of 370 kW or more were subject to a new maximum allowable NOX emission rate of 2.3 g/bhp-h.
When the new state regulations went into effect, the prior owner decided not to invest in new pollution control equipment. RC Cape May Holdingsthe new ownersdecided it was worthwhile to install the equipment and selected CCA’s SCR system.
In the CCA SCR Systems, ureaa nonhazardous reagent is metered into the exhaust gas stream just upstream of a catalyst. Once injected into the exhaust gas stream, the urea decomposes to ammonia which reacts with NOX compounds forming nitrogen, water vapor and carbon dioxide. The major system components are a reactor, a mixing duct, an injection control module and urea injectors.
At the heart of the CCA SCR system is an injection system with a single-fluid atomizer designed for optimum urea distribution. The standardized injector is self-cooling and is capable of operating with high turndown. One advantage of CCA’s injector design is that it is capable of providing a 50 to 60 micron droplet size distribution without an atomizing medium, such as steam or compressed air.
The injector ECU is programmed to control the urea injection rate as a function of engine parameters related to NOX emissions, such as load and exhaust gas temperature. It can also be operated as a closed-loop system based on a NOX output signal. Injector cycle frequency is factory set and the period of time that the injector remains open is controlled by modulating the signal to a solenoid actuated injector valve. These features help reduce system lifecycle costs.
The combined exhaust train flow rate for each of the four 2,100 kW diesel generators is approximately 25,694 ACFM at 625 F. The CCA system reduced NOX emissions from a baseline, full-load level of 8.4 g/bhp-h to a final level of 2.3 g/bhp-h, a total reduction of 73 percent. The engines had three separate criteria for CO compliance: parts per million, pounds per hour and g/bhp-h, which were not consistent. To meet all criteria, the owners decided to install diesel oxidation catalysts. Carbon moNOXide reductions of 60 percent to 85 percent using DOCs are accepted as generally applied control technology.
CCA worked with the owner’s contractor to reconfigure the SCR catalyst to allow installation of the DOC catalyst in the SCR reactor box. CCA’s DOC add-on to the SCR system demonstrated a 90+ percent CO reduction. Carbon moNOXide emissions were reduced from a full load baseline level of 500 ppm to a final level of less than 50 ppm.