Scr-Equipped Diesel Gen-Sets Beat Carb Claim On Nox - Brief Article

Diesel generator sets for backup power generation can achieve far lower emissions of nitrogen oxides (NOx) and "toxic" particulate matter (PM) than California Air Resources Board (CARB) estimated in a recent letter to local air pollution district officials.
Example: Installing a 90% efficiency urea-selective catalytic reduction (SCR) system on today's 5.5 grams/brake-horsepower hour NOx (engine-out) diesel gen-sets can cut NOx to just 0.55 g/bhp-hr -- or, in CARB's electric generation comparison terms, 1.6 pounds of NOx per megawatt-hour.
This isn't theoretical. Today, Clean Diesel Technologies Inc. (CDTI) is one of several companies actively marketing SCR (for NOx reduction) and it also markets a particle trap fuel additive system (for particulate matter control) for diesel gen-sets (and other applications). Current diesel gen-sets in Washington/Oregon could likewise be suitable for California with appropriate exhaust controls.
No special fuel required: CDTI's combination SCR/PM trap system technologies can achieve ultra-low emissions with today's ordinary CARB diesel fuel, rather than the ultra low-sulfur diesel (ULSD) required for certain highly catalyzed filter systems, CDTI chief operating officer Jim Valentine points out.
CDTI calculates diesel gen-set ability to hit 0.55 g/bhp-hr NOx based on recent tests with an SCR catalyst designed for 80% NOx reduction.
The company hit 0.68 g/bhp-hr NOx with the 80% SCR catalyst in 13-mode steady state tests at Southwest Research Institute. Running a 90% SCR catalyst thus yields 0.55 g/bhp-hr with a 5.5 grams NOx engine, Valentine explains.
* Beats 7-lbs. NOx Claim
By contrast, CARB claimed in a Feb. 21, 2001, letter to all of California's local air pollution control officers that "diesel engine with best available control" could only limit NOx to 7 lbs./MW-hr.
Yet the SCR technology clearly slashes that level dramatically, to NOx emissions levels well below CARB's estimate for "uncontrolled gas-fired power plant" (2 to 4 lbs./MW-hr) and even fairly competitive with what CARB terms the "typical mix of existing gas-fired California power plants" (0.5 lbs./MW-hr NOx).
What's more, new data shows that CARB's letter greatly underestimates the ability of diesel PM filters to achieve dramatic reductions in "toxic" PM, to the same 0.03 lbs./MW hr level CARB cites for "gas-fired power generation."
CARB's letter claimed that "existing diesel engine with trap retrofit" produces 0.1 to 0.5 lbs./MW-hr PM, equivalent to 0.034 to 0.17 b/bhp-hr.
Yet CDTI has found that engines tested with its trap-additive system achieve ultra-low 0.01 to 0.015 g/bhp-hr PM levels, equivalent to 0.03-0.045 lbs./MW-hr - matching what CARB shows for gas-fired electric power PM emissions.
Given these new data on ultra-clean emissions levels achievable for SCR/PM trap equipped diesel gen-sets, CARB's diesel gen-set "cancer risk" warnings and claims that diesels will produce some vastly greater amount of ozone-forming emissions, compared to gas-fired power, look dubious.
These alarmist claims unfortunately have been repeated by "green" groups in California newspaper stories about the state's power crisis.
* 'Cancer' Threat?
"Operation of an uncontrolled one-MW diesel engine for 250 hours per year would in crease cancer risk to nearby residents (within one city block) by 250 in a million," CARB's letter to air districts says, apparently failing to mention that PM trap-equipped diesels would virtually eliminate the PM "toxic" risk.
"On average this represents a 50% in crease in the cancer risk due to exposure to diesel exhaust," the CARB letter alarmingly concludes.
Meantime, CDTI is among a group of well-known technology companies applying to CARB for retrofit certification for a PM filter system for many diesel applications.
CDTI has produced test data showing it can hit the 0.01 g/bhp-hr PM limit CARB asks for -- and now, like many other technology developers, it's awaiting CARB's final decision on retrofit durability requirements.
CDTI's SCR system hasn't been certified with CARB, but it passed an earlier NESCAUM retrofit evaluation. It's now pending before an internal EPA diesel fuel/additives retrofit verification group, along with diesel water emulsions and other fuel technologies.
(Note: This internal EPA group review just took over from the outside "Environmental Technology Verification" panel that continues to develop emissions retrofit verifications for catalyst/trap devices (see Diesel Fuel News 11/13/2000, p1).
Meantime, over 100 diesel engines are either using or have ordered CDTI's urea-SCR system, Valentine said.
"There are several PM filter systems operating on large engines in California, and so we hope to combine the SCR and our fuel-borne catalyst/diesel particle filter technology soon to provide very low emissions diesels to the California market," Valentine said.
"CDTI is planning to team with Clean Air Systems of New Mexico to offer this additive/filter combination in conjunction with our urea-SCR licensee, RJM."