Several fossil-fueled power plants are meeting tough new restrictions on NOx emissions without the cost and operational concerns of a Selective Catalytic Reduction (SCR) technology. Case in point, the gas fired Hunters Point Unit #4 in San Francisco, CA. The efforts at Hunters Point reflect RJM¡¦s layered approach to NOx reduction, which enables fossil-fueled power plants to achieve 30% and 90% NOx reduction in baseline emissions. Environmental regulations on large power boilers are becoming stricter across North America. Conforming to legislation inevitably involves capital outlay and conflicts with the current need in the power industry to reduce costs and be competitive. Installing and operating technology to reduce NOx emissions can cost a utility millions of dollars, which has caused many utilities to look for innovative solutions for cost-effective NOx control. A layered approach to NOx reduction is one such cost-effective approach that can achieve up to a 90% NOx removal at a fraction of the cost of an SCR. Additionally, with no catalyst management program to deal with, the approach offers the power producer a unique balance between capital & operating costs, efficiency and NOx reduction. Clean Enough for California - Power Plant Achieves NOx Emission Levels of 26 ppm without an SCR Recently, Pacific Gas & Electric¡¦s Hunters Point Unit #4 in San Francisco, CA, a 170 MW CE boiler achieved NOx emission levels of 26 ppm without an SCR. With BAAQMD¡¦s ratcheting regulations of 95 ppm in 1999, 87 ppm in 2000, 47 ppm in 2002 and 31 ppm in 2004, PG&E had no choice but to choose a very aggressive NOx reduction strategy. SCR¡¦s emerged as the foremost technology to achieve such reductions but were deemed to be extremely expensive. The cost per ton of NOx reduced using an SCR for this unit was estimated at greater than $3,000. This encouraged PG&E Hunter¡¦s Point to investigate alternative NOx reduction technologies that were efficient, cost effective and met the following objectives:

1. Reduce NOX emissions by 65%+ with more efficient technologies than SCRs
2. Maintain low CO emissions.
3. Balance the average airflow between burners to within ¡Ó5% of the unit mean.
4. Improve flame stability.

The unit, a front wall fired natural circulation boiler that operates at 1,135,000 lb/hr. The burners on the unit included 15 Peabody H-26 Gas Ring Registers. The firing arrangement was front-fired 5 wide x 3 high with a furnace plan that is 44¡¦ wide x 25¡¦ deep. The combustion air temperature is 530o F. The baseline NOx was 130 ppm after being modified in the late 1960¡¦s for lower NOx emissions. After evaluating the problem, RJM Corporation recommended:

1. Very stable low NOx burner modifications,
2. Flue Gas Recirculation (FGR), and
3. RJM¡¦s patented NOx Tempering System (NT3TM).

All these technologies are part of RJM¡¦s layered approach (RJM-LT„§) to NOx reduction. The air to each burner was balanced using RJM¡¦s Air Distribution Analysis (ADA) method to + 5%, the fuel to each burner was balanced to + 5%. NOx Reduction Strategy
Low NOX Flame Stabilizer & Gas Pokers - The RJM low NOX flame stabilizer is an air-staged, vane cascade device optimized for performance on the existing burners. Installing the low NOX flame stabilizer at Hunter¡¦s Point produced a stable flame front that created a cyclonic vortex that aerodynamically stabilized the flame front in a fixed position. The flame stabilizer provided absolute control of flame stabilizing dynamics. Undesirable over-swirl at the burner throat was avoided. The flame stabilizer is a vane cascade device fabricated with high temperature resistant materials. The stabilizer slides over the jacket tube and is clamped in place with locking screws. A new gas header with gas pokers was utilized for each burner. Gas pokers branched off a center gas header to a position around the flame stabilizer.

By using all the five layers, a power plant can achieve up to 90% NOx reduction, eliminating the need for an SCR. As seen in this chart, Hunters Point Unit # 4, achieved a 68% reduction by using only 2 layers of the RJM-LT system NOx or Combustion Tempering - The patented NOx tempering system targets cooling media towards the NOX production zone to limit its formation. Injection nozzles are mounted around the flame stabilizer. Water supplied to the burner front is atomized and targeted by the nozzles. The water is atomized into distinct streams of micronized water. The latent heat of evaporation absorbed by the combustion gas in these zones limits the amount of NOX formed. Targeting the streams using computer modeling reduced the amount of water used at the unit. RJM designed the combustion tempering spray system into the upgraded burner and supplied flex hoses for each burner. PG&E supplied water to each burner.. CFD Modeling Helps Reduce NOx Combustion modeling was used to determine the baseline burner NOx and CO emissions and to design the burner modifications. The final burner design, including the flame stabilizer and gas poker was modeled to ensure that complete burnout of the gas fuel is accomplished with low CO and NOX emissions. The difference between the baseline and modified burner emissions determined the percent NOx reduction from the burner modifications. Computer modeling was also utilized to determine the optimum gas poker shoe exit angle and the optimal split ratio between rich and lean gas pokers. Final Results at Hunters Point Challenge the Cost-Effectiveness of Expensive Alternative Controls Such as an SCR Final performance testing indicated that the unit NOx at all loads was reduced to 26 ppm, a 68% reduction from an already low NOx baseline. CO was held to below 20 ppm. The modifications worked in concert with the FGR system modifications designed by Stone & Webster that increased FGR up to 30% through the windbox and some through the hopper. The startup was quick and easy, almost no tuning was required to achieve 26 ppm. While SCRs may get a power plant the reduction it anticipates, maintaining this high-efficiency may not always be practical from a cost perspective. At a higher efficiency level, the catalyst requirements increase several times resulting in enormous SCR capital & operating costs. Industry estimates indicate that SCR can cost up to 10-15 times more than other available combustion control technologies depending on extent of NOx reduction required. The reduction achieved through innovative and cost-effective NOx reduction technologies enabled PG&E to save the cost of an SCR. The plant achieved close to SCR level reductions at a fraction of SCR costs.