Applications of REACH Technology to Meet PM and NOx Emissions Limits

Applications of REACH Technology to Meet PM and NOx Emissions Limits at Oil-Fired Boilers in Europe

Robert C. Carr, Coen Company, Inc.
Rodolfo De Santis, Electric Power Technologies, Inc.
SUMMARY:

Emissions regulations for fossil-fired steam boilers in the European Union have become more stringent in recent years. In this regard, lower limits of 50 mg/Nm3 for particulate matter (PM) emissions and 650 mg/Nm3 for NOx emissions have been promulgated for new and existing units. To comply with these emissions regulations, owners and operators of existing plants must choose between low-cost combustion upgrades and complex, expensive postcombustion control technologies. For combustion upgrades, simultaneous control of NOx and PM emissions is difficult because NOx reduction techniques tend to increase PM emissions.

This paper describes applications of Reduced Emissions and Advanced Combustion Hardware (REACH) to reduce PM and NOx emissions at several tangential- and wall-fired steam boilers in Europe that burn heavy oil. Application of REACH typically involves the custom design of retrofittable oil atomizers and flame stabilizers. Significant changes to air registers, burner auxiliary equipment, pumping and heating equipment, or combustion controls are not required.

Results of REACH retrofits described in previous symposia are reviewed here[8] as well as new data from a REACH retrofit at a 480 t/h steam boiler. Results show reductions in PM emissions of 46 to 90%, with measured PM emissions between 42 and 136 mg/Nm3. Simultaneous reductions in NOx emissions of 13 to 60 percent were documented, with measured NOx emissions between 450 and 670 mg/Nm3. The largest reductions in PM and NOx emissions were achieved at boilers equipped with steam atomization.

REACH TECHNOLOGY:

REACH can be easily retrofit to existing burners to solve a variety of problems related to poor combustion conditions, including, high stack opacity, high unburned carbon and NOx emissions, acidic stack fallout, flame impingement, poor boiler turndown, and high excess oxygen[1]. The main retrofit components are specially designed compound-curved-vane (CCV) flame stabilizers and oil atomizers that optimize combustion performance and reduce emissions[2]. Two versions of REACH are available. Combustion Performance REACH (CP-REACH) is designed to reduce PM emissions and opacity and to provide operational improvements including increased burner turndown, reduced excess air requirements, improved flame stability, and elimination of flame impingement on furnace walls. Low-NOx REACH (LN-REACH) is designed for retrofit projects where NOx reduction is the major goal. The key difference between CP-and LN-REACH is the design of the oil atomizer.

REACH oil atomizers are custom-designed to adapt to the existing oil supply equipment and operating conditions (i.e., pressure, temperature, and capacity)[2]. For steam-atomized systems, REACH uses internal-mix (I-Mix) atomizers, which produce superior spray quality compared to other common atomizer designs (The quality of the oil spray is characterized by Sauter Mean Diameter (SMD), which is defined as the diameter of a hypothetical droplet that has the same surface-to-volume ratio as that of the total spray. SMD is most often used to characterize oil sprays because it is relevant to evaporation and combustion of oil droplets.). For reducing NOx emissions in steam-atomized systems (LN-REACH), the V-jet atomizer (patented) is used- which divides the oil spray into distinct segments at the base of the flame. Simultaneous NOx and PM reduction is obtained with LN-REACH. For mechanically atomized burners, CP-REACH oil atomizers can be designed to operate at supply pressures from 14 to 90 barg. Special low-NOx mechanical atomizers that produce oil spray characteristics similar to the V-Jet atomizer are also available. Detailed descriptions of these technologies have been published elsewhere[3-7].

REACH components can be adapted to a wide range of burner and boiler designs to maximize applicability, while retaining as much of the original burner as possible. In the majority of retrofit applications, REACH flame stabilizers and oil atomizers replace existing stabilizers and atomizers, while other burner components including air registers, oil guns, flame detection equipment, ignitors, and control systems can be left intact. Capital costs, installation costs, and outage duration are kept low by this limited scope of modifications. Consequently, REACH offers substantial cost advantages relative to other retrofit options (e.g., complete burner replacement).

REACH is installed at more than 130 boilers with 21,000-MWe of equivalent generating capacity. Previous papers have described the application of REACH technology to a 550-MWe, opposed-wall fired boiler[3], to a group of 70 t/h industrial boilers[5], and several large (140 to 450 t/h) industrial boilers in Europe[8]. A review of results from the European installations and a recent REACH retrofit at a 480 t/h boiler are presented below.

REACH INSTALLATIONS IN EUROPE:

In response to environmental and economic pressures described in the introduction, a large European petrochemical company and an oil refiner retrofitted REACH to reduce PM and/or NOx emissions from several co-generation plants within large petrochemical and refinery complexes. Table 1 summarizes the REACH modifications at fourteen boilers. The retrofits primarily included modifications to flame stabilizers and oil atomizers. In a few cases, modifications were also made to burner throats to reduce air velocity, and new oil guns were supplied to replace aging and under-performing equipment. None of the boilers listed were equipped with flue gas recirculation (FGR) to the windbox, and only the tangential fired boilers had upper auxiliary-air nozzles which could be used for simulated overfire air (OFA).

Emissions results for all of the boilers except G1 were published previously[8]. The retrofit scope and results obtained for plant G1 installed at a petroleum refinery are described here. Unit G1 is a Breda 480 t/h SWF boiler with three elevations and three burners in each elevation. The boiler was retrofit with LN-REACH technology in 1999. The original burners were equipped with Y-jet type steam atomizers and bluff body diffusers. Baseline PM and NOx emissions at 480 t/h were approximately 250 mg/Nm3 and 1,500 mg/Nm3, respectively. For the LN-REACH retrofit, the bluff body diffusers and Y-jet atomizers were replaced with CCV flame stabilizers and V-jet atomizers, and a larger atomizing steam valve was installed. Further, new oil guns were installed and the burner throats were enlarged from 711 mm to 813 mm for reasons cited elsewhere[8]. No pressure-part modifications were required.

RESULTS:

Results reported previously[8] for the first 13 boilers retrofitted with REACH showed reductions in PM emissions of 46 to 90% with measured PM emissions between 42 and 136 mg/Nm3. Simultaneous reductions in NOx emissions of 13 to 60 percent were also documented, with measured NOx emissions between 450 and 670 mg/Nm3. Emissions results for boiler G1 retrofitted with REACH are presented in Table 2. At 480 t/h, NOx emissions were reduced to 636 mg/Nm3 (reduction of 58%). Simultaneously, PM emissions were reduced to 64 mg/Nm3 (reduction of 74%). Excess oxygen was 2.2%. The results were comparable to data reported previously for similar Breda units[8].

Table 2, PM and NOx Emissions with REACH Technology at 480 t/h

COST:

The scope of supply for the REACH project at Boiler G1 included engineering analysis of existing hardware and operating conditions; design and supply of atomizers, CCV swirlers, oil guns, and new atomizing steam valve with controller; and field technical service for installation, start-up, and acceptance testing. The total cost for this scope of work (excluding installation) was about $400 per t/h of steam capacity, or approximately $200,000 (US).

CONCLUSIONS:

The following conclusions can be drawn from the implementation of REACH technology in 14 industrial boilers, ranging in capacity from 140 to 530 t/h of steam generating capacity:


  • REACH provided reductions in PM emissions, ranging from 45 to 85%, with absolute values of PM emissions after the REACH installations, ranging from 130 mg/Nm3 with mechanical atomization to as low as 42 mg/Nm3 with steam atomization.
  • LN-REACH provided significant reductions in NOx emissions, ranging from 50 to 60%, with absolute values of NOx emissions from 450 to 670 mg/Nm3. In all cases, NOx reductions were accomplished with a simultaneous reduction in PM emissions.
  • The improved combustion performance provided by REACH enabled further NOx reduction through the use of OFA without increases in PM emissions or opacity.
  • The small scope of modifications required for REACH retrofits enabled these emissions reductions with a fraction of the outage time and cost of burner replacement.
REFERENCES:


1. Giovanni, D.V., M.W. McElroy, and S.E. Kerho, “REACH: A Low-cost Approach to Reducing Stack Emissions and Improving the Performance of Oil-fired Boilers,” EPRI/EPA Joint Symposium on Stationary Combustion NOx Control, Kansas City, Missouri (May 1995).

2. Kerho, S. E., and D. V. Giovanni, “Atomizer and Swirler Design for Reduced NOx and Particulate Emissions,” EPRI Workshop on NOx Controls for Utility Boilers, Boston, Massachusetts (July 1992).

3. Giovanni, D.V., R.C. Carr and S.E. Kerho, “Reduction in NOx Emissions by Retrofit of Low-NOx Atomizers on a 550 MW Oil-fired Boiler,” Third International Conference on Combustion Technologies for a Clean Environment, Portugal (July 1995).

4. Carr, R. C., Marco Alberti, and Christopher J. Nagel, “Retrofit of Gas Combustion Equipment and Low-NOx Oil Atomizers at a 550-MW Oil-Fired Utility Boiler,” International Joint Power Generation Conference, Houston, Texas (October 1996).

5. Conti, A.V., S.E. Kerho and J. Lucente, “Low Cost Retrofit Combustion Hardware for Emissions Control on Industrial Boilers,” ASME/EPRI International Joint Power Generation Conference & Exposition, Minneapolis, Minnesota, (October 1995).

6. Conti, A.V. and J. Lucente, “Reduction of NOx Emissions on Oil Firing at Bowline Point Unit No. 2,” ASME/EPRI International Joint Power Generation Conference & Exposition, Minneapolis, Minnesota (October 1995).

7. Giovanni, D.V. and R.C. Carr, “Applications of REACH Technology to Reduce NOx and Particulate Matter Emissions at Oil-Fired Boilers,” EPRI-DOE-EPA Combined Utility Air Pollutant Control Symposium, Washington, DC (August, 1997).

8. Mosso, R.J. and D. V. Giovanni, “Low-Cost Combustion Technologies to Control NOx and PM Emissions from Oil and Gas-Fired Boilers,” PowerGen Europe Symposium, Milan, Italy (June 1998).