CFD Modeling of NOx Reduction Technologies in Utility Boilers

2000 ◽  
Author(s):  
Marc A. Cremer ◽  
Bradley R. Adams ◽  
David H. Wang ◽  
Michael P. Heap
Keyword(s):  
Nox Reduction ◽  
Electric Utility ◽  
Cfd Modeling ◽  
Nox Formation ◽  
Modeling Tools ◽  
Chemical Mechanisms ◽  
Utility Boilers ◽  
Clean Air ◽  
Nox Control ◽  
Selective Noncatalytic Reduction

Abstract This paper discusses the development and application of CFD modeling tools that have been utilized to assess and design NOx reduction systems that are currently being evaluated by the electric utility industry. Stringent limits on NOx emissions have been imposed by the Clean Air Act Amendments, and a number of NOx reduction technologies are available to help meet these limits including selective noncatalytic reduction (SNCR) and reburning, as well as various combinations of these. This paper discusses the development and implementation of global and reduced chemical mechanisms for NOx formation/destruction into a comprehensive CFD code so that these various options for NOx control can be evaluated. Also, some examples showing the application of these tools to full-scale utility boilers utilizing low-NOx burners, air staging, and SNCR are presented.

NOx Emissions in a Steel Reheat Furnace Firing By-Product Fuels

2001 ◽  
Author(s):  
Bradley R. Adams ◽  
Dave H. Wang
Keyword(s):  
Low Cost ◽  
Nox Reduction ◽  
Coke Oven ◽  
Cfd Modeling ◽  
Stoichiometric Ratio ◽  
Nox Emissions ◽  
Confined Space ◽  
Nox Formation ◽  
Reheat Furnace ◽  
Bottom Zone

Abstract A DOE-funded program was used to understand the mechanisms that control the formation of NOx during the combustion of steelmaking by-product fuels and to investigate possible low-cost control options to minimize the NOx emissions. This paper discusses the CFD modeling results of NOx emissions in a reheat furnace. The reheat furnace has a total of 20 burners distributed over three firing zones. The furnace is fired at a rate of 250 × 106 Btu/hr and an overall stoichiometric ratio of 1.06 (fuel lean). Fuels with heating values of approximate 500 Btu/SCF were examined, including coke oven gas (COG), blast furnace gas (BFG) and a blend of COG, BFG, natural gas (NG) and nitrogen. A good range of process variables was modeled to examine effects of fuel type, air preheat, stoichiometric ratio, firing rate and burner stoichiometry distribution on NOx emissions. Modeling results indicated that NOx formation in the reheat furnace is dominated by thermal NO, with some variation depending on the fuel fired. Temperature profiles showed an effective separation of the furnace interior into top and bottom zones as a result of the steel slab barrier. Higher temperatures characterized the bottom zone and elevated NOx levels as a result of the confined space and enhanced fuel air mixing provided by the slab supports. Results also showed that reburning of NOx plays a significant role in final NOx emissions with 30–40% of NOx formed being reduced by reburning in most cases. Modeling identified that operating the side burners in each burner zone slightly substoichiometric (while maintaining the overall furnace stoichiometry at 1.06) provided significant NOx reduction via reburning. NOx reductions of 23% and 30% were predicted when firing with COG and COG-NG-Air fuels, respectively. Overall furnace exit temperatures and heat flux profiles were not significantly affected by the biased firing.

Use of CFD Modeling for Design of NOx Reduction Systems in Utility Boilers

2002 ◽  
Author(s):  
Bradley Adams ◽  
Marc Cremer ◽  
James Valentine ◽  
Venkata Bhamidipati ◽  
David O’Connor ◽  
...  
Keyword(s):  
Nox Reduction ◽  
Field Testing ◽  
Nox Emission ◽  
Injection System ◽  
Cfd Modeling ◽  
Unburned Carbon ◽  
Port Placement ◽  
Utility Boilers ◽  
Ammonia Slip ◽  
Combustion Optimization

CFD modeling has found increasing use in the design and evaluation of utility boiler retrofits, combustion optimization and NOx reduction technologies. This paper reviews two recent examples of CFD modeling used in the design and evaluation of NOx reduction technologies. The first example involves the staging of furnace combustion through use of overfire air (OFA) to reduce NOx emission in a B&W opposed-wall fired pc furnace. Furnace simulations identified locations of highest flue gas mass flows and highest CO concentrations and were used to identify OFA port placement for maximum NOx reduction with lowest increases in unburned carbon in fly ash and CO emission. Simulations predicted a 34% reduction in NOx emission with OFA. The second example summarizes the design and application of RRI with OFA and SNCR in a 138 MW cyclone-fired boiler. Simulations were used to design an aminebased injection system for the staged lower furnace and to evaluate NOx reduction and ammonia slip of the RRI system. Field-testing confirmed modeling predictions and demonstrated that the RRI system alone could achieve 25–30% NOx reduction beyond OFA levels with less than 1 ppm ammonia slip and that RRI in combination with SNCR could achieve 50–55% NOx reduction with less than 5 ppm slip.

NOx Control for Stationary Sources and Utility Applications

2003 ◽  
Author(s):  
Thomas F. McGowan
Keyword(s):  
Gas Turbines ◽  
Cost Effective ◽  
Nox Formation ◽  
Industrial Plants ◽  
Clean Air ◽  
Corporate Goals ◽  
Ozone Transport ◽  
Electric Generation ◽  
Nox Control ◽  
Stationary Sources

NOx control is coming to electric generation utilities and industrial plants in a big way. Federal regulations, ozone non-attainment areas, ozone “transport regions,” acid rain provisions of the Clean Air Act, and corporate goals for emission reductions are all motivators. This paper explores regulations, the chemistry of NOx formation, and practical and cost-effective ways to reduce NOx at its source, as well as “end-of-pipe” methods for the major targets: coal fired boilers, gas and oil boilers, and gas turbines.

Low-Cost NOx Reduction Retrofit for Pump Scavenged Compressor Engines

1995 ◽  
Vol 117 (4) ◽  
pp. 804-809 ◽  
Author(s):  
E. N. Balles ◽  
R. C. Peoples
Keyword(s):  
Low Cost ◽  
Nox Reduction ◽  
Nox Emission ◽  
Emission Rates ◽  
Natural Gas Pipeline ◽  
Initial Work ◽  
Clean Air ◽  
Nox Control ◽  
Performance Results ◽  
Implementation Plans

The Clean Air Act Amendments of 1990 and the resulting individual State Implementation Plans will require many natural gas pipeline operators to install NOx reduction equipment on existing compressor station engines. A program was undertaken to develop lower cost NOx control options for these engines as compared to traditional techniques. The initial work, described in this paper, focused on the development of a low-cost retrofit package for Cooper-Bessemer GMV and GMV-TF pump scavenged integral compressor engines. The retrofit concept relied on highly dilute combustion to achieve low engine-out NOx emission rates. A significant portion of the effort concentrated on low-cost methods for delivering the required air charge and ignition enhancements to achieve reliable and robust combustion. The prototype retrofit kit has been installed on a GMV-6 in gas compressor service. Performance results showed a 70 percent reduction in NOx emission rates without a corresponding increase in HC emission rates.

A CFD Model Based Evaluation of Cost Effective NOx Reduction Strategies in a Roof-Fired Unit

2003 ◽  
Author(s):  
James Valentine ◽  
Marc Cremer ◽  
Kevin Davis ◽  
J. J. Letcavits ◽  
Scott Vierstra
Keyword(s):  
Fly Ash ◽  
Nox Reduction ◽  
Water Injection ◽  
Cost Effective ◽  
Cfd Modeling ◽  
Unburned Carbon ◽  
Cfd Model ◽  
Reduction Strategies ◽  
Nox Control ◽  
The Impact

To meet aggressive NOx reduction requirements, a range of NOx reduction strategies are currently available for application to pulverized coal fired furnaces. Utilities must assess the benefits and drawbacks of each viable NOx control technology to develop the best strategy for unit specific NOx control that fits within the utilities’ overall compliance plan. The installation of high capital and operating cost NOx reduction technologies, such as selective catalytic reduction, is cost prohibitive on many units. Lower cost technologies, although not capable of SCR level NOx reductions, can provide a more cost-effective approach and still achieve compliance over the fleet. This paper describes how computational fluid dynamic (CFD) modeling has been utilized by an experienced group of combustion engineers to evaluate and design cost effective NOx reduction strategies applied to a relatively unique PC fired unit, a B&W 150 MW roof-fired furnace. The unit fires bituminous coal through 10 multi-tip burners and is equipped with 10 NOx ports located below the burners. A baseline CFD model was first constructed and the predicted model results were compared with available data including NOx and CO emissions, as well as unburned carbon in fly ash. Upon completion of the baseline model, combustion alterations, including deeper staging, were evaluated. Specific burner adjustments were evaluated to allow for the deeper staging without significantly increasing unburned carbon in the fly ash, CO emissions, or near burner slagging. The CFD model was also utilized to evaluate the impact of water injection. AEP has previously utilized water injection to reduce peak combustion temperatures and thermal NOx formation rates in coal fired units for incremental NOx reductions. It is crucial that the NOx production zones in the downstream portion combustion field be identified, since these regions are most likely to produce NOx that will not be subsequently reduced prior to exiting the furnace. The CFD model was utilized to identify the most appropriate regions for water injection combined with the other combustion alterations. The results showed that NOx emissions could be reduced in this unit by approximately 37% from baseline full load emissions with no associated increase in unburned carbon in the fly ash or furnace exit CO. Burner alterations and water injection equipment based on the CFD model evaluation are currently being installed. Comparisons between the model predictions and the post retrofit performance will be provided.

Utilization of the MK Combustion Optimization System™ to Maximize Combustion Efficiency in an Environment-First Fashion

2004 ◽  
Author(s):  
David Krzysik
Keyword(s):  
Fine Particles ◽  
Effective Means ◽  
Nox Reduction ◽  
Cost Effective ◽  
Combustion Efficiency ◽  
Contributing Factors ◽  
Nox Formation ◽  
Trade Offs ◽  
Clean Air ◽  
Combustion Optimization

Nitrogen oxide (NOx) emissions discharged into the atmosphere from fossil fuel combustion prove to have adverse effects on the environment and human health. Contributing factors include the formation of acid rain, ozone, degradation of visibility, and inhalable fine particles. In addressing these problems, environmental regulations are becoming more stringent on electric utilities. Low NOx burner (LNB) technology was developed to provide a cost-effective means of complying with the NOx Reduction Program under Title IV of the Clean Air Act Amendments (CAAA) of 1990. Prior to LNB technology, standard burners were designed to rapidly mix the fuel and oxidant, producing high combustion efficiency and large quantities of NOx. Limiting the reaction rate at which the air and fuel mix, particularly during the early stages of combustion, can effectively control NOx formation; however, this rate limitation tends to diminish combustion efficiency and proves to be the compromise of LNB technology. Controlling one aspect or the other can be intuitively easy, but controlling both is challenging and trade-offs are necessary. Identifying a happy medium between the standards of yesterday and today is necessary in the optimization of coal-fired combustion. The ultimate effect will improve commercial availability in an environment-first fashion.

Equilibrium Chemistry Calculations for Assessment of NOx Abatement Strategies in IC Engines

2011 ◽  
Author(s):  
S. M. Aithal
Keyword(s):  
Natural Gas ◽  
Temporal Variation ◽  
Nox Reduction ◽  
Air Separation ◽  
Working Fluid ◽  
Nitrogen Enrichment ◽  
Nox Formation ◽  
Modeling Tools ◽  
Natural Gas Engines ◽  
Crank Angle

Nitrogen Enriched Air (NEA) has shown great potential in NOx reduction without the drawbacks of exhaust gas recirculation (EGR). Use of NEA in stationary natural gas engines has shown up to 70% NOx reduction with a modest 2% nitrogen enrichment. However, nitrogen enrichment beyond a point leads to degradation in engine performance in terms of power density, brake thermal efficiency and unburned hydrocarbons. Optimizing the nitrogen enrichment levels to reduce NOx without performance degradation of the engine would greatly benefit the advancement of the air separation membrane technology. Development of fast and robust modeling tools to compute the temporal variation of the incylinder engine pressure, temperature and NOx formation can aid experimental efforts in determining the optimum enrichment levels for a given engine operating condition. This work presents a methodology to compute engine-out NOx for engines with and without nitrogen enrichment. Temporal variation of in-cylinder engine pressure and temperature can be obtained by a solution of the energy equation. Using these temperature and pressure values, along with the instantaneous composition of the working fluid, one can evaluate the equilibrium concentration of the combustion products. Since the NOx formation freezes a few crank angle degrees after the completion of combustion, it is instructive to examine whether the equilibrium computation can provide a reasonable estimate of engine-out NOx. To this end, engine-out NOx computed by using the above-mentioned procedure was obtained as a function of equivalence ratio for cases with nitrogen enrichment of 2% and no nitrogen enrichment. The results showed that the equilibrium NOx concentrations a few crank angle degrees after end of combustion were close to those reported experimentally in stationary natural gas engines. These results suggest that it would be possible to use equilibrium chemistry computations to evaluate various NOx mitigation strategies.

Application of Reburning for NOx Control to a Firetube Package Boiler

1985 ◽  
Vol 107 (3) ◽  
pp. 739-743 ◽  
Author(s):  
J. A. Mulholland ◽  
W. S. Lanier
Keyword(s):  
Natural Gas ◽  
Reaction Order ◽  
Nox Reduction ◽  
Process Variable ◽  
Nox Emission ◽  
Boiler Load ◽  
Second Stage ◽  
Primary Zone ◽  
Dominant Process ◽  
Nox Control

A 730 kW (2.5 × 106 Btu/hr) firetube package boiler was used to demonstrate the application of reburning for NOx emission control. An overall reduction of 50 percent from an uncontrolled NOx emission of 200 ppm was realized by diverting 15 percent of the total boiler load to a natural-gas-fired second stage burner. Tests indicate that the overall reaction order of destruction with respect to initial NOx is greater than one; thus, larger reductions can be expected from reburning applications to systems with higher initial NOx. Rich zone stoichiometry has been identified as the dominant process variable. Primary zone stoichiometry and rich zone residence time are parameters that can be adjusted to maximize NOx reduction. Reburning applied to firetube package boilers requires minimal facility modification. Natural gas would appear to be an ideal reburning fuel as nitrogen in the reburning fuel has been shown to inhibit NOx reduction.

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