Improvement of NOx formation model for pulverized coal combustion by increasing oxidation rate of HCN

Zhang, Juwei; Ito, Tetsuo; Okada, Takuya; Oono, Emi; Suda, Toshiyuku

doi:10.1016/j.fuel.2013.06.030

Cited by 29 publications

(9 citation statements)

References 32 publications

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“…To describe the formation mechanism of fuel NO x , user-defined functions (UDFs) are applied to substitute the default models in the Fluent software. Zhang et al 40 and Zha et al 20 summarized that when the preexponential factor of HCN oxidation reaction formula was increased 13 times (A N1 in Equation 7 as 1.3 × 10 11 s −1 increased from 1.0 × 10 10 s −1 ) based on De Soete's global scheme, the predicted NO x distributions were consistent with experimental results. In addition, the NO x was reduced to N 2 by heterogeneous reaction on the char surface, which was calculated by the research of Levy et al 41 The NO x model was verified in our previous studies.…”

Section: Methodssupporting

confidence: 59%

Numerical study on combustion characteristics and heat flux distributions of 660‐MW ultra‐supercritical double‐reheat tower‐type boiler

Deng

Zhang

et al. 2021

Asia-Pacific J Chem Eng

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Ultra‐supercritical double‐reheat technology, as one of the most advanced coal‐fired power generation technology, is an important direction for emission reduction and energy saving in the world. In this study, the numerical calculation was executed in a 660‐MW ultra‐supercritical double‐reheat tower‐type boiler under deep‐air‐staging conditions. The refined HCN oxidation model was adopted to substitute the default model implemented by the user‐defined functions to calculate the NOx emission. The influences of the boiler load, over‐fire air (OFA) ratio, and excess air coefficient on temperature, species, and heat flux distributions were investigated. Results show that the decrement of the boiler load from boiler maximum continuous rating to 50% turbine heat acceptance gives rise to an increase of NOx emission. The heat flux distributions along with the furnace width direction present bell shaped. When the OFA ratio rises from 17% to 43%, NOx emission descends from 357.7 to 179.3 mg m−3 at the furnace outlet, and the heat flux distributions become more uniform along with the furnace width direction with lower peaks. Temperatures, species, and heat flux distributions are similar under the three different excess air coefficients. The NOx emission is the lowest when the excess air coefficient is 1.15. The results could provide a reference for combustion characteristics optimization and hydrodynamic calculation of ultra‐supercritical double‐reheat tower‐type boiler.

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Section: Methodssupporting

confidence: 59%

Numerical study on combustion characteristics and heat flux distributions of 660‐MW ultra‐supercritical double‐reheat tower‐type boiler

Deng

Zhang

et al. 2021

Asia-Pacific J Chem Eng

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“…Within the NO X postprocessing scheme, the key influencing parameters in the NO X models include the fraction of N released along with VM ( δ ), fraction of HCN converted from VM ‐N ( η ) and the available pore surface area of char in the NO X reduction model. Based on the previous works, 32–35 δ is set to 0.2 and 0.785 and η is set to 0.9 and 0.33 for coal and biomass in this work, respectively. The Brunauer–Emmett–Teller (BET) theory is a commonly used way to identify the specific surface area for porous particles.…”

Section: Numerical Modeling Detailsmentioning

confidence: 99%

Effect of biomass co‐firing position on combustion and NO_X emission in a 300‐MWe coal‐fired tangential boiler

DONGFENG

et al. 2021

Asia-Pacific J Chem Eng

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Co‐firing biomass in an existing coal combustion boiler is a promising way to mitigate carbon emission in the context of global carbon neutrality. This paper investigated the effect of biomass injection location on combustion and NOX formation characteristics in a 300‐MWe tangential boiler co‐firing with coal. Numerical models have been validated against experimental measurement for both pure coal firing and biomass/coal co‐firing cases. Compared to pure coal firing, co‐firing case with biomass injected into the highest layer can sustain a comparable temperature distribution profile along the furnace height, and generate a lower NO emission by around 20 ppm. By moving the biomass injection location downward, the temperature difference between co‐firing and pure coal firing cases becomes larger, and the final NO emission increases continually from 222 to 240 ppm. When biomass is injected through the lowest layer, N element in biomass volatile is oxidized to NO directly because of the abundant oxygen; thus, NO emission turns to be the highest among all co‐firing cases. Contrarily, when biomass is injected through the highest layer, the majority of N in biomass volatile is released as NH3, and it further acts as a reduction agent for NO, thus leading to the lowest NO emission.

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“…In order to understand NO chemistry and minimize NO emissions, the mechanisms of NO formation and reduction in coal combustion have to be taken into consideration, as shown in Figure . More detailed information on nitrogen chemistry in combustion can be found in the literature. − In coal combustion, fuel NO x has been acknowledged as the main NO x source. , According to the major fuel-N conversion reactions, , the N-intermediates HCN and NH 3 are subsequently converted into NHi radicals, which can either be oxidized to NO under oxygen-rich atmosphere or can serve as reducing agents themselves to reduce the generated NO to N 2 in a reducing atmosphere. Therefore, NHi radicals are the driving force in NO x reduction, and reactions within the NHi pool could lead to the formation of N 2 under fuel-rich conditions .…”

Section: Introductionmentioning

confidence: 99%

“…19−22 In coal combustion, fuel NO x has been acknowledged as the main NO x source. 23,24 According to the major fuel-N conversion reactions, 20,21 the N-intermediates HCN and NH 3 are subsequently converted into NHi radicals, which can either be oxidized to NO under oxygen-rich atmosphere or can serve as reducing agents themselves to reduce the generated NO to N 2 in a reducing atmosphere. Therefore, NHi radicals are the driving force in NO x reduction, and reactions within the NHi pool could lead to the formation of N 2 under fuel-rich conditions.…”

Section: Introductionmentioning

confidence: 99%

Effect of Stoichiometry and Temperature on NO_x Reduction by Reagent Injection in the Fuel-Rich Zone of Pulverized Coal Combustion

Zhang

Dong

et al. 2018

Energy Fuels

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In this paper, the characteristics of NO x reduction by reagent injection into the fuel-rich zone (RIFR) in coal combustion were investigated, under high temperatures and reducing atmosphere conditions. The stoichiometry and temperature have a major influence on the chemistry of NO and NH3 reagent (ammonia or urea). Therefore, experiments were conducted on a bench-scale test system with urea solution as the reagent to investigate the key factors influencing NO x reduction, including primary stoichiometric ratio (SR1), temperature in the reaction zone, and normalized stoichiometric ratio (NSR) of the injected reagent. The results indicated that the primary stoichiometric ratio SR1 was the key parameter affecting the reduction of NO x emissions. Better NO x reduction was achieved with a decrease in the SR1 for bare air staging. However, there was no benefit for NO x reduction by reagent injection in the very fuel-rich zone (SR1 ≤ 0.75), which depended on the distribution of N-intermediates and initial NO concentration. On the other hand, a negative NO x reduction was obtained by reagent injection when SR1 ≥ 0.95 because the added reagent was oxidized to form NO. The optimum SR1 for RIFR was found to be 0.85 in this study. A higher SR1 greatly improved the NO x reduction by RIFR only when SR1 was less than 1, and high temperatures (1473–1673 K) were required for the generation of more OH free-radicals in the fuel-rich zone, which promoted NO x reduction by NH3 in the absence of oxygen. Therefore, RIFR is different from the traditional selective non-catalytic reduction technology, which has a strong temperature dependency from 1100–1300 K. The NO x reduction efficiency was increased by 21.4% with RIFR compared to the bare air-staged method, under the optimum conditions of SR1 = 0.85, T = 1673 K, and NSR = 2. More urea solution led to greater NO x formation in the burnout zone but with no ammonia slip. This method can be applied as a new alternative technology to further reduce NO x in combination with the existing low NO x combustion technologies.

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Improvement of NOx formation model for pulverized coal combustion by increasing oxidation rate of HCN

Cited by 29 publications

References 32 publications

Numerical study on combustion characteristics and heat flux distributions of 660‐MW ultra‐supercritical double‐reheat tower‐type boiler

Numerical study on combustion characteristics and heat flux distributions of 660‐MW ultra‐supercritical double‐reheat tower‐type boiler

Effect of biomass co‐firing position on combustion and NO_X emission in a 300‐MWe coal‐fired tangential boiler

Effect of Stoichiometry and Temperature on NO_x Reduction by Reagent Injection in the Fuel-Rich Zone of Pulverized Coal Combustion

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Improvement of NOx formation model for pulverized coal combustion by increasing oxidation rate of HCN

Cited by 29 publications

References 32 publications

Numerical study on combustion characteristics and heat flux distributions of 660‐MW ultra‐supercritical double‐reheat tower‐type boiler

Numerical study on combustion characteristics and heat flux distributions of 660‐MW ultra‐supercritical double‐reheat tower‐type boiler

Effect of biomass co‐firing position on combustion and NOX emission in a 300‐MWe coal‐fired tangential boiler

Effect of Stoichiometry and Temperature on NOx Reduction by Reagent Injection in the Fuel-Rich Zone of Pulverized Coal Combustion

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Effect of biomass co‐firing position on combustion and NO_X emission in a 300‐MWe coal‐fired tangential boiler

Effect of Stoichiometry and Temperature on NO_x Reduction by Reagent Injection in the Fuel-Rich Zone of Pulverized Coal Combustion