Low Nitrogen Combustion Research Articles

High-temperature corrosion behavior of TP91, C22 alloy and C22 based on laser coatings in simulated reducing corrosion environment

To explore corrosion characteristics of TP91, C22 alloy and C22 laser coatings in reducing environment caused by low-nitrogen combustion at 500 °C–600 °C, a synthetic corrosive medium containing 0.2 vol% H2S-0.1 vol% O2–N2 were selected. Results showed that the order of corrosion resistance is: C22 laser coatings>C22 alloy>TP91. 550 °C was the limit corrosion temperature for C22 alloy and C22 laser coatings. The reason for the strong corrosion resistance of C22 alloy and C22 laser coatings is that a dense layer of Cr-rich corrosion products due to the is produced in the inner layer, thus protecting the matrix from direct corrosion by corrosive gas. Finer grains before corrosion tests and the formation of dense Cr2O3 inner layers in much speedier process were the main reasons for the best corrosion resistance of C22 laser coatings.

Theoretical and experimental investigation on the effect of CO on N migration and conversion during air-staged coal combustion

Air-staging combustion is the widely-used low-nitrogen combustion technology. In this process of NOx reduction, the role played by CO resulted from the air-staged combustion cannot be ignored. In this study, quantum chemistry method is used to investigate the effects of the CO on the NOx generation/reduction and on the char surface. Theoretical calculations indicate that CO is involved in nitrogen fixation during the migration and transformation of N. During the oxidation of N-containing char, CO increases the binding energy of N of pyridine with adjacent C atoms, which is not conducive to the N precipitation. During reduction of NOx by char, CO decreases the desorption energy barrier of N2 and promotes NO heterogeneous reduction. On the other hand, CO promotes the re-embedding of N in generated NO into the char to form char-N. XPS experiments are carried out for the coal char samples after the air-staged combustion. The experimental results show that high CO concentration is conducive to retention N. When the excess air coefficient (α) is 0.8, the increase of N-6 content is 7.2% larger than that of α = 0.9. This work discovers the nitrogen fixation of CO, enriches and expands the understanding of the role of CO.

Thermal deviation analysis of high-temperature reheater for single-tangential π type boiler

• The thermal deviation adjusting experiments of a 660 MW ultra-supercritical boiler were carried out. • The grid distribution of radiation intensity for particles at the high-temperature reheater area was measured by radiation spectroscopy. • Thermal deviation analysis of high-temperature reheater were presented. • A new type principle of reforming combustion system was proposed. For some π type boilers with four-corner tangential and deep air staged low nitrogen combustion technology, under full load condition, the steam temperature deviation for both sides of reheater outlet can reach as high as 15 °C. The left and right cross arrangement of steam between two stage reheaters increases the steam temperature deviation at the outlet, and the large amount input of desuperheating water makes the economic efficiency of the unit decrease. The thermal deviation adjusting experiments of a 660 MW ultra-supercritical boiler were carried out by adjusting the level and up-and-down swing angle of the separated over-fire air nozzle, and the grid distribution of radiation intensity for particles at the high-temperature reheater area was measured by radiation spectroscopy. The results show that there exists strong visible radiation in this area. Under the 600 MW-load condition, the radiation heat transfer of particle accounts for 25.95% of the total heat absorption of the high-temperature superheater and particle combustion still exists, whose combustion share accounts for about 1.83% of the received carbon content of coal. The particle temperature and emittance data fitted from the Planck's law indicate that the high-temperature particles are enriched at single side due to the inertial effect of residual rotation of flue gas. The residual rotation momentum of the separated over-fire air is insufficient to balance the temperature rise of both sides of the low-temperature reheater. Therefore, a new type principle of reforming combustion system was proposed, which changes a five-layer Separated Over-fire Air (SOFA) nozzle to two-section of six-layer SOFA nozzle to mitigate the combustion delay of pulverized coal particles and sets the wall-type tangent circle arrangement of the upper separated over-fire air nozzle to improve the residual rotation momentum of flue gas.

Investigation and Research on the Treatment of Air Pollution by Heating Boiler of Beijing University of Chemical Technology

On June 10, 2015, Beijing Municipal Environmental Protection Bureau issued “Boiler Atmospheric Pollutant Emission Standard” DB11/139-2015. Starting from April 1, 2017, NOx emissions from newly built boilers must be below 30mg/m3 and from in-use boilers must be below 80mg/m3. For implementing the emission reduction work in Beijing, according to current situation of boiler room in Beijing University of Chemical Technology, the school authorities do a series of work, including visits, market research and data analysis, attend academic conferences. On how to deal with the problem of air pollutant discharge standard of boilers in our university, we analyse the relevant emission standards at home and abroad, pollution prevention and control technology, low-nitrogen combustion principle of gas-fired industrial boilers and its technical development status, and put forward three solutions[1][2]. Through the comparison of advantages and disadvantages, the optimal solution is obtained.

Study on energy-saving operation technology of environmental protection facilities of ultra-low emission coal-fired unit

The operation optimization of low nitrogen combustion, denitrification and desulfurization facility of a 335 MW coal-fired unit met ultra-low requirements has been conducted in order to lower energy and material consumption. The operation mode of low nitrogen combustion with consideration of boiler efficiency and furnace exit nitrogen oxides concentration is determined. The boiler efficiency is 0.4% higher and the power supply coal consumption is reduced by 1.4 g/(kW h). The furnace exit nitrogen oxides concentration is reduced by 16 mg/m3. The SCR outlet nitrogen oxides concentration distribution uniformity is improved by ammonia spraying optimization, and the response speed and control quality of denitrification automatic control is improved by control logic optimization, therefore the liquid ammonia consumption is decreased by 0.13 kg/(104 kW h). The combination methods of absorber slurry pumps have been improved and the total mean running current of the pumps is lowered 33 amperes. The effect of limestone slurry feed automatic control is improved. The limestone slurry flow is reduced by 18.7 kg/(104 kW h).

Ultra-low emission transformation of 600 MW supercritical circulating fluidized bed boilers unit

With the introduction of ultra-low emission environmental protection policies in national and local coal-fired power plants, ultra-low emission transformation of coal-fired power plants is required to be carried out in an all-round way. Under this background, the first 600 MW supercritical circulating fluidized bed (SCCFB) boiler unit in the world have carried out the demonstration of the technical route of ultra-low emission transformation and the research of key technologies. By adopting limestone desulphurization and low nitrogen combustion in furnace, selective non-catalytic reduction (SNCR) technology outside furnace and the integrated desulfurization and dust removal process of flue gas circulating fluidized bed (CFB-FGD), the unit realizes the technical route of ultra-low emission, and has good investment and operation economy, which can adapt to the development trend of environmental protection in the future. The CFB-FGD and dust removal system can further improve the operation economy of the boiler by setting pre-electrostatic precipitator (pre-ESP), designing double-tower and optimizing the single-tower switching mode, optimizing the pressure margin of the induced draft fan, and adopting the coordinated desulphurization operation mode inside and outside the furnace. The research results can provide a reference for the selection of ultra-low emission transformation for 660MW ultra-supercritical CFB boiler unit.

A thermal and chemical fuel pretreatment process for NOx reduction from cement kiln

NOx emission has noticeably hindered cement industry from developing sustainably. A novel fuel pretreatment is developed to lower NOx emission. Besides, a pilot scale experimental facility was used to investigate differences between the fuel pretreatment and that of traditional low-nitrogen combustion with two different size ranges of coal (0–0.18 mm and 0.1–0.5 mm). The results shown that NOx emission attributed to fuel pretreatment is 40–45% lower than that of traditional low-nitrogen combustion with both size ranges of coal. Fuel pretreatment can maximally cut NOx emission as follows: partial fuel-N is reduced in situ to stable N2 at the preprocessing stage, thereby lowering the possibility of fuel-N oxidation in the precalciner; compared with parent coal, the reducing capacity of preprocessing product is enhanced for its larger specific surface area and lower graphitized degree in carbonaceous framework. Furthermore, particle size distribution could significantly influence above process. It is therefore revealed that the proposed approach more applies to NOx emission control in practical cement manufacture.

Influence of the Inner and Outer Secondary Air Ratios on the Combustion Characteristic and Flame Shape of a Swirl Burner with a Prechamber

The swirl burner with a prechamber was used in a 14 MW pulverized-coal combustion experiment to investigate the influence of inner and secondary air ratios (ISA/OSA) on the combustion characteristic and flame shape in this work. The temperatures and species concentrations in the prechamber were measured via the flue gas analyzer and thermocouples. The flame shape beyond the prechamber outlet was captured by using a high-speed camera. The results showed that the combustion efficiency was increased and low nitrogen combustion was achieved by adopting the swirl burner with a prechamber. The high temperature corrosion and slagging phenomenon did not occur in the prechamber. The influence of ISA/OSA on temperature and species concentration profiles at different areas in the prechamber was different. The flame shape size exhibited an inflection point with increasing ISA/OSA. Considering, comprehensively, the temperature peak, near wall temperature, oxygen-free zone, CO concentration, flame length, flame diameter, and divergence angle, the case of ISA/OSA =1 : 2 had great processing on combustion efficiency and NOx emission. Thus, ISA/OSA = 1 : 2 was selected as the optimized case under experiment conditions.

Research and Application of Low Nitrogen Burner for 600 MW Unit Boiler

High temperature corrosion on water wall is easily caused by burning high sulfur coal in low nitrogen burner of boilers in power station. Based on the combustion adjustment test of 600 MW unit boilers, this paper introduces the technical means of burner air distribution and coal mill operation optimization under low nitrogen combustion mode, realizes the optimal distribution of aerodynamic field in reductive and oxidative zones of boilers, and achieves the balanced control of boiler safety, environmental protection and energy saving when burning high sulfur coal. This technical means can provide reference for the operation of other similar boilers.

The ultra-low NOx emission characteristics of pulverized coal combustion after high temperature preheating

Preheating combustion is a promising low-nitrogen combustion technology. The article mainly describes the ultra-low NOx emission characteristics during preheating combustion, including preheating characteristics, combustion characteristics, and fuel nitrogen migration and transformation characteristics. Under the condition of fluidized bed equivalence ratio of 0.63 and preheating temperature of 980 °C, the calorific value of high-temperature coal gas is about 1.75 MJ/Nm3. Compared with raw coal, preheated char is modified and upgraded with a smaller particle size, larger specific surface area, and more pore structure. The combustion temperature is about 1045 °C, and the main form of NOx (NO2 or NO) along the DFC changes with the intensity of combustion. During the preheating process, 76.1% of the fuel nitrogen is converted to N2. Only 5.9% of the fuel nitrogen is converted to NH3, and NH3 is the only precursor of NOx. The average NOx emission is 31 mg/m3 (@6% O2), and corresponding conversion ratio of fuel nitrogen to NOx is 0.85%. This experimental results will play a vital role in the development of efficient and clean coal combustion technology.

Analysis on the cause of crack in connection pipeline of subcritical boiler reheater

Several coal-fired thermal power boilers with the same sub-critical parameters in Mengxi area of Inner Mongolia have successively suffered from cracking and leakage failure events of reheater connecting pipes, most of which occur at chamfered back tool grooves on the inner wall grooves of pipe welding joints. In order to find out the cause of cracking, typical failure samples were intercepted for macro-morphology, microscopy, SEM, chemical composition, mechanical properties, wall thickness measurement analysis and design and operation data investigation of several boiler equipment. The results show that comprehensive factors such as deviation of burning coal type from design of boiler, automatic dispatching of AGC load in power grid, low nitrogen combustion modification and so on cause changes in boiler combustion conditions and operation, which results in excessive high input level of reheater cooling water, resulting in long-term alternating thermal stress and non-periodic vibration of straight pipe and elbow arranged after fine-tuning of refrigerant flow direction in reheater. Finally, thermal fatigue cracks are induced to initiate and propagate through the stress concentration area of the chamfered knife groove of the inner wall of pipe welded joints.

Simulation analysis of boiler high temperature corrosion atmosphere under lean oxygen operation

High-temperature corrosion is a major threat to the safe operation of thermal power plants. The reducing atmosphere induced by boiler lean oxygen combustion has close relation with the water walls corrosion. In this paper, the reducing atmosphere such as CO, H2S concentration distribution was simulated targeted on a boiler. Under the full load, the atmosphere and the temperature distribution in low nitrogen combustion mode were further studied on different excess air ratios and the rates and position of the SOFA air conditions. With the SOFA rate increasing, the flame centre moved up, the boiler temperature is more uniform, and the temperature at the furnace outlet increased. the concentration of CO and H2S in the main combustion zone is obviously increased. In the burnout zone, there is almost no CO and H2S due to the supplement of SOFA.

Low-nitrogen combustion reformation for boiler burner

In view of the current reformation for denitrification and cost reduction in coal-fired power plants, the boiler burner was upgraded in our company. On the basis of the comprehensive study of the low nitrogen burners of the major coal-fired power plants, the following low nitrogen retrofit measures were implemented: low NOx retrofit measures of the burners, anti-slagging and anti-corrosion measures, as well as high-efficiency measures for stable combustion. The results showed that the improved burner had better air counterweight ratio and could ensure the stable combustion of pulverized coal. Under the pure coal condition, NOx was reduced from 600mg/m3 to 210mg/m3. Under the mixed combustion condition, NOx in the flue gas decreased from 410mg/m3 to 160mg/m3. The boiler efficiency was slightly improved after the reformation, for the boiler efficiency increased from 91.49% to 91.79% under the condition of gas mixing and increased from 92.92% to 93.79% under pure coal condition. As shown above, the NOx emission for burner was reduced without affecting the working efficiency and the cost of denitration was also controlled after reformation.

A numerical investigation of NOx concentration at the outlet of a coal-fired chain grate boiler

ABSTRACTA 3D computational fluid dynamic (CFD) simulation is performed on a 35t/h grate boiler to investigate the compound combustion, consisting of grate firing of lump coal on the fire grate and suspension combustion of pulverized coal sprayed in the middle of the stoker. A grate boiler-based low-nitrogen combustion method is proposed in the present study. The influences of this technology on the boiler temperature field and flue gas components as well as NOxare studied by comparing two different combustion modes before and after the transformation. Results show that the compound combustion technology can significantly improve the boiler efficiency and reduce the NOx concentration at the outlet. Therefore, the proposed method may have favorable applications in different industries. It is found that the boiler NOx emission can reach an optimal status, when the pulverized coal feed rate of the burner and the proportion of pulverized coal are set to 20m/s and 20%, respectively. It is observed that when the forward spinning arrangement form is adopted, the emission can be reduced up to 58.08%. The NOx at the outlet of a 35t/h boiler was reduced by 35.71% after retrofitting, which is in consistency with the obtained results.

Study on the influence of low nitrogen combustion on boiler operation

With the national emphasis on improving the quality of atmospheric environment and protecting the ecological environment, the standards for pollutant emission from power station boilers are becoming more and more strict. In response to national environmental requirements, low nitrogen combustion technology has been adopted in coal-fired power plants. However, the introduction of low nitrogen combustion technology has also brought a series of negative effects on boiler operation. It not only includes a dramatic rise in the high ash carbon content and heating water flow, slow load response rate and such influence on the unit economy, but also includes great reduction of reheat steam temperature under low load, rapid sharp rise of load steam temperature. The steam temperature decreases when load decreasing rate greatly reduces, the effects, such as big deviation between steam temperature and wall temperature, slagging furnace, high water wall, temperature corrosion and so on, have an impact on the stability of the security unit. This paper investigates 13 coal-fired power plants with capacity of 300 MW to 600 MW in Inner Mongolia autonomous region, to study the effects of low nitrogen combustion of boiler operation, pointing out the necessity of reasonable control of the export of nitrogen oxide content.

Numerical Simulation Analysis of the Optimized and Transformed 200MW Pulverized Coal Fired Boiler Burner

With the use of computational fluid mechanics software – FLUENT, the numerical simulation computation of combustion process inside a certain 200MW corner tangential firing boiler whose combustor is transformed by the multi-grade efficient low-nitrogen combustion technology was conducted, thus the furnace temperature, velocity, mixture and NOx concentration field at rated conditions before and after the transformation were obtained. The calculation results were highly identical with the industrial test results. The results show that after using the multi-grade efficient low-nitrogen combustion technology, the NOx emissions significantly lowered down with the drop of about 40% compared with the emissions before transformation, while the furnace coking and high temperature corrosion were effectively controlled, achieving good economic and social benefits and providing a reference to the design and transformation of the same types of boilers.