燃煤电站锅炉NOx排放的控制措施

基于我国燃煤电站锅炉NOx排放的实际情况,在对影响其NOx排放各因素进行分析的基础上,细化了低氧燃烧、空气分级燃烧、低NOx燃烧器和燃料分级燃烧技术在我国电站锅炉的应用,指出锅炉设计中应尽可能选用切向燃烧方式,将再燃技术应用于降低燃用低挥发分煤的固态排渣电站锅炉设计和改造中以进一步降低NOx排放并满足国家标准的要求,锅炉运行中尽量减小各喷口风粉量的偏差,合理组织沿炉膛水平方向和高度方向(倒梯形、缩腰形等)的分级燃烧实现降低NOx排放的最佳效果.     

The effect of air staged combustion on NOx emissions in dried lignite combustion

Experiments were carried out in a multi-path air inlet one-dimensional furnace to assess NOx emission characteristics of the staged combustion of BRXL lignite and its dried coals. The impact of moisture content, multiple air staging, pulverized coal fineness and burnout air position on NOx emissions under deep, middle and shallow air-staged combustion conditions. Moreover, the impact of blending coals on NOx emissions was investigated in this paper. The unburned carbon concentration in fly ash was also tested. Experimental results based on the combustion of BRXL lignite and its dried coals show that NOx emissions can be reduced drastically by air-staged combustion. NOx emissions reduce with the increase of the air that is staged and the distance between the burner and burnout air position. Dried coal of BRXL lignite emits a smaller amount of NOx than that of BRXL lignite. However, the dried degree of BRXL lignite is closely related to R₉₀ fineness. Dried coal with optimal moisture content yields least NOx emissions. When deep or middle staged combustion was adopted, the application of multi-staged combustion is conducive to NOx reduction. However, when shallow staged combustion was adopted, NOx emissions are higher in multi-staged combustion than that in single-staged combustion with M_S = 0.54. Thus, the existence of a certain concentration of O₂ in reduction zone would significantly reduce NOx emissions. The blending coals that dried coals of BRXL lignite were blended with bituminous coals emit a larger amount of NOx than that of the dried coal alone. NOx emissions decrease with the increase of the proportion of dried coal in the blending coal. Moreover, the unburned carbon concentration in fly ash of dried coal in staged combustion is lower than that of BRXL lignite in staged combustion. On the whole, the dried coal of BRXL lignite is conducive to NOx reduction in staged combustion.     

Emission characteristics and axial flame temperature distribution of producer gas fired premixed burner

This paper presents the emission characteristics and axial flame temperature distribution of producer gas fired premixed burner. The producer gas fired premixed burner of 150 kW capacity was tested on open core throat less down draft gasifier system in the present study. A stable and uniform flame was observed with this burner. An instrumented test set up was developed to evaluate the performance of the burner. The conventional bluff body having blockage ratio of 0.65 was used for flame stabilization. With respect to maximum flame temperature, minimum pressure drop and minimum emissions, a swirl angle of 60° seems to be optimal. The experimental results also showed that the NO_x emissions are inversely proportional to swirl angle and CO emissions are independent of swirl angle. The minimum emission levels of CO and NO_x are observed to be 0.167% and 384 ppm respectively at the swirl angle of 45–60°. The experimental results showed that the maximum axial flame temperature distribution was achieved at A/F ratio of 1.0. The adiabatic flame temperature of 1653 °C was calculated theoretically at A/F ratio of 1.0. Experimental results are in tune with theoretical results. It was also concluded that the CO and UHC emissions decreases with increasing A/F ratio while NO_x emissions decreases on either side of A/F ratio of 1.0.     

天然气锅炉NOx及CO排放控制试验研究

为了响应政府业及民用天然气锅炉达到超低氮排放,要求绝大多数天然气锅炉采用低氮燃烧器+烟气再循环系统的技术路线,实施后普遍出现NO_x、CO含量偏高、炉膛振动较大等问题。借助116 MW天然气锅炉进行试验研究,研究了燃烧器燃料配比、燃烧火焰长度、助燃空气氧含量三个因素对NO_x及CO的影响,并对投入烟气再循环前后炉膛振动情况进行了检测。试验表明:燃烧器燃料内外配比对NO_x、CO生成影响较大,两者呈现相反趋势变化;燃烧火焰长度对NO_x生成影响较大,对CO含量影响较小;助燃空气氧含量对NO_x、CO生成以及锅炉振动影响较大。三种影响因素相比,助燃空气氧含量影响更为突出。     

Simulation of emission performance and combustion efficiency in biomass fired circulating fluidized bed combustors

In this study, the combustion efficiency and the emission performance of biomass fired CFBs are tested via a previously published 2D model [Gungor A. Two-dimensional biomass combustion modeling of CFB. Fuel 2008; 87: 1453–1468.] against two published comprehensive data sets. The model efficiently simulates the outcome with respect to the excess air values, which is the main parameter that is verified. The combustion efficiency of OC changes between 82.25 and 98.66% as the excess air increases from 10 to 116% with the maximum error of about 8.59%. The rice husk combustion efficiency changes between 98.05 and 97.56% as the bed operational velocity increases from 1.2 to 1.5 m s^?1 with the maximum error of about 7.60%. CO and NO_x emissions increase with increasing bed operational velocity. Increasing excess air results in slightly higher levels of NO_x emission. A significant amount of combustion occurs in the upper zone due to the high volatile content of the biomass fuels.     

大型亚临界无烟煤电站锅炉的开发设计

本文介绍哈尔滨锅炉厂有限责任公司开发设计的３００ＭＷ亚临界循环无烟煤锅炉的技术特点和运行业绩。着重论述耿保证低挥发份煤种的着火、稳燃、燃尽和防止炉膛结焦、降低不投油稳燃负荷、减少ＮＯｓ排放量所采取的有效技术措施。特别是在燃烧器设计中,采用了哈锅与清华大学联合开发研制的,并获得国家创造发明专利金奖的“双一次风通道自稳式燃烧器”,该燃烧器具有明显的低负荷稳燃特性和综合性能,使大型无烟煤锅炉的设计达到了     

Influence of swirl number and fuel equivalence ratio on NO emission in an experimental LPG-fired chamber

The well-known kinetic mechanism of nitrogen oxides formation by thermal fixation of atmospheric nitrogen suggests the control of these pollutants by modifying the equivalence ratio and/or the temperature in the combustion region. In this experimental investigation a burner was specifically designed to take advantages of these chemical kinetic aspects. In particular, it was used to investigate the influence of swirl number and fuel equivalence ratio on nitric oxide concentration formed in a cylindrical combustion chamber. A set of 14 experimental runs was carried out to examine the influence of these factors, which were varied at seven and two levels (7¹ × 2¹) in the range of 0.36–1.32 and between 0.61 and 0.84, respectively. Liquefied petroleum gas (LPG) was always fired in the experiments. Temperature, O₂ and NO concentration were monitored in 42 different radial and axial positions along the chamber at four different operating conditions in terms of NO formation. The effect of increasing the swirl number and reducing the fuel equivalence ratio was to reduce approximately 31% and 33% the nitric oxide emission, respectively.     

Full-scale co-firing trial tests of sawdust and bio-waste in pulverized coal-fired 230 t/h steam boiler

Co-firing trial tests of sawdust and bio-waste coming from cereal production with hard coal were carried out at Skawina Power Plant in Poland (1532 MW in fuel, currently belonging to CEZ Group). Skawina Power Plant is a tangentially-fired pulverized coal unit with nine boilers (4 boilers of 210 t/h and five boilers of 230 t/h live steam respectively) that produces 590 MW electricity and 618 MW of heat (district heating and process steam).The paper presents an analysis of energy and ecological effects of sawdust and bio-waste co-firing in the existing pulverized hard coal boiler. The mixture of coal and biomass was blended in the coal yard, and fed into the boiler through the coal mills. During the tests, combustion of mixtures composed of hard coal and sawdust (with mass share of 9.5%) and hard coal – bio-waste (6.6% mass basis) were examined. The co-firing tests were successful. Based on the analysis of the test results, the influence of biomass co-firing on specific components of energy balance (e.g. stack losses and boiler thermal efficiency) was discussed, in comparison to combustion of coal alone. The emission indices during coal combustion were calculated and compared to the emission indices for biomass co-firing. It was proved that co-firing of both biomass sorts leads to a decrease of CO and SO₂ emissions. Due to the possibility of considering the part of the energy generated during biomass co-firing as renewable energy, the procedure for biomass based renewable energy share determination is presented and illustrated with an example.     

低氮燃烧技术在旺隆电厂420t/h燃煤锅炉上的应用

主要介绍了利用低氮燃烧技术实现对燃煤锅炉氮氧化物排放的控制,并以旺隆电厂为例,详细阐述了低氮燃烧器加空气分级燃烧技术在420 t/h燃煤锅炉上的工程应用并对不同燃尽风门开度下低氮燃烧的效果进行了试验研究.通过测试数据显示,改造前,此锅炉炉膛出口NO<,x>浓度为500 mg/m<'3>(干态,6%氧量);改造后,在保证...     

Mathematical modeling of combustion in a grate-fired boiler burning straw and effect of operating conditions under air- and oxygen-enriched atmospheres

A three-dimensional mathematical model has been developed as a tool for furnace structure design and operation conditions optimization when the straw combustion is in oxygen-enriched or conventional air atmospheres. Mathematical methods have been used based on a combination of FLIC (A fluid Dynamic Incinerator Code) code for the in-bed incineration and commercial software FLUENT for the over-bed combustion. Oxygen-enriched atmospheres promote the destruction of most pollutants due to the high oxygen partial pressures and temperatures, which is reflected by very low residual amounts of organic combustion by-products in the bottom ash and flue gas of the straw-fired boiler unit. The predictions indicated that the maximum combustion temperature is around 1500 K, CO emission is 201 vppm and O₂ concentration is about 6.9 vol% at furnace exit, and it is shown that mathematical models can serve as a reliable tool for detailed analysis of straw combustion processes in the packed-bed furnace when compared with literature measurement data. In comparison to traditional straw combustion, the deviation of flue gas CO and NO is 27.5% and 62.1%, respectively. The numerical simulation results showed that combustion under the oxygen-enriched atmosphere excelled combustion under conventional air.     

Influence of division cone angles between the fuel-rich and the fuel-lean ducts on gas–particle flow and combustion near swirl burners

Radial bias combustion pulverized coal swirl burners are used in boilers when burning low-grade coals, which are often low-volatility anthracite and lean coals that do not burn stably. In a gas–particle test facility, a three-dimensional particle-dynamics anemometer was used to measure gas–particle flows in the near-burner region. Division cones between the fuel-rich and the fuel-lean ducts of the burner were set at angles of 43.2° and 0°. Velocity and particle volume flux profiles were obtained and the influence of the cones on combustion was analyzed. Burners with a division cone angle of 43.2° were used in a lean-coal fired boiler (volatility 13.2% as received, ash 27.46% as received), rated at 670 t/h. Pulverized coal was conveyed by cold moisture-laden exhaust air from the pulverizer. In situ aerodynamic field measurements in cold state were made and combustion tests were carried out. Low NO_x emission and high thermal efficiency resulted and the turn-down ratio was 50%.     

Effect of injection pressure on performance,emission and combustion characteristics of high linolenic linseed oil methyl ester in a DI diesel engine

Due to the increasing demand for fossil fuels and environmental threat, a number of renewable sources of energy have been studied worldwide. In the present investigation a high linolenic linseed oil methyl ester has been investigated in a constant speed, DI diesel engine with varied fuel injection pressures (200, 220 and 240 bar). The main objective of this study is to investigate the effect of injection pressures on performance, emissions and combustion characteristics of the engine. The test results show that the optimum fuel injection pressure is 240 bar with linseed methyl ester. At this optimized pressure the thermal efficiency is similar to diesel and a reduction in carbon monoxide, unburned hydrocarbon and smoke emissions with an increase in the oxides of nitrogen was noticed compared to diesel. The combustion analysis shows that, the ignition delay is lower at higher injection pressures compared to diesel and the peak pressure is also higher at full load. The combustion duration was almost same at all the injection pressures. It is concluded that linseed methyl ester at 240 bar injection pressure is more efficient than 200 and 220 bar, except for nitrogen oxides emission.     

Residential pellet boilers in Belgium: Standard laboratory and real life performance with respect to European standard and quality labels

Nine residential wood pellet boilers were tested for the emissions of carbon monoxide (CO), nitrogen oxide (NO_x), dust and combustion efficiency in real life and standard laboratory conditions and values were compared with the permissible values of Blue Angel, Swan Mark and EN-303-5. The test setup consisted of six boilers equipped with bottom feed burner (BF), one with top feed (TF) and two with horizontally feed burner (HF). Wood pellets used as fuel were DINplus certified.     

污泥掺烧方式对燃煤锅炉燃烧影响的模拟研究

为了确保燃煤锅炉掺烧污泥后炉内燃烧安全稳定并控制NO_x的生成,以国内某典型1 000 MW超超临界燃煤锅炉为研究对象,利用CFD软件计算研究了不同的污泥掺烧方式对锅炉温度场和NO_x生成的影响。结果表明：在燃煤锅炉不同层的燃烧器掺烧污泥,掺烧污泥的燃烧器对应高度均出现了温度的下降和NO_x排放浓度的降低;随着污泥分别由下往上在B,D,F层燃烧器进行掺烧,在炉膛出口处烟温升高,NO_x排放浓度降低;在保持F层燃烧器总热值不变的情况下进行掺烧时,能保证锅炉整体温度水平,掺烧污泥比例越高,炉膛出口烟温越低,NO_x生成量越少;在F层燃烧器掺烧污泥燃烧效果较好,有利于NO_x减排,是最适合污泥掺烧的燃烧器层。     

空气分级切向燃烧锅炉炉膛配风优化模型

为实现空气分级低NOx燃烧锅炉主燃烧区过剩空气系数的在线监控,提高该类燃烧系统的运行水平,以二次风挡板作为一次元件,利用二次风箱到炉膛出口的压降模型对二次风喷嘴的空气流量进行测量;在此基础上,根据锅炉冷热态试验数据,综合考虑颗粒燃烬、NOx排放量以及风机输送电耗等因素,建立空气分级低NOx燃烧锅炉炉内风粉分布的优化模型,在给定燃料喷嘴运行方式和炉膛出口过剩空气系数的条件下,对二次风挡板开度进行优化。一台300 MW锅炉的应用表明,炉膛配风优化后,烟气NOx排放和颗粒燃尽度得到良好协调,且在保证NOx排放量为255 mg/m~3的情况下,优化后风箱-炉膛差压降低191 Pa,减少了风机电耗。     

四角切向燃烧锅炉煤粉射流逆向稳燃技术的研究开发

本文首次提出并分析了四角切向燃烧锅炉煤粉射流逆向稳燃技术的设计思想。根据炉内三维湍流流场的数值模拟，优化设计了本项技术应用于焦作电厂Ｎｏ．３炉的燃烧器改造方案。计算结果及现场应用证实，采用煤粉射流逆向稳燃技术能够大幅度延长一次风射流中煤粉颗粒在着火初期的停留时间，改善煤粉气流的着火条件，同时能够有效地削弱炉膛出口气流的残余旋转，从而减轻烟温偏差，并能改变煤粉颗粒的切圆运动轨迹，从而缓解了炉膛燃烧器区域水冷壁的结渣与高温腐蚀。     

通过煤粉浓缩预热低NOx燃烧器实现高温空气燃烧技术的研究

以煤粉浓缩预热低NOx燃烧器(PRP)为例,说明了通过组织高温烟气回流快速预热低风煤比的一次风煤粉气流,可以在燃煤锅炉上实现具有高稳燃和低NOx排放性能的高温空气燃烧.工业试验和应用表明:PRP燃烧器特殊的预热室结构可以有效控制一次风粉的预热,快速加热煤粉颗粒并使之在达到燃烧器喷口时接近着火温度,因而具有优异的煤种适应性、低负荷稳燃能力和低NOx排放特性,是在燃煤锅炉上实现高温空气燃烧的一种良好的燃烧器.     

Characterisation of an oxy-coal flame through digital imaging

This paper presents investigations into the impact of oxy-fuel combustion on flame characteristics through the application of digital imaging and image processing techniques. The characteristic parameters of the flame are derived from flame images that are captured using a vision-based flame monitoring system. Experiments were carried out on a 0.5 MW_th coal combustion test facility. Different flue gas recycle ratios and furnace oxygen levels were created for two different coals. The characteristics of the flame and the correlation between the measured flame parameters and corresponding combustion conditions are described and discussed. The results show that the flame temperature decreases with the recycle ratio for both test coals, suggesting that the flame temperature is effectively controlled by the flue gas recycle ratio. The presence of high levels of CO₂ at high flue gas recycle ratios may result in delayed combustion and thus has a detrimental effect on the flame stability.     

Methanol decomposition fuel processor for portable power applications

A new fuel processor approach for portable fuel cell power sources significantly improves upon microreformers by overcoming the difficulties with heat deficiencies and contaminants in the product hydrogen. Instead of reforming, the processor uses methanol decomposition to enable the byproduct, carbon monoxide (CO), to be used as the heat source. A hydrogen permselective membrane segregates the CO for combustion in an integrated burner, maximizes the decomposition conversion, and provides pure hydrogen for a fuel cell. Discharging the CO-rich retentate through an ejector to draw combustion air into the burner greatly simplifies the system. High and stable hydrogen yields are attained with optimized catalysts and fuel compositions. The resultant simple, efficient, and self-heating processor produces 85% of the hydrogen content of the fuel. A 20 W autonomous power source based on this novel fuel processor demonstrates a fuel energy density >1.5 Wh g^?1_(electrical), nearly twice as high as microreformer power sources.     

Estimation of methane and nitrous oxide emissions from paddy fields in Taiwan

To investigate the greenhouse gases emissions from paddy fields, methane and nitrous oxide emissions were estimated with the local measurement and the IPCC method during 1990–2006 in Taiwan. Annual methane emission ranged from 9001 to 14,980 ton in the first crop season for 135,314–242,298 ha of paddy fields, and it was between 16,412 and 35,208 ton for 101,710–211,968 ha in the second crop season with the local measurement for intermittent irrigation. The value ranged from 31,122 to 55,729 ton of methane emission in the first crop season, and it was between 29,493 and 61,471 ton in the second crop season with the IPCC guideline for continuous flooding. Annual nitrous oxide emission from paddy fields was between 371 and 728 ton in the first crop season, and the value ranged from 163 to 365 ton in the second crop season with the local measurement. Methane emission from paddy fields in Taiwan for intermittent irrigation was only 26.72–28.92%, 55.65–57.32% and 41.19–43.10% with the IPCC guidelines for continuous flooding and mean temperature of transplanting stage in the first crop, the second crop and total paddy fields, respectively. The values were 53.44–57.84%, 111.29–114.55% and 82.38–86.20% with the IPCC guidelines for single aeration and mean temperature of transplanting stage, respectively; and the values were 133.60–144.61%, 282.56–286.62% and 205.96–215.49% with the IPCC guidelines for multiple aeration and mean temperature of transplanting stage, respectively. Intermittent irrigation in paddy fields reduces methane emission significantly; appropriate application of nitrogen fertilizer and irrigation in paddy fields also decreases nitrous oxide emission.