SNCR+循环氧化吸收脱硝联合工艺在CFB锅炉超低排放中的应用

简述了选择性非催化还原(SNCR)和循环氧化吸收脱硝技术原理,以洛阳石化循环流化床(CFB)锅炉为例,对锅炉SNCR、循环氧化吸收脱硝改造后的运行进行分析,探讨了该联合脱硝技术应用于CFB锅炉超低排放改造的优点和不足。     

还原剂雾化效果对燃煤循环流化床锅炉SNCR脱硝性能影响研究

为提升燃煤循环流化床锅炉的选择性非催化还原（SNCR）脱硝性能,进行了还原剂雾化效果对燃煤循环流化床锅炉SNCR脱硝性能影响的研究。以Fluent软件中的离散模型为基础完成SNCR模型的构建。选择壁面喷射模拟喷枪类型,在氨氮比（理论等效比）为1.5的条件下,以喷枪位置、喷枪数量、喷射速度、雾化粒径和角度作为还原剂雾化效果评价指标,测试了燃煤循环流化床锅炉SNCR脱硝效率。结果表明：当喷枪位置处于X=5 m、喷枪个数为6个、喷射速度为25 m/s、喷枪雾化粒径为100μm、雾化角度为25°时,还原剂雾化效果最好,燃煤循环流化床锅炉SNCR脱硝效率最高为48.23%。     

气流床煤粉工业锅炉非催化还原脱硝试验

选择性非催化还原(SNCR)脱硝技术是燃煤工业锅炉领域重要的脱硝技术之一，目前电站锅炉SNC■脱硝效率普遍偏低，且工业锅炉SNCR应用研究较少。针对一台20 t/h气流床煤粉工业锅炉测量了炉膛温度以及不同喷枪位置和气液压力下炉膛出口的NO_x排放浓度，研究了气流床煤粉工业锅炉中SNCR的脱硝性能。结果表明，采用尿素进行脱硝反应的最佳温度窗口为790～850℃,最佳温度窗口位于炉膛中心截面附近，喷枪设置在炉膛侧壁中心优于炉膛顶部，喷枪插入深度和角度对脱硝效率的影响较小，喷枪位于最优位置时，脱硝效率可达87.2%,出口NO_x质量浓度为38 mg/m³,满足超低排放。喷枪流量随液压升高和气压降低而增大，气压大于液压时，喷枪雾化较好，整个扇面液滴分布较均匀，2.38≤氨氮物质的量比≤3.00时，液压越低，脱硝效率越高，0.30 MPa≤液压≤0.35 MPa, 0.29 MPa≤气压≤0.40 MPa时，SNCR脱硝效率较高，且氨逃逸较少。喷枪液滴雾化情况对脱硝效率的影响高于扇面角度。     

煤粉燃烧过程强化脱硝技术研究

为进一步提高炉内燃烧过程的脱硝效率,尤其是解决燃用挥发分低的贫煤和无烟煤时炉内NO_x排放浓度高的问题,基于高温燃尽区喷氨还原NO机理,提出了多级燃尽风布置区的高温强化还原区喷氨脱硝技术——多级强化还原煤粉燃烧技术(MERC)。借助50 kW下行燃烧炉,开展了氨氮比(RNSR)、还原剂与烟气混合程度、还原剂载气等关键技术参数对脱硝效率的影响,同时开展了MERC和SNCR对比试验研究,并进行了MERC技术的工程应用试验。结果表明:采用双支喷枪对喷能提高还原剂与炉内烟气的混合程度,双支喷枪对喷使脱硝效率从单支喷枪的45%提高到70%;空气作为载气,氨氮比超过1. 2时,NO浓度在500～700 mg/Nm~3,随着氨氮比增加,NO_x浓度先升后降;烟气作为载气时NO_x浓度大幅降低,仅为100 mg/Nm~3左右,因此还原剂的载气中含氧量越低,越有利于增强高温中喷氨还原NO的效果,还原剂载气需尽可能降低氧含量或采用无氧媒介。通过对比SNCR和MERC试验结果发现,氨氮比小于2时,常规SNCR的NH3耗量高于MERC;氨氮比超过2. 5后,NH3同NO的反应趋于饱和,过量的NH3同SO_2发生反应生成(NH4)2SO3和NH4HSO3,这是工程上出现SNCR过量喷尿素后造成空气预热器堵塞的原因。对某电厂125 MW燃煤锅炉进行低氮改造,由于该电厂1、2号锅炉燃用无烟煤+贫煤+烟煤的混煤,2015年低氮燃烧系统改造后一直存在锅炉出口NO_x浓度不稳定的情况,尾部脱硝装置入口最低在500 mg/m~3以下,最高为1 200 mg/m~3。为确保改造达到超低NO_x排放目标值,在原有燃烧优化试验+SNCR改造+SCR优化提效的设计方案的基础上增加了燃尽风前的尿素喷枪。结果表明:炉内脱硝效率高于65%,结合锅炉尾部SCR装置能实现烟囱位置NO_x浓度不高于30 mg/m~3的超低排放,达到了预期效果。     

SNCR烟气脱硝技术在330MW级CFB锅炉的应用

针对1180t／hCFB锅炉采用华能清能院选择性非催化还原（SNCR）脱硝专利技术,结合CFB锅炉炉内低NOx燃烧控制技术,NOx排放量由改造前的300mg／m3可有效控制在50mg／m3以下,脱硝效率达80％以上,对应氨氮比低于1．5,氨逃逸值可控制在1．5mg／m3以下,系统自动化投入率100％。通过对SNCR系统运行参数优化,得到较佳尿素给入浓度及合理的氨氮比控制参数,提高了脱硝系统的运行经济性、稳定性。该项技术首次成功应用于330MW等级CFB锅炉,为中国大型CFB锅炉实现高环保标准的氮氧化物减排探明了方向。     

燃煤锅炉低氮燃烧改造联合SNCR脱硝技术应用

文章介绍了3台65 t/h自然循环式煤粉锅炉采用低氮燃烧改造+SNCR脱硝技术脱硝的应用实例,监测数据表明,该技术成熟可靠,综合脱硝效率约为70%,同时采用已有液氨做SNCR脱硝的还原剂,节省了投资,具有良好的环境效益和经济效益。     

SNCR脱硝技术在45t循环流化床锅炉中的应用

介绍了开封龙宇45 t/h循环流化床燃煤锅炉烟气排放现状,对SNCR脱硝技术进行了对比并选择了氨法SNCR脱硝技术进行应用。改造后烟气中氮氧化物(以下简称NO_x)排放浓度降低了70%以上,达到了预期效果。     

“低氮燃烧技术+SNCR”在循环流化床燃煤锅炉上的应用

文章主要简述了低氮燃烧技术及选择性非催化还原法(SNCR)脱硝工艺的原理,循环流化床锅炉低氮燃烧改造方式,低氮燃烧技术+SNCR组合式工艺在实际工程案例中的应用情况,这种组合式脱硝工艺的优势,及这种组合式脱硝工艺所带来的经济和社会效益。     

基于环保超低排放的管式空预器长周期运行策略

针对管式空预器磨损、腐蚀和堵塞等问题,以河坡350 MW超临界循环流化床锅炉机组为例,通过空预器入口风温智能温控策略,根据酸露点的预测结果确定空预器管壁温度,从而调整暖风器出力,保证空预器的入口风温始终在酸露点以上,从而减小空预器末端低温腐蚀。结合低氧量燃烧技术,通过运行试验,最终确定锅炉在不同负荷下的氧量：350 MW负荷时氧量为2.7%～3.0%,310 MW负荷时氧量为3.0%～3.2%,230 MW负荷时氧量为3.2%～3.5%,有效减少了空预器低温段腐蚀。采用二次风口喷入石灰石快速响应炉内脱硫技术,使石灰石可以直接喷入炉内微氧化稀相区域,缩短了脱硫响应速率时间,减少了炉内脱硫剂石灰石的用量,避免了烟气中SO₂含量大幅波动,有效提高炉内脱硫效率。对比各脱硝喷枪效率以及脱硝喷枪的位置,确定喷枪效率,对SNCR系统的喷枪进行优化,在二次风管倾斜段增设脱硝喷枪,提高了全负荷平均脱硝效率,降低氨逃逸量,有效减少了该机组脱硝还原剂的消耗量,并且大幅降低氨逃逸硫酸氢氨对空预器腐蚀和堵塞的风险。通过以上技术手段,空预器运行6 a来,工作状态良好,运行平稳,可为同类机组空...     

锅炉脱硝SNCR系统提效降耗优化应用

提效降耗是锅炉脱硝SNCR系统优化的主要方向。文章以一个锅炉脱硝SNCR系统为例,简单介绍了锅炉脱硝SNCR系统运行现状,并对其提效降耗优化应用方案进行了进一步探究,希望为锅炉脱硝S N C R系统的应用优化提供一些参考。     

The kinetic rate of combustion of electrode carbon in the temperature range of 1000-1200 k

Kinetic rates of combustion of electrode carbon particles were measured in a temperature range of 1000-1200 K. Spherical carbon particles of size 7-9 mm are burnt in hot streams of nitrogen-oxygen mixtures. The velocity and the temperature of the mixture were varied. To compensate for the mass transfer resistance to the flow of oxygen to the carbon surface a mass transfer experiment was carried out in the same apparatus. By using mass transfer coefficients from the above experiment kinetic rates are analysed statistically to give the following Arrhenius type correlation of the kinetic rate: where n is in the range of 0.3 to 0.5.     

先进的低污染煤粉燃烧技术

本文分析了先进的煤粉燃烧技术应该具有的多种效能，即安全可靠、不结渣、燃烧稳定；具有低ＮＯ＿ｘ燃烧性能；有利于降低ＳＯ＿２的排放。论证了在我国研究开发低ＮＯ＿ｘ煤粉燃烧技术和推广应用不需耗费大量资金，却可大幅度减少ＮＯ＿ｘ的污染。还论证了先进的煤粉燃烧技术应采用炉内喷钙并附加增湿技术或排烟循环流化床脱硫技术。     

Devolatilization and char burning of coal particles in a fluidized bed combustor

Devolatilization and char burning were studied in an electrically heated bench-scale fluidized-bed reactor at 750 to 900°C bed temperature, gas oxygen mole fractions ranging from zero to 0.21, superficial gas velocities from 0.3 to 0.7 m/s and coal particle diameters 5 to 35 mm. The coals investigated include lignite, bituminous and anthracite. The coal devolatilization and char burning times, H/C ratio histories, and particle fragmentation were measured. Statistical correlations with the operating variables were developed for the devolatilization time. A mathematical model is given for the combustion of char. Most predictions of the model agree quite well with the experimental results.     

Transition Processes in Filtration Gas Combustion

The behavior of gas filtration combustion waves in the lowvelocity regime has been studied experimentally with variation in the parameters of the gas flow and porous medium. It is shown that in transition processes there may be quenching or formation of a stable combustionwave structure that does not correspond to the initial or final conditions. A nontrivial type of transition process accompanied by spatial transfer of the combustion zone is found.     

Homogeneous vs. catalytic combustion of lean methane—air mixtures in reverse-flow reactors

To carry out a comparative assessment of a recently proposed idea of using thermal flow-reversal reactors (TFRR) for mine ventilation air, the results for the catalytic flow-reversal reactor (CFRR) investigated within the European Project (2003) are briefly presented. Next, experimental investigations of thermal combustion are presented in this paper. These consisted of the kinetic study of homogeneous combustion in the pelletized bed and in the monolith. Kinetic equations for the two cases are derived and discussed. Experimental autothermal reverse-flow operation in a laboratory setup was performed. Due to the high heat capacity of the wall and insulation of the pelletized bed reactor, with considerable heat losses to the surroundings, autothermal operation was successful only in the monolithic reactor. It is finally concluded that the thermal combustion can be competitive compared with the catalytic oxidation.     

Free-convective regime of flame spread over a fuel film on a substrate

Flame spread over a liquid fuel film on a thin metallic substrate under free convection was studied experimentally. Instantaneous flame velocities correlate with the flame length. The average flame velocity increases from 2 to 30–40 cm/sec with the slope angle of the substrate to the horizon varying in the range of 0–90°. For a substrate of specified width, the flame velocity is inversely proportional to the heat capacity of the unit area of the substrate-fuel system and to the differences between the temperature corresponding to the formation of a stoichiometric mixture of the saturated fuel vapor and air and the ambient temperature. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 21–30, September–October, 2007.     

煤粉无焰富氧燃烧的数值模拟方法进展

无焰富氧燃烧是煤粉清洁燃烧技术的前沿发展方向之一,可在捕集高浓度CO₂的同时显著降低NOx排放,并提升富氧燃烧稳定性和热力性能。计算流体力学(CFD)作为燃烧研究的重要手段之一,具有快捷、成本低和数据丰富等优点,有效促进了无焰富氧燃烧技术发展。基于笔者团队对煤粉富氧燃烧和无焰燃烧的多年研究积累,对近十几年来煤粉无焰富氧燃烧CFD模拟方法和模拟研究进展进行了总结:首先强调了煤粉无焰燃烧的试验和数学定义,其由于存在非均相反应而区别于气体燃料无焰燃烧;然后详述了煤粉无焰富氧燃烧CFD模拟方法进展,包括模拟流动、传热、燃烧和污染物生成方面的子模型和机理,其中考虑强烈烟气卷吸的可实现k-ε湍流模型、P1或DO辐射模型及针对富氧气氛修正的WSGG气体辐射模型、CPD挥发分析出模型、考虑湍流与化学反应交互的有限速率EDC均相燃烧模型、针对无焰及富氧燃烧开发验证的均相反应机理、考虑气化反应的多步表面焦炭非均相燃尽模型、含氮化学详细反应机理氮转化模拟、动态自适应反应机理加速算法等可显著提高煤粉无焰富氧燃烧的模拟精度和计算效率。总结了煤粉无焰富氧燃烧在基准对照试验、微观反应区域分析、宏观反应特征、污染物生成及大型化锅炉概念设计方面的模拟研究情况;最后以大涡模拟、燃烧模型、高精度反应机理及动态自适应反应机理、工业应用优化等角度展望了煤粉无焰富氧燃烧CFD研究的发展方向。     

Application concepts and evaluation of small-scale catalytic combustors for natural gas

Basic application concepts of catalytic combustion are roughly classified into three types, and the development of catalysts, combustion performance and applicability are stated. On the diffusive catalytic combustion method, completeness of methane combustion and its reaction mechanism have been demonstrated by detailed combustion analysis of the burner and reaction kinetics. On the adiabatic lean premixed catalytic combustion method, applicability of a high-temperature catalyst system based on Mn-substituted hexaaluminate monolithic honeycomb to a 1.5 MW gas turbine combustor has been investigated through pressurized combustion tests and prototype engine-rig tests. As a result, a good outlook of the basic technical problems to overcome including the catalyst durability and the combustor control method was obtained, but another problem was that of the combustor capacity. In view of the progress of the non-catalytic lean premixed combustion method, it was concluded that a hybrid catalytic combustion method limiting catalytic combustion to the low-temperature range in this concept might become efficient in the future, but that it would depend on the development of efficient catalysts initiating their activity at about 350°C and having durability at 1000°C.     

Combustion limits of liquid monofuels

A mathematical model for steady-state nonadiabatic waves of filtration combustion of liquid monofuels in narrow tubes is proposed. Using this model, it is shown that combustion in this system can proceed in two regimes with different dominant mechanisms of heat transfer from combustion products to the preflame zone. The nature and parametric dependences of the limits of both regimes are analyzed. Calculations using the model are in good agreement with experimental data on the combustion of liquid hydrazine in narrow tubes. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 29–39, March–April, 2008.     

Operation of an internal combustion engine: Lean conditions with hydrogen produced in an onboard methanol reforming unit

A way of achieving quality regulation in running a conventional internal combustion engine is presented. The fuel stream (methanol) is divided into two parts one of which goes to a conventional fuel injection device, the other to an onboard decomposing reactor for the production of the necessary hydrogen. The reactor methanol flow is taken as proportional to the air flow to the carburettor, i.e., to the rotational speed in the quality regulation region. This rather easily achieved system is evaluated using a model calculated to include most of the parameters. Information is also included on the necessary regulation equipment. The resulting low emission of hazardous gases, as reported earlier, is an advantage but the main interest is in the high efficiency of the engine. To verify the calculations bench-scale tests were carried out. The differences between the model and the test results are analysed.