20t/h生物质燃气蒸汽锅炉燃烧特性的数值模拟研究

Numerical simulation study on combustion characteristics of 20 t/h biomass steam boiler

某电厂的生物质燃气蒸汽锅炉系统取消了气化炉出口的水冷装置,气化所得800℃生物质燃气直接送入锅炉中燃烧。考虑到燃气高温、低热值的特点,采取预燃室燃烧、空气分级、切圆送风等燃烧技术,设计了燃气锅炉的燃烧器。为探究不同运行参数下锅炉的燃烧性能,设计了四因素四水平正交试验,利用FLUENT软件探究了燃尽风比例、燃尽风位置(停留时间)、二次风投入方式、过量空气系数对锅炉烟气中NOx浓度的影响,发现燃尽风比例、燃尽风位置两个因素对NOx的排放影响较大,并且在燃尽风比例30%、停留时间为0.8 s、α=1.05、二次风按照工况3投入的情况下,烟气中NOx的浓度最低。然后在正交试验所得最佳工况基础之上,分别探究了不同燃尽风比例、燃尽风停留时间对NOx排放的影响,发现空气分级技术的脱硝效果明显,随着燃尽风比例的增大,脱硝效率逐渐提高,但同时会影响燃烧效率;停留时间在0.4~0.8 s时,推迟燃尽风的送入起到更好的效果,但此后进一步推迟燃尽风的送入位置对控制NOx的排放没有明显作用。

The water cooling device was cancelled in a biomass gas steam boiler system of power plant at the outlet of the gasifier, and the 800 ℃ biomass gas is directly sent to the boiler for combustion. Considering the characteristics of high temperature and low calorific value of biomass gas, the combustion system of gas boiler is designed by the following technology: pre-combustion chamber, air staged combustion and tangential combustion. A four-factor four-level orthogonal test was designed, using FLUENT to explore the combustion performance of boilers under the following operating factors: the proportion of SOFA, position of SOFA(residence time), secondary air input mode, excess air ratio, and found that the proportion of SOFA and the position of SOFA have a great influence on NO_x emission. When the proportion of SOFA is 30%, the residence time is 0.8 s, the excess air ratio is 1.05, and the secondary air is sent in under the condition 3, the best combustion performance are obtained. Then, based on the orthogonal experiment, the emission of NO_x of different SOFA proportion and SOFA position were calculated. It is found that the denitration effect of the air classification technology is effective. As the proportion of the SOFA increases, the denitration efficiency gradually increases, but the combustion efficiency decreases at the same time;When the residence time is 0.4~0.8 s, the longer the residence time is, the better the combustion performance of boiler attained.However, delaying the feeding of the SOFA has no obvious effect on the control of NO_x emission.