高准确性火电厂CO_(2)排放连续监测系统测点布置的数值模拟研究

Numerical simulation study on the measurement points arrangement of highaccuracy continuous CO_(2)emission monitoring system for thermal power plants

高准确性CO_(2)排放连续在线监测是计量我国火电领域碳排放的重要手段。为改进测点布置方案以提升现有CO_(2)在线监测方法的测量精度,本文以1台新建机组和1台旧机组的原烟道作为模拟对象,采用数值模拟的方法对不同负荷、不同测试断面、不同布点方式下的烟气流场和CO_(2)浓度场进行模拟,结合现场实测结果检验模拟的准确性,以改进CO_(2)排放连续在线监测中的测点布置方式。实测结果表明,2台机组的流速测点均匀布置,测点密度≥1个/m2时,在测试断面不满足GB/T 16157中“烟道监测断面应设置在距弯头、阀门、变径管下游方向≥6倍烟道直径,以及距上述部件上游方向≥3倍烟道直径处”要求的情况下,测试结果仍能准确反应断面平均速度,误差<2.3%;提升测点密度能有效增加流速测量的精确度;由于CO_(2)在断面分布均匀,仅需布置1~2个CO_(2)测点即可满足测量不确定度的要求,测试误差小于0.5%;机组负荷降低至75%和50%,或测试断面沿流向在2.5 m范围内移动,测试误差均可控制在4%以内。在此基础上,提出了一种非均匀测点布置法,借助数值模拟将测试断面按流速大小划分为若干连续区域,以各区域面积为权重,每个区域内布置较少测点以测试断面流速。该方法每个测试断面上的测点只需6~9个,测试误差小于4%。改进的方法简化了现有的在线监测布点方式。

Continuous on-line monitoring of high-accuracy CO_(2)emissions is an important means to measure carbon emissions in China's thermal power sector.In order to improve the measuring point arrangement scheme to improve the measurement accuracy of the existing CO_(2)on-line monitoring method,this paper takes the original flue of a new unit and an old unit as the simulation object,and uses the numerical simulation method to simulate the flue gas flow field and CO_(2)concentration field under different loads,different test sections and different distribution modes.The accuracy of the simulation is verified by the field measurement results to improve the arrangement of measuring points in the continuous on-line monitoring of CO_(2)emissions.The results show that when the flow velocity measuring points of the two units are evenly arranged and the density of measuring points is≥1/m2,the test section does not meet the requirements of GB/T 16157 that the flue monitoring section should be set at≥6 times the diameter of the flue in the downstream direction of the elbow,valve and variable diameter pipe,and≥3 times the diameter of the flue in the upstream direction of the above components.The test results can still accurately reflect the average speed of the section,and the error is less than 2.3%.Increasing the density of measuring points can effectively increase the accuracy of flow velocity measurement.Due to the uniform distribution of CO_(2)in the cross section,only 1~2 CO_(2)measuring points can be arranged to meet the requirements of measurement uncertainty,and the test error is less than 0.5%.When the unit load is reduced to 75%and 50%,or the test section moves in the range of 2.5 m along the flow direction,the test error can be controlled within 4%.On this basis,a non-uniform measuring point arrangement method is proposed.With the help of numerical simulation,the test section is divided into several continuous regions according to the flow velocity.With the area of each region as the weight,fewer measuring points are arranged in each region to test the flow velocity of the section.This method only needs 6~9 measuring points on each test section,and the test error is less than 4%.The improved method simplifies the existing on-line monitoring distribution method.