大尺度煤热解多环芳烃生成及排放规律

Formation and distribution of polycyclic aromatic hydrocarbons during large size coal pyrolysis

煤层热解是煤田火灾和煤层气化的重要过程，也是多环芳烃（PAHs）生成及排放的重要来源。选用4种低变质煤，在水平管式炉内进行煤层热解模拟实验，研究了16种USEPA优控PAHs在不同热解温度条件下的生成和分布特征。结果表明：PAHs的生成受热解温度的影响显著。热解产物中PAHs分布以3环PAHs为主，占80％以上；2环萘的生成随热解温度的升高快速下降；热解温度高于700℃时，4环类PAHs生成显著增加；5环、6环类PAHs生成量小于1．0mg／kg；高毒性苯并（a）芘的峰值出现在500～700℃，二苯并（a，h）蒽在400℃时生成量最大。热传导及传质阻力是影响大尺度煤非等温慢速热解过程PAHs生成及排放的主要因素。随煤变质程度的增加，高毒性PAHs生成量增大。400，900℃热解条件下PAHs毒性当量最高。

Being an important process of coal fires and underground coal gasification, coal seam pyrolysis is a crucial source of PAHs discharging into the air. Four kinds of low rank coals were pyrolyzed in the horizontal tube furnace to simulate coal seam pyrolysis ,and the formation and distribution of the 16 kinds of US EPA prior controlled PAHs at different temperatures were studied. The results show that with temperature increasing, four kinds of large size coals produce PAHs continually and PAHs yield is remarkably affected by temperature. 3-ring PAHs are the main species which takes up more than 80%. The yield of 2-ring PAHs attains the maximum at 400 ~C , and decreases rapidly with increasing temperature. Above 700 ~C, the yield of 4-ring PAHs rises significantly, and the yields of 5-ring and 6-ring are less than 1.0 mg/kg. The formation of the most toxic specie, benzo（a） pyrene, peaks between 500-700℃, and the maximum discharge of Dibenz（ a, h）anthracene occurs at 400℃. Resistance of heat conduction and mass transfer dur- ing the low speed pyrolysis process for the large size coal is the main affecting factor for the formation and discharge of PAHs. With the coal rank increasing, the discharge of toxic PAHs is enhanced. The maximum of TEQ occurs at 400 and 900 ℃.