Wang Yujue, Huang He, Cannon Fred S, Voigt Robert C, Komarneni Sridhar, Furness James C
Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Environ Sci Technol. 2007 Apr 15;41(8):2957-63. doi: 10.1021/es0628295.
This research studied a relative comparison of the hydrocarbon emissions during pyrolysis of four carbonaceous additives that can be used in green sand foundries. These included a highly volatile bituminous coal, anthracite, lignite, and cellulose. Analytic pyrolysis was conducted to simulate the heating conditions that the carbonaceous additives would experience during metal pouring. Specifically, the samples were flash pyrolyzed in a Curie-point pyrolyzer at 920 degrees C with a heating rate of about 3000 degrees C/sec. This simulated some key features of the fast heating conditions that the carbonaceous additives would experience at the metal-mold interface when molten metal is poured into green sand molds. The samples were also pyrolyzed in a thermogravimetric analyzer (TGA) from ambient temperature to 1000 degrees C with a heating rate of 20 degrees C/min; and this simulated key features of the slow heating conditions that the carbonaceous additives would experience within the bulk of green sand molds that is further away from the metal-mold interface. Hydrocarbon emissions from flash pyrolysis were analyzed with GC-FID, while those from TGA pyrolysis were monitored with mass spectroscopy and GC-FID. The anthracite exhibited very low volatile hydrocarbons during both flash pyrolysis and TGA pyrolysis. The cellulose released less hydrocarbons than bituminous coal or lignite in TGA pyrolysis, but more hydrocarbons than those two during flash pyrolysis. This means that cellulose can release sufficient volatile hydrocarbons at the intensely heated molten metal-mold interface where they are most desired for ensuring casting quality, but much less within the bulk of the mold where they are undesirable. This characteristic of cellulose offers an important opportunity for green sand foundries to diminish their hazardous air pollutant (HAP) emissions.
本研究对可用于湿型铸造厂的四种含碳添加剂在热解过程中的碳氢化合物排放进行了相对比较。这些添加剂包括高挥发性烟煤、无烟煤、褐煤和纤维素。进行了分析热解以模拟含碳添加剂在金属浇注过程中会经历的加热条件。具体而言，样品在居里点热解器中于920℃下进行快速热解，加热速率约为3000℃/秒。这模拟了含碳添加剂在将熔融金属倒入湿型砂模具时在金属 - 模具界面处会经历的快速加热条件的一些关键特征。样品还在热重分析仪（TGA）中从室温加热到1000℃，加热速率为20℃/分钟；这模拟了含碳添加剂在远离金属 - 模具界面的湿型砂模具主体内会经历的缓慢加热条件的关键特征。快速热解产生的碳氢化合物排放用气相色谱 - 火焰离子化检测器（GC - FID）进行分析，而热重分析仪热解产生的排放则用质谱仪和气相色谱 - 火焰离子化检测器进行监测。无烟煤在快速热解和热重分析仪热解过程中均表现出极低的挥发性碳氢化合物。在热重分析仪热解过程中，纤维素释放的碳氢化合物比烟煤或褐煤少，但在快速热解过程中比这两种煤释放的碳氢化合物多。这意味着纤维素能够在强烈加热的熔融金属 - 模具界面处释放足够的挥发性碳氢化合物，而在该界面处这些碳氢化合物对于确保铸件质量最为关键，同时在模具主体内释放的量则少得多，而在模具主体内这些碳氢化合物是不需要的。纤维素的这一特性为湿型铸造厂减少其有害空气污染物（HAP）排放提供了一个重要机会。
