Study on Pyrolysis of Carbonaceous Additives in Green Sand Foundries

This research evaluated the hydrocarbon emission characteristics 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. The samples were flash pyrolyzed in a Curie-point pyrolyzer at 920 C with a heating rate of about 3000 C/sec. This simulated 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 C with a heating rate of 20 C/min; and this simulated 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, defined herein as the 189 compounds that are categorized in Title III: Hazardous Air Pollutants of the 1990 Clean Air Act Amendments.) emissions.