Evaluation of Volatile Hydrocarbon Emission Characteristics of Carbonaceous Additives in Green Sand Foundries

Abstract

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.