Hazardous Waste and Tire Incineration in the US and Me：美国危险废物和轮胎焚烧和我.pptVIP

Hazardous Waste and Tire Incineration in the U.S. and Mexican Cement Industries: Environmental and Health Problems Cement Processing in US Cement Plants in Mexico Making Cement Entire process is environmentally destructive Extraction and mining of limestone Transportation of materials Combustion in kilns Toxic ash (cement kiln dust) Cement Kilns Very energy-intensive, especially wet kilns. Major air pollution sources, even when only burning fossil fuels. Worse when burning tires or hazardous waste. Cement Production Process Extraction of prime materials: limestone (70%) and other materials like clay, aluminum oxide, iron, shale and silica. Materials are ground and stored separately. Material is measured to achieve a specific combination, depending upon the type of cement desired, and ground to produce a very fine powder. Powder is pumped to silos, where the blend is standardized. The blend is placed in long, rotating kilns, where it is heated at high temperatures (approximately 1,500 degrees centigrade), causing chemical and physical reactions. This process where heat is used to break down the material is called “calcination.” A new material is formed, which is called pre-cement or “clinker,” which are composed of small balls about the size of a nut. The clinker is ground up, combined with gypsum and packaged. When this product – cement – is mixed with sand, stone, other materials and water, concrete is produced. The calcination process, turning the limestone into clinker in the kiln, is the fundamental step described above. This process requires a substantial amount of energy, provided by the burning of fuels, which are injected at the opposite end of the kiln, and it represents the major economic cost in cement production. Wet and Dry Process Kilns Wet Process (old process) Material ground using a rotating ball mill with water Resulting slurry is fed to rotary kiln Processing temperatures of 1450°C Uses more energy (burns more fuels) than dry process Dry P