Iron Steel And Metal Finishing Operations Summary

Essay, Research Paper

Iron, Steel and Metal Finishing Operations SummaryBy:Kevin WorleySouthwestern Oklahoma State University Production, forming, and cleaning of steel products creates several waste-outputs. These outputs range from the benign to RCRA regulated hazardous waste. Listed below are the steps associated with a metal product from ore to finished product, detailing the various wastes. Production of CokeConverting iron ore into steel involves using coke, limestone, and ore to create the reduced metal. Cokemaking is one of the industry s greatest environmental concerns. Quench water, coal, and heat are used to produce coke. This creates various byproducts, mainly from the coal. Several of these outputs are RCRA regulated as hazardous wastes from specific industries and are designated with a K’. Materials that have a hazardous characteristic (ignitability, corrosivity, reactivity, or toxicity) are designated with a D’. The following list describes the results of producing coke. Process residues from coke by-product recovery (RCRA K143, K148) Coke oven gas by-products such as coal tar, light oil, ammonia liquor, and the remainder of the gas stream is used as fuel. Coal tar is typically refined to produce commercial and industrial products including pitch, creosote oil, refined tar, naphthalene, and bitumen. Charging emissions (fine particles of coke generated during oven pushing, conveyor transport, loading and unloading of coke that are captured by pollution control equipment). Ammonia, phenol, cyanide and hydrogen sulfide Oil (K143, K144) Lime sludge, generated from the ammonia still (K060) Decanter tank tar sludge (K087) Benzene releases in coke by-product recovery operations Naphthalene residues, generated in the final cooling tower Tar residues (K035, K141, K142, and K147) Sulfur compounds, emitted from the stacks of the coke ovens Wastewater from cleaning and cooling (contains zinc, ammonia still lime (K060), or decanter tank tar (K087), tar distillation residues (K035)) Coke oven gas condensate from piping and distribution system; may be a RCRA characteristic waste for benzene. These products are produced because water is used to quench the coke; this contaminates the water with the various residues listed above. Iron Making In the iron making process iron ore, coke, and Limestone are fed into the blast furnace heated air is forced through the iron ore by bustle pipes located around the circumference of the blast furnace. Carbon dioxide from the coke reduces the ore into iron. The acid part of the ore reacts with limestone and creates slag, which is drawn off periodically. The slag contains a fair amount of sulfur and other unwanted impurities. Sulfur dioxide and hydrogen sulfide are driven off from the slag.Slag is the largest byproduct of iron production. Reheating and attempting to capture any left over metals reclaims slag. The remainder is considered hazardous waste. Blast furnace flue gas is cleaned and is used to supply heat to other processes in a plant or used to make steam to preheat air coming into the furnace. Sludge is also produced in the process. Wet scrubbers are used to remove fine particles. Wet scrubbers and sludge are another land disposed waste.

SinteringSintering is the mixing together of the leftover pollutants resulting of ironmaking (sludge iron ore fines, pollution control dust, coke breeze and flux). The pollutants are ignited and fused together to form an agglomerate. The agglomerate is then added to the next batch of iron ore in the blast furnace. Particulate matter is created in the operation but is picked up by the air pollution control equipment. Steel making using an Electric Arc FurnaceElectric arc furnaces are used when scrap metal is used to make steel. The scrap metal is heated by electric power. Since it is melted by electric power there is no need to make coke so there are less environmental concerns. During melting phosphorous, silicon, manganese, carbon and other materials are oxidized, and a slag containing these materials forms at the top. Oxygen is used to decarburize the molten steel and provide energy. Slag, metal dust and gases are produced when using this process. The gases and dust are cleaned either by the wet or dry system. The primary concern with the dust is that it contains lead and cadmium. Twenty to forty pounds of dust are produced with each ton of steel. FormingThe steel now needs to be shaped into a usable form. This involves several more steps and has its own pollution concerns. In order to form metal; for example, a spoon, the metal has to be shaped into sheet metal. This is accomplished by using rolling units. The most common operation to produce sheet metal is to used cold forming methods. The process is to generally reduce the cross-sectional area incrementally until the steel is at the desired thickness. The metal must be lubricated and annealed to keep the it ductile. This results in sludge for waste treatment plants. Another source of waste is the grindings from resurfacing of the rollers and disposal of worn out rollers. FinishingFinishing is the process of making the surface of the metal part suitable for painting, resistant to corrosion, or removal or scale, rust, oxides and other unwanted substances that will degrade the final product. The waste products derive from spent pickle liquor. Usually sulfuric acid is used as a pickle liquor to remove the oxides, rust and scale. This spent pickle liquor can be listed as hazardous waste (RCRA K062) if it contains residual acidity and high concentrations of metals. After pickling, the steel then passes through water rinses that becomes waste after use due to the presence of oils, metals and an acidic pH. The steel can also be coated with various materials, either paint or metallic coatings. The metallic coatings include: zinc (galvanizing), tin, chromium, aluminum, and terne (lead and tin). The coating can be applied by hot-dipping, spray coating, electroplating, or metal cladding.