Coke byproducts

Coke byproduct wastes. Coke, used in the production of iron, is made by heating coal in high-temperature ovens. Throughout the production process many byproducts are created. The refinement of these coke byproducts generates several listed and characteristic wastestreams. However, to promote recycling of these wastes, U.S. EPA provided an exclusion from the definition of solid waste for certain coke byproduct wastes that are recycled into new products. 

Coke production was formerly the most important demonstrated technology associated with the direct production of chemicals from coal. Industrial chemicals currently obtained in significant amounts as coke byproducts include benzene, toluene, xylene, naphthalene, anthracene, phenanthrene, phenol, ammonia, ammonium sulfate, sulfitr, and carbon dioxide. The vast majority of aromatics production from coal occurs in Eastern Europe, India, and Japan.75... 

Figure 16-25. Simplified fiow diagram of a coke-byproduct recovery plant. (Kroll and Barry, 1991)...

Naphthalene is adequately removed in the oil-washing operation for benzol recovery, and a separate naphthalene removal step is not required if benzol is recovered. This type of operation is shown in the overall coke byproduct recovery flow diagram (Figure 16-25) where residual naphthalene in the gas from the final cooler is removed by the light oil scrubber. However, in some cases it is advantageous to remove naphthalene in a separate step before the gas is processed for the removal of benzol and other impurities. This is usually accomplished hy oil washing. 

The main feedstock for catalytic reforming is heavy gasoline (80 to 180°C) available from primary distillation. If necessary, reforming also converts byproduct gasoline from processes such as visbreaking, coking, hydroconversion and heart cuts from catalytic cracking. 

The principal sources of feedstocks in the United States are the decant oils from petroleum refining operations. These are clarified heavy distillates from the catalytic cracking of gas oils. About 95% of U.S. feedstock use is decant oil. Another source of feedstock is ethylene process tars obtained as the heavy byproducts from the production of ethylene by steam cracking of alkanes, naphthas, and gas oils. There is a wide use of these feedstocks in European production. European and Asian operations also use significant quantities of coal tars, creosote oils, and anthracene oils, the distillates from the high temperature coking of coal. European feedstock sources are 50% decant oils and 50% ethylene tars and creosote oils. 

Coke The grinding characteristics of coke vary widely. Byproduct coke is hard and abrasive, while certain foundry and retort coke is extremely hard to grind. For certain purposes it may be necessary to produce a uniform granule with minimum fines. This is best accomplished in rod or bah mihs in closed circuit with screens. Hourly capacity of a 1.2- by 3-m (4- by 10-ft) rod mill with screens, operating on by-product-coke breeze, was 8.1 Mg (9 tons), 100 percent through No. 10 sieve, and 73 percent on No. 200 sieve power requirement, 30kW(40 hp). 

Out of the 900 million tons of coal produced in the United States for domestic purposes in 1992, about 34 million tons were used for coking [10]. The overw helmmg majority of coal is consumed by the electric utilities. Nevertheless, in 1990, the United States steel industry required about 23 million tons of coke which was produced by the byproduct recovery slot oven [15] For a typical blast furnace, this translates to 0 5 tons of coke per ton of iron metal. 

Coal-based pitches are predommantly byproducts of metallurgical coke operations in recovery-type coke ovens. The volatile products from the coke oven are recovered and processed, in simplest terms, into gas, light oils, and tar. The quantity and character of the materials are influenced by the type of coal charge, the design of the cokmg equipment, and the temperature and time profile of carboni2ation. Table 1 shows a typical yield of products from the... 

A typical modem phosphorus fumace (12 m diameter) can produce some 4 toniKs per hour and is rated at 60-70 MW (i.e. 140000A at SOOV). Three electrodes, each weighing 60 tonnes, lead in the current. The amounts of raw material required to make 1 tonne of white phosphorus depend on their purity but are typically 8 tonnes of phosphate rock. 2 tonnes of silica, 1.5 tonnes of coke, and 0.4 tonnes of electrode carbon. The phos rfKmis vapour is driven off from the top of the fumace together with the CO and some H2 it is passed through a hot electrostatic precipitator to remove dust and then condensed by water sprays at about 70 (P4 melts at 44.T). The byproduct CO is used for supplementary heating. 

From a practical standpoint, coal, because of its abundance, has received the most attention as a source for synthetic fuels. As early as 1807, a coal-gas system was used to light the streets of London, and until the 1930s, when less expensive and safer natural gas started to flow through newly constructed pipelines, gas piped to homes in the Eastern United States was derived from coal. Kerosene, originally a byproduct from the coking of coal tor metallurgical applications, can be considered the first synthetic lic -uid fuel made in quantity. But once crude oil became cheap and abundant, there was little serious research on synthetic liquid fuels in the industrial world until the Energy Crisis of 1973. The main exceptions to... 

In a cat cracker, a portion of the feed, mostly from secondary cracking and polymerization reactions, is deposited on the catalyst as coke. Coke formation is a necessary byproduct of the FCC operation the heat released from burning coke in the regenerator supplies the heat for the reaction. 

Catalytic coke is a byproduct of the cracking of FCC feed to lighter products. Its yield is a function of conversion, catalyst type, and hydrocarbon/catalyst residence time in the reactor. 

Raw materials for obtaining benzene, which is needed for the production of alkylbenzenes, are pyrolysis gasoline, a byproduct of the ethylene production in the steam cracking process, and coke oven gas. Reforming gasoline contains only small amounts of benzene. Large amounts of benzene are further produced by hydrodealkylation of toluene, a surplus product in industry. 

The characteristic times on which catalytic events occur vary more or less in parallel with the different length scales discussed above. The activation and breaking of a chemical bond inside a molecule occurs in the picosecond regime, completion of an entire reaction cycle from complexation between catalyst and reactants through separation from the product may take anywhere between microseconds for the fastest enzymatic reactions to minutes for complicated reactions on surfaces. On the mesoscopic level, diffusion in and outside pores, and through shaped catalyst particles may take between seconds and minutes, and the residence times of molecules inside entire reactors may be from seconds to, effectively, infinity if the reactants end up in unwanted byproducts such as coke, which stay on the catalyst. 

Produces strong, blocky coke having good reactivity. Involves low capital and running costs. Production process delinks with availability of markets for byproducts. Allows shut down without any detrimental effects to refractory. Produces hard coke for foundry. The process is characterized by simplicity. There involves no requirements of extra fuel for heating as in by-product oven practice. 

Heat (from coke oven gas, blast Coke oven gas and byproducts including coal tar, light oil, and... 

Benzene releases in byproduct recovery operations Naphthalene residues generated in the final cooling tower Sulfur and sulfur compounds recovered from coke oven gas Wastewater from cleaning and cooling (contains zinc, ammonia still lime, decanter tank tar, or tar distillation residues)... 

About 100 gal of process wastewater is typically generated from 1 t of coke produced.15 These wastewaters from byproduct coke making contain high levels of oil and grease, ammonia nitrogen, sulfides, cyanides, thiocyanates, phenols, benzenes, toluene, xylene, other aromatic volatile components, and polynuclear aromatic compounds. They may also contain toxic metals such as antimony, arsenic, selenium, and zinc. Water-to-air transfer of pollutants may take place due to the escape of volatile pollutants from open equalization and storage tanks and other wastewater treatment systems in the plant. 

Conventional wastewater treatment techniques consist of physical/chemical treatments, including oil separation, dissolved gas flotation, and ammonia distillation (for removal of free cyanides, free sulfides, and ammonia) followed by biological treatment (for organics removal) and residual ammonia nitrification. Almost all residuals from coke-making operations are either recovered as crude byproducts (e.g., as crude coal tar, crude light oil, ammonium sulfate, or other sulfur compounds)... 

In this process EAF dust, other zinc-bearing wastes, recycled materials, coke or coal, lime, and silica are mixed and fed to a rotary furnace. The zinc and other volatile nonferrous metals in the feed are entrained in the furnace off-gas and are carried from the furnace to an external dust collection system. The resulting oxide (zinc calcine) is a crude zinc-bearing product that is further refined at zinc smelters. A byproduct of the process is a nonhazardous, iron-rich slag that can be used in road construction. Solidification technologies change the physical form of the waste to produce a solid structure in which the contaminant is mechanically trapped. 

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