ASSIGNMENT PRESENTATION APPLIED CHEMISTRY ii MANUFACTURE OF METALLURGICAL COKE ON February 10, 2011PRESENTED BY: (10A247 – 10A253) SHREERAMAN L SHYLENDRAN R SIDDHARTH NARAYANAN C SIVA SANKAR NATESAN SUDALAI MUTHU M SUGEEBAN S SUKI M A 10A247 10A248 10A249 10A250 10A251 10A252 10A253 .5 m high. Beehive’s Oven Method: It is the earliest and most economical method for the manufacture of metallurgical coke. It has two openings one at the top for the charging of coal and the other at the side through which the coke formed is removed.MANUFACTURE OF METALLURGICAL COKE Metallurgical coke can be made by two methods: o Beehive’s oven method o Otto Hoffman’s by-product oven method. It is about 4 m wide and 2. Construction of Beehive oven: The Beehive’s oven is dome-shaped structure made of bricks. This side opening also acts as inlet for air supply as and when desired. Combustion is allowed to proceed in a gradually diminishing supply of air so that slow carbonization from the top layer to the bottom layer. Some air is supplied in from the side opening and the coal is ignited.Process: From the top opening.6-0.75 m thick coal. . takes place. Limitations of Beehive’s oven method: Most of the volatile matter having plenty of valuable chemicals escapes out into the atmosphere as waste. This also creates problems of air pollution. the coal is charged to give a layer of about 0. The yield of coke is about 60-80% of the coal charged and averages about 5-6 tonnes of coke per oven. This partial combustion furnishes heat which melts or fuses the coal and the evolved volatile matter burns at the partially closed side opening. This process of carbonization completes in about 3-4 days. The hard metallurgical coke formed is quenched with water and taken out from the discharge side opening. It is possible to make this process more economical by operating a series of beehive’s ovens in such a way that hot gases escaping from an oven are utilized to ignite the charge in the adjacent oven. Otto Hoffmann’s By-product Oven Product Method: Construction: The by-product coke oven consists of a number of narrow silica chambers.45m wide. . These chambers are erected side.by-side with vertical flues in between them to form a sort a battery.40—0. a gas off lake (for the removal of volatile matter) and a refractory line cast iron door at each end (for discharging coke). Each chamber is provided with a charging hole at the top (for charging the coal). Each chamber is about 10-12meter long 3-4 meter high and 0. The contraction at lower temperatures (around 500OC) corresponds to the loss of volatile matter in the form of gas and tar. The coals adjacent to the oven walls get heated and the plastic zone formed in the case of caking coals moves away from the walls towards the central zone. while that at 750OC corresponds to the solidification of the plastic mass of coal. . which are heated from both sides because coal is poor conductor of heat. The ovens are heated to 1200OC by burning gaseous fuel (like producer gas) and usually employing a regenerative principle to achieve as economical heating as possible (utilizing the waste flue gases for heating the checker-work of bricks). The coking is accompanied by a contraction in volume. the semi coke at the outer zones would have been converted into coke. The plastic zone through mobile is such a bad conductor of heat that while the inner zones are getting heated. These charging holes are then closed tightly to cut off the supply of air. This has been attributed to dehydrogenation leading to aromatization in the coal structure.Theory: Coking processes are always carried out in narrow retorts or ovens. Working: Finely crushed coal is introduced through the charging holes at the top of chamber. The heating is continued. When carbonization process is over. and non reactive. “dry quenching” can also be done and it offers advantages. The flue gases produced during combustion. graphitized. the red hot coke is placed in a chamber and cooled by passing inert gases from boilers (like N2). In place of wet quenching. The inert gases are then circulated to boilers where they generate steam. both the fuel and combustion of air are preheated. until all the volatile matter has escaped. before escaping to chimney. The coke produced by dry quenching is cheaper. While the flue gases leave their acquired heat to one generator. a massive ram pushes the red hot coke into a truck. because the coke produced is stronger. pass on their sensible heat to one of the two sets of checker brick-work. It takes about 11-18 hours. for carbonization of a charge of coal. In dry quenching. The inlet gases are passed through the heated checker brickwork. . which thus serves to preheat the inlet gases. denser. drier and contains lesser dust than wet quenched coke. blast furnace gas). It is then quenched by spraying water (wet quenching). It is enough if air is preheated in the case of a fuel (coal gas) with high calorific value but if the calorific value of the fuel is low (producer gas. the other generator is used for preheating the incoming air. until this brick work has been raised to a temperature of about 1000OC. Here ammonia goes into solution as ammonium hydroxide. It mainly consists of ammonia. moisture. Recovery of Naphthalene: o The gases are then passed through another tower in which water is sprayed at lower temperature when naphthalene gets condensed. naphthalene. Recovery of ammonia: o The gases from the chamber are then passed through in which water is sprayed. . Recovery of Hydrogen Sulphide: o The gases are then passed through a purifier. packed with moist Fe2O3. Recovery of Benzene: o The gases are then sprayed with petroleum when benzene and its homologues are recovered. benzene. tar. etc. hydrogen sulphide. Here H2S is retained. Here dust and tar get collected in a tank below. Recovery of tar: o The gas is first passed through a tower in which liquid ammonia is sprayed.Recovery of by products: The gas is coming out from the oven is known as ‘coke oven gas’. o The ammonia is used again. which is heated by steam coils to recover back the ammonia sprayed. Hydrogen Sulphide: . which are the starting materials for obtaining numerous drugs. o Ammonia is removed by absorption in water in scrubber or dissolved in dilute sulphuric acid to form ammonium sulphate which is used as a fertilizer. may cause blocking of the gas pipes. so that Fe2O3 is regenerated. the purifier is exposed to atmosphere. toluene and xylenes: o These are industrially important solvents and raw materials for plastics. creosote oil.o After sometime. etc. toluene. These are improved from the coal gas mainly because of their utility value and also to improve the quality of the gas. Significance of recovery of by-products: Coke-Oven gas contains large number of valuable impurities. present in tarry vapours. Naphthalene: o Naphthalene and other higher aromatics. perfumes and explosives. naphthalene. Tar on fractional distillation gives benzene. Benzene. when all Fe2O3 is changed into Fe2S3. Tar: o Tar pitch is used for road making and for preserving timber. Ammonia: o The removal of ammonia from the gas is necessary to avoid the blockage of gas pipes by ammonium carbonate. o Hydrogen Sulphide and other sulphur compounds present in coal may give a foul smell (offensive odours) to the gas. Sulphur compounds may get oxidized to sulphur dioxide and finally to sulphuric acid which promotes corrosion. Thank you .