U.S. heat recovery coking and combined power generation units

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This post was last edited by angryant on 2017-7-22 at 13:08. The non-recycling coking and combined power generation facility of Inner Continental Steel Company – The world’s first non-recycling coking and combined power generation facility is being built at the Indiana Harbor steel plant of Inner Continental Steel Company, with an annual production capacity of 1.33 million tons of coke. The coking plant consists of 4 non-recycling coke ovens, with 67 chambers per oven, for a total of 268 chambers. The type of these ovens is the same as that of the 143-chamber non-recycling coke ovens at the Fansheng plant of Yangguang Coal Coke Company. The combined power generation unit is capable of producing 87,000 kW of steam and electricity; coke is supplied to Blast Furnace No. 7 at an inland plant for the production of 9,000 tons of pig iron per day, with a total investment of 350 million dollars in this facility. The design for this project began at the end of 1996, construction started on January 14, 1997, and it was completed and put into operation on June 30, 1998. 1 Coke ovens: The non-recycling coke-making technology used at the Indiana Harbor Coke Plant is a patented technology of Sunshine Coal Coke Company. Compared with other coking processes, it has advantages such as environmental cleanliness and low costs. Since non-recycling coking is carried out under negative pressure, all the tar and gas are burned completely inside the furnace; as a result, by-products such as ammonia, naphthalene, benzene, and sulfur that are produced in conventional coke ovens are also burned away. However, this method provides a direct heat source for the coking process, and it converts the sensible heat of the waste gases into steam and electricity. The Jewell-Thompson type non-recycling coking unit at the Fan Sheng Coking Plant of Jewell Coal & Coke Company, which is affiliated with Sunshine Coal & Coke Company, is the only such unit in use in the United States. Its special heating channels are located at the bottom of the coke ovens, and since it came online in 1962, it has produced 600,000 tons of coke per year. The coke oven under construction at the Habo coking plant is an improved version of the coke oven used at the Fansheng plant; Figure 1 shows the structure of the coke oven at Fansheng plant. The oven is 3.66 m wide and 14.33 m long, with a coal loading capacity that can vary between 25 and 50 tons. The 4 coke ovens at the Habo plant are located adjacent to Blast Furnace No. 7 of the Neiland Steel Company. The plant covers an area of 152m in width and 800m in length. For this entire project, 9.2 million refractory bricks, 46,000 cubic meters of concrete, 13,000 tons of steel, and 5,000 tons of rebar are required. To ensure construction in winter, each coke oven requires a construction shed that is 9.14 m high and has an area of 18.29 × 320.04 m2, with 800 skilled workers employed for the work. The height of the coke ovens at the Habo plant is slightly lower than that at the Van Sant plant, with a coal loading capacity of 45 tons per carbonization chamber. When the coal loading amount is 42 tons, the coke production cycle time is 48 hours. http://www.meijiaohua.com/WebUpLoadFile/ArticlePhoto/200861256210049.gif Figure 1: Structure of the Jewell-Thompson type coke oven without recycling. This coke oven uses a relatively small number of brick types, namely 23. The carbonization chambers are constructed using silica bricks at the bottom of the furnace, where the furnace floor is made of silico-alumina bricks; the side walls are also made of silica bricks. The arch roof is composed of silica bricks, thermal insulation castables, ceramic fibers, and further thermal insulation castables. The furnace door lining is made of thermal insulation castables and thermal insulation ceramic blocks ； The bottom plate of the coke oven is made of insulated refractory bricks and cast refractory materials; Figure 2 shows the shape of the coke oven door. Coke ovens use conveyors for horizontal coal charging; therefore, the coal-charging and coke-pushing machine is different from the locomotives used in conventional coke ovens. As it has both coal-charging and coke-pushing functions, it is installed on the machine side of the coke oven. During the coal loading process, the coal is conveyed from the belt conveyor located at the top on the machine side to a horizontally arranged coal loading conveyor with water cooling. This coal loading conveyor extends into the carbonization chamber, loading the coal to the specified height while moving forward until it reaches the coke side; when the conveyor retracts, it compresses the coal flat. As soon as the coal conveyor was retracted, the furnace door was closed to start coking. The primary air for combustion enters the furnace top space through air holes in the furnace door; these holes are equipped with flaps that control the amount of air supplied, thereby enabling temperature control. Part of the combustion exhaust gases enter the heating flue at the bottom of the furnace through the downward air ducts in the side walls; the heating flue is also equipped with flap valves to control the amount of air entering, ensuring complete combustion of the exhaust gases. The gases resulting from combustion then enter the common gas collection duct through the upward pipes in the furnace walls. Here, the unburned remaining volatiles can be further burned. Figure 2: Door of a coke oven without recycling. The carbonization chamber is heated by heat sources from two sources: one is the introduction of controlled primary air into the carbonization chamber for combustion ； Secondly, some of the combustion exhaust gases burn in the bottom heating channel, heating the coal from below through the refractory bottom plate; the temperature of the coke cake at the end of coking can reach 1150°C. During coke pushing, the furnace door is opened, and the coke is pushed into the coke quenching car using a coke pusher; coke quenching is carried out using the conventional wet method, with the coke quenching car moving slowly while receiving the coke. The head of the coke pusher is horizontal and much larger than that of conventional coke oven pushers. http://www.meijiaohua.com/WebUpLoadFile/ArticlePhoto/200861256078393.gif Figure 3: Flow diagram of the combined power generation unit. 2. Processes and equipment for recovering thermal energy: The coke oven flue gas at 980°C is used to recover thermal energy in 16 waste heat boilers (4 boilers per coke oven). The rated steam production capacity of this system is 450 t/h; each boiler is capable of producing steam at a pressure of 5.72 MPa and a temperature of 400°C, with a steam output of 26.31 t/h. The temperature of the flue gas leaving the boilers is 180°C, and approximately 82% of the sensible heat is converted into steam. Steam from 16 waste heat boilers is collected in a common main pipe and then sent to the turbine generator. The flue gas exiting the waste heat boilers merges together and enters a common pipeline, where it is sent to a desulfurization unit for treatment. Figure 3 shows the process flow of the combined power generation plant. The output power of the turbogenerator at full load is 94,000 kW, and the steam pressure at the back pressure of the condenser is 0.01 MPa. The turbogenerator consists of a single-cylinder turbine that automatically extracts condensate, which is connected to a fully enclosed water-air cooled synchronous generator; the steam leaving the turbine is sent to Innerland Steel Company. The flue gas desulfurization unit is of the lime milk type, equipped with 2 fully spray-type absorption towers, followed by an air-backblowing bag filter for dust collection; it is capable of removing over 70% of the sulfides and 99.5% of the suspended particles from the flue gas. The rated handling capacity of the bag filter dust collector is 24,400 m3/min, with 24 sets in operation and 8 sets in standby. Two exhaust fans operating at full capacity maintain a negative pressure in the system, with waste gases being discharged into the atmosphere through the same chimney. The entire flue gas desulfurization and steam turbine power generation system was designed, manufactured, and installed by Fluor Company. Figure 4 shows a panoramic view of the 67-chamber coke oven without recovery system that is under construction. Figure 4: Panoramic view of the Habo plant under construction, featuring coke ovens without recycling systems