The invention relates to a process for avoiding the dissipation of unpurified flue gas from the coke oven process during the stoppage times of individual waste heat boilers, wherein said waste heat boiler serves for producing steam or hot water during the operation of at least one coke oven chamber, and the process makes it possible to keep the coke oven chambers of a battery of coke ovens hot, wherein the coke oven chambers are kept hot not by coking but by externally heated burners, the pollutant emission of which is low owing to the manner of the heating, such that a reduced emission of pollutants is effected during the stoppage. The invention also relates to an apparatus for keeping coke oven chambers hot during the stoppage of a waste heat boiler, said apparatus comprising coke oven chambers which comprise at least one externally heated burner, where “externally heated” is to be understood as meaning in particular a gas-heated or oil-heated burner.
During the operation of coke oven chambers, it is necessary to overhaul or clean the so-called waste heat boiler from time to time or at regular intervals. In normal operation, the waste heat boiler serves for cooling the flue gases from at least one coke oven chamber and for obtaining steam or hot water from the heat which is thus obtained. These waste heat boilers are often also referred to as recuperators and the associated technology is referred to as heat-recovery technology. During an overhaul or cleaning, however, these waste heat boilers have to stop, and are therefore no longer available for cooling the flue gas. It is often the case that the coking process in the coke oven chamber is continued, and therefore the hot flue gases, which are often laden with a considerable quantity of pollutants, have to be emitted into the atmosphere in an unpurified state. This is undesirable. The cooling down of the coke oven chamber for overhaul or cleaning purposes results in the refractory structure of the coke oven chambers being damaged, and this is not carried out for this reason.
There is therefore a need to find a process with which the coke oven, chambers of a coke oven bench can be kept hot without pollutant-containing coking gases being undesirably emitted. Coke oven chambers are often combined to form groups, since the cycle of charging, coking and emptying of coke oven chambers is not continuous and is therefore distributed over a plurality of coke oven chambers. Groups of coke oven chambers are also referred to as coke oven chamber benches. Typical coke oven chambers of the heat-recovery type use the coking gas obtained during the coking for combustion and therefore for producing heat.
The completely combusted flue gas thus obtained, which can be taken from the combustion chamber, is guided into a collection line, which is placed transversely with respect to the coke oven chambers, receives the hot flue gases from each coke oven chamber and guides said gases via an export line into the waste heat boiler or boilers. The waste heat boilers cool the flue gas by indirect heat exchange for producing steam or hot water, such as to give a cooled waste gas. This is often guided through a waste gas purification system. An apparatus for removal by suction and for producing a negative pressure in order to suck the combustion air into the oven chambers is arranged downstream of the waste gas purification. If the waste heat boiler is no longer being used for cooling the flue gas, it is also the case that the waste gas purification system is no longer available. During stoppage of the waste heat boilers, however, the coke oven chambers continue to operate, for the reasons mentioned, and the flue gas is conducted away via a directly connectable flue gas chimney, such that a considerable quantity of pollutants which are present in the completely combusted coking gas passes into the atmosphere.
U.S. Pat. No. 4,045,299 A describes an arrangement of coke oven chambers with coke oven chamber side walls, coke oven chamber front doors, charging openings in the roof and a coke oven chamber floor, onto which the coal cake for coking is charged. Secondary air soles are located underneath the floor, and these are connected via channels in the sides of the coke oven chamber to the gas chamber above the coke cake. In turn, the secondary air soles are connected to a post-combustion chamber, which is equipped with externally heated burners, as a result of which uncombusted residual gases in the coking gas can be completely combusted before they are introduced into the recuperator. If need be, the post-combustion chamber can be supplied with coking gas from the gas chamber above the coke cake, such that the flue gas is always completely combusted and is provided with a temperature which is suitable for flue gas combustion. However, the structure serves for ensuring complete combustion at a minimum temperature level, not for heat retention.
Rick Waddell et al. describe a process in which a number of coke oven chambers are combined to form a coke oven bench for producing coke and this bench is connected in each case in pairs or multiply to a waste heat boiler, wherein an emergency chimney is located upstream of the waste heat boiler and a waste gas purification system is located downstream of the waste heat boiler, and the hot purified waste gas is used via the waste heat boiler for generating electricity. The process does not disclose any possible ways of avoiding a continued flow of pollutant-containing flue gas into the atmosphere when the waste heat boiler is shut off. In addition, the process does not disclose any possible way of keeping coke oven chambers hot during the stoppage of the waste heat boiler.
In the article “Sun Coke Company's heat-recovery cokemaking technology high coke quality and low environmental impact”, Revue de metallurgie, cahiers d'informations techniques, Revue de metallurgie, Paris, Fr. vol. 100, no. 3, pages 233-241, dated Mar. 1, 2003, D. N. Walker et al. describe a novel system for producing coke which produces coke proceeding from various types of coal, wherein the coke has a defined stability and a defined proportion of volatile constituents depending on the type of coal used, and the system consists of coke oven chambers, which comprises a coke oven chamber with downcomer channels, an oven floor, a coke oven sole, upwardly directed flue gas channels, a flue gas channel arranged the coke oven chambers, an emergency chimney, a waste heat boiler with a secondary electricity generating unit, and a waste gas purification system with a downstream waste gas chimney. The system described in the article does not disclose any possible way of continuing the coking cycle during the stoppage of a waste heat boiler without conducting pollutant-containing flue gas into the atmosphere.
WO 01/18150 A2 describes a process for producing coke using a system for recovering energy with low investment costs at emission levels which lie well below permissible waste gas standards, wherein this system is equipped with a waste gas channel which has inlets for the admission of tertiary air in order to allow for complete combustion of the combustible constituents, such that the waste heat boilers receive an influx of pollutant-free waste gas, and the production process proceeds with low emission levels and good environmental compatibly, and at the same time electrical energy is produced at low cost per kilowatt hour. The article does not describe any additional burners in the coke oven chambers for heat retention or continued production of hot and pollutant-free flue gas during stoppage of waste heat boilers.
In their article “Sesa Energy Recovery Ovens”, Ironmaking Conference Proceedings 2001, P. F. X. D'Lima et al. describe a process for producing coke from a system for producing coke in accordance heat-recovery process, which comprises 84 coke oven chambers in two batteries each of 42 coke oven chambers, wherein the emissions are kept low by the use of low-sulfur type of coal, and an additional admission of tertiary air ensures that the carbon monoxide content of the waste gas is low, and an excess oxygen content of above 6% is present in the waste gas, such that all the particles in the waste gas are combusted. The article does not describe any additional burners in the coke oven chambers for heat retention or the continued production of hot and pollutant-free flue gas during the stoppage of the waste heat boilers.
The problem which arises during the stoppage of waste heat boilers is the cooling of the coke oven chambers. Coke oven chambers are ordinarily constructed from materials which have to withstand high temperatures but, owing to their properties, can be damaged upon cooling. Certain materials can change their properties at relatively low temperatures, and therefore these are unusable for the desired purpose.