GB2185993A

GB2185993A - Cogeneration method for producing coke, and electric power from steam

Info

Publication number: GB2185993A
Application number: GB08700182A
Authority: GB
Inventors: David Horace Archer; M Mushtaq Ahmed
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1986-01-31
Filing date: 1987-01-06
Publication date: 1987-08-05
Also published as: BE906160A; DE3701875A1; ZA87184B; IN167374B; JPS62209193A; GB8700182D0; GB2185993B; IN166708B; AU6797587A; AU586910B2; AU6760087A; AU590815B2

Abstract

In a cogeneration method coke and electrical energy are generated wherein a non-recovery coke oven is used, with addition of air to its coking chamber and to downcomers to the flue, and with an incineration chamber to effect full combustion of combustible products in the gases produced. Means are provided to remove sulfur dioxide from the hot gases prior to use of the hot gases in a steam generation unit wherein steam is produced for electric power production before the cooled combustion gases are discharged. The discharge gases are low in nitrogen oxide and sulfur dioxide and environmentally acceptable.

Description

SPECIFICATION Cogeneration method for producing coke, and electric power from steam The present invention is to a method for the cogeneration of coke, and electric powerfrom steam, that provides efficient heat recovery and environmentally acceptable discharge gases.

Interest has risen in the developing and implementing oftechnologiesfor more efficient use of coal in an environmentally acceptable and economic manner. Thecurrentuse as well as the proposed environmental regulations have significant effect on the use of coal, both as a power generation fuel and as a raw material for metallurgical coke. The coke industry is looking for environmentally acceptable coke production technology.

One type of such technology is the non-recovery coke making process developed by Pennsylvania Coke Technology Inc., such as described in United States Patents 3,912,597; 4,045,299; 4,111,757 and 4,124,450, the contents of which four patents are incorporated by reference herein. U.S. 3,912,597 teaches a nonrecovery type coke oven having a flue below the oven where combustible gases from the coke oven are passed through the flue and then through an associated ignition chamber prior to discharge of the gases to the atmosphere.An improvement over that smokeless and non-recovery type of coke oven is described in U.S. 4,045,299 wherein an independent heating means, such as a fuel burner, and a secondary air source are provided to maintain the ignition chamber at high temperatures, with temperature sensing means provided to actuate the burner and air source. Afurther improvement is described in U.S. 4,111,757 where a quenching means is provided on the coke side of the oven and a smoke hood provided over the quenching means, with smoke and effluent from quenching passed through a separate, closeable, passageway through the ignition chamber to convert the smoke and effluents produced during quenching to clean hot air.In the method described in U.S. 4,124,450, primary air to the coking chamber is decreased during coking and secondary air is fed to downcomers to the sole heating fluid, and the ignition chambertemperature controlled, with a negative draft pressure of between 0.15 and 0.17 inch water gage being maintained in the coking chamber by means of a stackfor discharge.

It is a further object of the present invention to provide a system which combines a non-recovery coking process with electric power production in an environmentally acceptable manner.

With this object in view the present invention resides in a method for the cogeneration of coke, and electric power by steam, wherein coal is heated in a non-recovery coke oven having a coking chamber and downcomers to a flue beneath the coking chamber, while,a negative pressure is maintained therein, to produce coke and hot combustion gases, the combustion gases containing nitrogen components and sulfur dioxide, characterized in that air is introduced to the coke oven chamber, and the downcomers, in an amountto maintain a reducing atmosphere not only in the oven chamber but also in the flue; from which the hot combustion gases containing combustible material are discharged to an incineration chamber, in which the combustible material in the hot combustion gases is then combusted with excess air at a temperature that minimizes formation of nitrogen oxides from nitrogen components in the hot combustion gases, the hot combustion gases are then contacted with a desulfurizing agent to remove sulfur dioxide therefrom and the hot desulfurized combustion gases so produced are passed to a steam production unit in which steam is generated by heat transfer from said hotdesulfurized combustion gases, which steam is used to produce electric power, and the desulfurized combustion gases after cooling by passage through the steam production unit are discharged to the atmosphere.

In one embodiment, the desulfurizing unit is a fluid bed desulfurizing unit located between the ignition chamber and the steam production unit, while in another embodiment, the sulfur dioxide is removed from the hot combustion gases by introduction of a desulfurizing agent to the ignition chamber with particulates removed from the hot combustion gas stream before entry into the steam production unit by the use of high temperature filters, such as ceramic filters.

The present method uses staged addition of air to the coke oven chamber and downcomers to maintain a reducing atmosphere therein and a temperature in the ignition chamber is maintained that minimizes the production of nitrogen oxides from nitrogen components in the hot combustion gases. The sulfur dioxide is removed from the hot combustion gases to produce an environmentally acceptable discharge gas to the atmosphere. Coke quenching is effected by steam at high coke temperatures and followed by water at low coke temperatures with hydrogen and carbon monoxide produced during steam quenching uses as afurther heat source in the ignition chamber.

The invention will become more readily apparent from the following description of a preferred embodimentthereofshown, by way of example only, in the accompanying drawings, wherein: Figure 1 schematically illustrates the integrated system and method for coke production and electric energy production from steam ofthe present invention; and Figure2 schematically illustrates another embodiment of the integrated system and method of the present invention wherein desulfurization of the hot combustion gases is effected by introduction of an agent to the ignition chamberforthe hot combustion gases.

Referring now to Figure 1, the present cogeneration system 1 is schematically illustrated. A non-recovery coke oven 3 has a coking chamber5which is operable under a slight negative pressureforcoke manufacture in a reducing environment. Coal isfed to the chamber Sthrough line 7. Airis introduced intothecoking chamber 5through a door9, or other entries along the length of the oven, through line 11, with the air introduction controlled so as to provide a reducing environmentwithin the coking chamber5. In the coking chamber5,the volatiles from the coal charge 13 are partially combusted to produce coke.The hotcombustion gases and volatiles produced in the coking chamber 5 are discharged therefrom through line 15to downcomers 17 and then through line 19to sole flues 21 beneath the coking chamber 5. Controlled air introduction to the downstream 17 is effected by passage of airfrom line 23 to the downcomer 17 to maintain a reducing atmosphere within the downcomers.

The staged addition ofairtothecoking chamber 5 and the downcomers 17 maintains a reducing atmosphere therein and minimizes the production of nitrogen oxide gases in the hot combustion gas that is produced during coking of the coal. The reducing atmosphere converts the nitrogen oxides (N Ox) formed by oxidation of nitrogen compounds in the coal, during coking, to nitrogen (N2) and combustion products such as carbon monoxide and water. The final lower combustion temperatures achieved by staged air admission interspersed with the transfer of heat to the coke oven minimizes the formation ofthermal NOx by the reaction: N2 + 02 < 2NO when ultimately the addition of excess air provides residual 02.

The hot combustion gases inthesoleflue 21 heatthe coal 13 contained in the coking chamber5 and are than passed through line 25to ignition or incineration chamber 27. In incineration chamber 27the combustible materials, volatiles and combustion gases, are combusted with air introduced thereto through line 29.

Excess air is introduced through line 29 into the incineration chamber so asto effect combustion of all of the coal volatiles in the hot combustion gases while minimizing the formation of thermal NOx.

Thermal energy for heating the coal and coking is transmitted through the oven walls from the downcomers 17, fromtheflue 21, and from the incineration chamber27.

Hot combustion gases from the incineration chamber27 are passed through line 31, which may contain an auxiliary burner33, to a means 35 for removing sulfur dioxide therefrom and a means 37 for producing steam by heattransferfrom the hot combustion gases following the removal ofthe sulfur dioxide.

In a preferred embodiment of the present invention, the means for removing sulfur dioxide from the hot combustion gases comprises a fluidized bed type gas desulfurizer 39. With the use of a fluidized bed desulfurizing unit, a superheater 41 is provided in conjunction with the means 37 for producing steam. The gases atthis pointare ata high temperature (790-1 1200C), suitableforsulfurcapture by a bed of alkaline earth metal absorbent particles, such as limestone or dolomite, of a mesh size of about4-100 mesh (US Standard Sieve) in diameter.In such desulfurization, by-products produced would include granular calcium sulfate or gypsum, which can subsequently be used as a building material or a raw material for cement production.

Solid sulfur absorbents are fed to the fluidized bed desulfurizing unit 39 through line 43 and spent material discharged therefrom through line 45. Solid particulates originating both in the coke oven units and in the fluid bed desulfurization unit are discharged from the desulfurization unitthrough line 47 and are removed from the hot combustion gases in initial separators, such as a cyclone 49. Separated particulates are returned to the desulfurization unit through line 50 and the solid-free hot combustion gases are then fed through line 51 to the means for producing steam 37.

A preferred means for producing steam 37, as illustrated, is a waste heat boiler 53 that has a high pressure evaporator 55 which produces a high pressure steam flow to line 57. A low pressure evaporator 59 is also provided in the waste heat boiler 53 which produces a low pressure steam flow to line 61. Boilerfeedwateris fed to the low pressure evaporator 59through line 63 having a directfeedwater heater 65 thereon which receives a portion of the low pressure steam flow through line 67, then to the high pressure evaporator 55 through line 61,to a pump 69, and through high pressure economizer coils 71 in the boiier system.The exhaust gases from the waste heat boiler are discharged therefrom through line 73.The high pressure steam flow in line 57 is passed through the superheater 41 that is positioned in line 31 between the incineration chamber 27, and the fluid bed desulfurization unit 39, with the superheated steam, heated further in coils 75 by the hot combustion gases, discharged through line 77 to means 79 for producing electric power from the steam, such as a steam turbine generatorfor production of electric power. The sensible heat in the exhausted combustion gas leaving the means to produce steam 37, in line73, can be used to preheat and dry coal being fed to the coke oven. The hot gases from line 73 are directed to a coal drier 81 to which coal is charged through line 83 and from which dry coal is discharged to line 7 for introduction into the coking chamber5.

Preferably, a fluidized bed drier is used which allows efficient heat transfer and temperature control, without excessive heating of coal particles that may result in volatiles release. The exhaust gases, environmentally acceptable, are then discharged to the atmosphere through line 85.

From the coking chamber5, hot coke is discharged through line 87 and must be cooled to acceptable temperatures. The present invention provides means for quenching the coke 89, using a steam and water quench. The hot coke, discharged through line 87 is passed to a coke quencher 91, wherein steam through line 93 is first contacted with the hot coke to cool the coke from its highest temperature (131 50C) to atemperature of about800 C by both transfer of sensible heat and the absorption of heat bythesteam-coke reaction: H2O+C#H2+CO.

The carbon monoxide (CO) and hydrogen (H2) produced during steam quenching ofthe hot coke are directed by line 95 to the incineration chamber 27 for combustion so as to provide additional energy to the hot combustion gases.

After the hot coke has been cooled to a temperature below about 800"C, where the steam-coke reaction becomes very slow, water is then introduced through line 97 to further cool the coke by the transfer of sensible heat and the latent heat of steam produced. Coke, following quenching by steam and then bywater is discharged from the coke quencher91 through line 99.

As illustrated in the schematic drawing of Figure 1, the present process produces coke and electric energy from steam while providing an environmentally acceptable exhaust gas from the system that has been desulfurized and is low in nitrogen oxides. Coal is heated in a coking chamber of a non-recovery coke oven under a reducing atmosphere to produce coke, with hot combustion gases passing through downcomersto a flue beneath the coke oven chamber, and with a negative pressure maintained therein. The reducing environment is maintained in the downcomers and the sole flues of the ovens by staged introduction of air. This minimizes the release of nitrogen oxide, NOx, pollutants in the gas, while generating enough heatforthe coking process.The reducing atmosphere converts the fuel derived NO,, formed by oxidation of the nitrogen compounds therein, to nitrogen and combustion products, carbon monoxide and water.

The hot combustion gases, containing nitrogen components and sulfur dioxide from the coking process, are discharged from the flue to an incineration chamber wherein combustion is effected at temperatures that minimize the formation ofthermal NOxfrom nitrogen and oxygen in the gases. All combustibles in the coal volatiles are combusted in the incineration chamber so as to obtain complete combustion with excess air ata temperature of between 1000-1 500 C, and thus minimize the formation ofthermal Now, while converting the carbon-containing combustibles (CO, hydrocarbons, etc.) to clean combustion products.The staged admis sion of air permits more effective control of heat transfer in the various zones of the oven, and bettertem- perature control.

Thermal energy for coal heating and coking is transmitted through the oven walls from the flues, the downcomers, and from the incineration chambers. Heat remaining in the gases discharged from the incineration chamber is used both in a heat recovery boilerto produce steam and in a coal drier.

The hot combustion gases from the incineration chamber are contacted with a desulfurizing agent, such as limestone or dolomite, to remove sulfur dioxide therefrom and are used in a steam production unit to pro- duce steam. The fluidized bed desulfurizer captures 90% or more of the sulfur dioxide in the combustion gas.

Cyclones associated with the fi uidized bed desulfurizerand particulate removal devices associated with the optional coal drier assure that the particulate emissionswill be minimal. The steam produced is passed to an electric power production unit such as a steam turbine to produce electric energy. The combustion gases discharged from the steam production unit may be used to preheat coal to be charged to the coking chambers of the coke ovens priorto discharge of the gases, which have been desu Ifurized and contains a minimal nitrogen oxide content, to the atmosphere as an environmentally acceptable discharge.

In another embodiment of the present invention, as schematically illustrated in Figure 2, the desulfuriza tion ofthe hot combustion gases is carried out in the incineration chamber 27, without the need for a separate desulfurization unit, to remove sulfur dioxide from the hot combustion gases. In this embodiment, fine part- icles (about 100-300 mesh in diameter, U.S. Standard Sieve) of a sulfur absorbent, such as limestone or dolomite, are introduced into the incineration chamber27 through line 101 and admixed with the coke oven gases therein. These particles absorb sulfur dioxide and flow with the hot combustion gases through line 31, which may contain an auxiliary burner 33, and to superheater 41. Upon discharge from the superheater4l through line 103, the particle laden, hot combustion gases are charged to a high temperature ceramicfilter unit 105wherein the particulates are removed, with the filtered hot combustion gases then passedthrough line 107 to the means for producing steam 37. The high temperature ceramic filter unit 105 may use ceramic bag filters, porous surfaces, or other such known high temperature ceramic filters usable to separate part iculates from high temperature gases.

Claims

1. A method for the cogeneration of coke, and electric power by steam, wherein coal is heated in a nonrecovery coke oven having a coking chamber and downcomers to a flue beneath the coking chamber, while a negative pressure is maintained therein, to produce coke and hot combustion gases, the combustion gases containing nitrogen components and sulfur dioxide, characterized in that air is introduced to the coke oven chamber, and the downcomers, in an amountto maintain a reducing atmosphere notonlyintheoven chamber but also in the flue; from which the hot combustion gases containing combustible material are discharged to an incineration chamber, in which the combustible material in the hot combustion gases is then combusted with excess air at a temperature that minimizes formation of nitrogen oxides from nitrogen components in the hot combustion gases, the hot combustion gases are then contacted with a desulfurizing agent to remove sulfur dioxide therefrom and the hot desulfurized combustion gases so produced are passed to a steam production unit in which steam is generated by heattransferfrom said hotdesulfurized combustion gases, which steam is used to produce electric power, and the desulfurized combustion gases after cooling by passage through the steam production unit are discharged to the atmosphere.

2. A method as defined in Claim 1, characterized in that a temperature of between 1000-1500 C is maintained in the incineration chamber.

3. A method as defined in Claim 1 or 2, characterized in that the hot combustion gases are contacted with a desulfurizing agentto remove sulfur dioxide therefrom in afluidized bed desulfurization unit.

4. The method as defined in Claim 2, characterized in that said desulfurizing agent is selected from the group consisting of limestone and dolomite of a particle size of between about 4-100 mesh.

5. A method as defined in Claim 3 or4, characterized in that said hot combustion gases in saidfluidized bed desulfurizing unit are at a temperature of between 790-1 1 20"C.

6. A method as defined in any of Claims 1 to 5, characterized in that said coal to be heated in the nonrecovery coke oven is preheated with the desulfurized combustion gases discharged from the steam production unit priorto discharge of the combustion gases to the atmosphere.

7. A method as defined in any of Claims 1 to 6 characterized in that said coke formed in the coking chamber is discharged and quenched by steam,to produce carbon monoxide and hydrogen, to atem perature of about 800#C, and then quenched with waterto a lowertemperature and that the carbon monoxide and hydrogen produced by said steam quenching are passed to said incineration chamber for combustion therein along with the combustible material in said hot combustion gases.

8. A method as defined in any of Claims 1 to 7, characterized in that the hot combustion gases are contac ted with a desulfurizing agent to remove sulfur dioxide therefrom by introduction of a desu Ifurizing agent into the hot combustion gases in the incineration chamber, and particulates in said hot combustion gases are removed therefrom priorto passing the same to the steam production unit.

9. A method as defined in Claim 8 characterized in that said desulfurizing agent if introduced into said ignition chamber is selected from the group consisting of limestone and dolomite of a particle size of about 100-300 mesh.