CA2027350A1

CA2027350A1 - Process for producing combustible gases in a melt-down gasifier

Info

Publication number: CA2027350A1
Application number: CA002027350A
Authority: CA
Inventors: Karl Faltejsek; Werner Kepplinger
Original assignee: Voestalpine Stahl GmbH; Voest Alpine Industrienlagenbau GmbH
Current assignee: Voestalpine Stahl GmbH; Primetals Technologies Austria GmbH
Priority date: 1989-02-16
Filing date: 1990-02-16
Publication date: 1990-08-17
Also published as: HUT58784A; KR0152427B1; WO1990009423A1; DE4004938C2; BR9005187A; HU901454D0; ZA901174B; KR910700322A; AT394201B; ATA35089A; EP0388395A1; JPH03504875A; DE4004938A1

Abstract

A b s t r a c t Process for producing combustible gases within a smelting gasifier In a process for producing combustible gases within a smelting gasifier operated with oxygen or, respectively, with air enriched in oxygen and being charged with pre-re-duced, preferably iron-containing, ores , coal and slag formers , in which process molten metal , liquid slag as well as combustible gas are discharge from the smelting gasifier and coal is used in a variable amount exceeding the amount required for the smelting reduction for the purpose of producing combustible gases the combustible gas produced is subdivided into at least two partial streams . In this case, a first partial stream of the produced combustible gas is used in the pre-reduction stage for the ore to be supplied into the smelting gasifier , noting that that portion of the combustible gas, which exceeds, the partial amount of gas required in the pre--reduction stage , is supplied to a desulfurizing reactor , from which are supplied as slag formers into the smelting gasifier the reaction products of the desulfuriz-ing reduction as well as not completely reacted slag formers.

Description

7 3 ~ U

PROCESS FOR PI~ODUCING COMBUSTIBLE GASES
IN A r~ELT-DO~lN G~SIFIER

BACXGROUND OF T~IE INVFNTION
Field of the Inventlon The invention refers to a process for producing combustible gases within a smelting gasifier operated with oxygen or, respectively, with air enriched in oxygen and being charged with pre-reduced, preferably iron-containing, ores, coal and slag foxm2rs, molten metal, liquid slag as well as c~mbustible gas ~ng discharged frcm the gasifier and ooal keing used in a variable amount exceeding the amount required for the ~ting reduction for the purpose of producing combustible gases.
Description of the Prior Art For the purpose of operating smelting gasifiers it is known to charge into the head of a smelting gasifier coal of suitable granulometry for the purpose of maintaining a fluidized bed of coal and gasifying the coal. For the purpose of obtaining tne desired melting temperature, the gasifying reaction requires oxygen, noting that substantially pure oxygen, i.e. oxygen containing only a small amount of nitrogen, must be used in a smelting gasifier on account of the usually maintained pressures. The pressure level within a smelting gasifier is, at least partially, predetermined by the peculiarities of discharging the molten bath, and such smelting ~asifiers can not be operated under arbitrarily high pressures if simultaneously the requirements of the '~2'7~

meltlng process shall be taken into consideration. Smelting gasifying processes simultaneously allow the productlon of li~uid pig ironlmake it possible to use coals containlng sulfur, because a smelting gasifying process allows to ~ix the g~ner~e~ hydxogen sulfide within the subsequent reduction shaf~ to the j~st reduced ixon~and allows the generated FeS to enter, via the fluidized bed, the liquid sump and to transfer same into the slag in the form of CaS after having been reacted with free CaO of the slag. In usual gasifying processes, the generated combustible gasified product is utilized for various purposes in caloric machines or combustion chambers, respectively.
Smelting gasifiers, except smelting gasifiers being free of any considerations with respect to tapping pig iron, are frequently operated within a pxessure range up to a maximum of 8 bar, as a rule 4 to 6 bar, for the purpose of not affecting the discharge of the melt.
The gas generated by such smelting gasifying processes in consideration of the existing metallurgical requirements can subsequently ~e used for produclngelectric energy, noting that, howe~er, the requirements for a subsequent energy production, in particular the requirements of a power plant, can only be considered to a limited degree on account of the metallurgical requirements. It is o~ extreme ~mportance for powex. plants to adapt the gas production to the momentarily xequixed ~mount o~. enexgy, and this is ~re~uently the reason for using ~n power plants gasifying processes performed 20'~735U

under pressure ~nd being operated under conditions not considering the requirements for reductively melting ores or pre-reduced me-tals, respectively.
There are known various orms of pressurized gasi~ying processes ~or coal for the purpose o~ operating power plants.
In this connection, there are proposed, as being particularly suitable, flue stream gasifiers, the burners of which have to be supplied with finely ground coal dust together with oxygen of high concentration. The residence time within such flue stream gasifiers and, respectively, the reaction time therein is relatively short and the gasifying products obtained by means of such flue stream gasifiers contain a plurality of noxious materials, in particular sulfur compounds, requiring an expensive purification o~ the product gas. These flue stream gasifiers must be operated with oxygen to make sure su~ficient gasification during such short residence times and for limiting the discharge of carbon together with the slag.
SUMMAR~ OF THE INVENTION
The invention now aims at providing a process of the initially mentioned type by means of which can simultaneously be considerated the metallurgical requirements for the smelting reduction process and the energetic requirements of a subsequent power plant. For solving this task, the process accoxding to the invention consists, in principle, in that the gas produced is subdivided into at least two partial streams, in that a first partial stream of the produced '~0~ 735U

comb~lstible gas is used for pre-reducing the ore to be charged into the smelting gasifier and in that khat partial amoun. of the gas, which exceeds the partial amount required for the pre-reduc~ion o~ ore, is supplied to a desulfurizing reactor from which the reaction products of the desulfurizing reaction as well as not completely reacted slag formers are supplied to the smelting gasifier. On account of subdividing the combustible gas produced within the smelting gasifier into at least two partial streams, a partial amount of the combustible gas considering the requirements for pre-reducing the charged material can be used for the pre-r~duction, noting that in course of the pre-reduction process there can simultaneously be chemically fixed any sulfur contained in the combustible gases. As a rule, slag formers for the subsequent smelting gasifying step are added in the pre-xeduction process. In this case, the pre-reduction process can be controlled such that the parameters xequired for operating the smelting gasifier, in particular the paramete~s for desulfurizing the melt (i.e. the transfer of the sulfur of the Fe~ contained in the metal melt into the slag) and the required basizity of the slag, are maintained, and by means of said partial stream it can ~imultaneo~sl~ be made sure that, during said pre-reduction, iron carbides are formed which allow subsequent carburizing of the bath within the smelting gasifier to the desired ~alue. The excess amount of combustible gases required for operatin~ the power ~lant need not be passed through the pre-reduction furnace, and it is/in particular when varying 2`7 3 ~

- J -amounts of excess gas shall be produced within~a short time interval and in a controllable manner for regulating the operation of the power plant/that the pre-reduction process can be operated in the metallurgicall~ necesqary manner and independent fro~ the just produced amount of gas by deriving said excessi~e partial stream. The excess amount is now, according to the invention, supplied as a second partial stream to a separate desulfurizing reactor, and the measure to desulfurize said excessive amount separate from the pre-reduction furnace provides the possibility to still con-sider the metallurgical requirements of the smelting gasi-fier in case of differing amounts of coal charged for producing differing amounts of gas. For this purpose, slag formers are equally used in the desulfurizing reactor, and, because a change of the slag basicity within the smelting gasifier could result on account of increasing the amount of fuel supplied to the smelting gasi~ier, a partial amount of slag former required for compensating purposes can be derived from the desulfurizing reactor and be supplied to the smelting gasifier. On account of no gangue being introduced, in contrast to the reduction shaft, via the desulfurizing shaft, the slag an~lysis and slag basicity would become changed on account of missing the elements contained in the gangue. For the purpose of counteracting this phenomenon, the slag formers are charged into the desulfurizing shaft in an other compo-sition, in particular with respect to the ratio of CaC03 and MgC03 and, respectively, with respect to the amounts of Al203 '~02'73~0 or SiO2~ As a whole, the feature of subdividing the produc~d amount o~ g~s into two partial stxeams provldes thus the possibility to maintain the metallurgically required slag basiclty and to rapidly change withln short the productlon of combustlble gases ~or a power plant, wlthout thereby detracting from the metallurgical process.
An optimum controi of the metallurgical re~uirements of the smelting gasi~ier can, in this case, reliably be obtained by adjusting the stream of solid matter discharged from the desulfurizing reactor and supplied to the smelting gasifier as a slag former such that the slag has the same slag basicity as the primary slag being formed from the coal ash, the gangue and the lumpy slag formers, being preferably carbonates, being charged together with the ore into the pre-reduction stage.
In a particularly advantageous manner, the process according to the invention is performed such that the stream of coal to the smelting gasifier and the stream o~ solid matter from the desulfurizing reactor is adjusted by means of controllable feeders in mutual quantitative dependency.
Control of the stream of solid matter for the chamber of the smelting gasifier and for the stream of solid matter being subsequently supplled to the smelting gasifier as a compensat-ing amount o~ the slag ~ormers makes it possible to take into consideration momentary variations of the requirements.
An~ change o~ the supplied amount of pre-reduced matexial could only incompletely provide for such a momentary 3 ~ ~

compensation, last not least, on account of cert~in residence times, of 6 to 8 hours ~or example, being required for the pre-reduction step and a momentary adaptatlon would thus not be possible by such a measure. Such a momentary adaptation can only be obtained by a compensating correction comprising the simultaneous variation of the amount of fuel and the separat~ly supplied amount of slag formers ~rom the desulfurizing reactor, thereby simultaneously obtaining the advantage that desulfurizing of this partial stream is, for the major part, effected by the slag formers and that the danger of enriching the molten bath in sulphur is reduced.
For the purpose of taking in consideration in an optimum manner and simultaneously the requirements of the desulfurizing reactor and the requirements of the pre-reducing furnace, the process according to the invention can in an optimum manner be performed such that MgC03 and CaC03 are supplied to the desulfurizing reactor in a proportion being different from the proportion applied in the pre-reduction step.
The smelting gasifier must be operated with gas exit temperatures of at least approximately 1000 CIto be in the position to thermally decompose higher hydrocarbons resulting by degassing the coal chaxged into said gasifier and ~arbon--nitrogen-com~ounds pxoduced in the degassing and, respectively, gasifying step within the head of the gasifier.
It is of substantial importance ~or the pre-reduction step that the introduced reductive gas, i.e. the combustible '~02'73~U

gas produced, be cooled to metallurgically required tempera-ture, noting that it is additionally necessary to maintain substantially constant the content of the combus~ible gas in reducing constltuents. For the purpose of cooling that S partial amount o~ the combustible gas which i9 supplied to the pre-reduction furnace, there shall, as far as possible, not be used the gas extracted from the pre-reduction furnace and having already a highex content in C02 but a gas con-taining CU in approximately the same concentration. This can in a particularly advantageous manner be achieved if a gas extracted from the desulfurizing reactor and having been cooled and purified is added to that partial amount of gas which is introduced into the pre-reduction step.
Accordin~ to a preferred procedure, the gas leaving the desulfurizing reactor is pre-cooled in a radiant heat exchanger under production o~ high-pressure steam, is cleaned of dust in centrifugal force separators, is further cooled in con~ecti~e heat exchangers under production of high--pressure steam and medium-pressure steam, is finally cooled in a last stage by txansferring heat to low-pressuxe steam or to feed water and is subse~uently washed. The gas can thus be further used in gas turbines.
A small partial stream of this gas is pressurized and added to the pre~iously mentioned partial stream of the gas to be supplied to the pxe-reduction stage.
Also the cooler effiluent gases of the pre-reduction stage are, as is in correspondence with a further preferred embodlment, treatecl in a similar manner, noting that the procedure is such that the partial stream of gas utilized in the pre-reduction sta~e is, a~ter havlng leEt the reduction shaft, cleaned o~ dust in centrifugal force separators, is cooled in convective heat exchangers ur.der production of medium-pressure steam, is finally cooled in a further cooling stage by transmitting heat to low-pressure steam or feed water and is finally washed. A partial stream of this gas is, as will be described later, used for controll-ing the exit temperature of the smelting gasifier.
The pre-reduction step is, as a rule, performed at temperatures being distinctly lower than the exit temperatures of the combustible gases from the smelting gasifier, noting that the partial gas stream used in the pre-reduction step is preferably cooled down to approximately 850 C. On the other hand, the desulfurizing process within the desulfurizing reactor can be effected directly at the pronouncedly higher exit temperatures of the combustible gas from the smelting gasifier, thereby improving the efficiency of the desulfurizing step.
On account of subdividing the gas produced into at least two partial streams, thexe is p~o~ided the possibility to adaptJwithin short and within broad limits and without affecting the metallurgical process/the just required amount of ~uel gas ~or the caloxific power plant, noting that for the purpose of maintainin~ the metallurgical requirements the procedure is pre~erably such that the gas stream used in S~ 3 ~ ~

the pre-reduction step is 25 to 95 %, pre~erably 40 to 80 %, of the combustible gas stream.
For the purpose of correc-tly consldering the compositlon of the gas, i.e. the~o~nt~nt in CH-compounds and CN-compounds of the combustible gas produced in the smelting gaslEier ln case of strongly varying amounts of coal, it is also required to control the temperature of the gases leavlng the smelt-ing gasifier. It is in particular when producing a great amount of gas for the subsequent power plant that the temperatures at the gasifier head are distinctly increased and must thus effectively be compensated.
For the purpose of gasifying coal within the smelting gasifier there can be used usual gasifying agents, noting that it is of advantage to introduce into the smelting gasi-fier as the gasifying agent pure ox~gen and/or oxygen having a residual nitrogen content of approximately 10 % and/or a mixture of 2 and steam and/or a mixture of hot air and 2 and/or, beside oxygen, C02 as a further oxygen carrier con-tained in recirculated effluent gas from the reduction stage.
~n particular when using as a gasifying agent an effluent gas from the pre-reduction stage results the energetic advantage that excessive sensible heat of the gas is consumed at a temperature level located above the temperature level re~uired for decomposing within the gasifier chamber CH-com-pounds and, respectively, CN-compounds, in particular at 1000 CIand is transferred into a calorific value of the gas produced. In this case, the C02 of the recirculated effluent ~'73'i~

gas ~rom t~le pre-reduction stage reacts in a heat-consuming manner within the fluidized bed of the smelting gasifier with C under the formation of 2 CO.
On account of the productlon of fuel gas belny freely selectable within broad limits, a greater proportion of senslble heat is, of course, at disposal in case of an increased pro-duction of fuel gas, which proportion can equally be utilized for maintaining the desired temperatures. In this case, the procedure is advantageously such that, when using hot air and 2 as the gasifying agent within the smelting gasifier, îhe hot air is heated by heat exchange against hot gases or by burning a small amount of fuel, preferably fuel gas, with-in the air stream to be supplied to the gasifier.
In case of a subsequent power plant with strongly variable power demand of the mains and in particular in case of an air--separation plant for the simultaneous production of the oxygen required for operating the smelting gasifier, the expenditure for equipment can substantially be reduced if the ~as produced is for the major part supplied to a steam power plant energiæed b~ gas turbines, noting that in case of minimum load there are burnt in this power plant the combustible effluent gases from the reduction stage partially or completely in the combustion chamber or combustion chambers of one ~as turbine~the hot effluent gases of which are utilized for producing steam being utilized in a steam turbine together with steam obtained by cooling hot ~as streams, and noting that in case o~ maximum load of the ~0~ 7351) power plant there is used for the ~o~uction of electrical ener~y, for the major part or as a whole, addltlonally the gas obtalned by gaslf~lng coal not re~uired ~or the operatlon of the reductlon stage and there i9 operated at least one further gas turblne.
On account of all elements of the equipment being, with the exception of the gas turbines,present as one single element, the expenditure for the equipment can substantially be reduced. Only one o~ the gas turbines would be operated for utilizin~, for example, the gas formed fro~ the metallurgically required coal, while two or more turbines would be opexated in case of full load of the power plant.
These elements, which are provided as one single element, of a power plant, are essentially the gas compressor, the steam turbine set, the main air compressor for compressing the major part of the air to be separated as well as the low temperature air-separator itself. Compressors can , as a rule, only within narrow li~its be adapted to different throughput, because their efficiency becomes distinctly reduced beyond these limits. There~o~e, it is of advantage to provide a speed-controlled pre-compxessor for gas in addition to the gas compressor, noting that the procedure is preferably such that the combustible gas is supplied to the combustion chamber or combustion cha~bers of one gas turbine or of the gas turbines via a gas comp~essor which is at full load of the power plant assisted by a pre-compressor, being preferably speed~controlled, for gas, so that the gas volume 3 ~ ~

sucked b~ the ~s compressor ~ ~ull lo~cl oE the power plant is distLnctly reduced ~nd an economic operation of this compressor is made sure. In this case it is sufficient that the speed-controlled pre-compressor for gas suppll~s, as ls in correspondence with a further preferred embodlment, approximately 20 % of the whole compressor work at full load of the steam power plant working with gas turbines.
Gas turbines are designed for being operated with natural gas or fuel oil. These fuels determine the ratio of the mass throughput in the compressor and the turbine, respectively. Coal gas has, however, a remarkedly higher specific weight and a substantially lower calorific value, so that the mass flow of the gas is greater fox the multiple of 5 to 10 (for the effluent gas of the reduction stage) as compared with the mass flow for which the turbines are designed. For the purpose of using essentially unchanged turbines, a partial stream of the compressed air is not supplied to the combustion within the combustion chamber and, respectively, not used for cooling the gas turbine but is discharged from the combustion chamber. In this case, the procedure is ad~antageously such that pressurized air is discharged from the combustion chamber~s) of the gas turbine(s), is cooled and is as a whole supplied to the air-separatin~ plant, noting that, at least at full-load operation of the powex plant, a pa~tial stream of this air is, preferably in a power-producing turbine, expanded down to the pxessuxe le~el re~uired for producing in the ~'735~) air-separating plant practically non-pressurized products and noting that this partially expanded stream of pressurized air of the air-separating plant ls supplied to the air--separating plant together with a further stream of pressurized air which is brought to a pressure level required for the air-separating step by an air compressor being preferably driven by the steam turbine, thereby, in particular~perform-ing the process such that the partial stream of pressurized air, which is derived from the combustion chamber(s) of the gas turbine(s) and is not expanded via the power-producing turbine, is condensed in the air-separator in countercurrent to give Iiq~id compresse~ oxygen, is expanded in liquid con-dition and is supplied into the sump within the separating column of the air separator.
With increasing load of the steam power plant equipped with gas turbines and thus with increasing amount of the coal to be gasified, also the mass stream of gases and the oxygen demand will be increased but not in the least in a proportional ratio. Above all, the oxygen demand will be increased to a sub-proportional degree because the proportion o~ steam or recirculated C02 from the effluent gas and serVing as an oxygen car~ieX will be increased to a supex-proportional degxee, while, on the other hand, the metallurgically necessary coal, which is gasified with the highest specific oxygen demand, is at disposal as a fuel gas only for approximately 40 or:50 % of its calorific value.
On the other hand, the main air compressor, which is '~G2 735~

at constant rotating speed conveniently drlven by the shaft of the steam turbine, would have to be operated in an in-economic overload condition in case of high load of the power plant and thus o khe alr-separator. For the purpose S of minimizing these effects, there is discharged ~rom the gas turbines a greater amount o~ air stream than would be required for evaporatin~ the oxygen and this additionally discharged amQunt of air is expanded in a power-producing manner within an air expansion turbine down to the pressure level of the main air compressor and is, together with the air supplied by the main air compressor, separated into its components within the air separator. In this case both air streams discharged from the gas turbines, i.e. the directly used air stream and the air stream being previously passed through the air expanding turbine, are cooled for producing preferably high-pressure steam and medium-pressure steam and subsequently purified in a suitable manner.
Within the combustion chambers of the gas turbine(s) there are generatbd thermally in a substantial amount nitrogen oxides in spite of the low calorific value of the coal gas, which calori~ic value is substantially lower than, for .example, ~hat of natural gas. . In this case, features being at disposal for burners ope~ated with natural gas, such as pre~iously mixing the gas with air, can not be used on account of the h~drogen content o~ coal gases. The thermal formation o~ nitrogen o~ides must.thus be counteracted by ef.fectively coolin~ the flame core.: ~n this case,.the proceduxe is ~i2 ~35l~

pr~ferably such that steam is supplied to the Euel gas to be supplied to the combustion chamber(s~ of the gas turbine(s) or to the burners and/or compressed nitrogen coming ~rom the air-separ~tln~ step i9 inter~lxed wlth the S fuel gas.
This is conveniently performed on occaslon of partlal load of the steam power plant equipped with gas turbines, i.e. on occasion of producing electrical power only by the effluent gases of the reduction stage, by simultaneously supplying steam into the burners of the combustion chambers of the gas turbine. On account of the high specific heat and dissociation heat of the steam, the thermal ~ormation of nitrogen oxides is drastically lowered, so that the effluent gases of the gas turbine can, without lowering to a greater extent the NOx-content of the gas by a catalytic reaction with NH3 for example, be discharged into the atmosphere. In case of full load of the steam power plant equipped with gas turbines, the higher calorific value of the uel gas results in a super-proportional and no more economic increase of the amount of steam used for suppressing the formation of nitrogen oxides in the burners. For the purpose of counteracting this phenomenon, nitrogen is con-veniently extracted from the air-separator ~eing equally operated with full load under the mentioned load condition, is compressed to the pressu~e level existing in the combustion ch~mbers of the ~as turbines and is intermixed with the uel gas. The thus drastically reduced calorific value o the coal 2 `7 3 tj ~

gas allows to agaln adjust economic amounts of steam for further suppressing the generation oE nitrogen o~ides.
Under full-load condition of the power plant, the effect of reducing the caloriflc value of the fuel gas ls domlnat-S lng the effect o inhibiting the formation of nitrogen oxides,and steam is supplied to the individual gas turbines in a dosed manner mainly for effecting a fine adjustment o~ the tolerated NOx-content o~ the waste gas. In this case, the procedure is advantageously such that in case of minimum load of the power plant, i.e. when consuming only the effluent gases of the reduction stage by one gas turbine, predominantly steam is supplied to this turbine for the purpose of mini-mizing the formation of nitrogen oxides, whereas in case of full load of the power plant the reauction of the calorific ~5 value within the fuel gas by adding nitrogen dominates in the effects suppressing the formation oE nitrogen oxides and steam is mainly supplied in a dosed manner to the individual gas turbines for effecting a fine adjustment of the tolerated NOx-cont.ents in the waste gas.
However, the mass stream of fuel gas to the gas turbines will be increased and for this reason further pressurized air must be extracted from the combustion chambers of the gas turbines. This air is expanded in a power-producing manner within the pxeviousl~ mentioned air expansion turbine, there-b~ further relieving the main air compressor from load. On account of the power produced by this expansion turbine in-creasing in the same:sense as the power. demand of the 3 ~ ~

nitrogen compressor, sai~ expansion turbine is conveniently alranged together with said nitrogen compressor on a common shaft and the small additionall~ required power is supplied by a motor, convenientl~ a motor o~ variable speed by frequency trans~ormation.
~ n case o~ minimum load of the steam power plant being equipped with gas turbines, i.e. when working only with the effluent gas of the reduction stage, this machine set is stopped. In this case, the process is preferably perfoxmed such that the compressor or the nitrogen is arranged together with the turbine for expanding pressurized air under ~ du~tion of power on one single shaft and is in principle driven by said turbine, is delivering a gradually increasing mass stream of nitrogen with increasing load of the power plant and receives any missing drive power from a further drive means being preferably controllable with respect to its rotating speed and being in particular designed as a polyphase induction motor being energized via frequency transformers.
BRIEF DESCRIPTION OF' THE DR~WING
In the ~ollowing, the invention is further explained with reference to the drawing schematically showing examples of embodiment o~ a plant for performing the process according to the invention. ~n the drawing Figure 1 shows a ~ixst embodiment o~ a plant for per-formin~ the process according to the invention and Figure 2 shows a modified embodiment of a plant '~0~ ~35~

includin~ gas turbi.nes and an air-separating plant, respectively.
DETAILED DESCRIPTION OF THE P~EFER~ED ~MBODIMENTS
In the block diagram shown in Flgure 1, a smeltlng gasiier designated by the re~erence numeral 1 i9 supplled with pre-reduced, preferably iron-containing, ores from a pre-reduction stage 2 as well with slag formers from a desulfurizing reactor 3. Coal is supplied to the smelting gasifier 1 via a conveyor means 4, while oxygen-containing fuel gas or pure oxygen, respectively, is supplied via a conduit 5. Pig iron is discharged from the smelting gasifier 1 at 6 while slag is discharged at 7.
Coal is supplied to the smelting gasif.ier 1 via a con-veyor means 4 in a variable amount and in an amount exceeding the amount re~uired for the melting reduction of the supplied, in particular iron-containing, ore, for the purpose of additionally producing a combustible gas. All of the gas pro-duced is extracted at the area of the head of the smelting gasifier via a conduit 8 and is subdivided in two partial streams 9 and 10, no*ing that the partial gas stream extracted via 9 is supplied to the pre-reduction stage 2, ; 8nd.-that-the.second partial~stream, which exceeds the partial stre~m o~ the gas re~uired for the pre-reduction stage, is supplied to the desul~urizing reactor 3. Iron-containing ores are supplied into the pre-~eduction stage:2 via a feed conduit 11 and slag formers, for examp.le CaC03 and MgC03, are supplied to the pre-reduction stage 2 via 12, noting that 3 ~ ~

subsequent to the pre-reduction stage 2, substantially Fe and FeS enter the smelting gasifier via 13 together with slag formers. Slag formers MgC03 and CaC03 are e~ually charged into the desulfurizing stage 3 vla 1~ but in a ratio being dif~erent fxom that in the pre-reduction sta~e. Sub-sequent to the desul~urizing stage, substantially CaO and CaS and MgO enter the smelting gasifier 1 via 15. ~he gas discharged from the smelting gasif.ler 1 is substantially formed of CO and H2 and of smaller proportions in H2S, C02 and H20. For the purpose of rapidly adapting and controlling the stream o~ materials into the smelting gasifier 1 there are provided in the supply conduit 4 for coal as well as in the supply conduit 15 controllable feeders 16 and 17 for solid material, whereby a compensating correction is made possible by simultaneously changing the amount of fuel and of the separately suppl.ied amount of slag formers from the desulfurizing reactor 3. This provides for maintaining the metallurgically re~uixed slag basicity.
Subdividing of the generated stream of combustible gases discharged from the gasifier head into partial streams 9 and 10 is now effected such that the gas stream used in the pre--reduction stage 2 amounts to about 25 to 95 % of the produced total stream of combustible gases. For providing the possibility to thermally decompose within the gasifier head higher hydrocarbons resulting from.degassing the coal charged into the smelting gasif.ie~.1 as well as car~on~nitro~en--compoundsproduced on occasion of the degassing step or, 3 ~j u respec~ively, ~asifying step, the exit temperature of the produced combustible gas is more than 1000 C.
Combustible gas being rich in C02 is ex~racted from the pre-reduction stage 2 via 18, is purlfied in a centrl-fugal force separator 19 and is, ~iA a-~ea-t exchanger 20 for producing medium-pressure steam 21, supplied to a scrubber 22 from which is extracted at 23 essentially puri-fied and cooled combustible gas, which is, for example, supplied into a combustion chamber of a gas turbine as will be explained in detail with reference to Figure 2.
A partial amount of the combustible gas extracted at 23 can, in this case, be supplied via a compressor 24 to the smelting gasifier as an oxygen-containing gasifying agent, for example via the conduit 5 or separate from the stream of oxygen.
A combustible gas poor in C02 is equally extracted from the desulfurizing reactor 3 at 25 and is passed through a radiant heat exchanger 26 for producing high-pressure steam 27, through a centrifugal force separator 28 as well as through a heat exchanger 29 forproducing high-pressure steam 30 and medium-pressure steam 31 and is purified in a scrubber 32.
Purified combustible gas is equally extracted from the scrubber 32 at 33 and can, as will be explained in detail by Figure 2, be supplied to a gas turbine. A branch conduit 34 is connected to the conduit 33 for the purpose of adding to the partial ~as stream 9 utilized in the pre-reduction stage 2 the purified and cooled combustible gas via a 73~

compressor 35 and thus or efecting coollng o~ this partial gas stream down to a temperature of approximately 850 C, which temperature is sultable for the pre-reduction 9tage~
Furthermore, there exists betwee~ the ~ as condult~ 23 and 33 a ~ranch conduit 37 ~eln-J controllable via a valve 36, so that the ratio o~ the partial gas streams passed through the pre-reduction sha~t 2 and the desulfurizing shaft 3, respectively, can be influenced.
In the embodiment shown in Figure 2, the reference numerals of Figure 1 have been maintalned fox e~ual con-structional parts. In the smelting gasifier.1, there is again produced a combustible ~as, which is supplied in two partial streams 9 and 10 to the pre-xeduction sta~e 2 as well as to the desul~uxizing stage 3, notin~ that the gas derived from the pre-reduction stage 2 and, respectivel~, from the desul~urizing stage 3 is again cooled in heat exchangers 20 and 29 and is used for producing high-pressure steam and mediu~-pressu~e steam, xespectivel~. In contrast to the arrangement accordin~ to Fi~ure 1, there is provided for the cooled gas streams in the conduits 18 and 25 a common scrubber 22 and the total amount o~ the purified combustible gas is extracted via the conduit 23. Within the conduit 23 supplying the combustible gas to a gas turbine or to sevexal gas turbines, thexe is provided a ~e-compresso~ 38 as well as a subse~uent ~as co~pXeSSor 39,. noting that.the pre--compXeSsor 38 ~ox the g~s iS dri~en by a h~pexs~nchronous dri~e motor 40-which is enexgized by a frequency trans-3 c~j ~

former 34. The thus compressed combustible gas is sub-se~uently supplied to combustion chambers 42 and 43. Within the combustion chambers 42, 43, the pur:lfied and compressed fuel gas is burnt with compressed air 46 and 47, notlng that S the effluent gases 48 and 49 emerging from the combustion chambers 42 and 43 are each supplied to a respective turbine 50 and 51. These turblnes 50 and 51 are each coupled to one respective compressox. 52 and 53 as well as to respective generators 54 and 55 fQr producing electrical energy as is 10 schematically indicated. Such systems of coupled compressors 52 and 53, turbines 50 and 51 as well as generators 54 and 55 a~d of associated combustion chambers 42 and 43 for burning the gases required for the operation of the turbines 50 and 51 are most frequently designed for using in the combustion 15 chambers natural gas or naphta, respectively. Because the combustible gas extracted from the smelting gasifier after having passed the pre-reduction stage 2 and, respectively, the desulfurizing stage 3 has as a rule a lower calorific value than naphta or, respectively, nahlral gas, and this greater 20 amount of product gas is required for producing the gas stream 23 re~uired for operating the turbines 50 and 51, there ~ould, in principle, exist the possibility to lower the supplied amount of compressed air 46 and 47 by modifying the compressors 52 and 53 and to adapt said amount to the absorp 25 tlon capadity of the turbines 50 and 51. Such modifications o~ compressors result, aS a xule, in problems also with respect of other constructional parts of the gas turbines, 3 5 l~

;~ ,, so tha-t p~rtlal st.reams 56 anA 57 are branched off the streams o~ compressed hot air and are, as will be explained later in greater detail, be supplied ~o an air-separating pl~nt.
The expanded gas extracted from the turbines 50 and 51 is passed through heat exchangers 58 and 59 in which is produced hi~h-pressure-steam 60 and 61 and, respectively, medium-pressure steam 62 and 63 as well as (here not shown in detail) additional low-pressure steam or in which feed water is pre-heated.
The high-pressure steam 30, 60, 61 and 76 produced in the various heat exchangers is supplied to a highpressure--steamturbine 64 ~rom which can be extracted via a conduit 65 steam at a ~edium pressure level, noting that this steam is supplied to the combustion chambers 42 and 43 of the gas turbines for the purpose o~ suppressing the formation of N0x. The medium-pxessure steam 66 extracted from the turbine 64 as well as the stxeams 21, 31,62,63,77 and 81 of medium--pressure steam produced in the various heat exchangers are supplied to a subse~uent stea~ turbine 67 and, after having been expanded, condensed within a condenser 68, the con-densate being returned into the circuit by means of a pump 69.
~n this case, the steam tuxbines are coupled with a generator 70, in its tuXn being coupled to the gas compressor 25 39 ~or the co~bustible ~asThe steam turbine 64 is further coupled with an air co~pxe$~X 31 ~X pxoducing-~edium--pressuxe alr 72 belng introduced.into an air-separating 7 3 ~ l~

plant 73.
Into the air-separating plant 73, there is introduced, in addition to the air having been compress~d within the alr compressor 71, also a partial stream of the high-pressure alr extracted from the compressors 52 and 53 of the combustion chambers 42 and 43 at 56 and 57, noting that a partial stream 74 is cooled b~ means of a heat exchanger 75 for producing high-pxessure steam and medium-pressure steam 76 and 77. These steam streams of different pressure are, as previously shown, equally supplied to the steam turbines 64 and 67, respectively. This air is li~uified within the air--separator in heat exchange a~ainst the previously compressed liquid oxygen, which will thereby evaporate, and is supplied into the separating column in this condition. Thus, this air stream is clearly defined by the mass stream of the extracted oxy~en. Under full load of the power plant it is, however, convenient to derive from the combustion chambers 42 and 43 pronouncedly m~re air as a partial stream 78.
The partial strea~ 78 of the high-pressure air, which is not passed through the heat exchan~er 75, is expanded, under production of poWer, in an expansion turbine 79 for high--pressure air and is, after having been cooled ~ithin a heat exchanger 80 with simultaneous production of medium--pressure steam.81 being equall~ utilized in the steam turbine 67, supplied to the medium-pressure air delivered by the compressor 71 and equally.introduced into the air-_separating plant 73. In this case,..the expansion turbine 79 - 2fi -is arr~nged on one shaft together with a motor 82 having adjoined thereto a frequency transformer 83 as well as with a nitrogen compressor 84. Ox~gen produced in the air-separat-in~ plant 73 is supplied via a conduit 85 as a gasifylng agent into the smelting gasifier, noting that, as mentioned above, further inert gases or oxygen-containing gases can, beside the pure oxygen, be supplied into the smelting gasi-fier ~ as is indicated by the conduit 5. Nitrogen produced in the alr-separating plant 73 is extracted via 86 and is, ~0 after having been compressed in the nitrogen compressor 84, added to the combustible gas to be supplied into the com-bustion cha~bers 42 and 43, noting that such an addition of nitrogen into the combustible gas to be utilized in the combustion chambers has, essentially at full load of the ~S steam power plant equipped with gas turbines, the result of lowering the calorific value of fuel gas, while any addition of steam into the combustion chambers of the ~as turbines ser~e the purpose of minimizing the formation of nitrogen oxides under the condition of partial lQad of the power plant and operating same with only one ~as turbine. In this manner, the air-separat~r not onl~ recei~es more air to be sepaxated in components at ~ull load of the power plant but, in parti-cular, the amount of compxessed air extracted from the gas turbines becomes increased.
Reference nu~eral 87 indicates the discharge of the waste product, which is rich in nit~ogen, o~.the air.separ~ting plant 73.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. Process for producing combustible gases within a smelting gasifier (1) operated with oxygen or, respectively, with air enriched in oxygen and being charged with pre-reduced, preferably iron-containing, ores (13), coal (4) and slag formers (15), melt (6), liquid slag (7) as well as combustible gas (8) being discharged from the gasifier and coal (4) being used in a variable amount exceeding the amount required for producing combustible gases (8), characterized in that the gas produced is subdivided into at least two partial streams (9, 10), in that a first partial stream (9) of the produced combustible gas is used for the pre-reduction (2) of the ore (13) to be charged into the smelting gasifier (1) and in that that partial amount of the gas, which exceeds the partial amount required for the pre-reduction (2), is supplied to a desulfurizing reactor (3), from which the reaction products of the desulfurizing reduction as well as not completely reacted slag formers are discharged and supplied to the smelting gasifier (1)as slag formers (15).

2. Process as claimed in claim 1, characterized in that the stream of coal (4) to the smelting gasifier (1) and the stream of solid material from the desulfurizing reactor (3) to the smelting gasifier (1) are adjusted in mutually quantitative dependency by means of controllable feeders (16, 17) for solid material.

3. Process as claimed in claim 1 or 2, characterized in that MgC03 and CaCo3 are supplied to the desulfurizing reactor (3) in a proportion being different from the pro-portion applied in the pre-reduction step (2).

4. Process as claimed in claim 1, 2 or 3, characterized in that combustible gas having been extracted behind the de-sulfurizing reactor (3) and having been cooled and purified is added to that partial amount (9) of the gas which is supplied to the pre-reduction stage (2).

5. Process as claimed in any of the claims 1 to 4, characterized in that the gas (25) leaving the desulfurizing reactor (3) is pre-cooled in a radiant heat exchanger (26) under the production of high-pressure steam (27), is freed of dust in a centrifugal force separator (28), is further cooled in convection heat exchangers (29) under the production of high-pressure steam (30) and medium-pressure steam (31), is finally cooled in a last stage (32) by transferring heat to low-pressure steam or feed water and is subsequently washed.

6. Process as claimed in any of the claims 1 to 5, characterized in that the partial gas stream (9) used in the pre-reduction stage (2) is, after having left the reduction shaft, cleaned of dust in centrifugal force separators (19), is cooled in convection heat exchangers (20) under the pro-duction of medium-pressure steam (21), is finally cooled in a further cooling stage (22) by transferring heat to low--pressure steam or feed water and is finally washed.

7. Process as claimed in any of the claims 1 to 6, characterized in that the partial gas stream (9) used for -the pre-reduction stage (2) is cooled down to approximately 850 oC.

8. Process as claimed in any of the claims 1 to 7, characterized in that the gas stream (9) used in the pre--reduction stage (2) amounts to 25 to 95 %, preferably to 40 to 80 %,of the produced combustible gas stream.

9. Process as claimed in any of the claims 1 to 8, characterized in that the stream of solid matter composed of the slag formers (15) having been discharged from the desulfurizing reactor (3) and being supplied to the smelting gasifier (1) is adjusted such that the slag (7) has the same slag basicity as the primary slag being formed from the coal ash, the gangue of the ore as well as that lumpy slag formers being preferably carbonates in nature, charged together with the ore (13) into the pre-reduction stage (2).

10. Process as claimed in any of the claims 1 to 9, characterized in that the gasifying agent utilized in the smelting gasifier (1) is pure oxygen and/or oxygen having a residual nitrogen content around 10 % and/or a mixture of O2 and steam and/or a mixture of hot air and O2 and/or, beside oxygen, C02 contained in the recirculated effluent gas of the reduction stage as a further oxygen carrier.

11. Process as claimed in any of the claims 1 to 10, characterized in that, when using effluent gas from the pre--reduction stage (2) as the gasifying agent, the sensible heat of the gas is consumed above that temperature level, in particular 1000 OC, which is required for decomposing CH-compounds and, respectively, CN-compounds within the gasifier chamber (1) and is transferred into calorific value of the produced gas.

12. Process as claimed in any of the claims 1 to 11, characterized in that,when using hot air and O2 as the gasi-fying agent within the smelting gasifier (1), the hot air is heated by heat exchange against hot gases or by burning a small amount of fuel, preferably a small amount of gas, within the air stream to be supplied to the gasifier.

13. Process as claimed in any of the claims 1 to 12, characterized in that the produced gas is supplied for the major part to a steam power plant equipped with gas turbines (42, 43, 50, 51, 54, 55) , noting,that in case of minimum load, there are burnt within this power plant, partially or as a whole and within the combustion chamber(s) (42, 43) of a gas turbine (50, 51) the effluent gases of the reduction stage, the hot effluent gases of said gas turbine being used for producing steam being utilized in a steam turbine (64, 67) together with steam resulting from cooling hot gas streams, and noting that, in case of full load of the power plant, the gas resulting from gasifying coal being not required for operating the reduction stage is, for the major part or as a whole, utilized for producing electric current, at least one further gas turbine being operated for this purpose.

14. Process as claimed in claim 13, characterized in that the combustible gas is supplied into the combustion chamber(s) (42, 43) of a gas turbine or of gas turbines (50,51) by means of a gas compressor (53, 62), which is, in case of full load of the power plant, assisted by a gas pre-compressor (38) being preferably regulated with respect to its rotating speed.

15. Process as claimed in claim 13 or 14, characterized in that the speed controlled gas pre-compressor (38) supplies, in case of full load of the steam power plant equipped with gas turbines, approximately 20 % of the total compressor work.

16. process according to any of the claims 13 to 15, characterized in that presurized air (56, 57) is removed from the combustion chamber(s) (42, 43) of the gas turbine(s) (50, 51), is cooled and is as a whole supplied to the air--separating plant (73), noting that a partial stream of said air is, at least at full load of the power plant, expanded, preferably within a power-producing turbine (79), down to a pressure level being necessary for producing in the air--separating plant (73) practically non-pressurized products, and noting that this partially expanded stream of pressurized air of the air-separating plant (73) is supplied to the air-separating plant (73) together with a further stream (72) of pressurized air which is brought by an air compressor (71), being preferably driven by the steam turbine (64), to a pressure level required for the air-separating step (73).

17. Process as claimed in claim 16, characterized in that the partial stream of pressurized air (56, 57) removed from the combustion chamber(s) (42, 43) of the gas turbine(s) (50, 51) is not expanded via the power-producing turbine (79), is condensed within the air separator (73) in countercurrent to oxygen being in a liquid condition, is expanded in a liquid condition and is supplied into the sump of the separating column of the air-separator.

18. Process as claimed in any of the claims 13 to 17, characterized in that steam is supplied into the fuel gas to be supplied into the combustion chamber(s) (42, 43) of the gas turbine(s) (50, 51) or into the burners and/or compressed nitrogen (86) derived from the air separating step (73) is admixed with the fuel gas.

19. Process as claimed in any of the claims 13 to 18, characterized in that, in case of minimum load of the power plant, i.e. when utilizing the effluent gases of the reduction stage (2) by means of a gas turbine, mainly steam is supplied to this gas turbine for the purpose of minimizing the formation of nitrogen oxides, whereas, in case of full load of the power plant, the reduction of the calorific value within the fuel gas by adding nitrogen dominates in the effects suppressing the formation of nitrogen oxides and steam is mainly supplied in a dosed manner to the individual gas turbines (50, 51) for effecting a fine adjustment of the tolerated NOx-content in the waste gas.

20. Process according to any of the claims 13 to 19, characterized in that the compressor (84) for nitrogen (85) is arranged together with the turbine (79) for expanding pressurized air (78) under control of power on one single shaft and is in principle driven by said turbine, is delivering a mass stream of nitrogen gradually increasing with increasing load of the power plant and receives any missing driving power from a further drive means (82) being preferably controllable with respect to its rotating speed and being in particular designed as a polyphase induction motor being energized via frequency transformers (83).