EP0154986B1 - Process and apparatus for obtaining flue gases poor in sox in incineration plants - Google Patents

Description

The invention relates to a method and to devices for obtaining low-SO _x flue gases in combustion plants operated with finely divided carbon-containing fuels, in particular coal, in which the sulfur contained in the fuel is converted into a finely divided additive, preferably limestone powder (CaCO _a ), quicklime powder ( CaO) or calcium hydroxide powder (Ca (OH) ₂ ) and then the desulfurized fuel is burned in the combustion chamber and the additive particles loaded with sulfur are sintered and removed with the ash.

Harmful by-products of fossil fuel combustion are well known. One of the main pollutants is sulfur dioxide, from which - according to the current state of technology - around 4 million tons are blown off into the air in the Federal Republic of Germany, whereby power plants and industry are the main causes. Despite the greatest efforts - worldwide - it has not yet been satisfactorily managed to control the harmful SO ₂ emissions and reduce them to a tolerable level.

The fossil fuel coal contains sulfur either as a mineral accompanying substance, in particular as pyrite (FeS ₂ ), or as so-called organic sulfur. Hardly any elemental sulfur is found in hard coal, not at all in the Federal Republic of Germany. The organic sulfur is part of the coal substance, the type of its binding to the coal is not yet known. Depending on its occurrence in the coal, it can be desulfurized by mechanical or chemical processes. Both processes are tedious, with the chemical processes requiring particularly high investment and operating costs.

It is important for the chemical desulfurization processes that coal is practically insoluble in common solvents and is therefore not susceptible to attack by selective reagents; Only the «cracking» of the whole structure allows a chemical intervention.

To reduce the amount of SO _x released in large-scale industrial combustion of fossil fuels, processes and systems for flue gas desulfurization or for desulfurization of the fuels are essentially used or tested. However, all measures known to date have resulted in a more or less sensitive increase in electricity sales prices, since the necessary systems can only be financed by them.

The most common method is the desulfurization of the flue gases. Since the S0 ₂ formed during the combustion of the fuel is eliminated here, the form of the original sulfur incorporation into the fuel is irrelevant. Wet desulfurization plants, in which gypsum is formed from the preferred additives and in which the sulfur is incorporated, have become the most popular. Such flue gas desulphurization increases the price of electricity by 1.9 pfennigs per kilowatt hour, which corresponds to a surcharge of DM 50 per ton of coal used.

In addition, the combustion chamber or the flue gas outlet of the boiler system must consist of materials that are compatible with the SOr components contained in the flue gas. As a result, the increased price for such materials must be accepted when the boiler system is being designed.

welches sich in der Asche ansammelt. Wird nicht Calciumoxid direkt sondern Calciumhydroxid oder Kalk als Additiv eingesetzt, müssen sich diese zuvor zersetzen:

A number of pilot projects are known for the desulfurization of the flue gases in the boiler, which pursue the dry desulfurization of the flue gases before the boiler emerges. They are based on the principle of adding sulfur-binding additives to the flue gas - still in the combustion chamber - in particular CaO (as quicklime powder), Ca (OH) ₂ (as calcium hydroxide powder) and CaC0 ₃ (as limestone or lime powder), which lead to inclusion of the sulfur content of the flue gas. For the incorporation of the sulfur content of the flue gas by the additive, it is assumed that calcium oxide reacts with SO ₂ and the excess oxygen or with SO ₃ to form calcium sulfate.

which accumulates in the ashes. If calcium hydroxide or lime is not used as an additive instead of calcium oxide, these must first decompose:

Without going into the reaction parameters or the reactions in detail, it should be noted that the effectiveness of desulfurization of flue gas in the boiler depends on a large number of parameters and is highly complex. Among other things, the type of coal, the partial pressure of SO ₂ , the excess of oxygen in the flue gas, the reaction temperature or the reaction temperature gradient, the dwell time of the additive in the flame zone, the turbulence in the combustion chamber, and the place where the additive is blown in play an important role into the combustion chamber, the speed of the additive blown in and other conditions, all of which are difficult or impossible to control. It is also important that calcium sulfate formed cleaves SO ₂ again at temperatures above 1200 ° C. and that the CaO particles begin to sinter at temperatures above 1250 ° C., as a result of which the surface of the additive becomes inactive. - Although this technology, which is still in the experimental stage, promises good approaches, it is still a long way from using it with economic success.

The above-mentioned technology for integrating SO ₂ by additives in the boiler, the predominant Concerning hard coal as fuel, a desulfurization process for lignite firing must be added, in which the additives are mixed with the fuel before the fuel is fed into the burner. Although this latter technique has been successfully tested on a pilot scale for lignite, its application for hard coal firing delivers much poorer levels of desulfurization. The reason for this obviously lies in the higher flame temperature of the hard coal, whereby the additives added to the fuel are subjected to the entire temperature spectrum of the flame, and must pass through temperature ranges which can lead to the decomposition of the sulfate already formed and to additive surface sintering.

A system has also been investigated in which additives are blown into the combustion chamber above the flame area by air jets. Desulphurization was far better than mixing fuel with additives in front of the combustion chamber. Such systems, however, only work promisingly in small steam generators, because the way in which the additives are blown into the combustion chamber, especially with large flue gas volumes, requires a very high mixing energy in order to achieve good mixing of the reactants. In addition, this mixing takes place for the most part in the boiler area, where there are no optimal reaction conditions for the incorporation of the sulfur in terms of temperature and residence time.

Worsened conditions also result in a large boiler with several burners, which are arranged next to and on top of each other. This creates very complex flow patterns and temperature fields. It should be decisive that an optimal temperature / time history of the injected additive cannot be guaranteed for a safe integration of the S0 ₂ into the additive.

In contrast, the invention has for its object to provide an inexpensive method and devices with which fossil fuels can be desulfurized so that when they are burned in the boiler room, significant amounts of SO _" no longer arise or can have a harmful effect.

This object is achieved in that the fuel and the additive are prepared in separate disintegration processes, that an amount of freshly prepared additive corresponding to its sulfur content is then added to the disintegrated fuel, and that this fuel-additive mixture is then under a controllable positive pressure and heated transport gas - while maintaining the mixing - is transported to a reactor designed as a leading section, in which the transport gas pressure suddenly relaxes and, in a low-oxygen inert gas atmosphere within a controllable temperature range above the boiling point of sulfur, the residence time of the mixture is adapted to the thermodynamic and reaction-kinetic sulfur transfer process taking place is, in which the sulfur is expelled from the fuel and the additives are loaded with the sulfur vapor or the gaseous sulfur compounds, whereupon in which fuel largely freed of sulfur is blown into the combustion chamber and burned at a temperature at which the loading of the additive particles likewise blown into the combustion chamber with the sulfur vapor or the gaseous sulfur compounds is maintained until sintering.

With the method characterized in claim 1 and in subclaims 1-15, it is possible to expel the sulfur content from the fuel even before the combustion chamber.

The disintegration of the fuel, for example the coal, normally takes place in an inert gas atmosphere in a disintegrator, preferably in accordance with German patent application DE-OS 3 034 849.3, in order to avoid self-ignition of the fuel when it is comminuted.

The disintegration of the additive, on the other hand, also takes place in a disintegrator, but in an independent disintegration process (preferably in a normal air or oxygen atmosphere), as a result of which oxygen is added to the additive particles, which causes the later loading of the additive Particles favored with the sulfur vapor or the gaseous sulfur compounds that are expelled from the fuel.

The fuels and additives prepared in separate disintegration processes are then mixed with one another, with the finely divided fuel being mixed with a quantity of freshly prepared fine-grained additive corresponding to its sulfur content — in no case deposited, already aged additive powder.

The mixture of finely divided fuel and highly active additive is then preferably transported through an inert transport gas heated to approximately 500 ° to 600 ° C. to a reactor designed as a leading section, this transport preferably taking place under a controllable excess pressure between 4 and 6 bar. This overpressure is necessary to prevent degassing of the fuel in the transport line, the length of which depends on the structural conditions available in front of the combustion chamber. For safety reasons, the disintegration of the fuel and the additive to fine dust is usually not carried out near the combustion chamber.

When the pressurized transport line flows into the reactor, the pressure of the hot transport gas (controllable) is suddenly released by the enlarged cross-section of the reaction chamber and the pressure drop is used via a control device to build up a vortex zone, in its agglomeration-inhibiting and agglomeration-dissolving turbu limits temperature and residence time are so controllable that the thermodynamic and reaction kinetic process of sulfur transfer from the fuel to the additive can be adapted to the chemophysical properties of the fuel-additive mixture.

Under these conditions, which can be controlled with an electronic process computer, a sulfur transfer takes place from the pulverized fuel heated up to the given reaction temperature in the advance conveyor section to the highly active, reactive additive, which is also brought to the given reaction temperature, due to the fact that the shock-like pressure release of the conveying gas when it flows into the Reactor of the leading section, the vaporization temperature of the sulfur and the reaction temperature of the gaseous sulfur compounds are also reduced in a shock, so that the sulfur is expelled from the fine fuel particles by almost explosive evaporation, or the gaseous sulfur compounds are suddenly split off and released from the more reactive additive with the release of oxygen in the spinal zone. The pressure in the vortex zone of the reactor is specified by the process control for this process sequence by 0.25 bar. A release of volatile components of the fuel is limited, which in no way negatively affect the combustion process.

The fine-grained solid fuel, which has largely been freed of its sulfur content, together with its already released volatile components and the sulfur-laden additive particles, is fed to the burner via a short delivery line behind the inlet section and blown into the combustion chamber there, enriched with combustion air. Due to the already released volatile constituents, the fuel burns out immediately after the burner nozzle. Under certain safety precautions, support torches can therefore be dispensed with.

By blowing the very fine-grained additive particles, which have already been heated to a temperature between 500 ° and 600 ° C in the lead section, into the hot flame zone of the combustion chamber immediately after the injection nozzle, the additive is sintered almost shockingly and thus does not “seal” together with the others combustible fiber of the fuel supplied to the ashes. For this process sequence, the combustion temperature can be operated below 1850 ° C, but above 1250 ° C, so that the sintering of the shock ensures that sulfur is incorporated into the additive, but that the sulfur molecules are broken down into individual sulfur atoms by thermal energy, which can occur explosively, before Sintering is prevented. By splitting the sulfur molecules, the binding to the additive is lost due to a spontaneous rejection reaction. In the lower-temperature flue gas zone, sulfur molecules can build up again and S0 ₂ formation can result from reaction with the residual oxygen contained in the flue gas. Such pollutant-laden flue gas immissions are avoided by the method according to the invention and the electronically process-controlled system technology used in connection therewith.

The new process enables gaseous, or at least gaseous, sulfur compounds to be transferred to an additive. It is important that due to the pressure and temperature control in the lead section, coking of the fuel, i.e. an unwanted complete degassing before the combustion chamber can be prevented.

Since the solid additive itself is not combustible, due to its special reactivity it can hold vaporized sulfur or gaseous sulfur compounds at the given combustion temperature spectrum in such a way that desorbation does not take place. The advantage here is that the burner, chimney and flue gas outlet can consist of less good material, since they are not - as before - exposed to the aggressive S0 ₂ influence.

The mixture of non-degassed, but freed from the sulfur constituents or fuel particles and additive particles with the incorporated sulfur reaches the combustion chamber in a well preheated state and does not extract as much thermal energy from the flame cone as cold-introduced mixtures of coal particles and additive Particles.

According to the invention, it is possible to achieve almost full desulfurization of fossil fuels upstream of the burner. Under special conditions, residual desulfurization of the fuel can also take place in the combustion chamber itself.

Particularly good results are achieved when highly active sulfur-binding additives are used which have been processed using a turbo-integration process. The quantity of additives must be matched to the fuel used. As a rule, good results are achieved if at least four times the amount of its sulfur content of freshly prepared highly active additive, preferably limestone or quicklime flour with a grain size of 50% below 30 °, is added to the fuel.

According to the invention, coal can be used as fuel, which is processed in a turbo disintegration process.

The expulsion of the sulfur from the fuel and the intensive reactions between the expelled sulfur and the additive are promoted according to the invention in that the sulfur transfer process takes place in a vortex zone, the turbulence of which builds up optimal reaction zones.

The system for achieving low-SO _x smoke gases in the operation of combustion systems for carrying out the method according to the invention with a device for injecting mixtures of fuels and finely divided additive parts into the combustion chamber and with a deashing plant, through which - with the ashes - the sintered additive particles loaded with sulfur are also removed, has a pressure transmitter vessel designed as a buffer for an intimate mixture of fuel and additive particles prepared in separate disintegration processes on. This pressure transmitter vessel is on the one hand connected to a line for compressed, heated, inert transport gas and on the other hand via an arrangement for loading this transport gas with the mixture of fuel and additive particles, via a further transport line to one for evaporating the sulfur to 500 ° C. to 600 ° C. ° C heatable flow lines connected. A shock-like relaxation of the pressure takes place in this lead section due to the widening of the cross section between the transport line and the lead section. As a result of this and because the residence time of the mixture in the vortex zone within the feed section can be controlled by throttling or deflecting devices and / or sieve plates, one is able to desulfurize practically any fuel according to the invention.

The temperature within the lead section must be above the equilibrium temperature of sulfur and its steam, preferably between 500 ° C and 600 ° C.

Further advantageous refinements of the system result from claims 16-28. All control valves, mixing valves, metering and throttling devices can be operated electrically, but also pneumatically or hydraulically, or via a process computer that controls the entire process in connection with an SO _Z measuring device installed in the flue gas outlet - if necessary also in connection with one in the lead section installed thermometer - can control. With the device according to the invention, an optimal desulfurization of the fuel can be made possible without the coal being completely degassed in front of the combustion chamber. According to the invention, the parameters for the proper course of the desulfurization process can be optimally set by many control means, for example in accordance with the coal. According to the invention, suitable measuring devices, evaluation circuits and control devices are therefore provided, with the aid of which the reaction temperature in the lead section or in the reactions and the pressure can be optimally adjusted.

Embodiments of plants according to the invention are explained below with reference to the drawing.

• Fig. 1 ein prinzipielles Verfahrensfließbild und
• Fig. 2 ein Verfahrensfließbild eines bevorzugten Ausführungsbeispieles der Erfindung.

It shows:

• Fig. 1 is a basic process flow diagram and
• Fig. 2 is a process flow diagram of a preferred embodiment of the invention.

1 schematically shows a furnace 1, of which a combustion chamber 2 and a flue gas outlet 6 are shown in simplified form. An evaporation pipeline 3 is indicated above the combustion chamber 2, for example.

A burner device 4 is supplied with combustion air in a conventional manner via a combustion air supply line 11 and a conveying fan 12.

Below the combustion chamber 2, a known ash removal system 5 is indicated schematically.

A dust separator 7 and a conventional SOr knife 8 are provided in the flue gas outlet 6.

The combustor 4 is supplied with the necessary fuel in the form of gas or fuel particles from a lead section 27 via a transport gas line 9, in which finely divided, preferably solid fossil fuels, the bound sulfur is removed. In the exemplary embodiment shown, the lead section 27 has a double wall 28 which is connected via a heating gas line 26 and a heat exchanger 25 in the combustion chamber 2 and via a further heating gas line 24 to a flue gas extraction 13 in the flue gas outlet 6. Via the flue gas extraction 13, inert flue gas is removed behind the dust separator 7 by means of a fan 15, behind which the flue gas line 14 is divided into the heating gas line 24 already mentioned and a transport gas line 16, which will be explained later.

In the heat exchanger 25, the heating gas portion of the amount of flue gas withdrawn is heated to the predetermined temperature in order to heat the lead section 27. For the process running thermodynamically in the leading section, pressure and temperature can be regulated so that the sulfur components are expelled from the fuel without the fuel, for example coal, being degassed. Depending on the size of the feed section 27 and the additive used to absorb the sulfur components expelled from the fuel, the temperature of the feed section 27 is kept between 500 ° and 600 ° C., ie above the boiling point of the sulfur. The temperature required in each case is regulated by means of temperature controllers known per se, which are not explained in detail here.

A floating-fluidized or fluidized bed 29, which is known per se, is arranged within the lead section 27 and the reaction space separated by the double wall 28 and is connected to the transport gas line 16 via an inlet line 30 and a control valve 31. The amount of flue gas extracted by the blower 15 passes via the transport gas line 16 and a suction filter 17 to a compressor 18 and then via a control valve 23 via the control valve 31 into the inlet line 30 or via a branched line to a transport gas inlet 47 at a pressure transmitter vessel 44.

A heat exchanger 20 for the transport gas is provided parallel to the control valve 23 and, like the heat exchanger 25, can be arranged in the combustion chamber 2. By means of the control valve 23, the temperature of the transport gas which is branched off for the floating fluidized bed or fluidized bed 29 and also at the Transport gas inlet 47 arrives, can be adjusted or controlled in a manner known per se. It should be noted here that the dedusted flue gases removed from the flue gas outlet already have a not inconsiderable initial temperature. The transport gas therefore does not need to be heated up from the relatively cold ambient temperature.

It is advantageous if the temperature of the transport gas is set between 500 ° and 600 ° C for both purposes. The temperature is controlled, for example, by an electronic process computer 55, which will be explained later.

The gases entering the lead section 27 through the inlet line 30 are used in the usual manner known per se to form a floating fluidized bed or fluidized bed 29, the intensity of which can be influenced by the control valve 31.

In addition, a further metering device 39 known per se can be provided, with which a further influencing of the floating-fluidized or fluidized bed within the lead section 27, for example the pressure within the lead section, is possible.

The intimately mixed fuel and additive particles are fed to the advance section 27 via a transport gas line 49 from a known pressure transmitter vessel 44 with an inlet slide 45 and an outlet slide 46 for secure shut-off, which in turn via a delivery line 42 to one in connection with the present invention not explained, known mixing device for coal dust and additive particles, is connected. Via an additional line 43 with a corresponding control valve 48, additive can be introduced into the delivery line 42 as required.

It is advantageous if a throttle device 38 is provided in front of the outlet slide 46.

All the control valves, preferably the control valves 23, 31, 48, but also the throttle device 38, can be influenced, for example, by means of an electronic process computer, generally designated 55, by the SO ₂₇ knife 8 in the flue gas outlet 6, if appropriate also by the temperature in the lead section. so that the reactions in the upstream section, ie the desulfurization of the fuel and the incorporation of the sulfur components into the additive particles, take place fully under the control of the electronic process computer 55.

If, for example, the SO ₂₇ values increase, more additive can be added to the mixture in line 42 via control valve 48. The temperature control via the electronic process computer 55 can be influenced by a thermometer 21 arranged, for example, in the lead section 27 by acting on the control valves 23 and / or 31. The electronic process computer 55 is also operatively connected to the metering devices 38, 39 in order to influence the dwell time in the lead section 27. Without changing anything at the core of the invention, the control or regulation of the fuel desulfurization in front of the combustion chamber 2 can also be carried out by other controls or by hand. A metering device 34 and a throttle valve 59 are provided in front of and behind the lead section 27, which are also connected to the electronic process computer 55. With these control elements, the dwell time in the lead section 27 and also the internal pressure conditions can be precisely controlled.

1 shows a very general process flow diagram to explain the new process for the desulfurization of fuel and a device suitable therefor. It is important that 4 short lines are provided between the lead section 27 and the burner device so that fuel and additive cannot cool down and agglomerate. 1 shows that with relatively simple means the new fuel desulfurization process can be used advantageously with the aid of the device explained both on new combustion plants and also on existing combustion plants 1. In all applications, the fuel particles are largely or completely desulfurized in front of the burner device 4. This minimizes or completely avoids the SO, 7 emissions in the combustion chamber and in the flue gas outlet 6, as well as the resulting contamination and destruction of these parts of the boiler system. The S0 ₂ is not blown off into the atmosphere.

A preferred embodiment of a plant according to the invention will now be explained in connection with a process flow diagram according to FIG. 2.

Insofar as the same device parts are used in a system according to FIG. 2 as in the system according to FIG. 1, and the corresponding implementations or the like are also used. play, reference is made to the preceding description.

A new feature of the first exemplary embodiment is that a storage container 19 for compressed transport gas is provided in the transport gas line 16 behind the compressor 18, and a control valve 54 for the transport gas is connected to the outlet thereof. In the part of the transport gas line 16 connected to the control valve 54, an oxygen meter 56 can be provided which, when the oxygen content in the conveying gas line 16 becomes too high, switches an inert gas source 50 on and off via a control valve 51 in order to introduce more or less inert gas into the Inject transport gas line 16. This ensures that the mixture of fuel and additive particles cannot ignite before or in the lead section.

The transport gas line 16 divides behind a further control valve 52. A bypass line 41 is guided over a heating device 37, in which the conveying gas is heated.

A line 40 for normal-temperature conveying gas branches off via a mixing valve 53, which line is connected to the bypass line 41 in front of the transport gas inlet 47 in the pressure transmitter vessel 44 reunited. The control valve 52 and the mixing valve 53 can be actuated by the electronic process computer 55, which can be influenced by the SO, 7 knife 8, in order to adjust the temperature of the transport gas for the intimately mixed fuel and additive particles. The heating device 37 can be arranged in the combustion chamber 2. In the present exemplary embodiment, it is installed in a double wall 36 of a fluidized bed reactor 32, which is heated via the heating gas line 26, in which a regulating valve 58 is provided, which can be controlled, for example, by a thermometer 57 in the fluidized bed reactor 32.

The temperature in the fluidized bed reactor is set depending on the fuels fired. In principle, the temperature has to be regulated so high that the sulfur components certainly escape from the fuel particles. It is advantageous if the temperature inside the fluidized bed reactor is above the boiling point of sulfur. Quick and good results can be achieved if the temperature inside the fluidized bed reactor is kept between 500 ° and 600 ° C.

An inlet 33 of the fluidized bed reactor 32 is connected via a metering device 34 connected to the process computer 55 and / or via a metering device 39 and via the transport gas line 49 to the outlet of the pressure transmitter vessel 44.

A throttle or deflection device 38 is arranged within the temperature-controlled fluidized bed reactor 32, behind which a fluidized bed 35 is formed from the transport gas loaded with the intimately mixed fuel and additive particles. In the fluidized bed, the sulfur components are driven out of the fuel and taken up by the additive. The dwell time required for this can be controlled via the metering device 34 and / or via the metering device 39, but also with the aid of a throttle valve 59 behind the lead section 27, for example by the electronic process computer 55. Due to the temperature control, the sudden drop in pressure and the adjustable dwell time, the additive is loaded with the sulfur components. If the sulfur components expelled from the fuel were not absorbed to the required extent by the additive, SO ₂ components would form during combustion in the combustion chamber and are displayed by the SOrMesser. The process control then either causes more additive powder to be fed into the line 42 via the control valve 48, the residence time in the fluidized bed reactor is increased, the reaction temperature is increased or the pressure difference between the transport line 49 and the flow path 27 is changed.

In the delivery line 42 for the intimately mixed fuel and additive particles, an additional amount of additive particles can be entered via an additional line 43 and a control valve 48. In the exemplary embodiment shown, the control valve 48 is likewise connected to the electronic process computer 55 in order to always ensure the excess of additive particles in the mixture which is necessary for the desulfurization. It is advantageous if at least four times the amount of additive particles contained in the fuel is available for the integration of the sulfur components.

Without changing anything at the core of the invention, the plants shown in FIGS. 1 and 2 can also be combined with one another if the fuel used requires that a residual desulfurization of the fuel must be carried out behind the fluidized bed reactor 32 in a reaction zone 27 before harmful combustion of the sulfur to S0 ₂ takes place in the combustion chamber 2. It is of great advantage if coal dust particles are used as fuel, which, for example, by means of the turbo disintegration process with impact speeds of over 100 m / sec. and a grain size of 50% under 40 µ has been prepared from coal if possible. Particularly good results are achieved when the carbon particles are processed at impact speeds of over 200 m / sec. he follows. The carbon particle surfaces are then not compressed - as is the case, for example, when the coal is crushed in ball mills - but "broken up" in preparation for a more effective desulfurization. The temperature and pressure control practiced in the leading sections according to the invention only cause the sulfur constituents to be expelled, but not a simultaneous full degassing of the fuel. Fuel particles that are led into the boiler room 2 over the short distance between the lead section and the burner chamber are therefore not coked, but rather fully-fledged, sulfur-free fuel.

Highly active sulfur-binding additives, for example limestone powder, quicklime powder or calcium hydroxide powder, are also obtained by processing these additives using the turbo disintegration process at high impact speeds of up to over 200 m / sec. With this preparation, grain sizes of 50% below 30 11m are achieved. The additive particles do not have a compacted surface, as is the case with comminution in ball mills, but a surface with a broken structure that is highly active. It can saturate faster with the expelled sulfur components at the temperatures maintained and during the adjustable dwell time.

The device according to the invention allows it to be adjusted to different fuels without difficulty. One is able to vary the constituents of fuel particles in the mixture and also to optimally adapt the temperature control and the dwell time in the leading sections to the fuel and its sulfur content. By removing the transport gas from the flue gas outlet 6, oxygen-poor gas is already available for pneumatic conveying addition. The mixture cannot ignite. If the oxygen content in the transport gas nevertheless exceeds the values to be observed for safety reasons, inert gas can also be added to the transport gas removed from the flue gas.

Before the fuel treated in this way burns in the combustion chamber, the sulfur is largely removed from it, so that the combustion chamber S0 ₂ can no longer be formed in a dangerous concentration or is no longer present.

The following generally applies to both exemplary embodiments of the invention:

The fuel and additive are processed in separate disintegration processes. The fuel is processed or comminuted in an inert gas atmosphere, primarily to prevent the fuel from spontaneously igniting. The additives, on the other hand, are processed in a normal air or oxygen atmosphere in which oxygen can accumulate on the additive particles, which contributes significantly to the activation of the additive particles and promotes the binding of the sulfur components to the additive.

List of terms used

• 1 furnace
• 2 combustion chamber
• 3 evaporation pipeline
• 4 burner device
• 5 ash removal system
• 6 flue gas extraction
• 7 dust separators
• 8 SOr knives
• 9 Transport gas line
• 10th
• 11 Combustion air supply
• 12 conveying fans
• 13 Flue gas extraction
• 14 flue gas pipe
• 15 blowers
• 16 Transport gas line
• 17 suction filter
• 18 compressors
• 19 storage container for compressed transport gas
• 20 heat exchangers for compressed transport gas
• 21 thermometers
• 22
• 23 control valve
• 24 heating gas line
• 25 heat exchangers
• 26 heating gas line
• 27 lead distance
• 28 double wall
• 29 Floating fluidized bed
• 30 inlet line
• 31 control valve
• 32 fluidized bed reactor
• 33 inlet
• 34 dosing device
• 35 fluidized bed
• 36 double wall
• 37 Heating device for transport gas
• 38 throttle device
• 39 dosing device
• 40 Transport gas line for normal temperature transport gas
• 41 Transport gas line for heated transport gas (bypass line)
• 42 delivery line
• 43 Additional line
• 44 pressure transmitter vessel
• 45 inlet valve
• 46 outlet slide
• 47 Transport gas inlet
• 48 Control valve for additive additive
• 49 Transport gas line
• 50 inert gas source
• 51 Inert gas control valve
• 52 Transport gas control valve
• 53 mixing valve
• 54 Transport gas control valve
• 55 electronic process computer
• 56 oxygen meter
• 57 thermometers
• 58 regulating valve
• 59 throttle valve

Claims (29)

1. A process for attaining flue gases low in SO, in furnaces operated with finely divided carbon- containing fuels, particularly coal, in which process the sulphur contained in the fuel is fused with a finely divided additive, preferably limestone powder (CaCO_a), caustic lime powder (CaO) or calcium hydroxide powder (Ca(OH)₂) and the desulphurized fuel is subsequently burned in the combustion chamber and the additive particles loaded with the sulphur are sintered and removed with the ash, characterized in that the fuel and the additive are prepared in separate disintegration processes, that the disintegrated fuel is then mixed with newly prepared additive in an amount corresponding to the sulphur content of the fuel, that this fuel-additive mixture is then transported by a heated-up transport gas under a controllable excess pressure - while maintaining the mixture- to a reactor designed as a leading zone (27, 32), wherein the transport gas pressure suddenly drops and that in a low-oxygen atmosphere of inert gas within an adjustable temperature range above the boiling point of sulphur the residence time of the mixture is adapted to the proceeding thermodynamic and reaction-kinetic sulphur transfer process, in which the sulphur is expelled from the fuel and the additives are loaded with the sulphur vapour and the gaseous sulphur compounds, whereupon the fuel substantially freed from sulphur and injected into the combustion chamber is burned at a temperature at which the loading of the likewise injected additive particles with the sulphur vapour and the gaseous sulphur compounds is maintained up to the sintering process.

2. A process according to claim 1, characterized in that the disintegration of the fuel takes place in an inert gas atmosphere, while the disintegration of the additive takes place in a normal atmosphere of air or oxygen, respectively.

3. A process according to claims 1 and 2, characterized in that the highly active sulphur-binding additives are prepared by means of the disintegration technique with high rates of impact, preferably by means of the turbo-disintegration technique with impact rates exceeding 100 m per second.

4. A process according to claims 1 to 3, characterized in that the fuel is mixed with newly prepared highly active additive, 50% of whose particle size is lower than 30 pm, in an amount of at least four times the sulphur content of the fuel.

5. A process according to claims 1 to 4, characterized in that finely divided coal is used as the fuel which is converted into coal dust by means of the turbo-disintegration technique with impact rates exceeding 100 m per second and that 50% of said coal dust has a particle size below 40 pm.

6. A process according to the claims 1 to 5, characterized in that the mixture of coal dust and finely divided additive is transported by means of a heated-up inert transport gas which is low in oxygen.

7. A process according to the claims 1 to 6, characterized in that the leading zone (27, 32) is heated to a temperature of between 500 and 600 °C.

8. A process according to claims 1 to 7, characterized in that for transporting the mixture of coal dust and finely divided additive and for heating the leading zone (27, 32) inert flue gas free from dust is drawn from the flue gas outlet (6) of the boiler plant (1).

9. A process according to the claims 1 to 8, characterized in that a partial amount of the transport-gas component of the amount of flue gas removed is heated to a temperature of between 500 and 600°C and mixed with an amount of non- heated transport gas for controlling the temperature prior to assuming the transport function.

10. A process according to the claims 1 to 9, characterized in that the transport-gas component of the amount of flue gas removed has an excess pressure of between 4 and 6 bars on assuming the transport function.

11. A process according to the claims 1 to 10, characterized in that the gas-tight leading zone includes a fluidized bed (29) and/or a fluidized-bed reactor (32) wherein the fluidized bed (35) is constructed by fluidizing the transport gas loaded with the mixture of coal dust and additive and/or by injecting heated flue gas into the transport gas flow leaded with the coal dust-additive mixture.

12. A process according to the claims 1 to 11, characterized in that the mixture ratio of coal dust and additive is controlled as a function of S0₂ measured in the flue gas outlet of the furnace.

13. A process according to the claims 1 to 12, characterized in that inert gas is added to the transport gas when its oxygen content is inadmis- sibly increased.

14. A process according to the claims 1 to 13, characterized in that the combustion of the fuel in the combustion chamber occurs at a temperature of between 1850 and 1250°C.

15. A process according to the claims 1 to 14, characterized in that the sulphur in the leading zone is expelled abruptly from the fuel with the drop of the transport gas pressure from 4 to 6 bars to 0,25 bar.

16. A process according to the claims 1 to 15, characterized in that the additive particles loaded with the sulphur vapour and the gaseous sulphur compounds are sintered abruptly in the combustion chamber.

17. A device for attaining flue gases low in SO_x in the operation of furnaces for carrying out the process according to the claims 1 to 16, comprising a means for injecting mixtures of fuels and finely divided additive particles into the combustion chamber and an ash removal plant by means of which the sintered additive particles loaded with ash as well as those loaded with sulphur are removed, characterized in that a pressure transfer vessel (44) designed for intermediate storage of an intimate mixture of fuel and additive particles prepared in separate disintegration processes is connected to a line (16) for compressed heated inert transport gas on the one hand and connected on the other via means (38, 46) for loading this transport gas with the mixture of fuel and additive particles and via a transport line (49) to a leading zone (27, 29, 32) which can be heated to a temperature sufficient for evaporating the sulphur and wherein the transport gas pressure drops as compared with that in the transport line (49) and the residence time of the mixture in the eddy zone is controllable by damper and reversing means (34, 38, 50) by screening plates (39).

18. A device according to claim 17, characterized in that flue gas is used for heating the leading zone (27, 29, 32) and as the transport gas for the mixture of fuel and additive particles and that for the extraction (13) of the flue gas there is provided a blower (15), which is linked up behind a dust separator (7) in a flue gas outlet (6) of the furnace (1).

19. A device according to the claims 17 and 18, characterized in that the flue gas line (14) is branched behind the blower (15) into a heating gas line (24) and a transport gas line (16).

20. A device according to the claims 17 to 19, characterized in that the heating gas line (24) is connected to the heating device (28) for the leading zone (27, 29, 32) via a heat exchanger (25) disposed in the combustion chamber (2) of the furnace (1).

21. A device according to the claims 17 to 20, characterized in that the transport gas line (16) is joined to a storage pressure tank (19) for the transport gas via a compressor (18).

22. A device according to the claims 17 to 21, characterized in that the outlet of the storage pressure tank (19) is connected to the pressure transfer vessel (24) via a control valve (54) and mixing valve (53) for adjusting pressure and temperature of the transport gas and that ahead of the mixing valve (53) a bypass line (41) branches off from the transport gas line and that said bypass line runs via a heating device (37) and before the transport gas line (40) is joined to the pressure transfer vessel (44) said bypass line is again connected to said transport gas line.

23. A device according to claim 22, characterized in that the heating device (37) for heating the transport gas component passed through the by- pass line (41) is disposed in the heated leading zone (27; 29, 32).

24. A device according to the claims 17 to 23, characterized in that an inert gas source is connected to the outlet of the storage pressure tank (50) via a control valve (51).

25. A device according to the claims 17 to 24, characterized in that the inlet and the outlet of the pressure transfer vessel (44) for loading the transport gas with the mixture of fuel and additive particles are lockable by means of an inlet slide (45) and an outlet slide (46).

26. A device according to claim 17, characterized in that the leading zone includes a fluidized-bed reactor (32) with impact and guide devices (35, 36) and/or a fluidized bed (29) having an additional inlet (30) for flue gas and a controllable damping and dosing device (59/39) for transport gas.

27. A device according to claim 26, characterized in that the fluidized-bed reactor (32) has a double wall (36) which is connected to the heating gas line (24, 26) and that the heating device (37) for the transport gas component passed through the bypass line (41) is disposed in said double wall.

28. A device according to claim 24, characterized in that the control valve (51) for the inert gas source (50) is in operative connection with an oxygen measuring device (56) in the transport gas line (16).

29. A device according to the claims 17 to 28, characterized by an S0_2-measuring device in the flue gas outlet (6) which is in operative connection, when required together with a thermometer (21) in the leading zone (27), via an electronic process computer (55) with the control valve (54) for transport gas behind the storage tank (19) for compressed transport gas, with a further control valve (23) for transport gas, with a control valve (48) in an auxiliary line (43) for additive and with a dosing device (34, 59) ahead of and behind the leading zone (27, 29, 32) as well as with a control valve (31) and damping and dosing devices (38, 39).

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