FI84561B - FOERFARANDE FOER FOERMINSKNING AV FASTA OCH GASFORMIGA EMISSIONER OCH FOER VAERMEAOTERVINNING VID FOERBRAENNING OCH SMAELTNING AV AEMNEN INNEHAOLLANDE ASKA OCH SVAVEL. - Google Patents

Description

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METHOD FOR REDUCING SOLID AND GASEOUS EMISSIONS AND RECOVERING HEAT WHEN COMBUSTING AND MELTING ASH AND SULFUR-CONTAINING SUBSTANCES

The invention relates to a method by which energy can be produced from ash-containing fuels (e.g. coal, peat, wood, bark) or by melting concentrates or other materials so that inorganic compounds 5 (e.g. fuel ash) in the gases are partially separated in a combustion chamber or melting chamber and possibly in the next melt separator, but mainly in the chamber following the incineration or smelting, which is referred to herein as a particle cooler, into which the temperature of the gases is so high that the ash is molten or steam. Regardless of the combustion or smelting method, the conditions of the particulate cooler can be chosen so that the separation of inorganic compounds and the removal of gaseous oxides (eg SO and NO) harmful to the environment or otherwise from the flue gases can be

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15 performed in the most efficient way possible.

As the use of coal has increased since 1973, the environmental impact of energy production has come to the fore. Looking at global developments, it can be estimated that the increase in energy demand 20 will be met mainly by coal and fission-based nuclear energy.

The competitiveness of conventional energy (coal, biofuels) is significantly weakened by the increasing investments required for environmental protection (NO, SO, dust).

25 This is particularly true of coal, the main source of conventional energy.

By main groups, the known combustion methods can be divided as follows: 1. Suspension or dust combustion: dusty substances, liquids, 30 gases.

2 84561 2. Fluidized bed combustion: suitable for almost all fuels 3. Grate combustion: solid fuel. Suspension combustion is currently the exclusive combustion method for high power units. The coal is then ground to a particle size of 50 to 150 μm and burned with a fusion burner in a furnace or process furnace of a steam boiler.

The suspension combustion of solid ash-containing substances, such as coal, in steam boilers is currently carried out by cooling the ash particles by radiation to a solid state 10 to avoid fouling, before the heating surfaces (e.g. superheaters) at the rest of the radiation section. Especially in large units (Φ> _ 100 MV \ Tt) the result is large radiation chambers with a power / volume level of 3 0.1 ... 0.2 MW / m. Because the combustion temperature cannot be precisely controlled, efficient SO 2 separation cannot be achieved in such boilers without a separate wet scrubber using an alkaline solution. Large coal-fired boilers based on slurry combustion are much larger and more expensive than gas and oil boilers of similar efficiency. An additional burden will be the separation system required to limit SO 2 emissions as environmental protection requirements become more stringent. Fuel ash cannot be recovered without separate filters either.

Fluidized bed combustion has rapidly become widespread in solid fuel plants of less than 100 MWt, as it is well suited to a wide variety of fuels, primarily due to its stability based on high heat capacity.

In fluidized bed combustion, the temperature can be kept almost constant throughout the combustion chamber and thus the possibility of simultaneous combustion and absorption of sulfur oxides into the Ca-based fluidized material is offered. Under oxidizing conditions, SC> x gases bind to calcium or other suitable metals as sulfate (MeSO 4). Today, a large number of different fluidized bed boilers for sulfur-containing combustion 3,84561 are commercially available, with simultaneous combustion and SO absorption in one fully mixed chamber. The problematic limitations of this technique are that sulphates decompose at temperatures above 900 ° C to form SO 2 and metal oxide and effective SO - 2 x absorption cannot be achieved at temperatures above 900 ° C.

Under reducing conditions, sulfur can in principle be bound to metal sulphide, but in practice efficient sulphide absorption requires a very high temperature T> 1300 ° C. In this case, the fuel ash usually melts, and fluidized bed combustion cannot be used due to the sintering of the fluidized material. The lower limit of the temperature range, on the other hand, is limited by the requirement of an adequate reaction rate. The practical limit for valid coal combustion (soot, PAH, CO emissions) is T> 850 ° C.

15 Sulphate decomposition, ash melting and efficient combustion requirement limit the temperature range of combustion and SO absorption in the same reactor to a very small

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850 ° C <T £ 900 ° C. The so-called fuel the organically bound ash is not appreciably recovered by any method based on fluidized bed combustion, but the boilers must always be equipped with dust separation devices. The narrow temperature range means that the load range of the boiler is limited and a compromise between efficient combustion and good SOx absorption.

Attempts have been made to solve these problems by dividing the circulating material of a fluidized bed boiler into two streams, one of which is cooled to maintain a constant temperature (typically 850 ° C) in the furnace over the entire capacity range. These principle solutions lead to technically cumbersome 30 structures that have not been successfully implemented in commercial facilities. This method also has the essential limitation that the cyclone-permeable ash stream (vaporized, small particles d <30 μm) cannot be separated, but a separate dust separation-35 equipment is required.

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European Patent Application 0 027 280 discloses a way to improve the ash separation by agglomerating the feedback of the secondary cyclone in a localized hot area in the fluidized bed. The agglomeration of the ash in the fluidized bed based on 5 local heating must be considered as a known method, of which there are several slightly different implementations. These methods are characterized in that the majority of the fluidized bed operates at a temperature below the melting or sintering temperature of the ash and the agglomeration of the ash is performed by increasing the temperature locally.

U.S. Patent 4,198,212 discloses a process for treating coal gasification product gas in which organic contaminants (tars, acids, carbon) contained in a fluidized bed gasifier are separated by passing the liquefied bed gasifier gases through a cooled fluidized bed to condense the contaminants on the surface of the fluidized bed material. Unreacted carbon is used as the fluidized bed material in the gasification reactor. The corresponding cleaning efficiency can be expected to be obtained in a conventional countercurrent carburetor, where the gases leave through a layer of new gasification material.

Grate combustion is only suitable for solid, combustible fuels. By treating the fuel in a suitable manner (e.g. peat pelletization), the ash separation 25 can be improved than by the known combustion methods described above. Grate incineration is not suitable for large plants because the ash easily melts in the grate, which usually results in a malfunction. In the case of gaseous emissions, grate combustion is poor, since the binding of SO compounds to metal sulphates is practically out of the question. Also for nitrogen oxides, conventional grate combustion is disadvantageous because the overall controllability of the grate combustion process is poor. Locally, areas with high temperatures and excess oxygen are always created locally.

35 In practice, flue gases from grate boilers also require dust separation equipment.

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The method according to the invention provides a decisive improvement in the above-mentioned drawbacks. To achieve this, the device according to the invention is characterized by what is set forth in the characteristic part-5 of claim 1.

The process according to claim 1 is characterized in that the incineration or smelting is carried out by a method known per se in such a way that the inorganic compounds melt or evaporate. The incineration can be carried out as conventional incineration or suspension incineration or multi-stage incineration. In multi-stage combustion, solid fuel gasification is first performed and combustion is continued by adding oxygen to the gasification products so that the ash of the gas entering the particle cooler is molten or steam. Conventional fluidized bed combustion 15 is not possible as a combustion part of the process according to the invention, because the melting of the ash would lead to sintering of the fluidized bed material. However, in a phased combustion, a fluidized bed gasifier can act as the first part. Multi-stage combustion is the preferred method because it does not require fines from the fuel 20 (average particle size of dust combustion <150 μm) and in the gasification stage the fuel nitrogen is obtained in the form of molecular nitrogen (Nj). It is well known that molecular nitrogen (Nj) reacts to nitric oxide more slowly than nitrogen-bound nitrogen. In addition, the excess oxygen from the post-gasification combustion can be kept small, mainly in the post-combustion of gaseous substances.

After combustion or melting, the gases containing inorganic compounds in the vapor and melt phase are passed to a particle cooler, where the inorganic melt and vapors in the gas are deposited on the surface of the particles as a solid material. The solid material forms spherical pellets which are easy to process further.

If the gases contain harmful oxides (e.g. SO 2), the material of the particles can be selected (e.g. CaCO 2) so that the oxides bind to it (e.g. CaSO 4). The temperature of the particles is adjusted by cooling, in the absorption of sulfur, typically to 500 to 900 ° C, so that the conditions for the reaction of the harmful substance with the particulate material are favorable.

By the particle cooler mentioned in the present invention is meant an apparatus in which particles colder than gas mix with the gas, whereby the molten and vaporized ash contained in the gases accumulates on the surface of the particles in a solid phase. To maintain the temperature difference between the particle and gas streams, the particles are cooled inside and / or outside the particle cooler. The walls of the particle cooler chamber may be uncooled or partially or completely cooled. As an example of a particle cooler, a conventional fluidized bed cooler or circulating fluid bed cooler can be mentioned, but the operation of the particulate cooler can also be realized by many other types of gas and particle flow and cooling and other arrangements. Based on the mutual movement of the particles and the gas, the particle cooler 20 may be a co-current cooler, a countercurrent cooler and a downstream countercurrent cooler, and the particle flow direction may be perpendicular or oblique to the gas flow direction. The longitudinal axis of the particle cooler chamber is preferably in the vertical direction, but may also be in an inclined or horizontal position.

There are five important advantages to be achieved by the invention. First, the method can be used to separate the inorganic substance in the gas, e.g. ash from the flue gases, so efficiently that significant savings are made in the investment in gas purification 30 and in the smelting the heat of the gases is better recovered. Second, a certain is achieved in the separation of SO

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level with a lower Ca / S ratio than, for example, in fluidized bed combustion, so the sulfur separation is cheaper. Third, the method solves the problem of vaporized 7,84561 ash compounds associated with solid fuel pressurized combustion in gas turbine operation. Fourth, when using the method, the boiler and boiler building are smaller and cheaper in combustion because flue gas cleaning equipment is not required or is smaller than before and a large tu-5 furnace is required to cool the gases with radiation below the ash melting point, which is an essential advantage in the case of a large boiler. Fifth, the combustion can be carried out separately for each fuel under the most favorable conditions, e.g. sulfur absorption and, to the extent necessary, heat recovery.

In the following, the invention will be explained in detail with reference to the accompanying drawing. Figure 1 shows a combustion method for low ash fuels. Figure 2 shows a combustion process in the phase combustion of high ash fuel kaxsi-15. Figure 3 shows a process according to the invention for the smelting of oxide concentrates. Figure 4 shows a process according to the invention for the combustion of sulfur-rich low ash fuel. Figure 5 shows a method according to the invention applied to an open gas turbine process using solid fuel.

Figure 1 shows a combustion method according to the invention for low ash materials. In the combustion chamber 1, into which the fuel and oxygen are introduced, the fuel burns at such a temperature that the ash contained in the gas 25 entering the lower chamber 2 is in the form of steam or melt. Above the outlet opening 3 of the chamber 2 there is a heat recovery part containing a particle cooler 4 and possibly additional heat flow and 5. The temperature of the particle cooler 4 is chosen so that the inorganic vapors and melts contained in the gases accumulate on the surface of the particles in solid form. If desired, efficient separation of sulfur oxides from the gases can also be provided in the particle cooler 4. The purified flue gases leave the opening 9. The inorganic substance 35 separated in the particle cooler can be removed via a separate outlet 10 8 84561 of the cooler or together with the melt separated in the chamber 2. From the opening in the bottom of the chamber 2, the molten ash flows into the granulation chamber 7 and is removed with the cooling water by means of a pump 8.

Figure 2 shows a process according to the invention for the two-stage combustion of rich ash fuel. In chamber 1, gasification (substoichiometric) combustion is carried out so that the ash can remain in solid form at this stage. In the part 2 10 between the gasifying part 1 and the molten cyclone 3, the additional air required for further combustion is introduced, whereby the temperature rises above the melting temperature of the ash components. In the molten cyclone 3, the separating droplets of melt flow through the opening 5 into the granulation chamber 9. The ash separated in the particle cooler is removed either through a separate outlet 12 or from the bottom of the granulation chamber 9 by means of a pump 10. The heat recovery section necessarily includes a particle cooler 6 and possibly an aftercooler 7. Pure gases escape through the opening 11.

The presented procedure avoids the problems of slurry combustion 20 (expensive boiler, expensive flue gas cleaning, fuel grinding to dust) because the combustion chamber can only be dimensioned according to combustion requirements and heat recovery is performed in a small condenser that can be built on a full heat transfer surface. Due to the small size of the boiler, there are also savings in boiler construction investments.

What is seen in the most commonly used fluidized bed technology today results in investment savings (gas cleaning, small and simple boiler) and a good sulfur-30 separation over a wide capacity range.

Figure 3 shows a process according to the invention for melting a concentrate or other solid. Fuel, melt and oxidant are introduced into the combustion chamber 1 and combustion 9 84561 is performed so that the solid melts. If it is desired to reduce the solid, the combustion in the chamber 1 can also be substoichiometric. Additional oxidant can be introduced in the outlet duct 2 of the combustion chamber 1 and the melt cyclone 3 so that the viscosity of the molten inorganic compounds in the gases 5 is suitable for the melt separator 3. In the melt cyclone, the molten compounds separate mainly on the walls and flow further into the lower furnace 4, where the different phases of the melt separate. The slag is removed through the opening 5 and the heavier phase through the opening 6.

10 Gases containing vapors and melt are passed to a particle separator, where the vapors and melt adhere to the surface of the particles in a solid state. The pelletized inorganic material is removed from the opening 9.

If necessary, the pure gases are further cooled in a condenser 8.

The smelting method can also be used for smelting aggregates and glass, so it can be applied e.g. in the insulation industry in the manufacture of glass and rock wool. The combustible gases generated during the smelting of the Vil process can be utilized in the drying parts of the process, because when using the smelting according to the invention they are sufficiently clean.

Figure 4 shows a process according to the invention for the combustion of sulfur-rich low ash fuel.

The combustion is carried out in chamber 1 as a conventional flame combustion. The flue gases containing sulfur oxides are passed to a Ca-containing particle cooler 2, where the temperature of the particles is chosen so that SO binds to calcium sulphate and at the same time the evaporated ash compounds 30 (e.g. vanadium compounds) of the fuel condense on the surface of the particles.

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The Ca-long material needed to absorb the sulfur is fed together through 5. The sulphate-containing material is removed together in 6 s. If necessary, the purified gases can be further cooled in a condenser 3.

5 It is of course clear that the thermal energy recovered in the coolers of Figures 1-4 can be used e.g. processes, power plants and heating.

Figure 5 shows a method according to the invention applied to an open gas turbine-10 process using solid fuel. The compressor 1 compresses the air, part of which is passed as an oxidizer to the carburetor 2 and the main part passes through the carburetor cooling pipe 3 and the particulate cooler cooling pipe 4 mainly into combustion air into the open gas turbine combustion chamber 5 and a smaller part into secondary combustion secondary air. a melt having a viscosity such that the separation of the molten ash in the molten cyclone 7 is efficient. Most of the ash exits from the opening 8 at the bottom of the cyclone. The gases containing molten ash and vapors pass through the opening 9 to the particle cooler 10, in which gases the remaining molten and vaporized ash often contains e.g. alkalis and vanadium compounds adhere to the surface of the particles mainly at the bottom of the particle cooler. Sulfur does not bind to sulfate-25 under reducing conditions, so particle cooler 10 primarily separates melt and vapors.

The gases purified from the ash compounds are led together through 13 to the combustion chamber 5 of an open gas turbine, to which, if necessary, air 14 is also fed directly to the compressor-30 dispute 1.

The gases 15 of the combustion chamber are led to a gas turbine 16, which rotates both the compressor 1 and the generator 17.

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The gases 18 leaving the turbine are passed to a second particle cooler 19 containing Ca compounds to absorb sulfur dioxide, the temperature of which is selected so as to achieve efficient SOx absorption.

5 The clean low-sulfur exhaust gases are preferably fed to an exhaust boiler or can be used as such for drying or heating.

Claims (9)

1. A process for the combustion of ash and sulfur-containing fuels or for the melting of the heat and for the recovery of heat, so as to simultaneously separate from the gases inorganic substances (ash) and, if necessary, sulfur oxides, characterized in that the combustion or melting is carried out on and off. known method, for example by combustion on rust or in suspension or incrementally and the melting as combustion in suspension, such that the ash components melt or expand and the gases containing molten and diluted gas components are conducted to a particle cooler where the material temperature is such that: the ash attaches firmly to the surface of the material. 2. A process according to claim 1, characterized in that the new particles, which are measured in the particle cooler to remove sulfur oxides from the gases, are made up of all or part sulfate-forming substance. 3. A process according to claim 1 or 2, characterized in that the gases are purified in a melt cyclone before the particle cooler, whereby melted ash or other substance flows into a melt or granulation chamber below the cyclone. 4. A process according to any one of claims 1-3, characterized in that the melted and evaporated components are separated and the sulfur oxides in separate particulate coolers. 5. A process according to any of claims 1-4, characterized in that the heat energy recovered in the coolers is used wholly or partly for processes or in power plants or for heating. Il is 84561 6. A process according to any one of claims 1 to 5 wherein the process is used for phase melting. Process according to Claim 6, characterized in that after the particle cooler, a portion of the purified gases is measured back into the melting chamber. 8. A process according to any one of claims 1-5, characterized in that in a gas turbine process, solid fuel is used, fully or partially the gasification part, the melting cyclone, the particle cooler, the combustion chamber and possibly the subsequent cooler with air are used. 9. A process according to any one of claims 1-5 or according to claim 7, characterized in that the gasification or reducing combustion of the furnace is carried out under the desired pressure and the purified gases are used as raw material or fuel for processes known per se in the industrial or power plant.