WO1995025248A1

WO1995025248A1 - Destructive, especially complete combustion, process

Info

Publication number: WO1995025248A1
Application number: PCT/AT1995/000042
Authority: WO
Inventors: Alfred Glasner; Kurt Kaufmann
Original assignee: Austrian Energy & Environment Spg/Waagner-Biro Gmbh
Priority date: 1994-03-17
Filing date: 1995-03-02
Publication date: 1995-09-21
Also published as: DE59500810D1; FI963664A0; EP0750731B1; ES2109815T3; EP0750731A1; FI111987B; CZ272096A3; AT404181B; ATA56494A; FI963664A

Abstract

For the purposes of the complete destruction, especially combustion, of carbon compounds like plastics, hydrocarbons, uncoated or coated paper, slurries and timber waste mixed with halogen-containing material like PVC, i.e. practically sorted domestic rubbish, the hydrocarbons are first mixed in a preliminary stage (7) with hot sand in a water vapour atmosphere, during which water gas is separated off. The degassed residue is taken with the now cooled sand to a fluidised bed combustion process and the gaseous fraction formed in the preliminary stage (7) is taken to a post-combustion process using the fluidised bed exhaust gas as the oxidizer. The hot exhaust gas produced can now be cooled in the ordinary way.

Description

Degradation processes, in particular for complete combustion

The invention relates to a process for degradation, in particular for the complete combustion of carbon compounds, such as. B. Kunst¬ materials, hydrocarbons uncoated or coated paper, sewage sludge and with halogen-containing material, such as PVC, mixed wood waste, in a fluidized bed combustion chamber in the presence of a fluidizing agent in the solid and gaseous state, such as. B. sand and water vapor.

It is known that plastic waste burns quickly with the formation of soot, resulting in a slag-like, difficult-to-burn melt which contains relatively large hydrocarbon molecules, soot but also dioxin units through condensation and causes a loss in calorific value due to non-wiring. It is also known that the sand used for fluidization melts due to excessively high bed temperatures and gives rise to difficulties due to grain size changes in the fluidized bed. The formation of soot and high-molecular hydrocarbons leads to increased CO values in the flue gas and increases the organic carbon content in the exhaust gas from the incineration plant. High combustion chamber temperatures improve the burnout. In a fluidized bed, however, the temperature of the combustion chamber is limited by the ash softening point.

From DE-OS 25 32 994 a process for drying and optionally pyrolyzing products is known, water and / or usable products being removed from the material to be burned by a heat treatment process. However, no two-stage combustion is disclosed. PCT 93/11388 shows a similar process for Drying substances to be burned, which in contrast to our invention intensifies the combustion and thus promotes clumping and only partial combustion in organic substances. From DE-OS 20 38 545 a plant for the destruction of solid waste in a combustion device under pressure and with the inclusion of a gas turbine is known, the exhaust gases of which are used to treat the solid waste to be burned, which after its coking and before its combustion is used for wastewater treatment, whereby water gas is generated.

The object of the invention is to remedy the disadvantages mentioned and to simplify the installation required for this purpose, the combustion of the carbon compounds being controlled in such a way that the formation of slag does not occur and the combustible part is completely converted into heat, with the volatile substances are first split off in water vapor atmosphere at temperatures between 300 ^° and 850 ^° C, whereby the calorific value of the substance is reduced before the actual combustion, so that the combustion temperature remains with certainty below the softening of the sand and the fluidizing property of the Sand is not influenced by coarsening.

A major advantage of the invention is seen in the possibility of removing sewage sludge, which is first dried under vacuum conditions and steam formation and then degassed and burned.

The invention is characterized in that, in order to avoid the formation of high molecular weight condensation products, the carbon compounds are first mixed in a preliminary stage with hot sand from the recirculation as a heat carrier, the carbon compounds being split in a water vapor atmosphere in a manner known per se to form water gas and volatile low molecular weight hydrocarbons and then the combustible residues are burned with the now cooled sand and the water vapor gas mixture generated in the preliminary stage is burned with the exhaust gas from the fluidized bed combustion chamber. Significant embodiments of the invention are specified in subclaims 2-17.

The invention is shown for example and schematically in the connected FIGS. 1 and 2.

1 shows a combustion based on the principle of a circulating fluidized bed. In the case of a circulating fluidized bed, the combustion chamber (1) is essentially filled with a turbulent gas / solid mixture which is separated into a gaseous and a solid fraction in a downstream cyclone (2). The solid is returned to the combustion chamber (1) via line (3, 4), and is enriched with fuel via line (11). In most cases, sand is used as a solid, which in its fine-grained form is a fluidizing agent for the fuel. The fuel sand mixture is fluidized in the combustion chamber (1) by air injection (12), the combustion being controlled by supplying secondary air (5) and the tertiary air (6) to achieve complete combustion. The ashes are separated out in line (3 or 4). In the case of combustion of carbon compounds, such as. B. plastics or hydrocarbons, uncoated or coated paper, sewage sludge and also of wood waste with or without PVC coatings, abbreviated to rubbish, local high temperatures arise in particular as a result of the rapid combustion of the plastics, which melt the fuel and form slag-like residues as well as complicating the further combustion of the substances to be burned and forming lumps which cause difficulties in fluidizing in the fluidized bed and include unburned substances. For the complete breakdown of these carbon compounds, a preliminary stage (7) is provided in the form of a fluidized-bed fluidized fluid chamber in which the volatile substances are split off from the carbon compounds in a water vapor atmosphere, with an endothermic conversion of the water vapor into hydrogen and the volatile Carbon occurs in carbon monoxide. By this measure the calorific value of the carbon compounds is reduced, so that a lower combustion chamber temperature Tempe ^¬ is achieved in the actual combustion in the combustion chamber (1) is no longer possible in which a slag formation. The The conversion of plastics in a water vapor atmosphere does not occur quantitatively to CO, CO2 and H2. Some of the hydrocarbons remain in the form of aliphatic C _X H _V compounds. The formation of aromatics is suppressed since they are only formed at very low oxygen partial pressures. At a higher temperature, the formation of aromatics takes place even at higher oxygen and is therefore more difficult to suppress. The formation of soot and aromatics is undesirable and leads to the precursors of dioxins. So indirectly for the formation of dioxins.

The precursor (7) passes hotter sand as heat transfer medium, which is cooled by the melting and gasification process and the endothermic water gas formation. In this sense, the fluidized bed combustion is expediently designed as a circulating fluidized bed, the circulating solid being sand and / or ash, in which carbon compounds to be split are introduced via a steam supply (13), but the carbon compounds melt due to the high temperature of the sand cannot burn due to lack of oxygen and spread in the sand. The volatile gaseous components react with the water vapor for the heat-consuming water gas reaction and hydrogen and carbon monoxide are formed. It is essential that the gas-forming reaction takes place in a highly turbulent zone, that is to say in a fluidized bed, so that the molten substances which partially decompose are distributed evenly in the sand and drop formation does not occur. The amount of sand is expediently more than 30 times greater in weight than that of the carbon compounds to be mined.

This fuel-sand mixture is now burned out with air supply in the actual fluidized bed combustion, so that practically burned-out sand and combustion exhaust gas are separated in the cyclone (2). This exhaust gas can now be mixed in a further combustion chamber (8) with the water gas formed in the preliminary stage (7), whereby the temperature of the exhaust gas rises further as a result of the combustion that occurs, which then is beneficial in the connected heat exchangers (9 and 10) Formation of water vapor, in particular for the generation of electrical energy, can be cooled. So that the gas does not contain undesirable components such. B. hydrochloric acid or hydrogen sulfide enters the combustion chamber (8), this can be cleaned in a dry absorption chamber (14) from the undesirable gas components and the heat exchanger (10) leaving the exhaust gas is low in pollutant. Part of this gas can be reintroduced into the fluidized bed of the combustion chamber (1) to improve the fluidization or temperature control of the fluidized bed.

In the case of sewage sludge preparation in particular, it makes sense to operate the preliminary stage (7) with negative pressure, the required steam being generated by vacuum evaporation in a degasser (15) and the sewage sludge thereby being dewatered or the liquid separated from the sewage sludge being evaporated.

It is essential that the distribution, melting and decomposition of the fuel takes place in a water vapor atmosphere and the resulting gaseous products are then burned with excess air, the temperature rise during the combustion of the now simplified hydrocarbon compounds resulting in no increased formation of aromatics and thus no formation of dioxins or formation Dioxin precursors leads. The CO and H2 formation (water gas reaction) thus lowers the temperature during the decomposition of the fuel without the formation of aromatic compounds and / or soot.

Within the scope of the invention, as shown in FIG. 2, a stationary fluidized bed can also be used, or the gas generated can also be blown into the fluidized bed, thus simplifying the circuit. If necessary, one of the two heat exchangers (9 and 10) can also be arranged between the fluidized bed and the injection of the degassing gas. The latter measure is particularly effective when the gas is blown in above the stationary fluidized bed.

In a simplified embodiment, the fuel is introduced into the fluidized bed (plenum 20) via line (11) with steam supply (13) into the combustion chamber 1 ^* , the edge zone (18) of the fluidized bed in the combustion chamber 1 'being fluidized with steam is, while the oxygen input for the combustion via the air injection (12) or recirculation gas injection takes place. As a result, the actual combustion in the center (19) of the fluidized bed is achieved and can be regulated simply by supplying air, while the fuel gasifies by supplying heat to the sinking sand (arrow 17 ') in the peripheral zone (18) and partially the fluidizing water vapor in hydrogen splits, the released oxygen is set off by the hot carbon with the formation of CO. These gaseous gasification points rise in the fluidized bed (arrow 17) and burn through the primary and secondary air supply (16) above the fuel inlet.

This results in a circulation of the sand (arrow 17 and 17 ') in the fluidized bed, which flows upwards in the center and downwards in the peripheral zone. Hot gas is thus continuously fed to the gasification in the edge zone (18), which is cooled in it and heated again at the combustion zone in the center (19) during its ascent.

Claims

PATENT CLAIMS

1. Process for the complete combustion of carbon compounds, such as. As plastics, hydrocarbons, uncoated or coated paper, sewage sludge and wood waste mixed with halogen-containing material such as PVC in a fluidized bed combustion chamber in the presence of fluidizing agents in the solid and gaseous state, such as, for. B. sand and water vapor, characterized in that to avoid the formation of high molecular weight condensation products, the carbon compounds are first mixed in a preliminary stage with hot sand from the recirculation as a heat carrier, the carbon compounds in a water vapor atmosphere in a manner known per se to form water gas and volatile low molecular weight hydrogens are split, and then the still combustible residues are burned with the now cooled sand and the water vapor-gas mixture generated in the preliminary stage is burned with the exhaust gas of the fluidized bed combustion chamber.

2. The method according to claim 1, characterized in that the partially outgassed substances in the fluidized bed of the preliminary stage are thoroughly mixed with the recirculated sand and are evenly distributed, the outgassing being carried out as the sand temperature drops and the volatile constituents in the water vapor atmosphere reacting preferably to hydrogen and carbon monoxide while consuming energy, and those that remain finely distributed and still combustible in the sand Solids are burned together with the sand in the downstream combustion chamber in the fluidized bed with the supply of oxygen.

3. The method according to claim 1, characterized in that in addition to the introduction of steam regulated oxygen is supplied in the preliminary stage, in particular in the form of air or recirculation gas, so that the temperature of the escaping partially outgassed substances-sand mixture decreases only slightly below the temperature of the entering hot sand, especially between 450 ^° C and 700 ^° C.

4. The method according to claim 1, characterized in that the combustion is carried out in a circulating fluidized bed and the gasification in the preliminary stage is integrated in the solids cycle.

5. The method according to claim 1 or 4, characterized in that the substances to be burned are mixed with more than 600 ^° C hot from the Wirbel¬ layer of the combustion chamber sand in a zone with water vapor and at least partially gasified, the hot Sand, which is introduced as a heat carrier in the preliminary stage, which supplies the energy required for hydrogen formation.

6. The method according to claim 1, characterized in that the conversion of the carbon takes place in two stages, the volatile substances with at least 30 times the amount by weight of hot sand in a low-oxygen atmosphere being introduced into a turbulent fluidized bed fluidized by water vapor supply, in which the decomposition reactions of the hydrocarbon formed during gasification take place when the substances are melted in a water vapor atmosphere at temperatures above 400 ° C, whereby the gaseous reaction products are separated from sand and unreacted volatile substances and the sand is partly returned to the gasification zone and / or at least partially led into the actual combustion chamber, in which the remaining solid or low volatile content of the introduced is under an oxidizing atmosphere Substances are burned in the form of hydrocarbons or soot formed, further fuels such as coal being used and / or the gases generated from the gasification reaction being burned in excess air.

7. The method according to claim 1, characterized in that water, steam and air or oxygen is introduced for temperature control in the preliminary stage.

8. The method according to claim β, characterized in that the gas generated in the gasification is supplied after leaving the preliminary stage of a gas purification, in which hydrochloric acid and other halogen compounds as well as optionally also hydrogen sulfide are removed.

9. The method according to claim 1, characterized in that the exhaust gases from the fluidized bed combustion, in particular with the gas mixture produced in the preliminary stage, are fed to a downstream combustion chamber.

10. The method according to claim 1 or 9, characterized in that the exhaust gases of the fluidized bed combustion, in particular after their complete combustion are cooled with energy.

11. The method according to claim 6, characterized in that the solids discharged from the gasification zone are heated by oxygen supply to over 600 ^° C and then brought back into a water vapor atmosphere for further degassing by cleavage.

12. The method according to claim 1, characterized in that the pressure is kept absolute during the gasification in the preliminary stage to below 1 bar.

13. The method according to claim 12, characterized in that the distribution of the fuel gas formed in the preliminary stage takes place in the fluidized bed of the combustion chamber via injectors which use air or recirculation gas with a higher pressure or water vapor as the propellant.

14. The method according to claim 12, characterized in that the requisite water vapor for the preliminary stage is obtained from cooling hot waste water by generating negative pressure in a vacuum degasser with steam jet apparatus.

15. The method according to claim 1, characterized in that the degassing and combustion is carried out in a fluidized bed, the fuel being evaporated in a gasification zone by mixing with water vapor and hot sand in a low-oxygen atmosphere, that the degassing gases are removed upward from the gasification zone and are burned locally with recirculation gas and / or primary air above the gasification zone and that the low-volatility fuel components and solid residues with the sand in a downstream combustion zone laterally or below the degassing zone are performed and subsequently burned with air and / or recirculation gas.

16. The method according to claim 15, characterized in that the fuel is introduced into the fluidized bed with steam.

17. The method according to claim 15 or 16, characterized in that the fuel and steam is premixed at low pressure, preferably negative pressure and is then blown into the fluidized bed in an injector by steam at higher pressure.