WO2000027952A1

WO2000027952A1 - Method for processing bottom ash of incinerator plants

Info

Publication number: WO2000027952A1
Application number: PCT/AT1999/000251
Authority: WO
Inventors: Alfred Edlinger
Original assignee: Holderbank Financiere Glarus Ag
Priority date: 1998-11-11
Filing date: 1999-10-19
Publication date: 2000-05-18
Also published as: AU6318899A; EP1047754A1

Abstract

The invention relates to a method for processing bottom ash of incinerator plants, notably of thermal power plants and industrial furnaces, such as blast furnaces, converters, glass tanks or refuse incinerators. According to said method the bottom ashes are transmitted to a fluid-bed gasifier (1), possibly together with fly ash. The fluid-bed gasifier (1) is subjected to hot air, oxygen and/or countercurrent steam and used as crushing chamber (6). The gases withdrawn from the crushing chamber (6) or the fluid-bed gasifier (1) are guided over heat exchangers (9, 11), filtered and at least partly condensed. In the heat exchangers (9, 11) feed water for producing the steam of the countercurrent crusher is heated and supplied to an evaporator (14) and a superheater. The gases of the fluid-bed gasifier (1) which remain after partial condensation are burned to evaporate the feed water.

Description

Process for processing bottom ash from incineration plants

The invention relates to a method for processing bottom ash from incineration plants, in particular from thermal power plants and industrial furnaces, such as e.g. Blast furnaces, converters, glass tanks, waste incineration plants.

For the grinding and disintegration of granular regrind and in particular routes, pozzolans, blastfurnace slag and also fly ash and pre-broken clinker, it has already been proposed to operate jet mills with combustion exhaust gases, in which water or water vapor was also injected. By using combustion exhaust gases together with water or steam, the enthalpy difference resulting from water evaporation was used energetically and a corresponding fineness of grinding was increased not least by introducing the combustion gases in a clocked manner. Due to the temperatures of the hot combustion gases, temperatures between 150 and 700 ° C were achieved in the grinding chamber, which at least around 700 ° C when using limestone or lime marl already enabled at least partial calcination.

In addition to fly ash, thermal power plants and industrial ovens also produce large amounts of bottom ash, the further use and simple grinding of which together with pozzolans, blastfurnace slag, fly ash or clinker would lead to undesired contamination of the end product obtained. Bottom ash of this type contains a high proportion of carbon, which is encapsulated in the bottom ash, so that digestion and sensible disposal of such bottom ash are not easily achieved.

The invention now aims to sensibly process bottom ash of the type mentioned at the beginning and to break it down mechanically and chemically, so that the resulting products can be used economically, for example as aggregates. fabric can be used in the construction industry. To achieve this object, the method according to the invention essentially consists in that the bottom ash, if appropriate together with fly ash, is fed to a fluidized bed gasifier, that the fluidized bed gasifier is subjected to hot air, oxygen and / or steam in the counter jet and is used as a milling chamber, that the from the milling chamber or Gases withdrawn from the fluidized bed gasifier are passed through heat exchangers, filtered and at least partially condensed, that feed water for the steam of the counter jet mill is heated in the heat exchangers and fed to an evaporator, and that the gases remaining in the fluidized bed gasifier after the condensation are burned to evaporate and overheat the feed water . Due to the fact that the bottom ash is fed to a fluidized bed gasifier together with fly ash, a corresponding thermal and chemical digestion takes place in such a fluidized bed gasifier. The fact that hot air, oxygen and / or water vapor is introduced into the fluidized bed at the temperatures of the fluidized bed gasifier and is used as a propellant for a counter jet mill means that fine grinding takes place at a high temperature level, the carbon particles released by mechanical digestion of the bottom ash on the one hand using hot air, Oxygen and / or water vapor are converted to fission gas and on the other hand increase the C content of the ground material. The gasification reaction in the fluidized bed gasifier thus essentially consists of a reaction of appropriately heated carbon with hot air, oxygen and / or water, the steam used for operating the mill being effective as an essential reagent in the fluidized bed gasifier. The steam drawn off from the counter jet mill can be cleaned in a simple manner by condensation, the gas phase remaining after the condensation of the water containing a high degree of chemical energy, since it is largely a cracked gas. The regrind enriched with coal particles and discharged from the counter jet mill can be separated from the coal particles, whereby high-quality graphite-like carbon can be obtained. Because now this gap gas is subsequently used to evaporate the feed water previously heated in heat exchangers, this chemical heat can be used by combustion in appropriate steam generators in the system, so that a particularly economical mode of operation is made possible at the same time as successful processing of bottom ash. The gases remaining after the partial condensation of the fluidized bed gasifier or the steam counter jet mill can be burned in a simple manner to evaporate the condensed water or the introduced feed water. Due to the high calorific value of fission gas, bottom ash can also be introduced into the fluidized bed gasifier or the steam counter jet mill as far as possible in the process according to the invention, since a corresponding partial combustion or heating can also take place in the fluidized bed gasifier.

The process according to the invention is advantageously carried out in such a way that granulated slags or pre-comminuted clinker are fed into the grinding chamber, so that slag or clinker can be effectively ground simultaneously with the processing of bottom ash. The bottom ash, which is largely freed of carbon, contributes to the hydraulic-pozzolanic properties of the resulting product, especially after appropriately fine grinding, so that correspondingly high-quality clinker dust or cement can be produced.

Depending on the composition of the bottom ash and on the amount of bottom ash to be processed, it may be desirable to set the hydraulic properties of the fine product produced in the grinding chamber of the steam jet mill correctly with appropriate additives. Due to the high temperature level, lime or calcium carbonate can be injected directly into the grinding chamber, as at least partially calcining can be observed at the prevailing temperature level of around 250 to 650 ° C. The desired properties of the ground clinker can be improved by adding lime and possibly basalt and / or or aluminum oxides, for example zeolites, are added as additives for adjusting the composition of the ground slags or of the ground clinker.

The greatest possible circulation of the steam required for the operation of the steam counter-jet mill can be achieved by condensation and recycling of the condensate, the condensate of the steam withdrawn from the jet mill being advantageously recycled as feed water. In order to ensure the corresponding pressure level required for the grinding process, the procedure is advantageously such that the feed water is fed to the evaporator under a pressure of 10 to 35 bar.

The process according to the invention is advantageously carried out in such a way that carbon particles are separated from the ground material and / or the product gas from the fluidized bed gasifier and, if appropriate, is used together with the cracked gas to generate steam.

The temperature in the fluidized bed gasifier is advantageously set to 300 to 700 ° C., for which purpose, if necessary, hot, preheated combustion air or oxygen can also be injected into the fluidized bed gasifier in order to set the desired temperature.

With particular advantage, the process is carried out in such a way that the exhaust steam from the jet mill or a downstream filter for separating solids is passed through a vapor compressor and then passed through a heat exchanger for heating feed water. In this way, by increasing the pressure of the exhaust steam in the manner of a heat pump, a large part of the latent heat of vaporization of the pocket filter can be recovered, which further increases the efficiency.

The invention is explained in more detail below on the basis of an exemplary embodiment shown schematically in the drawing. 1 shows a schematic illustration of the Overall system and FIG. 2 shows a section of the system shown in FIG. 1, in which a vapor compressor is connected downstream of the filter for separating solids.

In Fig. 1, 1 denotes a fluidized bed gasifier, via the feed nozzle 2 bottom ash, if appropriate, are added together with fly ash. A fluidized bed 3 is formed in the interior of the fluidized bed gasifier 1, water vapor being blown in via a ring line 4 and nozzles 5 to form a counterflow grinding chamber 6. The ashes gasified in the fluidized bed gasifier are comminuted accordingly in the grinding chamber 6, whereupon the regrind together with the cracked gas which is formed as the gasification product of the fluidized bed gasifier and the water vapor are drawn off via a classifier 7 and a line 8 and passed through a heat exchanger 9. The regrind is separated from the gases in a pocket filter 10, whereupon the gases are passed through a further heat exchanger 11 and the water vapor is condensed. The condensate is separated from the cracked gas in a liquid separator 12 and can then be added to the feed water for the counter jet mill. After increasing the pressure to a pressure of 10 to 35 bar, the feed water for the counter-jet mill is conducted via line 13 via heat exchangers 11 and 9 and via an evaporator 14, whereupon the steam is injected into the fluidized bed gasifier 1 to form a counterflow grinding chamber 6 . The evaporator 14, the fission gas extracted from the condensate is fed via a line 15 as fuel, whereby the high calorific value of the fission gas can be used.

Fig. 2 shows a section of the system shown in Fig. 1. The reference numerals have been retained for the same parts. To increase the efficiency, the vapor filter 10 is followed by a vapor compressor 16. A throttle 17 is connected downstream of the liquid separator 12, via which the condensate reaches another air cooler 18 and is subsequently added to the feed water for the counter jet mill.

Claims

Claims:

1. Process for processing bottom ash from incineration plants, in particular from thermal power plants and industrial furnaces, such as e.g. Blast furnaces, converters, glass tubs, waste incineration plants, characterized in that the bottom ash, if appropriate together with fly ash, are fed to a fluidized bed gasifier (1), that the fluidized bed gasifier (1) is subjected to hot air, oxygen and / or steam in the counter jet and as a grinding chamber (6 ) is used that the gases drawn off from the grinding chamber (6) or the fluidized bed gasifier (1) are passed through heat exchangers (9, 11), filtered and at least partially condensed, that feed water for the steam is present in the heat exchangers (9, 11) the counter jet mill is heated and fed to an evaporator (14) and superheater and that the gases remaining in the fluidized bed gasifier (1) after the partial condensation are burned to evaporate the feed water.

2. The method according to claim 1, characterized in that the grinding chamber (6) granulated slags or pre-shredded clinker are abandoned.

3. The method according to claim 1 or 2, characterized in that the grinding chamber (6) lime and optionally basalt and / or aluminum oxides, e.g. Zeolite A, as additives to adjust the composition of the ground slags or the ground clinker.

4. The method according to claim 1, 2 or 3, characterized in that the condensate of the vapor withdrawn from the jet mill is recycled as feed water.

5. The method according to any one of claims 1 to 4, characterized in that the feed water is supplied to the evaporator under a pressure of 10 to 35 bar.

6. The method according to any one of claims 1 to 5, characterized in that carbon particles from the regrind and / or the product gas of the fluidized bed gasifier (1) are separated and optionally used together with the cracked gas to generate steam.

7. The method according to any one of claims 1 to 6, characterized in that the evaporation of the jet mill or a downstream filter (10) for separating solids out via a vapor compressor (16) and then via a heat exchanger for heating (11) feed water to be led.