FI124206B - Process for the treatment of ash and plant for the treatment of ash - Google Patents

Description

Method for ash treatment and ash treatment plant

The invention relates to a method for treating ash according to the preamble of claim 1. The invention also relates to an ash treatment plant according to the preamble of claim 6.

One way to produce fuel is to gasify a carbonaceous raw material, which produces gas that can be burned. The raw materials are particularly popular waste materials, which are usually organic materials such as 10 different types of wood waste and packaging waste (for example, cardboard and paper). The material is also referred to as recycled fuel.

The gasification is usually effected as a fluidized bed treatment at elevated temperature under undetermined conditions. The resulting product gas is suitable for combustion in, for example, 15 conventional power plant boilers.

The gasification of waste generates fly ash, which is separated from the product gas stream from the gasifier when hot. kuumasuodintuhkana. This ash contains e.g. unreacted carbon (carbon black), bed material, and ash components (including alkali metals, heavy metals, and chlorides) of fuel.

The hot filter ash is high in carbon, about 20-30% by weight. However, the hot filter ash cannot be recovered, but must be delivered to a waste handler to convert it to a disposal form. Due to the high lecithin content, the hot filter ash is a hazardous waste.

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i g Due to its carbon content, the calorific value of the hot filter ash is approximately 8-11 MJ / kg.

i co 30 In order to avoid losing the ash calorific value and reducing the amount of ash x that becomes waste, processes have been developed to burn the ash. Is

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for example, a CFB combustion apparatus has been developed in which the combustion flue gases are introduced into the flue gas channel g after the gasification product gas boiler to the point before the bag filters, whereby they are cooled to below 200 ° C.

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Finnish patent Fl 110266 discloses a method for treating sooty solids in the gasification product gas already in the gasification plant. In this process, the high carbon black ash, which is separated from the product gas stream, is fed to a fluidized bed reactor as an oxidizer, where it is incinerated at 800 to 900 ° C to oxidize the carbon to carbon dioxide. The combustion flue gases are recycled back to the carburettor as secondary gasification gas. Before this, ash is separated from the flue gases.

However, such flue gas recycling is problematic as a solution 10 because the auxiliary gas stream from oxidation is rich in oxygen which complicates the control of the gasification process. Capacity also decreases because the flue gas stream, which increases the inert flow through the carburetor, consumes part of the capacity.

WO 03/055962 discloses incineration of the ash from the gasification in a CFB combustion reactor, where the flue gases are introduced into the product gas from the gasifier, where they are transported through the product gas cooler and the ash filter to the product gas burning boiler. According to the publication, it is also sought to obtain ash particles in the flue gas stream from the combustion reactor which bind the tar in the product gas so that it does not adhere to the product gas cooler.

It is an object of the present invention to provide a process for burning carbonaceous hot filter ash from a gasification process to reduce carbon (soot) and treating the flue gases from the combustion with a simple solution that can be better utilized.

In order to accomplish this purpose, the process according to the invention is characterized essentially by what is shown in the characterizing part of the appended claim co 30. 1 2 3 4 5 2

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The ash separated from the product gas of the gasification process is oxidized in fluidized bed combustion, and the flue gases produced by combustion are introduced into the combustion air of a 4 g boiler (main boiler) product of the gasification process.

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In addition to lowering the carbon content of the gasification hot filter ash, reducing the mass to be disposed of, and utilizing the thermal content of the ash 3, the flue gases containing CO can first be burned in the main boiler combustion air. At the same time, the heat content of the flue gases from the ash combustion can be used to preheat the combustion air. In the main boiler CO 5 oxidizes.

The flue gases from ash combustion are preferably filtered before being introduced into the combustion air of the boiler, whereby the finer ash fraction still present can be separated from them.

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The invention will now be described in more detail with reference to the accompanying drawing, which is a process diagram of an ash treatment plant.

The gasification process is known per se and is not described in further detail. 15 The most common raw material is so-called. recycled fuel, which is a different type of municipal and industrial waste, usually a carbonaceous solid fuel suitable for power generation.

Fly ash separated from the flow of combustible product gas obtained from gasification of fuel is treated in the plant shown in the drawing. Normally, such a plant is located in the same power plant as the gasifier itself and the main boiler of the power plant burning the product gas, which produces energy. The gasification process and the supply of ash (hot filter ash) separated from it as a raw material for the plant are shown in dashed lines. This ash, which contains 25 unreacted carbon (soot) from the gasified fuel, is fed to the fluidized bed reactor 1, which is burned by the oxygen-containing combustion air (arrow A) supplied to the reactor. The fluidized bed reactor also contains solid bed material (sand, limestone, etc.) which can be added if required Reactor 1 is a bricked or fully heat-insulated CFB-i30 reactor (circulating fluidized bed reactor) with no heat exchange surfaces. The combustion temperature in the reactor is below 900 ° C and is adjusted to the desired air coefficient.

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j? The flue gases produced by the combustion process pass through cyclone 2, where the solid material entrained in the flue gases is separated into the circulating fluidized bed reactor ° 35 return circuit. After the return material has been separated, the flue gases are transported along the flue duct 3 via a heat exchanger 4 where their temperature is lowered to about 400 ° C. Filtration is generally preferred 4 to be carried out at a temperature in the range 300 to 550 ° C. Because the flue gases are only cooled to about 400 ° C, no large heat exchanger (cooler) is required.

The coarser fraction of ash is removed from the fluidized bed reactor 1 below the bottom ash chicken 5, and the finer fraction which is not separated in cyclone 2 into the circulating fluidized bed reactor return passes along the flue gas channel 3 through the heat exchanger 4 to the ash separator 5. The ash separator is a gas filter where the fine ash is separated by filtration. The gas filter is so called. a heat filter, for example a fiber-ceramic filter 10.

By means of the heat exchanger 4, the energy obtained from the combustion of the ash coal can be recovered, while the temperature of the flue gases can be lowered to be suitable for filtration. In heat exchanger 4, heat exchange takes place on the 15 indirect principles, i.e., heat is transferred without direct contact from the flue gases to the heat transfer medium.

After the ash separator 5, the flue gas duct 3 is connected to the combustion air duct 6 which supplies combustion air to the main boiler 8 of the gasification plant. Along the combustion air duct 6, the flue gases and combustion air are conveyed to the combustion process of the main boiler 8, where product gas is fed through the duct 7 from the gasification process. 1 The heat exchange in the combustion air duct 6 thus takes place by direct contact between gaseous media. Preferably, the flue gases are connected to the combustion air stream so early that they are mixed with the combustion air and the? Combustion air temperature is stabilized at the time when the combustion air g is injected into the main boiler 8.

cö 30 i The carbon monoxide contained in the flue gases is oxidized to carbon dioxide in the main boiler 8

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the combustion process. Due to the high air coefficient of ash incineration, Sut is also rich in oxygen.

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C \ 1 g 35 From the material balances, it can be estimated that the amount of flue gases from ash combustion does not exceed 10% of the combustion air (expressed as a mass ratio) of the main boiler 8.

Claims (9)

A method for treating ash, comprising separating fly ash from the product gas stream from fuel gasification 5 to be burned in a fluidized bed combustion to reduce the carbon in the ash, and then treating the flue gases obtained in the combustion process with the ash separated from the product gas gasification process. the ash is incinerated in a fluidized bed combustion at a temperature below 900 ° C to reduce the amount of carbon, - the flue gases from the ash combustion are introduced into the combustion air duct (6) where they are mixed with the combustion air, and the flue gases and combustion air product gas as fuel. Method according to Claim 1, characterized in that the fine ash entrained in the flue gases from the fluidized bed combustion is separated off before being introduced into the combustion air. Process according to Claim 2, characterized in that the separation takes place by filtration, before which the flue gases are preferably cooled by a heat exchange. 25 Method according to one of the preceding claims, characterized in that the ash fluidized bed combustion takes place in a circulating fluidized bed (CFB). δ C \ J An ash treatment plant having a fluidized bed reactor (1) arranged to incinerate fly ash separated from the product gas stream x from the gasification of the fuel, characterized in that the flue gas channel (3) of the fluidized bed reactor (1) is connected to the combustion air duct (6) which goes to the same boiler (8) provided with a fuel gasification <J) <3 channel (7) for fuel gasification to burn the product gas in the boiler (8). δ 35 C \ J An ash treatment plant according to claim 5, characterized in that the flue gas duct (3) has an ash separator (5) for separating the ash fraction carried with the flue gases. The ash processing plant according to claim 5 or 6, characterized in that the fluidized bed reactor (1) is a circulating fluidized bed reactor (CFB). The ash processing plant according to any one of claims 5 to 7, characterized in that the fluidized bed reactor (1) furnace is completely heat insulated. 10 An ash treatment plant according to any one of claims 5 to 8, characterized in that the flue gas duct (3) has a heat exchanger (4) for cooling the ash gas, and after the heat exchanger (4) there is an ash separator (5) which is a gas filter. 15 δ CvJ co cp co X IX Q. σ> σ> LO C \ J δ C \ J