Combustion assembly

Abstract

The invention relates to a combustion plant with a first pass (8), with at least one fuel feed (1) for burning a fuel, and with a fluidized bed (2). It is characterized primarily in that a supply of secondary air (4, 4a) for complete combustion in a second pass (5), ideally with downward flow, is arranged in a region separated from the fluidized bed (2) by a deflection (3). The invention also relates to a method in a combustion plant. This arrangement prevents slag adhering to the walls from falling into the fluidized bed and thus avoids unnecessary downtime.

Description

[0001] The invention relates to an incineration plant comprising a fluidized bed; a first pass with a first combustion chamber and at least one fuel inlet for burning a fuel. The invention further relates to a method in an incineration plant.

[0002] At industrial sites where combustible waste is generated, it has proven advantageous to construct incineration power plants. This allows the mass and volume of the waste generated to be significantly minimized, while also allowing the site to partially or entirely cover its own energy needs. Fluidized bed combustion systems are often used for this purpose. Fluidized bed combustion systems have the advantage of being able to burn a wide range of fuels due to the high storage capacity of the bed material. In addition, the excellent mixing in a fluidized bed allows for very homogeneous combustion and thus very low emissions. Many waste materials form ash during combustion, which has a melting point below the typical combustion temperature of such a plant.This occurs primarily in agricultural products such as grasses, straw, grains, energy crops, animal waste products with high alkali contents in the ash or municipal or commercial waste fuels or shredder fractions from metal processing.

[0003] JP2009139043 A discloses a sludge incineration plant comprising a fluidized-bed furnace equipped with a separation device and a post-combustion furnace arranged downstream of the fluidized-bed furnace. JP S58 156107 A discloses a fluidized-bed boiler in which flue gas is fed into a second combustion chamber. The flue gas from the fluidized-bed boiler is diverted through an outlet into the second combustion chamber. EP 0 908 672 A1 discloses a device for treating solid waste. It depicts a fluidized-bed gasification furnace and a fluidized-bed melting furnace, with the gas from the fluidized-bed gasification furnace being fed to the fluidized-bed melting furnace.

[0004] The problems with conventional fluidized bed systems using these fuels are as follows: The formation of eutectics in the fuel ash and the bed material can lead to melting in the fluidized bed, resulting in sintered lumps. These lumps can no longer be fluidized and continue to grow in the fluidized bed until they no longer allow the boiler to operate within the required emission limits. Technological solutions exist for ash melting points up to approximately 600°C. Staged combustion and suitable bed materials can prevent ash from sintering in the fluidized bed. Here, after the fuel is added, air is added again to continue or complete the combustion. This air is also referred to as secondary air. Air is often added again somewhat later (tertiary air).

[0005] A second mechanism, however, has not yet been solved. The low-melting ash, especially when the air supply, particularly the secondary (or tertiary) air, is arranged one above the other and above the fluidized bed in a common combustion chamber, forms deposits on the walls of the combustion chamber. These deposits grow with continued operation of the plant. At a certain size or when combustion conditions change due to load changes, they detach from the wall and fall into the fluidized bed. There they hinder fluidization, which also leads to uncontrolled combustion conditions that necessitate shutdown of the plant. This situation can theoretically be avoided by constant, continuous cleaning of the walls in the combustion chamber. This prevents deposits from growing beyond a critical size; small deposits can be removed from the fluidized bed during operation.In practice, however, this method is difficult to implement because it is not possible to reach every surface and corner of the combustion chamber with heating surface cleaning devices, and constant cleaning results in a loss of efficiency and can cause increased wear on the walls due to corrosion and erosion mechanisms. The system requires frequent cleaning, which causes further high costs, particularly due to the shutdown of the combustion plant. WO 2014 / 184437 A discloses a boiler in which the lower section is divided to create a fluidized bed area and a free area for the removal of slag and ash. Furthermore, the gas is diverted by baffles during the upward flow. JP S58156107 A discloses a boiler in which the gas is fed to a cyclone into which water is injected for cooling. JP S602817 A shows a single-stage combustion with a downward-flow cooler.

[0006] The object of the invention is therefore to provide an incineration plant and a method for burning such fuels which avoids or reduces the above-mentioned disadvantages and enables the direct feeding of fuels with low-melting ashes as fuel into the fluidized bed.

[0007] The incineration plant according to the invention is defined in claim 1. This ensures that ash deposits and slag only form in the second pass without negatively affecting the fluidized bed.

[0008] According to the invention of claim 2, low-melting ash and slag can be removed separately.

[0009] According to the invention of claim 3, complete combustion can be ensured.

[0010] The invention also relates to the method defined in claim 4 in an incineration plant.

[0011] According to the invention, the gases from the fluidized bed are passed into the first pass and the complete combustion takes place in the second pass.

[0012] The invention will now be described by way of example with reference to the drawings, in which Fig. 1 a variant of the invention and Fig. 2 another variant of the invention Fig. 3 an embodiment which is not part of the invention, represents.

[0013] In Fig. 1 A fluidized bed combustion plant is schematically shown, in which bed material such as sand, blast furnace slag, or similar materials is fluidized in a fluidized bed 2 by injection 9 of combustion air and, if necessary, recirculation gas. The solid fuel is thrown or blown into the combustion chamber of the first pass 8 via one or more fuel feed points 1. The combustion chamber in the first pass 8 and the combustion chamber in the second pass 5, separated from it by a 180-degree deflection 3, can be designed to be gas-tight either by pipe walls conducting water and / or steam or by a sheet metal construction. The wall can be protected by brick lining or metallic coatings.

[0014] The fuel from fuel feed 1 is partially combusted in fluidized bed 2, which typically has a temperature of 600-750°C. However, other temperature profiles are also possible.

[0015] Carbonization gases and products of incomplete combustion such as CO, H2, CO2, H2O enter the combustion chamber 8 from the fluidized bed. An embodiment of the invention as described in Fig. 1 shown has several air openings for supporting air 7. This supporting air can combust a portion of the gas emerging from the fluidized bed 2, thereby raising the temperature of the gas to prevent the gas temperature from falling below the ignition temperature of the gas before reaching the secondary air supply 4.

[0016] The combustible gas mixture emerging from the combustion chamber of the first pass is guided in the deflector 3 into the downward-flowing second pass 5.

[0017] Secondary air 4 ensures complete combustion of the gas exiting the deflector 3. The secondary air is injected via lances or nozzles and typically consists of several air inlets.

[0018] In another embodiment of the invention according to Fig. 2 The secondary air supply can also be distributed over several levels (4, 4a).

[0019] After the addition of secondary air, the combustion gas typically has a temperature above 850°C, often even above 1000°C. In the downward-flowing second pass 5 of the combustion chamber, sufficient residence time is ensured for high burnout. Slag accumulations can form on the walls of the downward-flowing combustion chamber due to the fuel properties. These deposits typically detach from the walls once they reach a certain size or are removed by heating surface cleaning devices.

[0020] In the lower section of the downward-flow combustion chamber is a slag discharge opening 6, through which the slag is removed by gravity or through mechanical discharge openings. After the flue gas passes through the discharge opening 6, it is fed into the subsequent energy recovery process—typically a steam boiler with superheater, evaporator, and / or economizer. These plant components are state-of-the-art. Due to the prior slag separation, there is also no risk of clogging of superheater, evaporator, or economizer surfaces.

[0021] In Fig. 3A design not forming part of the invention is described in which the flue gas is deflected only 90 degrees 3 after the first pass. The second pass 5 is thus designed horizontally. The air supply 4 or 4a also takes place in the second pass 5, and the ash extractor 6 is also installed below the horizontal second pass in this case. The disadvantages of this design are the more difficult mixing of the combustion air 4 or 4a with the flue gas and the lack of cooling options for the ash and slag, which fall into the ash hopper directly after complete combustion and cannot cool down in the second pass 5.

Claims

1. Combustion plant with - a fluidized bed (2), - a first pass (8) with a first combustion chamber and at least one fuel addition (1) for burning a fuel, - a second pass (5) with a second combustion chamber, in which a supply for secondary air (4, 4a) is arranged for complete combustion, and which is traversed downwards, and - a deflection (3) of 90 to 180 degrees, ideally 180 degrees, by which the second pass (5) is separated from the fluidized bed (2) and the first pass (8).

2. Combustion plant according to claim 1, characterized in that at least one discharge opening (6) for low-melting ashes and slag is provided in the second pass (5).

3. Combustion plant according to one of claims 1 to 2, characterized in that further air additions (4a) are provided in the second pass (5) through which the air passes downward.

4. Method in a combustion plant with a fluidized bed (2); a first pass (8) with a first combustion chamber and at least one fuel addition (1) for burning a fuel; a second pass (5) with a second combustion chamber, in which a supply for secondary air (4, 4a) is arranged for complete combustion, and which is flowed through downwards; and a deflection (3) of 90 to 180 degrees, ideally 180 degrees, by which the second pass (5) is separated from the fluidized bed (2) and the first pass (8); wherein the secondary air (4, 4a) is fed into the second pass (5) in an area separated from the fuel addition (1) after the deflection (3) for complete combustion, the flue gas flowing downwards in the second pass (5).

5. Method according to claim 4, characterized in that further air additions (4a) are introduced in the second pass (5), through which the air flows downward.

6. Method according to one of claims 4 to 5, characterized in that the temperature is heated to above 750°C by further combustion.

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