EP3537043A1 - Combustion assembly - Google Patents

Abstract

The invention relates to a combustion system with a first train (8), with at least one fuel addition (1) for burning a fuel and with a fluidized bed (2). It is primarily characterized in that a supply for secondary air (4, 4a) for complete combustion is arranged in an ideally downward-flowing second train (5) in a region separated from the fluidized bed (2) by a deflection (3). The invention also relates to a method in an incinerator. With this arrangement, slag adhering to the walls can fall into the fluidized bed and thereby unnecessary downtimes can be prevented.

Description

The invention relates to a combustion system with a first train, with at least one fuel addition for burning a fuel and with a fluidized bed. The invention further relates to a method in an incinerator.

In industrial sites where flammable waste material is produced, it has proven useful to build combustion power plants. On the one hand, the mass and volume of waste generated can be greatly minimized, and on the other hand, the site can cover its energy needs, in part or in full. For this purpose, fluidized bed furnaces (fluidized bed firing) are often used. Fluidized bed burns have the advantage that, due to the high storage capacity of the bed material, they are able to burn a wide fuel band. In addition, the excellent mixing in a fluidized bed allows a very homogeneous combustion and thus very low emission levels. Many waste materials form ashes on combustion, which have a melting point below the usual combustion temperature of such a plant. This is especially true of agricultural products such as grasses, straw, grains, energy crops, animal waste products with high levels of alkali in the ash, or municipal or commercial waste fuels or shredder fractions from metal processing. The problems with conventional fluidized bed systems with these fuels are the following: formation of eutectics of the fuel ashes and of the bed material can lead to melting in the fluidized bed, which leads to sintered lumps in the fluidized bed. These can no longer be fluidized and continue to grow in the fluidized bed until they no longer allow operation of the boiler with the emission limits to be met. For this problem exist up to ash melting points of approx. 600 ° C technological solutions. By staged combustion and suitable bed materials sintering of the ash in the fluidized bed can be prevented. Here, after the addition of fuel again air is supplied to continue to perform the combustion or complete. This air is also called secondary air. Often a little later air (tertiary air) is supplied.

A second mechanism is not yet solved. The low-melting ashes form, especially when the addition of air in particular the secondary (or tertiary) air in a common furnace above the other and above the fluidized bed, deposits on the walls of the furnace, which grow with continuous operation of the plant and a determined size or changes in combustion conditions due to load changes from the wall and fall into the fluidized bed. There they obstruct the fluidization which also leads to uncontrolled combustion conditions that make a shutdown of the plant necessary. This fact can theoretically be circumvented by continuous, continuous cleaning of the walls in the furnace. This prevents deposits over a critical size grow, small deposits can be discharged in operation from the fluidized bed. Practically, however, this method is difficult to carry out, because you can not reach each area and corner of the furnace with Heizflächenreinigungsseinrichtungen and a constant cleaning efficiency losses and can cause increased wear due to corrosion and erosion mechanisms on the walls. The system requires frequent cleaning, which, in particular by the stoppage of the furnace, causes further high costs. It is from the WO 2014/184437 A a boiler is known in which the lower part is divided to create a fluidized bed area and a free area to remove slags and ashes. Furthermore, the gas is diverted by baffling in the upward flow. From the JP S58156107 A a boiler is known in which the gas is fed to a cyclone, in which water is injected for cooling. The JP S602817 A shows a one-stage combustion with a down-flow radiator.

The object of the invention is therefore to provide an incinerator and a method for burning such fuels available, which avoids or reduces the above-mentioned disadvantages and allow the direct abandonment of fuels with low-melting ash as fuel in the fluidized bed.

The invention is therefore characterized in that, in a region separated from the fluidized bed by, for example, a deflection, a supply for secondary air for complete combustion in a second flow, which is preferably flowed through downward Train is arranged. This ensures that ash caking and slag form only in the second train without affecting the fluidized bed negative.

An advantageous development of the invention is characterized in that a trigger for low-melting ash and slag is provided in the second train. As a result, they can be removed separately.

A favorable embodiment of the invention is characterized in that further air additions are provided in the second train, which is preferably flowed downward. This can ensure complete combustion.

The invention also relates to a method in a combustion system with a first train, with at least one fuel addition for burning a fuel and with a fluidized bed. It is inventively characterized in that the secondary air is supplied in a separated from the fuel addition area after a deflection in an ideally downwardly flowed through the second train.

An advantageous development of the invention is characterized in that further air additions take place in the second train, which is preferably flowed downward. A favorable embodiment of the invention is characterized in that the gases are passed from the fluidized bed in a first train and that the complete combustion takes place in a second train.

A favorable development of the invention is characterized in that the temperature is heated to over 750 ° C by the further combustion.

• Fig. 1 eine Variante der Erfindung und
• Fig. 2 eine weitere Variante der Erfindung
• Fig. 3 eine weitere Variante der Erfindung

darstellt.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 another variant of the invention

represents.

In Fig. 1 For example, a fluidized bed incinerator is schematically illustrated, in which bed material such as sand, blast furnace slag or the like Materials in a fluidized bed 2 by injection 9 with combustion air and, if necessary, fluidized by recirculation gas. About one or more fuel feed points 1, the solid fuel is thrown or blown into the combustion chamber of the first train 8. The combustion chamber in the first train 8 and the combustion chamber separated by a deflection 3 of 90 to ideally 180 degrees thereof in the second train 5 can be made gas-tight either by water and / or steam pipe walls or by a sheet metal construction. The wall may be protected by bricking or metallic coatings.

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

From the fluidized bed carbonization and incomplete combustion products such as: CO, H2, CO2, H2O enter the combustion chamber 8. An embodiment of the invention, as in Fig. 1 is shown has a plurality of air openings for supporting air 7. By this supporting air, a part of the gas leaving the fluidized bed 2 can be burned and thereby the temperature of the gas can be raised, in order to prevent the gas temperature from falling below the ignition temperature of the gas before reaching the secondary air supply 4.

The flammable gas mixture emerging from the combustion chamber of the first train is conducted in the deflection 3 into the second train 5, which, ideally, flows downwards.

By secondary air 4 is a complete combustion of the leaking from the deflection 3 gas. The secondary air is injected via lances or nozzles and typically consists of several air inlets.

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

After the secondary air addition, the combustion gas typically has a temperature above 850 ° C, often even over 1000 ° C. In the second train 5 of the combustion chamber, which flows downwards ideally, a sufficient residence time is ensured for a high burn-out. On the walls of the Ideally downwardly flowed combustion chamber may form due to the fuel properties slag accumulations. These typically separate from the wall above a certain size or are replaced by Heizflächenreinigungseinrichtungen.

In the lower region of the ideally downwardly flowed combustion chamber is a slag discharge opening 6 in which the slag is removed by gravity or by mechanical discharge openings. After the flue gas has passed the discharge opening 6, it is fed to the further process for energy recovery - typically a steam boiler with overheating, evaporator and / or economizer. These parts of the plant correspond to the state of the art. By the previous separation of slag there is also no risk for the installation of superheater, evaporator or Economizerflächen.

In Fig. 3 is a similar embodiment of the invention described by the flue gas deflected only 90 degrees after the first train 3 is. The second train 5 is thus carried out horizontally. The air supply 4 and 4a is also in the second train 5, the ash deduction 6 is also mounted in this case under the horizontal second train. A disadvantage of such an embodiment, the more difficult mixing of the combustion air 4 and 4a with the flue gas and the lack of cooling ability of the ashes and slags that fall directly after complete combustion in the ash hopper and 5 can not cool in the second train.

The invention is not limited to the illustrated examples. Thus, e.g. also a further addition of, for example, liquid fuels done.

Claims (6)

Combustion system with a first train (8), with at least one fuel addition (1) for burning a fuel and with a fluidized bed (2), characterized in that a second train (5) separated from the fluidized bed (2) by a deflection (3) ) is arranged a secondary air supply (4, 4a) for complete combustion, wherein the deflection (3) 90 is carried out to ideally 180 degrees. Incinerator according to claim 1, characterized in that in the second train (5) at least one trigger (6) is provided for low-melting ash and slag. Combustion plant according to one of claims 1 to 2, characterized in that further air additions (4a) are provided in the second train (5), which is preferably flowed downwards. Method in an incinerator with a first train (8), with at least one fuel addition (1) for combusting a fuel and with a fluidized bed (2), characterized in that the secondary air (4, 4a) in one of the fuel addition (1) separated area after a deflection (3) for complete combustion in a second train (5) is fed, the flue gas in the second train (5) flows horizontally to ideally downwards. Method according to Claim 4, characterized in that further air additions (4a) take place in the second train (5), which is preferably flowed downwards. Method according to one of claims 4 or 5, characterized in that the temperature is heated to over 750 ° C by the further combustion.

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