KR20000011104A - Method for minimizing nox dosage in flue gas - Google Patents

Abstract

PURPOSE: A method for minimizing the NOx dosage in flue gas is provided to prevent the turbulence from increasing in the combustion area by controlling the flue gas with the turbulent motion in the free space. CONSTITUTION: The method for minimizing the NOx content in flue gas comprises the steps of:burning the combustion product in a combustion chamber(2) of a furnace(1); exhausting the produced flue gas(12) through a free space(4) on the upper area of the combustion area(2); distributing the turbulence to the flue gas(12) of the free space(4) without increasing the turbulence in the combustion area(2); and reducing the NOx content of the flue gas(12) with the relatively simple method.

Description

How to minimize NOx content in flue gas

The present invention relates to a combustion furnace for combustion materials such as waste sludge, waste or coal, in which the combustion material is combusted in the furnace combustion zone and the resulting flue gas is discharged through the free space above the combustion zone. It's about how it works.

Free space in this context is a space where combustion is greatly reduced. In this space, it is separated into flue gas and dust, a small amount of CO and organic carbon after combustion, and this space is also called a calming space. A method of the abovementioned type is described, for example, in German Patent Publication No. 3703568 A1. This publication describes, for example, how to operate a fluidized bed furnace in which dirt sludge is combusted in a fluidized bed located in the combustion zone of a fluidized-bed furnace. In this method, the fluidized bed is prepared by flowing the air used in the form of a mixture of combustion air and flue gas, the flue gas being mixed with the combustion air under temperature and velocity control. By this method, the concentration of NO _{X in the} flue gas can be reduced. Nevertheless, since the residues of NO _X remain in the flue gas, it is required to further reduce NO _X emissions in terms of environmental protection, in particular in avoiding air pollution.

Therefore, it is an object of the present invention to further reduce the NO _x content in the flue gas.

Now surprisingly when the flue gas is regulated by turbulent motion in free space above the combustion zone, the NO _X content without substantially adversely changing the behavior of the combustion plant without substantially increasing turbulence in the combustion zone It has been found that the sewage sludge combustion plant can be further reduced. It is even more surprising that flue gases in free space above the combustion zone generally have to maintain laminar flow, so that as few coarse dust or soot particles as possible are discharged together from the combustion zone.

Therefore, an object of the present invention is obtained by the method of the above-mentioned type, comprising adjusting the flue gas to turbulent movement in free space to substantially increase turbulence in the combustion zone.

Thus, the present invention includes adjusting the flue gas to turbulent movement in free space to substantially increase turbulence in the combustion zone, so that the combustion material is combusted in the combustion zone of the furnace and the resulting flue gas is above the combustion zone. A method of operating a combustion furnace for combustion materials, such as waste sludge, waste or coal, which is discharged through free space located in the.

The combustion itself may proceed in one or two stages according to DE 3703568. Combustion furnaces that can be used are, in particular, fluidized bed furnaces, multiple-hearth furnaces, or grate-fired furnaces with fluidized beds in the combustion zone. The method is preferably suitable for burning waste sludge because it is expected that a relatively large amount of NO _X will be burned due to the protein content of the waste sludge. The turbulent flow of flue gas is easily produced by injecting a gas, preferably an inert gas or a noble gas, particularly preferably by injecting steam or nitrogen. However liquids or solids are also suitable for injection. Injection is advantageously carried out in a free space above the combustion zone in such a way that the turbulent flow in the combustion zone or fluidized bed does not substantially increase, preferably does not increase. This method is particularly suitable for combustion furnaces having a combustion area of at least 5 m 2, preferably 40 m 2, particularly preferably 100 m 2, and very particularly preferably at least 200 m 2.

The invention also relates to a combustion furnace, which has a combustion zone and a free space above the combustion zone, the means by which flue gas can be adjusted to turbulent movement in the free space so that it does not substantially increase turbulence in the combustion zone. This may be a fluid bed furnace with nozzles and / or baffles in free space above the fluid bed. Suitable baffles are, for example, guide plates. However, tubes installed for steam formation are also suitable.

The process according to the invention provides substantially the following advantages.

Minimization of NO _x by relatively simple measurements. With two-stage combustion, no secondary measurement by SNCR or selective (non-) catalytic reduction (SCR) methods. The CO formed during combustion can act as a reducing agent and for this reason it is not necessary to reduce the CO formation in the fluidized bed. In the SNCR or SCR method, a reducing agent is additionally added.

Elimination of disadvantages in the SNCR or SCR method: in particular the slip of NH ₃ , the corrosion of the plant and the reheating of the flue gases (SCR method).

Reduction of operating costs due to savings of reducing agent.

In addition, the reduction of NO _X and organic C loadings in the flue gas.

Improvement of combustion efficiency of blowing ash.

Increased homeostasis of combustion conditions due to improved regulating behavior of fluidized bed furnaces.

Compared to the high pressure steam injection (e.g. injection of heating oil) method and some SNCR methods in which the steam injection into the flue gas only performs the injection function of the medium to be dispersed into the flue gas, the method according to the present invention is pure water injected and flue The turbulence of the gas is increased, thereby improving the cross mixing of the flue gas.

The process according to the invention is also suitable for combustion furnaces with low heat dissipation amounts of 2000 kJ, also 1000 kJ and even less than 500 kJ / (kg of fuel).

The measuring action according to the invention is assumed to be explained below.

Nitrogen present in the waste sludge is essentially converted to NH ₃ , N ₂ and a small amount of NO _X fuel in the fluidized bed. The proportion of NO _{2 in} total nitrogen is about 5%. By minimizing the O ₂ supply during dirt sludge combustion, fuel NO formation is substantially suppressed, but CO formation is promoted.

In the free space above the fluidized bed, it is assumed that the NO _X formed in the waste sludge combustion will be reduced to N ₂ by the presence of C, CO and NH ₃ with the catalytic action of ash. Therefore, the reduction of NO _X can be improved by the following measurement.

An increase in the reducing agent concentration in the flue gas (e.g. an increase in CO concentration);

-Increase in residence time

Improved turbulence and reaction rates

The injection of steam into the free space above the fluidized bed is believed to lead to a concentration gradient and a temperature gradient naturally in the flue gas, resulting in improved turbulence and cross mixing. This greatly improves the reduction of NO _X to N ₂ . If not injected, the free space above the combustion zone is in a laminar flow state, whereby the reduction of NO _x proceeds less fully. When injected into the fluidized bed, these or other methods increase turbulence and combustion in the fluidized bed, and less CO is formed in the fluidized bed to enhance the reduction of NO _{X in} the free space.

The method according to the invention and the fluidized bed furnace according to the invention will be described in more detail below in an exemplary embodiment with reference to FIG. 1. It is not intended that the invention be limited in any way.

The fluidized bed furnace 1 is designed in two stages, in which the fluidized bed 11 is located and has a combustion zone 2 in which the industrial waste sludge 3 is combusted. The combustion zone 2 containing the fluidized bed 11 is located above the gas-compartment plate 9, via which the combustion air 7 is introduced into the fluidized bed 11 via an air disperser device which is not shown. At this time, in the first combustion step, the dirt sludge 3 is combusted in the fluidized bed 11 at about 1 volume% of O ₂ content in combustion air 7 (primary air) to reduce fuel NO _X formation. The generated flue gas 12 is discharged through the free space 4 past the free space 4 above the fluidized bed and transferred to the second combustion stage. In the second reaction the region 6 of the combustion step, the reducing CO formed by the combustion conditions, the second by supplying the air (8) is re-burned to CO ₂ (O ₂ content of> 6, the volume in the reaction the region 6 %). Injection of the steam 10 according to the invention is carried out directly into the free space 4 via one or more nozzles 5. Turbulent flow in the fluidized bed 11 is not or slightly affected by this injection.

The dirt sludge 3 is preferably supplied from the top of the height which ensures that the dirt sludge 3 is further dried by the hot flue gas 4 during the dropping into the fluidized bed 11.

The plant experiments described below demonstrate the beneficial action.

In the industrial mass scale plant according to FIG. 1, the waste sludge is combusted under the following conditions.

Sludge sludge feed rate: approx. 10 metric t / h (40% of dry matter)

Flue gas velocity: about 45000㎥ (S.T.P) / h (wet)

35000㎥ (S.T.P) / h (dry)

Fluidized Bed Temperature: 750-850 ℃

Temperature in free space: 900-1000 ℃

Temperature in the post-reaction zone: 860-900 ° C

Flow gas velocity (primary air): approx. 20000m3 (S.T.P) / h

NO _X concentration in free space: about 3000 mg / m 3 (STP)

CO concentration: about 0.5% by volume

Water content of flue gas: about 30% by volume

Area of gas compartment: 16.6㎡

Diameter of fluidized bed furnace: 5.65m

Height of fluidized bed furnace: 10.6 m

In a plant experiment, about 500 m 3 (STP) / h of superheated steam (4.2 bar _abs ) is injected into the free space above the fluidized bed, and the NO _X concentration is measured and recorded. The results are shown in the graph of FIG. 2 where the NO _X concentrations before, during and after steam injection are plotted against time (minutes). Immediately after steam injection, the NO _X concentration drops from about 220 to 100 mg / m 3 and increases back to its original value after the injection is stopped. In addition, the O ₂ concentration was plotted in the graph of FIG. 2 and the O ₂ concentration was about 0.5% by volume during the experiment.

Claims (12)

Sludge sludge 3 causes combustion zone 2 of furnace 1, including flue gas 12 being adjusted for turbulent movement in free space 4 to substantially increase turbulence in combustion zone 2. A method of operating a combustion furnace (1) for waste sludge (3), in which flue gas (12) burned and produced in the furnace is discharged through a free space (4) located above the combustion zone (2). (delete) The process according to claim 1 or 2, wherein the combustion is carried out in two stages. The method according to any one of claims 1 to 3, wherein the turbulent movement of the flue gas 12 is formed by injecting a gas 10 or a liquid or solid into the free space 4 above the combustion zone 2. . The method of claim 4 wherein the inert gas is injected. The method according to claim 4 or 5, wherein steam or nitrogen or noble gas is injected. The fluidized bed elderly method according to any one of the preceding claims, wherein the combustion furnace (1) has a fluidized bed (11) in the combustion zone (2). Means having a combustion zone 2 and a free space 4 above the combustion zone 2, wherein flue gas can be regulated by turbulent movement in the free space 4 so as not to substantially increase turbulence in the combustion zone ( Combustion furnace (1) for carrying out the process according to claim 1, in particular 5. 9. The gas or liquid according to claim 8, wherein the combustion furnace 1 is a fluidized bed furnace having a fluidized bed 11 in the combustion zone 12 and the means 5 are arranged above the combustion zone and directed towards the free space 4. Combustion furnace nozzle. 10. Combustion furnace according to claim 8 or 9, wherein the combustion furnace (1) has a gas-compartment plate (9) below the combustion zone (2) and an air dispersing device under the gas-compartment plate (9). Combustion furnace according to claim 8, wherein the baffles are stacked in a free space (4) above the combustion zone (2). The combustion furnace of claim 11, wherein the baffle is a guide plate.