KR100899105B1 - Ammonia tunning method applicable to burning gas exhaust system - Google Patents

Abstract

The present invention relates to an air pollution prevention technology, and more particularly, to a technique for removing nitrogen oxides (NOx) by adding an appropriate amount of ammonia to combustion gas discharged from a large combustion facility such as a waste incinerator and a boiler of a power plant.

In the present invention, the upstream gas measuring unit (2), the flow rate measuring unit (3), the ammonia spraying unit (4), the catalytic reaction layer (5), and the downstream gas measuring unit (6) from the upstream of the flue (1). And inlet gas measuring step; Initial tuning step; Outflow gas measuring step; Intermediate tuning step; Final tuning step; And setting the fixed gas measuring point; sequentially decomposing NOx in the exhaust gas into nitrogen and water.

When the present invention is applied, it is possible to effectively remove the nitrogen oxides in the combustion gas without leaving excess ammonia by optimally adjusting the amount of ammonia injected for each part in the large flue discharged combustion gas. In addition, when the method of the present invention is applied, the existing flue can be used as it is without the need to supplement the facility such as partitioning the inside of the flue, so that NOx in the combustion gas can be economically removed.

Air Pollution, NOx, Ammonia, Tuning, Catalyst, SCR

Description

Ammonia Tunning Method Applicable to Burning Gas Exhaust System}

The present invention relates to an air pollution prevention technology, and more particularly, to a technique for removing nitrogen oxides (NOx) by adding an appropriate amount of ammonia to combustion gas discharged from a large combustion facility such as a waste incinerator and a boiler of a power plant.

When combustion materials are combusted in a combustion device such as a waste incinerator or a large boiler, organic nitrogen in the combustion materials reacts with oxygen to generate nitrogen oxides such as NO, NO ₂ , and NO ₃ , commonly called NOx. This nitrogen oxide is a representative air pollutant, causing pollution problems such as causing acid rain when released into the atmosphere.

In facilities that emit combustion gases, such as waste incinerators, large boilers, and engines, the emission of nitrogen oxides is strictly regulated by applicable laws, and therefore, the combustion gas discharge device is provided with means for removing nitrogen oxides. Is common.

Selective Catalytic Reduction (SCR) is used as a means to remove nitrogen oxides from the combustion gas. The SCR method injects ammonia into the combustion gas and mixes ammonia with the combustion gas. Is passed through a catalytic reactor, and the nitrogen oxide reacts with ammonia to turn into nitrogen gas and water vapor (water). Examples of chemical reactions between nitrogen compounds and ammonia are as follows.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O

6NO + 4NH ₃ → 5N ₂ + 6H ₂ O

As can be seen from the above equation, when ammonia is added to the combustion gas containing nitrogen oxide and passed through the catalyst layer, the nitrogen oxide in the combustion gas and the added ammonia react to generate nitrogen gas and water vapor to remove the pollutants.

In order to remove nitrogen oxides in the combustion gas through the above chemical change, an appropriate amount of ammonia should be added according to the type and concentration of nitrogen compounds contained in the combustion gas (hereinafter referred to as "gas quality"). If less than the required amount of ammonia is added, the nitrogen oxides cannot be removed to a sufficient degree. If more ammonia is added than necessary amount, the excess ammonia remaining after reacting with nitrogen oxide is discharged to the outside and becomes another pollutant by itself, or it reacts with oxygen to produce nitrogen compound again as the following formula. do.

4NH ₃ + 5O ₂ → 4NO + 6H ₂ O

Therefore, in the apparatus for removing nitrogen oxides from the combustion gas by the SCR method, it is important to add the correct amount of ammonia required for the reaction.

At present, SCR method is mainly used to remove nitrogen oxides from engine combustion gas, which is used in engine exhaust system such as automobile exhaust system. In the case of engine exhaust system, the exhaust pipe is relatively small, and the flow rate of combustion gas is very fast, which creates turbulence. The distribution of nitrogen compounds in the combustion gas is almost uniform, and the catalytic reactor is also compact. Therefore, if the gas quality of the combustion gas is known, the amount of ammonia required for this can be calculated relatively accurately, and when it is injected into the combustion gas pipe, the ammonia is introduced into the catalytic reactor in a state in which the ammonia is uniformly mixed with the combustion gas having a very high flow rate, and nitrogen is introduced. The oxide decomposes.

However, in large combustion facilities such as waste incinerators and boilers in thermal power plants, the flue gas is very large (over several meters each) and the flow rate of the combustion gas is not so fast that the combustion gas flow is close to laminar flow. The flow velocity in the year is differently distributed depending on the site of the year section. Therefore, in order to apply the SCR method to such a large combustion apparatus, a special ammonia injector and method are required.

In Korean Patent Laid-Open Publication No. 10-2003-0003045, the combustion gas exhaust pipe passage is divided into several channels, and each channel is provided with an injection grid (AIG, Ammonia Injection Grid) formed of an ammonia spray pipe, and measures the flow rate for each channel. The SCR method for spraying the amount of ammonia required for the reaction is described.

However, in the case of the above-mentioned patent, it is expensive to divide the inside of the exhaust pipe into a plurality of channels, and a method for obtaining an appropriate amount of ammonia required for the reaction is not described.

As described above, in the flue gas flue of the large combustion apparatus, the flow rate of the discharged flue gas is not fast to form a laminar flow, so that the flue gas flowing in the flue does not mix well with each other and is distributed differently according to the flow rate. Therefore, the flow rate is different for each part on the cross section of the year, and the type and concentration of nitrogen oxide in the exhaust gas are also different for each part, and the amount of nitrogen oxide flowing for each part on the cross section of the year is also different. And the gas quality of the emitted flue gas also changes with time.

As described above, in the large flue gas flue, the gas quality flowing inside each part and each time is different from each other, so that the amount of ammonia injected in each part must also be different to effectively remove nitrogen oxides in the combustion gas without leaving excess ammonia. can do.

Therefore, in the large combustion gas discharge apparatus, in order to effectively remove nitrogen oxides, a means for injecting an optimum amount of ammonia for each part of the year and a method for determining an optimal amount of ammonia should be devised.

In order to achieve the above technical problem, the present invention provides the upstream gas measuring unit 2, the flow rate measuring unit 3, the ammonia spray unit 4, and the catalytic reaction layer 5 from the upstream inside the flue 1. And, the downstream gas measuring unit 6 is provided, the ammonia injection unit 4 is arranged in a lattice form a plurality of injection holes (41) horizontally and vertically at regular intervals. Each of the ejection holes 41 is connected to the ammonia tank by the supply pipe 42, and the supply pipe 42 is provided with a control valve 43 to adjust the amount of ammonia ejected into the ejection holes.

Then, the ammonia in the combustion gas is decomposed into nitrogen and water vapor through the following steps sequentially using the facility.

First step: inflow gas measurement, which measures the quality and flow rate of the combustion gas at each part of the flue in the upstream gas measurement unit 2 and the flow rate measurement unit 3 while operating the combustion device in the combustion gas decomposition device normally. step;

Second step: calculating the flow rate of ammonia to be ejected to each of the ejection holes 41 of the ammonia injection unit 4 on the basis of the quality and flow rate of the combustion gas measured in the inlet gas measurement step, based on each adjustment An initial tuning step of injecting ammonia into the flue 1 by adjusting the opening degree of the valve 43;

Step 3: After performing the initial tuning step, measuring the gas quality at each gas measuring point 62 of the downstream gas measuring unit 6, the outflow gas measuring step;

Step 4: Calculate the flow rate adjustment amount of ammonia to be ejected to each ejection hole 41 of the ammonia injection unit 4 based on the quality of the effluent gas measured in the effluent gas measurement step, and based on this, each control valve An intermediate tuning step of readjusting and correcting the opening degree of 43;

A fifth step: a final tuning step of determining the opening degree of each control valve 43 by repeating the third and fourth steps so that the concentration and distribution of NOx in the effluent gas fall within a target value;

Step 6: After the final tuning step is completed, the installation position of the fixed gas detection sensor 64 is determined as a gas measuring point 62 representing the average concentration of NOx concentration in the exhaust gas, and the fixed gas detection sensor at this point. A fixed gas measuring point setting step of fixing 64;

When the present invention is applied, it is possible to effectively remove the nitrogen oxides in the combustion gas without leaving excess ammonia by optimally adjusting the amount of ammonia injected for each part in the large flue gas flue.

When the method of the present invention is applied, the existing flue can be used as it is without the need to supplement the facility such as dividing the inside of the flue, thereby economically removing NOx in the combustion gas.

Combustion gas decomposition apparatus to which the ammonia tuning method of the present invention is applied is as shown in FIG. 1, the upstream gas measuring unit (2), flow rate measuring unit (3), ammonia spraying unit (4) from upstream in the flue (1) ), A catalytic reaction layer (5), and a downstream gas measurement unit (6). As used herein, the term "ammonia tuning" means an operation of controlling the amount of ammonia injected into each nozzle in a device having a plurality of ammonia injection holes.

The flue 1 is a passage through which the combustion gas passes and may be straight or bent in a b-, c-, or U-shape.

The upstream gas measurement unit 2 is an upstream side where the combustion gas is introduced into the combustion gas cracking device (usually in a device in a direction in which the fluid is constant, the inflow side of the fluid is called 'upstream', and the outflow side of the fluid It is a part for measuring the quality of the combustion gas flowing into each part of the flue cross section which is located in the flow path. The upstream gas measuring part is provided with a plurality of gas measuring holes 21 at regular intervals on one side of the year, and the gas measuring sensor 22 of the measuring device such as a gas analyzer is inserted into the gas measuring hole to supply the gas at each gas measuring point 22. Measure the quality. Each gas measuring hole 21 may be provided with a stopper so as to be prevented except during measurement.

The gas measuring point 22 is selected at a predetermined interval horizontally and vertically on the cross section of the flue, and is selected by varying the insertion depth of the gas detecting sensor from the respective gas measuring holes 21. The more gas measurement points 22, the more accurate gas distribution can be obtained, but if it is too much, it takes a lot of time to work, so it is appropriate number. For the year of 2m each, about 20 points are enough. .

The flow rate measuring unit 3 is a portion that is connected to the gas measuring unit 2 on the upstream side where the combustion gas flows into the combustion gas decomposition device and measures the flow rate of the combustion gas flowing into each part of the flue cross section. The flow rate is multiplied by the cross-sectional area. The flow rate measuring section 3 is also a portion having a plurality of flow rate measuring holes 31 at regular intervals on one side of the year, and a pitot tube is introduced into the flow rate measuring hole to measure the flow rate of each measuring point. The method of selecting the flow rate measuring point 32 is the same as the method of selecting the gas measuring point 22.

The flow rate measuring unit 3 may be provided separately, but may not be provided separately when the flow rate may be measured using the gas measuring hole 21 of the upstream gas measuring unit 2.

The ammonia spray unit 4 is a portion in which a plurality of ejection holes 41 are arranged in a lattice form at regular intervals in a horizontal direction. Each blowing hole 41 is connected to the ammonia tank (not shown) by the supply pipe 42, the supply pipe 42 is provided with a control valve 43 to adjust the amount of ammonia that is ejected into the blowing hole.

Since the ammonia ejected from the respective ejection holes 41 should be evenly dispersed in the combustion gas, the larger the number of ejection holes 41 is, the better the actual plant is provided with dozens to hundreds of ejection holes. Most preferably, the control valve 43 is provided in all of the supply pipes 42 connected to each of the ejection holes 41, so that the amount of ammonia ejected to each of the ejection holes may be controlled. Difficult and also requires a large number of control valves 43, the installation cost increases, there is a problem such as a lot of time for tuning work.

In general, the distribution of flow velocity and gas quality in each section of a flue in a large flue-gas discharge flue is formed by a relatively simple pattern according to the shape and arrangement of the flue. For example, the flow rate and the concentration of nitrogen oxides are high at one side (upper, lower, left, right, etc.) of the year, and the other side has a layered distribution in a low manner. Therefore, it is possible to group the ejection holes, configure the supply pipes connected to the ejection holes belonging to each group by branching in one group supply pipe, and install a control valve in the group supply pipes. Typically, the ejection holes 41 are attached to a plurality of ejection holes 41 at a predetermined interval in the longitudinal direction to one long pipe, the pipe is made to act as a group supply pipe, these pipes are made horizontally or vertically The ammonia injection unit is configured in such a manner that the nozzles are arranged at regular intervals so as to form a grating hole.

The catalytic reaction layer 5 is the same as that used in the conventional SCR method, where ammonia and nitrogen oxides undergo chemical reactions and decompose into nitrogen gas and water vapor (water).

In addition, the downstream gas measuring unit 6 has the same configuration as the upstream gas measuring unit 2, and is a place for measuring the quality of the combustion gas passing through the catalytic reaction layer 5 and released to the outside. The downstream gas measuring unit also includes a plurality of gas measuring holes 61 at one side of the year 1 at regular intervals, and a gas detecting sensor of a measuring device such as a gas analyzer is inserted into the gas measuring hole to measure each gas measuring point 62. Measure the concentration of nitrogen oxides.

The downstream gas measuring unit 6 has one fixed measuring point 63, and the fixed measuring point 64 is fixedly provided at the fixed measuring point. This fixed gas sensor exists for the operation of the plant.

The ammonia tuning method of the present invention is performed as shown in the flowchart shown in FIG. 2, by sequentially performing the following steps.

First step: Inflow gas for measuring the quality and flow rate of the combustion gas at each part of the flue cross section by the upstream gas measuring unit 2 and the flow rate measuring unit 3 while operating the combustion device in the combustion gas cracker normally. Measuring step;

The second step: calculate the flow rate of ammonia to be injected into each of the ejection holes 41 of the ammonia injection unit 4 on the basis of the quality and flow rate of the combustion gas measured in the inlet gas measurement step, based on each adjustment An initial tuning step of injecting ammonia into the flue 1 by adjusting the opening degree of the valve 43;

Step 3: After performing the initial tuning step, measuring the gas quality at each gas measuring point 62 of the downstream gas measuring unit 6, the outflow gas measuring step;

Step 4: Calculate the flow rate adjustment amount of ammonia to be injected into each of the ejection holes 41 of the ammonia injection unit 4 based on the quality of the gas measured in the outflow gas measurement step, and based on this control valve ( An intermediate tuning step of readjusting and correcting the opening degree of 43);

5th step: final tuning step of determining the opening degree of each control valve 43 by repeating said 3rd and 4th steps;

Step 6: After the final tuning step is completed, the fixed gas detection sensor 64 is determined as a gas measuring point 62 representing the average concentration of NOx concentration in the exhaust gas, and the fixed gas detection sensor 64 at this point. Fixing, fixed gas measuring point setting step;

The inflow gas measuring step of the first step is a step of measuring the distribution of the quality of the combustion gas and the flow rate of the combustion gas flowing for each part in the year (1) in the combustion gas discharge apparatus to which the present invention is applied. This step is carried out in the state of normal operation of the combustion device.In the normal operation state, the amount and quality of NOx in the combustion gas such as the type of fuel used, the flow rate of the fuel, the grade of the fuel, the amount of air required for combustion, the temperature of the combustion chamber, etc. The influencing factors correspond to the steady-state operating conditions in which the plant is mainly operated.

The initial tuning step of the second step is a step of adjusting the opening degree of each control valve 43 based on the calculation of the flow rate of ammonia to be ejected to each ejection hole 41 of the ammonia ejection unit 4. NOx generated in the combustion gas is removed by changing to nitrogen and water vapor when it meets ammonia and causes the following chemical reaction.

iNOx + jNH ₃ + k0 ₂ → mN ₂ + nH ₂ O

In the above formula, i, j, k, m, and n are integers indicating the number of moles of the molecule, NOx is a generic name for nitric acid compounds such as NO, NO ₂ , NO ₃ and the like. The reaction of ammonia and NOx as described above occurs mainly in the catalytic reaction layer (5), and the harmful pollutants contained in the combustion gas, NOx, are converted into safe nitrogen and water vapor and discharged to the outside.

As can be seen from the above formula, if the flow rate of the combustion gas flowing into each part of the year (1) and the type and concentration of the NOx of the part are measured by the inflow gas measuring step of the first step, the NOx is removed. In order to calculate the flow rate of ammonia to be injected into each ammonia jet hole 41, the calculated value is corrected by an empirical value to adjust the opening degree of the control valve 43 connected to each jet hole. At this time, ammonia used is liquid ammonia water or gaseous ammonia gas.

The outflow gas measuring step of the third step is a step of measuring the gas quality at each gas measuring point 62 of the downstream gas measuring unit 6 after the initial ammonia tuning as described above. In general, the number of factors involved in the chemical reaction between NOx and ammonia is very high, and after the initial tuning step, the quality of the combustion gas downstream of the year (1) shows that ammonia is insufficient for each measurement point, so NOx is not sufficiently removed. And where ammonia is oversupplied and excess ammonia is released.

In the intermediate tuning step of the fourth step, the control valve 43 connected to the ejection hole of the excessively ammonia-supplied part based on the gas quality measured in the effluent gas measuring step is closed a little, and The control valve connected to the ejection hole is further opened to adjust the flow rate of ammonia to be injected into each ejection hole 41.

Typically, the third and fourth steps are repeated several times for final ammonia tuning. However, no matter how precise the tuning, it is impossible to bring the NOx concentration below the target in all years. Therefore, the NOx concentration distribution is tuned to fall within a certain range of deviation, but empirically tuned so that the standard deviation of NOx concentration at each gas measurement point 62 of the downstream gas measurement unit 6 falls within 20% of the average value. It was found that the emission gas can be controlled to meet the Korean legal regulations.

The standard deviation (σ) is computed by the following equation, which is one of the measures of the scatter plot of the characteristic values of a statistical group.

Where x _k is each measured value at the measuring point, m is the mean value, and n is the number of measuring points.

The control variable CV is a value obtained by dividing the standard deviation by an average value.

 CV = σ / m

When ammonia tuning, this control variable should be within 0.2 (= 20%).

Normally, the NOx concentration in the combustion gas flowing to each part of the flue varies somewhat over time. Therefore, for the ammonia tuning, the measured value measured at each gas measuring point 62 of the downstream gas measuring unit 6 is an average value for a predetermined time (for example, 1 minute, etc.), so that more accurate ammonia tuning can be performed. Since some gas measuring instruments used in recent years have a function of measuring an average concentration during a predetermined time, it is possible to measure an average gas quality for a predetermined time.

 The fixed gas measuring point setting step of the sixth step is to determine the position of the fixed gas detection sensor 64 for monitoring and measuring the quality of the exhaust gas at all times during the operation of the combustion facility. The fixed position is set as the fixed measuring point 63. The fixed measuring point is selected from the respective gas measuring points 62 of the downstream gas measuring unit 6 as the point representing the average gas concentration after the final tuning is completed. Fix the fixed gas sensor 64 to the

The present invention can be used for pollution reduction of a facility for discharging a gas containing NOx, which is a pollutant.

1 is a block diagram of a gas discharge device to which the present invention is applied.

2 is a flowchart of the ammonia tuning method of the present invention.

※ Important Component Number

1: year, 2: upstream gas measuring part, 3: flow rate measuring part, 4: ammonia injection part,

5: catalytic reaction layer, 6: downstream gas measuring unit;

Claims (3)

Upstream gas measuring unit 2 having a plurality of gas measuring holes 21 at regular intervals on one side of the year from upstream, and a flow rate measurement having a plurality of flow rate measuring holes 31 at regular intervals on one side of the year Part 3, a plurality of blow holes 41 are arranged in a lattice shape at regular intervals horizontally and vertically, each blow hole 41 is connected to the ammonia tank by the supply pipe 42 and the control valve in the supply pipe 42 An ammonia spraying unit 4 configured to control the amount of ammonia ejected into the ejection hole by means of 43, a catalytic reaction layer 5 in which nitrogen oxide reacts with ammonia to change into nitrogen gas and water vapor, In addition, a fixed gas detection sensor 64 having a plurality of gas measuring holes 61 at one side of the year at regular intervals and a gas detection sensor 64 for measuring and monitoring the quality of the combustion gas at all times during the operation of the combustion facility is provided.In the downstream gas measuring unit 6, which is non-sequentially arranged with a flue (1) the gas discharge device, and ammonia tuning method, the following steps of sequentially removing the NOx in the combustion gas. First step: Inflow gas measurement in which the gas discharge device is normally operated and the upstream gas measuring unit 2 and the flow rate measuring unit 3 measure the quality and flow rate of the combustion gas at various portions of the cross section of the year. step; The second step: calculate the flow rate of ammonia to be injected into each blow hole 41 of the ammonia injection unit 4 on the basis of the quality and flow rate of the combustion gas measured in the inlet gas measurement step, based on each An initial tuning step of adjusting the opening degree of each control valve 43 provided in the supply pipe 42 connected to the ball 41 to inject ammonia to various portions of the cross section inside the flue 1; Third step: after performing the initial tuning step, the downstream gas measuring unit 6 to measure the quality of the combustion gas of the various parts of the cross section of the flue, outflow gas measuring step; Step 4: Calculate the flow rate adjustment amount of ammonia to be ejected to each of the ejection holes 41 of the ammonia injection unit 4 based on the quality of the combustion gas measured in the effluent gas measurement step, based on each An intermediate tuning step of modifying the opening degree of each control valve 43 provided in the supply pipe 42 connected to the 41; Step 5: Repeating the third and fourth steps, final tuning step of determining the opening degree of each control valve 43 so that the quality of the combustion gas discharged to the year meets the regulatory standard; Step 6: After the final tuning step is completed, the fixed gas detection point 64 is installed at the point where the NOx concentration in the combustion gas shows the average concentration in the flue gas cross section of the downstream gas measuring unit 6, the fixed gas measuring point Setting step; The method of claim 1, The final tuning step of the fifth step is a final tuning step of tuning the ammonia so that the standard deviation of the NOx concentration measured in the various sections of the year in the downstream gas measuring unit 6 falls within 20% of the average value. Made, Ammonia Tuning Method. The method according to claim 1 or 2, In the outflow gas measuring step of the third step, the downstream gas measuring unit 6 measures the average gas quality for a predetermined time at various parts of the cross section of the year. Ammonia Tuning Method.

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