A method for efficiently regulating ammonia injection grid and calculating ammonia injection rate in flue gas denitrification.

Abstract

This invention relates to a method for efficiently controlling ammonia injection grids and calculating ammonia injection volume in flue gas denitrification. It includes a detection facility and multiple ammonia injection grid units. Each ammonia injection grid unit comprises multiple branch pipes surrounding and connecting to the main pipe. Each ammonia injection grid unit is equipped with a regulating valve and a differential pressure sampling point. Each differential pressure sampling point is connected to a differential pressure transmitter outside the flue gas duct via its own instrument conduit. The differential pressure transmitter is connected to the regulating valve information of each ammonia injection grid unit. This invention sets a differential pressure sampling point at the center of each ammonia injection grid, calculates the flue gas flow rate of each ammonia injection grid unit using the differential pressure value, and precisely controls the ammonia injection volume of each ammonia injection grid based on the distribution of the flue gas flow rate at each grid across the flue gas duct cross-section, achieving precise and uniform ammonia injection. Compared to traditional ammonia injection grids, the denitrification efficiency is increased by more than 1.4 times, ammonia slip is significantly reduced, and ammonia consumption is saved, thereby greatly reducing operating costs.

Description

Technical Field

[0001] This invention relates to a high-efficiency control grid for flue gas denitrification and a method for calculating the amount of ammonia injected. It is an environmental protection auxiliary facility and method for a combustion furnace, and a facility for purifying pollutants in flue gas from a combustion furnace, particularly an environmental protection auxiliary facility for flue gas denitrification and a method for calculating the amount of catalyst injected. Background Technology

[0002] Flue gas denitrification (FGD) engineering aims to reduce nitrogen oxide (NOx) emissions and mitigate their threat to the atmospheric environment and human health. Selective reduction (SCR) FGD technology is widely used in FGD projects due to its simple operation and high denitrification efficiency. SCR FGD technology involves injecting a certain concentration of ammonia into the flue gas through an ammonia injection grid. The ammonia mixes with the flue gas, and a chemical reduction reaction occurs under the action of a downstream catalyst, thereby reducing the concentration of NOx in the flue gas. Currently, although ammonia injection grids have undergone several upgrades, they still cannot overcome the problems caused by uneven ammonia injection due to uneven flue gas flow field and velocity, and the inability to precisely control the ammonia injection volume of each injection unit. These problems lead to significant NOx escape from the flue gas, resulting in excessive NOx and ammonia emissions, and difficulties in adjusting the ammonia injection volume during the grid adjustment process. Therefore, improving the uniformity of ammonia injection to further reduce NOx in the flue gas and increase the efficiency of the environmentally friendly ammonia injection grid is a problem that needs to be solved. Summary of the Invention

[0003] To overcome the problems of existing technologies, this invention proposes a method for efficiently regulating ammonia injection grids and calculating ammonia injection volume in flue gas denitrification. The ammonia injection grids monitor the flue gas flow rate at the center of each grid unit. Utilizing the direct proportionality between the ammonia injection volume of each grid unit and the flue gas flow rate, the ammonia injection volume is calculated, achieving precise ammonia injection.

[0004] The objective of this invention is achieved as follows: a high-efficiency ammonia injection grid for flue gas denitrification includes a detection facility for detecting nitrogen oxides installed in the flue of a combustion furnace and multiple ammonia injection grid units evenly distributed in the flue. Each ammonia injection grid unit includes multiple branch pipes surrounding and connecting to the main pipe, and multiple ammonia injection ports are provided on the branch pipes. Each main pipe of each ammonia injection grid unit is provided with a regulating valve and a differential pressure sampling point. Each differential pressure sampling point is connected to a differential pressure transmitter outside the flue via its own instrument conduit, which can calculate the flue gas flow rate through each ammonia injection grid unit from the differential pressure value. The differential pressure transmitter is connected to the regulating valve information of each ammonia injection grid unit.

[0005] Furthermore, the ammonia injection grid units are evenly distributed in a grid pattern in the flue with a rectangular cross-section, and the branch pipes of the ammonia injection grid units are H-shaped. The differential pressure sampling point is set at the midpoint of the line connecting the H-shapes.

[0006] Furthermore, the two sampling ports of the differential pressure sampling point are set in the direction of flue gas flow.

[0007] Furthermore, each of the aforementioned instrument conduits is equipped with a back-blowing device.

[0008] Furthermore, the regulating valve is an electrically controlled regulating valve.

[0009] Furthermore, the electrically controlled regulating valve is connected to the operational controller, and the operational controller is connected to the nitrogen oxide detection facility and the pressure transmitter.

[0010] A method for calculating the ammonia injection rate using the above-mentioned high-efficiency ammonia injection grid for flue gas denitrification, the steps of which are as follows:

[0011] Step 1, Measure the pressure difference: Measure the pressure difference Δp through the sampling points of the ammonia injection grid unit;

[0012] Step 2, calculate flue gas flow rate: Calculate the flue gas velocity q at the current sampling point using the formula based on the pressure difference measured at the sampling point. m :

[0013]

[0014] Where: K is the calculation coefficient;

[0015] Step 3, Calculate the flow rate: Considering moisture, pressure, temperature, and oxygen content, use q. m Calculate the flue gas flow rate Q under standard conditions. 烟气 ;

[0016] Step 4, Calculate NOx: Obtain the NOx concentration in the flue gas from the nitrogen oxide detection facility, and calculate the amount of NOx in the flue gas per unit time.

[0017] NOx amount = Q 烟气 ×NOx concentration;

[0018] Step 5, calculate the number of ammonia moles: Calculate the amount of NH3 sprayed per unit time based on the amount of NOx per unit time. The formula is:

[0019] The number of moles of NH3 equals the number of moles of NOx;

[0020] The required number of moles of ammonia to be injected is calculated based on the actual chemical reaction equation. Chemical reaction equation:

[0021]

[0022] Step 6, convert the ammonia injection amount: convert the number of ammonia moles calculated from the chemical reaction formula into the industrial unit ammonia injection amount.

[0023] The advantages and beneficial effects of this invention are as follows: This invention sets pressure difference sampling points at the center of each traditional ammonia injection grid, calculates the flue gas flow rate of each ammonia injection grid unit using the pressure difference value, and calculates the precise ammonia injection amount based on the distribution of flue gas flow rate at each ammonia injection grid across the flue cross-section. This allows for precise control of the ammonia injection amount at each grid, achieving accurate and uniform ammonia injection. Compared to traditional ammonia injection grids, the denitrification efficiency is increased by more than 1.4 times, ammonia slip is significantly reduced, and ammonia consumption is saved, thereby greatly reducing operating costs. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a schematic diagram of the ammonia injection grid described in Embodiment 1 of the present invention;

[0026] Figure 2 These are schematic diagrams of the ammonia injection grid described in Embodiments 1 and 2 of the present invention;

[0027] Figure 3 These are schematic diagrams of the sampling port arrangement and back-blowing device in embodiments three and four of the present invention;

[0028] Figure 4 This is a block diagram illustrating the electronic control principle of the ammonia injection grid described in Embodiment Six of the present invention;

[0029] Figure 5 This is a flowchart of the method described in Embodiment Seven of the present invention. Detailed Implementation

[0030] Example 1:

[0031] This embodiment is a high-efficiency controlled ammonia injection grid for flue gas denitrification, such as... Figure 1 , 2 As shown. This embodiment includes a detection facility 2 for detecting nitrogen oxides installed in the flue gas duct 1 of the combustion furnace and multiple ammonia injection grid units 3 evenly distributed in the flue gas duct. Each ammonia injection grid unit includes multiple branch pipes 302 surrounding and connecting to the main pipe 301. Each branch pipe is provided with multiple ammonia injection ports 303. Each main pipe of each ammonia injection grid unit is provided with a regulating valve 304 and a differential pressure sampling point 305. Each differential pressure sampling point is connected to a differential pressure transmitter 4 outside the flue gas duct, which can calculate the flow rate of the flue gas passing through each ammonia injection grid unit from the differential pressure value, via its own instrument conduit 306. The differential pressure transmitter is connected to the regulating valve information of each ammonia injection grid unit.

[0032] The principle of this embodiment is as follows: a differential pressure sampling point is set at the center of each ammonia injection grid unit. The differential pressure is transmitted to a differential pressure transmitter outside the flue gas duct via an instrument conduit. The flue gas flow rate and nitrogen oxide content of each ammonia injection grid unit are calculated from the differential pressure value. Based on the flue gas flow rate and nitrogen oxide distribution in the flue gas duct cross-section at each ammonia injection grid, the ammonia injection rate of each ammonia injection grid is precisely controlled to achieve precise and uniform ammonia injection. The sampled differential pressure is transmitted to the differential pressure transmitter outside the flue gas duct via a pressure guide pipe. Each ammonia injection grid is equipped with an independent ammonia control valve (regulating valve), and the ammonia injection rate is controlled by adjusting the valve opening.

[0033] Figure 1 The flue described in Figure 1 , 2 The image shown (represented by a thick dashed box) is a horizontal cross-sectional view of a rectangular flue of a combustion furnace. There are 12 H-shaped ammonia injection grid units evenly distributed on one horizontal cross-section of the flue. In practice, there can also be multiple layers of ammonia injection grids, that is, multiple ammonia injection grid units are distributed on multiple horizontal cross-sections at different heights, and a certain distance is maintained between each horizontal cross-section so that the ammonia, as a catalyst, can be fully integrated with the flue gas.

[0034] To ensure that ammonia water can be sprayed evenly from each nozzle, the main pipe of the ammonia spraying grid unit is located at the center of the ammonia spraying grid unit. If the branch pipes are distributed in a circle, the main pipe can be located at the center of the circle. If the branch pipes are distributed in an H-shape, the main pipe can be located at the midpoint of the short connecting line in the middle of the H-shape.

[0035] The differential pressure transmitter includes two sampling ports, an instrument conduit, and a pressure transmitter. The sampling ports are arranged sequentially along the flue gas flow path to detect the pressure at two different locations and obtain the pressure difference. The instrument conduit typically consists of two lines, each connecting to one of the two sampling ports. The pressure transmitter can be a general-purpose pressure sensor. To prevent dust in the flue gas from clogging the sampling ports and instrument conduit, the sampling ports are positioned in the direction of flue gas flow, and a backflush system is installed on the instrument conduit to blow out any dust adhering to the conduit and sampling ports.

[0036] Each ammonia injection grid unit is equipped with a regulating valve on its main pipe. These valves can be manually or electrically controlled. When the regulating valve is manual, the operator can read the NOx parameter value from the nitrogen oxide detection device and the differential pressure parameter value measured by each differential pressure transmitter. By calculating the required ammonia injection quantity for each grid unit using these differential pressure and NOx parameter values, the operator can then manually control the regulating valve to achieve the desired injection quantity. If an electrically controlled regulating valve is used, fully automated control can be achieved. The electrical signal output from the pressure transmitter is sent to the arithmetic controller, which calculates the ammonia injection quantity, determines the opening degree of the electric valve, and then the electric valve actuates accordingly.

[0037] Detection facilities for nitrogen oxides (NOx) include sensors specifically designed to detect NOx in flue gas, and devices capable of outputting and displaying the parameters measured by the sensors as electrical signals, such as CEMS instruments. There are various existing technologies for detecting NOx in flue gas ducts. For example, some existing technologies assume that NOx is non-uniform across a certain cross-section of the flue gas duct, so multiple sensors are installed in a plane of the flue gas duct to detect NOx. However, in practice, such detection methods are too costly (CEMS instruments are expensive instruments), and equipment costs are a significant burden. Therefore, this embodiment measures the NOx levels at one point or a limited number of points in the flue gas duct, assuming that NOx in the flue gas duct is uniform, with variations in NOx levels within the same cross-section caused only by differences in flue gas flow rate. Therefore, this embodiment can achieve precise control of ammonia injection by installing one or a few NOx sensors in the flue gas duct.

[0038] Example 2:

[0039] This embodiment is an improvement upon Embodiment 1, specifically a refinement of the ammonia injection grid unit. In this embodiment, the ammonia injection grid units are evenly distributed in a grid pattern within a rectangular cross-section flue. The branch pipes of the ammonia injection grid units are H-shaped, and the differential pressure sampling point is located at the midpoint of the connecting line of the H-shape. Figure 2 As shown.

[0040] In this embodiment, the branch pipes of the ammonia injection grid are distributed in an H-shape, that is, two long pipes on both sides and a short pipe in the middle connecting the midpoints of the two long pipes. The connection point to the main pipe is set at the midpoint of the short pipe. In this way, the center of each ammonia injection grid is located at the connection between the main pipe and the branch pipe. Therefore, setting the differential pressure sampling point at this position means setting the differential pressure sampling point at the center of each ammonia injection grid unit. Since the ammonia injection grid units are evenly distributed in the flue, the differential pressure sampling points are also evenly distributed in a grid pattern across the flue cross-section.

[0041] Example 3:

[0042] This embodiment is an improvement upon the above embodiment, detailing the sampling ports of the differential pressure sampling point. In this embodiment, the two sampling ports 3051 and 3052 of the differential pressure sampling point are positioned in the direction of flue gas flow, as shown below. Figure 3 As shown.

[0043] To prevent backflow of smoke and dust from clogging the sampling ports, this embodiment adopts a design where both sampling ports are positioned leeward. The two sampling ports may or may not be in a straight line, but they must be positioned one in front of the other in the direction of smoke flow to ensure a pressure difference.

[0044] Example 4:

[0045] This embodiment is an improvement upon the above embodiment, and is a refinement of the instrument conduit in the above embodiment. Each instrument conduit described in this embodiment is equipped with a back-blowing device 5, such as... Figure 3 As shown.

[0046] To prevent clogging of the differential pressure sampling instrument conduit and sampling port, an anti-clogging backflush device can be installed on the instrument conduit. This involves installing a branch pipe at the rear end of the instrument conduit (or, if the connection between the instrument conduit and the sampling port is the front end, then the connection between the instrument conduit and the pressure transmitter is the rear end). This branch pipe is connected to a compressed air source, and compressed air is continuously used for backflush during or after flue gas detection. Figure 3 (In the direction of the arrow in the image), blow the dust adhering to the instrument conduit and sampling port back into the flue to keep the instrument conduit and sampling port unobstructed.

[0047] Example 5:

[0048] This embodiment is an improvement upon the above embodiment, and a refinement of the control valve described in the above embodiment. The control valve described in this embodiment is an electrically controlled control valve.

[0049] Electrically controlled regulating valves allow for convenient manual adjustment of valve opening, or electronic control of valve opening to achieve automatic control.

[0050] Example 6:

[0051] This embodiment is an improvement upon the above embodiment, detailing the electrically controlled regulating valve. In this embodiment, the electrically controlled regulating valve is connected to the operational controller 6, which in turn is connected to the nitrogen oxide detection facility and pressure transmitter, as described above. Figure 4 As shown.

[0052] The automated control scheme in this embodiment uses signal feedback to control the ammonia injection quantity. The control process is as follows: first, the average nitrogen oxide content in the flue is detected; then, the flue gas flow rate through each ammonia injection grid is detected using differential pressure detection. The amount of nitrogen oxides flowing through each ammonia injection grid is calculated using these two parameters, and the ammonia injection quantity for each grid is calculated accordingly. Finally, the ammonia injection quantity is converted into the opening degree of each regulating valve and executed, achieving precise ammonia injection control.

[0053] The computing controller described in this embodiment is an electronic device with computing and storage capabilities, such as a microcontroller, an industrial PC, or other electronic devices.

[0054] Example 7:

[0055] A method for calculating the ammonia injection rate using the high-efficiency controlled ammonia injection grid for flue gas denitrification described in the above embodiments. The calculation method in this embodiment is based on the ammonia injection grid unit, assuming the NOx concentration at the inlet of each ammonia injection grid is the same, with units of mg / Nm³. 3 (Dry flue gas, 6% O2). The calculation process is based on the principle of: pressure difference → flue gas flow rate → amount of nitrogen oxides → ammonia injection rate, and the valve is controlled by the calculated ammonia injection rate.

[0056] The steps of the method are as follows (the process is as follows): Figure 5 As shown):

[0057] Step 1, Measure the pressure difference: Measure the pressure difference Δp through the sampling point of the ammonia injection grid unit.

[0058] In the above embodiments, the ammonia injection grid is divided into units, and each unit has its own differential pressure sampling point to obtain the differential pressure sample at the ammonia injection grid. In this embodiment, it is referred to as the "current" ammonia injection grid unit.

[0059] Step 2, calculate flue gas flow rate: Calculate the flue gas velocity q at the current sampling point using the formula based on the pressure difference measured at the sampling point. m :

[0060]

[0061] Where: K is the calculation coefficient.

[0062] The calculated coefficient K is related to environmental factors and the characteristics of the measuring instrument itself. Usually, the measuring instrument will provide a reference value for the calculated coefficient K.

[0063] Step 3, Calculate the flow rate: Considering moisture, pressure, temperature, and oxygen content, use q. m Calculate the flue gas flow rate Q under standard conditions. 烟气 ;

[0064] The flow velocity is obtained, and then the flue gas flow rate at that unit is calculated. The calculated flue gas flow rate is the actual flue gas flow rate. It needs to be converted to the standard flue gas flow rate under standard conditions, taking into account factors such as moisture, pressure, temperature, and oxygen content in the flue gas. That is, dry basis flue gas, 6% O2, unit: Nm 3 / h.

[0065] Step 4, Calculate NOx: Obtain the NOx concentration in the flue gas from the nitrogen oxide detection facility, and calculate the amount of NOx in the flue gas per unit time.

[0066] NOx amount = Q 烟气 ×NOx concentration;

[0067] The standard flue gas flow rate measured at the sampling point of the ammonia injection grid unit is multiplied by the NOx concentration (unit: mg / Nm³). 3 The amount of NOx per unit time was calculated from dry flue gas (6% O2) (unit: mg / h dry flue gas, 6% O2).

[0068] Step 5, calculate the number of ammonia moles: Calculate the amount of NH3 sprayed per unit time based on the amount of NOx per unit time. The formula is:

[0069] The number of moles of NH3 equals the number of moles of NOx;

[0070] The required number of moles of ammonia to be injected is calculated based on the actual chemical reaction equation. Chemical reaction equation:

[0071]

[0072] Step 6, convert the ammonia injection amount: convert the number of ammonia moles calculated from the chemical reaction formula into the industrial unit ammonia injection amount.

[0073] In industrial production, all instruments and meters typically display units such as grams and kilograms. Therefore, it is necessary to convert molar numbers into industrial units: mg / h or kg / h, so that industrial instruments can adjust the ammonia injection rate and control the ammonia injection operation.

[0074] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of the present invention (such as the form of the ammonia injection grid, the form of ammonia injection quantity adjustment, etc.) without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A high-efficiency controlled ammonia injection grid for flue gas denitrification, comprising a detection facility for detecting nitrogen oxides installed in the flue of a combustion furnace and multiple ammonia injection grid units uniformly distributed in the flue, wherein each ammonia injection grid unit comprises multiple branch pipes surrounding and connecting to the main pipe, and each branch pipe is provided with multiple ammonia injection ports, characterized in that, Each of the ammonia injection grid units has a regulating valve and a differential pressure sampling point on its main pipe. Each differential pressure sampling point is connected to a pressure transmitter outside the flue via its respective instrument conduit. The pressure transmitter can calculate the flow rate of the flue gas passing through each ammonia injection grid unit based on the differential pressure value. The pressure transmitter is connected to the regulating valve information of each ammonia injection grid unit. The ammonia injection grid units are evenly distributed in a grid pattern in the flue with a rectangular cross-section. The branch pipes of the ammonia injection grid units are H-shaped. The differential pressure sampling point is located at the midpoint of the connecting line of the H-shape. The two sampling ports of the differential pressure sampling point are set in the direction of flue gas flow. Each of the instrument conduits is equipped with a back-blowing device.

2. The high-efficiency controlled ammonia injection grid according to claim 1, characterized in that, The regulating valve mentioned is an electrically controlled regulating valve.

3. The high-efficiency controlled ammonia injection grid according to claim 2, characterized in that, The electrically controlled regulating valve is connected to the operational controller, which in turn is connected to the nitrogen oxide detection facility and pressure transmitter.

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