Coal-fired boiler flue gas treatment system and control system thereof

Abstract

The invention relates to the technical field of coal-fired boiler flue gas treatment, in particular to a coal-fired boiler flue gas treatment system and a control system thereof.The coal-fired boiler flue gas treatment system comprises a first boiler, a second boiler and a desulfurizing tower which are communicated, an SNCR denitration process is conducted in the first boiler, an SCR denitration reaction buffer tank is conducted in the second boiler, and the second boiler and the desulfurizing tower are communicated. The second boiler is used for storing flue gas conveyed from the second boiler; the acid tank is communicated with the buffer tank and provides an acid solution to the buffer tank; the alkali reaction tank is arranged behind the buffer tank in the flue gas flow direction, is communicated with the buffer tank and the desulfurization tower, and is used for providing an alkaline solution for the flue gas; and the reducing agent tank communicates with the first boiler, the second boiler and the desulfurization tower and provides a reducing agent for the first boiler and the second boiler. The flue gas treatment device has the effects of reducing the flue gas treatment cost of the coal-fired boiler and reducing the risk of ammonia escape.

Description

Technical Field

[0001] The present application relates to the field of coal-fired boiler flue gas treatment technology, and in particular to a coal-fired boiler flue gas treatment system and a control system thereof. Background Art

[0002] With the acceleration of industrialization and the growth of energy demand, coal-fired boilers, as an important energy conversion equipment, play a key role in electricity production and industrial heating. However, coal-fired boilers produce a large amount of pollutants during operation, especially nitrogen oxides and sulfur oxides, which pose a serious threat to the environment and human health.

[0003] Therefore, in coal-fired plants such as power plants and heating plants, a flue gas treatment system is installed at the tail of the coal-fired boiler to physically and chemically transform the main nitrogen oxides and sulfur oxides in the flue gas so that the coal-fired flue gas meets the atmospheric emission standards.

[0004] At present, most coal-fired plants mainly choose the combined denitrification technology of selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), and use ammonia solution as the reducing agent. The most widely used desulfurization method is the limestone / gypsum method. Although the denitrification method combining SNCR and SCR is relatively mature, there are still some problems. For example, the risk of ammonia escape caused by improper control of the denitrification system is still common. Ammonia that does not participate in the reaction is discharged into the atmosphere with the flue gas to change the acid-base balance of the atmosphere. Long-term emission will harm the surrounding environment and ecosystem. For example, the catalyst used in the denitrification system is expensive, resulting in a high denitrification cost. Summary of the invention

[0005] In order to reduce the cost of coal-fired boiler flue gas treatment and reduce the risk of ammonia escape, the present application provides a coal-fired boiler flue gas treatment system and a control system thereof.

[0006] On the one hand, the present application provides a coal-fired boiler flue gas treatment system, which adopts the following technical solution: A coal-fired boiler flue gas treatment system, comprising a first boiler, a second boiler and a desulfurization tower connected to each other, wherein a SNCR denitration process occurs in the first boiler, and an SCR denitration reaction occurs in the second boiler, characterized in that it also includes: a buffer tank connected to the second boiler and the desulfurization tower and used for storing the flue gas transmitted from the second boiler; an acid tank, connected to the cache tank, and providing an acid solution to the cache tank; An alkaline reaction tank is arranged behind the buffer tank where the flue gas flows upward, connected to the buffer tank and the desulfurization tower, and is used to provide an alkaline solution to the flue gas; The reducing agent tank is connected to the first boiler, the second boiler and the desulfurization tower, and provides the reducing agent to the first boiler and the second boiler.

[0007] By adopting the above technical solution, a technical solution combining the traditional SCR and SNCR denitrification technologies is adopted, and the technology of the traditional solution is improved by adding acid tanks, alkali tanks and other related devices that utilize the denitrification reaction products. The investment cost is reduced by utilizing the denitrification reaction products, and the unused ammonia is purified and collected. While reducing the flue gas treatment cost, the risk of ammonia escape is reduced by recycling the ammonia with improved purity; Its basic process and principle are as follows: in the direction of flue gas flow, the first boiler is the front end of the flue gas treatment system and is connected to the gas boiler. The flue gas containing a large amount of nitrogen oxides and sulfur oxides after combustion in the gas boiler is discharged into the first boiler. The first boiler provides a high temperature of 900℃-1100℃, and an SNCR denitration reaction is carried out in the first boiler. Then the flue gas is transported from the first boiler to the second boiler along the pipeline. The second boiler provides a high temperature of 300℃-400℃, and an SCR denitration reaction is carried out in the second boiler. After two denitration reactions, the flue gas is transported to the desulfurization tower for desulfurization. The desulfurization tower provides a reaction temperature of 80℃-170℃ to remove a large amount of remaining sulfur oxides in the flue gas. The flue gas is denitrated to generate nitrogen and water. The flue gas is desulfurized to generate water, which is discharged out of the system with the filtered flue gas. The above desulfurization process adopts the limestone / gypsum method, that is, a calcium carbonate aqueous solution is sprayed into the desulfurization tower, and the weakly alkaline calcium carbonate aqueous solution is used to contact the sulfur oxides in the flue gas to generate calcium sulfate and carbon dioxide by chemical reaction. Therefore, in the above process After the flue gas flows out from the second boiler, it is transported to the buffer tank for buffering and accumulation. After sufficient accumulation, the acid tank sprays acidic liquid into the buffer tank. The acidic liquid reacts with ammonia mixed in the flue gas and volatilized from the reducing agent without undergoing denitration reaction to generate ammonium salt. The acidic solution is preferably carbonic acid, which is relatively common and has a low cost. If carbonic acid is used, a mixture of ammonium carbonate and ammonium bicarbonate is generated. After a reaction cycle, the solution containing ammonium carbonate and ammonium bicarbonate is transported to the subsequent alkaline reaction tank. The technicians add alkaline solution to the alkaline reaction tank to react chemically with ammonium carbonate and ammonium bicarbonate. The above-mentioned alkali is preferably slaked lime, that is, calcium hydroxide. Silicon oxide reacts with ammonium carbonate and ammonium bicarbonate to generate calcium carbonate, water, and ammonia. Among them, calcium carbonate is the raw material for the subsequent desulfurization reaction. The purity of the ammonia generated after the above-mentioned acid-base reaction and salt-base reaction is higher than that of the ammonia discharged from the second boiler, and is not mixed with gas impurities. It can be collected and directly used for proportioning the reducing agent; further, the carbon dioxide generated by the desulfurization reaction can be collected and used to manufacture carbonic acid; In summary, two chemical reaction processes are added between the traditional desulfurization tower and the second boiler for SCR denitration reaction to purify ammonia and directly generate calcium carbonate solution required for subsequent desulfurization reaction. The calcium carbonate solution can be used for spraying in the subsequent desulfurization tower after simple treatment. The gas output from the subsequent deoxygenation tower contains nitrogen, ammonia, carbon dioxide, etc., which can be collected, separated and recycled. Since the above scheme is an improvement of the denitrification system, the SCR, SNCR denitrification technology and the denitrification technology combining SCR and SNCR used in the denitrification system are all existing technologies, and their reaction principles and reaction chemical formulas are not described in detail.

[0008] Optionally, also include: A dust collector is arranged between the buffer tank and the first boiler, the flue gas inlet of the dust collector is connected to the first boiler, and the flue gas outlet of the dust collector is connected to the buffer tank and the reducing agent tank; The separation tank is connected to the reducing agent tank and the desulfurization tower, collects and stores the flue gas exhausted from the desulfurization tower, and separates carbon dioxide and ammonia.

[0009] By adopting the above technical solution, the coal used in the combustion boiler contains a certain amount of combustible inorganic minerals, which will form ash during combustion, while the non-combustible inorganic minerals will form solid residues, which will be mixed in the flue gas to form dust, fly ash, etc.; in the above solution, considering that the first boiler and the second boiler also need coal combustion to provide high temperature, the dust collector is set in the part after the denitrification reaction in the flue gas flow upward, and the impurities in the flue gas of the first boiler, the second boiler and the combustion boiler are removed at one time to avoid; in the above solution, the dust collector adopts an electrostatic precipitator; The separation tank receives the flue gas discharged from the desulfurization tower, and uses the physical property of ammonia being highly soluble in water to inject water into the separation tank to separate ammonia and carbon dioxide. The ammonia water is then transported to the reducing agent tank and simply mixed as a new reducing agent solution, while the carbon dioxide is recycled as a raw material for the preparation of carbonic acid.

[0010] Optionally, the first boiler is divided into two independent and non-connected parts, namely a first denitration part and a second denitration part; The first denitration section and the second denitration section are both connected to the reducing agent tank, the first denitration section is connected to the gas boiler and the second boiler, and the second denitration section is connected to the second boiler and the dust collector.

[0011] By adopting the above technical solution, the first boiler is divided into a first denitration part and a second denitration part, and the above reducing agent tank provides reducing agent to both parts; the first denitration part is the front end of the flue gas denitration system in the above solution, and the second denitration part is connected to the second boiler and the dust collector, and is located after the second boiler in the flue gas flow upward; The flue gas flow is from the first denitration part of the first boiler → the second boiler → the second denitration part of the first boiler → the dust collector, so that the flue gas from the second boiler that has completed the SCR denitration reaction flows back to the first boiler, and then undergoes the SNCR denitration reaction to improve the denitration rate; The technical solution of flue gas recirculation is not a necessary process. When the denitrification rate of the SCR is insufficient due to a malfunction or other accidental factors, that is, when the nitrogen oxide concentration near the SCR outlet is monitored to be too high, the technicians can switch the flue gas flow direction to make the flue gas reflux and ensure the denitrification rate of the flue gas denitrification system.

[0012] Optionally, the second denitrification section is formed with baffles on the inner walls on two opposite sides in the flue gas flow direction, and adjacent baffles are formed on different sides to form a flue gas flow channel.

[0013] By adopting the above technical solution, improvements are made on the basis of flue gas reflux, baffles are arranged at intervals to extend the flow channel of the flue gas, and at the same time, the flow velocity of the flue gas is slowed down under the action of the baffles, thereby ensuring the denitrification rate of the flue gas during flue gas reflux.

[0014] Optionally, the pipe between the second denitrification section and the dust collector is made of a heat-sensitive material, or the pipe between the second boiler and the dust collector is made of a heat-sensitive material, and is used to cool the flue gas flowing out of the second denitrification section.

[0015] By adopting the above technical solution, after denitration is completed, the flue gas needs to be further desulfurized to remove sulfur oxides mixed in the flue gas. Since the optimum temperature range of the chemical reaction for removing sulfur oxides is 80℃-170℃, and after denitration in the second denitration section, the flue gas temperature is about 900℃, if the high-temperature flue gas is directly cooled, the rapid drop in the flue gas temperature will easily lead to the formation of condensed water in the flue gas, increase the humidity of the flue gas, and the condensed water and the sulfur oxides in the flue gas will form an acidic sulfur solution to corrode the pipeline and damage the equipment, and it is easy to cause the condensed water mixed with dust and fly ash to adhere to the inner wall of the equipment, affecting the operation of the equipment; therefore, the temperature should not be cooled too quickly; In practical applications, the above solution can be adopted to appropriately extend the length of the pipeline between the second denitrification section and the dust collector, and only set a protective layer on the pipeline surface without setting a thermal insulation layer. When the flue gas flows along the pipeline, it can effectively exchange heat with the outside world and dissipate heat to the outside world. Furthermore, in order to improve the heat dissipation effect, this section of the pipeline can be made of heat-sensitive materials, such as ceramic materials such as silicon carbide and silicon nitride, high-temperature alloy materials such as iron-based alloys and nickel-based alloys, etc. Semiconductor heat sinks can also be installed on the pipeline wall to better utilize the temperature difference between the flue gas in the pipeline and the ambient temperature to accelerate heat dissipation; Both of the above technical solutions can be adopted, based on achieving effective heat dissipation with higher cost performance.

[0016] Optionally, a hot gas bin is provided on the inner wall of the desulfurization tower body, and the hot gas bin is connected to the second denitrification part and the dust collector.

[0017] By adopting the above technical solution, the heat of the flue gas is used to set the desulfurization tower body near the first boiler, and the hot gas discharged from the first boiler is used to heat the internal environment of the desulfurization tower, so that the temperature of the desulfurization tower meets the requirements; The specific structure may include setting a hot gas bin in the hot desulfurization tower body, so that the desulfurization tower wall is double-layered, and the high-temperature flue gas discharged from the second denitrification part of the first boiler is introduced into the hot gas bin, and the air inside the desulfurization tower is heated through the desulfurization tower wall by heat transfer, and then discharged from the hot gas bin outlet of the desulfurization tower to the pipeline between the dust collector and the second denitrification part, thereby further realizing the recovery and utilization of heat energy and reducing the heating cost of the desulfurization tower.

[0018] On the other hand, the present application provides a control system for a coal-fired boiler flue gas treatment system, which adopts the following technical solution: A control system applied to a coal-fired boiler flue gas treatment system as claimed in claim 1, characterized in that it comprises a central control module, a system monitoring module, and a system control module; The system monitoring module is used to detect the temperature of the flue gas discharged into the first boiler, and to monitor the ambient temperature inside the first boiler, the second boiler, and the desulfurization tower in real time, and to upload the temperature monitoring data to the central control module in real time; the system monitoring module is used to detect the pH value of the solution in the acid tank, the alkali reaction tank, and the buffer tank, and to upload the pH value monitoring data to the central control module in real time; the system monitoring module is used to monitor the reducing agent concentration in the reducing agent tank and the ammonia concentration in the buffer tank, and to upload the concentration monitoring data to the central control module in real time; The central control module receives and retrieves the monitoring data of the system monitoring module in real time, analyzes, processes and calculates, generates corresponding instructions according to the calculation results, and sends them to the system control module, and the system control module operates according to the instructions.

[0019] Optionally, the system control module receives relevant instructions from the central control module, adjusts the input flow of the acid solution in the acid tank, the input flow of the reducing agent in the reducing agent tank, and the input amount of the alkali solution in the alkali reaction tank, so that the acid solution, the reducing agent, and the alkali solution adapt to the real-time concentration of ammonia.

[0020] By adopting the above technical solution, the central control module, the system monitoring module and the system control module constitute the core part of the control system of the flue gas denitrification system. In practical applications, the flue gas denitrification system occupies a large volume, so the central control system is generally set in a separate control room. Specifically, the central control system can be a single chip microcomputer or a computing network composed of multiple computers, and its scale is determined by the specific scale of the flue gas denitrification system. The system monitoring module is set inside the flue gas denitrification, specifically inside the first boiler, inside the second boiler, and inside the desulfurization tower. It collects the reaction temperature in real time, and collects the concentration of nitrogen oxides flowing into the first boiler and the second boiler, and the concentration and pH value of sulfides flowing into the deoxidation tower. According to the current concentration, temperature, and pH value, the central control module estimates the denitrification reaction efficiency inside the first and second boilers, as well as the desulfurization reaction efficiency in the desulfurization tower, fits the efficiency-time curve, and intuitively displays the denitrification and desulfurization rates to the observers. The optimal efficiency value is pre-written in the central control module by the technicians, and the optimal efficiency is displayed in the form of a straight line. The central control module synchronously displays the optimal efficiency straight line and the real-time efficiency curve, and calculates the difference; In summary, the system detection module focuses on reaction efficiency, monitors all important numerical information related to denitrification and desulfurization efficiency, and sends the monitoring results to the central control module. The central control module then issues specific control instructions to the system control module to make adjustments. For example, when the amount of reducing agent injected into the first boiler is too much and is not suitable for the current nitrogen oxide concentration, continuing to maintain the current amount of reducing agent injected will lead to ammonia escape problems. The above-mentioned system control module can reduce the amount of reducing agent injected by controlling the reducing agent delivery pump. For example, when the internal ambient temperature of the desulfurization tower is too high, the system control module can cut off the flow path of the second denitrification section into the hot gas bin in the desulfurization tower, that is, close the valve between the second denitrification section and the hot gas bin, so that the flue gas flows directly from the second denitrification section into the desulfurization tower. When the internal ambient temperature of the desulfurization tower is lower than the preset temperature value, the flue gas flow path between the second denitrification section and the desulfurization tower is reopened.

[0021] In summary, the present application includes at least one of the following beneficial technical effects: 1. The integration of SNCR and SCR denitrification technologies, coupled with the partition design of the first boiler and the use of baffles, improves the denitrification efficiency and the flexibility of flue gas treatment, more efficiently reduces nitrogen oxide emissions in flue gas, and improves the effect of environmental governance; 2. Introducing components such as a buffer tank, an acid tank, and an alkali reaction tank to purify ammonia and generate a calcium carbonate solution necessary for the desulfurization reaction, and also generating carbon dioxide that can be used to prepare carbonic acid. Compared with the traditional method of using quicklime to dissolve in acid to generate a calcium carbonate solution, the present invention reduces the cost of use; 3. Use heat-sensitive materials and heat sinks to cool the flue gas in time, which improves energy efficiency, reduces system operating costs, and creates favorable conditions for subsequent desulfurization treatment; 4. The present invention finely adjusts the input flow of acid, reducing agent and alkali solution to adapt the ammonia gas at the real-time concentration, which not only optimizes the treatment process, but also greatly reduces material consumption and operating costs, bringing a more economical solution to the flue gas treatment industry; 5. Through the synergistic effect of the central control module, the system monitoring module and the system control module, the present invention realizes the full monitoring and intelligent management of the entire flue gas treatment process, improves the automation and intelligence level of the system, and provides a more convenient and efficient tool for factory operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the overall logic block diagram of the flue gas denitrification system in the embodiment of the present application.

[0023] Figure 2 It is a cross-sectional view of the first boiler in the embodiment of the present application.

[0024] Figure 3 It is a cross-sectional view of the deoxygenation tower in the embodiment of the present application.

[0025] Figure 4 It is an operation logic block diagram of the control system in the embodiment of the present application.

[0026] Explanation of the accompanying drawings: 1. first boiler; 11. first denitration section; 12. second denitration section; 121. baffle; 13. first gas valve; 14. second gas valve; 15. reducing agent tank; 151. reducing agent valve; 152. reducing agent pump; 16. delivery pump; 161. delivery valve; 17. separation tank; 2. second boiler; 3. dust collector; 4. desulfurization tower; 41. hot gas bin; 5. buffer tank; 51. acid tank; 52. acid valve; 53. acid pump; 6. alkali reaction tank; 61. alkali tank; 62. alkali valve; 63. alkali pump; 7. system monitoring module; 71. concentration monitoring unit; 72. temperature monitoring unit; 73. pH monitoring unit; 8. central control module; 81. wireless transmission module; 9. system control module; 91. valve control unit; 92. pump control unit. DETAILED DESCRIPTION

[0027] The following is combined with Figure 1-4 This application is described in further detail.

[0028] The present application embodiment discloses a coal-fired boiler flue gas treatment system. Figure 1A coal-fired boiler flue gas treatment system includes a first boiler 1 and a reducing agent tank 15. The first boiler 1 is connected to a gas boiler and receives flue gas containing nitrogen oxides and sulfur oxides generated after combustion in the gas boiler. The flue gas flows from the gas boiler to the first boiler 1, and a selective non-catalytic reduction (SNCR) denitration reaction is performed in the first boiler 1 to reduce the nitrate content of the flue gas. The denitration reaction in the first boiler 1 is provided with a reducing agent by the reducing agent tank 15. The first boiler 1 and the reducing agent tank 15 are connected by an industrial pipeline, and a reducing agent pump 152 is provided on the industrial pipeline to provide power for the reducing agent to be transported from the reducing agent tank 15 to the first boiler 1. In this embodiment, the reducing agent is an ammonia solution, and ammonia and nitrogen oxides are reduced in the first boiler 1 without a catalyst and at a high temperature to generate nitrogen and water, and are mixed with ammonia that has not fully reacted with nitrogen oxides, dust generated by the combustion of the gas boiler, fly ash and other small particles of coal slag.

[0029] Reference Figure 1 In the flue gas flow direction, a second boiler 2 is arranged behind the first boiler 1, and the second boiler 2 is connected with the first boiler 1. The flue gas that completes the SNCR denitration reaction in the first boiler 1 flows to the second boiler 2, and a selective catalytic reduction (SCR) denitration reaction is carried out in the second boiler 2. The reducing agent tank 15 is connected to the second boiler 2 bracket through an industrial pipeline, and a reducing agent pump 152 and a reducing agent valve 151 are arranged. The reducing agent pump 152 provides power for transporting the reducing agent from the reducing agent tank 15 to the second boiler 2, and the reducing agent valve 151 is used to control the conduction between the reducing agent tank 15 and the first boiler 1. The SNCR denitration reaction of the first boiler 1 relies on the high temperature conditions generated by combustion. Under the condition of no catalyst, the conversion rate of nitrogen oxides is 30%-40%. The furnace temperature of the first boiler 1 is 900℃-1100℃. The SCR denitration reaction in the second boiler 2 relies on high temperature and catalyst. Under catalytic conditions, the conversion rate of nitrogen oxides reaches more than 90%. Relying on the catalytic conditions of the catalyst, the reaction temperature of the second boiler 2 does not need to be very high, generally 300℃-400℃; therefore, in practical applications, considering the flue gas temperature difference under the optimal conversion rate of nitrogen oxides between the first boiler 1 and the second boiler 2, an economizer is generally set between the first boiler 1 and the second boiler 2 to absorb the flue gas temperature to heat water, reduce the flue gas temperature, and transfer part of the flue gas heat to the water, thereby improving the utilization rate of thermal energy.

[0030] In actual applications, the catalyst of the SCR denitrification reaction needs to be replaced regularly, and the effective catalytic life of the catalyst is related to the furnace temperature and humidity of the second boiler 2. Different furnace temperatures and different humidity make it impossible for professionals to accurately predict the effective catalytic life of each batch of catalysts. Therefore, this can easily lead to the end of the effective life of the catalyst and the denitrification rate of the second boiler 2 being less than 90%, which in turn leads to the nitrogen oxide content in the exhaust gas not meeting the standard.

[0031] Reference Figure 1 and Figure 2 , a partition is vertically arranged inside the first boiler 1, dividing the inside of the first boiler 1 into two equal-volume, independent, and unconnected parts, namely the first denitration part 11 and the second denitration part 12. The first denitration part 11 connected to the gas boiler is the first denitration part 11 inside the first boiler 1, and the second denitration part 12 is connected to the second boiler 2, and the high-temperature flue gas inside the second boiler 2 is discharged back to the second denitration part 12 of the first boiler 1, and the SNCR denitration reaction is carried out again in the second denitration part 12. The partition is arranged vertically, and the top and bottom ends are respectively fixed to the center of the top wall and the bottom wall of the first boiler 1, so that the first denitration part 11 and the second denitration part 12 are symmetrical semi-cylindrical structures. A plurality of horizontally arranged baffles 121 are fixed to a vertical curved inner wall and a vertical inner wall of the second denitration part 12, and the plurality of baffles 121 are evenly spaced along the vertical direction, and adjacent baffles 121 are spaced and distributed on the opposite side walls to form a serpentine gas flow channel. When the flue gas is transported to the second denitration section 12, the airflow is reciprocated in the horizontal direction through the baffle 121, thereby extending the flow time of the flue gas in the second denitration section 12 and ensuring sufficient denitration reaction time.

[0032] It should be noted that, in the present embodiment, the first denitration section 11 of the first boiler 1, the second denitration section 12 of the second boiler 2, and the flue gas inlet of the second boiler 2 are all arranged at the bottom, and the flue gas outlet is arranged at the top, that is, inside the first boiler 1 and the second boiler 2, the flow direction of the flue gas is from top to bottom, and under the action of gravity, the flue gas diffuses slowly from bottom to top, providing a longer reduction reaction time.

[0033] Reference Figure 1 and Figure 2 Therefore, the reducing agent tank 15 should also be provided with a section of industrial pipeline corresponding to the second denitration section 12 to make it connected, and a reducing agent pump 152 is provided on this section of industrial pipeline. Therefore, three sections of industrial pipelines are provided on the outflow side of the reducing agent tank 15 to provide reducing agent to the first denitration section 11 of the first boiler 1, the second denitration section 12 and the second boiler 2.

[0034] The above-mentioned reducing agent pumps 152 are all electrically controllable electromagnetic pumps commonly used in the chemical industry.

[0035] Reference Figure 1A dust collector 3 is arranged behind the second boiler 2 in the direction of flue gas flow. The dust collector 3 is used to connect the second denitration section 12 with the second boiler 2, and is used to remove solid coal slag mixed in the flue gas, dust and fly ash generated by the combustion of inorganic substances contained in coal, and coal slag and fly ash generated by the combustion of coal inside the first boiler 1 and the second boiler 2, so as to prevent them from scratching the inner wall of the subsequent equipment. The dust collector 3 is provided with a gas valve on the industrial pipeline connecting the second denitration section 12 and the second boiler 2. For the convenience of distinction, the gas valve between the second boiler 2 and the second denitration section 12 is the first gas valve 13, and the gas valve between the second boiler 2 and the dust collector 3 is the second gas valve 14. The second gas valve 14 is arranged on the industrial pipeline close to one end of the second boiler 2 to prevent the opening and closing of the second gas valve 14 from affecting the first gas valve 13. As described above, two pipelines are set at the front end of the dust collector 3 in the flue gas flow direction. First, under normal circumstances when the denitration rate meets the standard, the first air valve 13 is closed, the second air valve 14 is opened, and the flue gas is directly transported from the second boiler 2 to the dust collector 3. Second, due to the aging of the catalyst and the technicians' failure to replace it regularly, before the system is suspended, the flue gas inside the second boiler 2 is introduced into the second denitration section 12 of the first boiler 1, the first air valve 13 is opened, and the second air valve is closed, and the flue gas is transported from the second denitration section 12 to the dust collector 3. In this embodiment, the dust collector 3 uses the electrostatic precipitator 3 commonly used in the industry. The electrostatic precipitator 3 is a common dust removal equipment in the industry, and this embodiment will not be repeated.

[0036] In summary, nitrogen oxides and small solid particles are effectively removed from the flue gas output from the dust collector 3. At this time, the flue gas output from the second boiler 2 or from the second denitrification section 12 of the first boiler 1 contains nitrogen converted by the reduction reaction, water vapor, ammonia that does not fully participate in the reduction reaction, negligible trace nitrogen oxides, a large amount of sulfur oxides that are not removed, and other common gas components in the air.

[0037] Reference Figure 1 and Figure 3A desulfurization tower 4 is arranged behind the flue gas upward dust collector 3 to remove a large amount of sulfur oxides mixed in the flue gas so that the flue gas can meet the emission standards. The desulfurization tower 4 needs to use a detergent to remove the sulfur oxides mixed in the flue gas during the desulfurization process. Generally, limestone slurry, that is, calcium carbonate solution, is selected. Therefore, an alkaline reaction pool 6 for providing calcium carbonate solution is arranged on one side of the desulfurization tower 4. When the flue gas flows into the deoxidation tower, the deoxidation tower sprays limestone slurry into the flue gas, which reacts with the sulfur oxides in the flue gas to form calcium sulfate precipitation, and at the same time generates harmless carbon dioxide to achieve the purpose of desulfurization. The temperature with the highest desulfurization efficiency is 80℃-170℃, and the temperature inside the tower is lower than that of the first boiler 1 and the second boiler 2. With reference to the heat energy utilization of the first boiler 1 and the second boiler 2, a hot gas bin 41 is opened inside the wall of the desulfurization tower 4, so that the wall of the desulfurization tower 4 is set as a double-layer structure. After the hot gas flows out from the second denitration part 12 of the first boiler 1 or directly from the second boiler 2, it can be pre-introduced into the hot gas bin 41 in the middle of the wall of the desulfurization tower 4, and the internal ambient temperature of the desulfurization tower 4 is heated by heat transfer, further improving the utilization rate of heat energy. After heating the air inside the deoxidation tower in the hot gas bin 41 for a preset period of time, it flows out from the hot gas bin 41 to the dust collector 3. When the subsequent flue gas is passed into the desulfurization tower 4, the tower temperature in the desulfurization tower 4 is continuously maintained within the ideal temperature range due to the continuous presence of hot gas passed into the hot gas bin 41.

[0038] Reference Figure 1 The temperature required by the second denitrification section 12 of the first boiler 1 and the second boiler 2 and the hot gas bin 41 are too high. If the flue gas is transported to the hot gas bin 41 while maintaining the source temperature, the temperature inside the deoxidation tower will rise rapidly, which will be higher than the optimal temperature range of the desulfurization reaction. Therefore, the temperature of the flue gas needs to be lowered during flue gas transportation to cool the high-temperature flue gas. Therefore, the pipeline part between the second denitrification section 12 and the desulfurization tower 4 is made of heat dissipation material, which dissipates heat to the outside through heat transfer during the transportation of high-temperature flue gas, thereby reducing the flue gas temperature.

[0039] Reference Figure 1In this embodiment, the alkaline reaction pool 6 is used as the necessary path for the flue gas to flow. A buffer tank 5 is arranged between the dust collector 3 and the alkaline reaction pool 6 in the direction of the flue gas flow, forming a flue gas flow channel of the dust collector 3→buffer tank 5→alkaline reaction pool 6, that is, the flue gas output from the dust collector 3 is input into the buffer tank 5 for buffering until the buffer tank 5 is filled with flue gas. An acid tank 51 connected to the buffer tank 5 is arranged on one side of the buffer tank 5. The acid tank 51 contains an acid solution pre-configured by a technician, which reacts with the ammonia in the buffer tank 5 to generate an ammonium salt. In this embodiment, the acid solution uses a weakly acidic carbonate solution to facilitate the subsequent adjustment of the pH value of the solution. Carbonic acid is more common and has a lower cost. In this embodiment, the use of carbonic acid can reduce the cost of raw materials. The acid tank 51 is connected to the buffer tank 5 through an industrial pipeline, and an acid pump 53 is arranged in this section of the industrial pipeline to provide power for the carbonate solution to be transported from the acid tank 51 to the buffer tank 5, and an acid valve 52 is arranged to control the solution delivery flow between the acid tank 51 and the buffer tank 5.

[0040] The acid is transported from the acid tank 51 to the buffer tank 5, and the ammonia is dissolved in the carbonic acid solution and reacts with the carbonic acid molecules therein and the ammonia in the flue gas to generate a mixture of ammonium carbonate and ammonium bicarbonate. During the reaction process, technicians are required to control the inflow of carbonic acid and control the operating status of the acid pump 53 and the acid valve 52 to adapt them to the real-time ammonia concentration.

[0041] Reference Figure 1 , a delivery pump 16 is provided on the industrial pipeline between the buffer tank 5 and the alkali reaction tank 6, and the delivery pump 16 delivers the ammonium carbonate and ammonium bicarbonate solutions that have completed the reaction in the buffer tank 5 to the alkali reaction tank 6. An alkali tank 61 is provided on one side of the alkali reaction tank 6, and the alkali tank 61 contains an alkaline solution, which has the same structure as the acid tank 51 and the buffer tank 5. An alkali liquid pump 63 and an alkali liquid valve 62 are provided between the alkali tank 61 and the alkali reaction tank 6, which are used by technicians to control the alkali liquid flow rate flowing into the alkali reaction tank 6 to adapt it to the above-mentioned ammonium carbonate and ammonium bicarbonate content. Ammonium carbonate and ammonium bicarbonate react with the alkali liquid in the alkali reaction tank 6. Considering the demand for limestone solution in the subsequent desulfurization tower 4, the alkali reaction tank 6 uses slaked lime powder, that is, calcium hydroxide. Calcium hydroxide reacts with ammonium carbonate and ammonium bicarbonate in the alkali reaction tank 6 to generate calcium carbonate solution and ammonia. The ammonia generated in this way has a high purity and can be directly collected. After the salt-alkali reaction in the alkaline reaction tank 6 has been carried out for a preset period of time and the alkaline reaction tank 6 contains a sufficient amount of calcium carbonate, the calcium carbonate solution is transported from the alkaline reaction tank 6 to the desulfurization tower 4 .

[0042] In the above process, when the flue gas passes through the alkaline reaction tank 6, part of the sulfur oxides (especially sulfur dioxide) contained in the flue gas reacts with the slaked lime aqueous solution to generate water and calcium sulfite, that is, part of the sulfur oxides have been filtered out in the alkaline reaction tank 6, thereby improving the desulfurization capacity of the system.

[0043] Reference Figure 1, the industrial pipeline between the alkali reaction pool 6 and the desulfurization tower 4 is provided with a delivery pump 16, which provides the power for delivering calcium carbonate in the alkali reaction pool 6 to the desulfurization tower 4. Limestone solution is used for desulfurization in the desulfurization tower 4, and the denitrified and desulfurized gases are discharged from the desulfurization tower 4. Therefore, the gas discharged from the desulfurization tower 4 contains nitrogen converted by the reduction reaction, water vapor, ammonia generated by the salt-alkali reaction, a large amount of carbon dioxide, negligible trace nitrogen oxides and sulfur oxides, and other common gas components in the air. Among them, the content of ammonia and carbon dioxide is relatively high. Ammonia is harmful and cannot be discharged directly. It can be collected and used to make a reducing agent. A large amount of carbon dioxide is directly discharged, which will aggravate the greenhouse effect for a long time. It can be collected to make the above-mentioned carbonic acid. Based on this, a separation tank 17 is provided behind the deoxygenation tower in the flue gas flow direction to receive the flue gas after denitrification, desulfurization and dust removal from the deoxygenation tower, and separate the ammonia and carbon dioxide contained therein. Taking advantage of the fact that ammonia is highly soluble in water, water is injected into the separation tank 17 to dissolve the ammonia contained therein to form an ammonia solution, which is used as one of the direct raw materials for the subsequent reducing agent tank 15. When the ammonia content drops to a level that meets the flue gas emission standard, part of the carbon dioxide is removed, and the remaining carbon dioxide is collected and used to make carbonic acid.

[0044] Reference Figure 1 A delivery pump 16 and a delivery valve 161 are provided on the industrial pipeline between the reducing agent tank 15 and the separation tank 17 to provide power for delivering the ammonia solution in the separation tank 17 to the reducing agent tank 15 .

[0045] In this embodiment, the acid pump 53, the delivery pump 16, and the alkali solution pump 63 are all common industrial pumps.

[0046] It should be noted that the detailed principle details of desulfurization and denitrification during the implementation process, and other necessary dust removal, heat exchange, and condensation equipment are installed between the denitrification equipment and the desulfurization equipment. Since they are existing technologies and are not technical points of this embodiment, they are not elaborated in this embodiment, but they cannot be ignored during implementation. The implementation principle of a coal-fired boiler flue gas treatment system in an embodiment of the present application is as follows: the flue gas transported by the gas boiler is mixed with harmful substances such as nitrogen oxides and sulfur oxides and cannot be discharged directly, and a flue gas treatment system is required to remove the harmful substances.

[0047] The flue gas is input to the first denitration section 11 of the first boiler 1 for SNCR denitration reaction, and then transported to the second boiler 2 for SCR denitration reaction. The technicians should keep measuring the nitrogen oxide content at the outlet of the second boiler 2 in real time to ensure that the nitrogen oxide content is lower than the standard value. The catalyst in the second boiler 2 has an aging problem. At the end of its effective catalytic life, it is easy to cause unsatisfactory catalytic effect due to temperature instability. When the technicians observe that the denitration effect is insufficient, they should quickly switch the flue gas flow channel and introduce the flue gas into the second denitration section 12 of the first boiler 1 for SNCR denitration reaction.

[0048] The flue gas flowing out of the second denitration unit 12 or the second boiler 2 is the flue gas after denitration, and the flue gas flows into the desulfurization tower 4 for the subsequent desulfurization step. The flue gas is dedusted in the dust collector 3 to remove the small solid particles mixed inside, avoid damaging the subsequent equipment, and prevent the generation of impurities in the subsequent acid-base reaction.

[0049] The flue gas is transported from the dust collector 3 to the buffer tank 5, and the acid tank 51 transports carbonic acid to the buffer tank 5. The carbonic acid reacts with ammonia mixed in the flue gas to generate ammonium bicarbonate and ammonium carbonate, which are mixed in the solution. The solution is then transported to the alkaline reaction tank 6 to allow the ammonium carbonate, ammonium bicarbonate and strong alkali to react to generate calcium carbonate necessary for the subsequent desulfurization process and regenerate ammonia. The flue gas is filtered and cleaned in the alkaline reaction tank 6 to filter out some sulfur oxides and improve the desulfurization rate in the desulfurization tower 4.

[0050] The desulfurized flue gas is transported to the separation tank 17, where water is added to separate the ammonia and carbon dioxide contained in the flue gas. Part of the carbon dioxide is discharged, and part of the carbon dioxide is collected in the acid tank 51 for making carbonic acid. The ammonia solution is discharged into the reducing agent tank 15.

[0051] Based on the above-mentioned coal-fired boiler flue gas treatment system, this embodiment further discloses a control system for the coal-fired boiler flue gas treatment system. Figure 4 A control system for a coal-fired boiler flue gas treatment system includes a central control module 8, a system detection module, a system control module 9, and a wireless transmission module 81.

[0052] The system monitoring module 7 includes a temperature monitoring unit 72, a concentration monitoring unit 71, and a pH value monitoring unit 73. The temperature monitoring unit 72 is used to monitor the temperature of each part of the flue gas denitration system. Specifically, the temperature detection unit includes a plurality of temperature sensors, which are respectively arranged in the first denitration section 11 of the first boiler 1, the second denitration section 12 of the first boiler 1, the second boiler 2, and the desulfurization tower 4, and are used to monitor the specific and real-time reaction temperature of the denitration reaction in the first boiler 1 and the second boiler 2, and monitor the specific temperature of the desulfurization reaction in the desulfurization tower 4; the concentration monitoring unit 71 is used to monitor the concentration of nitrogen oxides and sulfur oxides in the flue gas, and is also used to monitor the real-time concentration of a solute in the solution. Specifically, the concentration monitoring unit 71 includes a gas inlet end of the first denitration section 11, the second denitration section 12 of the first boiler 1, the second boiler 2, and the desulfurization tower 4. The electrochemical sensors arranged at the gas outlet end, the gas outlet end of the second denitrification unit 12, the gas outlet end of the second boiler 2, the desulfurization unit inlet end, the desulfurization unit outlet end, and the inside of the buffer tank 5 are used to analyze the concentration values ​​of nitrogen oxides and sulfur oxides in the gas. The electrochemical sensors also include those arranged in the buffer tank 5, the alkali reaction tank 6, and the separation tank 17 for monitoring the ammonia concentration and the ammonium salt concentration in the solution. The pH value monitoring unit 73 is used to monitor the pH value of the solution of the acid-base reaction and the salt-base reaction in the flue gas denitrification system. Specifically, it includes a potentiometric pH sensor arranged in the acid tank 51, the alkali tank 61, the buffer tank 5, and the alkali reaction tank 6. The above-mentioned sensors maintain real-time detection of the environment of each important part of the flue gas denitrification system, and upload the temperature, concentration, and pH value values ​​to the central control module 8.

[0053] The central control module 8 is usually set in the control room, and the technicians in the control room comprehensively control the operation status of the flue gas denitrification system by observing the data displayed on the screen; in practical applications, computers with equivalent computing power are adapted according to the number and complexity of the components of the flue gas denitrification system, which can be as small as a single microcontroller or as large as a computing network composed of multiple computers. The central control module 8 receives various monitoring data from the system detection module, calculates and estimates the efficiency of various chemical reactions in the flue gas treatment system, especially the denitrification and desulfurization reactions according to the categories, and usually needs to fit the curve to show the technicians. For example, the SNCR denitrification efficiency, reaction temperature and other values ​​of the first denitrification part 11 in the first boiler 1 are fitted with the real-time efficiency-time curve according to the monitoring information received in real time from the system monitoring module 7, and compared with the standard efficiency line, so that the technicians can understand intuitively and can issue reminders to the technicians in time when it is lower than the standard efficiency curve, and the technicians can also change the operation status of a part of the flue gas denitrification system by typing and clicking the corresponding instructions.

[0054] The system control module 9 receives instructions from the central control module 8 to control the operation of various parts in the flue gas denitrification system. Specifically, the system control module 9 includes a valve control unit 91 and a pump control unit 92, wherein the valve control unit 91 includes an electronic control program arranged on the reducing agent valve 151, the first gas valve 13, the second gas valve 14, the acid valve 52, the alkali valve 62, and the valve body of the delivery valve 161; the pump control unit 92 includes an electronic control program arranged on the reducing agent pump 152, the acid pump 53, the alkali pump 63, and the pump bodies of each delivery pump 16.

[0055] The wireless transmission module 81 is a wireless transmission component arranged on each of the valve body, pump body and sensor body, and is used for communication between each component part in the system control module 9 and the central control module 8 .

[0056] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A coal-fired boiler flue gas treatment system, comprising a first boiler (1), a second boiler (2), and a desulfurization tower (4) which are connected to each other, wherein an SNCR denitration process occurs in the first boiler (1), and an SCR denitration reaction occurs in the second boiler (2), characterized in that: Also includes: a buffer tank (5), connected to the second boiler (2) and the desulfurization tower (4), and used for storing the flue gas transmitted from the second boiler (2); an acid tank (51), connected to the buffer tank (5), and providing an acid solution to the buffer tank (5); An alkaline reaction tank (6) is arranged behind the buffer tank (5) where the flue gas flows upward, is connected to the buffer tank (5) and the desulfurization tower (4), and is used to provide an alkaline solution to the flue gas; The reducing agent tank (15) is connected to the first boiler (1), the second boiler (2) and the desulfurization tower (4) to provide the reducing agent to the first boiler (1) and the second boiler (2).

2. A coal-fired boiler flue gas treatment system according to claim 1, characterized in that: Also includes: A dust collector (3) is arranged between the buffer tank (5) and the first boiler (1), the flue gas inlet of the dust collector (3) is connected to the first boiler (1), and the flue gas outlet of the dust collector (3) is connected to the buffer tank (5) and the reducing agent tank (15); The separation tank (17) is connected to the reducing agent tank (15) and the desulfurization tower (4), collects and stores the flue gas exhausted from the desulfurization tower (4), and separates carbon dioxide and ammonia.

3. A coal-fired boiler flue gas treatment system according to claim 1, characterized in that: The first boiler (1) is divided into two independent and non-connected parts, namely a first denitration part (11) and a second denitration part (12); The first denitration section (11) and the second denitration section (12) are both connected to the reducing agent tank (15); the first denitration section (11) is connected to the gas boiler and the second boiler (2); and the second denitration section (12) is connected to the second boiler (2) and the dust collector (3).

4. A coal-fired boiler flue gas treatment system according to claim 3, characterized in that: The second denitration section (12) is provided with baffles (121) on the inner walls of two opposite sides in the flue gas flow direction, and adjacent baffles (121) are formed on different sides to form a flue gas flow channel.

5. A coal-fired boiler flue gas treatment system according to claim 4, characterized in that: The pipeline between the second denitrification section (12) and the dust collector (3) is made of a heat-sensitive material, or the pipeline between the second boiler (2) and the dust collector (3) is made of a heat-sensitive material, and is used to cool the flue gas flowing out of the second denitrification section (12).

6. A coal-fired boiler flue gas treatment system according to claim 3, characterized in that: The inner wall of the desulfurization tower (4) is provided with a hot gas bin (41), and the hot gas bin (41) is connected to the second denitration section (12) and the dust collector (3).

7. A control system applied to a coal-fired boiler flue gas treatment system according to claim 1, characterized in that: It includes a central control module (8), a system monitoring module (7), and a system control module (9); The system monitoring module (7) is used to detect the temperature of the flue gas discharged into the first boiler (1), and to monitor the ambient temperature inside the first boiler (1), the second boiler (2) and the desulfurization tower (4) in real time, and to upload the temperature monitoring data to the central control module (8) in real time; the system monitoring module (7) is used to detect the pH value of the solution in the acid tank (51), the alkali reaction tank (6) and the buffer tank (5), and to upload the pH value monitoring data to the central control module (8) in real time; the system monitoring module (7) is used to monitor the reducing agent concentration in the reducing agent tank (15) and the ammonia concentration in the buffer tank (5), and to upload the concentration monitoring data to the central control module (8) in real time; The central control module (8) receives and retrieves the monitoring data of the system monitoring module (7) in real time, analyzes, processes and calculates, generates corresponding instructions according to the calculation results, and sends them to the system control module (9), and the system control module (9) operates according to the instructions.

8. The control system of a coal-fired boiler flue gas treatment system according to claim 7, characterized in that: The system control module (9) receives relevant instructions from the central control module (8), adjusts the input flow rate of the acid solution in the acid tank (51), the input flow rate of the reducing agent in the reducing agent tank (15), and the input amount of the alkali solution in the alkali reaction tank (6), so that the acid solution, the reducing agent, and the alkali solution are adapted to the ammonia gas at the real-time concentration.

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