Energy-saving system for preparing nitric acid by absorbing nitric oxide tail gas

Abstract

The utility model discloses an energy-saving system for preparing nitric acid by absorbing nitrogen oxide tail gas, which comprises a gas inlet buffer tank, a compressor, a compressed air inlet system and a NOx absorption tower system, the gas inlet buffer tank is connected with a NOx inlet pipe and an air inlet pipe, the air inlet pipe is provided with an air flow meter, nitrogen oxide tail gas is introduced into the NOx inlet pipe, and the NOx absorption tower system is connected with the compressor. A gas outlet of the gas inlet buffer tank is connected with a gas inlet of the compressor through a mixed gas inlet pipe, a gas outlet of the compressor is connected with the NOx absorption tower system through a mixed gas outlet header pipe, and the compressed air inlet system is connected with the mixed gas outlet header pipe; an air inlet pipe opening of the air inlet pipe is directly communicated with the atmosphere. Self-sucked air and NO in the tail gas react in the gas inlet buffer tank to generate NO2, so that the oxidation degree of the tail gas before entering the absorption tower is improved, the equilibrium concentration of nitric acid in the tower kettle of the absorption tower is improved, and the standing time required by the absorption tower is reduced; the self-sucked air can effectively reduce the usage amount of compressed air, and the energy consumption of the compressed air is reduced.

Description

Technical Field

[0001] The utility model relates to an energy-saving system for preparing nitric acid by absorbing nitrogen oxide tail gas, and belongs to the technical field of air pollution control. Background Art

[0002] Chemical production processes such as nitrification, nitric acid oxidation, nitric acid production, and denitrification of nitric sulfuric acid generate large quantities of nitrogen oxide exhaust gases, primarily NO and NO₂. These exhaust gases, with high concentrations, form a yellow or brown smog, commonly known as "yellow dragon," which is highly toxic to humans. When these gases come into contact with water, they form acid rain, causing acidification of water bodies, leaching and impoverishment of soil, burning and damaging crops and forests, and corrosive damage to buildings and cultural relics. Furthermore, nitrogen oxide gases damage the ozone layer, thinning it and even forming holes, adversely affecting human life. Therefore, the absorption and treatment of nitrogen oxide exhaust gases is a crucial component of nitric acid production and use. The nitric acid produced during absorption can be reused, providing both environmental protection and significant economic value. Currently, meeting nitrogen oxide exhaust emission standards is a mandatory requirement for the approval of nitric acid production and use projects.

[0003] Currently, there are two main methods for treating nitrogen oxide tail gas: dry and wet methods. Dry methods are commonly used for low-concentration, low-value nitrogen oxide recovery from automobile exhaust, industrial furnace exhaust, and power plant exhaust. Common methods include reduction, biological denitrification, biological adsorption, and physical adsorption. However, nitrogen oxide tail gas generated during chemical production processes is high in concentration and large in total volume, and has strong recovery value, so wet methods are commonly used for treatment. The wet method generally uses water, dilute nitric acid, and alkaline solution to absorb nitrogen oxide tail gas. Alkaline solution absorption can be carried out at normal pressure, requiring low investment and simple operation. However, the resulting salt product is either treated as high-concentration nitrogen-containing waste brine to meet discharge standards after biochemical treatment or treated as waste salt after multi-effect evaporation. This results in high treatment costs, and the nitrogen oxides are not truly recovered.

[0004] Therefore, the current mainstream treatment process uses water or dilute nitric acid for absorption. Dilute nitric acid is generally a by-product acid produced in the previous process. After the concentration of dilute nitric acid after absorbing nitrogen oxides meets the process requirements, it can be directly applied to the previous reaction process or sold as a by-product. The reaction in the absorption process is cyclical (for example, NO in the exhaust gas reacts with O2 to produce NO2, and NO2 reacts with water to produce nitric acid, which in turn produces NO). According to actual operation, it is difficult for exhaust emissions to meet national standards using the atmospheric pressure absorption method. Additional alkali solution absorption towers and urea absorption towers are required to meet the standards.

[0005] From the analysis of the reaction mechanism, the reaction rate of NO and O2 is proportional to the cube of the pressure. Therefore, pressurized absorption can greatly increase the reaction rate. Pressurization is also beneficial to the rate at which NO2 reacts with water to generate nitric acid and the equilibrium concentration of nitric acid. Pressurized operation can effectively reduce the height and number of absorption towers, and easily ensure that exhaust gas emissions meet standards.

[0006] The current mainstream process uses pressurized absorption. Since most nitrogen oxide exhaust is at atmospheric pressure, it needs to be pressurized by a compressor before entering the absorption tower. The structure of the pressurized absorption device is that the nitrogen oxide inlet pipe is connected to the air inlet buffer tank, which is then connected to the air compressor inlet via a pipe. Since the nitrogen oxides need to be pressurized by the compressor when entering, and the supplementary air required for the reaction with NO also needs to be provided by the air compressor, the energy consumption cost of exhaust gas treatment increases. Furthermore, the amount of nitrogen oxide exhaust gas generated by the previous process often fluctuates to a certain extent, especially when the previous reaction is intermittent, the fluctuation is even greater. Therefore, when selecting compressors in industry, a 20-50% margin is always considered. When the actual air intake volume is less than the operating air intake volume of the compressor, the compressor inlet must be maintained at a slight negative pressure. The existing technology is to add an internal circulation pipeline with a regulating valve at the compressor outlet. The compressor outlet is connected to the air intake buffer tank through the internal circulation pipeline. By adjusting the opening of the regulating valve on the internal circulation pipeline, the compressor inlet pressure is stabilized at a slight negative pressure. Although this approach can make the compressor operate under normal working conditions, it loses the compressor's margin capacity in vain and consumes a lot of energy. Summary of the Invention

[0007] In view of the above technical problems existing in the prior art, the purpose of this application is to provide an energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas.

[0008] The technical solutions adopted in this application are as follows:

[0009] An energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas includes an air intake buffer tank, a compressor, a compressed air intake system and NO x Absorption tower system, the inlet buffer tank is connected to NO x Intake pipe and air intake pipe, the air intake pipe is provided with an air flow meter, NO x The intake pipe is connected to the exhaust gas of nitrogen oxides generated in the chemical production process. The outlet of the intake buffer tank is connected to the air inlet of the compressor through the mixed gas intake pipe. The outlet of the compressor is then connected to the NOx exhaust gas through the mixed gas outlet main pipe. x The absorption tower system is connected, and the compressed air intake system is connected to the mixed gas outlet main pipe, for replenishing compressed air into the mixed gas outlet main pipe;

[0010] The air intake pipe opening of the air intake pipe is directly connected to the atmosphere. When the flow rate of nitrogen oxide tail gas generated in the chemical production process is less than the intake volume of the compressor under working conditions, the insufficient air volume is directly drawn into the air intake buffer tank by negative pressure self-priming from the air intake pipe opening of the air intake pipe connected to the atmosphere, so as to maintain the inlet pressure of the compressor stable at a slight negative pressure.

[0011] Furthermore, the air flow meter is connected to the compressed air intake system signal through the PLC or DCS control system. When the air flow meter detects that the air flow of the self-priming air in the air intake pipe increases or decreases, the PLC or DCS control system is used to feedback and control the compressed air intake system to correspondingly reduce or increase the amount of compressed air added to maintain the total amount of air entering the mixed gas outlet main pipe unchanged.

[0012] Furthermore, the compressed air intake system includes a compressed air intake pipe provided with a compressed air regulating valve and a compressed air flow meter, and the compressed air intake pipe is connected to the mixed gas outlet main pipe so as to replenish compressed air into the mixed gas outlet main pipe; the air flow meter is connected to the compressed air regulating valve and the compressed air flow meter signal through a PLC or DCS control system. When the air flow meter monitors that the air flow of the self-priming air in the air intake pipe increases or decreases, the PLC or DCS control system feeds back and controls the compressed air regulating valve to adjust the opening so as to correspondingly reduce or increase the amount of compressed air added. During this period, the compressed air flow meter feeds back the monitored compressed air addition flow to the PLC or DCS control system.

[0013] Furthermore, the compressed air intake system also includes an air compressor and an air buffer tank. The air compressor is connected to the air buffer tank through a pipeline, and the air outlet of the air buffer tank is connected to the mixed gas outlet main pipe through a compressed air intake pipe.

[0014] Furthermore, a one-way valve is provided on the air intake pipe.

[0015] Furthermore, the NO x The absorption tower system includes an absorption tower, the lower air inlet of the absorption tower is connected to the mixed gas outlet main pipe, the bottom liquid outlet of the absorption tower is connected to the inlet of a circulation pump through a pipeline, the outlet of the circulation pump is divided into two paths, one path discharges dilute nitric acid, and the other path is connected to the upper liquid inlet of the absorption tower through a pipeline, forming a circulating absorption system for the absorption liquid; water or dilute nitric acid as a raw material for the absorption liquid is also introduced into the upper liquid inlet of the absorption tower, and the top air outlet of the absorption tower discharges tail gas.

[0016] Furthermore, the NO x The absorption tower system includes at least two absorption towers, and adjacent absorption towers are connected in series.

[0017] Compared with the prior art, the beneficial effects achieved by this application are:

[0018] 1) Compared with the prior art, the present application eliminates the internal circulation pipeline at the compressor outlet and adds an air intake pipe to the air intake buffer tank. The intake port of this air intake pipe is directly connected to the atmosphere. When the flow rate of nitrogen oxide tail gas generated in the chemical production process is less than the working intake volume of the compressor, the insufficient air volume is directly sucked in by negative pressure from the pipe port connected to the atmosphere, thereby maintaining the compressor inlet pressure stable at a slight negative pressure. In addition, the air flow meter of the present application is connected to the compressed air intake system signal through a PLC or DCS control system. When the air flow meter detects that the air flow rate of the self-priming air in the air intake pipe increases or decreases, the PLC or DCS control system is used to feedback and control the compressed air intake system to reduce or increase the amount of compressed air added accordingly. That is, the air flow rate on the compressed air addition pipeline is reduced according to the air flow rate on the self-priming pipeline, thereby reducing the amount of compressed air added and thus achieving energy saving.

[0019] 2) The self-inhaled air reacts with the NO in the tail gas in the air inlet buffer tank to generate NO2, which increases the oxidation degree of the tail gas before entering the absorption tower, increases the equilibrium concentration of nitric acid in the bottom of the absorption tower and reduces the residence time requirement of the absorption tower.

[0020] 3) The compressor inlet pressure control of this technical solution is more stable, especially when the amount of nitrogen oxide exhaust fluctuates greatly. The air control valve on the compressed air intake pipe will have a certain lag in following, while the self-priming solution directly through the intake buffer tank pipe outlet follows very sensitively. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a structural schematic diagram of an energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas in the present application. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0023] Example: Control Figure 1

[0024] An energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas includes an air intake buffer tank 1, a compressor 2, a compressed air intake system and a NO x Absorption tower system, the inlet buffer tank 1 is connected to NO x Intake pipe and air intake pipe, the air intake pipe is provided with an air flow meter 6, NO x The intake pipe is connected to the nitrogen oxide tail gas generated in the chemical production process, and the outlet of the intake buffer tank 1 is connected to the air inlet of the compressor 2 through the mixed gas intake pipe 9. The outlet of the compressor 2 is then connected to the NO xThe absorption tower system is connected, and the compressed air intake system is connected to the mixed gas outlet main pipe 8, which is used to supplement compressed air into the mixed gas outlet main pipe 8.

[0025] comparison Figure 1 The air intake pipe is directly connected to the atmosphere. When the flow rate of nitrogen oxide tail gas generated in the chemical production process is less than the air intake volume of the compressor under working conditions, the insufficient air volume is directly sucked into the air intake buffer tank 1 by negative pressure from the air intake pipe connected to the atmosphere, so as to maintain the inlet pressure of the compressor 2 stable at a slight negative pressure.

[0026] In order to prevent the flow rate entering the intake buffer tank 1 from being too large instantly, which may cause the NO in the intake buffer tank 1 to x The gas escapes into the outside atmosphere through an air inlet pipe, which is equipped with a one-way valve.

[0027] The compressed air intake system of the present application includes an air compressor, an air buffer tank, and a compressed air intake pipe equipped with a compressed air regulating valve 4 and a compressed air flow meter 7. The air compressor is connected to the air buffer tank through a pipeline, and the air outlet of the air buffer tank is then connected to the mixed gas outlet main pipe 8 through the compressed air intake pipe so as to replenish compressed air into the mixed gas outlet main pipe 8.

[0028] The air flow meter 6 is connected to the compressed air intake system signal through the PLC or DCS control system. Specifically, the air flow meter 6 is connected to the compressed air control valve 4 and the compressed air flow meter 7 through the PLC or DCS control system. When the air flow meter 6 detects that the air flow of the self-priming air in the air intake pipe increases or decreases, the PLC or DCS control system feeds back and controls the opening size of the compressed air control valve 4. At the same time, the compressed air flow meter 7 feeds back the monitored compressed air supplementary flow to the PLC or DCS control system so as to adjust the compressed air supplementary amount to the appropriate range (maintaining the total amount of air entering the mixed gas outlet main pipe 8 unchanged). Thus, when the air flow meter 6 detects that the air flow of the self-priming air in the air intake pipe increases or decreases, the PLC or DCS control system feeds back and controls the compressed air intake system to adjust the compressed air supplementary amount to the appropriate range so as to maintain the total amount of air entering the mixed gas outlet main pipe 8 unchanged.

[0029] comparison Figure 1 , NO xThe absorption tower system includes an absorption tower 3, the lower air inlet of the absorption tower 3 is connected to the mixed gas outlet main pipe 8, the bottom liquid outlet of the absorption tower 3 is connected to the inlet of the circulation pump 5 through a pipeline, and the outlet of the circulation pump 5 is divided into two paths, one path discharges dilute nitric acid, and the other path is connected to the upper liquid inlet of the absorption tower 3 through a pipeline, forming a circulating absorption system for the absorption liquid; water or dilute nitric acid as a raw material for the absorption liquid is also introduced into the upper liquid inlet of the absorption tower 3, and the top air outlet of the absorption tower 3 discharges tail gas.

[0030] In order to enhance the absorption of NO by water or dilute nitric acid as the raw material of the absorption liquid x The absorption effect of exhaust gas, NO x The absorption tower system includes at least two absorption towers 3, and adjacent absorption towers 3 are connected in series.

[0031] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. An energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas, characterized in that It includes an air intake buffer tank (1), a compressor (2), a compressed air intake system and NO x Absorption tower system, the inlet buffer tank (1) is connected to a NO x Intake pipe and air intake pipe, the air intake pipe is provided with an air flow meter (6), NO x The intake pipe is connected to the exhaust gas of nitrogen oxides generated in the chemical production process. The outlet of the intake buffer tank (1) is connected to the intake of the compressor (2) through the mixed gas intake pipe (9). The outlet of the compressor (2) is connected to the NOx exhaust gas through the mixed gas outlet main pipe (8). x The absorption tower system is connected, and the compressed air intake system is connected to the mixed gas outlet main pipe (8) for replenishing compressed air into the mixed gas outlet main pipe (8); The air intake pipe opening of the air intake pipe is directly connected to the atmosphere. When the flow rate of nitrogen oxide tail gas generated in the chemical production process is less than the air intake volume of the compressor under working conditions, the insufficient air volume is directly sucked into the air intake buffer tank (1) by negative pressure from the air intake pipe opening of the air intake pipe connected to the atmosphere, so as to maintain the inlet pressure of the compressor (2) stable at a slightly negative pressure.

2. The energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas according to claim 1, characterized in that The air flow meter (6) is connected to the compressed air intake system signal through the PLC or DCS control system. When the air flow meter (6) detects that the air flow of the self-priming air in the air intake pipe increases or decreases, the PLC or DCS control system is used to feedback and control the compressed air intake system to correspondingly reduce or increase the amount of compressed air added, so as to maintain the total amount of air entering the mixed gas outlet main pipe (8) unchanged.

3. The energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas according to claim 2, characterized in that The compressed air intake system includes a compressed air intake pipe provided with a compressed air regulating valve (4) and a compressed air flow meter (7), the compressed air intake pipe being connected to a mixed air outlet main pipe (8) so as to replenish compressed air into the mixed air outlet main pipe (8); the air flow meter (6) is connected to the compressed air regulating valve (4) and the compressed air flow meter (7) via a PLC or DCS control system, and when the air flow meter (6) detects that the air flow rate of the self-priming air in the air intake pipe increases or decreases, the compressed air regulating valve (4) is fed back and controlled by the PLC or DCS control system to adjust the opening so as to reduce or increase the amount of compressed air added accordingly, during which the compressed air flow meter (7) feeds back the monitored compressed air addition flow rate to the PLC or DCS control system.

4. The energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas according to claim 2, characterized in that The compressed air intake system further comprises an air compressor and an air buffer tank. The air compressor is connected to the air buffer tank via a pipeline, and the air outlet of the air buffer tank is connected to the mixed gas outlet main pipe (8) via a compressed air intake pipe.

5. The energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas according to claim 1, characterized in that A one-way valve is provided on the air intake pipe.

6. The energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas according to claim 1, characterized in that The NO x The absorption tower system comprises an absorption tower (3), wherein the lower air inlet of the absorption tower (3) is connected to the mixed gas outlet main pipe (8), the bottom liquid outlet of the absorption tower (3) is connected to the inlet of a circulation pump (5) through a pipeline, and the outlet of the circulation pump (5) is divided into two paths, one path discharges dilute nitric acid, and the other path is connected to the upper liquid inlet of the absorption tower (3) through a pipeline, thereby forming a circulating absorption system for the absorption liquid; water or dilute nitric acid as a raw material of the absorption liquid is also introduced into the upper liquid inlet of the absorption tower (3), and the top air outlet of the absorption tower (3) discharges tail gas.

7. The energy-saving system for producing nitric acid by absorbing nitrogen oxide tail gas according to claim 1, characterized in that The NO x The absorption tower system comprises at least two stages of absorption towers (3), and adjacent absorption towers (3) are connected in series.

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