Online adjustment device for micro-flow ammonia for denitration

Abstract

The application discloses an online adjusting device for micro-flow ammonia for denitration, which comprises intermittent ammonia supply units, vaporization units, buffer units and vapor-gas mixing units which are sequentially communicated; the intermittent ammonia supply units are communicated with liquid ammonia delivery pipes; the vapor-gas mixing units are communicated with ammonia injection lattices; the intermittent ammonia supply units are used for providing quantitative liquid ammonia supply; the vaporization units are used for vaporizing liquid ammonia; the vapor-gas mixing units comprise primary mixers and secondary mixers; the primary mixers are used for ammonia gas dilution; and the secondary mixers are used for online adjustment; adjusting valves are arranged between two adjacent units; and each adjusting valve is electrically connected with a DCS control system. The application combines intermittent ammonia supply and two-stage mixing, guarantees micro adjustment of ammonia flow under the condition of small ammonia consumption, realizes ultra-low emission transformation of industrial flue gas with low background nitrogen oxides, and has great engineering practical value.

Description

Technical Field

[0001] This invention relates to the field of denitrification equipment technology, and specifically to an online regulating device for a small flow of ammonia used in denitrification. Background Technology

[0002] Industrial flue gas must undergo denitrification treatment before it can be emitted, making denitrification an essential step in its emission process. Some industrial flue gases that were originally low in NOx also require ultra-low emission retrofitting. However, due to the small volume and low initial concentration of the flue gas, the required ammonia consumption is relatively small, with a minimum ammonia consumption of less than 0.2 kg / h. Furthermore, online adjustment of the ammonia flow rate is necessary, posing a significant challenge to engineering practice.

[0003] On the one hand, the supply pressure at the source of liquid ammonia is generally above 1.0 MPa, while the pressure required at the ammonia injection grid is relatively small, generally 0.01 MPa. If an ordinary pressure reducing valve is used, the pressure reduction process is adiabatic throttling, and the liquid ammonia vaporizes after pressure reduction, resulting in a large temperature drop (about 87°C), which exceeds the boiling point temperature of liquid ammonia at the corresponding pressure, and the equipment cannot operate normally.

[0004] On the other hand, for ammonia operating conditions where the minimum flow rate can be less than 0.2 kg / h, the flow rate is so small that the pipeline cross-section is too small, approximately the diameter of a needle. In actual engineering practice, there will inevitably be problems such as pipeline corrosion and solid impurities in liquid ammonia itself, which can easily lead to pipeline blockage. Existing adjustment methods cannot achieve such small ammonia flow rate adjustments, and are therefore impractical in engineering. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to propose an online adjustment device for a small flow rate of ammonia for denitrification. By combining intermittent ammonia supply and two-stage mixing, it ensures minute adjustment of the ammonia flow rate even when the ammonia usage is small, thereby achieving ultra-low emission transformation of industrial flue gas with low background nitrogen oxides. This has significant practical engineering value.

[0006] To achieve the above objectives, the present invention employs the following technical solutions.

[0007] An online regulating device for a small flow of ammonia for denitrification is installed between a liquid ammonia delivery pipe and an ammonia injection grid. The online regulating device includes: an intermittent ammonia supply unit, a vaporization unit, a buffer unit, and a vapor-gas mixing unit connected in sequence. The intermittent ammonia supply unit is connected to the liquid ammonia delivery pipe, and the vapor-gas mixing unit is connected to the ammonia injection grid.

[0008] The intermittent ammonia supply unit is used to provide a fixed amount of liquid ammonia; the vaporization unit is used to vaporize the liquid ammonia, and the vapor outlet of the vaporization unit is connected to the vapor inlet of the buffer unit.

[0009] The steam-air mixing unit includes a primary mixer and a secondary mixer. The ammonia inlet of the primary mixer is connected to the steam outlet of the buffer unit, and the air outlet of the primary mixer is connected to the air inlet of the secondary mixer. The air inlets of the primary mixer and the secondary mixer are respectively connected to compressed air delivery pipes. The air outlet of the secondary mixer is connected to the ammonia injection grid.

[0010] Each of the intermittent ammonia supply unit, vaporization unit, buffer unit, and steam-gas mixing unit has a regulating valve installed on the connecting pipe between two adjacent units, and each regulating valve is electrically connected to the DCS control system.

[0011] The features and further improvements of the technical solution of this invention are as follows:

[0012] Furthermore, the intermittent ammonia supply unit includes a temporary storage tank and shut-off valves installed at the liquid ammonia inlet and liquid ammonia outlet at both ends. The liquid ammonia inlet of the temporary storage tank is connected to the liquid ammonia delivery pipe, and the liquid ammonia outlet of the temporary storage tank is connected to the liquid inlet of the vaporization unit. Each shut-off valve is electrically connected to the DCS control system.

[0013] Furthermore, the two shut-off valves are interlocked; when one shut-off valve is open, the other shut-off valve is closed.

[0014] Furthermore, the vaporization unit is a heat exchanger, the tube side of the heat exchanger contains liquid ammonia and vaporized ammonia, the shell side of the heat exchanger contains heat storage material, and a heater is installed in the shell side of the heat exchanger.

[0015] Furthermore, the heat exchanger is arranged vertically and includes a heat exchange coil, an inner cylinder, and an outer cylinder arranged from the inside out. The upper and lower ends of the inner cylinder and the outer cylinder are connected, and heat storage materials are filled between the inner cylinder and the heat exchange coil, and between the inner cylinder and the outer cylinder.

[0016] Furthermore, the heat storage substance is ethylene glycol antifreeze.

[0017] Furthermore, a check valve is provided at each inlet and outlet of the primary mixer and the secondary mixer.

[0018] Furthermore, the ammonia pressure in the primary mixer is 1-2 kPa higher than the compressed air pressure.

[0019] Furthermore, a pressure gauge is provided on the buffer unit.

[0020] Furthermore, it also includes a support frame, on which the online adjustment device is detachably mounted.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention uses an intermittent ammonia supply unit (liquid ammonia), which solves the problem of temperature drop caused by liquid ammonia pressure reduction during the adiabatic throttling process of traditional pressure reducing valves.

[0023] (2) The liquid ammonia vaporization process of the present invention adopts an indirect heating method, and the heating medium is ethylene glycol antifreeze, which has a low saturated vapor pressure and a high heat transfer coefficient, preventing freezing in winter and vaporization in summer, thus improving system safety. At the same time, the heating medium in the shell side adopts a dual-channel natural convection method for heat transfer. In the shell side, the liquid is heated at the bottom to form a heat difference between the top and bottom, which is used as the power to achieve a natural convection heat cycle from bottom to top. No circulation power is required, which is energy-saving and simple to implement in engineering.

[0024] (3) The mixing of ammonia and compressed air in this invention adopts a two-stage mixing process. The first-stage mixer dilutes the ammonia to increase the flow rate. The second-stage mixer enables online dynamic adjustment, allowing the ammonia flow rate of a small amount to be adjusted online for engineering applications. This achieves online adjustment of ammonia flow rate of less than 0.2 kg / h, which has great engineering application value. Attached Figure Description

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] Figure 1 This is a three-dimensional structural schematic diagram of an online regulating device for micro-flow ammonia in denitrification according to the present invention;

[0027] Figure 2 for Figure 1 A three-dimensional view of the device after the front cover of the heat exchanger has been removed;

[0028] Figure 3 This is a process flow diagram of the online adjustment device for micro-flow ammonia for denitrification according to an embodiment of the present invention;

[0029] Figure 4 This is a cross-sectional view of the self-operated differential pressure balancing mixing valve according to an embodiment of the present invention;

[0030] Figure 1-4 The components are as follows: 1. Intermittent ammonia supply unit; 11. Shut-off valve; 12. Temporary storage tank; 2. Vaporization unit; 21. Heat exchange coil; 22. Heater; 3. Buffer unit; 31. Pressure gauge; 4. Steam-gas mixing unit; 41. Primary mixer; 42. Secondary mixer; 5. Liquid ammonia delivery pipe; 6. Ammonia injection grille; 7. Support frame; 8. Compressed air delivery pipe; 9. Self-operated differential pressure balancing mixing valve; 91. Hollow valve body; 92. Valve seat; 93. Valve core; 94. Cylinder; 95. Spring; 96. Fixed shaft; 97. Air inlet; 98. Annular baffle. Detailed Implementation

[0031] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0032] refer to Figures 1-4 This invention provides an online regulating device for a small flow of ammonia for denitrification, installed between a liquid ammonia delivery pipe 5 and an ammonia injection grid 6. The online regulating device includes: an intermittent ammonia supply unit 1, a vaporization unit 2, a buffer unit 3, and a vapor-gas mixing unit 4 connected in sequence. The intermittent ammonia supply unit 1 is connected to the liquid ammonia delivery pipe 5, and the vapor-gas mixing unit 4 is connected to the ammonia injection grid 6. The intermittent ammonia supply unit 1 is used to provide a fixed amount of liquid ammonia. The vaporization unit 2 is used to vaporize the liquid ammonia, and the steam outlet of the vaporization unit 2 is connected to the steam inlet of the buffer unit 3. The steam-gas mixing unit 4 includes a primary mixer 41 and a secondary mixer 42. The ammonia inlet of the primary mixer 41 is connected to the steam outlet of the buffer unit 3, and the air outlet of the primary mixer 41 is connected to the air inlet 97 of the secondary mixer 42. The air inlets of the primary mixer 41 and the secondary mixer 42 are respectively connected to the compressed air delivery pipe 8. The air outlet of the secondary mixer 42 is connected to the ammonia injection grille 6. Each air inlet and outlet of the primary mixer 41 and the secondary mixer 42 is equipped with a check valve. The connecting pipes between adjacent units in the intermittent ammonia supply unit 1, vaporization unit 2, buffer unit 3 and steam-gas mixing unit 4 are respectively equipped with regulating valves, and each regulating valve is electrically connected to the DCS control system.

[0033] This embodiment takes the sulfur recovery process of Puhua as an example. Because the concentration of nitrogen oxides in the industrial flue gas generated by this process is low, the amount of ammonia used in its denitrification process is also small, reaching as low as less than 0.2 kg / h. Existing equipment cannot achieve such a small ammonia usage. In this embodiment, the online regulating device of this invention is installed between the liquid ammonia conveying pipe 5 and the ammonia injection grid 6 to achieve online regulation of the minute flow rate of ammonia.

[0034] Specifically, such as Figure 1 As shown, in this embodiment, the liquid ammonia pressure in the liquid ammonia delivery pipe 5 is 1.2 MPa, while the gas pressure entering the mixer is 0.01 MPa. This invention achieves the purpose of quantitative ammonia supply by using an intermittent ammonia supply unit 1 and setting shut-off valves 11 at both ends of a liquid ammonia pipeline of a fixed size. The shut-off valves 11 are interlocked, one opening and one closing, and are electrically controlled by a DCS control system. This solves the problem of temperature drop caused by liquid ammonia pressure reduction during the adiabatic throttling process of existing pressure reducing valves.

[0035] After depressurization, the liquid ammonia is vaporized in vaporization unit 2 (i.e., heater 22). The vaporized liquid ammonia then enters buffer unit 3 (buffer tank) for pressure stabilization. The buffer tank pressure is 0.01 MPa, with a fluctuation range of ±0.0005 MPa. The pressure-stabilized ammonia gas enters the primary mixer 41 through a pipeline from the ammonia inlet. Simultaneously, compressed air enters the primary mixer 41 through the air inlet. In the primary mixer 41, a fixed amount of ammonia and air are mixed, ensuring the ammonia / air mixing ratio is within a safe range (below 5%). The primary mixer 41 mixes the required amount of ammonia and air, and the volume of the mixed gas is more than 20 times greater than the actual amount of ammonia used. This volume ratio can be adjusted according to the actual ammonia usage. After ammonia dilution in the primary mixer 41, the ammonia / air mixture enters the secondary mixer 42, where it is further mixed with compressed air, achieving online regulation of the final output ammonia usage. The regulation method of this invention is to control the opening degree of each regulating valve through a DCS control system to achieve online regulation of the ammonia usage. The structural design of this invention enables online adjustment of the ammonia dosage at a very low flow rate, realizing the engineering implementation of the denitrification process for flue gas with low nitrogen oxide emissions, and providing theoretical and engineering technical support for ultra-low nitrogen oxide emissions.

[0036] refer to Figure 1 and Figure 2 According to one embodiment of the present invention, the intermittent ammonia supply unit 1 includes a temporary storage tank 12 and shut-off valves 11 installed at the liquid ammonia inlet and liquid ammonia outlet at both ends. The liquid ammonia inlet of the temporary storage tank 12 is connected to the liquid ammonia delivery pipe 5, and the liquid ammonia outlet of the temporary storage tank 12 is connected to the liquid inlet of the vaporization unit 2. Each shut-off valve 11 is electrically connected to the DCS control system.

[0037] Furthermore, the two shut-off valves 11 are interlocked, with one shut-off valve 11 opening and the other shut-off valve 11 closing.

[0038] In the above embodiments, the temporary storage tank 12 is part of the liquid ammonia delivery pipe 5. In this embodiment, only two shut-off valves 11 need to be set at both ends of the liquid ammonia delivery pipe 5 with a fixed length at one end to realize the intermittent quantitative ammonia supply process. When ammonia is introduced, the shut-off valve 11 at the inlet is opened and the shut-off valve 11 at the outlet is closed; when ammonia is discharged, the shut-off valve 11 at the inlet is closed and the shut-off valve 11 at the outlet is opened, thus achieving the purpose of quantitative ammonia supply, solving the temperature drop problem during the pressure reduction process, and the engineering implementation is simple and requires no equipment modification.

[0039] refer to Figure 2 According to one embodiment of the present invention, the vaporization unit 2 is a heat exchanger, the tube side of the heat exchanger contains liquid ammonia and vaporized ammonia, the shell side of the heat exchanger contains heat storage material, and a heater 22 is provided in the shell side of the heat exchanger.

[0040] refer to Figure 2According to one embodiment of the present invention, the heat exchanger is arranged vertically and includes a heat exchange coil 21, an inner cylinder and an outer cylinder arranged from the inside to the outside. The upper and lower ends of the inner cylinder and the outer cylinder are respectively connected, and heat storage material is filled between the inner cylinder and the heat exchange coil 21 and between the inner cylinder and the outer cylinder.

[0041] refer to Figure 1 and Figure 2 According to one embodiment of the present invention, the heat storage substance is ethylene glycol antifreeze.

[0042] In the above embodiments, liquid ammonia is vaporized through a heat exchanger, and ethylene glycol antifreeze is injected into the shell side. An electric heater 22 is used to replenish the heat required for the vaporization of liquid ammonia. Ethylene glycol antifreeze has a low saturated vapor pressure, a boiling point as low as -45°C, a large heat storage capacity, low viscosity, and a high heat transfer coefficient, which can prevent freezing when the ambient temperature is low. It can also achieve natural convection heating. Specifically, an inner cylinder and an outer cylinder are arranged in the shell side of the heater 22. The lower and upper ends of the inner cylinder and the outer cylinder are connected. The heater 22 is arranged in the inner cylinder and is located at the bottom of the shell side, forming a dual-channel natural convection heat transfer mode. The outer cylinder and the outer shell serve as a natural circulation channel, allowing the hot fluid heated by the electric heater 22 to rise to the top of the inner cylinder and then flow down from the outer cylinder back into the bottom of the inner cylinder, forming a cycle of natural convection heat circulation.

[0043] refer to Figure 1 and Figure 2 According to one embodiment of the present invention, a check valve is provided at each inlet and outlet of the primary mixer 41 and the secondary mixer 42 to prevent gas backflow.

[0044] refer to Figure 1 and Figure 2 According to one embodiment of the present invention, the check valve at the ammonia inlet of the primary mixer 41 is a self-regulating differential pressure balancing mixing valve 9, such as... Figure 4 As shown, it includes a hollow valve body 91. Inside the hollow valve body 91, from the inlet end to the outlet end, are sequentially arranged a valve seat 92, a valve core 93, and a cylinder 94. The valve core 93 and the cylinder 94 are connected by a soft seal. A fixed shaft 96 is provided on the valve core 93, and a spring 95 is sleeved on the free end of the fixed shaft 96. The spring 95 is fixedly connected to the base plate of the cylinder 94. Corresponding positions on the cylinder 94 and the valve body have air inlets 97. The two air inlets 97 are connected by an air inlet pipe, and each air inlet 97 is a compressed air inlet.

[0045] refer to Figure 4 According to one embodiment of the present invention, an annular baffle 98 is provided inside the cylinder 94, and the spring 95 is abutted between the bottom plate of the cylinder 94 and the annular baffle 98.

[0046] In the above embodiments, the pressure and flow rate of the incoming ammonia gas can be dynamically adjusted by controlling the axial movement of the valve core 93 based on the compressed air pressure in the cylinder 94 and the force of the spring 95, thereby controlling the opening of the valve core 93 and the valve seat 92. During normal operation, the pressure of the compressed air and the force of the spring 95 are used to balance the pressure of the ammonia gas, controlling the opening of the valve core 93 and the valve seat 92 to achieve the purpose of adjusting the ammonia gas pressure and flow rate. When the inlet ammonia gas pressure drops to a certain value, under the action of the compressed air pressure and the force of the spring 95, the valve core 93 inserts into the valve seat 92, and the valve closes. When the ammonia gas stops flowing, the valve closes by stopping the compressed air pressure. The adjustment principle of the self-operated differential pressure balancing mixing valve 9 of the present invention is that the difference between the compressed air pressure and the ammonia gas pressure is equal to the force of the spring 95. Since the magnitude of the spring 95 force is related to the opening, flow rate adjustment can be achieved. When the denitrification dilution gas is compressed air, this valve, while reducing the pressure of the ammonia gas, avoids the explosion safety hazard caused by the ammonia gas flowing into the compressed air, ensuring the safety of the ammonia gas mixing with air. Simultaneously, it works in conjunction with the intermittent ammonia supply unit 1 to ensure that the pressure of ammonia in the mixer is greater than that of air, thereby ensuring safety during the mixing process.

[0047] refer to Figure 1-3 According to one embodiment of the present invention, the ammonia pressure in the primary mixer 41 is 1-2 kPa higher than the compressed air pressure. In this embodiment, the ammonia pressure is 10 kPa and the compressed air pressure is 8 kPa.

[0048] refer to Figure 1-3 According to one embodiment of the present invention, the buffer tank is equipped with a pressure gauge 31 to monitor the pressure stabilization status in real time.

[0049] refer to Figure 1 and Figure 2 According to one embodiment of the present invention, it further includes a support frame 7, and the online adjustment device is detachably mounted on the support frame 7 for easy installation and disassembly.

[0050] In this invention, pressure gauges can be installed at other locations where pressure monitoring is required, such as between the primary mixer 41 and the secondary mixer 42, or on the compressed air delivery pipe 8. Each instrument is electrically connected to the DCS control system for easy control and adjustment.

[0051] This invention addresses the engineering problem of ultra-low emission retrofitting of industrial flue gas with low background nitrogen oxide content. By combining intermittent ammonia supply and multi-stage mixing, it achieves online ammonia flow regulation at a very low flow rate (the minimum ammonia consumption can be less than 0.2 kg / h of ammonia), which has broad engineering application value.

[0052] Although the present invention has been described in detail in this specification with general description and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. An online regulating device for a small flow rate of ammonia used in denitrification, installed between the liquid ammonia delivery pipe and the ammonia injection grid, characterized in that, The online regulating device includes: an intermittent ammonia supply unit, a vaporization unit, a buffer unit, and a vapor-gas mixing unit connected in sequence, wherein the intermittent ammonia supply unit is connected to a liquid ammonia delivery pipe, and the vapor-gas mixing unit is connected to an ammonia injection grid. The intermittent ammonia supply unit is used to provide a fixed amount of liquid ammonia; the vaporization unit is used to vaporize the liquid ammonia, and the vapor outlet of the vaporization unit is connected to the vapor inlet of the buffer unit. The steam-air mixing unit includes a primary mixer and a secondary mixer. The ammonia inlet of the primary mixer is connected to the steam outlet of the buffer unit, and the air outlet of the primary mixer is connected to the air inlet of the secondary mixer. The air inlets of the primary and secondary mixers are respectively connected to compressed air delivery pipes. The air outlet of the secondary mixer is connected to the ammonia injection grid, so as to achieve online adjustment of the ammonia flow rate of less than 0.2 kg / h. Each of the intermittent ammonia supply unit, vaporization unit, buffer unit and gas-gas mixing unit is equipped with a regulating valve on the connecting pipe between two adjacent units, and each regulating valve is electrically connected to the DCS control system. The intermittent ammonia supply unit includes a temporary storage tank and shut-off valves at its liquid ammonia inlet and outlet. The liquid ammonia inlet of the temporary storage tank is connected to the liquid ammonia delivery pipe, and the liquid ammonia outlet of the temporary storage tank is connected to the liquid inlet of the vaporization unit. Each shut-off valve is electrically connected to the DCS control system. The two shut-off valves are interlocked; when one shut-off valve is open, the other shut-off valve is closed. The intermittent ammonia supply unit is used to solve the temperature drop problem caused by liquid ammonia pressure reduction during the adiabatic throttling process of traditional pressure reducing valves. The vaporization unit is a heat exchanger, in which liquid ammonia and vaporized ammonia are contained in the tube side, and heat storage material is contained in the shell side. A heater is installed in the shell side of the heat exchanger. The heat exchanger is arranged vertically and includes a heat exchange coil, an inner cylinder and an outer cylinder arranged from the inside to the outside. The upper and lower ends of the inner cylinder and the outer cylinder are connected respectively, and the space between the inner cylinder and the heat exchange coil and the space between the inner cylinder and the outer cylinder are filled with heat storage material. Each inlet and outlet of the primary mixer and the secondary mixer is equipped with a check valve. The ammonia pressure in the primary mixer is 1-2 kPa higher than the compressed air pressure. The check valve at the ammonia inlet of the primary mixer is a self-operated differential pressure balancing mixing valve, which includes a hollow valve body. The hollow valve body is provided with a valve seat, a valve core, and a cylinder in sequence from the inlet end to the outlet end. The valve core and the cylinder are connected by a soft seal. A fixed shaft is provided on the valve core. A spring is sleeved on the free end of the fixed shaft. The spring is fixed to the cylinder base plate. Air inlets are opened at corresponding positions of the cylinder and the valve body. The two air inlets are connected by an air inlet pipe. The air inlets are compressed air inlets.

2. The online regulating device for micro-flow ammonia for denitrification according to claim 1, characterized in that, The heat storage substance is ethylene glycol antifreeze.

3. The online regulating device for micro-flow ammonia for denitrification according to claim 1, characterized in that, The buffer unit is equipped with a pressure gauge.

4. The online regulating device for micro-flow ammonia for denitrification according to claim 1, characterized in that, It also includes a support frame, on which the online adjustment device is detachably mounted.

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