Waste gas liquefaction safety recovery system for urea medium-pressure system

Abstract

The utility model provides a waste gas liquefaction safety recovery system for a urea medium-pressure system, and relates to the technical field of urea production, the waste gas liquefaction safety recovery system comprises a medium-pressure ammonia recovery tower, a medium-pressure inert gas washing tower and a gas conveying pipeline, a gas outlet of the medium-pressure inert gas washing tower is connected with a blow-down pipe, and an oxygen content online analyzer is arranged on the blow-down pipe; the medium-pressure ammonia recovery tower is connected with the medium-pressure inert gas washing tower, the medium-pressure inert gas washing tower is connected with a nitrogen delivery pipe, and a condensation assembly is arranged between the medium-pressure ammonia recovery tower and the medium-pressure inert gas washing tower. The concentration of oxygen in the waste gas is reduced, the content of the waste gas is prevented from entering the explosion limit value range, the equipment safety and the process operation safety are guaranteed, the waste gas entering the medium-pressure inert gas washing tower can be pre-condensed through the condensation assembly, ammonia components in the waste gas are collected after condensation, the medium-pressure pressure is reduced, and the energy consumption is reduced. Meanwhile, the ammonia consumption during normal operation is also reduced.

Description

Technical Field

[0001] The present application relates to the technical field of urea production, and in particular to a waste gas liquefaction safety recovery system for a urea medium-pressure system. Background Art

[0002] The urea medium-pressure system is a part of the urea plant and an important link in the urea production process. In the existing process, after the gaseous ammonia passes through the ammonia condenser, the gaseous ammonia is converted into liquid ammonia and recovered to the ammonia receiving tank. The gas phase in the ammonia receiving tank is directly passed through the medium-pressure ammonia recovery tower and the medium-pressure inert gas washing tower to add water to absorb the uncondensed gaseous ammonia, and the remaining gas is transported to the vent pipe.

[0003] During normal production and operation of the urea plant, passivation air must be added for the purpose of corrosion protection. However, as an inert gas, passivation air does not participate in the urea synthesis reaction. It eventually enters the medium-pressure system and is washed and condensed by a medium-pressure ammonia recovery tower and a medium-pressure inert washing tower to recover part of the ammonia component before being vented in a closed manner. The exhaust gas components vented here contain combustible gases of different concentrations, including NH3, CO, CH4 and H2. The O2 in the passivation air, as a combustion aid, mixes with the combustible components, which can easily cause the exhaust gas content to reach the explosion limit range, threatening the safety of equipment and process operation. Summary of the invention

[0004] The purpose of the embodiment of the present application is to provide a waste gas liquefaction safety recovery system for a urea medium-pressure system, which can solve the technical problem that after the O2 in the passivated air of the urea medium-pressure system is mixed with the combustible components in the waste gas, it is easy to cause the waste gas to reach the explosion limit, threatening the safety of equipment and process operation.

[0005] An embodiment of the present application provides a waste gas liquefaction safety recovery system for a medium-pressure urea system, comprising a medium-pressure ammonia recovery tower, a medium-pressure inert gas washing tower and a gas transmission pipeline, wherein the gas outlet of the medium-pressure ammonia recovery tower is connected to the gas inlet of the medium-pressure inert gas washing tower through the gas transmission pipeline, the gas outlet of the medium-pressure inert gas washing tower is connected to a vent pipe, the vent pipe is provided with an oxygen content online analyzer, the medium-pressure inert gas washing tower is connected to a nitrogen delivery pipe, and a condensation component is provided between the medium-pressure ammonia recovery tower and the medium-pressure inert gas washing tower.

[0006] Furthermore, the condensation component includes a first circulating water cooler, a second circulating water cooler, a first shut-off valve, a second shut-off valve, a first pipeline, a second pipeline and a third pipeline, the first shut-off valve is arranged on the gas pipeline, one end of the first pipeline is connected to the gas pipeline and is located between the shut-off valve and the medium-pressure ammonia recovery tower, the other end of the first pipeline is connected to the air inlet of the first circulating water cooler, the second shut-off valve is arranged on the first pipeline, the air outlet of the first circulating water cooler is connected to the air inlet of the second circulating water cooler through the second pipeline, and the air outlet of the second circulating water cooler is connected to the air inlet of the medium-pressure inert gas washing tower through the third pipeline.

[0007] Furthermore, a low-point exhaust valve is provided on the second pipeline, a connecting pipe is provided on the second pipeline, two ends of the connecting pipe are respectively located on both sides of the low-point exhaust valve, and a high-point exhaust valve is provided on the connecting pipe.

[0008] Furthermore, a flow regulating valve is provided on the nitrogen delivery pipe.

[0009] Furthermore, a variable flow meter is provided on the nitrogen delivery pipe, and the variable flow meter is located at the rear side of the flow regulating valve.

[0010] Furthermore, a pressure gauge transmitter is provided on the nitrogen delivery pipe, and the pressure gauge transmitter is located in front of the flow regulating valve.

[0011] Furthermore, a secondary line pipe is provided on the nitrogen delivery pipe, one end of the secondary line pipe is located between the variable flow meter and the flow regulating valve, the other end of the secondary line pipe is located between the flow regulating valve and the pressure gauge transmitter, and a secondary line valve is provided on the secondary line pipe.

[0012] Beneficial effects of the utility model:

[0013] The utility model is provided with an oxygen content online analyzer on the vent pipe to provide a basis for controlling the oxygen content in the vented waste gas within a safe range. The medium-pressure inert gas washing tower is connected with a nitrogen delivery pipe, and nitrogen is input into the medium-pressure inert gas washing tower through the nitrogen delivery pipe to reduce the oxygen content concentration in the waste gas, avoid the waste gas content from entering the explosion limit value range, and ensure the safety of equipment and process operation. A condensation component is provided between the medium-pressure ammonia recovery tower and the medium-pressure inert gas washing tower, and the condensation component can pre-condense the waste gas entering the medium-pressure inert gas washing tower, and recover the ammonia component in the waste gas after condensation to reduce the medium pressure, and also reduce the ammonia consumption during normal operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 This is a schematic diagram of the structure of some embodiments of the present application;

[0016] The reference numerals are:

[0017] 1. Medium-pressure ammonia recovery tower; 2. Medium-pressure inert gas washing tower; 3. Gas transmission pipeline; 4. Vent pipe; 5. Oxygen content online analyzer; 6. Nitrogen transmission pipe; 61. Flow control valve; 62. Transmitting flow meter; 63. Pressure gauge transmitter; 64. Sub-line pipe; 65. Sub-line valve; 7. Condensation assembly; 71. First circulating water cooler; 72. Second circulating water cooler; 73. First shut-off valve; 74. Second shut-off valve; 75. First pipeline; 76. Second pipeline; 761. Low-point exhaust valve; 762. Connecting pipe; 763. High-point exhaust valve; 77. Third pipeline, 8. Shut-off valve; 9. Exhaust valve; 10. Medium-pressure ammonia absorption tower. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0020] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0021] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0022] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0023] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances. Specific embodiment:

[0025] like Figure 1 As shown, the present application provides a waste gas liquefaction safety recovery system for a urea medium-pressure system, comprising a medium-pressure ammonia recovery tower 1, a medium-pressure inert gas washing tower 2 and a gas pipeline 3, the gas outlet of the medium-pressure ammonia recovery tower 1 is connected to the gas inlet of the medium-pressure inert gas washing tower 2 through the gas pipeline 3, the gas outlet of the medium-pressure inert gas washing tower 2 is connected to a vent pipe 4, and an oxygen content online analyzer 5 is provided on the vent pipe 4 to provide a basis for controlling the oxygen content in the vented waste gas within a safe range, the medium-pressure inert gas washing tower 2 is connected to a nitrogen delivery pipe 6, and nitrogen is input into the medium-pressure inert gas washing tower 2 through the nitrogen delivery pipe 6 to reduce the oxygen content concentration in the waste gas, avoid the waste gas content from entering the explosion limit value range, and ensure the safety of equipment and process operation, and a condensation component 7 is provided between the medium-pressure ammonia recovery tower 1 and the medium-pressure inert gas washing tower 2, and the condensation component 7 can pre-condense the waste gas entering the medium-pressure inert gas washing tower 2, and recover the ammonia component in the waste gas after condensation to reduce the medium pressure, and also reduce the ammonia consumption during normal operation.

[0026] like Figure 1As shown, the condensation assembly 7 includes a first circulating water cooler 71, a second circulating water cooler 72, a first shut-off valve 73, a second shut-off valve 74, a first pipeline 75, a second pipeline 76 and a third pipeline 77. The first shut-off valve 73 is arranged on the gas pipeline 3, one end of the first pipeline 75 is connected to the gas pipeline 3 and is located between the shut-off valve and the medium-pressure ammonia recovery tower 1, the other end of the first pipeline 75 is connected to the air inlet of the first circulating water cooler 71, the second shut-off valve 74 is arranged on the first pipeline 75, and the second pipeline 76 is connected to the third pipeline 77. The air outlet of the first circulating water cooler 71 is connected to the air inlet of the second circulating water cooler 72 through the second pipe 76, and the air outlet of the second circulating water cooler 72 is connected to the air inlet of the medium-pressure inert gas washing tower 2 through the third pipe 77. When in use, the interiors of the first circulating water cooler 71 and the second circulating water cooler 72 are connected to the medium-pressure ammonia medium-pressure inert gas washing tower 2 through pipes, and a suction pump is provided on the pipes, and the medium-pressure ammonia medium-pressure inert gas absorption tower 2 is installed in combination with the medium-pressure ammonia absorption tower 10 in the prior art. When the first shut-off valve 73 is closed and the second shut-off valve 74 is opened, the waste gas enters the first circulating water cooler 71 from the medium-pressure ammonia recovery tower 1 through the gas pipeline 3 and the first pipeline 75, then enters the second circulating water cooler 72 through the second pipeline 76, and finally enters the medium-pressure inert gas washing tower 2 through the third pipeline 77. When the gas phase passes through the first circulating water cooler 71 and the second circulating water cooler 72, a small amount of water is added to the first circulating water cooler 71 and the second circulating water cooler 72 to absorb the ammonia component in the gas phase to form ammonia water. The heat released is taken away by the circulating water. The ammonia water enters the medium-pressure inert gas washing tower 2 through the ammonia water pump and then flows into the medium-pressure ammonia absorption tower 10 for recycling, thereby reducing the loss of ammonia water and reducing the pressure of the waste gas entering the medium-pressure inert gas washing tower 2. It is avoided that the medium-pressure rear system is over-pressurized after the nitrogen enters the medium-pressure inert gas washing tower 2, thereby improving the safety of equipment operation. The first shut-off valve 73 and the second shut-off valve 74 are set to enable the gas phase to switch between the condensation component 7 and the gas pipeline 3.

[0027] like Figure 1 As shown, a low-point exhaust valve 761 is provided on the second pipeline 76, and a connecting pipe 762 is provided on the second pipeline 76. Both ends of the connecting pipe 762 are respectively located on both sides of the low-point exhaust valve 761. A high-point exhaust valve 763 is provided on the connecting pipe 762. In actual applications, the installation height of the high-point exhaust valve 763 is higher than the installation height of the low-point exhaust valve 761, and the high-point exhaust valve 763 is installed at the highest point of the connecting pipe 762. The high-point exhaust valve 763 is used to exhaust the gas in the connecting pipe 762, and the low-point exhaust valve 761 is used to automatically exhaust the liquid in the second pipeline 76. By intermittently opening the high-point exhaust valve 763 and the low-point exhaust valve 761, the connecting pipe 762 and the second pipeline 76 can be kept unobstructed.

[0028] like Figure 1As shown, a flow regulating valve 61 is provided on the nitrogen delivery pipe 6. The staff can control the opening of the flow regulating valve 61 according to the data information provided by the oxygen content online analyzer 5, and then control the input of nitrogen to the medium-pressure inert gas washing tower 2 to adjust the oxygen concentration in the exhaust gas.

[0029] like Figure 1 As shown, a variable flow meter 62 is provided on the nitrogen delivery pipe 6. The variable flow meter 62 is located at the rear side of the flow regulating valve 61. The nitrogen flow in the nitrogen delivery pipe 6 is accurately measured by the variable flow meter 62 so as to accurately control the nitrogen flow entering the medium-pressure inert gas washing tower 2.

[0030] like Figure 1 As shown, a pressure gauge transmitter 63 is provided on the nitrogen delivery pipe 6, and the pressure gauge transmitter 63 is located in front of the flow control valve 61. The pressure gauge transmitter 63 accurately measures the nitrogen pressure in the nitrogen delivery pipe 6, and assists the flow control valve 61 and the transmission flow meter 62 to accurately control and adjust the delivery of nitrogen.

[0031] like Figure 1 As shown, a secondary line pipe 64 is provided on the nitrogen delivery pipe 6, one end of the secondary line pipe 64 is located between the transmission flow meter 62 and the flow regulating valve 61, and the other end of the secondary line pipe 64 is located between the flow regulating valve 61 and the pressure gauge transmitter 63. A secondary line valve 65 is provided on the secondary line pipe 64. Specifically, both sides of the flow regulating valve 61 are provided with stop valves 8 on the nitrogen delivery pipe 6, and an exhaust pipe is connected to the nitrogen delivery pipe 6 between the two stop valves 8, and an exhaust valve 9 is provided on the exhaust pipe. When the flow regulating valve 61 fails, the secondary line valve 65 is opened, and the stop valves 8 on both sides of the flow regulating valve 61 are closed at the same time to ensure the continued circulation of the gas phase, and then the exhaust valve 9 is opened to drain the waste gas remaining in the nitrogen delivery pipe 6 section between the valves on both sides of the flow regulating valve 61, and then the flow regulating valve 61 can be replaced.

[0032] Working principle:

[0033] When in use, the interiors of the first circulating water cooler 71 and the second circulating water cooler 72 are connected to the medium-pressure ammonia absorption tower through pipelines, and a suction pump is provided on the pipelines. The medium-pressure ammonia recovery tower 1 is connected to the ammonia receiving tank in the prior art, the first shut-off valve 73 is closed, and the second shut-off valve 74 is opened. The gas phase in the ammonia receiving tank directly enters the medium-pressure ammonia recovery tower 1, and then enters the first circulating water cooler 71 through the gas transmission pipeline 3 and the first pipeline 75, and then enters the second circulating water cooler 72 through the second pipeline 76, and finally enters the medium-pressure inert gas washing tower 2 through the third pipeline 77. When the gas phase passes through the first circulating water cooler 71 and the second circulating water cooler 72, a small amount of water is added to the first circulating water cooler 71 and the second circulating water cooler 72 to absorb the gas phase. Ammonia components are formed into ammonia water, and the heat released is taken away by the circulating water. The ammonia water enters the medium-pressure inert gas washing tower 2 through the ammonia water pump and then flows into the medium-pressure ammonia absorption tower 10 for recycling, thereby reducing the loss of ammonia water and reducing the pressure of the exhaust gas entering the medium-pressure inert gas washing tower 2. After the exhaust gas enters the medium-pressure inert gas washing tower 2, water will be added again to absorb the uncondensed ammonia. At the same time, the nitrogen gas pipeline 3 controls the input of nitrogen into the medium-pressure inert gas washing tower 2 through the flow regulating valve 61, the transmission flow meter 62 and the pressure gauge transmitter 63 based on the exhaust gas oxygen content provided by the oxygen content online analyzer 5, to ensure that the oxygen content concentration in the exhaust gas is within a safe range to prevent explosion. At the same time, it is avoided that the medium-pressure rear system is overpressured after the nitrogen enters the medium-pressure inert gas washing tower 2, thereby improving the safety of equipment operation.

[0034] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A waste gas liquefaction safety recovery system for a urea medium pressure system, characterized by: The invention comprises a medium-pressure ammonia recovery tower, a medium-pressure inert gas washing tower and a gas transmission pipeline. The gas outlet of the medium-pressure ammonia recovery tower is connected to the gas inlet of the medium-pressure inert gas washing tower through the gas transmission pipeline. The gas outlet of the medium-pressure inert gas washing tower is connected to a vent pipe, and an online oxygen content analyzer is arranged on the vent pipe. The medium-pressure inert gas washing tower is connected to a nitrogen delivery pipe, and a condensation component is arranged between the medium-pressure ammonia recovery tower and the medium-pressure inert gas washing tower.

2. The waste gas liquefaction safety recovery system for a urea medium pressure system according to claim 1, characterized in that: The condensation component includes a first circulating water cooler, a second circulating water cooler, a first shut-off valve, a second shut-off valve, a first pipeline, a second pipeline and a third pipeline. The first shut-off valve is arranged on the gas pipeline. One end of the first pipeline is connected to the gas pipeline and is located between the shut-off valve and the medium-pressure ammonia recovery tower. The other end of the first pipeline is connected to the air inlet of the first circulating water cooler. The second shut-off valve is arranged on the first pipeline. The air outlet of the first circulating water cooler is connected to the air inlet of the second circulating water cooler through the second pipeline. The air outlet of the second circulating water cooler is connected to the air inlet of the medium-pressure inert gas washing tower through the third pipeline.

3. The waste gas liquefaction safety recovery system for a urea medium pressure system according to claim 2, characterized in that: The second pipeline is provided with a low-point exhaust valve, the second pipeline is provided with a connecting pipe, the two ends of the connecting pipe are respectively located on both sides of the low-point exhaust valve, and the connecting pipe is provided with a high-point exhaust valve.

4. The waste gas liquefaction safety recovery system for a urea medium pressure system according to claim 1, characterized in that: The nitrogen delivery pipe is provided with a flow regulating valve.

5. The waste gas liquefaction safety recovery system for a urea medium pressure system according to claim 4, characterized in that: The nitrogen delivery pipe is provided with a variable flow meter, and the variable flow meter is located at the rear side of the flow regulating valve.

6. The waste gas liquefaction safety recovery system for a urea medium pressure system according to claim 5, characterized in that: The nitrogen delivery pipe is provided with a pressure gauge transmitter, and the pressure gauge transmitter is located at the front side of the flow regulating valve.

7. The waste gas liquefaction safety recovery system for a urea medium pressure system according to claim 6, characterized in that: The nitrogen delivery pipe is provided with a secondary line pipe, one end of the secondary line pipe is located between the variable flow meter and the flow regulating valve, the other end of the secondary line pipe is located between the flow regulating valve and the pressure gauge transmitter, and the secondary line pipe is provided with a secondary line valve.

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