Urea emptying tail gas treatment device

Abstract

The utility model discloses a urea emptying tail gas treatment device which comprises a first-stage tail gas absorption washing tower and a second-stage tail gas absorption washing tower which are both packed towers, a tower top gas outlet of the first-stage tail gas absorbing and washing tower is connected with a lower section pipeline of the second-stage tail gas absorbing and washing tower; the first-stage washing liquid circulating pump provides circulating washing liquid for the first-stage circulating cooler and sends out part of the circulating washing liquid to the ammonia recovery system; and the second-stage washing liquid circulating pump provides circulating washing liquid for the second-stage circulating cooler and delivers part of the circulating washing liquid to the ammonia recovery system. Through the combination of circulating cooling and desalted water cooling, washing liquid and desalted water can be kept at the optimal working temperature, so that the absorption efficiency is improved, and ultra-clean up-to-standard emission of tail gas is realized through secondary washing and absorption of two sections of fillers.

Description

Technical Field

[0001] The utility model belongs to the field of tail gas purification, and particularly relates to a treatment device for urea vent tail gas. Background Art

[0002] The carbon dioxide stripping process is a production process widely used in domestic large and medium-sized urea plants. This process has the advantages of relatively low steam specific consumption and relatively low production cost, but at the same time, there is also a problem of large ammonia loss. In the carbon dioxide stripping urea production process, the ammonia content in the vent tail gas is relatively high, about 1% - 3%, which not only increases the ammonia consumption, weakens the economic benefits of the enterprise, but also brings serious environmental pollution problems.

[0003] With the increasingly strict environmental protection regulations and the improvement of people's awareness of environmental protection, the ammonia emission problem in the urea plant vent tail gas has become one of the key factors restricting the development of the industry. By introducing and digesting advanced technologies, upgrading and transforming existing devices, improving production efficiency and environmental protection level, and developing a treatment device for the vent tail gas of the urea low-pressure absorption tower, it has become an urgent need. Summary of the Invention

[0004] The utility model provides a urea vent tail gas treatment device. The vent tail gas of the low-pressure absorption tower is washed by two-stage tail gas absorption and washing towers, so that the ammonia in the vent tail gas of the low-pressure absorption tower is reduced to 20mg / Nm³, and at the same time, ammonia products are recovered.

[0005] The technical solution of the utility model is as follows: a urea vent tail gas treatment device includes a primary tail gas absorption and washing tower and a secondary tail gas absorption and washing tower; characterized in that, a primary circulating liquid cooler and a primary washing liquid circulating pump are provided for the primary tail gas absorption and washing tower; a secondary circulating liquid cooler and a secondary washing liquid circulating pump are provided for the secondary tail gas absorption and washing tower; the gas outlet at the top of the primary tail gas absorption and washing tower is connected to the lower section pipeline of the secondary tail gas absorption and washing tower; the first layer of packing and the second layer of packing are respectively filled in the primary tail gas absorption and washing tower and the secondary tail gas absorption and washing tower; one end of the demineralized water cooler is connected to the external demineralized water pipeline, and the other end is led into the upper part of the second layer of packing in the upper section of the secondary tail gas absorption and washing tower through a pipeline;

[0006] One end of the primary circulating liquid cooler is led into the upper part of the first layer of packing in the middle of the primary tail gas absorption and washing tower through a pipeline, and the other end is connected to the primary washing liquid circulating pump through a pipeline. The primary washing liquid circulating pump is connected to the bottom of the primary tail gas absorption and washing tower. The primary washing liquid circulating pump provides circulating washing liquid for the primary circulating cooler and sends a part of it to the ammonia recovery system;

[0007] After the secondary circulating liquid cooler, it is divided into two parts. One part is introduced into the upper part of the first layer of packing in the middle of the secondary tail gas absorption and scrubbing tower through a pipeline, and one end of the other part is introduced into the upper part of the first layer of packing in the upper section of the primary tail gas absorption and scrubbing tower through a pipeline, and the other end is connected to the secondary scrubbing liquid circulating pump through a pipeline. The secondary scrubbing liquid circulating pump is connected to the bottom of the secondary tail gas absorption and scrubbing tower. The secondary scrubbing liquid circulating pump provides circulating scrubbing liquid for the secondary circulating cooler and sends a part of it to the ammonia recovery system.

[0008] Furthermore, a wire mesh demister is installed at the gas outlet of the secondary tail gas absorption and scrubbing tower.

[0009] Furthermore, a low-pressure steam gas pipeline is provided in the gas outlet pipeline of the secondary tail gas absorption and scrubbing tower.

[0010] The utility model has the following beneficial effects

[0011] 1. Significantly reduce the ammonia content in the vent gas of the low-pressure absorption tower: The treatment device of the utility model successfully controls the ammonia content in the vent gas of the urea low-pressure absorption tower at an extremely low level of less than 20 mg / Nm³.

[0012] 2. Environmental protection contribution: The extremely low ammonia emission helps to reduce air pollution, protect the ecological environment, and has a positive contribution to improving air quality and other aspects.

[0013] 3. Reduce the explosion risk: By efficiently absorbing and recovering ammonia in the tail gas, the utility model significantly reduces the ammonia concentration, fundamentally eliminating the explosion risk caused by ammonia accumulation. At the same time, introducing a low-pressure steam pipeline reduces the hydrogen partial pressure, further enhancing the safety of the system. Description of the drawings

[0014] Figure 1 is a schematic diagram of the system of the utility model;

[0015] Explanation of the reference numerals in the drawings: Primary tail gas absorption and scrubbing tower 1, secondary tail gas absorption and scrubbing tower 2, demineralized water cooler 3, primary circulating liquid cooler 4, secondary circulating liquid cooler 5, primary scrubbing liquid circulating pump 6, secondary scrubbing liquid circulating pump 7, first layer of packing 8, second layer of packing 9, wire mesh demister 10, low-pressure steam pipeline 11. Detailed implementation manners

[0016] As Figure 1 shown, a urea vent gas treatment device includes a primary tail gas absorption and scrubbing tower 1 and a secondary tail gas absorption and scrubbing tower 2. The first layer of packing 8 and the second layer of packing 9 are respectively filled in the primary tail gas absorption and scrubbing tower 1 and the secondary tail gas absorption and scrubbing tower 2.

[0017] The primary tail gas absorption scrubbing tower 1 is a packed tower, which is divided into upper and lower sections. The lower section uses circulating liquid for cooling and circulating scrubbing, and the upper section uses the scrubbing liquid from the primary scrubbing liquid circulation pump 6 for cooling absorption scrubbing;

[0018] The secondary tail gas absorption tower 2 is a packed tower, which is divided into upper and lower sections. The lower section uses the circulating liquid from the secondary scrubbing liquid circulation pump 7 for cooling and circulating scrubbing, and the upper section uses the cooled demineralized water for scrubbing.

[0019] At the gas outlet of the secondary tail gas absorption scrubbing tower 2, a wire mesh demister 10 is installed to effectively remove the entrained mist in the tail gas, making the discharged tail gas purer and achieving effective ammonia removal.

[0020] One end of the demineralized water cooler 3 is connected to the external demineralized water pipeline, and the other end is introduced into the upper part of the first layer of packing 9 in the upper section of the secondary tail gas absorption scrubbing tower 2 through a pipeline.

[0021] One end of the primary circulating liquid cooler 4 is introduced into the middle of the primary tail gas absorption scrubbing tower 1 through a pipeline, and the other end is connected to the primary scrubbing liquid circulation pump 6 through a pipeline. The primary scrubbing liquid circulation pump 6 is connected to the bottom of the primary tail gas absorption scrubbing tower 1. The primary scrubbing liquid circulation pump 6 provides circulating scrubbing liquid for the primary circulating cooler 4 and sends a part of it to the ammonia recovery system.

[0022] After the secondary circulating liquid cooler 5, it is divided into two parts. One part is introduced into the middle of the secondary tail gas absorption scrubbing tower 2 through a pipeline, and one end of the other part is introduced into the upper part of the primary tail gas absorption scrubbing tower 1 through a pipeline, and the other end is connected to the secondary scrubbing liquid circulation pump 7 through a pipeline. The secondary scrubbing liquid circulation pump 7 is connected to the bottom of the secondary tail gas absorption scrubbing tower 2. The secondary scrubbing liquid circulation pump 7 provides circulating scrubbing liquid for the secondary circulating cooler 5 and sends a part of it to the ammonia recovery system.

[0023] A low-pressure steam gas pipeline 11 is provided in the gas outlet pipeline of the secondary tail gas absorption scrubbing tower 2. The proportion of oxygen and hydrogen in the tail gas is relatively high, while the ammonia content is relatively low. This tail gas composition is prone to explosion, so explosion-proof measures need to be taken. During the tail gas absorption process, low-pressure steam is introduced into the tail gas pipeline. The addition of low-pressure steam changes the partial pressure of hydrogen in the tail gas, making the component ratio deviate from the explosion area and reducing the explosion risk. The input amount of low-pressure steam is adjusted according to different tail gas components.

[0024] The tail gas absorption system of this device adopts a two-stage absorption system: the first-stage tail gas absorption scrubber 1 adopts a segmented scrubbing design. Through the scrubbing design of the upper and lower sections, first, the scrubbing liquid of the first-stage circulating liquid cooler 4 is cooled and circulated to realize the pre-cooling of the tail gas, efficiently remove harmful substances such as ammonia in the tail gas, and at the same time reduce the energy consumption and cost in the treatment process, with the advantages of simple operation and convenient maintenance. Then, through the scrubbing liquid cooling circulation of the second-stage circulating liquid cooler 5, the pre-scrubbing of the tail gas is realized. The tail gas that has undergone pre-scrubbing and pre-cooling enters the lower part of the second-stage tail gas absorption scrubber 2. The demineralized water passing through the demineralized water cooler 3 fully absorbs and washes, improving the washing efficiency. The combination of circulating cooling and demineralized water cooling enables both the scrubbing liquid and the demineralized water to maintain the optimal working temperature, thereby improving the absorption efficiency. After re-scrubbing and absorption through two sections of packing, the tail gas is discharged up to the ultra-clean standard.

[0025] The working process is as follows:

[0026] The vent tail gas of the low-pressure absorption tower enters from the lower section of the first-stage tail gas absorption scrubber 1 and comes into full contact with the circulating scrubbing liquid passing through the first-stage circulating liquid cooler 4 in the first layer of packing 8 for temperature reduction treatment. After the temperature reduction treatment, the tail gas rises and passes through the second layer of packing 9. After pre-scrubbing and absorption, it enters the second-stage tail gas absorption scrubber 2 by using the residual pressure, comes into full contact in the first layer of packing 8 for scrubbing and absorption, rises and passes through the second layer of packing 9 for re-scrubbing and absorption.

[0027] The 40°C demineralized water from outside the plant enters from the top of the second-stage tail gas absorption scrubber 2 after being cooled by the demineralized water cooler 3, and comes into full gas-liquid contact with the tail gas entering the upper section of the second-stage tail gas absorption scrubber 2. The demineralized water cooled to the optimal absorption temperature by the demineralized water cooler 3 performs secondary full scrubbing on the ammonia in the tail gas, fully absorbs the ammonia in the tail gas, and the washed tail gas is discharged after removing the entrained liquid droplets by the wire mesh demister 10.

[0028] Steam is introduced into the vent tail gas outlet pipeline of the second-stage tail gas absorption scrubber 2 for explosion-proof treatment, and at the same time, the ammonia content in the vent tail gas is further reduced to ensure that the content of NH3 in the tail gas is less than 20 mg / Nm3.

[0029] A device for treating urea vent tail gas proposed by the utility model shows significant advantages and effects in solving the ammonia emission problem, ensuring safe production, and resource recovery and utilization.

Claims

1. A urea vent gas treatment device, comprising a primary tail gas absorption and scrubbing tower (1) and a secondary tail gas absorption and scrubbing tower (2); characterized in that, A first-stage tail gas absorption scrubbing tower (1) is equipped with a first-stage circulating liquid cooler (4) and a first-stage scrubbing liquid circulating pump (6); a second-stage tail gas absorption scrubbing tower (2) is equipped with a second-stage circulating liquid cooler (5) and a second-stage scrubbing liquid circulating pump (7); the gas outlet at the top of the first-stage tail gas absorption scrubbing tower (1) is connected to the lower section pipeline of the second-stage tail gas absorption scrubbing tower (2); a first layer of packing (8) and a second layer of packing (9) are respectively filled in the first-stage tail gas absorption scrubbing tower (1) and the second-stage tail gas absorption scrubbing tower (2); one end of the desalted water cooler (3) is connected to the external desalted water pipeline, and the other end is led into the second-stage tail gas absorption scrubbing tower (2) above the second layer of packing (9) in the upper section through a pipeline. One end of the first-stage circulating liquid cooler (4) is led into the first-stage tail gas absorption scrubbing tower (1) above the first layer of packing (8) in the middle through a pipeline, and the other end is connected to the first-stage scrubbing liquid circulating pump (6) through a pipeline. The first-stage scrubbing liquid circulating pump (6) is connected to the bottom of the first-stage tail gas absorption scrubbing tower (1). The first-stage scrubbing liquid circulating pump (6) provides circulating scrubbing liquid for the first-stage circulating liquid cooler (4) and sends a part of it to the ammonia recovery system. After the second-stage circulating liquid cooler (5), it is divided into two parts. One part is led into the second-stage tail gas absorption scrubbing tower (2) above the first layer of packing (8) in the middle through a pipeline, and one end of the other part is led into the first-stage tail gas absorption scrubbing tower (1) above the first layer of packing (8) in the upper section through a pipeline, and the other end is connected to the second-stage scrubbing liquid circulating pump (7) through a pipeline. The second-stage scrubbing liquid circulating pump (7) is connected to the bottom of the second-stage tail gas absorption scrubbing tower (2). The second-stage scrubbing liquid circulating pump (7) provides circulating scrubbing liquid for the second-stage circulating liquid cooler (5) and sends a part of it to the ammonia recovery system.

2. The urea vent gas treatment device according to claim 1, characterized in that, A wire mesh demister (10) is installed at the gas outlet of the second-stage tail gas absorption scrubbing tower (2).

3. The urea vent gas treatment device according to claim 2, characterized in that, A low-pressure steam gas pipeline (11) is provided in the gas outlet pipeline of the second-stage tail gas absorption scrubbing tower (2).

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