Self-adaptive regulation and control method for recycling urea emptying tail gas

Abstract

The invention discloses a self-adaptive regulation and control method for recycling urea emptying tail gas. The self-adaptive regulation and control method comprises the following steps: S1, data detection; s2, performing real-time judgment; s3, explosion-proof control is carried out; and S4, tail gas recycling. The method has the advantages that the currently emptied 4Bar emptied tail gas is completely recovered to the steam generation boiler for combustion, so that the coal consumption of the boiler can be reduced, and the purposes of saving energy and reducing carbon are achieved; meanwhile, emission of components such as alkane in the tail gas can cause VOCs pollution to the atmosphere, after the tail gas is recycled through the method, a 4Bar absorption tower of the urea device is not emptied any more, pollution of tail gas emission to the atmosphere is greatly reduced, and good environmental protection benefits are achieved. The carbon dioxide absorbed by the methanol washing section is used as inert gas to be doped into the tail gas, so that oxygen in the tail gas can be diluted, the oxygen content is further reduced, burning explosion is prevented, and safe recycling of the tail gas is ensured.

Description

Technical Field:

[0001] The present invention relates to the field of tail gas recycling, and particularly to an adaptive control method for recycling urea vent tail gas. Background Art:

[0002] In the process of producing urea, coal needs to be gasified into raw gas first, and then the raw gas reacts with steam to be converted into carbon dioxide and hydrogen. After methanol washing, methanol is used to absorb components such as carbon dioxide and hydrogen sulfide in the raw gas. Then, the crude hydrogen enters the liquid nitrogen washing to react with nitrogen to generate liquid ammonia, which is sent to the urea plant as a raw material for preparing urea. The methanol that absorbs carbon dioxide is flashed and purified, and then carbon dioxide is sent to the urea plant. In the urea plant, ammonia and carbon dioxide react to form urea, and the tail gas after the reaction is discharged after removing ammonia through a scrubber.

[0003] The raw material carbon dioxide purity of the urea plant of Hulunbeier Jinxin Chemical Industry is 98.5%, and it also contains a small amount of combustible gases such as alkanes, hydrogen, carbon monoxide, and ammonia. Since these combustible gases do not participate in the reaction during the production of urea, they will eventually accumulate in the gas phase. To prevent excessive accumulation of hydrogen in the gas phase and reach the explosion limit, a dehydrogenation reactor is set in the urea production process, and air is added. Under the action of a catalyst, hydrogen reacts with oxygen to form water. Therefore, there is also oxygen and nitrogen in the tail gas accumulation. These gases that do not participate in the urea production reaction finally enter the 4Bar absorption tower for washing and then are discharged. The content of combustible gases in the tail gas discharged from the 4Bar absorption tower of the urea plant is about 16%, with a relatively high calorific value and a large discharge amount, about 1800 Nm 3 / h. However, because the vent tail gas contains oxygen, once the oxygen content is too high, there will be a risk of combustion and explosion for the recycled gas, so the recycling is difficult. Summary of the Invention:

[0004] In order to solve the above problems, the purpose of the present invention is to provide an adaptive control method for recycling urea vent tail gas.

[0005] The present invention is implemented by the following technical solutions:

[0006] An adaptive control method for recycling urea vent tail gas includes the following steps:

[0007] S1. Data detection: Monitor the tail gas flow rate and the oxygen content in the tail gas discharged from the absorption tower;

[0008] S2. Real-time judgment: According to the monitored oxygen content in the tail gas, judge whether the explosion condition is satisfied. If it is satisfied, execute S3. Explosion-proof control; if not, execute S4. Tail gas recycling;

[0009] S3. Explosion-proof control: An inert gas is incorporated into the tail gas discharged from the absorption tower. Based on the monitored flow rate of the tail gas discharged from the absorption tower and the oxygen content in the tail gas, the incorporation flow rate of the inert gas is determined to ensure that the oxygen content in the tail gas does not meet the explosion conditions, and then S4. Tail gas recycling is executed;

[0010] S4. Tail gas recycling: The tail gas is sent to a steam generating boiler as fuel for combustion.

[0011] Further, in the S2. Real-time judgment, the explosion conditions are: the volume percentage of oxygen in the monitored tail gas ≥ 4%.

[0012] Further, in the S3. Explosion-proof control, the calculation method of the incorporation flow rate of the inert gas is:

[0013]

[0014] In formula (1), Q i is the incorporation flow rate of the inert gas, Q w is the monitored flow rate of the tail gas discharged from the absorption tower, is the oxygen content in the monitored tail gas discharged from the absorption tower.

[0015] Further, in the S1. Data detection, the moisture content in the tail gas discharged from the absorption tower also needs to be detected;

[0016] In the S2. Real-time judgment, first, based on the monitored moisture content in the tail gas, it is judged whether the moisture content is qualified. If it is qualified, then it is judged whether the explosion conditions are met; if it is unqualified, the tail gas needs to be first passed through condensation and gas-liquid separation and then judged whether the explosion conditions are met.

[0017] Further, in the S2. Real-time judgment,

[0018] If the volume percentage of moisture in the monitored tail gas ≥ 10%, it is judged as unqualified;

[0019] If the volume percentage of moisture in the monitored tail gas < 10%, it is judged as qualified.

[0020] Further, in the S3. Explosion-proof control, the inert gas is carbon dioxide from the methanol washing section.

[0021] Further, the carbon dioxide from the methanol washing section is first heat-exchanged and heated with the purified water from urea hydrolysis, and then mixed with the tail gas discharged from the absorption tower.

[0022] Further, in the S1. Data detection, the calorific value of the tail gas discharged from the absorption tower also needs to be detected;

[0023] S4. During the reuse of tail gas, first calculate the combustion calorific value provided by the tail gas according to the monitored calorific value and flow rate of the tail gas, and determine the fuel coal addition amount of the steam generation boiler according to the calorific value of the fuel coal.

[0024] Further, the calculation method for the fuel coal addition amount of the steam generation boiler is as follows:

[0025]

[0026] In formula (2), m t is the fuel coal addition amount of the steam generation boiler, m0 is the initial fuel coal addition amount of the steam generation boiler, Q w is the monitored tail gas flow rate discharged from the absorption tower, q w is the monitored calorific value of the tail gas discharged from the absorption tower, q c is the calorific value of the fuel coal.

[0027] Advantages of the present invention:

[0028] 1. All the currently vented 4Bar vent tail gas is recovered and burned in the steam generation boiler, which can save the coal consumption of the boiler and achieve the purpose of energy conservation and carbon reduction. At the same time, the emission of components such as alkanes in the tail gas will cause atmospheric VOCs pollution. After the tail gas is recovered by the present invention, the 4Bar absorption tower of the urea plant no longer vents, greatly reducing the pollution of the tail gas emission to the atmosphere and having good environmental benefits.

[0029] 2. By mixing the carbon dioxide absorbed in the methanol washing section into the tail gas as an inert gas, the oxygen in the tail gas can be diluted, thereby reducing the oxygen content, preventing combustion and explosion, and ensuring the safe reuse of the tail gas.

[0030] 3. Using the waste heat carried by the purified water from urea hydrolysis to heat the mixed-in carbon dioxide gas can prevent excessive liquid water from precipitating in the tail gas, thereby preventing pipeline corrosion.

[0031] 4. When the water content in the tail gas is too high, most of the water in the tail gas can be removed through condensation and gas-liquid separation, thereby improving the combustion efficiency of the steam generation boiler. Specific embodiments:

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] Example 1:

[0034] An adaptive control method for the recovery and utilization of urea vent tail gas, comprising the following steps:

[0035] S1. Data detection: Monitor the tail gas flow rate and the oxygen content in the tail gas discharged from the absorption tower;

[0036] S2. Real-time judgment: According to the monitored oxygen content in the tail gas, judge whether the explosion and combustion conditions are met. If so, execute S3. Explosion-proof control; if not, execute S4. Tail gas recycling;

[0037] S3. Explosion-proof control: Incorporate inert gas into the tail gas discharged from the absorption tower, and determine the incorporation flow rate of the inert gas according to the monitored tail gas flow rate and the oxygen content in the tail gas discharged from the absorption tower, ensuring that the oxygen content in the tail gas does not meet the explosion and combustion conditions, and execute S4. Tail gas recycling;

[0038] S4. Tail gas recycling: Send the tail gas to the steam generation boiler for fuel combustion.

[0039] Further, in S2. Real-time judgment, the explosion and combustion conditions are: the volume percentage of oxygen in the monitored tail gas ≥ 4%;

[0040] Further, in S3. Explosion-proof control, the calculation method for the incorporation flow rate of the inert gas is:

[0041]

[0042] In formula (1), Q i is the incorporation flow rate of the inert gas, Q w is the monitored tail gas flow rate discharged from the absorption tower, is the oxygen content in the monitored tail gas discharged from the absorption tower.

[0043] Further, in S1. Data detection, the moisture content in the tail gas discharged from the absorption tower also needs to be detected;

[0044] In S2. Real-time judgment, first, judge whether the moisture content is qualified according to the monitored moisture content in the tail gas. If it is qualified, then judge whether the explosion and combustion conditions are met; if it is unqualified, the tail gas needs to be passed through condensation and gas-liquid separation first and then judge whether the explosion and combustion conditions are met.

[0045] Further, in S2. Real-time judgment,

[0046] If the volume percentage of moisture in the monitored tail gas ≥ 10%, it is judged as unqualified;

[0047] If the volume percentage of moisture in the monitored tail gas < 10%, it is judged as qualified.

[0048] Further, in S3, explosion-proof control, the inert gas is carbon dioxide from the methanol washing section.

[0049] Further, the carbon dioxide from the methanol washing section is first heat-exchanged with the purified water from urea hydrolysis to increase the temperature, and then mixed with the tail gas discharged from the absorption tower.

[0050] Further, in S1, data detection, the calorific value of the tail gas discharged from the absorption tower also needs to be detected;

[0051] In S4, tail gas reuse, first, according to the monitored calorific value and flow rate of the tail gas, calculate the combustion calorific value provided by the tail gas, and determine the fuel coal addition amount of the steam generation boiler according to the calorific value of the fuel coal.

[0052] Further, the calculation method of the fuel coal addition amount of the steam generation boiler is as follows:

[0053]

[0054] In formula (2), m t is the fuel coal addition amount of the steam generation boiler, m0 is the initial fuel coal addition amount of the steam generation boiler, Q w is the monitored flow rate of the tail gas discharged from the absorption tower, q w is the monitored calorific value of the tail gas discharged from the absorption tower, q c is the calorific value of the fuel coal.

[0055] Since the tail gas volume, tail gas composition, and calorific value of the tail gas will all change with the changes in the urea plant load, operating conditions, and raw coal, therefore, in the present invention, the tail gas volume, tail gas calorific value, moisture content, and oxygen content in the tail gas are monitored in real time. When the oxygen content is relatively high, in order to prevent the pipeline from catching fire and exploding, the carbon dioxide absorbed in the methanol washing section is used as an inert gas and incorporated into the tail gas, which can dilute the oxygen in the tail gas, thereby reducing the oxygen content and preventing fire and explosion. At the same time, according to the real-time tail gas volume, the amount of incorporated carbon dioxide is regulated to ensure that the oxygen content in the tail gas does not meet the fire and explosion conditions, further ensuring the safe reuse of the tail gas.

[0056] Since the present invention was implemented, according to the statistically monitored data, the average combustion calorific value is 4.37×10 6 kcal / h, the boiler thermal efficiency of the enterprise is about 85%, and calculated according to this thermal efficiency, the utilization amount of the combustion calorific value is 3.71×10 6 kcal / h. Calculated according to the combustion calorific value of 3200 kcal / kg of the fuel coal in Jinxin Chemical Industry, the coal consumption can be reduced by 1.19 t / h. Calculated according to the price of 176.99 yuan / ton of the fuel coal, the annual energy-saving benefit is 1.668 million yuan.

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An adaptive control method for the recovery and utilization of urea vent tail gas, characterized in that It includes the following steps: S1. Data detection: Monitor the tail gas flow rate discharged from the absorption tower and the oxygen content in the tail gas. S2. Real-time judgment: According to the monitored oxygen content in the tail gas, judge whether the explosion and combustion conditions are met. If so, execute S3. Explosion-proof control; if not, execute S4. Tail gas recycling. S3. Explosion-proof control: Incorporate inert gas into the tail gas discharged from the absorption tower, and determine the incorporation flow rate of the inert gas according to the monitored tail gas flow rate discharged from the absorption tower and the oxygen content in the tail gas, ensuring that the oxygen content in the tail gas does not meet the explosion and combustion conditions, and execute S4. Tail gas recycling. S4. Tail gas recycling: Send the tail gas to the steam generation boiler to burn as fuel.

2. An adaptive regulation method for the recycling of urea vent tail gas according to claim 1, characterized in that, In the S2. Real-time judgment, the explosion and combustion conditions are: the volume percentage of oxygen in the monitored tail gas ≥ 4%.

3. An adaptive regulation method for recycling and utilization of urea vent tail gas according to claim 1, characterized in that, In the S3. Explosion-proof control, the calculation method of the incorporation flow rate of the inert gas is as follows: In formula (1), Q i is the inflow rate of the inert gas, and Q w is the tail gas flow rate discharged from the monitored absorption tower, and is the oxygen content in the tail gas discharged from the monitored absorption tower.

4. An adaptive control method for the recycling of urea vent tail gas according to claim 1, characterized in that, In the S1. Data detection, it is also necessary to detect the moisture content in the tail gas discharged from the absorption tower. In the S2. Real-time judgment, first judge whether the moisture content is qualified according to the monitored moisture content in the tail gas. If it is qualified, then judge whether the explosion and combustion conditions are met; if it is unqualified, the tail gas needs to be passed through condensation and gas-liquid separation first and then judge whether the explosion and combustion conditions are met.

5. An adaptive regulation method for the recovery and utilization of urea vent tail gas according to claim 4, characterized in that In the S2. Real-time judgment, if the volume percentage of moisture in the monitored tail gas ≥ 10%, it is judged as unqualified; if the volume percentage of moisture in the monitored tail gas < 10%, it is judged as qualified.

6. An adaptive regulation method for the recovery and utilization of urea vent tail gas according to claim 1, characterized in that, In the S3. Explosion-proof control, the inert gas is carbon dioxide from the methanol washing section.

7. An adaptive control method for the recovery and utilization of urea vent tail gas according to claim 6, characterized in that, The carbon dioxide from the methanol washing section is first heat-exchanged and heated with the purified water from urea hydrolysis, and then mixed with the tail gas discharged from the absorption tower.

8. An adaptive control method for the recycling of urea vent tail gas according to claim 1, characterized in that, In the S1. Data detection, it is also necessary to detect the calorific value of the tail gas discharged from the absorption tower. In the S4. Tail gas recycling, first calculate the combustion calorific value provided by the tail gas according to the monitored calorific value and flow rate of the tail gas, and determine the fuel coal addition amount of the steam generation boiler according to the calorific value of the fuel coal.

9. An adaptive control method for the recovery and utilization of urea vent tail gas according to claim 8, characterized in that, The calculation method of the fuel coal addition amount of the steam generation boiler is as follows: In formula (2), m t is the coal addition amount of the steam generating boiler, m0 is the initial coal addition amount of the steam generating boiler, Q w is the tail gas flow rate discharged from the monitored absorption tower, q w is the calorific value of the tail gas discharged from the monitored absorption tower, q c is the calorific value of the coal.

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