Ammonia desulfurization device for preventing ammonia escape and production method thereof

Abstract

The present invention discloses an ammonia desulfurization device for preventing ammonia escape, characterized in that it comprises a desulfurization tower, a circulation tank connected to the desulfurization tower through a first pipeline, wherein an ammonia-containing absorption liquid for absorbing sulfur oxides in flue gas is placed in the circulation tank; a primary circulation pump arranged on the first pipeline and located between the circulation tank and the desulfurization tower, wherein the number of the primary circulation pumps is at least two or more, wherein the primary circulation pump delivers the circulating absorption liquid in the circulation tank to the desulfurization tower to form a first spray layer; an ammonia injection main pipeline connected to the first pipeline, wherein the ammonia injection main pipeline is provided with the same number of first ammonia injection branch pipelines as the primary circulation pumps, and one end of the first ammonia injection branch pipeline is connected to the ammonia injection main pipeline. The present invention accurately controls the amount of ammonia injection to achieve a gradual increase in the pH value of the first spray layer from the upper layer to the lower layer, which can significantly reduce ammonia escape while maximizing the absorption rate of sulfur dioxide by the absorbent, and effectively controls ammonia escape in the outlet flue gas.

Description

Technical Field

[0001] The invention belongs to the technical field of ammonia desulfurization devices, and in particular relates to an ammonia desulfurization device for preventing ammonia escape and a production method thereof. Background Art

[0002] The Petroleum Refining Industry Pollutant Emission Standard (GB31570-2015) promulgated on April 16, 2015 requires that the sulfur dioxide emission concentration of acid gas recovery equipment should be ≯400mg / m 3 The limit is ≯100mg / m 3 The special emission restrictions were implemented on July 1, 2015. Currently, the optional processes for reducing sulfur dioxide emissions from flue gas of sulfur recovery units include: flue gas sodium desulfurization, flue gas by-product ammonium sulfate fertilizer, flue gas sulfur dioxide recovery desulfurization, etc.

[0003] The flue gas by-product ammonium sulfate fertilizer process uses ammonia solution to absorb sulfur dioxide, and then generates ammonium sulfate after oxidation. It is a comprehensive utilization technology for tail gas. This technology does not produce waste liquid or solid waste, is environmentally friendly, and has a good promotion prospect. The process of using ammonia to absorb sulfur dioxide has been widely used in flue gas treatment of catalytic devices and power plants. However, there are significant differences between the flue gas of the sulfur recovery unit and the former flue gas, mainly:

[0004] 1) Sulfur recovery: The sulfur dioxide content in the flue gas after the incineration of Claus tail gas is generally 10000~30000mg / Nm 3 , far exceeding the 1000-5000mg / Nm 3 The high sulfur dioxide content leads to high concentrations of ammonium sulfite and ammonium bisulfite in the absorption liquid, making it easier for ammonia to escape from the absorption liquid.

[0005] 2) Sulfur recovery The water content of Claus tail gas after incineration is generally 20-30%, far exceeding the 5% of catalytic and power plants. The high water content leads to less water evaporated when the flue gas reaches water vapor saturation when in contact with the absorption liquid, the absorbed gasification latent heat is small, and the operating temperature of the desulfurization tower is difficult to drop below 60 degrees Celsius. The high temperature of the desulfurization tower is not only not conducive to absorption, but also makes it easier for ammonia to escape from the absorption liquid.

[0006] 3) Sulfur recovery The carbon dioxide content in the flue gas after the Claus tail gas is incinerated is generally less than 5%, which is much lower than the 20% in catalytic and power plants. Carbon dioxide reacts with ammonia in water to form ammonium carbonate. Since sulfuric acid is more acidic than carbonic acid, carbon dioxide will not replace sulfur dioxide from the absorption liquid, but carbon dioxide can absorb part of ammonia as a buffer, which is beneficial to absorption and can also reduce ammonia escape in the exhaust gas to a certain extent.

[0007] 4) Sulfur recovery The flue gas temperature after incineration of Claus tail gas is generally 260-280°C, which is much higher than the 110-150°C of catalytic and power plants. The high flue gas temperature makes it difficult to cool the desulfurization tower, resulting in the escape of ammonia in the exhaust flue gas.

[0008] The high sulfur dioxide concentration, small carbon dioxide buffer, and high water content in sulfur recovery flue gas are not conducive to cooling. The high flue gas temperature leads to high temperature of the desulfurization tower. The existing sulfur recovery by-product ammonium sulfate fertilizer technology has ammonia escape problem, which not only adds a new pollution source to the sulfur flue gas, but also causes ammonia waste. The latest version of the "Emission Standard for Malodorous Pollutants" GB14554 was publicly solicited for opinions in 2019 and is about to be implemented. This version of the standard stipulates that the maximum allowable emission rate of ammonia in exhaust pipes above 30 meters is 3.5kg / h, which is significantly lower than the GB14554-93 version. Therefore, the ammonia escape problem has become the main technical difficulty that plagues the promotion and application of sulfur recovery by-product ammonium sulfate fertilizer technology. Ammonia escape refers to the phenomenon that gaseous ammonia is discharged with the flue gas. In the sulfur recovery by-product ammonium sulfate fertilizer technology, the main cause of ammonia escape is the excessively high concentration of free ammonia in the circulating absorption liquid.

[0009] At present, there are many ways to inject ammonia for ammonia-based desulfurization. Some methods directly spray gaseous ammonia or ammonia water into the flue gas, resulting in a large amount of escaping ammonia in the flue gas, causing environmental impact and ammonia waste; some methods inject all the ammonia into the desulfurization tower, but the amount of injected ammonia is difficult to control, and it is difficult to avoid ammonia escape in the flue gas. Summary of the invention

[0010] The first technical problem to be solved by the present invention is to provide an ammonia desulfurization device for preventing ammonia escape by injecting ammonia in stages to reduce the concentration of free ammonia in the circulating absorption liquid in response to the above-mentioned existing technical status.

[0011] The technical solution adopted by the present invention to solve the first technical problem is: an ammonia desulfurization device for preventing ammonia escape, characterized in that:

[0012] Desulfurization tower;

[0013] A circulation tank is connected to the desulfurization tower through a first pipeline, wherein an ammonia-containing absorption liquid for absorbing sulfur oxides in the flue gas is placed in the circulation tank;

[0014] A primary circulation pump is provided on the first pipeline and is located between the circulation tank and the desulfurization tower. The number of the primary circulation pumps is at least two. The primary circulation pump delivers the circulating absorption liquid in the circulation tank to the desulfurization tower to form a first spray layer; and

[0015] The ammonia injection main pipeline is connected to the first pipeline, and the ammonia injection main pipeline is provided with the same number of first ammonia injection branch pipelines as the primary circulation pump, one end of the first ammonia injection branch pipeline is connected to the ammonia injection main pipeline, and the other end of the first ammonia injection branch pipeline is located between the circulation tank and the primary circulation pump, so as to realize independent ammonia injection to the inlet of each primary circulation pump; the first ammonia injection branch pipeline is provided with a third regulating valve for controlling the amount of ammonia injected into the inlet of the primary circulation pump to realize a gradual increase in the pH value of the first spray layer from the upper layer to the lower layer.

[0016] In order to achieve precise control of the amount of ammonia injected, preferably, the desulfurization tower is provided with a second pipe for flue gas to enter, the second pipe is provided with a feedforward detection system for detecting the sulfur oxide content in the flue gas, and the main ammonia injection pipeline is provided with a first regulating valve which controls the ammonia injection amount in real time by the feedforward detection system.

[0017] There are many ways to calculate the sulfur oxide content in flue gas. Preferably, the feedforward detection system includes a module for detecting flue gas flow, a module for detecting sulfur oxide concentration in flue gas, and a module for calculating sulfur oxide content in flue gas; the module for calculating sulfur oxide content in flue gas controls the first regulating valve.

[0018] In order to achieve precise control of the amount of ammonia injected, preferably, a feedback detection system is arranged on the first pipeline, and the feedback detection system includes a first module for detecting the pH value in the outlet of the primary circulation pump; a second regulating valve for controlling the amount of ammonia injected in the ammonia injection main pipeline in real time by the first module is arranged on the ammonia injection main pipeline; the second regulating valve is arranged in parallel with the first regulating valve to realize independent control of the ammonia injection amount.

[0019] In order to achieve accurate control of the amount of ammonia injected, preferably, the desulfurization tower is provided with a third pipeline for the exhaust of the purified flue gas, the feedforward detection system includes a second module capable of detecting the content of sulfur oxides in the third pipeline, and the feedforward detection system also includes a selection switch, and the selection switch selects to control the second regulating valve according to the detection value of the first module or the detection value of the second module. Under normal circumstances, the second regulating valve is controlled according to the pH value at the outlet of the primary circulation pump. If the content of sulfur oxides in the purified flue gas is greater than the preset value, the content of sulfur oxides in the third pipeline is used to control the second regulating valve. The first regulating valve is the main valve, and the control amount is about 70%. The second regulating valve is the secondary valve, and the control amount is about 30%. The feedforward detection system and the feedforward detection system are combined to meet the purpose of accurate control.

[0020] In order to facilitate the isolation of the unoxidized circulating absorption liquid from the oxidized circulating absorption liquid, preferably, a pipeline for the unoxidized circulating absorption liquid in the circulating tank to pass through is provided in the circulating tank, and the pipeline is connected to the circulating pump; an opening is provided on the pipeline for the unoxidized circulating absorption liquid to flow into the oxidized circulating absorption liquid in the circulating tank; a first connecting pipe is provided between the circulating tank and the desulfurization tower for the absorption liquid after passing through the first spray layer to flow into the pipeline. The purpose of the opening is to allow the excess unoxidized absorption liquid generated during the absorption process in the pipeline to enter the circulating tank through the opening of the pipeline to maintain the balance of the liquid in the pipeline. The first connecting pipe returns the absorption liquid after passing through the first spray layer to the pipeline.

[0021] Preferably, it also includes a secondary circulation pump connected to the desulfurization tower, the secondary circulation pump discharges the absorption liquid in the desulfurization tower and returns it to the desulfurization tower to form a second spray layer, the second spray layer is located below the first spray layer, a first static mixer is arranged between the desulfurization tower and the secondary circulation pump to facilitate uniform mixing of the absorption liquid in the desulfurization tower, and a second ammonia injection pipeline is arranged between the ammonia injection main pipeline and the first static mixer to inject liquid ammonia into the first static mixer. The absorption liquid in the desulfurization tower is an oxidized ammonium sulfate solution, and an ammonia injection point is arranged on the pipeline from the outlet of the ammonium sulfate secondary circulation pump of the desulfurization tower back to the desulfurization tower, and the ammonia is evenly mixed into the ammonium sulfate solution through the first static mixer, and the pH value of the ammonium sulfate solution at the bottom of the tower is controlled between 2 and 3 to reduce corrosion to the bottom of the tower.

[0022] An ammonia injection point is set on the pipeline from the ammonium sulfate solution at the bottom of the desulfurization tower to the evaporation crystallization unit, and the pH value is controlled between 3 and 5 to reduce the corrosion of the equipment and pipelines of the evaporation crystallization unit. Preferably, it also includes a discharge pump connected to the desulfurization tower to deliver the absorption liquid in the desulfurization tower to the evaporation crystallization unit, a second static mixer is set between the desulfurization tower and the discharge pump to facilitate uniform mixing of the absorption liquid in the desulfurization tower, and a third ammonia injection pipeline is set between the ammonia injection main pipeline and the second static mixer to inject liquid ammonia into the second static mixer.

[0023] Preferably, it also includes a chimney connected to the desulfurization tower for discharging purified flue gas.

[0024] The second technical problem to be solved by the present invention is to provide a production method of an ammonia desulfurization device for preventing ammonia escape in view of the above-mentioned existing technical status.

[0025] The technical solution adopted by the present invention to solve the second technical problem is: a production method of an ammonia desulfurization device for preventing ammonia escape, characterized in that: the amount of ammonia injected into the first spray layer increases by 8 to 15wt% from the upper layer to the lower layer, and the pH value of the bottom spray layer of the first spray layer is controlled below 6. The pH value of the absorption liquid in the sulfur recovery process of by-product ammonium sulfate fertilizer has a great influence on the absorption of sulfur dioxide and sulfur trioxide. When the pH is less than 6, the desulfurization efficiency increases rapidly with the increase of pH. When the pH value is 6, the desulfurization efficiency reaches 98%. Thereafter, the desulfurization efficiency increases slowly as the pH value continues to increase. However, as the pH value increases, the ammonia escape amount also increases. For this reason, the pH value of the absorption liquid in the sulfur recovery process of by-product ammonium sulfate fertilizer is generally controlled between 5.0 and 6.0. By independently injecting ammonia at the inlet of each primary circulation pump, the ammonia injection amount of the first spray layer from the upper layer to the lower layer is increased by 8 to 15% successively, so that the pH value of the first spray layer from the upper layer to the lower layer gradually increases by about 0.1. Within this range, free ammonia in the circulating absorption liquid is not easy to escape and the desulfurization efficiency is optimal.

[0026] Compared with the prior art, the advantages of the present invention are: the main ammonia injection pipeline is provided with the same number of first ammonia injection branch pipelines as the primary circulation pumps, so as to realize independent ammonia injection to the inlet of each primary circulation pump; the first ammonia injection branch pipeline is provided with a third regulating valve for controlling the amount of ammonia injected into the inlet of the primary circulation pump to realize the gradual increase of the pH value of the first spray layer from the upper layer to the lower layer. Accurately controlling the amount of ammonia injection to realize the gradual increase of the pH value of the first spray layer from the upper layer to the lower layer can significantly reduce ammonia escape while maximizing the absorption rate of the absorbent to sulfur dioxide, and effectively controlling the ammonia escape in the outlet flue gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to the accompanying drawings.

[0029] like Figure 1 The figure shows an ammonia desulfurization device for preventing ammonia escape of the present invention, which includes a desulfurization tower 1, a circulation tank 2, a primary circulation pump 3, an ammonia injection main pipeline 4, a feedforward detection system 5, a feedback detection system, a chimney 7, a secondary circulation pump 8, and a discharge pump 9.

[0030] The circulation tank 2 is connected to the desulfurization tower 1 through the first pipeline 21, and an ammonia-containing absorption liquid for absorbing sulfur oxides in the flue gas is placed in the circulation tank 2; a pipeline 22 is provided in the circulation tank 2 for the unoxidized circulating absorption liquid in the circulation tank 2 to pass through, and the pipeline 22 is connected to the circulation pump 3; an opening 22a is provided on the pipeline 22 for the unoxidized circulating absorption liquid to flow into the circulation tank 2 and then into the oxidized circulating absorption liquid; a first connecting pipe 2a is provided between the circulation tank 2 and the desulfurization tower 1 for the absorption liquid after passing through the first spray layer 31 to flow into the pipeline 22.

[0031] The sulfur oxides in flue gas are mainly sulfur dioxide, with a small amount of sulfur trioxide.

[0032] The primary circulation pump 3 is arranged on the first pipeline 21 and is located between the circulation tank 2 and the desulfurization tower 1 . There are four primary circulation pumps 3 . The primary circulation pump 3 delivers the circulating absorption liquid in the circulation tank 2 to the desulfurization tower 1 to form the first spray layer 31 .

[0033] The ammonia injection main pipeline 4 is connected to the first pipeline 21, and the ammonia injection main pipeline 4 is provided with a first ammonia injection branch pipeline 41. The number of the first ammonia injection branch pipelines 41 is four. One end of the first ammonia injection branch pipeline 41 is connected to the ammonia injection main pipeline 4, and the other end of the first ammonia injection branch pipeline 41 is located between the circulation tank 2 and the primary circulation pump 3, so as to realize independent ammonia injection to the inlets of the four primary circulation pumps 3; the ammonia injection main pipeline 4 is provided with a first regulating valve 4a for the amount of ammonia injection. The ammonia injection main pipeline 4 is provided with a second regulating valve 4b for controlling the amount of ammonia injection, and the second regulating valve 4b is arranged in parallel with the first regulating valve 4a to realize independent control of the amount of ammonia injection. The first ammonia injection branch pipeline 41 is provided with a third regulating valve 3a for controlling the amount of ammonia injected into the inlet of the primary circulation pump 3 to realize a gradual increase in the pH value of the first spray layer 31 from the upper layer to the lower layer. The ammonia injection main pipeline 4 is provided with a second ammonia injection branch pipeline 42. The ammonia injection main pipeline 4 is provided with a third ammonia injection branch pipeline 43.

[0034] The desulfurization tower 1 is provided with a second pipe 11 for flue gas to enter, and a feedforward detection system 5 for detecting the sulfur oxide content in the flue gas is provided on the second pipe 11. The desulfurization tower 1 is provided with a third pipe 12 for the purified flue gas to be discharged.

[0035] The feedforward detection system 5 comprises a module 51 for detecting flue gas flow rate, a module 52 for detecting sulfur oxide concentration in flue gas, and a module 53 for calculating sulfur oxide content in flue gas; the module 53 for calculating sulfur oxide content in flue gas controls the first regulating valve 4a.

[0036] The feedback detection system is arranged on the first pipeline 21, and the feedback detection system includes a first module 61 for detecting the pH value in the outlet of the primary circulation pump 3. The feedback detection system is connected to the third pipeline 12. The feedback detection system includes a second module 62 capable of detecting the content of sulfur oxides in the third pipeline 12. The feedback detection system also includes a selection switch 63. The selection switch 63 selects to control the second regulating valve 4b according to the detection value of the first module 61 or the detection value of the second module 62.

[0037] The secondary circulation pump 8 is connected to the desulfurization tower 1. The secondary circulation pump 8 discharges the absorption liquid in the desulfurization tower 1 and returns it to the desulfurization tower 1 to form a second spray layer 81. The second spray layer 81 is located below the first spray layer 31. A first static mixer 82 is provided between the desulfurization tower 1 and the secondary circulation pump 8 to facilitate uniform mixing of the absorption liquid in the desulfurization tower 1. The second ammonia injection pipeline 42 injects liquid ammonia into the first static mixer 82.

[0038] The discharge pump 9 is connected to the desulfurization tower 1, and the discharge pump 9 delivers the absorption liquid in the desulfurization tower 1 to the evaporation crystallization unit. A second static mixer 91 is arranged between the desulfurization tower 1 and the discharge pump 9 to facilitate uniform mixing of the absorption liquid in the desulfurization tower 1. The third ammonia injection pipeline 43 injects liquid ammonia into the second static mixer 91.

[0039] The chimney 7 is connected to the desulfurization tower 1 for discharging the purified flue gas.

[0040] The method of the present invention is used to independently inject ammonia into the inlets of four primary circulation pumps 3, and the third regulating valve 3a is adjusted to control the ammonia injection amount of the four first ammonia injection branch pipes 41. The first spray layer 31 forms four spray layers in the desulfurization tower 1. The ammonia injection amount of the absorption liquid in the four spray layers increases by 10wt% from the upper layer to the lower layer, and the pH values ​​from the upper layer to the lower layer are 5.2, 5.3, 5.4, and 5.5. Compared with the traditional method of directly spraying gaseous ammonia or ammonia water into the flue gas or injecting all ammonia into the desulfurization tower, the ammonia escape in the outlet flue gas is reduced by more than 30%, and the ammonia escape in the outlet flue gas is effectively controlled.

Claims

1. An ammonia desulfurization device for preventing ammonia escape, characterized in that: include Desulfurization tower (1); A circulation tank (2) is connected to the desulfurization tower (1) via a first pipeline (21), wherein an ammonia-containing absorption liquid for absorbing sulfur oxides in the flue gas is placed in the circulation tank (2); a primary circulation pump (3), which is arranged on the first pipeline (21) and is located between the circulation tank (2) and the desulfurization tower (1), wherein the number of the primary circulation pumps (3) is at least two or more, and the primary circulation pump (3) delivers the circulating absorption liquid in the circulation tank (2) to the desulfurization tower (1) to form a first spray layer (31); and an ammonia injection main pipeline (4) connected to the first pipeline (21); the ammonia injection main pipeline (4) is provided with the same number of first ammonia injection branch pipelines (41) as the primary circulation pump (3); one end of each of the first ammonia injection branch pipelines (41) is connected to the ammonia injection main pipeline (4); the other end of each of the first ammonia injection branch pipelines (41) is located between the circulation tank (2) and the primary circulation pump (3), so as to realize independent ammonia injection at the inlet of each primary circulation pump (3); and the first ammonia injection branch pipeline (41) is provided with a third regulating valve (3a) for controlling the amount of ammonia injected into the inlet of the primary circulation pump (3) so as to realize a gradual increase in the pH value of the first spray layer (31) from the upper layer to the lower layer; The desulfurization tower (1) is provided with a second pipeline (11) for flue gas to enter, the second pipeline (11) is provided with a feedforward detection system (5) for detecting the sulfur oxide content in the flue gas, and the ammonia injection main pipeline (4) is provided with a first regulating valve (4a) for controlling the ammonia injection amount in real time by the feedforward detection system (5); The feedforward detection system (5) comprises a module for detecting flue gas flow rate (51), a module for detecting sulfur oxide concentration in flue gas (52), and a module for calculating sulfur oxide content in flue gas (53); the module for calculating sulfur oxide content in flue gas (53) controls the first regulating valve (4a); The first pipeline (21) is provided with a backfeed detection system, the backfeed detection system comprising a first module (61) for detecting the pH value in the outlet of the primary circulation pump (3); the ammonia injection main pipeline (4) is provided with a second regulating valve (4b) for controlling the amount of ammonia injected into the ammonia injection main pipeline (4) in real time by the first module (61); the second regulating valve (4b) is arranged in parallel with the first regulating valve (4a) to realize independent control of the amount of ammonia injected; The desulfurization tower (1) is provided with a third pipe (12) for discharging purified flue gas, the feedback detection system comprises a second module (62) capable of detecting the content of sulfur oxides in the third pipe (12), and the feedback detection system further comprises a selection switch (63), wherein the selection switch (63) selects to control the second regulating valve (4b) according to the detection value of the first module (61) or the detection value of the second module (62).

2. The ammonia desulfurization device for preventing ammonia escape according to claim 1, characterized in that: The circulation tank (2) is provided with a pipe (22) for the unoxidized circulating absorption liquid in the circulation tank (2) to pass through, and the pipe (22) is connected to a primary circulation pump (3); the pipe (22) is provided with an opening (22a) for the unoxidized circulating absorption liquid to flow into the oxidized circulating absorption liquid in the circulation tank (2); and a first connecting pipe (2a) is provided between the circulation tank (2) and the desulfurization tower (1) for the absorption liquid after passing through the first spray layer (31) to flow into the pipe (22).

3. The ammonia desulfurization device for preventing ammonia escape according to claim 1, characterized in that: The invention also comprises a secondary circulation pump (8) connected to the desulfurization tower (1), wherein the secondary circulation pump (8) discharges the absorption liquid in the desulfurization tower (1) and returns it to the desulfurization tower (1) to form a second spray layer (81), wherein the second spray layer (81) is located below the first spray layer (31), and a first static mixer (82) is arranged between the desulfurization tower (1) and the secondary circulation pump (8) to facilitate uniform mixing of the absorption liquid in the desulfurization tower (1), and a second ammonia injection branch pipeline (42) is arranged between the ammonia injection main pipeline (4) and the first static mixer (82) to inject liquid ammonia into the first static mixer (82).

4. The ammonia desulfurization device for preventing ammonia escape according to claim 1, characterized in that: The invention also comprises a discharge pump (9) connected to the desulfurization tower (1) for delivering the absorption liquid in the desulfurization tower (1) to the evaporation crystallization unit; a second static mixer (91) is arranged between the desulfurization tower (1) and the discharge pump (9) to facilitate uniform mixing of the absorption liquid in the desulfurization tower (1); and a third ammonia injection branch pipeline (43) is arranged between the ammonia injection main pipeline (4) and the second static mixer (91) to inject liquid ammonia into the second static mixer (91).

5. The ammonia desulfurization device for preventing ammonia escape according to claim 1, characterized in that: It also includes a chimney (7) connected to the desulfurization tower (1) for discharging the purified flue gas.

6. A production method of an ammonia desulfurization device for preventing ammonia escape according to any one of claims 1 to 5, characterized in that: The amount of ammonia injected into the first spray layer (31) increases by 8-15wt% from the upper layer to the lower layer, and the pH value of the lowest spray layer of the first spray layer (31) is controlled to be below 6.

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