A method and apparatus for corrosion control of a condensate stripper overhead reflux system

Abstract

A corrosion control method and device for changing the condensate stripping tower overhead reflux system, the method comprising the following steps: 1) setting a cyanide ion control content index for the condensate to be refluxed into the ammonia stripping tower overhead, and monitoring the content of cyanide ions in the subsequent reflux condensate; 2) when the cyanide ion content exceeds the control content index, inject polysulfide into the condensate to be stripped. The method finds out the corrosion reason from the perspective of corrosion aggravation, establishes a cyanide ion control index, and when the cyanide ion control index exceeds the standard, the content of cyanide ions in the condensate is consumed by polysulfide. The reduction of cyanide ions can slow down the corrosion efficiency of ammonium carbamate, control the corrosion of the stripping device during the stripping of the condensate, and effectively control the corrosion from the root cause, reducing the risk of unplanned shutdown and subsequent inspection and maintenance costs.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, specifically to a corrosion control method and apparatus for the top reflux system of a shift converter condensate stripping tower. Background Technology

[0002] With the increasing scale of domestic coal chemical plants and the growing awareness of energy conservation and environmental protection among enterprises, more and more companies are beginning to pay attention to the ammonia recovery problem in the condensate of shift conversion processes. For companies using coal-water slurry gasification processes, if ammonia can be recovered from the shift conversion condensate for ammonia-based desulfurization, waste can be turned into treasure, saving more than 40% of liquid ammonia annually.

[0003] The condensate from the conversion process mainly originates from the condensation and washing of crude coal gas, and primarily contains NH3, CO2, and a small amount of H2S. Currently, most enterprises use ammonia stripping to treat the condensate, with typical processes including single-tower low-pressure stripping, single-tower pressurized side-stream ammonia stripping, and double-tower pressurized stripping. However, due to the presence of corrosive substances such as NH3, CO2, H2S, and HCN in the condensate, and the fact that some of the condensate is recycled within the stripping system, a vicious cycle has formed. This has resulted in significant corrosion problems in the entire condensate stripping unit, especially in the top reflux system of the condensate stripping tower. Unplanned shutdowns have frequently occurred within the first six months of operation, severely impacting the long-term stable operation of the unit and negatively affecting the enterprise's safe production, cost reduction, and environmental protection.

[0004] To address the prominent corrosion problem in condensate stripping units, the inventors proposed a method and apparatus (publication number CN111760320B) for mitigating corrosion in the top reflux system of a condensate stripping tower. This patent uses a spray tower as the cooling system for non-condensable gases, replacing the traditional top condenser. This effectively solves or mitigates the severe localized corrosion problem of ammonia in the top reflux system of existing condensate stripping processes, reduces maintenance costs, avoids or minimizes unplanned downtime due to leaks, lowers maintenance expenses, and ensures the safe, stable, and long-term operation of the entire stripping system. While this patent provides a solution by replacing the traditional top condenser with a spray tower for non-condensable gas cooling, it only considers the gas-liquid distribution of ammonia and does not address the causes of sudden corrosion problems in the short term. Therefore, it cannot fundamentally solve the problem, and the long-term corrosion risk remains significant, while also increasing the investment cost of related equipment. Summary of the Invention

[0005] The purpose of this invention is to provide a corrosion control method and apparatus for the top reflux system of a stripping tower, which can control the corrosion of the stripping tower top reflux system by the condensate during stripping.

[0006] To address the shortcomings of the aforementioned technical problems, the present invention provides a corrosion control method for the top reflux system of a shift converter condensate stripping tower, comprising the following steps:

[0007] 1) Establish a cyanide ion control index for the condensate to be returned to the top of the ammonia stripping tower, and monitor the cyanide ion content in the subsequent reflux condensate;

[0008] 2) When the cyanide ion content exceeds the control index, polysulfides are injected into the condensate to be stripped to reduce the cyanide ion content, thereby preventing cyanide ions from aggravating the corrosion intensity of ammonium carbamate.

[0009] 3) A portion of the condensate to be returned to the top of the ammonia stripping tower is transported to the feed inlet of the acid stripping tower. The ammonium carbamate in the condensate is decomposed under high temperature conditions to prevent the accumulation of corrosive substances returning to the top of the ammonia stripping tower.

[0010] As a further optimization of the corrosion control method of the top reflux system of the conversion condensate stripping tower of the present invention, the content index of cyanide ions in step 1) is ≤40μg / g.

[0011] As a further optimization of the corrosion control method of the top reflux system of the conversion condensate stripping tower of the present invention, the content index of cyanide ions in step 1) is 20 μg / g.

[0012] As a further optimization of the corrosion control method of the top reflux system of the condensate stripping tower of the present invention, a sampling port for detecting cyanide ions is set on the pipeline path through which the condensate is circulated back to the top of the ammonia stripping tower.

[0013] As a further optimization of the corrosion control method of the top reflux system of the conversion condensate stripping tower of the present invention, the polysulfide injection position is set at the condensate feed pipe of the acid stripping tower.

[0014] As a further optimization of the corrosion control method of the top reflux system of the condensate stripping tower of the present invention, a diversion pipe is set on the reflux pipe that circulates the condensate back to the top of the ammonia stripping tower. The diversion pipe is used to transport part of the condensate in the reflux pipe to the feed port of the acid stripping tower.

[0015] As a further optimization of the corrosion control method of the top reflux system of the condensate stripping tower of the present invention, the polysulfide injection method is nozzle injection.

[0016] As a further optimization of the corrosion control method of the top reflux system of the conversion condensate stripping tower of the present invention, the polysulfide is sodium polysulfide or ammonium polysulfide.

[0017] As a further optimization of the corrosion control method of the top reflux system of the conversion condensate stripping tower of the present invention, the polysulfides are sodium polysulfide and ammonium polysulfide.

[0018] As a further optimization of the corrosion control method of the top reflux system of the conversion condensate stripping tower of the present invention, the pH of the polysulfide is greater than 7.5.

[0019] A reflux device for the top of a shift condensate stripping tower includes an acid stripping tower, an ammonia stripping tower, a heat exchanger, a gas-liquid separator, a reflux tank, and a reflux pump. The inlet of the acid stripping tower is connected to a condensate pipe for conveying condensate, the outlet of the acid stripping tower is connected to an external sulfur recovery device, the outlet of the acid stripping tower is connected to the inlet of the ammonia stripping tower, the outlet of the ammonia stripping tower is connected to the inlet of the heat exchanger, the outlet of the heat exchanger is connected to the inlet of the gas-liquid separator, and the gas outlet of the gas-liquid separator... The gas-liquid separator is connected to an external ammonia settling unit. The liquid outlet of the gas-liquid separator is connected to the inlet of the reflux tank. A reflux pump is provided at the outlet of the reflux tank. The outlet of the reflux pump is connected to the reflux port of the stripping tower through a reflux pipe. The reflux tank is characterized in that a corrosion control agent tank is connected to the end of the condensate pipe near the stripping tower. The corrosion control agent tank is filled with polysulfides. A sampling port for easy detection of circulating condensate is provided between the reflux tank and the reflux pump. A drain pipe for connection is directly provided between the inlet end of the condensate pipe and the outlet end of the reflux pipe.

[0020] As a further optimization of the reflux device at the top of the condensate stripping tower of the present invention, the guide pipe is provided with a shut-off valve to control the flow state of the guide pipe.

[0021] The present invention has the following beneficial effects: The method of the present invention addresses the root causes of corrosion by identifying the source of corrosion and establishing a cyanide ion control index. When the cyanide ion control index exceeds the limit, polysulfides consume the cyanide ion content in the condensate. The reduction of cyanide ions slows down the corrosion efficiency of ammonium carbamate, controlling the corrosion of the stripping unit by the condensate during the stripping process. This effectively controls corrosion at its source, reducing the risk of unplanned downtime and subsequent maintenance costs. Simultaneously, a guide pipe is installed on the condensate circulation return pipe to guide the ammonium carbamate enriched in the return pipe to the feed inlet of the acid stripping tower. The high-temperature hot air decomposes the ammonium carbamate, further controlling the corrosion of the stripping unit by the condensate during the stripping process. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the implementation structure of the control method in Example 1;

[0023] Attached reference numerals: 1. Corrosion control agent tank; 2-1. Acid stripping tower; 2-2. Ammonia stripping tower; 3. Heat exchanger; 4. Gas-liquid separator; 5. Reflux tank; 6. Reflux pump; 7. Shut-off valve; 8. Sampling port; 9. Drain pipe; 10. Reflux pipe. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0025] Example 1

[0026] like Figure 1 As shown, this embodiment provides a corrosion control method for the top reflux system of a stripping tower, which can control the corrosion of the stripping tower top reflux system by the condensate during the stripping process.

[0027] The corrosion control method provided in this embodiment includes the following steps:

[0028] 1) Establish a cyanide ion control index for the condensate to be returned to the top of the ammonia stripping tower 2-2, and monitor the cyanide ion content in the subsequent reflux condensate; According to the inventor's research, ammonium carbamate (also known as methylamine, NH4COONH2) is generated during the circulating condensation process of the condensate in the stripping system, which can cause severe corrosion to metal materials. At the same time, cyanide ions are present during the stripping process of the condensate, and cyanide ions can increase the corrosion efficiency of ammonium carbamate. Therefore, in order to control the corrosion of the stripping unit by the condensate during the stripping process, it is necessary to control the cyanide ion content. Therefore, it is necessary to establish a cyanide ion control index to prevent the cyanide ion content from exceeding the standard, thereby controlling the degree of system corrosion.

[0029] 2) When the cyanide ion content exceeds the control limit, polysulfides are injected into the condensate to be stripped. The polysulfide injection point is located at the condensate feed pipe of the acid stripping tower 2-1. The polysulfides reduce the cyanide ion content, thereby preventing cyanide ions from exacerbating the corrosion of ammonium carbamate. Reducing the cyanide ion content prevents cyanide ions from increasing the corrosion efficiency of ammonium carbamate, thus controlling severe corrosion of the stripping unit by the condensate. The injected polysulfides are one or more of sodium polysulfide and ammonium polysulfide. Simultaneously, the pH of the polysulfides injected into the condensate should be greater than 7.5. A pH value below 7.5 will cause the polysulfides to decompose, and oxygen can decompose them, generating elemental sulfur and other corrosion reaction products, and even clogging the pipeline.

[0030] 3) A portion of the condensate to be returned to the top of the ammonia stripping tower 2-2 is transported to the feed inlet of the acid stripping tower 2-1. The ammonium carbamate in the condensate is decomposed under high temperature conditions to prevent the accumulation of corrosive substances at the top of the ammonia stripping tower 2-2 and further control the corrosion of the stripping unit caused by the condensate during the stripping process.

[0031] In step 3, to ensure that a portion of the condensate to be returned to the top of the ammonia stripping tower 2-2 is transported to the feed inlet of the acid stripping tower 2-1, a guide pipe 9 is installed on the reflux pipe 10 where the condensate is circulated back to the top of the ammonia stripping tower 2-2. The guide pipe 9 has a unidirectional flow effect, guiding only a portion of the condensate from the reflux pipe 10 to the inlet of the stripping tower 2. The heat from the feed height of the stripping tower 2 is used to decompose the ammonium carbamate in the condensate. This way, some condensate will also return to the stripping tower 2, preventing the outlet temperature of the stripping tower 2 from rising and affecting the stripping separation effect.

[0032] In step 1, the cyanide ion content should be controlled to be ≤40 μg / g, preferably 20 μg / g. The goal is simply to control the corrosion rate and maintain a state of mild corrosion. The controlled cyanide ion content in this process was determined through field testing.

[0033] In step 1, a sampling port 8 for detecting cyanide ions is installed on the pipeline path from the condensate recirculation to the top of the ammonia stripping tower 2-2. Samples are taken through sampling port 8 to monitor the cyanide ion content in the recirculated condensate.

[0034] In step 2, the polysulfide injection method is nozzle spraying. Polysulfide spraying injection can make the polysulfide and condensate mix more evenly.

[0035] Example 2

[0036] This embodiment is a reflux device for the top of a stripping tower designed according to the control method of Embodiment 1. While extracting ammonia from the condensate, it can also control the corrosion of the stripping tower top reflux system by the condensate during stripping.

[0037] This embodiment provides an existing structure for a top reflux device of a conversion condensate stripping tower, including an acid stripping tower 2-1, an ammonia stripping tower 2-2, a heat exchanger 3, a gas-liquid separator 4, a reflux tank 5, and a reflux pump 6. The inlet of the acid stripping tower 2-1 is connected to the condensate pipe that transports the condensate, the outlet of the acid stripping tower 2-1 is connected to an external sulfur recovery device, the outlet of the acid stripping tower 2-1 is connected to the inlet of the ammonia stripping tower 2-2, the outlet of the ammonia stripping tower 2-2 is connected to the inlet of the heat exchanger 3, the outlet of the heat exchanger 3 is connected to the inlet of the gas-liquid separator 4, the gas outlet of the gas-liquid separator 4 is connected to an external ammonia settling unit, the liquid outlet of the gas-liquid separator 4 is connected to the inlet of the reflux tank 5, and a reflux pump 6 is provided at the outlet of the reflux tank 5. The outlet of the reflux pump 6 is connected to the reflux port of the stripping tower 2 through a reflux pipe 10.

[0038] The difference from the existing structure is that the end of the condensate pipe near the stripping tower 2 is connected to the corrosion control agent tank 1. A material valve for controlling the discharge of the corrosion control agent tank 1 should be provided at the connection between the condensate pipe and the corrosion control agent tank 1. The corrosion control agent tank 1 is filled with polysulfides. Polysulfides are added to the condensate pipe through the corrosion control agent tank 1 to control the cyanide ion content in the condensate.

[0039] A sampling port 8 is provided between the reflux tank 5 and the reflux pump 6 to facilitate the testing of the circulating condensate. By taking samples through the sampling port 8, the content of cyanide ions in the reflux condensate can be monitored.

[0040] A guide pipe 9 is directly connected to the inlet end of the condensate pipe and the outlet end of the return pipe 10. The guide pipe 9 has a unidirectional flow effect, guiding only a portion of the condensate from the return pipe 10 to the inlet of the stripping tower 2. By guiding this portion of the condensate to the inlet of the stripping tower 2, the heat from the feed height of the stripping tower 2 decomposes the ammonium carbamate in the condensate, further controlling the corrosion of the stripping unit caused by the condensate during the stripping process.

[0041] The drain pipe 9 is equipped with a shut-off valve 7 to control the flow status of the drain pipe 9. The shut-off valve 7 is designed to facilitate the shut-off and material discharge when the stripping unit is under low load or during the shutdown of the stripping unit.

[0042] Example 3

[0043] This embodiment is based on field test data from the stripping device in Embodiment 2.

[0044] The process employs a dual-tower stripping system with 304L stainless steel. The cyanide ion content in the on-site material is 180 μg / g. By continuously injecting polysulfides into the condensate and monitoring the corrosion rate of ammonium carbamate under different cyanide ion contents, the system can effectively address the corrosion problem.

[0045]

[0046] The table above shows the relationship between control indicators and material corrosion rates.

[0047] The comprehensive corrosion evaluation method in the embodiments was evaluated in accordance with HG / T 20580-2020.

[0048]

[0049] The table above shows the comparison between overall corrosion rate and corrosion allowance in the HG / T 20580-2020 standard.

[0050] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A corrosion control method for the top reflux system of a shift converter condensate stripping tower, characterized in that, Includes the following steps: 1) Establish a cyanide ion control index for the condensate to be returned to the top of the ammonia stripping tower (2-2), and monitor the cyanide ion content in the subsequent reflux condensate; 2) When the cyanide ion content exceeds the control index, polysulfides are injected into the condensate to be stripped to reduce the cyanide ion content, thereby preventing cyanide ions from aggravating the corrosion intensity of ammonium carbamate. 3) A portion of the condensate to be returned to the top of the ammonia stripping tower (2-2) is transported to the feed inlet of the acid stripping tower (2-1) to decompose the ammonium carbamate in the condensate under high temperature conditions, thus preventing the accumulation of corrosive substances returning to the top of the ammonia stripping tower (2-2).

2. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 1, characterized in that: The cyanide ion content in step 1) is ≤40μg / g.

3. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 2, characterized in that: The cyanide ion content in step 1) is 20 μg / g.

4. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 1, characterized in that... A sampling port (8) for detecting cyanide ions is set on the pipeline path through which the condensate is circulated back to the top of the ammonia stripping tower (2-2).

5. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 1, characterized in that: The polysulfide injection point is located at the condensate feed pipe of the acid stripping tower (2-1).

6. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 1, characterized in that: A guide pipe (9) is installed on the reflux pipe (10) at the top of the ammonia stripping tower (2-2) where the condensate is circulated back to the tower. The guide pipe (9) is used to transport part of the condensate in the reflux pipe (10) to the feed inlet of the acid stripping tower (2-1).

7. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 1, characterized in that: The polysulfide injection method is nozzle spraying.

8. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 1, characterized in that: The polysulfide is sodium polysulfide or ammonium polysulfide.

9. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 1, characterized in that: The polysulfides are sodium polysulfide and ammonium polysulfide.

10. The corrosion control method for the top reflux system of a shift converter condensate stripping tower according to claim 1, characterized in that: The polysulfide has a pH greater than 7.

5.

11. A top reflux device for a shift converter condensate stripping tower, characterized in that: The system includes an acid stripping tower (2-1), an ammonia stripping tower (2-2), a heat exchanger (3), a gas-liquid separator (4), a reflux tank (5), and a reflux pump (6). The inlet of the acid stripping tower (2-1) is connected to a condensate pipe for conveying condensate, the outlet of the acid stripping tower (2-1) is connected to an external sulfur recovery device, the outlet of the acid stripping tower (2-1) is connected to the inlet of the ammonia stripping tower (2-2), the outlet of the ammonia stripping tower (2-2) is connected to the inlet of the heat exchanger (3), the outlet of the heat exchanger (3) is connected to the inlet of the gas-liquid separator (4), and the gas outlet of the gas-liquid separator (4) is connected to an external ammonia stripping device. The settling unit is connected, the liquid outlet of the gas-liquid separator (4) is connected to the inlet of the reflux tank (5), the outlet end of the reflux tank (5) is equipped with a reflux pump (6), the outlet end of the reflux pump (6) is connected to the reflux port of the deammoniation stripping tower (2-2) through the reflux pipe (10), the end of the condensate pipe near the acid stripping tower (2-1) is connected to a corrosion control agent tank (1), the corrosion control agent tank (1) is filled with polysulfides, a sampling port (8) is provided between the reflux tank (5) and the reflux pump (6) to facilitate the detection of circulating condensate, and a drain pipe (9) is directly provided between the inlet end of the condensate pipe and the outlet end of the reflux pipe (10) for connection.

12. A top reflux device for a shift converter condensate stripping tower according to claim 11, characterized in that: The drainage tube (9) is equipped with a shut-off valve (7) to control the flow state of the drainage tube (9).

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