A process and apparatus for stripping of a transformed condensate

Abstract

The application discloses a transformation condensate stripping process and a device thereof, and the process comprises extracting ammonia gas in the condensate by using a stripping tower, and injecting polysulfide into the condensate before the condensate enters the stripping tower, and the polysulfide is used for consuming the content of cyanide ions in the condensate. By adding the polysulfide into the condensate, the content of cyanide ions in the condensate is consumed by the polysulfide, the reduction of the cyanide ions can slow down the corrosion efficiency of the ammonium carbamate, the corrosion of the condensate to the stripping device in the stripping process is reduced, the effective control of the corrosion is realized from the root, the risk of unplanned shutdown and the subsequent inspection and maintenance cost are reduced, and the operation cycle of the condensate stripping system is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, specifically to a conversion condensate stripping process and its apparatus. 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, the inventors' research has shown that the condensate generates ammonium carbamate (also known as methylamine, NH4COONH2) during the circulating condensation process in the stripping system. This carbamate can cause severe corrosion to metallic materials. Furthermore, cyanide ions (CN-2) are present during the condensate stripping process. － Cyanide ions can enhance the corrosion efficiency of ammonium carbamate. Therefore, as corrosive substances accumulate, they can cause severe corrosion in the entire condensate stripping system, gradually becoming a bottleneck affecting the long-term operation of the unit. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems and deficiencies by providing a condensate stripping process and apparatus, which can greatly reduce the corrosion of the stripping device caused by the condensate during the stripping process.

[0005] To address the shortcomings of the aforementioned technical problems, the present invention employs the following technical solution: a condensate stripping process that utilizes a stripping tower to extract ammonia from the condensate. Before the condensate enters the stripping tower, polysulfides are injected into the condensate to consume the cyanide ion content in the condensate.

[0006] As a further optimization of the condensate stripping process of the present invention, a sampling port is set on the path of the condensate circulation reflux. The cyanide ion content in the reflux condensate is monitored by sampling through the sampling port. If the content exceeds the standard, polysulfides are added to the condensate to be introduced into the stripping tower.

[0007] As a further optimization of the condensate stripping process of the present invention, a guide pipe is installed on the reflux pipe of the condensate circulating back to the stripping tower, and part of the condensate in the reflux pipe is guided to the inlet of the stripping tower, so as to decompose the ammonium carbamate in the condensate by utilizing the heat of the feed height of the stripping tower.

[0008] As a further optimization of the condensate stripping process of the present invention, the polysulfide injection location is the condensate feed point of the stripping tower.

[0009] As a further optimization of the condensate stripping process of the present invention, the polysulfide is sodium polysulfide or ammonium polysulfide.

[0010] As a further optimization of the condensate stripping process of the present invention, the polysulfides are sodium polysulfide and ammonium polysulfide.

[0011] As a further optimization of the condensate stripping process of the present invention, the pH of the polysulfide is greater than 7.5.

[0012] As a further optimization of the condensate stripping process of the present invention, the content of cyanide ions is controlled to be ≤40μg / g.

[0013] As a further optimization of the condensate stripping process of the present invention, the cyanide ion content is controlled at 20 μg / g.

[0014] As a further optimization of the condensate stripping process of the present invention, the polysulfide injection method is nozzle injection.

[0015] A condensate stripping device includes a stripping tower, a heat exchanger, a gas-liquid separator, a reflux tank, and a reflux pump. The liquid inlet of the stripping tower is connected to a condensate pipe for conveying condensate. The gas outlet of the 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. The gas outlet of the gas-liquid separator is connected to an external sulfur recovery unit. The liquid outlet of the gas-liquid separator is connected to the inlet of the reflux tank. A reflux pump is installed 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. 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.

[0016] As a further optimization of the condensate stripping device of the present invention, a sampling port for easy detection of circulating condensate is provided between the reflux tank and the reflux pump.

[0017] As a further optimization of the condensate stripping device of the present invention, the inlet end of the condensate pipe and the outlet end of the return pipe are directly provided with a drain pipe for connection.

[0018] As a further optimization of the condensate stripping device of the present invention, the guide pipe is provided with a shut-off valve to control the flow state of the guide pipe.

[0019] The present invention has the following beneficial effects:

[0020] I. This invention adds polysulfides to the condensate, thereby consuming the cyanide ion content in the condensate. The reduction of cyanide ions can slow down the corrosion efficiency of ammonium carbamate, reduce the corrosion of the stripping unit caused by the condensate during the stripping process, achieve effective corrosion control from the root, reduce the risk of unplanned downtime and subsequent maintenance costs, and effectively extend the operating cycle of the condensate stripping system.

[0021] Second, in a further optimization of the present invention, a guide pipe is provided on the condensate circulation return pipe. The condensate in the return pipe is led out to the feed position of the stripping tower through the guide pipe. The hot gas of the stripping tower is used to decompose the ammonium carbamate in the condensate, thereby further reducing the corrosion of the stripping device caused by the condensate during the stripping process. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the stripping process in Example 1;

[0023] Attached reference numerals: 1. Corrosion control agent tank, 2. 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 conversion condensate stripping process, which can greatly reduce the corrosion of the stripping device during the condensate stripping process while using the stripping tower (2) to extract ammonia from the condensate.

[0027] According to the inventors' research, the condensate will produce ammonium carbamate (also known as methylamine, NH4COONH2) during the cyclic condensation process of the stripping system. Ammonium carbamate can cause severe corrosion to metal materials. At the same time, cyanide ions will be present during the stripping process of the condensate. Cyanide ions can increase the corrosion efficiency of ammonium carbamate. Therefore, in order to reduce the corrosion of the stripping device by the condensate during the stripping process, it is necessary to control the content of cyanide ions or ammonium carbamate.

[0028] Therefore, before the condensate enters the stripping tower 2, polysulfides need to be injected into the condensate to consume it, reduce the content of cyanide ions in the condensate, avoid cyanide ions from aggravating the corrosion efficiency of ammonium carbamate, and reduce the severe corrosion of the stripping unit caused by the condensate during the circulating stripping process.

[0029] In this process, the polysulfide is injected at the condensate feed inlet of stripping tower 2, and the injected polysulfide is one or more of sodium polysulfide and ammonium polysulfide. Simultaneously, the pH of the polysulfide injected into the condensate should be greater than 7.5, because a pH value below 7.5 will cause the polysulfides to decompose. Oxygen can decompose polysulfides, generating elemental sulfur and other corrosion products, and may even block pipelines.

[0030] In the process, the polysulfide injection method is nozzle spraying, which allows the polysulfides to mix more evenly with the condensate.

[0031] Meanwhile, in order to ensure that the cyanide ion content in the circulating condensate remains at a low level, sampling port 8 is set up on the path of the condensate circulation return. Sampling is carried out through sampling port 8 to monitor the cyanide ion content in the return condensate. If the content exceeds the standard, polysulfides are added to the condensate that is about to enter the stripping tower 2, thereby controlling the cyanide ion content in the circulating condensate to remain at a low level and reducing the corrosion of the stripping unit caused by the condensate during the stripping process.

[0032] In this process, the cyanide ion content is 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] Meanwhile, in order to eliminate the corrosive factor ammonium carbamate, a guide pipe 9 is installed on the reflux pipe 10 where the condensate is circulated back to the stripper 2. Part of the condensate in the reflux pipe 10 is guided to the inlet of the stripper 2. The heat from the feed height of the stripper 2 is used to decompose the ammonium carbamate in the condensate, further reducing the corrosion of the stripping unit caused by the condensate during the stripping process.

[0034] In the above process, the diversion pipe 9 only guides a portion of the condensate in the return pipe 10 to the inlet of the stripping tower 2. In this way, some condensate will flow back into the stripping tower 2, which prevents the temperature at the top outlet of the stripping tower 2 from rising and affecting the stripping separation effect. At the same time, the diversion pipe 9 only has a unidirectional flow effect, and the diversion pipe 9 can only guide a portion of the condensate in the return pipe 10 to the inlet of the stripping tower 2.

[0035] Example 2

[0036] This embodiment is a condensate stripping device designed according to Example 1. The stripping device extracts ammonia from the condensate while controlling and greatly reducing the corrosion of the stripping device during the condensate stripping process.

[0037] The existing structure of the stripping device provided in this embodiment includes a stripping tower 2, a heat exchanger 3, a gas-liquid separator 4, a reflux tank 5, and a reflux pump 6. The liquid inlet of the stripping tower 2 is connected to the condensate pipe that transports condensate, the gas outlet of the stripping tower 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 sulfur recovery 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 introduced into the condensate pipe through the corrosion control agent tank 1 to reduce 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 in the return pipe 10 to the inlet of the stripping tower 2. By guiding a portion of the condensate in the return pipe 10 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 reducing 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] A single-tower stripping process with full reflux was adopted. The equipment was made of 304L stainless steel. The cyanide ion content in the material on site was 210μg / g. Polysulfides were continuously injected into the condensate, and the corrosion rate of ammonium carbamate was monitored under different cyanide ion contents.

[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] The 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 process for stripping condensate, wherein ammonia is extracted from condensate using a stripping tower (2), characterized in that: Before the condensate enters the stripper (2), polysulfides are injected into the condensate to consume the cyanide ion content in the condensate. A guide pipe (9) is installed on the reflux pipe (10) through which the condensate is circulated back to the stripper (2) to guide part of the condensate in the reflux pipe (10) to the inlet of the stripper (2) and use the heat of the feed height of the stripper (2) to decompose the ammonium carbamate in the condensate.

2. The shift condensate stripping process according to claim 1, characterized in that: A sampling port (8) is set up on the path of the reflux of the condensate. The cyanide ion content in the reflux condensate is monitored by sampling through the sampling port (8). If the content exceeds the standard, polysulfides are added to the condensate to be introduced into the stripping tower (2).

3. The shift condensate stripping process according to claim 1, characterized in that: The polysulfide injection point is the condensate feed point of the stripping tower (2).

4. The shift condensate stripping process according to claim 1, characterized in that: The polysulfide is sodium polysulfide or ammonium polysulfide.

5. The shift condensate stripping process according to claim 1, characterized in that: The polysulfides are sodium polysulfide and ammonium polysulfide.

6. The shift condensate stripping process according to claim 1, characterized in that: The polysulfide has a pH greater than 7.

5.

7. The shift condensate stripping process according to claim 1, characterized in that: The controlled content of cyanide ions is ≤40 μg / g.

8. The shift condensate stripping process according to claim 7, characterized in that: The controlled content of cyanide ions is 20 μg / g.

9. The shift condensate stripping process according to claim 1, characterized in that: The polysulfide injection method is nozzle spraying.

10. A condensate stripping device, comprising a stripping tower (2), a heat exchanger (3), a gas-liquid separator (4), a reflux tank (5), and a reflux pump (6), wherein the inlet of the stripping tower (2) is connected to a condensate pipe for conveying condensate, the outlet of the stripping tower (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 sulfur recovery 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) being connected to the reflux port of the stripping tower (2) via a reflux pipe (10), characterized in that: The end of the condensate pipe near the stripping tower (2) is connected to a corrosion control agent tank (1), which is filled with polysulfides. The inlet end of the condensate pipe and the outlet end of the return pipe (10) are directly connected by a drain pipe (9).

11. A shift condensate stripping apparatus according to claim 10, characterized in that: A sampling port (8) is provided between the reflux tank (5) and the reflux pump (6) to facilitate the detection of circulating condensate.

12. A shift condensate stripping apparatus according to claim 10, 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).

Images