An auxiliary water circulation system for natural gas to acetylene

Abstract

The present application relates to the technical field of natural gas acetylene production, in particular to an auxiliary water circulation system for natural gas acetylene production, comprising a cracking device and a concentration device connected in sequence, and the cracking device and the concentration device are respectively connected with a first cooling tower and a second cooling tower. The present application can solve the problem of high COD content after the existing carbon black water is discharged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas acetylene production, in particular to an auxiliary water circulation system for natural gas acetylene production. BACKGROUND

[0002] The process technology of natural gas partial oxidation acetylene production is one of the important technologies of natural gas chemical industry. The process is as follows: natural gas and oxygen are added to the acetylene furnace, and the methane in the natural gas is cracked to generate acetylene in the acetylene furnace at 1500℃. In the high-temperature environment, acetylene is further decomposed to produce carbon black. In order to reduce the generation of carbon black and other by-products, a large amount of cooling water is used to quench the cracked gas instantaneously to terminate the reaction. In this process, carbon black is mixed into the quenching water to form carbon black water. Then, the dilute acetylene generated by the cracking reaction is absorbed and desorbed several times using N-methyl pyrrolidone (NMP) as a solvent to obtain acetylene product.

[0003] Among them, the quenching water used in cracking and the cooling water used in concentration are collected and treated, and then reused as circulating water (this circulating water is commonly known as carbon black water). At present, for the treatment of carbon black water, the carbon black water treatment device is improved or increased, such as the Chinese patent documents with publication numbers CN214010069U and CN113041674A. However, in the actual use process, there are still the following technical problems: a large amount of carbon black water is needed in the process of natural gas acetylene production, and due to different process conditions, some solid impurities (such as carbon black particles) or by-products such as diphenylacetylene, vinylacetylene and other unsaturated hydrocarbons and aromatic compounds produced in the acetylene production process are entrained after the carbon black water enters different devices. The removal of different by-products and impurities is inconsistent, so the COD content of the waste water discharged after the carbon black water produced in the existing natural gas acetylene production technology is treated is relatively high, which is 200-400ppm, and cannot meet the higher environmental protection requirements. SUMMARY

[0004] The present application aims to provide an auxiliary water circulation system for natural gas acetylene production to solve the problem of high COD content after the existing carbon black water is discharged.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] An auxiliary water circulation system for natural gas acetylene production, comprising a cracking device and a concentration device connected in sequence, and the cracking device and the concentration device are respectively connected with a first cooling tower and a second cooling tower.

[0007] The inventor found in actual use that the carbon black water generated in the cracking device mainly contains part of carbon black particles, which is relatively easy to handle, and the COD (commonly used to indicate water pollution) of the discharged wastewater after treatment is low, only 50-100 ppm; while the carbon black water used for spray cooling in the concentration device has a high COD of 1000-2000 ppm of the discharged wastewater; after analysis, it is found that it is due to the direct contact of the carbon black water and the NMP solvent vapor entrained in the process gas, which inevitably leads to the entry of organic solvents into the water circulation, thereby polluting the water quality; and this part of the carbon black water and the carbon black water of the cracking device are usually cooled in the same cooling tower, which leads to mutual pollution of the two parts of water, increases the treatment amount of NMP and other organic solvents in the production system, thereby increasing the treatment difficulty and cost, and the COD content of the finally discharged wastewater can only reach 200-400 ppm.

[0008] Therefore, after research, the inventor changes part of the water circulation system in the natural gas acetylene process, and the carbon black water in the cracking device and the concentration device is treated and collected separately, which has the following beneficial effects:

[0009] 1. By using different cooling towers to cool the backwater and water supply system of the carbon black water in the cracking device and the concentration device, mutual pollution of the carbon black water in the two systems can be avoided, the purpose of separate treatment of the carbon black water generated by the two systems is achieved, the total amount of wastewater containing NMP organic solvent pollutants is reduced, the wastewater treatment difficulty and cost are reduced, and the increasingly stringent environmental protection emission requirements can be met.

[0010] 2. The temperature inconsistency of the carbon black water required to be circulated by the cracking device and the concentration device can be solved; in the process of using natural gas to produce acetylene, it is required that the temperature of the carbon black water entering the concentration device is stably controlled at 30-40℃; but in actual use, the recycled carbon black water in the cracking device is mainly used for rapid quenching of cracked gas, and the temperature of natural gas when cracking acetylene in the cracking device is as high as 1500℃, therefore, separate water circulation treatment of the carbon black water of the cracking device and the concentration device can increase the temperature of the quenching water used in the cracking device from 30-40℃ to 40-50℃, which does not affect the cooling of the cracked gas, and creates conditions for waste heat recovery of the carbon black water.

[0011] 3. By separating the carbon black water in the concentration device and the cracking device for cooling, the temperature of the carbon black water in the concentration device can be more easily and stably controlled at 30-40℃; especially in the extreme high temperature working condition in summer, the cooling effect of the cooling tower is insufficient, and the optimal control temperature of 30-40℃ cannot be reached, which leads to too high water temperature affecting the stable operation of the concentration device, and further affecting the acetylene product quality.

[0012] 4. The quenching water with higher temperature is supplied to the cracking device, and according to the operation data analysis, the cracking device can also increase the acetylene yield by about 0.1-0.2%.

[0013] Further, the cracking device and the concentration device are at least two groups, all the cracking devices are communicated with the first cooling tower, and all the concentration devices are communicated with the second cooling tower.

[0014] The multiple groups of cracking devices and concentration devices are arranged, the production line is conveniently expanded, the carbon black water used by the two groups of cracking devices and the two groups of concentration devices is cooled in two different cooling towers, the mutual pollution of the carbon black water used in different processes of the two production lines can be avoided, and the requirements of different temperature carbon black water for the cracking device and the concentration device can be simultaneously met.

[0015] Further, the first cooling tower and the second cooling tower are both hyperbolic cooling towers; the cooling tower is powered by the chimney effect, so that power is not needed, the purpose of saving power is achieved, and the cost of cables, power distribution cabinets, control cabinets and the like required for controlling the electric fan is saved.

[0016] Further, the first overflow pipe is arranged on the tower wall of the first cooling tower and communicated with the first cooling tower, and the second overflow pipe is arranged on the tower wall of the second cooling tower and communicated with the second cooling tower.

[0017] The carbon black water from the cracking device and the concentration device enters the cooling tower for cooling, but a small part of the carbon black in the carbon black water entering the cooling tower still floats in the cooling water, and the overflow pipe arranged on the cooling tower can ensure that the carbon black flows out from the overflow pipe.

[0018] Further, the carbon black separation device is arranged between the cracking device and the first cooling tower.

[0019] The working principle of the carbon black water separation device is that a closed distributed large-capacity water tank is used to reduce the water flow rate for static placement, so that the carbon black floats in the water, and then a continuous automatic scraping device is used to remove the carbon black, so that the purpose of carbon black separation is achieved.

[0020] Further, the water outlet end of the first overflow pipe is connected with the pollution cleaning device.

[0021] The pollution cleaning device is a cyclone pollution removal equipment, which is mainly used for removing the carbon black suspended pollutants in the first cooling tower, so that the COD of the waste water discharged from the pollution cleaning device is reduced.

[0022] Further, the water outlet end of the second overflow pipe is connected with the rectification device.

[0023] The rectification device is mainly used for removing the organic pollutants with high COD concentration overflowing from the second cooling tower, further treating the waste water, so that the COD of the waste water after discharge is reduced and meets the discharge standard. Attached Figure Description

[0024] Figure 1 This is a flowchart of the auxiliary water circulation system of the present invention. Detailed Implementation

[0025] The following detailed description illustrates the specific implementation method:

[0026] Example 1

[0027] An auxiliary water circulation system for acetylene production from natural gas includes a cracking unit, an enrichment unit, and a cooling tower. The outlet of the cracking unit is connected to the inlet of the enrichment unit, so that the cracked gas generated in the cracking unit enters the enrichment unit for cooling and enrichment. In this embodiment, there are two cracking units, two enrichment units, and two cooling towers. Specifically, the cooling towers are hyperbolic cooling towers, including a first hyperbolic cooling tower E380A and a second hyperbolic cooling tower E380B (hereinafter referred to as the first cooling tower and the second cooling tower). The cracking unit includes cracking unit A and cracking unit B. The outlets of cracking unit A and cracking unit B are both connected to the inlet of the first cooling tower. The outlet of the first cooling tower is connected to the inlet of cracking unit A and cracking unit B. The inlet of pyrolysis unit B is connected to supply cooling carbon black water to pyrolysis units A and B; the concentration unit includes concentration unit A and concentration unit B, the outlets of both concentration unit A and concentration unit B are connected to the inlet of the second cooling tower, and the outlet of the second cooling tower is connected to the inlet of concentration unit A and concentration unit B, for supplying cooling carbon black water to concentration unit A and concentration unit B; a first overflow pipe is provided on the wall of the first cooling tower, and the outlet end of the first overflow pipe is connected to a cleaning and purification device; a second overflow pipe is provided on the wall of the second cooling tower, and the outlet end of the second overflow pipe is connected to a distillation device; in this embodiment, all connections are made by pipelines.

[0028] A carbon black separation device is installed between the pyrolysis unit and the first cooling tower. The carbon black separation device includes a distributed large-capacity water tank and a continuous automatic scraping device. The carbon black water flowing out of the pyrolysis unit contains a large amount of carbon black. First, the water flow rate is reduced and the carbon black is allowed to settle in the closed-loop distributed large-capacity water tank, causing the carbon black to float to the surface. After the carbon black floats, it is removed by the continuous automatic scraping device, resulting in relatively clean carbon black water. Then, the carbon black water enters the first cooling tower for cooling treatment. The outlet of the first cooling tower is connected to the inlets of pyrolysis units A and B, so that the cooled carbon black water returns to pyrolysis units A and B for use as quenching water. The carbon black wastewater overflowing from the first overflow pipe enters the cleaning and purification device, which is a cyclone separator. It is mainly used to remove suspended pollutants from the carbon black in the first cooling tower, thereby reducing the COD of the wastewater discharged from the cleaning and purification device.

[0029] The carbon black water flowing out of the water outlets of the concentration devices A and B is raised in temperature after once spray heat exchange, needs to be cooled in the second cooling tower, and then is recycled to the concentration devices A and B as cooling water. Since the carbon black water carries organic solvents, it cannot be directly discharged after use, and is mainly flowed into the rectification device through the second overflow pipe. The organic pollutants with high concentration of COD are removed in the rectification device, so that the discharged wastewater is further treated, and the COD of the discharged wastewater is reduced to meet the discharge standard. The carbon black water in the cracking device and the concentration device is collected and treated separately in the present application. The carbon black water generated by the two devices can be prevented from polluting each other, and the temperature requirements of the carbon black water in different devices are met. In summary, the present application has more beneficial effects compared with the prior art.

[0030] Comparative Example 1

[0031] The difference from Example 1 is that the cracking device and the concentration device share one cooling tower. Specifically, the cracking gas generated by the cracking device enters the concentration device through a pipeline, and the carbon black water used by the cracking device and the concentration device all enters one cooling tower for cooling treatment. After cooling, it is reused. An overflow pipe is arranged on the cooling tower, and a sewage purification device for treating mixed sewage is arranged at the water outlet of the overflow pipe.

[0032] Table 1- The auxiliary water for natural gas acetylene production is treated by using the mode of Example 1 and Comparative Example 1 respectively, and the obtained wastewater discharge COD, carbon black water outlet temperature, acetylene yield, acetylene product purity and other parameters are shown in the following table:

[0033]

[0034] From Table 1, it can be seen that:

[0035] 1. The carbon black water in the cracking device and the concentration device is collected and treated separately in the present application. The COD of the finally discharged wastewater is reduced from 200-400 ppm to 50-100 ppm, which meets the increasingly stringent environmental protection discharge requirements.

[0036] 2. The contradiction that the temperature of the recycled carbon black water required by the cracking device and the concentration device is inconsistent is solved. The temperature of the quenching water can be increased from 30-40℃ to 40-50℃ by adjusting the first cooling tower, so that the cooling of the cracking gas is not affected, and the conditions for waste heat recovery of the carbon black water are created. At the same time, the quenching water with higher temperature is supplied to the cracking device. According to the operation data analysis, the acetylene yield of a single cracking device can be increased by about 0.1-0.2%.

[0037] 3、The carbon black water from the cracking device and the enrichment device into the cooling tower in the prior art has a certain temperature difference itself, so when the cooling treatment is carried out in the cooling tower, especially in the extremely high temperature working condition in summer, the cooling effect of the cooling tower is insufficient, and the optimal control temperature of 30-40℃ cannot be reached, which leads to the water temperature being too high to affect the stable operation of the enrichment device, and further affects the quality of the acetylene product; by separately collecting and treating the carbon black water of the enrichment device, there is no temperature difference when cooling, and the temperature of the carbon black water out of the second cooling tower can be more easily maintained at 30-40℃, so that the enrichment device is stably operated, and the purity of the acetylene product is improved to 98.75% to 99.10%.

[0038] The above is only an embodiment of the present application, and common technical solutions and / or characteristics in the scheme are not described in detail. It should be noted that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the present application. The protection scope of the present application should be subject to the content of its claims, and the specific implementation mode and the like in the specification can be used to explain the content of the claims.

Claims

1. An auxiliary water circulation system for acetylene production from natural gas, comprising a cracking unit and a concentration unit connected in sequence, characterized in that, The pyrolysis unit and the concentration unit are respectively connected to a first cooling tower and a second cooling tower; The outlet of the pyrolysis unit is connected to the inlet of the first cooling tower, and the outlet of the first cooling tower is connected to the inlet of the pyrolysis unit. The first cooling tower is used to supply cooling carbon black water to the pyrolysis unit. The outlet of the concentration unit is connected to the inlet of the second cooling tower, and the outlet of the second cooling tower is connected to the inlet of the concentration unit. The second cooling tower is used to supply cooling carbon black water to the concentration unit. The first cooling tower is equipped with a first overflow pipe connected to it on its tower wall, and the second cooling tower is equipped with a second overflow pipe connected to it on its tower wall; the outlet end of the first overflow pipe is connected to a cleaning and purification device. A carbon black separation device is installed between the pyrolysis unit and the first cooling tower; a distillation device is connected to the outlet of the second overflow pipe.

2. The auxiliary water circulation system for acetylene production from natural gas according to claim 1, characterized in that: The pyrolysis unit and the concentration unit are at least two sets, all of which are connected to the first cooling tower and all of which are connected to the second cooling tower.

3. An auxiliary water circulation system for acetylene production from natural gas according to claim 2, characterized in that: Both the first and second cooling towers are hyperbolic cooling towers.

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