Gas-liquid separation process for hydrogenation reaction product
Technical Field
The invention belongs to the technical field of petrochemical hydrogenation processes, and relates to a gas-liquid separation process method for hydrogenation reaction products, in particular to a gas-liquid separation process of a high-pressure hydrogenation reaction device.
Technical Field
With the global heavy and inferior crude oil, the deep refining and cleaning of petroleum products and the fine development of downstream chemical industry, the petroleum processing technology is from simple to complex, from thermal processing to catalytic processing, from single technology to coexistence of multiple technologies, from extensive to environment-friendly, and has made a leap forward. Among them, as the most important means for producing clean traffic fuels and environment-friendly oil products, an effective way for converting residual oil and heavy and poor crude oil into products with high added values, a main method for improving the service performance or processing performance of oil products or oil materials, a leading process for combining oiling and producing chemical raw materials, and a catalytic hydrogenation technology are developed most rapidly. Since the last 90 s, the construction of hydrogenation units and the development of hydrogenation technology are accelerated in all countries of the world, and the processing capacity of catalytic hydrogenation in the global oil refining industry reaches more than 57% of the primary processing capacity of crude oil and is far higher than the secondary processing capacity of any other crude oil.
According to different properties of raw materials and product requirements, petrochemical enterprises are respectively provided with various hydrogenation process devices of different types such as naphtha hydrogenation, aviation kerosene hydrogenation, gasoline refining (including S Zorb), diesel oil hydrogenation, wax oil hydrogenation, residual oil hydrogenation, lubricating oil hydrogenation, hydroisomerization, pour point depression and the like on the arrangement of a production total processing flow from crude oil distillation to delivery of various qualified products. The flow of the hydrogenation process unit is basically not very different and mainly comprises a reaction part and a separation part. The reaction part is divided into fixed bed hydrogenation, boiling bed hydrogenation, slurry bed hydrogenation and moving bed hydrogenation according to the state of a reactor bed catalyst; according to the reaction pressure, the method is divided into high-pressure hydrogenation, medium-pressure hydrogenation and low-pressure hydrogenation. Generally, as the hydrogenated feedstock oil becomes heavier in nature, the pressure presentation required by the hydrogenation unit increases; at the same time, the hydrogen partial pressure required is also increased in order to ensure the catalyst activator and the plant cycle. Such as residual oil hydrogenation, hydrocracking, wax oil hydrogenation and lubricating oil hydrogenation for producing high-quality base oil, generally require higher reaction pressure (12.0-20.0 MPa). The separation part generally comprises a gas-liquid separator, a stripping tower, a fractionating tower and auxiliary equipment parts such as heat exchange, pressure boosting and the like. The hydrogenation reaction product is a multi-component gas-liquid mixture, and enters a separation part after coming out of the reaction part to obtain various target products.
In the existing gas-liquid separation system for hydrogenation reaction products, the reaction products with high temperature and high pressure enter a heat high-pressure separator after heat exchange. The liquid phase of the hot high-pressure separator after gas-liquid separation is decompressed and then enters a hot low-pressure separator, and the gas phase of the hot high-pressure separator enters a cold high-pressure separator after heat exchange and cooling. And the gas phase of the cold high-pressure separator enters a circulating hydrogen system after desulfurization treatment, and the liquid phase of the gas phase is mixed with the gas phase of the gas-liquid separation of the hot low-pressure separator and enters the cold low-pressure separator. The gas phase of the cold low-pressure separator is the low-pressure gas, and the gas phase can be used as a hydrogen-rich gas dehydrogenation gas recovery unit after desulfurization treatment. And the liquid phase of the cold low-pressure separator and the liquid phase of the hot low-pressure separator enter a stripping tower respectively after heat exchange. The gas-liquid separation process is based on the characteristics of large heat release and high temperature of hydrogenation products in the hydrogenation process, and aims to balance the energy of a hydrogenation reaction part and a separation part, and from the aspect of energy recycling, a liquid phase at a high temperature position is sent to a fractionation unit which needs a large amount of heat to carry out hydrogen sulfide removal and distillation cutting, so that the aim of reducing the overall energy consumption of a hydrogenation device is fulfilled.
USP4,159,937 proposes a separation method of hydrocracking products, which is a method of separating and fractionating various hydrocracking products by adopting a multi-stage separation of a hydrocracking gas-liquid mixture. Firstly, the hydrocracking product enters a hot high-pressure separator, gas-liquid separation is carried out at high temperature and high pressure, wherein the liquid phase enters a low-pressure hot flash tank for flash evaporation, and two products of gas and liquid are obtained. And the gas phase of the hot high-pressure separator enters a cold high-pressure separator after being condensed to separate hydrogen-rich gas. The hot low-pressure gas is condensed and then enters a flash tank together with the liquid phase from the cold high-pressure separator, and is separated at a lower pressure.
For more deeply carrying out energy comprehensive utilization and energy conservation, CN100510021C proposes a separation flow of hydrogenation reaction effluent. The effluent of the hydrogenation reaction enters a hot high-pressure separator, the separated gas phase enters a medium-temperature high-pressure separator after being cooled, the gas phase separated from the medium-temperature high-pressure separator enters a cold high-pressure separator after being cooled, and the gas phase separated from the cold high-pressure separator is used as circulating hydrogen. And a heat exchange tower is arranged, liquid phases separated by the hot high-pressure separator, the medium-temperature high-pressure separator and the cold high-pressure separator respectively enter the lower part, the middle part and the upper part of the heat exchange tower, the liquid phase of the heat exchange tower is sent to a stripping tower for treatment, and the gas phase of the heat exchange tower is cooled and then enters a gas-liquid separator for separation. The existing gas-liquid separation process only starts from the aspects of energy balance and comprehensive utilization, and heat exchange equipment is required to be arranged to recover heat with different temperature levels.
Hydrogen, however, differs from light hydrocarbons in that its solubility in hydrocarbons increases with increasing temperature at constant pressure, particularly at higher pressures. Thus, while the prior art is advantageous in reducing the energy usage of the plant, the thermal high pressure separation arrangement greatly increases the solubility of hydrogen in hydrocarbons. For refineries processing heavy crude oil and achieving high product yields, hydrogen consumption can reach at most 290 normal cubic meters per ton of crude oil. Typical hydrogen production costs from coal to natural gas are 10,000-20,000 yuan/ton. Hydrogen has become the second largest source of cost next to the cost of crude oil in refinery feedstock costs. Therefore, reducing the cost of hydrogen has become an important issue for the daily management of refining enterprises.
Disclosure of Invention
Aiming at the technical defects in the prior art and the urgent need of reducing the hydrogen cost, the invention provides a gas-liquid separation process for a high-pressure hydrogenation reactant, which can effectively reduce the hydrogen cost of enterprises and improve the hydrogen utilization rate.
The gas-liquid separation process of the high-pressure hydrogenation reaction product comprises the following steps:
(1) the high-temperature and high-pressure hydrogenation reaction product enters a hot high-pressure separator after heat exchange;
(2) the gas phase of the hot high-pressure separator enters a cold high-pressure separator after heat exchange and cooling; the gas phase of the cold high-pressure separator enters a circulating hydrogen system after being subjected to desulfurization treatment; the liquid phase of the hot high-pressure separator is decompressed and then enters a hot medium-pressure separator, and the pressure of the hot medium-pressure separator is 5.0-12.0 MPa, preferably 7.0-9.0 MPa;
(3) the gas phase of the hot medium-pressure separator enters the cold medium-pressure separator together with the liquid phase of the cold high-pressure separator after heat exchange; the liquid phase of the hot medium-pressure separator is decompressed and then enters a hot low-pressure separator;
(4) the gas phase of the hot low-pressure separator enters the cold low-pressure separator together with the liquid phase of the cold medium-pressure separator after heat exchange, and the liquid phase of the hot low-pressure separator enters a stripping tower of the fractionation unit;
(5) the gas phase of the cold medium-pressure separator and the gas phase of the cold low-pressure separator are sent out together, and can be used as a hydrogen-rich gas dehydrogenation gas recovery unit after desulfurization treatment;
(6) the high-purity hydrogen recovered by the hydrogen recovery unit is returned to the inlet of the device supplementing hydrogen compressor, so that the demand of the device on the hydrogen of the public works is reduced, and the utilization efficiency of the hydrogen is improved.
In the invention, the pressure of the heat and high pressure separator in the step (1) is set to be 10.0-20.0 MPa, preferably 11.0-15.0 MPa according to the requirements of the type and property of the processing raw materials, the performance of the reaction catalyst and the like; the temperature is 180 ℃ to 380 ℃, preferably 200 ℃ to 300 ℃.
The concrete pressure setting in the step (2) considers the recovery of the pressure energy of the hydraulic turbine from the liquid phase of the hot high-pressure separator to the hot medium-pressure separator. The pressure of the hot high-pressure separator is generally 5-10 MPa, preferably 5-7 MPa higher than that of the hot medium-pressure separator.
And (4) setting the pressure of the hot and low pressure separator in the step (3) to be 0.8-2.5 MPa, preferably 1.2-2.0 MPa. The specific pressure setting mainly considers the pressure drop of the pipeline and equipment in the subsequent flow from the low-pressure separator to the stripping tower.
The pressure of the cold high pressure separator corresponds to the pressure of the hot high pressure separator, and there is only a pressure drop of the fluid through the piping and/or equipment. The temperature of the cold high-pressure separator is determined by the heat exchange process of the device and the desulfurization requirement of the recycle hydrogen.
The temperature of the hot medium-pressure separator is consistent with that of the hot high-pressure separator, and only a certain flash evaporation temperature drop exists.
The pressure of the cold intermediate pressure separator corresponds to the pressure of the hot intermediate pressure separator, and there is only a pressure drop of the fluid through the piping and/or equipment. The temperature of the cold medium pressure separator is determined by the heat exchange flow of the device and the requirements of the vortex tube.
The temperature of the hot low-pressure separator is consistent with that of the hot high-pressure separator and the hot medium-pressure separator, and only a certain flash evaporation temperature drop exists.
The pressure of the cold low pressure separator corresponds to the pressure of the hot low pressure separator, and there is only a pressure drop of the fluid through the piping and/or equipment. The temperature of the cold low-pressure separator is determined by the heat exchange process of the device and the oil-gas separation temperature.
The hydrogen recovery unit can be a PSA pressure swing absorption hydrogen purification process, or a membrane separation hydrogen purification process and a cryogenic separation process.
The process method is suitable for various hydrogenation processes, such as wax oil hydrogenation, residual oil hydrogenation, hydrocracking, catalytic diesel oil hydrogenation modification, lubricating oil hydrogenation, hydrogenation pour point depression and other process processes.
Other technologies such as heat exchange flow, high-pressure water injection, desulfurization and the like in the gas-liquid separation in the hydrogenation process are consistent with the conventional technologies. The invention adds a process of injecting desalted water before the processes of a hot medium-pressure separator, a hot low-pressure separator gas-phase pipeline and a heat extraction device.
Compared with the prior art, the separation process has the following beneficial effects:
1. the process method changes the outlet path with large amount of dissolved hydrogen in the flow of the hot high-pressure separator by arranging the medium-pressure separator, so that a large amount of dissolved hydrogen is discharged from the gas phase of the product separator, the content of the hydrogen in the gas phase of the separator is ensured, and the economic recovery of the hydrogen is facilitated. The invention can recycle hydrogen by utilizing the existing flow, thereby reducing the hydrogen cost of enterprises.
2. And a medium-pressure separator is arranged, so that a large amount of hydrogen is flashed from the medium-pressure separator, and the separation energy consumption and equipment investment of a fractionation unit of a hydrogenation device are reduced.
3. The process reduces the demand of the device on the hydrogen of the public works and improves the utilization efficiency of the hydrogen of the device. In a word, the process is scientific and reasonable, the device is less in modification, and the cost of hydrogen for the device can be greatly reduced.
Drawings
FIG. 1 is a schematic flow chart of the gas-liquid separation process of the hydrogenation reaction product of the present invention.
FIG. 2 is a flow chart of the principle of gas-liquid separation in the conventional hydrogenation process.
The main notations in FIGS. 1-2 illustrate: 1. hydrogenation reaction products; 2. a hot high pressure separator; 3. a cold high pressure separator; 4. a hot intermediate pressure separator; 5. a cold medium pressure separator; 6. a hot low pressure separator; 7. a cold low pressure separator; 8. a thermal high-pressure-distribution gas-phase water cooler; 9. a cold low oil separation heat exchanger; 10. stripping the overhead gas of the column; 11. stripping a top liquid phase, 12 and a bottom liquid phase; 13. a stripping column; 14. a hydrogen-rich gas; 15. cooling high-pressure gas; 16. cooling and separating oil; 17. hot low oil separation; 18. cooling and separating gas; 19. cool and divide the gas.
Detailed Description
As shown in fig. 1, the process flow of the gas-liquid separation process of the hydrogenation reaction product of the present invention is as follows:
the hydrogenation reaction product 1 after heat exchange enters a hot high-pressure separator 2 for gas-liquid separation, and the gas phase (called hot high-pressure gas for short) of the hot high-pressure separator 2 is further cooled in a hot high-pressure gas phase cooler 8 after heat exchange and cooling and then enters a cold high-pressure separator 3. And the gas-phase cold high-pressure gas 15 of the cold high-pressure separator is used as recycle hydrogen to enter a recycle hydrogen desulfurization and compression system. After being pressurized, the mixture returns to the reaction system for recycling.
The liquid phase (called thermal high-pressure oil for short) of the thermal high-pressure separator 2 is decompressed and then enters a thermal medium-pressure separator 4. The gas phase after gas-liquid separation in the hot medium-pressure separator 4 enters the cold medium-pressure separator 5 together with the liquid phase in the cold high-pressure separator 3 after heat exchange and cooling. The gas-phase cold medium-pressure gas 19 from the cold medium-pressure separator 5 is combined with the cold low-pressure gas 18 and sent to the hydrogen recovery unit as the hydrogen-rich gas 14.
The liquid phase after gas-liquid separation in the hot medium pressure separator 4 is decompressed and enters a hot low pressure separator 6. The gas phase of the hot low-pressure separator 6 enters the cold low-pressure separator 7 together with the liquid phase of the cold medium-pressure separator 5 after heat exchange and cooling. The gaseous cold low-pressure gas 18 of the cold low-pressure separator 7 is combined with the cold medium-pressure gas 19 and sent out as the hydrogen-rich gas 14. The liquid-phase cold low-fraction oil 16 of the cold low-pressure separator 7 enters the upper part of the stripping tower 13 after being subjected to heat exchange by the cold low-fraction oil heat exchanger 9. The liquid phase hot low fraction oil 17 of the hot low pressure separator 6 enters the middle part of the stripper 13.
Cold low-fraction oil 16 and hot low-fraction oil 17 enter stripper 13 from different locations, respectively, and stripper overhead gas 10 is sent out as sour gas. The stripping column bottom liquid phase 12 enters a subsequent fractionation unit, and the stripping column top liquid phase 11 is sent out of the device.
Comparative example 1
The hydrocracking is taken as an example for explanation, the scale of the device is 200 ten thousand tons per year, the raw materials are second-line-reduced straight-run wax oil and coking wax oil, and the production scheme is a once-through process for producing more aviation kerosene.
The gas-liquid separation of the reaction product adopts a conventional process flow, as shown in figure 2. The hydrogenation reaction product after heat exchange enters a hot high-pressure separator for gas-liquid separation, and the gas phase (hot high-pressure gas for short) of the hot high-pressure separator enters a cold high-pressure separator after heat exchange and cooling. The gas phase of the cold high-pressure separator is used as recycle hydrogen to enter a recycle hydrogen desulfurization and compression system.
The liquid phase of the hot high-pressure separator (hot high-pressure oil for short) enters the hot low-pressure separator after being decompressed. The gas phase of the hot low-pressure separator enters the cold low-pressure separator together with the liquid phase of the cold high-pressure separator after heat exchange and cooling. The gas phase of the cold low-pressure separator is discharged as low-partial gas. The liquid phase cold low-pressure oil of the cold low-pressure separator enters the upper part of the stripping tower. The liquid phase hot low-pressure oil of the hot low-pressure separator enters the middle part of the stripping tower.
Cold low-fraction oil and hot low-fraction oil respectively enter the stripping tower from different positions, and the overhead gas of the stripping tower is sent out by acid gas. The liquid phase at the bottom of the stripping tower enters a subsequent fractionation unit. The operating conditions of the gas-liquid separation section are shown in table 1.
TABLE 1 comparative example gas-liquid separation operating conditions
The existing flow is thermal high-grade (13 MPa) -thermal low-grade (2.7 MPa), and after Pro-II simulation, the composition simulation data of low-grade gas and stripping tower top gas are shown in the following table 2.
Table 2 simulation results of comparative examples
Example 1
The hydrocracking is taken as an example to explain, the scale of the device is 200 ten thousand tons per year, the raw materials are second-line reduced straight-run wax oil and coking wax oil, and the production scheme is a once-through process for producing more aviation kerosene.
The gas-liquid separation of the reaction product adopts the technology, and the specific flow is shown in figure 1. The hydrogenation reaction product after heat exchange enters a hot high-pressure separator for gas-liquid separation, and the gas phase (short for hot high-pressure gas) of the hot high-pressure separator is subjected to heat exchange and cooling and then enters a cold high-pressure separator together with the cold medium-pressure gas of the gas phase (short for medium-pressure gas) of the medium-pressure separator after being further cooled by a hot high-pressure gas phase cooler. The gas phase of the cold high-pressure separator is used as recycle hydrogen to enter a recycle hydrogen desulfurization and compression system.
The liquid phase of the hot high-pressure separator (hot high-pressure oil for short) enters a hot medium-pressure separator after being decompressed. And the gas phase after gas-liquid separation in the hot medium-pressure separator enters the cold medium-pressure separator together with the liquid phase in the cold high-pressure separator after heat exchange and cooling. And the gas phase of the cold medium-pressure separator is combined with the gas phase of the cold low-pressure separator and then sent out as hydrogen-rich gas.
And the liquid phase after gas-liquid separation in the hot medium-pressure separator is decompressed and enters the hot low-pressure separator. The gas phase of the hot low-pressure separator enters the cold low-pressure separator together with the liquid phase of the cold medium-pressure separator after heat exchange and cooling. The gas phase of the cold low-pressure separator is combined with cold medium-separation gas and is sent out of the hydrogen recovery unit as hydrogen-rich gas. The liquid phase cold low-pressure oil of the cold low-pressure separator exchanges heat with the hot medium-pressure gas and then enters the upper part of the stripping tower. The liquid phase hot low-pressure oil of the hot low-pressure separator enters the middle part of the stripping tower.
Cold low-fraction oil and hot low-fraction oil respectively enter the stripping tower from different positions, and the overhead gas of the stripping tower is sent out by acid gas. The liquid phase at the bottom of the stripping tower enters a subsequent fractionation unit. The operating conditions of the gas-liquid separation section are shown in Table 3.
TABLE 3 gas-liquid separation operating conditions of the examples
The compositions and flow rates of low-split GAS (LPG) and stripping overhead acid GAS (SOUR GAS) after Pro-II simulation according to the operating conditions of Table 3 are shown in Table 4.
Table 4 simulation results of the examples
The results of the comparative and example simulations are shown in table 5 for low gas and acid gas in tables 2 and 4.
TABLE 5 COMPARATIVE TABLE
As can be seen from Table 5, with the present invention, the flow rate of hydrogen in the low-molecular gas from which the dissolved hydrogen in the hydrogenation process came was increased by 28kg-mol/hr as compared with the comparative example, while the flow rate from the acid gas at the top of the stripping column was decreased by 28 kg-mol/hr. The hydrogen can be recovered due to the low-gas dehydrogenation recovery unit. The recovery rate of the hydrogen recovery unit is assumed to be 90%, and the amount of hydrogen mostly recovered by enterprises is 25.2 kg-mol/hr. The annual benefit is about 616.4 ten thousand yuan calculated according to the conventional hydrogen cost price of the refining enterprises.