Evacuating system and method for fixed bed propane dehydrogenation device

Abstract

The invention provides an evacuation system and method for a fixed bed propane dehydrogenation device, and in the system and method, about 600 DEG C high-temperature process tail gas to be vacuumized from a fixed bed reactor of the fixed bed propane dehydrogenation device firstly enters a waste heat recovery unit, and the process tail gas mainly comprises hydrocarbons and steam / mixed air; the waste heat recovery unit recovers high-temperature-level sensible heat, the waste heat recovery unit is a waste heat boiler or a waste heat generator, heat is fully utilized, the overall energy utilization efficiency is improved, then the waste heat is introduced into the spray cooling unit, process tail gas is cooled to the working temperature permitted by the liquid ring vacuum pump unit, and the temperature is about 60 DEG C; according to the liquid ring vacuum pump unit, the rotary impeller is used for driving working liquid to form a liquid ring, volume change is formed in a pump cavity, suction and compression of process tail gas are achieved, and therefore a traditional steam ejector is replaced, energy is saved, and efficiency is improved.

Description

Technical Field

[0001] This invention relates to vacuum technology for the reaction product separation system in a fixed-bed propane dehydrogenation to propylene unit, and particularly to a high-efficiency, energy-saving vacuum system based on a liquid ring pump and its application method. Background Technology

[0002] Currently, mature propane dehydrogenation (PDH) reactors mainly include two types: fixed-bed and fluidized-bed. Fixed-bed reactors typically employ a sequential control method involving multiple reactors to achieve continuous production. Each reactor undergoes a cycle consisting of: dehydrogenation reaction, steam purging, catalyst regeneration and preheating, evacuation, and then dehydrogenation again. Evacuation includes two conditions: hydrocarbon + steam and mixed air.

[0003] Among the most commonly used technical solutions, the following drawbacks and shortcomings mainly exist:

[0004] High steam consumption: The core equipment, the steam ejector, requires a large amount of medium- or high-pressure steam as a power source. The production cost of steam (fuel consumption, water treatment, boiler operation) is high, making it one of the main energy consumption and cost items in the operation of the plant.

[0005] There is still room for improvement in energy utilization efficiency: Although existing technologies recover the waste heat of the mixed steam (working steam + suction gas) at the steam ejector outlet by setting up a waste heat boiler (HRSG) to generate low-pressure steam or generate electricity, the efficiency of the steam ejector itself is relatively low (not high thermodynamic efficiency), and there are unavoidable energy losses (such as heat dissipation loss and condensation heat loss) in the process of steam generation, transportation, injection, and recondensation / recovery.

[0006] The system is highly complex: Steam injection systems typically require multi-stage ejectors and are equipped with auxiliary equipment such as post-stage condensers and condensate pumps. Waste heat power generation systems also require steam turbines, generators, lubrication systems, and control systems, resulting in a complex structure, numerous pieces of equipment, and a large footprint for the entire vacuuming and waste heat recovery system.

[0007] High investment and maintenance costs: The complex steam jet-waste heat power generation system has a high initial investment cost. Steam ejectors are susceptible to corrosion and scaling, and the maintenance workload for valves, condensate systems, etc., is also significant. The operation and maintenance of the waste heat power generation system also requires professional personnel and incurs costs.

[0008] Limited operational flexibility: The steam system is relatively slow to start up, shut down, and adjust its load, and is sensitive to pressure fluctuations in the steam pipeline network.

[0009] Based on this, the core technical problem that this invention needs to solve is: how to provide a vacuum system for a fixed-bed propane dehydrogenation unit that can significantly reduce operating energy consumption, especially steam consumption, simplify system structure, reduce investment and maintenance costs, while ensuring stable and reliable system vacuum and maintaining or improving energy recovery efficiency. Summary of the Invention

[0010] Based on the above technical background, the inventors provide a vacuum system and method for a fixed-bed propane dehydrogenation unit. In this system and method, the high-temperature process tail gas (approximately 600°C) from the fixed-bed reactor of the fixed-bed propane dehydrogenation unit, to be evacuated, first enters a waste heat recovery unit. The main components of this process tail gas are hydrocarbons and steam / mixed air. The waste heat recovery unit recovers the high-temperature sensible heat. This waste heat recovery unit is a waste heat boiler or waste heat generator, making full use of the heat and improving the overall energy utilization efficiency. Then, it is introduced into a spray cooling unit to cool the process tail gas to the allowable operating temperature of the liquid ring vacuum pump unit, approximately 60°C. The liquid ring vacuum pump unit uses a rotating impeller to drive the working fluid to form a liquid ring, creating a volume change in the pump chamber, thereby achieving the suction and compression of the process tail gas, thus replacing the traditional steam ejector, saving energy, and improving efficiency, thus completing the present invention.

[0011] This invention provides a evacuation system for a fixed-bed propane dehydrogenation unit.

[0012] The system includes a waste heat recovery unit 1, a spray cooling unit 2, and a liquid ring vacuum pump unit 3;

[0013] The waste heat recovery unit 1 is connected to the fixed bed reactor of the fixed bed propane dehydrogenation unit, and is used to receive the high-temperature process tail gas to be evacuated in the fixed bed reactor, and after absorbing and utilizing the heat in the high-temperature process tail gas, it is connected to the spray cooling unit 2.

[0014] The spray cooling unit 2 is used to spray and cool the process exhaust gas to obtain cooled saturated gas. The spray cooling unit 2 is connected to the liquid ring vacuum pump unit 3.

[0015] The liquid ring vacuum pump unit 3 is used to draw in and compress the cooled saturated gas, and to draw in the pressure at the outlet of the fixed bed reactor to the required vacuum level within a predetermined time.

[0016] The waste heat recovery unit 1 includes a waste heat boiler or a waste heat generator.

[0017] The saturated gas temperature that exits from the spray cooling unit 2 and enters the liquid ring vacuum pump unit 3 is 50-60℃.

[0018] The spray cooling unit 2 includes a cooling spray tower 21, a circulating washing pump 22 and a circulating liquid cooler 23 that are connected to each other.

[0019] The process exhaust gas is cooled by spraying circulating liquid in the cooling spray tower 21.

[0020] The circulating washing pump 22 is used to provide power for the circulating flow of the circulating liquid;

[0021] The circulating liquid cooler 23 is used to control the temperature of the circulating liquid;

[0022] Preferably, in the spray cooling unit 2, the circulating liquid is demineralized water.

[0023] The liquid ring vacuum pump unit 3 includes one or more liquid ring vacuum pumps 31 arranged in parallel.

[0024] Preferably, the liquid ring vacuum pump unit 3 further includes a working fluid cooler 32 and a gas-liquid separator 33.

[0025] The working fluid cooler 32 is used to cool the working fluid of the liquid ring vacuum pump 31, and the working fluid is demineralized water.

[0026] The gas output from the liquid ring vacuum pump 31 is sent to the downstream system after passing through the gas-liquid separator 33.

[0027] A ventilation pipe 4 is connected between the outlet pipe of the gas-liquid separator 33 and the inlet pipe of the liquid ring vacuum pump 31, and a first regulating valve 5 is installed on the ventilation pipe 4.

[0028] The system also includes a pressure gauge 6 installed at the gas outlet of the fixed-bed reactor.

[0029] The pressure gauge 6 is connected to the first regulating valve 5. Based on the pressure information detected by the pressure gauge 4, the opening state of the first regulating valve 5 is adjusted, and the pressure in the liquid ring vacuum pump unit 3 is stabilized by controlling the return gas flow rate.

[0030] The present invention also provides a evacuation method for a fixed-bed propane dehydrogenation unit.

[0031] This method is achieved through the evacuation system described above for a fixed-bed propane dehydrogenation unit.

[0032] The method includes the following steps:

[0033] Step 1: Connect the waste heat recovery unit 1, the spray cooling unit 2 and the liquid ring vacuum pump unit 3 sequentially to the outside of the gas outlet of the fixed bed reactor of the fixed bed propane dehydrogenation unit, and start them in operation.

[0034] Step 2: The high-temperature process tail gas at the outlet of the fixed bed reactor is drawn by the liquid ring vacuum pump unit 3 and passed through the waste heat recovery unit 1 and the spray cooling unit 2 in sequence.

[0035] Step 3: Control the opening state of the first regulating valve 5 based on the detected normal pressure at the gas outlet of the fixed bed reactor, that is, control the return gas flow rate.

[0036] In step 3, when the pressure at the outlet of the fixed bed reactor is typically 115 kPaA-60 kPaA, the return gas flow rate is 15% of the normal flow rate.

[0037] When the pressure at the outlet of the fixed-bed reactor is typically 60 kPaA-28 kPaA, the return gas flow rate is 30% of the normal flow rate.

[0038] The beneficial effects of this invention are as follows:

[0039] (1) The evacuation system and method of the present invention for fixed bed propane dehydrogenation unit has outstanding economic benefits compared with the traditional steam injection and waste heat power generation system; it completely eliminates the high steam consumption of steam ejectors, and the operating cost is mainly converted into electricity consumption, which significantly reduces the operating cost;

[0040] (2) The vacuum system and method of the present invention for fixed bed propane dehydrogenation unit, compared with the traditional steam jet plus waste heat power generation system, eliminates the need for steam ejector, post condenser, condensate pump and waste heat power generation system layout, the equipment investment is expected to be reduced, and the costs of installation, civil engineering, pipelines etc. are also reduced accordingly, so the investment cost is lower.

[0041] (3) The evacuation system and method of the present invention for a fixed bed propane dehydrogenation unit are simpler than the traditional steam jet plus waste heat power generation system, and the maintenance of core equipment is relatively simple, thus reducing maintenance costs.

[0042] (4) The vacuum system and method of the present invention for fixed bed propane dehydrogenation unit, compared with the traditional steam injection plus waste heat power generation system, has a significantly shorter investment payback period than the traditional scheme, even considering the investment in liquid ring pump and pre-heat recovery unit, due to the significant operating cost savings.

[0043] (5) The present invention provides an evacuation system and method for a fixed-bed propane dehydrogenation unit. The system and method use a pre-waste heat boiler to directly and efficiently recover the high-temperature sensible heat of the process tail gas, generating valuable steam for the unit to use. The energy recovery efficiency is higher and the heat energy grade utilization is more reasonable.

[0044] (6) The present invention provides an evacuation system and method for a fixed-bed propane dehydrogenation unit. The system and method have a greatly simplified system structure, a significantly reduced number of devices, a clearer process, and a more intuitive operation.

[0045] (7) The present invention provides an evacuation system and method for a fixed-bed propane dehydrogenation unit. The liquid ring pump of the system and method starts and stops quickly, and the load is adjusted by controlling the outlet return inlet pressure. The system and method are responsive and accurate. The system is less affected by fluctuations in the external steam pipeline network, and a front-mounted spray cooling unit is provided to ensure the stable operation of the pump.

[0046] (8) The present invention provides a vacuum system and method for a fixed-bed propane dehydrogenation unit. The liquid ring pump technology in the system and method is mature and reliable. With the support of the optimized operating condition waste heat recovery unit and the spray cooling unit, it operates stably and can meet the strict vacuum requirements of the PDH unit.

[0047] (9) The present invention provides an evacuation system and method for a fixed-bed propane dehydrogenation unit. The equipment layout in the system and method is more compact, significantly saving equipment space. The operating noise of the liquid ring pump is lower than that of the multi-stage steam ejector and steam turbine generator set.

[0048] (10) The present invention provides an evacuation system and method for a fixed-bed propane dehydrogenation unit, which eliminates the need for a large amount of cooling water required by a steam injection system and helps to reduce carbon emissions. Attached Figure Description

[0049] Figure 1 This diagram shows the overall layout of the evacuation system for a fixed-bed propane dehydrogenation unit according to the present invention.

[0050] Explanation of icon numbers

[0051] 1-Waste heat recovery unit

[0052] 2-Spray cooling unit

[0053] 21-Cooling Spray Tower

[0054] 22-Circulating Washing Pump

[0055] 23-Circulating liquid cooler

[0056] 24-Thermometer

[0057] 25-Second regulating valve

[0058] 26-First Liquid Level Gauge

[0059] 27-Third regulating valve

[0060] 28-Fourth regulating valve

[0061] 3-Liquid Ring Vacuum Pump Unit

[0062] 31-Liquid Ring Vacuum Pump

[0063] 32-Working fluid cooler

[0064] 33-Gas-Liquid Separator

[0065] 34-Second Liquid Level Gauge

[0066] 35-Fifth regulating valve

[0067] 36-Sixth regulating valve

[0068] 4-Ventilation duct

[0069] 5-First regulating valve

[0070] 6-Pressure gauge Detailed Implementation

[0071] The present invention will now be described in detail, and its features and advantages will become clearer and more apparent from these descriptions.

[0072] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0073] This invention provides a evacuation system for a fixed-bed propane dehydrogenation unit, such as... Figure 1 As shown, the system includes a waste heat recovery unit 1, a spray cooling unit 2, and a liquid ring vacuum pump unit 3;

[0074] The waste heat recovery unit 1 is connected to the fixed bed reactor of the fixed bed propane dehydrogenation unit, and is used to receive the high-temperature process tail gas to be evacuated in the fixed bed reactor, and after absorbing and utilizing the heat in the high-temperature process tail gas, it is connected to the spray cooling unit 2.

[0075] Preferably, the high-temperature process tail gas to be evacuated in the fixed-bed reactor has an initial temperature of about 600°C. The waste heat recovery unit 1 includes a waste heat boiler or a waste heat generator. The waste heat boiler can use the high-temperature process tail gas for heating and hot water supply, and the waste heat generator can use the high-temperature process tail gas for power generation. Both methods can significantly reduce the temperature of the high-temperature process tail gas so that it can meet the operating temperature requirements of the liquid ring vacuum pump unit after passing through the spray cooling unit 2.

[0076] The spray cooling unit 2 is used to spray and cool the process exhaust gas to obtain cooled saturated gas. The spray cooling device 2 is connected to the liquid ring vacuum pump unit 3.

[0077] Preferably, the saturated gas temperature exiting the spray cooling unit 2 and entering the liquid ring vacuum pump unit 3 is 50-60°C, that is, the spray cooling unit 2 cools the process exhaust gas to 50-60°C.

[0078] The spray cooling unit 2 includes a cooling spray tower 21, a circulating washing pump 22, and a circulating liquid cooler 23 that are connected to each other.

[0079] The process exhaust gas is cooled by spraying circulating liquid in the cooling spray tower 21.

[0080] The circulating washing pump 22 is used to provide power for the circulating flow of the circulating liquid;

[0081] The circulating liquid cooler 23 is used to control the temperature of the circulating liquid;

[0082] Preferably, in the spray cooling unit 2, the circulating liquid is demineralized water.

[0083] Preferably, a thermometer 24 is installed at the top of the cooling spray tower 21 to monitor the outlet temperature in real time. The thermometer 24 is connected to a second regulating valve 25 on the circulating liquid inlet pipe of the cooling spray tower 21. The flow rate of the circulating liquid is adjusted by controlling the second regulating valve 25 through the thermometer 24, so as to ensure that the process exhaust gas is cooled to 50-60°C.

[0084] Preferably, a first level gauge 26 is provided in the lower middle part of the cooling spray tower 21 to measure the liquid level in the cooling spray tower 21 in real time. The first level gauge 26 is connected to a third regulating valve 27 on the circulating liquid inlet pipe of the spray cooling unit 2 and a fourth regulating valve 28 on the circulating liquid outlet pipe to adjust the total amount of circulating liquid in the spray cooling unit 2 according to the detection value of the first level gauge 26, so as to ensure that the liquid level in the cooling spray tower 21 meets the spray cooling requirements.

[0085] The liquid ring vacuum pump unit 3 is used to draw in and compress the cooled saturated gas, and to draw in the pressure at the outlet of the fixed bed reactor to the required vacuum level within a predetermined time.

[0086] The liquid ring vacuum pump unit 3 includes one or more liquid ring vacuum pumps 31 arranged in parallel; more preferably, at least two liquid ring vacuum pumps 31 are provided to ensure that at least one liquid ring vacuum pump 31 is in backup state in order to deal with unexpected situations such as sudden failures and ensure that the evacuation system can operate continuously and efficiently.

[0087] Preferably, the liquid ring vacuum pump unit 3 further includes a working fluid cooler 32 and a gas-liquid separator 33.

[0088] The working fluid cooler 32 is used to cool the working fluid of the liquid ring vacuum pump 31, and the working fluid is demineralized water.

[0089] The gas output from the liquid ring vacuum pump 31 is sent to the downstream system after passing through the gas-liquid separator 33.

[0090] Preferably, a ventilation pipe 4 is connected between the outlet pipe of the gas-liquid separator 33 and the inlet pipe of the liquid ring vacuum pump 31, and a first regulating valve 5 is provided on the ventilation pipe 4.

[0091] The system also includes a pressure gauge 6 installed at the outlet of the fixed-bed reactor. This pressure gauge 6 is connected to the first regulating valve 5 and adjusts the opening state of the first regulating valve 5 based on the pressure information detected by the pressure gauge 4. By controlling the return gas flow rate, the pressure in the liquid ring vacuum pump unit 3 is stabilized, thereby stabilizing the load on the liquid ring vacuum pump unit 3. Furthermore, the pressure gauge 6 is also connected to the motor signal of the liquid ring vacuum pump 31, allowing for adjustment of the motor speed.

[0092] Preferably, a second level gauge 34 is provided on the gas-liquid separator 33. The gas-liquid separator 33 is also provided with an inlet pipe and a drain pipe. A fifth regulating valve 35 is provided on the inlet pipe and a sixth regulating valve 36 is provided on the drain pipe. Demineralized water is added to the gas-liquid separator 33 through the inlet pipe and sewage is discharged through the drain pipe. The second level gauge 34 is signal-connected to the fifth regulating valve 35 and the sixth regulating valve 36 to realize the automatic adjustment of the working fluid level in the gas-liquid separator 33.

[0093] The present invention also provides a evacuation method for a fixed-bed propane dehydrogenation unit, which is implemented by the evacuation system for a fixed-bed propane dehydrogenation unit described above.

[0094] Preferably, the method includes the following steps:

[0095] Step 1: Connect the waste heat recovery unit 1, the spray cooling unit 2 and the liquid ring vacuum pump unit 3 sequentially to the outside of the gas outlet of the fixed bed reactor of the fixed bed propane dehydrogenation unit, and start them in operation.

[0096] Step 2: The high-temperature process tail gas at the outlet of the fixed bed reactor is drawn by the liquid ring vacuum pump unit 3 and passed through the waste heat recovery unit 1 and the spray cooling unit 2 in sequence.

[0097] Step 3: Control the opening state of the first regulating valve 5 based on the detected normal pressure at the gas outlet of the fixed bed reactor, that is, control the return gas flow rate.

[0098] The evacuation system in this application is a constant-volume evacuation system. The return gas flow rate varies with time and control pressure to satisfy the pressure / flow rate operating curve of the liquid ring pump. The outlet pressure of the liquid ring pump is mainly considered based on the system back pressure, which is usually around 150 kPaA. Therefore, when the inlet operating pressure, i.e., the pressure at the outlet of the fixed-bed reactor, is usually around 115 kPaA-60 kPaA, according to the pressure / flow rate operating curve of the liquid ring pump, the return gas flow rate is about 15% of the normal flow rate, i.e., the opening degree of the first regulating valve 5 is 15%, to maintain the stability of the liquid ring pump. When the inlet operating pressure, i.e., the pressure at the outlet of the fixed-bed reactor, is usually around 60 kPaA-28 kPaA, according to the pressure / flow rate operating curve of the liquid ring pump, the return gas flow rate is about 30% of the normal flow rate, i.e., the opening degree of the first regulating valve 5 is 30%, to maintain the stability of the liquid ring pump.

[0099] More preferably, the method further includes step 4, which involves measuring the liquid level in the cooling spray tower 21 in real time using the first liquid level gauge 26, and then automatically adjusting the total amount of circulating liquid in the spray cooling unit 2 to ensure that the liquid level in the cooling spray tower 21 meets the spray cooling requirements, and that the liquid level is maintained between 30% and 60% of the total height.

[0100] More preferably, the method further includes step 5, which involves measuring the liquid level in the gas-liquid separator 33 in real time using the second liquid level gauge 34, and then automatically adjusting the liquid level in the gas-liquid separator 33 to maintain it between 60% and 80% of the total liquid level.

[0101] Example

[0102] A fixed-bed process based on Lummus's Catofin technology was selected, using a propane dehydrogenation catalyst from Klein. The fixed-bed reactor of the propane dehydrogenation unit in this process was chosen, and the unit was evacuated. This method includes:

[0103] Step 1: Install a vacuum system on the device. This vacuum system, such as... Figure 1 As shown, it includes a waste heat recovery unit 1, a spray cooling unit 2, and a liquid ring vacuum pump unit 3;

[0104] The waste heat recovery unit 1 is a waste heat boiler, which is connected to the fixed bed reactor of the fixed bed propane dehydrogenation unit. It is used to receive the high-temperature process tail gas of about 600°C that is to be evacuated in the fixed bed reactor, and after absorbing and utilizing the heat in the high-temperature process tail gas, it is connected to the spray cooling unit 2.

[0105] The spray cooling unit 2 is used to spray and cool the process tail gas to obtain a cooled saturated gas with a temperature of 50-60℃. The spray cooling unit 2 is connected to the liquid ring vacuum pump unit 3.

[0106] The liquid ring vacuum pump unit 3 is used to pump and compress the cooled saturated gas. The air evacuation stage lasts 20 seconds and the reduction stage lasts 140 seconds, which can pump the pressure at the outlet of the fixed bed reactor to the required vacuum level of 28 kPaA.

[0107] The liquid ring vacuum pump unit 3 includes three liquid ring vacuum pumps 31 arranged in parallel. The liquid ring vacuum pumps are selected from the CBF730-2 model liquid ring vacuum pumps of Guangdong Kenfulai Pump Industry Co., Ltd.

[0108] Step 2: The high-temperature process exhaust gas from the outlet of the fixed-bed reactor is drawn in by the liquid ring vacuum pump unit 3, and then passed sequentially through the waste heat recovery unit 1 and the spray cooling unit 2; the flow rate through the waste heat recovery unit 1 and the spray cooling unit 2 during the air evacuation stage is 47548 m³ / h. 3 The flow rate through waste heat recovery unit 1 and spray cooling unit 2 during the reduction stage is 39832 m³ / h. 2 / h.

[0109] Step 3: Control the opening state of the first regulating valve 5 based on the detected normal pressure at the gas outlet of the fixed bed reactor, that is, control the return gas flow rate.

[0110] In step 3, at the start of operation, the pressure at the outlet of the fixed bed reactor is usually 115 kPaA. At this time, the speed of the liquid ring pump at the liquid ring vacuum pump unit 3 is controlled to be 330 rpm, and the opening of the first regulating valve 5 is controlled to be 15%.

[0111] After the air evacuation stage of 15s and the reduction stage of 110s, the pressure at the outlet of the fixed bed reactor is usually 60kPaA. At this time, the speed of the liquid ring pump at the liquid ring vacuum pump unit 3 is controlled to be maintained at 330rpm, and the opening of the first regulating valve 5 is controlled to be 30%.

[0112] After a total of 20 seconds of air evacuation and 140 seconds of reduction, the 265m section was completed during the air evacuation phase. 3 The gas evacuation process was completed at 222m during the reduction phase. 3 The gas evacuation operation consumed 167 kWh of electricity and 207 tons of circulating water. During operation, the pressure at the outlet of the liquid ring vacuum pump unit 3 was maintained at around 150 kPaA, indicating that the working effect of this method can meet the expected requirements.

[0113] During operation, the waste heat boiler produces a total of 240 kg of 4.3 MPa high-pressure steam.

[0114] Comparative Example

[0115] A company in Qingdao uses the same fixed-bed process of Lummus's Catofin technology as in the example for production operations. It has the same scale as in the example, with a total of 8 reactors. It adopts sequential control, and the evacuation time and evacuation requirements are also the same as in the example. The company uses steam vacuum technology, and the steam consumption for evacuation is 20t / h. The steam is supplied by the industrial park and the price is 180 yuan / ton.

[0116] Based on economic benefit analysis, with an electricity price of 0.65 yuan / kWh and 8000 hours per year, the emission factor for electricity in Shandong Province is 0.641tCO2 / MWh. For steam, considering 230℃@1.0MPag, the emission factor is 0.11tCO2 / GJ.

[0117] As can be seen, by adopting the technology in the embodiments, the operating cost can be saved by approximately RMB 32.52 million per year, and the carbon dioxide emissions can be reduced by approximately 46,325.3 tons per year.

[0118] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0119] The present invention has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present invention based on these embodiments, all of which fall within the scope of protection of the present invention.

Claims

1. A evacuation system for a fixed-bed propane dehydrogenation unit, characterized in that, The system includes a waste heat recovery unit (1), a spray cooling unit (2), and a liquid ring vacuum pump unit (3); The waste heat recovery unit (1) is connected to the fixed bed reactor of the fixed bed propane dehydrogenation unit, and is used to receive the high temperature process tail gas to be evacuated in the fixed bed reactor, and after absorbing and utilizing the heat in the high temperature process tail gas, it is connected to the spray cooling unit (2). The spray cooling unit (2) is used to spray and cool the process exhaust gas to obtain cooled saturated gas. The spray cooling device (2) is connected to the liquid ring vacuum pump unit (3). The liquid ring vacuum pump unit (3) is used to draw in and compress the cooled saturated gas, and to draw in the pressure at the outlet of the fixed bed reactor to the required vacuum level within a predetermined time.

2. The evacuation system for a fixed-bed propane dehydrogenation unit according to claim 1, characterized in that, The waste heat recovery unit (1) includes a waste heat boiler or a waste heat generator.

3. The evacuation system for a fixed-bed propane dehydrogenation unit according to claim 1, characterized in that, The saturated gas temperature exiting the spray cooling unit (2) and entering the liquid ring vacuum pump unit (3) is 50-60°C.

4. The evacuation system for a fixed-bed propane dehydrogenation unit according to claim 1, characterized in that, The spray cooling unit (2) includes a cooling spray tower (21), a circulating washing pump (22), and a circulating liquid cooler (23) that are connected to each other; The process exhaust gas is cooled by spraying circulating liquid in the cooling spray tower (21); The circulating washing pump (22) is used to provide power for the circulating flow of the circulating liquid; The circulating liquid cooler (23) is used to control the temperature of the circulating liquid; Preferably, in the spray cooling unit (2), the circulating liquid is demineralized water.

5. The evacuation system for a fixed-bed propane dehydrogenation unit according to claim 1, characterized in that, The liquid ring vacuum pump unit (3) includes one or more liquid ring vacuum pumps (31) arranged in parallel; Preferably, the liquid ring vacuum pump unit (3) further includes a working fluid cooler (32) and a gas-liquid separator (33). The working fluid cooler (32) is used to cool the working fluid of the liquid ring vacuum pump (31), and the working fluid is demineralized water. The gas output from the liquid ring vacuum pump (31) is sent to the downstream system after passing through the gas-liquid separator (33).

6. The evacuation system for a fixed-bed propane dehydrogenation unit according to claim 5, characterized in that, A ventilation pipe (4) is connected between the outlet pipe of the gas-liquid separator (33) and the inlet pipe of the liquid ring vacuum pump (31), and a first regulating valve (5) is installed on the ventilation pipe (4). The system also includes a pressure gauge (6) installed at the outlet of the fixed-bed reactor. The pressure gauge (6) is connected to the first regulating valve (5) and adjusts the opening state of the first regulating valve (5) according to the pressure information detected by the pressure gauge (4). By controlling the return gas flow rate, the pressure in the liquid ring vacuum pump unit (3) tends to stabilize.

7. A method for evacuating a fixed-bed propane dehydrogenation unit, characterized in that, The method is implemented using the evacuation system for a fixed-bed propane dehydrogenation unit as described in any one of claims 1 to 6.

8. The evacuation method for a fixed-bed propane dehydrogenation unit according to claim 7, characterized in that, The method includes the following steps: Step 1: Connect the waste heat recovery unit (1), the spray cooling unit (2) and the liquid ring vacuum pump unit (3) to the outside of the gas outlet of the fixed bed reactor of the fixed bed propane dehydrogenation unit in sequence, and start them. Step 2: The high-temperature process tail gas at the outlet of the fixed bed reactor is drawn by the liquid ring vacuum pump unit (3) and then passed through the waste heat recovery unit (1) and the spray cooling unit (2) in sequence. Step 3: Control the opening state of the first regulating valve (5) based on the detected normal pressure at the outlet of the fixed bed reactor, that is, control the return gas flow rate.

9. The evacuation method for a fixed-bed propane dehydrogenation unit according to claim 8, characterized in that, In step 3, when the pressure at the outlet of the fixed bed reactor is typically 115 kPaA-60 kPaA, the return gas flow rate is 15% of the normal flow rate. When the pressure at the outlet of the fixed-bed reactor is typically 60 kPaA-28 kPaA, the return gas flow rate is 30% of the normal flow rate.

Images