Methods for shutting down the Fischer-Tropsch reactor

Abstract

This invention describes a method for shutting down a Fischer-Tropsch reactor, wherein a reaction gas mixture comprising syngas and recycle gas recovered from the Fischer-Tropsch reactor is fed into the reactor in a synthesis loop. The Fischer-Tropsch reactor contains a Fischer-Tropsch catalyst indirectly cooled by a pressurized coolant. The method comprises the steps of: (a) depressurizing the coolant to cool the reaction gas mixture, thereby quenching the Fischer-Tropsch reaction occurring in the reactor; (b) stopping the syngas feed to the Fischer-Tropsch reactor; and (c) maintaining the recycle gas circulating through the Fischer-Tropsch reactor during steps (a) and (b) to remove heat from the reactor. Compared to a complete shutdown, this method safely facilitates a faster return to operating conditions.

Description

[0001] This invention relates to methods for shutting down Fischer-Tropsch reactors and processes.

[0002] The Fischer-Tropsch process involves producing a gas with the formula (C) from a feed gas containing hydrogen and carbon monoxide. n H 2n+2 This process involves a series of catalytic chemical reactions of various hydrocarbons. The process can be operated in one or more Fischer-Tropsch reactors using iron-based or cobalt-based catalysts at pressures ranging from 0.1 MPa to 10 MPa and temperatures ranging from 170°C to 350°C.

[0003] The Fischer-Tropsch reaction is exothermic, and various arrangements have been developed to prevent overheating and damage to the Fischer-Tropsch reactor and catalyst, as well as the potential corresponding reduction in productivity, activity, and selectivity. In one arrangement, the fixed bed of Fischer-Tropsch catalyst is cooled by heat exchange with a coolant such as pressurized boiling water.

[0004] When necessary, the Fischer-Tropsch reactor and process must be shut down in a safe and effective manner, i.e., changed from an operating state where hydrocarbons are synthesized to a non-operating state.

[0005] GB2223237A discloses a process for shutting down a reactor used to produce at least a portion of liquid hydrocarbons, which are generated by the catalytic reaction of syngas, consisting of carbon monoxide, with hydrogen at elevated temperature and pressure. The reactor is equipped with a cooling device and a device for circulating gas through the catalyst to equalize its temperature. The process includes the following steps: (i) interrupting the syngas feed; (ii) depressurizing the reactor downstream of the catalyst and supplying an inert gas to the reactor upstream of the catalyst; and (iii) cooling the catalyst to ambient conditions.

[0006] US10329492 discloses a process for shutting down a Fischer-Tropsch reactor, the process comprising: a) stopping the fresh feed to the reactor; b) opening or increasing the flow rate to the reactor tail gas purge line to maintain sufficient flow through the reactor; c) reducing the pressure inside the reactor to a level below the pressure of the purge gas reservoir; d) opening the purge gas valve to allow flow from the purge gas reservoir to the reactor inlet; e) allowing purge gas to purge through the reactor to substantially remove the fresh feed gas; and f) closing the purge gas valve and blocking the purge gas line such that the flow rate through the reactor is zero.

[0007] While using inert or purge gases for reactor depressurization and quenching is effective, it lacks flexibility and requires extended start-up times. Furthermore, this shutdown process wastes syngas and reserves from the synthesis loop.

[0008] The applicant has developed an alternative closure method that overcomes the problems of existing methods.

[0009] Therefore, the present invention provides a method for shutting down a Fischer-Tropsch reactor, wherein a reaction gas mixture comprising syngas and recycle gas recovered from the Fischer-Tropsch reactor is fed into the Fischer-Tropsch reactor in a synthesis loop, the Fischer-Tropsch reactor comprising a Fischer-Tropsch catalyst indirectly cooled by a pressurized coolant, the method comprising the steps of: (a) depressurizing the coolant to cool the reaction gas mixture, thereby quenching the Fischer-Tropsch reaction occurring in the Fischer-Tropsch reactor; (b) stopping the syngas feed to the Fischer-Tropsch reactor; and (c) maintaining the recycle gas circulating through the Fischer-Tropsch reactor during steps (a) and (b) to remove heat from the Fischer-Tropsch reactor.

[0010] This method circulates the recirculated gas through the Fischer-Tropsch reactor, and can therefore be called a partial shutdown, which is the opposite of a complete shutdown, in which the reactant gas can be replaced by an inert gas such as nitrogen.

[0011] The advantages of the partial shutdown method include:

[0012] i. The purging of reactants is minimized because the entire loop is not purged with inert gas every time.

[0013] ii. Restart time is minimized because a complete depressurization and purging process is not required before repressurization with fresh feed.

[0014] iii. It saves on expensive inert gas.

[0015] iv. Ensure catalyst protection by allowing the reactant gases to continue flowing instead of relying on inert gases to remove reactants from the catalyst.

[0016] The method is applied to a Fischer-Tropsch reactor containing a cooled Fischer-Tropsch catalyst, the reaction gas mixture is fed into the Fischer-Tropsch reactor, and the Fischer-Tropsch reactor operates in a loop.

[0017] The reactant gas mixture fed into the Fischer-Tropsch reactor consists of syngas plus recycle gas recovered from the Fischer-Tropsch reactor product stream. Syngas used in the Fischer-Tropsch process contains hydrogen and carbon monoxide. Recycle gas typically contains unreacted syngas, carbon dioxide, and potentially light hydrocarbons.

[0018] Syngas can be formed using any suitable Fischer-Tropsch syngas generation technology. For example, syngas can be formed by processes including one or more steps selected from vaporization, partial oxidation, and catalytic partial oxidation, applied to feedstocks such as coal, biomass, carbonaceous materials, and waste plastics, or equivalents containing non-biological carbon. Syngas preferably consists essentially of hydrogen and carbon monoxide. In cases where the resulting syngas contains carbon dioxide, a carbon dioxide removal stage is typically required to remove carbon dioxide from the reaction gas mixture upstream of the Fischer-Tropsch reactor. Carbon dioxide removal methods are known and typically involve the absorption of carbon dioxide from the syngas using a chemical or physical scrubbing system. One or more contaminant removal stages may also be used before or after any carbon dioxide removal stage to advantageously remove impurities or contaminants that could poison the Fischer-Tropsch catalyst upstream of the Fischer-Tropsch reactor by scrubbing (absorption) and / or passing the reaction gas mixture through one or more beds of suitable adsorbent.

[0019] The Fischer-Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally possessing the formula (C1, C2, C3). n H 2n+2 A more useful reaction produces alkanes from the reaction gas mixture, as shown below:

[0020] (2n+1)H2+n CO→C n H 2n+2 +n H2O,

[0021] Where n is typically 5 to 100 or higher, and preferred products have n in the range of 10 to 20.

[0022] The Fischer-Tropsch reactor operates in a synthesis loop, where a mixture of reactant gases is fed into the reactor and reacted on a Fischer-Tropsch catalyst to form a product mixture comprising liquid and gaseous hydrocarbons, vapors, and unreacted gases. The product gas mixture exiting the Fischer-Tropsch reactor is cooled to condense vapors and facilitate the recovery of liquid hydrocarbons. A portion of the unreacted gases, optionally after light hydrocarbon separation, is returned to the Fischer-Tropsch reactor as recycle gas, thus forming the synthesis loop. The recycle gas is combined with the synthesis gas to form a reactant gas mixture outside the Fischer-Tropsch reactor, allowing for more efficient temperature control of the feed to the Fischer-Tropsch reactor. Operating the Fischer-Tropsch reactor in a loop improves the conversion efficiency of the process. To prevent the buildup of inert gases, the loop can be purged as Fischer-Tropsch tail gas, which can be further treated.

[0023] The synthesis gas fed into the Fischer-Tropsch reactor may have a hydrogen to carbon monoxide molar ratio in the range of 1.6:1 to 2.5:1, preferably 2.0:1 to 2.2:1.

[0024] Before shutdown, the Fischer-Tropsch reactor can be operated at pressures ranging from 10 bar absolute to 100 bar absolute (0.1 MPa to 10 MPa) and temperatures ranging from 170°C to 350°C. Operation on the cobalt catalyst can be carried out at pressures ranging from 20 bar absolute to 50 bar absolute and temperatures ranging from 200°C to 320°C. The gas hourly space velocity (GHSV) for continuous operation can reach 1000 hr. -1 Up to 25000hr -1 Within the range.

[0025] A Fischer-Tropsch reactor contains a Fischer-Tropsch catalyst indirectly cooled by a pressurized coolant. A Fischer-Tropsch reactor can be any reactor suitable for containing a catalyst indirectly cooled by a pressurized coolant. Indirect cooling in a Fischer-Tropsch reactor can be achieved through indirect heat exchange with the coolant, and the Fischer-Tropsch reactor is a convenient heat exchange reactor. Fischer-Tropsch processes typically operate at elevated pressures; therefore, Fischer-Tropsch reactors are typically pressure vessels, such as cylindrical vessels with rounded apexes. The flow through the catalyst can be axial and / or radial. The Fischer-Tropsch catalyst can be provided in the form of a bed through which tubes or plates carrying the coolant are placed, or the catalyst can be provided in multiple reaction tubes immersed in a coolant flowing around their exterior. The latter reactor technology is preferred.

[0026] Any Fischer-Tropsch catalyst can be used, but iron and cobalt Fischer-Tropsch catalysts are preferred. Cobalt-based Fischer-Tropsch catalysts are superior to iron-based catalysts due to their lower selectivity for carbon dioxide. Any cobalt Fischer-Tropsch catalyst can be used, but preferred catalysts contain 9% to 25% by weight of Co supported on a suitable support material. Therefore, suitable catalysts include agglomerates, pellets, or extrusions containing metal oxides such as alumina, zinc oxide, titanium dioxide, or silica, or mixtures thereof, on which a catalytically active metal is deposited.

[0027] In a particularly preferred arrangement, the Fischer-Tropsch catalyst is used in combination with a catalyst support suitable for a tubular Fischer-Tropsch reactor, wherein the catalyst support containing the catalyst is disposed within one or more tubes cooled by a circulating coolant such as pressurized water. The term "catalyst support" refers to a catalyst vessel, for example, in the form of a cup or canister, configured to allow gas and / or liquid to flow into and out of the support and through a bed of catalyst or catalyst precursor disposed within the support. Any suitable catalyst support may be used. In one arrangement, the catalyst support is the catalyst support described in WO2011 / 048361, the contents of which are incorporated herein by reference. In an alternative arrangement, the catalyst support may comprise the monolithic catalyst disclosed in WO2012 / 136971, the contents of which are also incorporated herein by reference. In yet another alternative arrangement, the catalyst support may be the catalyst support disclosed in WO2016 / 050520, the contents of which are also incorporated herein by reference. In a preferred embodiment, the Fischer-Tropsch synthesis unit includes a tubular Fischer-Tropsch reactor, wherein a catalyst support containing a Fischer-Tropsch catalyst is disposed within one or more tubes cooled by a cooling medium.

[0028] The pressure of the coolant can be the same as or similar to the pressure of the reactant gas mixture fed into the Fischer-Tropsch reactor.

[0029] The coolant can be any pressurized coolant effective for removing heat from the Fischer-Tropsch reactor, but is preferably pressurized boiling water. Water can be any suitable cooling water. The heat from the Fischer-Tropsch reactor is thus removed by generating steam, which is preferably fed into a steam drum connected to the Fischer-Tropsch reactor.

[0030] The Fischer-Tropsch reaction described above produces FT water as a byproduct. In the Fischer-Tropsch hydrocarbon synthesis unit, this FT water is separated from the hydrocarbon mixture generated by the Fischer-Tropsch reaction. Separation can be conveniently performed using one or more gas-liquid or liquid-liquid separators.

[0031] Separating byproduct water from the product mixture produced in the Fischer-Tropsch reactor stage allows for the recovery of hydrocarbons from the product mixture. Gaseous hydrocarbons can be recovered for sale or recycled back into the process, for example, as part of the Fischer-Tropsch tail gas or as feed to the syngas generation unit along with the Fischer-Tropsch tail gas. Liquid hydrocarbons can be recovered for sale or undergo upgrading to provide more valuable hydrocarbon products. Thus, the Fischer-Tropsch hydrocarbon synthesis unit advantageously produces one or more hydrocarbon streams, including but not limited to molten hydrocarbon waxes and / or light hydrocarbon condensates that are liquid at ambient temperatures. The hydrocarbon products synthesized in the Fischer-Tropsch hydrocarbon synthesis unit can be used directly, for example, to prepare base oils, or can be subsequently processed to prepare other products.

[0032] The shutdown method includes step (a): depressurizing the coolant to cool the reaction gas mixture, thereby quenching the Fischer-Tropsch reaction occurring in the Fischer-Tropsch reactor. Preferably, in this step, the coolant and the Fischer-Tropsch reactor are cooled to 150°C or lower by reducing the pressure of the coolant, for example, to a temperature in the range of 100°C to 150°C, such as when the coolant is boiling water, by reducing the pressure to approximately 5 bar absolute or lower. Depressurization can be accomplished by depressurizing the steam drum connected to the Fischer-Tropsch reactor. Depressurization step (a) can be conveniently provided using orifices and / or control valves connected to the steam drum. Depressurization alone via orifices or in combination with one or more control valves provides an improved level of control for this method. Ideally, the depressurization rate should be fast enough to rapidly quench the reaction and prevent the decomposition of carbon monoxide on the carbon deposits formed on the catalyst, but not fast enough to cause mechanical damage to the Fischer-Tropsch reactor and its cooling system. For example, excessively rapid depressurization in a water-cooled system can cause liquid water to enter the steam line, leading to steam hammer and potential equipment / piping damage. Depending on the catalyst activity, coolant depressurization can appropriately occur within 5 to 10 minutes. The initial pressure, i.e., the pressure during normal operation, can range from 15 bar absolute to 35 bar absolute, depending on the operating temperature used to obtain optimal catalyst performance. The final pressure, i.e., the pressure after depressurization, can be 5 bar absolute or less. The depressurization rate is preferably in the range of 2 to 6 bar per minute. If only an orifice is used, the depressurization rate will decay over time, but if a valve control system is used, the depressurization rate can be constant.

[0033] The shutdown method further includes step (b): stopping the syngas feed to the Fischer-Tropsch reactor. Step (b) is preferably performed simultaneously with the depressurization step (a), i.e., steps (a) and (b) are preferably performed concurrently. A small delay between the initial start step (a) and the subsequent start step (b) is permissible, but since the delay between the initial start step (b) and the subsequent start step (a) carries the risk of carbon formation on the catalyst, step (a) is preferably the first step. Stopping the syngas mixture feed reduces the amount of reaction occurring in the Fischer-Tropsch reactor. The syngas stream diverted from the Fischer-Tropsch reactor can be discharged or returned to the syngas production stage or used as fuel.

[0034] The shutdown method further includes step (c): during steps (a) and (b), the recycle gas is kept circulating in the loop and through the Fischer-Tropsch reactor to remove heat from the reactor. The recycle gas stream is typically at a lower pressure than the syngas and is therefore circulated via a recycle compressor. This circulation is maintained after the syngas feed to the Fischer-Tropsch reactor is stopped. Since the recycle gas contains some hydrogen and carbon monoxide, some additional Fischer-Tropsch synthesis may occur, but this is limited by the cooling of the Fischer-Tropsch reactor caused by the depressurization of the coolant. Any liquid hydrocarbons and byproduct water formed during step (c) are normally recovered. Therefore, although the Fischer-Tropsch reactor and loop are not depressurized, for example, by purging, the loop pressure will decrease slightly due to the conversion of the reactant gas into a liquid until the Fischer-Tropsch reaction is quenched.

[0035] The Fischer-Tropsch reactor loop can be safely kept in circulation in this mode whenever needed. This method allows the Fischer-Tropsch reactor and process to enter a standby state without having to discharge (e.g., vent) the entire stock of the reactor system, i.e., the system remains under pressure ready for restart. Even though a full reactor purging is required before restarting, this still has operational benefits because it allows the operator to do so in a controlled manner when making their choice.

[0036] This method can precede process restart, or, if necessary, complete shutdown.

[0037] When it is necessary to restart the process after a partial shutdown, the method may further include the following steps: (d1) reducing the pressure of the Fischer-Tropsch reactor and the circulating gas, (e1) adjusting the inert gas content of the circulating gas to a minimum, (f1) repressurizing the Fischer-Tropsch reactor with syngas feed, and (g1) repressurizing the coolant to increase the temperature of the Fischer-Tropsch reactor until the Fischer-Tropsch reaction begins to occur, and (h1) introducing syngas into the Fischer-Tropsch reactor.

[0038] In step (d1), the pressure reduction of the circulating gas in the Fischer-Tropsch reactor and loop can be conveniently achieved by purging the synthesis loop. The Fischer-Tropsch reactor pressure can be reduced to a range of 5 to 10 bar absolute pressure, with the optimal value depending on the specific equipment. Preferably, this pressure is lower than the inert gas supply, such as nitrogen, to facilitate a rapid supply of inert gas to the Fischer-Tropsch reactor and loop (if necessary).

[0039] In step (e1), the inert gas may include nitrogen, carbon dioxide, methane, and other light hydrocarbons. The reactants, non-inert gases namely hydrogen and carbon monoxide, will also be present because the Fischer-Tropsch reactor and catalyst temperatures have been reduced in step (a) to quench the Fischer-Tropsch reaction. The minimum inert gas content in the circulating gas can range from 60% to 80% vol%. The optimal value will depend on the specific equipment design and the pressure reduced to the selected level in step (d1). If the inert gas level is too low, the pressure can be further reduced and replenished with an inert gas such as nitrogen. If the inert gas level is too high, the system pressure can be further reduced without subsequent replenishment with inert gas. Step (e1) is necessary because the inert gas content present in the circulating gas can vary depending on the activity of the catalyst when the shutdown method is started and how long it takes for the Fischer-Tropsch reactor to be quenched in step (a). Excessive inert gas levels can lead to slow start-up, which may cause the Fischer-Tropsch reactor temperature to rise too rapidly, potentially leading to catalyst damage or even runaway. Conversely, excessively low inert gas levels can make startup more difficult to control, potentially damaging the catalyst due to the exothermic reaction.

[0040] In step (f1), the pressure can be increased to a level equal to or lower than the initial operating pressure, but typically 60% to 100% of the operating pressure prior to shutdown. During this stage, the Fischer-Tropsch catalyst will be below the normal pre-shutdown temperature, so there is essentially no conversion or consumption of syngas; therefore, pressurization is stopped once the desired reactor pressure is reached.

[0041] In step (g1), the repressurization should be sufficient to raise the temperature of the Fischer-Tropsch catalyst to the operating conditions, i.e., the temperature at which the Fischer-Tropsch reaction begins. When the coolant is pressurized boiling water, this can be achieved by repressurizing the steam drum connected to the Fischer-Tropsch reactor using a suitable device such as a steam ejector / ejector pump circuit.

[0042] In step (h1), the syngas feed to the Fischer-Tropsch reactor is restarted. Ideally, the syngas feed is introduced together with the recirculated gas to provide the desired hydrogen to carbon monoxide molar ratio at the inlet of the Fischer-Tropsch reactor. Loop purging can be used to control the pressure in the Fischer-Tropsch reactor and the loop. If the syngas in step (f1) is repressurized to a pressure below the desired operating pressure, such as the operating pressure before partial shutdown, the pressure can be increased back to the desired operating pressure in step (h1).

[0043] As an alternative to process restart, the Fischer-Tropsch reactor can be completely shut down from a partially shut-down state. If a complete shutdown of the process is required after a partial shutdown, the method may further include the following steps: (d2) stopping the circulation of the recirculated gas; (e2) feeding an inert gas feed into the Fischer-Tropsch reactor and the recirculation under a pressure greater than that of the Fischer-Tropsch reactor and the recirculation; and (f2) purging the Fischer-Tropsch reactor and the reaction gas recirculation using the inert gas feed instead of the recirculated gas.

[0044] In step (d2), the circulation of the circulating gas is stopped.

[0045] In step (e2), an inert gas, such as nitrogen, is supplied to provide safe inertization of the Fischer-Tropsch reactor system. The inert gas displaces the non-inert gases (i.e., hydrogen and carbon monoxide) from the catalyst and prevents catalyst damage, for example, due to carbon buildup. The inert gas can be conveniently stored in a pressurized tank specifically for this purpose, or a constant high-pressure inert gas supply can be used. The pressure at which the inert gas supply, such as nitrogen, is supplied to the Fischer-Tropsch reactor and loop can be suitably 10 to 30 bar higher than the pressure of the Fischer-Tropsch reactor and loop.

[0046] In step (f2), the purging of the Fischer-Tropsch reactor and the circulating gas can be conveniently achieved using synthesis loop purging. If the pressure of the inert gas supply decreases as the circulating gas is replaced, the Fischer-Tropsch reactor pressure can be reduced via a purging device such as an orifice or valve to maintain a pressure differential sufficient to replace the reactant gas and provide a sufficient cooling flow to the Fischer-Tropsch reaction tubes. If a constant-pressure inert gas supply is used, it is not necessary to reduce the pressure in the Fischer-Tropsch reactor and the loop.

[0047] Steps (d2), (e2), and (f2) can be performed simultaneously or rapidly in sequence. In emergency shutdown situations, performing (d2) as the first step can be particularly advantageous.

[0048] In an alternative scenario not according to the invention, a complete shutdown method may be conceivable including the steps of: (a) depressurizing the coolant to cool the reactant gas mixture to quench the Fischer-Tropsch reaction occurring in the Fischer-Tropsch reactor; (b) stopping the synthesis gas feed to the Fischer-Tropsch reactor; (c) stopping the circulation of the recirculating gas; (d) feeding an inert gas feed into the Fischer-Tropsch reactor and the recirculating gas loop at a pressure greater than that of the Fischer-Tropsch reactor and the loop; and (e) purging the Fischer-Tropsch reactor and the reactant gas loop using the inert gas feed instead of the recirculating gas. Steps (a), (b), (c), (d), and (e) may be performed simultaneously or rapidly and continuously. This method does not possess the advantages of the present invention.

[0049] The shutdown method of this invention can be used for planned or emergency shutdowns, for example, to maintain process safety, facilitate maintenance, or protect the Fischer-Tropsch catalyst. The process can be started manually or operated automatically using conventional computerized equipment control systems and / or equipment safety instrumented systems.

[0050] When the equipment control system trips in response to unexpected or unplanned conditions in the process, a partial shutdown can be used, where the trip poses no danger to the Fischer-Tropsch reactor and catalyst. Conversely, a complete shutdown can be performed to protect the Fischer-Tropsch catalyst from deactivation due to flow loss, or to provide greater integrity protection for the catalyst against other failures, such as high temperatures / runaway in the Fischer-Tropsch reactor.

[0051] When a partial shutdown method is initiated, the equipment control system and / or equipment safety instrumented system may additionally instruct upstream and / or downstream operations to shut down or enter a safe operating state. For example, if the coolant is pressurized boiling water that generates steam, the equipment control system may activate an auxiliary steam generation unit, such as a flame heater or boiler, to provide steam to replace the steam lost from the steam drum. Alternatively or otherwise, the equipment control system may deactivate downstream units to treat liquid and gaseous hydrocarbons recovered from the product gases of the Fischer-Tropsch reactor, and / or to treat Fischer-Tropsch tail gas.

[0052] The invention is further described with reference to the accompanying drawings, in which:

[0053] Figure 1 This is a description of one embodiment of a system to which the method of the present invention can be applied.

[0054] Those skilled in the art will understand that the accompanying drawings are illustrative and that commercial equipment may require additional equipment items such as feed cylinders, pumps, vacuum pumps, compressors, gas recirculation compressors, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, collection tanks, storage tanks, etc. The provision of such auxiliary equipment does not constitute part of this invention and is consistent with conventional chemical engineering practice.

[0055] exist Figure 1In this process, syngas generation unit 10 produces a purified syngas mixture of hydrogen and carbon monoxide under elevated temperature and pressure. Syngas is fed from syngas generation unit 10 via line 12 and combined with a circulating stream in line 14 to produce a reactant gas mixture, which is fed via line 16 into a Fischer-Tropsch reactor 18 containing multiple reaction tubes 20 containing Fischer-Tropsch catalysts. The Fischer-Tropsch catalysts may be contained within multiple catalyst supports in each reaction tube. The tubes 20 are cooled by pressurized boiling water supplied to the reactor via line 22 from steam drum 24. Steam is recovered from the Fischer-Tropsch reactor 18 via line 26 and returned to steam drum 24. Boiler feedwater (not shown) is fed into the steam drum, and steam is recovered from the steam drum via line 28. Hydrocarbons are synthesized through the reaction of hydrogen and carbon monoxide on the Fischer-Tropsch catalysts. The product mixture is recovered from the Fischer-Tropsch reactor 18 via line 30 and fed into a first gas-liquid separator 32, where the liquid wax product is separated from the product and unreacted gas, and recovered via line 34 for optional further processing. The gaseous product and unreacted gas are fed from the first gas-liquid separator 32 via line 36 into one or more heat exchangers 38, where they are cooled to condense a mixture of byproduct water and condensable hydrocarbon products. The cooled mixture formed in the one or more heat exchangers 38 is fed via line 40 into a second gas-liquid separator 42, where the condensed water and hydrocarbons are separated and recovered via line 44 for further processing. The unreacted gas mixture, containing hydrogen, carbon monoxide, and possibly carbon dioxide and / or non-condensable hydrocarbons, is recovered from the second gas-liquid separator 42 via line 46 and compressed in a recirculating compressor 48 to form a recirculating gas stream 14. A purge line 50 is taken from the unreacted gas mixture line 46 located upstream of the compressor 48.

[0056] Optionally, a pressure vessel 52 containing high-pressure nitrogen gas, with a pressure greater than that of the compressed recirculating gas in line 14 and the synthesis gas feed in line 12, can be connected to the recirculating gas in line 14 via a feed line 54 located downstream of compressor 48 for use in emergency situations. Alternatively, it may be advantageous to directly connect a branch line of line 54 to the reactant gas feed line 16 located near the inlet of Fischer-Tropsch reactor 18 to help purge reactants from the reactor as quickly as possible.

[0057] To operate the partial shutdown method, valve 56 in steam line 28 is opened to depressurize the coolant in steam drum 24, which is fed into Fischer-Tropsch reactor 18 via line 22. Simultaneously, valve 58 in syngas feed line 12 is closed to stop the flow of syngas to reaction tube 20. The depressurization of the steam drum lowers the temperature of the coolant, thereby quenching the reaction occurring in reaction tube 20. Recirculating compressor 48 is operated to maintain gas flow in the cooling reaction tube 20 within Fischer-Tropsch reactor 18.

[0058] To restart the process, valve 60 on purge line 50 can be opened. Nitrogen, for example, from a local low-pressure nitrogen source (not shown), can be used to adjust the inert gas content of the recycle gas to a level that prevents overheating of reaction tube 20 in Fischer-Tropsch reactor 18 when restarting the syngas feed. Valve 58 is then reopened to allow pressurization of reaction tube 20 in Fischer-Tropsch reactor 18. Once the desired pressure is reached, valve 58 is closed. Valve 56 is then closed to allow repressurization of steam drum 24 and the coolant supplied to the reactor via line 22. This allows Fischer-Tropsch reactor 18 and reaction tube 20 to reach the temperature required for Fischer-Tropsch reaction restart. Once the desired temperature is reached, valve 58 is reopened to supply syngas to reaction tube 20 in Fischer-Tropsch reactor 18 via line 12.

[0059] In cases where a complete system shutdown is required, such as in an emergency, the circulating compressor 48 is stopped and valve 62 in the high-pressure nitrogen feed line 54 is opened to allow nitrogen to enter the reaction tube 20 of the Fischer-Tropsch reactor 18. Valve 60 in the purge line 50 is opened to allow inert gas to flow through the entire system.

Claims

1. A method for shutting down a Fischer-Tropsch reactor, wherein a mixture of reaction gases comprising synthesis gas and recycle gas recovered from the Fischer-Tropsch reactor is fed into the Fischer-Tropsch reactor in a synthesis loop, the Fischer-Tropsch reactor comprising a Fischer-Tropsch catalyst indirectly cooled by a pressurized coolant, the method comprising the steps of: (a) depressurizing the coolant to cool the reaction gas mixture, thereby quenching the Fischer-Tropsch reaction occurring in the Fischer-Tropsch reactor; (b) stopping the synthesis gas feed to the Fischer-Tropsch reactor; and (c) maintaining the circulating gas through the Fischer-Tropsch reactor during steps (a) and (b) to remove heat from the Fischer-Tropsch reactor, wherein the Fischer-Tropsch reactor includes a pressure vessel, wherein the Fischer-Tropsch catalyst is provided in a plurality of reaction tubes immersed in a coolant flowing around its exterior.

2. The method of claim 1, wherein the Fischer-Tropsch catalyst is used in combination with a catalyst support suitable for a tubular Fischer-Tropsch reactor, wherein the catalyst support is a catalyst container configured to allow gas and / or liquid to flow into and out of the support and through a bed of catalyst disposed within the support, and wherein the catalyst support containing the catalyst is disposed within one or more tubes cooled by the pressurized coolant.

3. The method according to claim 1 or 2, wherein the coolant is pressurized boiling water supplied by a steam drum connected to the Fischer-Tropsch reactor, and the depressurization step (a) is provided using an orifice and / or control valve connected to the steam drum.

4. The method according to any one of claims 1 to 3, wherein the decompression rate in step (a) is 2 to 6 bar per minute.

5. The method according to any one of claims 1 to 4, wherein the temperature of the coolant and the Fischer-Tropsch reactor in step (a) is reduced to 150°C or lower.

6. The method according to any one of claims 1 to 5, wherein the process is started directly after the method.

7. The method of claim 6, wherein the method further comprises the following steps: (d1) Reduce the pressure of the Fischer-Tropsch reactor and the circulating gas, (e1) Adjust the inert gas content of the circulating gas to a minimum, (f1) Repressurize the Fischer-Tropsch reactor with syngas feed, (g1) Repressurize the coolant to increase the temperature of the Fischer-Tropsch reactor until the Fischer-Tropsch reaction begins, and (h1) Introduce syngas into the Fischer-Tropsch reactor.

8. The method according to claim 7, wherein in step (d1), the pressure of the Fischer-Tropsch reactor is reduced to a pressure in the range of 5 bar absolute pressure to 10 bar absolute pressure.

9. The method according to claim 7 or claim 8, wherein in step (e1), the minimum inert gas content of the circulating gas is in the range of 60% to 80% by volume.

10. The method according to any one of claims 7 to 9, wherein in step (f1), the pressure is increased to 60% to 100% of the operating pressure prior to shutdown.

11. The method according to any one of claims 7 to 10, wherein in step (g1), when the coolant is pressurized boiling water, repressurization is achieved by prepressurizing the steam drum connected to the Fischer-Tropsch reactor using a steam ejector / ejector pump circuit.

12. The method according to any one of claims 1 to 5, wherein the process is completely shut down after the method.

13. The method of claim 12, wherein the method further comprises the following steps: (d2) Stop the circulation of the circulating gas, (e2) feed an inert gas into the Fischer-Tropsch reactor and the circuit at a pressure greater than that of the Fischer-Tropsch reactor and the circuit, and (f2) purge the Fischer-Tropsch reactor and the reaction gas circuit with the inert gas feed instead of the circulating gas.

14. The method according to claim 13, wherein in step (e2), the inert gas feed is a nitrogen feed.

15. The method according to claim 13 or claim 14, wherein in step (e2), the inert gas is supplied from a pressurized tank dedicated to the method.

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