A method for controlling a process including a steam system coupled to a reactor system.

Abstract

A method for controlling a process including a steam system coupled to a reactor system, the steam system comprising a steam vessel that supplies a stream of liquid water under pressure to the reactor system to cool the reactor system, thereby generating a steam stream, and receives a steam stream from the reactor system, the method comprising: (i) obtaining a first total liquid level measurement in the steam vessel using an inferred level device; (ii) obtaining a second total liquid level measurement in the steam vessel using a direct level device; (iii) calculating, using a control system, a difference between the first total liquid level measurement and the second total liquid level measurement; and (iv) activating an alarm using the control system if the difference between the first total liquid level measurement and the second total liquid level measurement is greater than or equal to 1% of the lower of the first total liquid level measurement and the second total liquid level measurement. A method is described.

Description

Technical Field

[0001] The present invention relates to a method for controlling a process including a steam system used to provide cooling to a reactor system, and more particularly to a method for a reactor system used to produce hydrocarbons by the Fischer-Tropsch process.

Background Art

[0002] The Fischer-Tropsch process involves a series of catalytic chemical reactions in a reactor system that produce various hydrocarbons having the formula (C n H 2n+2 ) from a feed gas containing hydrogen and carbon monoxide. The process can be operated in one or more Fischer-Tropsch reactors using an iron or cobalt-based catalyst at a pressure within the range of 0.1 to 10 MPa and a temperature within the range of 170 to 350 °C. The process can be operated to generate waxy hydrocarbons, which can be further processed into fuels in downstream processing.

[0003] The Fischer-Tropsch reaction is exothermic, and various configurations have been developed to prevent overheating and damage of the Fischer-Tropsch reactor and catalyst. In some configurations, a reactor system including a fixed bed of Fischer-Tropsch catalyst is cooled in heat exchange with boiling water under pressure. In some configurations, water can flow through coolant tubes within the bed of particulate catalyst. In other configurations, catalyst tubes containing particulate catalyst can be immersed in water. In any case, heat is transferred to the water, causing the water to boil and generate steam. Thus, the steam system is typically coupled to the reactor system to provide water and receive the steam generated by heat exchange within the reactor system.

[0004] There is a risk that hydrocarbon products from the Fischer-Tropsch reaction may leak into the steam system during the operating period when the steam system is operating at a lower pressure than the reactor system. The steam system typically comprises a steam vessel, often described as a steam drum, which supplies pressurized water to the reactor system and receives steam from the reactor system. Thus, the steam vessel contains both steam and liquid water.

[0005] The applicants recognized that hydrocarbons can accumulate in steam vessels due to their lower density (than water). Conventional steam drum level monitoring devices typically operate by measuring the displacement or pressure difference between two heights within the drum, so as hydrocarbons accumulate in the steam vessel over time, the effectiveness of these devices can gradually diminish. If a difference develops between the measured liquid level and the water level, there is a risk of insufficient reactor cooling, which could lead to runaway reactions and damage to the catalyst or reactor.

[0006] The applicants have found that process operation and control can be improved by using a combination of different technologies. [Overview of the project]

[0007] Accordingly, the present invention provides a method for controlling a process comprising a steam system coupled to a reactor system, wherein the steam system comprises a steam vessel that supplies a pressurized stream of liquid water to the reactor system to cool the reactor system, thereby generating a steam stream, and receiving the steam stream from the reactor system, the method comprising: (i) using an estimation level device to obtain a first total liquid level measurement in the steam vessel; (ii) using a direct level measuring device to obtain a second total liquid level measurement in the steam vessel; (iii) using a control system to calculate the difference between the first total liquid level measurement and the second total liquid level measurement; and (iv) using the control system to activate an alarm if the difference between the first total liquid level measurement and the second total liquid level measurement is 1% or more of the lower of the first and second total liquid level measurements.

[0008] The present invention provides a method for controlling a process comprising a steam system coupled to a reactor system, wherein the steam system comprises a steam vessel that supplies a pressurized stream of liquid water to the reactor system to cool the reactor system, thereby generating a steam stream, and receiving the steam stream from the reactor system, the method comprising: (i) using an estimation level device to obtain a first total liquid level measurement in the steam vessel; (ii) using a direct level measuring device to obtain a second total liquid level measurement in the steam vessel; (iii) using a control system to calculate the difference between the first total liquid level measurement and the second total liquid level measurement; and (iv) using the control system to activate an alarm if the difference between the first total liquid level measurement and the second total liquid level measurement is 5% or more of the lower of the first and second total liquid level measurements.

[0009] The present invention can be applied when the reactor system is operated at a higher pressure than the steam system, but it can also be applied when the system pressures are the same, or even when the steam system pressure is higher than the reactor system pressure.

[0010] The temperature of the liquid water coolant provided by the steam system may be in the range of 150 to 250°C. The pressure of the liquid coolant and the steam in the steam container may be in the range of 0.4 to 4.0 MPa (absolute).

[0011] The reactor system may be a Fischer-Tropsch reactor system containing a Fischer-Tropsch catalyst, but the present invention can be applied to any exothermic reactor system coupled to a steam system, which optionally provides cooling.

[0012] The steam container contains both steam and liquid water. This method uses two different types of measuring devices. This overcomes the drawbacks of using two devices of the same type.

[0013] This method involves obtaining a first total liquid level measurement in a steam vessel using an estimation level device. The estimation level device measures by estimating the total liquid level in the steam vessel using the difference in density or pressure within the vessel. Such devices include positive displacement devices or differential pressure devices. Such devices are used in the chemical industry and are commercially available. Since the liquid may include both liquid water and another liquid that may be immiscible with water, the liquid level is the total liquid level. In a preferred embodiment, the total liquid level includes the sum of the liquid water level and the immiscible liquid level, such as the liquid hydrocarbon level. If the immiscible liquid is a hydrocarbon or a mixture of hydrocarbons such as Fischer-Tropsch liquid, it typically forms a layer on top of the liquid water in the steam vessel because it is less dense than water. Therefore, the level detected will be the hydrocarbon level above the liquid water in the steam vessel. Since the estimated level is typically based on the density of water, the presence of a liquid hydrocarbon layer can cause errors in the measurement of the estimation level device. Therefore, the presence of a lower-density liquid causes the estimation level device to read a lower level than the actual level, because the weight of the liquid measured by the estimation level device is lighter.

[0014] This method also includes simultaneously or sequentially acquiring a second total liquid level measurement in the steam vessel using a direct level measuring device. The direct level measuring device may measure the total liquid level in the steam vessel using a direct scanning method. Such devices include ultrasonic or guided wave radar (GWR) devices. Such devices are used in the chemical industry and are commercially available. Alternatively, a float level device may be used to directly measure the liquid water level, connected to the steam vessel and using a magnet attached to a float that indicates the level.

[0015] When the reactor system includes a Fischer-Tropsch reactor, using both an estimated level device and a direct level measuring device offers certain advantages, such as the tendency for the level indication to deviate when hydrocarbons begin to deposit in the liquid being measured.

[0016] In some configurations, guided wave radar (GWR) equipment may be provided to the steam vessel in addition to existing displacement or differential pressure equipment.

[0017] This method includes the step of using a control system to compare a first total liquid level measurement with a second total liquid level measurement and calculating the difference between the first total liquid level measurement and the second total liquid level measurement. This comparison involves subtracting a smaller or lower liquid level measurement from a larger or higher liquid level measurement. In this way, the difference is a positive number. The comparison may use statistical methods known in the art, such as an n-point moving average of the two values ​​over time, where n is a number between 2 and 100.

[0018] Steps (i), (ii), and (iii) of the method may be performed while taking measurements continuously or at regular intervals of a few seconds, a few minutes, or a few hours. The calculations are performed using a control system. The control system may be any suitable control system used to control chemical reactors and processes. The control system may be a distributed control system (DCS). Distributed control systems are used to control a number of chemical processes and are commercially available.

[0019] The method of the present invention includes using a control system to calculate the difference between a first total liquid level measurement and a second total liquid level measurement, and if the difference between the first and second total liquid level measurements is 1% or more or 5% or more of the lower of the two total liquid level measurements, the control system activates an alarm. If the difference is lower than this value, the control system does not activate an alarm, but simply repeats the previous step to monitor the steam vessel. This can be done continuously or periodically.

[0020] If the difference between the measurements is 1% or more, or 5% or more, of the lower of the first total liquid level measurement and the second total liquid level measurement, an alarm is triggered so that the process operator can investigate the cause of the difference. This may include, in response to the alarm, one or more of the following steps: monitoring the flow and temperature of liquid water from the steam vessel; monitoring the temperature of the reaction vessel in the reactor system; and monitoring the chemical composition of the liquid in the steam vessel, for example, by taking a liquid sample and analyzing its pH.

[0021] A display system with a visible or audible alarm may be connected to the control system. The connection of the control system to any alarm system may be wireless or by direct hardwiring.

[0022] The operator may use the reactor system to shut down the process. Shutting down the reactor system may be necessary if the calculated difference is 1% or more, or 5% or more, particularly 5% or more. Therefore, in some embodiments, the method includes a further step of shutting down the reactor system to prevent overheating of the reactor and catalyst. Methods for shutting down a reactor system are known. Methods for shutting down a Fischer-Tropsch reactor system are described, for example, in British Patent Application Publication No. 2223237(A), U.S. Patent No. 10329492, and International Publication No. 2022 / 11784(A1), the contents of which are incorporated herein by reference. In such methods, the steam vessel may be depressurized to cool the liquid water coolant and the supply of fresh synthesis gas may be stopped. Alternatively or additionally, if desired, an inert gas such as nitrogen gas may be injected into the reactor system.

[0023] This method can be usefully applied to processes involving a Fischer-Tropsch reactor containing a cooled Fischer-Tropsch catalyst, which is supplied with a reaction gas mixture and operated within a loop.

[0024] The reaction gas mixture fed to the Fischer-Tropsch reactor typically contains, in addition to synthesis gas, recycled gas recovered from the Fischer-Tropsch reactor product stream. The synthesis gas for the Fischer-Tropsch process contains hydrogen and carbon monoxide. The recycled gas will typically contain unreacted synthesis gas, carbon dioxide, and possibly light hydrocarbons.

[0025] The Fischer-Tropsch process ideally involves a series of chemical reactions that produce various hydrocarbons having the formula (C n H 2n+2 ). A more useful reaction produces alkanes from the reaction gas mixture as follows: (2n + 1)H2 + nCO → C n H 2n+2 + nH2O where n is typically 5 to 100 or more, and the preferred products have n in the range of 10 to 20.

[0026] The Fischer-Tropsch reactor is typically operated within a synthesis loop. That is, the reaction gas mixture is fed to the Fischer-Tropsch reactor where it reacts on a Fischer-Tropsch catalyst to form a product mixture containing liquid and gaseous hydrocarbons, steam, and unreacted gas. The product gas mixture is cooled after exiting the Fischer-Tropsch reactor to condense steam and facilitate the recovery of liquid hydrocarbons. A portion of the unreacted gas is optionally returned to the Fischer-Tropsch reactor as recycled gas after separation of light hydrocarbons, thereby forming the synthesis loop. The recycled gas is combined with synthesis gas to form the reaction gas mixture outside the Fischer-Tropsch reactor, which allows for more efficient temperature control of the feed to the Fischer-Tropsch reactor. Operating the Fischer-Tropsch reactor within a loop improves the conversion efficiency of the process. A purge may be taken from the loop as Fischer-Tropsch tail gas for further processing to prevent the accumulation of inert gases.

[0027] The Fischer-Tropsch reactor can be operated at pressures within the range of 10 to 100 bar absolute (0.1 to 10 MPa) and temperatures within the range of 170 to 350 °C. Operation on a cobalt catalyst can be at 20 to 50 bar absolute and 200 to 320 °C. The gas hourly space velocity (GHSV) for continuous operation can be in the range of 1000 to 25000 hr -1 -1.

[0028] The Fischer-Tropsch reactor contains a Fischer-Tropsch catalyst that is indirectly cooled by water under pressure. The Fischer-Tropsch catalyst can be provided as a bed in which tubes or plates carrying the coolant are installed, or the catalyst can be provided in a plurality of reaction tubes immersed in a coolant flowing around the outside of the plurality of reaction tubes. The latter reactor technology is preferred.

[0029] Any Fischer-Tropsch catalyst may be used, but iron and cobalt Fischer-Tropsch catalysts are preferred. Cobalt-based Fischer-Tropsch catalysts are preferred over iron-based catalysts due to their lower carbon dioxide selectivity. In a particularly preferred configuration, the Fischer-Tropsch catalyst is used in combination with a catalyst support suitable for use in a tubular Fischer-Tropsch reactor, where the catalyst-containing catalyst support is placed in one or more tubes cooled by circulating pressurized water. "Catalyst support" means a catalyst container, for example, in the form of a cup or can, configured to allow gas and / or liquid to enter and exit the support and flow through a bed of catalyst or catalyst precursor placed within the support. Any suitable catalyst support may be used. In one configuration, the catalyst support is as described in International Publication 2011 / 048361, the contents of which are incorporated herein by reference. In an alternative configuration, the catalyst support may include a catalyst monolith as disclosed in International Publication 2012 / 136971, the contents of which are also incorporated herein by reference. In yet another alternative configuration, the catalyst support may be one disclosed in International Publication No. 2016 / 050520, the contents of which are also incorporated herein by reference. In a preferred embodiment, the reactor system includes a tubular Fischer-Tropsch reactor in which a catalyst support containing a Fischer-Tropsch catalyst is placed in one or more tubes that are cooled by a cooling medium. [Brief explanation of the drawing]

[0030] The present invention will be further described with reference to the drawings. [Figure 1] This is a diagram of one embodiment of a system to which the method of the present invention may be applied.

[0031] Those skilled in the art will understand that the drawings are schematic and that commercial plants may require additional equipment such as raw material drums, pumps, vacuum pumps, compressors, gas recirculation compressors, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, and storage tanks. The provision of such ancillary equipment does not form part of the present invention and follows conventional chemical engineering practices. [Modes for carrying out the invention]

[0032] In Figure 1, the steam system 10 is coupled to the Fischer-Tropsch reactor system 12. The DCS control system 14 controls the steam system and the reactor system by valves 16, 18, and 20. The steam system 10 includes a steam vessel 22 to which a stream of boiler feedwater is supplied via line 24. This steam vessel supplies a stream of pressurized liquid water via line 26 to the Fischer-Tropsch reactor 28, where the liquid water is used to cool tubes 30 containing multiple Fischer-Tropsch catalysts. The feed gas 32, including a fresh synthesis gas stream 34 and a recycled gas stream 36, is supplied to the reactor 28, where the feed gas reacts on the catalysts in tubes 30 to produce hydrocarbon liquid products. These hydrocarbon liquid products, along with unreacted gas and by-product water, are recovered from the reactor as a product stream 38 for further processing. The fresh synthesis gas stream 34 and the recycled gas stream 36 are compressed by a compressor (not shown). The pressure of the supply gas mixture 32 is higher than the pressure of the pressurized water supplied through line 26. The recycled gas stream 36 is recovered from the product stream 38 using one or more gas-liquid separators (not shown).

[0033] The formation of the hydrocarbon liquid generates heat, which converts a portion of the liquid water supplied by line 26 into steam in reactor 28. The mixture of steam and liquid water is recovered from reactor 28 and supplied to steam vessel 22 via line 40. The steam system 10 further comprises an estimation level device 42 that obtains a first total liquid level measurement in steam vessel 22, and a direct level measuring device 44 that obtains a second total liquid level measurement in steam vessel 22. The levels detected by devices 42 and 44 are communicated to a controller 14 (indicated by dashed lines 48 and 50), which compares the first total liquid level measurement and the second total liquid level measurement and calculates the difference between them. The control system 14 is connected to a display system 46 having visible and audible alarms (indicated by dashed line 52). If the difference between the first total liquid level measurement and the second total liquid level measurement is 5% or more of the lower of the first and second total liquid level measurements, the control system 14 is used to activate an alarm in the display system 46.

[0034] The control system 14 is connected to valves 16, 18, and 20 (as indicated by dashed lines 54, 56, and 58), and the valves 16, 18, and 20 can be adjusted to bring about a controlled shutdown of the reactor system 12 based on commands from the control system or an operator, for example, based on the temperature of the catalyst in the tube 30. For example, valve 16 can be opened to reduce the pressure in the steam vessel 22, thereby lowering the temperature of the liquid water and suppressing the Fischer-Tropsch reaction. Alternatively or additionally, the supply of fresh synthesis gas may be stopped by closing valve 20. The circulating compressor continues to supply the recycle gas stream 32 to the reactor. Optionally, a pressure vessel (not shown) containing high-pressure nitrogen at a higher pressure than the feed gas 32 may be connected to the recycle gas line 36 or the feed line 32 to inject nitrogen gas into the catalyst-filled tube 30 in an emergency. Subsequently, valve 18, which controls the supply of boiler feedwater to the steam vessel 22, may also be closed to shut off the feedwater. Furthermore, the disclosure of the present invention may include the following embodiments. (Aspect 1) A method for controlling a process comprising a steam system coupled to a reactor system, wherein the steam system comprises a steam vessel that supplies a pressurized stream of liquid water to the reactor system to cool the reactor system, thereby generating a steam stream, and receiving the steam stream from the reactor system, the method comprising: (i) obtaining a first total liquid level measurement in the steam vessel using an estimation level device; (ii) obtaining a second total liquid level measurement in the steam vessel using a direct level device; (iii) calculating the difference between the first total liquid level measurement and the second total liquid level measurement using a control system; and (iv) if the difference between the first total liquid level measurement and the second total liquid level measurement is 1% or more of the lower of the first total liquid level measurement and the second total liquid level measurement, the control system activating an alarm. (Aspect 2) The method according to embodiment 1, wherein the reactor system is operated at a higher pressure than the steam system. (Aspect 3) The method according to embodiment 1 or 2, wherein the estimation level device is a positive pressure device or a differential pressure device. (Aspect 4) The method according to any one of embodiments 1 to 3, wherein the direct level measuring device is a guided wave radar device or a float device. (Appendix 5) The method according to any one of embodiments 1 to 4, wherein steps (i), (ii), and (iii) are performed sequentially. (Aspect 6) The method according to any one of embodiments 1 to 4, wherein the method steps (i), (ii), and (iii) are performed by measurements every few seconds, every few minutes, or every few hours. (Aspect 7) The method according to embodiment 1, wherein the difference between the first total liquid level measurement and the second total liquid level measurement is calculated using a time average or a statistical method. (Pattern 8) The method according to any one of embodiments 1 to 7, wherein the control system is a distributed control system. (Aspect 9) The method according to any one of embodiments 1 to 8, wherein a display system having a visible or audible alarm is connected to the control system. (Aspect 10) The method according to any one of embodiments 1 to 9, wherein, in response to the alarm, the method further comprises one or more of the steps of monitoring the flow and temperature of the liquid water from the steam vessel, monitoring the temperature of the reaction vessel in the reactor system, and monitoring the chemical composition of the liquid in the steam vessel. (Aspect 11) The method according to any one of embodiments 1 to 10, wherein the method further includes the step of shutting down the reactor system in response to the alarm. (Aspect 12) The method according to any one of embodiments 1 to 11, wherein the reactor system is a Fischer-Tropsch reactor system comprising a Fischer-Tropsch catalyst that is indirectly cooled by water under pressure. (Aspect 13) The method according to embodiment 12, wherein the Fischer-Tropsch catalyst is provided as a floor on which water-carrying pipes or plates are installed, or the Fischer-Tropsch catalyst is provided in a plurality of water-cooled reaction tubes. (Aspect 14) The method according to embodiment 12 or 13, wherein the Fischer-Tropsch catalyst is used in combination with a catalyst support in a tubular Fischer-Tropsch reactor, and the catalyst support containing the Fischer-Tropsch catalyst is arranged in one or more tubes that are cooled by circulating water under pressure. (Aspect 15) A method for controlling a process comprising a steam system coupled to a reactor system, wherein the steam system comprises a steam vessel that supplies a pressurized stream of liquid water to the reactor system to cool the reactor system, thereby generating a steam stream, and receiving the steam stream from the reactor system, the method comprising: (i) obtaining a first total liquid level measurement in the steam vessel using an estimation level device; (ii) obtaining a second total liquid level measurement in the steam vessel using a direct level device; (iii) calculating the difference between the first total liquid level measurement and the second total liquid level measurement using a control system; and (iv) if the difference between the first total liquid level measurement and the second total liquid level measurement is 5% or more of the lower of the first total liquid level measurement and the second total liquid level measurement, the control system activating an alarm.

Claims

1. A method for controlling a process comprising a steam system coupled to a reactor system, wherein the steam system comprises a steam vessel that supplies a pressurized stream of liquid water to the reactor system to cool the reactor system, thereby generating a steam stream, and receiving the steam stream from the reactor system, the method comprising: (i) obtaining a first total liquid level measurement in the steam vessel using an estimation level device; (ii) obtaining a second total liquid level measurement in the steam vessel using a direct level measuring device; (iii) calculating the difference between the first total liquid level measurement and the second total liquid level measurement using a control system; and (iv) the difference between the first total liquid level measurement and the second total liquid level measurement being the first A method for controlling a process comprising a steam system coupled to a reactor system, the step of using the control system to activate an alarm if the total liquid level is 1% or more of the lower of the first total liquid level measurement and the second total liquid level measurement, wherein the reactor system is a Fischer-Tropsch reactor system comprising a Fischer-Tropsch catalyst that is indirectly cooled by a stream of liquid water from the steam vessel, the Fischer-Tropsch reactor system is operated at a higher pressure than the steam system, and the difference between the first total liquid level measurement and the second total liquid level measurement that activates the alarm is caused by hydrocarbon products of the Fischer-Tropsch reactor system that leak into the steam system and accumulate in the steam vessel.

2. The method according to claim 1, wherein the estimation level device is a volumetric type device or a differential pressure device.

3. The method according to claim 1, wherein the direct level measuring device is a guided wave radar device or a float device.

4. The method according to claim 1, wherein steps (i), (ii), and (iii) are performed in sequence.

5. The method according to claim 1, wherein steps (i), (ii), and (iii) are performed by measurements every few seconds, every few minutes, or every few hours.

6. The method according to claim 1, wherein the difference between the first total liquid level measurement and the second total liquid level measurement is calculated using a time average or a statistical method.

7. The method according to claim 1, wherein the control system is a distributed control system.

8. The method according to claim 1, wherein a display system having a visible or audible alarm is connected to the control system.

9. The method according to claim 1, wherein, in response to the alarm, the method further comprises one or more of the steps of monitoring the flow and temperature of the liquid water from the steam vessel, monitoring the temperature of the reaction vessel in the reactor system, and monitoring the chemical composition of the liquid in the steam vessel.

10. The method according to claim 1, wherein the method further includes the step of shutting down the reactor system in response to the alarm.

11. The method according to claim 1, wherein the Fischer-Tropsch catalyst is provided as a floor on which water-carrying pipes or plates are installed, or the Fischer-Tropsch catalyst is provided in a plurality of water-cooled reaction tubes.

12. The method according to claim 1, wherein the Fischer-Tropsch catalyst is used in combination with a catalyst support in a tubular Fischer-Tropsch reactor, and the catalyst support containing the Fischer-Tropsch catalyst is arranged in one or more tubes that are cooled by circulating water under pressure.

13. The method according to claim 1, wherein the control system is used to activate the alarm if the difference between the first total liquid level measurement and the second total liquid level measurement is 5% or more of the lower of the first total liquid level measurement and the second total liquid level measurement.

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