System for methanol synthesis
By arranging an electric heater inside the steam drum to heat the feedwater, the problem of insufficient hot steam in the green methanol synthesis process was solved, ensuring stable operation of the system under startup and load changes, reducing costs and improving system flexibility.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CASALE SA
- Filing Date
- 2024-10-22
- Publication Date
- 2026-05-19
AI Technical Summary
In methanol synthesis, especially in green processes, there are challenges such as the lack of hot steam for heating the converter during startup and the need to control the converter under load changes. Traditional methods are particularly problematic in systems that rely on renewable energy.
An electric heater is installed inside the steam drum to heat the feedwater sent to the converter, providing additional heat input to compensate for insufficient hot steam, and stabilizing the reaction system under transient conditions through control modes.
It enables stable system operation in the absence of hot steam or under load changes, reduces structural costs and improves system flexibility and controllability.
Smart Images
Figure CN122070170A_ABST
Abstract
Description
Technical Field
[0001] This invention pertains to the field of methanol industrial production. Background Technology
[0002] Methanol is industrially produced by reacting supplementary syngas (“supplementary gas” or “syngas”) containing hydrogen and carbon oxides.
[0003] A reaction system for converting the makeup gas typically includes at least one catalytic converter in a synthesis loop. The synthesis loop includes a catalytic converter, one or more heat exchangers, a condenser, a separator, and piping arranged to return at least a portion of the gaseous fraction to the converter via a compressor. Methanol is formed in the catalytic converter, the converter hot effluent is cooled in one or more heat exchangers, and the reaction effluent is condensed in the condenser after cooling to produce a methanol-containing liquid product, which is separated from the gaseous fraction containing unreacted gases in the separator.
[0004] The makeup gas is characterized by its stoichiometric coefficient, which is a function of the molar numbers of hydrogen, carbon monoxide, and carbon dioxide, and is characterized by the molar ratio CO / CO2. The stoichiometric coefficient is defined as SN = (H2-CO2) / (CO+CO2), and a makeup gas with a stoichiometric coefficient equal to or greater than 2.0 is highly desirable for methanol synthesis. A high CO / CO2 ratio indicates high reactivity of the gas, meaning less catalyst is needed to produce a given amount of methanol.
[0005] In the converter, the significant amount of heat released by the exothermic conversion is typically removed via an internal heat exchanger connected to the steam system. The heat from the reaction can be used to generate steam at fairly high pressure, which is an attractive way to recover energy within the process.
[0006] The heat exchanger can be directly immersed in the catalyst. A converter with a heat exchanger immersed in the catalyst is called an isothermal converter because the temperature of the catalytic bed is maintained within a narrow, almost constant range. Converters that utilize the heat of reaction to generate steam are called steam rise converters.
[0007] Make-up gas can be produced through coal gasification or through steam reforming or partial oxidation of hydrocarbons such as natural gas. Recently, methods for producing hydrogen using renewable energy sources have emerged to reduce emissions and lower the carbon intensity of the entire process. Traditionally, process sustainability has been indicated by color. Coal-based processes are referred to as "brown"; natural gas-based processes as "grey"; processes featuring carbon dioxide capture as "blue"; and processes where hydrogen is produced from biofuels or renewable electricity as "green." Interest in green hydrogen has increased dramatically in recent years.
[0008] In some cases, it may be desirable to provide a heat input to the methanol converter. This is typically the case during startup, when the catalyst and process stream contained in the converter must be heated to operating temperatures. Due to the high hydrogen partial pressure and harsh CO conditions, installing additional heaters on the process side (in direct contact with the makeup gas) is technically challenging.
[0009] The known approach is to utilize the internal heat exchanger (steam side) of the converter to heat it. The heat is provided by hot steam (“start-up steam”) generated elsewhere in the process. In conventional coal- or natural gas-based plants, there is typically a large quantity of sufficiently hot steam, for example, from the reforming section. However, there are practical cases where the availability of steam at a sufficient temperature for heating the converter is limited or insufficient. This lack of hot steam may occur when there is a small amount of thermal process stream available for heat recovery and steam production, or when the heat for this purpose is unavailable for any reason. An example of considerable interest is the so-called green process, where some or all of the hydrogen or syngas contained in the makeup gas is produced from renewable energy sources. Compared to conventional combustion reforming processes, green processes inherently have fewer thermal process streams from which steam can be generated.
[0010] Another problem that typically, but not exclusively, plagues green processes involves syngas production relying on intermittent power sources. In this case, fluctuations in the amount of hydrogen produced in the front end cause significant variations in the load on the synthesis loop. The load can be defined as the amount of fresh makeup gas fed into the loop and converted into methanol, or the amount of methanol produced in the loop.
[0011] A common problem arises when equipment needs to operate smoothly at very low loads (such as 20% or 10% of rated capacity), raising the question of how to manage control loops operating at partial load. This issue is less common in coal- or gas-based equipment, which typically relies on a nearly constant fuel input and is designed to operate almost always close to 100% of rated capacity. In contrast, the problem is frequently encountered in green equipment, as most renewable energy sources, such as solar and wind power, are naturally susceptible to fluctuations.
[0012] WO 2023 / 110479 discloses an apparatus and process for producing methanol, wherein an electric heater is arranged on the inlet line of the converter. Summary of the Invention
[0013] The present invention solves the aforementioned problems of lack of hot steam for heating the converter when needed (e.g., during startup) and / or for controlling the converter and synthesis loop under load variations.
[0014] The above-mentioned problems are solved by the reaction system for methanol synthesis and the method for controlling the reaction system according to the claims.
[0015] This invention uses an electric heater to heat the boiling feedwater supplied to the internal heat exchanger of the converter. Therefore, the heat generated in the electric heater is transferred to the reaction system, and this invention compensates for reduced or no availability of hot steam during the process. The electric heater is strategically located inside the pressure vessel of the steam drum connected to the converter. According to embodiments of the invention, the electric heater can be fixed or removable. Furthermore, the electric heater provides an additional means of controlling the reaction system during transients or when operation under reduced loads is required.
[0016] Compared to the in-line electric heater taught in WO 2023 110479, the electric heater located inside the steam drum has significant advantages. First, it eliminates the need for a separate container for the electric heater. Second, the significant pressure drop introduced by in-line electric heaters is avoided in this invention. If the circulation from the steam drum to the converter is forced circulation via a pump, this means less power is absorbed by the pump. If the circulation is natural circulation by gravity, this invention reduces the static head required to ensure circulation, thereby reducing the height of the steam drum relative to the converter, and thus significantly reducing structural costs.
[0017] This invention relates to a reaction system for methanol synthesis, comprising a catalytic converter and a steam system, wherein the converter includes at least one internal heat exchanger connected to the steam system and arranged to generate steam using the heat from the methanol synthesis reaction, wherein the steam system includes: a steam drum separate from the converter, the steam drum being connected to the heat exchanger via a water inlet line arranged to supply water from the steam drum to the heat exchanger; and a steam collection line adapted to collect the steam generated in the heat exchanger, wherein the steam system includes an electric heater installed inside the steam drum, and the electric heater being arranged to heat the feedwater sent to the converter.
[0018] In a preferred embodiment, the electric heater includes an electric heating tube bundle inside the pressure vessel of the steam drum.
[0019] Electric heaters can have a modular structure, for example, formed by multiple electric heating elements.
[0020] In one embodiment, in addition to the electric heater integrated in the steam drum, the system includes at least one online electric heater. Preferably, the online electric heater is located on the water inlet line and / or steam outlet line connected to the steam drum. According to some embodiments of the invention, the online heater can be added during retrofitting.
[0021] This invention is applicable to new methanol plants and the retrofitting of existing ones. Retrofitting according to the invention includes providing the aforementioned electric heater in the steam drum of the steam system. This invention is particularly meaningful for retrofitting brown (coal-based) or grey (natural gas-based) methanol plants when, for example, a portion of the original hydrogen or syngas source is replaced by hydrogen or syngas produced from renewable energy sources. Retrofitting according to the invention can also be carried out to allow smooth operation under variable loads, particularly when the plant needs to operate at low loads (e.g., less than 50% of rated capacity, such as 20% or less).
[0022] Another aspect of the invention is a method for controlling the aforementioned reaction system for methanol synthesis, wherein the reaction system is selectively controlled according to a first mode or a second mode, in which a steam system removes heat from the converter, and in the second mode, a steam system supplies heat to the converter. In the first mode, heat is removed primarily through the evaporation of feedwater sent to the converter. In the second mode, heat is transferred to the converter through feedwater heated by the electric heater in the steam drum.
[0023] Typically, the conversion of the make-up gas to methanol releases heat (an exothermic reaction), therefore, the system operates in the first mode. The second mode can be selected during transient periods when the converter requires heat input. For example, the second mode can be selected during the start-up of the reaction system. The second mode can also be selected during load changes in the reaction system.
[0024] In a highly preferred embodiment, at least a portion of the supplemental gas production relies on renewable energy sources. Specifically, the hydrogen in the supplemental gas can be produced partially or entirely from renewable sources, such as water electrolysis driven by renewable energy. Examples of renewable sources include solar, wind, biomass, hydropower, and other naturally occurring sources. In such embodiments, periods of reduced availability of renewable sources (e.g., day / night solar activity) reduce hydrogen production and the amount of supplemental gas that can be fed into the reaction system. The intermittent input of renewable energy may also be determined by changes in energy prices. The second operating mode can be selected during periods of temporary lack or reduced availability of renewable energy to maintain appropriate temperatures in the converter.
[0025] The method of this invention is applicable to all device embodiments described herein. Modifications to the method of this invention may include providing a control system configured to operate according to the method of this invention. Attached Figure Description
[0026] Now using Figure 1 The schematic diagram illustrates the invention. Figure 1 An embodiment of the present invention is shown.
[0027] Figure 1This is a simplified schematic diagram of a reaction system used to produce methanol. The diagram shows the following items:
[0028] 100 reaction system
[0029] 1. Methanol converter
[0030] 2. Internal heat exchanger (evaporator) of the converter
[0031] 3. Fresh replenishment gas containing hydrogen and carbon oxides
[0032] 4. Product effluent from the converter
[0033] 5. Treatment of converter effluent, including cooling / condensation and separation of liquid fractions.
[0034] 6. Liquid products containing methanol (crude methanol)
[0035] 7 Unreacted gases (gaseous fractions separated from the effluent after cooling / condensation)
[0036] 8. Circulating compressor
[0037] 9. Unreacted gas recirculated to converter 1
[0038] 10 Steam System
[0039] 11. Steam drum
[0040] 12 pumps
[0041] 13 Feed water to heat exchanger 2
[0042] 14 Steam pipeline
[0043] 15. Makeup water for the steam drum
[0044] 16 Steam extracted from the steam drum
[0045] 20 Electric heaters Detailed Implementation
[0046] Converter 1 is typically part of the synthesis loop. Figure 1 Block 5 represents the treatment of product effluent 4, which typically includes cooling, methanol condensation, and separation of the liquid fraction 6 containing methanol (crude methanol) from the gaseous fraction 7 containing unreacted gases. At least a portion of the unreacted gases is returned to the converter via a recirculating compressor 8, thus forming a loop. Purge gas (not shown) is removed from the loop, for example upstream of compressor 8. The feed to converter 1 consists of fresh make-up gas from line 3 and recirculated gas from line 9.
[0047] Fresh supplement gas 3 is a mixture of hydrogen and carbon oxides obtained at a suitable front end of the methanol plant. In a preferred embodiment, the hydrogen or syngas contained in the fresh gas is produced partly or entirely from renewable energy sources, such as solar-powered water electrolysis. In some embodiments, the carbon dioxide contained in the fresh gas can be obtained from a carbon dioxide capture process to reduce emissions.
[0048] The heat exchanger 2 inside the converter 1 removes some of the heat of reaction to generate steam. An electric heater 20, for example, an electrically heated tube bundle, is housed within the pressure vessel of the steam drum 11. The heater 20 can increase the temperature of the water supplied to the heat exchanger 2 via line 13 to provide temporary heat input to the converter 1 when needed. In an embodiment, additional online electric heaters are provided on the inlet water line 13 and / or the steam line 14.
Claims
1. A reaction system (100) for synthesizing methanol from supplemental gas, comprising a catalytic converter (1) and a steam system (10), wherein, The converter (1) includes at least one internal heat exchanger (2) arranged to generate steam using the heat from the methanol synthesis reaction. The steam system includes a steam drum (11) separate from the converter, which is connected to the heat exchanger via a water inlet line (13) to supply water to the heat exchanger and collects the steam generated in the heat exchanger via a steam line (14). The steam system includes an electric heater (20) installed inside the steam drum (11) and the electric heater is arranged to heat the feed water sent to the converter.
2. The system according to claim 1, wherein, The electric heater includes an electric heating tube disposed inside the pressure vessel of the steam drum.
3. The system according to claim 1 or 2, wherein the electric heater is integrated with the steam drum or is removable from the steam drum.
4. The system according to any one of claims 1 to 3, in addition to the electric heater (20) of the steam drum, includes at least one online electric heater, which is disposed on the water inlet line (13) and / or steam outlet line (14) connected to the steam drum.
5. A method for controlling a reaction system (100) for synthesizing methanol from supplemental gas, wherein: The reaction system includes a catalytic converter (1) and a steam system (10), wherein the converter includes at least one internal heat exchanger (2) connected to the steam system and arranged to generate steam using the heat from the methanol synthesis reaction, wherein the steam system includes a steam drum (11) separate from the converter, the steam drum being connected to the heat exchanger via a water inlet line to supply water to the heat exchanger and collecting the steam formed in the heat exchanger via a steam line, wherein the steam drum includes an electric heater (20) installed inside the steam drum, and the electric heater being arranged to heat the feed water to the converter, wherein the method includes: The reaction system is selectively controlled according to a first mode or a second mode. In the first mode, the steam system removes heat from the converter by evaporation of feedwater sent to the converter. In the second mode, the steam system supplies heat to the converter by feedwater heated by the electric heater in the steam drum.
6. The method according to claim 5, wherein, The second mode is selected at least during the startup of the reaction system.
7. The method according to claim 5 or 6, wherein, The second mode shall be selected at least during load changes in the reaction system.
8. The method according to claim 7, wherein, The load variation includes operating the reaction system at a partial load of 50% or 20% less than the system's rated load.
9. The method according to claim 7 or 8, wherein, The production of at least part of the supplemental gas relies on renewable energy, and the second mode is selected during periods of temporary lack or reduced availability of the renewable energy.
10. The method according to claim 9, wherein, At least some of the hydrogen in the supplementary gas is produced by water electrolysis using renewable energy sources, such as solar, wind, or hydropower.
11. The method according to any one of claims 5 to 10, wherein, The reaction system further includes at least one online electric heater located on the water inlet line (13) and / or steam transmission line (14) connected to the steam drum, wherein, in the second operating mode, heat is supplied to the converter through the heater (20) installed in the steam drum and through the online heater.
12. A method for modifying a methanol production line, wherein, In the original equipment, the makeup gas for methanol synthesis is produced from hydrocarbons, such as coal or natural gas, via any of the following methods: steam reforming, partial oxidation, or gasification. The equipment includes a steam-rising methanol converter with an internal heat exchanger connected to a steam drum. This internal heat exchanger is used to utilize the heat released from the methanol synthesis chemical reaction to produce steam. The method includes: The steam drum is modified by installing an electric heater inside the steam drum, the electric heater being arranged to heat the feedwater sent to the internal heat exchanger of the converter.
13. The method of claim 12, further comprising the step of replacing at least a portion of the hydrogen or syngas contained in the supplemental gas with hydrogen or syngas generated from renewable energy.
14. The method of claim 12 or 13, further comprising the step of adding an online heater to a water line or steam line connected to the steam drum.
15. The method according to any one of claims 12 to 14, comprising providing an S control system configured to operate according to any one of claims 5 to 11.