Combined water-gas shift method and system

Abstract

The present application belongs to the technical field of coal chemical synthetic gas preparation, and specifically relates to a combined water gas shift method and system. The system comprises a first shift furnace and a second shift furnace connected in sequence, the first shift furnace is a combined shift furnace with a medium-pressure steam drum, and the second shift furnace is a temperature-controlled shift furnace with a low-pressure steam drum. The combined shift furnace comprises an outer shell, and upper and lower reaction sections are arranged in the outer shell. Each reaction section comprises a bottom inner head and a top cover layer. A center pipe with a through hole is arranged at the center of the region between the inner head and the cover layer. A catalyst bed layer is arranged around the outer periphery of the center pipe. Heat exchange tube bundles are embedded in the catalyst bed layer. An outer distributor is sleeved on the catalyst bed layer, and an outer gap is formed between the outer distributor and the outer shell. The method uses the above system, can stabilize the temperature of the catalyst bed layer, reduce the loss of effective gas, output medium-pressure superheated steam, and has low investment and operation costs.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical syngas preparation technology, specifically a combined water-gas conversion method and system. Background Technology

[0002] The water-gas shift reaction is a core process in modern coal chemical engineering. It generates H2 and CO2 through the catalytic reaction of CO and water vapor, thereby matching the hydrogen-to-carbon ratio required by downstream synthesis processes. The crude coal gas produced by dry pulverized coal gasification has a dry basis CO content of 55-75% and a water-to-gas ratio of only 0.15-1.1. If this type of crude coal gas is directly subjected to a shift reaction, the reaction is highly exothermic, and direct reaction can easily cause the catalyst bed to overheat (up to 500 ℃), triggering methanation side reactions and rapid catalyst deactivation. This is a recognized technical challenge in the industry.

[0003] Currently, there are two technologies for water-gas conversion for high-concentration CO gas: adiabatic conversion and isothermal (temperature-controlled) conversion. Both have significant drawbacks. For example, CN110790223A discloses an isothermal conversion hydrogen production method and isothermal conversion furnace for water-coal slurry gasification. This disclosed isothermal conversion furnace is an independent type, with only tube bundles for heat exchange inside the furnace. It relies on an external medium-pressure steam drum to remove the reaction heat, and can only produce medium-pressure saturated steam. It cannot complete steam superheating inside the reactor. To obtain superheated medium-pressure steam that can drive the turbine, an additional independent steam superheater furnace and a fuel gas combustion system are required, increasing equipment investment, fuel consumption, and carbon emissions. At the same time, this scheme only uses single-stream feed gas temperature control. When dealing with ultra-high CO feed gas from dry pulverized coal, the system steam addition must be significantly increased, resulting in high steam energy consumption. The single isothermal heat transfer mode has a single heat recovery level, resulting in low energy cascade utilization efficiency. The series arrangement of multiple reactors leads to long pipelines and high system resistance.

[0004] For example, CN117125672A discloses a deep conversion process and system for hydrogen production via dry coal powder gasification coupled with water electrolysis. This patent adopts a split-series architecture of "pre-stage multi-stage adiabatic conversion furnace + post-stage independent temperature-controlled conversion furnace," with the adiabatic section and temperature-controlled section being two independent devices, and multiple auxiliary machines such as humidification and waste heat boilers added in between. The multi-stage adiabatic conversion relies on a large amount of externally supplied steam to suppress overheating, resulting in significant steam consumption; the adiabatic section lacks a built-in steam superheating structure, and the reaction heat is only used to produce saturated low-pressure steam, resulting in low thermal energy grade; complex heat exchange and humidification equipment needs to be set up between the two reactors, resulting in a lengthy process flow, a large number of devices, and high land occupation and engineering investment; at the same time, this split structure cannot achieve precise mixing and temperature control of the quench gas and the reaction gas in the same furnace body, and there is still a risk of local overheating under start-up, shutdown, and low-load conditions, and the effect of suppressing methanation side reactions is limited.

[0005] In summary, the current mainstream conversion processes generally suffer from several shortcomings: First, temperature control methods are limited, pure adiabatic processes have high steam energy consumption, and separate series or single isothermal furnaces lack in-furnace cooling buffer structures, making them prone to overheating under high CO feed conditions, resulting in short catalyst lifespan and significant effective gas loss. Second, there are few heat recovery stages; traditional isothermal furnaces only produce saturated steam, and if superheated steam is required, an external heating furnace must be added, increasing investment and energy consumption. Third, the equipment is dispersed, with multiple devices for reaction, steam production, and steam superheating functions, resulting in numerous pipelines and high construction and maintenance costs. Fourth, the adaptability to operating conditions is poor, making it difficult to flexibly switch between shallow and deep conversion modes. If the conversion depth needs to be adjusted, significant modifications to pipelines or the addition of bypasses are required, making operation cumbersome. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned technical problems and provide a combined water-gas conversion method that can stably control the catalyst bed temperature during the CO concentration crude gas conversion process, prevent overheating deactivation and side reactions, reduce effective gas loss, and recover reaction heat in stages to directly produce high-grade medium-pressure superheated steam, while having low investment and operating costs.

[0007] The present invention also provides a system for the above-mentioned combined water-gas conversion method that simplifies device configuration and reduces engineering investment and operating energy consumption.

[0008] The combined water-gas conversion system of the present invention includes a first converter and a second converter connected in sequence. The first converter is a combined converter with a medium-pressure steam drum, and the second converter is a temperature-controlled converter with a low-pressure steam drum. The combined converter includes an outer shell, within which are an upper reaction section and a lower reaction section. Each reaction section includes a bottom inner head and a top covering layer. A central tube with through holes is disposed in the center of the area between the inner head and the covering layer. A catalyst bed is arranged around the outer periphery of the central tube. A heat exchange tube bundle is embedded in the catalyst bed. An outer distributor is fitted over the catalyst bed, and an outer gap is formed between the outer distributor and the outer shell. The bottom of the outer shell has a first raw material gas inlet, a second raw material gas inlet, and a boiler water inlet; the middle of the outer shell has a water vapor outlet and a saturated steam inlet; and the top of the outer shell has a shift gas outlet and a superheated steam outlet. The first raw material gas inlet is connected to the outer gap inlet of the lower reaction section, the second raw material gas inlet is connected to the central tube of the lower reaction section, the boiler water inlet is connected to the steam outlet via the heat exchange tube bundle of the lower reaction section, the gas outlet of the central tube of the lower reaction section is connected to the outer gap of the upper section, the saturated steam inlet is connected to the hot steam outlet via the heat exchange tube bundle of the upper reaction section, and the gas outlet of the central tube of the upper reaction section is connected to the shift gas outlet.

[0009] This application is the first to integrate temperature-controlled steam generation, in-furnace cooling, adiabatic reaction, and steam superheating into a single combined converter, significantly improving equipment integration, reducing the number of reactors and heat exchangers, lowering engineering investment and system resistance. Combined with a downstream temperature-controlled converter, it forms a two-stage integrated converter system. Under high-CO dry pulverized coal and crude gas conditions, it can suppress bed overheating without large amounts of supplemental steam, significantly reducing steam energy consumption, suppressing methanation side reactions, increasing effective gas yield, and directly producing medium-pressure superheated steam in the furnace, eliminating the need for an external fuel-type steam superheater, thus reducing fuel consumption and carbon emissions. Preferably, the upper and lower reaction sections of the combined converter are each provided with an upper header at the top and a lower header at the bottom. The upper header and the lower header are each composed of an inner cavity and an annular gap. The lower header has an inner cavity and a tube sheet on the top surface. In the lower reaction section, the second raw material gas inlet is connected to the lower central tube inlet via the annular gap in the lower header, the boiler water inlet is connected to the lower heat exchange tube bundle inlet via the inner cavity in the lower header, the outlet of the lower central tube is connected to the annular gap in the upper header, and is connected to the outer gap of the upper section via the gas redistribution hole in the upper section of the annular gap, and the outlet of the lower heat exchange tube bundle is connected to the steam outlet via the inner cavity of the upper header. In the upper reaction section, the saturated steam inlet is connected to the inner cavity of the lower header of the upper section, and is connected to the inlet of the upper heat exchange tube bundle through the tube sheet. The outlet of the upper heat exchange tube bundle is connected to the superheated steam outlet through the inner cavity of the upper header of the upper section. The upper end of the upper central tube is connected to the shift gas outlet through the annular gap of the upper header of the upper section.

[0010] The double-layer header structure achieves simultaneous closed-loop steam-water circulation and uniform redistribution of process gas, resolving potential issues such as gas flow deviation and heat exchange medium cross-flow within the furnace. It is particularly suitable for combined converter furnaces with integrated structures, ensuring uniform gas flow distribution, preventing localized catalyst overheating, eliminating the risk of steam-water leakage, and extending equipment lifespan. Preferably, in the combined converter, the lower reaction section is a temperature-controlled reaction section, and a raw material gas distribution pipe with vent holes is provided in the lower central tube along the axial direction. The second raw material gas inlet is connected to the lower central tube through the raw material gas distribution pipe. The upper reaction section is an adiabatic reaction section, and the upper catalyst bed provided on the outer periphery of the upper central tube consists of an outer catalyst bed and an inner catalyst bed. The upper heat exchange tube bundle is embedded in the inner catalyst bed.

[0011] This invention integrates the raw material gas distribution pipe inside the lower central pipe, utilizing the limited space inside the furnace to achieve rapid and uniform mixing of high-temperature gas and cold quench gas, with uniform dispersion of the cold quench gas and minimal temperature fluctuations during mixing. The upper reaction section adopts a double-layer catalyst bed design with inner and outer layers. The outer layer forms an adiabatic reaction zone for simple adiabatic heating, while the inner layer forms a steam superheating zone, where superheated steam is exchanged simultaneously with the reaction. The coupling of the two reaction zones ensures a stable output of medium-pressure superheated steam, enabling staged utilization of reaction heat and significantly improving steam superheating efficiency.

[0012] Preferably, in the adiabatic reaction section, the catalyst loading volume ratio of the upper catalyst outer bed layer and the catalyst inner bed layer is 1.0~1.5.

[0013] This ratio is the optimal range obtained by the inventors through thousands of operating tests on dry pulverized coal with high CO feedstock. Outside this range, two defects will occur: if the ratio is too small, the heat exchange area of ​​the superheated section will be insufficient, and the steam will not reach the superheated temperature; if the ratio is too large, the heat release of the adiabatic section will be insufficient, and the reaction depth will be insufficient. Within this ratio range, qualified superheated steam at 360~400℃ can be stably produced while ensuring the CO conversion depth, balancing catalyst life and steam quality.

[0014] Preferably, in the temperature-controlled reaction section, the total cross-sectional area of ​​the vent holes on the feed gas distribution pipe is greater than twice the cross-sectional area of ​​the second feed gas inlet; the total cross-sectional area of ​​the gas redistribution holes in the annular gap of the upper header in the lower section is greater than twice the cross-sectional area of ​​the central pipe in the lower section. This multiple is required for the radial uniform distribution of a large flow of feed gas; a multiple lower than this may cause gas flow deviation and local catalyst overheating.

[0015] Preferably, in the combined converter, the heat exchange tube bundle in the temperature-controlled reaction section is a shell-and-tube heat exchange tube bundle, and the heat exchange tube bundle in the adiabatic reaction section is a wound-type heat exchange tube bundle. The shell-and-tube type is suitable for natural circulation of water in low-pressure boilers and has a large heat exchange area; the wound-type tube bundle can offset high-temperature thermal stress, reduce the heat exchange area, and quickly superheat steam.

[0016] Preferably, in the combined converter, the steam outlet is connected to the intermediate-pressure steam drum, the steam outlet at the top of the intermediate-pressure steam drum is connected to the saturated steam inlet, and the feedwater outlet at the bottom flows back to the boiler water inlet, forming a steam-water circulation loop. This invention uses the intermediate-pressure steam drum as a transfer hub for both water supply and saturated steam delivery, forming a closed-loop cycle of lower-stage steam generation, steam drum separation, and upper-stage superheating. Natural circulation is achieved through the density difference between steam and water, and the arrangement height of the intermediate-pressure steam drum is also reduced.

[0017] Preferably, it also includes a raw gas preheater, a medium-pressure waste heat boiler, and a medium-pressure boiler feedwater heater; the first raw gas inlet of the combined converter is connected to the outlet of the raw gas preheater; the converted gas outlet of the combined converter is connected in series with the raw gas preheater, the medium-pressure waste heat boiler, and the medium-pressure boiler feedwater heater, and then connected to the gas phase inlet of the temperature-controlled converter; the outlet of the medium-pressure boiler feedwater heater is connected to the saturated steam inlet of the combined converter via the saturated steam outlet of the medium-pressure waste heat boiler and the medium-pressure steam drum.

[0018] The combined water-gas conversion method of the present invention, employing the above-mentioned combined water-gas conversion system, includes the following steps: The raw gas is divided into two streams. The first stream of raw gas is preheated by the raw gas preheater and then sent to the first raw gas inlet of the combined converter. The second stream of raw gas is directly sent to the second raw gas inlet of the combined converter. The raw gas undergoes a conversion reaction in the combined converter and produces medium-pressure superheated steam as a byproduct. The converted gas drawn from the top of the combined converter is sent to the temperature-controlled converter for deep conversion after heat recovery. In the combined shift converter, the first stream of raw gas enters the lower outer gap of the temperature-controlled reaction section from the first raw gas inlet, and then is radially introduced into the catalyst bed of the lower section through the lower outer distributor to carry out the shift reaction. The heat released by the reaction is absorbed by the boiler water inside the lower heat exchange tube bundle. The shifted gas after the reaction continues to flow radially into the lower central tube. The second stream of raw gas, as quench gas, is introduced into the lower central tube through the raw gas distribution pipe, mixes with the shifted gas flowing into the lower central tube and is cooled down, and finally led out from the upper end of the lower central tube. Boiler feedwater is introduced into the lower heat exchange tube bundle through the boiler feedwater inlet to absorb the reaction heat and generate a water-steam mixture, which is led out through the water-steam outlet and sent to the medium-pressure steam drum. The mixed gas drawn from the central tube of the temperature-controlled reaction section is introduced upward into the outer gap of the upper section of the adiabatic reaction section, and then radially into the catalyst bed of the upper section through the external distributor to continue the reaction. The reaction heat is absorbed by the saturated steam inside the heat exchange tube bundle of the upper section. The reacted gas flows into the central tube of the upper section and is finally led out from the gas outlet. The medium-pressure saturated steam from the medium-pressure steam drum is introduced into the heat exchange tube bundle of the upper section through the saturated steam inlet to absorb the reaction heat and generate medium-pressure superheated steam, which is led out from the superheated steam outlet.

[0019] In the method of this invention, the raw materials are fed in two ways. The lower section of the furnace is first water-cooled and temperature-controlled, and the central tube of the furnace is cooled in situ. The upper section simultaneously completes the adiabatic reaction and saturated steam superheating. There is no need to add a large amount of steam for temperature control, and the effective gas loss is reduced. The external fuel-type superheater is eliminated, which effectively reduces fuel consumption and investment.

[0020] Preferably, the first feed gas accounts for 20-40% of the total gas volume, and the remaining feed gas is the second feed gas. By controlling the amount of the two feed gas streams, the heat release and cooling range of the upper and lower sections can be well stabilized and balanced, the bed temperature can be controlled throughout the process, and steam production and CO conversion depth can be taken into account. If the ratio is too low, the heat release in the lower section will be insufficient, making it difficult to produce qualified saturated steam; if the ratio is too high, the amount of cooling gas will be insufficient, and the cooling of the mixed gas will not reach 230-260℃, causing the upper section to easily overheat.

[0021] Preferably, in the combined converter furnace, the reaction temperature in the temperature-controlled reaction section is controlled at 300℃~380℃, and the temperature drops to 230℃~260℃ after the two gases are mixed in the central tube of the lower section. The dry basis molar concentration of CO in the mixed gas is 35~48%. The reaction temperature in the adiabatic reaction section is controlled at 380℃~420℃. The multi-stage temperature windows work together to adapt to the three-stage reaction of tube-and-tube water cooling, cold quench temperature control, and adiabatic coupling superheating, while avoiding the catalyst overheating range throughout the process, significantly suppressing methane side reactions, and ensuring sufficient reaction heat in the upper section for steam superheating.

[0022] Preferably, in the adiabatic reaction section, the mixed gas first undergoes an adiabatic shift reaction in the outer catalyst bed, raising the reaction temperature to 380℃~420℃. Subsequently, the gas radially enters the inner catalyst bed for further shift reaction, where its heat is absorbed by the steam in the upper heat exchange tube bundle within the inner catalyst bed, maintaining the reaction gas temperature at 380℃~420℃. After the reaction is complete, the gas flows into the upper central tube. This stepwise reaction coupled with superheating fully utilizes the waste heat from the adiabatic reaction, allowing saturated steam to be superheated to the target temperature without an additional heat source, significantly improving the efficiency of thermal energy utilization.

[0023] Preferably, the shifted gas drawn from the top of the combined shift converter is fed into the temperature-controlled shift converter for deep shifting after heat recovery via a medium-pressure waste heat boiler and a medium-pressure boiler feedwater heater. The medium-pressure boiler feedwater is first heated indirectly by heat exchange with the shifted gas via the medium-pressure boiler feedwater heater, and then further heated by heat exchange with the shifted gas in the medium-pressure waste heat boiler to generate medium-pressure saturated steam. The medium-pressure saturated steam produced by the medium-pressure waste heat boiler and the medium-pressure saturated steam from the medium-pressure steam drum are mixed and then fed into the saturated steam inlet of the combined shift converter. This method can fully recover low-grade waste heat, reduce the external heating load on the boiler feedwater, and lower the energy consumption for steam preparation in the system.

[0024] Beneficial effects: 1. For crude coal gas produced by dry coal powder gasification with a CO content exceeding 55%, this invention combines a multi-stage temperature control structure with lower-stage water-cooled heat transfer, in-furnace cold quenching and mixing, and upper-stage constant-temperature reaction. It can stably maintain the catalyst temperature in each stage within a suitable range without the need for a large amount of additional steam, completely solving the overheating problem of high CO feed gas conversion, significantly reducing effective gas loss caused by methane side reactions, and effectively extending the catalyst service life.

[0025] 2. Traditional isothermal converters can only produce saturated steam. To obtain superheated steam usable by the turbine, an additional combustion heater must be added, increasing fuel consumption and carbon emissions. This invention utilizes waste heat from the reaction in stages within the same furnace: the lower stage absorbs heat to generate medium-pressure saturated steam, while the upper stage directly utilizes the heat from the adiabatic reaction to achieve steam superheating on-site. This is equivalent to integrating a steam superheater directly within the catalyst bed, improving steam quality and the overall system's thermal efficiency, and eliminating the need for an external superheater. The entire unit recovers heat in stages through steam production, steam heating, and feedwater preheating, resulting in a significantly higher heat utilization rate than conventional converter processes.

[0026] 3. This invention integrates water-cooled conversion, adiabatic reaction, steam generation, steam superheating, and in-furnace cold mixing into a single combined conversion furnace, simplifying the process flow, reducing the number of equipment, and lowering investment and operating costs.

[0027] 4. The lower section of the furnace adopts a tube-and-shell structure, which is suitable for the design requirements of natural boiler water circulation. This reduces the arrangement height of the intermediate-pressure steam drum and facilitates natural steam-water circulation. The upper section of the catalytic bed uses wound heat exchange tube bundles, which helps to disperse thermal stress under high-temperature conditions, reduces the heat exchange area, and increases the equipment safety factor. At the same time, the area of ​​each ventilation opening is reasonably limited, ensuring uniform airflow distribution in the furnace and preventing problems such as gas flow deviation and localized overheating of the catalyst.

[0028] 5. Precise temperature control effectively suppresses side reactions such as methanation, reduces the loss of H2 and CO, and improves the yield and economy of the target product. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the present invention.

[0030] Wherein: 41-Raw gas preheater; 42-Combined converter; 43-Medium-pressure steam drum; 44-Medium-pressure waste heat boiler; 45-Medium-pressure boiler feedwater heater; 46-Temperature-controlled converter; 47-Low-pressure steam drum.

[0031] Figure 2 This is a schematic diagram of a combined converter furnace.

[0032] The components are: 1. Outer shell; 2. Upper head; 3. Lower head; 4. Upper inner head; 5. Lower inner head; 6. Upper outer distributor; 7. Upper central tube; 8. Lower outer distributor; 9. Lower central tube; 10. Raw material gas distributor; 11. First raw material gas inlet; 12. Second raw material gas inlet; 13. Boiler water inlet; 14. Steam outlet; 15. Saturated steam inlet; 16. Shift gas outlet; 17. Superheated steam outlet; 21. Lower outer annular gap; 22. 23. Upper outer annular gap; 24. Lower lower header inner cavity; 25. Lower lower header annular gap; 26. Lower upper header inner cavity; 27. Lower upper header; 28. Upper lower header tube sheet; 29. ​​Upper upper header inner cavity; 30. Upper upper header annular gap; 31. Shell and tube heat exchanger bundle; 32. Spiral heat exchanger bundle; 33. Lower catalyst bed; 34. Catalyst outer bed; 35. Catalyst inner bed; 36. Cover layer; 37. Gas redistribution pores. Detailed Implementation

[0033] The present invention will be further explained below with reference to the accompanying drawings: System Implementation Example: See Figure 1 The conversion system of the present invention includes a raw gas preheater 41, a first converter, a medium-pressure waste heat boiler 44, a medium-pressure boiler feedwater heater 45, and a second converter, which are connected in sequence. The first converter is a combined converter 42 equipped with a medium-pressure steam drum 43, and the second converter is a temperature-controlled converter 46 equipped with a low-pressure steam drum 47.

[0034] Combination Figure 2 Description of the internal structure of the combined conversion furnace 42: The top of the outer shell 1 has an upper end cap 2 and the bottom has a lower end cap 3; the interior of the cavity is divided into a lower reaction section (a temperature-controlled reaction section) and an upper reaction section (an adiabatic reaction section) along the height; the bottom of the lower reaction section is provided with a lower inner end cap 5 (filled with inert ceramic balls), and the bottom of the upper section is provided with an upper inner end cap 4, filled with inert ceramic balls. The covering layer 36 of the upper and lower reaction sections is also formed by filling inert ceramic balls.

[0035] In the temperature-controlled reaction section, a lower section central tube 9 is arranged vertically in the center. The lower section catalyst bed 33 and the lower section outer distributor 8 are arranged sequentially from the inside to the outside of the lower section central tube 9. The lower section outer distributor 8 and the inner wall of the outer shell 1 form a lower section outer annular gap 21. The lower section catalyst bed 33 is embedded with a tubular heat exchange tube bundle 31. The lower section central tube 9 is axially penetrated by a raw material gas distributor 10, and the tube wall of the raw material gas distributor 10 is evenly opened with small ventilation holes.

[0036] In the adiabatic reaction section, an upper central tube 7 is arranged vertically in the center. Outside the upper central tube 7, from the inside to the outside, a catalyst inner bed 35, a catalyst outer bed 34, and an upper outer distributor 6 are arranged in sequence. An upper outer annular gap 22 is formed between the upper outer distributor 6 and the inner wall of the outer shell 1. A spiral heat exchange tube bundle 32 is embedded inside the catalyst inner bed 35. The catalyst loading volume ratio of the catalyst outer bed 34 to the catalyst inner bed 35 is 1.0-1.5, which is 1.2 in this embodiment.

[0037] In the temperature-controlled reaction section (lower reaction section), the bottom is equipped with a lower lower header, which is divided into a lower lower header inner cavity 23 and a lower lower header annular gap 24; the top is equipped with a lower upper header, which is divided into a lower upper header inner cavity 25 and a lower upper header annular gap 26. Multiple sets of gas redistribution holes 37 are opened on the upper side wall of the lower upper header annular gap 26. In the adiabatic reaction section (upper reaction section), an upper lower header 27 is set at the bottom, and an upper lower header tube sheet 28 is fixed on the top surface of the inner cavity of the upper lower header 27; an upper upper header is set at the top, which is divided into an upper upper header inner cavity 29 and an upper upper header annular gap 30.

[0038] The lower head 3 has a first raw material gas inlet 11, a second raw material gas inlet 12, and a boiler water inlet 13; the middle side wall of the outer shell 1 has a steam outlet 14 and a saturated steam inlet 15; the upper head 2 has a shift gas outlet 16 and a superheated steam outlet 17. Among them, the first raw material gas inlet 11 and the second raw material gas inlet 12 can be a sleeve structure for easy arrangement.

[0039] Pipeline connections: The first raw material gas inlet 11 connects to the outer annular gap 21 of the lower section; the second raw material gas inlet 12 connects to the annular gap 24 of the lower header of the lower section, and finally connects to the raw material gas distributor 10 inside the central pipe 9 of the lower section; the total cross-sectional area of ​​all vents of the raw material gas distributor 10 is 2.2 times the cross-sectional area of ​​the second raw material gas inlet 12. The boiler water inlet 13 connects to the inner cavity 23 of the lower header of the lower section, and connects to the shell-and-tube heat exchanger bundle 31; the upper end of the shell-and-tube heat exchanger bundle 31 connects to the inner cavity 25 of the upper header of the lower section, and the upper header inner cavity 25 connects to the steam outlet 14; the gas outlet at the top of the central pipe 9 of the lower section connects to the annular gap 26 of the upper header of the lower section, and passes through the gas redistribution hole 37 into the outer annular gap 22 of the upper section; the total cross-sectional area of ​​the gas redistribution hole 37 is 2.2 times the cross-sectional area of ​​the central pipe 9 of the lower section. The saturated steam inlet 15 connects to the interior of the upper section lower header 27 and is distributed to the spiral heat exchanger tube bundle 32 via the upper section lower header tube sheet 28; the upper end of the spiral heat exchanger tube bundle 32 is connected to the inner cavity 29 of the upper section upper header, and after collection, it is connected to the hot steam outlet 17; the top of the upper section central tube 7 is connected to the annular gap 30 of the upper section upper header, and after collection in the annular gap 30 of the upper section upper header, it is connected to the change gas outlet 16.

[0040] Steam-water circulation pipeline: Steam outlet 14 is connected to the bottom of medium-pressure steam drum 43 via a pipeline; the saturated steam pipeline at the top of medium-pressure steam drum 43 is led out and connected to saturated steam inlet 15; the feedwater return pipeline at the bottom of medium-pressure steam drum 43 is connected to boiler water inlet 13, forming a natural circulation steam-water loop. Waste heat recovery pipeline: The outlet of raw material gas preheater 41 is connected to the first raw material gas inlet 11; the shift gas outlet 16 is connected in series with raw material gas preheater 41, medium-pressure waste heat boiler 44, and medium-pressure boiler feedwater heater 45, and finally connected to the inlet of temperature-controlled shift furnace 46; the water outlet of medium-pressure boiler feedwater heater 45 is sent to medium-pressure waste heat boiler 44 for vaporization and steam production; the saturated steam pipeline produced by medium-pressure waste heat boiler 44 is merged with the steam pipeline of medium-pressure steam drum 43 and then connected to saturated steam inlet 15.

[0041] In the temperature-controlled reaction section, the catalyst filling the outer bed of the lower section of the catalyst can be an oxidized sulfur-resistant shift catalyst or a pre-sulfurized sulfur-resistant shift catalyst. In the adiabatic reaction section, the inner bed 35 and the outer bed 34 of the catalyst can be oxidized sulfur-resistant shift catalysts or pre-sulfurized sulfur-resistant shift catalysts, which can be the same or different. All of them are commercially available. The specific selection is existing technology and will not be described in detail.

[0042] Process Example 1: In this embodiment, pretreated dry coal powder gasification crude coal gas is used as the feed gas. The feed gas temperature is 204℃, the pressure is 3.9 MPaA, and the molar flow rate is 12299 kmol / h. The molar composition is shown in the table below. The above-mentioned raw material gas has a dry basis CO molar content of 59.35% and a water-to-gas ratio of 0.69.

[0043] The complete process steps are as follows: S1: Raw material gas splitting: All raw material gas is split into two streams. The first stream, accounting for 20-40% (mole percentage) of the total gas volume, is sent to the raw material gas preheater 41 to be heated to 260°C and then sent to the first raw material gas inlet 11 of the combined converter 42. The remaining raw material gas is used as quench gas and is sent directly from the second raw material gas inlet 12 through the lower section lower header cavity 23 of the combined converter 42 to the raw material gas distributor 10.

[0044] S2: Lower-stage temperature-controlled shift reaction: In the lower section of the combined shift furnace 42, the preheated first stream of raw material gas enters the outer annular gap 21 of the lower section, is evenly dispersed by the lower external distributor 8, and radially passes through the lower catalyst bed 33 to undergo a shift reaction. The reaction temperature in the lower section is stably maintained at 300~380℃. Boiler water enters the tubular heat exchange tube bundle 31 from the boiler water inlet 13 through the lower header annular gap 24 of the lower section, absorbs the heat of reaction to form a steam-water mixture, and is sent to the medium-pressure steam drum 43 through the steam-water outlet 14 to complete the steam-liquid separation. The high-temperature gas after the reaction in the lower section flows into the lower central pipe 9 and is fully mixed with the cold quench gas (second stream of raw material gas) sprayed from the raw material gas distributor 10 to form a mixed gas. The temperature after mixing is 230~260℃, and the dry basis CO concentration of the mixed gas is 35~48%.

[0045] S3: Upper section adiabatic reaction and steam superheating: The mixed gas enters the upper section outer annular gap 22 through the gas redistribution hole 37 of the lower section upper header annular gap 26, and is evenly distributed by the upper section outer distributor 6. It first flows radially through the upper section catalyst outer bed 34 to undergo an adiabatic reaction, and the gas temperature rises to 400℃; then it enters the upper section catalyst inner bed 35 to continue the reaction; the saturated steam from the medium-pressure steam drum 43 is introduced into the wound heat exchange tube bundle 32 through the upper section lower header 27 via the saturated steam inlet 15, continuously absorbing the reaction heat, and the medium-pressure superheated steam heated to 380℃ is sent out through the upper section upper header annular gap 30 and the superheated steam outlet 17; the shift gas after the upper section reaction is completed is collected into the upper section central pipe 7, and after passing through the upper section upper header inner cavity 29, it is sent out through the shift gas outlet 16.

[0046] S4: Waste Heat Recovery and Deep Conversion: The converted gas discharged from the top of the combined converter 42 passes sequentially through the raw material gas preheater 41, the medium-pressure waste heat boiler 44, and the medium-pressure boiler feedwater heater 45 to recover waste heat in stages. The boiler feedwater is first preheated by the medium-pressure boiler feedwater heater 45 and then sent to the medium-pressure waste heat boiler 44 to vaporize and generate saturated steam. The saturated steam from the medium-pressure waste heat boiler 44 and the medium-pressure steam drum 43 is combined and sent to the saturated steam inlet 15. The cooled converted gas is sent to the temperature-controlled converter 46 to complete deep conversion. This converter is equipped with a heat transfer unit and can produce low-pressure steam as a byproduct. The converted gas leaving the temperature-controlled converter 46 enters the waste heat recovery system to complete the final heat recovery and finally obtain the product converted gas.

[0047] The operating parameters and composition of the inlet and outlet of the combined converter furnace 42 and the temperature-controlled converter furnace 26 are shown in the table below. The final product gas had a temperature of 40℃, a pressure of 3.65 MPaA, and a molar flow rate of 11442.6 kmol / h. The molar composition is shown in the table below. Using the system and method described in this invention, the CO conversion rate in the feed gas is 96.28%, and the produced shift gas can be used for hydrogen production or ammonia synthesis.

[0048] 1. Steam Production: This invention produces 39.9 t / h of medium-pressure superheated steam at 4.0 MPa and 380℃, without the need for an external superheater; the isothermal conversion produces 47.2 t / h of saturated steam at 4.0 MPa, with the superheater consuming 206 Nm³ of fuel gas (calorific value 2000). 3 / h; 2. Effective gas loss: The methanation loss of this invention is ≤0.3% throughout the entire process, while the loss of traditional adiabatic conversion is 1.0%; 3. Catalyst lifespan: Under the same operating conditions, the catalyst of this invention has a continuous operating cycle of 36 months, while that of a traditional adiabatic furnace is only 24 months, representing a 33% increase in service life; 4. Investment and Energy Consumption: Compared with adiabatic conversion, the investment in the construction of the entire set of equipment is reduced by 25%, and the process steam consumption is reduced by 68.6%.

Claims

1. A combined water-gas conversion system, comprising a first conversion furnace and a second conversion furnace connected in sequence, characterized in that, The first converter is a combined converter with a medium-pressure steam drum, and the second converter is a temperature-controlled converter with a low-pressure steam drum. The combined converter includes an outer shell, within which are an upper reaction section and a lower reaction section. Each reaction section includes a bottom inner head and a top covering layer. A central tube with through holes is disposed in the center of the area between the inner head and the covering layer. A catalyst bed is arranged around the outer periphery of the central tube. A heat exchange tube bundle is embedded in the catalyst bed. An outer distributor is fitted over the catalyst bed, and an outer gap is formed between the outer distributor and the outer shell. The bottom of the outer shell has a first raw material gas inlet, a second raw material gas inlet, and a boiler water inlet; the middle of the outer shell has a water vapor outlet and a saturated steam inlet; and the top of the outer shell has a shift gas outlet and a superheated steam outlet. The first raw material gas inlet is connected to the outer gap inlet of the lower reaction section, the second raw material gas inlet is connected to the central tube of the lower reaction section, the boiler water inlet is connected to the steam outlet via the heat exchange tube bundle of the lower reaction section, the gas outlet of the central tube of the lower reaction section is connected to the outer gap of the upper section, the saturated steam inlet is connected to the hot steam outlet via the heat exchange tube bundle of the upper reaction section, and the gas outlet of the central tube of the upper reaction section is connected to the shift gas outlet.

2. The combined water-gas conversion system as described in claim 1, characterized in that, The combined converter furnace has an upper header at the top of both the upper and lower reaction sections and a lower header at the bottom. The upper header and the lower header are both composed of an inner cavity and an annular gap. The lower header has an inner cavity and a tube sheet on the top surface. In the lower reaction section, the second raw material gas inlet is connected to the lower central tube inlet via the annular gap in the lower header, the boiler water inlet is connected to the lower heat exchange tube bundle inlet via the inner cavity in the lower header, the outlet of the lower central tube is connected to the annular gap in the upper header, and is connected to the outer gap of the upper section via the gas redistribution hole in the upper section of the annular gap, and the outlet of the lower heat exchange tube bundle is connected to the steam outlet via the inner cavity of the upper header. In the upper reaction section, the saturated steam inlet is connected to the inner cavity of the lower header of the upper section, and is connected to the inlet of the upper heat exchange tube bundle through the tube sheet. The outlet of the upper heat exchange tube bundle is connected to the superheated steam outlet through the inner cavity of the upper header of the upper section. The upper end of the upper central tube is connected to the shift gas outlet through the annular gap of the upper header of the upper section.

3. The combined water-gas conversion system as described in claim 1, characterized in that, In the combined converter, the lower reaction section is a temperature-controlled reaction section, and a raw material gas distribution pipe with vent holes is provided in the lower central tube along the axial direction. The second raw material gas inlet is connected to the lower central tube through the raw material gas distribution pipe. The upper reaction section is an adiabatic reaction section, and the upper catalyst bed provided on the outer periphery of the upper central tube consists of an outer catalyst bed and an inner catalyst bed. The upper heat exchange tube bundle is embedded in the inner catalyst bed.

4. The combined water-gas conversion system as described in claim 3, characterized in that, In the adiabatic reaction section, the catalyst loading volume ratio of the upper outer catalyst bed to the inner catalyst bed is 1.0~1.

5.

5. The combined water-gas conversion system as described in claim 3, characterized in that, In the temperature-controlled reaction section, the total cross-sectional area of ​​the vent holes on the raw material gas distribution pipe is more than twice the cross-sectional area of ​​the second raw material gas inlet; the total cross-sectional area of ​​the gas redistribution holes in the annular gap of the lower section header is more than twice the cross-sectional area of ​​the lower section central pipe.

6. The combined water-gas conversion system as described in claim 3, characterized in that, In the combined converter furnace, the heat exchange tube bundle in the temperature-controlled reaction section is a shell-and-tube heat exchange tube bundle, and the heat exchange tube bundle in the adiabatic reaction section is a wound heat exchange tube bundle.

7. The combined water-gas conversion system as described in claim 1, characterized in that, In the combined converter, the steam outlet is connected to the medium-pressure steam drum, the steam outlet at the top of the medium-pressure steam drum is connected to the saturated steam inlet, and the feedwater outlet at the bottom flows back to the boiler water inlet, forming a steam-water circulation loop.

8. The combined water-gas conversion system according to any one of claims 1-7, characterized in that, It also includes a raw gas preheater, a medium-pressure waste heat boiler, and a medium-pressure boiler feedwater heater; the first raw gas inlet of the combined converter is connected to the outlet of the raw gas preheater; the converted gas outlet of the combined converter is connected in series with the raw gas preheater, the medium-pressure waste heat boiler, and the medium-pressure boiler feedwater heater, and then connected to the gas phase inlet of the temperature-controlled converter; the outlet of the medium-pressure boiler feedwater heater is connected to the saturated steam inlet of the combined converter via the saturated steam outlet of the medium-pressure waste heat boiler and the medium-pressure steam drum.

9. A combined water-gas conversion method, characterized in that, The combined water-gas conversion system according to any one of claims 1-8 includes the following steps: The raw gas is divided into two streams. The first stream of raw gas is preheated by the raw gas preheater and then sent to the first raw gas inlet of the combined converter. The second stream of raw gas is directly sent to the second raw gas inlet of the combined converter. The raw gas undergoes a conversion reaction in the combined converter and produces medium-pressure superheated steam as a byproduct. The converted gas drawn from the top of the combined converter is sent to the temperature-controlled converter for deep conversion after heat recovery. In the combined shift converter, the first stream of raw gas enters the lower outer gap of the temperature-controlled reaction section from the first raw gas inlet, and then is radially introduced into the catalyst bed of the lower section through the lower outer distributor to carry out the shift reaction. The heat released by the reaction is absorbed by the boiler water inside the lower heat exchange tube bundle. The shifted gas after the reaction continues to flow radially into the lower central tube. The second stream of raw gas, as quench gas, is introduced into the lower central tube through the raw gas distribution pipe, mixes with the shifted gas flowing into the lower central tube and is cooled down, and finally led out from the upper end of the lower central tube. Boiler feedwater is introduced into the lower heat exchange tube bundle through the boiler feedwater inlet to absorb the reaction heat and generate a water-steam mixture, which is led out through the water-steam outlet and sent to the medium-pressure steam drum. The mixed gas drawn from the central tube of the temperature-controlled reaction section is introduced upward into the outer gap of the upper section of the adiabatic reaction section, and then radially into the catalyst bed of the upper section through the external distributor to continue the reaction. The reaction heat is absorbed by the saturated steam inside the heat exchange tube bundle of the upper section. The reacted gas flows into the central tube of the upper section and is finally led out from the gas outlet. The medium-pressure saturated steam from the medium-pressure steam drum is introduced into the heat exchange tube bundle of the upper section through the saturated steam inlet to absorb the reaction heat and generate medium-pressure superheated steam, which is led out from the superheated steam outlet.

10. The combined water-gas conversion method as described in claim 9, characterized in that, The first stream of raw gas accounts for 20-40% of the total gas volume, and the remaining raw gas is the second stream of raw gas.

11. The combined water-gas conversion method as described in claim 9, characterized in that, In the combined converter furnace, the reaction temperature in the temperature-controlled reaction section is controlled at 300℃~380℃. After the two gases are mixed in the central tube of the lower section, the temperature drops to 230℃~260℃, and the dry molar concentration of CO in the mixed gas is 35~48%. The reaction temperature in the adiabatic reaction section is controlled at 380℃~420℃.

12. The combined water-gas conversion method as described in claim 11, characterized in that, In the adiabatic reaction section, the mixed gas first undergoes an adiabatic shift reaction in the outer catalyst bed, raising the reaction temperature to 380℃~420℃. Subsequently, the gas enters the inner catalyst bed radially to continue the shift reaction. Its heat is absorbed by the steam in the upper heat exchange tube bundle in the inner catalyst bed, maintaining the reaction gas temperature at 380℃~420℃. After the reaction is complete, the gas flows into the upper central tube.

13. The combined water-gas conversion method according to any one of claims 9-12, characterized in that, The shifted gas drawn from the top of the combined shift converter is fed into the temperature-controlled shift converter after heat recovery by the medium-pressure waste heat boiler and the medium-pressure boiler feedwater heater. The medium-pressure boiler feedwater is first heated by indirect heat exchange with the shifted gas through the medium-pressure boiler feedwater heater, and then further heated by heat exchange with the shifted gas through the medium-pressure waste heat boiler to generate medium-pressure saturated steam. The medium-pressure saturated steam produced by the medium-pressure waste heat boiler and the medium-pressure saturated steam from the medium-pressure steam drum are mixed and fed into the saturated steam inlet of the combined shift converter.

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