System and method for preparing combustible gas by pulverized coal steam hydrogen-rich gasification

Abstract

The present application relates to the technical field of coal gasification, and particularly relates to a system and method for preparing combustible gas by coal powder steam hydrogen-rich gasification, which comprises a gasification reactor, in which coal powder and high-temperature steam provided by a heat accumulating heat exchanger are reacted to produce hydrogen-rich fuel gas, the hydrogen-rich fuel gas is cooled by a heat exchanger and then enters a spray tower for secondary cooling to condense water vapor and release sensible heat and latent heat, the hydrogen-rich fuel gas is discharged from the spray tower, the heat released by the condensate water is recovered by the spray water provided by a flash tank to the spray tower, the condensate water and the spray water enter the flash tank again to be converted into steam, and the steam is absorbed by the heat exchanger to enter the heat accumulating heat exchanger after absorbing the sensible heat of the hydrogen-rich fuel gas, and high-temperature steam reaching the temperature of the coal powder gasification reaction is obtained; the present application uses high-temperature steam as a single gasification agent to participate in the coal powder gasification reaction, the high-temperature steam produced by the heat accumulating heat exchanger provides the required H element and reaction temperature for the gasification reaction, and the proportion of H2 in the hydrogen-rich fuel gas is increased.

Description

Technical Field

[0001] This invention relates to the field of pulverized coal gasification technology, and in particular to a system and method for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam. Background Technology

[0002] Hydrogen energy boasts advantages such as high calorific value, convenient transportation, wide application, and clean combustion, and is considered one of the most promising energy sources for the future. To meet the large-scale demand for hydrogen energy, hydrogen-rich fuel gas can be produced through pulverized coal gasification.

[0003] Coal gasification is a strongly endothermic process, typically using H2O, CO2, pure O2, or air as gasifying agents. The participation of O2 or air provides the necessary heat and temperature for the gasification reaction, but it increases the CO2 / CO concentration in the produced gas. Furthermore, existing coal gasification systems using pure O2 as a gasifying agent require an additional air separation unit, increasing system construction and operating costs; using air as a gasifying agent increases the N2 concentration in the produced gas, resulting in a decrease in the calorific value of the produced gas and an increase in equipment size. Summary of the Invention

[0004] The purpose of this invention is to provide a system and method for producing combustible gas through pulverized coal steam hydrogen-rich gasification, thereby solving the problems of high CO / CO2 / N2 content and high energy and water consumption in existing hydrogen-rich gas preparation methods. To achieve the above objective, this invention provides the following technical solution:

[0005] In a first aspect, the present invention provides a system for producing combustible gas by hydrogen-rich gasification of pulverized coal steam, comprising:

[0006] Gasification reactor, used for the gasification reaction of high-temperature steam and pulverized coal;

[0007] The energy-saving device includes a spray tower and a flash tank, which establish a circulating heat exchange channel. The spray tower is connected to the gasification reactor and a heat exchanger is installed between them.

[0008] A regenerative heat exchanger is connected to the flash tank, and the steam in the pipeline exchanges heat through the heat exchanger. The regenerative heat exchanger is connected to the gasification reactor and provides it with high-temperature steam.

[0009] Secondly, the present invention provides a method for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam, wherein the method employs the system for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam as described in the first aspect, and includes the following steps:

[0010] In the gasification reactor, pulverized coal reacts with high-temperature steam provided by a regenerative heat exchanger to produce hydrogen-rich fuel gas. After being cooled by the heat exchanger, the hydrogen-rich fuel gas enters a spray tower for secondary cooling, causing the water vapor in it to condense and release sensible and latent heat. The hydrogen-rich fuel gas is discharged from the spray tower and the heat released by the condensate is recovered by the spray water supplied to the spray tower by the flash tank. The condensate and the spray water enter the flash tank together and are converted into steam again. After absorbing the sensible heat of the hydrogen-rich fuel gas through the heat exchanger, it enters the regenerative heat exchanger to obtain high-temperature steam that reaches the coal gasification reaction temperature.

[0011] As a further technical solution, the tar in the hydrogen-rich gas phase is collected in a spray tower. After the tar and water are statically separated, they are pumped to a gasification reactor. Under the action of high-temperature steam, they are gasified and cracked into small molecule alkanes, and then further reformed into hydrogen-rich gas.

[0012] As a further technical solution, alkaline substances are added to the spray tower and / or flash tank to neutralize and remove acidic substances during the pulverized coal gasification process.

[0013] As a further technical solution, a gas-liquid separation device is installed at the hydrogen-rich gas outlet of the spray tower.

[0014] As a further technical solution, a pressure swing adsorption purification device is installed at the hydrogen-rich gas outlet of the spray tower.

[0015] As a further technical solution, the hydrogen extraction waste gas generated by the pressure swing adsorption purification device is used as fuel for a regenerative heat exchanger.

[0016] As a further technical solution, the regenerative heat exchanger is equipped with multiple regenerative chambers, which continuously switch operation to generate high-temperature water vapor.

[0017] As a further technical solution, the spray tower is equipped with a water replenishment device.

[0018] As a further technical solution, the gas and liquid are transported by a compressor and a water pump during the preparation process.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) This invention utilizes high-temperature steam as a single gasifying agent to participate in the coal powder gasification reaction, which can provide a large amount of H element for the coal powder gasification process, thereby increasing the hydrogen concentration in the gasified gas; at high temperature, steam can be reformed with the tar produced by gasification into small molecule gaseous products, which helps to increase the concentration of combustible components; it reduces the dilution effect of N2 on combustible components when air is used as the gasification medium, thereby increasing the calorific value of the gas; compared with existing preparation methods, the proportion of CO / CO2 / N2 and other gases in the prepared hydrogen-rich gas is lower; it does not require oxygen as the gasification medium, omits the air separation device, simplifies the production process, and reduces equipment investment.

[0021] (2) This invention utilizes a spray tower and flash tank to recover water vapor from hydrogen-rich fuel gas, returning the sensible and latent heat of the water vapor to the system, reducing the system's cold source heat loss. Furthermore, a heat exchanger is used to heat the recovered low-temperature saturated steam and send it to the pulverized coal gasification reactor, realizing the recycling of water vapor. This improves the system's economic efficiency and has broad application prospects.

[0022] (3) The present invention recovers the heat released by the condensate from the spray water supplied by the flash tank to the spray tower. The condensate and the spray water enter the flash tank together and are converted into steam again, realizing the heat recovery and mass recovery of water vapor in hydrogen-rich gas. In particular, the latent heat of water vapor is huge, which has obvious energy saving, consumption reduction and water saving effects. Attached Figure Description

[0023] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute a limitation thereof. It should also be understood that these drawings are for simplicity and clarity and are not necessarily drawn to scale. The invention will now be described and explained with additional features and details using the drawings, wherein:

[0024] Figure 1 A schematic diagram of a system for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam is shown in an embodiment of the present invention.

[0025] In the diagram: 1. Coal mill; 2. Gasification reactor; 3. Heat exchanger; 4. Spray tower; 5. Flash tank; 6. Condenser; 7. Compressor; 8. Regenerative heat exchanger; 9. Water pump. Detailed Implementation

[0026] The technical solutions in typical embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0027] Example 1

[0028] like Figure 1 As shown, this embodiment provides a system for producing combustible gas by hydrogen-rich gasification of pulverized coal steam, including a coal mill 1, a gasification reactor 2, a heat exchanger 3, a spray tower 4, a flash tank 5, a condenser 6, a compressor 7, a regenerative heat exchanger 8, and a water pump 9.

[0029] Among them, gasification reactor 2 is used for the gasification reaction of high-temperature steam and pulverized coal; the gasification feedstock can be pulverized coal, or raw materials with high carbon content such as biomass and organic solid waste. Gasification reactor 2 can take many forms, such as rotary kiln, moving bed, entrained flow bed, fluidized bed, boiling bed, bubbling bed, spouted bed, settling bed, etc.

[0030] The energy-saving device includes a spray tower 4 and a flash tank 5, which establish a circulating heat exchange channel. The spray tower 4 is connected to the gasification reactor 2 and a heat exchanger 3 is installed between them.

[0031] The flash tank 5 is the core of the energy-saving device. It has a spray layer at the top and a slag discharge valve at the bottom. It forms a water circulation loop with the spray tower 4. The liquid outlet of the flash tank 5 is connected to the spray pipe inlet of the spray tower 4, and the liquid inlet of the flash tank 5 is connected to the pipe outlet of the spray tower 4. Both pipes are equipped with circulating water pumps 9.

[0032] The steam from flash evaporation in flash tank 5 is first pressurized and heated by compressor 7 to reach the required steam pressure for the process. The steam exiting compressor 7 enters regenerative heat exchanger 8 for further heating to reach the required steam temperature for the process.

[0033] The regenerative heat exchanger 8 is connected to the flash tank 5 and the steam in the pipeline exchanges heat through the heat exchanger 3. The regenerative heat exchanger 8 is connected to the gasification reactor 2 and provides it with high-temperature steam.

[0034] The internal heat storage medium of the regenerative heat exchanger 8 is made of high-temperature and corrosion-resistant porous ceramic bricks. Multiple regenerative heat exchangers 8 can be arranged to facilitate heat exchange. After the temperature of the heat storage medium is raised by burning hydrogen extraction waste gas or other gaseous fuels, the process switches to the steam path, where the heat storage medium transfers heat to steam. Multiple heat storage chambers can continuously switch operation, continuously generating high-temperature steam.

[0035] Example 2

[0036] This embodiment provides a method for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam, using the system for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam in Example 1, including the following steps:

[0037] Coal is ground to a specific particle size range by a coal mill 1, and then conveyed to a gasification reactor 2. There, it undergoes a steam-coal gasification reaction with steam generated at 1000–1200℃ from a regenerative heat exchanger 8, producing hydrogen-rich fuel gas. The main hydrogen-rich gasification reactions are: C + H₂O = CO + H₂, CO + H₂O = CO₂ + H₂, CH₄ + H₂O = CO + 3H₂, C + 2H₂O = CO₂ + 2H₂, C + CO₂ = 2CO, and C + 2H₂ = CH₄. The organic macromolecules produced by the rapid pyrolysis of coal powder also undergo a reforming reaction with H₂O. n H m O p +(2n-p)H2O=nCO2+(m / 2+2n-p)H2. The hydrogen-rich gas discharged from gasification reactor 2 has a temperature of approximately 800–1000℃, with a dry basis H2 volume percentage of 40–70%, CO2 volume percentage of 10–20%, and CO volume percentage of 10–30%.

[0038] Using high-temperature steam as a single gasifying agent in the coal powder gasification reaction can provide a large amount of H elements for the coal powder gasification process and increase the H2 ratio in hydrogen-rich gas. However, there are also some problems that need to be solved: (1) The coal powder-steam gasification process is a strongly endothermic process, which requires external energy supplementation to maintain the effective gasification reaction; (2) In order to ensure the efficiency of coal powder-steam gasification, steam is generally in excess, and the combustible products contain a lot of unreacted steam, making it difficult to recover water in the high-temperature gasification gas, resulting in a large water consumption in the coal powder gasification process; (3) The sensible heat and latent heat of the high-temperature gasification gas produced by the gasification reaction are difficult to recover effectively, resulting in low energy recovery and utilization efficiency and large operating energy consumption.

[0039] Therefore, this embodiment solves the above problems by setting up heat exchangers, energy-saving devices, and regenerative heat exchangers to work together.

[0040] The high-temperature steam generated by the regenerative heat exchanger 8 not only provides the necessary hydrogen (H) for the gasification reaction but also provides the reaction temperature. The hydrogen-rich gas produced by the gasification reactor 2 is cooled to 80–250°C by the heat exchanger 3, recovering sensible heat to heat the low-temperature saturated steam generated by the flash tank 5 to 100–500°C. Multiple heat exchangers 3 can be used, and the recovered sensible heat can be utilized elsewhere.

[0041] The cooled hydrogen-rich gas, at 80–250°C, does not reach the dew point temperature (70–90°C) for steam condensation, so the water vapor in the gas will not condense. It enters spray tower 4, where water at 60–90°C in flash tank 5 is sprayed to cool the gas. Simultaneously, the water vapor in the gas decreases to its dew point temperature, condensing and releasing sensible and latent heat within spray tower 4. The spray water recovers the sensible and latent heat released by the condensate and is pumped to flash tank 5, where low-temperature saturated steam at 80–99°C is flashed out. This steam is then pressurized by compressor 7 and passes through a heat exchanger to recover the sensible heat of the hydrogen-rich gas, raising the steam temperature to 100–500°C.

[0042] Hydrogen-rich gas is discharged from spray tower 4, and the heat released by the condensate is recovered by the spray water supplied to spray tower 4 by flash tank 5. The condensate and spray water enter flash tank 5 together and are converted into steam again. The energy-saving device realizes the heat and mass recovery of water vapor in hydrogen-rich gas. In particular, the latent heat of water vapor is huge (2257.2kJ / kg), which has obvious energy-saving, consumption-reducing and water-saving effects.

[0043] Tar in the hydrogen-rich gas phase is collected in spray tower 4. After the tar and water settle and separate, they are pumped to gasification reactor 2. Under the action of high-temperature steam, they are gasified and cracked into small molecule alkanes, and further reformed into hydrogen-rich gas.

[0044] Alkaline substances are added to the spray tower 4 and / or flash tank 5 to neutralize and remove acidic substances such as Cl, F, and S from the coal during the pulverized coal gasification process, thereby achieving further purification of the hydrogen-rich gas.

[0045] The exhaust gas from spray tower 4 may contain unseparated steam or small droplets. A gas-liquid separator can be added to the outlet of the spray device. In this embodiment, condenser 6 is used to purify the hydrogen-rich fuel gas. The hydrogen-rich fuel gas can be further purified by pressure swing adsorption to remove gaseous impurities, increasing the H2 concentration to 99.99%. The CO in the hydrogen extraction exhaust gas, which contains a relatively high amount of oxygen, can be used as fuel. The hydrogen extraction exhaust gas produced by the pressure swing adsorption purification device is used as fuel for the regenerative heat exchanger 8.

[0046] The steam, initially heated by heat exchanger 3, then passes through regenerative heat exchanger 8, raising its temperature to 1000–1200°C. The high-temperature steam then enters gasification reactor 2 to participate in the pulverized coal gasification reaction. During the reaction, H2O is continuously consumed and converted into H2; therefore, a water replenishment device can be installed at spray tower 4 to maintain system water balance.

[0047] In this embodiment, high-temperature steam is used as a single gasifying agent in the pulverized coal gasification reaction. The sensible heat of the high-temperature steam maintains the temperature required for the reaction. The water vapor in the hydrogen-rich gas is recovered by the spray tower 4 and flash tank 5. The sensible heat and latent heat of the water vapor are returned to the system, reducing the heat loss of the cold source of the system. Furthermore, a heat exchanger 3 is used to heat up the recovered low-temperature saturated steam and send it to the pulverized coal gasification reactor 2, realizing the recycling of water vapor.

[0048] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam, characterized in that, The systems used include: Gasification reactor, used for the gasification reaction of high-temperature steam and pulverized coal; The energy-saving device includes a spray tower and a flash tank, which establish a circulating heat exchange channel. The spray tower is connected to the gasification reactor and a heat exchanger is installed between them. The flash tank is equipped with a spray layer at the top and a slag discharge valve at the bottom; A regenerative heat exchanger is connected to the flash tank and the steam in the pipeline exchanges heat through the heat exchanger. The regenerative heat exchanger is connected to the gasification reactor and provides it with high-temperature steam. The method for preparing combustible gas using the system includes the following steps: In the gasification reactor, pulverized coal reacts with high-temperature steam provided by a regenerative heat exchanger to produce hydrogen-rich fuel gas. This hydrogen-rich fuel gas is cooled by the heat exchanger and then enters a spray tower for secondary cooling, causing the steam to condense and release sensible and latent heat. The hydrogen-rich fuel gas is discharged from the spray tower and the heat released by the condensate is recovered by the spray water supplied to the spray tower from the flash tank. The condensate and spray water enter the flash tank together and are converted back into steam. After absorbing the sensible heat of the hydrogen-rich fuel gas, the steam enters the regenerative heat exchanger to obtain high-temperature steam reaching the coal gasification reaction temperature (1000-1200℃). The steam flashed in the flash tank is pressurized and heated by a compressor to reach the required steam pressure for the process. The steam exiting the compressor enters the regenerative heat exchanger for further heating to reach the required steam temperature for the process. Tar in the hydrogen-rich gas phase is collected in a spray tower. After the tar and water settle and separate, they are pumped to a gasification reactor. Under the action of high-temperature steam, they are gasified and cracked into small molecule alkanes, and then further reformed into hydrogen-rich gas. A pressure swing adsorption (PSA) purification device is installed at the hydrogen-rich gas outlet of the spray tower, and the hydrogen-refining waste gas generated by the PSA purification device is used as fuel for a regenerative heat exchanger.

2. The method for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam as described in claim 1, characterized in that, Alkaline substances are added to the spray tower and / or flash tank to neutralize and remove acidic substances during the pulverized coal gasification process.

3. The method for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam as described in claim 1, characterized in that, A gas-liquid separation device is installed at the hydrogen-rich gas outlet of the spray tower.

4. The method for preparing combustible gas by pulverized coal steam hydrogen-rich gasification as described in claim 1, characterized in that, The regenerative heat exchanger is equipped with multiple regenerative chambers, which continuously switch operation to generate high-temperature water vapor.

5. The method for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam as described in claim 1, characterized in that, The spray tower is equipped with a water replenishment device.

6. The method for preparing combustible gas by hydrogen-rich gasification of pulverized coal steam as described in claim 1, characterized in that, During the preparation process, the gas and liquid are transported by a compressor and a water pump.

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