Method and system for developing yield-increasing hydrogen through underground coal gasification

Abstract

The invention discloses a method and system for increasing yield of hydrogen through coal underground gasification development, and relates to the technical field of coal underground gasification development. The method comprises the following steps that a water injection well, an oxidizing agent injection well and a production well are formed in an area with a coal layer; the underground coal layer is ignited through the oxidizing agent injection well, and a cavity is formed in the coal layer; injecting water vapor into the cavity through the water injection well; and monitoring the content of hydrogen produced by the production well, and when the daily hydrogen production has an obvious decreasing trend, controlling the end, located in the cavity, of the water injection well to move upwards and backwards, so that the end, located in the cavity, of the water injection well moves to the outer boundary area of the cavity. When the hydrogen production rate is detected to be reduced, the water injection retraction operation is performed, so that the water injection point is aligned with the boundary of the current underground coal layer, the gasification reaction with water is recovered, and the yield of H2 is increased.

Description

Technical Field

[0001] This invention relates to the field of underground coal gasification development technology, specifically a method and system for increasing hydrogen production through underground coal gasification development. Background Technology

[0002] Despite a century of development in UCG (Underground Coal Gasification) and numerous mine trials and scientific studies worldwide, several significant scientific and engineering challenges remain hindering its progress. These include unstable syngas production and calorific value, and underground environmental protection. The calorific value of syngas is primarily influenced by coal quality and gasification processes; therefore, increasing the hydrogen content in the syngas is a current research objective. Furthermore, limitations in monitoring conditions can reduce the sealing of the coal seam caprock, potentially leading to caprock rupture and syngas leakage into groundwater, causing severe environmental pollution and exacerbating the complexity of the underground coal gasification environment.

[0003] To maximize hydrogen production, some researchers have concluded through experiments that reverse gasification should be employed, involving withdrawing the oxidant injection well at different time steps to eliminate the negative impact of a shrinking reduction zone that cannot meet hydrogen production requirements. Besides Chinese coal, experiments have demonstrated that, under laboratory conditions, Polish lignite and hard coal can be gasified under different oxygen and steam conditions to produce hydrogen-rich syngas. Experimental results show that the high moisture content in lignite eliminates the need for artificial water supply, providing favorable conditions for hydrogen production from uranium conversion gas. However, neither the reverse gasification nor the two-stage steam / air mixing injection into the UCG cavity used in the aforementioned studies combines controlling heat transfer from the cavity's overburden layer with increased hydrogen production. Furthermore, given the prohibitive cost of large-scale experiments, current research primarily focuses on laboratory-scale experiments, which has certain limitations. Therefore, this invention provides a method for increasing hydrogen production through underground coal gasification to address the aforementioned problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for increasing hydrogen production through underground coal gasification. This method combines heat transfer from the overburden layer above the underground coal gasification control chamber with hydrogen production enhancement. A retractable water injection technology is designed for deep coal seams to effectively control constant hydrogen production and the upward vertical expansion of the combustion air zone during UCG operations. To achieve the above objectives, this invention provides the following technical solution:

[0005] This invention provides a method for increasing hydrogen production through underground coal gasification, the method comprising the following steps:

[0006] In areas with coal seams, water injection wells, oxidant injection wells, and production wells are to be constructed.

[0007] The underground coal seam is ignited by injecting an oxidant into a well, and a cavity is formed in the coal seam.

[0008] Water vapor is injected into the cavity through the injection well;

[0009] The hydrogen content produced by the production well is monitored. When the daily hydrogen production shows a significant downward trend, the end of the injection well located in the cavity is controlled to move upward and backward, so that the end of the injection well located in the cavity moves to the outer boundary area of ​​the cavity.

[0010] Furthermore, the end wellheads of the water injection well, oxidant injection well, and production well all extend into the coal seam.

[0011] Furthermore, after a stable cavity is formed in the underground coal seam, water vapor is injected into the cavity through a water injection well to prevent the ignition process from failing.

[0012] Furthermore, the water injection well is configured with a telescopic wellhead at one end within the cavity.

[0013] Furthermore, the oxidant injected into the oxidant injection well is pure oxygen.

[0014] Furthermore, the oxidant content injected into the oxidant injection well gradually increases over time.

[0015] Furthermore, the bottom ends of both the water injection well and the production well are connected to the cavity.

[0016] The present invention also provides a system for increasing hydrogen production through underground coal gasification, the system comprising:

[0017] The module is designed for drilling water injection wells, oxidant injection wells, and production wells in areas with coal seams.

[0018] The ignition module is used to ignite the underground coal seam through an oxidant injection well and form a cavity in the coal seam.

[0019] The injection module is used to inject water vapor into the cavity through the injection well;

[0020] The monitoring module is used to monitor the hydrogen content produced by the production well. When the daily hydrogen production shows a significant downward trend, it controls the end of the water injection well located in the cavity to move upward and backward, so that the end of the water injection well located in the cavity moves to the outer boundary area of ​​the cavity.

[0021] The technical effects and advantages of this invention are as follows:

[0022] (1) The method for increasing hydrogen production through underground coal gasification involves performing a water injection and retraction operation when a decrease in hydrogen production rate is detected, so that the water injection point is aligned with the current boundary of the underground coal layer, thereby restoring the gasification reaction with water and thus increasing the production and yield of H2.

[0023] (2) The method of increasing hydrogen production through underground coal gasification can significantly control the formation temperature, greatly prevent the conduction of heat in the cavity in the vertical direction, effectively reduce the possibility of thermal rupture of the caprock, and greatly reduce a series of environmental problems such as groundwater pollution caused by the release of harmful gases produced during underground coal gasification.

[0024] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A flowchart of a method for increasing hydrogen production through underground coal gasification is provided by the present invention.

[0027] Figure 2 This is a conceptual diagram of the modeling of the present invention;

[0028] Figure 3 This is a 3D view of the model created using the STAR simulator in this invention;

[0029] Figure 4 This is a comparison chart of the daily H2 production rate of the model of this invention and conventional steam injection technology;

[0030] Figure 5 This is a comparison chart of the cumulative H2 yield between the model of this invention and conventional steam injection technology;

[0031] Figure 6 This is a comparison diagram of the temperature distribution of the cavity in the model of this invention and the model of a non-retractable, non-injection well.

[0032] Figure 7 This invention provides a schematic diagram of a system for increasing hydrogen production through underground coal gasification. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The flowchart shown in the attached diagram is merely an illustrative example and does not necessarily include all steps. For example, some steps may be broken down, while others may be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0035] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0036] To address the shortcomings of existing technologies, this invention discloses a method for increasing hydrogen production through underground coal gasification. Figure 1 A flowchart of a method for increasing hydrogen production through underground coal gasification development provided by this invention is shown below. Figure 1 As shown, the method includes the following steps:

[0037] Step S1: In areas with coal seams, water injection wells, oxidant injection wells, and production wells are constructed, with the end wellheads of the water injection wells, oxidant injection wells, and production wells extending into the coal seam.

[0038] Step S2: Ignite the underground coal seam by injecting an oxidant into the well and form a cavity in the coal seam;

[0039] Step S3: Inject water vapor into the cavity through the water injection well, wherein one end of the water injection well located in the cavity is configured as a telescopic wellhead;

[0040] Step S4: Monitor the hydrogen content produced by the production well. When the daily hydrogen production shows a significant downward trend, control the end of the water injection well located in the cavity to move upward and backward, so that the end of the water injection well located in the cavity moves to the outer boundary area of ​​the cavity.

[0041] Preferably, in step S2, after a stable cavity is formed in the underground coal seam (assuming the cavity is of a certain size so that the cooling effect of the injected water will not directly stop the cavity development), water vapor is injected into the cavity through a water injection well to avoid failure of the ignition process.

[0042] Preferably, the oxidant injected into the oxidant injection well is pure oxygen.

[0043] Preferably, the oxidant content injected into the oxidant injection well gradually increases over time.

[0044] Preferably, the bottom ends of both the injection well and the production well are connected to the cavity.

[0045] Example:

[0046] This invention provides a method for increasing hydrogen production through underground coal gasification, comprising the following steps:

[0047] Step S1: In areas with coal seams, water injection wells, oxidant injection wells, and production wells are constructed, with the end wellheads of the water injection wells, oxidant injection wells, and production wells extending into the coal seam.

[0048] Step S2: Ignite the underground coal seam by injecting an oxidant into the well and form a cavity in the coal seam;

[0049] Step S3: Inject water vapor into the cavity through the water injection well, wherein one end of the water injection well located in the cavity is configured as a telescopic wellhead;

[0050] Step S4: Monitor the hydrogen content produced by the production well. When the daily hydrogen production shows a significant downward trend, control the end of the water injection well located in the cavity to move upward and backward, so that the end of the water injection well located in the cavity moves to the outer boundary area of ​​the cavity.

[0051] Figure 2 This is a modeling concept diagram for the present invention. Figure 3 The three-dimensional view of the model created by the STAR simulator in this invention is as follows: Figure 2-3 As shown, this invention uses the STAR simulator from CMG Ltd. for modeling. To ensure the practical applicability of the simulation results, the physical properties of deep coal seams in the Santanghu Basin of Xinjiang, China, were employed. The model simulates the ignition process using a two-day heater in the oxidant injection well. From the third day onwards, pure oxygen is injected into the coal seam, with the oxygen supply gradually increasing over time to accommodate the continuously growing underground cavities. As time progresses, the expansion of the underground coal seam boundary renders the optimal water injection location less ideal, and the hydrogen production rate begins to decline. To mitigate this trend and achieve a sustained high hydrogen production rate, a water injection retraction operation is performed when a decline in hydrogen production is detected. This aligns the water injection point with the real-time coal-rich coke boundary, thereby restoring its gasification reaction with water.

[0052] To verify the feasibility of using this model to maintain a high H2 production rate, a comparative model of a steam injection well without a retraction function was constructed. The steam injection time for both models was 30 days, and the daily hydrogen production was measured. When the water injection well in the model of this invention was injected on the 5th day, it was retracted upward by 3 subdivision grids, i.e., 1.5 meters. The steam injection point of the comparative model did not change position. Figure 4 This is a comparison chart of the daily H2 yield of the model of this invention and conventional steam injection technology, from... Figure 4 As can be seen, the downward trend in H2 production rate was reversed on the 6th day after steam injection, while in the control scheme, the H2 rate continued to decline. Figure 5 This is a comparison chart of the cumulative H2 yield between the model of this invention and conventional steam injection technology, as shown in the figure. Figure 5 As shown, at a more suitable injection location, the H2 production rate steadily increases until it reaches a relatively stable state, with an average H2 production rate approaching 10,000 cubic meters per day. Furthermore, the high-yield period is longer compared to before the upward retraction, reflecting that water injection helps suppress the vertical growth of the cavity.

[0053] In addition to preventing the formation process of the cavity from weakening the sealing performance of the capping layer, the temperature field distribution within the cavity should be controlled to reduce its impact on the capping layer. Figure 6 This is a comparison diagram of the temperature distribution of the cavity in the model of this invention and the model of the non-withdrawal water injection well. In the diagram, a corresponds to the model of this invention and b corresponds to the non-withdrawal water injection well model. The instantaneous temperature data of the two selected grid points at the same time show that the model of this invention can significantly control the formation temperature, greatly prevent the conduction of heat in the cavity in the vertical direction, and effectively reduce the possibility of thermal rupture of the caprock.

[0054] Based on the same concept, this invention also discloses a system for increasing hydrogen production through underground coal gasification. Figure 7 This invention provides a schematic diagram of a system for increasing hydrogen production through underground coal gasification, as shown in the figure. Figure 7 As shown, the system includes:

[0055] The module is designed for drilling water injection wells, oxidant injection wells, and production wells in areas with coal seams.

[0056] The ignition module is used to ignite the underground coal seam through an oxidant injection well and form a cavity in the coal seam.

[0057] The injection module is used to inject water vapor into the cavity through the injection well;

[0058] The monitoring module is used to monitor the hydrogen content produced by the production well. When the daily hydrogen production shows a significant downward trend, it controls the end of the water injection well located in the cavity to move upward and backward, so that the end of the water injection well located in the cavity moves to the outer boundary area of ​​the cavity.

[0059] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for increasing hydrogen production through underground coal gasification, characterized in that, The method includes the following steps: In areas with coal seams, water injection wells, oxidant injection wells, and production wells are to be constructed. The underground coal seam is ignited by injecting an oxidant into a well, and a cavity is formed in the coal seam. Water vapor is injected into the cavity through the injection well; The hydrogen content produced by the production well is monitored. When the daily hydrogen production shows a significant downward trend, the end of the injection well located in the cavity is controlled to move upward and backward, so that the end of the injection well located in the cavity moves to the outer boundary area of ​​the cavity.

2. The method for increasing hydrogen production through underground coal gasification development according to claim 1, characterized in that, The terminal wellheads of the water injection well, oxidant injection well, and production well all extend into the coal seam.

3. A method for increasing hydrogen production through underground coal gasification development according to claim 1 or 2, characterized in that, After a stable cavity is formed in the underground coal seam, water vapor is injected into the cavity through a water injection well to prevent the ignition process from failing.

4. The method for increasing hydrogen production through underground coal gasification development according to claim 2, characterized in that, The water injection well is located at one end of the cavity and is configured with a telescopic wellhead.

5. The method for increasing hydrogen production through underground coal gasification development according to claim 1, characterized in that, The oxidant injected into the oxidant injection well is pure oxygen.

6. The method for increasing hydrogen production through underground coal gasification development according to claim 5, characterized in that, The oxidant content injected into the oxidant injection well gradually increases over time.

7. The method for increasing hydrogen production through underground coal gasification development according to claim 1, characterized in that, The bottom ends of both the injection well and the production well are connected to the cavity.

8. A system for underground coal gasification to increase hydrogen production, characterized in that, The system includes: The module is designed for drilling water injection wells, oxidant injection wells, and production wells in areas with coal seams. The ignition module is used to ignite the underground coal seam through an oxidant injection well and form a cavity in the coal seam. The injection module is used to inject water vapor into the cavity through the injection well; The monitoring module is used to monitor the hydrogen content produced by the production well. When the daily hydrogen production shows a significant downward trend, it controls the end of the water injection well located in the cavity to move upward and backward, so that the end of the water injection well located in the cavity moves to the outer boundary area of ​​the cavity.

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