WO2013090979A1

WO2013090979A1 - Ucg product gas quenching method and apparatus

Info

Publication number: WO2013090979A1
Application number: PCT/AU2012/001350
Authority: WO
Inventors: Greg Martin Parry PERKINS; Casper Jan Hendrik BURGER; Shafraz Zafrullah
Original assignee: Linc Energy Ltd
Priority date: 2011-12-21
Filing date: 2012-11-02
Publication date: 2013-06-27

Abstract

The invention relates to systems and methods for treating underground coal gasification (UCG) product gas within an underground coal gasifier. In one aspect, the invention concerns systems and methods for lowering UCG product gas temperature within an underground coal gasifier such that the physical and/or chemical properties of the product gas are altered before reaching a production well of the gasifier. In another aspect, the invention concerns a method for active decommissioning of a gasifier, whereby a downstream spent gasifier cavity is decommissioned while an upstream gasifier cavity remains in active operation for UCG product gas production.

Description

UCG PRODUCT GAS QUENCHING METHOD AND APPARATUS TECHNICAL FIELD

[0001] This invention relates to a method and apparatus for lowering (quenching) underground coal gasification (UCG) product gas temperature within an underground coal gasifier such that the physical and/or chemical properties of the product gas are altered before reaching a production well of the gasifier. This invention also concerns a method for active decommissioning of a gasifier, whereby a downstream spent gasifier cavity is

decommissioned while an upstream gasifier cavity remains in active operation for UCG product gas production.

BACKGROUND ART

[0002] Underground coal gasification is a process by which product gas is produced from a coal seam by combusting and gasifying the coal in situ in the presence of an oxidant. The product gas is typically referred to as synthesis gas or syngas and can be used as a feedstock for various applications, including clean fuels production, chemical production, and electricity generation.

[0003] Wells are drilled into the coal seam to allow for oxidant injection and product gas extraction. The wells are linked or extended to form an in-seam well channel to facilitate oxidant injection, cavity development, and product gas flow. The well allowing the injection of oxidant is called an injection well. The well from which product gas emerges is called a production well. Both horizontal and vertical well regions can be used for injection and production. Underground coal gasification can also utilise one or more vertical wells (service wells) located between the injection and production wells.

[0004] A coal seam having an injection well and a production well, with a well channel linking the two wells, is typically referred to as an underground coal gasifier. The gasifier will have a combustion zone within which coal is combusted in the presence of an oxidant, a gasification zone located downstream of the combustion zone in which coal is gasified and partially oxidized to produce product gas, and a downstream pyrolysis zone in which pyro lysis of coal occurs. Hot product gas flows downstream from the gasification zone and exits the ground from a well head of the production well. As coal is consumed or gasified, a gasifier (gasification) cavity within the coal seam develops and grows in size.

[0005] Typically, UCG product gas will contain: (1) main syngas components (e.g., CO, ¾, C0₂, N₂, and CHU); (2) solid particles/particulates (e.g., soot, ash, and coal particles); (3) water; (4) minor components such as C₂-C₆ hydrocarbons, oxygen, argon, sulphur containing components (e.g., H₂S, COS, CS₂, mercaptans, and thiophenes), nitrogen based components (e.g., NH₃ and HCN), hydrocarbon components (e.g., coal condensate, BTEX (benzene, toluene, ethylbenzene and xylenes), and PAHs (polycyclic aromatic hydrocarbons)); and (5) trace components such as heavy metals (arsenic and mercury) and chlorides.

[0006] High product gas temperatures can have undesirable impacts on the mechanical integrity and hydrocarbon containment capability of a underground coal gasifier's production well. At most risk is the heel of the production well, where the production casing, cement, and coal formation are in close proximity and exposed to high temperatures and product gas, which can cause deformation of the well design (including casing deformation, shearing, failure, and plastic deformation), corrosion of the well materials, and cracking and failure of the cement.

[0007] Additionally, high product gas temperatures can increase the production of contaminants such as BTEX, PAHs, and heavy hydrocarbons (i.e., C₅+) in the downstream pyrolysis zone of an underground coal gasifier. Such contaminants are of environmental concern.

[0008] Thus, there is a need for methods and systems of lowering UCG product gas temperature within an underground coal gasifier prior to it reaching a production well, particularly the heel of the production well.

SUMMARY OF INVENTION

[0009] It is an object of the present invention to provide a method and apparatus for lowering UCG product gas temperature within an underground coal gasifier, which minimises or overcomes at least one of the problems of the prior art. [0010] In one aspect, the invention provides a method of lowering UCG product gas temperature within an underground coal gasifier, including the step of injecting a sufficient quantity of a quenching fluid into a UCG product gas stream having a temperature of between about 500 and 1,200 °C to lower the temperature of the product gas stream to about 200 to 400 °C, wherein the quenching fluid is injected into the product gas stream via a service well located downstream of an active gasifier cavity and upstream of a production well.

[0011 ] In one embodiment, the service well is located between the active gasifier cavity and a downstream spent gasifier cavity.

[0012] Any suitable type of quenching fluid can be used. The quenching fluid can be a liquid or a gas (including a liquid or a gas with particulates suspended therein), or any combination thereof. The quenching fluid can consist of more than one type of liquid or gas. The choice of quenching fluid will depend on the desired outcome. For example, the quenching fluid can be used to lower the temperature of a UCG product gas stream such that less damage is caused to mechanical components used in underground coal gasification, particularly the production well. Alternatively (and/or additionally), the quenching fluid can be used to alter the chemical composition of the product gas stream prior to it reaching or leaving the production well.

[0013] The quenching fluid can optionally contain one or more chemicals that can be beneficial to decommissioning a spent gasifier cavity and/or can beneficially condition the UCG product gas prior to the product gas reaching or leaving the production well.

[0014] In one embodiment of the invention, the quenching fluid is a liquid. The liquid can be water. The water can be obtained from a naturally occurring water source, such as surface water or ground water. The water can be either fresh water or brine. The water can be treated water, such as demineralised water or raw water separated from UCG product gas.

[0015] In another embodiment of the invention, the quenching fluid is a gas, such as any available gas at surface. The gas can be treated syngas. The syngas can be cooled syngas from the same or another underground coal gasifier. Alternatively, the quenching fluid can be carbon dioxide. The carbon dioxide can be recycled from a downstream processing facility that separates carbon dioxide from UCG product gas. [0016] While the quenching fluid can be injected into a UCG product gas stream at any suitable location within the underground coal gasifier, it is preferably injected upstream of a production well via a service well. The positioning of the service well for quenching fluid injection can be chosen with respect to various design criteria, including sufficient distance from the injection location to the production well and/or a spent gasifier cavity so as to ensure good mixing between the injected quenching fluid and the hot product gas stream, and appropriate temperature reduction of the product gas stream.

[0017] As will be understood by one of ordinary skill in the art, the quenching fluid can be injected at any suitable injection rate and quantity. The injection rate can be chosen with respect to various design criteria, including ensuring that injection of the quenching fluid via a service well is sufficient to lower the UCG product gas stream temperature to the desired lower temperature prior to it reaching a production well and/or a spent gasifier cavity. One of ordinary skill in the art will be able to formulate the rate and quantity of quenching fluid injection necessary to achieve desired outcomes.

[0018] The quenching fluid can be injected into a UCG product gas stream in any suitable way. The quenching fluid can be injected by way of an injection welL an ignition well, a production well, a service well, or any other vertically extending or inclined well. Preferably, the quenching fluid is injected upstream of a production well via a service well.

[0019] The injection method can include the step of using a quenching fluid delivery system to deliver the quenching fluid, and this can be of any suitable size, shape, and construction. In one embodiment of the invention, the quenching fluid delivery system includes an existing well/well casing (e.g., a service well) for conveying the quenching fluid to a UCG product gas stream. The delivery system can further include a circulation pump and fluid reservoir connected to a well head of the well for pumping the quenching fluid into the well. Alternatively, the delivery system can further include a gas compressor connected to the well head for injecting quenching gas into the well.

[0020] In another embodiment of the invention, the quenching fluid delivery system includes a pipe for conveying the quenching fluid, and optionally a nozzle or pig tail fitted to a lower end of the pipe for spraying the quenching fluid into a UCG product gas stream. This type of delivery system can be extended to the desired in-seam location via an injection, ignition, service, production, or other type of well that extends from ground surface. The pipe can be flexible, such that it can be unwound from a spool.

[0021 ] The delivery system can further include a circulation pump and fluid reservoir connected to the upper end of the pipe. Alternatively, the delivery system can further include a gas compressor connected to the upper end of the pipe. The pipe can have a diameter of anywhere between, for example, 0.5 and 4 inches, and preferably between 1 and 2 inches. The pipe can be made of steel, including carbon steel and stainless steel, for example.

[0022] In a further embodiment of the invention, the quenching fluid delivery system includes a pipe arranged concentrically with a casing of a well (e.g., the casing of a service well) and the pipe can extend to the bottom of the well, or any location above the bottom of the well (e.g., the top of the coal seam).

[0023] A lower end of the pipe for conveying the quenching fluid can have a plurality of openings in the form of perforations, slots, or other types of holes. Quenching fluid can be injected into the annular space between the pipe and the well casing (or the pipe and the coal seam), such that the quenching fluid mixes with a UCG product gas stream in a mixing zone at or near the bottom of the well to lower the temperature of the product gas stream prior to it reaching a production well.

[0024] If desired, the pipe can be insulated to minimise heat exchange with the quenching fluid flowing in the annular space. The pipe can have a diameter of anywhere between, for example, 0.5 and 4 inches, and preferably between 1 and 2 inches. The pipe can be made of steel, including carbon steel and stainless steel, for example.

[0025] The delivery system can include one or more spacers for the spacing the pipe relative to the well casing. Preferably, the pipe is spaced centrally of the well casing.

[0026] The desired temperature for the quenched UCG product gas can be a precise temperature or a temperature range. As is well known to one of ordinary skill in the art, the desired temperature will be dependent on the gasifier pressure and the dew point of the product gas at that pressure. Differing product gas compositions will have differing dew points. Typically, the product gas should not be allowed to reach its dew point prior to leaving the production well.

[0027] For example, in order to prevent high-temperature damage to the production well or other mechanical components used in UCG and/or the production of contaminants, the temperature of the quenched UCG product gas can be anywhere between about 200 and 400 °C, more preferably between about 300 and 350 °C, and most preferably below about 300 °C. Quenching can improve mechanical longevity and avoid the use of costly materials which may be needed when operating the gasifier under extreme temperatures.

[0028] For example, in order to promote favourable chemical reactions with a UCG product gas stream, such that a specific product gas composition is manifest at the well head of a production well, the quenching fluid can be injected into the product gas stream when at temperatures of between about 500 and 1200 °C, such that the temperature of the product gas stream is lowered to about 200 to 400°C, and preferably less than about 300 °C.

[0029] The disclosed methods can include the step of monitoring the temperature in-seam and/or within a well, such as a production well and/or a service well, and regulating the injection rate and quantity of quenching fluid according to the temperature reading. To that end, the quenching fluid delivery system can include at least one thermocouple (located in- seam or within a well) electrically connected to a computer-operable valve for regulating flow of the quenching fluid.

[0030] In one embodiment of the invention, the quenching fluid is used to quench the temperature of the product gas stream prior to the stream reaching a heel or casing of the production well. As discussed herein, high product gas temperatures can have undesirable impacts on the mechanical integrity and hydrocarbon containment capability of the production well, particularly by causing deformation of the well design.

[0031] In another aspect, the invention provides a method of lowering UCG product gas temperature within an underground coal gasifier prior to it reaching a production well, including the step of injecting a quenching fluid into a UCG product gas stream having a temperature of between about 500 and 1,200 °C such that the temperature of the product gas stream is lowered to about 200 to 400 °C prior to it reaching the production well. [0032] In one embodiment of the invention, the quenching fluid is injected upstream of the production well via a service well.

[0033] In yet another aspect, the invention provides a method of underground coal gasification in a coal seam provided with an injection well, a production well, and an in-seam well channel linking the injection well and the production well, including the steps of: a) establishing a first gasifier cavity in the coal seam so as to produce UCG product gas, b) injecting a quenching fluid into the UCG product gas downstream of the first gasifier cavity and upstream of the production well so as to lower the temperature of the product gas to about 200 to 400 °C prior to the product gas reaching the production well, c) establishing a second gasifier cavity upstream of the first gasifier cavity so as to produce UCG product gas, and d) injecting quenching fluid into the UCG product gas downstream of the second gasifier cavity and upstream of the first gasifier cavity so as to lower the temperature of the product gas to about 200 to 400 °C prior to the product gas reaching the production well.

[0034] By progressively repeating these steps, gasifier cavities that are no longer in use can be actively decommissioned via steam stripping during the UCG process, thereby reducing the need for end of life decommissioning steps, including a dedicated steam injection step. Additionally, the active decommissioning step is continued for as long as upstream active gasification is required, which would typically continue for many years.

[0035] In this way, active decommissioning of a gasifier having multiple gasifier cavities can be realised, whereby a downstream gasifier cavity is decommissioned while an upstream gasifier cavity remains in operation for active gasification.

[0036] In some embodiments of the invention, injecting a quenching fluid to lower the temperature of the UCG product gas within an underground coal gasifier changes the chemical composition of the product gas prior to it reaching or leaving a production well. For example, where the quenching fluid is carbon dioxide, injecting carbon dioxide has the advantage of shifting the equilibrium of the water gas shift reaction (CO + H₂0 <→ H₂ + C0₂) to the left, thereby increasing the carbon monoxide content of the product gas and reducing the H₂/CO ratio. This is particularly helpful for product gas applications where control of the H₂/CO ratio is desired. [0037] The inventive concept further concerns apparatuses and systems for carrying out the methods described herein.

[0038] In a further aspect, the invention provides an apparatus for lowering UCG product gas temperature within an underground coal gasifier prior to it reaching a production well, including a quenching fluid delivery system for injecting quenching fluid into a UCG product gas stream such that the temperature of the product gas stream is lowered to about 200 to 400 °C.

[0039] In one embodiment of the invention, the quenching fluid delivery system injects quenching fluid into a service well located upstream of the production well.

[0040] The quenching fluid delivery system can include one or more thermocouples for monitoring temperature in-seam and/or within a well (e.g., one or more thermocouples located in a well liner that extends upstream from a heel of a production well). The quenching fluid delivery system can include at least one thermocouple (located in-seam or within a well) electrically connected to a computer-operable valve for regulating flow of the quenching fluid.

[0041] It is to be understood that features of the methods as described herein are interchangeable with features of the apparatuses as described herein and vice- versa.

[0042] In order that the invention may be more readily understood and put into practice, one or more preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying figures.

BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a side section view depicting part of an underground coal gasifier having a service well, a production well, and a quenching fluid delivery system, according to an embodiment of the present invention. [0044] Figure 2 is a side section view depicting part of an underground coal gasifier having a service well, a production well, and a quenching fluid delivery system, according to another embodiment of the present invention.

[0045] Figure 3 depicts a method for active decommissioning of an underground coal gasifier that has multiple gasifier cavities, whereby a downstream gasifier cavity is decommissioned while an upstream gasifier cavity remains in operation for active

gasification, according to a further embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0046] The inventors have detennined that a UCG product gas stream having a temperature of between about 500 and 1,200 °C can be lowered to a temperature of about 200 to 400 °C prior to it reaching a production well by introducing a quenching fluid into the product gas stream via a service well located upstream of the production well in an underground coal gasifier.

[0047] Furthermore, the inventors have developed a method for minimising the formation of contaminants such as BTEX, PAHs, and heavy hydrocarbons (i.e., C +) in UCG product gas by maintaining a pyro lysis zone of an underground coal gasifier at a temperature below about 300 °C.

[0048] The inventors have also developed a method for active decommissioning of an underground coal gasifier, whereby a downstream spent gasifier cavity is decommissioned while an upstream gasifier cavity remains in active operation for UCG product gas production.

[0049] In the figures, like reference numerals refer to like features.

[0050] Referring to Figure 1 , there is generally depicted an underground coal gasifier 10 illustrating certain aspects of the invention. A coal seam 12 is located underground and surrounded by overburden 14 and underburden 16, and includes a generally horizontally- extending well channel 18 linking an injection well (which is not shown) and a production well 20. The underground coal gasifier 10 also includes a service well 22. Production well 20 and service well 22 include casing 23 secured by cement 24.

[0051 ] Use of water 25 as a quenching fluid introduced via the service well 22 to lower the temperature of hot product gas 26 prior to it reaching the production well 20 was trialled. Figure 1 shows the service well 22 and a quenching fluid delivery system 28, including a pipe 30 for conveying water 25, and a nozzle 32 fitted to a lower end of the pipe 30 for spraying the water 25 into a 500 to 1,200 °C product gas 26 stream.

[0052] The delivery system 28 further includes a circulation pump 34 and water tanks 36 that are connected to pipe 30. Pipe 30 extends through a well head 38 of the service well 22.

[0053] The delivery system 28 further includes a plurality of thermocouples 40 that monitor the temperature of the gasifier, including the service well 22, well liner 42, and production well 20, and automatically regulate the flow of water 25 injection by way of a computer-operable valve 44 located downstream of the pump 34.

[0054] The sizing of the pipe 30 and nozzle 32 provide for a high enough linear velocity to ensure that the water 25 in the pipe 30 remains as water before exiting the nozzle 32. The vaporisation of water 25 cools the product gas 26 to a temperature of about 200 to 400 °C.

[0055] The production well 20 is fitted with a perforated well liner 42. The well liner 42 extends from a heel of the production well 20 almost to a gas mixing zone 46 upstream of the production well 20, beneath the service well 22.

[0056] In use, water 25 is injected into the service well 22 via the pipe 30 and spray nozzle 32 where it mixes with the product gas 26, cooling it to the desired temperature. The delivery system 28 is designed to cool the product gas 26 at maximum production flow conditions from a maximum temperature of about 1,200 °C down to a minimum temperature of about 200 °C. The thermocouples 40, predominantly located in the production well 20 and well liner 42, measure the temperature of the quenched product gas 26 and the water 25 injection rate is optimally controlled to achieve the desired temperature. [0057] Although not illustrated, injected water 25 can be recycled from product gas 26 that is produced by the same gasifier (following appropriate surface treatment of the water). This provides significant benefits in reducing water treatment costs.

[0058] Depending on UCG operation conditions, the delivery system 28 need not have the nozzle 32, and the well liner 42 need not be present.

[0059] Referring to Figure 2, there is generally depicted an underground coal gasifier 10 illustrating additional aspects of the invention. A coal seam 12 is located underground and surrounded by overburden 14 and underburden 16, and includes a generally horizontally- extending well channel 18 linking an injection well (which is not shown) and a production well 20. The underground coal gasifier 10 also includes a service well 22. Production well 20 and service well 22 include casing 23 secured by cement 24.

[0060] Use of water 25 as a quenching fluid introduced via the service well 22 to lower the temperature of hot product gas 26 prior to it reaching the production well 20 was trialled. Figure 2 shows the service well 22 and a quenching fluid delivery system 28, including a pipe 30 for conveying water 25 to a well head 38 of the service well 22. Pipe 30 extends through the well head 38 of the service well 22 for injection of water 25 into the service well 22, The delivery system 28 further includes a circulation pump 34 and water tanks 36 that are connected to pipe 30.

[0061] The delivery system 28 further includes a plurality of thermocouples 40 that monitor the temperature of the gasifier, including the service well 22, well liner 42, and production well 20, and automatically regulate the flow of water 25 injection by way of a computer-operable valve 44 located downstream of the pump 34.

[0062] Injected water 25 travels down the service well 22 into the well channel 18, where it vaporises as it mixes with a 500 to 1,200 °C product gas 26 stream moving downstream to the production well 20. In this way the product gas 26 is cooled to a temperature of about 200 to 400 °C. [0063] The production well 20 is fitted with a perforated well liner 42. The well liner 42 extends from a heel of the production well 20 almost to a gas mixing zone 46 upstream of the production well 20, beneath the service well 22.

[0064] In use, water 25 is injected into the service well 22 via the pipe 30 where it mixes with the product gas 26, cooling it to the desired temperature. The delivery system 28 is designed to cool the product gas 26 at maximum production flow conditions from a maximum temperature of about 1,200 °C down to a minimum temperature of about 200 °C. The thermocouples 40, predominantly located in the production well 20 and well liner 42, measure the temperature of the quenched product gas 26 and the water 25 injection rate is optimally controlled to achieve the desired temperature.

[0065] Although not illustrated, injected water 25 can be recycled from product gas 26 that is produced by the same gasifier (following appropriate surface treatment of the water). This provides significant benefits in reducing water treatment costs.

[0066] Depending on UCG operation conditions, the well liner 42 need not be present.

[0067] Figure 3 depicts a method of active decommissioning of an underground coal gasifier 10 having multiple gasifier cavities, whereby a downstream spent gasifier cavity 50 is decommissioned while an upstream active gasifier cavity 52 remains in operation.

[0068] The underground coal gasifier 10 includes an injection well 48, a production well 20, a generally horizontally- extending well channel 18 linking the injection well 48 and the production well 20, and several service (quench) wells 22 (i.e., 22a, 22b, and 22c) located between the injection well 48 and the production well 20.

[0069] The injection well 48 includes an encased pipe and has a heel located adjacent the well channel 18. Likewise, the production well 20 is an encased pipe and has a heel located adjacent the well channel 18.

[0070] Each service well 22 includes an encased pipe having a lower end in fluid communication with the well channel 18. Each service well 22 has an upper end having a well head (which is not shown) which has an inlet for quenching fluid. [0071 ] The quenching fluid is water 25 (including treated waste water), that is pumped into the service well 22. The water 25 is initially injected at a rate of about 0.2m /hour to about l.OnrVhour, and then the rate is modified as required according to thermocouple readings at the production well 20 and/or according to thermocouple readings from other regions of the underground coal gasifier 10. Thermocouples (which are not shown) that monitor the temperature of the gasifier 10 can automatically regulate water 25 injection by way of a computer-operable valve (which is not shown) located downstream of a pump (which is not shown) and upstream of the service well 22.

[0072] As injected water 25 travels down the service well 22 into the well channel 18 (and/or gasifier cavity), it vaporises as it mixes with hot product gas 26 moving downstream to the production well 20. In this way the hot product gas 26 is cooled.

[0073] A first step of the method (which is not shown) involves establishing a first gasifier cavity 50 upstream of the first service well 22a so as to produce product gas. Water 25 is injected into the well channel 18 via the service well 22 a downstream of the first gasifier cavity 50 and upstream of the production well 20 so as to lower the temperature of the hot product gas 26 to below about 400 °C (preferably less than about 300 °C) prior to the product gas 26 reaching the production well 20. Temperature readings taken at the production well 20 or from within the well channel 18 inform a UCG operator as to whether more or less water 25 is to be injected into the service well 22a.

[0074] As depicted in Figure 3, a further step of the method involves establishing a second gasifier cavity 52 upstream of the service well 22b and the first gasifier cavity 50 so as to produce additional product gas. The second gasifier cavity 52 is established once gasification using the first gasifier cavity 50 has come to an end (i.e., the coal has been gasified and the cavity is spent).

[0075] Figure 3 further depicts injecting water 25 into the well channel 18 via the service well 22b downstream of the second gasifier cavity 52 and upstream of the first gasifier cavity 50 so as to lower the temperature of the hot product gas 26 to below about 400 °C (preferably less than about 300 °C) prior to the product gas 26 reaching the production well 20.

Temperature readings taken at the production well 20 or from within the well channel 18 inform a UCG operator as to whether more or less water 25 is to be injected into the service well 22b.

[0076] Although not depicted in Figure 3, further gasifier cavities can be established and further quenching can be carried out in a similar way to that described herein. Service well 22c would be the next service well to be used. It is possible that a single underground coal gasifier can have 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more gasifier cavities with accompanying service wells.

[0077] As discussed herein, by progressively repeating the steps of this method, gasifier cavities that are no longer in use can be actively decommissioned during the actual UCG process, thereby reducing the need for end of life decommissioning steps, including a dedicated steam injection step. Additionally, the active decommissioning step can be continued for as long as upstream active gasification is required, which would typically continue for many years.

[0078] Table 1 below shows what water injection rates are required in order to quench product gas streams generated using different types of oxidant.

TABLE 1

Water cooling calculation in service well

[0079] Throughout this specification, unless the context requires otherwise, the words "comprise", "comprises" and "comprising" will be understood to mean the inclusion of a stated integer, group of integers, step, or steps, but not the exclusion of any other integer, group of integers, step, or steps. [0080] Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. It will therefore be appreciated by those of skill in the art that, in light of the instant disclosure, various modifications and changes can be made in the particular embodiments exemplified without departing from the scope of the present invention.

Claims

1. A method of lowering underground coal gasification (UCG) product gas temperature within an underground coal gasifier, comprising the step of injecting a sufficient quantity of a quenching fluid into a UCG product gas stream having a temperature of between about 500 and 1 ,200 °C to lower the temperature of the product gas stream to about 200 to 400 °C, wherein the quenching fluid is injected into the product gas stream via a service well located downstream of an active gasifier cavity and upstream of a production well.

2. The method of claim 1 , wherein the quenching fluid is water.

3. The method of claim 1, wherein the quenching fluid is carbon dioxide.

4. The method of claim 1 , wherein the service well is located between the active gasifier cavity and a downstream spent gasifier cavity.

5. The method of any one of claims 1 to 4, wherein the temperature of the UCG product gas stream is lowered to less than about 300 °C.

6. The method of any one of claims 1 to 5, wherein the the chemical composition of the UCG product gas is altered prior to it reaching or leaving the production well.

7. A method of lowering underground coal gasification (UCG) product gas temperature within an underground coal gasifier prior to it reaching a production well, comprising the step of injecting a quenching fluid into a UCG product gas stream having a temperature of between about 500 and 1,200 °C such that the temperature of the product gas stream is lowered to about 200 to 400 °C prior to it reaching the production well.

8. The method of claim 7, wherein the quenching fluid is water.

9. The method of claim 7, wherein the quenching fluid is carbon dioxide.

10. The method of any one of claims 7 to 9, wherein the quenching fluid is injected upstream of the production well via a service well.

11. The method of any one of claims 7 to 10, wherein the temperature of the UCG product gas stream is lowered to less than about 300 °C.

12. The method of any one of claims 7 to 11, wherein the the chemical composition of the UCG product gas is altered prior to it reaching or leaving the production well.

13. A method of underground coal gasification in a coal seam provided with an injection well, a production well, and an in-seam well channel linking the injection well and the production well, comprising the steps of:

a. establishing a first gasifier cavity in the coal seam so as to produce underground coal gasification (UCG) product gas;

b. injecting a quenching fluid into the UCG product gas downstream of the first gasifier cavity and upstream of the production well so as to lower the temperature of the product gas to about 200 to 400 °C prior to the product gas reaching the production well; c. establishing a second gasifier cavity upstream of the first gasifier cavity so as to produce UCG product gas; and

d. injecting quenching fluid into the UCG product gas downstream of the second gasifier cavity and upstream of the first gasifier cavity so as to lower the temperature of the product gas to about 200 to 400 °C prior to the product gas reaching the production well.

14. The method of claim 13, wherein the quenching fluid is water.

15. The method of claim 13, wherein the quenching fluid is carbon dioxide.

16. The method of any one of claims 13 to 15, wherein the temperature of the product gas stream is lowered to less than about 300 °C.

17. The method of any one of claims 13 to 16, wherein the the chemical composition of the UCG product gas is altered prior to it reaching or leaving the production well.

18. An apparatus for lowering underground coal gasification (UCG) product gas temperature to about 200 to 400 °C within an underground coal gasifier prior to it reaching a production well, comprising: a) a quenching fluid delivery system for injecting quenching fluid into a UCG product gas stream via a service well located upstream of the production well; and

b) one or more thermocouples,

wherein the one or more thermocouples are located in a well liner that extends upstream from a heel of the production well.

19. The apparatus of claim 18, further comprising one or more thermocouples located in the production well.

20. The apparatus of claim 18 or claim 19, wherein the one or more thermocouples are electrically connected to a computer-operable valve for regulating flow of the quenching fluid.