DERIVED FROM UCG PRODUCT GAS

TECHNICAL FIELD

[0001 ] This invention relates to a method and system for treating a waste stream derived from product gas produced by underground coal gasification (UCG). In particular, the invention concerns a method and system for separating aqueous components from nonaqueous components of the waste stream.

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 reaction produces hot product gas, which is typically referred to as synthesis gas or syngas. The product gas is a mixture of combustible gases which can be treated and used as fuel or for chemical production.

[0003] Typically, product gas will contain: (1) main syngas components (e.g., CO, H ₂ , C0 ₂ , N ₂ , and CH ₄ ); (2) solid particles/particulates (e.g., soot, ash and coal particles); (3) water; (4) minor components such as C ₂ -C ₆ hydrocarbons, oxygen, argon, sulphur containing components (e.g., H ₂ S, COS, CS ₂ , mercaptans, and thiophenes), nitrogen based components (e.g., N¾ 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.

[0004] Surface treatment of product gas can include separating out liquid and solid components from gaseous components of the product gas stream (either in a single treatment step or in separate treatment steps, in which case separate waste components can be pooled), and these are collectively referred to herein as a "waste stream". A waste stream derived from product gas will typically contain a mixture of water ("aqueous component") and

coal/hydrocarbon condensate ("non-aqueous component") which may or may not further include particulates, such as coal ash.

[0005] One problem with UCG is that a waste stream will always be produced and the waste stream will require treatment on site before disposal, storage or release to the environment. This problem is expected to intensify when UCG is carried out on a large commercial scale due to increasing volumes of waste streams.

[0006] Another problem is that the waste stream contains components that could be used in the manufacture of chemicals and in industrial processes, but cost-efficient treatment steps for recovering these components do not exist.

[0007] Yet another problem is that working with waste streams derived from product gas produced by UCG can be hazardous.

[0008] The applicant has trialled separating aqueous from non- aqueous components of waste streams using settling tank technology and using manually-operated drainage valves to drain the different components, but this has proven to be unsatisfactory. It will most certainly be unsatisfactory when carrying out UCG on a large commercial scale. One general problem is that light and heavy hydrocarbons of the non-aqueous component take a long time to separate from the aqueous component and, in fact, fail to completely separate from the aqueous component.

[0009] Handling and separation of the waste stream is complicated due to the following reasons: (1) the presence of coal condensate (hydrocarbons) and coal tar, which have a high melting temperature and are therefore difficult to keep in a liquid phase; (2) the presence of ash and other particulate matter which upon mixing and settling with coal tar are prone to solidify under ambient conditions; and (3) the similar bulk fluid properties of the waste water components, in particular the densities of the hydrocarbon liquid phase and water, make separation difficult and often impossible due to the propensity of the mixed waste water components to emulsify.

[0010] Thus there is a need for an improved method and system of treating a waste stream derived from product gas produced by UCG.

SUMMARY OF INVENTION

[0011 ] It is an object of the present invention to provide a method and system for treating a waste stream derived from product gas produced by UCG, which minimises or overcomes at least one of the problems mentioned herein.

[0012] According to an aspect of the present invention, there is provided a method for treating a waste stream derived from product gas produced by underground coal gasification, the method including the steps of dosing the waste stream with a demulsifier, conveying the demulsifier-dosed waste stream to at least one settling tank, wherein the waste stream separates into aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components, and recovering the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components.

[0013] In one embodiment, the waste stream is at a temperature of about 20 °C to about 85 °C when it is dosed with the demulsifier.

[0014] In another embodiment, the temperature of the demulsifier-dosed waste stream in the at least one settling tank is maintained at a temperature of about 20 °C to about 40 °C.

[0015] The method can also include the step of sensing one or more interfaces between the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components prior to recovering the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components.

[0016] In an embodiment of the present invention, the method for treating a waste stream derived from product gas produced by UCG when implemented can reduce the settling time taken for the waste stream to separate into its respective components, thereby increasing the capacity of a waste stream treatment system to process waste streams and decreasing storage tank requirements. By reducing settling time, the aforementioned problem of the mixture of coal condensate, coal tar and ash, and other particulate matter solidifying is mitigated, thereby eliminating the task of heating storage tanks. Furthermore, effective separation of the waste stream components can result in the production of saleable hydrocarbon liquid products, which can be used as fuel sources, for example.

[0017] According to a further aspect of the present invention, there is provided a system for separating aqueous and non-aqueous components in a waste stream recovered from product gas produced by underground coal gasification, the system including a settling tank, a demulsifier dosing unit fluidly connected to the settling tank, and a flow connection from a source of the recovered waste stream to the settling tank.

[0018] In one embodiment, the system includes a plurality of settling tanks. [0019] In another embodiment, the waste stream is dosed with demulsifier in the settling tank(s).

[0020] In yet another embodiment, the waste stream is dosed with demulsifier immediately before being received by the settling tank(s).

[0021] In a further embodiment, the flow connection from the source of the recovered waste stream to the settling tank(s) is a feed pipe.

[0022] Suitably, the demulsifier dosing unit is fluidly connected to the settling tank(s) via the feed pipe and the waste stream is dosed with demulsifier prior to the waste stream being received by the settling tank(s).

[0023] An advantage of the present invention is that, due to efficient separation of components, the method and system lend themselves to automation.

[0024] Accordingly, in yet another embodiment, the settling tank(s) includes a sensor- controlled drainage system having a sensor for sensing an interface between separated aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components of the waste stream and operating one or more drainage valves to individually drain the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components.

[0025] In still another embodiment, the settling tank(s) includes a sensor-controlled floating suction system calibrated to float within separated aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components of the waste stream and individually drain the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components.

[0026] The settling tank for receiving the demulsifier-treated waste stream and allowing separation of the aqueous and non-aqueous components from one another can be of any suitable size, shape and constructions and can be formed from any suitable material or materials. Any number of settling tanks can be used depending on the volume of waste stream to be treated. One or more settling tanks can be used in a parallel or series arrangement to process large volumes of waste stream. One or more settling tanks can be used to blend two or more hydrocarbon phases in the production of a saleable hydrocarbon liquid product, for example. [0027] Each settling tank can have one or more drainage valves for draining separated components of a waste stream. The one or more drainage valves can be located at any suitable location within or on the settling tank. Preferably, each settling tank can have one or more drainage valves for individually draining separated components of the waste stream (i.e., aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components).

[0028] Preferably, for large commercial operations, demulsified waste streams can be received by more than one settling tank in a parallel arrangement.

[0029] Any suitable type of demulsifier (i.e., emulsion breaker) and demulsifier unit can be used. The demulsifier can be a chemical agent or a physical process that promotes effective separation of components. Preferably, the demulsifier is a chemical agent or combination of agents, including, for example, polyoxyalkylenes, vinyl polymers, polyamines, polyamides, phenolics, and silicone polyethers. A more complete description and listing of demulsifiers can be found in Chapter 22 of Fink, Oil Field Chemicals, Gulf Professional Publishing, 2003.

Exemplary commercially available demulsifiers include KLARAID™ PCI 190, KLARAID™ PCI 192, KLARAID™ PCI 195, KLARAID™ PC2712, KLARAID™ PC4000, KLARAID™ IC1170, KLARAID™ IC1172, NOVUS™ CE 2666, and NOVUS™ CE 2680 (GE Betz, Inc, Trevose, PA, USA). Preferably, the chemical agent or combination of agents are selected depending on the type of emulsion to be broken.

[0030] The amount of demulsifier to be used can vary broadly. In general, the amount will be at least an amount sufficient to enhance the separation between aqueous and non-aqueous components of the waste stream introduced into the settling tank. While the most effective amount will generally depend upon the relative quantities of the aqueous and non-aqueous components in the waste stream, this amount can readily be determined by one of ordinary skill in the art using known testing procedures.

[0031 ] The demulsifier unit can be of any size, shape and constructions and formed from any material or materials. The demulsifier unit can feed the demulsifier into the settling tank or into a feed pipe conveying the waste stream to the settling tank. The demulsifier unit can include an injection system for injecting the demulsifier under pressure into the settling tank or into the feed pipe conveying the waste stream to the settling tank. Preferably, the demulsifier unit includes a pump for pumping the demulsifier at a suitable rate into the settling tank or into the feed pipe conveying the waste stream to the settling tank. [0032] The demulsifier unit can be directly attached to the settling tank such that the waste stream is dosed with the demulsifier immediately before being received in the settling tank or directly in the settling tank. Preferably, however, the demulsifier unit is located upstream of the settling tank proximal a feed pipe conveying the waste stream to the settling tank.

[0033] The demulsifier unit can include a flow sensor to detect the flow of the waste stream being conveyed to the settling tank, and the flow sensor can activate and deactivate the demulsifier unit according to whether or not there is a flow of waste stream detected.

[0034] Operation of the demulsifier unit can be linked to upstream processes such that the demulsifier unit can be activated and deactivated according to whether upstream processes are active and producing a flow of waste stream.

[0035] Preferably, a warm or heated waste stream is dosed by the demulsifier unit and this can be achieved in any suitable way.

[0036] As discussed herein, the system for separating aqueous and non-aqueous components in a waste stream recovered from product gas produced by UCG can further include at least one sensor-controlled drainage valve for draining at least one separated component of the waste stream. Any suitable type of sensor can be used. The sensor can sense the boundary/interface between separated components of the waste stream The sensor can be a probe that extends into the settling tank. The sensor can be an electromagnetic-based sensor, for example, a Guided Wave Radar (GWR) sensor.

[0037] Alternatively, the sensor can be located externally to the settling tank. The sensor can be a nuclear level or gamma ray gauge. Preferably, the sensor is a probe that extends into the settling tank and preferably the sensor uses GWR. In use, the sensor can sense the boundary/interface of a separated component of the waste stream and operate a drainage valve or drainage valves to drain the separated component or components.

[0038] As also discussed herein, the system for separating aqueous and non-aqueous components in a waste stream recovered from product gas produced by UCG can further include at least one sensor- controlled floating suction system calibrated to float within a predetermined liquid phase (i.e., an aqueous, non-aqueous light condensate, and/or nonaqueous heavy condensate phase) and drain the associated liquid. In conjunction with a sensor located either in the settling tank (e.g., a probe using GWR) or externally to the settling tank (e.g., a nuclear level or gamma ray gauge) for sensing the boundary/interface between separated components of the waste stream, the at least one sensor-controlled floating suction system can have an additional sensor located on a float. The additional sensor can be a densitometer. In use, the sensors can sense the boundary/interface of a separated component of the waste stream (i.e., an aqueous, non-aqueous light condensate, and/or non-aqueous heavy condensate component of the waste stream) and operate the floating suction system to remove the separated component.

[0039] It is to be appreciated that integers/features of the methods and systems according the to the different aspects can be interchangeable. That is, a feature of a method can be a feature of a system according to the present invention, and vice versa. Moreover, any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

[0040] 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

[0041] Figure 1 is a block flow diagram for treating a waste stream derived from product gas produced by an underground coal gasifier, according to an embodiment of the present invention.

[0042] Figure 2 depicts a system for separating aqueous and non-aqueous components in a waste stream recovered from product gas produced by UCG, according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0043] According to an embodiment of the invention, there is provided a method for treating a waste stream derived from product gas produced by UCG. The method includes the steps of dosing the waste stream with a demulsifier, conveying the demulsifier-dosed waste stream to at least one settling tank, wherein the waste stream separates into aqueous, nonaqueous light condensate, and non-aqueous heavy condensate components, and recovering the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components.

[0044] In some embodiments, the method includes sensing one or more interfaces between the separated aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components and individually isolating the aqueous, non-aqueous light condensate, and nonaqueous heavy condensate components.

[0045] In the figures, like reference numerals refer to like features.

[0046] Referring to Figure 1, raw product gas produced by an underground coal gasifier 2 is conveyed from a production well 4 to a knock-out vessel 6 for primary removal of liquid and solid wastes.

[0047] Wastes removed by the knock-out vessel 6 (including an aqueous component and a non-aqueous component with solids/particulates) are then conveyed to a settling tank 20, whilst product gas is conveyed to a wellhead separation device 8, wherein further entrained liquids are separated from the product gas and conveyed to the settling tank 20. The syngas component is then conveyed for further downstream processing 9.

[0048] Prior to being received by the settling tank 20, the waste stream including aqueous and non-aqueous components is dosed with a demulsifier via a demulsifier dosing unit 10. The demulsifier is injected/pumped into a feed pipe 11 which conveys the waste stream to the settling tank 20. The demulsifier demulsifies the aqueous and non-aqueous components into aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components.

[0049] The inventor has found that it is advantageous to dose the waste stream prior to it being received by the settling tank 20 as the waste stream is still hot/warm and elevated temperatures enhance the effectiveness of the demulsifier and prevent solids from forming. Additionally, dosing the waste stream prior to it being received by the settling tank 20 improves mixing of the demulsifier and the waste stream as a result of turbulence produced in the feed pipe 11 while the demulsifier and the waste stream are flowing into the settling tank 20.

[0050] In the settling tank 20 the demulsifier-treated waste stream separates into the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components via gravity. Any dissolved gases are routed from the settling tank 20 by a flare line 51 and routed off to a flare 50.

[0051] A sensor-controlled drainage system 30 includes a probe 32 (i.e., a sensor) that extends into the settling tank 20. The probe 32 utilizes GWR to detect boundaries/interfaces between the separated aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components and operates one or more drainage valves to individually recover the aqueous 30a, non- aqueous light condensate 30b, and non-aqueous heavy condensate 30c components.

[0052] Isolated non-aqueous light condensate 30b and non-aqueous heavy condensate 30c components can then be conveyed for further downstream processing/blending 15.

[0053] The isolated aqueous component 30a can undergo further treatment at a process water treatment plant 14 before being recirculated 16.

[0054] According to another embodiment of the invention, there is provided a system for separating aqueous and non-aqueous components in a waste stream recovered from product gas produced by UCG (i.e., a waste stream treatment system). The system includes a settling tank 20, a demulsifier dosing unit 10, and a flow connection from a source of the recovered waste stream to the settling tank 20. The demulsifier dosing unit 10 demulsifies the recovered waste stream having an aqueous component and a non-aqueous component into aqueous, nonaqueous light condensate, and non-aqueous heavy condensate components. The settling tank 20 receives the demulsifier-treated waste stream, which then settles via gravity and separates into the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components.

[0055] The waste stream treatment system also includes a sensor-controlled drainage system 30. The sensor-controlled drainage system 30 can individually drain the separated aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components by operating one or more drainage valves of the settling tank 20/drainage system 30.

[0056] Referring to Figure 2, to handle large volumes of waste streams, multiple settling tanks 20 are used in parallel to effectively treat the waste streams. Raw product gas is first conveyed from the production well 4 via the knock-out vessel 6 and wellhead separation device 8, after which the waste stream is dosed with demulsifier by the demulsifier dosing unit 10 and conveyed to multiple settling tanks 20 in parallel. [0057] Once the demulsifier-treated waste stream separates into the aqueous, non-aqueous light condensate, and non-aqueous heavy condensate components via gravity, these

components are isolated via the sensor-controlled drainage system 30.

[0058] As described above, the isolated components of the non-aqueous light condensate and non-aqueous heavy condensate components can then be conveyed for further downstream processing/blending, whereas the isolated aqueous component can undergo further treatment at a process water treatment plant 14 before being recirculated.

[0059] A person of ordinary skill in the art will appreciate that many embodiments and variations can be made without departing from the ambit of the present invention.

[0060] In a variation of the sensor-controlled drainage system 30, rather than using sensor-controlled drainage valves to drain the separated components of the waste stream, the system 30 can use a calibrated floating suction system. The calibrated floating suction system involves the calibration of one or more floats to stay in a particular respective liquid phase and remove the associated separated component. In this variation, the probe 32 operates the calibrated floating suction system and disables the suction system once a separated component had been removed.

[0061 ] Advantages of the instant invention include: treatment of a waste stream with a demulsifier is a quicker way of separating components rather than relying on gravity separation alone, and hence the process lends itself to automation; the separated components are of greater purity than those separated by gravity alone, and hence one or more of the components can be used as a feedstock for chemical production; since separation of the components occurs at a greater rate, the components can be disposed of in a more regular manner, in smaller volumes; less handling and manual processing of hazardous components is required, as well as in smaller volumes; the method and system enables heavy condensates to remain in solution and to be more conveniently handled and disposed of in liquid form; and by processing waste streams more effectively, smaller volumes are deposited in settling ponds and tailings dams, which makes remediation process at the end of the operative life of the underground coal gasifier simpler and cheaper.

[0062] 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.

[0063] 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 Ught 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.