AU2011202102B2

AU2011202102B2 - Processing of Coal Seam Gas (CSG) Water

Info

Publication number: AU2011202102B2
Application number: AU2011202102A
Authority: AU
Inventors: Roy Ian Doveton
Original assignee: PENRICE SODA PRODUCTS Pty Ltd
Current assignee: PENRICE SODA PRODUCTS Pty Ltd
Priority date: 2010-05-06
Filing date: 2011-05-06
Publication date: 2013-05-02
Anticipated expiration: 2031-05-06
Also published as: AU2011202102A1

Abstract

-21 A method for the treatment of coal seam gas (CSG) water, the CSG water containing at least sodium carbonate, sodium bicarbonate and sodium chloride, 5 the method including the steps of: heating the CSG water to convert a portion of the sodium bicarbonate to sodium carbonate; precipitating sodium bicarbonate crystals by carbonation of the heated CSG water; and 10 treating the sodium bicarbonate crystals to form a dry sodium bicarbonate and/or a dry sodium carbonate. F- 0 cw C:

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Processing of Coal Seam Gas (CSG) Water Applicant: Penrice Soda Products Pty Ltd The following statement is a full description of this invention, including the best method of performing it known to me: r)' A .g RECEIVED 0 6 MAY 2011 6067 KAE -2 PROCESSING OF COAL SEAM GAS (CSG) WATER This application claims benefit of Australian provisional patent application 201090985, filed 6 May 2010, which is incorporated herein in its entirety. 5 Field of the Invention The present invention relates to the processing of water associated with coal seam gas, the water being the main by-product of the extraction of natural gas 10 (primarily being methane) from coal seams. The present invention relates to a method for the processing of coal seam gas water, hereafter referred to as CSG water. Background of the Invention 15 Coal seams (sometimes referred to as "coal beds") are often saturated with water. In areas where the dominant chemistry of the water in the coal seam is sodium bicarbonate, and where the coal seam is buried deeply enough to maintain sufficient water pressure to hold gas in place, the hydrostatic pressure 20 of the water will hold large amounts of natural gas such as methane within the coal. Because the gas moves with the water, extraction of the gas from the coal seam involves drilling to the coal seam and pumping the available water from the coal seam, thereby reducing the water pressure. As the gas has a relatively low solubility in the water, the gas and water readily separate as the pressure 25 decreases, allowing water to be piped out of a well separately to gas. The coal seam gas industry, particularly in Queensland, Australia, is increasing in importance as an alternative source of energy and is likely to increase even more drastically in the near future with the ongoing development of a few very 30 large natural gas projects. As the annual volume of coal seam gas extracted increases, so will the volume of CSG water extracted increase. In 2007, 12.5 GL of CSG water was extracted from some of the early gas producing bores in -3 Queensland, with the water generally being disposed of in evaporation ponds at the surface in a manner that has tended to be ecologically undesirable and thus unacceptable. The expectation of the Queensland Government is that in Queensland alone, the average annual production of CSG water is likely to be 5 between 25 and 50 GL, with possible annual peaks of up to 100 GL. As a result, the Queensland Government is proposing to limit the use of evaporation ponds, requiring the coal seam gas industry to develop alternative techniques for the disposal and/or use of CSG water. 10 CSG water is generally high in sodium chloride, sodium carbonate and sodium bicarbonate, making it difficult to easily dispose of and rendering the water unusable (without further treatment) for many of the normal agricultural, mining, industrial or domestic uses for water. For example, the total dissolved solids (TDS) values for dissolved salt in CSG water is stated to range to more than 15 10,000 milligrams/litre, with TDS values in the range of 1,000 to 6,000 mg/ being quite typical. By comparison, drinking water has a TDS value for dissolved salt of about 500 mg/, while seawater has a TDS value for dissolved salt of about 35,000 mg/. 20 Importantly, CSG water is different from seawater in that its levels of sodium bicarbonate and sodium carbonate are comparatively high. Indeed, some figures have shown that the dissolved solids in some CSG waters comprise as much as 62.5% sodium bicarbonate, 12.5% sodium carbonate and only 25% salt, although these relativities can vary significantly from one source to 25 another. On this basis, assuming an average salinity concentration of 2,500 mg/I and a CSG water volume of 25 GL/annum, a total of 62,500 tpa of sodium chemicals could be produced by the suitable processing of CSG water. The aim of the present invention is to provide both a method and apparatus 30 suitable for the processing of CSG water in order to provide the coal seam gas industry with a useful alternative for the disposal and/or use of the CSG water it produces.

-4 The above discussion of the background to the invention is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known, or part of the common general knowledge (in any country) as at the priority date of any of the claims. 5 Summary of the Invention Coal seam gas and its associated CSG water are firstly pumped to the surface (or flows freely to the surface) where the gas is separated from the water by 10 traditional means using a gas-liquid separator where flow rates are reduced in a vessel to allow droplets of water to settle out and gas to continue. The coal seam gas and CSG water are typically transported through pipelines to a central processing facility where the method of the present invention may be utilised. 15 The present invention provides a method for the treatment of coal seam gas (CSG) water, the CSG water containing at least sodium carbonate, sodium bicarbonate and sodium chloride, the method including the steps of: heating the CSG water to convert a portion of the sodium bicarbonate to 20 sodium carbonate; precipitating sodium bicarbonate crystals by carbonation of the heated CSG water; and treating the sodium bicarbonate crystals to form a dry sodium bicarbonate and/or a dry sodium carbonate. 25 Before heating the CSG water to convert the sodium bicarbonate, the CSG water may be treated to remove undesirable organic materials, such as by the use of activated carbon filters or the like, and may also be subjected to a water softening process in order to remove calcium and magnesium. In a preferred 30 form, the water softening process would be by the use of ion exchange resins.

-5 Furthermore, before heating the CSG water to convert the sodium bicarbonate, the CSG water will ideally be subjected to a concentration process. Ideally, the concentration process will be a filtration process such as a reverse osmosis process that removes large molecules and ions (such as the sodium carbonate, 5 the sodium bicarbonate and the sodium chloride) by applying pressure to the CSG water on one side of a selective membrane, to trap the large molecules and ions and allow a purified solution to pass therethrough. This filtration process thus produces a purified CSG water (ideally with a purity 10 better than reticulated mains water) that can be collected for distribution to end users such as irrigators, plus a concentrated CSG water having a higher concentration (ideally up to a tenfold increase) of the sodium carbonate, sodium bicarbonate and sodium chloride. In this respect, it should be possible for as much as 90% of the water to be beneficially used as purified CSG water. 15 The concentrated CSG water is preferably then further concentrated, such as by evaporation, in order to increase the concentration of the sodium carbonate, sodium bicarbonate and sodium chloride. The preferred extent of concentration is such that the liquid is moved close to its saturation point. It will of course be 20 appreciated that this saturation point is dependent upon the chemical composition of the liquid and thus will be dictated by the composition of the original CSG water. The concentrated CSG water is then subjected to heating to convert a portion of 25 the (now concentrated) sodium bicarbonate to sodium carbonate ready for the subsequent precipitation step, with the reference throughout this specification to "a portion" meaning that more than about 50% of the sodium bicarbonate is converted to sodium carbonate. Indeed, while it is preferred that all of the sodium bicarbonate converts to sodium carbonate, it tends not to be practically 30 achievable to convert more than about 95%, and so a broad aim is to adopt heating conditions that permit a substantial portion of the sodium bicarbonate to convert to sodium carbonate, such that the conversion level is in the range of -6 from 60 to 95% or in the range of from 70 to 90%, or in the range of from 75 to 80%. Ideally, in order to effect the conversion, the concentrated CSG water will be 5 heated to a temperature in the range of from 60*C to 120*C, or to a temperature in the range of from 70 0 C to 1 10 C, or to a temperature in the range of from 80 0 C to 105 0 C, or to a temperature in the range of from 90 0 C to 100 0 C,.in order to effect the conversion and evaporation. More preferably the concentrated CSG water will be heated to about 100 *C. 10 In this conversion process, the sodium bicarbonate decomposes to sodium carbonate, releasing carbon dioxide, leaving a solution containing predominantly sodium carbonate and sodium chloride, in accordance with the following equation; 15 2 NaHCO 3 -- Na 2

CO

3 + H 2 0 + CO 2 T The heating of course plays the dual role of converting the sodium bicarbonate to sodium carbonate and also further concentrating the CSG water through evaporation. Also, it will be appreciated that the adoption of a temperature that 20 is towards the higher ends of the above ranges is preferred due to the decomposition reaction occurring faster at higher temperatures. However, the competing desires of minimizing energy consumption and avoiding complete evaporation of the liquid tend to dictate the adoption of lower temperatures. With this in mind, it will be appreciated that the heating could be conducted 25 under a slight vacuum, to lower the temperature at which boiling occurs and allow a lower temperature to be adopted. At this point, there will be three main chemicals remaining within the heated CSG water, namely sodium carbonate, sodium chloride and unconverted 30 sodium bicarbonate. In this respect, it has been found that the relative concentrations of sodium carbonate, sodium chloride and sodium bicarbonate in -7 the heated CSG water at this point should be such as to avoid precipitation of unwanted salts when cooled and prior to the fractional crystallization step. In relation to the precipitation step, it is preferred that sodium bicarbonate 5 crystals are precipitated via fractional crystallisation, ideally in a series of continuously stirred, pressurised carbonation vessels, by reducing the temperature of the heated CSG water and subjecting it to carbonation at a temperature and pressure preferably selected to maximise precipitation of sodium bicarbonate crystals. Ideally, the carbonation conditions (including the 10 carbon dioxide concentration, which will ideally be between 70% and 95%) are selected such that substantially all of the sodium carbonate in the heated CSG water reacts to form sodium bicarbonate, in accordance with the following equation: Na 2

CO

3 + H 2 0 + CO 2 -+ 2NaHCO 3 I 15 The carbonation preferably occurs at a temperature in the range of 25*C to 70 0 C, or at a temperature in the range of 30 0 C to 65 0 C, or at a temperature in the range of 30*C to 50 0 C. In this respect, it will be appreciated by a skilled addressee that the selection of a suitable temperature from these ranges will be 20 dependent upon the starting temperature of the heated CSG water, the amounts, relative proportions and saturation levels of the sodium carbonate, sodium bicarbonate and sodium chloride in the heated CSG water, the partial pressures in the carbonation vessels, and also the number and type of vessels used, amongst other things. 25 While it is preferred that all of the sodium carbonate precipitates out as sodium bicarbonate crystals, it tends not to be practically achievable to convert more than about 95%, and so a broad aim is to adopt conditions (particularly temperature conditions) that permit a substantial portion of the sodium 30 carbonate to precipitate, such that the precipitation level is in the range of from 70 to 95% or in the range of from 80 to 90%. Also, the conditions will ideally be selected such that the sodium bicarbonate crystals are larger rather than -8 smaller (in order to assist with subsequent filtration and separation steps). In this respect, the average crystal size would preferably be greater than 50 micron and ideally greater than 100 micron. 5 The precipitation of sodium bicarbonate crystals is aided by the use of pressurised carbonation vessels. Indeed, it is preferable to adopt a carbonation vessel, and carbonation conditions, that ensure the formation of few larger crystals of bicarbonate rather than many smaller crystals, which again would make filtering and washing more difficult. In this respect, the pressure will 10 preferably be in the range of from 1 OOkPa to 650kPa (gauge) in the carbonation vessels, or in the range of from 150kPa to 600kPa (gauge), or in the range of from 300kPa to 500kPa (gauge). Therefore, the present invention also provides a method for the treatment of 15 coal seam gas (CSG) water, the CSG water containing at least sodium carbonate, sodium bicarbonate and sodium chloride, the method including the steps of: separating coal seam gas from its associated CSG water; subjecting the CSG water to a water softening process; 20 concentrating the CSG water to produce a purified CSG water and a concentrated CSG water; heating the concentrated CSG water to convert a portion of the sodium bicarbonate to sodium carbonate and further concentrate the CSG water; precipitating sodium bicarbonate crystals by carbonation of the heated 25 CSG water; and treating the sodium bicarbonate crystals to form a dry sodium bicarbonate and/or a dry sodium carbonate. Following precipitation of the sodium bicarbonate crystals, the crystals are 30 preferably filtered and simultaneously washed to remove a filtrate containing high levels of sodium chloride. This sodium chloride filtrate may then be transferred to a salt purifying and crystallisation process capable of converting -9 the sodium chloride in solution into a dry sodium chloride, which process will be described later. A counter current multistage washing process is preferably used to wash the 5 sodium bicarbonate crystals, utilizing purified CSG water obtained from earlier in the process, with the wash water being collected and returned to the CSG water concentrating step mentioned above. In this form, the further dissolution of the bicarbonate is minimized as the first two washing stages are able to be operated having a higher bicarbonate content and hence having a lower 10 potential to dissolve bicarbonate. Indeed, ideally the washing is conducted at low temperatures (such as temperatures in the order of ambient temperature) to further minimize dissolving of the sodium bicarbonate. In this respect, the losses of bicarbonate at the washing stage will ideally be less than about 4 wt%. 15 The filtered and washed sodium bicarbonate crystals can then either be dried at low temperature to avoid decomposition and then graded, packed and sold, or can be decomposed by heating to high temperatures to sodium carbonate (soda ash). Indeed, it is envisaged that the overall method of the present invention may split the filtered and washed sodium bicarbonate crystals into two 20 streams, with one stream being dried at low temperature to form the dry sodium bicarbonate and other being decomposed at high temperature to form the dry sodium carbonate. With this in mind, the dry sodium bicarbonate may be formed by drying at a temperature of from 65 to 75 *C using a flash drier, or at a temperature of from 55 to 65 *C using a fluid bed drier. 25 In relation to the decomposition of the sodium bicarbonate to form sodium carbonate (soda ash), the decomposition is time and temperature dependent and thus it will be appreciated that higher temperatures require less time for the transformation. Ideally, the temperature will be in the range of 160 to 1800C, 30 but more preferably will be about 170*C. It will also be noted that carbon dioxide is liberated at this stage and that this C02 is able to be reused during the carbonation step mentioned above.

- 10 Supplementary carbon dioxide for the method of the present invention can be manufactured via, for example, an amine concentration process using a carbon fuel burnt stack / exhaust emission. The method of manufacturing soda ash via the method described above would thus be self-supporting in that there would 5 be sufficient carbon dioxide liberated within the method. If refined sodium bicarbonate was produced, then there would need to be supplementary carbon dioxide provided. Also with regard to the decomposition to form soda ash, it should be 10 appreciated that soda ash formed in this manner is light soda ash where the bulk density is low (about 500 kg/m 3 ). In this form, the light soda ash is very dusty and not easily usable by most potential customers. Therefore, the light soda ash would ideally be further processed to form a dense soda ash with a bulk density closer to 1000 kg/M 3 . Such further processing is ideally conducted 15 by reconstituting the crystals, such as by mixing the light soda ash with water to form a sodium carbonate monohydrate and then re-drying to form larger, heavier crystals. Such dense soda ash can then be packed and sold. Alternatively, if a high purity refined sodium bicarbonate is required, higher than 20 perhaps might be possible simply by drying the sodium bicarbonate at low temperatures, sodium carbonate produced from the decomposition (being the light soda ash) could be dissolved in water to a concentration of about 22% v/v (for example), heated to about 60*C and reacted with carbon dioxide to thus form refined sodium bicarbonate crystals which can then be filtered and 25 washed. The refined sodium bicarbonate thus formed will be of a higher purity. Finally, and as mentioned above, the filtrate solution from the sodium bicarbonate filtering process will contain a residual amount of sodium carbonate and sodium bicarbonate which cannot easily be removed, these thus remaining 30 in the liquid that may then be subjected to the salt purifying and crystallization process mentioned above that removes sodium carbonate and sodium - 11 bicarbonate and further concentrates the liquid until solid salt crystals form for subsequent harvesting and sale. The filtrate from the sodium bicarbonate filtering process is preferably reacted 5 with lime to produce calcium carbonate and sodium hydroxide in a three stage purification step. Substantially all of the sodium hydroxide is converted to sodium chloride by addition of hydrochloric acid or calcium chloride. The solids underflow is filtered and the overflow is sent on to the salt crystallization process, with the waste preferably decomposed to form carbon dioxide. This 10 decomposition is ideally achieved by burning normally in a kiln, with the with the resulting product being lime (CaO) and carbon dioxide. The lime can then be reused in the salt purification step described above. Therefore, the present invention also provides a method for the treatment of 15 coal seam gas (CSG) water, the CSG water containing at least sodium carbonate, sodium bicarbonate and sodium chloride, the method including the steps of: - separating coal seam gas from its associated CSG water; - subjecting the CSG water to a water softening process; 20 concentrating the CSG water to produce a purified CSG water and a concentrated CSG water; - heating the concentrated CSG water to convert a portion of the sodium bicarbonate to sodium carbonate and further concentrate the CSG water; - precipitating sodium bicarbonate crystals by carbonation of the heated 25 CSG water; - filtering and simultaneously washing the sodium bicarbonate crystals to separate the sodium bicarbonate crystals from a filtrate rich in sodium chloride; - treating the sodium bicarbonate crystals to form a dry sodium 30 bicarbonate via a low temperature heating and/or a dry sodium carbonate via a high temperature heating; purifying the filtrate rich in sodium chloride; -12 - precipitating sodium chloride crystals from the sodium chloride rich filtrate; and - treating the sodium chloride crystals to form a dry sodium chloride. 5 Brief Description of the Drawings An embodiment of the present invention will now be described, by way of example only, with brief reference to the general flowsheet in the accompanying Figure 1 and to Figure 2 which is a ternary phase diagram showing the sodium 10 bicarbonate phase boundaries for a saturated solution in a sodium bicarbonate / sodium carbonate / sodium chloride system. However, it is to be appreciated that the following description of the flowsheet only exemplifies this one particular way of putting the present invention into practise. The following description is thus not to be read as limiting the above general description. 15 Brief Description of a Preferred Embodiment With reference to Figure 1, coal seam gas and its associated CSG water are firstly pumped to the surface where the gas is separated from the water by 20 traditional means (not shown) such as those mentioned above, resulting in separated CSG water being stored in pond 10. The separated CSG water will vary in components and concentration quite markedly from operation to operation, However, a typical composition might be 25 as follows: * Carbonate expressed as calcium carbonate 123mg/l * Bicarbonate expressed as calcium carbonate 885mg/I . Chloride 2400mg/I 30 The separated CSG water is subjected to a concentration process in the form of a reverse osmosis process 12 that produces, in this embodiment, three purified CSG water streams 14a, 14b and 14c and a concentrated CSG water stream - 13 16. The two purified streams 14a and 14b are shown being re-utilised in the process in the two wash stages 18 and 20, while the concentrated CSG water stream 16, following pretreatment and evaporation, is passed to a heat exchanger 22 where the stream is cooled prior to fractional crystallisation. The 5 evaporation step is conducted by a mechanical vapour recompression process where the concentrated CSG water stream is heated to 100 0 C so that the sodium bicarbonate decomposes to sodium carbonate, releasing carbon dioxide. In this embodiment, where the CSG water is of a type that contains relatively high initial levels of sodium chloride compared to sodium bicarbonate 10 and sodium carbonate, the heated CSG water contains the following (wt%):

H

2 0 82.9% NaCl 13.1% Na 2

CO

3 2.7% NaHCO 3 1.3% 15 Sodium bicarbonate crystals are precipitated in the carbonation and crystallisation stage 24 via fractional crystallisation, by reducing the temperature of the heated CSG water in the heat exchanger 22 and subjecting it to carbonation at a temperature and pressure in pressurised 20 carbonation/crystallisation vessels selected to precipitate sodium bicarbonate crystals. The carbonation conditions (including the carbon dioxide concentration) are selected such that substantially all of the sodium carbonate reacts to form sodium bicarbonate. 25 In this embodiment, five continuously stirred, pressurised carbonation vessels, connected in series, are adopted for use in the carbonation and crystallisation stage, operated at a constant pressure of about 500kPa but at decreasing temperatures from one vessel to the next, with the reduction in temperature being from an initial 50*C in the first vessel to 45 0 C in the second vessel, 40'C 30 in the third vessel, 350C in the fourth vessel, and 300C in the fifth vessel. Indeed, as will be appreciated from the ternary phase diagram of Figure 2, these ideal temperatures can be determined with reference to the temperature - 14 phase lines for different compositions of CSG water, in a manner that promotes the precipitation of the desirable sodium bicarbonate crystals. With a flow-rate of about 3000 kg/hr through the carbonation vessels, the outlet 5 stream, providing about 130kg/hr of crystallised product (at about 4.5 wt% solids) for use in the next stage, contains about 92.7 wt% sodium bicarbonate crystals, about 3.8 wt% sodium chloride crystals, and about 3.5 wt% sodium carbonate crystals. 10 Following precipitation of the sodium bicarbonate crystals, the crystals are filtered 28 and simultaneously washed 18 in a countercurrent multistage washing process to remove a filtrate 30 containing high levels of sodium chloride and to produce a solids cake at about 85 wt% solids containing about 96.3 wt% sodium bicarbonate, about 3.6 wt% sodium carbonate and less than 15 0.05 wt% sodium chloride. The sodium chloride filtrate 30 may then be transferred to a salt purifying process 20 and a crystallisation process 32 capable of converting the high levels of sodium chloride in solution into a dry sodium chloride 34. 20 The filtered and washed sodium bicarbonate crystals 36 can then either be dried 38 at low temperature to avoid decomposition and then graded, packed and sold 40, or can be decomposed by heating 42 to high temperatures to sodium carbonate (soda ash). Indeed, and as mentioned above in the general description, operation of the method is able to split the crystals 36 into two 25 streams, with one stream being dried 38 and the other being decomposed at high temperature 42. As a result, the operation of the method of the present invention is able to extract between 75 and 80% of the sodium bicarbonate in the initial CSG water 30 and turn it into useful products such as soda ash and dried sodium bicarbonate.

-15 Finally, it will be appreciated that this embodiment has been described by way of example only, and that variations and modifications within the spirit and scope of the invention are also envisaged.

Claims

26. - 16 What is claimed is: 1. A method for the treatment of coal seam gas (CSG) water, the CSG water containing at least sodium carbonate, sodium bicarbonate and sodium 5 chloride, the method including the steps of heating the CSG water to convert a portion of the sodium bicarbonate to sodium carbonate, precipitating sodium bicarbonate crystals by carbonation of the heated CSG water, and subsequently treating the sodium bicarbonate crystals to form a dry sodium bicarbonate and/or a dry sodium carbonate. 10 2. A method according to claim 1, wherein the CSG water is subjected to a water softening process prior to the heating step. 3. A method according to claim 2, wherein the water softening process is 15 conducted by passing the CSG water through an ion exchange resin device. 4. A method according to claim 2 or claim 3, wherein the CSG water is subjected to a concentration process after the water softening process but prior to the heating step. 20 5. A method according to claim 4, wherein the concentration process is a flitration process that produces a purified CSG water and a concentrated CSG water. 25 6. A method according to claim 5, wherein the filtration process is a reverse osmosis filtration process. 7. A method according to claim 5 or claim 6, wherein it is the concentrated CSG water that is subjected to heating to convert a portion of the sodium 30 bicarbonate to sodium carbonate. -17 8. A method according to claim 7, wherein the heating occurs at a temperature in the range of 60 to 120 *C. 9. A method according to claim 7, wherein the heating occurs at a 5 temperature in the range of 70 to 110 *C. 10. A method according to claim 7, wherein the heating occurs at a temperature in the range of 80 to 105 *C. 10 11. A method according to claim 7, wherein the heating occurs at a temperature in the range of 90 to 100 *C. 12. A method according to claim 7, wherein the heating occurs at a temperature of about 100 C. 15 13. A method according to claim 7, wherein the conversion level is in the range of from 60 to 95% sodium bicarbonate to sodium carbonate. 14. A method according to claim 7, wherein the conversion level is in the 20 range of from 70 to 90% sodium bicarbonate to sodium carbonate. 15. A method according to any one of claims 1 to 14, wherein the sodium bicarbonate crystals are precipitated via fractional crystallisation. 25 16. A method according to claim 15, wherein the fractional crystallisation is conducted by reducing the temperature of the heated CSG water and subjecting it to carbonation at a temperature and pressure selected to precipitate sodium bicarbonate crystals. 30 17. A method according to claim 15 or claim 16, wherein substantially all of the sodium carbonate reacts to form sodium bicarbonate. - 18 18. A method according to claim 15 or claim 16, wherein 70 to 95 % of the sodium carbonate crystallises as sodium bicarbonate. 19. A method according to any one of claims 15 to 18, wherein crystallisation 5 conditions are selected such that the sodium bicarbonate crystals are greater than 50 micron. 20. A method according to any one of claims 15 to 18, wherein crystallisation conditions are selected such that the sodium bicarbonate crystals are greater 10 than 100 micron. 21. A method according to claim 15, wherein the CSG water is cooled to a temperature in the range of 25 to 70 *C, with carbon dioxide being passed through the concentrated CSG water in a carbonation vessel. 15 22. A method according to claim 15, wherein the CSG water is cooled to a temperature in the range of 30 to 65 *C, with carbon dioxide being passed through the concentrated CSG water in a carbonation vessel. 20 23. A method according to claim 15, wherein the CSG water is cooled to a temperature in the range of 30 to 50 *C, with carbon dioxide being passed through the concentrated CSG water in a carbonation vessel. 24. A method according to claim 21, wherein a carbon dioxide concentration 25 of between 70% and 95% is used for the carbonation. 25. A method according to claim 21, wherein the pressure is in the range of from 1OOkPa to 650kPa (gauge) in the carbonation vessel. 30 26. A method according to claim 21, wherein the pressure is in the range of from 300kPa to 500kPa (gauge) in the carbonation vessel. - 19 26. A method for the treatment of coal seam gas (CSG) water, the CSG water containing at least sodium carbonate, sodium bicarbonate and sodium chloride, the method including the steps of: - separating coal seam gas from its associated CSG water; 5 subjecting the CSG water to a water softening process; - concentrating the CSG water to produce a purified CSG water and a concentrated CSG water; - heating the concentrated CSG water to convert a portion of the sodium bicarbonate to sodium carbonate and further concentrate the CSG water; 10 precipitating sodium bicarbonate crystals by carbonation of the heated CSG water; and - treating the sodium bicarbonate crystals to form a dry sodium bicarbonate and/or a dry sodium carbonate. 15 27. A method according to claim 26, wherein the sodium bicarbonate crystals are filtered and simultaneously washed to remove a filtrate containing high levels of sodium chloride.
28. A method according to claim 27, wherein the sodium chloride filtrate is 20 transferred to a salt crystallisation process capable of converting the sodium chloride in solution into a dry sodium chloride.
29. A method according to any one of claims 26 to 28, wherein a counter current multistage washing process is used to wash the sodium 25 bicarbonate crystals, utilizing purified CSG water, with the wash water being collected and returned to the CSG water concentrating step.
30. A method according to claim 29, wherein the filtered and washed sodium bicarbonate crystals are then either dried at low temperature to avoid 30 decomposition, or are decomposed by heating to high temperatures to sodium carbonate. -20
31. A method according to claim 30, wherein the high temperature is in the range of from 160 to 180 *C, and the low temperature is in the range of from 55 to 75 *C. 5 32. A method for the treatment of coal seam gas (CSG) water, the CSG water containing at least sodium carbonate, sodium bicarbonate and sodium chloride, the method including the steps of: - separating coal seam gas from its associated CSG water; subjecting the CSG water to a water softening process; 10 concentrating the CSG water to produce a purified CSG water and a concentrated CSG water; - heating the concentrated CSG water to convert a portion of the sodium bicarbonate to sodium carbonate and further concentrate the CSG water; 15 precipitating sodium bicarbonate crystals by carbonation; - filtering and simultaneously washing the sodium bicarbonate crystals to separate the sodium bicarbonate crystals from a filtrate rich in sodium chloride; - treating the sodium bicarbonate crystals to form a dry sodium 20 bicarbonate via a low temperature heating and/or a dry sodium carbonate via a high temperature heating; - purifying the filtrate rich in sodium chloride; - precipitating sodium chloride crystals from the sodium chloride rich filtrate; and 25 treating the sodium chloride crystals to form a dry sodium chloride.