WO2014153623A1

WO2014153623A1 - Silica removal from coal seam gas water

Info

Publication number: WO2014153623A1
Application number: PCT/AU2014/050006
Authority: WO
Inventors: Terence Michael COLLINS
Original assignee: Ghd Pty Ltd
Priority date: 2013-03-26
Filing date: 2014-03-20
Publication date: 2014-10-02

Abstract

A process for the removal of dissolved silica from a high alkalinity silica rich water stream produced from the extraction of coal seam gas, the process including: contacting the high alkalinity silica rich water stream 202 with the silica lean activated alumina media 206 in a contact vessel 200, dissolved silica adsorbing to the 5 activated alumina media 206, to form a silica lean water stream 208 and a silica rich activated alumina media 218; removing the silica lean water stream 208 from the contact vessel; removing the silica rich activated alumina media 218 from the contact vessel 200 to a regeneration vessel 240;10 regenerating the silica rich activated alumina media 245 with a regenerant solution in the regeneration vessel 240, dissolved silica desorbing from the activated alumina media into the regenerant solution, to form a regenerated silica lean activated alumina media 256; and returning the regenerated silica lean activated alumina media 256 as the silica 15 lean activated alumina media 206 to the contact vessel 200.

Description

Silica removal from coal seam gas water

Field of the invention

The invention relates to the removal of silica from a water stream produced from the extraction of coal seam gas. Background of the invention

Water produced from the extraction of Coal Seam Gas (CSG), also known as coal bed methane, contains a number of impurities. Typically, associated water includes various sodium salts, such as: sodium chloride, sodium carbonate and sodium bicarbonate; as well as variable levels of other minor constituents the most significant of which are calcium, magnesium, barium, strontium, fluoride, bromide and reactive (dissolved) silica. The range in quality of the associated water varies widely between sedimentary basins, and between wells within each sedimentary basin.

As part of existing treatment processes, this water is passed through a reverse osmosis (RO) system to produce a permeate stream which is suitable for beneficial reuse. The higher the recovery that can be achieved, the lower the volume of CSG brine produced for further treatment and/or disposal. The RO recovery is limited by the concentration of certain constituents in the RO feedwater; principally the hardness components (calcium, magnesium, barium and strontium) and reactive (dissolved) silica. The hardness components are readily removed by existing ion exchange technologies. However, the removal of silica (which is typically present at concentrations of about 150 to about 250 mg/L) in CSG brine poses a significant problem due to the high level of alkalinity that is a characteristic of CSG brine streams.

Proprietary antiscalants can be dosed to the RO feedwater which allow concentration of silica to 200 - 250 mg/L (depending on operating conditions). Further concentration of the CSG brine can be achieved using thermal desalination technologies due to the increased solubility of silica at higher temperatures. In this case, the peak concentration of silica will be typically limited to around 400 mg/L, limiting the recovery of the downstream thermal desalination process to 37.5 - 50%. The solubility of silica can be increased by raising the pH of the brine stream but this imposes significant additional operating costs and may also create environmental issues with respect to subsequent disposal of the brine.

While technologies exist for the removal of silica from low alkalinity waters, for example by co-precipitation of silica with magnesium hydroxide, these processes have reduced effectiveness at high alkalinity concentrations. These processes also often produce significant quantities of sludge requiring disposal.

In light of the foregoing, there is a need to provide a mechanism to address the issue of high reactive silica concentrations in CSG water, and in particular CSG brine.

Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Summary of the invention

In one aspect, this invention is directed toward a process for removal of reactive silica from a high alkalinity silica rich water stream, such as a brine stream produced from the treatment of coal seam gas water (which may be by reverse osmosis), resulting in a silica lean water stream. The high alkalinity silica rich water stream will generally have a high dissolved solids concentration with high alkalinity component. Ideally, the treatment process removes the constraints imposed by the presence of silica and allows enhanced reduction of CSG brine volumes using secondary reverse osmosis or other brine concentration technology. This reduces the requirements for subsequent disposal of brine by deep well injection or evaporation ponds, or in the case of salt recovery it will provide a more concentrated brine stream for subsequent crystallisation.

It is expected that the concentration of reactive silica in the high alkalinity silica rich water stream is from about 150 mg/L to about 250 mg/L. The silica lean water stream is expected to have a variable concentration of reactive silica depending on the degree of removal required. Preferably, the concentration of reactive silica in the silica lean water stream will be about 50 mg/L to about 100 mg/L.

In one aspect of the invention, there is provided a method for the removal of reactive silica from a high alkalinity silica rich water stream produced from the extraction of coal seam gas, the method including: contacting the high alkalinity silica rich water stream with a silica lean activated alumina media, reactive silica adsorbing onto the activated alumina media, to form a silica lean water stream and a silica rich activated alumina stream; separating the silica lean water stream and the silica rich activated alumina stream; regenerating the silica rich activated alumina media with a regenerant solution, reactive silica desorbing from the activated alumina media into the regenerant solution, to form a regenerated silica lean activated alumina media; returning the regenerated silica lean activated alumina media as the silica lean activated alumina stream in the contacting step.

Preferably, the contacting step is a counter-current contacting step. By moving the activated alumina media in a counter current direction to the flow of the high alkalinity silica rich water stream, the chemical efficiency of the adsorption reaction is maximised. The use of a continuous counter-current contacting step provides a more efficient means of adsorption than conventional batch adsorption operations, or where the activate alumina media is used as a fixed bed.

Preferably, the contact time for the contact step in respect of the activated alumina media is from about 10 to about 30 minutes.

In a preferred embodiment, the activated alumina stream is a moving bed of the activated alumina. The use of a moving bed of activated alumina media allows this process to be operated as a continuous process. This moving bed system provides a number of advantages over conventional fixed bed arrangements, for example smaller footprint, smaller media inventory, improved chemical efficiency, and greater operational flexibility. Additionally, by moving the activated alumina media in a counter-current direction to the flow of the water stream, the driving force for the adsorption reaction is maximised, thereby resulting in a more efficient adsorption process than compared with batch operation. In a preferred embodiment, the high alkalinity silica rich water stream has a total alkalinity above 1 ,000 mg/L. Preferably, the total alkalinity is at least about 2000mg/L. The alkalinity is present as the carbonate and bicarbonate salts of sodium. Alkalinity is generally expressed in mg/L of equivalent calcium carbonate.

In a preferred embodiment, the pH of the high alkalinity silica rich water stream is from about 8 to about 9.4. Preferably, the pH of the high alkalinity silica rich water stream is from about 8.8 to about 9.2. Silica removal efficiencies decrease outside this pH range. At high pH values, for example progressively above pH 9.4, the hydroxide ion concentration in the water competes for the active sites on the activated alumina media and inhibits the adsorption of the reactive silica. The volume ratio of water to activated alumina media in the contacting step (or in an adsorption column) is variable. Generally, the ratio that is used will be dependent on the feedwater silica, the operating capacity of the activated alumina media, and the desired reduction in reactive silica concentration.

In a preferred embodiment the regenerant solution is an aqueous solution of about 1 % to about 1 .5% sodium hydroxide. In an alternative embodiment, dilute calcium hydroxide slurry is the regenerant.

In another aspect of the invention, there is provided a process for the removal of dissolved silica from a high alkalinity silica rich water stream produced from the extraction of coal seam gas, the process including: contacting a high alkalinity silica rich water stream with a silica lean activated alumina media in a contacting region of the contact vessel, dissolved silica adsorbing to the activated alumina media, to form a silica lean water stream and a silica rich activated alumina media; removing the silica lean water stream from the contact vessel; removing the silica rich activated alumina media from the contact vessel ; regenerating the silica rich activated alumina media with a regenerant solution in a regeneration vessel, dissolved silica desorbing from the activated alumina media into the regenerant solution, to form a regenerated silica lean activated alumina media ; and returning the regenerated silica lean activated alumina media to the contact vessel as the silica lean activated alumina media.

Preferably, a high alkalinity silica rich water stream inlet and a silica rich activated alumina media outlet are located at a the lower region of the contact vessel, and a silica lean activated alumina media inlet and a silica lean water stream outlet are located at an upper region of the contact vessel; such that the flow of the high alkalinity silica rich water stream is counter-current to the silica lean activated alumina media.

Preferably, the residence time in the adsorption column will be from about 10 to about 30 minutes.

In a preferred embodiment the activated alumina media is a moving bed. In a preferred embodiment the high alkalinity silica rich water stream has a total alkalinity of at least 1000 mg/L. Preferably the total alkalinity is at least about 2000mg/L.

In a preferred embodiment the pH of the high alkalinity silica rich water stream is from about 8 to about 9.4. Preferably the pH of the high alkalinity silica rich water stream is from about 8.8 to about 9.2. In a preferred embodiment the regenerant solution is an aqueous solution of about 1 % to about 1 .5% sodium hydroxide.

Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawing. Recitation of ranges of values herein are merely intended to serve as a short hand method of referring individually to each separate value and each potential range encompassed within, unless otherwise recited. Furthermore, each separate value and each potential range is incorporated into the specification as if it were individually recited herein.

Brief description of the drawings

Figure 1 provides an illustration of an embodiment of the invention. Figure 2 provides an illustration of another embodiment of the invention.

Detailed description of the embodiments

The invention relates to the removal of reactive silica from a high alkalinity water stream, such as a brine stream, associated with the extraction of coal seam gas (CSG).

The invention involves contacting high alkalinity coal seam gas water containing reactive silica with activated alumina media in a counter current adsorption step. The reactive silica adsorbs onto the activated alumina media from the coal seam gas water stream resulting in a coal seam gas water stream with a substantially reduced reactive silica concentration, i.e. a silica lean water stream. The silica lean water stream and the silica containing activated alumina media are then separated. The silica lean water stream can be used in other process steps, stored, or further treated depending on operational requirements.

The ratio of activated alumina media to coal seam gas water can be adjusted to provide the desired degree of silica removal. Setting of this ratio is one of the primary parameters for control of the silica removal process. An operator will adjust the ratio until targeted performance is attained. Once the process is optimised the plant will be able to operate with minimal operator attention. The residence time of the adsorption contacting step will be about 10 to about 30 minutes.

The invention also involves the step of regenerating the silica rich activated alumina media. The regeneration step involves contacting the silica rich activated alumina media in a counter current fashion with a regenerant solution. In this contact step, the silica desorbs from the activated alumina media, into the regenerant solution, resulting in a regenerated activated alumina media and a silica rich regenerant solution. The regenerated activated alumina media and the silica rich regenerant solution are then separated. The regenerated alumina can then be reused to treat further silica containing coal seam gas water.

The process is configured to be operated as a continuous process for the removal of reactive silica from coal seam gas water and the regeneration of an activated alumina media.

Other process or method steps may be required as necessary. For example, a wash step may be required after the adsorption step to clean the media. Similarly a rinse step may be required after the regeneration step to remove traces of regenerant. This will depend on the specifics of the adopted process or method.

A typical composition of a high alkalinity silica rich water stream (i.e. a brine stream) from the reverse osmosis treatment of coal seam gas water is given in Table 1 below:

Table 1 : Typical CSG Brine Quality

The activated alumina media used for this application is granular in nature with a preferred particle size of either 0.3 - 0.6mm or 0.6 - 1 .2mm. A summary of typical activated alumina properties is provided in Table 2 below. Table 2: Typical Activated Alumina properties

The process and/or method will now be described below in more detail with reference to preferred embodiments.

Figure 1 provides an illustration of an embodiment of the invention. In this embodiment, a high alkalinity silica rich water stream 100 from a coal seam gas extraction process is introduced into an adsorption column 102. A typical composition for a silica rich water stream from a coal seam gas extraction process is given in Table 1.

The silica rich water stream 100 is introduced via an inlet 104 into an upper region of the adsorption column 102. The silica rich water stream 100 moves downwardly through the adsorption column 102, and is extracted as a silica lean water stream 106 through an outlet 107 located in a lower region of the adsorption column 102. As the silica rich water stream 100 moves downwardly through the adsorption column, it moves through a silica lean activated alumina stream 108. The silica lean activated alumina stream 108 is a bed of activated alumina that moves downwardly through the column 102. The activated alumina media used for this application is granular in nature with a preferred particle size of either 0.3 - 0.6mm or 0.6 - 1.2mm. A summary of typical activated alumina properties is provided in Table 2. The silica lean activated alumina stream 108 is introduced via an inlet 110 at the top of the column 102 and is removed from the column 102 as a silica rich activated alumina stream 1 12 via an outlet 1 14 at the base of the column.

In this way, the silica rich water stream 100 contacts with the silica lean activated alumina stream 108 in a co-current manner. Silica from the silica rich water stream 100 is adsorbed to the activated alumina in the activated alumina stream 108, this results in a silica lean water stream 106 and a silica rich activated alumina stream 112. The silica lean water stream 106 is removed from the adsorption column 102 via outlet 108 for post treatment use. The silica rich activated alumina stream 1 12 is then removed from the adsorption column 102 via outlet 1 14 for further treatment including regeneration. In this embodiment, after exiting the adsorption column 102 the silica rich activated alumina stream is rinsed in a rinsing zone 1 16. The rinse step involves brief fluidisation of the activated alumina for the purpose removing particles that were retained as a result of the counter-current contact between the activated alumina bed and the water stream. After the rinse process, the silica rich activated alumina stream 1 12 passes from the rinsing zone 1 16 to the regeneration zone 1 18.

In the regeneration zone 1 18, the silica rich activated alumina stream is mixed with a regenerant solution 120, such as sodium hydroxide solution. The regenerant solution 120 is provided to the regeneration zone through an inlet 124. The regenerant solution 120 can be diluted with dilution water if required. The regenerant solution 120 desorbs the silica from the silica-rich activated alumina into the regenerant solution resulting in a spent regenerant solution 128 and a regenerated activated alumina stream 130. The spent regenerant solution 128 is then removed via an outlet 132. The spent regenerant solution 128 may be recovered through further processing and recycled back into the system. The regenerated activated alumina stream 130 can then pass through a pulse zone 134 and backwash zone 136. In these zones, the regenerated activated alumina stream is rinsed to remove entrained regenerant solution.

The pulse zone 134 includes inlets 138 and 140 which introduce deionised water into the pulse zone 134. The deionised water is fed by a pulse pump. The deionised water helps to remove residual regenerant solution. Excess water, including the residual regenerant solution is then removed as backwash 144 in the backwash zone 136. Any activated alumina that is removed in the backwash 144 is captured in a trap tank (not shown). The activated alumina can then be returned to the process into the pulse zone 134 via the pulse pump and inlet valves 138 and 140.

After exiting the backwash zone 136, the rinsed and regenerated activated alumina stream is then reintroduced into the adsorption column 102 as the silica lean activated alumina stream 108.

In an alternative arrangement of the embodiment depicted by Figure 1 , the silica rich water stream may be introduced via an inlet in a lower region of the adsorption column, and the silica lean water stream outlet may be taken from an upper region of the adsorption column. For example, outlet 107 may be used as the inlet for the silica rich water stream 100, and inlet 104 may be used as the outlet for the silica lean water stream 106. In this way, a counter current flow path between the silica rich water stream and the silica lean activated alumina media can be established.

Figure 2 provides an illustration of an embodiment of a process according to the invention. The process of this embodiment includes four columns that are operated together in a continuous manner. In this embodiment, the treatment process is treating a high alkalinity silica rich water stream that is a brine stream from a coal seam gas extraction process. The raw water from the extraction of the CSG is initially treated, for example in a reverse osmosis process, to produce the brine stream.

The first column is an adsorption column 200. The adsorption column 200 is fed a high alkalinity silica rich water stream 202 via an inlet 204. The high alkalinity silica rich water stream 202 is CSG brine that is at a pH in the range 8.8 - 9.4 and has an alkalinity in the range of 1000 to 8000 mg/L. The high alkalinity silica rich water stream 202 rises from a lower portion of the adsorption column 200 to an upper portion of the adsorption column 200, during which the high alkalinity silica rich water stream 202 contacts a silica lean activated alumina media 206 in a counter-current flow direction. The reactive silica in the high alkalinity silica rich water stream 202 is adsorbed to the activated alumina resulting in a silica lean water stream 208. The silica lean water stream 208 is then removed from an upper portion of the adsorption column 200 via an outlet 210. The silica lean water stream 208 is effectively a brine solution. This can be transferred to a holding tank for further treatment. The silica lean activated alumina media 206 enters the adsorption column 200 through an inlet 212 located in an upper portion of the adsorption column 200, such as through the top. The silica lean activated alumina media 206 is present in the adsorption column 200 as a bed of activated alumina media 214 that descends through the adsorption column 200. As the bed of activated alumina descends, it contacts the rising high alkalinity silica rich water stream. As stated above, silica in the high alkalinity silica rich water stream adsorbs to the activated alumina in the bed of activated alumina 214. This results in a silica lean water stream 208 and a silica rich bed of activated alumina 214. The silica rich bed of activated alumina media 214 is removed from a lower portion of the adsorption column 200 via an outlet 216 as a silica rich activated alumina media 218. The residence time of bed of activated alumina media 214 in the adsorption column 200 is from about 10 to about 30 minutes. The silica rich activated alumina media 218 is then transferred in small batches from the bottom of the adsorption column 200 via an airlift 220 to the fluidised wash column 222.

The silica rich activated alumina media 218 is fed into the fluidised wash column 222 via an inlet 224 in an upper portion of the fluidised wash column 222, such as through the top. The silica rich activated alumina media then moves downwardly through the fluidised wash column 222 as a bed of silica rich activated alumina media 226. Wash water 228 (which may be treated water) is fed into the fluidised wash column via an inlet 230 in a lower portion of the fluidised wash column 222. The wash water 228 rises upwardly through the bed of silica rich activated alumina media 226, causing the bed of silica rich activated alumina media 226 to be fluidised. This fluidisation process assists in the removal of any particulates retained by the silica rich activated alumina media 226 in the adsorption column 200. Typically, the fluidised wash column 222 allows for 100% expansion of the bed of silica rich activated alumina media 226 to remove solid fines, which may also include silica rich activated alumina media fines. Any silica rich activated alumina media fines lost in this manner may be replenished in this column through the introduction of supplementary activated alumina media. The wash water 228, including any solid fines then exits from an upper portion of the fluidised wash column 222 via a trough 232 as dirty wash water 234. The dirty wash water 234 can be returned to an upstream pond for settlement and subsequent reprocessing. After exiting the fluidised wash column 222 via an outlet 236 at a lower portion of the fluidised wash column 222, the washed silica rich activated alumina media 238 is then fed to a regeneration column 240 via an airlift 242.

The washed silica rich activated alumina media 238 enters the regeneration column 240 via an inlet 244 in the top of the regeneration column 240 as a bed 245. The bed of silica rich activated alumina 245 moves downwardly through the column. A regenerant solution 246 is fed from a reservoir 248 into the regeneration column 240 via an inlet 250. In this case, the regenerant solution is a 1 - 2wt% sodium hydroxide solution to elute the silica from the media.

The regenerant solution 246 flows upwardly through the regeneration column 240 and contacts the activated alumina media in the bed of silica rich activated alumina in a counter-current flow direction. This causes the silica to be desorbed from the activated alumina media 245, forming a regenerated activated alumina media and a silica rich regenerant. The silica rich regenerant is then removed via an upper portion of the regeneration column 240 through an outlet 252 as a silica rich regenerant stream 254. The silica rich regenerant stream 254 is then further processed to remove the silica from the regenerant solution so that the regenerant solution can be reused. The regenerated activated alumina media is removed from a lower portion of the regeneration column 240 as a regenerated activated alumina media 256.

The regenerated activated alumina media 256 then exits the regeneration column 240 via exit 257 then transferred via an airlift line 258 from the regeneration column 240 to a rinse column 260. The regenerated activated alumina media 256 may be transferred intermittently from the bottom of the regeneration column 240 to the rinse column 260. The regenerated activated alumina media 256 enters the rinse column 260 via an inlet 262 in the top of the rinse column 260. Rinse water 264 is fed into the rinse column 260 via an inlet 266 in a lower region of the rinse column 260. In this particular embodiment, the rinse water 264 is a side stream taken from the silica lean water stream 208. However, the rinse water may alternatively be sourced from plant deionised or demineralised water. The rinse water 264 rises through the rinse column 260 and contacts with the descending regenerated activated alumina in a counter-current fashion. The rinse water 264 removes residual regenerant from the regenerated activated alumina media. The rinse solution, including any residual regenerant solution is then removed from the rinse column 260 via an outlet 268 in an upper portion of the rinse column 260. The rinse solution is then sent to the regenerant solution reservoir where it may be mixed with concentrated regenerant solution to produce a regenerant of the desired concentration for use in the regenerant column 240. The rinsed regenerated activated alumina media is then removed via an outlet 270 at the bottom of the rinse column 260. The rinsed regenerated activated alumina media can then be transported back to the adsorption column 200 via an airlift 272 for use as the silica lean activated alumina media 206.

In this manner a continuous process for the removal of silica from a coal seam gas associated water stream and the regeneration of an activated alumina adsorbent is provided.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1 . A continuous method for the removal of reactive silica from a high alkalinity silica rich water stream produced from the extraction of coal seam gas, the method including: contacting the high alkalinity silica rich water stream with a silica lean activated alumina media, reactive silica adsorbing onto the activated alumina media, to form a silica lean water stream and a silica rich activated alumina media; separating the silica lean water stream and the silica rich activated alumina stream; regenerating the silica rich activated alumina media with a regenerant solution, reactive silica desorbing from the activated alumina media into the regenerant solution, to form a regenerated silica lean activated alumina media; returning the regenerated silica lean activated alumina media as the silica lean activated alumina media in contacting step.

2. The method of claim 1 wherein the contacting step is a counter-current contacting step.

3. The method of claim 1 or 2, wherein the activated alumina media is a moving bed.

4. The method of any one of the preceding claims wherein the high alkalinity silica rich water stream has a total alkalinity of at least 1 ,000 mg/L.

5. The method of claim 4 wherein the total alkalinity is at least 2000mg/L.

6. The method of any one of the preceding claims wherein the pH of the high alkalinity silica rich water stream is from about 8 to about 9.4.

7. The method of claim 6 wherein the pH of the high alkalinity silica rich water stream is from about 8.6 to about 9.2.

8. The method of anyone of the preceding claims wherein the regenerant solution is an aqueous solution of about 1 % to about 1 .5% sodium hydroxide.

9. A process for the removal of dissolved silica from a high alkalinity silica rich water stream produced from the extraction of coal seam gas, the process including: contacting the high alkalinity silica rich water stream with the silica lean activated alumina media in a contact vessel, dissolved silica adsorbing to the activated alumina media, to form a silica lean water stream and a silica rich activated alumina media; removing the silica lean water stream from the contact vessel; transferring the silica rich activated alumina media from the contact vessel to a regeneration vessel; regenerating the silica rich activated alumina media with a regenerant solution in the regeneration vessel, dissolved silica desorbing from the activated alumina media into the regenerant solution, to form a regenerated silica lean activated alumina media; and returning the regenerated silica lean activated alumina media to the contact vessel as the silica lean activated alumina media.

10. The process of claim 9, wherein a high alkalinity silica rich water stream inlet and a silica rich activated alumina media outlet are located at a the lower region of the contact vessel, and a silica lean activated alumina media inlet and a silica lean water stream outlet are located at an upper region of the contact vessel; such that the flow of the high alkalinity silica rich water stream is counter-current to the silica lean activated alumina media.

1 1 . The process of claim 9 or 10, wherein the activated alumina media is a moving bed.

12. The process of any one of claims 9 to 1 1 wherein the high alkalinity silica rich water stream has a total alkalinity of at least 1000 mg/L.

13. The process of claim 12 wherein the total alkalinity is at least 2000mg/L.

14. The process of any one of claims 9 to 13 wherein the pH of the high alkalinity silica rich water stream is from about 8 to about 9.4.

15. The process of claim 14 wherein the pH of the high alkalinity silica rich water stream is from about 8.6 to about 9.2.

16. The process of anyone of claims 9 to 15 wherein the regenerant solution is an aqueous solution of about 1 % to about 1 .5% sodium hydroxide.