The present invention generally relates to gas component extraction, and, more particularly, to a process for extracting a gas component from a gas mixture.

The extraction of gases, such as carbon dioxide or nitrogen oxides, from air in substantial quantity requires the processing of large volumes of air. Creating a continuous movement of large volumes of air typically requires the input of significant energy by the use of fans. Wind can move large volumes of air, but is rarely continuous and hence will not provide optimal use of gas capture equipment. A continuous flow of air is required for this. Inducing air flows by the evaporation of water using the chimney effect is described in patent application WO2010/032049. In this process, water in its conventional form is sprayed at the top of a chimney such that water evaporates. This cools the air and due to the stack effect and the entrainment of air by the falling water, air is moved down the column. Large flows of slow moving air may be induced in this manner.

When water evaporates, the process is generally governed by temperature, surface area and the humidity of the air. In a flowing air stream, humidity defines the amount of water that can be further evaporated. Increased temperature increases the rate of evaporation and the amount of humidity that can be added to the air. However, raising the temperature of large flows of air requires significant energy input which not feasible in a low energy process. This leaves surface area as being the only parameter over l which useful control can be applied. Ideally, to minimize energy use, droplet size needs to be as small as possible so as to create the maximum surface area to volume ratio. In this way less energy is expended pumping water to create the greatest surface area. However, creating finer and finer droplets has practical limits and in most instances requires increased energy use as finer droplets are created. Nozzle clogging and coalescence also are significant problems. As a result, spraying water for evaporation means that most of the water pumped will not evaporate unless the height of the chimney is very high. Very high chimneys are expensive to build and are generally not practical.

Bubbles offer a useful way of reducing the energy expended pumping water to create large surface areas for evaporation. Bubbles are self assembling structures that naturally self limit the thickness of the bubble walls. Equally bubbles present two surfaces to the air which doubles the useful surface area. The energy to form bubbles is very small. Bubbles form easily if sufficient foaming agent is present and have very large surface area to volume ratios. The ratio of water volume to surface area is unaffected by bubble size. Bubble thickness can vary but is limited to a maximum thickness. Bubbles typically start out with thicker walls which steadily reduce as the water evaporates from the bubbles' surfaces until the wall thickness reduces to the point of popping. When the bubble breaks, fine particles of water are formed which further aids evaporation. While bubble size has no effect on the ratio of water volume to surface area, bubble size does affect the amount of bubbles that can be packed into a given space: the smaller the bubble, the greater the surface area to water volume ratio per cubic metre of air. For this reason, decreasing bubble size is generally useful. Ideally, the bubbles need to be sufficiently small such that they do not excessively bump into each other and stick together which reduces the surface area but at the same time not so small that the air inside of the bubble becomes so reduced that little evaporation occurs and the double surface is wasted. Equally, the bubbles need to interact with as much of the air column as possible to achieve saturated humidity. This can be aided by spreading out the formation of the bubbles across the top of the column so that the falling bubbles can mix with all parts of the incoming air.

An example of a typical application would be to have a chimney where bubbles of modest size are created evenly across the column cross-section towards the top of a column such that passing wind does not draw out the created bubbles. The bubbles fall and water evaporates from the large surface areas that have been created. The air cools from evaporation. Towards the bottom of the column, most of the bubbles walls have sufficiently thinned so that the bubbles pop. The remaining bubbles and the shattered bubble fragments fall to the bottom of the column. The majority fall into a water sump. Some bubbles and fragments are entrained in the air leaving the air chimney. The air flow passes across a series of sharp points to break the remaining bubbles and then passes through drift eliminators to trap the entrained water particles. The cooled air within the chimney creates a downward falling flow of air due to the stack effect. The high ratio of surface area to volume ratio that bubbles offer mean that a very high percentage of the total water that is pumped is directly evaporated. The use of falling bubbles within a chimney creates large volumes of cooled air for low energy input.

In the majority of applications of the induced flow bubble tower, the induced draft will be redirected by 90 degrees at the bottom of the tower so that broken bubble particles can fall into a sump and air exit on the horizontal. This is ideal for gas capture from the created air flow which can then pass through a series of sprays, fill packs, or bubbles of sorbent to capture or destroy the desired gases from the air.

The described induced flow bubble tower has applications that extend beyond selective gas capture from gas streams. The falling bubble tower offers a means to evaporate water for very low energy. This is useful for applications such as waste water concentration or creating cool air streams. The described process uses sufficiently low energy that it could be used to modify the local or regional water cycle by increasing the humidity of the region's air and reducing the temperature of large volumes of air. The effects will be dependent upon local geography, weather conditions, and the amount of water evaporated.

The process may be for evaporating water, concentrating materials dissolved within the water, and/or supplying air that is saturated with respect to humidity. As outlined in patent application WO2010/032049, it has been found that the following reaction sequence is particularly useful for capturing carbon dioxide from the air:

1) CaSCv 2H ₂ 0 → CaS0 ₄ + 2H ₂ 0

(Gypsum) (Calcium sulphate) (Water)

3.91g → 3.09g + 0.82g

NH ₃ + H ₂ 0 → NH ₄ OH

(Ammonia) (Water) (Ammonium hydroxide)

0.77g + 0.82g → 1.59g

CaS0 ₄ + C0 ₂ + 2NH ₄ OH CaC0 ₃ + H ₂ 0 + (NH ₄ ) ₂ S0 ₄

(Calcium sulphate) (Carbon dioxide) (Ammonium hydroxide) (Calcium carbonate) (Water) (Ammonium sulphate)

3.09g + 1g + 1.59g 2.27g + 0.41g + 3.00g

It has been found through experimentation that reaction 3 can be optimized to capture higher percentages of a given air flow if the level of suspended gypsum and ammonia is increased. Ammonia and ammonium hydroxide are alkali and the greater the concentration of ammonia, the greater the pH. Overall, the greater the level of ammonia/ammonium hydroxide, the greater the rate of carbon capture. However, higher ammonia concentrations mean greater vapour pressures of ammonia. This means that ammonia gas increasingly strips out of solution as the pH of the working sorbent rises. This is undesirable. From the discussion that is to follow, it will become apparent how the above-mentioned deficiencies associated with known constructions and techniques are addressed by the present invention, while providing numerous additional advantages not hitherto contemplated or possible with said known constructions.

According to an aspect of the present invention, there is provided a process for extracting a gas component from a gas mixture, said process comprising the steps of:

providing a gas mixture;

passing the gas mixture through a sorbent medium, thereby selectively extracting said component; and

recycling the sorbent medium;

wherein the sorbent medium includes a concentration gradient.

The sorbent medium may comprise at least one of gypsum, ammonia and water.

In at least some embodiments, this may prevent spillage of sorbent materials, such as ammonia vapour, from the process. The concentration gradient also allows a user to manage medium such as water vapour as well. In at least some embodiments, this may allow a user to improve the ratio of created calcium carbonate, for instance, to the gypsum reactant. Further, it also enables concentration of the ammonium sulphate solution, for instance. The process may include the step of forming bubbles from the gas mixture and passing it vertically along a column.

The flow of the gas mixture may be redirected by about 90° at the end of the column.

In embodiments, an induced flow chimney may be employed to create the air/gas mixture flow and then to have the carbon/gas component capture part of the process run along the ground. The carbon capture part of the process may be up to 26 metres long, for example. In this way, the column may not necessarily be vertical. Equally, in some embodiment it may be more desirable to operate the linked capture pairs to manage the ammonia vapour in a configuration where the column is not completely vertical. However, it must be borne in mind that that best result may be achieved when the induced air flow column is vertical to make the stack effect work most efficiently. The carbon capture with the joined pairs may be only practical in the horizontal configuration, for instance.

The flow of the gas mixture may be substantially perpendicular to the flow of the sorbent medium on contact therewith.

This arrangement may be desirable because it creates a simpler arrangement of linked capture sections. There are alternatives, but they can be more complicated and expensive to build, which is an unwelcome cost. In this arrangement, it becomes possible to build what is essentially a tube with walls of fill pack set into it. Optionally, it is possible to have a series of mini towers where air flows up one tower and then may be redirected and then enter another tower and rise up again. However, such an arrangement may be more expensive to build and more complicated to run. Potentially, it may also use more energy.

The process may include the step of using a foaming agent to induce bubble formation.

The gas component may include at least one of carbon dioxide, nitrogen oxide, ammonia, methane and water vapour.

The gas mixture may include air.

The air may be enriched with gases created from combustion or another industrial process.

The sorbent medium may be in the form of a spray, a fill pack, a solution or a collection of bubbles.

Bubble are particularly advantageous because they require low energy to form. They have huge surface area in relation to the liquid volume which means that the amount of fluid pumped is used to best advantage. Bubbles can create vast surface areas for very low energy. Bubbles provide a very low capital cost method of generating large surface areas, compared with other sorbent medium forms. Equally, bubbles create less back pressure as compared with other sorbent medium forms which provide significantly more wind resistance.

The process may include the step of using sulphuric acid to scrub ammonia vapour.

The cost of complete removal of ammonia vapour from the gas mixture prior to exit using capture and release pairs can be reduced by incorporating a sulphuric acid scrubbing step which removes low level ammonia vapour. The addition of a final acid scrubber reduces the energy and capital cost of controlling the ammonia vapour. If the carbon capture reaction outlined below in reaction three is used, using sulphuric acid as the acid in the final acid scrubber is an advantage because ammonium sulphate is produced which is one of the products produced by reaction three.

The extraction of the gas component may be for the capture and/or destruction thereof.

It may be that using the process described above, carbon dioxide is extracted from air according to the following reactions:

1) CaS0 ₄ - 2H ₂ 0 → CaS0 ₄ + 2H ₂ 0

2) NH ₃ + H ₂ 0 → NH ₄ OH

3) CaS0 ₄ + CO2 + 2NH ₄ OH → CaC0 ₃ + H ₂ 0 + (NH ₄ ) ₂ S0 ₄ According to another aspect of the present invention, there is encompassed a process of cooling air using water, comprising the steps of:

generating water bubbles;

providing a column open at its top end;

feeding the water bubbles into the column at its top end;

allowing the bubbles to sink and evaporate, thereby generating cool air and inducing a downward air flow.

In at least some embodiments, by using bubbles, virtually all the water pumped is evaporated if the chimney is made high enough and, perhaps, if it is not raining (this makes the air have 100% humidity). This make the process a substantially lower energy cost means of inducing very large air flows. Bubbles offer the advantage of being able to create large surface areas and not creating significant air resistance and not requiring high energy input.

The use of bubbles in this manner may produce a process which requires up to about 1000 times less energy to generate cool air and induce air flow than conventional processes.

The water may be fresh water, salt water, or sourced from waste water that is contaminated with impurities. According to a further aspect of the present invention, there is envisaged an apparatus for extracting a gas component from a gas mixture, comprising at least one pair of sorbent sections which are in fluid communication with one another, and means for storing a sorbent medium for extraction of said gas component, the sorbent sections being operable to recycle a sorbent medium by fluid communication, wherein the at least one pair of sorbent sections effect a concentration gradient of the sorbent medium.

The apparatus may be for capture and/or destruction of a gas component of a gas mixture,

The apparatus may comprise a further gas component extraction section.

The gas component extraction section may be situated between the at least one pair of sorbent sections.

Of course, it will be appreciated that in a series of pairs of sorbent sections, all the pairs may capture a gas component, for instance C0 ₂ or other gases, but they may do this at reduced efficiency as you move away from the centre of the process cascade as this has the optimal conditions. It may be possible to configure the cascade as only having capture pairs but by doing this, you can have a section where the ammonia concentration is higher and gives you higher capture rates. The process may be seen as a self-refining process. The concentration of the products may, therefore, be managed in an efficient way (for instance of the chalk). The bubbles offer a manner of manage the concentrations of the media to a greater extent than known methods.

The gas component extraction section and/or the at least one pair of sorbent sections may be containers and/or columns.

The apparatus may comprise means for feeding the gas mixture to the at least one pair of sorbent sections.

The said feeding means may be configured to feed the gas mixture in direction substantially perpendicular to the flow of sorbent medium.

The sections may comprise a sump for receiving sorbent medium.

The sump of one of the pair of sorbent sections may be in fluid communication with the top of the other of the pair of sorbent sections.

The apparatus may be adapted for a sorbent medium which comprises at least one of gypsum, ammonia and water. The apparatus may comprise means for forming bubbles from the gas mixture, and a column for passing the bubbles therethrough.

The end of the column may be operable to redirect the flow of the gas mixture by about 90°.

The apparatus may be adapted for a gas component which includes at least one of carbon dioxide, nitrogen oxide, ammonia, methane and water vapour.

The gas mixture may include air.

The air may be enriched with gases created from combustion or another industrial process.

The apparatus may be adapted for a sorbent medium which is in the form of a spray, a fill pack, a solution or a collection of bubbles.

The apparatus may comprise rotating arm spreaders to deliver fluids and solids across a fill pack sorbent medium.

If fill packs are used to create large surface areas, it has been found to be beneficial to use rotating arm water spreaders to distribute the fluid across the top of the fill packs. Rotating arm spreaders have been widely used to spread water within cooling towers

13 and in the waste water industries for many years. They represent a low energy method of spreading water. This is useful but rotating spreaders have another particularly useful advantage for carbon capture. Rotating spreaders do not continuously deliver fluid to all parts of the fill pack at the same time. The carbon capture or gas absorbing process is limited by the rate of gas molecules diffusing into the liquid surface. This happens relatively slowly. Fluids and materials delivered to a fill pack surface do not immediately fall off the fill pack and continue to create thin films for some time after they are delivered onto the fill pack surfaces. This means that fluids to create films do not need to be added continuously. A rotating spreader is a uniquely useful device in this application which periodically refreshes fluid across the fill packs while also delivering fluid to the surface of the fill pack for low energy. This means that fewer reactants and fluid have to be delivered across the fill packs to capture a given amount of carbon. The reduced pumping means that less energy is required as compared to continuously pumping fluid across the top of the fill packs which is a significant and useful advantage. The rate of rotation of the spreader directly correlates to the rate of the fluid refreshment rate. Adjustment of this rate means that the energy of pumping can be optimized to deliver minimal energy input.

According to yet another aspect, the present invention encapsulates the use of the apparatus as described herein in the process as described herein. The present invention will now be described more particularly, by way of example only, according to the accompanying drawing, in which:

Fig 1 is a schematic diagram of an apparatus for extracting a gas component from a gas mixture, the apparatus formed according to an embodiment of the present invention.

A brief outline of the features and processes of figure 1 is as follows; the incoming air or gas stream is indicated 1. The recirculation pump 2 of first unit 101 feeds solution to the top of third unit 303. The second unit 202 comprises recirculation pump 16. The recirculation pump 3 of third unit 303 feeds solution to the top of first unit 101. Fluid trickles downwards as a thin film over the fill pack 17 of first unit 101. Air passes through at a 90° angle to the falling fluid. Fill packs 4 and 5 that have the same configuration but are in second and third units 202 and 303, respectively. First unit 101 comprises a conical tank 6 to collect the falling fluid that falls from fill pack 17. The second and third units 202 and 303 comprise sumps 7 and 8, respectively. Fluid distribution system 12 evenly spreads the fluid across the top of fill packs 17, 4 and 5. Indicated 13, is air or gas that has ammonia gas mixed in from the stripping process that occurred in fill pack 17. Indicated 14, is air or gas that has further ammonia gas that has evaporated from the high ammonia concentration in second unit 202. Indicated 15, is air or gas that has reduced ammonia concentration relative to 14 due to the absorption of ammonia into solution in fill pack 5. Referring now in more detail to Fig 1 , in this system/apparatus, a gas mixture (air) 1 enters the first unit (section) 101 where ammonia vapour is released from the falling fluid solution. This air 13 then passes to the second unit 202 where carbon capture occurs. The high concentration of ammonia from the sorbent system means that ammonia vapour is unavoidably added to the air 13. This air 14 then passes to the third unit 303. The pumped liquid falling through the third unit 303 is supplied from the sump 6 of the first unit 101. This solution is low in ammonia which was released into the air 1 in the first unit 101. The low ammonia solution is sprayed in the third unit 303 and absorbs ammonia from the air 14 that passes through the third unit 303. The air 15 that leaves the third unit 303 has reduced ammonia vapour. The liquid that is within the sump 8 of the third unit 303 has increased ammonia concentration and is then passed to the top of the first unit 101 where it gives up its excessive ammonia as it falls through the first unit 101. In this way, a balance of ammonia absorption in the third unit 303 and release in the first unit 101 is maintained.

A single pair of ammonia capture and release units will be insufficient to contain all the ammonia vapour in a commercial system. The number of absorption pairs required is dependent upon the operating pH of the central capture tower, the air temperature and the air velocity in ratio to the absorption surface area. Temperature has a particular bearing on this. In colder conditions, there is less ammonia vapour and in warmer conditions, more. Any commercial carbon capture system will need to plan for the warmest part of the year. This can be done through insuring that enough pairs of capture and release units are present for the warmest possible day or plan to reduce ammonia capture requirements on excessively hot days by reducing operating ammonia concentration. Due to continuous consumption of ammonia by the process (reaction 3), adjusting the ammonia concentration is possible.

The cost of complete removal of ammonia vapour from the gas mixture prior to exit using capture and release pairs can be reduced by incorporating a sulphuric acid scrubbing step which removes low level ammonia vapour. The addition of a final acid scrubber reduces the energy and capital cost of controlling the ammonia vapour. If the carbon capture reaction outlined in reaction three is used, using sulphuric acid as the acid in the final acid scrubber is an advantage because ammonium sulphate is produced which is one of the products produced by reaction three.

A single pair of capture and release units have been found to be able to control excessive ammonia vapour and produce no odour if the pH of the sorbent solution for capture was 10.2 (air temperature was a 28°C for this test). The process of the ammonia capture is seen by the pH differential of the different capture units. The steady state recorded pHs were:

First unit (the ammonia release unit): 9.5

Second unit (the carbon capture unit): 10.22

Third unit (the ammonia capture unit): 9.65 In each unit, fluid is sprayed across the top of a fill pack to create a falling thin film of solution that has a large surface area to volume ratio. This fluid interacts with the air 1 , 13, 14 and 15 that is moving horizontally through the fill pack 17, 4 and 5 holes. There are alternative methods to create large surface to area volume ratios for good gas interaction such as fine sprays of water or bubbles of solution. The described process is not exclusive to any one method of creating large surface area to volume of sorbents/solvents. It is possible to use a mixture of fill packs for the inner units that contain ammonium sulphate and precipitated chalk and, bubbles created by the addition of foaming agents to fully absorb and release the ammonia vapour in the outer units. This configuration avoids contaminating the created ammonium sulphate solution with foaming agents and is less expensive to build as fewer fill packs are required. Ammonium sulphate and precipitated calcium carbonate are removed in the outer pair 101 and 303 of units before the bubbles and foaming agents are used. To prevent drift of particles of water and foaming agent, drift eliminators are fitted between the units that use bubbles and the units that are based upon fill packs. In situations where mixing ammonium sulphate with foaming agent is not seen as an issue, bubbles can be used throughout the process and fill packs avoided. This embodiment has the advantage of low capital build costs as fill packs are not required.

The sorbent solution is contained within the second unit 202 (gas component extraction section). A useful sorbent solution that uses reaction 3 to capture CO2 from the gas stream is a mixture of suspended ground powdered gypsum, ammonia and water. As the mixture reacts with carbon dioxide from the air, precipitated calcium carbonate and ammonium sulphate (which is highly soluble) are produced, this creates a dilute solution of ammonium sulphate and a mixture of gypsum and chalk. The mixture is continuously recycled to increase the concentration of ammonium sulphate and raise the concentration of chalk. The sorbent is transferred from the main capture unit 202 in the centre of the process to the pair of ammonia capture units 101 and 303 directly next to it. Within the ammonia capture and release units, carbon capture occurs that increases the ratio of chalk to gypsum. Sorbent from the first pair of ammonia capture and release units is then moved progressively outward through the pairs of ammonia capture and release units. In the outer pair of units, high purity chalk and high strength ammonium sulphate solution are removed. This arrangement is particularly advantagous because it generally avoids the need to separate the created chalk from the input gypsum by a differential settling cascade. The gypsum concentration is progressively reduced by reaction three as the gypsum/chalk mixture moves through the process until gypsum contamination levels become low at the point where the purified chalk is removed.

The described system means that ammonia concentration increases as you move towards the central unit 202 where it is at a maximum. The rate of carbon capture, which is tied to ammonia concentration, decreases as you move outward from the central capture unit 202. The concentration of ammonium sulphate increases as you move outward towards the outer pair of units. Equally the purity of the chalk mixture improves as you move outward from the centre. The concentration gradients have another useful property, water vapour control. High concentration salt solutions tend to reach equilibrium with the moisture within the atmosphere such that at sufficient concentration, they absorb moisture from the air. In this way, the full size process will evaporate little to no fresh water because the outer pair of units will end up creating an ammonium sulphate solution that has a water vapour pressure that is in equilibrium with the air. In this way, little fresh water is required to be added to the process except to make-up for water removed when ammonium sulphate solution is extracted and to balance the small amount of drift losses. A small amount of water evaporation does occur if ammonium hydroxide solution is supplied to the central carbon capture unit 202.

If the described induced flow bubble tower is used, saturated humidity air will then pass through the progression of carbon capture units. Essentially, no water vapour will be lost from the series of capture units as the air entering the units will be saturated with water vapour. Consequently, the content of water will remain constant throughout the series of carbon capture units and ammonium sulphate will concentrate to a lower concentration than if water evaporation could take place. Further, concentration of the ammonium sulphate to create saturated solutions will require water evaporation. This can be done outside of the capture process.

An embodiment of the invention would be to have an induced flow bubble tower that supplies air flow to a series of capture units that maximize carbon dioxide capture and fully contains the ammonia vapour used in the process. Concentrated ammonium sulphate and high purity precipitated calcium carbonate is removed from the outer pair of capture towers. Water is only evaporated from the induced flow bubble tower which can use fresh, waste, brackish or salt water as a supply source. The described arrangement can be used with other chemical reactions. A number of variations will be apparent to skilled users and priority is claimed over these.

According to an aspect of the present invention, there is provided a process where water is evaporated from bubbles within a column that is open at the top and the bottom such that the air is cooled due to evaporation and creates a downward air flow due to the stack effect and the water used is fresh, salt or sourced from waste water that is contaminated with impurities.

According to another aspect of the present invention, there is provided a process of water evaporation from bubbles in moving air to create a low energy process to evaporate water and/or to concentrate materials dissolved within the water and/or to supply air that is saturated with respect to humidity.

According to a further aspect of the present invention, there is provided a process of using a series of paired sections where the fluid that has falien to the bottom of one section is delivered to the top of the opposite section to absorb or release ammonia or water vapour and the paired sections are joined such that fluid and solids can progressively move outwards from the centre of the conjoined sectional pairs. In embodiments, the process above may be such that the reactants are feed into the centre of the progression of paired sections and purified reaction products are removed from the outer joined pair.

In embodiments, the process above may be used to capture carbon dioxide, nitrogen oxides and methane gases.

In embodiments, the process above may operate on air that is enriched with gases created from combustion or another industrial process.

According to another aspect of the present invention, there is provided the use of rotating arm spreaders to deliver fluids and solids across a fill pack section that is being used to capture carbon dioxide and/or manage ammonia and water vapour.

According to yet a further aspect of the present invention, there is provided the dissolved/suspending of reactants within the fluid used to make-up bubbles within a gas stream to capture or release a gas within said gas stream.

In embodiments, the process above may be such that it is used to:

- Capture carbon dioxide

- Capture and release ammonia

- Capture and release water vapour.