AU2011212316A1

AU2011212316A1 - Method and arrangement for removing gas from a liquid

Info

Publication number: AU2011212316A1
Application number: AU2011212316A
Authority: AU
Inventors: Teemu Ritasalo; Niclas Tylli; Jussi Vaarno
Original assignee: Outotec Oyj
Current assignee: Metso Corp
Priority date: 2010-02-02
Filing date: 2011-01-31
Publication date: 2012-07-26
Also published as: CA2786684A1; FI123403B; PE20130350A1; FI20100032A; EA201290648A1; WO2011095685A1; FI20100032A0; CL2012002120A1; EP2531270A1; CN102740943A; EP2531270A4; BR112012019081A2

Abstract

The invention relates to a method and arrangement for removing gas, particularly inert gas bubbles, from process solutions. A container (1) containing process solution is provided with means both for feeding gas and solution into a container and for removing gas and solution from the container, said container (1) comprising a separate gas removal tank (2) set therein, into which tank the solution is fed tangentially at the lower part (3) of the gas removal tank, and in which gas removal tank the solution is conducted in a helical, upwardly oriented motion, as the gas bubbles (7) are removed from the top part (14) of the gas removal tank.

Description

WO 2011/095685 PCT/F12011/050077 1 Method and arrangement for removing gas from a liquid Background of invention The invention relates to a method according to claim 1 for removing gas, particularly inert gas bubbles, from process solutions. Moreover, the invention 5 also relates to an arrangement according to claim 15 for removing gas from a solution. Generally in hydrometallurgical processes, such as recovery processes, gas is contained in the solutions. It is a well-known fact that gas bubbles which 10 have not been discharged from the process cause problems in many hydrometallurgical dissolution, cooling and precipitation processes. Problems arise for example when separating in a thickener the solids contained in a solution, because bubbles slow down the settling of the slurry and raise the tiny solid particles on the surface of the thickener and further to the overflow. 15 A functioning liquid-solid-separation and particularly a clear overflow are extremely important for an efficient operation of a hydrometallurgical process, for instance for minimizing recovery losses and environmental emissions. Gas bubbles may consume the reagent, thus resulting in problems for example in extraction. Moreover, the bubbles cause aerosol emissions, such as acid and 20 metal emissions to the environment, when being released from the liquid surface of the reactor. Emissions cause health hazards when a possibly toxic gas is emitted from process conditions to the environment, and problems related to corrosion may also occur. It is well known that the removal of gas bubbles from solutions is difficult, and various different arrangements have 25 been developed to solve the problem. From the patent publication GB 1325816, there is known one arrangement for degassing a solution. According to said solution, it is suggested that the degassing equipment includes a cylindrical container, into which liquid is fed 30 tangentially, as it is set in a rotary, downwardly oriented motion. The released WO 2011/095685 PCT/F12011/050077 2 gas bubbles are removed in countercurrent to the flow from the top part of the container, which is the most essential drawback of said invention. 5 Brief description of invention The object of the invention is to solve problems related to gas removal. The invention relates to eliminating the hazardous effects caused by gas bubbles when processing liquids containing solid substances. The preferred embodiments of the invention are set forth in the dependent claims. 10 The object of the invention is realized by means of a method according to the independent claim 1 for removing gas, particularly inert gas bubbles, from process solutions, wherein a container containing process solution is provided with means both for feeding gas and solution into a container and for 15 removing gas and solution from the container, said container comprising a separate gas removal tank set therein, into which tank the solution is fed tangentially at the lower part of the gas removal tank, and in which gas removal tank the solution is conducted in a helical, upwardly oriented motion, while the gas bubbles are removed from the top part of the gas removal tank. 20 Preferably solution is removed at the lower part of the tank. According to an embodiment of the invention, the gas removal tank is installed concentrically in the surrounding container. In that case there is achieved an advantageous arrangement, as the solution is removed from the 25 gas removal tank into the surrounding container. For the implementation of the invention, it is also advantageous that the solution is fed to the gas removal tank in an essentially horizontal direction with respect to the lengthwise axis of the gas removal tank. Now the helical flow of the solution inside the gas removal tank is conducted in a desired motion. 30 According to an embodiment of the invention, the solution is conducted into the gas removal tank through a feed pipe, the maximum width of the WO 2011/095685 PCT/F12011/050077 3 transversal surface of said feed pipe being no more than a fifth of the gas removal tank diameter, at least at the spot where it is connected to the gas removal tank. According to an embodiment of the invention, solution is fed to 5 the gas removal tank advantageously at the rate 1-6 m/s, so that an advantageous helical flow is achieved. The diameter and height of the gas removal tank are chosen so that the delay time of the solution containing gas bubbles in the gas removal tank is advantageously at least 10 seconds. The faster the achieved helical flow and the longer the achieved delay time of the 10 solution in the gas removal tank, the more effective is the merging together of gas bubbles. According to the invention, after gas removal the solution is conducted to proceed into an intermediate space left in between the gas removal tank and 15 the container. According to the invention, gas removal is made more effective by adjusting the solution flow rate in the intermediate space. According to an embodiment of the invention, the maximum flow rate of the solution in the intermediate space is no more than 8 cm/s, in which case there is achieved a good separation of the gas bubbles from the solution. 20 According to an embodiment, the gas removal tank is placed in the container prior to concentrating the solution. According to another embodiment of the invention, the gas removal tank is placed in the container prior to precipitating the solution. 25 According to an embodiment of the invention, solids contained in the solution are removed through the lower part of the gas removal tank. Thus there are advantageously removed the solids which would otherwise be left on the bottom of the gas removal tank. According to an embodiment of the invention, 30 solids carried along with the solution are removed through the lower part of the container.

WO 2011/095685 PCT/F12011/050077 4 The object of the invention is achieved by using an arrangement according to the invention for removing gas, particularly inert gas, from process solutions, said arrangement comprising, in connection with a container containing 5 process solution, means for feeding both gas and solution to the container and for removing both gas and solution from the container, in which case the container includes a separate gas removal tank, at the lower part of which there is tangentially arranged a solution feed pipe, and in which gas removal tank the solution is conducted in a helical, upwardly oriented motion, the top 10 part of said gas removal tank being provided with means for removing gas. It is advantageous for the invention that the lower part of the container is provided with means for removing solution. According to an advantageous embodiment of the invention, the gas removal tank is installed concentrically 15 in the surrounding container. The lower part of the gas removal tank is at least partially conical and open for removing solids contained in the solution. Consequently, the solids contained in the solution are advantageously removed. According to an embodiment of the invention, the means for removing solids from the container are placed as near as possible to the 20 outlet aperture of the gas removal tank. According to an embodiment of the invention, the maximum width of the transversal surface of the feed pipe is no more than a fifth of the diameter of the gas removal tank, at least at the spot where it is connected to the gas removal tank. 25 The arrangement according to the invention provides for a fast and controlled removal of gas bubbles from the solution. When a motion directed upwards from below is made use of in gas removal, bubble clusters are advantageously removed through the top part of the gas removal tank. The diameter of the container surrounding the gas removal tank can be chosen to 30 be suitable, depending on the desired diameter of the gas bubbles to be removed. An embodiment according to the invention can be included in an existing process, when gas removal problems occur therein. According to the invention, an effective separation of gas bubbles can be affected by adjusting WO 2011/095685 PCT/F12011/050077 5 the flow rate of the solution and by designing the measures of the gas removal tank with respect to the existing process requirements. 5 List of drawings Preferred embodiments of the invention are described below with reference to the appended drawings, wherein Figure 1a is an illustration in principle of an arrangement according to the 10 invention, Figure 1 b is an illustration in principle of an arrangement according to the invention, Figure 2 illustrates an example according to an embodiment of the invention, and 15 Figure 3 illustrates an example according to an embodiment of the invention. Detailed description of the invention An arrangement according to the invention for removing gas is illustrated in more detail in Figures 1 a and 1 b, of which 1 b shows the target of Figure 1 a 20 as viewed from the direction A. Solution is fed into a container 1, provided with a separate cylindrical gas removal tank 2, which is installed concentrically with respect to the container and is conical at the lower part 3. Solution is fed into the gas removal tank tangentially through the lower part 3, in which gas removal tank 2 the solution 4 is set in a helical, upwardly 25 oriented motion owing to the effect of the centrifugal force. The feed flow is conducted from the feed pipe 5 to the gas removal tank 2, so that at the feeding spot, it is perpendicular to the lengthwise axis 6 of the gas removal tank. Light smaller gas bubbles 7 rise, along with the flow, towards the top part of the gas removal tank 2 and are further merged into larger gas bubble 30 clusters, the flow rate of which is further increased. Gas bubbles are released through the surface 8 of the container 1, from where they are recovered as overflow through a pipework 9 installed in the top part of the container.

WO 2011/095685 PCT/F12011/050077 6 From the gas removal tank, the liquid flow turns towards the bottom of the container 1, where the non-separated bubbles move downwardly in the intermediate space 10 left between the container 1 and the gas removal tank 5 2. The flow in the intermediate space 10 left between the container 1 and the gas removal tank 2 continues in the downwardly direction, and further both solution and larger solid particles are removed through the lower part 11 of the container. In order to achieve good bubble separation, the flow rate of the solution is adjusted to be suitable in the intermediate space 10. 10 Consequently, by means of an arrangement according to the invention, gas removal from a solution can be made more effective by adjusting the flow rate in the intermediate space 10. Advantageously the maximum flow rate in the intermediate space is no more than 8 cm/s, preferably no more than 5 cm/s. It is advantageous that the lower part 3 of the gas removal tank 2 is conical, in 15 order to carry out the removal of solution and solids through the outlet aperture 13 of the gas removal tank 2 further to the lower part 11 of the container 1. In the lower part 11 of the container 1, there are provided means, such as a pipework 12, for conveying the solution out, and said means are most advantageously set as near to the outlet aperture 13 of the gas removal 20 tank as possible. The width B of the transversal surface of the feed pipe 5 is proportioned to the length of the diameter C of the gas removal tank 2, so that it is advantageously no more than a fifth of the tank diameter at the point where 25 the feed pipe is connected to the tank. By feeding solution into the gas removal tank 2 at a certain speed, such as 1-6 m/s, there is achieved an advantageous delay time for the solution in the gas removal tank, said delay time being at least 10 seconds. Bubble separation can be further boosted by increasing the helical flow in the gas removal tank and by increasing the 30 solution delay time therein. The size of a gas removal tank 2 according to the invention can be adjusted to be desirable depending on the solution feed rate and the turbulent speed of the solution in the gas removal tank.

WO 2011/095685 PCT/F12011/050077 7 The invention is further illustrated by means of the following example. Example 1 5 The functional capacity of the arrangement according to the invention was tested in laboratory-scale conditions. An arrangement according to the invention for removing gas is described in this example as follows. A gas removal arrangement according to the example comprises a gas removal 10 tank, which in this example is described as a cyclone, as well as a tank surrounding said cyclone. Water was treated in a gas removal arrangement according to the example, in which case air was fed in the feed pipe of the cyclone. The cyclone is set concentrically in the tank, so that solution can be fed tangentially through the lower part of the cyclone. Now the solution is set 15 in a helical, upwardly oriented motion, so that bubbles are removed at the top part of the cyclone, while part of them is carried along with the flow into the intermediate space left between the tank and the cyclone. The diameter of the cyclone used in the arrangement according to the example was 300 mm and the height 700 mm; these sizes fluctuate as a function of the feed rate and the 20 turbulent speed. In that case the solution was fed into the cyclone through a feed pipe with a diameter of 40 mm. Three different flow rates were used in the tests: 5.1 m 3 /h, 7.4 m 3 /h, and 10.6 m 3 /h. The solution feed rates into the cyclone corresponding to said flow rates were 1.1 m/s, 1.6 m/s, and 2.3 m/s, and the flow rates in the intermediate space left in between the cyclone and 25 the tank were 2.9 cm/s, 4.2 cm/s and 6.0 cm/s. The functional capacity of the invention was estimated by measuring the sizes of the gas bubbles in the intermediate space left in between the cyclone and the tank, at the depth of 630 mm from the free fluid level. The measurement volume is background illuminated by an immersed light, and the pictures were recorded with a digital 30 camera. The contours of the gas bubbles, and therethrough the size of the gas bubbles, could be defined through the gradient of the image intensity. In the tests it was observed that the solution flow rate in the intermediate space has an effect on the separation capacity of the bubbles. By reducing said flow WO 2011/095685 PCT/F12011/050077 8 rate in the intermediate space, the separation of smaller bubbles from the solution is made possible, as is seen from Figure 2. 5 In addition, the functionality of an industrial-scale gas removal tank was estimated by means of computational flow modeling. The flow rate into the gas removal tank was 6500 m 3 /h. With the allowed pressure loss (1.5 m of aqueous column) as a boundary condition, the diameter of the cyclone tank was optimized. Figure 3 shows the results for three different diameters of the 10 cyclone tank. Here the graphs illustrate a percentage share of the fed gas bubbles that remain in the solution after the gas removal tank. As the graph shows, in the case of the example, gas removal was most effective in a cyclone tank with a diameter of 3 meters. 15 For a man skilled in the art, it is obvious that along with the development of technology, the principal idea of the invention can be realized in many different ways. Thus the invention and its embodiments are not restricted to the above described examples, but they may vary within the scope of the appended claims. 20

Claims

1. A method for removing gas, particularly inert gas bubbles from process solutions, in which case a container (1) containing process solution includes 5 means for feeding both gas and solution to the container and for removing both gas and solution from the container, characterized in that the container (1) includes a separate gas removal tank (2) installed therein, when the lower part of the gas removal tank (2) is conical, into which 10 tank the solution is fed tangentially at the lower part (3) of the gas removal tank, and in which gas removal tank the solution is set in a helical, upwardly oriented motion as the gas bubbles (7) are removed through the top part (14) of the gas removal tank. 15

2. A method according to claim 1, characterized in that solution is removed through the lower part (11) of the tank.

3. A method according to claim 1 or 2, characterized in that the gas removal tank (2) is set concentrically in the surrounding container (1). 20

4. A method according to claim 1, 2 or 3, characterized in that the solution is fed into the gas removal tank (2) essentially horizontally with respect to the lengthwise axis (6) of the gas removal tank. 25

5. A method according to claim 1, 2, 3 or 4, characterized in that the solution is conducted into the gas removal tank (2) through a feed pipe (5), the maximum width (B) of the transversal surface of said feed pipe being no more than a fifth of the feed pipe diameter (C), at least at the spot where it is connected to the gas removal tank. 30 WO 2011/095685 PCT/F12011/050077 10

6. A method according to any of the claims 1-5, characterized in that the solution is fed into the gas removal tank (2) advantageously at the rate 1-6 m/s. 5

7. A method according to any of the claims 1-6, characterized in that the diameter (C) and the height (D) of the gas removal tank (2) are chosen so that the delay time of the solution containing gas bubbles in the gas removal tank is advantageously at least 10 seconds. 10

8. A method according to any of the preceding claims, characterized in that after gas removal, the solution is conducted to proceed into the intermediate space (10) between the gas removal tank (2) and the reactor. 15

9. A method according to any of the claims 1-8, characterized in that gas removal is made more effective by adjusting the solution flow rate in the intermediate space (10).

10. A method according to any of the claims 1-9, characterized in that the 20 maximum flow rate of the solution in the intermediate space (10) is no more than 8 cm/s.

11. A method according to any of the claims 1-10, characterized in that the gas removal tank (2) is placed in the container (1) prior to the concentration of 25 the solution.

12. A method according to any of the claims 1-11, characterized in that the gas removal tank (2) is placed in the container (1) prior to the concentration of the solution. 30

13. A method according to any of the preceding claims, characterized in that solids contained in the solution are removed through the lower part (3) of the gas removal tank (2). WO 2011/095685 PCT/F12011/050077 11

14. A method according to any of the preceding claims, characterized in that solids carried along with the solution are removed through the lower part (11) of the container (1). 5

15. An arrangement for removing gas, particularly inert gas from process solutions, said arrangement comprising means, provided in connection with a container (1) containing process solution, for feeding both gas and solution into the container and for removing both gas and solution from the container, 10 characterized in that the container (1) includes a separate gas removal tank (2), when the lower part of the gas removal tank (2) is conical, at the lower part (3) whereof there is tangentially installed a solution feed pipe (5), and in which gas removal tank (2) the solution is set in a helical, upwardly oriented motion, the 15 upper part (14) of said gas removal tank (2) being provided with means for removing gas.

16. An arrangement according to claim 15, characterized in that the lower part of the container is provided with means for removing solution. 20

17. An arrangement according to claim 15 or 16, characterized in that the gas removal tank (2) is set concentrically in the surrounding container (1).

18. An arrangement according to any of the claims 15-17, characterized in 25 that the lower part (3) of the gas removal tank is at least partially conical and open for removing solids contained in the solution.

19. An arrangement according to any of the claims 15-18, characterized in that the means (12) for removing solids from the container (1) are placed as 30 near as possible to the outlet aperture (13) of the gas removal tank (2).

20. An arrangement according to any of the claims 15-19, characterized in that the maximum width (B) of the transversal surface of the feed pipe (5) is WO 2011/095685 PCT/F12011/050077 12 no more than a fifth of the diameter (C) of the gas removal tank, at least at the spot where it is connected to the gas removal tank. 5