Method and installation for removing any gas from a gas mixture stream

Abstract

A method and apparatus for removing gas from a gas mixture stream. A first liquid (82) is introduced into a stream (106) for evaporative cooling and saturation of the gas mixture. Small droplets of a second liquid (84) capable of absorbing and dissolving the gas are provided, small enough to not settle by gravity and large enough to be centrifuged. The small droplets are sprayed into the stream to absorb and dissolve the gas into the droplets, and the small droplets are centrifuged out of the stream.

Description

[Technical Field]

[0001] The present invention relates to a method for removing any gas from a gas mixture stream.

[0002] The invention also relates to an installation for carrying out the above method. [Background technology]

[0003] Conventional systems for reducing sulfur oxides (SOx), such as sulfur dioxide, in exhaust gases from ship diesel engines are primarily based on various types of scrubbers. For this purpose, wet scrubbers are primarily used, in which an aerosol of an alkaline solution (such as sodium hydroxide (NaOH)) is sprayed into the scrubber in a so-called closed-loop system and reacts with the sulfur oxides to form, for example, water-soluble salts or other disposable reaction products. This is often done when the ship is in port or when seawater is not sufficiently alkaline. If the seawater itself is sufficiently alkaline, so-called open-loop systems can be used at sea, in which an aerosol of seawater is added to react with the sulfur oxides in the exhaust gases for sulfur oxide removal.

[0004] Such scrubber systems require large amounts of water spray to break the exhaust gas into aerosol droplets, and the droplets must be very large and the exhaust gas flow must be very slow to allow the droplets to settle by gravity relative to the air flow through the scrubber, making the system very large.

[0005] To improve upon such systems, a compact system, disclosed in WO 2018 / 231105 and forming the basis of the present invention, proposes spraying an aerosol under high pressure into the exhaust gas stream and using centrifugal techniques to separate the droplets from the exhaust gas stream. This allows for the use of a smaller amount of water to obtain very small droplets with a larger total surface area that can react quickly with sulfur dioxide. In this case, the amount of water required to spray is only about 2.5-5% of the amount required in prior art systems, while maintaining separation effectiveness. Summary of the Invention

[0006] The object of the present invention is to further improve the methods and installations of the prior art generally, and in particular to make systems such as those disclosed in WO 2018 / 231105 better compliant with new requirements that do not allow emissions above those corresponding to 0.1% sulfur in diesel fuel.

[0007] According to one aspect of the invention, the method comprises: introducing a first liquid in the stream for evaporative cooling and saturation of the gas mixture; providing small droplets of a second liquid capable of absorbing and dissolving said gas, small enough not to settle by gravity and large enough to be centrifuged; spraying the small droplets into the stream to dissolve the gas in the droplets; centrifuging the small droplets from the stream; and Includes:

[0008] Although the present invention may be generally implemented in a variety of applications for removing any gas from a gas mixture stream, the present disclosure is particularly exemplified as applied above to removing sulfur dioxide from combustion exhaust gases, for example, from marine diesel engines. Examples of such various applications may be found in the following documents:

[0009] European Patent Application Publication No. 2499091, European Patent Application Publication No. 2747877, U.S. Patent No. 8444942, European Patent Application Publication No. 2298957, European Patent Application Publication No. 1524023, International Publication No. 2016 / 062731, European Patent Application Publication No. 3393625

[0010] Providing the liquid in two separate steps has the following advantages in general and in specific applications:

[0011] In the initial step of introducing the first liquid (e.g., water), evaporation leads to saturation and cooling of the high-temperature (e.g., 300-400°C) gas mixture (e.g., exhaust gas mixture), and saturation stops evaporation. Importantly, evaporation and saturation in the first liquid introduction step ensure that the small droplets of the second liquid maintain their size. Otherwise, as in the single spray step of WO 2018 / 231105, water would continue to evaporate from the droplets due to cooling, and control of droplet size would subsequently be lost. Therefore, saturation in the water introduction step effectively prevents evaporation from the droplets introduced in the spray step. Cooling is also advantageous in that typical centrifuges cannot withstand excessive heat.

[0012] The droplets of the second liquid are small enough not to settle by gravity and large enough to be centrifuged, so that the droplets of the second liquid are carried forward in the stream and separated from the stream in the centrifugation step.

[0013] The first liquid may be introduced by spraying small droplets of the first liquid into the stream, which provide rapid cooling and consequent saturation.

[0014] Small droplets of the first liquid can be formed by atomization with pressurized air using a two-fluid nozzle, or by atomization with high-pressure liquid atomization using a single-fluid nozzle. Two-fluid nozzles can be advantageous for producing very small droplets for the fastest possible cooling.

[0015] Small droplets of the second liquid can also be formed by atomization with pressurized air using a two-fluid nozzle, or by atomization with high-pressure liquid spray using a single-fluid nozzle. Single-fluid nozzles can be advantageous for producing more droplets per time unit, and as a result, fewer nozzles may be required.

[0016] Atomization of the liquid creates an aerosol with small droplets to provide a large total surface area, allowing for a short reaction time between the first and second liquids with little or no slowdown required for a given flow rate, especially in the case of diesel engine exhaust streams, resulting in rapid cooling and saturation of the vaporized water in the first step, neutralizing sulfur oxides with alkali in the droplets, which also allows the system to remain very compact.

[0017] By atomizing with pressurized air, the size of the droplets can be controlled by changing the flow rate of the air and the flow rate of the alkaline aqueous solution.

[0018] The droplet size can also be controlled by varying only the pressure of the pressurized air, which may be the case if the spray nozzle and alkaline solution flow rate are already determined.

[0019] The droplet size can be controlled to vary between about 20 and 200 μm, typically about 50 μm. Smaller droplets in the gas stream may pass through the separation step in an undesirable manner. The droplet size is more formally understood as the size of medium-sized droplets. For example, medium-sized droplets v50 is the volume of the droplet that is 50% of the v50 This means that the droplets have a diameter greater than 50 μm. v50 A typical distribution of droplets includes droplets between 20 and 130 μm (10% of the volume is droplets smaller than 20 μm, and 90% of the volume is droplets smaller than 130 μm).

[0020] Small droplets of the second liquid may be sprayed downstream of the spray of the first liquid into the stream, allowing time for the stream to become fully saturated.

[0021] The spray of aerosol droplets may be co-current with the flow of exhaust gases.

[0022] The first liquid may be water and the second liquid may be an alkaline aqueous solution.

[0023] The gas mixture may be a combustion exhaust gas and the gas being removed may be a gas containing sulfur oxides.

[0024] In particular, the gas mixture may be an exhaust gas stream from a marine diesel engine and the gas to be removed may be a gas containing oxides of sulfur.

[0025] The equipment for carrying out the method of the present invention is inserted into the exhaust flow path of the exhaust pipe for carrying out the method, and the equipment comprises a spray nozzle for water and a spray nozzle for an alkaline aqueous solution, and at least one centrifugal separator downstream of these spray nozzles in the flow. The spray nozzles comprise at least one water spray nozzle and at least one atomizing spray nozzle downstream of the at least one water spray nozzle in the flow for producing droplets of the alkaline solution.

[0026] The exhaust pipe may be the exhaust pipe of a marine diesel engine.

[0027] Atomization can also be achieved by a single-fluid high-pressure nozzle, but in one embodiment, at least one atomizing spray nozzle is a two-fluid (alkaline solution and pressurized air) nozzle. Such nozzles, not used in the prior art, can be selected and controlled to obtain the desired droplet size.

[0028] The installation may also comprise a control and drive unit capable of controlling the size of the droplets depending on the engine load during operation.

[0029] Other features and advantages of the invention may be apparent from the claims and the following detailed description. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a diagram illustrating an exemplary installation for treating exhaust gases from a marine diesel engine.

[0031] The drawings are generally illustrative in nature and therefore the scale, orientation, size, etc. of components relative to one another may not correspond to those of the actual installation.

[0032] Components having functions corresponding to each other may be designated by the same reference numerals. DETAILED DESCRIPTION OF THE INVENTION

[0033] Although the present invention may be implemented in other areas of gas processing, in the detailed description that follows the invention is implemented in a marine installation.

[0034] The marine installation 10 of Figure 1 is shown diagrammatically inserted in the path of the exhaust stream of an exhaust pipe 104 of a large diesel propulsion engine 102 of a vessel 100. The diesel fuel of the engine 102, which may be in the megawatt range, typically contains large amounts of sulfur, which contributes to the production of sulfur oxides (SO), such as SO, in the exhaust stream 106. x )

[0035] Generally, such an installation 10 for reducing sulfur oxides can be considered to consist of an atomizing section 20 and a centrifugal separation section 50 forming a continuous partition of the exhaust pipe 106. Atomizing fluid is supplied to the nozzles 32, 42 of the atomizing section 20 by a control and drive unit 80.

[0036] The spray section 20 is sequentially and continuously divided into a water spray section 30 and an alkaline solution spray section 40, each including a nozzle 32 and a nozzle 42, which may be arranged in a single or multiple circular arrays surrounding the exhaust stream. The water may be seawater 82, and the alkaline solution 84, such as sodium hydroxide (NaOH), may include seawater.

[0037] The nozzles 32 of the water spray section 30 may be of a single-fluid type, for example, as shown by the dashed lines in Figure 1, which utilizes the kinetic energy of pressurized water to break it into droplets and spray the water droplets into the exhaust stream 106. The water droplets cool the exhaust stream and vaporize in the exhaust stream, saturating the exhaust stream with water vapor. However, the nozzles 32 may also be of a two-fluid (two-phase) type, as shown by the solid lines in Figure 1.

[0038] Nozzle 42 of alkaline solution spray section 40 may similarly be of a single-fluid type, as shown in dashed lines in Figure 1, or in the embodiment shown in solid lines, nozzle 42 is shown as a two-fluid (two-phase) type, capable of atomizing the stream of liquid alkaline solution 84 into an aerosol of fine droplets by pressurized / compressed air and spraying the aerosol into steam-saturated exhaust stream 106. The enlarged, solid-circled area at the bottom of Figure 1 shows an external-mixing type two-fluid atomizing spray nozzle 42, although other types of two-fluid atomizing nozzles may be used as well.

[0039] Because the exhaust stream is already saturated with steam, the alkaline solution droplets maintain their size. The basic alkaline solution in the droplets reacts with and neutralizes the acidic sulfur oxides, turning them into salt and water in the droplets. This reaction can occur and be completed in reaction zone 62, which forms an interior space throughout separator section 50 and extends somewhat upstream throughout alkaline solution spray section 40.

[0040] The separation section 50 is provided with a plurality of centrifugal separators 52. As is apparent from the enlarged, circled area at the top of FIG. 1 , each separator 52 comprises a rotor 54, which in turn comprises a stack of closely spaced conical separating discs 56 (plural conical separating discs 56) projecting into the reaction section 62. The separators may also be of a more basic type, with radial vanes in the rotor instead of conical discs (not shown). Each separator 52 is of a counterflow type, i.e., the exhaust flow is radially inward (arrow P) through the gaps between the discs 56 relative to the pumping effect generated by the rotating rotor 52. Such rotor-type centrifugal separators 52 for centrifuging solid and / or liquid particles from a gas flow, such as crankcase gas, are known per se from the prior art, for example from WO 2012 / 052243.

[0041] Each separator rotor 54 further includes a fan 64 that rotates with the rotor 54. The fan 64 is disposed within a chamber 58 that is separate from and surrounds the separator section 68 of the reaction section 62 to enhance the flow of purified gas from the gas outlet 60 of the rotor 52 to the chamber 58 and then to the purified exhaust gas outlet 70. Optionally, instead of individual fans 64 for each separator 52, a common fan (not shown) may be disposed upstream or downstream of the reaction section 62 to feed the mixture of exhaust gas, water, and reaction products through the disk stack of the rotor 54 and discharge gas with reduced sulfur oxide content to the exhaust gas outlet 70. The separator rotors 54 are driven by individual electric motors 72 or by a common electric motor and belt transmission (not shown), similar to that shown in FIG. 2 of WO 2012 / 052243. The reaction section 62 has at least one outlet 74 for discharging the reaction products and liquid separated by the separator rotor 54. Different separator configurations similar to those described above and usable in the present invention are described in detail in the above-mentioned WO 2018 / 231105.

[0042] The control and drive unit 80 is shown in an exemplary and simplified manner. It operates as follows and is briefly configured as follows: A plurality of pumps 88 draw and pressurize seawater and alkaline solution from respective sources 82 and 84. A compressor 86 draws and pressurizes ambient air, which can be temporarily stored in an accumulator 92. A plurality of valves 90 distribute the respective pressurized fluids to the nozzles 32 and 42. A regulator 94 maintains pressure and / or flow setpoints. The settings of the valves 90 and regulators 94 are controlled by a control unit 96. The settings, such as liquid and air pressure settings for controlling droplet size, are controlled by the exhaust gas flow rate, which varies with engine load during operation of the vessel 100. The exhaust gas flow rate is obtained by a flow sensor 108 in the exhaust pipe 102.

[0043] The unit 80 may in particular be configured to control, in a manner known per se, the size of the droplets produced by a selected type of atomizing nozzle 42 by varying the speed of the air and liquid flow through the atomizing nozzle 42. Since the type of atomizing nozzle and the liquid flow rate are already determined, only the air pressure may need to be changed.

[0044] The foregoing detailed description has been given primarily for clarity of understanding, and no unnecessary limitations should be understood therefrom. Modifications will become apparent to those skilled in the art upon reading this disclosure, and may be made without departing from the spirit of the invention or the scope of the appended claims.

Claims

1. 1. A method for removing optional gases from a gas mixture stream, comprising: introducing a first liquid into said stream for evaporative cooling and saturation of said gas mixture; providing small droplets of a second liquid capable of dissolving the gas and of a size that will not settle by gravity and will be centrifuged; spraying the small droplets into the stream to absorb and dissolve the gas into the droplets; centrifuging the small droplets from the stream; and Including, the gas mixture is combustion exhaust gas; The method according to claim 1, wherein the first liquid is water and the second liquid is an alkaline aqueous solution.

2. 10. The method of claim 1, comprising introducing said first liquid by spraying small droplets of said first liquid into said stream.

3. 3. The method of claim 2, comprising forming small droplets of the first liquid by atomization.

4. 4. The method of claim 3, comprising producing atomization of the first liquid by pressurized air using a two-fluid nozzle or by high pressure liquid atomization using a single-fluid nozzle.

5. 5. The method of claim 4, comprising forming small droplets of the second liquid by atomization.

6. 6. A method according to claim 5, characterized in that the atomization of the second liquid is produced by pressurized air using a two-fluid nozzle or by high pressure liquid atomization using a single-fluid nozzle.

7. 7. The method according to claim 2, further comprising controlling the size of the droplets of the first liquid and the droplets of the second liquid to vary between 20 and 200 μm.

8. 8. A method according to any one of claims 2 to 7, characterized in that it comprises spraying droplets of the second liquid downstream of the spray of droplets of the first liquid into the stream.

9. 9. A method according to any one of claims 2 to 8, characterized in that it comprises spraying droplets of the second liquid co-currently with the flow.

10. 10. The method according to any one of claims 1 to 9, characterized in that the gas to be removed is a gas containing sulfur oxides.

11. 11. A method according to any one of claims 1 to 10, characterized in that the gas mixture is an exhaust gas stream from a marine diesel engine and the gases to be removed are gases containing oxides of sulfur.

12. 12. An installation (10) for carrying out the method according to any one of claims 1 to 11, which is inserted in the path of an exhaust flow of an exhaust pipe (104), comprising: spray nozzles (32, 42) for the water and the alkaline aqueous solution; at least one centrifugal separator (52) downstream of said spray nozzle in said flow; Equipped with The spray nozzle is at least one water spray nozzle (32); at least one atomizing spray nozzle (42) downstream of the at least one water spray nozzle (32) in the flow for producing droplets of the alkaline solution; An installation (10) comprising:

13. 13. The installation (10) according to claim 12, characterized in that the exhaust pipe (104) is the exhaust pipe of a marine diesel engine.

14. 14. The installation (10) according to claim 12 or 13, characterized in that the spray nozzle (32, 42) is a single-fluid nozzle or a two-fluid nozzle.

15. 15. The installation (10) of any one of claims 12 to 14, wherein the at least one atomizing spray nozzle (42) is oriented to spray co-currently with the flow and the at least one spray nozzle (32) is oriented to spray counter-currently with the flow.

16. 16. Installation (10) according to any one of claims 12 to 15, characterized in that it comprises a control and drive unit (80) capable of controlling the size of said droplets depending on the engine load during operation.

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