Method and installation for removing a gas from a flow of a gas mixture

Abstract

A method and installation for removing a gas from a flow of a gas mixture. A first liquid (82) is introduced in the flow (106) for evaporative cooling and saturation of the gas mixture. Small droplets of a second liquid (84) are provided which are capable of adsorbing and dissolving said gas and of a size small enough not to be sedimented by gravitation and big enough to be centrifugally separated. The small droplets are sprayed into the flow for adsorbing and dissolving said gas into the droplets, and the small droplets are centrifugally separated from the flow.

Claims

1. A method of removing a gas from a flow of a gas mixture, characterized by: introducing a first liquid in the flow for evaporative cooling and saturation of the gas mixture; providing small droplets of a second liquid capable of dissolving said gas and of a size small enough not to be sedimented by gravitation and big enough to be centrifugally separated; spraying the small droplets into the flow for adsorbing and dissolving said gas into the droplets; and centrifugally separating the small droplets from the flow, wherein the gas mixture is a combustion exhaust gas.

2. The method of claim 1, comprising introducing the first liquid by spraying small droplets thereof into the flow.

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

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

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

6. The method of claim 5, comprising generating the atomization of the second liquid by pressurized air using a two-fluid nozzle or by high-pressure liquid spray using a single-fluid nozzle.

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

8. The method of claim 2, comprising spraying the droplets of the second liquid downstream of spraying the droplets of the first liquid into the flow.

9. The method of claim 2, comprising spraying the droplets of the second liquid co-currently with the flow.

10. The method of claim 1, wherein the first liquid is water and the second liquid is an alkaline water solution.

11. The method of claim 1, wherein the gas to be removed is a gas comprising sulphur oxides.

12. The method of claim 1, wherein the gas mixture is an exhaust gas flow from a marine diesel engine and the gas to be removed is a gas comprising sulphur oxides.

13. The method of claim 1, wherein the first liquid and the second liquid are introduced by spraying small droplets thereof into the flow by atomization, generating said atomization by pressurized air using a two-fluid nozzle or by high-pressure liquid spray using a single-fluid nozzle and further comprising controlling the size of the droplets of the first and second liquids to vary between 20 and 200 μm.

14. An installation (10) to be inserted in a path of an exhaust flow of an exhaust pipe (104) for performing the method of claim 10, characterized by spray nozzles (32, 42) for the water and the alkaline water solution; and at least one centrifugal separator (52) downstream of the spraying nozzles in the flow; said spray nozzles comprising at least one water spray nozzle (32); and at least one atomizing spray nozzle (42) downstream of the at least one water spray nozzle (32) in the flow for producing the droplets of the alkaline solution.

15. The installation (10) of claim 14, wherein the exhaust pipe (104) is an exhaust pipe of a marine diesel engine.

16. The installation of claim 14 or 15, wherein the spray nozzles (32, 42) are single fluid nozzles or two-fluid nozzles.

17. The installation of claim 14, wherein the at least one spray nozzle (42) is oriented for spraying co-currently with the flow and the at least one spray nozzle (32) is oriented for spraying counter-currently with the flow.

18. The installation of claim 14, comprising a control and actuation unit (80) capable of controlling the size of the droplets in dependence of engine load during operation.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a view showing diagrammatically an exemplary installation for treatment of exhaust gases from a marine diesel engine.

(2) The drawing is generally of an explanatory nature, so that scale, orientation, size etc. of mutually related components may not correspond to those of a realized installation.

(3) Components having mutually corresponding functions may be designated with same numerals.

DETAILED DESCRIPTION

(4) While the invention may be practised in other fields of treating gases, in the following detailed description the invention is practised on a marine installation.

(5) The marine installation 10 of FIG. 1 is diagrammatically shown inserted in an exhaust flow path of an exhaust pipe 104 of a large diesel propulsion engine 102 of a marine vessel 100. Diesel fuel for engine 102 that may be in the megawatt range regularly contains large quantities of sulphur which are converted to sulphur oxides (SOx) such as SO.sub.2 in an exhaust flow 106.

(6) Generally, the installation 10 for reducing these sulphur oxides can be considered as composed of a spraying section 20 and a centrifugal separation section 50 forming serial partitions of the exhaust pipe 106. Spraying fluids are supplied to nozzles 32, 42 of the spraying section 20 by an actuation and control unit 80.

(7) Spraying section 20 is in turn serially partitioned into a water spray section 30 and an alkaline solution spray section 40 having the respective nozzles 32 and 42 that can be arranged in single or in one or more circular arrays surrounding the exhaust flow. The water may be sea water 82, and the alkaline solution 84, such as sodium hydroxide (NaOH), may contain sea water.

(8) The nozzles 32 in the water spray section 30 may be of a single-fluid type as indicated in phantom in FIG. 1, for example, capable of utilizing the kinetic energy of pressurized water to break it up into droplets and spraying the water droplets into the exhaust flow 106. The water droplets cool the exhaust flow and evaporate in the exhaust flow to saturate the exhaust flow with water vapor. They may likewise, however, also be of a two-fluid (two-phase) type, as indicated in full line in FIG. 1.

(9) While the nozzles 42 in the alkaline solution spray section 40 may likewise also be of the single-fluid type as illustrated in phantom in FIG. 1, in the shown full line embodiment they are shown as two-fluid (two-phase) type, capable of atomizing a flow of the liquid alkaline solution 84 into an aerosol of fine droplets by pressurized/compressed air and spraying the aerosol into the vapor-saturated exhaust flow 106. The enlarged encircled full line lower area of FIG. 1 shows a two-fluid atomizing spray nozzle 42 of external-mix type but other types of two-fluid atomizing nozzles may, however, likewise be used.

(10) The droplets of alkaline solution will keep their size as the exhaust flow is already saturated by vapor. The basic alkaline solution in the droplets will react with and neutralize the acid sulphur oxides into salt and water in the droplets. This reaction may take place and be completed in a reaction compartment 62 forming an inner space throughout the separator section 50 and extending upstream more or less throughout the alkaline solution spray section 40.

(11) The separation section 50 has a plurality of centrifugal separators 52. As apparent from the enlarged circular upper area of FIG. 1, each separator 52 has a rotor 54 with a stack of narrowly spaced conical separation discs 56 projecting into the reaction compartment 62. The separators may also be of a more basic type, having radial wings instead of conical discs (not shown) in the rotor. Each separator 52 is of a counter-current type, i.e. where the exhaust flow is radially inwards (arrows P) through the interspaces between the discs 56, against the pumping effect generated by the rotating rotors 52. Such rotor-type centrifugal separators 52 for centrifugal separation of solid and/or liquid particles from a flow of gas, e.g. crank case gases, are previously known per se from e.g. WO 2012/052243 A1.

(12) Each separator rotor 54 is further provided with a fan 64 which rotates together with the rotor 54. The fan 64 is located in a chamber 58 which is separate from and encloses a separator section 68 of the reaction compartment 62 for enhancing the flow of cleaned gas from gas outlet 60 of the rotors 52 to the chamber 58 and further to an outlet 70 of the cleaned exhaust gas. Optionally, instead of an individual fan 64 for each separator 52, a common fan (not shown) may be arranged upstream or downstream of the reaction compartment 62 for feeding the mixture of exhaust gases, water and reaction products through the disc stack of the rotors 54 and discharging the gas of reduced sulphur oxide content to the exhaust gas outlet 70. The separator rotors 54 are driven either by an individual electric motor 72 or by a common electric motor and a belt transmission (not shown), similar to what is shown in FIG. 2 of WO 2012/052243 A1. In the reaction compartment 62 there is at least one outlet 74 for discharging the reaction products and liquids separated-out by the separator rotors 54. Different separator arrangements similar to that described above and usable in the present invention are described in detail in the initially mentioned document WO2018/231105 A1.

(13) The control and actuation unit 80 is shown in an exemplary and simplified manner. Control and actuation unit 80 operates and is briefly configured as follows: Pumps 88 draw and pressurize sea water and alkaline solution from respective sources 82 and 84. A compressor 86 draws and pressurizes ambient air that can be temporarily stored in a pressure accumulator 92. Valves 90 distribute the respective pressurized fluids to the nozzles 32 and 42. Regulators 94 maintain set values of pressure and/or flow. Settings for 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 governed by the exhaust gas flow rate that varies in dependence of engine load during operation of vessel 100. Exhaust gas flow rate is obtained by a flow sensor 108 in the exhaust pipe 102.

(14) Unit 80 can be specifically configured to control the size of the droplets generated by a selected type of atomizing nozzles 42 by varying the rates of air and liquid flow therethrough in a manner known per se. With atomizing nozzle type and liquid flow rate already determined, only the air pressure may need to be varied.

(15) The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom. Modifications will become obvious 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.