METHOD AND SYSTEM FOR THE REMOVAL OF PARTICULATE MATTER AND HEAVY METALS FROM ENGINE EXHAUST GAS

Abstract

Method and system for removal of soot, ash and heavy metals, and optionally additionally NOx and SOx being present in exhaust gas from an engine operated on heavy fuel oil.

Claims

1. A method for removal particulate matter, hydrocarbons, and heavy metals being present in exhaust gas from an engine operated on heavy fuel oil, comprising the steps of operating the engine at a load to obtain an exhaust temperature of the exhaust gas of at least 325 C.; passing the exhaust gas at exhaust gas temperatures of 325 C. to 550 C. through the at least one filter unit each comprising at least one particulate filter and capturing the particulate matter and heavy metals contained in the exhaust gas; continuously burning the captured soot and adhered hydrocarbons off the at least one particulate filter by contact with a catalyst being arranged on the particulate filter; periodically disconnecting the at least one filter unit from flow of the exhaust gas; applying a pneumatic pulse at the outlet of the at least one particulate filter by pulse injecting air into the outlet in reverse to the previous flow of the exhaust gas and blowing off the captured particulate matter together with the heavy metals from the at least one particulate filter; applying suction at inlet of the at least one particulate filter; and conveying the blown off particulate matter and heavy metals from the at least one particulate filter, optionally through an external auxiliary filter unit, to a container.

2. The method of claim 1, wherein the at least one particulate filter is in form of a wall flow filter.

3. The method of claim 2, wherein the catalyst is coated on or inside the walls of the at least one particulate filter.

4. The method of claim 1, wherein the catalyst comprises of titanium dioxide, oxides of vanadium and tungsten and metallic palladium.

5. The method of claim 1, wherein body of the at least one particulate filter is prepared from silicon carbide, cordierite, mullite, aluminium titanate or sintered metal.

6. The method of claim 1, wherein the air is pulse injected with injection pulse duration of between 10 and 600 msec, preferably 300 msec.

7. The method of claim 1, wherein the air for pulse injection is withdrawn from an accumulator tank with compressed air at a pressure 4 to 10 bar abs, preferably 6.5 bar abs.

8. The method of claim 1, wherein the at least one filter unit is arranged in a pressure vessel upstream an engine turbocharger.

9. The method of claim 8, wherein the exhaust gas is passed through the at least one filter unit at a pressure of between 0 and 3 bar abs.

10. The method according to claim 1, comprising the further step of selective catalytic reduction of nitrogen oxides in the exhaust gas prior to the gas is passed through the at least one filter unit or after the gas has passed through the at least one filter unit.

11. The method according to claim 1, comprising the further step of reducing amounts of sulphur oxides contained in the exhaust gas by scrubbing the gas with an alkaline solution or sea water in an open or closed loop, downstream of the at least one filter unit.

12. A system for removal of particulate matter comprising soot, ash and heavy metals being present in exhaust gas from an engine operated on heavy fuel oil comprising one or more exhaust gas inlet pipes connecting each the engine with inlet of each of one or more filtration units; one or more exhaust gas outlet pipes connected to outlet of each of the one or more filtration units; arranged within the one or more filtration units at least one particulate filter catalyzed with a catalyst for effectuating burning off of soot and hydrocarbons; an air pulse jet arrangement mounted at the outlet of the at least one particulate filter for blowing off the particulate matter collected at the at least one particulate filter; and the air pulse jet arrangement comprises one or more air blow pipes connected to an air supply, nozzles in the air blow pipes and an eductor arranged at the outlet of the at least one particulate filter for pulse injection of air into the at least one particulate filter; and a suction pipe installed close to the inlet of the least one particulate filter, the suction pipe being connected to a suction source.

13. The system of claim 12, wherein the at least one particulate filter is in form of a wall flow filter.

14. The system of claim 13, the at least one particulate filter is coated on walls or inside walls with a catalyst catalysing burning of captured soot of the filters.

15. The system of claim 12, wherein the catalyst consists of titanium dioxide, oxides of vanadium and tungsten and metallic palladium.

16. The system according to claim 12, wherein body of the at least one particulate filter is prepared from silicon carbide, cordierite, or mullite or aluminium titanate or sintered metal.

17. The system of claim 12, wherein the one or more air blow pipes are connected to an accumulator tank with compressed air.

18. The system of claim 12, wherein the one or more filtration units are arranged in a pressure vessel upstream an engine turbocharger.

19. The system of claim 12, wherein the one or more filtration units are arranged downstream an engine turbocharger.

20. The system of claim 12, wherein the one or more exhaust gas outlet pipes connect the one or more filtration units to a downstream selective catalytic reduction unit comprising a denitrification catalyst.

21. The system of claim 12, wherein the one or more exhaust gas inlet pipes connect the one or more filtration units to an upstream selective catalytic reduction unit comprising a denitrification catalyst.

22. The system of claim 12, wherein the one or more exhaust gas outlet pipes connect the one or more filtration units to a scrubber unit.

23. The system of claim 12, wherein a selective catalytic reduction unit comprising a denitrification catalyst unit is connected upstream to the one or more filtration units and downstream to a scrubbing unit.

24. The system of claim 20, wherein the selective catalytic reduction unit is arranged upstream or downstream an engine turbocharger

25. The system of claim 12, further comprising a by-pass pipe by-passing the exhaust gas at least one of the one or more filtration units.

26. The system of claim 12, further comprising one or more auxiliary filter units connected to the suction pipe.

27. The system of claim 12, wherein the air pulse jet arrangement further comprises an isolation valve at outlet of the at least one particulate filter.

28. The system of claim 12, wherein the suction pipe connects an exhaust gas inlet side of the filter unit/s or the particulate filter/s with an exhaust gas outlet side from the filter unit/s or the particulate filter/s.

Description

[0068] A more detailed description of the method and system is apparent from the following description of a specific embodiment with reference to the drawings in which

[0069] FIG. 1 shows a schematic flow sheet of the method and system according to the invention; and

[0070] FIG. 2 is en exploded view of the cleaning arrangement and the valve and nozzle configuration arranged at outlet of a particulate filter.

[0071] Referring now to FIG. 1, the system for use in the method according to an embodiment of the invention comprises a filtration unit 4 connected at outlet via exhaust turbine 12 of a turbocharger 10 to an SCR unit 6. SCR unit 6 is connected to SO.sub.xscrubber 8.

[0072] The filtration unit 4 is divided by a wall 14 into an exhaust gas inlet section 4a and a filtrated exhaust gas outlet section 4b. The unit 4 comprises three particulate filters 16 a,b,c.

[0073] The particulate filters are modular and spaced apart arranged in unit 4, which allows individual regeneration or replacing of spent filters as described below.

[0074] Outlets 18 a, b, c of the particulate filters are lockable and connected to pulse jet cleaning valves 20 a, b, c. The cleaning valves can lock the outlet of the filters sequentially or all at once after a predetermined time on stream or otherwise determined, e.g. by the pressure drop created over the filters. The jet cleaning valves may be connected to an accumulator tank with compressed air (not shown)and provide a pressurized and pulsed air stream with a duration as disclosed above in reverse flow to the previous exhaust gas flow through filters 16a,b,c. By these means, ash and remaining amount of soot together with heavy metals accumulated in the filters are blown off to a discharge sluice 22. During regeneration of filters 4 a,b,c, exhaust gas flow to the actual filtration units, unit 4 in FIG. 1 is disrupted by means of valve 30 and the gas is by-passed to another filtration unit (not shown).

[0075] The filtration unit 4 is connected to a downstream air compressor 24 of a turbocharger 10 via the engine 2 by an exhaust gas pipe 26. The advantage of such a configuration is described hereinbefore.

[0076] When connected upstream of turbocharger air compressor 24, it is preferred to arrange the filtration unit 4 within a pressure vessel 28 in order to allow the filtration unit to better utilize the pressure drop gain with the same soot load obtained by the pressurized engine exhaust gas. The soot combustion increases with higher temperature that is always present upstream a turbocharger and may eliminate support heating.

[0077] The filtrated exhaust gas is passed from filtration unit 4 in line 32 via exhaust turbine 12 of turbocharger 10 to SCR catalyst unit 6. Prior to be introduced into unit 6, urea is injected into the gas as reductant for the SCR of nitrogen oxides. The SCR reaction and catalysts for use in the reaction are widely disclosed and known in the art and need no further description.

[0078] Finally, the SCR treated exhaust gas in pipe 34 is passed to scrubber unit 8 for the removal of SO.sub.x. In unit 8 the exhaust gas is scrubbed with a diluted alkaline solution, e.g. an aqueous solution of sodium hydroxide wherein the SO.sub.x are converted to sodium sulphite and/or sodium sulphate dissolved in the scrubber solution. The pH value of spent scrubber solution can easily be adjusted to a value around 7 and because heavy metals, soot and ash have been removed from the exhaust gas prior to scrubbing it is possible to distribute spent scrubber solution into the environment with negligible risk thus fulfilling foreseen IMO regulations.

[0079] The thus cleaned exhaust gas is withdrawn from scrubber unit 8 and passed in pipe 36 to an exhaust stack (not shown).

[0080] FIG. 2 is an exploded view of an air pulse jet valve arrangement 20 connected to outlet 18 of the particulate filters 16, shown in FIG. 1.

[0081] The air pulse jet valve arrangement 20 according to an embodiment of the invention comprises air blow pipes 21a and 21b with air nozzles (not shown) at outlet of the pipes. The air blow pipes are connected through pipe 23 to a pressurized air supply from a compressed air tank (not shown). Valve arrangement 20 comprises further an isolation valve 25 at outlet 18 of a filtration unit 4. The filtration unit 4 is provided with two filters 16a and 16b with outlet pipes 19a and 19b, respectively. The outlet pipes are in form of eductors.

[0082] During filtration operation, the outlet 18 is open and filtered exhaust gas leaving filters 16a and 16b from outlet pipes 19a and 19b is withdrawn through outlet 18.

[0083] In regeneration mode as shown in FIG. 2, outlet 18 is locked by isolation valve 25 and pressurized air from pipe 23 is passed sequentially to air blow pipes 21a and 21b and pulse injected into eductors 19a and 19b, respectively. The air pulse injected into filters 16a and 16b in reverse to the previous exhaust gas flow causes ash and remaining amounts of soot accumulated in the filters to peel off from the filter surface and then being blown to a perforated grid 23a and 23b close to the outlet of filter 16a and 16b. The blown off particulate matter is sucked through the grids to suction pipe 22 connected to grids 23a and 23b. Suction pipe 22 is connected to a vacuum pump (not shown) establishing a sufficient suction pressure in the line to suck the particulate matter through an external filter 24. Captured particulate matter is removed from filter 24 and conveyed to a disposal container 26.

[0084] In FIG. 2, filter 16a is under regeneration. An air pulse 27 is injected through air blow pipe 21a into eductor 19a in outlet of filter 16a for about 300 msec. Particulate matter 28 is hereby blown off from filter 16a and collected on grid 23a facing the outlet of filter 16a. During the air pulse or after the finished air pulse, suction is applied in line 22 and the collected particulate matter on grid 23a is sucked in line 26 through auxiliary filter 27 and captured. The captured particulate matter is disposed to container 22.