Method and system for the removal of particulate matter from engine exhaust gas or process equipment

Abstract

Method and system for removal of particles such as soot, ash and heavy metals, and optionally additionally NO.sub.X and SO.sub.X being present in exhaust gas from an engine or process equipment.

Claims

1. Method for removal of soot, hydrocarbons, ash and heavy metals being present in exhaust gas from an engine or process equipment, comprising the steps of: passing the exhaust gas at exhaust gas temperature through at least one filtration unit, each comprising at least one particulate filter and capturing particles, soot, ash and heavy metals contained in the exhaust gas, wherein the at least one filtration unit is arranged in a pressure vessel upstream or downstream an engine turbocharger or a cement production process; continuously burning the captured soot and adhered hydrocarbons off the at least one particulate filter by contact with a catalyst being arranged on the filter; periodically opening at least one particle discharge valve in a particle discharge valve arrangement comprising a particle collector mounted at each of the inlets for the filtration units; subsequently pulse injecting air into the outlet of at least one of the filtration units in reverse to the previous flow of the exhaust gas and blowing the particles off the at least one particulate filter; closing the at least one particle discharge valve; and subsequently repeating the reverse pulse process for all the one or more filtration units without shutting off said filtration units from the exhaust gas.

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, and wherein the particle discharge valve is opened between 1 and 5 sec before the injection pulse duration and closed between 2 and 15 sec after the injection pulse duration.

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 barg.

8. The method of claim 1, wherein the exhaust gas is passed through the at least one filtration unit at a pressure of between 0 and 3 barg.

9. The method of 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 filtration unit or after the gas has passed through the at least one filtration unit.

10. 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 filtration unit.

11. The method according to claim 1, wherein the exhaust gas temperature of the exhaust gas which is passed through the at least one filtration unit is kept in the temperature range of 380 C.-420 C. to avoid that any particles, soot, ash and heavy metals contained in the exhaust gas are fixed too hard to said filtration unit for the reverse pulse to remove them.

12. Filtration assembly for removal of particles of soot and ash present in exhaust gas from an engine or process equipment, comprising: one or more exhaust gas inlet pipes connecting each the engine or process equipment with the inlet of each of one or more filtration units, wherein the one or more filtration units are arranged in a pressure vessel upstream or downstream an engine turbocharger or a cement production process; one or more exhaust gas outlet pipes in fluid communication with the outlet of each of the one or more filtration units; at least one particulate filter catalyzed with a catalyst for effectuating burning off of soot with adhered hydrocarbons connected in parallel within the one or more filtration units; an air pulse jet valve arrangement mounted at the outlet of the one or more filtration units for pulse cleaning, blowing off ash from the at least one particulate filter, where the air pulse jet valve arrangement comprises one or more pulse valves, one or more air blow pipes connected to an air supply and nozzles in the blow pipes for pulse injection of air through the nozzles in the blow pipes into the at least one particulate filter; and a particle discharge valve arrangement mounted at the inlet of the one or more filtration units, for collecting soot and ash from the at least one particulate filter during air pulse cleaning, said particle discharge valve arrangement comprising one or more particle discharge valves, one or more dust discharge pipes and one or more particle collectors mounted at the exhaust gas inlet of the one or more filtration units.

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

19. 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.

20. 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.

21. 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.

22. The system of claim 12, wherein the selective catalytic reduction unit is arranged upstream or downstream an engine turbocharger.

23. 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.

24. The system of claim 12, wherein a heat exchanger is arranged up-stream the one or more filtration units to ensure that the exhaust gas temperature of the exhaust gas which is passed through said filtration units is kept below 420 C.

Description

(1) A more detailed description of the method and system will be apparent from the following description of a specific embodiment with reference to the drawings in which

(2) FIG. 1 shows a schematic flow sheet of the method and system according to the invention between cleaning pulses; and

(3) FIG. 2 shows a schematic flow sheet of the method and system according to the invention during a cleaning pulse.

POSITION NUMBERS

(4) 01. Filtration assembly 02. Filtration unit with particulate filter(s). 03. Blow pipe nozzles. 04. Air pulse jet valve arrangement. 05. Particle discharge valve arrangement. 06. Particle collector. 07. Exhaust gas inlet pipe. 08. Exhaust gas outlet pipe.

(5) Referring now to FIG. 1, a filtration assembly is shown having three filtration units 02 with particulate filters mounted inside. Exhaust gas with particles from an engine or other process is led to the filtration assembly by the exhaust gas inlet pipe 07. Within the housing of the assembly, the exhaust gas flows through all three of the filtration units, where the particle filters retains the particles. The cleaned exhaust gas flows out of the filtration units and exits the filtration assembly by the exhaust gas outlet pipe 08.

(6) As the particles build up during operation, the pressure loss through the particle filters increases and they need to be cleaned. This is done by shortly providing a back flush of air at a pressure high enough to provide a pulse through the particle filters in opposite direction of the exhaust gas flow. The cleaning back flush is provided to one filtration unit at a time in a cycle.

(7) The cleaning pulse is provided by an air pulse jet valve arrangement 04, which has a blow pipe nozzle 03 mounted near or at the exit of each filtration unit, pointed in a direction towards the particle filters in reverse direction of the exhaust gas flow. The blow pipe nozzles are connected via piping to pulse valves which controls the air pulse cycle. One valve at a time opens in a short time for the flow of cleaning air back through the one or more particle filters in each of the filtration units one by one.

(8) The particles which are released from the particle filters during each cleaning incident in the cycle is collected and extracted from the filtration assembly by particle collectors 06 which are mounted near or at the inlet of the filtration units, at least one for each filtration unit. All the particle collectors are connected by piping to the particle discharge valve arrangement 05, which conveys the particles from the filtration assembly and out to a separate container (not shown) which may have a further auxiliary filter mounted (not shown). The particle discharge valve arrangement also operates in a cycle, which is related to the air pulse cleaning cycle. I.e. before a jet pulse is blown through one of the filtration units, the particle valve connected to the particle collector of the same filtration is opened. A relative higher pressure within the filtration assembly than in the particle discharge valve arrangement provides a flow of gas from the filtration assembly and out through the opened particle collector. Shortly after a particle collector is opened and an outflow of gas is obtained through said particle collector, the related pulse valve is opened and the cleaning air pulse jet is provided to the related filtration unit, as seen on FIG. 2. In the embodiment shown in FIG. 2 the pressure difference between the filtration assembly and the particle discharge valve arrangement is 30 mbar, which drives the outflow of gas from the filtration assembly through the opened particle collector, the connected piping and further out through the opened particle discharge valve. As the particle collector is connected near or in the inlet opening of the filtration unit, the released particles due to the air jet pulse is conveyed to and through the particle collector due to the out-flow driven by the pressure difference.

(9) As seen on FIG. 2, and essential for the invention, the exhaust gas continues to flow through the filtration assembly unhindered by the cleaning pulse, since the pulse flow is relative small compared to the total exhaust gas flow. Therefore no valves are needed to shut-off the filtration unit during pulse cleaning, it is momentarily by-passed by the exhaust gas stream due to the local pressure difference. This makes the lay-out of the filtration assembly more simple than known systems, and also renders the filtration assembly more compact, since no extra filter capacity is needed during the short back-pulse cleaning cycle, which may last only a few seconds or less than a second. To avoid that particles, soot, ash or the like contained in the exhaust gas which is passed through the one or more filtration units are fixed too hard to the filters it may be necessary to keep the exhaust gas temperature below 460 C. or preferably in the range of 380 C.-420 C. Otherwise said particles may melt or burn and thereby fix so hard to the filters that the reverse pulse flow through the filters is not able to remove the particles sufficiently to keep a base pressure drop over the filters, depending on the composition of the fuel.

(10) It may be advantageous to install a heat exchanger upstream the one or more filtration units to ensure a sufficiently low exhaust gas temperature up-stream the filtration units.

EXAMPLES

(11) The purpose of this test was triggered by a severe observation made on Queen Victoria where the reactor by mistake was exposed to a temperature close to 480 C. This generated a high dP across the BMC-101WF filter due to deposits of a white/yellow metal sulfate ash compounds found on the inlet surface inside the channels. This ash was difficult to remove by reverse air pulsing as the ash was stuck to the filter surface probably due to melting at this high temperature.

(12) Especially sulfate compounds of vanadium, nickel and sodium were identified to have low melting ash phases. To reproduce these conditions and find a reliable temperature process window, metal additives of V, Na and S were added to MGO during these tests. The pressure-drop was measured at 400-420-440-460 and 480 C. (graph 7). During these different test conditions no un-expected increase in pressure drop has been observed. But at the inlet temperature 480 C. some white/yellow deposits was found on the filter connected to the SO 2/SO 3 sampling probe, which indicate the same ash deposits as seen on Queen Victoriathe oil contained 66 ppm V, 36 ppm Na, 31 ppm Ni and 2.52% S at this temperature. At the lower temperatures 400-460 C. black ash was found on inlet filter sample as expected indicating an unmelted ash with a carbon rest.