APPARATUS FOR NITROGEN OXIDES REMOVAL BY OXIDATION WITH OZONE AND SCRUBBING OR ABSORBING THE REACTION PRODUCTS

Abstract

The present invention provides an apparatus for the treatment of exhaust gas from diesel engine or other combustion type processes, the apparatus comprising liquid and Ozone gas injection means (2) and (3) respectively, for delivering the liquid and Ozone gas into a pressurised exhaust gas stream pipe (1) when the diesel engine or other type internal combustion processes are in use. The liquid and the Ozone gas commingle as the liquid is reduced to a spray of very fine droplets in order to capture sub micron particulate materials before entering a shortened reaction/contacting chamber (4) where the contents undergo a phase change before exiting and entering a gas liquid separator (5) where the liquid droplets are separated from the treated particulate materials, which are subjected to a scrubbing regime in a downstream scrubber (11) before exiting the apparatus through an exit pipe (7). When in use, the apparatus uses the diesel engine or other combustion type process pressure to create high velocities and Reynolds numbers in the shortened reaction/contacting chamber (4) in which NOx is rapidly mixed and reacted with the injected Ozone gas and converted through to N.sub.2O.sub.5 and wherein the sub micron particulate materials, with condensed hydrocarbons, are simultaneously wetted and efficiently captured by the injected and finely sheared liquid droplets.

Claims

1. An apparatus for injecting liquid into a pressurised gas stream containing suspended solids in the form of fine particles as well as NOx vapours or gases, which apparatus comprises a gas-liquid-vapour contacting pressure duct (1) including a droplet generator (1a) comprising liquid introducing means (2), which lead into said duct (1) and terminate in one or more spray nozzles for producing a very fine spray of liquid droplets, the apparatus also comprising a droplet separator (5) where the liquid and the particulate laden exhaust gas are separated, the apparatus also comprising a scrubber/absorber (11) wherein the reacted gas product N.sub.2O.sub.5 is liberated from the surrounding carrier gas, characterised in that the apparatus further comprises means (3) for injecting Ozone gas into the pressure duct (1) and the pressurised gas stream contained therein when the apparatus is in use, the apparatus further comprising a combined atomising/reacting contacting chamber (4) in which injected liquid in very fine droplet form commingles with the Ozone gas as the liquid droplets collide with and capture the fine particulate solids suspended in the pressurised gas stream, which fine particles are removed in the droplet separator and the commingled Ozone gas passes through the droplet separator (5) whereafter the N.sub.2O.sub.5 reaction product enters the scrubber (11) whereat, when the apparatus is in use, the pressurised gas is freed of any N.sub.2O.sub.5 and residual droplets before passing to atmosphere through an outlet (7).

2. An apparatus as claimed in claim 1, characterised in that the liquid spray is directed co-currently with the Ozone into the pressurised gas stream.

3. An apparatus as claimed in claim 1, characterised in that the droplets in mist form have a diameter in the range of 10 to 300 by maintaining the liquid to gas ratio between 0.15 and 2.0 litre/m3.

4. An apparatus as claimed in claim 3, characterised in that the liquid to gas ratio is preferably maintained between 0.2 and 1.2 litres/m3.

5. An apparatus according to claim 1, characterised in that the liquid is one or more of town water, rainwater, river water, seawater, domestic or industrial wastewater.

6. An apparatus according to claim 1, characterised in that the chamber (1) at the liquid introducing means (2) is circular, ellipsoidal, square or rectangular.

7. An apparatus according to claim 1, characterised in that the duct (1) incorporating the chamber (1a) is straight, curved, rounded, bent, tapered or in a full or partial vena contracta, i.e. reducing then opening.

8. An apparatus according to claim 7, characterised in that the chamber (1a) includes a venturi section, one or more orifice plates or other pressure loss generating restriction.

9. An apparatus according to claim 1, characterised in that the value of the square root of the product of the chamber (4) gas velocity U.sub.g and its length L (UgL).sup.0.5 lies between 0.2 and 20.0 and preferably lies between 1.5 and 15.0.

10. An apparatus according to claim 1, characterised in that the molar ratio of the injected Ozone as compared to the total NOx (NO+NO.sub.2) gas is at least 1.2:1 and is preferably greater that 1.5:1.

11. An apparatus according to claim 1, characterised in that the residence time of the gas does not exceed 200 milliseconds and where the L/d, i.e length to diameter, ratio of the chamber (4) lies between 1.0 and 20.0 and more preferably between 2.0 and 8.0.

12. An apparatus according to claim 1, characterised in that a re-circulating system including one or more pumps (8, 8a) are provided to re-circulate the liquid from the separator (5) to the liquid injecting means (2).

13. An apparatus according to claim 12, characterised in that the re-circulating system includes one or more filters (9, 9a) for the removal of particulates from the liquid before it returns to the water storage tank (10) for

Description

[0055] There now follows, by way of example, a detailed description of the present invention, which description is to be read with reference to the accompanying drawings in which:

[0056] FIG. 1 illustrates a block diagram of the present invention;

[0057] FIG. 2 is a side elevation of a contacting chamber of the present invention; and,

[0058] FIG. 3 is a plan elevation of the contacting chamber of FIG. 2.

[0059] The present invention, see FIG. 1, provides a mist injector apparatus for the treatment of exhaust gas from a diesel or internal combustion engine and generally comprises an exhaust pipe 1 for conveying the exhaust gas from the engine, not shown, a duct la leading to a combined atomising/reacting or contacting chamber 4, hereinafter referred to as the contacting chamber 4, a gas/liquid separator 5, a water storage tank 10 and a scrubber 11 that leads to an outlet 7 for the treated gas.

[0060] The present invention also comprises an Ozone generator 13 connected to the exhaust pipe 1 by a feed pipe 13a and by a pipe 13b to the scrubber 11, see FIG. 1. The pipe 13a terminates in an Ozone injecting tube, not shown, located within the exhaust pipe 1.

[0061] The water storage tank 10 is connected by a pipe 10a to the exhaust pipe 1 at a point downstream from the Ozone injecting tube and upstream of the contacting chamber 4 by a pipe 10a, which terminates in a water injecting tube, not shown, located within the exhaust pipe 1. The pipe 10a is provided with a pump 8 and filters 9 for the delivery of clean water to the water injecting tube within the exhaust pipe 1 as aforesaid.

[0062] The contacting chamber 4 is provided by an elongate tubular member 4a having dimensions of length to diameter ratio L/d of between 1.0 and 20.0 and a preferred range of 2.0 to 8.0 across the full design range and operating spectrum. The tubular member 4a of the contacting chamber 4 is connected at a downstream end thereof to the gas/liquid separator 5, see especially FIGS. 2 and 3.

[0063] The gas/liquid separator 5, which is generally as described and shown in Applicants European Patent No. EP1787016B, is connected downstream to the scrubber 11 by a pipe 5a, see FIG. 1. The gas/liquid separator 5 is also connected by a return pipe 6 for spent water that is fed back to the water storage tank 10 by a pump 8a and through filters 9a provided along the return pipe 6 between the gas/liquid separator 5 and the water storage tank 10, see FIG. 1.

[0064] When the mist injector apparatus of the present invention is in use for the treatment of exhaust gas emitted from a diesel or an internal combustion engine, Ozone is delivered from the Ozone generator 13 via the pipe 13a to be injected into the exhaust pipe 1 through one or more Ozone injection nozzles, not shown, located within the exhaust pipe 1. Concomitantly therewith, liquid, i.e. water is fed by the pump 8 from the water storage tank 10 through the pipe 10a and the filters 9 into the exhaust pipe 1 through one or more liquid injection nozzles, not shown, located within the exhaust pipe 1 downstream of the Ozone injection nozzles.

[0065] The liquid injection nozzles provide a fine spray of very small water droplets that co-mingles with the Ozone from the Ozone injecting nozzles to capture small particulate materials that are carried by the exhaust gas, the size of which particulate materials are usually in the 0.02-0.3 micron (um) size range, which particulate materials are often coated with condensed hydrocarbons that are emitted simultaneously along with the exhaust gas.

[0066] Thus the exhaust gas co-mingled with the Ozone and the very fine water droplets enter the compacting chamber 4 wherein, because of the length to diameter size ratio of the chamber, the Ozone gas reacts with NOx to rapidly produce water absorbable N.sub.2O.sub.5.

[0067] The treated particulate materials pass from a downstream end of the compacting chamber 4 and into the gas/liquid separator 5 where the water is drained off at a lower portion of the separator and into the pipe 6 to be fed by the pump 8a through the filter 9a back to the water storage tank 10 to be re-circulated through the system.

[0068] From the gas/liquid separator 5, the rapidly generated N.sub.2O.sub.5(g) is conveyed through the pipe 5a to the Turboscrubber where the N.sub.2O.sub.5(g) is removed leaving the treated exhaust gas to exit to atmosphere through the outlet pipe 7.

[0069] The pumps 8 and 8a are electrically driven and powered by the vehicle electric power if mounted on a train or ship.

[0070] The filters 9 and 9a are easily cleaned or readily replaced every 3 to 6 months if necessary. Likewise, the water storage tank 10 is equipped with suitable connections for ease of filling, draining and cleaning.

[0071] Modifications to the mist injector apparatus is envisaged to be within the scope of the Claims appended hereto.

[0072] For example: [0073] 1. The subject apparatus is effective in separating PM/HC from NOx, via N.sub.2O.sub.5 product removal to the benefit of allowing a cleaner formation of recoverable HNO.sub.3 product. [0074] 2. The apparatus may also be used for either NOx or PM/HC removal on their own, from industrial emissions, in cases where only one pollutant is present, for example, low NOx boilers still generate PMs and HCs. [0075] 3. The liquid used in the subject apparatus may also include oils and aqueous reagents.