Exhaust Gas Treatment

Abstract

A device 1 , capable of being placed in-line in the exhaust conduit of an IC engine upstream of an SCR catalyst, which produces a gaseous hydrolysis product, containing ammonia, which is added to the exhaust gas in a controlled manner to pass therewith through the SCR catalyst to reduce the NOx content of the exhaust gas. The device 1 has an inlet 2 and an outlet 3 for the exhaust gas flowing therethrough and comprises an outer body 4 , which forms a pressure barrier, and passing through the outer body 4 is an inner body 5 which comprises a flowpath longitudinally therethrough from the inlet 2 to the outlet 3 . The device 1 is split into two sections, a reactor section with an inlet for pressurised aqueous urea and comprising an upper and lower area connected by a plurality of tubes 10 which pass through the exhaust gas for heat exchange and wherein the hydrolysis of urea occurs at elevated temperature and pressure and a reservoir section connected to the reactor section via a pressure release valve to allow the gaseous hydrolysis product to pass from the reactor to the reservoir. The device further comprises a valve 17 for dosing the gaseous hydrolysis product into the exhaust gas.

1 . A unitary device for generating and feeding gaseous hydrolysis product comprising ammonia, formed by the hydrolysis of an aqueous solution of urea (as hereinbefore defined) at elevated temperature and pressure, into the exhaust gas of an IC engine as it flows through the exhaust system of the engine to an SCR catalyst, the device being adapted to be placed in the exhaust system so that the exhaust gas will flow through it during use, and comprising
 a) a housing having an inlet for the exhaust gas and an outlet for the exhaust gas;   b) a reaction vessel located at least partially within the housing between the inlet and the outlet for containing an aqueous solution of urea and arranged such that, in use, the vessel and therefore the urea solution become heated by means of heat exchange with the exhaust gas as it flows from the inlet to the outlet;   c) a urea solution inlet to the reaction vessel and a gaseous hydrolysis product outlet from the reaction vessel;   d) a reservoir for receiving and storing gaseous hydrolysis product;   e) a valve in the outlet from the reaction vessel and adapted to permit the contents of the reaction vessel, in use, to attain an elevated pressure as it becomes heated, and periodically to discharge gaseous hydrolysis product into the reservoir; and   f) a conduit for interconnecting the reservoir and the exhaust system, the conduit including a valve to selectively control the feed of hydrolysis product stored in the reservoir into the exhaust gas via the conduit.   
   
   
       2 . The device according to  claim 1  wherein the valve in the outlet is placed at least partially outside the housing such that it is at least partially protected from direct exposure to the hot exhaust gasses 
   
   
       3 . The device according to  claim 1  wherein the conduit for interconnecting the reservoir and the exhaust system is placed at least partially outside the housing such that it is at least partially protected from direct exposure to the hot exhaust gasses 
   
   
       4 . The device according to  claim 1 , wherein the valve in the outlet actuates in response to the pressure within the reaction vessel. 
   
   
       5 . The device according to  claim 4  wherein the valve in the outlet is a mechanical back pressure valve and allows excess gas to pass through once the pressure within the reaction vessel exceeds a specific predetermined pressure. 
   
   
       6 . The device according to  claim 4  wherein the valve in the outlet is actuated via a control system in response to a signal received from a pressure transducer situated in the reaction vessel indicating the pressure therein is above a specific value. 
   
   
       7 . The device according to  claim 1 , wherein the valve in the outlet is actuated via a control system in response to a signal received from a temperature sensor situated in the reaction vessel indicating the temperature of the aqueous solution of urea therein is above a specific value. 
   
   
       8 . The device according to  claim 1 , further comprising an SCR catalyst within the unitary device. 
   
   
       9 . The device according to  claim 8  wherein the downstream end of the SCR catalyst is coated with a catalyst that converts any un-reacted ammonia in the exhaust gas into harmless gasses such that ammonia is not released into the environment. 
   
   
       10 . The device according to  claim 1 , wherein the gaseous hydrolysis product is introduced substantially on the axis of the exhaust gas flow path substantially perpendicularly to the direction of the exhaust gas flow. 
   
   
       11 . The device according to  claim 10  wherein a number of radially spaced inlets are situated adjacent to one another substantially perpendicularly to the flow. 
   
   
       12 . The device according to  claim 1 , wherein the point of introduction of the gaseous hydrolysis product is substantially at the mouth of a truncated conical section of the flowpath and the flow of exhaust gas and gaseous hydrolysis product into the cone induces mixing. 
   
   
       13 . The device according to  claim 1 , wherein the flowpath between the point of introduction of the gaseous hydrolysis product and the SCR catalyst has at least one substantially 90 degree bend therein causing turbulence in the flowpath. 
   
   
       14 . The device according to  claim 1 , further comprising a substantially cylindrical vortex chamber, upstream of the SCR catalyst, wherein the exhaust gas and gaseous hydrolysis product enter the vortex chamber substantially perpendicularly to its radius and exit the chamber along its central axis, the vortex within the chamber further inducing mixing of exhaust gas and gaseous hydrolysis product. 
   
   
       15 . The device according to  claim 1 , further comprising an oxidation catalyst within the single unit and through which the exhaust gas flows prior to introduction of the gaseous hydrolysis product. 
   
   
       16 . The device according to  claim 1 , further comprising a diesel particulate filter and through which the exhaust gas flows prior to introduction of the gaseous hydrolysis product. 
   
   
       17 . The device according to  claim 1 , further comprising: an oxidation catalyst within the single unit and through which the exhaust gas flows prior to introduction of the gaseous hydrolysis product; and
 a diesel particulate filter and through which the exhaust gas flows prior to introduction of the gaseous hydrolysis product, wherein the diesel particulate filter is upstream of the oxidation catalyst   
   
   
       18 . A device according to  claim 1 , further comprising a NO x  sensor placed within the exhaust gas flow to measure the quantity of NOx therein. 
   
   
       19 . The device according to  claim 18  wherein the NOx sensor is placed in the exhaust flow upstream of the point of introduction of the gaseous hydrolysis product and the signal is used to predict the required volume of the gaseous hydrolysis product required to be dosed into the gas to effect its removal. 
   
   
       20 . The device according to  claim 18  wherein the NOx sensor is placed in the exhaust flow downstream of the SCR catalyst and a greater or lesser amount of gaseous hydrolysis product will be dosed into the exhaust gas depending whether the sensed NOx level is above or below a target level. 
   
   
       21 . The device according to  claim 1 , further comprising an ammonia sensor placed downstream of the SCR catalyst to measure ammonia slip. 
   
   
       22 . The device according to  claim 1 , wherein the device comprises an outer body, which forms a pressure barrier, and passing through the outer body is an inner body which comprises a flowpath longitudinally therethrough with an inlet and an outlet for the exhaust gas, the outer and inner bodies forming two chambers therebetween, one substantially above the inner body and one substantially below the inner body, the two chambers connected by at least one fluid passageway. 
   
   
       23 . The device according to  claim 22  wherein the two chambers and the at least one fluid passageway comprise the reaction vessel. 
   
   
       24 . The device according to  claim 23  wherein the at least one fluid passageway is in thermal contact with the exhaust gas. 
   
   
       25 . The device according to  claim 24  wherein the at least one fluid passageway between the two chambers passes through the exhaust gas flowpath formed by the inner body. 
   
   
       26 . The device according to  claim 25  wherein the at least one fluid passageway passes around the sides of the inner body. 
   
   
       27 . The device according to  claim 22 , wherein the inner and outer bodies extend beyond the reaction vessel, the volume defined between said inner and outer bodies in their extended sections being separated from the reaction vessel at one end by a bulkhead and enclosed at the other end to form a reservoir area abutting the reaction vessel and through which the inner body passes. 
   
   
       28 . The device according to  claim 27  wherein the valve in the outlet is located in the bulkhead separating the reaction vessel and the reservoir. 
   
   
       29 . The device according to  claim 22 , where a by-pass valve is provided to selectively bypass a proportion of the exhaust gas so that it does not directly heat the fluid passageways of the reaction vessel. 
   
   
       30 . The device according to  claim 29  wherein the inner body comprises two exhaust gas flowpaths, only one of which is in thermal contact with the fluid passageways of the reaction vessel. 
   
   
       31 . The device according to  claim 1 , wherein the device comprises a rear section comprising two substantially cylindrical upright tubes and an enclosed cavity therebetween, said tubes adapted to house the reaction vessel and reservoir respectively. 
   
   
       32 . The device according to  claim 31  wherein the tube housing the reaction vessel has an inlet for the exhaust gas and is in fluid communication with the enclosed cavity such that the hot exhaust gasses flow in the inlet, over the reaction vessel and exit the tube into the enclosed cavity. 
   
   
       33 . The device as claimed in  claim 31  wherein at least a part of the tube housing the reservoir is in direct fluid contact with the hot exhaust gasses. 
   
   
       34 . The device as claimed in  claim 33  wherein the reservoir is isolated from direct heat contact with the part of the tube in direct fluid contact with the hot exhaust gasses by an air gap. 
   
   
       35 . The device as claimed in  claim 34  wherein heat transfer through the wall of the tube containing the reservoir and across the air gap is sufficient to maintain the reservoir at a high enough temperature to prevent solidification of salts out of the hydrolysis gas. 
   
   
       36 . The device as claimed in  claim 31 , wherein the enclosed cavity has an opening therein for the exhaust gas to pass through prior to entering a diesel particulate filter and/or an oxidation catalyst. 
   
   
       37 . The device according to  claim 31 , wherein the catalysts and at least one mixing means is attached to the exterior of the rear section via a framework. 
   
   
       38 . The device according to  claim 37  further comprising an outer casing that fits over the catalysts and mixing elements forming a treatment enclosure. 
   
   
       39 . The device according to  claim 38  wherein the outlet for the exhaust gas passes from the treatment enclosure through the enclosed cavity in the rear section to allow the exhaust gas to exit the unit for eventual discharge. 
   
   
       40 . The device according to  claim 31 , wherein the reservoir and reaction vessel abut a manifold plate, said manifold plate providing a barrier between a hot area below it and a cooler area above it. 
   
   
       41 . The device according to  claim 40  wherein the valves and any sensors are placed at least partially in the cooler area such that their electronics and some other function critical parts can be protected from direct exposure to the hot environment. 
   
   
       42 . The device according to  claim 40  wherein the manifold plate includes a heat shield between the hot area and the cooler area. 
   
   
       43 . The device according to  claim 41  wherein the valves and any sensors have covers sealed thereover to prevent water ingress into the electronics. 
   
   
       44 . The device according to  claim 43  wherein said covers comprise a thermally conductive material and include a number of cooling fins to assist in removing any heat from this area. 
   
   
       45 . The device according to  claim 31 , mounted on a commercial vehicle such that the rear section is closest the centre of the vehicle and treatment enclosure extends outwards therefrom such that, in event of a collision, the treatment area forms a sacrificial ‘crumple zone’ to absorb the energy of impact and protect the pressurised reaction vessel and reservoir from direct impact. 
   
   
       46 . The device according to  claim 1 , further provided with a heating element for the reservoir. 
   
   
       47 . A hydrolysis gas reservoir for receiving ammonia containing gas from a hydrolysis reaction vessel, the reservoir comprising a body and a manifold, said manifold having passageways therein to accommodate various sensors and at least one valve and having heating means associated therewith to maintain said manifold at an elevated temperature. 
   
   
       48 . The reservoir according to  claim 47  wherein the heating means comprises one or more electric heating elements. 
   
   
       49 . The reservoir according to  claim 48  wherein the heating means comprises a plurality of finger heaters inserted substantially radially into the manifold. 
   
   
       50 . The reservoir according to  claim 47 , wherein the heating means is adapted to maintain the manifold at a temperature in the range 130 to 300 degrees centigrade. 
   
   
       51 . The reservoir according to  claim 50  the heating means is adapted maintain the manifold at a temperature in the range 210 to 230 degrees centigrade. 
   
   
       52 . The reservoir according to  claim 47 , wherein attached to a passageway of the manifold is a pressure relief valve that releases the hydrolysis product from the reservoir should the pressure therein exceed a certain value. 
   
   
       53 . The reservoir according to  claim 52  wherein any gas being released via the pressure relief valve is released into a small reservoir of water to condense the gaseous hydrolysis product and prevent it being released directly into the atmosphere. 
   
   
       54 . The reservoir according to  claim 52  wherein any gas being released via the pressure relief valve is released directly into the exhaust gas flow. 
   
   
       55 . The reservoir according to  claim 47 , wherein attached to a port of the manifold is a dosing valve for dosing the ammonia-containing gas into an exhaust gas stream. 
   
   
       56 . The reservoir according to  claim 47 , wherein the manifold has a valve seat therein between two of said passageways, one passageway leading from the interior of the reservoir and forming a valve inlet and the other passageway exiting the side of the manifold forming a valve outlet. 
   
   
       57 . The reservoir according to  claim 56  wherein a valve actuator and associated valve armature are connected to said manifold, the valve actuator operable to move the valve armature on and off the valve seat thereby allowing or preventing flow therethrough. 
   
   
       58 . The device according to  claim 47 , wherein the reservoir manifold has means for attaching it to a manifold plate such that the valves and sensors protrude through the manifold plate into the cool area above it. 
   
   
       59 . The reservoir according to  claim 58  wherein said means for attaching the manifold to the manifold plate comprise a plurality of flanges adapted to take a screw or bolt. 
   
   
       60 . A system for the reduction of NOx in the exhaust gas of an IC engine comprising a reactor for producing ammonia, a reservoir to temporarily store ammonia a means of introducing ammonia to the exhaust gas and an SCR catalyst, the reservoir including
 a body and a manifold, said manifold having passageways therein to accommodate various sensors and at least one valve and having heating means associated therewith to maintain said manifold at an elevated temperature.   
   
   
       61 . A device for generating gaseous hydrolysis product comprising ammonia, formed by the hydrolysis of an aqueous solution of urea at elevated temperature and pressure, the device being adapted to be placed in the exhaust system so that the exhaust gas will flow through it during use, and comprising
 a) a first substantially upright and cylindrical tube enclosed at its upper end and open at its lower end and having an inlet and an outlet on its sides for the exhaust gas;   b) an elongate reaction vessel located in the tube for containing an aqueous solution of urea and arranged such that, in use, the vessel and therefore the urea solution become heated by means of heat exchange with the exhaust gas as it flows from the inlet to the outlet; and   c) a urea solution inlet to the reaction vessel and a gaseous hydrolysis product outlet from the reaction vessel;   
     wherein said reaction vessel is attached to the upper enclosed end of the first tube and sealingly engages with the first tube at its lower end preventing the exhaust gas from escaping out of the open lower end of the first tube. 
   
   
       62 . The device according to  claim 61  wherein the reaction vessel is provided with a structurally weak point in its upper end that will rupture at a lower pressure that the rest of the reaction vessel ensuring that, in the case of excessive pressure build up in the reaction vessel, the structurally weak point will rupture and the gas in the reaction vessel will expand therethrough forcing the reaction vessel downwards. 
   
   
       63 . The device according to  claim 61  wherein the reaction vessel has a circumferential seal attached to the outer surface of its lower end and the said seal slides in the tube as the reaction vessel expands and contracts. 
   
   
       64 . The device according to  claim 61  wherein the tube has a circumferential seal attached to the inner surface of its lower end and the reaction vessel slides past the seal as it expands and contracts. 
   
   
       65 . The device according to  claim 61 , wherein the device further comprises a second substantially upright and cylindrical tube having an enclosed upper end and an open lower end, said second tube housing a substantially elongate reservoir to collect the gaseous hydrolysis product produced in the reaction vessel, said reservoir being attached to the upper enclosed end of the tube and sealingly engaging with the tube at its lower end. 
   
   
       66 . The device according to  claim 65  wherein the exterior of the second tube is at least partially heated by the hot exhaust gasses. 
   
   
       67 . The device according to  claim 65  wherein the reservoir is provided with a structurally weak point in its upper end that will rupture at a lower pressure that the rest of the reservoir ensuring that in the case of excessive pressure build up in the reservoir the structurally weak point will rupture and the gas in the reservoir will expand therethrough forcing the reservoir downwards. 
   
   
       68 . The device according to  claim 65 , wherein reservoir has a circumferential seal attached to the outer surface of its lower end and the said seal slides in the tube as the reservoir expands and contracts. 
   
   
       69 . The device according to  claim 65 , wherein the tube has a circumferential seal attached to the inner surface of its lower end and the reservoir slides past the seal as it expands and contracts. 
   
   
       70 . The device according to  claim 65 , wherein the first and second substantially upright tubes form the two substantially upright tubes.