DEVICE AND METHOD FOR GENERATING A REDUCING AGENT GAS FROM A LIQUID OR SOLID REDUCING AGENT

Abstract

A device for generating a reducing agent gas from a solid or liquid reducing agent, where the reducing agent gas is preferably suited for nitrogen oxide reduction in an exhaust gas of a combustion engine, the device including a reactor with an inner volume and an inlet for a reducing agent solution and an outlet for the reducing agent gas. The device further including a heating system disposed at least partially in the inner volume and a heating control unit for controlling the heating system, wherein the inner volume includes first and second heating zones each including at least one heating element and controlled independently of each other by the heating control unit.

Claims

1. A device for generating a reducing agent gas from a solid or liquid reducing agent comprising: at least one reactor with an inner volume and an inlet for a reducing agent solution and an outlet for a reducing agent gas; a heating system disposed at least partially in the reactor and comprising at least one heating element; a heating control unit for controlling the heating system; wherein at least one of: the inner volume comprises a first and a second heating zone where the first and the second heating zone each comprise at least one heating element and where the first and second heating zones are controllable independently of each other by the heating control unit; and the reactor comprises a mixing unit in the inner volume.

2. The device according to claim 1, wherein the inner volume comprises at least three heating zones, wherein each heating zone comprises at least one heating element.

3. The device according to claim 1 wherein the heating zones each comprise at least two heating elements, wherein each heating element is controllable independently.

4. The device according to claim 1, wherein each heating zone comprises a direct or indirect temperature sensor.

5. The device according to claim 1, wherein the heating element or the heating elements comprise a heating rod or heating rods.

6. The device according to claim 0, wherein the inner volume includes a longitudinal which extends in a direction substantially perpendicular to a direction of a force of gravity during intended use, wherein at least one of the heating rods extend substantially in the direction of longitudinal axis and the heating rods are arranged substantially perpendicular to a direction of a force of gravity during intended use.

7. The device according to claim 1, wherein, the reactor comprises a dome for collecting gas.

8. The device according to claim 1, wherein the device comprises a dosage unit which is disposed upstream of the inlet.

9. An engine comprising a device according to claim 1.

10. A marine vessel including at least one of a device according to claim 1 and an engine according to claim 9.

11. A method for generating a reducing agent gas from a solid or liquid reducing agent the method comprising: introducing a reducing agent solution into an inner volume of a reactor through an inlet; heating the reducing agent solution in the inner volume with a heating system comprising at least one of a first and a second heating zone in the inner volume, where the first and the second heating zones each comprise at least one heating element and where the heating zones are controllable independently of each other by a heating control unit for controlling the heating system, and at least one heating element and a mixing unit in the inner volume such that the reducing agent solution is uniformly heated; reacting the reducing agent solution to a reducing agent gas; and removing the reducing agent gas through an outlet of the reactor.

12. The method according to claim 0, wherein in the heating step, if one heating zone is in a liquid phase in the reactor and another heating zone is in a gaseous phase in the reactor, a heating power is higher in the heating zone in the liquid phase.

13. The method according to claim 0, wherein the method further comprises: mixing the reducing agent solution by solving solid urea in water in a mixing tank; guiding the reducing agent solution from the mixing tank to the reactor through an inlet piping.

14. A method for reducing NO.sub.x in an exhaust gas comprising a method according to claim 0, wherein the method further comprises: injecting the reducing agent gas into an exhaust gas of a combustion engine.

15. The device according to claim 4, wherein each heating zone comprises at least one heating element that includes one of the temperatures sensors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Non-limiting embodiments of the invention are described, by way of example only, with respect to the accompanying drawings, in which:

[0051] FIG. 1 is a process scheme for generating gaseous ammonia;

[0052] FIG. 2 is a detailed process scheme with a reactor and heating zones; and

[0053] FIG. 3 is a cross-section of a reactor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Ammonia is a highly volatile gas with adverse physiological effects, which can be intolerable at very low concentration. At high concentrations ammonia presents substantial environmental and operating hazards and risks. It is classified as a hazardous material and many precautions are required in transporting and handling it safely. Solid urea, on the other hand is a stable, non-volatile and environmentally friendly material that is safely transported. Solid urea or urea solution may be safely stored and handled with fewer risks and can serve as safe source of ammonia. A reactor 2 as shown in the following is used for converting urea solution to ammonia. The basic chemistry employed in the conversion of urea to ammonia comprises the following two reaction steps:

CO(NH2)2.fwdarw.HNCO+NH3(urea) (isocyanic acid) (Ammonia) (1)

HNCO+H.sub.2O.fwdarw.NH.sub.3+CO.sub.2(isocyanic acid) (water) (Ammonia) (Carbon dioxide) (2)

[0055] The first reaction, in which isocyanic acid is formed, is a thermolysis and endothermic, while the second, in which ammonia and carbon dioxide are produced is exothermic. In total, the overall reaction is endothermic. Thus, the reaction requires heat and quickly stops when a supply of heat is withdrawn. Excess water may promote the reaction. Thus the overall reaction is as follows:

CO(NH.sub.2).sub.2+H.sub.2O.fwdarw.2NH.sub.3+CO.sub.2(urea) (water) (Ammonia) (Carbon dioxide) (3)

[0056] The reaction commences at around 110 C. and accelerates at around 150 C. to 160 C.

[0057] A device 1 for generating ammonia is shown in FIG. 1. The ammonia is generated from a liquid solution 22. The liquid solution 22 is stored in a tank 21 and comprises urea, which is solved in water. From the tank 21 the urea solution is pumped with a pump 23 to a reactor 2. The urea solution is let into the reactor 2 through an inlet 26 and out of the reactor 2 through an outlet 27. An inner volume 3 of the reactor comprises a heating system 4. The reactor is a pressure tank and rated for pressures up to 80 bar. The heating system 4 heats up the urea solution to 300 C. Thus, the endothermic reaction of urea and water to ammonia is enabled.

[0058] Furthermore, a pressure within the reactor rises due to the heating. The pressure rises because the reactants are liquid, while the reaction products are gaseous. A pressure relief valve 24 controls the pressure within the reactor. Since all reaction products are gaseous, only gaseous products are let through the pressure relief valve 24. The gaseous products are then injected into an exhaust gas stream 25. The exhaust gas stream 25 is let through an exhaust pipe 30 to a mixing zone 29. In the mixing zone 29 the reaction products, in particular the ammonia, are mixed with the exhaust gas stream 25. The mixture of gases is then let to an SCR catalyst 28. The catalyst accelerates the reduction of nitrogen oxides with ammonia in the exhaust gas to nitrogen and water. Thus, the exhaust gas 25, which is let out, is cleaned.

[0059] FIG. 2 shows a detailed process scheme for the device 1. The tank 21 includes a tank sensor 31. The tank sensor 31 measures a current filling level of the tank 31. Further, the pump 23 includes a motor 32, which is electrical. After the pump 23, an inlet piping 34 comprises a pressure sensor 33. The inlet piping 34 guides the urea solution 22 from the tank 21 to the inlet 26 of the reactor 2.

[0060] The inlet piping 34 comprises a check valve 43. The check valve 43 prevents a backflow from the reactor 2 to the tank 21. At the same time the valve 43 allows a flow from the tank to the reactor, provided the pump generates sufficient pressure, i.e. a higher pressure than in the reactor 2.

[0061] The inlet piping 34 leads the urea solution 22 to the reactor 2 and into the inner volume 3 of the reactor 2. The reactor itself is separated into two heating zones 6 and 7. The solution 22 enters the reactor 2 at a bottom of the inner volume 3. The bottom of the reactor forms the first heating zone 6. In the first heating zone 6, a heating element 11 starts heating up the urea solution, which is at the temperature of the inlet piping 34. A temperature in the first heating zone 6 is measured by a first temperature sensor 16. Since the urea solution enters the reactor at a temperature below 110 C., for example at room temperature, the first heating zone transfers a high amount of energy to the urea solution. As the urea solution 22 is heated up, it rises in the inner volume 3 of the reactor 2 to the second heating zone 7. In the second heating zone 7, heat is transmitted to the urea solution by a second heating element 12. Since the reaction products are gaseous, there may be a phase boundary in the inner volume 3 between gaseous reaction products and the liquid solution 22. The heating elements 11, 12 are electrical heating rods. Each heating element 11, 12 belongs to one of the heating zone 6, 7.

[0062] The liquid solution heats up until a target temperature is reached. Thus, the heating power transferred to the solution 22 in the lowest heating zones, i.e. in the first heating zone 6 is higher than in the second heating zone 7.

[0063] The heating system 4 allows an independent control of the individual heating elements 11, 12 in the respective heating zones 6, 7. A control unit 5, which controls heating elements 11 and 12, can control each heating element 11, 12. Like the temperature in the first heating zone 6, the temperature of the second heating zone 7 is monitored by a second temperature sensor 17. The control unit 5 is set to maintain a pre-set temperature in the inner volume 3. The sensors 16, 17 provide a control loop to regulate the temperature.

[0064] At a top portion, the reactor 2 includes the outlet 27. To the outlet 27, an outlet piping 44 with an outlet pressure sensor 35 is connected. Downstream of the outlet pressure sensor 35, a pressure relief valve 24 controls the pressure in the outlet piping 44. The pressure sensor 35 and the pressure relief valve 24 in connection with the pump 23 and the check valve 43 allow a control of a pressure within the reactor 2.

[0065] The device 1 further includes a pressure control unit (not shown). The pressure control unit regulates the pressure in reactor 2 via the valve 24. The sensors 33 and 35 provide a feedback to the pressure control unit. The pressure control unit is set to a target pressure.

[0066] An output is determined by a delivery rate of the pump 23 as well as a temperature within the reactor, which is controlled by the heating system 4 and a pressure inside the reactor 2. The pressure and the temperature are kept constant by the respective control units. The output is thus only determined by the delivery rate of the pump 23 and dosage system. This output is then measured by a mass flow meter 36. Lastly, the reaction products are injected via an injector 37 into the exhaust pipe 30. A filling level in the reactor 3 is monitored with a reactor sensor 38.

[0067] FIG. 3 shows a cross section of the reactor 2 and its inner volume 3. The heating zones 6, 7 are indicated by dotted lines in FIG. 3. The heating elements 11, 12 comprise temperature sensors, which are integrated within the heating elements 11, 12. Further, the reactor 2 comprises thermocouples, which additionally measure a temperature of the urea solution or the reaction products in the gaseous phase.

[0068] As can be seen from FIG. 3, the reactor is partly filled with urea solution and partly filled with gaseous products of the reaction. The heating elements 12 of the second heating zone 7, which are in the gaseous phase, do not need to heat the inner volume as much and thus transmit less energy.

[0069] The reactor 2 comprises a dome 40. The reactor 2 comprises a circular cylindrical shape. The dome 40 extends from the circular cylindrical shape in an upward direction. The dome 40 allows a collection of the gaseous reaction products and in particular of gaseous ammonia 39. The gaseous reaction products are then let out of the outlet 27, which is on top of the dome. Further, the dome allows a separation of the liquid solution and the gaseous reaction products. Thus, gaseous ammonia 39 is extracted from the reactor 2.

[0070] In the foregoing description, it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed herein. Such modifications are to be considered as included in the following claims, unless these claims by their language expressly state otherwise. In removing claims or multiple dependencies, unpatentability of any deleted claim or combination or sub-combination of claims is not admitted, and reserve the right to change the claims and their dependency during prosecution.