EXHAUST GAS RECOMBINER

Abstract: An exhaust gas recombiner for restoring hydrogen and oxygen gases in gases extracted from a condenser of a steam engine into water by reaction of the hydrogen and oxygen gases includes a vertical cylinder vessel (1) having an extracted gas iniet (2) at its lower end and an outlet (3) at its upper end. To improve performance and reduce pressure loss, the diameter of the vessel (1) is substantially the same as that of an outlet piping connected to the outlet (3) of the vessel for introducing gases leaving the vessel into an exhaust gas condenser. The apparatus further includes a plurality of units in the vessel (1), each unit having a honeycomb structure (4) for flow-rectifying gases flowing into the vessel through the extracted gas inlet (2) and a honeycomb catalyst (5) carrying on its surfaces a catalyst and positioned at the upper side of the honeycomb structure (4).

Description: This invention relates to an exhaust gas recombiner for restoring hydrogen and oxygen gases in gases extracted from a condenser of a steam engine such as steam turbine and the like into water by reaction of the hydrogen and oxygen gases. With a steam engine, water vapor used for lowering back pressure is cooled by a condenser to restore the vapor into water and the condensed water is recovered so as to be used again. In this case, when the water vapor is mixed with air or hydrogen or oxygen gas produced by decomposition of the water vapor, the degree of vacuum in the condenser will lower, detrimentally affecting the thermal efficiency of the steam engine. As shown in Fig. 1, therefore, an air extractor 31 is connected to the condenser 30 of the steam engine to extract air, hydrogen and oxygen gases and the like from the condenser 30. As the steam used for a steam turbine in an atomic power station includes tritium and the like, extracted gases as they are may not be exhausted into the ambient atmosphere. Therefore, in order to reduce the volume of the extracted gases, after the gases are preheated by an exhaust gas preheater 32, hydrogen and oxygen gases are caused to react with each other to produce water vapor which is then condensed in an exhaust gas condenser 34 so as to be used again. For such an exhaust gas recombiner 33, a unit has been generally used, which comprises a large tank filled with pellet catalysts each including porous alumina pellets supporting catalysts on their surfaces. With such a hitherto used recombiner, however, in order to obtain sufficient reaction efficiency, the filled layers must be thick or bulky. Such thick filled layers exhibit various disadvantages in that pressure losses become larger, the apparatus unavoidably becomes large, and the pellet catalysts are vibrated so as to collide with each other to be pulverized with resulting deterioration of the catalysts, and the construction for filling the pellet catalysts becomes complicated. GB-A-1 115 815 discloses a coolant purifier for a nuclear reactor having a vertical vessel containing adsorbant portions for fission products separated by heat exchanges. It is a primary object of the invention to provide an improved exhaust gas recombiner which at least partly removes the disadvantages of the prior art, e.g. operates with less pressure losses without pulverization and deterioration of catalyst caused by gas flows and is designed simple in construction and compact as a whole. The exhaust gas recombiner according to the invention is set out in claim 1. The term "flow-rectifying" used herein is intended to mean that gas flows are conditioned to make them steady flows in parallel without causing any disturbance. The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings. Fig. 1 is one example of a block diagram of a condensing process line; Fig. 2 is a sectional view illustrating one embodiment of the exhaust gas recombiner according to the invention; and Fig. 3 is a graph illustrating a relation between space velocities and degree of hydrogen conversion. Referring to Fig. 2 illustrating an embodiment of the invention, the apparatus comprises a vertical cylindrical vessel 1 having a reduced diameter lower end, an extracted gas inlet 2 provided at the lower end, and an exhaust gas outlet 3 provided at an upper end of the vessel 1. An extracted gas preheated to a temperature of about 140°C by an exhaust gas preheater 32 as above described is supplied into the extracted gas inlet 2. The extracted or exhaust gas is treated in the vessel 1 by heating to a high temperature of about 350°C by the heat of reaction and is fed from the exhaust gas outlet 3 through an outlet piping into an exhaust gas condenser 34. In the illustrated exhaust gas recombiner according to the invention, the vessel 1 has a diameter substantially the same as that of the outlet piping, thereby preventing pressure loss which would otherwise occur in a vessel having a reduced diameter outlet of the prior art. There are provided in the vertical cylindrical vessel 1 honeycomb structures 4 for rectifying gas flows and honeycomb catalysts 5 in layers. The honeycomb structure 4 used in this embodiment is cylindrical and includes therein rectangular or square cells whose pitch is in the range 1.7-5.9 mm. It carries no catalyst. The honeycomb structure 4 includes a number of through-apertures extending in axial or vertical directions formed by the cells to flow-rectify the gas flow flowing thereinto through the exhaust gas inlet 2 into parallel flows. On the other hand, the honeycomb catalyst 5 is a honeycomb support structure of cordierite which is coated on its surfaces with alumina on which is carried the catalyst such as platinum, palladium or the like for combining hydrogen and oxygen gases. The concentration of platinum, palladium or the like as the active component is of the order of 0.5-3 g/lit. Like the honeycomb structure 4, the honeycomb catalyst 5 includes therein rectangular or square cells with pitch of 1.7-5.9 mm. The axial length of the honeycomb catalyst 5 is very much longer than that of the honeycomb structure 4. In order to easily exchange the honeycomb structure 4 and the honeycomb catalyst 5 as one set, the vessel 1 is made separable at flanges 6 into a plural parts. Heaters 7 are provided on outer circumferential surfaces or the vessel 1 so that the inner temperature of the vessel 1 is kept constant by on-off control of the heaters 7, thereby accomplishing a stable reaction. In using the recombiner, an extracted gas including for example 3.2 volume % of hydrogen gas and 1.6 volume % of oxygen gas is obtained from the main condenser 30 by means of the air extractor 31. The extracted gas is preheated to about 140°C in the exhaust gas preheater 32 and is then introduced through the extracted gas inlet 2 into the vessel 1. The extracted gas is flow-rectified into parallel flows by the honeycomb structure 4 and then passes through the honeycomb catalyst 5 arranged above the honeycomb structure 4. During such a passage through the honeycomb catalyst 5, the hydrogen and oxygen gases in the extracted gas are recombined with each other by the action of the catalyst to convert them into water vapor. The water vapor is then fed into the exhaust gas condenser 34 through the outlet piping connected to the exhaust gas outlet 3 at the upper end of the vessel 1 and having substantially the same diameter as that of the vessel 1. The water vapor is condensed in the exhaust gas condenser 34 and the condensed water is then returned to the original circulating system. The performance of the exhaust gas recombiner of this kind is estimated by degree of hydrogen conversion %. In this case, the degree of hydrogen conversion is given by (H₂ concentration on the inlet side - H₂ concentration on the outlet side)/H₂ concentration on the inlet side (%). As shown in Fig. 3, with the exhaust gas recombiner according to the invention, the degree of hydrogen conversion was 99.99% when space velocity was 15×10⁴ 1/hr and also when space velocity was 21.6×10⁴ 1/hr. When space velocity was 28.8×10⁴ 1/hr, the degree of hydrogen conversion was 99.19%. Data shown by a white circle in Fig. 3 are for the case that the vessel 1 is horizontal. Within a range of the space velocity less than 21.6×10⁴ 1/hr, the horizontal type apparatus exhibited substantially the same effect as that of the vertical type apparatus. In case of the space velocity of 28.8×10⁴ 1/hr, the degree of hydrogen conversion with the horizontal type apparatus lowered to 93.7%. The reason why the vertical type apparatus is superior to the horizontal type is probably based on the fact that vertically flowing hydrogen gases in the vertical type apparatus are more sufficiently mixed with each other than in the horizontal type because the hydrogen gases are lighter than the air. Nevertheless, although the invention has been illustrated by the vertical vessel described above, a horizontal cylindrical vessel may be used instead. In the illustrated apparatus according to the invention, there are provided the honeycomb structures 4 and the honeycomb catalysts 5 in the vertical cylindrical vessel 1 without arranging any moving members in the vessel as used in the prior art. Therefore, no collision and pulverization of the catalysts occur and hence their deterioration scarcely occurs. Moreover, the gases introduced into the extracted gas inlet 2 provided at the lower end of the apparatus are flow-rectified into parallel flows and then pass through the through-apertures of the honeycomb catalysts 5 in the form of honeycomb structures. In this manner, the apparatus according to the invention can reduce the pressure losses to the order of one fiftieth of those in the prior art. As shown by the data of the embodiments, high degree of hydrogen conversion can be accomplished by the feature of the invention in conjunction with the vessel 1 in the form of a vertical cylinder. Even if the diameter of the vessel 1 is made substantially the same as that of the outlet piping, the apparatus can exhibit sufficient performance as a recombiner. Therefore, it is possible to minimize the entire apparatus to a size less than one fiftieth of that of the prior art. Moreover, as the exhaust gas recombiner is of small type, a plurality of the apparatuses may be arranged in parallel so that if catalysts of one apparatus are deteriorated, the apparatus can be immediately replaced with other apparatus. As can be seen from the above explanation, as the exhaust gas recombiner according to the invention can maintain a high degree of hydrogen conversion within the range of high space velocity with less pressure losses without causing any pulverization and deterioration of catalysts caused by gas flows so that the apparatus is simple in construction and compact as a whole. Therefore, the apparatus according to the invention eliminates all the disadvantages of the prior art and greatly contributes to development of industries. Of course the apparatus according to the invention can be applied to not only steam turbines in atomic power stations but also condensing process lines of general steam prime movers. While the invention has been particularly illustrated with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details can be made therein.

Claims: An exhaust gas recombiner comprising a cylindrical vessel (1) having a gas inlet (2) at one end and an outlet (3) at its other end, at least one honeycomb structure (4) in said cylindrical vessel having its through passages in the axial direction of the vessel (1) for flow-rectifying gases flowing into the vessel through the gas inlet (2) and at least one honeycomb catalyst support (5) in said vessel (1) carrying on its surfaces a catalyst which catalyses the combination of hydrogen and oxygen into water, said catalyst support (5) being positioned downstream of flow-rectifying honeycomb structure (4). An exhaust gas recombiner as set forth in claim 1, wherein a plurality of units, each consisting of one said flow-rectifying honeycomb structure (4) and one said honeycomb catalyst support (5) downstream of the flow-rectifying honeycomb structure (4) are arranged to form in a plurality of stages. An exhaust gas recombiner as set forth in claim 2, wherein said vessel (1) is made separable at portions having flanges (6) into a plurality of parts whose number is the same as the number of the units, thereby enabling the units to be easily exchanged. An exhaust gas recombiner as set forth in any one of claims 1 to 3, wherein said vessel (1) has a diameter substantially the same as the diameter of outlet piping connected to said outlet (3) for introducing the gases leaving from the vessel into a condenser. An exhaust gas recombiner as set forth in any one of claims 1 to 4 wherein said flow-rectifying honeycomb structure (4) is cylindrical and its cells are rectangular in cross-section with a pitch in the range 1.7-5.9 mm. An exhaust gas recombiner as set forth in any one of claims 1 to 5 wherein said honeycomb catalyst support (5) is made of cordierite and is coated on its surfaces with alumina for carrying the catalyst. An exhaust gas recombiner as set forth in any one of claims 1 to 6, wherein said honeycomb catalyst support (5) is cylindrical and its cells are rectangular in cross-section with a pitch in the range 1.7-5.9 mm. An exhaust gas recombiner as set forth in any one of claims 1 to 7, wherein said vessel (1) is provided on its outer circumference with heating means (7) to keep the interior temperature constant. An exhaust gas recombiner as set forth in any one of claims 1 to 8 wherein said cylindrical vessel (1) is vertical, with said inlet (2) at its lower end.

Inventors: IWATA, KATSUICHI, OKAMOTO, MAGOJI
Applicants: NGK INSULATORS, LTD.
Application year: 1989
Main classification: G21C19
IPC codes: F01K19, G21F9, G21C19, B01J19