JPS6283301A - oxygen hydrogen recombiner - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention mainly relates to recombining hydrogen and oxygen gas produced by radiolysis of reactor water in a boiling water nuclear power plant using a catalyst to reduce explosive properties. This article relates to an oxyhydrogen recombiner for safely processing gas without any waste.

[Background of the invention]

Figure 1 shows the flow of the radioactive waste treatment system in a boiling water nuclear power plant. Hydrogen gas and oxygen gas generated by radiolysis of cooling water in the reactor 1 are transported to the main condenser 3 via the turbine 2 along with radioactive rare gases such as krypton and quinanone. The mixed air is extracted by the air extractor 4, diluted by the driving steam of the air extractor to below the detonation limit of hydrogen gas, and then transported to the exhaust gas treatment system. The carried exhaust gas is heated to a temperature higher than the saturation temperature of the treated gas using in-house steam in an exhaust gas preheater 5 to remove moisture, and then a catalyst 7 in a recombiner 6 performs a recombination reaction of oxygen and hydrogen. This is done to reduce the hydrogen concentration at the outlet of the recombiner 6 during rated plant operation to 1 ppm or less, and the water resulting from the recombination is condensed and removed in the exhaust gas condenser 8 together with the driving steam.

The radioactive exhaust gas from which hydrogen, oxygen, and water vapor have been removed is attenuated to a radioactive concentration below the specified value by adding krypton and xenon, which have long half-lives, to a rare gas hold-up device 9.
The air is discharged into the atmosphere from the exhaust stack 11 by the air extractor 10.

The amounts of hydrogen, oxygen, air, and steam in the treated gas of such an exhaust gas treatment system vary greatly when the plant is started, rated, and stopped.
While the hydrogen gas is 3 to 4% and the air amount is 4ONηhr or less, at startup, the hydrogen gas varies from 0 to the above rated value of 3 to 4% in accordance with changes in the furnace output of the plant. Also, under conditions where the hydrogen gas concentration is low at startup, the degree of vacuum in the main condenser 3 is low, so a large amount of air flows into the air extractor 4.
The air is extracted. At the time of shutdown, the leakage air from the main condenser 3 is the same as at the rated time, but the amount of hydrogen gas decreases depending on the output of the reactor. (Note that oxygen gas and hydrogen gas are generated by decomposition of reactor water, so oxygen and hydrogen are always treated as equivalent gases in a 1:2 ratio in the recombiner 8.
Needless to say, there will be an inflow into In addition, in the oxyhydrogen recombiner 8, oxygen and hydrogen undergo an exothermic reaction, so that a temperature rise of about 70° C. occurs with 1% hydrogen gas. Therefore, at the rated output of 100%, the hydrogen concentration is 3
Since the temperature of the recombiner 8 is as high as 1, the temperature of the recombiner 8 is not high.
At startup and shutdown, the hydrogen concentration is low, so the temperature of the recombiner 8 is low.

Furthermore, the allowable pressure loss of the exhaust gas recombiner is determined by the back pressure of the air extractor 4 on the upstream side and the pressure loss of equipment piping in the system. The maximum back pressure of the air extractor 4 is at most 0.
It is about 5atg. Further, the back pressure at the connection point with the main condenser 3 of the exhaust gas treatment system including the air extractor 4 changes as the amount of treated gas t decreases, and the back pressure decreases as the amount of treated gas decreases.

Therefore, the allowable pressure loss of the exhaust gas recombiner is the starting rating,
It is determined from the amount of gas to be processed under each operating condition of shutdown, each operating mode and its required back pressure.

Taking these into consideration, the allowable pressure loss for the exhaust gas recombiner system is generally about 1000. , ) must be less than or equal to ψ.

The pressure drop in the recombiner varies greatly depending on the porosity of the catalyst, the flow rate of the exhaust gas, and the amount of catalyst packed in the recombiner.

Furthermore, since the oxyhydrogen recombination reaction causes an exothermic reaction within the catalyst, the actual flow rate inside the recombiner reaches more than twice that on the inlet side at the rated time.

Based on the above, when designing the catalyst for the exhaust gas recombiner,
The gas flow rate and the melting medium are determined from the catalyst performance and allowable pressure loss under startup, rating, and shutdown conditions.

By the way, the exhaust gas treatment profile (flow rate) is 1, which must be approximately proportional to the plant's furnace output, so if the flow rate of the treated gas in the exhaust gas recombiner is the same, the required catalyst passage cross-sectional area is equal to the amount of treated gas This will vary depending on the reactor power, and as a result, the required column diameter of the recombiner will vary depending on the plant reactor power. In addition, the upper limit of the flow rate in the recombiner must be set within a range where the pressure loss when passing through the catalyst in the recombiner is within the range where the system is affected, and the flow rate must be kept low. This will increase the required column diameter of the recombiner, increasing the size of the vessel and increasing the cost of the recombiner due to the required plate thickness, so it is preferable to lower the lower limit of the flow rate. do not have.

However, in conventional catalysts for exhaust gas recombiners, noble metals such as palladium are attached to ceramics such as porous alumina. This ceramic catalyst is used by filling pellet-shaped or spherical catalysts.The carrier material of this ceramic catalyst is alumina and its shape is granular, so the catalysts collide with each other during filling. There is a possibility that the catalyst surface may become powdered and fall off, or the catalyst itself may be pulverized due to its own dancing due to the gas flow in the recombiner. There is a risk that the catalytic reaction may proceed in the equipment and piping before and after the coupler), and the performance of the catalyst itself is low. In addition, because the catalyst is pellet or spherical, the packing density of the catalyst is very low, and the pressure loss associated with the gas flow increases. Therefore, the body diameter of the exhaust gas recombiner must be increased and it must be used in a low process gas flow rate range. Moreover, this has the problem of increasing the size of the recombiner and increasing the cost.

[Purpose of the invention]

The purpose of the present invention is 1. These conventional drawbacks have been overcome, and the oxyhydrogen removal performance is much superior, the pressure loss is low, and high performance is maintained within the range of reducing the catalyst loading and increasing the processing gas flow rate in the recombiner. The purpose is to provide an oxygen-hydrogen recombiner that can be used.

[Summary of the invention]

The present invention is an oxygen/scale recombiner for recombining oxygen and hydrogen for exhaust gas treatment as described above, in which alumina is impregnated as a binder on the surface of a sponge-like metal carrier to impart catalytic activity to the alumina. Particles of platinum-based noble metals such as platinum and palladium having a concentration of 0.1 y-/l to 5. of-
The above-mentioned recombiner is equipped with a metal catalyst formed in the shape of a thread so that each catalyst has a pore diameter of 0.5 van to 6.0 van. The space velocity (SV value) of the exhaust gas in the recombiner is set to 500 to 1.
50000, pressure loss below 1000tttxH2O,
It is characterized in that the flow velocity is in the range of INm/m to 4Nm/s.

As a result, hydrogen gas having a hydrogen concentration of 4 mol % or less, which is the flammable limit value at the inlet of the recombiner, is diluted to 1 ppm or less at the outlet of the recombiner.

In this way, the present invention replaces the catalyst in the recombiner with a pellet-type or spherical ceramic catalyst impregnated with a noble metal such as palladium, using a ceramic such as a porous alumina material, which has high oxygen removal performance. By changing to a sponge-like porous metal catalyst with high porosity and low pressure loss,
Improving recombination performance, reducing pressure loss, and improving catalyst
Under the condition that the ratio of the amount of treated gas is constant, the flow rate of the treated gas is increased to reduce the size of the recombiner in a region where the oxyhydrogen removal performance does not deteriorate, and at the same time reduce the possibility of catalyst pulverization and scattering. This makes maintenance and inspection easier.

[Embodiments of the invention]

An experiment was conducted to measure the catalytic performance of the recombiner by simulating the same exhaust gas conditions as in a real plant.

The catalytic performance of the recombiner was evaluated by the ratio of the inlet hydrogen concentration flowing into the recombiner to the outlet hydrogen concentration (hydrogen conversion ratio) flowing out from the recombiner after silica hydrogen bonding with the catalyst. The exhaust gas condition in the exhaust gas treatment system of a boiling water nuclear power plant is that the majority (approximately 90% or more) of the exhaust gas is heated steam, so the outlet hydrogen concentration is the A trace amount of unreacted hydrogen ai was amplified and measured with an analyzer such as a gas chromatograph, and the hydrogen humidity measured with this analyzer was calculated to be converted to the state before the steam was converted to drain.

FIG. 2 shows the results of measuring the pressure loss when the passage flow rate was changed using the opening of the pore diameter of the catalyst as a parameter under the gas conditions of the oxyhydrogen recombiner in a state where the cylinder was packed with a constant layer of catalyst. Curve 12 shows the change in pressure loss when the opening is 0.5 mm, and curve 13 shows the change in pressure loss when the opening is 6.0 mm.

The double hatched range between curves 12 and 13 indicates the range that satisfies the system allowable pressure loss of the recombiner. Note that when the opening is increased to 6 beads or more, the contact time between the exhaust gas and the catalyst becomes shorter, resulting in a decrease in performance.

FIG. 3 shows the results of measuring the catalytic performance of the recombiner, with the horizontal axis representing the exhaust gas flow rate and the vertical axis representing the hydrogen conversion ratio. Curve 14 shows that alumina is applied as a binder to the surface of a plate-shaped Nl-Cr alloy sponge-like metal support by, for example, a chemical method (impregnation, coating, spraying, electrodeposition, etc.) in order to increase the surface area of the catalyst. Fi 0.1 t/l to 5.0 by impregnating with platinum or a platinum-based catalytically active precious metal such as 4-radium, or by chemical methods such as baking with fallen cloth.
Do not carry I/L, and adjust the eye opening from 0.5 to 6. Or
Curve 15 shows the oxygen-hydrogen bonding performance of the metal catalyst according to the present invention as a function of the trx pore diameter. Curve 16 shows the oxyhydrogen bonding performance of a metal catalyst in which palladium is supported by an electrodeposition method, and curve 16 shows the oxyhydrogen binding performance of a conventional ceramic catalyst in which palladium is supported on a carrier such as a porous alumina material.

From this figure, in the oxyhydrogen recombination reaction, curve 14
The metal catalyst according to the present invention shown in FIG.
The same capacity as the ceramic catalyst of Curve 15 and the metal catalyst supported by the electrodeposition method of Curve 15.

It can be seen that at the same flow rate, the oxyhydrogen removal reaction is more than one order of magnitude better than these.

In addition, Figure 4 shows the relationship between the flow rate of the catalyst self-processing gas in the recombiner and the pressure loss under high-performance conditions, and curve 1
Curve 7 shows a conventional ceramic catalyst, and curve 18 shows a metal catalyst using alumina as a binder. From this figure, it can be seen that at the same flow rate, the metal catalyst has a lower pressure loss than the conventional catalyst, at less than A, and that it is possible to increase the gas flow rate with respect to the pressure loss allowed by the system. Recognize.

In general catalytic reactions, the space velocity SV value can be used as a numerical value representing catalytic performance.

The space velocity is determined by the ratio between the flow rate of the process gas passing through the catalyst and the catalyst lid contributing to the catalytic reaction. In other words, the space velocity is the reciprocal of the contact time between the catalyst and the reaction gas.

FIG. 5 schematically shows the packed catalyst in a cylindrical shape. When the capacity of the catalyst is doubled from W to W, as shown in the figure (&), the flow velocity of the reactant gas passing through the catalyst increases from V to V. If it is doubled, the contact time between the catalyst and the gas is the same, and the SV value is the same.

That is, Vs: V, x=l: 2W, :W, zl
: 2,', sv凰;Sv.

In this figure, the height of the catalyst layer is changed to change the catalyst capacity, but the same is true even if the diameter of the catalyst is changed.

It is known that with a normal catalyst, the catalytic reaction is the same outside the thread where the SV value is constant.

For example, in the decomposition reaction of acetylene and the thermal decomposition reaction of N2O5, when the SV value is constant, the decomposition performance is almost the same even if the catalyst capacity (bed height) and the process gas flow rate (flow rate) are changed.

In contrast, tests have shown that a recombiner using a metal catalyst as described above according to the present invention exhibits a different tendency. FIG. 6 shows the results of this test, in which the horizontal axis represents the exhaust gas flow rate and the vertical axis represents the hydrogen conversion ratio.
, Hm yH, ) as parameters is shown by a solid line, and a curve using different constant sv values (SVl, SVl) as parameters is shown by a dotted line. From this figure, it was found that when the exhaust gas flow rate was changed gracefully under the condition that the SV value was constant, the catalyst performance tended to improve as the flow rate increased. This can be achieved, for example, by decreasing the recombiner's body diameter to increase the flow rate and increasing the catalyst bed height, or by increasing the recombiner's body diameter to lower the process gas flow rate within the catalyst. Under the condition that the gas space velocity (SV value) in both cases is constant, the recombination reaction progresses more when the flow velocity in the former recombiner is increased than when the catalyst layer height is lowered. It means that. Conventional ceramic catalysts do not exhibit such a troublesome tendency due to oxyhydrogen bonding, nor are they allowed to increase the flow rate to this extent. In addition, the flow rate was changed from 2 to 3 to 4.
It was found that as the flow rate increases to Nm/see, this tendency becomes larger, and there is no difference in the flow rate in the range of 1 Nm/see or less, where the flow velocity is small. It is assumed that this is because increasing the gas flow rate causes a phenomenon in which the gas on the surface of the catalyst is stirred, which thins the gas barrier and increases the reaction rate. .

From the above, in an actual ground recombiner, the steady state flow rate of 0, 5 to 0.7, which is used in conventional ceramic catalysts, is
Nm/sec, based on the present invention, alumina is impregnated as a binder on the surface of a sponge-like metal carrier made of a chromium alloy, and a platinum-based noble metal such as platinum or radium having catalytic activity is added to the alumina. Particles are supported in the generally used range of 0.1 - 71 - 5.0 f/ (in addition, regarding the support of noble metals, it is better to support them finely and uniformly, and if the amount of supported metals is large, the supported thickness By using a sponge-like metal catalyst with a pore size of 0.5 nm to 6.0 nm, each metal catalyst has a pore size of 0.5 nm to 6.0 nm. By increasing the flow rate and reducing the body diameter of the recombiner, it becomes possible to create a more compact oxyhydrogen recombiner. In addition, the applicable range of the SV value of this recombiner is 500 to 1so in steady state, taking into account the following three parameters: flow rate, catalyst loading and horizontal placement, and pressure loss.
It is best to use the ooo range.

By the way, it has been found that when the exhaust gas treatment speed is as high as possible when the contact time with the metal catalyst and the Sv value is constant, the oxyhydrogen bonding reaction is promoted. The air extractor (blower) installed on the upstream side of the recombiner also has a limited capacity, and it is difficult to increase the size of the air extractor (blower) because it will affect other downstream equipment. For this reason, the flow velocity must be selected in a flow velocity range near the allowable pressure loss limit of the system mentioned above.

Figure 7 shows the exhaust gas treatment conditions at the actual plant rating (high hydrogen concentration accelerates the exhaust gas recombination reaction, and the reaction heat is not high) when the recombiner is filled with the essential catalyst in an actual plant. This figure shows the relationship between pressure loss and flow velocity under conditions where the pressure loss is maximum. The pressure loss curve is approximately proportional to the square of the flow rate, and as the flow rate increases, the pressure loss increases rapidly. Therefore, the upper limit of the flow rate that can be selected within the pressure loss that can be applied to the system is 4 Nm/se.
It is up to c. However, if the pressure loss is 5 Nm/sec, the pressure loss will be nearly twice that of 4 Nm/sec, far exceeding the allowable pressure loss. On the other hand, the lower limit of flow velocity is
It is determined by the shape of the container of the recombiner containing the metal catalyst. When filling the recombiner with a metal catalyst, in this embodiment, since the catalyst has a plate shape, the catalyst is filled and stored in a cartridge, a tank, or the like.

It is also possible to have a structure in which the container is directly filled with it. Since the required plate thickness of the recombiner increases in proportion to the body diameter, S
When the flow rate is lowered under the condition of a constant v value, the barrel diameter increases and the weight of the recombiner increases rapidly.

In addition, the size of the container support legs is limited by the length of the recombiner body, so even if the flow velocity is lowered and the packed bed height is lowered, the support legs, comb fittings, and other structures that are susceptible to welding problems will make it difficult to keep the cage low. Since it is difficult to reduce the flow rate under a condition where the Sv value is constant, the weight of the recombiner will be significantly increased, which will significantly increase the cost. When we actually calculate the weight of the metal catalyst recombiner and the exhaust gas flow rate in the recombiner (which varies depending on the recombiner body diameter), we find that the recombiner has a flow rate below I Nm/wc as shown in Figure 8. It turns out that the weight, and thus the price, becomes significantly more expensive.

From the above, in this example, the exhaust gas treatment rated flow rate in the new type recombiner filled with the metal catalyst as described above is approximately IN
It has been found that a value of approximately 4 Nm/s6e is appropriate. This rated flow velocity range is much improved over the conventional rated flow velocity range of 0.5 to 0.7 Nm156e.

FIG. 9 is a schematic sectional view of a recombiner according to an embodiment of the present invention, in which 19 is a shell, 2O is an exhaust gas inlet, 21 is an outlet, 2
2 is a cartridge; 23 is a plate-shaped metal catalyst as described above; as shown in FIG. .

FIG. 11 shows a conventional recombiner for comparison, and 25 is a pellet or spherical ceramic catalyst packing as described above.

The oxyhydrogen recombiner according to the present invention shown in Fig. 9 has a recombination reaction that is one order of magnitude better than that using a conventional ceramic catalyst, has a smaller pressure loss, and has a lower space velocity due to the contact time between the catalyst and the exhaust gas. Since the performance is improved by increasing the flow rate under the condition that the flow rate is constant, compared to the conventional recombiner shown in Fig. 11, the catalyst capacity is approximately V5, the vessel column diameter is approximately V3, and the recombiner weight is approximately A. This made it possible to create a large hut.

12 to 14 show other embodiments of the present invention.

FIG. 12 shows that the recombiner container is made into a fuselage 7 lunge 26,
This structure has a cartridge 22 filled with a plate-shaped metal catalyst 23 of the present invention.

Furthermore, FIG. 13 shows a structure in which the plate-shaped metal catalyst 23 of the present invention is directly filled inside the recombiner without the cartridge 22.

Moreover, FIG. 14 shows a metal catalyst 23 having high performance of the present invention.
This is an example of a structure in which the pellets are made into pellets (preferably pellet size is 5 to 50 tm) and filled into a conventional recombiner. According to this embodiment, it is possible to replace the conventionally used ceramic catalyst with a high-performance metal catalyst, thereby increasing the reliability of equipment and systems.

〔Effect of the invention〕

The oxyhydrogen recombiner according to the present invention has less pulverization and scattering of the catalyst, far superior recombination reaction, and lower pressure loss than those using conventional ceramic catalysts. Moreover, if the space velocity is the same, the performance is improved by increasing the flow velocity due to the contact time between the catalyst and the exhaust gas. can be made significantly smaller. In addition, since it has become possible to downsize, it is possible to adopt a pre-clock head structure on the top of the recombiner, and it is possible to create a structure that allows easy maintenance and inspection of the inside of the recombiner. Moreover, it is advantageous in terms of transportability and installation space.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a gaseous waste treatment system in a boiling water nuclear power plant, and Fig. 2 is a schematic diagram of a gaseous waste treatment system in a boiling water nuclear power plant. Figure 3, a diagram showing the results of measuring pressure loss, shows recombination using the metal catalyst of the example of the present invention, a metal catalyst with a catalytically active noble metal directly electrodeposited on a metal carrier, and a conventional ceramic catalyst, respectively. Figure 4 is a diagram showing the relationship between the hydrogen conversion ratio of the recombiner and the exhaust gas flow rate, and Figure 5 is a diagram showing the relationship between the pressure loss and exhaust gas treatment flow rate of the recombiners of the embodiment of the present invention and the conventional example under actual machine rated conditions. Figure (a). Figure 6 is a diagram showing the relationship between the performance of oxyhydrogen bonding and the exhaust gas treatment flow rate according to the embodiment of the present invention, and Figure 7 is a model diagram for explaining the space velocity. Figure 7 is a model diagram for explaining the space velocity. Figure 8 is a diagram showing the relationship between the weight of the recombiner and the exhaust gas flow rate in the recombiner, and Figure 9 is a diagram showing the relationship between the weight of the recombiner and the exhaust gas flow rate in the recombiner, and Figure 9 is an example of the present invention. Fig. 10 is a partial diagram of the new recombiner, Fig. 1
FIG. 1 is a structural diagram of a recombiner filled with a conventional pellet-type ceramic catalyst, and FIGS. 12 to 14 are structural diagrams of new recombiners according to other embodiments of the present invention. l; Nuclear reactor 2; Turbine 3; Main condenser 4; Air extractor A5; Exhaust gas preheater 6; Exhaust gas oxyhydrogen recombiner 7; Oxygen hydrogen combination catalyst 8: Exhaust gas condenser 9; Rare gas hold Appu Electric Manufacturing 10; Air extractor B 11; Main exhaust stack 19; Container body
2O; Exhaust gas population 21; Exhaust gas outlet 23
; Metal catalyst 24; Support spacer 25; Ceramic catalyst 26; Fuselage 7 Lanjinico agent Hondako XfL-" Figure 2 Figure 3 Exhaust gas flow rate Figure 6 Surrender ◆I? tlf1 0/2.345 θ Flow velocity (oval

Claims (1)

[Claims] In an oxygen-hydrogen recombiner that introduces exhaust gas containing hydrogen gas, oxygen gas, superheated steam, and a small amount of air, and recombines the hydrogen gas and oxygen gas through a catalytic reaction, alumina is applied as a binder to the surface of a sponge-like metal carrier. 0.1 g/l to 5.0 g of platinum-based precious metal particles such as platinum and palladium having catalytic activity are impregnated onto the alumina.
/l and each has an opening of 0.5 mm to 6.
A sponge-like metal catalyst formed to have a pore diameter of 0 mm is filled in the recombiner, and the flow rate of the exhaust gas in the recombiner is set to 1 to 4 Nm/s, and the space velocity (SV value) is set to 500 to 15.
0000, an oxygen-hydrogen recombiner characterized by having a pressure loss of 1000 mmH_2O or less.