MXPA98005569A - Apparatus and method for reducing oxygen content in a cald exhaust gas - Google Patents

Abstract

When using an apparatus comprising a portion for catalyzing the fuel disposed downstream or in an intermediate portion of the conventional portion for heat transfer from the boiler and an apparatus for the supply of a fuel with a reduced amount of oxygen in the position just before the catalytic portion for combustion, fuel with a reduced oxygen content is supplied to an exhaust gas from the radiation portion of the boiler and burned in the catalytic portion for combustion, thereby increasing the of CO2 and reducing the content of oxygen gas, so that an exhaust gas is obtained that is composed mainly of nitrogen gas and that has a concentration of oxygen gas that does not exceed 1,000 p

Description

APPARATUS AND METHOD TO REDUCE THE OXYGEN CONTENT IN THE EXHAUST GAS OF A BOILER BACKGROUND OF THE INVENTION The present invention relates to an apparatus and method for reducing the oxygen content in the exhaust gas of a boiler. A conventional practice has been the introduction of nitrogen gas pressure in a field to maintain the pressure of an oil reservoir or dissolving nitrogen gas in oil to form a condition known as miscible, so that fluidity is increased of the oil in the oil tank. Here, as a source of nitrogen gas, nitrogen gas is used separated from oxygen by means of a process of air at low temperature, however, it requires a huge energy and also, the cost of the apparatus is really high. In accordance with the above, there is a request for countermeasures to obtain nitrogen gas with little energy and at a low cost. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an apparatus and method for reducing the oxygen content in the exhaust gas of a boiler, which makes it possible to prepare nitrogen gas with little energy and at low cost. According to the present invention, the above-described objective is achieved by means of an apparatus for reducing the oxygen content in the exhaust gas of a boiler, comprising a portion of catalysis for combustion, which is arranged downstream, or in an intermediate portion of the conventional heat transfer portion in the boiler and a fuel supply apparatus for providing a fuel with a reduced oxygen content in the position just before the portion for combustion of the catalyst. The present invention includes a method for reducing the oxygen content in an exhaust gas of a boiler, comprising the supply of fuel with reduction of oxygen in the exhaust gas just before the portion for catalysis of the fuel, arranged downstream or in the intermediate portion of the conventional portion for heat transfer from the boiler, burning the fuel with a reduced content oxygen in the combustion catalysis portion to increase the CO 2 content and reduce the gas content, and obtain an exhaust gas that is composed mainly of nitrogen gas and has a gas concentration that does not exceed 1,000 ppm.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view illustrating an embodiment of the single pass boiler, including an apparatus hereof for reducing the oxygen content in the boiler exhaust gas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment of the present invention will now be described with reference to the accompanying drawing. Figure 1 illustrates an embodiment of a boiler unit including an apparatus for reducing the oxygen content in the boiler exhaust gas according to the present invention. The boiler 1 to which this embodiment has been applied is called a boiler of the single-pass type. The heat transfer system of the boiler 1 is usually equipped with a portion for evaporation that is divided into two parts. One of the evaporation portions is a radiation evaporator 2 and the other is a waste evaporator 3. In the heat transfer system of the boiler 1, the water is fed from a port for water supply 4 through a pre-heater (not illustrated) and then sent to the evaporator by radiation 2 through the fuel economizer 5. The radiation evaporator 2 has many water pipes 6 arranged in parallel. The confluence and separation of water is repeated in the collector 7 arranged in the middle of the path, so that the water flow in each water tube is made uniformly. Approximately 85% of the water that is supplied in this way is evaporated in the evaporator by radiation 2 by the heat of combustion of the fuel of the boiler, while evaporation of the remaining water potion and partial heat (by conventional heat transfer) is carried out in the subsequent waste evaporator 3. Most of the impurities in the supplied water adhere to the inner wall of the waste evaporator tube 3, so that the waste evaporator is housed in the low temperature gas duct in order to protect it from overheating. Then, the vapor passes through the radiation superheater 8 and a convection superheater 9, is taken from the steam outlet of the superheater 10 and then fed to the generating turbine and the heating system (not shown) in the subsequent stage. Incidentally, the arrows A, B and C in Figure 1 indicate the flows of the combustion gas (A, B) and the exhaust gas (C), respectively.

The radiation evaporator described above 2 and the radiation superheater 8 form the radiation portion of the boiler, which is a relatively high temperature portion. On the other hand, the convection superheater 9, the waste evaporator 3 and the fuel economizer 5 form the conventional heat transfer portion of the boiler which is a relatively low temperature portion. The radiation evaporator 2 described above has the form of a descending unit with a group of risers, however a boiler of the single-pass type using a spiral-type or meander type evaporator does not detract from the purpose of the present invention. The heat transfer system described above (water supply system) by the fuel combustion of the boiler is controlled by means of an automatic controller that is not illustrated. The embodiment of the present invention, as illustrated in FIG. 1, further comprises a portion for the catalysis of combustion 11 and an apparatus for the supply of fuel 12, which forms a main portion of the apparatus for the reduction of oxygen according to the present invention.

The portion for combustion catalysis 11 is disposed downstream of the conventional portion for heat transfer from the boiler as illustrated in Figure 1. Examples of the catalyst used for the catalyst portion of the combustion 11 include those that contain a metal that belongs to the elements of the platinum group and its oxides. The catalysts shown below can be used, for example. (1) a catalyst that is obtained by coating powders in a heat resistant base such as cordierite, these powders are prepared having at least one active component that is selected from platinum, palladium or rhodium disposed in a carrier containing at least an oxide selected from a group consisting of alumina, silica, titania and zirconia. (2) a catalyst that is obtained by adding to the catalyst described above at least one oxide selected from the group consisting of oxides of an alkaline earth element and oxides of a rare earth element as a co-catalyst. (3) a catalyst containing at least one substance selected from a group consisting of metals such as copper, vanadium, chromium, iron and nickel, and oxides thereof.

In relation to the amount of catalyst, when the amount of the exhaust gas is determined at 1,600,000 Nm3 / H (corresponding to a 600 MW boiler), the amount of catalyst is 16M3. When the amount of catalyst is smaller than the previous amount, the combustion does not accelerate sufficiently, while if it is used in excess it is expensive. Preferably, the temperature of the exhaust gas from the boiler that is fed to the catalyst portion of the combustion 11 is between 150 and 350 ° C. The temperature of the exhaust gas in the combustion catalysis portion 11 is preferably between 300 and 500 ° C, more preferably between 350 ° and 500 ° C. The combustion catalysis portion 11 can be disposed downstream of the conventional heat transfer portion of the boiler that is illustrated in the embodiment of Figure 1. Alternatively, it can be arranged in the middle part of the portion. for the conventional heat transfer of the boiler since up to now, it satisfies the temperature of the exhaust gas as described above. The fuel delivery apparatus 12 is an apparatus for supplying the fuel with a reduced oxygen content in the portion for combustion catalysis 11 and is disposed in the position just before the combustion catalysis portion 11. Generally , in the present invention, a reduction in the concentration of oxygen in the exhaust gas containing 2 to 3 vol% oxygen by 1 is sought., 000 ppm or less by secondary combustion in the portion for combustion catalysis 11. Accordingly, it is appropriate to add a natural gas (composed mainly of CH4) in an amount of 16.00 to 20,000 Nm3 / H when the quantity of the exhaust gas is determined at 1,600,000 Nm3 / H (corresponding to a 600 MW boiler). In other words, the amount that falls within a range from (an amount of exhaust gas) x 102 to 1.25 x (an amount of exhaust gas) is adequate 102 Nm3 / H. Generally, the exhaust gas contains an amount of oxygen that is between 2 to 3 vol%, so that amounts smaller than the range specified above do not allow sufficient reduction of oxygen. When the quantity exceeds the previous range, the exhaust gas contains natural gas as an unburned portion, but there is no problem if the gas is introduced under pressure in an oil field. As the apparatus for the supply of fuel 12, the injection apparatus which is well known to those skilled in the art can be used. Incidentally, in the boiler equipped with the oxygen reduction apparatus according to the present invention, the temperature increases in the catalysis portion of the fuel 11. Therefore, an air heater 14 is provided for the purpose of. carry out the heat exchange between the exhaust gas and the air from an air suction fan. As the air heater 14, a heat exchanger of the free air flow type is preferred. Through the air heater 14, the dehydrator (not illustrated), the compressor (not shown) and the like, the exhaust gas is transferred to the place where it is used. In the apparatus for reducing oxygen according to this embodiment, the oxygen in the exhaust gas is reduced and the CO 2 content increases by means of combustion of the fuel with reduced oxygen. The heat generated here is used by the air heater 14 to heat the air for primary combustion. Similar to other apparatuses, these apparatuses are controlled, appropriately and automatically by the control portion that is not illustrated. By using the apparatus for oxygen reduction according to this embodiment in the manner described above, a substantially oxygen-free exhaust gas can be obtained at a very low cost and with really little energy compared to that which is obtained by the process at low temperature. Furthermore, the resulting exhaust gas has a C02 content higher than the ordinary exhaust gas belonging to the secondary combustion by means of the apparatus for reducing oxygen. C02 is more effective than nitrogen gas when injected under pressure in the oil field. When the exhaust gas from the boiler after the primary combustion is injected under pressure as such into the oil tank of an oil field, it clogs the oil reservoir and a marked corrosion is created in the production or oil equipment due to the remaining oxygen. On the other hand, the exhaust gas available by the present invention hardly contains oxygen but contains sufficient C02, so that it has greater effects when it is injected under pressure in an oil field. In other words, by injecting C02-rich nitrogen gas that is obtained in accordance with the present invention into an oil field, the pressure of the oil reservoir can be maintained and the fluidity of the oil in the reservoir can be significantly increased. .

Other embodiments The apparatus for reducing the oxygen content in the exhaust gas of a boiler and the method for using the apparatus, each according to the present invention, are not limited to the embodiment described above but they can be subjected to various modifications within the range of the technical idea of the present invention. The boiler shown in Figure 1 is a boiler known as Benson, but the present invention can be applied to other boilers of a single pass such as the Zulzer boiler. The present invention can also be applied to boilers that is not a single step as long as they do not go beyond the scope of the present invention.

Working Example Example 1 In a single pass boiler having an exhaust gas amount of 1,600,000 Nm3 / H, a Pt catalyst (having platinum, as an active ingredient, which is carried by the silica and is coated with a base cordierite) is placed, as a portion of the combustion catalysis, downstream of the conventional heat transfer portion of the boiler. The amount of catalyst was set at 16 m3. The temperature of the exhaust gas supplied to the fuel catalysis potion was 200 ° C and the gas had the following compounds: N2: 73%, C02: 9%, H20: 16%, 02: 2% Natural gas was added (composed mainly of CH4) as a fuel with reduced oxygen in an amount of 16,000 Nm3 / H. As a result of combustion in the combustion catalysis portion, the gas composition showed a change as follows: N2: 73%, C02: 10%, H20: 17%, 02: (not detected) The temperature of the combustion was 400 ° C. As described above, the nitrogen gas rich in CO 2, free of oxygen can be obtained in a large quantity only by supplying a small amount of fuel with reduced oxygen, whereby the effectiveness of the present invention is confirmed. The filing of Japanese Patent Application No. 9-190924 filed on July 16, 1997, including the specifications, claims, drawings and summary, is hereby incorporated by reference in its entirety.

Claims (20)

1. An apparatus for reducing the oxygen content in the exhaust gas of a boiler, comprising a potion for combustion catalysis which is disposed downstream or in an intermediate portion of the conventional heat transfer portion of the boiler; and an apparatus for supplying fuel that supplies a fuel with a reduced oxygen content at the position just before the portion of combustion catalysis.

2. The apparatus according to claim 1, wherein the exhaust gas has passed through the radiation portion of the boiler.

3. The apparatus according to claim 1, wherein the boiler is of the single-pass type.

4. The apparatus according to claim 1, wherein the catalyst in the catalytic portion of the combustion for catalysis is a catalyst that is obtained by means of powders coated in a resistant base such as cordierite, these powders are prepared to have the minus one selected active component of platinum, palladium and rhodium, carried in a carrier containing at least one oxide selected from a group consisting of alumina, silica, titania and zirconia.

5. The apparatus according to claim 4, wherein the catalyst in the combustion portion for catalysis is a catalyst that is obtained by adding to the catalyst described above at least one oxide selected from a group consisting of oxides of an alkaline earth element and oxides of a rare earth element as co-catalyst.

6. The apparatus according to claim 1, wherein the catalyst in the combustion portion for catalysis is a catalyst containing at least one substance selected from a group consisting of metals such as copper, vanadium, chromium, iron and nickel and the oxides thereof.

7. The apparatus according to claim 1, wherein the temperature of the exhaust gas fed to the portion for the catalysis of combustion is 150 ° to 350 ° C.

8. The apparatus according to claim 1, wherein the temperature of the exhaust gas in the portion for the catalysis of combustion is 300 ° to 500 ° C.

9. The apparatus according to claim 1, wherein the fuel with the reduced oxygen content is a natural gas that is composed mainly of CH4.

10. The apparatus according to claim 9, wherein the fuel with the reduced oxygen content is provided in an amount ranging from (an amount of exhaust gas) x 102 to 1.25 x (a quantity of gas of exhaust) 102 Nm3 / H.

11. A method for reducing the oxygen content in an exhaust gas from a boiler, which comprises supplying a fuel with reduced oxygen content in an exhaust gas just before the portion for 1 to catalysis of combustion that is disposed downstream or in an intermediate portion of the conventional portion for heat transfer from the boiler, burning the fuel with reduced oxygen in this portion for the catalysis of combustion to increase the CO 2 content and reduce the oxygen gas content, and obtain an exhaust gas that consists mainly of nitrogen gas and has an oxygen gas concentration that is not higher than 1,000 ppm.

12. The method according to claim 11, wherein the exhaust gas has passed through the radiation portion of the boiler.

13. The method according to claim 11, wherein the boiler is of the one-step type.

14. The method according to claim 11, wherein the catalyst in the portion of combustion for catalysis is a catalyst that is obtained by powders coated in a heat resistant base such as cordierite, these powders are prepared to have at least an active ingredient selected from platinum, palladium and rhodium, carried in a carrier containing at least one oxide selected from a group consisting of alumina, silica, titania and zirconia.

15. The method according to claim 14, wherein the catalyst in the portion for the combustion of the catalyst is obtained by adding the catalyst as described above to at least one oxide which is selected from a group consisting of the oxides of an element of alkaline earth and the oxides of a rare earth elements as a co-catalyst.

16. The method according to claim 11, wherein the catalyst in the portion for combustion of the catalyst contains at least one substance which is selected from a group consisting of metals such as copper, vanadium, chromium, iron and nickel and oxides thereof .

17. The method according to claim 11, wherein the temperature of the exhaust gas fed from the catalysis portion for combustion is 150 ° to 350 ° C.

18. The method according to claim 11, wherein the temperature of the exhaust gas in the catalysis portion for combustion is from 300 ° C to 500 ° C.

19. The method according to claim 11, wherein the fuel with the reduced oxygen content is a natural gas that is composed mainly of CH4.

20. The method according to claim 19, wherein the fuel with the reduced oxygen content is provided in an amount in the range from (an amount of exhaust gas) x 102 to 1.25 x (a quantity of gas of exhaust) 102 Nm3 / H.