JP2000130706A - Method for reducing oxygen from exhaust gas of boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the oxygen concentration in the exhaust gas of a boiler to zero by completely burning a natural gas containing CH4 as a main component by using a small amount of fuel catalyst, by adding fuel having a lower combustion stating temperature than CH4 has to the natural gas as oxygen reducing fuel. SOLUTION: A boiler 1 is provided with a radiant evaporator 2 and a balance evaporator 3. The principal section of an oxygen reducing device comprises a combustion catalyst section 11 and a fuel supplying device 12, and the oxygen concentration in the exhaust gas of the boiler 1 is reduced to <=1,000 ppm through secondary combustion in the section 11. The catalyst used in the section 11 contains a metal of the platinum group, such as platinum, etc., or the oxide of aluminum, etc., as an active component. CH4 is a hardly burned combustible gas, because the combustion starting temperature of CH4 is 370-380 deg.C when the catalyst is used. When H2, etc., is added to a natural gas containing CH4 as a main component, therefore, the combustion starting temperature of the gas can be lowered and oxygen can be removed surely from the exhaust gas of the boiler 1 by means of the oxygen reducing device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for reducing oxygen in boiler exhaust gas.

[0002]

2. Description of the Related Art Conventionally, nitrogen gas is injected into an oil field to maintain the pressure of an oil reservoir, or nitrogen gas is dissolved in oil to form a so-called miscible state, and oil flows in the oil reservoir. Enhancement is being made. Here, in general, a nitrogen gas separated from oxygen by a cryogenic separation method of the atmosphere is used as a nitrogen gas source. However, in order to separate nitrogen gas, not only a large amount of power is required but also the cost of the apparatus is excessive. Therefore, measures have been desired for obtaining nitrogen gas with low power and low cost.

[0003]

On the other hand, as an inexpensive inert gas production process, a nitrogen production process in which a combustible gas is introduced into a boiler exhaust gas of 1 to 2% oxygen to make oxygen zero by catalytic combustion can be considered. However, the temperature of the boiler exhaust gas is about 350 ° C., the catalytic combustion is insufficient with the flammable gas normally used, and it is difficult to zero oxygen, and a large amount of catalyst is required. Therefore, the present invention has been proposed for the purpose of completely burning at the above-mentioned exhaust gas temperature and enabling the removal of oxygen from the boiler exhaust gas.

[0004]

SUMMARY OF THE INVENTION The present invention provides an inert gas having a boiler exhaust gas having an oxygen concentration of 1000 ppm or less by supplying a fuel for reducing oxygen to a combustion catalyst section provided downstream of a boiler convection heat transfer section. In doing so, a fuel having a combustion start temperature lower than that of CH ₄ is added to a natural gas mainly composed of CH ₄ as a fuel for reducing oxygen, and used.

[0005]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described. FIG. 1 shows an embodiment of a boiler apparatus including an apparatus for reducing oxygen in boiler exhaust gas according to the present invention. Boiler 1 to which this embodiment is applied
Is a type called a once-through boiler. The boiler 1 is generally provided with two evaporators in a heat transfer system. One of the evaporators is a radiation evaporator 2, and the other is a residual evaporator 3.

In the heat transfer system of the boiler 1, water is supplied from a water supply port 4 via a preheater (not shown), and water is sent to a radiant evaporator 2 via a economizer 5. The radiation evaporator 2 has a large number of water pipes 6 arranged in parallel, and the joining and splitting of water are repeated by a header 7 provided on the way to make the flow of each water pipe 6 uniform. About 85% of the feedwater is evaporated by the radiation evaporator 2 by the heat of combustion of the boiler fuel, and the remaining feedwater is evaporated and partially heated (by convection heat transfer) in the next remaining evaporator 3. . Most of the impurities in the feed water adhere to the pipes of the remaining evaporator 3, and this part is contained in a flue with a low gas temperature to avoid overheating. Further, the steam passes through the radiant superheater 8 and the contact superheater 9, is taken out from the superheated steam outlet 10, and sent to a power generation turbine, a heating system (not shown), and the like at the subsequent stage. Note that arrows A, B, and C in FIG. 1 indicate flows of the combustion gas (A, B) and the exhaust gas (C).

The radiant evaporator 2 and the radiant superheater 8 are portions called boiler radiating portions, which are relatively high temperatures. The contact superheater 9, the remaining evaporator 3, and the economizer 5 are portions called boiler convection heat transfer portions, which are relatively low temperature portions. The above-mentioned radiation evaporator 2 is of a rising pipe group-downcoming pipe type, but a so-called meander type or a once-through boiler using a spiral type does not adversely affect the object of the present invention. . Heat transfer system (water supply system)
Control of boiler fuel combustion and the like is performed by an automatic control function (not shown).

Further, as shown in FIG. 1, in the present embodiment, a combustion catalyst section 11 and a fuel supply device 12 are provided.
These constitute a main part of the oxygen reduction apparatus according to the present invention. The combustion catalyst section 11 is provided downstream of the boiler convection heat transfer section as shown. Examples of the catalyst used in the combustion catalyst section 11 include a catalyst containing a metal of a platinum group element or an oxide thereof. For example, the following catalysts can be used. (1) On a carrier containing at least one oxide selected from the group consisting of alumina, silica, titania, and zirconia, at least one of platinum, palladium, and rhodium is used as an active ingredient. A catalyst in which the supported powder is coated on a heat-resistant substrate such as cordierite. (2) A catalyst in which at least one oxide selected from the group consisting of an oxide of an alkaline earth element and an oxide of a rare earth element is further added as a promoter to the above catalyst. (3) A catalyst containing a metal such as copper, vanadium, chromium, iron and nickel, and at least one selected from the group consisting of oxides of these metals.

The fuel supply device 12 is a device for supplying the oxygen reducing fuel to the combustion catalyst unit 11.
Is provided immediately before. The purpose of the present invention is to reduce the concentration of oxygen in exhaust gas generally containing 2 to 3% by volume of oxygen by the secondary combustion in the combustion catalyst section 11 to 1,000 ppm or less. From this, when the exhaust gas amount is set to 1,600,000 Nm ³ / H (corresponding to a 600 MW boiler), natural gas (having CH ₄ as a main component) is reduced to 16,000 to 20,000 Nm ³ / H. It is preferred to add in an amount. That is, in general,
(Exhaust gas amount) × 10 ^{2 to} 1.25 × (Exhaust gas amount) 10 ²
An amount of Nm ³ / H is preferred. Generally, the amount of oxygen contained in the exhaust gas is 2 to 3% by volume. If the amount is less than the above range, it is not possible to sufficiently reduce oxygen. If the amount is too large, the natural gas is contained in the exhaust gas as unburned matter, but there is no inconvenience for the purpose of injecting this gas into the oil field. As the fuel supply device 12, an injection device known to those skilled in the art can be used.

In the boiler provided with the oxygen reducing device according to the above embodiment, the temperature rises in the combustion catalyst section 11. Therefore, an air heater 14 for exchanging heat between the exhaust gas and the air from the air suction blower is provided. The air heater 14 is preferably a heat exchange type having no air leakage. The exhaust gas is transferred to a place of use via an air heater 14, a dehydrator (not shown), a compressor (not shown), and the like.

[0011] The amount of the catalyst, for example, a 80～16M ³ in the case of setting the amount of exhaust gas and 1,600,000Nm ³ / H (corresponding to 600MW boiler). If the amount of the catalyst is less than this, sufficient combustion promotion is not performed, and if the amount is too large, it is uneconomical.

The temperature of the boiler exhaust gas supplied to the combustion catalyst section 11 is about 350 ° C. at the maximum. However, since natural gas generally used as fuel contains methane at 90% or more, it may be difficult to remove natural gas by combustion with a combustion catalyst in the above exhaust gas temperature range. In this case, it is conceivable to increase the exhaust gas temperature by installing the combustion catalyst section in the intermediate section from the downstream side of the boiler convection heat transfer section, but it is not always possible to change the installation location due to installation space restrictions. Do not mean.

The inventors of the present invention have investigated the combustion start temperature of various combustible gases with a catalyst, and found that CH ₄ :
370-380 ° C, LPG: 190-210 ° C, H ₂ :
30 to 50 ° C., carbon monoxide: 80 to 100 ° C., benzene: 130 to 135 ° C., etc., indicating that CH ₄ is the most combustible gas.

That is, natural gas containing CH ₄ as a main component is L
By adding PG or H ₂ or the like, it is possible to reduce the combustion initiation temperature, it becomes possible to reliably removed oxygen by oxygen reducing apparatus of the current boiler exhaust gas.

In the oxygen reducing apparatus according to the present embodiment,
A fuel oxygen reduction is burned, to reduce the oxygen in the exhaust gas, to increase the content of CO _2. The heat generated here is used in the air heater 14 to heat the air for primary combustion. The control of these devices is appropriately and automatically controlled by a control unit (not shown) similarly to the other devices.

As described above, by using the oxygen reducing apparatus according to the present embodiment, it is possible to obtain an exhaust gas containing much less oxygen at a much lower power and lower cost than the cryogenic separation method. In addition, in this exhaust gas, the amount of CO ₂ is increased in the secondary combustion by the oxygen reduction device as compared with the normal exhaust gas. CO ₂ has a great effect when injected into an oil field more than nitrogen gas.

Generally, the boiler exhaust gas after the primary combustion is
When the oil is injected into the oil field of the oil field as it is, clogging of the oil layer and significant corrosion of the oil well or the production equipment proceed due to the remaining oxygen. On the other hand, the exhaust gas obtained by the present invention is a nitrogen gas containing almost no oxygen and containing a large amount of CO ₂ , and has a great effect when injected into an oil field.
That is, by injecting the CO ₂ rich nitrogen gas obtained according to the present invention into an oil field, it is possible to maintain the reservoir pressure,
The fluidity of the oil in the oil reservoir can be significantly increased.

[0018]Other embodiments  The method for reducing oxygen in boiler exhaust gas according to the present invention is as described above.
The present invention is not limited to the above-described embodiments, but is within the scope of the technical idea of the present invention.
Various modifications are possible. The boiler of FIG.
This is a Benson type boiler.
It can be applied to other once-through boilers such as la. In addition, the present invention
Not only for once-through boilers, but also for other boilers
Can be

[0019]

EXAMPLE Assuming the present boiler exhaust gas oxygen removal device,
An oxygen removal test by adding a combustible gas was performed using a combustion catalyst. These examples are shown below.

Example 1 (Catalyst preparation) γ-Al ₂ O ₃ powder was immersed in an aqueous palladium nitrate solution, water was evaporated to dryness, and calcined at 550 ° C. for 5 hours to obtain a powdery combustion catalyst ( Pd / Al ₂ O ₃ ... Pd
Supported amount 5%). Water and silica gel were added to the powdered catalyst to form a slurry, and the resulting powder was coated on a 400 cpsi cordierite substrate at 100 g / l to obtain a honeycomb-shaped combustion catalyst 1.

(Evaluation of activity)
An oxygen removal test was performed under the following test conditions. <Gas composition> O₂ 1%, CO₂ 12%, H₂O 1
7%, CH₄ 6000ppm + C ₃H₈4000pp
m (C₁Conversion) GHSV: 20,000h^-1(catalyst
20cc), gas amount: 400Nl / h, temperature 3
00-450 ° C

When CH ₄ is used, oxygen removal is represented by the following reaction formula.

Embedded image CH ₄ + 2O ₂ → CO ₂ + 2H ₂ O The flammable gas is CH ₄ , the main component of natural gas, and C ₃
H ₈ is assumes a major component of the LPG. Table 1 shows the outlet oxygen concentration after activity evaluation at each inlet temperature.
From this result, it was confirmed that the outlet oxygen concentration was almost 0 at the inlet temperature of 350 ° C.

Example 2 Using the same catalyst and the same activity evaluation conditions as in Example 1, the composition and concentration of the flammable gas to be added were examined. The composition and concentration of the flammable gas are shown below. Combustible gas (all hydrocarbons _{C 1} terms) No. No. 2 CH ₄ 4000 ppm, C ₃ H ₈ 4000 ppm (main component of LPG) No. 3 6000 ppm of CH _4, 4000 ppm of C ₂ H ₆ (high boiling point of LNG) No. ₄ 6000 ppm of CH _4, 4000 ppm of CO (main component of reformer gas) No. 5 CH ₄ 6000 ppm, H ₂ 4000 ppm (main component of reformer gas) No. 6 6000 ppm CH _4, 4000 ppm benzene (main component of gasoline) 7 CH ₄ 6000 ppm, light oil 4000 ppm (main component of light oil)

The thing that the combustible gas is combustible gas to CH ₄ which is the main component of any natural gas LPG, LNG, reformer gas, gasoline, typical components of light oil was added. The activity evaluation results are shown in Table 1. From this result,
No. 2-No. It was found that the oxygen concentration at the inlet was 350 ° C. and the oxygen concentration at the outlet was 0 in each case.

[0025] Comparative Example 1 Example 1 In the same catalyst and activity evaluation condition and, as a combustible gas added, CH ₄ only 10,000ppm a typical natural gas components CH _4, the main component of natural gas 9,200 ppm + C ₃ H
₈ each, addition of 800 ppm _{(C 1} terms) No.
8, no. An evaluation test was performed as No. 9. The activity evaluation results are shown in Table 1.

According to the results, CH _{4 of} 8,10,0
With only 00 ppm, a large amount of oxygen remains at the inlet temperature of 350 ° C. 9 natural gas equivalent gas (CH ₄
Even at 9,200 ppm + C ₃ H ₈ ppm), the combustion removal of oxygen is insufficient.

[0027]

[Table 1]

[0028]

As is clear from the above description, according to the present invention, by injecting a flammable gas which is more excellent in combustibility than methane, the amount of combustion catalyst in the boiler exhaust gas can be reduced with a smaller amount than when methane is injected. Can be reduced to zero, and an existing boiler can be used as it is, thereby realizing a cheap inert gas production process.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating an embodiment of a once-through boiler including an apparatus for reducing oxygen in an exhaust gas boiler for carrying out the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 boiler 2 radiant evaporator 3 residual evaporator 4 water supply port 5 energy saving device 6 water pipe 7 header 8 radiant superheater 9 contact superheater 10 superheated evaporation outlet 11 combustion catalyst section 12 fuel supply device

Claims (3)

[Claims] 1. A fuel provided downstream of a boiler convection heat transfer section.
The fuel for oxygen reduction is supplied to the combustion
Produce an inert gas with an oxygen concentration of 1000 ppm or less
In this case, CH₄The main component
CH to natural gas ₄Add fuel with lower combustion start temperature
Oxygen reduction in boiler exhaust gas characterized by using
Method. 2. The boiler exhaust gas according to claim 1, wherein paraffins, olefins, naphthenes, aromatics, hydrogen or carbon monoxide are added as a fuel which can be burned at a lower temperature than CH _4. Oxygen reduction method. 3. A method for reducing oxygen in boiler exhaust gas, comprising using a catalyst containing a noble metal as an active component as a combustion catalyst.