JPS5824687B2 - Method and device for reducing residual carbon monoxide in exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is aimed at reducing residual CO (carbon monoxide) in exhaust gas, and in particular, reducing residual CO (carbon monoxide) in exhaust gas that does not self-combust at a low concentration in exhaust gas when carbon-containing substances are combusted using a fluidized bed. This invention relates to reducing residual CO in exhaust gas when the exhaust gas contains entrained particles containing carbon monoxide and unburned carbon.

The exhaust gas of devices intended to burn carbon-containing substances necessarily contains residual CO.

Therefore, various methods have been developed to remove residual CO from exhaust gas.

Among these methods, for example, methods for reducing residual CO in the exhaust gas from a boiler etc. include a method of increasing the combustion temperature and a method of supplying excess oxygen 02.

However, when the combustion temperature is raised, the generation of NoX (nitrogen oxides) tends to increase, so in equipment that uses liquid fuel such as heavy oil, it is necessary to improve the spray nozzle of the burner, etc. Methods are being used to suppress the occurrence of flames and at the same time maintain a high average flame temperature.

Furthermore, when solid fuel is used, the use of a fluidized bed makes it possible to make the temperature of the combustion region more uniform, which is said to be very advantageous with respect to NOx.

On the other hand, it is possible to reduce the residual CO by supplying an excess of 0□, but an increase in the amount of 0□ supplied will result in an increase in the required power, which will increase the combustion temperature and increase NOx. There are many.

In particular, in a device using a fluidized bed, non-uniformity in the passage path on the gas side is unavoidable, resulting in partial incomplete combustion, so it is necessary to increase the amount of oxygen supplied per unit fuel. Although it is possible to increase the average combustion efficiency, it is difficult to effectively reduce the residual CO concentration in exhaust gas.

Additionally, in order to continuously and stably burn flammable gas alone, the amount of gas generated is generally 300 to 500 kc at the minimum.
al/Nm3 is required.

If the only combustible gas component is CO, the CO concentration is 10% (
The same applies to gases below 701%) and approximately 300 kca
l/Nrr? bawl.

Therefore, in order to burn gas with a concentration lower than this, it is necessary to add other auxiliary fuel, such as propane gas, or to burn it in advance, or to burn other fuels in advance and contain trace amounts of flammable gas. Introduce gas containing components.

This requires measures such as a so-called afterburner, which poses an economical problem.

The purpose of the present invention is to economically reduce the low concentration of CO, which cannot self-combust, remaining in exhaust gas. in,
If the combusted exhaust gas contains a low concentration of CO that cannot self-combust and entrained particles containing unburned carbon, after performing an operation to reduce the entrained particles in advance, under the 02 concentration at that point, This method is characterized by holding the exhaust gas at a predetermined temperature for a predetermined period of time to oxidize CO in the exhaust gas.

That is, in the present invention, particles containing unburned carbon accompanying the exhaust gas, mainly unburned solid fuel, are used to remove residual CO in the exhaust gas.
We found through experiments that the concentration of 0
As a result, the entrained particles were removed before the temperature of the exhaust gas decreased, and the residual CO in the exhaust gas was then reduced to the 02 concentration at that point. By providing residence time to maintain the exhaust gas at the temperature necessary for oxidation at the source, it is possible to reduce the residual CO concentration in the exhaust gas without using additional auxiliary fuel. be.

Examples of the present invention will be described below.

FIG. 1 shows an example in which the present invention is applied to a regenerating apparatus for a catalyst whose activity has deteriorated due to the adhesion of solid carbons to the surface of the catalyst after catalytic cracking of hydrocarbons.

Catalyst regeneration tower 1 is a regeneration device using a fluidized bed, and a catalyst (average particle size 210μ, specific gravity 380) used for catalytic cracking of hydrocarbons and having an average of 3.5 wt% of carbon attached to its surface is connected to a supply pipe. 2 to the catalyst layer 3.

Combustion air is supplied to the catalyst regeneration tower 1 from a supply pipe 4, is made uniform by a dispersion plate 5, and is supplied to the catalyst layer 3.

This air is not only used for combustion, but also serves as a gas that fluidizes the catalyst layer 3.

The regenerated catalyst from which carbon has been removed by combustion with the supplied air (carbon deposition rate 0.3 wt% or less) is transferred to the overflow pipe 6.
It flows into the pipe, is led out of the thread through the take-out pipe 7, and is used again for catalytic cracking.

Here, part of the amount of heat generated by combustion is used to raise the temperature of the catalyst layer 3, and the rest is recovered by the heat transfer tube 8 provided in the catalyst layer 3.

On the other hand, while the combustion air passes through the catalyst layer 3, most of the 02 is consumed in combustion, and when it leaves the catalyst layer 3, the so-called
It rises inside the freeboard 9 as exhaust gas.

During this time, some of the accompanying catalyst particles are sedimented and removed, and the rest are removed by the cyclone 1 installed in the freeboard 9.
0 and 11.

Here, the accompanying catalyst particles are removed as much as possible.

The removed particles are returned to the catalyst layer 3 through the pipe 12.

The exhaust gas from which entrained particles have been removed in the cyclones 10 and 11 is guided by a pipe 13 to a heat transfer tube 14 installed in the catalyst layer 3, where residual CO is reduced, and then exhausted to the outside through an exhaust pipe 15. be done.

The effects of this embodiment will be explained below.

Table 1 shows the results of sampling the exhaust gas from the inlet of the pipe 130 and the exhaust pipe 15 and measuring the residual CO concentration.The residence time of the exhaust gas at this time was approximately 2
2 seconds, including the piping 13, it was about 2.2 seconds.

This result shows that even if the residual 0□ concentration in the exhaust gas is low, the residual CO concentration can be reduced by passing it through the pipe 13 and the heat exchanger tube 14, and the temperature of the exhaust gas flowing inside the heat exchanger tube 14 can be adjusted by controlling the temperature of the exhaust gas flowing through the catalyst layer. 3, and even if the temperature of the catalyst layer 3 is relatively low, the residual CO
This shows that scales can effectively reduce the concentration.

However, when the temperature of the catalyst layer 3 becomes 750° C. or lower, the reduction effect is almost not observed. Therefore, the temperature of the catalyst layer needs to be 750° C. or higher.

In addition, in the conventional case (corresponding to the gas composition at the inlet of the pipe 130), when the residual CO concentration is reduced from about 3% to about 1.5%, the residual CO concentration doubles by 1.5 to 2 degrees. However, in the case of this example, no increase in the residual CO concentration was observed.

Further, when the residual 0□ concentration is lowered to about 1%, the residual CO concentration increases also in this example, but the effect of reducing the residual CO is still observed.

Further, if the final residual CO concentration in the exhaust gas is not required, the same type of heat transfer tube 15 as the heat recovery heat transfer tube 8 can be used.

In such a case, the pipe 13 may be installed outside the catalyst regeneration tower 1.

On the other hand, when a strict reduction in the residual CO concentration is required, the volume of the heat exchanger tubes 14 cannot be ignored, so it is necessary to give sufficient consideration to the dimensions, shape, total area, piping, etc. of the heat exchanger tubes 14.

Next, Table 2 shows the effect of reducing the residual CO concentration due to the removal of entrained particles in this example.

This is a comparison between using both cyclones 10 and 11, using only cyclone 10 and not using cyclone 11, and using neither cyclone 10 nor 11. The temperature of the catalyst layer is 847-852℃, and the residual 0□ concentration is 1.5-1.6.
%Met.

When both the cyclones 10 and 11 are not used, that is, when the conventional method is used, the residual CO in the heat exchanger tubes 15 is hardly reduced.

This is thought to be due to incomplete combustion of a small amount of carbon remaining on the surface of the entrained catalyst particles under the low 02 concentration and newly generating CO.

On the other hand, it can be seen that the reduction in the residual CO concentration when the entrained particles are removed using a cyclone is extremely significant.

Note that if the cyclones 10 and 11 have sufficient capacity, the height of the freeboard 9 can be lowered, so it is also possible to downsize the catalyst regeneration device.

FIG. 2 shows another embodiment, which has the structure of FIG. 1.

The difference from the conventional structure is that a heat transfer tube is installed inside the freeboard 9 to keep the exhaust gas warm.

In this device, exhaust gas exiting the cyclone 11 is guided to a heat exchanger tube 16 through a pipe 13, and further into a pipe 17,
It passes through the heat transfer tube 18 and is discharged to the outside of the yarn through the exhaust pipe 15.

Other parts are the same as in FIG. Table 3 shows the measurement results of the residual CO concentration at the inlet, middle, and outlet of the heat exchanger tubes. 13.
17, approximately 3.3 seconds (all at around 850°C).

This experimental result shows that the exhaust gas temperature is lower at the same catalyst layer temperature than in the case of the above-mentioned example. The concentration was almost the same as in the previous example.

The method of this embodiment can achieve the same residual CO concentration reduction effect by increasing the gas residence time to some extent even when there is no space to install a heat exchanger tube for gas heat retention in the catalyst layer.

FIG. 3 shows still another embodiment, which is applied to a small-sized fluidized bed combustion furnace for coal.

In this device, coal serving as a fuel is mixed with limestone at a constant ratio, and then co-supplied from a supply pipe 32 to a combustion furnace 31 .

Room-temperature air is introduced from the lower part of the combustion furnace 31 through the air supply pipe 33 and the distribution plate 35 to form a fluidized bed of particles supplied into the combustion furnace 31 .

This air is a fluidizing gas as well as a source of oxygen necessary for the combustion of coal.

Unburned content in the coal, which is mostly composed of char, and limestone, the surface of which has partially changed to calcium sulfate, are extracted from the system through the overflow pipe 36.

After the combustion gas passes through the freeboard 37 and removes fine particles with the cyclone 310, it is led out of the combustion furnace through a pipe 313.

Furthermore, after keeping the temperature high in the heat exchanger tube 314 provided outside the combustion layer 34 to reduce the residual CO concentration, the exhaust gas 1 tube 31
It is discharged by 5.

The temperature of the combustion furnace is controlled by the flow rate of coal supplied from the supply pipe 32.

The air flow rate was roughly set based on the coal supply amount, and the final concentration of residual 02 in the exhaust gas was set to 2 to 3%.

Collected gas from the piping 313 and exhaust pipe 315 and remaining gas
When the O concentration was analyzed, they were 540 ppm and 540 ppm, respectively.
2501) pIn.

At this time, the temperature of the combustion layer 34 was 863° C., and the gas residence time within the heat exchanger tube 314 was about 1.4 seconds.

In this way, the residual CO concentration can be reduced even in a small device in which it is difficult to install a heat-retaining heat exchanger tube inside the device.

In this way, the device described in the example can effectively reduce residual CO in exhaust gas containing unnaturally low concentrations of CO without using new fuel, and the effect is greater than that of conventional methods. Since the remaining 02 concentration does not change to about 1.5%, which is lower than the remaining 02 concentration, it is possible to reduce the power required to supply 02 or gas containing 02.

Furthermore, since a fluidized bed is used and there is no need for excessive supply of 0□ or for raising the combustion temperature, it is also possible to suppress the increase in NOx.

As described above, the method and apparatus for reducing residual CO in exhaust gas according to the present invention can reduce the amount of residual CO remaining in exhaust gas that cannot self-combust.
It makes it possible to reduce O2 economically and has great industrial effects.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of an embodiment of the apparatus for reducing residual carbon oxide in exhaust gas of the present invention, and FIG.
The figures are also explanatory diagrams showing the schematic configurations of different embodiments. Explanation of symbols 1... Catalyst regeneration tower, 3...
・Catalyst pipe, 4... Air supply pipe, 10.11...
...Cyclone, 13...Piping, 14,1
6, 18... Heat exchanger tube, 15... Exhaust pipe.

Claims (1)

[Claims] [1] A carbon-containing substance is burned in the presence of oxygen using a fluidized bed, and the exhaust gas contains an unnaturally low concentration of carbon monoxide and entrained particles containing unburned carbon. In this case, after performing an operation to reduce the entrained particles in advance, the exhaust gas is held at a predetermined temperature for a predetermined time under the oxygen concentration at that time, and the residual carbon oxide in the exhaust gas is oxidized. 1. A method for reducing residual carbon oxide in exhaust gas. 2. The method for reducing residual carbon oxide in exhaust gas according to claim 1, wherein the exhaust gas is maintained at a temperature of 750° C. or higher. 3. The residual carbon oxide reduction method according to claim 1, wherein the retention time of the exhaust gas is a residence time during which the exhaust gas passes through a predetermined temperature range. 4. A means for burning a carbon-containing substance in the presence of oxygen, a means for reducing entrained particles that generate carbon monoxide through combustion contained in the exhaust gas generated by the means, and a method for reducing the entrained particles by the means. In order to oxidize the carbon monoxide in the exhaust gas by holding the exhaust gas at a predetermined temperature for a predetermined time under the oxygen concentration at that time, the combustion means is provided at a position where heat from the combustion means can be transferred. 1. A device for reducing residual carbon oxide in exhaust gas, comprising a heat transfer means. 5. The device for reducing residual carbon oxide in exhaust gas according to claim 4, wherein the means for reducing the entrained particles is a cyclone. 6. The exhaust gas according to claim 4 or 5, wherein the combustion means is a catalyst regeneration tower using a fluidized bed, and the heat transfer means is a heat transfer tube provided in the fluidized bed. Residual carbon oxide reduction device inside. 7. Claim 4 or 5, wherein the combustion means is a catalyst regeneration tower using a fluidized bed, and the heat transfer means is a heat transfer tube provided on a freeboard of the catalyst regeneration tower. Remaining carbon oxide reduction device in exhaust gas. 8. The apparatus for reducing residual carbon oxide in exhaust gas according to claim 4 or 5, wherein the heat transfer means is a heat transfer tube provided on the outer periphery of the combustion means.