JPS6111656B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a regeneration process of activated carbon used in flue gas desulfurization, and a method for reducing SO ₂ in the gas purged in this regeneration process.
Combined with the process of reducing sulfur to sulfur using coal,
An inert gas containing substantially no oxygen is generated from the semi-coked coal by-produced in the reduction process and the flue gas desulfurized, and this inert gas is used as the regeneration gas in the regeneration process described above. This relates to a method for regenerating activated carbon used for flue gas desulfurization.

As one of the so-called flue gas desulfurization methods for desulfurizing exhaust gas from fixed sources, activated carbon is used as an adsorbent for sulfur oxides, and the activated carbon is brought into contact with the exhaust gas to adsorb the sulfur oxides in the exhaust gas onto the activated carbon. has been put into practical use. In this flue gas desulfurization method, sulfur oxides gradually accumulate on the activated carbon due to contact with the exhaust gas, and the adsorption capacity of the activated carbon declines, so it is necessary to regenerate it at an appropriate time to restore its adsorption capacity. It won't happen.

Activated carbon whose adsorption capacity has declined can be regenerated by using, for example, an AC moving bed regenerator, which maintains the activated carbon in a moving bed state and indirectly heats it while injecting oxygen-free inert gas into the moving bed of the activated carbon. This can be carried out by bringing sulfur oxides (mainly SO ₂ ) into contact with activated carbon to remove sulfur oxides (mainly SO 2 ). From the SO ₂ -containing gas obtained during this regeneration, elemental sulfur can be recovered by bringing it into contact with coal to reduce SO ₂ to sulfur.

By the way, the substantially oxygen-free inert gas required when regenerating activated carbon can be obtained by burning gaseous fuel such as LPG or liquid fuel such as light oil while adjusting the amount of air, or by nitrogen gas separation method using air deep cooling. , a coke bed flow method of oxygen-containing gas, a method of adsorption and separation of oxygen using a molecular sieve, and the like. However, in this method, the fuel used is expensive, and the amount of
The major drawback is that it requires a large amount of fuel and is uneconomical since it requires 21% of the oxygen consumed. This method is relatively economical if it is carried out on a large scale and at the same time the oxygen obtained can be used effectively. Not suitable. Although the method described above is suitable for obtaining nitrogen gas on a relatively small scale, it is not suitable for obtaining a large amount of nitrogen gas. This method has the advantage of being able to use a gas with a relatively low oxygen concentration, such as flue gas, and therefore also consuming less coke.

On the other hand, considering the process of bringing SO ₂ -containing gas obtained during activated carbon regeneration into contact with coal to reduce SO ₂ in the gas to sulfur, the SO ₂ -containing gas obtained during activated carbon regeneration is H ₂ SO ₄・_nH2O ＋1/2C
→1/2CO ₂ + (n+1)H ₂ O As can be understood from the regeneration reaction formula, each 1 mole of SO ₂ contains (n+1) moles of water vapor, so when reducing SO ₂ in this gas to sulfur, It is extremely difficult to completely avoid the by-product of H ₂ S caused by the presence of water vapor. Therefore, when attempting to recover sulfur from SO ₂ -containing gas obtained during activated carbon regeneration, the contact temperature (reaction temperature) and residence time between coal and gas must be properly controlled to recover H ₂ S. It is necessary to suppress by-products as much as possible. According to the knowledge obtained by the present inventors regarding this point, in order to suppress the by-product of H ₂ S and increase the reaction rate from SO ₂ to S,
It is important that the coal in the reactor is discharged from the reduction reactor without reacting sufficiently, in other words, in a semi-coked state in which the coal is not completely coked. However, there is a disadvantage in that the coal utilization rate decreases.

The present invention focuses on the fact that the above-mentioned semi-coked coal can be used as a raw material for obtaining the inert gas necessary for regenerating activated carbon, and the present invention has been developed in a process of regenerating activated carbon and reducing _SO2- containing gas with coal. By combining these methods, the disadvantage of reduced coal utilization in the reduction process can be eliminated, and an inert gas for regenerating activated carbon can be easily obtained.

That is, the present invention provides a method for regenerating activated carbon for flue gas desulfurization, in which activated carbon used for flue gas desulfurization is brought into contact with an inert gas at an elevated temperature to purge SO ₂ -containing gas from the activated carbon. The SO ₂ -containing gas purged from the activated carbon is introduced into a moving bed type coal-packed tower to reduce SO ₂ to sulfur, and the semi-coked coal produced as a by-product of this reduction reaction is taken out from the coal-packed tower. , (b) supplying this semi-coked coal and flue gas desulfurized combustion flue gas to an inert gas generating furnace,
(c) The inert gas obtained here is used as a regeneration gas for activated carbon used in flue gas desulfurization. The present invention provides a method for regenerating activated carbon for flue gas desulfurization.

Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings. FIG. 1 shows an example of a flow sheet suitable for carrying out the method of the present invention.
Reference numerals 1, 4, and 9 in the figure indicate an activated carbon regeneration tower, a moving bed packed tower, and an inert gas generating furnace, respectively. 1st
In the figure, activated carbon (hereinafter referred to as deactivated activated carbon) that has been used for flue gas desulfurization and whose sulfur oxide adsorption ability has declined is fed into the regeneration tower 1 from the top thereof. Activated carbon regeneration tower 1 also receives a substantially oxygen-free inert gas (the source of which will be described below) through line 2, which contacts the deactivated activated carbon at a relatively low temperature of 300 to 400°C. . Through this contact, the deactivated activated carbon is regenerated by releasing SO ₂ without burning, and the SO ₂ desorbed from the activated carbon is purged from the regenerated activated carbon by an inert gas, and SO _{2 is} released.
It is taken out to the pipe line 3 as a contained gas. Although not shown, the regenerated activated carbon is usually continuously taken out from the regeneration tower 1 and sent to the flue gas desulfurization equipment, where it can of course be reused for adsorption and removal of sulfur oxides in the combustion flue gas. .

The SO ₂ -containing gas taken out from the activated carbon regeneration tower 1 is supplied to a moving bed type coal packed tower 4 through a pipe 3 . In the packed tower 4, the moving bed of coal supplied from the top of the tower comes into contact with the SO2 _- containing gas, and under the conditions described in, for example, Japanese Patent Publication No. 54-36159, the _SO2 in the gas is converted into vapor form. is reduced to elemental sulfur. As mentioned above, in this reduction reaction,
It is important to discharge coal, which is a reducing agent, from the bottom of the packed tower 4 in a semi-coked state in order to suppress the by-product of H ₂ S, and generally the movement speed of the coal within the packed tower 4 is adjusted. By doing so, the coal can be discharged from the packed tower in a semi-coked state. The vaporized elemental sulfur produced by the reduction reaction in the packed column 4 is taken out along with other gases into a pipe 5 and sent to a sulfur condenser (not shown), where sulfur is recovered.

On the other hand, the coal discharged from the bottom of the packed tower 4 into the pipe 7 in a semi-coked state is passed through the sieve 7 to remove ash, etc., and then sent to the inert gas generating furnace 9 via the pipe 8. It is introduced from the top and forms a moving bed within the furnace. The inert gas generating furnace 9 is supplied with flue gas desulfurized from a pipe 10 . This combustion exhaust gas comes into contact with semi-coked coal under elevated temperature and is inactivated. That is, substantially all the oxygen contained in the exhaust gas is consumed by contact with the semi-coked coal. By the way, taking boiler exhaust gas as an example, the oxygen concentration in combustion exhaust gas is 3 to 8 in a coal boiler.
%, and is 1 to 6% for heavy oil-fired boilers, and this value fluctuates in the range of 50 to 100% depending on load fluctuations of each boiler. However, even in such a case, by supplying auxiliary air in a controlled amount to the inert gas generating furnace 9 as necessary to maintain the furnace temperature at 600 to 900°C, preferably 700 to 800°C. , can consume virtually all the oxygen supplied into the furnace. The substantially oxygen-free inert gas thus obtained is taken out from the inert gas generating furnace 9 into the pipe line 2 and supplied to the activated carbon regeneration tower 1.

In addition, in the inert gas generating furnace 9, it is possible to control the movement speed of the semi-coked coal so that it turns into ash at the furnace outlet, but in order to avoid troubles due to ashing, it is possible to control the movement speed of the semi-coked coal control so that it is discharged from the furnace outlet in a state where it remains,
As shown in the figure, after the semi-coked coal coming out of the pipe 11 is passed through a sieve 7 to remove ash,
Circulating to the inert gas generating furnace 9 via the pipe line 8 allows for more stable operation.

FIG. 2 shows another flow when implementing the present invention. In this example, combustion exhaust gas is supplied to the indirect heat exchanger 20 attached to the activated carbon regeneration tower 1, and the activated carbon regeneration tower receives heat. The combustion exhaust gas discharged from the heat exchanger 20 to the pipe line 21 is supplied to the inert gas generating furnace 9. After removing ash in the sieving machine 7, a part of the semi-coked coal is sent to the inert gas generating furnace 9 through a pipe line 8, and is then diverted to a pipe line 22 and supplied to the moving bed type coal packed tower 4. . The rest of the flow is the same as the flow shown in FIG.

If you follow the flow shown in Figure 2, you can supply heat to the activated carbon regenerator 1 and the combustion exhaust gas discharged from the heat exchanger 20 at a temperature of about 300 to 350°C to the inert gas generation furnace. This has the advantage of making it easier to control the temperature inside the furnace. In addition, since the semi-coked coal can be reused in the moving bed type coal-filled tower, there is also the advantage that the coal can be used without wasting it as a whole.

As is clear from the above explanation, according to the present invention, the inert gas necessary for regenerating activated carbon can be produced by using semi-coked coal, which is produced as a by-product when reducing SO ₂ to sulfur. It can be generated.

[Brief explanation of the drawing]

FIGS. 1 and 2 show an example of a flow sheet for carrying out the method of the present invention. 1; Activated carbon regeneration tower, 2; Inert gas pipe, 3;
SO2 _- containing gas pipe, 4; moving bed coal-filled tower,
7; Sieving machine, 8; Semi-coked coal pipeline,
9; Inert gas generator, 10; Combustion exhaust gas pipe,
20; indirect heat exchanger, 21; combustion exhaust gas pipe, 2
2; Semi-coked coal distribution pipe.

Claims (1)

[Claims] 1. In a method for regenerating activated carbon for flue gas desulfurization, in which activated carbon used for flue gas desulfurization is brought into contact with an inert gas at an elevated temperature to purge SO ₂ -containing gas from the activated carbon, (a ) The SO ₂ -containing gas purged from the activated carbon is introduced into a moving bed type coal-packed tower to reduce SO ₂ to sulfur, and the semi-coked coal produced as a by-product of this reduction reaction is transferred from the coal-packed tower. (b) supplying this semi-coked coal and flue gas desulfurized combustion flue gas to an inert gas generating furnace;
(c) The inert gas obtained here is used as a regeneration gas for activated carbon used in flue gas desulfurization. A method for regenerating activated carbon for flue gas desulfurization, characterized by: