JPS6111653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas desulfurization method, and particularly to a dry exhaust gas desulfurization method using semiformed coke as an adsorbent.

Conventionally, the so-called lime-gypsum method is well known as a method for removing sulfur oxides (sulfur dioxide and sulfur trioxide are collectively referred to) from flue gas. However, with this method, as the equipment becomes larger, such as in thermal power plants, the amount of gypsum and other waste that is discharged becomes enormous, and it costs a lot of money to transport it. The disadvantage is that it is not easy to secure a place.

Therefore, in recent years, methods have been proposed to reduce emissions by recovering sulfur oxides in exhaust gas as easily treated elemental sulfur or hydrogen sulfide, rather than in the form of sulfates such as gypsum, and various processes have been developed. has been done. One of the processes for recovering elemental sulfur from sulfur oxides in exhaust gas is called the wet method.
An aqueous solution of alkali or the like is used to absorb sulfur oxides. This method requires a lot of water and
Also, waste water is unavoidable from the process,
The disadvantage is that new wastewater treatment equipment is required.

On the other hand, as a so-called dry process that does not use a large amount of water, a method is known in which sulfur oxides in exhaust gas are adsorbed and removed using activated carbon or a certain type of catalyst. In this method, sulfur oxides adsorbed on activated carbon or the like are reduced to elemental sulfur using a reducing gas, and the regenerated activated carbon and catalyst are recycled and reused in the adsorption process. As the reducing gas in this case, it is necessary to use a hydrogen-rich gas, such as naphtha or natural gas obtained by steam reforming. For this reason, conventional dry processes require the installation of a hydrogen generation plant or a hydrocarbon harvesting plant.
Another drawback was that the cost of hydrogen in the entire process was high.

The purpose of the present invention is to eliminate the drawbacks of the conventional dry desulfurization process described above, efficiently remove sulfur oxides contained in exhaust gas, and use hydrogen generated within the system without requiring a special hydrogen generation plant. An object of the present invention is to provide an exhaust gas desulfurization method that enables regeneration of an adsorbent.

In order to achieve the above object, the present invention
Semi-formed coke obtained by carbonization at 500 to 800°C is activated with water vapor and oxygen-containing gas and used as an adsorbent, and the exhaust gas is brought into contact with it to adsorb and remove sulfur oxides in the exhaust gas. The sulfuric acid generated on the adsorbent is reduced using the hydrogen-containing gas generated during activation of the semi-formed coke and/or the hydrogen-containing gas obtained from the carbonization gas of the coal, to produce hydrogen sulfide (H ₂ S). The method is characterized in that the adsorbent is desorbed from the semi-formed coke and the adsorbent is regenerated.

Typically, the present invention utilizes a portion of coal, which is a raw material for, for example, a coal-fired boiler, carbonizes it to produce semi-formed coke, and further activates it with steam and oxygen-containing gas. , the step of producing an adsorbent for sulfur oxides in exhaust gas and regenerating semi-formed coke attached in the form of sulfuric acid after adsorbing sulfur oxides in exhaust gas; In this system, hydrogen-rich gas generated by hydrogen gas is introduced to decompose sulfuric acid into H ₂ S-rich gas and eliminate it.

In the present invention, semi-formed coke is made of coal with a
Although it is produced by carbonization at 800°C, an adsorbent with sufficient adsorption capacity cannot be obtained outside the above temperature range. Next, the activation process of semi-formed coke is
This is carried out, for example, by partial oxidation of semiformed coke with steam and an oxygen-containing gas (for example air) at a temperature of 700 DEG to 900 DEG C., thus obtaining a porous surface-active adsorbent. The adsorbent produced in this way is contacted with exhaust gas under the formation of a moving or fluidized bed, usually at a temperature of about 100-150°C. Although it is desirable that the adsorption temperature be low, if the temperature is too low, the emitted processing gas may turn into white smoke, and if it is too high, the ability to adsorb sulfur oxides may be reduced.

Since the exhaust gas generally contains steam and oxygen in addition to sulfur oxides, the sulfur oxides are oxidized and adsorbed on the semi-formed coke in the form of sulfuric acid. This is then reduced by contact with a hydrogen-containing gas and desorbed from the semi-coke as hydrogen sulfide. As this hydrogen-containing gas, the carbonized coal gas or a reformed gas thereof, and/or the hydrogen-containing gas generated during activation of the semi-formed coke is used. Carbonization of coal produces approximately hydrogen
It is well known that so-called carbonized gas containing 50 vol% or more is generated, and in the activation process of semi-formed coke, the so-called partial oxidation reaction occurs because the semi-formed coke is treated with steam and oxygen-containing gas. This occurs and gases rich in hydrogen, carbon monoxide, carbon dioxide, etc. are generated. Therefore, in the present invention, all of the reducing gas can be provided by the hydrogen-containing gas generated within the system. This process of regenerating the adsorbent (semi-formed coke) is easily carried out by bringing the hydrogen-containing gas into contact with the adsorbent at a temperature of 250 to 350°C, for example, using a moving bed or fixed bed apparatus.

Next, one embodiment of the present invention will be explained according to the flow sheet shown in FIG.

In the figure, fuel coal is supplied to a coal-fired boiler 6 through a conduit 2. The boiler exhaust gas enters the sulfur oxide adsorber 10 via conduit 8;
After coming into contact with the semi-formed coke and removing most of the sulfur oxides, it is led to a subsequent process (for example, a chimney) through a conduit 12. The semi-formed coke and a part of the semi-formed coke pulverized in this step are sent to the boiler 6 through the conduit 20 and burned.

A portion of the coal supplied to the boiler 6 is supplied to the conduit 4
The coke is sent to the carbonization device 24 and carbonized at a temperature of 500 to 800°C, producing tar and carbonization gas along with semi-formed coke. The heavy tar content is extracted via conduit 22 and sent to boiler 6, for example.

The semi-formed coke is sent to an activator 30 via a conduit 28, where it undergoes a partial oxidation reaction with an oxygen-containing gas and steam (not shown) and is activated. after that,
Conduits 31 and 16 feed into adsorber 10.

The carbonization gas generated in the carbonization device 24 is a gas rich in hydrogen and methane, and is further converted into a gas rich in hydrogen by a known reformer 34 as necessary.
Conduit 36 sends it to desorber 14 .

In the activator 30, a portion of the carbon in the semi-formed coke is gasified by steam and oxygen, so that gas rich in hydrogen, carbon monoxide (CO), and carbon dioxide (CO ₂ ) is generated. Although the temperature of the activator 30 varies depending on the type of coal, it is appropriate to keep it in the range of 700 to 900°C. The gas generated here is sent to the desorber 14 via a conduit 32.

The sulfuric acid-adhered semi-coke enters the desorber 14 from the adsorber 10 via a conduit 18, where it comes into contact with the hydrogen-containing gas introduced from the conduits 32 and 36 to regenerate semi-coke. In this step, hydrogen-rich gas generated from the carbonization device 24 or hydrogen-rich gas generated from the activator 30 is used to
Sulfuric acid adhering to the semi-formed coke is desorbed in the form of H ₂ S. As the reducing gas used in this step, both of the gases generated in the above two steps may be used, but depending on the amount of gas produced, either one of the gases may be used. Also, the reaction temperature of this step is
250-350℃ is appropriate, but depending on the reaction conditions
In addition to H ₂ S, SO ₂ is also produced as a by-product, so the conduit 38
In this way, it can be introduced into the next step, for example, a known Claus reactor, and recovered as elemental sulfur. The semi-formed coke regenerated in the desorber 14 passes through the conduit 16, is combined with the semi-formed coke sent from the activator 30, and is returned to the adsorber 10.

A specific example of the present invention using the flow sheet shown in FIG. 1 will be described below.

Example 1 When 65.5 t/h of Australian coal containing a sulfur concentration of 0.7 wt% was charged into coal-fired boiler 6 and burned, the amount of exhaust gas was 500,000 Nm ³ /h, and the sulfur oxide concentration in the exhaust gas was was 632ppm. The temperature of the adsorber 10 was set to 150° C., and activated semi-formed coke was circulated between the moving bed 12 and the desorber 14 at a rate of 34.5 t/h. Since the semi-formed coke is consumed by pulverization etc., coal is supplied to the carbonizer 24 at a rate of 7.5 t/h,
Activated semi-formed coke was supplied through conduit 31. In the carbonizer 24, coal is carbonized at 700°C, and in the activator 30, the obtained semi-formed coke is heated to 850°C with steam and oxygen-containing gas while forming a moving bed.
It was activated by In the carbonization process, 2250Nm ³ /h of carbonization gas with the following composition is used along with 4.5t/h of semi-formed coke.
was generated.

_H2 : 54.1%, _CH4 : 31.6%, CO: 7.6%,
_CO2 : 2.8%, CnHm: 3.9% This gas is passed through a known reformer to partially oxidize _CH4, etc., and _CO2 is removed, resulting in a gas with the following composition.
2995m ³ /h was generated.

_H2 : 76.3%, CO: 23.7% In the activation process, gas with the following composition is 1463
m ³ /h produced.

_H2 : 36.5%, CO: 8.1%, ^CO2 : 18.8%, _N2 :
36.7% The desorber 14 is maintained at 250 to 350°C with a moving bed,
Hydrogen-rich gas generated in the carbonization device 24 or activator 30 described above was introduced, and the sulfur oxides adhering to the semi-formed coke in the form of sulfuric acid were desorbed as H ₂ S-rich gas. Since SO ₂ was mixed with H ₂ S in this gas, this gas was introduced into a known Claus reactor to recover 0.4 t/h of elemental sulfur.

Normally, in order to recover elemental sulfur from SO ₂ rich gas using a Claus reactor, new H ₂ S
A generator must be installed, but in the case of the present invention, H ₂ S is generated by reduction in the process of desorbing sulfuric acid adsorbed on semi-formed coke, so a new H ₂ S generator is installed. There will be no need.

Example 2 When Pacific coal with a sulfur concentration of 0.2 wt% is used as a raw material and treated in the same manner as in Example 1, the amount of sulfuric acid recovered by the adsorber 12 per unit time decreases, so The generated gas could be effectively used as it is for reduction in the desorber 14 without being particularly reformed.

As described above, according to the present invention, semi-coke is produced by carbonizing coal, and this is activated with steam and oxygen-containing gas to be used as an adsorbent for removing sulfur oxides from exhaust gas. Sulfur oxides in the exhaust gas can be easily treated by using a reducing gas containing H ₂ generated in the semi-formed coke manufacturing process in the process of removing sulfur oxides attached to the coke in the form of sulfuric acid. It can be recovered in the form of H ₂ S. Therefore, an economical dry desulfurization process is possible without requiring expensive activated carbon or catalysts or hydrogen gas generators for regeneration as in the past. Furthermore, in the treatment of exhaust gas from coal-fired boilers, it is particularly advantageous because an adsorbent can be produced from coal as a raw material.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. 6... Boiler, 10... Adsorber, 14... Desorber, 24... Carbonization device, 30... Activator, 34...
...Riff Ohmer.

Claims (1)

[Claims] 1. Semi-formed coke obtained by carbonizing coal at 500 to 800°C and activated with steam and oxygen-containing gas is used as an adsorbent, and exhaust gas is brought into contact with this to remove the After adsorbing and removing sulfur oxides,
The sulfuric acid produced on the adsorbent is reduced using the hydrogen-containing gas produced during activation of the semi-coke and/or the hydrogen-containing gas obtained from the carbonization gas of the coal, and the semi-coke is converted into hydrogen sulfide. An exhaust gas desulfurization method characterized in that the adsorbent is desorbed from the adsorbent and the adsorbent is regenerated. 2. The exhaust gas desulfurization method according to claim 1, wherein the exhaust gas is exhaust gas from a coal-fired boiler.