JPS6127645B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a desulfurization method using a three-stage combustion method.
Conventionally, one method for desulfurizing combustion exhaust gas from fuel containing a large amount of ash was to supply alkali directly into the furnace and remove it as salt removal or sulfite. However, with this method, as the temperature inside the furnace increases, reactions such as CaO + SO ₂ +1/2O ₂ →CaSO ₄ ...(1) Na ₂ O + SO ₂ +1/2O ₂ →Na ₂ SO ₄ ...(2) become less likely to occur. As is clear from the relationship between furnace temperature and desulfurization rate shown in Figure 1, 1000
There was a problem that the desulfurization rate decreased at high temperatures above ℃. On the other hand, in a reducing atmosphere, sulfides such as CaO+H ₂ S→CaS+H ₂ O…(3) Na ₂ O+H ₂ S→Na ₂ S+H ₂ O…(4) Na ₂ O+SO ₂ +3C→Na ₂ S+3CO…(5) The main reaction is to produce , and the sulfides produced by these reactions are stable even at high temperatures.

Therefore, a method has been devised in which a staged combustion method known as a two-stage air combustion method is used to carry out reductive combustion in the primary combustion zone in the absence of air, and a reducing agent is supplied to the primary combustion zone. However, in this method, 1
Most of the sulfides generated in the secondary combustion zone are oxidized again after the secondary combustion zone where excess air is supplied and combustibles are completely burned, and the captured S is converted into CaO+3/2O ₂ →CaO+SO ₂ ...( 6) Since it is released through reactions such as Na ₂ S + 3/2O ₂ →NaO + SO ₂ (7), there was a problem that the results were not much different from conventional desulfurization methods.

Furthermore, when the ash content is high, most of the alkali supplied to the primary combustion zone reacts with silicic acid, which is the main component of the ash content, before reacting with S, creating complex silicate compounds and reducing the desulfurization effect. Another problem was that in many cases the value was very low.

The present invention aims to solve such problems, and in a three-stage combustion method in which fuel and air are separately supplied, the furnace is divided into at least a primary combustion chamber and a secondary combustion chamber, and the primary combustion chamber The primary fuel is combusted in the primary combustion chamber by maintaining the ash at a high temperature higher than the pour point of the ash, the ash is taken out in a molten state from the primary combustion chamber, and then the primary combustion in the primary combustion chamber is performed. Exhaust gas is supplied to a secondary combustion chamber, and in the secondary combustion chamber, excess secondary fuel is supplied to combust while maintaining the secondary combustion area in a reducing atmosphere, and a desulfurization agent is supplied to perform desulfurization. The sulfur content is extracted as sulfide, and then the secondary combustion exhaust gas is
Secondary air is supplied and tertiary combustion is performed to completely burn and oxidize the unburned components contained in the secondary combustion exhaust gas, while the sulfides generated in the secondary combustion chamber are sent to a carbonation device and converted into carbonate. At the same time, the carbonate is supplied as a desulfurization agent to the secondary combustion chamber for circulation use, and the H ₂ S generated in the carbonation device is recovered as elemental sulfur in a Claus furnace. By providing a desulfurization method using a staged combustion method,
This objective is achieved by providing a process in which the desulfurization rate of combustion exhaust gas can be improved compared to conventional methods, and the desulfurization agent can be recycled.

The method of the present invention will be explained in detail below based on the drawings showing one embodiment thereof. In FIG. 2, 1 is a primary combustion chamber that is supplied with primary fuel 2 and primary air 3 and performs primary combustion; 4 is a primary combustion chamber into which primary combustion exhaust gas 5 of the primary combustion chamber 1 is introduced; A secondary combustion chamber 8 is supplied with a secondary fuel 6 and a carbonate 7 as a desulfurizing agent and performs secondary combustion.The secondary combustion exhaust gas 9 of the secondary combustion chamber 4 is introduced into the secondary combustion chamber 8, and the secondary combustion chamber 8 is supplied with secondary air 10. A tertiary combustion chamber performs tertiary combustion, and the furnace is formed by three combustion chambers, a primary combustion chamber 1, a secondary combustion chamber 4, and a tertiary combustion chamber 8. 11 is the tertiary combustion exhaust gas 1 of the tertiary combustion chamber 8
The combustion gas that has passed through the exhaust gas secondary treatment device 11, such as a dust collector or, in some cases, a denitration device, which performs secondary treatment of the tertiary combustion exhaust gas 12 by introducing the 13 is released into the atmosphere 14. 15 is a carbonation device into which sulfide 16 generated from carbonate 7 is introduced in the secondary combustion chamber 4 and returns the sulfide 16 to carbonate 7; ash 17 is also taken out from the sulfide 16; is H ₂ S18
occurs. The carbonate 7 obtained in the carbonation device 15 is circulated to the secondary combustion chamber 4. _Reference numeral 19 denotes a Claus furnace into which H ₂ S 18 generated in the carbonation device 15 is introduced and O ₂ 20 is supplied to recover elemental sulfur 21 _from the H ₂ S 18.
The exhaust gas 24 containing the above is circulated to the secondary combustion chamber 4.

The operation of this configuration will be described next. First, primary fuel 2 and primary air 3 are supplied to primary combustion chamber 1, and primary combustion is performed while maintaining primary combustion chamber 1 at a high temperature higher than the pour point of ash. As a result, the ash 22 is taken out in a molten state. At this time, if the primary air 3 is supplied in an amount equal to or greater than the theoretical air amount of the primary fuel 2, the inside of the primary combustion chamber 1 can be maintained in an oxidizing atmosphere to avoid corrosion of the heat absorption pipes and the like. Next, the primary combustion exhaust gas 5 of the primary combustion chamber 1 is introduced into the secondary combustion chamber 4, and the excess secondary fuel 6 and alkali carbonates (CaCO ₃ , Na ₂ CO ₃ , etc.) to perform secondary combustion while maintaining the secondary combustion area in a reducing atmosphere. As a result, sulfur content is extracted as sulfide 16. At this time, the main reactions are CaCO ₃ +H ₂ O→CaS+CO ₂ +H ₂ O (8) Na ₂ CO ₃ +H ₂ S→Na ₂ S+CO ₂ +H ₂ O (9), etc. Note that if a fuel with a low ash content is used as the secondary fuel 6, consumption of the carbonate 7 by silicic acid in the ash can be greatly reduced, and the reaction can be promoted. Next, 2 of secondary combustion chamber 4
The secondary combustion exhaust gas 9 is introduced into the tertiary combustion chamber 8, and the secondary air 10 is also supplied to the tertiary combustion chamber 8 for tertiary combustion. As a result, the unburned components contained in the secondary combustion exhaust gas 9 are completely combusted and oxidized. As mentioned above, the secondary air 1 is also in the tertiary combustion chamber 8.
If a large amount of 0 is supplied and burned while maintaining an oxidizing atmosphere, corrosion of the heat absorbing tubes etc. can be avoided. Next, the tertiary combustion exhaust gas 12 in the tertiary combustion chamber 8,
The tertiary combustion exhaust gas 12 is introduced into a secondary exhaust gas treatment device 11 and further treated, and then released into the atmosphere 14 as a combustion gas 13. On the other hand, the secondary combustion chamber 4
The sulfide 16 produced in is introduced into a carbonation device 15, where it is brought into contact with steam 23 and combustion gas 13 and returned to carbonate 7. The combustion gas 13 is transferred from the exhaust gas secondary treatment device 11 to the atmosphere 1.
A part of the combustion gas 13 to be released into the carbonator 1
It is recommended to supply it to 5 and make effective use of it. The reaction in which the sulfide 16 returns to the carbonate 7 is the reverse reaction of the above formulas (8) and (9). The carbonate 7 obtained in the carbonation device 15 is 2
It is supplied to the next combustion chamber 4 and used for circulation as an alkali absorbent. Next, H ₂ S18 generated by the reverse reaction in the carbonation device 15 is introduced into the Claus furnace 19, and H ₂ S + 3/2O ₂ →SO ₂ +H ₂ O …(10) 2H ₂ S+SO ₂ →3S+2H ₂ O …( 11) It is recovered as elemental sulfur 21 through the reaction.

As described above, according to the method of the present invention, the desulfurization rate does not decrease even when the temperature inside the furnace is high, and since the desulfurization agent is not supplied to the primary combustion chamber, the desulfurization agent is reacted with silicic acid, which is the main component of the ash. This method does not reduce the desulfurization effect due to the production of complex silicate compounds, and the desulfurization rate of combustion exhaust gas can be improved compared to conventional methods. Moreover, it is possible to provide a process in which the sulfur content taken out from the secondary combustion chamber is recovered as elemental sulfur, and the desulfurization agent can be recycled.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between furnace temperature and desulfurization rate in a conventional desulfurization method, and FIG. 2 is a flow sheet diagram showing an embodiment of the method according to the present invention. 1...Primary combustion chamber, 2...Primary fuel, 4...2
Secondary fuel chamber, 5... Primary combustion exhaust gas, 6... Secondary fuel, 7... Carbonate, 8... Tertiary combustion chamber, 9... 2
Secondary combustion exhaust gas, 10... Secondary air, 15... Carbonation device, 16... Sulfide, 17... Ash content, 18...
...H ₂ S, 19...Klaus reactor, 21...Elementary sulfur.

Claims (1)

[Claims] 1 In the three-stage combustion method where fuel and air are supplied separately, the furnace is divided into at least a primary combustion chamber and a secondary combustion chamber.
The primary combustion chamber is divided into secondary combustion chambers, the primary combustion chamber is maintained at a high temperature above the pour point of the ash, the primary fuel is combusted in the primary combustion chamber, and the ash is removed from the primary combustion chamber in a molten state. , Next, the primary combustion exhaust gas in the primary combustion chamber is supplied to a secondary combustion chamber, and in the secondary combustion chamber, excess secondary fuel is supplied and burned while maintaining the secondary combustion area in a reducing atmosphere. At the same time, a desulfurizing agent is supplied to perform desulfurization, thereby extracting the sulfur content as sulfide, and then removing the secondary combustion exhaust gas from its downstream side.
Secondary air is supplied and tertiary combustion is performed to completely burn and oxidize the unburned components contained in the secondary combustion exhaust gas, while the sulfides generated in the secondary combustion chamber are sent to a carbonation device and converted into carbonate. At the same time, the carbonate is supplied as a desulfurization agent to the secondary combustion chamber for circulation use, and the H ₂ S generated in the carbonation device is recovered as elemental sulfur in a Claus furnace. Desulfurization method using staged combustion method.