JP2007144298A - Efficient flue gas desulfurization method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To resolve problems wherein, in desulfurization of sulfur-containing flue gas generated in combustion of coal, a limestone-gypsum method requires power and a large amount of water for circulation of slurry causing enlargement and complication of the desulfurization facility, while in an adsorption method by activated carbon, a large amount of heat is needed for heating sulfur content adsorbed in activated carbon for decomposition and recovering, also causing enlargement and complication of the facility. <P>SOLUTION: High efficiency of the whole of the desulfurization system, durability, economic performance, easiness in maintenance and management of the desulfurization facility can be obtained, by combining a wet type ammonia absorbing method with a dry type activated carbon and alkaline absorption method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a flue gas desulfurization apparatus for removing sulfur oxide (SOx) in exhaust gas generated by combustion of coal or the like.

Conventionally, a limestone-gypsum method has been adopted as a desulfurization method for exhaust gas. As another method, an adsorption method using activated carbon is known as a dry method.

  In the above limestone-gypsum method, limestone or slaked lime fine powder is sprayed into the exhaust gas as a slurry liquid, and the exhaust gas is cooled and SOx is absorbed at the same time, so that the power required for circulating the slurry and a large amount of water are required. The by-product slurry gypsum requires a device for separating the water and collecting the gypsum. Therefore, the limestone-gypsum method is required to increase the size and complexity of the desulfurization equipment.

  On the other hand, in the case of an adsorption method using activated carbon as a dry method, the sulfur content adsorbed on the activated carbon is heated to be decomposed and recovered, so a large amount of heat is required, and the equipment is required to be large and complicated.

However, according to the above technique, the limestone-gypsum method requires power and a large amount of water required for the circulation of the slurry, and the desulfurization equipment cannot be increased in size and complexity. On the other hand, in the adsorption method using activated carbon, the sulfur component adsorbed on the activated carbon is heated to be decomposed and recovered, so that a large amount of heat is required, and the equipment must be enlarged and complicated.
Therefore, an object of the present invention is to provide a compact and simplified desulfurization facility that does not require a large amount of power, a large amount of water, and a large amount of heat.

In order to solve the above-mentioned problems, the invention of claim 1 introduces an exhaust gas containing sulfur produced by combustion of coal or the like into a lower desulfurization chamber of a desulfurization tower, and evaporates under an atmosphere where the exhaust gas temperature is 130 ° C. or higher. Primary desulfurization treatment is performed by mixing reaction with ammonia that has become gas due to the heat of the bed, and the first-treated exhaust gas is introduced into the upper desulfurization chamber, and residual sulfur content in the exhaust gas is absorbed by the lamination of the alkaline desulfurization block. It is characterized by the following desulfurization treatment.
The invention according to claim 2 is that in the lower desulfurization chamber, a mixture of water and ammonia is sprayed with a nozzle, gasified by the heat of the evaporating bed in an atmosphere with an exhaust gas temperature of 130 ° C. or higher, and mixed with the exhaust gas containing sulfur. It reacts and performs a primary desulfurization process.
The invention of claim 3 absorbs residual sulfur in the exhaust gas entering from the lower desulfurization chamber by laminating an alkaline desulfurization block composed of activated carbon, concrete, iron powder and quicklime, slaked lime, etc. in the upper desulfurization chamber. It is characterized by performing a secondary desulfurization process.

According to the first invention, the second invention, or the third invention, a desulfurization facility that does not require a large amount of power, a large amount of water, and a large amount of heat and that is highly efficient, compact, and simplified can be realized.

Embodiments of the present invention will be described below.
As shown in FIG. 1, the present invention includes a desulfurization tower 3, an evaporating bed 4, a nozzle 5, a lower desulfurization chamber 6, a desulfurization block 7, a desulfurization block stack 17, an upper desulfurization chamber 8, a water tank 9, a pump 10, and a pump 11. , An ammonia tank 12, a mixer 13, a vent hole 16, and the like.

Exhaust gas containing sulfur produced by combustion of coal or the like enters the lower desulfurization chamber 6 of the desulfurization tower 3 and rises through the vent hole. Ammonia supplied by the mixer 13 or the like is sprayed through the nozzle 5 and becomes a gas by the heat of the evaporating bed in an atmosphere where the exhaust gas temperature is 130 ° C. or more, and is mixed with the exhaust gas containing the rising sulfur content. This is a primary desulfurization treatment, that is, desulfurization by ammonia absorption. This reaction is considered as follows.
2NH ₃ + SO ₂ + H ₂ O → (NH ₄ ) ₂ SO ₃

The exhaust gas containing the mixed gas that has undergone this primary desulfurization process rises and enters the stack of alkaline desulfurization blocks such as activated carbon, concrete, iron powder and quicklime and slaked lime in the upper desulfurization chamber, and is produced by ammonia absorption (NH ₄ ) ₂ SO ₃ is adsorbed on the activated carbon part of the desulfurization block. In addition, partially unreacted SO ₂ reacts with H ₂ O and is adsorbed on activated carbon of the desulfurization block to become H ₂ SO ₄ , and NH ₃ reacts with H ₂ SO ₄ to form NH ₄ HSO on the activated carbon surface. ₄ and (NH ₃ ) ₂ SO ₃ are produced. On the other hand, the remaining sulfur oxides are neutralized with the alkaline material of the desulfurization block and absorbed by the alkaline material. On the other hand, the iron powder contained in the desulfurization block undergoes an oxidation reaction with SO ₂ and H ₂ O to become FeSO ₄ and Fe ₂ (SO ₄ ) ₃ , which undergoes oxidative expansion and has already been adsorbed on activated carbon (NH ₄ ). ₂ SO ₃ and the neutralized material absorbed by the alkaline material are peeled off from the wall surface of the desulfurization block vent hole. Thus, new activated carbon and alkaline material wall surfaces are exposed again. The secondary desulfurization treatment is performed by these adsorption, absorption reaction, and oxidation reaction. The alkali absorption reaction is considered as follows.
SO ₂ + H ₂ O = H ₂ SO ₃ = H ⁺ + HSO ₃ ⁻
SO ₂ + 2OH ⁻ = SO ₃ ²⁻ + H ₂ O
2SO ₃ ^2- + O ₂ = 2SO ₄ ^2-

In addition, due to the strong dehumidifying ability of the desulfurized block alkaline material, water vapor in the exhaust gas is absorbed, the moisture content of the exhaust gas becomes 1.2%, and the temperature of the exhaust gas becomes 130 ° C or higher, so it is necessary to reheat the exhaust gas In addition, there is no risk of condensation on equipment such as a suction fan.

Since the desulfurization block has a fine porous structure by special processing, it can efficiently absorb and adsorb (NH ₄ ) ₂ SO ₃ , residual sulfur and water vapor in the exhaust gas passing through the vent holes. However, the desulfurization block has poor performance after a certain period of time because absorption and adsorption are becoming saturated. Therefore, a new desulfurization block must be replaced at regular intervals to maintain the desulfurization efficiency. The exchange cycle is once every 6 months.

By-products such as ammonium sulfate produced by desulfurization are taken out of the system, separated, recovered and disposed of when the desulfurization block is replaced.

It is a systematic diagram of a desulfurization apparatus. It is the elements on larger scale of an evaporating bed. It is a desulfurization block diagram.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Boiler 2 Dust collector 3 Desulfurization tower 4 Evaporation bed 5 Nozzle 6 Lower desulfurization chamber 7 Desulfurization block 8 Upper desulfurization chamber 9 Water tank 10 Pump 11 Pump 12 Ammonia tank 13 Mixer 14 Suction fan 15 Chimney 16 Vent hole 17 Desulfurization block lamination

Claims (3)

An exhaust gas containing sulfur produced by combustion of coal or the like is introduced into the lower desulfurization chamber of the desulfurization tower, and the primary reaction is performed by a mixed reaction with ammonia that has become a gas due to the heat of the evaporating bed in an atmosphere with an exhaust gas temperature of 130 ° C. A high-efficiency flue gas desulfurization method characterized by introducing desulfurized and primary-treated exhaust gas into the upper desulfurization chamber, and performing secondary desulfurization treatment of residual sulfur content in the exhaust gas by absorbing a stack of alkaline desulfurization blocks; apparatus. In the lower desulfurization chamber, a mixture of water and ammonia is sprayed with a nozzle, gasified by the heat of the evaporating bed in an atmosphere with an exhaust gas temperature of 130 ° C. or higher, mixed with the exhaust gas containing sulfur, and subjected to primary desulfurization treatment The high-efficiency flue gas desulfurization method and apparatus according to claim 1, wherein: In the upper desulfurization chamber, secondary desulfurization treatment is performed by absorbing residual sulfur in the exhaust gas entering from the lower desulfurization chamber by laminating alkaline desulfurization blocks composed of activated carbon, concrete, iron powder and quicklime, slaked lime, etc. The high-efficiency flue gas desulfurization method and apparatus according to claim 1.