JPH02194836A - Drying method for desulfurizing agent - Google Patents

Abstract

PURPOSE:To economically and efficiently dry a desulfurizing agent by supplying the precursor of the desulfurizing agent to the top part of a fluidized bed type absorption tower and drying it by desulfurized waste gas or high-temp. air for the combustion of a boiler. CONSTITUTION:Coal ashes, lime component and gypsum component are supplied to a mixer 4 through a conduit 11 and mixed. The mixture is sent to a kneader 5 through a conduit 12 as a powdery raw material and kneaded with water 13. The obtained kneaded material is sent to a heater 6 through a conduit 14 and heat-treated by steam 15 and thereafter sent to the top part of an absorption tower 2 through a conduit 16 as the precursor of a desulfurizing agent. One part of desulfurized exhaust gas is supplied to the top part of the absorption tower 2 through a conduit 21. Therefore the precursor of the absorbent is dried while it is transferred through the top part of the absorption tower 2. The dried desulfurizing agent is brought into contact with waste gas supplied through a conduit 7 and absorbs gaseous SO2 and thereafter discharged to the outside of the system through a conduit 31 as the spent desulfurizing agent. A part of flue gas desulfurized in the absorption tower 2 is resupplied to the top part thereof and the other part is discharged through a stack 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for drying a desulfurizing agent, and particularly to a method for drying a desulfurizing agent that can efficiently dry an absorbent for treating exhaust gas.

[Conventional technology]

Conventional desulfurization methods for removing sulfur dioxide gas (So□) from exhaust gas include wet desulfurization, in which an alkaline agent is mixed with water and brought into contact with the exhaust gas, and dry desulfurization, in which solid particles of an alkaline agent are injected into the boiler furnace. There is a law.

The wet desulfurization method has a higher utilization rate of alkaline agent and desulfurization rate than the dry desulfurization method, but has the disadvantage that the exhaust gas temperature decreases, requiring reheating of the exhaust gas, and that desulfurization wastewater is generated.

On the other hand, the dry desulfurization method has a high exhaust gas temperature, does not require reheating of the exhaust gas, and does not generate desulfurization wastewater, but has the drawbacks of low utilization rate of alkali agent and low desulfurization rate.

[Problems to be Solved by the Invention] The present inventors have developed a method using coal ash, silicon oxide, or alumina oxide containing silica, alumina, etc. as a high-performance desulfurization agent.
Ca (OH) 2, lime components such as CaO, and CaS
We proposed a desulfurization agent obtained by mixing gypsum components such as O4'2H20 and CaSO4, adding water to make a clay-like mixture, and then heating and solidifying the mixture with steam. This desulfurization agent is
As shown in the diagram of the relationship between gas contact time and desulfurization rate due to changes in desulfurization agent water content, the desulfurization rate improves as the water content in the desulfurization agent decreases. In addition, A in the figure is a desulfurizing agent with a moisture content of 34%, B with a moisture content of 15 to 17%, and C with a moisture content of 1% or less.

When kneading coal ash, etc., lime component, and gypsum component with water, 30 to 30 parts by weight per 100 parts by weight of the raw material mixture.
50% by weight of water is preferably used, but this water is retained in the desulfurizing agent precursor after heat treatment in a steam atmosphere without evaporating. This desulfurizing agent precursor is ncao・A/
, zO,, mCaSO4-fH20 (however, n, m,
j2 is an integer), and is stably solidified by crystal water.

However, in order to obtain a desulfurizing agent with higher performance, it is advantageous to increase the number of pores that can sufficiently diffuse the absorbed gas into the absorbent, and since stable substances have low reaction activity, the desulfurizing agent It is necessary to dry the agent precursor to remove crystal water and increase the number of pores.

On the other hand, in the moving bed type absorption tower used in the dry desulfurization method, the desulfurization agent is supplied from the top of the absorption tower and passes through the absorption tower.
During that time, it comes into contact with exhaust gas and absorbs S02 gas,
The desulfurizing agents are piled up so that the height H of the desulfurizing agent at the top of the absorption tower is greater than the gas passage length Z, that is, so that the relationship Z<H holds (see FIG. 2). This relationship is Z
>H, the untreated gas from the gas inlet side causes a short path, flows into the top of the absorption tower, and flows to the gas outlet side without being desulfurized. Therefore, in a moving bed type absorption tower, a space corresponding to the height H is not necessary.

An object of the present invention is to provide a method for drying a desulfurizing agent that can economically and efficiently dry the desulfurizing agent using a conventional moving bed absorption tower.

[Means for Solving the Problems] The method for drying a desulfurizing agent of the present invention involves supplying a precursor of a desulfurizing agent used for absorbing and removing sulfur oxides in exhaust gas to the upper part of a moving bed type absorption tower, It is characterized by drying with desulfurized exhaust gas or high temperature air for boiler combustion.

The desulfurizing agent precursor used in the present invention is preferably obtained by kneading coal ash, silicon oxide, or aluminum oxide, a lime component, and a gypsum component with water and heat-treating the mixture in a steam atmosphere.

〔Example] Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a system diagram of a desulfurization apparatus according to an embodiment of the present invention;
FIG. 2 is an enlarged sectional view of the absorption tower in FIG. 1. This device includes a boiler 1, an absorption tower 2 to which combustion exhaust gas generated from the boiler 1 is supplied, a conduit 21 to supply a part of the desulfurized exhaust gas to the top of the absorption tower 2, and a desulfurization agent. A mixer 4 that mixes raw materials, a kneader 5 that kneads the mixture with water 13, and a kneader 5 that mixes the mixture with water vapor (or water-containing high-temperature heat medium).
It consists of a heater 6 that performs the heat treatment in step 15, and a chimney 3 that discharges the desulfurized exhaust gas to the outside of the system. In such a configuration, the coal ash, lime components and gypsum components are transferred to the conduit 11.
The raw material powder is supplied to the mixer 4 and mixed therein, and then sent as raw material powder through the conduit 12 to the kneader 5, where it is kneaded with water 13. The obtained kneaded material is sent to the heater 6 via a conduit 14, where it is heat-treated with steam (or high-temperature heat medium containing moisture) 15, and then supplied to the upper part of the absorption tower 2 through a conduit 16 as a precursor of a desulfurizing agent. . A part of the desulfurized exhaust gas is supplied to the upper part of the absorption tower 2 through the conduit 21, so that the precursor of the absorbent is dried while moving at the top of the absorption tower.

The dried desulfurization agent comes into contact with the exhaust gas supplied from the conduit 7, absorbs the SO□ gas, and is discharged out of the system from the conduit 13 at the bottom of the absorption tower as a spent desulfurization agent.

A part of the exhaust gas desulfurized in the absorption tower 2 is supplied again to the upper part of the absorption tower 2, and the rest is discharged from the chimney 3 to the outside of the system.

Desulfurization was carried out under the following conditions using the apparatus shown in FIG. 1, and the desulfurization rate was measured to be 90%. The desulfurization rate was 50% when the desulfurization agent precursor was used without being dried.

<Desulfurization conditions> (1) Absorbent after heat treatment (desulfurization agent precursor, conduit 16)
O flow rate: 470 kg/h O moisture content: 31% ○ Particle size: 3 to 10 bars (2) Drying gas (exhaust gas after desulfurization treatment, conduit 21) O
Flow rate: 620 ON/h ○Temperature = 130°C ○Moisture concentration: 12-13% by volume (3) Desulfurization agent after drying ○Moisture content: 1% or less (sampled at the upper part of absorption tower 2) ○Drying time: 10h (4) Desulfurization processing gas (boiler exhaust gas, conduit 7) ○Flow rate:
50,0OONrrr/h ○SO, concentration: 5001) Pm As mentioned above, the area where desulfurization agents were conventionally piled up simply to prevent short baths of untreated gas can now be effectively used for drying desulfurization agents. Equipment costs and utility costs can be reduced.

FIG. 3 is a system diagram of a desulfurization apparatus according to another embodiment of the present invention. The difference between FIG. 3 and FIG. 1 is that the desulfurizing agent precursor heated in the heater 6 is supplied to the dryer 20 installed downstream of the absorption tower 2 through a conduit 16; The drying process is performed using the desulfurized exhaust gas supplied from 8, and is supplied to the upper part of the absorption tower 2 through a conduit 41. This device is particularly advantageous for treating exhaust gas with a high concentration of SO□ gas.

The amount of desulfurizing agent supplied increases in proportion to the amount (concentration) of 802 gas in the exhaust gas, and is in the relationship of supplied desulfurizing agent amount=treated gas amount×SO□ concentration. For example, under the desulfurization conditions described above, with the same processing gas amount (50,00ONrrr/h), the drying gas amount is changed from 620ONrrf/h to 50,00ONn(/h).
h, the amount of desulphurizing agent precursor that can be dried increases from 470 kg/h to approximately 3,790 kg/h. Therefore, with this amount of desulfurization agent, the SO□ concentration is 4,
000 ((50000/6200)X500) p
This means that it is possible to treat exhaust gas that is pm.

FIG. 4 is a diagram showing the relationship between the required amount of drying gas and the supplied desulfurizing agent (desulfurizing agent precursor). When the processing gas amount is constant, when the SO□ concentration ratio is 3, the supplied desulfurizing agent amount ratio is 3, and the drying gas amount ratio is 3. However, when the SO2 concentration ratio becomes 6, the supplied absorbent amount ratio becomes 6, and the amount of drying gas required to dry this supplied desulfurization agent also increases proportionally, and the drying gas amount ratio increases to 6. . Therefore, when the SO□ concentration becomes high, it is advantageous to install a dedicated dryer 20.

In this embodiment, the desulfurized exhaust gas is used as the drying gas, but the gas supplied from the conduit 21 may be any other high-temperature medium, such as high-temperature air for boiler combustion. Furthermore, in the dryer 20 shown in Fig. 2, the entire amount of the desulfurized exhaust gas is introduced as a high-temperature medium, but some of the desulfurized exhaust gas is supplied in proportion to the amount of absorbent, or other It goes without saying that the same effect can be obtained by supplying dry air or the like.

〔Effect of the invention〕

According to the desulfurizing agent drying method of the present invention, it is possible to effectively utilize the short-path prevention space of the moving bed absorption tower and to dry the desulfurizing agent precursor using the high temperature gas after the desulfurizing treatment. This eliminates the need for special drying equipment or heat sources, reducing equipment costs and running costs.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a desulfurization apparatus according to an embodiment of the present invention;
FIG. 2 is an enlarged sectional view of the absorption tower in FIG. 1, FIG. 3 is a system diagram of a desulfurization apparatus according to another embodiment of the present invention, and FIG. 4 shows drying gas when the amount of gas to be treated is constant. FIG. 5 is a diagram showing the relationship between the gas contact time and the desulfurization rate with respect to the change in the moisture content of the desulfurization agent. l... Boiler, 2... Absorption tower, 3... Chimney, 4...
... Mixer, 5... Kneading machine, 6... Heater, 7.8
．． 11.12.14.16.21.41.51... Conduit.

Claims (2)

[Claims] (1) A precursor of a desulfurizing agent used to absorb and remove sulfur oxides from exhaust gas is supplied to the upper part of a moving bed absorption tower, and this is dried using desulfurized exhaust gas or hot air for boiler combustion. A method for drying a desulfurizing agent, characterized by: (2) Claim characterized in that the precursor of the desulfurization agent is one obtained by kneading coal ash, silicon oxide, or aluminum oxide, a lime component, and a gypsum component with water and heat-treating the mixture in a steam atmosphere. 1) The method for drying the desulfurizing agent described above.