JPS58150416A - Treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To reduce running cost, by a method wherein in-furnace desulfurization is carried out by limestone and spray dryer type wet desulfurization is carried out by using coal ash recovered in a dust collecting apparatus in a slurry form to utilize inexpensive limestone. CONSTITUTION:In-furnace desulfurization is carried out by directly blowing limestone into a coal fired boiler 1. In the next step, the exhaust gas from the boiler 1 is introduced into a spray dryer type wet desulfurization apparatus 8 through an air preheater 3. Coal ash containing dust from a succeeding electric dust collecting apparatus 9 and the desulfurization apparatus 8 is recirculated and supplied to a slurry tank 11 to be mixed with water and the prepared slurry is contacted with the exhaust gas to remove SOx. The exhaust gas issued from the desulfurization apparatus 8 is passed through the electric dust collecting apparatus to remove dust therein and discharged out of a system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas treatment method for removing sulfur oxides and dust from exhaust gas discharged from a coal-fired boiler.

In conventional exhaust gas treatment methods that include flue gas desulfurization of flue gas discharged from coal-fired boilers, as shown in Figure 1,
The exhaust gas is first introduced into the high-temperature dust collector 2, and coal ash containing dust in the exhaust gas is removed.

The coal ash generated at this time is discharged from the lower part of the dust collector 2 to the outside of the thread. Thereafter, the combustion air passes through an air preheater 3, is heated, and is then pressurized by a pressure booster fan 4 and introduced into a wet desulfurization device 6 using a lime/gypsum method or a soda ash method.

In these wet desulfurization equipment 6, lime (quicklime, slaked lime),
A desulfurizing agent such as soda ash is extracted and desulfurized, and then it is discharged from the chimney 7 to the outside of the system.

However, in such a method, the amount of lime/soda ash and water used as desulfurization agents is large, and these desulfurization agents are expensive, resulting in high running costs.

On the other hand, although the technology of in-furnace desulfurization in a boiler itself is publicly known,
Even if this method is used alone, it has the disadvantage that very little desulfurization effect can be expected.

The present invention was made to solve the above-mentioned drawbacks, and by injecting inexpensive limestone directly into the boiler furnace as a desulfurizing agent without using lime and soda ash, it increases the desulfurization effect in the boiler furnace and improves the concentration of limestone. It is characterized by desulfurization by extracting the coal ash collected by the dust device as a slurry into a spray dryer type wet desulfurization device.

Hereinafter, one embodiment of the present invention will be described with reference to FIG.

1 is a coal-fired boiler in which coal is charged, combustion air heated by an air preheater 3 (described later) is introduced, and the coal is combusted. Reference numeral 3 denotes an air preheater that heats the air supplied via the blower 5 using heat in the exhaust gas, and converts it into combustion air to be introduced into the coal-fired boiler 1.

8 is a spray dryer type wet desulfurization equipment, which ejects slurry as a liquid absorbent from a slurry tank 11 containing slurry mixed with water, coal ash, etc., and further discharges exhaust gas passing through an air preheater 3. By introducing and bringing into contact, sulfur compounds are removed.

9 is a low-temperature electrostatic precipitator that removes dust from exhaust gas. 5 is a forced draft fan, and 10 is an induced draft fan.

In the above configuration, first, limestone is directly blown into the coal-fired boiler 1 to perform in-furnace desulfurization. The limestone injected at this time immediately decomposes into quicklime (Cab) in the combustion gas at a temperature of 900°C or higher, and reacts with sulfur dioxide gas and oxygen in the gas at a temperature of 1250°C or lower to produce calcium sulfate.

900'C or more CaCO3CaO+CO2・・・・・・・・・(1)C
aO+S(), +JzO, -Shiyaku Mikkomi Ca EA
-"- (2) Next, the exhaust gas discharged from the coal-fired boiler passes through the air preheater 3 and is introduced into the spray dryer type wet desulfurization device 8.

The introduced exhaust gas comes into contact with the slurry stored in the slurry tank 11 to remove sulfur compounds. This slurry is made by circulating coal ash containing dust from the downstream low-temperature electrostatic precipitator 9 and this spray dryer type wet desulfurization device 8, supplied to the slurry tank 11, and mixed with water.

The coal ash including coal ash is discharged to the slurry tank 11, and the cleaned gas from which dust has been removed is discharged from the chimney 7 to the outside of the system via the induced draft fan 10.

According to the present invention, since the boiler main body is used as a reactor, additional equipment such as a spray dryer-type wet desulfurization device and a dust collector installed downstream can not only be downsized, but also inexpensive limestone can be used. In addition, since the non-plated dryer type wet desulfurization equipment does not require new limestone, it has the advantage that the consumption amount is small and the ramming cost is low.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an exhaust gas treatment method including a conventional lime/gypsum method or soda ash type wet desulfurization equipment, and Figure 2 is an exhaust/gas treatment blade including a spray dryer type wet desulfurization equipment of the present invention. FIG. 1...Coal-fired boiler 2...High temperature dust collector 3.
... Air preheater 4 ... Boost blower 5 ...
Forced air blower 6... Lime-gypsum method or soda ash type wet desulfurization device 7... Chimney 8... Spray dryer type wet desulfurization device 9... Low temperature dust collector 10... Induced draft Machine 110/Slurry tank

Claims (1)

[Claims] A method for removing sulfur compounds and coal ash from the exhaust gas by passing the exhaust gas discharged from a coal-fired boiler through a spray dryer-type thermal desulfurization device and a dust collector, in which limestone is directly blown into the boiler. An exhaust gas treatment method characterized by: