JPH0232006B2 - HAIENDATSURYUNISAISURUGASUONDONOCHOSEIHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting the gas temperature during flue gas desulfurization using a heat medium, and in particular to a method for adjusting the gas temperature during flue gas desulfurization with a large dust content, such as flue gas from a coal-fired boiler. This invention relates to a method for adjusting the temperature by circulating a heat medium.

Combustion exhaust gas after treatment in the wet flue gas desulfurization equipment is saturated with water vapor and contains small amounts of corrosive components such as sulfur dioxide (SO ₂ ), so it is necessary to prevent corrosion of steel chimneys and prevent white smoke. After being heated in a reheating device, it is released into the atmosphere. Conventionally, the afterburning method was used as a reheating method, but
Due to the rapid rise in energy costs, energy-saving types have been put into practical use that reheat by replacing the high-temperature untreated gas at the desulfurization inlet with the low-temperature treated gas at the desulfurization outlet. A rotary regenerative heat exchanger has been adopted as an energy-saving type, but this method uses corrugated elements stacked up as heat storage plates, so the gas passage is narrow, making it difficult to collect dust, especially when used for coal-fired boilers. Due to adhesion and solidification due to repeated drying and wetting of dust, passages become blocked and operation becomes impossible. Furthermore, this method has the disadvantage that the desulfurization equipment becomes large because untreated gas leaks from the high temperature side to the low temperature side.

As described above, the rotary regenerative heat exchanger used as a reheating device in a wet flue gas desulfurization system for a coal-fired boiler is likely to become inoperable due to passage blockage caused by dust, and leakage of untreated gas into the treated gas may cause damage after desulfurization. In order to eliminate the increase in the concentration of sulfur dioxide (SO ₂ ) in the processed gas, in the process of researching an alternative method to the rotary regenerative heat exchange method, we decided to develop a closed multi-tube heat exchange method using a heating medium circulation method ( We have confirmed that it is appropriate to use a gas heater (hereinafter referred to as GGH) for this purpose, but the heat exchanger tube for the process gas (gas that has completed desulfurization) of the gas heater is It has been found that corrosion is extremely severe due to exposure to water vapor saturated processing gas containing absorbed mist, and that the condition becomes even more severe as the heat medium temperature decreases due to load fluctuations. Therefore, the inventors of the present invention have conducted further studies on the closed multi-tube heat exchange method using a heating medium circulation method, which improves the corrosion resistance of the equipment without reducing the heating medium temperature as much as possible even when load fluctuations occur, and have developed the present invention. I was able to complete it.

That is, the present invention provides a method for cooling untreated gas with a heating medium circulating between an untreated gas cooling section and a treated gas heating section and reheating the treated gas, in which the heating medium heated by the untreated gas is After mixing with the heating medium that bypassed the untreated gas cooling section to adjust the untreated gas outlet temperature, a part of it is used to adjust the temperature of the heating medium sent to the untreated gas cooling section, and the remainder is used to cool the untreated gas. This is a method for adjusting gas temperature during flue gas desulfurization, characterized in that the gas is further heated with a medium heater and then used for heating the process gas.

Hereinafter, a specific example of the present invention will be described in more detail with reference to the accompanying drawings. Figure 1 shows a schematic flow of a specific example, and Figure 2 shows the gas flow of Figure 1.
FIG. 3 is an explanatory diagram showing the control relationship of the gas heater.

In Figure 1, 33 is an exhaust gas fan, 1 is an untreated gas side gas heater, 34 is a cooling tower, 3
5 is an absorption tower, 2 is a processing gas side gas/gas heater,
36 is a steam gas heater, 37 is a stack, 2
8 is the heat exchanger tube of the untreated gas side gas/gas heater, 2
9 is a heat transfer tube of the gas/gas heater on the processing gas side, 5 is a heat medium pump, 3 is a heat medium heater, 38 is a heat transfer tube of the steam gas heater, 10, 11, 12, 13, 3
9, 40, 41 are gas ducts, and 17, 24 are heat medium pipes. Further, in Fig. 2, 1 is a gas/gas heater on the untreated gas side, 2 is a gas/gas heater on the treated gas side, 3 is a heat medium heater, 4 is a heat medium expansion tank,
5 is a heat medium pump, 6 and 7 are heat medium flow control valves, 8 is a steam flow control valve, 9 is a steam trap, 10,
11, 12, 13 are gas ducts, 14, 15, 1
6 is a temperature detector, 17, 18, 19, 20, 2
1, 22, 23, 24, 25 are heat medium pipes, 26,
Reference numeral 27 indicates a steam pipe, 28 indicates a heat exchanger tube for the gas/gas heater on the untreated gas side, 29 indicates a heat transfer tube for the gas/gas heater on the treated gas side, and 30, 31, and 32 indicate temperature regulators.

In Figure 1, the untreated gas is transferred to the gas duct 39.
The gas is pressurized by the exhaust gas fan 33, passes through the gas duct 10, and enters the untreated gas side gas/gas heater 1 (hereinafter abbreviated as untreated GGH). Untreated
In the GGH 1, the untreated gas heats the heat medium sent by the heat medium pump 5 in the heat transfer tube 28 of the untreated GGH to lower its temperature, and enters the cooling tower 34 via the gas duct 11. In the cooling tower 34 , the untreated gas is cooled by water sprinkling, dust and soluble gas are partially removed, and the untreated gas passes through the gas duct 40 and enters the absorption tower 35 . In the absorption tower 35, the sulfur dioxide in the untreated gas is absorbed by the absorption liquid, and after removing the mist, it enters the treated gas side gas/gas heater 2 (hereinafter abbreviated as treatment GGH) via the gas duct 12. process
In the GGH2, the processing gas is supplied to the heat medium heater 3
The temperature is further raised by
The heat medium introduced into the heat transfer tube 29 of the GGH heats and raises the temperature, and enters the steam gas heater 36 via the gas duct 13. In the steam gas heater 36, the processing gas is further heated by the steam flowing through the heat transfer tube 38 of the steam gas heater 36, and is radiated into the atmosphere from the stack 37 via the gas duct 41. In Fig. 2, to explain the operation of the gas gas heater in more detail, the untreated gas that passes through the gas duct 10 and enters the untreated GGH1 is untreated.
Heating the heat medium flowing inside the heat transfer tube 28 of GGH1,
The temperature drops and reaches the gas duct 11. On the other hand, the heat medium is sent by the heat medium pump 5, and the heat medium pipes 18, 1
9 and is sent to the heat exchanger tube 28 of the untreated GGH1. The opening degree of the heating medium flow rate control valve 6 installed in the heating medium piping 20 is controlled by the temperature controller 30 so that the outlet temperature of the untreated gas does not fall below a certain level using the temperature detector 14 installed in the gas duct 11. adjust,
Perform a partial bypass of the heating medium.

The heat medium after heat exchange in the untreated GGH 1 is mixed with the heat medium that has bypassed the heat medium pipe 20, and is transferred to the heat medium pipe 2.
1 and 23, a portion of the heat medium enters the heat medium heater 3. on the other hand,
A temperature detector 15 installed in the heat medium pipe 18 controls the flow rate of the heat medium installed in the heat medium pipe 22 using a temperature regulator 31 so that the temperature of the heat medium in the heat medium pipe 18 does not fall below a certain level. The opening degree of the valve 7 is adjusted to partially recirculate the heat medium. The heating medium introduced into the heating medium heater 3 is controlled by the temperature detector 16 installed in the gas duct 13, and the opening degree of the steam flow rate control valve 8 is adjusted by the temperature regulator 32 so that the temperature at the outlet of the treated gas is constant. and adjust the heat medium heating amount. The heat medium heating steam passes through the steam pipe 26, heats the heat medium in the heat medium heater 3, condenses, and is discharged through the steam pipe 27 and the steam trap 9. On the other hand, the heat medium heated and heated by the heat medium heater 3 passes through the heat medium pipe 24, enters the heat transfer tube 29 of the processing GGH2, and enters the gas duct 12.
The processing gas introduced by the processing gas is processed in GGH2.
The heated medium is heated to a predetermined temperature, enters the heat medium expansion tank 4 via the heat medium pipe 25, mixes with the heat medium flowing back through the heat medium pipe 22 via the heat medium pipe 17, and is pumped into the heat medium pump 5.
reach.

The effects of the present invention are listed below.

(1) The following effects are produced by installing the heat medium heater 3 between the heat medium pipes 23 and 24 after heating the untreated GGH1.

Boilers in thermal power plants are operated over a fairly wide range from maximum combustion load operation (hereinafter abbreviated as MCR) to 1/4 load operation, so the raw gas flow rate and raw gas inlet temperature drop considerably. In addition, since the untreated gas outlet temperature of the untreated GGH 1 cannot be lowered below a certain level in order to avoid sulfuric acid dew point corrosion of the heat transfer tube 28 of the untreated GGH 1, the amount of heat exchange of the untreated GGH 1 is limited. Especially during 1/4 load operation, the amount of heat exchange is small, so the temperature of the heat medium entering the processing GGH2 decreases, and furthermore, the heat transfer tubes of the processing GGH2 are exposed to water vapor-saturated processing gas over a wide range. This results in severe corrosion over a wide area. However, as in the present invention, by installing the heat medium heater 3 and setting the processing gas outlet temperature to a temperature close to the MCR (at maximum load), the processing
The temperature of the heat medium entering the heat exchanger tube 29 of GGH2 becomes high, and furthermore, the temperature distribution of the entire heat exchanger tube 29 of the treated GGH2 becomes close to MCR.
The area exposed to the water vapor saturated process gas is much smaller and corrosion is considerably reduced.

The processing gas is heated to a white smoke prevention temperature by the steam gas heater 36, but as the load becomes smaller, the required capacity of the steam gas heater 36 reaches a maximum at a certain point. However, by installing the heat medium heater 3 in the gas/gas heater when the load is reduced and keeping the processing gas outlet temperature constant, the required capacity of the steam gas heater 36 can be significantly reduced, leading to cost reduction. Furthermore, since the heat exchanger tube 38 of the steam gas heater 36 is constantly exposed to dry processing gas, it can be sufficiently handled using a low-grade material.

(2) The following effects are produced by installing the bypass heat medium pipe 20 and the circulation (reflux) heat medium pipe 22.

When the load decreases, by increasing the amount of heat medium bypassing the bypass heat medium pipe 20, the amount of heat exchange between the untreated gas and the gas heater can be reduced, and the untreated gas outlet temperature can be kept constant. Therefore, sulfuric acid dew point corrosion of the outlet side heat exchanger tube of the untreated gas gas heater can be avoided.

If the difference between the untreated gas outlet temperature and the heating medium temperature of the untreated gas and gas heater becomes too large (20°C
(above), the sulfuric acid dew point corrosion of the heat transfer tube becomes severe, but a part of the high temperature heat medium is returned to the circulation line 22 so that the temperature at the heat medium inlet on the untreated gas/gas heater side does not fall below a certain temperature. Corrosion as described above does not occur.

[Brief explanation of drawings]

FIG. 1 shows a schematic flow of a specific example of the present invention, and FIG. 2 is an explanatory diagram showing the control relationship between the gas and the gas heater shown in FIG.

Claims (1)

[Claims] 1 In a method of cooling untreated gas and reheating treated gas by a heating medium circulating between an untreated gas cooling section and a treated gas heating section, the heating medium heated by the untreated gas is After mixing with the heating medium that bypassed the untreated gas cooling section to adjust the gas outlet temperature, a part of it is used to adjust the temperature of the heating medium sent to the untreated gas cooling section, and the remainder is used in the heating medium heater. A method for adjusting gas temperature during flue gas desulfurization, characterized in that the gas temperature is further heated at , and then used for heating the process gas.