JPH04141214A - Exhaust gas desulfurizer - Google Patents

Abstract

PURPOSE:To prevent the accumulation of a solid in a dust collecting apparatus, in an exhaust gas desulfurizer equipped with a desulfurizing reactor and a dust collector, by providing a gas heater controlling the temp. of the gas flowing in the dust collector. CONSTITUTION:The temp. of the exhaust gas 2 from a boiler 1 is lowered by an air heater 3 to guide the exhaust gas 2 to a desulfurizing reactor 4. A desulfurizing agent 5 is sprayed to a flue 6 by a nozzle 11 and the exhaust gas is guided to the desulfurizing reactor 4. Water is sprayed into the desulfurizing reactor 4 from a nozzle 12 to lower the temp. of the exhaust gas. The exhaust gas issued from the desulfurizing reactor 4 is guided to a dust collector 8 while the temp. thereof is controlled to the condensing point of water or the dew point of sulfuric acid or higher. By this method, the condensation of water or sulfuric acid causing scale can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flue gas desulfurization device using at least one compound selected from alkali metals and alkaline earth metal compounds as a desulfurization agent, and particularly to a dust collector. The present invention relates to a flue gas desulfurization device that can operate stably over a long period of time.

[Prior Art] Exhaust gas discharged from heavy oil-fired and coal-fired boilers in thermal power plants usually contains acidic harmful substances such as sulfur compounds (SOx) and HCI at a rate of 100 to 3000 Ppm. Since it is said to be a causative agent of acid rain and photochemical smog, effective treatment methods are desired. Conventionally, wet methods (e.g. limestone-gypsum method) or dry methods (activated carbon method) have been used, but while the wet method has a high removal rate of harmful substances, it is difficult to treat wastewater and requires reheating of exhaust gas. However, there were problems in that the equipment costs and operating costs were high, and a high removal rate could not be obtained with the dry method.

Therefore, it is desired to develop a desulfurization method that can obtain a high removal rate with a wastewater-free, low-cost process.

In addition to the methods mentioned above, desulfurization methods for exhaust gas from boilers include a semi-dry method in which slaked lime or its slurry is sprayed into the exhaust gas, and limestone is directly dispersed in the high-temperature gas in the furnace or flue to remove acidic harmful substances. A dry method has been proposed, which is characterized by low equipment and operating costs, but both methods have the problem of low removal rates.

FIG. 5 shows a typical flow sheet of a method in which slaked lime or quicklime is sprayed into exhaust gas to react with SO in the exhaust gas, and then removed by a dust collector. Exhaust gas 2 from the boiler 1 is lowered in temperature by an air heater 3 and guided into a desulfurization reactor 4. A desulfurizing agent 5 such as slaked lime is supplied to a flue 6 or a desulfurizing reactor 4
At this time, by also supplying water, the temperature of the exhaust gas is lowered and the humidity is increased.1 The reacted desulfurizing agent 5 is collected together with the ash in the exhaust gas by a dust collector 8 and discarded. .

[Problems to be Solved by the Invention] In the prior art described above, desulfurization performance improves when the gas temperature of the desulfurization reactor 4 is lowered. Therefore, a water spray nozzle is placed inside the desulfurization reactor 4 in order to lower the gas temperature. At this time, desulfurization performance is improved by lowering the gas temperature in the desulfurization reactor 4, but water condensation and/or sulfuric acid condensation occurs in the dust collector 8 on the downstream side of the desulfurization reactor 4, and the dust in the gas and desulfurizing agent 5 adheres to form scale,
Furthermore, problems such as corrosion of the material in the scale portion may occur. For this reason, long-term stable operation of the desulfurization reactor 4 was not possible, and the operation of the entire system was sometimes hindered.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a flue gas desulfurization method that prevents solid matter in flue gas after flue gas desulfurization treatment from accumulating in a dust collector and enables long-term stable operation of the dust collector. It is.

[Means to solve the problem J The above object of the present invention is achieved by the following configuration.

In other words, a desulfurization reactor that desulfurizes sulfur oxides in combustion exhaust gas by adding at least one compound selected from alkali metals or alkaline earth metal compounds to exhaust gas as a desulfurization agent, and a desulfurization reactor that desulfurizes sulfur oxides in combustion exhaust gas, and solids in the gas after desulfurization In a flue gas desulfurization system equipped with a dust collector that separates and collects substances, a temperature detection means for detecting the temperature of the gas at the entrance of the dust collector is provided in the dust collector inlet flue, and the temperature detected by the temperature detection means is Flue gas desulfurization involves installing a gas heater between the desulfurization reactor and the precipitator to control the temperature of the gas flowing into the precipitator to a temperature higher than the condensation point of water or the dew point based on the temperature of the gas at the inlet of the precipitator. A bypass passage equipped with a bypass damper is provided at the inlet of the device or the flue that introduces the flue gas into the desulfurization reactor to directly introduce the flue gas into the dust collector without passing through the desulfurization reactor. The exhaust system is equipped with a bypass damper driving means that controls the temperature of the gas flowing into the precipitator to a temperature higher than the condensation point of water or the dew point of sulfuric acid based on the temperature of the gas detected by the temperature detection means installed at the inlet of the dust collector. This is a smoke desulfurization equipment.

[Function] The temperature of the gas after flowing through the desulfurization reactor is further lowered by heat radiation in the flue or the like before entering the dust collector.

At this time, the moisture in the gas condenses or the sulfuric acid reaches its dew point and adheres to the inner walls of the dust collector. Then, dust and desulfurization agent in the exhaust gas adhere to this adhered water or sulfuric acid, forming scale.

Therefore, in order to prevent condensation of water or film that causes scale, it is necessary to keep the exhaust gas temperature at or above the adiabatic saturation temperature while monitoring the gas temperature at the inlet of the precipitator.

Therefore, the gas temperature inside the dust collector is controlled by a gas heater installed at the entrance of the dust collector. This prevents water from condensing, thereby eliminating scaling problems on the inner walls of the dust collector.

In addition, dust can also be collected by installing a bypass damper path in place of the gas heater to directly introduce the combustion exhaust gas into the dust collector without going through the desulfurization reactor, and by controlling the opening and closing of the inlet bypass damper depending on the gas temperature at the entrance of the dust collector. Scale problems on the inner walls of the vessel can be prevented.

[Examples] The present invention will be explained in more detail by the following examples, but is not limited thereto.

Example 1 A case of desulfurizing exhaust gas from a coal-fired boiler using slaked lime as a desulfurizing agent will be described using an example in which an apparatus according to the present invention is applied.

In FIG. 1, exhaust gas 2 from a boiler 1 is lowered in temperature by an air heater 3, and then introduced into a desulfurization reactor 4. The desulfurizing agent 5 is sprayed into the flue 6 from a nozzle 11. The desulfurization agent 5 is introduced into the desulfurization reactor 4 through a flue 6. Water is sprayed from the nozzle 12 in the desulfurization reactor 4 to lower the temperature in the exhaust gas.

The exhaust gas exiting the desulfurization reactor 4 is guided to the dust collector 8 via the gas heater 54. Here, the inlet gas temperature of the dust collector 8 is set to 7
Adjust the amount of fuel in the gas heater 54 to maintain the temperature at 5°C,
Oil is used as a heating source for the gas heater 54.

In the desulfurization reactor 4, the desulfurization agent 5 reacts with the acidic toxic gas of the SO2 gas, and the reacted desulfurization agent 5 is collected together with the ash in the exhaust gas in the dust collector 8 and discarded.

Using this device, coal A (S02 concentration in exhaust gas 101
A desulfurization test was conducted when 000pp was burned. However, slaked lime is used as the desulfurization agent 5, and the molar ratio of slaked lime to S02 contained in the exhaust gas is twice (hereinafter, Ca/
(abbreviated as S = 2) was added.

Water was sprayed from the nozzle 12 so that the gas temperature in the desulfurization reactor 4 became 70°C.

After removing moisture from the gas at the boiler 1 outlet and dust collector 8 outlet, SO2 concentrations were measured and found to be 11,000 ppm and 300 PPm, respectively. In other words, 70% of the 802 in the exhaust gas was removed.

This test was continuously operated for 100 hours, and after the apparatus was stopped, the inside of the dust collector 8 was inspected, and no solid matter such as a desulfurizing agent was observed.

Example 2 Using the same apparatus as in Example 1, the desulfurization rate was measured under the same conditions. However, as a heating source for the gas heater 54, LP
A gas such as G is used. Furthermore, water was sprayed from the nozzle 12 so that the gas temperature in the desulfurization reactor 4 became 65°C.

After removing moisture from the gas at the boiler 1 outlet and dust collector 8 outlet, SO2 concentrations were measured and found to be 11,000 ppm and 200 ppm, respectively. In other words, 80% of the SO2 in the exhaust gas was removed.

As in Example 1, a test was conducted in which the vehicle was operated for 100 hours. After the test, when the dust collector 8 was internally inspected, no solid substances such as the desulfurizing agent 5 were observed.

Example 3 As shown in FIG. 2, the desulfurization rate was measured under the same conditions using steam as the heating source for the gas heater 54 and using the same apparatus as in Example 1 except for the same.

A temperature detection sensor 61 is provided on the inner wall surface of the dust collector 8, and the amount of steam supplied is adjusted by a temperature controller 34 and a control valve 35. Water is sprayed through the nozzle 12 so that the temperature of the gas in the desulfurization reactor 4 reaches 65°C, and the temperature of the inner wall surface of the dust collector 8 is maintained at 70''C.

After removing moisture from the gas at the boiler 1 outlet and dust collector 8 outlet, the S02 concentration was measured and found to be 11000 ppm and 300 ppm, respectively. In other words, 70% of the SO2 in the exhaust gas was removed.

As in Example 1, a test was conducted in which the vehicle was operated for 100 hours. After the test, when the dust collector 8 was internally inspected, no solid substances such as the desulfurizing agent 5 were observed.

Comparative Example 1 A desulfurization test was conducted on coal A under the same conditions as in Example 1 using an apparatus based on the prior art shown in FIG.

As in Example 1, a test of continuous operation for 100 hours was conducted. After the test, when the dust collector 8 was internally inspected, solid substances such as the desulfurizing agent 5 were observed (approximately 1 kg accumulated), and furthermore, corrosion of the material surface of the inner wall of the dust collector 8 was observed.

Embodiment 4 Another embodiment of the present invention is shown in FIGS. 3 and 4.
The example shown in the figure divides the internal space of the desulfurization reactor 4 into two, and is provided with a partition wall 60 through which the gas flow within the desulfurization reactor 4 detours.

A damper 55 for bypassing the gas flow is provided in a part of the partition wall 60. By partially bypassing the inlet gas introduced into the desulfurization reactor 4 via the bypass damper 55, the temperature of the precipitator 8 artificial gas is made to be equal to or higher than the adiabatic saturation temperature of the exhaust gas temperature. Bypass damper 55
The opening/closing control is performed by measuring the inlet gas temperature of the dust collector 8 with a temperature detection sensor 56 attached to the flue 6 between the desulfurization reactor 4 and the dust collector 8, and calculating the measured temperature value with a calculator 57. Then, the drive motor 59 of the bypass damper 55 is controlled by the calculated signal. In addition, the example shown in FIG. 4 has a bypass flue 6 in which the exhaust gas passes through the desulfurization reactor 4 and is directly introduced into the dust collector 8, in addition to the exhaust gas population 62 of the desulfurization reactor 4.
3 will be provided. A bypass damper 55 is attached to the entrance of this bypass flue 63.

In FIGS. 3 and 4, although not shown, the temperature of the exhaust gas from the boiler is lowered by an air heater as in FIG.
It is guided into the desulfurization reactor 4. The desulfurizing agent 5 is sprayed from a nozzle 11 in the flue 6. The desulfurization agent is led into the desulfurization reactor 4 via the flue 6. Water is sprayed from the nozzle 12 in the desulfurization reactor 4 to lower the temperature in the exhaust gas. Further, within the desulfurization reactor 4, a part of the gas is bypassed by a bypass damper 55. By controlling the opening and closing of the bypass damper 55,
Water is sprayed from the nozzle 12 so that the gas temperature in the desulfurization reactor 4 is 65°C, and the gas temperature at the inlet of the dust collector 8 is 75°C.
to hold. The desulfurization rate was measured under the same conditions as in Example 2 except for the other conditions.

After removing moisture from the gas at the boiler 1 outlet and dust collector 8 outlet, SO2 concentrations were measured and found to be 11,000 ppm and 300 ppm, respectively. That is, 70% of SO□ in the exhaust gas was removed.

As in Example 2, a test was conducted in which the vehicle was operated for 100 hours. After the test, when the dust collector 8 was internally inspected, no solid matter such as dust collector 5 was observed.

In the above embodiments, slaked lime was used as the desulfurizing agent 5, but in addition to this, oxides, hydroxides, and carbonates of alkali and alkaline earth metals such as quicklime, sodium hydroxide, and sodium carbonate can be used.

In addition, in order to effectively monitor the gas temperature at the inlet of the dust collector 8, in addition to measuring the gas at the outlet of the desulfurization reactor 4, we also measure the outside air temperature, the temperature outside and inside the flue 6 between the desulfurization reactor 4 and the dust collector 8. It is also possible to measure the temperature of the gas at the inlet of the precipitator 8 and control the temperature of the gas at the inlet of the precipitator 8 based on the signal or the signal of the SO2 concentration at the outlet of the desulfurization reactor 4.

[Effects of the Invention] According to the present invention, the long-term stable operation of the dust collector is achieved by controlling the gas heater or bypass damper installed at the entrance of the dust collector while monitoring the inlet gas of the dust collector. be able to.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of a flue gas desulfurization method in an embodiment of the present invention, FIGS. 2, 3, and 4 are schematic diagrams of a desulfurization reactor and a dust collector in other actual km of the present invention, FIG. 5 shows flow sheets of conventional desulfurization equipment. 1...Boiler, 4...Desulfurization reactor, 5...Desulfurization agent,
8 Dust collector, 54 Gas heater, 55 Bypass damper, 56 Temperature detection sensor Applicant Babcock Hitachi Co., Ltd. Agent Patent attorney Takayoshi Matsunaga 1 person Figure Figure Figure

Claims (2)

[Claims] (1) A desulfurization reactor that desulfurizes sulfur oxides in combustion exhaust gas by adding at least one type of alkali metal or alkaline earth metal compound to the exhaust gas as a desulfurization agent, and In a flue gas desulfurization equipment equipped with a dust collector for separating and recovering solid matter, a temperature detection means for detecting the temperature of the gas at the entrance of the dust collector is provided in the flue at the entrance of the dust collector, and the temperature detected by the temperature detection means is provided. A gas heater is installed in the exhaust gas flue between the desulfurization reactor and the dust collector to control the temperature of the gas flowing into the dust collector to a temperature higher than the condensation point of water or the sulfuric acid dew point based on the temperature of the gas at the dust collector inlet. A flue gas desulfurization device characterized by: (2) A bypass passage equipped with a bypass damper at the inlet to introduce the flue gas directly into the dust collector without passing through the desulfurization reactor is provided in the flue gas flue, and the temperature at the inlet of the dust collector is 2. A bypass damper driving means for controlling the temperature of the gas flowing into the precipitator to a temperature higher than the condensation point of water or the dew point of sulfuric acid based on the temperature of the gas detected by the detection means. flue gas desulfurization equipment.