JPH0494721A - Waste combustion gas purifying device - Google Patents

Abstract

PURPOSE:To form a water film on the surface of a desulfurizing agent while preventing dew condensation on the inner wall of a desulfurization tower and to attain sufficient desulfurization efficiency by surely lowering the temp. on the desulfurization side at the inlet of the desulfurization tower close to the water temp. CONSTITUTION:The waste gas contg. SOx from a coal or heavy oil-fired boiler 1 is cooled by an air heater 2 and sent to a desulfurization tower 3. A desulfurizing agent such as slaked lime is supplied from a supply port 4 and water from a supply port 5, and the waste gas is desulfurized. In this case, the desulfurizing agent is cooled by a cooler 6 while being gas-floated. Consequently, a thin water film is formed on the surface of the desulfurizing agent, the reaction with the gaseous SOx in the waste gas is remarkably promoted, and the gaseous SOx is mostly removed. High desulfurization efficiency is stably attained in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a desulfurization device using an alkali or alkaline earth metal compound as a desulfurization agent, and particularly to a device suitable for improving the desulfurization rate.

[Conventional technology] 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 HC6 at a rate of 100 to 3,000 ppm. Therefore, in order to prevent air pollution, an effective method for removing this is desired.

Wet exhaust gas purification methods have traditionally been widely used in large boilers, but while they have a high rate of removal of harmful substances, they have problems such as difficulty in wastewater treatment, large costs in processing by-products, and high equipment costs. was there.

In order to solve the problems of these wet exhaust gas purification methods, dry desulfurization methods have been developed. Dry methods can be broadly divided into two methods: ■ A method in which a slurry of carbonates, hydroxides, or oxides of alkali metals and alkaline earth metals is sprayed into the furnace or flue as a desulfurizing agent; There are two methods: one involves blowing metal compound powder into a furnace or flue.

However, the above-mentioned method of spraying slurry has the technical problem of easily clogging the nostle and making it difficult to adjust the slurry.On the other hand, the latter method avoids problems such as nostle clogging, but the desulfurization rate is not sufficient. The problem was that it was not achieved.

Further, a typical flow of the method (2) above is shown in FIG.

The exhaust gas from the boiler is lowered in temperature by an air heater 2, and is led to a desulfurization tower 3. A desulfurizing agent such as slaked lime or quicklime is supplied into the desulfurizing tower 3 from the desulfurizing agent supply port 4, and at the same time water is also supplied from the water supply port 5, thereby lowering the temperature of the exhaust gas and increasing the humidity. The desulfurizing agent that has reacted with SOX in the exhaust gas is collected together with the ash in the exhaust gas by a dust collector 7 and discarded.

[Problems to be Solved by the Invention] In the exhaust gas purification method described in (1) above, the removal rate of acidic harmful substances is increased by forming a water film on the surface of the desulfurizing agent. It is necessary to control the operation to a temperature as close to the adiabatic saturation temperature as possible.

However, in order to prevent dew condensation on the inner wall of the desulfurization tower 3, it is necessary to operate at a temperature above the adiabatic saturation temperature +10°C, and the desulfurization efficiency under this condition was not sufficient.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an exhaust gas purification method that prevents dew condensation on the inner wall of a desulfurization tower and forms a water film on the surface of a desulfurization agent to achieve a sufficient desulfurization rate.

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

That is, an apparatus used in a combustion exhaust gas purification method that removes acidic harmful substances by spraying fine powder of a desulfurizing agent made of an alkali metal compound or an alkaline earth metal compound into the combustion exhaust gas containing acidic harmful substances, This is a combustion exhaust gas purification device in which a desulfurizing agent supply section for introducing the desulfurizing agent into exhaust gas is provided with a cooler for cooling the desulfurizing agent.

[Function] - The temperature of the desulfurizing agent entering the desulfurizing tower is lowered to below the saturation temperature of the desulfurizing tower by a cooler, and a water film is formed on the surface of the desulfurizing agent. This improves the reactivity of the desulfurizing agent with acidic harmful substances such as SO2.

Exhaust gas containing acidic harmful substances such as SO2 is treated with alkali metals,
When removing sulfur using a desulfurizing agent such as an alkaline earth metal compound, relative humidity is said to control desulfurization performance, but the microscopic reaction mechanism is unknown. However, the fact that it is controlled by relative humidity suggests that the reaction may be dominated by slight condensation of water on the surface of the desulfurizing agent.
Using an experimental device that can control the supply temperature of the desulfurization agent, we investigated its effect on the desulfurization rate.

Using slaked lime as a desulfurizing agent, the reactor scum temperature (S○2
The amount of scum (N2 gas) was controlled to be constant at 65°C, and the water vapor concentration was set to 15%, resulting in approximately 2Q OOp p
The desulfurization performance was examined by flowing a simulated exhaust gas containing SO2 gas.

The results are shown in FIG. 2, and it was found that the supply temperature of slaked lime greatly affected the desulfurization performance, and lowering the temperature of the desulfurization agent was advantageous for the desulfurization reaction.

[Example] Specific examples and experimental results suitable for carrying out the present invention will be described below.

Embodiment 1 FIG. 1 shows an example in which the present invention is applied to a commercial boiler. SOX from coal-fired or heavy oil-fired boiler 1
The temperature of the exhaust gas containing .

At this time, in the case of a coal-fired boiler, the exhaust gas contains 7 to 10
%, and in the case of heavy oil-fired boilers, it contains 12 to 15% water. This exhaust gas enters the desulfurization tower 3. A desulfurizing agent such as slaked lime is supplied to the desulfurizing tower 3 from a desulfurizing agent supply port 4, water is introduced from a water supply port 5, and SoX gas in the exhaust gas is removed.

At this time, what largely controls the desulfurization performance is the surface temperature of the desulfurizing agent entering the desulfurization tower 3, as is clear from the experimental results shown in FIG. 2, under conditions of constant relative humidity within the desulfurization tower.

In the apparatus shown in FIG. 1, the cooler 6
Since the temperature of the desulfurizing agent is lowered by this, when the desulfurizing agent is supplied into the desulfurizing tower 3, a thin water film is formed on the surface of the desulfurizing agent. Therefore, the reactivity with the SOy dregs in the discharged dregs is greatly improved, and most of the SOy dregs are removed.

Note that the water used for cooling the desulfurization agent in the cooler 6 can be the spray water used to control the humidity inside the desulfurization tower 3, and there is no problem in terms of utility.

The cooler 6 can be provided in the supply line for pneumatic transportation of the desulfurizing agent, at the bottom of the desulfurizing agent hopper, or in the powder extraction section. Moreover, it may be provided in all of these.

Experimental Example Next, the results of an experiment using an apparatus having the same system configuration as in FIG. 1 will be described below.

20ONm with approximately 10% moisture in a light oil-fired combustion furnace
Generate hot air at a rate of 3/h and use an S○2 gas cylinder for 20
00 ppm of SO2 gas was mixed in, and the simulated waste gas corresponding to this boiler waste gas was led to the desulfurization tower.

On the other hand, slaked lime used as a desulfurization agent was either supplied from the hopper to the desulfurization tower by air conveying air, or at this time, it was cooled by a cooler using spray water for humidity control in the desulfurization tower. was sprayed on.

At this time, the thermometer in the air flow conveying pipe installed just before the desulfurization tower was
It showed a temperature of 3 to 25°C.

The amount of slaked lime was supplied so that the molar ratio with SO2 gas was 2, and the spray water used for cooling the desulfurization agent was provided in the desulfurization tower so that the relative humidity in the desulfurization tower was 80 to 82%. A constant amount was supplied while monitoring the temperature and humidity meter.

The S02 monitor value at the desulfurization tower outlet obtained in this experiment is
The desulfurization rate was 290 to 300 ppm, and a desulfurization rate of 85% was obtained.

Comparative Experiment A comparative experiment was conducted using the above-mentioned apparatus in which the desulfurizing agent was bypassed and directly supplied to the desulfurizing tower without passing through the cooler. As in the previous experiment, a blower was used as an air source for conveying the desulfurizing agent, but the thermometer installed in the air conveyance showed a value of 45 to 50°C. The SO2 monitor value at the desulfurization tower outlet obtained in this comparative experiment was 68 oppm, and the desulfurization rate was 66.
The value was as low as %.

Example 2.3 Other embodiments of the invention are shown in FIGS. 3 and 4.

Embodiment 2 shown in FIG. 3 is an example in which the desulfurization agent and spray water are directly supplied to the duct instead of the desulfurization tower, and the embodiment shown in FIG. Although this is an example in which the desulfurizing agent is collected in the dust bag W7 and the desulfurizing agent is recycled, the present Example 2.3 also has the same effect of improving the desulfurizing performance.

In order to further ensure the temperature drop of the desulfurizing agent, it is also effective to add a volatile substance to the desulfurizing agent and use the latent heat of vaporization to lower the temperature. Alcohol or water can be used as the volatile substance.

In this way, if the desulfurizing agent is not actively cooled, the temperature will be 30 to 50℃ due to the influence of the ambient temperature where the desulfurizing agent hopper and airflow conveying pipe are installed and the airflow conveying air itself. It was found that the sulfur content easily rises to the vicinity and can be a major factor in lowering the desulfurization rate.

[Effects of the Invention] According to the present invention, the temperature of the desulfurizing agent entering the desulfurization tower can be reliably cooled to around the water temperature, and when it enters the desulfurization tower,
A water film suitable for reaction can be easily formed and a high desulfurization rate can be stably obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the flow of an exhaust gas purification device showing one embodiment of the present invention, Fig. 2 is a graph showing experimental data regarding desulfurization agent temperature and desulfurization rate, and Fig. 3 is another embodiment of the present invention. (
Fig. 4 is a diagram showing the flow of the exhaust gas purification device according to another embodiment (part 2) of the present invention, and Fig. 5 is the flow diagram of the exhaust gas purification device of the prior art. A diagram showing each is shown. 1 Boiler, 2... Air heater, 3... Desulfurization tower, 4
・ Desulfurizing agent supply port, 5. Water supply port, cooler Applicant Babcock Hitachi Co., Ltd. Representative Patent attorney Takayoshi Matsunaga 1 person (%) *'! J! agent

Claims (3)

[Claims] (1) A device used in a combustion exhaust gas purification method that removes acidic harmful substances by spraying fine powder of a desulfurizing agent made of an alkali metal compound or alkaline earth metal compound into the combustion exhaust gas containing acidic harmful substances, A combustion exhaust gas purification device characterized in that a desulfurization agent supply section for introducing the desulfurization agent into exhaust gas is provided with a cooler for cooling the desulfurization agent. (2) The combustion exhaust gas purification device according to claim 1, wherein a volatile substance such as alcohol or water is added to the desulfurizing agent. (3) The combustion exhaust gas purification apparatus according to claim 1, characterized in that a cooler is used to adjust the temperature so that the supply temperature of the desulfurizing agent is equal to or lower than the adiabatic saturation temperature in the desulfurizing tower.