JPS60227845A - Treating apparatus of exhaust gas - Google Patents

Abstract

PURPOSE:To improve the collectivity by providing a temp. control means of exhaust gas on the upstream side of an electrical dust collector, and regulating the heat absorption of the heat retained by boiler exhaust gas in the treating apparatus of exhaust gas. CONSTITUTION:The combustion gas discharged from a boiler 1 is heat-exchanged with combustion air at an air preheater 4. The gas temp. at the inlet to an electrical dust collector 6 or the contained ash content is detected by a detector 20, and the amt. of a medium for controlling the gas temp. at the inlet to the electrical dust collector which is supplied into a gas temp. controller 17 is controlled through a control valve 18 so that the inlet gas temp. or the electric resistance may be regulated to a specified value to prevent a decrease in the dust collecting performance due to the variation in the kind of coals, etc. A low-pressure feed-water heater, and air- or seawater-cooled exhaust gas cooler, a cold-water spray, etc. are used as the gas temp. controller. The gas freed of dust at the electrical dust collector is pressurized by an induced draft blower 8, SO2, etc. is removed at a stack gas desulfurizer 9, and the gas is discharged into the atmosphere from a stack 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas treatment device, and more particularly to an exhaust gas treatment device that can be applied to a coal-fired boiler or the like.

In a conventional exhaust gas treatment device, for example, as shown in FIG. 1, combustion gas discharged from a combustion section 2 in a boiler 1 passes through a boiler outlet flue 3 and exchanges heat with combustion air in an air preheater 4. After that, the air flows into the electrostatic precipitator 6 through five air preheater outlet flues. Coal combustion gas usually contains a large amount of ash (ash contained in coal) (20 to 50 rr/N7y for bituminous coal), but the electrostatic precipitator 6 can remove the ash contained in this combustion gas. This is to remove the ash that has been removed. The combustion gas from which dust has been removed by the electrostatic precipitator 6 passes through the dust collector outlet flue 7, increases its pressure in the induced draft fan 8, removes SO2 and residual soot in the flue gas desulfurization device 9, and passes through the flue 10 to the chimney 11. more waste is being disposed of into the atmosphere.

As described above, the conventional exhaust gas treatment apparatuses do not have an inlet gas temperature adjustment function, and therefore, the following problems occur, especially in exhaust gas treatment apparatuses for coal-fired boilers.

Characteristics of the gas properties at the inlet of an electrostatic precipitator for coal-fired boilers include: (1) Depending on the coal properties, especially the moisture content, the coal drying air (-
The required amount of air) changes. Therefore, the amount of air passing through the air preheater changes, and the gas temperature at the air preheater outlet (electrostatic precipitator inlet) changes.

(11) Coal combustion gas contains a large amount of coal ash, and the amount depends on the amount of ash contained in the coal. Is the concentration in the combustion gas of common bituminous coal 10 to 50? r/N-
It is. If these are not removed, they will be discarded into the atmosphere and pollute the air.

011) Coal ash is composed of many types of minerals,
Its collection ability changes depending on the ash properties and also changes depending on the temperature. This is because the electrical resistance of ash is greatly affected by temperature.

As mentioned above, the collection performance of coal ash is affected by the gas temperature.
There is an appropriate temperature range depending on its properties, but conventional exhaust gas treatment equipment does not have a gas temperature adjustment function as mentioned above.
When the coal properties change, the temperature of the exhaust gas is not maintained at an appropriate temperature, so there are drawbacks such as a significant drop in the collection efficiency.

The present invention has been proposed in view of the above circumstances, and its purpose is to improve the dust collection performance of the electrostatic precipitator by controlling the inlet gas temperature of the electrostatic precipitator to an appropriate temperature. The purpose of this invention is to provide a processing device.

An exhaust gas treatment device according to the present invention is an exhaust gas treatment device that guides exhaust gas to an electrostatic precipitator to collect dust in the exhaust gas, and includes temperature control means for the exhaust gas provided upstream of the electrostatic precipitator. The feature is that, upstream of the t/% electrostatic precipitator, for example, a low-pressure feed water heater, an air or seawater cooling type exhaust gas cooler, a cold air introduction device, a cold water spray device, etc. are installed to absorb the heat held in the boiler exhaust gas. The above-mentioned drawbacks of the conventional methods can be overcome by adjusting the amount and maintaining a proper exhaust gas temperature to improve collection performance.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 2 is a diagram showing the configuration of an embodiment of the present invention, Fig. 3 is a diagram showing the relationship between combustion gas temperature and electrical resistance of ash, and Fig. 4 is a diagram showing the decrease in electrical resistance depending on combustion gas temperature. , Figure 5~
FIG. 8 is a diagram showing an example of a gas temperature control device according to an embodiment of the present invention, and FIG. 9 is a diagram showing the relationship between SO, concentration, and acid dew point in combustion gas in an embodiment of the present invention. be.

What is shown in Fig. 2 is an example in which the present invention is applied to a device for treating gas discharged from a boiler, and the properties and dust collection performance of the ash discharged from the boiler in this case are The relationship will be explained with reference to FIGS. 3 and 4.

Coal generally contains carbon, hydrogen, oxygen, nitrogen, and sulfur as its main components, as well as organic compounds, 17 ash, and moisture, and is burned in a furnace to become combustion gas. Although its composition and ash composition vary widely depending on the coal, the collection performance of ash is controlled by its electrical resistance, and the lower the electrical resistance, the better the collection performance.

The components that control the electrical resistance of the ash are SOs in the combustion gas and alkali metals such as Na2OmKto in the ash.

The former adsorbs to the surface of the ash at low temperatures and lowers the electrical resistance (dominated by surface conduction), while the latter increases the volume conductivity and lowers the electrical resistance. Therefore, volume conduction becomes dominant in the high temperature region, and surface conduction becomes dominant in the low temperature region. Low-temperature dust collectors are used in areas where the gas temperature is low (usually below 180°C), and their ability to collect blood is affected by the amount of SO3 ash attached (surface conduction). Figure 3 shows the relationship between combustion gas temperature and electrical resistance of ash. (A), (B), (C) in Figure 3,
(D) shows the characteristics of coal. (5) is coal with low sulfur and alkali content, (B) is coal with low sulfur content but high alkali content, (C) is coal with high sulfur content and low alkali content, and (to) is coal with low sulfur content and alkali content. It shows the electrical resistance of ash in the combustion gas of coal, which has many components.

As shown in FIG. 3, the electrical resistance changes depending on the gas temperature, and the temperature at which it reaches its maximum value exists in the temperature range where the low-temperature electrostatic precipitator is applicable. Here, the combustion gas temperature of a coal-fired boiler changes not only depending on the boiler load, but also on the coal properties, and the electrical resistance characteristics differ depending on the coal properties, so the temperature of the combustion gas in a coal-fired boiler is designed for the following conditions (coal, gas temperature conditions). The dust collection performance of an electrostatic precipitator may deteriorate significantly under other conditions (when the coal is different from the designed coal) (in Figure 4, the usage point is different from the design point A due to a change in the coal). 3 points, the electrical resistance increases and the dust collection performance decreases) In this way, in the conventional method, if the charcoal used is different from the designed charcoal, the dust collection performance decreases significantly, and the amount of soot and dust scattered from the chimney exceeds the allowable limit. This is a serious problem in terms of air pollution. The present invention is cooled to solve the above problems, and the problems shown in Figs. 2 and 5 to M7
In the figures, the same parts as those shown in FIG. 1 will be described using the same reference numerals.

In FIG. 2, 17 is a gas temperature control device, 18 is a control valve, 19 is a control valve activation relay, and 2° is a gas temperature or electric resistance detector for contained ash.
This is an addition to the conventional example shown in the figure.

The operation of the above-mentioned embodiment of the present invention will be explained below. As shown in FIG. The amount of inlet gas temperature control medium of the electrostatic precipitator 6 supplied to the device 17 is controlled by the control valve activation relay 19 and the control valve 1.
By controlling the inlet gas temperature or electrical resistance to a predetermined value through the precipitator 8, it is possible to prevent the dust collection performance of the electrostatic precipitator 6 from deteriorating due to variations in coal type or the like.

What is shown in FIG. 5 is an embodiment in which a low-pressure feed water heating type gas temperature control device 17 is used as the gas temperature control device 17 in FIG. 2. According to this embodiment, the combustion gas temperature At the same time, it is possible to improve the thermal efficiency of the plant by recovering the heat retained in the combustion gas. In FIG. 5, the condensate obtained from the condenser 21 is pressurized by the rear water pump 22, passes through the first low-pressure water heater 23 and the second low-pressure water heater 24, and then is sent to the third low-pressure water heater (not shown) or desorbed. This leads to the respiratory organs (not shown),
A part of this low-pressure feed water is guided to a gas temperature control device (combustion gas/low-pressure feed water heater) 77 of a low-pressure feed water heating type, and the heat retained in the combustion exhaust gas is recovered.

In this case, the inlet gas temperature of the electrostatic precipitator 6 is controlled by controlling the amount of water supplied to the feed water heater, adjusting the heat transfer area of the feed water heater, or adjusting the amount of passing combustion gas.

What is shown in Fig. 6 is an example in which a cold water spray type gas temperature control device [77] is used as the gas temperature control device Noah in Fig. 2. In this example, the latent heat of vaporization of water is used to The combustion gas temperature is controlled (lowered) using water @ fog. In this case, the partial pressure of water vapor in the combustion gas increases due to fog water, but as shown in Figure 9, for example, the acid dew point increases and the amount of SO adsorbed by the ash increases, so the electrical resistance of the ash is further improved. It has the effect of Incidentally, the combustion gas temperature is 10
The amount of spray water required to lower the temperature is approximately 0.4 of the amount of gas.
It is about %. The control valve 18 in FIG. 6 is a spray control valve, and the gas temperature control device 17 is a nozzle.

What is shown in FIG. 7 is an example in which a cold air introduction method is used as the gas temperature control device I7 in FIG.
The gas is introduced into a mixer installed at the inlet flue of the engine, and is mixed with combustion gas to lower the gas temperature. In this case, the amount of air required to lower the combustion gas by 10° C. is approximately 9 inches of the gas amount. The control valve 18 in FIG. 7 is a cold air control damper, and 13 is a forced draft fan.

What is shown in Fig. 8 is the gas temperature control device 1 in Fig. 2.
7 is an example of using air or seawater cooling method,
In this method, an air-cooled or water-cooled cooler is installed in the inlet flue of the electrostatic precipitator 6 to control the gas temperature. In this case, there is an advantage that the amount of processing gas does not increase.

The control valve 18 in FIG. 8 is an air or seawater amount control valve, and the gas temperature control device 17 is a heat exchanger.

As described above, according to the present invention, the combustion gas temperature is controlled to an appropriate temperature by the combustion gas temperature control device installed at the inlet flue (upstream) of the electrostatic precipitator of the exhaust gas treatment device, for example, as shown in FIG. As shown in Figure 2, when using coal different from the designed coal, conventionally the electrical resistance of the ash increases from A to B, resulting in a significant drop in dust collection, but according to the present invention, the combustion gas temperature By lowering the temperature to an appropriate temperature, the electrical resistance C can be lowered to, for example, the same level as (5) in FIG. 4, so the dust collection performance of the electrostatic precipitator can be improved.

Furthermore, for example, if a low-pressure feed water heating system is used as a gas temperature control device, it is possible to adjust the combustion gas temperature to improve dust collection, and at the same time recover the heat retained in the combustion gas to improve the thermal efficiency of the plant. When a cold water spray method is used as a gas temperature control device, the increased moisture in the combustion gas can further reduce its electrical resistance, further improving dust collection performance, and other excellent effects can be achieved. be.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of a conventional example, Fig. 2 is a diagram showing the configuration of an embodiment of the present invention, Fig. 3 is a diagram showing the relationship between combustion gas temperature and electrical resistance of ash, and Fig. 4 is a diagram showing a decrease in electrical resistance due to combustion gas temperature, and FIGS. 5 to 8 are diagrams each showing an example of a gas temperature control device in an embodiment of the present invention.
Figure 9 shows SO8 in the combustion gas in one embodiment of the present invention.
FIG. 3 is a diagram showing the relationship between concentration and acid dew point. 17... Gas temperature control device, 18... Control valve, 19
...Control valve operation relay, 20...Detector. Applicant's Sub-Attorney Patent Attorney Takehiko Suzue No. 1 Figure 5 Figure 3: 6-force degree of entry □ Figure 4: Birth of child/su transition □

Claims (1)

[Claims] What is claimed is: 1. An exhaust gas treatment device for guiding exhaust gas to an electrostatic precipitator to collect dust in the exhaust gas, characterized in that an exhaust gas temperature control means is provided upstream of the electrostatic precipitator.