JPS6248131B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waste incinerator, and particularly to an incinerator that can efficiently cool high-temperature exhaust gas generated by incineration and reduce acid gas in the exhaust gas.

When incinerating various types of waste, high-temperature exhaust gas is generated, which is cooled to some extent before being transferred to processes such as dust collection. Methods for cooling the exhaust gas include water injection, boiler, and combinations of these. There is,
They are used differently for each incinerator.

On the other hand, exhaust gas contains hydrogen chloride gas (HCl) and/or sulfur oxide gas (SO _x ), and in order to prevent air pollution, these acidic gases must be reduced before exhaust gas is released into the atmosphere. Can be done. The reduction of these oxidizing gases has been carried out separately and independently from the cooling of the high-temperature gas by various methods as shown below, but each method has the drawbacks described below.

(1) Wet alkaline absorption method A promising method for reducing HCl and SO _x has been developed, but because it is a wet method, there are technical problems such as processing of waste liquid and white smoke generation due to the low temperature and high humidity. There are many problems, and the equipment is also large, and the construction and running costs are high.

(2) Wet evaporation tower method Combustion exhaust gas, etc. is led to a reaction evaporation tower or a packed tower, and a slurry of calcium hydroxide [Ca(OH) ₂ ] is evaporated in the tower and mixed in contact with the exhaust gas. This method removes HCl and/or SO _x by converting them into calcium chloride (CaCl ₂ ) and calcium sulfate (CaSO ₄ ), respectively, but the exhaust gas temperature is between 200 and 350.
℃, the gas temperature decreases due to the evaporation of the slurry, so the gas produced by the above reaction
There is a risk of low-temperature corrosion of the electrostatic precipitator installed to collect dust such as CaCl ₂ , CaSO _{4 ,} and unreacted Ca(OH) ₂ , and there are also problems such as generation of white smoke. Another disadvantage is that the equipment is large and construction costs are high, and the slurry is not easy to handle.

(3) High-temperature dry reduction method Calcium carbonate (CaCO ₃ ) or Ca(OH) ₂ is added to HCl and/or SO _x contained in high-temperature gas of 750 to 950°C during the combustion process.
is brought into contact with the gas in powder or slurry form.
Convert HCl and SO _x to CaCl ₂ and CaSO ₄ respectively, and collect them with a dust collector such as an electrostatic precipitator.
Although this is a method to remove HCl _{and SO}
Other salts (NaCl, Na ₂ SO ₄ ) mixed in
It has the property of forming a complex salt and melting it.
If the combustion equipment is equipped with a heat exchanger such as an air preheater, it will melt and adhere to the combustor wall near the injection point and downstream, or to the tube group of the heat exchanger, producing clinker and clogging the tube group, respectively. This results in a significant adverse effect on plant performance, which poses various practical problems.

(4) Low _- temperature dry reduction method For gas containing HCl and/or _SO This method involves contacting and mixing the powder with the gas, converting HCl and SO _x into CaCl ₂ and CaSO ₄ respectively, and collecting them with a dust collector to remove HCl and SO _x . The reduction rate that can be stably obtained in an actual plant is about 50%.

In the conventional acid gas reduction methods mentioned above, the main issue is the contact mixing of the exhaust gas and chemicals after combustion is completed, and methods of increasing the residence time of the chemicals to improve miscibility, or methods of increasing the residence time of chemicals in the exhaust gas pipes are considered. Methods such as placing obstacles in the area have been considered, but no significant results have been achieved.

The present inventors have developed a method for reducing HCl and SO _x that is more effective and practical than conventional acid gas reduction methods, that is, it requires a high mixing ratio of acid gas and chemicals, reduces equipment costs,
As a result of intensive research to develop a method that has low running costs, easy equipment operation, and a higher reduction rate than the conventional low-temperature dry reduction method, we succeeded in developing a method that simultaneously cools exhaust gas and removes acid gas. This is what the present invention has achieved.

That is, the present invention provides a method for injecting alkaline earth metal compounds (oxides, hydroxides, carbonates, etc.) into the high-temperature gas existing region in the upper part of the combustion chamber (hereinafter referred to as the upper part of the furnace) of a waste incinerator.
Waste that can be integrated with exhaust gas cooling and acid gas removal using alkaline earth metal compound powder, characterized in that a powder injection device is provided and a water injection device is provided near the downstream of the injection device. Regarding incinerators. In the present invention, when the alkaline earth metal compound powder is injected into the high-temperature exhaust gas near the upstream of the water injection device in the upper part of the furnace, the volume of the water injected into the high-temperature exhaust gas increases as it evaporates, and this volume change causes As a result, the contact mixing ratio increases, and the reaction between acidic gas and alkaline earth metal compound powder, which was previously a solid-gas reaction, becomes a solid-liquid reaction due to the injected water, increasing reactivity. By integrating water jet cooling and alkaline earth metal compound powder jetting, the reduction rate of acid gas is increased.

In the present invention, the following effects can be achieved by integrating exhaust gas cooling and acid gas reduction, which have conventionally been performed separately, in the upper part of the furnace.

A higher reduction rate can be obtained than the conventional low-temperature dry reduction method, and running costs are also lower.

Since it is only necessary to newly install an alkali chemical injection device to an existing furnace that has a water injection device in the upper part of the furnace, the equipment cost is low and it does not take up space unlike conventional acid gas reduction devices.

Even if reaction products and surplus chemicals fall, they fall into the furnace, making maintenance management easy and the equipment easy to operate.

Although the present invention can be applied to various waste incinerators, it is suitable for municipal waste incinerators, industrial waste incinerators, etc. that have a water injection exhaust gas cooling device in the upper part of the incinerator.

A specific example to which the present invention is applied is shown in FIG. This is a water-injection gas-cooled waste incinerator with a new nozzle for injecting Ca(OH) ₂ .

First, the alkaline earth metal compound powder (hereinafter referred to as chemical) supply system will be explained. The amount of conveying air is adjusted by a blower 1 and a gate valve 2, the flow rate is measured by a flow meter 3, and the air is sent to a powder supply device through a pipe 4. The powder supply device is composed of a hopper section 5 and an ejector section 6, and the conveying air from the line 4 and the chemical from the hopper section 5 are mixed by this device. The mixed chemicals pass through the pipe 7 and the valve 8, reach the injection nozzle 15, and are injected.

On the other hand, the water-injected gas-cooled waste incinerator is Hoppa 1.
Garbage is supplied into the furnace from 0 and burned on the stoker 11. The exhaust gas that has completed combustion is cooled by water droplets injected from the water injection nozzle 12, and the water droplets are completely evaporated inside the gas cooling chamber 13. Thereafter, the combustion air passes through a heat exchanger 14 for preheating and reaches a dust collector.

On the other hand, the chemical injection nozzle 15 is the water injection nozzle 1.
It was installed upstream of 2. In this case, the moment the powder injected from the chemical injection nozzle 15 enters the gas cooling chamber 13, it enters the zone where water evaporates, where it comes into contact with the exhaust gas and mixes with the powder. The acidic gas is greatly reduced by the solid-liquid reaction. In addition, some of the excess Ca(OH) ₂ and reaction products fall onto the stoker 11.

EXAMPLE FIG. 2 shows the results of an experiment conducted using a water-injected gas-cooled waste incinerator (150 t/d) equipped with the chemical supply device shown in FIG. 1. The experimental conditions at this time were as follows.

Gas temperature at the chemical injection nozzle position Approximately 1000℃ Gas flow rate at the chemical injection nozzle position
Approx. 34000Nm ³ /h Exhaust gas cooling chamber diameter 2.7m Water injection amount Approx. 10t/h Reduction rate (%) calculation method HCl concentration before chemical injection - HCl concentration after chemical injection / HCl concentration before chemical injection x 100 HCl concentration before chemical injection
300 to 450 ppm (calculated as O ₂ 12%) In this example, an experiment was conducted by injecting Ca(OH) ₂ powder from the following two locations.

a When the gas is injected from the upper part of the gas cooling chamber 13 (Fig. 2) b When it is injected from the chemical injection nozzle 15 (the second
As is clear from FIG. 2, at the same equivalence ratio, the acidic gas reduction rate is highest when water is injected immediately after chemical injection. This is because in case a, the water is all water vapor and the reaction is mainly a solid-gas reaction, so it is considered that the desalination effect of the injected water is not observed. In case b, it is thought that this is because the reaction is mainly a solid-liquid reaction and a gas-liquid reaction when the chemical comes into contact with the injected water, increasing the reaction efficiency.

[Brief explanation of the drawing]

Figure 1 shows a specific example of the incinerator of the present invention, and the second
The figure is a graph showing the relationship between the chemical injection position and the acid gas reduction rate of the present invention.

Claims (1)

[Claims] 1. A waste incinerator, characterized in that an alkaline earth metal compound powder injection device is provided in a high-temperature gas presence region above a combustion chamber of the waste incinerator, and a water injection device is provided near the downstream of the injection device.