JPS62119316A - Method of controlling temperature of fluidized bed - Google Patents

Abstract

PURPOSE:To suppress the generation of dioxine or the like by supplying pressure air of a predetermined air excess ratio to a particle dilute layer in the vicinity of the upper surface of the fluidized bed as a part of secondary air in the titled control of a fluidized bed refuse incinerator. CONSTITUTION:Air having an air excess ratio of 0.1-0.3 is supplied to a particle dilute layer 8 placed at the directly upper part of a fluidized bed 2 under a high pressure. By this procedure, air from the fluidized bed 2 and a vaporized burnable gas are mixed and caused to react sufficiently with each other to raise the furnace temperature as shown by curve B, and the fluidized bed 2 is heated with the radiation heat of a combustion flame to maintain the temperature of the fluidized bed at 800 deg.C or more. Particles which have sprung out into a dilute layer 8 come into direct contact with the high temperature gas and the temperature of the particles is raised, and again return to the fluidized bed 2 to maintain the temperature of the fluidized bed 2 to a high value. By this organization, the generation of dioxine or the like can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of operating a fluidized bed waste incinerator, and particularly to a method of controlling the temperature of a fluidized bed to suitably perform intermittent operation.

<Conventional technology and its problems> Urban areas, which are increasing year by year, have traditionally been incinerated using stoker type incinerators, but recently fluidized bed type incinerators have begun to be used. The advantages of fluidized incinerators include fewer breakdowns, dry ash with less unburned matter, and ease of intermittent operation.

The fluidized bed is filled with silica sand having a particle size of about Lffiffi to a height of about 1 m in a so-called stationary state without supply of fluidizing gas, and is fluidized. Because the fluidized bed packing has a large heat retention capacity, the temperature inside the furnace decreases slowly after shutdown, which is particularly advantageous for intermittent operation furnaces called semi-continuous furnaces.

Here, intermittent operation refers to an operation in which the vehicle is operated for 8 hours or 16 hours during the day per day, for example.

However, conventional operating methods have various problems, and there are many points that require further improvement.

FIG. 1 shows the relationship between the combustion air supply position and the temperature inside the furnace in a fluidized bed waste incinerator as a diagram.

Fluidized air is supplied as combustion air 5 to a fluidized bed 2 provided at the lower part of the fluidized bed furnace 1 via a wind box 3.

Secondary air 6 is supplied to the empty tower section 4 above the fluidized bed 2 for complete decomposition and cooling of the combustible gas. This is the typical operating mode of a normal waste fluidized bed incinerator, which takes a temperature pattern as shown by curve A in FIG. The state of temperature change in the furnace from the bottom to the top will be explained using the A curve.

From the wind box 3 at the bottom of the furnace, combustion air 5 which also serves as fluidization is supplied to the fluidized bed 2. At this time, the pressure of the secondary air 5 is changed by a forced blower (not shown), and the temperature is raised to around 50°C. In some cases, it may be heated to about 100 to 250°C by an air preheater (not shown).

In any case, when the primary air from the wind box 6 flows into the fluidized bed 2, it contacts the fluidized medium and is instantly heated to the same temperature as the fluidized bed 2, 600 to 700°C.

The air leaving the fluidized bed 2 comes into contact with combustible gas from the combustible content in the waste vaporized in the fluidized bed 2 or in the empty tower section 4, causing a combustion reaction, and the temperature rises toward the top of the furnace. By supplying secondary air near the top, the combustible matter completely burns, reaching the highest temperature at the supply point (900°C in the figure), mixing, averaging the temperature, and cooling (800°C in the figure).
00℃) and flows out of the furnace.

As shown in curve A, the conventional operating mode of waste incineration using a fluidized bed furnace has the following drawbacks.

First, in the case of waste incineration, the temperature of the fluidized bed is controlled by convective heat transfer and radiation heat transfer between the combustion gas and fluidized medium particles on the fluidized bed. In the case of fluidized waste incineration, the amount of primary air is supplied at an excess air rate of about 19 to 11, and the excess air is supplied as secondary air 6, but under these conditions, the Become. In this mode, the fluidized bed temperature is 600
The temperature can only be maintained at about 700°C, which is considered a drawback of fluidized bed furnaces for the following reasons.

The fluidized bed type waste incinerator is called a semi-continuous type and burns 8 to 16 kg per day.
The temperature of the fluidized bed should be high, considering the start of the furnace the next day.
If it is 0 to 850℃, the layer temperature at the start of the next day will be 600℃.
As described above, there is an advantage in immediately putting in garbage and starting steady operation without using oil supplementary combustion. However, when the fluidized bed operating temperature is 600 to 700°C, the next day the bed temperature drops to 500°C or less. In this case, it is necessary to raise the bed temperature to 600 to 650°C by auxiliary combustion of oil. This is the first drawback.

Recently, problems such as dioxins have emerged as new pollution factors in waste incineration. Although the toxicity of dioxin is extremely severe, it is thermally unstable and can reach temperatures of 800°C.
It is known that the above decomposes easily, and it is also known that a reaction (residence) time of about 1 second is sufficient.

The dioxin problem in waste incineration is related to fly ash and combustion residue (incineration ash) on the gas side.

It is said that this occurs more easily when the reaction temperature is low, and it has been confirmed in practice.

In order to eliminate these drawbacks, high-pressure injection air is supplied directly above the fluidized bed to allow operation along the 8 curves shown in FIG. 1.

<Objective of the Invention> The present invention eliminates the operational disadvantages of conventional fluidized bed waste incinerators, maintains a high fluidized bed temperature before shutting down the operation, facilitates intermittent operation, is economical, and eliminates dioxins, etc. Regarding technology to suppress outbreaks.

Outline of the means for achieving this> By supplying high-pressure injection air to the particle-diluted layer on the upper surface of the fluidized bed, the mixing and twisting of the combustible gas is promoted and the temperature directly above the layer is maintained at a high temperature, thereby lowering the fluidized bed temperature. It is maintained at a higher temperature than the operating temperature of conventional methods.

An embodiment of the present invention will be described with reference to FIG.

・A high-pressure injection air supply lower is provided just above the fluidized bed, and by injecting and supplying a relatively small amount of high-pressure air, the area directly above the fluidized bed is maintained at a high temperature, and convection and radiation heat transfer with the fluidized medium particles is activated. The temperature of the fluidized bed is maintained at a higher temperature than in conventional operation methods, making intermittent operation easier and ensuring complete decomposition of dioxins, etc.

The 8 curves in FIG. 1 are the furnace temperature change curves according to this operating method. The combustible components of the waste supplied to the fluidized bed furnace are quickly vaporized (gasified) in or directly above the fluidized bed, and are ignited and combusted by air flowing from below the fluidized bed. Normally, urban air is burned at an excess air ratio of 1.2 to 2.5, although it varies depending on the amount of heat. Among these, the fluidizing air as combustion air is supplied in the range of α9 to 1.1 as described above. Therefore, as secondary air, the excess air rate is 0.1 to 1.6.
A corresponding portion is supplied to the empty column section 4 above the fluidized bed. However, if the entire amount of secondary air is supplied directly above the fluidized bed as in the present invention,
There is a drawback that the gas temperature becomes locally high from around the point where the supply amount of secondary air exceeds the excess air ratio of 0.4, and the NOx concentration rapidly increases.

The apparent specific gravity of the fluidized bed is approximately 1 when the fluidized particles are silica sand. Therefore, the contact between air and the vaporized gaseous body of combustible substances is worse in a fluidized bed than in a normal gas-filled space. In other words, it is impossible for all the oxygen in the air present in the fluidized bed to react with the vaporized gas. This results in a low fluidized bed temperature, as shown by curve A in FIG. 1, and after the fluid has evaporated to the top of the bed, a reaction occurs in the empty column and the temperature rises.

In order to eliminate this drawback, in the present invention, air corresponding to an air excess ratio of 0.1 to 0.5 is supplied to the particle diluted layer 8 immediately above the fluidized bed, and this is further supplied at high pressure. , the air from the fluidized bed and the vaporized combustible gas are mixed and reacted sufficiently, the temperature of the 8th curve is raised, and the fluidized bed is heated by the radiant heat of the combustion flame to raise the fluidized bed temperature to 800℃ or higher. Hold. Further, the upper surface of the fluidized bed is not clearly separated from the gas like the water surface, but particles that have jumped from the fluidized bed dance like boiling water, forming a so-called dilute layer 8. These flying particles come into direct contact with the high-temperature gas produced by the ejected air, raise their temperature, and then return to the fluidized bed by gravity, which has the effect of increasing the bed temperature.

Further, reducing the amount of injected air to an excess air ratio of 0.1 to 0.6 suppresses the generation of NOx.

By this operation, it becomes extremely easy to maintain the fluidized bed temperature at 750° C. or higher.

The advantage of keeping the fluidized bed temperature high is in the case of intermittent operation.
The next day, the fluidized bed should be operated without heating the oil by burning the oil.

<Effect of the invention> By implementing the present invention, the temperature of the fluidized bed can be reduced to 800°C.
When the operation is stopped in the above manner, in so-called intermittent operation, which is a start-up/stop of daily operation, the temperature drop is small and it is easy to start even if garbage is directly supplied at the time of start-up, and auxiliary fuel is not required.

In addition, highly toxic substances such as dioxins in the incineration ash extracted through the fluidized bed can be completely decomposed at high temperatures. Furthermore, by instantaneously raising the gas temperature above the fluidized bed to a high temperature, the residence time of the fly ash in the high-temperature gas can be extended, and the decomposition of dioxins and the like contained therein can be completely completed.

When desulfurization is performed using limestone particles as a fluid medium,
It is particularly noteworthy as an effect of this invention that the optimum temperature for the desulfurization reaction is 800 to 850°C.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the air supply position and the furnace temperature. 1...Fluidized bed furnace 2...Fluidized bed 3...Wind box 4...Sky tower section 5...-Next air 6...
・Secondary air 7...Injection air

Claims (1)

[Claims] 1. In a method of incinerating waste in a fluidized bed furnace, pressurized air is used as part of secondary air in a particle diluted layer near the top surface of the fluidized bed, and the air excess coefficient is equivalent to 0.1 to 0.3. A fluidized bed temperature control method characterized by supplying an amount of . 2. The fluidized bed temperature control method according to claim 1, wherein the fluidized bed temperature is maintained at 800° C. or higher and the fluidized bed is operated intermittently.