JPH0152652B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to a fluidized bed thermal reactor such as a fluidized bed incinerator or a fluidized bed pyrolysis furnace for municipal waste or industrial waste. The present invention relates to a method of controlling a fluidized bed thermal reactor that detects and grasps the amount of materials unsuitable for fluidization, such as incombustible materials, and operates while maintaining the amount substantially constant.

Note that in this specification, the term "non-combustible material" refers to not only non-combustible materials but also materials that do not thermally decompose.

[Prior art]

For example, in a fluidized bed incinerator that incinerates materials to be treated such as municipal garbage and industrial waste in a fluidized bed formed of a fluidized medium such as sand, bottles, cans, etc. Since non-combustible materials such as stones and metal products accumulate in the furnace, it is necessary to extract the non-combustible materials along with the sand.

In this case, when the amount of incombustibles extracted is less than the amount of incombustibles supplied, the incombustibles will accumulate more and more in the furnace, eventually leading to poor flow. Also, when the amount of incombustibles extracted is greater than the amount supplied,
Incombustibles will not accumulate further in the furnace, but
This results in a larger amount of sand being discharged together with incombustibles being extracted than necessary, resulting in increased heat loss.

[Problem that the invention seeks to solve]

Conventionally, it was difficult to detect the concentration of noncombustibles in the furnace (the content of noncombustibles in the fluid medium), so a certain amount of the mixture of sand and noncombustibles was constantly extracted, and only the sand was kept in the furnace. The concentration of incombustibles inside the furnace was adjusted by returning it to

In this case, if the balance between the amount of noncombustibles in the supplied combustible material and the amount of noncombustibles in the discharged sand is lost, poor flow may occur, or heat loss may become excessive, resulting in low-quality waste not combusting on its own or undergoing thermal decomposition. The drawback was that the amount of heat required increased.

From the above, it is desirable that the concentration of incombustibles in the fluidized medium such as sand in the furnace is kept within a certain range.For example, in the case of a municipal waste incinerator, the concentration of incombustibles is between 5 and 10%. % range is desirable. In particular, when incinerating industrial waste with a high content of noncombustibles, the balance between the supply and discharge of noncombustibles must be
It is essential to achieve this while keeping the amount of sand removed to a minimum. To do this, it is necessary to detect the concentration of noncombustibles in the furnace as accurately as possible, and if the concentration of noncombustibles is high, increase the amount of sand extracted, and if it is low, reduce the amount of sand removed, or increase or decrease the supply of combustibles. However, there was no easy way to detect the concentration of noncombustibles.

The present invention solves the above-mentioned problems of the conventional incinerator, detects the concentration of incombustibles in a fluidized bed incinerator by a simple method, keeps this value within a substantially constant range, and incinerates the fluidized bed. The purpose is to always maintain a good fluid state and achieve complete incineration of the combustible material.

[Means for solving problems]

The present invention was made by focusing on the fact that the pressure fluctuation waveform of flowing air changes with the change in the concentration of noncombustibles in the incinerator. In a method for controlling a fluidized bed thermal reactor that is equipped with a fluidized gas distributor and forms a fluidized bed above the fluidized bed thermal reactor, the pressure fluctuation frequency of the gas blown into the fluidized bed from the distributor is detected, and based on the detected value. By controlling the supply amount of the material to be treated or the amount of fluidized medium withdrawn from the fluidized bed,
A method for controlling a fluidized bed thermal reactor is provided, which is characterized in that the content of substances unsuitable for fluidization, such as incombustible substances, in a fluidized medium is maintained within a substantially constant range.

〔Example〕

Hereinafter, the present invention will be described based on an example in an incinerator with reference to the drawings.

In Fig. 1, reference numeral 1 denotes an incinerator main body, the bottom of which is equipped with an air disperser 2 having a large number of air ejection holes, and above which sand is placed at a considerable height to form a fluidized bed 12. are doing. A wind box 3 is provided below the air distributor 2 for supplying flowing air.

At the bottom of the furnace is a non-combustible material removal conveyor 7 for removing sand and non-combustible materials, from which a mixture of sand and non-combustible materials is extracted and then classified by a vibrating sieve 9. The incombustible materials, ie, the materials unsuitable for fluidization, are discharged from the furnace as residue, and the sand, ie, the fluidizing medium, is returned to the furnace by a moving means (not shown) and reused.

It is known that the fluidized air supplied from the wind box 3 to the fluidized bed through the air distributor 2 exhibits pressure fluctuations specific to the fluidized state of the fluidized bed. The pressure fluctuation frequency f is expressed as f=K・L ^x・V ^Y. Here, L: Height of the fluidized bed at rest V: Flow velocity X, Y: Constant K: Constant determined by the fluid medium.

Therefore, if L and V are constant, the pressure fluctuation frequency f is determined by the flowing medium. As shown in FIG. 1, this pressure fluctuation frequency f is determined by installing a strain gauge 4 in a wind box 3, amplifying the detected value with a dynamic strain meter 5, and then frequency-analyzing it using an FFT analyzer 6. By doing
can be easily found.

Therefore, when considering the pressure fluctuation phenomenon in a fluidized bed, when the fluidized air from the disperser is gradually increased, at first the air appears to flow quietly between the sand (fixed bed), but then When the amount exceeds a certain level, the air flows between the sand in the form of bubbles, causing the sand to move. This is called a fluidized bed. In this state, air generates bubbles when it is ejected directly above the disperser, the bubbles coalesce and gradually grow as they rise, and when they reach the surface of the layer they burst and are discharged. The pressure fluctuation phenomenon in the layer is caused by the formation, growth, and bursting of these bubbles, and shows a random fluctuation waveform, but the waves are quite periodic.

Analysis of this pressure fluctuation was performed by obtaining a power spectrum using the following equation.

φ=1/T|∫X(t)・e ^-j2 〓 ^ft・dt| ^2where f: pressure fluctuation frequency, t: time.

This calculation was performed after collecting 512 samples.
This was done using an FFT analyzer. The results are shown in FIGS. 2a and 2b, and it can be seen that the waveform is periodic because it has a fairly steep peak.

The position of this peak changes depending on the concentration of noncombustibles, and this is because the conditions of bubble generation, growth, and bursting change depending on the concentration of noncombustibles, that is, fluidization unsuitable materials. In particular, the pressure fluctuation frequency f is
There is a close relationship with the number of bubbles, and the larger the number, the smaller the pressure fluctuation frequency f tends to be. Therefore, it is thought that the non-combustibles, that is, the fluidizing materials, promote the coalescence and growth of bubbles and reduce the number of bubbles, so that the higher the concentration of non-combustibles, the smaller the peak frequency becomes (see Figure 3).

As mentioned above, it is understood that when L and V are constant, the pressure fluctuation frequency f is determined by the nature of the fluid medium, ie the concentration of non-combustibles. As shown in FIG. 3, in order to maintain the concentration of incombustibles in the sand within an appropriate range, for example within a range of 5 to 10%, it is preferable to adjust the concentration so that 0.6<f<0.7.

This is achieved by controlling the raw material input conveyor 8 installed at the top of the incinerator 1 and the incombustible material removal conveyor 7 installed at the bottom of the incinerator 1 using the control device 13. In other words, when f<0.6, By lengthening the extraction time when 0.6<f<0.7, and shortening the extraction time when 0.6<f<0.7, it is possible to ensure the best flow condition without generating heat loss due to extraction of excess sand. Otherwise, it is of course possible to control the concentration of non-combustibles by controlling the speed of the conveyor supplying the combustibles.

The above description has been made regarding a fluidized bed incinerator, but the same applies to a fluidized bed pyrolysis furnace.

〔Effect of the invention〕

As described above, the present invention detects the fluctuating frequency of the fluidizing gas blown into the fluidized bed from the air disperser, and based on this, accurately grasps the content of noncombustibles in the fluidized bed, which changes from time to time, Since appropriate countermeasures can be taken, the concentration of incombustibles in the fluidized bed can always be maintained within the desired range, thereby ensuring the best fluidization state of the fluidized bed and therefore the best operation of the fluidized bed incinerator. state can be secured. Therefore, stable incineration operations are possible even for items containing large amounts of non-combustible materials, such as bottles and cans.
In addition, even for waste with a low calorific value, it is expected that auxiliary combustion will become unnecessary or will be reduced.
It greatly contributes to the treatment of municipal garbage or industrial waste.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a fluidized bed incinerator implementing the present invention, Figures 2a and b are diagrams showing the frequency analysis results of air pressure fluctuations, and Figure 3 shows the relationship between the concentration of incombustibles and the frequency of air pressure fluctuations. This is a graph showing. 1... Incinerator main body, 2... Air disperser, 3...
Wind box, 4...Strain gauge, 5...
Dynamic strain meter, 6... FFT analyzer, 7... Non-combustible material removal conveyor, 8... Raw material input conveyor, 9
... vibrating sieve, 12 ... fluidized bed, 13 ... control device.

Claims (1)

[Claims] 1. In a method of controlling a fluidized bed thermal reactor that is equipped with a fluidizing gas distributor at the bottom and forms a fluidized bed above the fluidized bed, the pressure fluctuation frequency of the gas blown from the distributor into the fluidized bed is detected; By controlling the supply amount of the material to be treated or the amount of fluidized medium withdrawn from the fluidized bed based on the value, the content of substances unsuitable for fluidization, such as incombustibles, in the fluidized medium can be maintained within a substantially constant range. A method for controlling a fluidized bed thermal reactor, characterized in that: