JPH01168335A - Process for detecting state of fluidized bed - Google Patents

Abstract

PURPOSE:To detect the state of fluidization in a fluidized bed easily, quantitatively, and on real time, by comparing the values of fluctuations in pressure in a fluidized bed with a reference value of fluctuation in pressure in a fluidized bed to detect the state of fluidization in the fluidized bed. CONSTITUTION:By conducting experiments in advance, reference values of fluctuations in pressure in a fluidized bed are preset corresponding to each state of fluidization in the fluidized bed of a fluidized bed apparatus 1. The values of fluctuation in pressure in the layer of the fluidized bed are detected by means of a pressure detector 10 to detect the state of fluidization of the fluidized bed by comparing the detected values with said preset values. As a result, the state of fluidization of the fluidized bed can be detected easily, quantitatively, and on real time as well. In this manner, control of a fluidized bed apparatus can be performed easily, precisely, and rapidly, manually or automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting the state of a fluidized bed in a circulating fluidized bed boiler, etc., which is an application technology of high-speed fluidized bed combustion.

[Conventional technology]

What is shown in FIG. 5 is a conceptual diagram of a conventional circulating fluidized bed coal-fired boiler.

In the figure, 50 is a combustion chamber, and the combustion chamber 50 is provided with a viewing window 51 for observing the fluidization state and a temperature sensor 52. A fuel hopper 53 is provided at the bottom of the combustion chamber 50.
Pulverized coal and limestone are supplied in fixed quantities from a limestone hopper 54, and air is supplied via a secondary air fan 55 and a secondary air fan 56, so that fuel coal is combusted within the combustion chamber 50.

The high temperature exhaust gas from the combustion chamber 50 is passed through the hot cyclone 57
, a superheater 58 , and a dust collector 59 , and is discharged into the atmosphere from a chimney by a fan 60 . Water is heated in the superheater 58 and steam is generated.

The fuel coal in the combustion chamber 50 exhibits the state shown in FIG. 6 depending on the amount of supplied air. That is, when air is pumped through the baffle plate to the coal-filled bed at the bottom of the combustion chamber 50, the speed of the air passing through the bed (hereinafter referred to as "superficial velocity") causes become a state.

The state shown in FIG. 6(1) is when the superficial velocity is small, the particles of fuel coal are apparently stationary, and this state is called a fixed bed.

In the state shown in Fig. 6 (2), when the superficial velocity increases and the pressure drop reaches a flow start velocity that almost balances the entire weight of the thermal coal particles, the thermal coal particles begin to move as if they were melting a solid. Start. This state is called uniform fluidization.

The state shown in FIG. 6(3) is a bubble fluidization state, and when the superficial velocity becomes higher than the above, bubbles are continuously generated from the bottom of the bed and rise within the bed. The generated bubbles repeatedly coalesce within the layer and grow with the layer height. However, when particles with a small particle density and a large particle size distribution are used, the frequency of bubble splitting increases at the same time as the bubbles coalesce, so the bubble diameter increases with the layer height. It remains almost constant within

When the superficial velocity is further increased, a slugging fluidization state occurs as shown in FIG. 6(4). This condition refers to a state in which, in a fluidized bed where the combustion chamber diameter (column diameter) is small and the bed height is excessive, bubbles grow to the column diameter and rise intermittently in the bed, making it impossible to form a bubble fluidized state. .

When the superficial velocity is further increased, the turbulent fluidization state shown in FIG. 6(5) is reached. That is, bubbles and slap collapse, and particles move violently.

If the superficial velocity is further increased from the turbulent fluidization region and the particle circulation amount is increased, the high-speed fluidization state shown in FIG. ) becomes 0.8 to 0.9.

When the superficial velocity is further increased, the thin transport state shown in FIG. 6 (7) is reached, and the particles are discharged out of the combustion chamber along with the airflow.

Each state of the fluidized bed in FIG. 6 can be distinguished by the relationship between the particle Raynozzle number and the Archimedes number, and FIG. 7 shows the relationship between the particle Raynozzle number Rep and the Archimedes number Ar.
It is a graph which shows the relationship between and each fluidization state. The symbols used in the figure are as follows.

Rep; Particle Reynozzle number dp; Particle diameter 2g; Gas density Uo: Gas superficial velocity μ; Gas viscosity coefficient 8r; Archimedes number ρp; Particle density g; Gravitational acceleration Fr; Froude number (Fr=Ar /Re”)Dt;
Fluidized bed column diameter ε; void ratio Remb i bubble fluidization start Ray nozzle number Remf
; Number of Rei nozzles at the start of uniform fluidization Reh i
Ray nozzle number to start turbulent fluidization In the circulating flow boiler, the lower part of the combustion chamber 50 is in a bubble fluidized state, the upper part is in a turbulent to high-speed fluidized state, and the combustion state (temperature) is controlled by finely controlling the particle density. , excess air ratio, etc.).

Optimal fluidization conditions and particle densities exist in fluidized bed devices other than circulating fluidized beds. Therefore, in order to keep the flow state and particle density appropriate, the flow state and particle density are detected and the amount of secondary air and the amount of secondary air are controlled accordingly.

Conventionally, methods have been used to detect this flow state, including (1) visual observation or visual observation through a television camera, and (2) indirect detection from measured values such as temperature.

[Problem that the invention seeks to solve]

In a fluidized bed device, in order to operate the device smoothly, the amount of fuel supplied, -
The amount of secondary air, amount of secondary air, amount of water supply, etc. must be appropriately controlled. Therefore, it is necessary to quickly and accurately detect the flow conditions within the bed.

However, conventional visual inspection methods lack quantitative properties, are subject to the subjectivity of the observer, and require the observer's skill.

In addition, the method of indirectly detecting the temperature or the like has poor responsiveness and also changes depending on other factors, so there is a problem that it lacks accuracy as a method for detecting the fluidized state of the layer.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for detecting the state of a fluidized bed that can easily detect the state of the fluidized bed quantitatively and in real time.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention has taken the following measures.That is, the feature of the present invention is that the fluidized bed in the fluidized bed apparatus is A reference pressure fluctuation value in the bed corresponding to each flow state is set, a pressure detection means detects the bed pressure fluctuation value in the fluidized bed, and the detected value is compared with the set value to determine the flow state of the fluidized bed. The point is to detect.

[Function] The inventors of the present application have found through various experiments that there is a close relationship between pressure fluctuations in the fluidized bed in a fluidized bed apparatus and each fluidization state.

Therefore, the intrabed pressure fluctuation value in each flow state is determined in advance through experiments, and this value is used as an index indicating each flow state. That is, an in-bed standard pressure fluctuation value corresponding to each flow state of the fluidized bed in the fluidized bed apparatus is set in advance.

During actual operation, the actual pressure fluctuations in the fluidized bed are measured by the pressure detection means. By comparing this measurement result with the reference set value, it is possible to know the flow state within the bed at the time of measurement.

[Example] Embodiments of the present invention will be described below based on the drawings.

What is shown in FIG. 1 is a conceptual diagram of a fluidized bed apparatus imitating a circulating fluidized bed coal-fired boiler.

In the figure, 1 is a combustion chamber (layer), and a baffle plate 2 is provided at the bottom of the combustion chamber 1, and a combustion ash outlet 3 is provided. A fuel hopper 4 and a feeder 5 are provided on the current plate 2 for supplying pulverized coal for fuel. An air supply valve 6 is partially connected to the wall surface of the combustion chamber below the current plate 2, and a secondary air supply valve 7 is connected to the wall surface of the combustion chamber above the current plate 2. Three secondary air supply valves 7 are provided at predetermined intervals in the height direction.

The primary and secondary air supply valves 6.7 are connected to a blower 9 via an air heater 8.

A pressure fluctuation sensor 10 for detecting the pressure within the combustion chamber 1 is provided on the wall surface of the combustion chamber above the rectifying plate 2. Five sensors 10 are provided at predetermined intervals in the height direction.

Each sensor 10 is electrically connected to an FFT analyzer 11. This FFT analyzer 11 is electrically connected to calculation means 12 and storage means 13, and these constitute control means 14. This control means 14 is electrically connected to the secondary and secondary air supply valves 6.7, and the opening degrees of these valves 6.7 are automatically controlled by commands from the control means 14.

A hot cyclone 16 is connected to the upper part of the combustion chamber 1 through a duct 15, and the lower part of the hot cyclone 16 communicates with the lower part of the combustion chamber 1 through a downcomer 17 and a loop seal 18, and the hot cyclone 16 is connected to the upper part of the combustion chamber 1 through a duct 15. A circulation path is formed between the cyclones 16.

An exhaust gas discharge duct 19 is connected to the top of the hot cyclone 16, and a gas cooler 20, a bag filter 21, a fan 22, and a chimney are connected in this order to the duct 19.

The combustion chamber 1 is provided with a thermocouple 23 that measures the temperature inside the combustion chamber, and a gas analyzer 24 that analyzes combustion gas is connected.
The gas analyzer 24 is connected to the data logger 25. This data logger 25 also constitutes a part of the control means 14.

In the fluidized bed apparatus, pressure fluctuations corresponding to various fluidization states in the combustion chamber 1 are determined in advance through experiments.

First, coal in the fuel hopper 4 is cut out by the feeder 5 and deposited in a predetermined amount on the rectifying plate 2, and the secondary air supply valve 6 and the secondary air supply valve 7 are opened and closed as appropriate to supply air into the combustion chamber 1. supply, burn the coal, and actively create various fluidized states. The sensor 10 detects pressure fluctuations within the combustion chamber 1 in various flow states.

What is shown in FIG. 2 is a frequency spectrum of pressure vibration obtained by analyzing the pressure vibration signal measured by the sensor 10 with the FFT analyzer 11. Figure 2 (1) shows single-stage combustion (
(air ratio 1.2), figure (2) shows the case of two-stage combustion (-stage air ratio 015). This is data at a position 0.4 m from the center.

Here, single-stage combustion refers to combustion in which the secondary air supply valve 7 is closed and air is supplied only from the secondary air supply valve 6.
Two-stage combustion refers to combustion in which air is supplied by opening both the secondary and secondary air supply valves 6.7.

The air ratio is used as a unit to indicate the amount of air, and is the ratio when the amount of air required to burn all of the supplied fuel is set to 1. In a normal combustion furnace, a 12th order air ratio is used at about 1.2. Therefore, there is an excess of 0.2 air.

In this example as well, the air ratio is 1.2, and therefore the -order air ratio (Prjmary air ratio
) 1.2 means that the secondary air ratio is 0, that is, single-stage combustion. Further, the secondary air ratio of 0.5 means that the secondary air ratio is 0.7 and two-stage combustion is performed.

Now, if the -order air ratio is determined, the gas (air) velocity at the bottom of the layer is determined, so the particle Reynozzle number (Rep) and Archimedes number (Ar) in Figure 7 are determined, and by reading Figure 7, , the state of the fluidized bed at the bottom of the bed can be known.

That is, it can be seen that in single-stage combustion with a negative air ratio of 1.2, there is a turbulent fluidized bed at the bottom of the bed, and in two-stage combustion with a negative air ratio of 0.5, there is a bubbly fluidized bed.

On the other hand, in the upper part of the bed, both the single-stage combustion and the two-stage combustion have the same superficial velocity, so Rap and Ar are the same in the upper part of the bed, so the flow state is the same.

Now, returning to FIG. 2 and considering, in the upper part of the bed, the peak of the pressure oscillation frequency is the same at 5 to 6 Hz in both the single-stage combustion and the two-stage combustion. On the other hand, in the case of single-stage combustion (second
In Figure (1)), the frequency peak is between 2 and 6 tlz, whereas in the case of two-stage combustion (Fig. 2 (2)), the frequency peak is between 1 and 2 tlz.
, and the two are different.

This means that if the flow state is the same, the characteristics of the pressure vibration frequency spectrum are the same, and if the flow state is different, the characteristics of the pressure vibration frequency spectrum are different.

Therefore, by creating various flow states by changing the air ratio and determining the pressure oscillation frequency characteristics at that time, each flow state can be made to correspond to each pressure oscillation frequency characteristic.

In this way, the pressure oscillation frequency characteristics corresponding to each flow state are determined through experiments, and this is used as a reference value in the storage means 1.
Please remember it in 3.

In actual operation, the pressure fluctuation value measured by the sensor 10 is analyzed by the FFT analyzer 11, and the calculation means 1
2, it is possible to quantitatively know the flow state of the combustion chamber 1 at that time by comparing it with the reference set value in the storage means 13, and thereby adjust the primary and secondary air supply valves to achieve the optimum flow state. 6.7.

What is shown in FIG. 3 shows the power of the pressure vibration obtained by analyzing the pressure vibration signal measured by the sensor 10 with the FFT analyzer 11. This power is an integral value of the energy density 2 up to each frequency.

In Figure 3, the horizontal axis shows four primary air ratios (1, 2
.
) shows the change in power corresponding to From this figure,
At the bottom of the layer (0, 4, 0, 9 m), the -order air ratio decreases (
1,2 → 0.7), although the power is increasing,
It can be seen that in the upper part of the layer (1, 4, 2, 4, 4, 4 m), the power decreases as the -order air ratio decreases (1, 2→0.5).

On the other hand, FIG. 4 shows the results of actually measuring the particle density distribution within the layer. The horizontal axis shows the particle density, the vertical axis shows the height from the stratification,
The figure shows the change in particle density for four conditions: −-order air ratio 1.2.1.0.0.7.0.5.

From this figure, it can be seen that at the bottom of the layer, the -order air ratio decreases (1, 2→
0.7), the particle density increases, whereas in the upper part of the layer, the particle density decreases as the primary air ratio decreases (1,2 → 0.5).

Now, by comparing this FIG. 4 and the above-mentioned FIG. 3, it can be seen that there is a correspondence between the power of pressure fluctuation and the particle density.

Therefore, by measuring the power of pressure oscillations, the particle density within the layer can be detected. Although this particle density corresponds to each flow state, it is possible to know the power of pressure vibration → particle density → flow state.

Note that the present invention is not limited to the above embodiments.

〔Effect of the invention] Changes in the flow state of the bed appear as changes in pressure oscillations.

Therefore, by measuring pressure vibrations, the flow state of the bed can be easily detected quantitatively and in real time. This allows the fluidized bed apparatus to be controlled easily, quickly and accurately, either manually or automatically.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a fluidized bed apparatus used in the method of the present invention;
Figure 2 shows the pressure oscillation frequency spectrum, Figure 3 shows the power of pressure oscillations, Figure 4 shows the particle density distribution in the bed, and Figure 5 shows the concept of a conventional fluidized bed device. figure,
FIG. 6 is an explanatory diagram showing various fluidization states, and FIG. 7 is a fluidization state diagram. 1... Combustion chamber, 6... Secondary air supply valve, 7...
- Secondary air supply valve, 10... pressure detection means (sensor), 14... control means. Patent applicant: Shinko Pyro Power Co., Ltd.
1 Kobe Steel, Ltd. P-ITP

Claims (1)

[Claims] (1) Set in advance an intra-bed standard pressure fluctuation value corresponding to each flow state of the fluidized bed in the fluidized bed apparatus, detect the intra-bed pressure fluctuation value of the fluidized bed by a pressure detection means, and combine the detected value with the above-mentioned A method for detecting the state of a fluidized bed, comprising detecting the state of the fluidized bed by comparing the state with a set value.