JPH1061932A - Combustion control method for waste incinerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stabilized generating amount of steam even in a case when the nature of wastes, supplied into an incinerator, is changed suddenly. SOLUTION: The generating amount of steam of a boiler 8b is measured by a flow meter 11 and the concentration of O2 in exhaust gas is measured by an O2 -concentration meter 14. When the concentration of O2 in the exhaust gas is lower than an upper limit concentration, the amount of combustion air is adjusted in accordance with an objective amount of air based on the generating amount of steam, however, the amount of combustion air is controlled so as to coincide with the amount of air of either smaller one when an objective amount of air or the concentration of O2 has exceeded the upper limit concentration at first when the concentration of O2 in the exhaust gas has exceeded the upper limit concentration. Further, a combustion air temperature is adjusted in accordance with the low calorific power of wastes. According to this method, drying is advanced with the optimum amount of air and the condition of combustion is restored quickly even when humid wastes are supplied suddenly whereby the generating amount of steam is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refuse incinerator that utilizes the combustion heat of refuse for steam power generation by adjusting the amount and temperature of combustion air to stabilize the combustion state and obtain a constant amount of generated steam. The present invention relates to a combustion control method.

[0002]

2. Description of the Related Art Municipal solid waste incinerators play an important role in treating various wastes discharged in social life. In addition to this, effective utilization of waste energy is being attempted, such as by performing steam power generation using heat generated by combustion of waste.

[0003] In a refuse incinerator, refuse is intermittently put into a hopper at intervals of several tens of minutes by a crane and is temporarily stored therein, and is supplied to the furnace at a constant supply rate by a drying grate serving as a feeder and a dryer. It is sent continuously. The sent refuse is burned by combustion air blown from below each grate on several stages of grate, and is discharged as ash behind the furnace. On the other hand, the combustion gas generated by the combustion passes through a heat exchanger at the furnace outlet, is converted into steam, and is exhausted.

[0004] In an incinerator that efficiently recovers the heat energy generated by the incineration of such refuse, combustion control that ensures a stable amount of steam generated in the boiler is an important technology. Then, automatic combustion control is performed for stable supply of steam and stabilization of the furnace outlet temperature. As a means, control of the amount of combustion air and cooling air or control of the grate speed for adjusting the amount of waste sent. And so on.

[0005] In general, these controls are based on the past steam generation amount, combustion air blowing amount, refuse input amount, etc., and calculate a target incineration amount corresponding to the required steam generation amount for each refuse input. Then, it is done according to this. If the actual amount of waste is less than the target incineration amount, the standard speed of the grate is increased to increase the standard combustion air amount, and if it is larger than the target incineration amount, the grate speed is reduced and the combustion air amount is reduced. Is adjusted so as to approach the target incineration amount.

However, the properties of refuse vary widely, and flammable refuse may be supplied followed by flammable refuse, or vice versa. In such a case, the amount of generated steam is not constant only by achieving the target amount of incineration set for each input of the waste. In order to maintain a constant amount of generated steam, it is necessary to perform control in accordance with the ever-changing nature of waste.

To solve this problem, the amount of generated steam is measured, and when the amount of generated steam is larger than the target amount, the amount of combustion air is reduced.
When the amount of generated steam is smaller than the target amount, there is a method of controlling combustion by increasing the amount of combustion air (hereinafter, referred to as a method of measuring the amount of generated steam).

Further, in order to stabilize the combustion state, a method of measuring the O ₂ concentration in the exhaust gas and controlling the amount of combustion air (hereinafter, referred to as a method).
A method for measuring the concentration of O _{2 in} exhaust gas) has also been proposed. For example, Japanese Patent Application Laid-Open No. Hei 6-331123 discloses that the amount of air supplied to a refuse incinerator, the concentration of O ₂ in exhaust gas, and the flow rate of exhaust gas are measured, and the excess air ratio is calculated from the measured values. And a method of controlling the amount of combustion air so that the two agree with each other.

[0009]

However, in the method of measuring the amount of generated steam or the method of measuring the concentration of O _{2 in} exhaust gas, the combustion is not always stable, and it may be difficult to keep the amount of generated steam constant. Was. For example, when malicious waste with a lot of moisture is supplied, the amount of waste that burns is small,
The amount of steam generated decreases, and at the same time, oxygen is not consumed, so that the O ₂ concentration in the exhaust gas increases.

At this time, in the steam generation amount measuring method, an attempt is made to activate combustion by increasing the amount of combustion air. However, even if the amount of combustion air is increased, it does not contribute to combustion until the refuse is dried, and the combustion air cools the inside of the furnace and blows wasteful air to worsen the combustion state.

At this time, in the method for measuring the O ₂ concentration in exhaust gas, the amount of combustion air is reduced to a standard excess air ratio. Therefore, drying of the refuse is delayed, and the combustion state is not improved. As described above, according to the conventional technique, it was not possible to normalize the combustion state in response to the change in the dust property.

The present invention has been made in order to solve the above-mentioned problems. The present invention adjusts the amount and temperature of combustion air based on the measurement of the O ₂ concentration in exhaust gas and the amount of generated steam to control combustion. The purpose of the present invention is to maintain a proper combustion corresponding to the change of the waste property and to obtain a constant steam generation amount.

[0013]

Means for achieving this object are the following inventions.

The first invention measures the amount of steam generated in a refuse incinerator and the concentration of O _{2 in} exhaust gas, and calculates the target amount of combustion air required to make the amount of steam equal to the target amount of steam generated. the combustion air target amount when the first reached mid O ₂ concentration limit the measured value predetermined for storing the combustion air temporarily set amount, and the measured value of the exhaust gas O ₂ concentration is below the upper limit When the combustion air amount is controlled to match the combustion air target amount, when the measured value of the O ₂ concentration in the exhaust gas exceeds the upper limit, the combustion air target amount at that time and the combustion air temporary set amount are compared. A combustion control method for a refuse incinerator, characterized in that the amount of combustion air is controlled so as to match the smaller amount of the combustion air.

Normally, the combustion air is blown according to a standard amount determined when the refuse is charged. This standard amount is
The amount of air is larger than the amount of air based on the theoretical amount of O ₂ required for combustion in order to achieve complete combustion of refuse, and is about 1.5 times the amount of air. At this time, the measured value of the O ₂ concentration in the exhaust gas is not more than the upper limit.

Therefore, when relatively flammable refuse is supplied, the amount of O ₂ consumed increases and the O ₂ concentration in the exhaust gas decreases, but at this time, the combustion is actively performed and the combustion state is good. . At this time, if the amount of steam generation exceeds the target amount, reduce the amount of combustion air to reduce the combustion speed, and if the amount of steam generation does not reach the target amount, increase the amount of combustion air to increase the combustion speed. In this case, the steam generation amount approaches the target amount. Therefore, if the target combustion air amount is calculated by the PID method or the like based on the measurement result of the steam generation amount so that the steam generation amount matches the target amount and the combustion air amount is controlled in a short cycle, the steam generation amount is always The target amount can be maintained.

However, when the measured value of the O ₂ concentration in the exhaust gas exceeds the upper limit, it differs from the normal case. in this case,
Since the amount of dust is low the amount of combustion air reaches the ignition point be appropriate, is less exhaust gas O ₂ concentration higher than the upper limit concentration O ₂ amount consumed, at the same time the combustion state Since it is bad, the amount of generated steam is also smaller than the target amount. At this time, if an attempt is made to control the amount of combustion air so that the amount of generated steam coincides with the target amount based on the measurement result of the amount of generated steam, the calculated target amount of combustion air is steadily increased, and the amount of combustion air is steadily increased. However, as mentioned above,
Increasing the amount of combustion air only cools the refuse and only increases the refuse that does not reach the ignition point. Conversely, reducing the amount of combustion air only delays the drying of the refuse.

In this case, the appropriate amount of combustion air is the temporarily set amount of combustion air. The temporarily set amount of combustion air is the target amount of combustion air when the measured value of the O ₂ concentration in the exhaust gas reaches the upper limit.
The amount of air is sufficient for combustion, and in this case, the amount exceeding this amount is an amount indicating a boundary that becomes wasteful air. By controlling the amount of combustion air to be equal to the temporarily set amount of combustion air, refuse having poor properties can be dried without cooling and quickly recovered to a normal state.

According to a second aspect of the present invention, when the measured value of the O ₂ concentration in the exhaust gas is equal to or lower than the upper limit, the combustion air temperature is reduced if the lower heating value of the waste is large, and the lower heating value of the waste is reduced. Control to increase the combustion air temperature,
When the measured value of the O ₂ concentration in the exhaust gas exceeds the upper limit, the combustion of the refuse incinerator according to the first aspect of the present invention is controlled to increase the combustion air temperature according to the difference between the upper limit and the measured value. It is a control method.

The lower calorific value is the calorific value of garbage per unit weight calculated from the balance of the amount of waste input, the amount of heat recovered by the boiler, the amount of heat exhausted, and the amount of heat dissipated from the furnace body. . Therefore, it is calculated every time the refuse is thrown into the hopper, but the lower calorific value obtained is the average calorific value of the refuse put in the last time or the last time, and has been incinerated on that day or in the last several hours. It is a guide to know the amount of water in garbage.

Normally, that is, when the measured value of the O ₂ concentration in the exhaust gas is equal to or less than the upper limit, the combustion air temperature may be low because the lower the heat value, the smaller the moisture content. Conversely, if the lower calorific value is small, there is more moisture, so the combustion air temperature is raised to enhance the drying of the refuse, thereby stabilizing the combustion state.

However, when the measured value of the O ₂ concentration in the exhaust gas exceeds the upper limit, abnormal waste is supplied to the furnace, and in this case, the combustion air based on the average lower heating value is used. The proper temperature cannot be determined. At this time,
Since abnormally high moisture waste is fed into the furnace, and controls so that the combustion air amount coincides with the combustion air target amount or combustion air temporarily set amount at that time, O ₂ concentration in the upper limit value and the measured value Is controlled so as to increase the temperature of the combustion air in accordance with the difference between. That is, the amount of combustion air is increased within a range without waste, and the higher the O ₂ concentration, the higher the temperature of combustion air.

The third aspect of the present invention, first the calculated excess air ratio from the measured values of the exhaust gas O ₂ concentration, to control the quantity of combustion air with the air excess ratio instead of the measured value of the exhaust gas O ₂ concentration It is a combustion control method for a refuse incinerator according to the first or second invention.

In the operation of a combustion furnace, the excess air ratio is generally used as one index for adjusting the amount of combustion air. Therefore, it is practical to control the amount of combustion air using the excess air ratio. In this case, the excess air ratio depends on the O ₂ concentration in the air and the O ₂ consumed.
It is calculated as the ratio of _two concentrations. That is, the excess air ratio λ
Is expressed by the following equation (1), where the O ₂ concentration in the exhaust gas is [O ₂ ].

[0025]

(Equation 1)

Since the O ₂ concentration in the exhaust gas and the excess air ratio have a one-to-one correspondence, if the upper limit of the excess air ratio is determined corresponding to the upper limit of the O ₂ concentration in the exhaust gas, the first invention or the second invention
In the control of the combustion air amount according to the invention, the combustion air amount can be controlled in the same manner by using the excess air ratio instead of the O ₂ concentration in the exhaust gas.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The outline of a waste incinerator to which the method of the present invention is applied and a control system will be described with reference to FIG. In the figure,
Reference numeral 1 denotes an incinerator, which has a hopper 2, a dry grate 3a, a combustion grate 3b, a post-combustion grate 3c, and an ash fallout port 4. Combustion air is sent from the combustion air blower 5 to the heater 12.
The air is blown up from under each grate through the combustion air damper 5a. The refuse is dried mainly by the combustion air blown up from below by the dry grate 3a, burned by the combustion grate 3b, and burned out to ash by the post-combustion grate 3c.

On the other hand, the exhaust gas generated by the combustion is guided from the furnace outlet 6 to the chimney 7 and discharged out of the furnace. O ₂ concentration is measured by the O ₂ concentration meter 14 at the time of discharge. Note that cooling air sent from a cooling air fan 10 is blown from a cooling air blowing port 9 so that the temperature inside the furnace does not excessively increase.

A boiler 8b provided with a heat exchanger 8a is installed at a furnace outlet 6 from which exhaust gas is discharged. The amount of generated steam is measured by the flow meter 11.

Numeral 15 denotes combustion control means which is deeply related to the present invention, and calculates a set value of the amount of combustion air by inputting signals from the flow meter 11 and the O ₂ concentration meter 14 to obtain a combustion air damper 5a.
And a signal from the lower heating value calculator 13 is input to calculate a combustion air temperature and output a temperature signal to the heater 12. As the combustion control means 15, for example, a computer is used.

The calculation of the control value by the combustion control means 15 is performed at a predetermined cycle. The procedure is as follows.

First, a method of controlling the amount of combustion air by using the measured value of the O ₂ concentration in the exhaust gas will be described. As described above, the relationship between the O ₂ concentration in the exhaust gas and the excess air ratio is (1) Since the expressions have a relationship and can be replaced with each other, an example using an excess air ratio will be described.

The excess air ratio λ _(k) is calculated from the measured value of the O ₂ concentration in the exhaust gas according to the equation (2). However, the subscript (k)
Indicates that this is a measured value.

[0034]

(Equation 2)

Then, the calculated value from several times before to this time is smoothed by the following equation (3 ₎ to calculate an air excess ratio smoothed value λ _{m (k)} .

[0036]

(Equation 3)

On the other hand, the measured value V of the steam generation amount and the target steam generation amount V ₀ are input to the PID controller, where they are compared, and the target combustion air amount F ₁ based on the steam generation amount is obtained by the equation (4). Is calculated.

[0038]

(Equation 4)

Here, PB is a proportional gain, T _i is an integral gain, T _d is a differential gain, and is an adjustment parameter.
Represents the Laplace operator. F ₁ is garbage state is combustion air amount should the target steam generation amount V ₀ would normally obtained.

Next, a judgment is made from λ _{m (k)} obtained by the above equation (3), and finally a combustion air amount set value F is determined. FIG. 2 shows a flow for determining the combustion air amount set value F.

First, the air excess ratio smoothed value λ _{m (k)} is compared with a predetermined air excess ratio upper limit λ _s . Excess air ratio upper limit value lambda _s is appropriate to define a range of about 1.5 to 2. When λ _{m (k)} is equal to or _smaller than λ _s , the combustion air amount set value F is determined as F ₁ .

The λ _{m (k)} is lambda When the difference exceeds a _s is, F ₁ and temporarily stored have combustion air temporarily set quantity F (flag =
0), and if F ₁ is smaller than F (flag = 0), the combustion air amount set value F is determined to be F ₁ and F ₁ is set to F (fl
ag = 0, the combustion air amount set value F is changed to F (f
lag = 0). Temporarily set amount of combustion air F (fla
g = 0) is the target combustion air amount when the excess air ratio smoothed value λ _m reaches the upper limit for the first time.

However, at this stage, it is also checked whether or not the previous air excess ratio smoothed value λm _(k-1) was equal to or _smaller than λs. It is temporarily stored as a set amount F (flag = 1). According to this calculation, if the excess air ratio smoothed value continuously exceeds the excess air ratio upper limit, the temporarily set amount of combustion air does not change. Is exceeded, the combustion air temporary set amount is updated. Then, in the next operation, F (flag = 1) becomes F
(Flag = 0) is used instead. As a result, the temporarily set amount of combustion air is determined according to the degree of abnormality of the property of the refuse at that time.

Next, a case where the combustion air temperature and the combustion air temperature are controlled simultaneously will be described. Excess air smoothed value λ
_{If m (k)} is equal to or less than the upper limit value λ _s , the combustion air temperature set value _TFSET based on the equation (5) is sent from the combustion control means 15 to the heater 12, and the combustion air temperature is set to the set value _TFSET. The combustion air temperature is controlled so that The same applies when the measured value of the O ₂ concentration in the exhaust gas is equal to or less than the upper limit.

[0045]

(Equation 5)

The combustion air temperature set value T _FSET is a function T _F (Hu) of the lower heating value Hu, and is, for example, a function as shown in FIG. When the lower heating value (Hu) is small, the combustion air temperature _TF is set high, and when the lower heating value (Hu) is large, the combustion air temperature _TF is set low.

When the excess air ratio smoothed value λ _{m (k)} exceeds the upper limit value λ _s , the combustion air temperature setting value T _FSET based on the equation (6) is _sent from the combustion control means 15 to the heater 12. And the combustion air temperature is controlled such that the combustion air temperature becomes the set value _TFSET . Measured value of O ₂ concentration in exhaust gas [O ₂ ]
_{If (k)} exceeds the upper limit [O ₂ ] _s , the set value _TFSET of the combustion air temperature is determined based on the equation (7).

[0048]

(Equation 6)

[0049]

(Equation 7)

Here, K _TF1 and K _TF2 are control parameters of the proportional gain. The equation (7) shows that the excess air ratio smoothed value λ _{m (k) of the} equation (6 ₎ and its upper limit value λ _s are expressed as O _{2 in the} exhaust gas.
The measured value of the concentration [O ₂ ] _(k) and its upper limit [O ₂ ] _s are respectively replaced.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Waste incineration is carried out using the apparatus shown in FIG.
The O ₂ concentration in the exhaust gas, the amount of combustion air, and the amount of generated steam were examined. The target steam generation amount was 20 t / h, and the upper limit of the O ₂ concentration in the exhaust gas was 9%. The measurement was performed continuously,
The measured values were collected in a cycle of 30 seconds, and the set value of the combustion air amount was calculated according to the flow of FIG. 2 to control the combustion air amount.

The investigation was carried out by measuring the amount of generated steam and O _{2 in the} exhaust gas.
A concentration measurement method was also performed, and the results were compared.

FIG. 4 shows the results of the practice of the invention, FIG. 5 shows the results of the method for measuring the amount of generated steam, and FIG. 6 shows the results of the method for measuring the O ₂ concentration. In each figure, the figure (a) shows the O ₂ concentration in the exhaust gas,
(B) shows the amount of combustion air, and (c) shows the change in the amount of generated steam.

In the embodiment of the invention, the combustion air amount was controlled to coincide with the combustion air temporary set amount at the point P when the O ₂ concentration in the exhaust gas temporarily increased and the steam generation amount decreased. As a result, the reduced steam generation recovered soon.

On the other hand, in the method for measuring the amount of generated steam, the amount of combustion air was increased at the point P, so that the refuse was cooled, the amount of generated steam continued to decrease, and the recovery was extremely delayed. Also, in the O ₂ concentration measurement method, drying of the refuse was delayed because the amount of combustion air was reduced at the time point P, and the reduction in the amount of generated steam did not progress as much as the method for measuring the amount of generated steam, but it took about the same time to recover. Cost.

[0056]

According to the present invention, the amount of generated steam and the O ₂ concentration in the exhaust gas are measured, and the target amount of combustion air is periodically calculated so that the amount of generated steam is normally constant. The combustion air amount is controlled. If the measured value of the O ₂ concentration in the exhaust gas or the excess air ratio exceeds the upper limit, the combustion air target amount at the time when the O ₂ concentration exceeds the upper limit is stored, and the calculated combustion air target amount is stored. While the amount exceeds the stored combustion air target amount, the combustion air amount is adjusted to the stored combustion air target amount. Or
Simultaneously with the control of the combustion air amount, the combustion air temperature is usually adjusted according to the lower heating value of the refuse, and when the measured value of the O ₂ concentration in the exhaust gas or the excess air ratio exceeds the upper limit,
The combustion air temperature is raised according to the degree of the difference.

For this reason, it is possible to avoid wasteful blowing of the combustion air to further cool the refuse, and to reduce the amount of the combustion air to delay the drying of the refuse, so that the steam generation amount approaches the target amount quickly. As described above, even if the property of the refuse abnormally changes, the refuse is efficiently burned to stabilize the combustion state, and the effect of the present invention to generate a certain amount of steam is great.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a refuse incinerator and a control system for explaining the invention.

FIG. 2 is a flowchart for determining a combustion air amount set value for explaining the invention.

FIG. 3 is a graph showing a relationship between a set value of a combustion air temperature and a lower heating value for explaining the invention.

FIG. 4 is a graph showing a result when control is performed by the method of the present invention.

FIG. 5 is a graph showing a result when control is performed by a conventional method for measuring the amount of generated steam.

FIG. 6 is a graph showing the results when control is performed by a conventional method for measuring the concentration of O ₂ in exhaust gas.

[Description of Signs] 1 Incinerator 2 Hopper 3a Dry grate 3b Combustion grate 3c Combustion grate 5 Combustion air blower 5a Combustion air damper 8a Heat exchanger 8b Boiler 11 Flow meter 12 Heater 13 Low calorific value calculator 14 O ₂ concentration meter 15 Combustion control means

Claims (3)

[Claims] 1. A measure of steam generation amount and the exhaust gas in the O ₂ concentration in the incinerator, the steam generation amount calculating a combustion air target amount necessary to match the target steam generation amount, exhaust gas O ₂ concentration of storing the combustion air target amount when the measured value is first reached a predetermined upper limit value as the combustion air temporarily set amount, and the combustion time measurement of exhaust gas O ₂ concentration is below the upper limit The combustion air amount is controlled so as to coincide with the air target amount, and when the measured value of the O ₂ concentration in the exhaust gas exceeds the upper limit, the smaller of the combustion air target amount at that time and the combustion air temporary set amount is smaller. A combustion control method for a refuse incinerator, comprising controlling the amount of combustion air so as to match the amount. _{2. When} the measured value of the O ₂ concentration in the exhaust gas is below the upper limit, the combustion air temperature is lowered if the lower heating value of the refuse is large, and the combustion air temperature is reduced if the lower heating value of the refuse is small. And controlling, when the measured value of the O ₂ concentration in the exhaust gas exceeds the upper limit value, the combustion air temperature in accordance with the difference between the upper limit value and the measured value. The combustion control method of the refuse incinerator described in the above. 3. The method according to claim 1, wherein an excess air ratio is obtained from the measured value of the O ₂ concentration in the exhaust gas, and the amount of combustion air is controlled using the excess air ratio in place of the measured value of the O ₂ concentration in the exhaust gas. Item 3. The combustion control method for a waste incinerator according to Item 2.