JPS5848805B2 - Natural draft heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a natural draft heating furnace, and particularly to a heating furnace that maintains good and safe combustion conditions and improves fuel economy.

In natural draft heating furnaces, which are widely used in petrochemical factories, etc., the amount of combustion air that is naturally ventilated into the furnace from the burner air inlet is controlled by the opening of a damper attached to the exhaust outlet. It's being fine-tuned.

In this case, if the amount of air supplied into the furnace is unnecessarily large, the inside of the furnace will be cooled by the air that is not used for combustion, and the furnace will be heated accordingly, resulting in poor fuel consumption and uneconomical performance.

In other words, it is preferable to supply the amount of combustion air required for the amount of heating heat of the object to be heated, and for this purpose, the draft pressure (ventilation pressure) in the furnace must be reduced to a minute negative pressure close to atmospheric pressure. It is best to maintain and supply the minimum amount of air required.

However, in a natural draft heating furnace, on the other hand, the draft pressure may locally increase or decrease within the furnace, and may not necessarily correspond to the amount of air, ie, the amount of oxygen, within the furnace.

Therefore, when trying to minimize the amount of supplied air by maintaining the draft pressure at a minute negative pressure close to atmospheric pressure, even if the locally measured draft pressure shows a normal value, the overall Insufficient amount of oxygen may cause incomplete combustion, and if the amount of air supplied increases suddenly thereafter, there is a risk of explosive combustion and destruction of the heating furnace.

Therefore, when the amount of oxygen is insufficient, it is necessary to temporarily increase the damper opening.

By the way, the conventional method of controlling the opening of the damper applied to a natural draft heating furnace is to manually control the opening of the damper according to the indicated pressure while watching the draft pressure gauge (the pressure indicating meter is installed in the control room, (often controlled remotely)
Alternatively, there is an automatic control method in which a damper is linked to a set opening degree in response to draft pressure detected by a draft pressure gauge.

However, the former manual control method has poor accuracy and does not have sufficient fuel economy, and the latter cannot deal with the above-mentioned temporary oxygen shortage in the reactor, resulting in safety problems. It's not used to much by women.

The present invention has been developed in view of these conventional drawbacks, and measures the draft pressure damper opening, the oxygen concentration in the exhaust gas, the flow rate of the heated object, the temperature at the entrance and exit of the heating furnace, etc. at regular intervals, and measures the draft pressure. In addition to a highly accurate and stable main control system that controls the damper opening corresponding to the average value of an appropriate number of times, including the current measured value, it also has a main control system that controls the damper opening according to the average value of a suitable number of times, including the current measured value. The damper opening control based on the draft pressure mentioned above is not performed normally, so it is stopped, and when the oxygen concentration in the exhaust air drops abnormally, the damper is opened regardless of the draft pressure, as this leads to a lack of oxygen in the furnace. A first object of the present invention is to provide a natural draft heating furnace equipped with a damper opening degree control device equipped with an auxiliary control system for operation.

Furthermore, since it is necessary to increase the air supply amount when the heat load of the heating furnace increases, we added an auxiliary control system to the damper control device to close the damper even if the draft pressure decreases. The second purpose is to provide a furnace.

An example in which the present invention is applied to a crude oil atmospheric distillation apparatus will be described below based on the drawings.

In Fig. 1, 1 is the heating furnace main body, and a burner 2 attached to the bottom raises the heated object passing through the furnace to a constant temperature by heating the wall of the flow pipe 3. .

A flow meter 4 and an inlet thermometer 5 are attached to the inlet portion of the main body 1 of the flow pipe 3, and an outlet thermometer 6 is attached to the outlet portion of the main body 1.

Depending on the temperature of the heated object measured by the outlet thermometer 6, the opening degree of the flow control valve 8 installed in the fuel supply pipe T leading to the burner 2 is automatically controlled, and the opening of the flow control valve 8 is automatically controlled. The amount of fuel is supplied to the burner 2 according to the required amount of heating heat.

A damper 9 for controlling the amount of air introduced into the main body 1 by controlling the exhaust flow rate is attached to the exhaust outlet 1a opened at the upper part of the main body 1.

A draft pressure gauge 10 and an oxygen concentration meter 11 are attached to the exhaust outlet 1a upstream and downstream of the damper 9, respectively, and the damper 9 is connected to an opening gauge 12 thereof and a drive machine 13 for rotationally driving the damper 9.

Then, the measurement signals emitted from the flow meter 4, thermometers 5, 6, draft pressure gauge 10, and oxygen concentration meter 11 of the heated body are input into the computer 14 at regular intervals,
The computer 14 transmits a damper opening degree control signal calculated according to the input signal to the driver 13 to drive it and control the damper 9 to an appropriate opening degree.

Further, as will be described later, when the computer 14 detects an abnormality in each measured value during control, it transmits the information to the television 15 and tie writer 16 to notify the abnormality.

A control program for the combustion control system having such a configuration will be explained with reference to FIG.

Measurement signals from each measuring meter are input to the computer 14 every three minutes, and the current measurement value, the previous measurement value, and the measurement value before the previous measurement are updated each time they are input and set in the data processing section.

Then, at the second time l after the start of input, the damper opening degree is maintained at the current level.

The control program from the third time after the start of input progresses as follows.

First, check for abnormalities in the oxygen concentration meter 11.

Determine whether the current measured value of the oxygen concentration in exhaust gas is within the range of 3 to 9%, and whether the difference between the current measured value and the previous measured value is within ±1φ, and if either of these is not satisfied. In this case, it is determined that the oxygen concentration meter is abnormal, and this is detected on TV 1.
5 and the typewriter 16 (hereinafter, notifications via the TV or typewriter will be abbreviated as "report"), and the measured value of the oxygen concentration in the exhaust gas and the target oxygen concentration will be compared as described below. After checking for abnormalities in the damper opening and draft pressure, the damper opening is controlled using the draft pressure.

Next, it is determined whether the current measured value of the oxygen concentration in the exhaust gas is, for example, 3.5% or less, and if it is 3.5% or less, the measured value is compared with the target oxygen concentration. Damper 9
For example, calculate the opening when the damper is opened by 3% (the damper opening is shown corresponding to the cross-sectional area ratio when the cross-sectional area of the exhaust outlet when the damper is fully open is 100), and the calculated opening is The damper 9 is controlled to the calculated opening degree when the opening degree is greater than or equal to the lower limit opening degree, and to the lower limit opening degree when the opening degree is less than the lower limit opening degree.

In other words, if the oxygen concentration in the exhaust gas is too low, the amount of oxygen in the furnace is often insufficient, and as mentioned above, incomplete combustion or explosive combustion is likely to occur, so temporarily increase the damper opening. to increase the amount of air supplied into the furnace.

In detail, this configuration causes the damper 9 to open when the above condition is detected for the first time, but when the measured value at the next input is continuously below 3.5%, the damper 9 is opened once more, that is, for 3 minutes. The damper opening degree is maintained at that time, and when the same state continues three times in a row, the damper 9 is again opened three times.

If the same condition occurs four or more times in a row despite the damper opening control, it is determined that the abnormality in the oxygen concentration measurement value is caused by an abnormality in the oxygen concentration meter 11, and the information is reported to the draft controller, which will be described later. The damper opening degree is controlled by pressure.

In this way, it is possible to prevent the damper 9 from being erroneously kept at a large opening for a long time due to an abnormality in the oxygen concentration meter 11, thereby preventing the actual oxygen concentration from increasing abnormally and deteriorating fuel economy.

Next, the amount of heat required to heat the heated object, that is, the heat load of the heating furnace, is calculated from the flow rate of the heated object and the temperature difference between the entrance and exit of the heating furnace, and the target value is calculated from the predetermined relational expression between the heat load and the oxygen concentration in the exhaust gas. Determine the oxygen concentration and set it in the memory.

Then, the measured value of the oxygen concentration in the exhaust gas is 0.0% lower than the target oxygen concentration.
If the condition continues to be lower than 5% for 12 hours or more, a value obtained by subtracting the target oxygen concentration by a predetermined amount (for example, by reducing the constant term of the target oxygen concentration formula by 0.2%) is set as a new target oxygen concentration, Conversely, if the target oxygen concentration is o. If the condition remains high for more than s% for two hours or more, this condition is reported and an instruction is given to reduce the air inlet opening of the burner 2 to reduce the air supply amount.

In other words, when the measured value of oxygen concentration is lower than the target oxygen concentration for a predetermined period of time or more, it is determined that the target oxygen concentration is too high, and the target oxygen concentration is automatically lowered, and the target oxygen concentration is the target oxygen concentration that the measured value is lowered. If it falls within the set range, this becomes the new target oxygen concentration.

In addition, when the measured value continues to be higher than the corrected target oxygen concentration for a predetermined period of time or more, the air supply amount is controlled to be reduced by notification, so the oxygen concentration ends up within the set range of the target oxygen concentration and the exhaust gas is being pumped out. It is possible to stabilize the oxygen concentration at a low concentration and further improve fuel economy.

Next, it is determined whether there is an abnormality in the damper opening degree meter 12, and if the damper opening degree is less than the set lower limit opening of 60φ or the difference between the current measurement value and the previous measurement value is ±5% or more, the damper opening degree meter 12 is detected. 12 is determined to be abnormal, the abnormal state is notified, and the damper opening is controlled by the draft pressure to maintain the damper opening at the current state.

Next, check for abnormalities in the draft pressure gauge 10, and check if the current measured value is outside the set pressure range, for example -4 to 3 trrm Aq, or if the pressure difference between the current measured value and the previous measured value is, for example, ±2 tan Aq. If the above condition exists, the damper opening degree is maintained at the current level as described above.

When an abnormality is reported in any of these abnormal items, the abnormality is promptly inspected or corrected to a normal state by manual control.

Next, if it is determined that the damper opening degree and the draft opening degree are normal, or if the abnormal measured value of the oxygen concentration in the exhaust gas is caused by an abnormality in the oxygen concentration meter 11, the main control is the draft pressure. Controls the damper opening.

First, calculate the average value Pm of the current measured value of the draft pressure and the previous and two previous measured values, and then calculate Pm.1. O
mAq (unit omitted below), the damper opening degree is calculated by opening the damper 9 by 2.0%, O (if Pm≦1.0, opening is 1.1%, and when the calculated opening degree is the lower limit opening degree, the damper opening degree is calculated by opening the damper 9 by 2.0%. At times,
When the opening degree falls below the lower limit opening degree, the opening degree is controlled to the lower limit opening degree.

Next, press Pm≦0.0 to check whether the heat load of the heating furnace is increasing based on the flow rate of the object to be heated and the temperature difference at the entrance and exit of the heating furnace. When the opening degree is equal to or higher than the lower eye opening degree, the opening degree is controlled to the current opening degree, and when it is below the lower limit opening degree, the opening degree is controlled to the lower limit opening degree.

That is, since the air supply amount is in the process of increasing while the heat load is increasing, the damper opening degree is set not to close even if Pm≦0.0.

If the heat load is not increasing, -1 (if Pm≦0.0, the damper opening is maintained as it is, -2 (if Pm≦-1.0, the damper opening is 1.1)
% closed, Pm -2 is calculated as 2.0% closed, and when the calculated opening is greater than or equal to the lower limit opening, the calculated opening is controlled to the lower limit when the opening is less than the lower limit.

As described above, the basic control is to adjust the amount of air supplied into the furnace to be an appropriate amount by closing or opening the damper in response to an increase or decrease in draft pressure.

In the example of control applied to the heating furnace of crude oil atmospheric distillation equipment, in the case of the equipment of the present invention, the set value of the draft pressure is set to O~-2 waA.
When q, the measured average value of draft pressure is -1.1 2
1IaILAq, and a negative pressure much closer to positive pressure was obtained than the actual measured average value -1.76 mmAq when the draft pressure management target of the conventional manual damper control system was similarly set to O~-2 tmAq.

Further, when the set value of the draft pressure was set from 0 to -1 mAq, the actual measured average value decreased to -(16 1 ttan Aq), and even in this case, positive pressure was almost never achieved.

This result is used as a fuel consumption index [”/,
) (amount of fuel required to heat the heated object 1B to a predetermined temperature) When the operating rate of the heating furnace is 90%, the actual measured average value - 1-1 2 mm▲q (draft 8. When the pressure setting value is O~-2m7ILAq).
0 7 (1/Kl) (point B in the diagram), measured average value -0
．． 6 When 1mAq (setting value 0 to -IWanAq) 8. 6 5 ('/kl) (point C in the figure) and 8.75 ["I'" when -1.76 mmAq (draft pressure management target value O ~ -2 Aq) of manual control method.
Compared to H3 (point A in the diagram), the number of threads is reduced by 0.6% and 1.1, respectively.

That is, the fuel consumption can be reduced to this extent, which is economically advantageous, especially in a furnace of this kind that is operated continuously for a long time.

As explained above, according to the present invention, the main air supply amount control is performed by controlling the damper opening based on the average value of the current and past several draft pressure measurements, so the draft pressure increases temporarily. Stable combustibility is maintained, and fuel economy is greatly improved.

In addition, when the oxygen concentration in the exhaust gas falls below the set concentration and the amount of oxygen in the furnace tends to be insufficient, the damper is opened without worrying about the draft pressure, which prevents incomplete combustion and explosive combustion. Also, when the damper opening degree is abnormal, the damper opening degree control using the draft pressure is stopped, so that erroneous control based on the abnormal measured value can be prevented.

Furthermore, if the damper is configured not to close even if the draft pressure decreases during an increase in heat load, it is possible to satisfy the increase in the amount of air required due to the increase in heat load, and to prevent a lack of oxygen in the furnace. It can be prevented.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of the device of the present invention, Fig. 2A
, B, and C are control program diagrams of the same device, and FIG. 3 is a graph showing the relationship between draft pressure and fuel consumption rate for the control method and manual control method of the same device. DESCRIPTION OF SYMBOLS 1... Heating furnace main body, 4... Flow meter, 5... Inlet part thermometer, 6... Outlet part thermometer, 9... Damper, 10
...Draft pressure gauge, 11...Oxygen concentration meter, 12.
...Damper opening gauge, 14...Computer.

Claims (1)

[Claims] 1. In a natural draft heating furnace in which the supply amount of combustion air naturally ventilated into the furnace is adjusted by controlling the opening of a damper attached to an exhaust outlet, the draft pressure in the heating furnace is , input the measured values of exhaust oxygen concentration and damper opening at regular intervals, and if the measured values of draft pressure and damper opening are normal and the exhaust oxygen concentration is above the set lower limit concentration. A first control system that controls the damper opening so that the current and past measurements of the draft pressure are averaged and the average value approaches atmospheric pressure, and each measured value of the draft pressure and the damper opening. a second control system that opens the damper by a predetermined amount regardless of the draft pressure when the exhaust oxygen concentration is normal and the oxygen concentration in the exhaust falls below the set lower limit concentration; and at least one of the draft pressure and the damper opening degree. A natural draft heating furnace comprising a damper opening control device comprising a third control system that unconditionally maintains the damper opening at the current state when a measured value is abnormal. 2. The natural ventilation according to claim 1, wherein the first control system controls the damper opening degree according to the average value of the current measurement value of the draft pressure, the previous measurement value, and the measurement value before the previous one. Type heating furnace. 3. The amount of combustion air naturally ventilated into the furnace is adjusted by controlling the opening of a damper attached to the exhaust outlet. Input the measured values of medium oxygen concentration, damper opening, flow rate of the heated object, and temperature of the heated object at the entrance and exit of the heating furnace at regular intervals, and make sure that the measured values of draft pressure and damper opening are normal, and a first control system that averages current and past several measured values of draft pressure and controls the damper opening degree so as to bring the average value close to atmospheric pressure when the oxygen concentration in the exhaust gas is higher than a set lower limit concentration; , a second control system that opens the damper by a predetermined amount regardless of the draft pressure when the measured values of the draft pressure and the damper opening degree are normal and the oxygen concentration in the exhaust gas is lower than the set lower limit concentration; and a third control system that unconditionally maintains the damper opening at the current level when at least one of the measured values of the damper opening is abnormal; A fourth control system that closes the damper opening when the pressure is negative and the heat load of the heating furnace is increasing, which is detected based on the flow rate of the heated object and the temperature difference at the entrance and exit of the heating furnace. A natural draft heating furnace characterized by being equipped with a damper opening control device comprising: