JPH0686634B2 - Reactor pressure control method for direct heating furnace - Google Patents

Description

The present invention relates to a furnace pressure control method for a direct-fired heating furnace.

In a direct-fired heating furnace (hereinafter simply referred to as “heating furnace”), when the exhaust gas exhaust power is excessive, (a) excess air increases, (b) heat loss due to exhaust gas increases, and (c) furnace There are problems such as the internal temperature decreasing and the temperature distribution becoming non-uniform. When exhaust gas is insufficient, (d) incomplete combustion causes soot, (e) large fuel loss, (f) flashback. However, the exhaust condition (furnace pressure) greatly affects the performance of the heating furnace.

Therefore, in order to maintain the exhaust state of the heating furnace at a desired value, an exhaust gas draft force is applied by the chimney and an appropriate pressure loss is added by the flue damper to control the exhaust state in the furnace, that is, the furnace pressure control.
If a chimney cannot be installed due to construction cost or location problems, an induction fan may be installed to provide an exhaust gas draft force, and a flue damper may be used to control the furnace pressure by adding an appropriate pressure loss. In addition, due to the height limitation of the chimney and the construction cost, there are cases where both the chimney and the induction fan are provided to provide an exhaust draft force, and an appropriate pressure loss is added by the flue damper to control the furnace pressure.

The conventional furnace pressure control method for a heating furnace equipped with both a chimney and an induction fan is mainly based on the control by opening and closing the flue damper. I was told. However, in the case of this method, when the combustion amount becomes small, the flue damper becomes the damper opening close to fully closed to suppress the excessive draft force, and the draft force of the attracting fan is reduced for the first time there. Since it is a method of lowering the rotation speed of the fan, the draft force of the attracting fan is changed within the range where the control characteristics of the flue damper are deteriorated, resulting in disturbance to the furnace pressure and stable furnace pressure. There was a problem that control could not be secured.

The present invention is a furnace pressure control method that solves the problems of the conventional method, the gist thereof is a furnace pressure control method for a direct-fired heating furnace of a method of discharging exhaust gas from a chimney while attracting exhaust gas with an induction fan, After setting the opening of the flue damper within a range where the control characteristics of the damper itself are good, the parameters indicating the combustion state of the heating furnace including the fuel gas amount of the heating furnace, the excess air ratio, and the temperature of the exhaust gas discharge system are set. The pressure loss and draft force of the exhaust gas exhaust system are calculated using these values, the reference rotational speed of the induction fan is calculated and set from these calculated values, and the furnace pressure is normally controlled by the damper opening control under the set induction fan rotational speed. A method for controlling a furnace pressure of a direct-fired heating furnace, which is characterized in that control is performed, and when the damper opening exceeds a range where the control characteristic is good, the induction fan rotational speed is corrected.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a control system in an embodiment of the present invention.

The exhaust gas burned in the furnace 1 is discharged to the atmosphere through the heat exchanger 3, the flue damper 4, the induction fan 5 and the chimney 6 which are provided in the exhaust gas discharge path. Reference numerals 7, 8 and 9 are thermocouples for measuring the exhaust gas temperature in each part of the discharge path. Reference numeral 10 is a thermocouple for measuring the furnace temperature, and its output signal is sent to the temperature indicating controller 11. Reference numeral 13 is a fuel flow rate indicator, and 16 is an air flow rate indicator which opens and closes the flow rate control valves 14 and 17 in response to the output signals of the orifices 15 and 18, the temperature indicator controller 11 and the excess air ratio setting device 12. Reference numeral 19 is a furnace pressure detector, and the furnace pressure indicating controller 20 receives the output signal thereof and opens and closes the flue damper 4. 2 is an arithmetic unit, and 21 is an adder.

Next, the operation of this device will be described.

Combustion is preferably carried out while maintaining the furnace pressure of the heating furnace slightly higher than atmospheric pressure. The furnace pressure is determined by the balance of the following formula (1).

(Chimney draft force) + (Attractive fan draft force) = (Flue damper pressure loss) + (Chimney flow pressure loss) + (Discharge path flow pressure loss) ... (1) Each term in the equation (1) The value of can be calculated by the following equations (2) to (7).

Chimney draft force; P _o = 355H _c (1 / T _o -1 / T _c ) ..
(2) Exhaust gas amount; Q _E = Q _Gas・ G + (m-1) Q _Gas・_Lo ...
(3) Stack flow pressure loss; P _c = K _c · Q ² E · 1 / T _c ··· (4) Discharge path flow compression loss; P _f = K _f · Q ² E · 1 / T _f · · (5) Flue damper pressure loss; P _d = f (Q _E , σ _o ) ・ ・ ・ (6) _{Induced fan} -and- _raft force; P _oF = P _c + P _f + P _d -P _o
(7) inducement Juan _{rpm; V = g (P oF,} Q E) ··· (8) T o; atmospheric temperature (° K), T _c; chimney temperature (° K), T _f; discharge path temperature (° K), H _c ; Chimney height (m), Q _Gas ; Total amount of fuel gas flow in each furnace zone (Nm ³ / h), G; Theoretical exhaust gas amount (Nm ³ / Nm)
³ ), _Lo ; theoretical air amount (Nm ³ / Nm ³ ), m; excess air ratio, f; flue damper characteristic function, g; attractive fan characteristic function, σ _o ; flue damper opening degree (%), V; Induction fan rotation speed (rpm),
K _c , K _f ; Coefficients In the equation (1), the stack draft force, stack flow pressure loss, and discharge path flow pressure loss are uniquely determined from the combustion state of the heating furnace, so the induced fan rafts force and flue damper pressure loss are The balance can determine the furnace pressure.

Therefore, in the present invention, the opening of the flue damper is set within a range in which the damper control characteristics are good, and the fuel gas flow rate is taken in from the orifice 15 and the excess air ratio is taken in from the excess air ratio setting device 12. , uptake temperature measurements from Matanetsu couple 7,8,9, calculator 2 in the (2) subjected to (7) of the calculation, calculates a reference rotational speed V _o attractant Juan in (8) and, to set the reference rotation speed V _o. After that, the furnace pressure is controlled by controlling the opening of the flue damper 4, and when the damper opening exceeds the range with good damper characteristics, the rotation speed of the induction fan is changed by ± ΔV _o and the flue damper is constantly operated. Are controlled within a range with good characteristics. Moreover, in equation (7)
When P _{oF ≈0} , the induction _fan is set to the state of minimum rotation speed, and furnace pressure control of only the flue damper is performed. When P _oF > 0, control is performed as described above. In the case of a heating furnace, the frequency of combustion amount change is not high, so the control cycle for calculating and setting the induction fan reference speed V _o should be set longer than the control cycle for furnace pressure control by the flue damper. To do.

By using the above control method, 1) the reference rotational speed V _o of the induction fan can be set in a feed-forward manner by calculating from the pressure loss and draft force of the exhaust gas discharge system, and then the furnace pressure control mainly of the flue damper. With this, the flue damper characteristics can be controlled within a good range, and the induction fan rotational speed is corrected with a small change amount ± ΔV _o , so the induction fan rotational speed change does not cause a large disturbance to the furnace pressure and is stable. The furnace pressure can be controlled.

2) From expressions (1) to (8), it is possible to properly distribute the induced fand raft force and the pressure loss of the flue damper, and it is possible to obtain an excellent effect that the controllability of the furnace pressure can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a control system in an embodiment of the present invention. 1 …… Furnace 2… Calculator 4 …… Flue damper 5 …… Induction fan 6 …… Chimney 7,8,9,10 …… Thermocouple 19 …… Furnace pressure detector 20 …… Furnace pressure indicating controller 21 ... Adder

Claims (1)

[Claims] Claim: What is claimed is: 1. A furnace pressure control method for a direct-fired heating furnace in which exhaust gas is discharged from a chimney while being attracted by an induction fan. After setting, the fuel gas amount of the heating furnace,
The pressure loss and draft force of the exhaust gas exhaust system are calculated using parameters indicating the heating furnace combustion state including the excess air ratio and the temperature of the exhaust gas exhaust system, and the reference rotational speed of the induction fan is calculated and set from these calculated values. It is characterized in that the furnace pressure control is always performed by the damper opening control under the set induction fan rotational speed, and the induction fan rotational speed is corrected when the damper opening exceeds the favorable range of the control characteristics. Control method for furnace pressure of direct-fired heating furnace.