JPS63243613A - Control method for operation of balanced draft furnace - Google Patents

Abstract

PURPOSE:To eliminate a large damper and to improve safety, by a method wherein, in inverter control operation of the forced and the induced draft fan of a balanced draft furnace, automatic reset of an inverter control circuit after instantaneous outage is effected such that the forced fan is reset after restoration of the induced draft fan. CONSTITUTION:On instantaneous outage, restarting of an induced draft fan 5 is detected by the relay of an inverter 5' for the induced draft fan. After receipt of a detecting signal, a starting signal is fed to an inverter 1' for a forced fan such that the starting signal is delayed a specified time by means of a timer, and a forced fan 1 is restarted. This constitution enables elimination of a large damper for regulation of combustion air and combustion gas. Further, consumption power is saved, and safe automatic reset is practicable without bringing a pressure in a furnace into a positive pressure state.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application) The present invention relates to a method for controlling the operation of an inverter-controlled forced fan and induction fan used in a balanced draft furnace.

Problems to be Solved by the Invention) The balanced draft system is used in large boilers, large heating furnaces, reforming furnaces for city gas production, and the like. The advantage of the balanced draft method is that combustion is carried out under forced draft that allows for stable combustion, and the furnace internal pressure can be maintained at a predetermined negative pressure despite fluctuations in the furnace load, making it suitable for large furnaces with large fluctuations in furnace load. However, a balanced ventilation furnace requires the installation of a forced fan for blowing combustion air, a damper for regulating its flow rate or pressure, an induction fan for exhausting combustion gas, and a damper for regulating its flow rate or pressure. FIG. 2 illustrates a conventional method for controlling the operation of a balanced draft furnace using an example of a reforming furnace for producing city gas. Referring to FIG. 2, reference numeral 1 denotes a forced fan for blowing combustion air, and a large damper (2) for a flow controller (FIC) is provided on the discharge side duct of the fan. 3 is a reforming furnace, and the pressure inside the furnace is controlled by a pressure regulator (PI).
C) It is controlled by adjusting the opening and closing of a large exhaust gas damper (4) provided on the suction side of the combustion gas induction fan (5). The above method of controlling the operation of a balanced draft furnace requires the installation of large dampers for combustion air and combustion exhaust gas, respectively, and the forced fan and induction fan are both driven by standard motors that rotate at a constant speed. There is a problem in that the required power is not significantly reduced even under load. In the present invention, by controlling the rotational speed of the fan using an inverter-controlled electric motor, the present invention eliminates the need for a large damper and also saves energy at low loads. With the recent development of microelectronics such as thyristors and transistors, inverter control has made remarkable technological progress, and the equipment cost of the inverter itself has become cheaper.

However, when controlling a balanced draft furnace with an inverter, there are the following problems to be solved. That is, as a matter of course, the inverter control circuit described above has a built-in measure for automatic recovery in the event of an instantaneous power outage (generally a voltage drop that recovers within one second, hereinafter referred to as an instantaneous power outage). In general-purpose inverters, in the event of a momentary power outage within the compensation time of the power supply, the output of the inverter is cut off for a certain period of time and then re-outputted to protect transistors and the like. As a method for re-outputting, after the power is restored, a reset signal is automatically issued to set the inverter to its initial state. Then, by detecting the residual voltage and rotational frequency of the free-running motor using inertia force, the inverter's output voltage is gradually applied and the output frequency is increased to match, automatically returning to the original steady operating state. There is.

However, when comparing the horsepower and rotational inertia of a forced fan, an induction fan, and an induction fan, the latter has a higher exhaust gas temperature and a larger air volume due to the leakage air from the furnace, so the equipment capacity is also larger. It also has great power. Therefore, after a momentary power outage, the residual voltage of the free-running motor in the forced fan attenuates faster, and the output voltage of the inverter can be applied more quickly and the fan returns to the operating state. In a balanced ventilation furnace, if the induced fan does not reach operating state and only the forced fan enters operating state, the pressure inside the furnace will become considerably pressurized (positive pressure), and the high temperature gas inside the furnace will blow out, which is critical for bone movement safety. is dangerous.

Means for Solving the Problems) The present invention was provided to solve the above problems, and is a method for controlling the operation of an inverter-controlled forced fan and induction fan for a balanced draft furnace. The gist is that when the forced fan and induction fan of a balanced draft furnace are driven by an inverter-controlled electric motor, the inverter control circuit automatically returns after a momentary power outage, and it is detected that the fully induced fan has recovered. This is a method for controlling the operation of a balanced draft furnace, characterized in that the forced fan is returned to its original position after

According to the present invention, by driving the forced fan and induction fan of a balanced ventilation furnace with an inverter-controlled electric motor, they can be operated at a rotation speed corresponding to the required air volume, so there is no need for a damper for landscape control, and the load is low. Unlike standard electric motors that rotate at a constant speed, it is possible to operate at low speeds, resulting in significant energy savings.Furthermore, even in the event of a momentary power outage, the pressure inside the furnace can be increased to blow high-temperature combustion gases out of the furnace. Remarkable effects can be obtained, such as preventing dangers such as exposure.

(for production) The operation of the present invention will be explained based on examples.

FIG. 1 is a system diagram showing an embodiment in which the present invention is applied to a reforming furnace for producing city gas. In the figure, 1 is a forced fan for blowing combustion air, and its inverter 1 receives a signal from a flow rate indicator controller (CFIC) and inputs the frequency and current to the conductive motor of the forced fan 1 to obtain the required air flow rate. Or adjust and control the voltage. Reference numeral 3 denotes a reforming furnace, and combustion gas of fuel supplied to a burner installed at the top of the furnace passes through a heat recovery section 3 and is sent to a stack B by an induction fan 5. The internal pressure of the reforming furnace 3 is detected by a pressure indicator controller (PiC), and the frequency and current or voltage input to the induced fan 5 are adjusted and controlled by the induced fan inverter 5 so as to maintain a predetermined constant negative pressure. When the power is restored from a momentary power outage, the restart of the induction fan is detected by a relay in the induction fan inverter panel, etc. After receiving the signal, a timer or a switch with a similar function is activated to hold the signal for a certain period of time. , sends a signal to the forced fan inverter to issue a reset signal and cause it to re-output and restart.

Effects of the Invention) According to the present invention, the following remarkable effects not seen before can be obtained, and therefore the present invention is extremely useful in industry.

In other words, it is not necessary to install a large damper for regulating the combustion air and combustion gas in a balanced draft furnace, and the power consumption of forced fans and induction fans can be reduced during low-load operation of the furnace, and the pressure inside the furnace can be maintained even during momentary power outages. It is possible to safely and automatically return the forced fan and induced fan without creating positive pressure.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment in which the present invention is applied to a reformer for producing city gas, and FIG. 2 is a system diagram of a conventional operation control method for the same reformer. DESCRIPTION OF SYMBOLS 1... Forced fan, 1... Inverter for forced fan, 2... Damper for combustion air, 3... Reformer, 4...
...Damper for combustion gas, 5...Induction fan, 5...
・Inverter for induced fan.

Claims (1)

[Claims] When driving the push-in fan and induction fan of a balanced ventilation furnace with an inverter-controlled electric motor, the automatic recovery of the inverter control circuit after a momentary power outage is performed after detecting that the induction fan has returned. A method for controlling the operation of a balanced draft furnace, characterized by restoring.