JPH0227325Y2 - - Google Patents

Description

[Detailed explanation of the invention] This invention is based on radiant tube furnaces (hereinafter referred to as
The present invention relates to a combustion control device using RTF (abbreviated as RTF), and more specifically to a combustion control device that improves the combustion control method during the minimum combustion time of RTF.

When product raw materials are fed into a furnace and heated to produce a product, some types of products are extremely reluctant to be oxidized. An example of this type of product is a long iron plate. When heating such products, it is not possible to heat them directly with a burner, so a
An indirect heating method using RTF radiant heat is used. That is, the COG and air are burned inside the tube, the tube is heated with the heat, and the heated tube gives heat to the product. In the case of this type of furnace, there is no way to cool it other than to stop combustion when the temperature inside the furnace exceeds a certain value. however,
It would not be efficient if combustion was stopped each time. Therefore, in such a situation, it is necessary to lower the furnace temperature without stopping combustion even if the furnace temperature control is ignored. Furnace temperature control using a furnace temperature controller is normally performed by adjusting the valve opening of the exhaust gas flow rate control valve, but for this purpose, the furnace temperature controller operating output is forced to a certain limit value. The furnace temperature is lowered while reducing the amount of fuel and achieving minimum combustion. Here, the specific sequence for lowering the furnace temperature is that the exhaust gas flow rate is reduced by throttling the exhaust gas flow rate control valve, and the set value of the cog flow rate controller, which converts the required cog amount from the exhaust gas flow rate, also decreases, and finally the cog flow rate decreases. The flow rate will decrease.

However, in such a conventional system in which the operating output limit value is fixed at one point, the opening degree of the exhaust gas flow rate control valve at the time of minimum combustion remains constant regardless of changes in the exhaust gas temperature. Therefore, the temperature-corrected exhaust gas flow rate value changes due to a change in exhaust gas temperature. If the exhaust gas flow rate value changes, the setting value of the cog flow rate controller based on it changes, and therefore, there is a problem that the cog flow rate changes depending on the exhaust gas temperature at that time.

The present invention was developed in consideration of these points, and it is based on the exhaust gas temperature and the valve opening of the exhaust gas flow rate control valve (the exhaust gas flow rate is such that the cog flow rate controller setting value is constant at any exhaust gas temperature). valve opening)
A function generator is provided in which the relationship between A combustion control device with good controllability is realized in which a constant set value is given to a cog flow rate controller.

The present invention will be described in detail below with reference to the drawings.

The figure is a configuration diagram showing an embodiment of the present invention. In the figure, 1 is a furnace in which the product is heated, and has an inlet A through which the product flows and an outlet B through which the product flows out. Reference numeral 2 is an RTF installed inside the furnace, and for example, about 300 RTFs are installed in the same furnace. 3
4 is a temperature detector that detects the temperature inside the furnace, such as a thermocouple; 4 is a control valve that adjusts the flow rate of fuel (for example, a cog); 5 is a flow rate detector that detects the fuel flow rate; and 6 is a measured value of the output of the flow rate detector. It is a cog flow rate controller that receives PV, and its operating output MV is given to the control valve 4. 7 is a temperature detector that detects the exhaust gas temperature on the RTF outlet side, 8 is a flow rate detector that detects the exhaust gas flow rate, 9 is a control valve that adjusts the exhaust gas flow rate, and 10 is the output of the flow rate detector 8 that is connected to the temperature detector 7. A first computing unit that corrects the output and calculates the flow rate at a reference temperature; 11 is a second computing unit that receives the output of the first computing unit and performs an oxygen correction calculation; 12 is the output of the second computing unit; A third computing unit calculates a necessary cog flow rate target value based on the received data, and the output of this computing unit is given to the cog flow rate controller 6 as a target cog flow rate value. 13 is a function generator which inputs the exhaust gas temperature and outputs a corresponding lower limit value of the operating output; 14 is an in-furnace temperature controller which uses the output of the in-furnace temperature detector 3 as a measured value PV. A lower limit value of the operating output is given to the furnace temperature controller from the function generator 13, and the operating output MV is set not to become smaller than a certain limit value. The operating output is then given to the exhaust gas flow rate control valve 9, and by adjusting the exhaust gas flow rate with the control valve, the temperature inside the furnace is adjusted. 1
5 is a buffer tank for temporarily storing exhaust gas, and the internal pressure of this tank is always maintained at a constant negative pressure.
16 is a damper, and 17 is a pump for forcibly drawing out exhaust gas. The operation of the device configured as described above will be explained as follows.

A temperature change in the exhaust gas is detected by a temperature detector 7 and provided to a function generator 13 . As described above, the function generator is set with an exhaust gas valve opening degree that provides an exhaust gas flow rate such that the set value SV of the cog flow rate controller 6 is constant at any exhaust gas temperature. Therefore, the operating output limit value at the exhaust gas temperature at that time is given to the furnace temperature controller 14, and a constant set value is always given to the cog flow rate controller 6 at the lowest combustion time regardless of changes in the exhaust gas temperature. Therefore, the cog flow rate does not change, and the optimum value of the cog flow rate at the lowest combustion time can be obtained.
In the above description, a case has been described in which a cog is used as the fuel, but the fuel is not limited to a cog, and other fuels such as BFG (blast furnace gas) may also be used.

As explained in detail above, according to the present invention, a function generator is provided that stores the relationship between the exhaust gas temperature and the valve opening of the exhaust gas flow rate control valve in advance, and the output of the generator is set as the lower limit of the operating output of the furnace temperature controller. By setting a limit value and always giving a constant set value to the cog flow rate controller at the time of minimum combustion regardless of changes in exhaust gas temperature, it is possible to obtain the optimum value of the cog flow rate at the time of minimum combustion.

[Brief explanation of the drawing]

The figure is a configuration diagram showing an embodiment of the present invention. 1... Furnace, 2... RTF, 3, 7... Temperature detector, 4, 9... Control valve, 5, 8... Flow rate detector,
6... Cog flow rate controller, 10-12... Arithmetic unit,
13...Function generator, 14...Furnace temperature controller, 15
...Batua tank, 16...Damper, 17...
extraction pump.

Claims (1)

[Scope of Claim for Utility Model Registration] The temperature inside the furnace is measured, and the flow rate value of the exhaust gas is determined by controlling a control valve that adjusts the flow rate of the exhaust gas of the radiant tube furnace so that the temperature inside the furnace becomes a predetermined value. In a combustion control device that controls the temperature inside the furnace by adjusting the fuel flow rate, there is a temperature detector that detects the exhaust gas temperature of the combustion gas, and the output of this temperature detector is input to set the lower limit of the operating output corresponding to the exhaust gas temperature. It has a function generator that outputs a limit value, and a furnace temperature controller that receives the output of this function generator and the furnace temperature value and controls the exhaust gas flow rate control valve. Also, the opening degree of the exhaust gas valve is set so that the set value of the fuel flow rate controller becomes constant and the exhaust gas flow rate is maintained, and the output of this function generator at the time of minimum combustion is set as the lower operating limit value of the furnace temperature controller. A combustion control device characterized in that the fuel flow rate is made constant regardless of changes in exhaust gas temperature during the lowest combustion time.