JPH0331609A - Fuel switching for heating furnace, and the like - Google Patents

Abstract

PURPOSE:To regulate instantaneously the opening of a flow rate regulating valve to the opening required for the new fuel by obtaining the time required for new fuel after fuel switching to reach a burner from a switching valve in a heating furnace, etc., in which two kinds of fuel are switched alternately. CONSTITUTION:Before switching from city gas to LPG fuel a required flow rate of the LPG fuel and the degree of opening of FIC-1 regulating valve which can be regulated to the required flow rate of the LPG fuel and from the primary pressure of the LPG fuel, the volume from the switching valve Hv-1 to a burner and Cv, etc., of the FIC-1 regulating valve, the time for the LPG fuel to reach the burner after its leaving Hv-1, are obtained from the load of a heating furnace at the time of switching by an electronic computer. When the above mentioned calculations are over, the operation of a three-way valve Hv-1 is switched to introduce the LPG fuel into a fuel piping. The inside of the fuel piping is replaced by the LPG fuel from the upstream section like a piston's flow, and reaches the burner after the time obtained by the calculation. At this time since the degree of opening of the FIC-1 regulating valve is regulated to the opening obtained by the calculation, the flow rate of the LPG fuel which corresponds to the load of a heating furnace is supplied to the burner.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a fuel switching method for a heating furnace or the like.

(Prior art) For equipment that uses hydrocarbons such as naphtha and LPG as raw materials to produce city gas through a steam reforming reaction.

A heating furnace for preheating raw material hydrocarbons and a reforming furnace for carrying out a steam reforming reaction are installed. These furnaces are equipped with two fuel supply systems that can separately supply two types of fuel so that city gas can be reliably and stably produced.

Figure 2 is a system diagram of a conventional fuel supply system when city gas and LPG are used as fuel for the heating furnace. In Figure 9, FIC-10 and FIC-20 indicate the flow rates of city gas and LPG, respectively Temperature indicating controller T, which is a controller and performs feedback control of the fuel flow rate and controls the temperature of the process fluid exiting the heating furnace to a predetermined temperature.
Cascade control is provided by IC-10. PIC-10
゜PIC-20 is FIC-10 and FIC-20 respectively
Hv-10 and Hv-20 are cutoff valves for the city gas flow path and LPG flow path, respectively.

The method of switching the fuel used in the conventional two-line fuel supply system described above is as follows.0For example, from city gas to LP
The case of switching to G will be explained. First, the load on the heating furnace is kept constant, the cascade control of TIC-40 is removed, and the LPG cutoff valve Hv-20 is opened. Next, the flow rate of city gas is slightly reduced using FIC-10, and LPGttFIC-20, which is equivalent to the same amount in terms of calorific value, is used.
Supplied by The above operation is repeated several times until only LPG is left.During this time, care is taken to keep the total calorific value of city gas and LPG constant and to maintain stable combustion, but in reality it takes several minutes. It takes more than 30 minutes (for example, 30 minutes).

When the switching is completed and the operation becomes stable, the cascade control of TIC-10 is utilized to return to normal operation.

In the conventional fuel switching method explained above, the time required for switching is long, and during this time, the combustion state is There is a problem in that a large amount of effort is required for various monitoring tasks and other operations during this period, as the amount of data changes greatly.

(Problems to be Solved by the Invention) The present invention has been devised in view of the above circumstances, and is a labor-saving fuel switching device for heating furnaces, etc., which can perform the switching operation automatically and in a short time. The objective is to provide a method.

(Means for Solving the Problems) The gist of the present invention is that in a heating furnace or the like in which two types of fuel are alternately switched, the time taken for new fuel to reach the burner from the switching valve after switching is , and instantaneously adjusts the valve opening of the fuel flow rate control valve to the opening required for the new fuel flow rate when this arrival time has elapsed from the time the changeover valve is switched. It's a method.

In other words, the time it takes for new fuel to reach the burner after operating the switching valve is comprehensively determined by a computer from the geometric volume between the switching valve and the burner, the Cv value of the flow rate control valve, the pressure and flow rate of new fuel, etc. A feature of the present invention is that when this time has elapsed since the valve was operated, the fuel flow rate control valve is instantly adjusted to the valve opening corresponding to a predetermined flow rate of new fuel. As a result, the valve opening of the fuel control valve is adjusted at the same time that new fuel reaches the burner, so that it can thereafter be supplied to the burner at a predetermined flow rate.

Although a three-way valve is suitable as the switching valve, a remote-controlled on-off valve may be provided in each flow path. The measuring end of the flow rate controller changes the specific gravity depending on the type of fuel.

A type of flowmeter 1 that can accurately measure even if the volumetric flow rate varies greatly, such as a Karman vortex flowmeter, is suitable.

According to this method, it is possible to perform the switching automatically and in a much shorter time than the conventional method, and moreover, the switching to the W4 key can be performed without any abnormality occurring during the switching.

(Example) The content of the present invention will be further explained below based on Examples.

FIG. 1 is a system diagram when the present invention is implemented in a heating furnace.

In the figure, PIC-1 and PIC-2 are pressure indicating regulators for the supply pressures of city gas and LPG, respectively, and these regulators maintain the primary pressure of the flow rate regulator, which will be described later, at a predetermined pressure. Hv-1 is a three-way Robor valve, and has a structure in which the flow path can be switched from city gas to LPG and from LPG to city gas by rotating the valve shaft. FIC-1 is a flow rate indicator controller that can be used for both city gas and LPG.

A Karman vortex flowmeter or the like is suitable, since it can measure even when the physical properties and flow rate of the gas vary greatly. TIC-1 is a temperature indicating controller for the process fluid exiting the heating furnace, and is used in cascade with the flow rate indicating controller FIC-1 to control the fuel flow rate. The fuel switching method of the present invention having the above configuration is as follows. Prior to switching, the load on the heating furnace was made constant, the TLC-1 cascade was also removed, and the FIC
The opening degree of the -1 control valve is kept constant. Prior to the Hv-1 switching operation, the following items are determined using a computer.

The required flow rate of fuel LPG based on the load on the heating furnace at the time of switching, and the valve opening degree of the FIC-1 control valve that can be adjusted to this flow rate.

The time it takes for LPG to leave HV-1 and reach the burner based on the primary pressure of the fuel LPG, the volume from HV-1 to the burner, and the Cv of the FIC-1 control valve.

Once the above calculations are completed, the three-way valve is switched and LPG is introduced into the fuel pipe.The inside of the pipe is replaced by LPG from the upstream part in a piston flow manner, and it reaches the burner after the arrival time determined by the above calculation. At this point, the opening degree of the control valve of FIC-1 is adjusted to the opening degree determined by the above calculation, so that the flow rate of LPG corresponding to the heating furnace load is supplied to the burner. After switching the fuel, if there is no abnormality in the operating state around the heating furnace and normal operation is confirmed, the feedback control of FIC-1 and the cascade control by TIC-1 are restored. The time required for switching was very short compared to the conventional method, less than several tens of seconds, and no abnormalities were observed during the switching.

Although the above embodiment is an example of switching from city gas to LPG, switching from LPG to city gas can be performed using exactly the same procedure, and the present invention can also be applied to other types of fossil fuels. Needless to say.

(Effects) According to the fuel switching method of the present invention described above, the fuel switching can be performed automatically in a much shorter time than the conventional method, so that the effect of saving labor in driving can be obtained. .

[Brief explanation of drawings]

FIG. 1 is a system diagram when the present invention is implemented in a heating furnace, and FIG. 2 is a system diagram of a conventional two-system fuel supply system. that's all

Claims (1)

[Claims] In heating furnaces, etc. that use two types of fuel by switching them alternately, find the time it takes for new fuel to reach the burner from the switching valve after switching, and calculate the fuel flow rate when this arrival time has elapsed from the time the switching valve was switched. A fuel switching method for a heating furnace, etc., characterized in that the opening degree of a control valve is instantly adjusted to the opening degree required for a predetermined flow rate of new fuel.