JPH0145526B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to provide a new air ratio control device when preheated air is used in combustion control.

Conventional air ratio control methods for combustion using preheated air include the double pressure equalization valve method, constant flow valve linkage method, exhaust gas analysis method, and flow rate measurement method. It must be controlled on the upstream side of the heat exchanger.
There was a problem that it could only be used in temperature-controlled zones. In addition, the exhaust gas analysis method has problems such as delayed response and is not suitable for cases with a large number of burners, while the flow rate measurement method is considered ideal, but has the problem of being expensive.

These problems are mainly caused by the fact that when preheated air is used for combustion, the combustion air temperature rises as the constant temperature rises, which changes the burner differential pressure, piping pressure loss, etc., making it impossible to control the air ratio to an appropriate level. This is due to this.

Further, when the combustion amount changes due to temperature control of the furnace, the preheated air temperature also changes, causing a similar problem.

The present invention focuses on this point and provides an air ratio control device for preheated air combustion with a simple device and high accuracy.

It can be said that there is a proportional relationship between the air temperature (absolute temperature), the burner differential pressure, the required pressure on the control valve outlet side such as piping resistance.

Therefore, by adopting a method in which a control valve controlled by air temperature is placed downstream of a pressure equalizing valve, the above-mentioned problems can be solved and an inexpensive and high-performance air ratio control device can be realized.

FIG. 1 shows a system diagram of an air ratio control device according to the present invention. In FIG. 1, an air ratio control system using a pressure equalizing valve 5 is used, but a butterfly valve linkage system may be used instead. That is, as shown in FIG. 1, the absolute temperature of the air line after preheating is detected by a thermocouple 8 or the like, and the flow rate of the gas line after pressure equalization is corrected and controlled by the control valve 6 at this temperature.

In FIG. 1, A is an air line G is a gas line, 1 is a burner, 3 is a heat exchanger, 2 is a temperature control valve, 5 is a pressure equalization valve, 4 is a signal air pressure cooling section, and 7 is a controller.

However, when using the method shown in Figure 1, although the required air pressure is low when the furnace is low, the pressure drop in the heat exchanger is small, and the temperature control valve needs to be adjusted to match when the furnace is high. Therefore, there is a problem in that the pressure on the temperature control valve outlet side increases and the flow rates of both gas and air become excessive.

In order to solve this problem, we invented a system in which a control valve 9, which is also controlled by the combustion air temperature, is installed upstream of the temperature control valve.

This is the system diagram shown in Figure 2.

In the case of a linkage type, the control valve 9 may be placed downstream of the temperature control valve. When there are many temperature control zones, the air piping after heat exchange is long and the temperature may drop due to heat dissipation along the way, so in that case, a control valve 9 is installed downstream of the temperature control valve.

The opening of the control valve 6 is adjusted proportionally depending on the preheated air temperature, and operates in the closing direction when the temperature is high and in the opening direction when the temperature is low. Conversely, the control valve 9 operates proportionally in the closing direction when the temperature is low and in the opening direction when the temperature is high.

An air ratio control system using the control system shown in Figure 2 can be used at low cost by adding a simple detection section and control valve to a normal air ratio control system, and can be used for preheating air combustion to accommodate multiple temperature control zones. An air ratio control device can be realized.

[Brief explanation of drawings]

FIG. 1, FIG. 2 are system diagrams showing one embodiment of the air ratio control device for preheated air combustion according to the present invention. 1: Burner, 2: Temperature control valve, 3: Heat exchanger,
4: Signal air cooling section, 5: Equalizing valve, 6, 9: Control valve, 7: Controller, 8: Thermocouple.

Claims (1)

[Claims] 1. Combustion air temperature after indirect heat exchange with waste gas in a control device that preheats combustion air and controls the air-fuel ratio with a pressure equalization valve, or a control device that controls air valves and fuel valves with a linkage mechanism. At the same time, a control valve is provided in the fuel line that detects the combustion air temperature and proportionally adjusts the opening in the closing direction when the temperature is high and in the opening direction when the temperature is low. An air ratio control device for preheated air combustion, characterized in that a control valve for adjusting the temperature is provided in the combustion air line.