JPH04126915A - Forced combustion type gas-burning hot water supply device - Google Patents

Abstract

PURPOSE:To contrive a lower NOx, by providing an exhaust duct which has an exhaust gas inlet end opened to the exhaust chamber side on the upper side of a heat exchanger and an exhaust gas outlet end opened into or in the vicinity of an intake port of a burner, and mixing a portion of a heatexchanged low-temperature combustion gas into combustion air. CONSTITUTION:An exhaust duct 15 is provided which has an exhaust gas inlet end 13 opened in a part of an exhaust chamber and an exhaust gas outlet end 14 opened in or in the vicinity of an intake port 8. At the time of forced combustion carried out by driving a motor-driven fan 4, a portion of an exhaust gas is introduced into a combustion air chamber (a) together with combustion air by utilizing a pressure difference between the exhaust gas inlet and outlet ends 13 and 14. In this gas-burning hot water supply device, the forced combustion by driving the fan 4 produces a positive pressure at the exhaust gas inlet end 13 and a negative pressure at the outlet end 14, and the resulting pressure difference causes a portion of the combustion (exhaust) gas at a relatively low temperature to flow through the intake port 8 into the combustion air chamber (a). Water vapor, CO2, etc., formed by combustion reaction in the combustion gas thus directed into the air chamber (a) are introduced into both primary air and secondary air, and are fed into the inside and the outside of a flame, thereby inhibiting the generation of a local high temperature region which would produce thermal NOx.

Description

[Detailed Description of the Invention]: 3- [Industrial Application Field] The present invention provides a combustion device having a Bunsen type or semi-Bunsen type gas burner constituted by a plurality of flame hole groups;
The present invention relates to a forced combustion type waste water heater for domestic use, which is equipped with a heat exchanger that heats water supply using combustion gas, and forcibly introduces combustion air using an electric fan.

[Conventional technology]

Gas-fueled water heaters and bathtubs with water heaters are widely used for household use, and in recent years, improvements have been made to make them more compact, have higher loads, and reduce noise.

On the other hand, from the standpoint of pollution prevention, household water heaters are also required to suppress the generation of NOx.

However, in gas combustion technology, there is a problem that it is difficult to achieve both compactness of appliances, increase in load, and reduction of NOx.

In other words, most conventional water heaters of this type use a Bunsen burner or semi-Bunsen burner as a combustion device, which forms a flame above the flame 1]I through a plurality of flame hole groups having a constant open area L1. The ratio of the combustion air is 1.4 to 1.7 as a whole, with secondary air (premixed air) being in the range of 20 to 40% of the theoretical air amount.
Most of the water heaters complete combustion within the range of 100~]5 in these water heaters.
N around 0 ppm.

X is discharged.

On the other hand, in order to reduce NOx, ceramic plate type fully premixed burners such as Schwank burners,
- It is known to use secondary flame formation Bunsen burners with a secondary combustion chamber.

Although it is possible to reduce NOx by using these combustion devices, the former has problems in that the combustion amount restriction cannot be widened and it is difficult to control the negative air ratio. Both methods are complicated and have a high production cost, making them unsuitable for use in general household water heaters.

Furthermore, in large boilers used for industrial purposes, combustion exhaust gas is recirculated to the combustion chamber and combustion flame zone, and NOx is suppressed through the two effects of lowering the flame temperature and lowering the oxygen partial pressure during the thermal NOx reduction method. It is known to do. In this exhaust gas recirculation, a part of the combustion exhaust gas in the flue is sucked up and pressurized by a recirculation blower and then reinjected into the combustion chamber. Approximately 250℃~300℃ input as air
The high-pressure recirculated exhaust gas allows for combustion with a low oxygen concentration, while maintaining sufficient diffusion power to complete combustion of the unburned air-fuel mixture in the combustion zone and maintaining the combustion zone in a hotter state. As a result, the flame enters a moderately slow combustion state, lowering the flame peak temperature and suppressing thermal NOx. In addition, this method also reduces waste heat loss for industrial plants, and is an effective means for energy saving.

(Figure 2 of the Japan Society of Mechanical Engineers technical material “Method for suppressing the production of environmental pollutants in stationary combustion equipment using gaseous/liquid fuels”)
・See 15 and related descriptions).

Note that Figures 2 and 15 of the above technical data are shown as Figure 13 in the attached drawings.

[Problem to be solved by the invention]

The above exhaust gas recirculation is effective for industrial plants, but for domestic water heaters, a recirculation fan is newly required, which becomes a new noise source. Exhaust gas recirculation is not performed in domestic water heaters because they are used for only about 1.5 to 2 hours a day in total and there is little benefit due to the usage conditions of severe load fluctuations.

In addition, the use of ceramic plate type fully premixed burners has been widely used, and the development of new combustion devices and new fuel power 'C control methods that are different from the conventional Bunsen or semi-Bunsen combustion devices and their control devices. etc., which makes it difficult to put it into practical use, and there is a problem that the varnish is 1 to 100% high.

The present invention improves the problems of the prior art as described above, applies it to a gas water heater using a Bunsen type or semi-Bunsen type burner that has been widely put into practical use, and improves its combustion mechanism and combustion control unit. The purpose of the present invention is to provide a gas water heater for home use that can reduce NOx without major modification.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a combustion device having a Bunsen type or semi-Bunsen type gas burner configured with a plurality of flame hole groups, a heat exchanger that heats water supply with combustion gas, and an electric fan. In a gas water heater configured to forcibly introduce combustion air, an exhaust inlet end is opened on the exhaust chamber side of the upper part of the heat exchanger, and an exhaust discharge end is opened at or near the intake port of the combustion device. It is characterized in that an exhaust duct with an opening is installed, and a part of the low-temperature combustion gas after heat exchange in the exhaust chamber is mixed into the combustion air.

[Effect]

As described above, the present invention has an exhaust gas inlet end opened on the side of the exhaust chamber of the second part of the heat exchanger, and the intake air of the combustion apparatus.
Since an exhaust duct with an open exhaust discharge end is installed at or near the exhaust duct, when an electric fan is driven to cause combustion, part of the combustion exhaust gas is transferred to the intake air due to the pressure difference between the exhaust introduction end and the exhaust discharge end. is introduced into the combustion chamber from the air supply port,
Water vapor, CO2, etc. generated by the combustion reaction in the combustion exhaust gas are introduced into the primary air and secondary air and thrown into the interior and exterior of the flame, suppressing the generation of localized high temperature areas that are the cause of thermal NOx generation. be able to.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 12.

FIG. 1(A) is a basic configuration diagram showing an example in which the present invention is applied to a combustion air forced type gas water heater, and FIG. 1(B) is a basic configuration diagram showing an example in which the present invention is applied to an exhaust suction type gas water heater. FIG.

In FIGS. 11(A) and (B), 1- is a Bunsen-type or semi-Bunsen-type gas burner (hereinafter simply referred to as a gas burner) composed of a plurality of burner ports, and 2 is a heat exchanger arranged on three sides thereof. These are surrounded by a combustion chamber 3, which forms a combustion air chamber a, a combustion chamber B, and a heat exchange chamber C.
In the case of FIG. 1(A), an electric fan 4 is disposed below the combustion air chamber a, and in the case of FIG. 1(B), an electric fan 4 is provided downstream of the exhaust chamber d. When the electric fan 4 is driven and gas is supplied to the gas burner 1 for combustion, the combustion air is sucked in from the intake air (co 8 and supplied as primary and secondary air to the gas burner 1, and The combustion exhaust gas is discharged from the exhaust port 9, and the water thus supplied from the water supply pipe 6 is heated by the heat exchanger 2 and is then supplied from the hot water tap 7.

This type of forced combustion type waste water heater has a built-in microcomputer control device 100, and after setting the desired hot water temperature on the remote control (not shown), turn on the operation switch, and then heat the hot water in this state. When the tap is opened, the flow sensor 10 detects the water supply, supplies gas to the gas burner, and ignites the ignition device (not shown). The water heater is detected, and based on these detected values, the microcomputer control section controls the opening degree of the gas proportional control valve 5 and the rotation of the electric fan 4 so that hot water at a desired temperature can be obtained. Incidentally, since the automatic control described above is well known, detailed explanation thereof will be omitted.

In the present invention, the exhaust gas introduction end 13 is opened in a part of the exhaust chamber (in the case of FIG. 1(A)) or the exhaust side of the electric fan (in the case of FIG. 1(B)), and the intake port 8 Or an exhaust duct 15 with an exhaust discharge end 14 opened in the vicinity thereof
is installed, and during forced combustion by driving the electric fan 4, a part of the exhaust gas is introduced into the combustion air chamber a along with the combustion air by utilizing the pressure difference between the exhaust gas introduction end 13 and the exhaust gas discharge end 4. Configure it as follows.

Since the gas water heater of the present invention has the configuration as described above,
During forced combustion by driving the electric fan 4, the exhaust gas introduction end 1
3 is a positive pressure, and the exhaust discharge end 14 is a negative pressure, and due to the pressure difference, a portion of relatively low-temperature combustion exhaust gas is introduced from the intake port 8 into the combustion air chamber a.

That is, water vapor, CO2, etc. generated by the combustion reaction during the combustion exhaust gas introduced into the combustion air chamber a are introduced into both the primary air and the secondary air.

In general, gas water heaters equipped with Bunsen or semi-Bunsen burners use around 20% of the secondary air to cool the inner wall of the heat exchanger, and electric fans for combustion air do not have sufficient wind pressure. Due to the conditions, the secondary air is around 130% of the theoretical air amount ratio, and the secondary air is around 30% of the theoretical air amount ratio, but this has a big impact on ensuring the required performance such as combustion stability and combustion completion performance. It is the primary air that has the power.

In the present invention, water vapor, CO2, etc. are introduced into both the primary air and the secondary air as described above. The water vapor and CO2 thus introduced into the visible flame of the combustion flame zone together with the combustion secondary air for premixing and the combustion secondary air for diffusion mixing increase the heat capacity of the respective combustion air; It takes heat from the inside and outside of the flame,
The combustion reaction will be moderately slow.

The atmosphere in the combustion air chamber a is 20 to 20 degrees higher than the temperature of the air introduced from the outside by an electric fan, due to radiant heat from the burner group arranged on one side and conductive heat transfer from other combustion zone structures. It will be about 30°C higher. Therefore, the saturated steam temperature in the combustion air chamber a rises, so that even if the combustion exhaust gas is mixed to a volume ratio of about 20% of the total input air, the combustion air will not condense in the combustion air chamber a. From the above, the heat removed from the flame due to the boiling water content is mainly sensible heat, and rapid heat removal does not occur locally, and the degree of slow combustion is very uniform, and the flame length is As a result, it is less likely to cause extremely long or incomplete combustion, and as a result,
The amount of NOx discharged is reduced in inverse proportion to the amount of water vapor added (see Figure 9).

In the embodiment shown in FIGS. 1(A) and 1(B), the pressure difference between the exhaust gas introduction end 13 and the exhaust gas discharge end 14 fluctuates as the pressure difference changes from the maximum combustion load to the minimum combustion load, and the exhaust gas is regenerated. The amount of circulation also changes. However, even in this example, depending on the setting of the diameter of the exhaust duct, a problem of 30,000 Kca
Considerable NO in the maximum load range of Q/H or higher
It has an effect of reducing x.

Figure 2 shows the exhaust duct 1 of the water heater shown in Figure (A).
By incorporating a flow rate adjustment mechanism such as a damper or variable orifice into part of 5, it is possible to adjust the return amount of low-temperature combustion gas according to the type of gas or needs such as when extending exhaust gas without changing the diameter of the duct. This is an example of how to do this.

FIG. 3 shows a microcomputer control device 10 for controlling the gas proportional control valve 5 so that the opening degree of the flow rate adjustment mechanism 16 shown in FIG. 2 can be adjusted by an actuator 7 such as a gear motor.
The flow rate adjustment mechanism 16 uses a control current value of 0 as an opening setting signal.
The opening degree can be adjusted in several steps or steplessly. In this way, the amount of recirculation of exhaust gas can be automatically controlled in accordance with the flow rate of gas.

In FIG. 4, the opening degree of the flow rate adjustment mechanism 16 can be adjusted by the actuator 17 as in FIG. 3, and a humidity sensor 18 and a temperature sensor 19 are provided in the combustion air chamber a.
The microcomputer control unit 100 is used to calculate an absolute humidity value from the output signals of the humidity sensor 18 and temperature sensor 19, and the absolute humidity value is used as an opening setting signal for the flow rate adjustment mechanism 16. The opening degree can be adjusted in several steps or steplessly.

This is because if the amount of water vapor added is used as a monitoring parameter and the amount of exhaust gas recirculation is increased, the C○/CO2 value, which is an indicator of the quality of combustion, will increase, the thermal efficiency of the hot water heat exchanger will decrease, and combustion will slow down. However, if the absolute humidity, which can be calculated from the humidity and temperature of the combustion air, is controlled as a parameter, the above-mentioned disadvantages will not occur. According to the experimental results, the absolute humidity control range is, for example], 5X]Okg/kg' to 21X], Ok
g/kg'(kg' is 1 kg of dry air), good combustibility and low NOx (90 to 70 ppm) can be obtained (see Figure 9). In addition, the heat exchange efficiency can be controlled to about 80 ± 2% at maximum combustion (first
(See figure 0).

Furthermore, in winter and summer, the absolute humidity in the combustion air fluctuates around 3×10 kg/kg' due to atmospheric humidity changes alone, and the NOx value also fluctuates around 3×10 kg/kg' (see Figure 11). Therefore, control using absolute humidity as a parameter is also effective against NOx value fluctuations in winter and summer.

In FIG. 5, as in FIG. 3, the opening degree of the flow rate adjustment mechanism [6] can be adjusted by an actuator]7, and an O2 concentration sensor 20 and a temperature sensor 19 are installed in the combustion air chamber a. , the amount of change in absolute humidity in the combustion air is calculated by the change in partial pressure of 02 by the microcomputer control device 100,
Using this as an opening setting signal, the opening of the flow rate adjustment mechanism 16 can be adjusted in several steps or steplessly.

Note that the temperature sensor] 9 is for correction. In this way, good control similar to the embodiment shown in FIG. 4 can be performed.

FIG. 6 shows an example in which an exhaust 021 degree sensor is installed in the exhaust chamber d instead of detecting the 02 concentration in the combustion air chamber of the embodiment shown in FIG.
1 and an exhaust temperature sensor 22 are installed to calculate the amount of change in absolute humidity in the combustion air based on the change in partial pressure, and use it as an opening setting signal to adjust the opening of the cylinder mechanism 16. This is what I did. In this way, good control similar to the embodiment shown in FIG. 5 can be performed.

FIG. 7 shows a non-completely sealed type using a shape memory alloy, bimetal, etc. whose shape changes depending on the temperature, instead of adjusting the opening degree of the flow rate adjustment mechanism 16 using the actuator J7 as shown in FIGS. 3 to 6. This self-control damper 23 is installed in the exhaust duct 15, and roughly controls the exhaust gas flow rate according to the change in exhaust gas temperature from the maximum combustion time to the minimum combustion time of the water heater. This is an example of how this could be done. That is, the self-control damper 23, as shown in FIG. 8(a),
At maximum load, the damper piece 23 changes depending on the exhaust gas temperature.
A is used which opens the damper piece 23a wide and closes the damper piece 23a while leaving the minimum flow path 23b at the minimum load as shown in FIG. 8(b).

In addition, in the embodiments shown in FIGS. 2 to 7,
Although illustrations of the exhaust suction type embodiments as shown in FIG. 3(B) are omitted, it goes without saying that these embodiments can also be applied to the exhaust suction type.

〔Effect of the invention〕

As described above, according to the present invention, the differential pressure between the exhaust gas introduction end and the exhaust gas discharge end can be reduced without making major changes to the combustion mechanism parts such as the burner, the gas proportional control valve, and the combustion control system. By installing an exhaust duct (exhaust duct) utilizing the above, it is possible to provide a forced combustion type gas water heater that is compact and has low NOx.

[Brief explanation of drawings]

Figures 1 (A) and (B) are schematic diagrams showing the basic configuration of a forced combustion gas water heater to which the present invention is applied, Figures 2 to 7 are schematic diagrams showing different embodiments, and Figure 8 ( a)(b)
) is a detailed diagram of the self-control damper used in Fig. 7, Fig. 9 is a graph showing the relationship between Co/CO2 and NOx in the combustion exhaust gas and absolute humidity in the combustion air, and Fig. 10 is a graph showing the combustion amount and combustion. Graph showing the relationship with Noxg degree in exhaust gas, No. 11
The figure is a graph showing the performance difference of a hot water boiler without NOx countermeasures in summer, Fig. 12 is a graph showing the relationship between 02W degree and absolute humidity in combustion air, and Fig. 13 is an explanation showing the conventional exhaust gas recirculation system. It is a diagram. 1... Burner, 2... Heat exchanger, 4... Electric fan, 5... Gas proportional control valve, 6... Water supply pipe, 7... Hot water outlet pipe, 8... Intake port, 9 ...Exhaust port, 10...Flow sensor 11...Water supply temperature sensor, 12...Output hot water temperature sensor, 13...Exhaust inlet end, 14...Exhaust discharge end, ]5...Exhaust Duct, 16... Flow rate adjustment mechanism, 17... Actuator, 18... Humidity sensor, 19... Temperature sensor, 20... O of combustion air chamber
2 concentration sensor, 21... 02 concentration sensor of exhaust chamber 22... temperature sensor of exhaust chamber, 23... self-control damper.

Claims (1)

[Claims] 1. A combustion device including a Bunsen-type or semi-Bunsen-type gas burner configured with a plurality of flame hole groups, a heat exchanger that heats water supply with combustion gas, and an electric fan that generates combustion air. In a forced combustion gas water heater designed to forcefully introduce gas, an exhaust gas introduction end is opened on the exhaust chamber side of the upper part of the heat exchanger, and an exhaust gas discharge end is opened at or near the intake port of the combustion device. A forced combustion characterized in that an exhaust duct is installed, and a part of the low-temperature combustion gas after heat exchange in the exhaust chamber is mixed into the combustion air due to the pressure difference between the exhaust introduction end and the exhaust discharge end. Type gas water heater. 2. The forced combustion system according to claim 1, wherein a low temperature combustion gas flow rate adjustment mechanism is disposed in the flow path of the exhaust duct, and the flow rate adjustment mechanism is configured to adjust the return amount of the low temperature combustion gas. Combustion gas water heater. 3. The low-temperature combustion gas flow rate adjustment mechanism disposed in the flow path of the exhaust duct is adjusted by an actuator, and the actuator is driven using the current value of the gas flow rate proportional control valve as an opening setting signal to adjust the flow rate. 3. The forced combustion gas water heater according to claim 2, wherein the opening degree of the mechanism is adjusted. 4. The low-temperature combustion gas flow rate adjustment mechanism installed in the flow path of the exhaust duct is adjusted by an actuator, and the actuator is set to an absolute value calculated from the detected values of the humidity sensor and temperature sensor installed in the combustion air chamber. 3. The forced combustion gas water heater according to claim 2, wherein the opening of the flow rate adjustment mechanism is adjusted by driving the humidity value as an opening setting signal. 5. The low-temperature combustion gas flow rate adjustment mechanism installed in the flow path of the exhaust duct is adjusted by an actuator, and the actuator is used to control the combustion rate calculated from the detected values of the O_2 concentration sensor and temperature sensor installed in the combustion air chamber. 3. The forced combustion gas water heater according to claim 2, wherein the opening degree of the flow rate adjustment mechanism is adjusted by driving the amount of change in absolute humidity in the air as an opening setting signal. 6. The flow rate adjustment mechanism for low-temperature combustion gas disposed in the flow path of the exhaust duct is adjusted by an actuator, and the actuator is operated to adjust the flow rate of the low-temperature combustion gas based on the detected value of the exhaust O_2 concentration sensor and exhaust temperature sensor installed in the exhaust chamber. 3. The forced combustion gas water heater according to claim 2, wherein the opening degree of the flow rate adjustment mechanism is adjusted by driving the amount of change in absolute humidity in the combustion exhaust gas as an opening setting signal. 7. Construct a non-completely sealed self-controlling damper using a shape memory alloy or the like that changes its shape depending on the temperature, and place the self-controlling damper in the flow path of the exhaust duct so that the damper changes its shape according to changes in the exhaust temperature. 2. The forced combustion gas water heater according to claim 1, wherein the amount of low-temperature combustion gas returned is roughly controlled.