JP7641116B2 - Heat recovery system, heat recovery method, and combustion control device - Google Patents

Description

One embodiment of the present invention relates to a heat recovery system, a heat recovery method, and a combustion control device. In particular, the present invention relates to a combustion control device having a function of controlling the oxygen concentration in a combustion chamber, and a heat recovery system equipped with the combustion control device.

Conventionally, heat recovery systems are known that recover and reuse heat generated during incineration at waste incineration facilities that incinerate municipal waste and other waste. In such heat recovery systems, collected municipal waste is burned in an incinerator, and the heat of the generated combustion gas is recovered by a heat exchanger such as an air preheater. The heat recovered by the air preheater is returned to the incinerator and used to raise the temperature of the combustion air, for example (see Patent Document 1, for example).

JP 2013-24504 A

In conventional heat recovery systems, exhaust gas generated in an incinerator is further completely combusted in a reburning chamber (secondary combustion chamber) to suppress the generation of harmful substances such as dioxins. At this time, the law requires that the exhaust gas be retained in the reburning chamber at a temperature of 850°C or higher (preferably 900°C or higher) for at least two seconds. Therefore, the temperature of the combustion gas discharged from the reburning chamber also becomes high, at over 900°C.

Here, if high-temperature gas of 900°C or more is directly supplied to the heat exchanger, there is a problem that the metal components that make up the heat exchanger (especially the parts that come into direct contact with the high-temperature gas) will deteriorate due to high-temperature corrosion. High-temperature corrosion is corrosion that does not involve liquid water and occurs in a high-temperature environment. For this reason, in conventional heat recovery systems, it was necessary to lower the temperature of the high-temperature gas generated in the reburning chamber to a temperature at which high-temperature corrosion would not occur. It is also known that dioxin resynthesis occurs at approximately 400°C or higher. Therefore, with consideration given to suppressing dioxin resynthesis, the combustion gas discharged from the reburning chamber was cooled to around 350°C before being supplied to the heat exchanger.

As described above, conventional heat recovery systems require heat recovery from combustion gas whose temperature has been reduced to around 350°C. Therefore, to ensure heat recovery efficiency, steam boilers were generally used as heat exchangers. However, steam boilers require the operation of qualified personnel (boiler engineers) because the vessel is highly pressurized, which leads to increased maintenance and equipment upkeep costs.

One of the objectives of the present invention is to provide a heat recovery system with a simple structure that suppresses high-temperature corrosion and improves heat recovery efficiency.

The heat recovery system in one embodiment of the present invention comprises a combustion chamber, a heat exchanger to which combustion gas generated in the combustion chamber is supplied, and a combustion control device that controls the oxygen concentration of the combustion gas, wherein the combustion chamber has an oxygen concentration meter that measures the oxygen concentration of the combustion gas, and the combustion control device controls the oxygen concentration so that the pressure difference between the dissociation pressure of the contact point of the heat exchanger and the oxygen partial pressure of the combustion gas is below a predetermined value.

In the heat recovery system, the combustion chamber may further include a thermometer for measuring a temperature of the combustion gas. In this case, the control device may calculate the dissociation pressure based on the temperature.

The heat recovery system may further include a gas supply device that supplies oxygen gas or an inert gas to the combustion chamber. In this case, the combustion control device may control the gas supply device according to the oxygen concentration.

The heat recovery system may further include an air flow rate adjustment device that adjusts the amount of air supplied to the combustion chamber. In this case, the combustion control device may control the air flow rate adjustment device in accordance with the oxygen concentration.

In the heat recovery system, the heat exchanger may be a vacuum or non-pressure hot water heater.

The heat recovery system may further include a cooling chamber to which the combustion gas that has passed through the heat exchanger is supplied.

The heat recovery system may further include an incinerator that supplies primary combustion gas to the combustion chamber.

In the heat recovery system, the oxygen concentration meter may be a laser oxygen concentration meter.

A heat recovery method in one embodiment of the present invention includes measuring the oxygen concentration of combustion gas generated in a combustion chamber, controlling the oxygen concentration so that the pressure difference between the dissociation pressure of the contact part of a heat exchanger connected to the combustion chamber and the oxygen partial pressure of the combustion gas is not more than a predetermined value, and supplying the combustion gas with the oxygen concentration controlled to the heat exchanger.

The heat recovery method may further include measuring a temperature of the combustion gas. In this case, the dissociation pressure may be calculated based on the temperature.

The heat recovery method may use a vacuum or non-pressure hot water heater as the heat exchanger.

The heat recovery method may further include supplying the combustion gas that has passed through the heat exchanger to a cooling chamber.

The heat recovery method may further include supplying primary combustion gas generated in the incinerator to the combustion chamber.

In the heat recovery method, the oxygen concentration may be measured using a laser oxygen concentration meter.

A combustion control device according to an embodiment of the present invention includes a storage unit that stores a control program, and a processor that executes the control program, which causes the processor to acquire a temperature inside a combustion chamber, calculate a dissociation pressure of a contact portion of a heat exchanger using the temperature, acquire an oxygen concentration inside the combustion chamber, calculate an oxygen partial pressure of a combustion gas generated in the combustion chamber using the oxygen concentration, determine whether or not a pressure difference between the oxygen partial pressure and the dissociation pressure is equal to or less than a predetermined value, and control the oxygen concentration inside the combustion chamber when the pressure difference is not equal to or less than the predetermined value.

In the combustion control device, the control program may further cause the processor to execute a process of determining whether the oxygen partial pressure is higher than the dissociation pressure when the pressure difference exceeds the predetermined value, and, when the oxygen partial pressure is higher than the dissociation pressure, reducing the oxygen concentration inside the combustion chamber, and, when the oxygen partial pressure is lower than the dissociation pressure, increasing the oxygen concentration inside the combustion chamber.

1 is a block diagram showing a configuration of a heat recovery system according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration of a heat exchanger in the heat recovery system according to one embodiment of the present invention. FIG. 4 is a flowchart showing an example of control of a combustion control device in the heat recovery system according to one embodiment of the present invention. FIG. 2 is a diagram showing a configuration of a heat exchanger in the heat recovery system according to one embodiment of the present invention. 1 is a block diagram showing a configuration of a heat recovery system according to an embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the drawings. However, the present invention can be implemented in various forms without departing from the spirit of the present invention, and should not be interpreted as being limited to the description of the embodiments exemplified below. In the drawings, the width, thickness, shape, etc. of each part may be shown diagrammatically compared to the actual form in order to make the explanation clearer, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, elements having the same functions as those explained with reference to the previous drawings may be given the same reference numerals, and duplicate explanations may be omitted.

First Embodiment
[Configuration of heat recovery system]
FIG. 1 is a diagram showing an example of a heat recovery system 100 according to an embodiment of the present invention. The heat recovery system 100 of this embodiment includes an incinerator 110, a combustion chamber 120, a heat exchanger 130, a cooling chamber 140, and a combustion control device 150. However, the system configuration shown in FIG. 1 is merely an example of the heat recovery system 100. Although not shown, other equipment may be provided, such as a garbage pit for accumulating collected garbage, an ash pit for accumulating ash generated in the incinerator, and a filter-type dust collector for collecting fine ash contained in the combustion gas.

The incinerator 110 is a facility that incinerates waste 202, such as municipal waste, that is brought in. The incinerator 110 converts the waste 202 into ash and renders it harmless through incineration. In this embodiment, a stoker-type incinerator is used as the incinerator 110, but this is not limited to this. When the waste 202 is incinerated in the incinerator 110, primary combustion gas 204 is generated. The primary combustion gas 204 generated in the incinerator 110 is supplied to the combustion chamber 120.

The combustion chamber 120 is a facility for reburning the primary combustion gas 204 generated in the incinerator 110. In this embodiment, the primary combustion gas 204 supplied from the incinerator 110 remains in the combustion chamber 120 for 2 seconds at a temperature of 950°C. In the combustion chamber 120, the unburned gas contained in the primary combustion gas 204 is burned, thereby completely burning the combustion gas. The secondary combustion gas 206 generated by complete combustion in the combustion chamber 120 is supplied to the heat exchanger 130 via a flue (not shown). Although not shown in FIG. 1, the combustion chamber 120 may be provided with a blower for blowing air and a damper for adjusting the amount of air supplied from the blower.

In this embodiment, the oxygen concentration meter 122 is disposed inside the combustion chamber 120. Specifically, the oxygen concentration meter 122 is disposed near the exhaust port inside the combustion chamber 120. However, the oxygen concentration meter 122 is not limited to being disposed near the exhaust port, and can be disposed at any position suitable for measuring the oxygen concentration. For example, the oxygen concentration meter 122 may be disposed in the flue connecting the combustion chamber 120 and the heat exchanger 130.

The oxygen concentration meter 122 measures the oxygen concentration contained in the secondary combustion gas 206. In this embodiment, a laser type oxygen concentration meter is used as the oxygen concentration meter 122, so it is possible to measure the oxygen concentration of the secondary combustion gas 206 in real time. Furthermore, a thermometer 124 is disposed inside the combustion chamber 120. In this embodiment, the configuration is such that the indoor temperature of the combustion chamber 120 (i.e., the gas temperature of the secondary combustion gas 206) is measured in real time. As described above, the combustion chamber 120 is suitable for measuring the oxygen concentration and indoor temperature with high accuracy because the combustion gas remains there for at least 2 seconds. The roles of the oxygen concentration meter 122 and the thermometer 124 will be described later.

In this embodiment, a gas supply device 126 is also connected to the combustion chamber 120. The gas supply device 126 is connected to the combustion control device 150, and supplies oxygen gas or an inert gas (e.g., nitrogen gas) to the combustion chamber 120 according to the control of the combustion control device 150. As described below, the combustion control device 150 is configured to measure the oxygen concentration inside the combustion chamber 120 and adjust the oxygen concentration when a predetermined condition is met. In this case, the gas supply device 126 functions as a supply source of oxygen gas or inert gas to the combustion chamber 120.

The heat exchanger 130 is a device that recovers heat from the secondary combustion gas 206 supplied from the combustion chamber 120. Specifically, in this embodiment, a vacuum hot water heater is used as the heat exchanger 130. The vacuum hot water heater is structured to reduce the pressure inside the container to a level lower than atmospheric pressure, reduce the pressure of the heat transfer water (water used as a heat transfer medium) to boil, and use the heat of the steam to extract hot water.

Figure 2 is a diagram showing the configuration of the heat exchanger 130 in the heat recovery system 100 of one embodiment of the present invention. As described above, the heat exchanger 130 is a vacuum type hot water heater. The inside of the housing 131 of the heat exchanger 130 is divided into a heating chamber 132 and a heat exchange chamber 133. The heating chamber 132 is supplied with secondary combustion gas 206 sent from the combustion chamber 120. The secondary combustion gas 206 supplied to the heating chamber 132 is used to heat the heat transfer water 134 filled in the heat exchange chamber 133, and is then discharged as combustion gas 208.

The metal member constituting the inner wall of the heating chamber 132 is exposed to the high-temperature secondary combustion gas 206 and serves to transfer the heat of the secondary combustion gas 206 to the heat exchange chamber 133. In this embodiment, the part of the heat exchanger 130 (here, a vacuum-type hot water heater) that comes into direct contact with the secondary combustion gas 206 is called the "contact part." The contact part is preferably made of an alloy material containing iron, which has excellent heat resistance and heat conductivity. For example, S-TEN steel (registered trademark), which has high corrosion resistance to sulfuric acid and hydrochloric acid, may be used as the metal material constituting the contact part.

The heat exchange chamber 133 is decompressed below atmospheric pressure. Therefore, the heat transfer water 134 boils at a reduced pressure at around 80°C, generating steam. A heat exchange section 135 is disposed above the heat transfer water 134, and heat exchange is performed using the heat of the generated steam. The heat exchange section 135 has a water supply pipe 136, through which water is supplied from an inlet 136a and hot water is obtained from an outlet 136b. The steam that has been reduced in temperature by heat exchange is exhausted from an exhaust port 131a provided at the top of the housing 131.

In this embodiment, the high-temperature (e.g., 950°C) secondary combustion gas 206 discharged from the combustion chamber 120 can be directly supplied to the heat exchanger 130. In other words, there is no need to cool the secondary combustion gas 206 discharged from the combustion chamber 120 to about 350°C before supplying it to the heat exchanger 130, as in the conventional technology. Therefore, there is no need to use a steam boiler as in the conventional technology, and heat can be recovered with high efficiency even if a heat exchanger such as a hot water heater is used.

In addition, since the vacuum type hot water heater is in a reduced pressure state inside the housing 131, it is not subject to boiler regulations. Therefore, unlike conventional technologies that use steam boilers, there is no need to appoint a boiler engineer to manage the heat exchanger 130. In this way, the heat recovery system 100 of this embodiment can use a hot water heater, which is not subject to boiler regulations, as the heat exchanger 130, thereby reducing the costs required for maintenance and equipment upkeep.

Returning to FIG. 1, the combustion gas 208 that has passed through the heat exchanger 130 is supplied to the cooling chamber 140. The cooling chamber 140 is a facility for lowering the temperature of the combustion gas 208 to approximately 350°C. The cooling chamber 140 is provided with a water injection device (not shown) that reduces the temperature of the combustion gas 208 by injecting water into the container. The combustion gas 210 that has been cooled in the cooling chamber 140 is sent to other downstream equipment (e.g., a filter-type dust collector) via a flue (not shown).

The above-described flow allows heat to be recovered from the combustion gas (specifically, the secondary combustion gas 206) generated by the incineration process of the waste 202. In this embodiment, the combustion control device 150 controls the oxygen concentration of the secondary combustion gas 206 inside the combustion chamber 120. Specifically, the combustion control device 150 adjusts the oxygen concentration inside the combustion chamber 120 using measurements obtained from the oxygen concentration meter 122 and the thermometer 124 arranged in the combustion chamber 120. By adjusting the oxygen concentration, the oxygen partial pressure of the secondary combustion gas 206 inside the combustion chamber 120 is controlled. This point will be described in detail below.

[Operation of the combustion control device]
In the heat recovery system 100 of this embodiment, the combustion control device 150 includes at least a processor and a storage unit, and executes a control program stored in the storage unit by the processor to perform combustion control of the combustion chamber 120. However, in addition to the combustion control of the combustion chamber 120, the combustion control device 150 may also perform control of other components constituting the heat recovery system 100.

In this embodiment, the combustion control device 150 adjusts the oxygen partial pressure of the secondary combustion gas 206 by controlling the oxygen concentration of the secondary combustion gas 206 generated in the combustion chamber 120. Specifically, the combustion control device 150 is configured to adjust the above-mentioned oxygen partial pressure so that the differential pressure between the dissociation pressure of the contact portion of the heat exchanger 130 and the oxygen partial pressure of the secondary combustion gas 206 is equal to or less than a predetermined value. Note that the "differential pressure" is the difference between the dissociation pressure and the oxygen partial pressure, and is expressed as a positive value. For example, the absolute value of the value obtained by subtracting the dissociation pressure from the oxygen partial pressure can be used as the differential pressure.

In this embodiment, since the secondary combustion gas 206 has a high temperature of 800° C. or more, metal materials in contact with the secondary combustion gas 206 are deteriorated by high-temperature corrosion. Here, the reaction formula of high-temperature corrosion in which a metal element M becomes _an oxide _MαOβ is expressed by formula (1).

・・・（１）

... (1)

In this case, the free energy (ΔG) of equation (1) is expressed by equation (2).

・・・（２）

... (2)

Here, ΔG ⁰ is the standard free energy of formation (also called the standard Gibbs energy of formation), R is the gas constant, T is the absolute temperature, α _x is the activity of x, and P _O2 is the partial pressure of oxygen.

The redox reaction of high-temperature corrosion is determined by the value of ΔG in formula (2). That is, if ΔG is negative, the reaction of formula (1) proceeds and the metal element M is oxidized. Conversely, if ΔG is positive, the reverse reaction of formula (1) proceeds and the oxide MαOβ is reduced. In other words, when ΔG = 0, the redox reaction of the metal element M is in equilibrium.

The oxygen partial pressure (P _O2 ) when ΔG=0 is the oxygen partial pressure at which the metal element M and the oxide M _α O _β are in equilibrium, and is called the dissociation pressure. The dissociation pressure (P _O2 ) is expressed by formula (3).

・・・（３）

...(3)

That is, when a metal element M exists in a gas containing oxygen, if the oxygen partial pressure of the gas exceeds the dissociation pressure, the metal element M is oxidized to become an oxide M _α O _β . Conversely, if the oxygen partial pressure of the gas falls below the dissociation pressure, the oxide M _α O _β is reduced to become the metal element M. This means that when the oxygen partial pressure of the gas is equal to the dissociation pressure, the metal element M is not oxidized and high-temperature corrosion does not occur.

In formula (3), the standard free energy of formation (ΔG0) is a value specific to the substance. Therefore, the dissociation pressure is also a value specific to the substance. However, as is clear from formula (3), the dissociation pressure changes with temperature. In other words, if the standard free energy of formation and temperature of a metal member are known, the dissociation pressure of the metal member can be calculated. Therefore, it can be seen that high-temperature corrosion of the metal member can be suppressed by matching the calculated dissociation pressure of the metal member with the oxygen partial pressure of the gas in contact with the metal member.

Therefore, in this embodiment, the oxygen concentration of the secondary combustion gas 206 is controlled to make the dissociation pressure of the contact portion of the heat exchanger 130 equal or approximately equal to the oxygen partial pressure of the secondary combustion gas 206, thereby bringing the oxidation-reduction reaction of the contact portion of the heat exchanger 130 into equilibrium. In other words, the combustion control device 150 can suppress deterioration of the heat exchanger 130 due to high-temperature corrosion by making the pressure difference between the dissociation pressure of the contact portion of the heat exchanger 130 and the oxygen partial pressure of the secondary combustion gas 206 equal to or less than a predetermined value.

The range within which the pressure difference between the dissociation pressure at the contact portion of the heat exchanger 130 and the oxygen partial pressure of the secondary combustion gas 206 should be kept may be appropriately selected depending on the extent to which deterioration of the heat exchanger 130 should be suppressed. For example, the combustion control device 150 may set 10% (preferably 5%, more preferably 3%) of the dissociation pressure at the contact portion of the heat exchanger 130 as a threshold value (predetermined value), and determine that the oxidation-reduction reaction at the contact portion of the heat exchanger 130 is in equilibrium when the pressure difference is equal to or less than the threshold value. The combustion control device 150 may also control the oxygen concentration so that the oxygen partial pressure of the secondary combustion gas 206 falls within a range of ±10% (preferably 5%, more preferably 3%) based on the dissociation pressure at the contact portion of the heat exchanger 130.

Since the material of the contact part of the heat exchanger 130 is known in advance, if the temperature can be specified, the dissociation pressure of the contact part can be obtained. Furthermore, if the oxygen concentration of the secondary combustion gas 206 (i.e., the oxygen concentration inside the combustion chamber 120) and the gas flow rate are known, the oxygen partial pressure of the secondary combustion gas 206 can be obtained. Therefore, in this embodiment, an oxygen concentration meter 122 is disposed near the exhaust port of the combustion chamber 120 to measure the oxygen concentration of the secondary combustion gas 206. The temperature measured by the thermometer 124 and the pressure inside the combustion chamber 120 measured by a pressure gauge (not shown) can be used to measure the gas flow rate.

In addition, in this embodiment, a thermometer 124 is disposed inside the combustion chamber 120 to measure the temperature inside the combustion chamber 120. Therefore, the combustion control device 150 can obtain the dissociation pressure of the contact part of the heat exchanger 130 in response to the temperature change based on the temperature obtained from the thermometer 124. For example, when the heat recovery system 100 is operated intermittently instead of continuously, the temperature of the secondary combustion gas 206 changes when the temperature of the combustion chamber 120 increases and decreases. Even in this case, by measuring the temperature of the combustion chamber 120 in real time, it is possible to obtain the change in the dissociation pressure at the contact part of the heat exchanger 130 in accordance with the change in the temperature inside the combustion chamber 120. Therefore, if the heat recovery system 100 is operated intermittently, even if the temperature of the combustion chamber 120 is increasing or decreasing, the high-temperature corrosion of the contact part can be suppressed by changing the oxygen partial pressure according to the change in the dissociation pressure.

In addition, when the heat recovery system 100 is operated continuously, or when it is not necessary to take into account the temperature rise or fall of the combustion chamber 120, the dissociation pressure of the contact part of the heat exchanger 130 may be obtained assuming that the indoor temperature of the combustion chamber 120 is constant. In this case, it is not necessary to know the indoor temperature of the combustion chamber 120, and the thermometer 124 can be omitted.

As described above, the combustion control device 150 in the heat recovery system 100 of this embodiment controls the oxygen concentration of the secondary combustion gas 206 generated in the combustion chamber 120, thereby adjusting the oxygen concentration of the secondary combustion gas 206 (oxygen concentration in the combustion chamber 120) so that the pressure difference between the dissociation pressure of the contact portion of the heat exchanger 130 and the oxygen partial pressure of the secondary combustion gas 206 is equal to or less than a predetermined value. This makes it possible to suppress deterioration due to high-temperature corrosion of the contact portion of the heat exchanger 130 (the portion of the heat exchanger 130 that contacts the secondary combustion gas 206) caused by the secondary combustion gas 206.

[Control flow of the combustion control device]
Fig. 3 is a flow chart showing an example of the control of the combustion control device 150 in the heat recovery system 100 according to one embodiment of the present invention. The control shown in Fig. 3 is performed by a processor included in the combustion control device 150 executing a control program stored in a storage unit. Note that Fig. 3 shows an example in which the control program is executed periodically at a predetermined interval, but the control program may be executed continuously by loop processing.

In FIG. 3, when the control program is executed, the combustion control device 150 acquires the temperature inside the combustion chamber 120 from the thermometer 124 (step S301). In this embodiment, the temperature inside the combustion chamber 120 is set to 950°C. In other words, the temperature of the secondary combustion gas 206 generated in the combustion chamber 120 can be considered to be 950°C.

Next, the combustion control device 150 calculates the dissociation pressure of the contact portion in the heat exchanger 130 based on the acquired temperature (step S302). In this embodiment, since a steel material such as S-TEN steel is used as the constituent material of the contact portion, the standard free energy of formation is known. Therefore, if the temperature can be acquired, the dissociation pressure of the contact portion can be calculated by the above-mentioned formula (3). Note that, although an example of calculating the dissociation pressure is shown here, the present invention is not limited to this example. For example, a reference table that associates temperatures with dissociation pressures may be prepared in advance, and the dissociation pressure may be acquired from the reference table based on the acquired temperature.

After calculating the dissociation pressure, the combustion control device 150 obtains the oxygen concentration inside the combustion chamber 120 from the oxygen concentration meter 122 (step S303). In this embodiment, a laser type oxygen concentration meter is used as the oxygen concentration meter 122, so that the oxygen concentration inside the combustion chamber 120 can be measured in real time. The oxygen concentration meter 122 is disposed so as to measure the oxygen concentration near the exhaust port of the combustion chamber 120. Therefore, the oxygen concentration measured by the oxygen concentration meter 122 can be regarded as the oxygen concentration of the secondary combustion gas 206 generated in the combustion chamber 120.

Next, the combustion control device 150 calculates the oxygen partial pressure of the secondary combustion gas 206 based on the acquired oxygen concentration (step S304). Since the shape of the combustion chamber 120 is known and the temperature inside the combustion chamber 120 has already been acquired, the gas flow rate of the secondary combustion gas 206 in the area where the oxygen concentration meter 122 is placed can also be calculated. Therefore, if the oxygen concentration can be acquired, the oxygen partial pressure of the secondary combustion gas 206 can be calculated. However, this is not limited to this example, and if the gas flow rate is known, a reference table that associates oxygen concentration with oxygen partial pressure may be prepared in advance, and the oxygen partial pressure may be acquired from the reference table based on the acquired oxygen concentration.

After the oxygen partial pressure of the secondary combustion gas 206 and the dissociation pressure of the contact portion of the heat exchanger 130 are obtained through the above-mentioned process, the combustion control device 150 calculates the differential pressure between the oxygen partial pressure and the dissociation pressure, and judges whether the calculated differential pressure is equal to or less than a predetermined value (i.e., whether the oxygen partial pressure falls within a predetermined range based on the dissociation pressure) (step S305). In this embodiment, the combustion control device 150 judges whether the differential pressure between the oxygen partial pressure and the dissociation pressure is equal to or less than a predetermined value (e.g., 10% of the dissociation pressure). Through this judgment process, the combustion control device 150 can grasp whether the oxygen partial pressure of the secondary combustion gas 206 and the dissociation pressure of the contact portion of the heat exchanger 130 are in equilibrium.

If the determination in step S305 is YES, the combustion control device 150 ends the control process because the oxygen partial pressure of the secondary combustion gas 206 is in equilibrium with the dissociation pressure of the contact portion of the heat exchanger 130. If the determination in step S305 is NO, the combustion control device 150 determines whether the oxygen partial pressure is higher than the dissociation pressure (step S306).

If the determination in step S306 is YES, the combustion control device 150 reduces the oxygen concentration inside the combustion chamber 120 (step S307). Specifically, the combustion control device 150 controls the gas supply device 126 to supply a predetermined amount of inert gas into the combustion chamber 120. By supplying the inert gas, the oxygen concentration inside the combustion chamber 120 can be relatively reduced. If the determination in step S306 is NO, the combustion control device 150 increases the oxygen concentration inside the combustion chamber 120 (step S308). Specifically, the combustion control device 150 controls the gas supply device 126 to supply a predetermined amount of oxygen gas into the combustion chamber 120. By supplying the oxygen gas, the oxygen concentration inside the combustion chamber 120 can be relatively increased. In this way, the combustion control device 150 can monitor the oxygen concentration in the combustion chamber 120 in real time and control the oxygen concentration inside the combustion chamber 120 (i.e., the oxygen partial pressure of the secondary combustion gas 206).

When the supply of gas by the control process of step S307 or step S308 is completed, the combustion control device 150 returns the control process to step S301. Thereafter, the combustion control device 150 again performs the control process from step S301 onwards, and continues to execute the control program until the differential pressure between the oxygen partial pressure and the dissociation pressure becomes equal to or less than a predetermined value. Finally, when the differential pressure between the oxygen partial pressure and the dissociation pressure becomes equal to or less than the predetermined value and the determination of step S305 becomes YES, the combustion control device 150 ends the execution of the control program.

As described above, the heat recovery system 100 of this embodiment is equipped with the combustion control device 150, and thus can monitor the oxygen concentration inside the combustion chamber 120 (i.e., the oxygen partial pressure of the secondary combustion gas 206). In addition, the heat recovery system 100 controls the oxygen concentration inside the combustion chamber 120 according to the result of comparing the oxygen partial pressure of the secondary combustion gas 206 calculated by the combustion control device 150 with the dissociation pressure of the contact part of the heat exchanger 130, and can keep the oxygen partial pressure and the dissociation pressure within the same or approximately the same range. As a result, the heat recovery system 100 can maintain an equilibrium state between the high-temperature secondary combustion gas 206 of about 950 ° C. even when it contacts the contact part of the heat exchanger 130. In this way, since heat exchange can be performed using the high-temperature secondary combustion gas 206, heat can be recovered with high efficiency even if a heat exchanger that is not subject to legal regulations such as a hot water heater is used. In other words, according to this embodiment, it is possible to provide a heat recovery system 100 that suppresses high-temperature corrosion with a simple structure and improves heat recovery efficiency.

In addition, the order of the control flow from step S301 to step S304 in Fig. 3 is not limited to this example. For example, the control flow in Fig. 3 may acquire the temperature after acquiring the oxygen concentration. Also, the control flow in Fig. 3 may calculate the dissociation pressure and oxygen partial pressure after acquiring the oxygen concentration and temperature.

(Variation 1)
In the present embodiment, the combustion control device 150 is controlled to keep the pressure difference between the dissociation pressure at the contact portion of the heat exchanger 130 and the oxygen partial pressure of the secondary combustion gas 206 below a predetermined value, but from the viewpoint of suppressing deterioration of the contact portion of the heat exchanger 130, the present invention is not limited to this example. For example, when the oxygen partial pressure of the secondary combustion gas 206 exceeds the dissociation pressure at the contact portion of the heat exchanger 130, the pressure difference is kept below the above-mentioned predetermined value, and when the oxygen partial pressure is below the dissociation pressure, no particular restriction may be set. In other words, the combustion control device 150 may adjust the oxygen concentration of the secondary combustion gas 206 so that the oxygen partial pressure of the secondary combustion gas 206 is below the dissociation pressure at the contact portion of the heat exchanger 130.

In this case, the contact parts of the heat exchanger 130 are always placed in a reducing atmosphere, which helps prevent deterioration of the contact parts due to high-temperature corrosion.

(Variation 2)
In this embodiment, an example is shown in which a vacuum type hot water heater is used as the heat exchanger 130, but the present invention is not limited to this example. For example, an atmospheric pressure type hot water heater can also be used as the heat exchanger 130. The atmospheric pressure type hot water heater is structured to boil heat transfer water with the inside of the container open to the atmosphere, and to extract hot water by using the heat of the steam. The atmospheric pressure type hot water heater is also called a non-pressure type hot water heater because no pressure is applied inside the container.

Figure 4 is a diagram showing the configuration of a heat exchanger 130 used in a heat recovery system 100 according to one embodiment of the present invention. Specifically, Figure 4 shows the configuration of an atmospheric pressure hot water heater 230 used as the heat exchanger 130. In the atmospheric pressure hot water heater 230, the inside of a housing 231 is divided into a heating chamber 232 and a medium chamber 233. The heating chamber 232 is supplied with secondary combustion gas 206 sent from the combustion chamber 120. The secondary combustion gas 206 supplied to the heating chamber 232 is used to heat the heat transfer water 234 filled in the medium chamber 233, and is then discharged as combustion gas 208.

The heat transfer water 234 heated in the medium chamber 233 is supplied to the heat exchange section 235, where heat exchange is carried out using the heat of the heated heat transfer water 234. The heat exchange section 235 has a water supply pipe 236, to which water is supplied from an inlet 236a and hot water is obtained from an outlet 236b. A pump 237 is provided between the medium chamber 233 and the heat exchange section 235. The pump 237 serves to circulate the heat transfer water 234 between the medium chamber 233 and the heat exchange section 235.

In this embodiment, the high-temperature (e.g., 950°C) secondary combustion gas 206 discharged from the combustion chamber 120 can be directly supplied to the heat exchanger 130. In other words, there is no need to cool the secondary combustion gas 206 discharged from the combustion chamber 120 to about 350°C before supplying it to the heat exchanger 130, as in the conventional technology. Therefore, there is no need to use a steam boiler as in the conventional technology, and high heat recovery efficiency can be ensured even when a heat exchanger such as a hot water heater is used.

In addition, the atmospheric pressure hot water heater 230 has an opening 231a at the top of the housing 231, and the inside of the housing 231 is maintained at atmospheric pressure. Therefore, the internal pressure of the housing 231 of the atmospheric pressure hot water heater 230 does not become high pressure, and the atmospheric pressure hot water heater 230 is not subject to boiler legal regulations. Therefore, when the atmospheric pressure hot water heater 230 is used as the heat exchanger 130, there is no need to assign a boiler engineer as a manager. In other words, since a hot water heater that is not subject to legal regulations can be used as the heat exchanger 130, the costs required for maintenance and equipment upkeep can be reduced.

(Variation 3)
In the heat recovery system 100 of this embodiment, any heat exchanger other than the above-mentioned vacuum type hot water heater and atmospheric pressure type hot water heater can be used as the heat exchanger 130. In this embodiment, since the high-temperature secondary combustion gas 206 discharged from the combustion chamber 120 can be directly supplied to the heat exchanger 130, high heat recovery efficiency can be achieved regardless of the type of heat exchanger used.

(Variation 4)
In the control flow shown in Fig. 3, an example is shown in which the differential pressure between the oxygen partial pressure and the dissociation pressure is calculated in step S305, and it is determined whether or not the calculated differential pressure is equal to or lower than a predetermined value (i.e., whether or not the oxygen partial pressure falls within a predetermined range based on the dissociation pressure), but the present invention is not limited to this example. For example, in Fig. 3, step S305 may be omitted.

In this case, the combustion control device 150 calculates the dissociation pressure of the contact portion of the heat exchanger 130 in step S302, calculates the oxygen partial pressure of the secondary combustion gas 206 in step S304, and then determines in step S306 whether the oxygen partial pressure is higher than the dissociation pressure. Then, depending on the result of this determination, the combustion control device 150 executes the control process of step S307 or step S308 to increase or decrease the oxygen concentration in the combustion chamber 120. After controlling the oxygen concentration in this way, the combustion control device 150 repeats the control process again from step S301.

The combustion control device 150 of this modification constantly executes the above-mentioned loop process, and feeds back the comparison result between the oxygen partial pressure and the dissociation pressure to keep the oxygen partial pressure and the dissociation pressure within the same or approximately the same range. This makes it possible to maintain an equilibrium state between the contact part of the heat exchanger 130 and the secondary combustion gas 206 generated in the combustion chamber 120.

Second Embodiment
In the first embodiment, an example in which the oxygen concentration inside the combustion chamber 120 is adjusted using the gas supply device 126 has been described, but the present invention is not limited to this example. For example, the oxygen concentration inside the combustion chamber 120 can also be adjusted by using an air flow rate adjustment device such as a damper or a valve to adjust the amount of air supplied to the combustion chamber 120.

Figure 5 is a block diagram showing the configuration of a heat recovery system 100a according to one embodiment of the present invention. In Figure 5, the same elements as those in the heat recovery system 100 described in the first embodiment are given the same reference numerals and will not be described.

As shown in FIG. 5, the heat recovery system 100a of this embodiment includes a blower 127 and a damper 128. The blower 127 supplies air to the combustion chamber. The damper 128 is provided between the blower 127 and the combustion chamber 120, and adjusts the amount of air supplied to the combustion chamber 120. In other words, the damper 128 functions as an air volume adjustment device that adjusts the flow rate of air supplied to the combustion chamber 120.

In this embodiment, the combustion control device 150a controls the damper 128. Specifically, the combustion control device 150a can adjust the amount of air supplied to the combustion chamber 120 by controlling the damper 128. That is, the combustion control device 150a can adjust the oxygen concentration inside the combustion chamber 120 by adjusting the amount of air supplied to the combustion chamber 120. For example, referring to the control flow shown in FIG. 3 in the first embodiment, the combustion control device 150a can lower (step S307) or raise (step S308) the oxygen concentration inside the combustion chamber 120 by controlling the damper 128 according to the judgment of step S306. In this way, the combustion control device 150a can monitor the oxygen concentration in the combustion chamber 120 in real time and control the oxygen concentration inside the combustion chamber 120 (i.e., the oxygen partial pressure of the secondary combustion gas 206).

The embodiments of the present invention and their variations can be combined as appropriate as long as they are not mutually inconsistent. Based on the heat recovery system of the above-mentioned embodiment, a person skilled in the art can add or remove components or modify the design, or add or omit processes or change conditions, and these are also included in the scope of the present invention as long as they include the gist of the present invention.

Furthermore, even if there are other effects and advantages different from those brought about by the above-mentioned embodiments, if they are clear from the description in this specification or can be easily predicted by a person skilled in the art, they are naturally understood to be brought about by the present invention.

100, 100a... heat recovery system, 110... incinerator, 120... combustion chamber, 122... oxygen concentration meter, 124... thermometer, 126... gas supply device, 127... blower, 128... damper, 130... heat exchanger, 131... housing, 131a... exhaust port, 132... heating chamber, 133... heat exchange chamber, 134... heat transfer water, 135... heat exchange section, 136... water supply pipe, 136a... inlet, 136b... outlet, 14 0...cooling chamber, 150, 150a...combustion control device, 202...waste, 204...primary combustion gas, 206...secondary combustion gas, 208...combustion gas, 210...combustion gas, 230...atmospheric pressure hot water heater, 231...casing, 231a...opening, 232...heating chamber, 233...medium chamber, 234...heat transfer water, 235...heat exchange section, 236...water supply pipe, 236a...inlet, 236b...outlet, 237...pump

Claims (16)

A combustion chamber;
a heat exchanger to which the combustion gas generated in the combustion chamber is supplied;
A combustion control device for controlling an oxygen concentration of the combustion gas;
Equipped with
The combustion chamber has an oxygen concentration meter for measuring an oxygen concentration of the combustion gas,
The combustion control device is a heat recovery system that controls the oxygen concentration so that the pressure difference between the dissociation pressure of a contact portion that is part of the heat exchanger and comes into contact with the combustion gas and the oxygen partial pressure of the combustion gas is equal to or less than a predetermined value. The combustion chamber further includes a thermometer for measuring a temperature of the combustion gas.
The heat recovery system according to claim 1 , wherein the combustion control device calculates the dissociation pressure based on the temperature. The combustion chamber further includes a gas supply device for supplying oxygen gas or an inert gas to the combustion chamber,
The heat recovery system according to claim 1 or 2, wherein the combustion control device controls the gas supply device in accordance with the oxygen concentration. The combustion chamber further includes an air flow rate adjusting device for adjusting the amount of air supplied to the combustion chamber.
The heat recovery system according to claim 1 or 2, wherein the combustion control device controls the air volume regulator in accordance with the oxygen concentration. The heat recovery system according to any one of claims 1 to 4, wherein the heat exchanger is a vacuum or non-pressure type hot water heater. The heat recovery system according to any one of claims 1 to 5, further comprising a cooling chamber to which the combustion gas that has passed through the heat exchanger is supplied. The heat recovery system according to any one of claims 1 to 6, further comprising an incinerator that supplies primary combustion gas to the combustion chamber. The heat recovery system according to any one of claims 1 to 7, wherein the oxygen concentration meter is a laser type oxygen concentration meter. Measure the oxygen concentration of the combustion gas generated in the combustion chamber,
controlling the oxygen concentration so that a pressure difference between a dissociation pressure of a part of a heat exchanger connected to the combustion chamber that comes into contact with the combustion gas and an oxygen partial pressure of the combustion gas is equal to or less than a predetermined value;
supplying the combustion gas, the oxygen concentration of which has been controlled, to the heat exchanger. further comprising measuring a temperature of the combustion gas;
The heat recovery method according to claim 9 , wherein the dissociation pressure is calculated based on the temperature . The heat recovery method according to claim 9 or 10, in which a vacuum or non-pressure hot water heater is used as the heat exchanger. The heat recovery method according to any one of claims 9 to 11, further comprising supplying the combustion gas that has passed through the heat exchanger to a cooling chamber. The heat recovery method according to any one of claims 9 to 12, further comprising supplying primary combustion gas generated in an incinerator to the combustion chamber. The heat recovery method according to any one of claims 9 to 13, wherein the oxygen concentration is measured by a laser type oxygen concentration meter. A combustion control device including a memory unit that stores a control program and a processor that executes the control program,
The control program includes:
Obtain the temperature inside the combustion chamber,
Obtaining an oxygen concentration inside the combustion chamber;
Calculating the oxygen partial pressure of the combustion gas generated in the combustion chamber using the oxygen concentration;
Calculating a dissociation pressure of a part of a heat exchanger that is in contact with the combustion gas using the temperature;
determining whether a differential pressure between the oxygen partial pressure and the dissociation pressure is equal to or less than a predetermined value;
A combustion control device that causes the processor to control the oxygen concentration inside the combustion chamber when the pressure difference is not equal to or less than the predetermined value. The control program further comprises:
When the differential pressure is not equal to or less than the predetermined value, it is determined whether the oxygen partial pressure is higher than the dissociation pressure;
16. The combustion control device according to claim 15, wherein the processor is configured to execute a process of decreasing the oxygen concentration inside the combustion chamber when the oxygen partial pressure is higher than the dissociation pressure, and increasing the oxygen concentration inside the combustion chamber when the oxygen partial pressure is lower than the dissociation pressure.

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