Heat recovery system and heat recovery method

Abstract

To provide a heat recovery system of a simple structure and improved heat recovery efficiency, capable of suppressing high-temperature corrosion.SOLUTION: The heat recovery system comprises a biogas generation device, an incineration furnace, a combustion chamber to which biogas generated in the biogas generation device and primary combustion gas generated in the incineration furnace are supplied, a heat exchanger to which combustion gas generated in the combustion chamber is supplied, and a combustion controller that controls the oxygen concentration in the combustion gas, with the combustion chamber comprising an oximeter measuring the oxygen concentration in the combustion gas, and the combustion controller controlling the oxygen concentration so that the differential pressure between the dissociation pressure of the contact part of the heat exchanger and the partial pressure of oxygen in the combustion gas is not greater than a predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a heat recovery system and a heat recovery method, and more particularly to a heat recovery system including a combustion control device having a function of controlling the oxygen concentration in a combustion chamber. [Background technology]

[0002] Conventionally, in waste incineration facilities that incinerate waste such as municipal waste, there is known a heat recovery system that recovers and reuses heat generated during the incineration process. In such a heat recovery system, collected municipal waste is burned in an incinerator, and then 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, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-24504 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional heat recovery systems, exhaust gas generated in an incinerator is further completely combusted in a re-burning 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 re-burning chamber at a temperature of 850°C or higher (preferably 900°C or higher) for more than two seconds. Therefore, the temperature of the combustion gas discharged from the re-burning chamber is also high, at 900°C or higher.

[0005] Here, if high-temperature gas of 900°C or more is directly supplied to a heat exchanger, there is a problem that the metal components constituting the heat exchanger (especially the parts that directly contact 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, in consideration of suppressing dioxin resynthesis, the combustion gas discharged from the reburning chamber was cooled to approximately 350°C before being supplied to the heat exchanger.

[0006] As described above, conventional heat recovery systems require heat recovery from combustion gas whose temperature has been reduced to around 350°C, and therefore generally use a steam boiler as a heat exchanger to ensure heat recovery efficiency. However, steam boilers require the operation of a qualified person (boiler engineer) because the vessel is highly pressurized, which leads to increased costs for maintenance and equipment upkeep.

[0007] An object of the present invention is to provide a heat recovery system having a simple structure, which suppresses high-temperature corrosion and improves heat recovery efficiency. [Means for solving the problem]

[0008] A heat recovery system according to one embodiment of the present invention includes a biogas generator, an incinerator, a combustion chamber to which the biogas generated in the biogas generator and the primary combustion gas generated in the incinerator are supplied, a heat exchanger to which the combustion gas generated in the combustion chamber is supplied, and a combustion control device that controls the oxygen concentration of the combustion gas. The combustion chamber has an oxygen concentration meter that measures the oxygen concentration of the combustion gas, and the combustion control device measures the oxygen concentration of the combustion gas at the contact portion of the heat exchanger. dissociation The oxygen concentration is controlled so that the pressure difference between the partial pressure of oxygen in the combustion gas and the pressure in the exhaust gas is equal to or less than a predetermined value.

[0009] A heat recovery system according to one embodiment of the present invention includes a biogas generator, an incinerator to which biogas generated in the biogas generator is supplied, a combustion chamber to which primary combustion gas generated in the incinerator is supplied, 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. The combustion chamber has an oxygen concentration meter that measures the oxygen concentration of the combustion gas, and the combustion control device is a device that measures the oxygen concentration of the combustion gas at a contact portion of the heat exchanger. dissociation The oxygen concentration is controlled so that the pressure difference between the partial pressure of oxygen in the combustion gas and the pressure in the exhaust gas is equal to or less than a predetermined value.

[0010] The heat recovery system may further comprise a gas generator supplied with the biogas.

[0011] In the heat recovery system, the biogas generator may include a treatment tank and a biological sludge bed provided inside the treatment tank. In this case, the biogas generator may further include a sludge settler provided above the biological sludge bed and having an inclined surface facing the biological sludge bed. The sludge settler may be movable in the vertical direction inside the treatment tank.

[0012] 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 determine the temperature of the combustion gas based on the temperature. dissociation The pressure may be calculated.

[0013] 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 in accordance with the oxygen concentration.

[0014] The heat recovery system may further include an air flow rate regulator that regulates the amount of air supplied to the combustion chamber. In this case, the combustion control device may control the air flow rate regulator in response to the oxygen concentration.

[0015] In the heat recovery system, the heat exchanger may be a vacuum or non-pressure type hot water heater.

[0016] The heat recovery system may further include a cooling chamber to which the combustion gas that has passed through the heat exchanger is supplied.

[0017] In the heat recovery system, the oxygen concentration meter may be a laser type oxygen concentration meter.

[0018] In one embodiment of the present invention, a heat recovery method includes supplying a biogas generated in a biogas generator and a primary combustion gas generated in an incinerator to a combustion chamber, burning the biogas and the primary combustion gas in the combustion chamber, measuring an oxygen concentration of the combustion gas generated, and measuring an oxygen concentration of a contact part of a heat exchanger connected to the combustion chamber. dissociation The present invention also includes controlling the oxygen concentration so that a pressure difference between the partial pressure of oxygen in the combustion gas and the pressure in the exhaust gas is equal to or less than a predetermined value, and supplying the combustion gas in which the oxygen concentration has been controlled to the heat exchanger.

[0019] In one embodiment of the present invention, a heat recovery method includes: supplying biogas generated in a biogas generating apparatus to an incinerator; supplying primary combustion gas generated in the incinerator to a combustion chamber; measuring an oxygen concentration of the combustion gas generated by burning the primary combustion gas in the combustion chamber; dissociation The present invention also includes controlling the oxygen concentration so that a pressure difference between the partial pressure of oxygen in the combustion gas and the pressure in the exhaust gas is equal to or less than a predetermined value, and supplying the combustion gas in which the oxygen concentration has been controlled to the heat exchanger.

[0020] In the heat recovery method, the biogas generator may include a treatment tank and a biological sludge bed provided inside the treatment tank. In this case, the biogas generator may further include a sludge settler provided above the biological sludge bed and having an inclined surface facing the biological sludge bed. The sludge settler may be movable in the vertical direction inside the treatment tank.

[0021] The heat recovery method may further include measuring a temperature of the combustion gas. dissociation The pressure may be calculated based on the temperature.

[0022] The heat recovery method may use a vacuum type or non-pressure type hot water heater as the heat exchanger.

[0023] The heat recovery method may further include supplying the combustion gas that has passed through the heat exchanger to a cooling chamber.

[0024] In the heat recovery method, the oxygen concentration may be measured by a laser type oxygen concentration meter. [Brief description of the drawings]

[0025] [Figure 1] 1 is a block diagram showing a configuration of a heat recovery system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a configuration of a heat exchanger in the heat recovery system according to the first embodiment of the present invention. [Diagram 3] FIG. 2 is a flow chart showing an example of control of a combustion control device in the heat recovery system according to the first embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing a configuration of a biogas generation device according to a first embodiment. [Diagram 5] FIG. 2 is a diagram showing the configuration of a sludge settler in the biogas production apparatus of the first embodiment. [Figure 6] FIG. 2 is a diagram showing the configuration of a flow straightening unit in the biogas production apparatus of the first embodiment. [Figure 7] FIG. 2 is a diagram showing the configuration of the biogas generation apparatus of the first embodiment in a first state. [Figure 8] FIG. 4 is a diagram showing the configuration of the biogas generation apparatus of the first embodiment in a second state. [Figure 9] FIG. 2 is a diagram for explaining the state of the reaction area in a first state. [Figure 10] FIG. 4 is a diagram showing the configuration of a modified example of the heat exchanger in the heat recovery system according to the first embodiment of the present invention. [Figure 11] FIG. 4 is a block diagram showing a configuration of a heat recovery system according to a second embodiment of the present invention. [Figure 12] FIG. 11 is a block diagram showing a configuration of a heat recovery system according to a third embodiment of the present invention. [Figure 13] FIG. 11 is a block diagram showing a configuration of a heat recovery system according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention can be implemented in various forms without departing from the gist 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 described with respect to the previous drawings may be given the same reference numerals, and duplicate explanations may be omitted.

[0027] (First embodiment) [Heat recovery system configuration] FIG. 1 is a diagram showing an example of a heat recovery system 100 in a first embodiment of the present invention. The heat recovery system 100 of this embodiment includes a biogas generator 110, an incinerator 115, 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 only one 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, an acid generator for denaturing high molecular organic matter contained in wastewater or sewage into low molecular organic matter using microorganisms, a storage tank for storing excess sludge discharged from the biogas generator, and a filter-type dust collector for collecting fine ash contained in the combustion gas.

[0028] The biogas generator 110 is a treatment facility that uses anaerobic microorganisms to decompose organic matter contained in wastewater 201, which includes industrial wastewater, human waste, domestic sewage, etc. In the biogas generator 110, organic matter in the wastewater 201, such as lower organic acids, is treated by the anaerobic microorganisms and decomposed into biogas 202, such as methane gas, carbon dioxide, and hydrogen. The biogas 202 generated in the biogas generator 110 is supplied to the combustion chamber 120. For ease of explanation, only the biogas generator 110 is shown in FIG. 1, but a facility for pre-treating the wastewater 201 (such as a heating tank or an acid generator) may be provided upstream of the biogas generator 110.

[0029] In this embodiment, an anaerobic treatment device of UASB (Upflow Anaerobic Sludge Bed) type is used as the biogas generator 110. The UASB type anaerobic treatment device is characterized in that it uses a biological sludge bed in which anaerobic microorganisms having methane fermentation ability are granulated and held at a high density. The granulated anaerobic microorganisms exist in the treatment tank as black granules, and the aggregate of the granules functions as the biological sludge bed. Note that, although anaerobic microorganisms are exemplified in the description of this embodiment, aerobic microorganisms can also be used. The specific structure of the biogas generator 110 of this embodiment will be described later.

[0030] The incinerator 115 is a facility for incinerating waste 203 such as urban waste that has been brought in. The incinerator 115 converts the waste 203 into ash and renders it harmless through incineration processing. In this embodiment, a stoker-type incinerator is used as the incinerator 115, but is not limited to this. When the waste 203 is incinerated in the incinerator 115, primary combustion gas 204 is generated. The primary combustion gas 204 generated in the incinerator 115 is supplied to the combustion chamber 120.

[0031] The combustion chamber 120 is a facility for reburning the primary combustion gas 204 generated in the incinerator 115. In this embodiment, in addition to the primary combustion gas 204, the biogas generated in the biogas generator 110 is also supplied to the combustion chamber 120. The supplied biogas can be used as ignition fuel at the start of operation, or as auxiliary energy to increase the internal temperature of the combustion chamber 120. In this embodiment, the supplied gas is retained for 2 seconds at a temperature of 950°C inside the combustion chamber 120. Therefore, in the combustion chamber 120, the combustible gas (e.g., methane gas) contained in the biogas 202 and the unburned gas contained in the primary combustion gas 204 are completely burned. 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.

[0032] 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 may be disposed at any position suitable for measuring the oxygen concentration. For example, the oxygen concentration meter 122 may be disposed in a flue connecting the combustion chamber 120 and the heat exchanger 130.

[0033] 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 combustion chamber 120 is configured to measure the indoor temperature of the combustion chamber 120 (i.e., the gas temperature of the secondary combustion gas 206) 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 therein for at least 2 seconds. The roles of the oxygen concentration meter 122 and the thermometer 124 will be described later.

[0034] A gas supply device 126 is also connected to the combustion chamber 120 of this embodiment. 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 satisfied. At that time, the gas supply device 126 functions as a supply source of oxygen gas or inert gas to the combustion chamber 120.

[0035] The heat exchanger 130 is a facility that recovers heat from the secondary combustion gas 206 supplied from the combustion chamber 120. Specifically, in this embodiment, a vacuum type hot water heater is used as the heat exchanger 130. The vacuum type hot water heater is structured to reduce the pressure inside a container to a pressure lower than atmospheric pressure, reduce the pressure of heat transfer water (water used as a heat transfer medium) to boil, and use the heat of the steam to extract hot water.

[0036] 2 is a diagram showing the configuration of the heat exchanger 130 in the heat recovery system 100 of the first embodiment of the present invention. As described above, the heat exchanger 130 is a vacuum type hot water heater. In the heat exchanger 130, the inside of the housing 131 is divided into a heating chamber 132 and a heat exchange chamber 133. A secondary combustion gas 206 sent from the combustion chamber 120 is supplied to the heating chamber 132. 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 then discharged as a combustion gas 208.

[0037] The metal member constituting the inner wall of the heating chamber 132 has a role of transferring heat of the secondary combustion gas 206 to the heat exchange chamber 133 while being exposed to the high-temperature secondary combustion gas 206. 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 against sulfuric acid and hydrochloric acid, may be used as the metal material constituting the contact part.

[0038] The heat exchange chamber 133 is decompressed below atmospheric pressure. Therefore, the heat transfer water 134 boils at a reduced pressure at about 80°C to generate 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, to which water is supplied from an inlet 136a and hot water is obtained from an outlet 136b. The steam whose temperature has been reduced by the heat exchange is exhausted from an exhaust port 131a provided at the top of the housing 131.

[0039] 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, unlike the conventional technology, it is not necessary 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. Therefore, it is not necessary 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.

[0040] In addition, the vacuum type hot water heater is not subject to boiler regulations because the inside of the housing 131 is in a reduced pressure state. Therefore, unlike the conventional technology that uses a steam boiler, 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 that is not subject to boiler regulations as the heat exchanger 130, and therefore the costs required for maintenance and equipment upkeep can be reduced.

[0041] Returning to the explanation of 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 about 350°C. A water injection device (not shown) is provided in the cooling chamber 140, and the temperature of the combustion gas 208 is reduced by injecting water into the container. The combustion gas 210 whose temperature has been reduced in the cooling chamber 140 is sent to other downstream equipment (for example, a filter-type dust collector) via a flue (not shown).

[0042] According to the flow described above, heat can be recovered from the combustion gas (specifically, the secondary combustion gas 206) obtained by burning the biogas 202 generated by the decomposition process of organic matter (organic matter in the wastewater 201) using anaerobic microorganisms and the primary combustion gas 204 generated by the incineration process of the waste material 203. At this time, 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 the measured values ​​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.

[0043] [Operation of 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 execute control of other components constituting the heat recovery system 100.

[0044] 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. dissociation The oxygen partial pressure is adjusted so that the pressure difference between the pressure of the combustion gas 202 and the oxygen partial pressure of the secondary combustion gas 206 is equal to or less than a predetermined value. dissociation It is the difference between the oxygen partial pressure and the oxygen pressure, and is expressed as a positive value. For example, from the oxygen partial pressure dissociation The absolute value of the pressure subtracted can be used as the differential pressure.

[0045] In this embodiment, the secondary combustion gas 206 is at a high temperature of 800° C. or more, and therefore, metal materials in contact with the secondary combustion gas 206 are deteriorated by high-temperature corrosion.α O β The reaction equation for high-temperature corrosion is expressed as follows:

[0046]

number

[0047] In this case, the free energy (ΔG) of equation (1) is expressed by equation (2).

[0048]

number

[0049] 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, P O2 is the partial pressure of oxygen.

[0050] 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 M is oxidized. α O β is reduced. In other words, when ΔG = 0, the oxidation-reduction reaction of the metal element M is in equilibrium.

[0051] The partial pressure of oxygen when ΔG=0 (P O2 ) is a metal element M and an oxide M α O β is the oxygen partial pressure at which equilibrium occurs. dissociation It's called pressure. dissociation Pressure (P O2 ) is expressed by equation (3).

[0052]

number

[0053] In other words, when metal element M exists in a gas containing oxygen, the oxygen partial pressure of the gas is dissociation When the pressure exceeds 1000 K, the metal element M is oxidized to form the oxide M. α O β Conversely, if the oxygen partial pressure of the gas is dissociation Below this pressure, the oxide M α O β is reduced to metal element M. This means that the oxygen partial pressure of the gas is dissociation This means that when the pressure is consistent with that of the metal element M, it will not be oxidized and will not be subject to high temperature corrosion.

[0054] In equation (3), the standard free energy of formation (ΔG 0 ) is a value specific to each material. Therefore, dissociation Pressure is also a value specific to the material. However, as is clear from equation (3), dissociation The pressure changes depending on the temperature. In other words, if the standard free energy of formation of a metal component and the temperature are known, the dissociation Therefore, the calculated pressure of the metal member can be calculated. dissociation It can be seen that high-temperature corrosion of the metal members can be suppressed by matching the oxygen partial pressure of the gas in contact with the metal members.

[0055] Therefore, in this embodiment, the oxygen concentration of the secondary combustion gas 206 is controlled to reduce the amount of oxygen in the contact area of ​​the heat exchanger 130. dissociation By making the pressure of the combustion gas 204 equal or approximately equal to the oxygen partial pressure of the secondary combustion gas 206, the oxidation-reduction reaction at the contact portion of the heat exchanger 130 is brought into equilibrium. dissociation By keeping the pressure difference between the partial pressure of the combustion gas 204 and the oxygen partial pressure of the secondary combustion gas 206 at a predetermined value or less, deterioration of the heat exchanger 130 due to high-temperature corrosion can be suppressed.

[0056] At the contact portion of the heat exchanger 130 dissociation The range of the pressure difference between the partial pressure of the secondary combustion gas 206 and the partial pressure of oxygen in the secondary combustion gas 206 should be appropriately selected depending on the extent to which deterioration of the heat exchanger 130 should be suppressed. dissociationA threshold value (predetermined value) may be set to 10% (preferably 5%, more preferably 3%) of the pressure difference, and when the pressure difference is equal to or less than the threshold value, it may be determined that the oxidation-reduction reaction of the contact portion of the heat exchanger 130 is in equilibrium. dissociation The oxygen concentration may be controlled so that the oxygen partial pressure of the secondary combustion gas 206 falls within a range of ±10% (preferably 5%, and more preferably 3%) based on the pressure.

[0057] Since the material of the contact part of the heat exchanger 130 is known in advance, if the temperature can be specified, the dissociation The oxygen partial pressure of the secondary combustion gas 206 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. For this reason, 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 gas flow rate can be measured using the temperature measured by a thermometer 124 and the pressure inside the combustion chamber 120 measured by a pressure gauge (not shown).

[0058] 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 determines the temperature of the contact part of the heat exchanger 130 based on the temperature obtained from the thermometer 124. dissociation 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, the pressure at the contact portion of the heat exchanger 130 can be obtained by measuring the temperature of the combustion chamber 120 in real time. dissociation It is possible to obtain the change in pressure following 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 rising or falling, dissociation By changing the oxygen partial pressure in response to the change in pressure, high temperature corrosion of the contact area can be suppressed.

[0059] In addition, when the heat recovery system 100 is operated continuously, or when there is no need to take into account the temperature rise or fall of the combustion chamber 120, the temperature of the contact portion of the heat exchanger 130 is assumed to be constant. dissociation In this case, it is not necessary to know the temperature inside the combustion chamber 120, and the thermometer 124 can be omitted.

[0060] 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 reducing the amount of oxygen in the contact area of ​​the heat exchanger 130. dissociation The oxygen concentration of the secondary combustion gas 206 (oxygen concentration in the combustion chamber 120) is adjusted so that the pressure difference between the pressure in the combustion chamber 120 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 caused by the secondary combustion gas 206 (the portion of the heat exchanger 130 that contacts the secondary combustion gas 206).

[0061] [Control flow of 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 of the first embodiment of the present invention. The control shown in Fig. 3 is executed 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.

[0062] 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. That is, the temperature of the secondary combustion gas 206 generated in the combustion chamber 120 can be considered to be 950°C.

[0063] Next, the combustion control device 150 controls the temperature of the contact part in the heat exchanger 130 based on the acquired temperature. dissociationIn this embodiment, since a steel material such as S-TEN steel is used as the material for the contact portion, the standard free energy of formation is known. Therefore, if the temperature can be obtained, the standard free energy of formation of the contact portion can be calculated by the above-mentioned formula (3). dissociation The pressure can be calculated. dissociation However, the present invention is not limited to this example. For example, the temperature and dissociation A look-up table is prepared that corresponds to the temperature and pressure, and the look-up table is used to select the temperature and pressure based on the obtained temperature. dissociation The pressure may be acquired.

[0064] dissociation After calculating the pressure, the combustion control device 150 acquires 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.

[0065] 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 and the like are 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 arranged can also be calculated. Therefore, if the oxygen concentration can be acquired, the oxygen partial pressure of the secondary combustion gas 206 can be found by calculation. However, this is not the only example, and if the gas flow rate is known, a reference table that associates oxygen concentrations with oxygen partial pressures may be prepared in advance, and the oxygen partial pressure may be acquired from the reference table based on the acquired oxygen concentration.

[0066] Through the above process, the oxygen partial pressure of the secondary combustion gas 206 and the contact point of the heat exchanger 130 dissociation After determining the oxygen partial pressure and dissociationThe differential pressure between the oxygen partial pressure and the oxygen partial pressure is calculated, and it is determined whether the calculated differential pressure is equal to or lower than a predetermined value (i.e., whether the oxygen partial pressure is dissociation In this embodiment, the combustion control device 150 determines whether the oxygen partial pressure and the pressure are within a predetermined range (step S305). dissociation When the pressure difference between the dissociation By this determination process, the combustion control device 150 determines whether the oxygen partial pressure of the secondary combustion gas 206 is equal to or lower than the oxygen partial pressure of the contact area of ​​the heat exchanger 130. dissociation It is possible to know whether the pressure is in equilibrium or not.

[0067] If the determination in step S305 is YES, the oxygen partial pressure of the secondary combustion gas 206 and the contact area of ​​the heat exchanger 130 are dissociation If the result of step S305 is NO, the combustion control device 150 determines that the oxygen partial pressure is dissociation It is then determined whether the pressure is higher than the predetermined pressure (step S306).

[0068] 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).

[0069] 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 onward, and adjusts the oxygen partial pressure and dissociation The control program continues to be executed until the pressure difference between the oxygen partial pressure and the combustion pressure becomes equal to or less than a predetermined value. dissociation When the pressure difference between the pressure in the intake duct and the pressure in the exhaust duct falls below the predetermined value, the determination in step S305 becomes YES, and the execution of the control program ends.

[0070] 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 is capable of monitoring the oxygen concentration inside the combustion chamber 120 (i.e., the oxygen partial pressure of the secondary combustion gas 206) calculated by the combustion control device 150 and the oxygen partial pressure of the contact part of the heat exchanger 130. dissociation The oxygen concentration in the combustion chamber 120 is controlled according to the result of comparing the oxygen partial pressure and dissociation The pressure can be kept within the same or approximately the same range as the pressure in the heat exchanger 130. 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 and the contact portion of the heat exchanger 130 even when the high-temperature secondary combustion gas 206 comes into contact with the contact portion 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.

[0071] 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. In addition, in the control flow in FIG. 3, after acquiring the oxygen concentration and the temperature, dissociation The blood pressure and oxygen partial pressure may be calculated.

[0072] [Biogas generator configuration] Fig. 4 is a diagram showing the configuration of a biogas generator 110 of the first embodiment. The biogas generator 110 includes at least a treatment tank 22, a biological sludge bed 24, and a sludge settler 26. Furthermore, the biogas generator 110 of this embodiment includes a raw water supply pipe 28, a cylindrical member (draft tube) 30, a return device 32, a scum blocking member 34, a treated water discharge trough 36, a treated water discharge port 38, and a lifting device 40. However, the example shown in Fig. 4 is merely an example, and the present invention is not limited to this example.

[0073] The treatment tank 22 is a cylindrical case made of steel plate or synthetic resin. The treatment tank 22 corresponds to the outer frame of the biogas generator 110 of this embodiment. The biogas generator 110 of this embodiment uses a hollow member having a long axis in the vertical direction as the treatment tank 22 in order to perform fermentation treatment by upward flow using the UASB method. A guide rail 22a (see Figs. 7 and 8) is provided on a part of the inner wall of the treatment tank 22 for moving the sludge sediment 26 described later in the vertical direction along the inner wall. In this embodiment, the treatment tank 22 is shaped like a cylinder, but may be shaped like a rectangular parallelepiped. It is also possible to have a structure in which multiple rectangular parallelepiped cases are connected together. Furthermore, the material is not limited to steel plate or synthetic resin, and may be a reinforced concrete structure (RC structure).

[0074] The biological sludge bed 24 is provided at the bottom inside the treatment tank 22. The biological sludge bed 24 is also called a sludge bed. The biological sludge bed 24 is an aggregate of granules formed by the self-granulation of anaerobic microorganisms. The granules are black granular substances with excellent settling properties that utilize the self-granulation function of anaerobic microorganisms. The granules can hold methanogens at high density and high activity without using a carrier for immobilizing microorganisms.

[0075] The sludge settler 26 is a member for settling the granules raised by the upward flow toward the biological sludge bed 24. The sludge settler 26 is provided above the biological sludge bed 24. The sludge settler 26 includes a cap-shaped main body 26a and a flow straightening section 26b provided on the upper surface of the main body 26a. The main body 26a of the sludge settler 26 has an inclined surface facing the biological sludge bed 24. In other words, the main body 26a of the sludge settler 26 has a shape of a truncated cone with the bottom surface facing downward in a side view. The flow straightening section 26b is a member including a plurality of tubular structures formed by stacking a plurality of inclined plates. The cross-sectional shape of the tubular structure is arbitrary, and may be, for example, a triangle, a rectangle, a pentagon, a hexagon, a diamond, or a circle.

[0076] Fig. 5 is a diagram showing the configuration of the sludge settler 26 in the biogas generator 110 of the first embodiment. As shown in Fig. 5, the main body 26a of this embodiment is formed by combining a plurality of fan-shaped members 26a-1. However, the main body 26a may be integrally formed by processing a single plate-shaped member. In any case, the main body 26a is preferably a cap-shaped member having an inclined surface facing the biological sludge bed 24.

[0077] As shown in FIG. 5, the flow straightening unit 26b of this embodiment is disposed with the open end of the tubular structure 26b-1 facing the vertical direction. A net cover for preventing the flow straightening unit 26b from floating up may be provided on the flow straightening unit 26b. Here, a plurality of through holes 26c are provided on the upper surface of the main body 26a. The tubular structure 26b-1 inside the flow straightening unit 26b is connected to each of the plurality of through holes 26c provided on the upper surface of the main body 26a. The water to be treated that has passed through the main body 26a flows upward through the plurality of tubular structures 26b-1.

[0078] Fig. 6 is a diagram showing the configuration of the rectifier 26b in the biogas generator 110 of the first embodiment. Specifically, Fig. 6(A) is a diagram showing the configuration of a plurality of inclined plates 26b-2. Fig. 6(B) is a diagram showing the rectifier 26b formed by combining a plurality of inclined plates 26b-2. Note that Fig. 6(B) shows an example of the rectifier 26b in which the cross-sectional shape of the tubular structure 26b-1 is hexagonal.

[0079] As shown in FIG. 6(A), the plurality of inclined plates 26b-2 are each composed of a plate-like member having a plurality of bent portions. The material of each inclined plate 26b-2 can be plastic, metal, or the like. When the plurality of inclined plates 26b-2 shown in FIG. 6(A) are stacked together, the rectifying portion 26b having a plurality of tubular structures 26b-1 can be formed as shown in FIG. 6(B). The rectifying portion 26b may be formed by bonding the plurality of inclined plates 26b-2 together with an adhesive or the like, or the rectifying portion 26b may be formed by covering the stacked plurality of inclined plates 26b-2 with the above-mentioned net cover or the like. In any case, it is sufficient that the structure shown in FIG. 6(B) is disposed on the upper surface of the main body portion 26a of the sludge settler 26.

[0080] In general, in UASB-type anaerobic treatment equipment, care must be taken to prevent the granules that make up the biological sludge bed from being carried by the upward flow and flowing out of the treatment tank (flushing out) during operation of the equipment. To achieve this, it is important to adjust the settling speed of the granules so that it is faster than the upward speed of the water to be treated. The settling speed of the granules can be calculated using Stokes' equation. According to Stokes' equation, the settling speed of the granules increases as the particle density and particle size of the granules increase. In addition, the upward speed of the water to be treated (water surface area load) is the value obtained by dividing the flow rate of the water to be treated by the cross-sectional area (separation area) of the treatment tank. Therefore, it is important to increase the separation area of ​​the treatment tank in order to reduce the upward speed of the water to be treated.

[0081] Considering the above, in the biogas generator 110 of this embodiment, the sludge settler 26 is disposed inside the treatment tank 22, thereby increasing the effective separation area of ​​the treatment tank 22 and slowing down the upward movement speed of the water to be treated. In particular, in the flow straightening section 26b, the surface area of ​​the inside of the hollow structure can be added as a separation area, so that the granules settle efficiently. The granules separated from the water to be treated again descend inside the treatment tank 22 and finally return to the biological sludge bed 24. In this way, the sludge settler 26 also greatly contributes to the separation of the granules.

[0082] Furthermore, the biogas generator 110 of this embodiment narrows the region below the sludge settler 26, i.e., the reaction region, for a predetermined period from the start of operation (specifically, the acclimatization period of the biological sludge bed 24), thereby promoting the growth of granules and improving the particle density of the granules. As described above, this contributes to increasing the settling speed of the granules.

[0083] In order to obtain the above-mentioned effects, in this embodiment, the sludge settler 26 is movable in the vertical direction along the inner wall of the treatment tank 22. In other words, by moving the sludge settler 26 in the vertical direction, the reaction area can be narrowed or widened depending on the operating conditions of the biogas generator 110. This control will be described later with reference to Figures 7 and 8.

[0084] Returning to Fig. 4, the description of the biogas generator 110 continues. The raw water supply pipe 28 supplies raw water (primary treated water supplied from the acid generator 110 shown in Fig. 1) to the inside of the treatment tank 22. Although only one supply pipe is shown in Fig. 4, this is not limiting, and multiple supply pipes may be arranged in parallel. Note that, as will be described in detail later, the open end of the raw water supply pipe 28 in this embodiment is located below the cylindrical member 30, and the supplied raw water is sent to the inside of the cylindrical member 30.

[0085] The tubular member 30 is a long, thin, hollow pipe, and is provided in the reaction zone of the treatment tank 22 (i.e., below the sludge settler 26). Specifically, the tubular member 30 is disposed away from the inner wall of the treatment tank 22 with its open end facing in the vertical direction. A biological sludge bed 24 is formed in the reaction zone of the treatment tank 22. Therefore, the tubular member 30 is located inside the biological sludge bed 24 during operation of the biogas generator 110.

[0086] The return device 32 has a role of returning the water to be treated from the upper part to the lower part of the treatment tank 22. Specifically, the return device 32 has a function of returning the water to be treated above the sludge sediment 26 (i.e., the water to be treated that does not contain granules) and / or the water to be treated below the sludge sediment 26 (i.e., the water to be treated that contains granules) to the lower end side of the tubular member 30 described above. In other words, the return device 32 has a role of returning the water to be treated in the separation zone to the reaction zone again and circulating the water to be treated in the reaction zone. As will be described later, the biogas generator 110 of this embodiment has a structure that increases the flow rate inside the tubular member 30 so that good convection occurs in the reaction zone. The water to be treated returned to the reaction zone again by the return device 32 is returned to the inside of the tubular member 30 from the opening on the lower end side of the tubular member 30, which contributes to an increase in the flow rate inside the tubular member 30.

[0087] The return device 32 forms a flow path that returns the water to be treated to the reaction area again using a circulation pump 111 and a return pipe 112. In addition to the circulation pump, a heater 113 and a water temperature sensor 114 are provided in the flow path. The heater 113 heats the water to be treated flowing through the return pipe 112. The water temperature sensor 114 measures the temperature of the water to be treated flowing through the return pipe 112.

[0088] The heater 113 may be any of various heaters, such as a coil heater, a specific heat contact tank, a multi-tube heat exchanger, or a plate heat exchanger. Instead of using the heater 113 to heat the water to be treated, it is also possible to heat the water to be treated by utilizing the residual heat of the secondary combustion gas 206. For example, the temperature of the water to be treated may be increased by using steam obtained by utilizing the residual heat in the heat exchanger 130.

[0089] The water temperature sensor 114 may be, for example, a thermistor. In this embodiment, the heater 113 is controlled based on the output signal of the water temperature sensor 114 to control the temperature of the water to be treated in the treatment tank 22. In this embodiment, a contact heater such as a coil heater is used as the heater 113. By using a contact heater as the heater 113, the temperature of the water to be treated that comes into contact with the heater 113 exceeds 60 degrees. Therefore, the heater 113 not only maintains the temperature inside the tank, but also decomposes excess granules and proteins in the water to be treated.

[0090] The scum blocking member 34 is provided above the sludge settler 26. Scum is excess sludge and the like that has risen to the surface due to the action of gas. The scum blocking member 34 is, in contrast to the sludge settler 26, a member that has a truncated cone shape in side view with the bottom facing upward, and has an opening near the center through which the water to be treated passes.

[0091] The treated water discharge trough 36 is provided above the scum blocking member 34. The treated water discharge trough 36 has an opening at its center that allows the treated water that has risen inside the treatment tank 22 to pass through, and has a groove around the opening for receiving the treated water that overflows. The treated water that has accumulated in this groove is discharged from a treated water discharge port 38.

[0092] The lifting device 40 is a drive device for moving the sludge settler 26 in the up and down direction. The lifting device 40 includes a support member 40a, one end of which is connected to the sludge settler 26, a lifter 40b connected to the other end of the support member 40a, and a support frame 40c that supports the support member 40a and the lifter 40b. The movement of the sludge settler 26 by the lifting device 40 may be performed manually or automatically. In this embodiment, a scale 40d is provided on the support frame 40c. For example, when the sludge settler 26 is moved manually by moving a lifter (e.g., a lifting cylinder), the sludge settler 26 can be placed at any position as long as the moving distance is known from the scale 40d.

[0093] The operation of the biogas generator 110 of this embodiment described above will be described with reference to FIGS.

[0094] [Biogas generator operation] FIG. 7 is a diagram showing the configuration of the biogas generator 110 of the first embodiment in a first state. FIG. 8 is a diagram showing the configuration of the biogas generator 110 of the first embodiment in a second state. For convenience of explanation, the biogas generator 110 shown in FIGS. 7 and 8 omits some of the configuration shown in FIG. 4. Although not shown in FIG. 4, as shown in FIGS. 7 and 8, the treatment tank 22 has guide rails 22a for moving the sludge sediment 26 up and down along the inner wall. However, the guide rails 22a are not essential. For example, when the treatment tank 22 is small, they may be omitted.

[0095] In the first state shown in FIG. 7, the sludge settler 26 is disposed below the treatment tank 22 (at the first position) and the reaction area 50 is relatively reduced (i.e., the separation area 60 is enlarged). For convenience of explanation, the lower end of the sludge settler 26 is illustrated as the upper limit of the reaction area 50 in FIG. 7, but in reality, any area below the sludge settler 26 can function as the reaction area 50. For convenience of explanation, the biological sludge bed 24 is represented by a rectangular area (hatched area) in FIG. 7. However, during actual operation, convection of the water to be treated occurs in the reaction area 50, so that granules are present in almost the entire reaction area 50. This is also the case in the second state shown in FIG. 8.

[0096] In this embodiment, the "first position" is a position where the sludge settler 26 is placed for a predetermined period from the start of operation (specifically, the acclimatization period of the biological sludge bed 24). The first position may be appropriately determined taking into consideration the depth of the treatment tank 22, etc. At the start of operation, since the granules are very vulnerable to load fluctuations, the reaction area 50 is narrowed to suppress the load fluctuations. This prevents the binding strength of the granules from decreasing, and prevents the granules from floating up due to internal gas. Furthermore, narrowing the reaction area 50 increases the organic matter concentration in the reaction area 50, promoting the growth of the granules.

[0097] As described above, in this embodiment, during the acclimatization period of the biological sludge bed 24, the treatment in the first state (first treatment) shown in Fig. 7 is performed, and emphasis is placed on promoting the growth of granules. As a result, the biogas generator 110 of this embodiment can shorten the acclimatization period of the biological sludge bed 24.

[0098] Furthermore, at the start of operation, the biological sludge bed 24 does not function adequately due to insufficient growth of granules. Also, since there are many granules with very small particle diameters, it is desirable to improve the solid-liquid separation performance in the separation zone 60. At the start of operation, the biogas generator 110 of this embodiment expands the separation zone 60 as the reaction zone 50 shrinks, so that it is possible to simultaneously promote the growth of granules in the reaction zone 50 and improve the solid-liquid separation performance in the separation zone 60.

[0099] Next, the second state shown in FIG. 8 is a state in which the sludge settler 26 is disposed above the treatment tank 22 (second position) and the reaction area 50 is relatively enlarged (i.e., the separation area 60 is reduced). In other words, the second state is a state in which the sludge settler 26 is disposed at a second position above the first position and the reaction area 50 is relatively enlarged. When it is determined that the granules have grown sufficiently and the acclimation period has elapsed, the next step is to focus on increasing the treatment capacity of the reaction area 50. In other words, by enlarging the reaction area 50, the contact time between the water to be treated and the granules is increased, and the efficiency of the treatment is improved. For this reason, in this embodiment, the sludge settler 26 is moved upward from the first position to the second position, and the treatment (second treatment) is performed in a state in which the reaction area 50 is enlarged.

[0100] In addition, an operator can visually check through a viewing window 22b (see Figure 4) provided in the treatment tank 22 to determine whether the granules have grown sufficiently, i.e., whether the acclimatization period of the biological sludge bed 24 has elapsed.

[0101] Furthermore, the biogas generator 110 of this embodiment can also expand or reduce the reaction zone 50 during operation in response to an increase or decrease in the supply amount of water to be treated. For example, when the supply amount of water to be treated (i.e., the supply amount of organic matter passing through the biological sludge bed 24) increases, it is desirable to move the sludge settler 26 upward to expand the reaction zone 50 and improve the efficiency of treatment in the reaction zone 50. For example, when the supply amount of water to be treated exceeds a predetermined amount, it is possible to switch from the second treatment to the first treatment.

[0102] Furthermore, in this embodiment, in the first state shown in Fig. 7, the growth of granules is promoted by generating convection in the reaction area 50. This point will be described with reference to Fig. 9.

[0103] 9 is a diagram for explaining the state of the reaction zone 50 in the first state. As described above, the biogas generator 110 of this embodiment includes the return device 32 that forms a flow path for returning the intermediate water in the separation zone 60 to the reaction zone 50 using the circulation pump 111. The water to be treated that has been returned to the lower end side of the tubular member 30 by the return device 32 again passes through the inside of the tubular member 30 and rises. At that time, the water to be treated whose flow rate has been increased by the circulation pump 111 is supplied to the inside of the tubular member 30, so that the flow rate inside the tubular member 30 increases locally.

[0104] Therefore, at the upper open end of the cylindrical member 30, an upward flow occurs due to the flow of the granules and the water to be treated flowing out at a high flow rate. At the lower open end of the cylindrical member 30, negative pressure is generated near the open end due to the flow of the water to be treated flowing into the cylindrical member 30. Due to the negative pressure, the granules and the water to be treated are drawn into the inside of the cylindrical member 30 at the lower open end of the cylindrical member 30. As a result, as shown in FIG. 9, a strong convection of the water to be treated occurs in the reaction area 50. At this time, since the sludge settler 26 moves to the first position and the reaction area 50 is narrowed, the fine granules become entangled with each other and grow larger. As a result, the growth of the granules is significantly promoted. Furthermore, when the granules flowing out upward from the cylindrical member 30 are blocked by the sludge settler 26 located directly above, they collide with other granules and form granules with even larger particle sizes.

[0105] As described above, according to this embodiment, the growth of granules can be promoted by lowering the sludge settler 26 to the first position and narrowing the reaction area 50. Furthermore, the growth of granules can be promoted by generating strong convection in the reaction area 50 using the cylindrical member 30.

[0106] The biogas generator 110 of this embodiment is equipped with a sludge settler 26 that can move up and down inside the treatment tank 22. This allows the range of the reaction zone and separation zone to be freely expanded or reduced depending on the operating conditions. During the acclimatization period of the biological sludge bed 24 at the beginning of operation, the sludge settler 26 can be moved downward to narrow the reaction zone 50 and promote the growth of granules.

[0107] The biogas generator 110 of this embodiment also includes a tubular member 30 spaced apart from the inner wall of the treatment tank, and a return device 32 that returns the water to be treated to the lower end side of the tubular member 30. As a result, during the acclimatization period of the biological sludge bed 24 at the beginning of operation, the sludge settler 26 is moved downward while the flow rate of the upward flow inside the tubular member 30 is increased, and strong convection is generated throughout the reaction area 50. As a result, the effect of convection is added to the effect of narrowing the reaction area 50, and the growth of granules can be significantly promoted.

[0108] (Variation 1) In this embodiment, the contact portion of the heat exchanger 130 is heated by the control of the combustion control device 150. dissociation In the above description, the pressure difference between the partial pressure of oxygen in the secondary combustion gas 206 and the pressure difference between the partial pressure of oxygen in the secondary combustion gas 206 is set to a predetermined value or less. However, 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, dissociation If the pressure exceeds the specified value, the pressure difference is kept below the specified value, and the oxygen partial pressure is dissociation In other words, the combustion control device 150 determines whether the oxygen partial pressure of the secondary combustion gas 206 is greater than the oxygen partial pressure of the contact portion of the heat exchanger 130. dissociation The oxygen concentration of the secondary combustion gases 206 may be adjusted to be below pressure.

[0109] In this case, the contact parts of the heat exchanger 130 are always placed in a reducing atmosphere, so that deterioration of the contact parts due to high-temperature corrosion can be suppressed.

[0110] (Variation 2) In this embodiment, an example in which a vacuum type hot water heater is used as the heat exchanger 130 has been shown, 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, since no pressure is applied inside the container.

[0111] Fig. 10 is a diagram showing the configuration of a modified example of the heat exchanger 130 used in the heat recovery system 100 of the first embodiment of the present invention. Specifically, Fig. 10 shows the configuration of an atmospheric pressure type hot water heater 230 used as the heat exchanger 130. In the atmospheric pressure type 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 then discharged as combustion gas 208.

[0112] The heat transfer water 234 heated in the medium chamber 233 is supplied to the heat exchange section 235, and heat exchange is performed using the heat of the heated heat transfer water 234. The heat exchange section 235 has a water supply pipe 236, and 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.

[0113] 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, unlike the conventional technology, it is not necessary 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. Therefore, it is not necessary to use a steam boiler as in the conventional technology, and high heat recovery efficiency can be ensured even if a heat exchanger such as a hot water heater is used.

[0114] In addition, the atmospheric pressure type 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 type hot water heater 230 does not become high pressure, and the atmospheric pressure type hot water heater 230 is not subject to boiler regulations. Therefore, when the atmospheric pressure type hot water heater 230 is used as the heat exchanger 130, it is not necessary 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.

[0115] (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.

[0116] (Variation 4) In the control flow shown in FIG. 3, in step S305, the oxygen partial pressure and dissociation The differential pressure between the oxygen partial pressure and the oxygen partial pressure is calculated, and it is determined whether the calculated differential pressure is equal to or lower than a predetermined value (i.e., whether the oxygen partial pressure is dissociation However, the present invention is not limited to this example. For example, in FIG. 3, step S305 may be omitted.

[0117] In this case, the combustion control device 150 performs the step S302 of dissociation In step S304, the oxygen partial pressure of the secondary combustion gas 206 is calculated. In step S306, the oxygen partial pressure is calculated as follows: dissociationThen, 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 manner, the combustion control device 150 repeats the control process again from step S301.

[0118] The combustion control device 150 of this modification constantly executes the above-mentioned loop process to obtain the oxygen partial pressure and dissociation The results of the comparison with the oxygen partial pressure are fed back to dissociation This allows an equilibrium state to be maintained between the contact portion of the heat exchanger 130 and the secondary combustion gas 206 generated in the combustion chamber 120.

[0119] 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.

[0120] Fig. 11 is a block diagram showing the configuration of a heat recovery system 100a according to a second embodiment of the present invention. In Fig. 11, the same elements as those in the heat recovery system 100 described in the first embodiment are given the same reference numerals and the description thereof will be omitted.

[0121] 11, 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. That is, the damper 128 functions as an air volume regulator that adjusts the flow rate of air supplied to the combustion chamber 120.

[0122] 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 determination in 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).

[0123] Third embodiment In the first and second embodiments, examples have been described in which the biogas 202 generated in the biogas generator 110 is supplied to the combustion chamber 120. In this embodiment, however, an example will be described in which the biogas 202 is supplied to an incinerator 115.

[0124] Fig. 12 is a block diagram showing the configuration of a heat recovery system 100b according to a third embodiment of the present invention. In Fig. 12, the same elements as those in the heat recovery systems 100 and 100a described in the first and second embodiments are denoted by the same reference numerals, and the description thereof will be omitted.

[0125] As shown in FIG. 12, in the heat recovery system 100b of this embodiment, the biogas 202 (e.g., methane gas) generated in the biogas generator 110 is supplied to the incinerator 115 and used for the incineration of waste 203. This allows the biogas 202 to be used as fuel (e.g., ignition fuel at the start of operation) required for the incineration process in the incinerator 115, and the amount of conventional fuel used, such as heavy oil, can be reduced. The biogas 202 can also be used to increase the internal temperature of the incinerator 115 during waste incineration. In FIG. 12, the biogas 202 is supplied directly from the biogas generator 110 to the incinerator 115, but the present invention is not limited to this example, and the biogas may be supplied to the incinerator 115 via other equipment, such as a gas refinery or a gas tank.

[0126] (Fourth embodiment) In the first and second embodiments, examples were described in which the biogas 202 generated in the biogas generation device 110 was supplied to the combustion chamber 120, but in this embodiment, an example will be described in which a portion of the biogas 202 is supplied to a gas generator 160.

[0127] Fig. 13 is a block diagram showing the configuration of a heat recovery system 100c according to a fourth embodiment of the present invention. In Fig. 13, the same elements as those in the heat recovery systems 100 and 100a described in the first and second embodiments are denoted by the same reference numerals, and the description thereof will be omitted.

[0128] As shown in FIG. 13, in the heat recovery system 100c of this embodiment, biogas 202 (e.g., methane gas) generated in the biogas generator 110 is supplied to the combustion chamber 120 and the gas generator 160. For example, a biogas generator can be used as the gas generator 160. The biogas generator is a facility that generates electricity using biogas such as methane gas as fuel. In this embodiment, by supplying the biogas 202 generated in the biogas generator 110 to the gas generator 160 as well, it is possible to recover electricity in addition to recovering heat. In FIG. 13, the biogas 202 is supplied directly from the biogas generator 110 to the gas generator 160. However, this is not limited to the example, and the biogas 202 may be supplied to the gas generator 160 via other facilities such as a gas refinery device or a gas tank.

[0129] The embodiments of the present invention and their modifications can be combined as appropriate as long as they are not mutually inconsistent. A heat recovery system according to the above-described embodiment, in which a person skilled in the art appropriately adds or removes components or modifies the design, or adds or omits a process or modifies conditions, is included in the scope of the present invention as long as it includes the gist of the present invention.

[0130] Furthermore, even if there are other effects and advantages different from those brought about by the aspects of the above-mentioned embodiment, those which are clear from the description in this specification or which can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention. [Explanation of symbols]

[0131] 22... treatment tank, 22a... guide rail, 22b... sight glass, 24... biological sludge bed, 26... sludge settler, 26a... main body, 26b... straightening section, 26b-1... tubular structure, 26b-2... inclined plate, 26c... through hole, 28... raw water supply pipe, 30... cylindrical member (draft tube), 32... return device, 34... scum prevention member, 36... treated water discharge trough, 38... treated water Discharge port, 40...lifting device, 40a...support member, 40b...lifter, 40c...support frame, 50...reaction zone, 60...separation zone, 100, 100a...heat recovery system, 110...biogas generator, 111...circulation pump, 112...return pipe, 113...heater, 114...water temperature sensor, 115...incinerator, 120...combustion chamber, 122...oxygen concentration meter, 124...thermometer, 1 26...gas supply device, 127...blower device, 128...damper, 130...heat exchanger, 131...casing, 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, 140...cooling chamber, 150, 150a...combustion control device, 160...gas generator, 201...sewage, 202...biogas, 203...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

1. A biogas generator; An incinerator, A combustion chamber to which the biogas generated in the biogas generator and the primary combustion gas generated in the incinerator are supplied; 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 controls the oxygen concentration so that the pressure difference between the dissociation pressure of the contact portion of the heat exchanger and the oxygen partial pressure of the combustion gas is equal to or less than a predetermined value.

2. A biogas generator; An incinerator to which the biogas generated in the biogas generator is supplied; A combustion chamber to which primary combustion gas generated in the incinerator is supplied; 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 controls the oxygen concentration so that the pressure difference between the dissociation pressure of the contact portion of the heat exchanger and the oxygen partial pressure of the combustion gas is equal to or less than a predetermined value.

3. The heat recovery system according to claim 1 or 2, further comprising a gas generator supplied with the biogas.

4. The heat recovery system according to claim 1 , wherein the biogas generator comprises a treatment tank and a biological sludge bed provided inside the treatment tank.

5. The biogas generating apparatus further includes a sludge settler disposed above the biological sludge bed and having an inclined surface facing the biological sludge bed; The heat recovery system according to claim 4 , wherein the sludge settler is vertically movable inside the treatment tank.

6. 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.

7. 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 , wherein the combustion control device controls the gas supply device in accordance with the oxygen concentration.

8. 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 , wherein the combustion control device controls the air volume regulator in accordance with the oxygen concentration.

9. The heat recovery system according to claim 1 , wherein the heat exchanger is a vacuum or non-pressure type hot water heater.

10. The heat recovery system according to claim 1 , further comprising a cooling chamber to which the combustion gas that has passed through the heat exchanger is supplied.

11. The heat recovery system according to claim 1 , wherein the oxygen concentration meter is a laser oxygen concentration meter.

12. The biogas generated in the biogas generator and the primary combustion gas generated in the incinerator are supplied to the combustion chamber, Measure the oxygen concentration of the combustion gas generated by burning the biogas and the primary combustion gas in a combustion chamber; controlling the oxygen concentration so that a pressure difference between a dissociation pressure at a contact portion of a heat exchanger connected to the combustion chamber 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.

13. The biogas generated by the biogas generator is supplied to the incinerator. Supplying the primary combustion gas generated in the incinerator to a combustion chamber; measuring an oxygen concentration of a combustion gas generated by burning the primary combustion gas in a combustion chamber; controlling the oxygen concentration so that a pressure difference between a dissociation pressure at a contact portion of a heat exchanger connected to the combustion chamber 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.

14. 14. The heat recovery method according to claim 12 or 13, wherein the biogas generator comprises a treatment tank and a biological sludge bed provided inside the treatment tank.

15. The biogas generating apparatus further includes a sludge settler disposed above the biological sludge bed and having an inclined surface facing the biological sludge bed; The heat recovery method according to claim 14 , wherein the sludge settler is vertically movable inside the treatment tank.

16. further comprising measuring a temperature of the combustion gas; The heat recovery method according to claim 12 , wherein the dissociation pressure is calculated based on the temperature.

17. The heat recovery method according to any one of claims 12 to 16, wherein a vacuum type or non-pressure type hot water heater is used as the heat exchanger.

18. The heat recovery method according to any one of claims 12 to 17, further comprising supplying the combustion gas that has passed through the heat exchanger to a cooling chamber.

19. The heat recovery method according to any one of claims 12 to 18, wherein the oxygen concentration is measured by a laser type oxygen concentration meter.

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