JP7478089B2 - Biogas Engine System - Google Patents

Description

The present invention relates to a biogas engine system equipped with a biogas engine that burns biogas.

In recent years, biogas engines have been attracting attention. Biogas engines use biogas, which is produced by methane fermentation of organic waste (e.g., food waste, sewage, livestock waste, and food waste), as fuel.

Biogas is carbon neutral, so using it can reduce the burden on the environment. On the other hand, methane fermentation of organic waste requires heating the organic waste to activate the fermentation.

It has therefore been proposed to use the thermal energy of a biogas engine to heat organic waste. For example, the following energy recovery system has been proposed. This energy recovery system is equipped with a methane fermentation tank that produces biogas by methane fermentation of a slurry containing food waste, and a cogeneration engine that uses the biogas as fuel to generate electricity and high-temperature, high-pressure steam. In this energy recovery system, the high-temperature, high-pressure steam discharged from the cogeneration engine is used to keep the methane fermentation tank warm (see, for example, Patent Document 1).

JP 2009-34569 A

On the other hand, energy recovery systems are required to recover and reuse energy more efficiently.

The present invention is a biogas engine system with excellent energy efficiency.

The present invention [1] is a biogas engine that burns biogas, a biogas generation unit that ferments organic waste to generate biogas, a refrigerant circulation line for cooling the biogas engine with a refrigerant, a heat medium circulation line for heating the biogas generation unit with a heat medium, a heat exchanger that exchanges heat between the refrigerant circulation line and the heat medium circulation line, a temperature sensor that detects the temperature of the biogas generation unit, and a control unit that controls the operation of the biogas engine and the refrigerant circulation line in accordance with the temperature of the biogas generation unit detected by the temperature sensor, The control unit includes a biogas engine system that can switch between an insulation operation mode in which the biogas engine is ignited at a predetermined timing and the refrigerant is circulated through the refrigerant circulation line at a predetermined flow rate when the temperature of the biogas generation section detected by the temperature sensor is equal to or higher than a predetermined value, and a heating operation mode in which the ignition timing of the biogas engine is delayed from the predetermined timing and/or the flow rate of the refrigerant through the refrigerant circulation line is increased when the temperature of the biogas generation section detected by the temperature sensor is less than a predetermined value.

In the biogas engine system of the present invention, when the temperature of the biogas generation section is equal to or higher than a predetermined value, the control unit operates in a heat retention operation mode, igniting the biogas engine at a predetermined timing and circulating the refrigerant at a predetermined flow rate through the refrigerant circulation line. When the temperature of the biogas generation section is lower than the predetermined value, the control unit operates in a heating operation mode, delaying the timing of ignition in the biogas engine from the timing in the heat retention operation mode and/or increasing the flow rate of the refrigerant in the refrigerant circulation line.

As a result, in the biogas engine system of the present invention, when the temperature of the biogas generation unit is equal to or higher than a predetermined value, the biogas generation unit is kept warm, and the biogas generation unit is heated only when the temperature of the biogas generation unit is below the predetermined value. Therefore, the biogas engine system of the present invention has excellent energy efficiency throughout the system.

FIG. 1 is a schematic diagram showing one embodiment of a biogas engine system of the present invention. FIG. 2 is a schematic diagram showing another embodiment of the biogas engine system of the present invention.

1. Configuration of the biogas engine system In Fig. 1, the biogas engine system 1 is, for example, a power source connected to a power generation device 100 (see the dashed line in Fig. 1). The biogas engine system 1 includes a biogas engine 2 that burns biogas, a biogas generation unit 3 that ferments organic waste to generate biogas, a refrigerant circulation line 4 for cooling the biogas engine 2 with a refrigerant, a heat medium circulation line 5 for heating the biogas generation unit 3 with a heat medium, a heat exchanger 6 for exchanging heat between the refrigerant circulation line 4 and the heat medium circulation line 5, a temperature sensor 8 that detects the temperature of the biogas generation unit 3, and a control unit 7 that controls the operation of the biogas engine 2, the refrigerant circulation line 4, and the heat medium circulation line 5 according to the temperature of the biogas generation unit 3 detected by the temperature sensor 8.

The biogas engine 2 includes a cylinder block 11, a crankshaft 10, a piston 12, a cylinder head 13, an oil pan 23, a biogas supply section 14, an air supply section 15, and a gas exhaust section 16.

The cylinder block 11 has a cylinder section 11a and a crankcase 11b. The cylinder section 11a houses the piston 12. The crankcase 11b is disposed vertically below the cylinder section 11a. The lower end of the crankcase 11b is connected to an oil pan 32 (described below). The crankcase 11b houses the crankshaft 10 (described below).

The shape of the cylinder block 11 is not particularly limited and is designed according to the number of cylinders. In other words, the biogas engine 2 is a single-cylinder or multi-cylinder biogas engine.

The piston 12 is provided to compress air in the cylinder portion 11a. The piston 12 is housed in the cylinder portion 11a so that it can slide. The crankshaft 10 is connected to the piston 12. The crankshaft 10 is housed in the crankcase 11b so that it can rotate.

The cylinder head 13 seals the cylinder block 11 on the vertically upper side of the cylinder block 11. A combustion chamber 20 is formed between the piston 12 and the cylinder head 13. In the combustion chamber 20, biogas injected from a biogas supply valve 19 (described below) can be mixed and combusted with air.

The cylinder head 13 also includes an intake port for introducing air supplied from an air supply section 15 (described later) into the combustion chamber 20, an exhaust port 22 for discharging exhaust gas generated in the combustion chamber 20 to a gas exhaust section 16 (described later), an intake valve 24 that can open and close the intake port 21, and an exhaust valve 25 that can open and close the exhaust port 22. Although not shown, the intake valve 24 and the exhaust valve 25 are connected to a control unit 7 (described later) and can be opened and closed as desired.

The oil pan 23 is a container for storing engine oil. The oil pan 23 is connected to the vertical lower end of the crankcase 11b. Engine oil is stored in the oil pan 23. The engine oil can be supplied to the piston 12 by a known method. Examples of the method for supplying the engine oil include a dry sump method, a wet sump method, and a semi-wet sump method. In addition, the engine oil can be supplied to the biogas engine 2 by contacting the crankshaft 10 with the engine oil and rotating the crankshaft 10. Supplying the engine oil to the piston 12 enables the piston 12 to move up and down, and for example, the intake stroke, compression stroke, explosion stroke, and exhaust stroke can be performed in sequence.

The biogas supply unit 14 is a unit that supplies biogas to the combustion chamber 20. The biogas supply unit 14 includes a biogas supply pipe 18 and a biogas supply valve 19.

The biogas supply pipe 18 is a pipe for supplying biogas from the biogas storage tank 34 (described later) to the combustion chamber 20. The upstream end of the biogas supply pipe 18 is connected to the biogas storage tank 34 (described later). The downstream end of the biogas supply pipe 18 is connected to the biogas supply valve 19. A pump (not shown) is interposed in the biogas supply pipe 18. When the pump is driven, the biogas in the biogas storage tank 34 (described later) is supplied to the biogas supply valve 19.

The biogas supply valve 19 is an injection valve for injecting biogas into the combustion chamber 20. The biogas supply valve 19 is connected to the cylinder portion 11a so as to face the inside of the combustion chamber 20. Although not shown, the biogas supply valve 19 is also connected to a control unit 7 (described below), allowing biogas to be injected at any timing.

The air supply unit 15 is a unit for introducing air into the combustion chamber 20. The air supply unit 15 is equipped with an intake pipe 30.

The intake pipe 30 is a pipe for introducing air into the combustion chamber 20 of the biogas engine 2. The upstream side of the intake pipe 30 is open to the outside (open air). The downstream side of the intake pipe 30 is connected to the intake port 21 of the cylinder head 13. Note that, when the biogas engine 2 has multiple cylinder blocks 11, the intake pipe 30 is formed as a branched manifold that branches out on the downstream side, and the branched ends are connected to the intake ports 21 of each cylinder head 13.

The intake pipe 30 may be provided with a compressor (not shown). The compressor (not shown) is a device for drawing in air from the outside. Although not shown, the compressor (not shown) is connected to a control unit 7 (described below) and can be operated as desired.

The gas exhaust unit 16 is a unit that exhausts the exhaust gas (biogas combustion gas) generated in the combustion chamber 20 from the combustion chamber 20. The gas exhaust unit 16 is equipped with an exhaust pipe 31.

The exhaust pipe 31 is a pipe for discharging exhaust gas from the combustion chamber 20 of the biogas engine 2 to the outside. The upstream side of the exhaust pipe 31 is connected to the exhaust port 22 of the cylinder head 13. The downstream side of the exhaust pipe 31 is open to the outside (outside air). Note that, when the biogas engine 2 has multiple cylinder blocks 11, the exhaust pipe 31 is formed as a branched manifold whose upstream side branches, and the branched ends are connected to the exhaust ports 22 of each cylinder head 13.

The biogas engine 2 also includes an ignition plug 29. The ignition plug 29 is an electrical component for igniting the mixture of biogas and air. Examples of the ignition plug 29 include a spark plug and a glow plug. The ignition plug 29 is provided facing the combustion chamber 20. The ignition plug 29 is also connected to the control unit 7 and can be operated as desired (see the thick dashed line in Figure 1).

The biogas engine 2 is equipped with a refrigerant supply port 35 through which a refrigerant (described later) can be supplied, and a refrigerant discharge port 36 through which the refrigerant (described later) can be discharged. This allows the biogas engine 2 to be cooled by the refrigerant (described later).

The biogas generation unit 3 is provided to ferment organic waste into methane and generate biogas. More specifically, the biogas generation unit 3 includes a fermentation tank 32, a biogas transport pipe 33, and a biogas storage tank 34.

The fermentation tank 32 is a tank for methane fermentation of organic waste. The fermentation tank 32 is made of a heat-resistant and pressure-resistant container. The fermentation tank 32 contains microorganisms capable of methane fermentation of organic waste.

The fermentation tank 32 is equipped with a heat medium supply port 37 through which a heat medium (described later) can be supplied, and a heat medium discharge port 38 through which the heat medium (described later) can be discharged. This allows the fermentation tank 32 to be heated by the heat medium (described later).

The biogas transport pipe 33 is a pipe for transporting biogas from the fermenter 32 to the biogas storage tank 34. One end of the biogas transport pipe 33 is connected to the fermenter 32. The other end of the biogas transport pipe 33 is connected to the biogas storage tank 34. Although not shown, a pump and a valve are interposed midway in the flow direction of the biogas transport pipe 33. By driving the pump and opening and closing the valve, the biogas can be transported from the fermenter 32 to the biogas storage tank 34.

Although not shown, a treatment device for pretreating the biogas by any method is interposed midway in the flow direction of the biogas transport pipe 33. Examples of treatment devices include a desulfurization device and a desiloxane device.

The biogas storage tank 34 is a storage tank that stores biogas. The biogas storage tank 34 is made of a heat-resistant and pressure-resistant container. The other end of the biogas transport pipe 33 is connected to the biogas storage tank 34. This allows the biogas generated in the fermenter 32 to be transported to the biogas storage tank 34 and stored there. The biogas storage tank 34 is also connected to the biogas supply pipe 18. This allows the biogas in the biogas storage tank 34 to be supplied to the combustion chamber 20 of the biogas engine 2 at any time.

The refrigerant circulation line 4 includes a refrigerant circulation pipe 41, a radiator 42, and a refrigerant circulation pump 43.

The refrigerant circulation pipe 41 is a pipe through which a refrigerant circulates. Examples of refrigerants include water, LLC (ethylene glycol aqueous solution), or oil. One end of the refrigerant circulation pipe 41 is connected to the refrigerant supply port 35 of the biogas engine 2. The other end of the refrigerant circulation pipe 41 is connected to the refrigerant discharge port 36 of the biogas engine 2.

The radiator 42 is interposed midway in the flow direction of the refrigerant circulation pipe 41. This allows the radiator 42 to cool the relatively high-temperature refrigerant, whose temperature has increased due to heat exchange with the biogas engine 2, through heat exchange. The cooled refrigerant circulates through the refrigerant circulation pipe 41 and is supplied to the biogas engine 2 again.

The refrigerant circulation pump 43 is disposed in the refrigerant circulation pipe 41 downstream of the radiator 42 and upstream of the heat exchanger 6. Examples of the refrigerant circulation pump 43 include known liquid delivery pumps. Examples of the liquid delivery pump include a rotary pump, a gear pump, a piston pump, and a diaphragm pump. The liquid delivery pump may be housed inside the biogas engine 2.

The refrigerant circulation line 4 is capable of cooling the biogas engine 2 (see dashed line in Figure 1). More specifically, the refrigerant circulation line 4 is capable of supplying a relatively low-temperature refrigerant from the refrigerant supply port 35 of the biogas engine 2 (see thin arrow C1 in Figure 1). The supplied refrigerant exchanges heat with the biogas engine 2, cooling the biogas engine 2. The refrigerant becomes relatively hot through heat exchange, is discharged from the refrigerant discharge port 36, and is supplied to the heat exchanger 6 (described below) (see thick arrow H1 in Figure 1).

The heat medium circulation line 5 includes a heat medium circulation pipe 51 and a heat medium circulation pump 52.

The heat medium circulation pipe 51 is a pipe through which a heat medium circulates. Examples of heat medium include water, LLC (ethylene glycol aqueous solution), and oil. One end of the heat medium circulation pipe 51 is connected to the heat medium supply port 37 of the fermenter 32. The other end of the heat medium circulation pipe 51 is connected to the heat medium discharge port 38 of the fermenter 32.

The heat medium circulation pump 52 is disposed in the heat medium circulation pipe 51. Examples of the heat medium circulation pump 52 include a known liquid delivery pump.

The heat medium circulation line 5 is capable of heating the fermenter 32. More specifically, the heat medium circulation line 5 is capable of supplying a relatively high-temperature heat medium from the heat medium supply port 37 of the fermenter 32 (see thick arrow H2 in Figure 1). The supplied heat medium exchanges heat with the fermenter 32, heating the fermenter 32. The heat medium becomes relatively cold through heat exchange, and is discharged from the heat medium discharge port 38 (see thin arrow C2 in Figure 1).

The heat exchanger 6 is a known heat exchanger. The heat exchanger 6 is provided to exchange heat between the refrigerant circulation line 4 and the heat medium circulation line 5. More specifically, the heat exchanger 6 is interposed in the refrigerant circulation pipe 41 upstream of the radiator 42 and downstream of the refrigerant circulation pump 43. In other words, the heat exchanger 6 can be supplied with a relatively high-temperature refrigerant that has undergone heat exchange in the biogas engine 2. The heat exchanger 6 is also interposed in the heat medium circulation pipe 51 downstream of the heat medium circulation pump 52 and upstream of the fermenter 32. In other words, the heat exchanger 6 can be supplied with a relatively low-temperature heat medium that has undergone heat exchange in the fermenter 32.

The temperature sensor 8 is a sensor for detecting the temperature of the fermenter 32. Examples of the temperature sensor 8 include an infrared radiation thermometer and a thermocouple thermometer. The location of the temperature sensor 8 is not particularly limited, but for example, the sensor portion of the temperature sensor 8 is located inside the fermenter 32. This allows the temperature sensor 8 to detect the internal temperature of the fermenter 32. The temperature sensor 8 is also electrically connected to the control unit 7 (described below) (see the thick dashed line in Figure 1). This allows the internal temperature of the fermenter 32 detected by the temperature sensor 8 to be input to the control unit 7 (described below).

The control unit 7 is a control unit that executes electrical control in the biogas engine system 1. The control unit 7 is equipped with a CPU, ROM, and RAM. The control unit 7 is electrically connected to the spark plug 29 of the biogas engine 2 (see the thick dashed line in Figure 1). This allows the control unit 7 to arbitrarily control the timing of ignition in the biogas engine 2.

The control unit 7 is also electrically connected to the temperature sensor 8 (see the thick dashed line in FIG. 1). This allows the temperature of the fermenter 32 detected by the temperature sensor 8 to be input as an electrical signal to the control unit 7. The control unit 7 is also electrically connected to the refrigerant circulation pump 43 and the heat medium circulation pump 52 (see the thick dashed line in FIG. 1). This allows the control unit 7 to control the operation and stop of the refrigerant circulation pump 43 and the heat medium circulation pump 52. The control unit 7 is also able to arbitrarily control the flow rate of the refrigerant circulating through the refrigerant circulation line 4 by controlling the refrigerant circulation pump 43. The control unit 7 is also able to arbitrarily control the flow rate of the heat medium circulating through the heat medium circulation line 5 by controlling the heat medium circulation pump 52.

The control unit 7 controls the operation of the biogas engine 2 and the refrigerant circulation pump 52 in response to the temperature of the fermenter 32 detected by the temperature sensor 8, as described in detail below, thereby making it possible to switch the operating mode of the biogas engine system 1 between a heat retention operating mode (described below) and a heating operating mode (described below).

2. Operation of the Biogas Engine System In the biogas engine system 1, biogas is generated in the biogas generation section 3. More specifically, organic waste (e.g., food waste, sewage, livestock waste, and food waste) is fed into the fermentation tank 32, where the organic waste undergoes methane fermentation. As a result, biogas containing methane gas as a main component is generated. The biogas is pretreated (desulfurization treatment and desiloxane treatment) as necessary, and transported to the biogas storage tank 34 via the biogas transport pipe 33.

Then, the biogas is supplied to the biogas engine 2, where the intake stroke, compression stroke, explosion stroke, and exhaust stroke are carried out in sequence.

More specifically, in the biogas engine 2, the intake valve 24 starts intake and the intake port 21 is opened, causing air to pass through the intake pipe 30 and be supplied to the combustion chamber 20 (intake stroke).

Then, the intake valve 24 is operated, the intake port 21 of the cylinder head 13 is closed, and the air is compressed by the piston 12 moving up and down (rising) in each cylinder block 11 (compression stroke).

When the piston 12 rises, the biogas in the biogas storage tank 34 is supplied to the combustion chamber 20 via the biogas supply pipe 18 and the biogas supply valve 19. This causes the mixture of air and biogas to be compressed. The compressed mixture is then ignited by the spark plug 29 at a predetermined timing (i.e., when the air compression rate reaches a predetermined value), causing an explosion (explosion stroke).

As a result, the biogas is combusted, producing water vapor and exhaust gases within the combustion chamber 20.

Then, the exhaust valve 25 is operated and the exhaust port 22 is opened, so that the water vapor and exhaust gas in the combustion chamber 20 pass through the exhaust pipe 31 and are discharged to the outside (exhaust stroke).

Then, in the power generation device 100 (see dashed line in Figure 1), the kinetic energy of the biogas engine 2 is used to rotate the magnet or coil. This generates electricity.

As described above, in the biogas engine system 1, the organic waste undergoes methane fermentation in the fermenter 32 to generate biogas. The biogas is then mixed with air in the biogas engine 2 and combusted.

On the other hand, in the biogas engine 1, a relatively high temperature is required to generate biogas. Therefore, when the internal temperature of the fermenter 32 is relatively low (e.g., below 40°C), the efficiency of methane fermentation decreases compared to when the internal temperature of the fermenter 32 is relatively high (e.g., 40°C or higher).

Therefore, in the biogas engine system 1, the operating mode of the biogas engine system 1 is switched between a heat retention operating mode (described later) and a heating operating mode (described later), and the fermenter 32 is kept warm or heated by the thermal energy of the biogas engine 2, thereby improving the efficiency of biogas generation.

More specifically, in the biogas engine system 1, first, the temperature of the fermenter 32 is detected by the temperature sensor 8 and input to the control unit 7. The control unit 7 then determines whether the temperature of the fermenter 32 is below a predetermined value or is equal to or greater than a predetermined value. The predetermined temperature value is, for example, 40°C.

When the temperature of the fermenter 32 is equal to or higher than a predetermined value (e.g., 40°C), the control unit 7 operates the biogas engine system 1 in a heat retention operation mode. In the heat retention operation mode, the control unit 7 ignites the biogas engine 2 at a predetermined timing and circulates the refrigerant through the refrigerant circulation line 4 at a predetermined flow rate.

That is, in the insulation operation mode, the control unit 7 first ignites the biogas engine 2 at a predetermined timing. The ignition timing is usually the timing when the output of the biogas engine 2 is at its maximum, for example, the timing when the piston 12 reaches top dead center. The control unit 7 also operates the refrigerant circulation pump 43 to circulate a predetermined flow rate of refrigerant through the refrigerant circulation line 4. The flow rate of the refrigerant is, for example, 25 to 50 L/min.

As a result, a relatively low-temperature refrigerant is supplied to the refrigerant supply port 35 of the biogas engine 2 while it is running, and exchanges heat with the biogas engine 2. As a result, the biogas engine 2 is cooled. Meanwhile, the temperature of the refrigerant rises, and it is discharged from the refrigerant discharge port 36 of the biogas engine 2 and supplied to the heat exchanger 6.

In addition, in the heat retention operation mode, the control unit 7 operates the heat medium circulation pump 52 to circulate a predetermined flow rate of the heat medium through the heat medium circulation line 5. The flow rate of the heat medium is, for example, 30 to 100 L/min.

As a result, the relatively high-temperature heat medium is supplied to the heat medium supply port 37 of the fermenter 32 and exchanges heat with the fermenter 32. As a result, the fermenter 32 is heated and the organic waste is efficiently fermented into methane. Meanwhile, the temperature of the heat medium decreases, and it is discharged from the heat medium discharge port 38 of the fermenter 32 and supplied to the heat exchanger 6.

Then, in the heat exchanger 6, the relatively high-temperature refrigerant discharged from the biogas engine 2 exchanges heat with the relatively low-temperature heat medium discharged from the fermenter 32. As a result, the temperature of the relatively high-temperature refrigerant drops, and the temperature of the relatively low-temperature heat medium rises. In other words, the thermal energy generated in the biogas engine 2 is recovered by the refrigerant, and then transferred to the heat medium.

Then, the heat medium with the increased temperature is circulated through the heat medium circulation pipe 51 by driving the heat medium circulation pump 52. As a result, the relatively high temperature heat medium is supplied to the fermenter 32 again. In other words, the heat generated by the biogas engine 2 keeps the organic waste at a relatively high temperature (for example, 40 to 80°C). As a result, biogas can be generated with energy efficiency.

Meanwhile, the refrigerant whose temperature has been reduced is circulated through the refrigerant circulation pipe 41 by driving the refrigerant circulation pump 43. As a result, the relatively low-temperature refrigerant is once again supplied to the biogas engine 2. As a result, the biogas engine 2 is once again cooled by the refrigerant.

In contrast, when the temperature of the fermenter 32 is below a predetermined value (e.g., 40°C), the control unit 7 operates the biogas engine system 1 in a heating operation mode. In the heating operation mode, the control unit 7 delays the timing of ignition in the biogas engine 2 from the predetermined timing in the heat retention operation mode and/or increases the flow rate of the refrigerant in the refrigerant circulation line 4.

For example, in the heating operation mode, the control unit 7 delays the timing of ignition in the biogas engine 2 from the specified timing in the heat retention operation mode. In other words, in the heating operation mode, the biogas engine 2 is ignited at a delayed angle.

In the biogas engine 2, the internal temperature and exhaust gas temperature of the biogas engine 2 vary depending on the timing of ignition of the biogas and air mixture. If the timing of ignition of the biogas is later than the timing in the heat retention operation mode, the internal temperature and exhaust gas temperature of the biogas engine 2 become relatively high. The timing of ignition in the heating operation mode is, for example, after the piston 12 reaches top dead center and a predetermined time (for example, 5 to 15 degrees in crank angle) has elapsed.

In other words, when the biogas engine 2 is ignited at a retarded angle, the internal temperature of the biogas engine 2 and the temperature of the exhaust gas rise relative to the above-mentioned heat retention operation mode.

Therefore, the refrigerant in the refrigerant circulation line 4 in the heating operation mode can recover more thermal energy from the biogas engine 2 than the refrigerant in the heat retention operation mode. The thermal energy of the refrigerant is then transferred to the heat medium circulating in the heat medium circulation line 5 in the heat exchanger 6. In other words, the temperature of the heat medium in the heating operation mode is higher than the temperature of the heat medium in the heat retention operation mode. In the heating operation mode, the fermenter 32 is heated by the higher temperature heat medium.

For example, in the heating operation mode, the control unit 7 operates the refrigerant circulation pump 43 to increase the flow rate of the refrigerant circulating through the refrigerant circulation line 4 to be greater than the flow rate of the refrigerant in the heat retention operation mode. The flow rate of the refrigerant in the heating operation mode exceeds the flow rate of the refrigerant in the heat retention operation mode, and is, for example, 50 to 100 L/min. Also, the flow rate of the refrigerant in the heating operation mode is, for example, 150% to 200% of the flow rate of the refrigerant in the heat retention operation mode.

This increases the cooling efficiency of the biogas engine 2 by the refrigerant circulation line 4. In other words, the refrigerant in the refrigerant circulation line 4 in the heating operation mode can recover more thermal energy from the biogas engine 2 than the refrigerant in the heat retention operation mode. The thermal energy of the refrigerant is then transferred to the heat medium circulating in the heat medium circulation line 5 in the heat exchanger 6. In other words, the temperature of the heat medium in the heating operation mode is higher than the temperature of the heat medium in the heat retention operation mode. In the heating operation mode, the fermenter 32 is heated by the higher temperature heat medium. As a result, the amount of biogas generated can be increased.

Then, the control unit 7 repeats the above heating operation mode until the temperature of the fermenter 32 reaches or exceeds a predetermined value (e.g., 40°C). When the temperature of the fermenter 32 reaches or exceeds a predetermined value (e.g., 40°C), the control unit 7 switches the operation mode of the biogas engine system 1 to the heat retention operation mode.

4. Function and Effects In such a biogas engine system 1, when the temperature of the fermenter 32 is equal to or higher than a predetermined value, the control unit 7 operates in a heat retention operation mode, igniting the biogas engine 2 at a predetermined timing and circulating the refrigerant at a predetermined flow rate through the refrigerant circulation line 4. When the temperature of the fermenter 32 is lower than the predetermined value, the control unit 7 operates in a heating operation mode, delaying the timing of ignition in the biogas engine 2 compared to the timing in the heat retention operation mode, and increasing the flow rate of the refrigerant in the refrigerant circulation line 4.

As a result, in the biogas engine system 1 described above, when the temperature of the fermenter 32 is equal to or higher than a predetermined value, the fermenter 32 is kept warm, and the amount of biogas generated can be maintained while maintaining the high thermal efficiency of the biogas engine 2 alone. Also, in the biogas engine system 1 described above, the fermenter 32 can be heated only when the temperature of the fermenter 32 is below a predetermined value. In this case, the thermal efficiency of the biogas engine 2 alone decreases, but the amount of biogas generated can be increased, so that a decrease in output can be suppressed and output can be maintained. Therefore, the biogas engine system 1 described above has excellent energy efficiency of the entire system.

In the above-described embodiment, the heat exchanger 6 performs heat exchange between the relatively high-temperature refrigerant discharged from the biogas engine 2 and the relatively low-temperature heat medium discharged from the fermenter 32 to recover the thermal energy generated in the biogas engine 2. However, in the biogas engine system 1, the thermal energy generated in the biogas engine 2 can also be recovered from the exhaust gas.

In FIG. 2, in addition to the above configuration, the biogas engine system 1 is equipped with an exhaust heat recovery line 9.

The exhaust heat recovery line 9 is equipped with an exhaust heat recovery pipe 81 and an exhaust heat exchanger 82.

The exhaust heat recovery pipe 81 is a pipe through which a heat medium circulates. Examples of heat medium include water, LLC (ethylene glycol aqueous solution), or oil. One end of the exhaust heat recovery pipe 81 is connected to the heat medium circulation pipe 51 downstream of the heat exchanger 6 and upstream of the fermenter 32. The other end of the exhaust heat recovery pipe 81 is connected to the heat medium circulation pump 52 upstream of the heat exchanger 6 and downstream of the fermenter 32.

The heat medium circulation pump 52 is a three-way pump. In other words, the heat medium circulation pump 52 can supply the relatively low-temperature heat medium discharged from the fermenter 32 to the heat exchanger 6 via the heat medium circulation pipe 51, and can further supply it to the exhaust heat exchanger 82 via the exhaust heat recovery pipe 81.

The exhaust heat exchanger 82 is a known heat exchanger. The exhaust heat exchanger 82 is provided to exchange heat between the exhaust pipe 31 and the exhaust heat recovery pipe 81. More specifically, the exhaust heat exchanger 82 is interposed in the exhaust heat recovery pipe 81. In other words, the exhaust heat exchanger 82 can be supplied with a relatively low-temperature heat medium that has undergone heat exchange in the fermenter 32. The exhaust heat exchanger 82 is also interposed in the exhaust pipe 31. In other words, the exhaust heat exchanger 82 can be supplied with exhaust gas generated by the biogas engine 2.

In this biogas engine system 1, the relatively low-temperature heat medium discharged from the fermenter 32 is supplied to the heat medium circulation pipe 51 and the exhaust heat recovery pipe 81 via the heat medium circulation pump 52. The heat medium supplied to the exhaust heat recovery pipe 81 is then supplied to the exhaust heat exchanger 82 (see arrow C3 in Figure 1). Meanwhile, the relatively high-temperature exhaust gas generated by the biogas engine 2 is supplied to the exhaust heat exchanger 82 via the exhaust pipe 31. As a result, the relatively low-temperature heat medium and the relatively high-temperature exhaust gas exchange heat in the exhaust heat exchanger 82.

As a result, the exhaust gas is cooled and discharged to the outside air. Meanwhile, the temperature of the heat transfer medium rises and is discharged from the exhaust heat exchanger 82 (see arrow H3 in Figure 1). The heat transfer medium then merges with the relatively high-temperature heat transfer medium discharged from the heat exchanger 6 in the heat transfer medium circulation pipe 51 and is supplied to the fermenter 32 (see arrow H2 in Figure 1). Therefore, according to the above-mentioned biogas engine system 1, the fermenter 32 can be more efficiently kept warm in the warm-retention operation mode.

In addition, when the biogas engine 2 is ignited at a retarded angle in the heating operation mode, the temperature of the exhaust gas becomes higher than the temperature of the exhaust gas in the heat retention operation mode. Therefore, the heat medium in the exhaust heat recovery pipe 81 in the heating operation mode can recover more thermal energy from the biogas engine 2 than the heat medium in the heat retention operation mode.

In addition, in the heating operation mode, for example, if the flow rate of the heat medium circulating through the exhaust heat recovery pipe 81 is increased compared to the flow rate of the heat medium in the heat retention operation mode, the heat exchange efficiency in the exhaust heat exchanger increases. In other words, the heat medium in the exhaust heat recovery pipe 81 in the heating operation mode can recover more thermal energy from the biogas engine 2 than the heat medium in the heat retention operation mode.

In this embodiment, the thermal energy of the exhaust gas from the biogas engine 2 can be recovered and used to heat the fermenter 32, thereby further improving energy efficiency.

In the heating operation mode, the timing of ignition in the biogas engine 2 may be delayed from a predetermined timing and the flow rate of the refrigerant in the refrigerant circulation line 4 may be increased. Also, the timing of ignition in the biogas engine 2 may be delayed from a predetermined timing and the flow rate of the refrigerant in the refrigerant circulation line 4 may not be increased. Also, the flow rate of the refrigerant in the refrigerant circulation line 4 may be increased and the timing of ignition in the biogas engine 2 may not be delayed.

1 Biogas engine system 2 Biogas engine 3 Biogas generation section 4 Coolant circulation line 5 Heat medium circulation line 6 Heat exchanger 7 Control unit 8 Temperature sensor

Claims (1)

A biogas engine that burns biogas;
a biogas generating unit that ferments organic waste to generate biogas;
A refrigerant circulation line for cooling the biogas engine with a refrigerant;
A heat medium circulation line for heating the biogas generation section with a heat medium;
a heat exchanger for exchanging heat between the refrigerant circulation line and the heat medium circulation line;
A temperature sensor that detects the temperature of the biogas generation unit;
a control unit that controls the operation of the biogas engine and the refrigerant circulation line in response to the temperature of the biogas generation unit detected by the temperature sensor,
The control unit
a heat retention operation mode in which, when the temperature of the biogas generation unit detected by the temperature sensor is equal to or higher than a predetermined value, the biogas engine is ignited at a predetermined timing and a refrigerant is circulated through the refrigerant circulation line at a predetermined flow rate;
When the temperature of the biogas generation section detected by the temperature sensor is below a predetermined value, the timing of ignition in the biogas engine is delayed from the predetermined timing and/or the flow rate of refrigerant in the refrigerant circulation line is increased.

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