Compressed-air-storing electricity generating system and electricity generating method using the same

Disclosed are a compressed air energy-storing electricity generating system and an electricity generating method using the same, in which air of a high pressure is injected into a tank laid under the ground using midnight electricity and surplus produced electricity, and the air of the high pressure in the tank is uniformly discharged so as to drive a generator during a time period when the consumption of electric power is high, thus efficiently managing energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compressed air energy-storing electricity generating system and an electricity generating method using the same, and more particularly to a compressed air energy-storing electricity generating system and an electricity generating method using the same, in which air of a high pressure is injected into a tank laid under the ground using midnight electricity and surplus produced electricity, and the air of the high pressure in the tank is uniformly discharged so as to drive a generator during a time period when the consumption of electric power is high, thus efficiently managing energy.

2. Description of the Related Art

Midnight electricity means electricity used late at night from 10 pm of one day to 8 am of the next day or from 11 pm of one day to 9 am of the next day when the consumption of electricity is low, and has an inexpensive electric charge due to the supply of surplus electric power. Thus, various methods for using midnight electricity have been proposed. Representative apparatuses for using midnight electricity include a regenerative boiler using midnight electricity and a regenerative water heater using midnight electricity. These apparatuses store midnight electricity by night and use the stored electricity by day so as to disperse the consumption of electricity power concentrated on the daytime.

Further, according to another method for using midnight electricity, compressed air is stored in an underground cave using midnight electricity and the stored compressed air is supplied to a turbine by day so as to drive a generator, thus reducing the consumption of electric power by day.

As shown inFIG. 4, in a conventional compressed air energy storage (CAES) system using midnight electricity, air compressed by a compressor20, driven using midnight electricity, is injected into a storage tank30, and the stored compressed air is discharged to the outside during a time period when the consumption of electric power is high. The discharged compressed air is mixed with a fuel in a burner50such that the mixture of the air and the fuel is burned, and a turbine40is driven by the pressure of the burnt gas. Thereby, a generator is driven.

Such a system compresses air using midnight electricity, and uses energy converted from the compressed air if necessary. However, as the compressed air is continuously discharged to the outside, the pressure in the storage tank30is gradually lowered and the pressure of the discharged compressed air is gradually lowered, and thus a turbine driving efficiency is depreciated. Accordingly, an apparatus, which can continuously discharge compressed air stored at a uniform pressure, has been strongly required.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a compressed air energy-storing electricity generating system and an electricity generating method using the same, in which at least two storage tanks storing compressed air are provided with lower portions connected by a connection pipe and respectively have separate spaces for containing storage water. Thus, when air is compressed and stored using midnight electricity, in the case that the compressed air of a desired pressure is injected into one storage tank connected to a compressor, the increase of pressure in the storage tank is sensed and storage water is forcibly transferred to a hydraulic pump installed on the connection pipe so that the pressure in the storage tank is uniformly maintained, and simultaneously the other storage tank, hermetically sealed, serves as an accumulator for storing hydraulic energy due to the compression of sealed air.

Further, the compressed air in the storage tank connected to a turbine is discharged by day, and then the decrease of the pressure in the storage tank is sensed and the hydraulic pump on the connection pipe serves as a hydraulic motor and supplies the storage water into the storage tank storing the compressed air so that the pressure in the storage tank is uniformly maintained, and simultaneously electricity is generated using the hydraulic energy stored in the accumulator through the hydraulic motor.

Accordingly, there are provided a compressed air energy-storing electricity generating system and an electricity generating method using the same, in which the pressure in the storage tank for storing the compressed air is uniformly maintained due to the transfer of the storage water so as to maximize efficiencies of the compressor and the turbine when the compressed air is stored in the storage tank or the compressed air in the storage tank is discharged, and hydraulic energy is stored in the accumulator by night and electricity is generated using the stored hydraulic energy by day.

In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a compressed air energy-storing electricity generating system, which comprises a compressor sucking and compressing external air through driving of a motor, storage tanks storing the compressed air, a burner mixing the compressed air, supplied from the storage tanks, with a fuel and burning the obtained mixture, and a generator driving a turbine using the obtained burnt gas and generating electricity through driving of the turbine, wherein the storage tanks include a first storage tank and a second storage tank, separately disposed such that the lower portions of the two tanks are connected by a connection pipe, the first storage tank is provided with an inlet hole and an outlet hole formed through the upper portion thereof so as to receive the compressed air supplied from the compressor and discharge the compressed air from the first storage tank, and storage water is contained in the first and second storage tanks such that the second storage tank is hermetically sealed so as to serve as an accumulator.

A hydraulic pump/motor unit may be installed on the connection pipe connecting the first and second storage tanks, and forcibly transfer the storage water from the first storage tank to the second storage tank by means of a pump function or transfer the storage water from the second storage tank in a high pressure state to the first storage tank in a low pressure state due to pressure equilibrium.

A pressure sensor may be installed in the first storage tank, compare a sensed value with a set value, and operate the hydraulic pump/motor as a result of the comparison.

Sealed air stored in the second storage tank may have a pressure higher than that of the compressed air stored in the first storage tank in an atmospheric state by a designated degree such that the storage water fills 90% or more of the total volume of the first storage tank when the inside of the first storage tank is in the atmospheric state.

A second generator may be installed in the hydraulic pump/motor unit, and when a hydraulic motor function of the hydraulic pump/motor unit is performed, the motor may be driven by the transfer of the storage water stored in the second storage tank so as to generate electricity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a compressed air energy-storing electricity generating system in accordance with the present invention will be described in detail with reference to the annexed drawings.

FIG. 1is a schematic view illustrating a compressed air energy-storing electricity generating system in accordance with the present invention,FIGS. 2 to 4are views illustrating the change of pressure in storage tanks of the compressed air energy-storing electricity generating system in accordance with the present invention, andFIG. 5is a block diagram illustrating an electricity generating method using the compressed air energy-storing electricity generating system in accordance with the present invention.

As shown inFIG. 1, a compressed air energy-storing electricity generating system10of the present invention includes a compressor20, storage tanks30, which store air compressed by the compressor20, and a turbine40, which is driven by the compressed air discharged from the storage tanks30.

The compressor20drives a motor using midnight electricity or surplus produced electricity, receives external air due to the driving of the motor, and compresses the external air. Here, one compressor may be installed or a plurality of compressors may be installed in parallel so as to shorten an air compressing time.

The storage tanks30are installed at the outside or buried under the ground. When the compressed air energy-storing electricity generating system10is installed in a city, on which many buildings are concentrated, it is preferable that the storage tanks30are buried under the ground and thus a ground space is utilized.

In the present invention, the two storage tanks30are used. However, if necessary, in order to increase the total storage capacity, the number of the storage tanks30is increased to three or more, or the volumes of the storage tanks30are increased.

As shown inFIGS. 1 to 5, the storage tanks30include a first storage tank31and a second storage tank32. The first storage tank31is provided with an inlet hole311, through which the air compressed by the compressor20is injected into the first storage tank31, and an outlet hole312, through which the compressed air in the first storage tank31is discharged to the outside. The lower portions of the first and second storage tanks31and32are connected by a connection pipe33. A designated amount of storage water34is contained in the lower portions of the first and second storage tanks31and32such that the storage water34flows between the first and second storage tanks31and32. That is, sealed air35is located in the upper portion of the second storage tank32, hermetically sealed, and the storage water34is located in the lower portion of the second storage tank32, and when the storage water34flows from the first storage tank31to the second storage tank32through the connection pipe33, the sealed air35has a reduced volume and a high pressure and thus the second storage tank32serves as an accumulator.

A hydraulic pump/motor unit331, which serves as both a hydraulic pump and a hydraulic motor, is installed on the connection pipe33passing the storage water34. For example, the hydraulic pump/motor unit331is operated as the hydraulic motor using midnight electricity by night so as to move the maximum amount of the storage water34to the second storage tank32, and the connection pipe33is opened by day when the consumption of electric power is high so as to move the storage water34in the second storage tank32to the first storage tank31due to the expansion of sealed air35in a high pressure state and to continuously discharge compressed air36stored in the first storage tank31to the outside. Of course, the hydraulic pump and the compressor20may use surplus produced electricity during a time period by day when the consumption of electric power is low.

The compressed air36discharged through the outlet hole312of the first storage tank31is mixed with the fuel in the burner50, and the mixture is burned and thus drives the turbine40. Then, a generator connected to a turbine shaft generates electricity due to the driving of the turbine40.

Further, a cooler21and a regenerator51are respectively installed in routes of the compressed air36supplied to and discharged from the storage tanks30. Since the compressed air36supplied to the storage tanks30has a high temperature, the compressed air36passes through the cooler21so that the compressed air36is stored after the volume of the compressed air36is reduced, and thus the storage capacity of the compressed air36in the storage tanks30is increased. Further, the compressed air36discharged from the storage tanks30passes through the regenerator51so that the compressed air36exchanges heat with gas of a high temperature exhausted from the turbine40, and thus the burning due to the mixing of the compressed air36and the fuel is easily achieved and a turbine driving efficiency due to the expansion of the volume of the compressed air36is increased.

A pressure sensor313is installed in the first storage tank31. The pressure sensor313senses the pressure in the first storage tank31, compares the sensed pressure with a set value, and operates the hydraulic pump of the hydraulic pump/motor unit331as a result of the comparison. That is, when the compressor20stores the compressed air36of a desired pressure in the first storage tank31using midnight electricity, the pressure sensor313senses the increase of the pressure in the first storage tank31and operates the hydraulic pump such that the storage water34in the first storage tank31is forcibly transferred to the second storage tank32, thus uniformly maintaining the pressure in the first storage tank31. On the contrary, when the compressed air36in the first storage tank31is supplied to the turbine40by day, the pressure sensor313senses the decrease of the pressure in the first storage tank31and opens the hydraulic pump/motor unit331such that the storage water34in the second storage tank32is transferred to the first storage tank31, thus uniformly maintaining the pressure in the first storage tank31. Although this embodiment describes the hydraulic pump/motor unit331including both the hydraulic pump and the hydraulic motor, the hydraulic pump and the hydraulic motor may be separately installed. Accordingly, this system further includes control units for respectively controlling the hydraulic pump and the hydraulic motor such that the hydraulic pump and the hydraulic motor can be smoothly operated.

A second generator is installed on a hydraulic motor shaft of the hydraulic pump/motor unit331. The storage water34in the second storage tank32is transferred to the first storage tank31due to the increase of the pressure of the sealed air35, and drives the hydraulic motor having a hydraulic turbine function, thus operating the second generator. That is, the hydraulic pump/motor unit331stores hydraulic pressure energy in the second storage tank32using midnight electricity. Further, during a time period by day when the consumption of electric power is high, the storage water34in the second storage tank32is transferred to the first storage tank31, drives the hydraulic motor, and operates the second generator installed on the hydraulic motor shaft, and the storage water34transferred to the first storage tank31allows the compressed air36in the first storage tank31to be discharged at a regular pressure so as to drive the turbine40. Thereby, the compressed air energy-storing electricity generating system10system10of the present invention generates electricity using hydraulic energy and compressed air.

Hereinafter, the change of the pressure in the storage tanks30of the above compressed air energy-storing electricity generating system10will be described in detail. Here, pressure of compressed air required to drive the turbine40is about 50 bar.

FIG. 2illustrates the fundamental setting of the compressed air energy-storing electricity generating system10before the system10is driven. The storage water34is contained in the first storage tank31provided with the inlet hole311and the outlet hole312, the sealed air35is contained in the hermetically sealed second storage tank32, and the two tanks31and32are connected by the connection pipe33. The hydraulic pump/motor unit331is installed on the connection pipe33.

Here, the pressure of the storage water34contained in the first storage tank31is 50 bar, and the pressure of the sealed air35in the second storage tank32is 51 bar. In the case that the pressure of the sealed air35in the second storage tank32is larger than that of the storage water34contained in the first storage tank31by a designated amount, as described above, the storage water34is collected in the first storage tank31due to the pressure of the sealed air35in the second storage tank20in a stand-by state.

With reference toFIG. 3, the compressor20is driven using midnight electricity under the state ofFIG. 2, and thus the compressed air36of a pressure of 50 bar is injected into the first storage tank31. When the compressed air36having an amount, which is more than the capacity of the first storage tank31, is injected into the first storage tank31, the pressure in the first storage tank31is increased, and the pressure sensor313in the first storage tank31senses the increase of the pressure and thus operates the hydraulic pump/motor unit331.

When the hydraulic pump of the hydraulic pump/motor unit331is operated using midnight electricity, the storage water34contained in the first storage tank31is forcibly transferred to the second storage tank32, and thus the pressure in the first storage tank31is decreased to 50 bar. Further, the pressures of the sealed air35and the storage water34in the second storage tank32are gradually increased, and respectively reach 100 bar when the storage water34in the second storage tank32has the same water level as that of the storage water34in the first storage tank31.

With reference toFIG. 4, when the hydraulic pump of the hydraulic pump/motor unit331is continuously operated, the storage water34in the first storage tank31is continuously transferred to the second storage tank32such that 75% of the storage water34is contained in the second storage tank32. Then, the sealed air35in the second storage tank32has a reduced volume and a pressure of 200 bar. Further, the compressor20is continuously driven, and thus the compressed air36is continuously injected into the first storage tank31such that the compressed air36of a pressure of 50 bar fills 75% of the total volume of the first storage tank31.

On the contrary, during a time period by day when the consumption of electric power is high, the connection pipe33is opened. Thus, the storage water34in the second storage tank32drives the hydraulic motor of the hydraulic pump/motor unit331and is transferred to the first storage tank31due to pressure equilibrium caused by a difference of pressures, and the compressed air36stored in the first storage tank31, as much as the volume of the transferred storage water34, is discharged through the outlet hole312.

In more detail, when the hydraulic pump/motor unit331is opened under the state ofFIG. 4, the sealed air35of a high pressure in the second storage tank32is expanded, and thus the storage water34in the second storage tank32is transferred to the first storage tank31. According to the transfer of the storage water34, the compressed air36of a pressure of 50 bar contained in the first storage tank31is discharged through the outlet hole312.

That is, the storage water34in the second storage tank32is continuously transferred to the first storage tank31until the pressure of the sealed air35in the second storage tank32is almost equal to the pressure of the compressed air36in the first storage tank31, and the compressed air36stored in the first storage tank31is continuously discharged due to the transfer of the storage water34.

Now, with reference toFIG. 5, an electricity generating method using the above compressed air energy-storing electricity generating system of the present invention will be described, as follows.

The electricity generating method using the above compressed air energy-storing electricity generating system, which has the compressor20, the first and second storage tanks31and32, the lower portions of which are connected by the connection pipe33, the hydraulic pump/motor unit331installed on the connection pipe33for transferring the storage water34between the first and second storage tanks31and32, and the turbine40driven by the compressed air36discharged from the first storage tank31so as to generate electricity, includes a compressed air injecting step (S1), a pumping step (S2), a discharging step (S3), and an electricity generating step (S4).

In the compressed air injecting step (S1), the compressor20is driven using midnight electricity and surplus produced electricity, and thus the compressed air36is injected into the first storage tank31.

Thereafter, in the pumping step (S2), the storage water34contained in the first storage tank31is forcibly transferred to the second storage tank32due to the pump function of the hydraulic pump/motor unit331, and thus presses the sealed air35in the second storage tank32and leaves a space in the first storage tank31, thereby increasing the inflow amount of the compressed air36using the compressor20.

In the discharging step (S3), the compressed air36stored in the first storage tank31is discharged so as to drive the turbine40, and the hydraulic pump/motor unit331installed on the connection pipe33is opened and thus the storage water34, as much as the amount of the discharged compressed air36, is transferred to the first storage tank31due to the increase of the pressure of the sealed air35in the second storage tank32.

Further, in order to uniformly set the pressure of the compressed air36stored in the first storage tank31and the pressure of the compressed air36discharged from the first storage tank31, a pressure controlling step (S5) may be achieved simultaneously with the pumping step (S2) and the discharging step (S3). That is, when the compressor20injects the compressed air36into the first storage tank31, in the case that the compressed air36injected into the first storage tank31has a designated amount or more, the pressure of the compressed air36in the first storage tank31is increased. Then, a value, obtained by sensing the pressure of the compressed air36in the first storage tank31using the pressure sensor313installed in the first storage tank31, is compared with a set value inputted by a user, and when the sensed value is more than the set value, the hydraulic pump of the hydraulic pump/motor unit331is driven and thus the storage water34is forcibly pumped into the second storage tank32.

When the compressed air36is used during a time period when the consumption of electric power is high, the compressed air36is discharged from the first storage tank31and thus the pressure of in the first storage tank31is lowered. Accordingly, when the sensed pressure is not more than the set value, the pressure sensor313opens the hydraulic pump/motor unit331so as to transfer the storage water34in the second storage tank32to the first storage tank31due to pressure equilibrium, thus uniformly maintaining the pressure of the compressed air36in the first storage tank31.

Thereafter, a hydraulic electricity generating step (S6) is further performed. In the hydraulic electricity generating step (S6), when the storage water34is transferred from the second storage tank32, serving as an accumulator, to the first storage tank31, the storage water34drives the hydraulic motor of the hydraulic pump/motor unit331installed on the connection pipe33, and the second generator60generates electricity due to the driving of the hydraulic motor.

Thereafter, in the electricity generating step (S4), the compressed air36discharged in the discharging step (S3) is mixed with the fuel in the burner50, and the mixture is burned. Then, the obtained burnt gas enters the turbine40and collides with turbine blades, thereby driving the turbine40so as to generate electricity.

Further, a heat exchanging step (S7) may be performed. In this case, after the heat exchanging step (S7) is completed, electricity is generated using the compressed air36discharged in the discharging step (S3). That is, the discharged compressed air36passes through the regenerator51so that the compressed air36exchanges heat with gas of a high temperature exhausted from the turbine40, and the compressed air36in a high temperature state is put into the burner50. Here, the volume of the compressed air, to which the heat is applied, is gradually increased, and is then rapidly increased simultaneously with burning, and thus the output of the turbine40is improved.

As apparent from the above description, the present invention provides a compressed air energy-storing electricity generating system and an electricity generating method using the same, in which at least two storage tanks storing compressed air are provided with lower portions connected by a connection pipe and respectively have separate spaces for containing storage water, and thus a hydraulic pump/motor unit installed on the connection pipe serves as a hydraulic pump and forcibly transfers the storage water so that the air in one storage tank, hermetically sealed, has a high pressure and compressed air of a desired pressure is injected into the other storage tank.

Thus, when the hydraulic pump/motor unit installed on the connection pipe is opened, the sealed air in the sealed storage tank is expanded due to pressure equilibrium and the storage water in the sealed storage tank passes through the hydraulic pump/motor unit serving as a hydraulic motor and is transferred to the other storage tank containing the compressed air, and the compressed air in the other storage tank is discharged to the outside as much as the volume of the transferred storage water.

As described above, there are provided the present invention provides an environmentally friendly compressed air energy-storing electricity generating system and an electricity generating method using the same, in which the storage water is transferred between the two storage tanks according to the compressed state of the air within the storage tanks and thus the pressure and the amount of the compressed air, finally discharged, are uniformly maintained so as to maximize efficiencies of a compressor and a turbine, and hydraulic energy is stored in the sealed storage tank, serving as an accumulator, by night and electricity is generated using the stored hydraulic energy by day.