Patent Application
20140190165
The present invention relates to a power plant using a medium having a lower boiling point than water as a working medium, equipped with an air removing device which removes an air intruding into the working medium.
A power plant, using a low boiling point medium, for recovering heat energy from a low-temperature heat source which has not been utilized in conventional geothermal power generation using a steam turbine and for generating a power has attracted special attention as an energy recovery device recently (see Patent Literature 1).
In general, when a medium with a high vapor pressure (i.e., a low boiling point) is used, vaporization by the vaporizer is easy but condensation by the condenser is difficult. To the contrary, when a medium with a low vapor pressure (i.e., a high boiling point) is used, vaporization is difficult but condensation is easy. From this point of view, a medium which maximizes an enthalpy difference (heat difference) between a turbine inlet and a turbine outlet is selected as a medium to be used. For example, n-pentane (nC5H12) is mainly used as a natural medium used in a condition where a temperature of a geothermal heat source is from 130° C. to 140° C. and a temperature of a cooling source is from 15° C. to 30° C.
The cooling source of the condenser is generally circulating cooling water or an atmosphere. Therefore, the temperature of the cooling source is largely different between winter and summer. Thus, in a case where the condenser is designed only based on a cooling performance required in summer, the cooling performance of the condenser is further enhanced when the temperature of the cooling source drops in winter.
As shown in
Thus, as a device for removing the air intruding the medium in a plant related to power generation, Patent Literatures 2 to 6 described below are known.
Patent Literature 2 discloses a binary power plant using water instead of a low boiling point medium, equipped with an air extraction device for extracting an air from drain water of a condenser.
Patent Literature 3 discloses a power system including a power cycle circuit 10 which circulates a working fluid in which a high boiling point medium and a low boiling point medium are mixed through a vapor generator 1 for heating a solution of the working fluid and generating a vapor, a steam turbine 2 which is driven by the vapor supplied by the vapor generator 1, a condenser 3 for cooling the vapor released from the steam turbine to condense it to the solution, and a feed pump 16 for supplying the solution supplied from the condenser 3 to the vapor generator 1, in that order, wherein a concentration of the low boiling point medium of the working fluid in the condenser 3 is determined to provide a pressure around the atmospheric pressure as the lowest pressure which can be generated in the condenser 3 in the power cycle circuit 10.
Patent Literature 4 discloses a plant which includes a chamber having a piston therein provided above an upper portion of a condenser, a valve connecting a space below the piston in the chamber to the condenser, a cooling means cooling a lower portion of the chamber by a coolant through a wall, and a discharge valve connected to the lower portion of the chamber.
Patent Literatures 5 and 6 disclose a plant including: a tightly sealed chamber above an upper portion of a condenser, the chamber being provided with a movable diaphragm for dividing the inside of the chamber into an upper portion and a lower portion; two flow rate control valves arranged between the condenser and the lower portion of the chamber in series; a cooling means for cooling the lower portion of the chamber with a coolant through a wall; and a discharge valve connected to the lower portion of the chamber.
Patent Literature 2 described above uses water as the medium and therefore requires the heat source of 100° C. or more. Thus, there is a problem that it cannot use a lower-temperature heat source.
Patent Literature 3 described above has problems that the pressure in the condenser increases in summer and the heat generation efficiency is reduced, because the concentration of the low boiling point medium is determined to provide a pressure around the atmospheric pressure as the lowest pressure which can be generated in the condenser in winter.
Patent Literatures 4, 5, and 6 described above disclose the plant for removing the air from the medium, but merely refer to an example in which the plant is regularly operated every 20 minutes as an operation timing of the plant. Thus, there is a problem that an outflow of the medium increases because the air removing operation is performed more than necessary.
In view of the above problems, it is an object of the present invention to provide a power plant equipped with an intruding air removing device which can detect an air intruding into a medium flow path of the power plant without stopping the power plant and reduce the amount of a working medium exhausted to the outside of the plant.
To achieve the aforementioned object, the present invention is characterized in that, in a power plant including: a heat exchanger configured to exchange heat between a medium having a lower boiling point than water and a heat source to generate a medium gas; a turbine configured to receive a pressure of the medium gas supplied from the heat exchanger to rotate; an electric generator configured to be connected to the turbine; a condenser configured to cool the medium gas discharged from the turbine; a circulation pump configured to supply the medium released from the condenser to the heat exchanger; a medium flow path configured to pass through the heat exchanger, the turbine, the condenser, and the circulation pump; and an air removing device configured to remove an air intruding into the medium, the air removing device includes: a gas retaining portion provided on an outlet side of the condenser and configured to retain a gas in the medium; a pressure gauge configured to measure a pressure in the gas retaining portion; a thermometer configured to measure a temperature in the gas retaining portion; a controller configured to calculate a pressure threshold value based on a saturated vapor pressure value of the medium calculated using the temperature of the thermometer, and compare a pressure value of the pressure gauge and the pressure threshold value to determine whether or not an air has intruded into the medium; and a release means configured to release the gas in the gas retaining portion in a case where it is determined that the air has intruded.
The release means includes: a first chamber to which the gas retained in the gas retaining portion is transferred in a case where the controller determines that the air has intruded; and a medium supply means configured to supply a liquid medium to the first chamber so that the gas is compressed. The gas remaining in the first chamber is released after the medium is supplied.
The medium supply means may include a liquid medium tank configured to store the liquid medium and a liquid medium feed pump configured to supply the liquid medium from the liquid medium tank to an inside of the first chamber. Also, the medium supply means may include a valve provided in the medium flow path on an outlet side of the circulation pump, a branching pipe configured to branch from a pipe between the circulation pump and the valve and connect to the first chamber, and another valve provided in the branching pipe, and when determining intrusion of the air, the controller may control the valve provided in the medium flow path on the outlet side of the circulation pump to be closed and the other valve provided in the branching pipe to be opened.
The release means is characterized by including: a first valve provided in a pipe connecting the gas retaining portion and a lower portion of the first chamber; a second valve provided in a pipe connecting the liquid medium feed pump and the first chamber; a third valve provided in a pipe connecting an upper portion of the first chamber to a second chamber; a fourth valve configured to release the gas from the second chamber; and a fifth valve provided in a pipe connecting the gas retaining portion to the upper portion of the first chamber.
The controller is characterized by, when determining that the air has intruded, controlling the second valve and the third valve to be closed and the first valve and the fifth valve to be opened so that the gas in the gas retaining portion is transferred to the first chamber, and then controlling the first valve and the fifth valve to be closed, the second valve to be opened, and the liquid medium feed pump to supply the liquid medium to the first chamber so that the gas is compressed, and subsequently controlling the third valve to be opened while the fourth valve is closed so that the gas in the first chamber is transferred to the second chamber, and then controlling the third valve to be closed and the fourth valve to be opened so that the gas in the second chamber is released to an outside of the second chamber.
The power plant may further include: a combustor configured to burn the medium remaining in the gas released from the second chamber; and an air supply portion configured to supply an air to the combustor. Furthermore, a sixth valve may be provided in a pipe connecting to the combustor and the air supply portion to each other, and the controller may control opening degrees of the fourth valve and the sixth valve to adjust a flow rate.
The controller preferably determines that the air has intruded when the pressure value of the pressure gauge is larger than the pressure threshold value which is preferably calculated by adding a margin value to the saturated vapor pressure value. The margin value is a preset fixed value or a proportional value obtained by multiplying the saturated vapor pressure value by a coefficient.
Furthermore, it is preferable that a spray nozzle is provided for spraying the liquid medium into the first chamber.
As the medium used in the present invention, an organic low boiling point medium such as various chlorofluorocarbons, especially R245fa, and n-pentane can be used.
According to the present invention, the pressure threshold value obtained by adding the margin value to the saturated vapor pressure value of the medium calculated based on the temperature in a liquid phase portion of the gas retaining portion and the pressure value of a gas phase portion of the gas retaining portion are compared with each other, thereby intrusion of an air is detected. Therefore, it is possible to automatically detect the intrusion of the air into the medium flow path of the power plant. Moreover, the amount of the working medium released to the outside of the plant can be reduced. Also, it is possible to prevent reduction in the power generation efficiency caused by a lowered condensing performance of the condenser because of intrusion of an air not condensed by the condenser into the medium.
Embodiments of the present invention will be described below based on the drawings. First, description is now made to an example of the embodiment of the present invention based on
A first chamber 2 is connected to the gas retaining portion 1 with a pipe via a valve 12. Moreover, a pipe is provided for connecting an upper portion of the first chamber 2 and the gas retaining portion 1 to each other. This pipe is provided with a valve 16. To the first chamber 2, a pressure gauge 7, a liquid level gauge (higher level) 8, and a liquid level gauge (lower level) 9 are provided in that order from the upper portion of the chamber.
A liquid medium feed pump 18 is connected to the inside of the first chamber 2 with a pipe via a flowmeter 6 for liquid pentane and a valve 13. At the outlet for the liquid pentane of this pipe, a spray nozzle 25 is provided.
A second chamber 3 is connected to an upper portion of the first chamber 2 with a pipe via a valve 14.
A combustor 4 is provided with combustion catalyst therein, and a lower portion of the combustor 4 is connected to the second chamber 3 with a pipe via a valve 15. An air supply means 19 is connected to the combustor 4 with a pipe via a valve 17. Pentane supplied from the second chamber 3 is mixed with an air supplied from the air supply means 19, and is burned by the combustion catalyst in the combustor 4 to produce an exhaust gas. The produced exhaust gas is released to the atmosphere. In the combustor 4, for making the combustion catalyst work, a heater 4a is provided which controls the combustion catalyst to a predetermined temperature. The combustor 4, the air supply portion 19, the valve 17 and the pipes connecting those are not essential components, but are unnecessary in a case where the gas released from the valve 15 is diluted by the atmosphere without being burned.
A controller 5 is connected to the thermometer 10, the pressure gauge 11, the pressure gauge 7, the liquid level gauge (higher level) 8, the liquid level gauge (lower level) 9, and the flowmeter 6 with signal lines, respectively. Signals from the instruments are respectively input to the controller 5. Moreover, the controller 5 is connected to the valves 12, 13, 14, 15, 16, and 17 with electric wires, respectively, to control opening and closing of the valves.
Another embodiment of this example may be configured to use the circulation pump 104 also as the liquid medium feed pump 18, substitute the pipe between the condenser 103 and the circulation pump 104 for a liquid medium tank 24, provide a valve in the pipe at the outlet of the circulation pump 104, provide a pipe branching from a portion between this valve and the circulation pump 104 and connecting to the first chamber 2, and provide the valve 13 in this branching pipe.
Next, an operation of this plant is described.
First, the air intrusion detection step S1 is described.
The controller 5 obtains the signal of the pressure gauge 11 provided in a gas phase portion of the gas retaining portion 1 and the signal of the thermometer 10 provided in a liquid phase portion of the gas retaining portion 1, and calculates a pressure threshold value obtained by adding a margin value (margin) to a saturated vapor pressure value of the medium calculated based on the temperature of the thermometer. If the pressure value of the pressure gauge 11 is equal to or less than the pressure threshold value, measurements of the pressure value and the temperature are continued. If the pressure value of the pressure gauge 11 is higher than the pressure threshold value, it is determined that an air has intruded into the medium and the control flow goes to the next step. The above-described margin value is set to a fixed value or a proportional value which is obtained by multiplying the aforementioned saturated vapor pressure value of the medium calculated based on the temperature of the thermometer by a coefficient. More specifically, the saturated vapor pressure (Ps) at a temperature (T1) is calculated using the following Equation 1.
Ps=0.0003(T1)3+0.0159(T1)2+1.1844(T1)+24.316 (Equation 1)
The margin value is determined via several tests considering the number and conditions of joints. In case of the fixed value, for example, the margin value is set to about 10% of a value at 1 atmosphere. In case of the proportional value, the aforementioned coefficient is set to about 0.1.
Next, the medium liquefaction step S2 is described. In this step, an air-containing gas retained in the gas retaining portion is transferred to the first chamber 2, and the gas is compressed by supplying a liquid medium into the first chamber 2, so that the medium in the gas is liquefied and the amount of the medium in the gas is reduced.
More specifically, after a state where the respective valves 12, 13, 14, 15, 16, and 17 of the intruding air removing device shown in
When liquid pentane is introduced into the first chamber 2 to compress the air-containing gas, the gas temperature rises. This rise in temperature is given by the following Equation 2.
T2=T1×[P2/P1](k-1)/mk (Equation 2)
T2: Gas temperature after compression (K)
T1: Gas temperature before compression (K)
P2: Gas pressure after compression (mPa)
P1: Gas pressure before compression (mPa)
k: Specific heat ratio
m: Stage number of compression
For example, when adiabatic compression of an air of 30° C. saturated with pentane is carried out from 101 kPa to 1 MPa, the temperature rise difference (ΔT) is 83° C. This rise in temperature can be suppressed by injecting liquid pentane which is made fine by the spray nozzle into the first chamber 2, instead of simply injecting liquid pentane into the first chamber 2. A portion of n-pentane saturated in the air-containing gas is cooled to be liquefied, and can be collected. Injection using the spray can reduce the temperature in the first chamber 2 more rapidly than in a method for injecting liquid pentane without spraying it.
When the detection value of the liquid level gauge (higher level) 8 exceeds the predetermined higher liquid level threshold value, the valve 13 is closed and the liquid medium feed pump 18 is stopped.
Next, the exhaust step S3 is described. First, a counter is initialized to 0. Then, the first chamber 2 and the second chamber 3 are made to communicate with each other, so that a portion of the gas compressed in the first chamber 2 is transferred to the second chamber 3. More specifically, a state where the valve 15 is closed and the valve 14 is opened is continued for a predetermined time. Then, the valve 14 is closed.
Subsequently, the gas is released from the second chamber 3 to the outside of the plant. At this time, the combustor 4, the air supply portion 19, the valve 17 and the pipes connecting those to one another are not essential components. For example, in a case where the gas released from the valve 15 is diluted by the atmosphere without being burned, the valve 15 may be opened to release the gas to the atmosphere as it is.
In a case where the gas is burned and is then released to the atmosphere, it is expected that the gas cannot be completely burned only by oxygen contained in the gas. In case of n-pentane, for example, when a ratio of mixing with an air exceeds the combustion range (1.5% to 7.8%) of n-pentane, oxygen has to be supplied. For adjusting the air amount to this range, an air is introduced via the valve 17. This air is desirably supplied from compressed air supply equipment. For example, an air for instrumentation for operating instrumentation devices of the plant may be used as this air. More specifically, the following procedure is performed. The combustor 4 is provided therein with a ceramic honeycomb filter carrying platinum fine particles as combustion catalyst. While the inside of the combustor 4 is heated to be at a temperature from 200° C. to 350° C. by the heater 4a, the valves 17 and 15 are opened to supply the gas and the air to the combustor 4, thereby the medium is burned. This state is continued for a predetermined time. Then, the valves 15 and 17 are closed. Subsequently, the counter is incremented by one. If the counter is less than N times which is a predetermined number of times, the procedure loops back, as shown in
Then, the pressure is released from the first chamber 2 to the gas retaining portion 1 and the medium is moved. More specifically, the valves 16 and 12 are opened and, after a predetermined time has passed, the valves 16 and 12 are closed. Then, the procedure loops back to the above-described air intrusion detection step S1.
Next, the reason why compressing the mixed gas of the air and the medium can reduce the amount of the medium in the mixed gas is described. The amount Fst of n-pentane saturated in an air is expressed by the following Equation 3.
Fst=Fa×(Ps/(Pc−Ps)) (Equation 3)
Fst: The amount of n-pentane which is saturated in an air at a temperature t in the standard state (Nm3)
Fa: The amount of an air in the standard state (Nm3)
Ps: The saturated vapor pressure of n-pentane at the temperature t (kPa)
Pc: The operation pressure (kPa)
The results of calculation are shown in
Next, the description is made with respect to the loss amount of n-pentane.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-179444 | Aug 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/070791 | 8/16/2012 | WO | 00 | 2/6/2014 |
