Two-stage turbine gas suspension ORC power generation system and control method
Technical Field
The invention relates to the technical field of industrial waste heat recovery and clean energy, in particular to a two-stage turbine gas suspension ORC power generation system and a control method.
Background
The Organic Rankine Cycle (ORC) is a technology for realizing Rankine cycle power generation by adopting a low-boiling-point organic working medium (such as a refrigerant) and completing the phase change of the organic working medium by utilizing a heat source with a lower temperature. The liquid organic working medium is heated by low-temperature waste heat in an evaporator (sometimes called a waste heat exchanger) to generate high-temperature high-pressure gas, the high-temperature high-pressure gas is expanded by an expander to drive a generator to generate electric energy, the low-temperature low-pressure gaseous working medium after passing through the expander is cooled into liquid in a condenser, and the liquid is pressurized by a refrigerant pump and sent back to the evaporator to complete a cycle. The ORC waste heat power generation technology has the problems of low cycle efficiency, less generated energy, high operation and maintenance cost and long investment return period. The expansion generator is a key device for restricting the performance of an ORC unit, and the expansion generator mainly comprises two types, namely a screw machine and a centripetal turbine expander. The screw machine can run at low speed to directly drive the power frequency generator to generate power, and the centripetal turbine rotates at high speed and drives the power frequency motor to generate power after being decelerated by the gear box.
The invention discloses a radial expansion generator set, which is an ORC (organic Rankine cycle) circulating system based on a static pressure air bearing, belongs to the prior art, has the application number of 2019108354914, and is named as a static pressure air bearing-based ORC circulating system, wherein two stages of centripetal turbines are adopted in the expansion generator set and are symmetrically arranged at two sides of a motor, one side of the expansion generator set is a high-pressure stage turbine, and the other side of the expansion generator; the support of the generator rotating shaft of the expansion generator set adopts a static pressure air bearing, and the lubricating liquid of the static pressure air bearing adopts a refrigerant in the system, so that the pollution of the lubricating oil is avoided, and the loss of the bearing is reduced; the air suspension bearing technology is a bearing technology which can achieve the effects of supporting load, lubricating and cooling by forming a fluid film on the surface of a bearing sliding pair through fluid with certain pressure. The cooling refrigerant of the expansion generator set enters from the bottom of the motor and is discharged into the condenser from the discharge port. The above-described prior art has the following problems: (1) when the flow rate and the pressure of a heat source are changed greatly, the pressure of a coolant which directly enters a cooling system of the motor through a cooling pump or/and a liquid storage device is also fluctuated greatly, so that the air suspension bearing cannot work normally and stably; (2) the coolant is required to be input into a cooling loop of the motor through a coolant pump, and the structure is complicated and is not beneficial to popularization and utilization. Therefore, a liquid supply cooling pipeline which can be switched into a power generation state or a shutdown state and a pressure stabilizing pump according to the operation parameters of the system is needed, so that accidents are effectively prevented, and the energy conversion efficiency is improved.
Disclosure of Invention
1. The technical problem to be solved is as follows:
the invention aims to provide a two-stage turbine gas suspension ORC power generation system, wherein an expansion generator set adopts a static pressure gas bearing, so that the friction loss is lower, and the power generation efficiency is high; by adopting a two-stage turbine structure, the working condition of high expansion ratio is practical, and the system efficiency is higher; the air inlet structure adopts a bypass loop to realize the protection of the expansion machine; the liquid supply cooling pipeline is provided with a pressure stabilizing pump with a bypass, and the on-off is controlled by an electromagnetic valve to ensure the stable pressure supply of the gas suspension bearing.
2. The technical scheme is as follows:
a two-stage turbine gas suspension ORC power generation system comprises an evaporator, an expansion generator set, a condenser, a working medium pump and an evaporator which are connected in a circulating manner; the method is characterized in that: the expansion generator set comprises a high-pressure stage turbine, a gas suspension bearing generator and a low-pressure stage turbine; and the outlet of the high-pressure stage turbine is communicated with the inlet of the low-pressure stage turbine.
The evaporator is a combined full liquid evaporator; the inner cavity of the combined flooded evaporator is internally provided with an internal clapboard with liquid equalizing holes to divide the evaporator into an upper part and a lower part which are communicated, the upper part is a flooded evaporation section, and the lower part is a working medium preheating section.
An outlet of the preheating section of the evaporator is connected with a generator of the expansion generator set through a liquid supply cooling pipeline; the liquid supply cooling pipeline comprises an evaporator preheating section outlet, a pressure stabilizing pump electromagnetic valve and a pressure stabilizing pump which are connected in sequence; the liquid supply cooling pipeline also comprises a bypass liquid supply cooling pipeline which is connected with the pressure stabilizing pump electromagnetic valve and a pipeline where the pressure stabilizing pump is arranged in parallel; the bypass liquid supply cooling pipeline comprises a pressure stabilizing pump bypass electromagnetic valve; the pressure stabilizing pump electromagnetic valve and the pressure stabilizing pump bypass electromagnetic valve are in an interlocking state. An air inlet pipeline is arranged between an outlet of an evaporation section of the evaporator and the expansion generator set; the air inlet pipeline comprises an evaporation section outlet of the evaporator, an air inlet valve and a high-pressure turbine air inlet which are connected in sequence; the air inlet pipeline also comprises a bypass pipeline of the air inlet pipeline; and the bypass path of the air inlet pipeline comprises an evaporation section outlet of the evaporator, a bypass valve and an outlet of the low-pressure turbine which are connected in sequence.
Furthermore, the expansion generator set is an integrated generator set, wherein the gas suspension bearing generator is a variable-speed permanent magnet generator; the rotor in the variable-speed permanent magnet generator rotates along with the rotating shaft; two ends of the rotating shaft are respectively provided with impellers to form two turbines; the outlet pipe of one turbine is connected with the inlet pipe of the other turbine, and a high-pressure stage turbine and a low-pressure stage turbine are correspondingly formed.
A control method of a two-stage turbine gas suspension ORC power generation system comprises the following steps:
the method comprises the following steps: the system starts to operate, the air inlet valve is in a closed state, the bypass valve is in an open state, the liquid working medium is heated and evaporated after the heat source enters the evaporator, and the liquid working medium firstly enters the condenser through the bypass valve to be condensed; detecting the temperature and the pressure of gaseous working media at an outlet of an evaporator, detecting the temperature and the pressure of the working media in a condenser, obtaining enthalpy values of the working media at the outlet of the evaporator and the working media at the outlet of the condenser through the temperature and the pressure, calculating to obtain enthalpy difference between the working media and the working media at the outlet of the condenser, calculating theoretical generated energy at the moment according to the enthalpy difference and a flowmeter, comparing the generated energy with preset starting generated energy of an expander, if the generated energy is more than or equal to the starting generated energy of the expander, opening an air inlet valve, closing a bypass valve, enabling working media gas to firstly enter a high-pressure stage.
Step two: detecting the working medium air pressure at the outlet of the working medium pump, and if the value of the compressed air pressure is higher than the preset air pressure of the cooling pipeline, opening the electromagnetic valve of the pressure stabilizing pump and closing the bypass electromagnetic valve of the pressure stabilizing pump; if the air pressure is lower than the preset air pressure of the cooling pipeline, closing the electromagnetic valve of the pressure stabilizing pump pipeline, opening the bypass electromagnetic valve of the pressure stabilizing pump, and pressurizing through the pressure stabilizing pump to keep the pressure obtained by the air suspension bearing stable.
Step three: when the system is stopped, the flow of the heat source is reduced, the heat exchange capacity of the evaporator is reduced, the temperature and the pressure of the organic working medium entering the expansion machine are gradually reduced, when the generated energy is lower than a preset stop power generation value, the bypass valve is opened from a closed state, the air inlet valve is closed from an open state, the organic working medium at the outlet of the evaporator directly enters the condenser to be condensed until the heat source stops entering the evaporator, and the system is completely stopped.
3. Has the advantages that:
(1) the expansion machine adopted in the invention is a two-stage turbine gas suspension expansion machine, the ORC system realizes oil-free operation, the structure is simple, and the power generation efficiency is high; two stages of turbines of the expansion machine are symmetrically arranged on two sides of the generator, and the stress of the structure is balanced; the two-stage turbine series design of the expansion machine is suitable for the working condition of ORC high expansion pressure ratio, and the system has higher power generation efficiency.
(2) The evaporator is a combined evaporator integrating a liquid storage tank, a preheater and the evaporator, so that the complexity of the system is greatly simplified, the unit size is reduced, and the cost is reduced.
(3) The expander bypass pipeline is arranged to realize the protection of the expander in the starting and stopping state; and a combined full-liquid evaporator with a liquid storage function is used for simultaneously supplying liquid to a liquid cooling pipeline to cool the motor and supply pressure to the air suspension bearing.
(4) The liquid supply cooling pipeline is provided with a pressure stabilizing pump with a bypass, so that the system can stably run under the working condition of large heat source fluctuation.
Drawings
FIG. 1 is a connection diagram of the overall structure of the present invention;
FIG. 2 is a schematic diagram of the modular flooded evaporator of the present invention.
Detailed Description
As shown in fig. 1 to fig. 2, a two-stage turbine gas suspension ORC power generation system comprises an evaporator, an expansion generator set, a condenser, a working medium pump and an evaporator which are connected in a circulating manner; the method is characterized in that: the expansion generator set comprises a high-pressure stage turbine, a gas suspension bearing generator and a low-pressure stage turbine; and the outlet of the high-pressure stage turbine is communicated with the inlet of the low-pressure stage turbine.
The evaporator is a combined full liquid evaporator; the inner cavity of the combined flooded evaporator is internally provided with an internal clapboard with liquid equalizing holes to divide the evaporator into an upper part and a lower part which are communicated, the upper part is a flooded evaporation section, and the lower part is a working medium preheating section.
An outlet of the preheating section of the evaporator is connected with a generator of the expansion generator set through a liquid supply cooling pipeline; the liquid supply cooling pipeline comprises an evaporator preheating section outlet, a pressure stabilizing pump electromagnetic valve and a pressure stabilizing pump which are connected in sequence; the liquid supply cooling pipeline also comprises a bypass liquid supply cooling pipeline which is connected with the pressure stabilizing pump electromagnetic valve and a pipeline where the pressure stabilizing pump is arranged in parallel; the bypass liquid supply cooling pipeline comprises a pressure stabilizing pump bypass electromagnetic valve; the pressure stabilizing pump electromagnetic valve and the pressure stabilizing pump bypass electromagnetic valve are in an interlocking state. An air inlet pipeline is arranged between an outlet of an evaporation section of the evaporator and the expansion generator set; the air inlet pipeline comprises an evaporation section outlet of the evaporator, an air inlet valve and a high-pressure turbine air inlet which are connected in sequence; the air inlet pipeline also comprises a bypass pipeline of the air inlet pipeline; and the bypass path of the air inlet pipeline comprises an evaporation section outlet of the evaporator, a bypass valve and an outlet of the low-pressure turbine which are connected in sequence.
Furthermore, the expansion generator set is an integrated generator set, wherein the gas suspension bearing generator is a variable-speed permanent magnet generator; the rotor in the variable-speed permanent magnet generator rotates along with the rotating shaft; two ends of the rotating shaft are respectively provided with impellers to form two turbines; the outlet pipe of one turbine is connected with the inlet pipe of the other turbine, and a high-pressure stage turbine and a low-pressure stage turbine are correspondingly formed.
A control method of a two-stage turbine gas suspension ORC power generation system comprises the following steps:
the method comprises the following steps: the system starts to operate, the air inlet valve is in a closed state, the bypass valve is in an open state, the liquid working medium is heated and evaporated after the heat source enters the evaporator, and the liquid working medium firstly enters the condenser through the bypass valve to be condensed; detecting the temperature and the pressure of gaseous working media at an outlet of an evaporator, detecting the temperature and the pressure of the working media in a condenser, obtaining enthalpy values of the working media at the outlet of the evaporator and the working media at the outlet of the condenser through the temperature and the pressure, calculating to obtain enthalpy difference between the working media and the working media at the outlet of the condenser, calculating theoretical generated energy at the moment according to the enthalpy difference and a flowmeter, comparing the generated energy with preset starting generated energy of an expander, if the generated energy is more than or equal to the starting generated energy of the expander, opening an air inlet valve, closing a bypass valve, enabling working media gas to firstly enter a high-pressure stage.
Step two: detecting the working medium air pressure at the outlet of the working medium pump, and if the value of the compressed air pressure is higher than the preset air pressure of the cooling pipeline, opening the electromagnetic valve of the pressure stabilizing pump and closing the bypass electromagnetic valve of the pressure stabilizing pump; if the air pressure is lower than the preset air pressure of the cooling pipeline, the electromagnetic valve of the pressure stabilizing pump is closed, the bypass electromagnetic valve of the pressure stabilizing pump is opened, and the pressure obtained by the air suspension bearing is kept stable through pressurization of the pressure stabilizing pump.
Step three: when the system is stopped, the flow of the heat source is reduced, the heat exchange capacity of the evaporator is reduced, the temperature and the pressure of the organic working medium entering the expansion machine are gradually reduced, when the generated energy is lower than a preset stop power generation value, the bypass valve is opened from a closed state, the air inlet valve is closed from an open state, the organic working medium at the outlet of the evaporator directly enters the condenser to be condensed until the heat source stops entering the evaporator, and the system is completely stopped.
The specific embodiment is as follows:
the power generation principle of the ORC system is as follows: the heat source is communicated with the evaporator 1 to transfer heat energy to the organic working medium through heat exchange, the organic working medium absorbs heat to evaporate, and the organic working medium enters the expansion machine to do work to push the turbine to rotate so as to drive the generator to generate electricity.
When the system is started, liquid organic working medium in the evaporator 1 absorbs heat of a heat source and is evaporated into gaseous working medium, the bypass valve 3 of the system is opened, the air inlet valve 2 is closed, organic working medium steam enters the condenser 7 through a bypass pipeline, is cooled by an external cold source in the condenser 7 and is condensed into liquid working medium, then the liquid working medium is pumped into a preheating section of the combined type full liquid evaporator 1 through the working medium pump 7, and high-pressure working medium is conveyed to a cavity of the generator 6 and the air suspension bearing through a liquid supply cooling pipeline and is used for cooling the generator and the air suspension bearing for air supply.
When the generated energy obtained through the pressure difference calculation of the evaporator and the condenser is larger than the preset generated energy, the air inlet valve 2 is opened, the bypass valve 3 is closed, the organic working medium firstly enters the high-pressure stage turbine 4, enters the low-pressure stage turbine 5 from the outlet of the high-pressure stage turbine 4 after expansion acting, continues to expand to act to generate power, the exhaust gas after acting enters the condenser 7 to be condensed into liquid working medium, and is pumped into the evaporator 1 through the working medium pump 8 to complete the whole cycle.
When the system needs to be stopped, the bypass valve 3 is opened from a closed state, the air inlet valve 2 is closed from an open state, and the gaseous organic working medium enters the condenser 7 through the bypass valve 3. And (4) until the external heat source is closed, the evaporator 1 does not exchange heat any more, and the working medium pump 8 is stopped.
In the system, the liquid supply cooling pipeline is provided with a pressure stabilizing pump 11, and the pressure of the liquid supply cooling pipeline is ensured to be stable through the pressure stabilizing pump 11 aiming at the working condition of large flow and pressure fluctuation of a heat source, so that the pressure obtained by the air suspension bearing is kept stable. Wherein the pressure stabilizing pump electromagnetic valve 12 and the bypass pressure stabilizing pump electromagnetic valve 13 are in an interlocking state and are kept to be turned on and off. And the start and stop of the pressure stabilizing pump are controlled by switching the electromagnetic valves.
Fig. 2 is a schematic diagram of the internal structure of the combined flooded evaporator, and the lower part of the heat exchanger is a preheating section with a liquid storage function. The inside of the heat exchanger is divided into an upper part and a lower part by an internal clapboard with liquid equalizing holes, the upper part is a flooded evaporation section 18, and the lower part is a working medium preheating section 19. In the figure, the solid line is the running direction of the organic working medium, and the dotted line is the flow direction of the heat source. In the figure, a heat source inlet 14 is provided, a heat source outlet 15 is provided, a working medium inlet 16 is provided, and a working medium outlet 17 is provided.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.