Hermetically sealed turbo expander system for use in organic rankine cycles and organic rankine cycle plant

The present invention is related to a hermetically sealed turbo expander system for use in organic rankine cycles, comprising a turbo expander, a rotatable rotor and a casing which is filled with an organic working medium in a gaseous condition, whereby the turbo expander is arranged around the rotor within the casing, at least two bearings for bearing the turbo expander around the rotor, with sealed openings in the casing for lines to and from the turbo expander. The invention is further related to an organic rankine cycle plant, comprising an evaporator, an turbo expander, a condenser, a pump and a recuperator, which are fluidically connected with each other in an organic rankine cycle, wherein an organic working medium can flow through a first line from the evaporator to the turbo expander, from the turbo expander through a second line to the condenser, from the condenser through a third line to the pump and from the pump through a fourth line to the evaporator, wherein the recuperator is arranged at the third line and the fourth line.

Organic rankine cycles (ORC) are an attractive technology for waste heat recovery and are gaining importance due to higher energy costs. Compared to the usual water/steam rankine cycle in today's steam power plants, organic rankine cycles use an organic working medium like R134a or R606. Organic working media have the advantage of lower boiling point as water.

Thus, lower temperature levels may be utilized for power gen- eration with these organic working media. On the other hand, the organic working medium is more expensive and cannot be replaced as easily as water. For that reason, loss of working medium should be avoided, which can be achieved by hermetically sealed components in the cycle. While it is comparatively easy to seal heat exchangers and pipe connections, rotating equipment like pumps or expanders need specific measures for effective sealing. A known solution is to enclose all rotating parts within one sealed cas- ing, e. g. the expander, the generator and the bearings. That means, all components, namely the expander, the bearings, which are lubricated with a gas film of working medium, and the generator, which is cooled by the working medium in the casing, would operate in an atmosphere of the working medium. The advantage of this solution is that only pipe connections for working medium are required. There is no other medium entering or leaving the casing and there are no moving seals . But, it has shown that gas lubricated bearings have restrictions in their load capacity, limiting the allowable ro- tor mass of the organic rankine cycle plant and the power output of the components. Solutions for hermetically sealed expanders with high rotor masses are not available.

Therefore, the invention is based on the object of increasing the rotor mass of a rotor and the power output of an organic rankine cycle plant.

Aforesaid object is solved by a hermetically sealed turbo expander system with the features according to independent claim 1 and an organic rankine cycle plant with the features according to independent claim 6. Further features and details of the present invention result from the sub claims, the description and the drawings. Features and details discussed with respect to the hermetically sealed turbo expander can also be applied to the organic rankine cycle plant and vice versa.

According to a first aspect of the invention aforesaid object is solved by a hermetically sealed turbo expander system for use in organic rankine cycles, comprising a turbo expander, a rotatable rotor and a casing which is filled with an organic working medium in a gaseous condition, whereby the turbo expander is arranged around the rotor within the casing, at least two bearings for bearing the turbo expander around the rotor, with sealed openings in the casing for lines to and from the turbo expander. The hermetically sealed turbo expander system is characterized in that the at least two bear- ings are liquid lubricated bearings. Further the hermetically sealed turbo expander system comprises at least one sealed supply opening in the casing for guiding one or more supply lines to the at least two bearings and a feedback opening in the casing for guiding a feedback line to the organic ranking cycle.

Such a hermetically sealed turbo expander system enables to use a rotor with a relative high mass and an increased power output of an organic rankine cycle plant. The hermetically sealed turbo expander system eliminates current limitations in rotor weight and less power output of an organic rankine cycle plant. The requirement of hermetically sealing the organic rankine cycle components is kept, by using an organic liquid working medium as lubricant. Using liquid lubricated bearings for bearing the turbo expander around the rotor of the hermetically sealed turbo expander system leads to a significant increase of the allowable rotor mass, eliminating current power output restrictions. The casing can be filled with an organic working medium at the outlet pressure of the expander. Therefore the organic working medium is in gaseous condition. The lubricating fluid for the liquid lubricate bearings needs to be in substantially liquid condition in order to provide a reliable bearing lubrication, in particular a hydrostatic and/or hydrodynamic lubrication. For this rea- son, the lubricating fluid can be guided through one or more supply lines from the outside of the casing from within the organic rankine cycle in liquid condition and therefore can be kept in substantially liquid condition within the liquid lubricated bearings. The one or more supply lines are guided through at least one sealed supply opening in the casing from the organic rankine cycle to the at least two bearings . The casing can have one sealed supply opening for one supply line, whereby the supply line is splitted within the casing into at least two parts for guiding the organic working medium through the splitted parts to the at least two liquid lubricated bearings. Alternative to that the casing can comprise two or more sealed supply openings for guiding two or more supply lines to the liquid lubricated bearings. It is possible that for each liquid lubricated bearing a separate supply line is guided through corresponding sealed supply openings in the casing. According to a preferred development of the invention a hermetically sealed turbo expander system is preferred which is characterized in that each liquid lubricated bearing comprises seals limiting a bearing-to-shaft gap of a liquid lubricated bearing, whereby each liquid lubricated bearing cora- prises an organic working fluid input line to be connected with a supply line and an organic working fluid output line. That means the organic working fluid input line of a liquid lubricated bearing is connected to one supply line, so that organic working fluid can be guided from a supply line into the organic working fluid input line of the liquid lubricated bearing. Each liquid lubricated bearing forms together with the seals, in particular two seals, between the liquid lubricated bearing and the rotor a bearing-to-shaft gap. The organic working fluid input line ends into the bearing-to-shaft gap and the organic working fluid output line is also connected to the bearing-to-shaft gap, so that organic working medium supplied by the supply line can flow through the liquid working fluid input line of the bearing through the bearing-to-shaft gap and from the bearing-to-shaft gap through the organic working fluid output line into the casing of the hermetically sealed turbo expander system.

In order to ensure a liquid condition of the organic working medium in the liquid lubricated bearings, the organic working medium should be pressurized above the casing internal pressure, so that it would not boil at the internal temperature at the bearing location. That means it is necessary to ensure that the pressure in the supply lines is substantially kept up to the point when the organic working medium leaves the bearings. This is achieved by sealing the liquid lubricated bearing area from the casing internal area by the seals.

Slight leakages are allowed as there will be leakage into the same working medium. No pollution can occur. Further no loss of organic working medium is possible. After passing the liquid lubricated bearing surfaces, the organic working medium can leave the bearings into the casing. To control the flow of the organic working medium from the liquid lubricated bearings into the casing a flow resistance is advantageous.

Therefore a hermetically sealed turbo expander system is preferred, wherein each organic working medium output line comprises a flow resistance. This can be achieved by a throttle, a gap, an internal flow or a valve. Such a flow resistance can control the organic working medium flow and the pressure of the organic working medium in the liquid lubricated bearings. The organic working medium which flows through the liquid lubricated bearings into the casing can leave the casing through the feedback line, so that the organic working medium can be kept constant at the same pressure in the casing.

Further a hermetically sealed turbo expander system is preferred which is characterized in that a generator is arranged inside the casing which is coupled to the rotor for producing electrical energy, whereby one of the at least two liquid lubricated bearings is arranged at the rotor at that side of the generator which is turned away from the turbo expander. Such an arrangement of the at least two liquid lubricated bearings leads to a significant increase of the allowable ro- tor mass and therefore of the power output of the generator of the hermetically sealed turbo expander system.

According to a second aspect of the invention the object is achieved by an organic rankine cycle plant, comprising an evaporator, a turbo expander, a condenser, a pump and a recuperator, which are fluidically connected with each other in an organic rankine cycle, wherein an organic working medium can flow through a first line from the evaporator to the tur- bo expander, from the turbo expander through a second line to the condenser, from the condenser through a third line to the pump and from the pump through a fourth line to the evaporator, wherein the recuperator is arranged at the third line and the fourth line. The organic rankine cycle plant is characterized in that the turbo expander is a hermetically sealed turbo expander system according to the first aspect of the invention, in particular according to claims 1 to 5. The organic rankine cycle plant further comprises at least one sup- ply line for guiding the organic working medium in a liquid condition from the pump to the at least two liquid lubricated bearings and a feedback line arranged between the feedback opening in the casing and one of the lines of the organic rankine cycle plant for discharging gaseous organic working medium from the inside of the casing back in the organic rankine cycle.

Such an organic rankine cycle plant enables an increased allowable rotor mass and an increased power output due to the liquid lubrication of the bearings of the hermetically sealed turbo expander system. Such an organic rankine cycle plant eliminates the current limitations in the rotor weight and thus the power output of organic rankine cycle plants. The requirement of hermetically sealing the cycle components is kept by such an organic rankine cycle plant by using liquid working medium as lubricant for the bearings .

The components of the organic rankine cycle plant are arranged and connected to each other in such a way that they build an organic rankine cycle. An advantage of such an organic rankine cycle plant is that the organic working medium can be used for lubricating the liquid lubricated bearings of the hermetically sealed turbo expander system. It is not necessary to use a separate lubricant fluid for lubricating the bearings arranged around the rotor of the hermetically sealed turbo expander system. The organic working medium which is supplied by the one or more supply lines to the liquid lubricated bearings can flow back into the organic rankine cycle through the casing and through the feedback line, so that the amount of the organic working medium can be kept constant in the organic rankine cycle. The organic working medium is transported through the supply lines by the pump. That means the organic working medium is pressurized by the pump. The pump ensures that the pressure is substantially kept up to the point when the organic working medium leaves the liquid lubricated bearings. After passing the liquid lubricated bearings the organic working medium can leave the liquid lu- bricated bearings into the casing. This can be controlled by a flow resistance in the organic working medium output lines of the bearings. That the organic working medium flows into the casing of the hermetically sealed turbo expander system, is beneficial from a generator cooling point of view. That means the resulting internal flow of the organic working medium in the casing has a cooling effect on the generator. The organic working medium can leave the casing through the feedback opening in the casing and then through the feedback line and can flow back to the organic rankine cycle. The feedback line can be arranged between the feedback opening in the casing and one of the lines of the organic rankine cycle plant. To which line the feedback line guides the organic working medium depends on the pressure of the organic working medium and the pressure in the lines of the organic rankine cycle.

Preferred is an organic rankine cycle plant, whereby the feedback line enters the second line, in particular in an area between the casing of the hermetically sealed turbo expander system and the condenser. This guarantees that the or- ganic working medium coming from the feedback line can be liquefied by the condenser and pressurized again by the pump of the organic rankine cycle plant. If the pressure of the organic working medium in the feedback line is high enough it is possible to guide the organic working medium to another suitable point in the organic rankine cycle.

It is possible that pressure losses occurs in lines, valves and other components in the flow pass of the organic working medium to the liquid lubricated bearings. Therefore it is advantageous that the organic working medium is supplied to the liquid lubricated bearings from an organic rankine cycle point of elevated pressure. Advantageously the organic work- ing medium is supplied to the liquid lubricated bearings by means of a pump or a compressor. Therefore an organic rankine cycle plant is preferred, which is characterized in that the at least one supply line is arranged between an area between the recuperator and the pump and the liquid lubricated bear- ings . Thus, the pump of the organic rankine cycle plant can be used to pressurize the organic working medium up to the suitable pressure for the liquid lubricated bearings. That means it is of advantage that the pump of the organic rankine cycle plant pressurizes the organic working medium not only for the evaporator, but also for the liquid lubricated bearings. Therefore, a split of the fourth line between the pump and the recuperator is of advantage, so that the main part of the organic working medium can flow through the recuperator to the evaporator, wherein a small part of the pressurized organic working medium can flow through the at least one supply line to the bearings in the casing of the hermetically sealed turbo expander system. The pump heats up the organic working medium. Therefore the condenser of the organic rankine cycle plant has to cool down the organic working medium before the organic working medium enters the pump.

The organic working fluid which is used for lubricating the bearings needs to be in substantially liquid condition in order to provide a reliable bearing lubrication. For this rea- son the lubricating organic working medium shall be supplied in liquid condition to the bearings and shall be kept in substantially liquid conditions within the bearings. In order to ensure the liquid condition, the organic working medium may either be sub-cooled, so that the organic working medium would not boil at the internal pressure in the casing, or pressurized above the casing internal pressure, so that the organic working medium would not boil at the internal temper- ature at the bearing location. Preferred is a combination of both measures .

In case of a sub-cooled organic working medium, the organic working medium temperature needs to be below the situation temperature belonging to the internal casing pressure. This can be achieved by cooling the organic working medium or by taking the organic working medium from a low-temperature point of the organic rankine cycle . It has to be considered that the temperature will rise due to heat transfer into lines, bearing structure and due to viscous friction within the bearings. The cooling is achieved by heat transfer to lower temperature organic working medium within the organic rankine cycle, for example condensate, or by some external medium of lower temperature, for example cooling water, refrigerant or air. The organic working medium is supplied to the liquid lubricated bearings from an organic rankine cycle point of elevated pressure or by the pump. The pump can be located before or after the organic working medium has passed the condenser.

Preferred is a combination of sub-cooling and pressurizing the organic working medium. The extent of the cooling and the pressurizing can be reduced by such a combination to those measures alone.

Substantially liquid condition of the organic working medium means that the organic working medium is in liquid or in liquid/gaseous condition, the latter provided that the lubrica- tion of the bearings will significantly differ from a purely gaseous lubrication. It is expected that the steam content of below 50 %, especially below 30 %, will be sufficient. This may depend on the actual conditions in the casing and the selected organic working medium.

The at least one supply line is guided through the sealed openings in the casing to the liquid lubricated bearings. Preferred is an organic rankine cycle plant which is characterized in that an additional cooling device is arranged at the at least one supply line or at the third line for cooling the organic working medium in the supply line or in the third line. This ensures that the organic working medium temperature is below the situation temperature belonging to the internal casing pressure.

Further an organic rankine cycle plant is preferred, which is characterized in that an additional pump is provided at the at least one supply line to compress the organic working medium in the at least one supply line. This measure ensures that the pressure of the organic working medium in the supply line is substantially kept up to the point when the organic working medium leaves the liquid lubricated bearings.

The present invention is further described with respect to the accompanying figures. The figures show schematically: Fig. 1 an organic rankine cycle plant with an inventive

hermetically sealed turbo expander system and

Fig. 2 a liquid lubricated bearing arranged around a rotor of a hermetically sealed turbo expander system.

In Fig. 1 an organic rankine cycle plant 30 is disclosed which comprises a hermetically sealed turbo expander system 1 according to the invention. The organic rankine cycle plant 30 comprises an evaporator 31, a turbo expander 2, a conden- ser 32, a pump 33 and a recuperator 34, which are fluidically connected with each other in an organic rankine cycle. In the organic rankine cycle an organic working medium 5 can flow through the first line 11 from the evaporator 31 to the turbo expander 2, from the turbo expander 2 through a second line 12 to the condenser 32, from the condenser 32 through a third line 13 to the pump 33 and from the pump 33 through a fourth line 14 to the evaporator, wherein the recuperator 34 is ar- ranged at the third line 13 and a fourth line 14 for exchanging heat from one line to the other line.

The hermetically sealed turbo expander system 1 is located in flow direction of the organic working medium 5 behind the evaporator 31.

The hermetically sealed turbo expander system 1 comprises a turbo expander 2, a rotatable rotor 3 and a casing 4 which is filled with an organic working medium 5 in a gaseous condition, whereby the turbo expander 2 is arranged around the rotor 3 within the casing 4. The hermetically sealed turbo expander system 1 further comprises two bearings 6 for bearing the turbo expander 2 around the rotor 3. The casing 4 has sealed openings 7 for lines 11, 12 to and from the turbo expander 2. The two bearings 6 are liquid lubricated bearings. In the casing 4 sealed supply openings 8 are arranged for guiding two supply lines 15 to the bearings 6 and a feedback opening 9 is arranged for guiding a feedback line 16 to the organic rankine cycle line 12.

The hermetically sealed turbo expander system 1 of the organic rankine cycle plant 30 enables the use of a rotor 3 with a high mass and therefore enables an increased power output. The hermetically sealed turbo expander system 1 eliminates current limitations in rotor weight and less power output of a known organic rankine cycle plant.

The casing 4 is filled with organic working medium 5 at the outlet pressure of the expander 2. The organic working medium 5 is in gaseous condition. The organic working medium 5 which is the lubricating fluid is guided through the supply lines 15 from outside of the casing 4 from the organic rankine cycle in liquid condition to the liquid lubricated bearings 6. The supply lines 15 are guided through sealed supply openings 8 in the casing 4 to the bearings 6. Each liquid lubricated bearing 6 has it own supply line 15. The components of the organic rankine cycle plant 30 are arranged and connected to each other in such a way that they build an organic rankine cycle. An advantage of such an organic rankine cycle plant 30 is that the organic working me- dium 5 can be used for lubricating the liquid lubricated bearings 6 of the hermetically sealed turbo expander system 1. The organic working medium 5 which is supplied to the liquid lubricated bearings 6 can flow back into the organic rankine cycle through the casing 4 and the feedback line 16, re- spectively. The amount of organic working medium 5 can be kept constant in the organic rankine cycle plant 30.

The organic working medium 5 is transported through the supply lines 15 by the pump 33. The pump 33 can be driven by a motor 35. The organic working medium 5 is pressurized by the pump 33. After passing the liquid lubricated bearings 6 the organic working medium 5 can leave the liquid lubricated bearings 6 into the casing 4. This can be controlled by a flow resistance 24, see fig. 2. Each liquid lubricated bear- ing 6 comprises an organic working fluid input line 22 and an organic working fluid output line 23. The flow resistance 24 is arranged in the organic working fluid output line 23.

Each liquid lubricated bearing 6 comprises seals 20 limiting a bearing-to-shaft gap 21 of a liquid lubricated bearing 6. The organic working fluid input line 22 of a liquid lubricated bearing 6 is connected to one supply line 15, so that organic working medium 5 can be transported through the supply line 15 into the organic working fluid input line 22 of the liquid lubricated bearing 6. Each liquid lubricated bearing 6 forms together with seals 20, in particular two seals 20, between the liquid lubricated bearing 6 and the rotor 3 the bearing-to-shaft gap 21. The organic working fluid input line 22 ends into the bearing-to-shaft gap 21 and the organic working fluid output line 23 is also connected to the bearing-to-shaft gap 21, so that organic working medium 5 can flow through the liquid working fluid input line 22 through the bearing-to-shaft gap 21 and from the bearing-to-shaft gap 21 through the organic working fluid output line 23 into the casing 4 of the hermetically sealed turbo expander system 1. The flow resistance 24 can be a throttle, a gap or a valve, in particular a ½-way valve. Such a flow resistance 24 can control the organic working medium flow and the pressure of the organic working medium 5 in the liquid lubricated bearings 6. The organic working medium 5 which flows through the liquid lubricated bearings 6 into the casing 4 can leave the casing 4 through the feedback line 16.

A generator 10 is arranged inside the casing 4 of the hermetically sealed turbo expander system 1. The generator 10 is coupled to the rotor 3 for producing electrical energy. One of liquid lubricated bearings 6 is arranged at that side of the generator 10 which is turned away from the turbo expander 2. Such an arrangement of the at least two liquid lubricated bearings 6 leads to a significant increase of the allowable rotor 3 mass and therefore of the power output of the generator 10 of the hermetically sealed turbo expander system 1.

Reference signs

1 hermetically sealed turbo expander system

2 turbo expander

3 rotor

4 casing

5 organic working medium

6 liquid lubricated bearings

7 sealed openings

8 sealed supply opening

9 feedback opening

10 generator

11 first line

12 second line

13 third line

14 fourth line

15 supply line

16 feedback line

20 seals

21 bearing-to-shaft gap

22 organic working fluid input line

23 organic working medium output line

24 flow resistance

30 organic rankine cycle plant

31 evaporator

32 condenser

33 pump

34 recuperator