EP2455658B1 - Method and device for vaporization of organic working media - Google Patents

Description

Field of the invention

The present invention relates to a device for direct evaporation of organic working media for generating electrical energy from heat sources by the use of organic media.

State of the art

The operation of expansion machines, such as steam turbines, using the Organic Rankine Cycle (ORC) process to generate electrical energy through the use of organic media, such as organic low evaporation temperature media, which at higher temperatures generally have higher evaporation pressures compared to water as the working medium is known in the art. ORC systems represent a realization of the Rankine cycle in which, for example, electric energy is obtained in principle via adiabatic and isobaric changes in the state of a working medium. About evaporation, expansion and subsequent condensation of the working medium in this case mechanical energy is recovered and converted into electrical energy. In principle, the working medium is brought to a working pressure by a feed pump, and it is supplied to it in a heat exchanger energy in the form of heat, which is provided by a combustion or a waste heat flow available. From the evaporator, the working fluid flows via a pressure tube to an ORC turbine, where it is expanded to a lower pressure. Subsequently, the expanded working medium vapor flows through a condenser, in which a heat exchange between the vaporous working medium and a cooling medium takes place, after which the condensed working medium is returned by a feed pump to the evaporator in a cyclic process.

However, organic media have significantly lower decomposition temperatures compared to water, i. H. Temperatures at which the molecular bonds of the medium break, resulting in destruction of the working medium and decomposition into corrosive or toxic reaction products. Even if the temperature of the live steam is lower than the decomposition temperature of the medium, the latter can be significantly exceeded at insufficiently flowed through points, as is possible in particular on steam-exposed areas of the heat exchanger. Also, a failure of the feed pump causes the flow through the heat exchanger is interrupted and the working fluid is thus exposed directly to the temperature of the heat source used for evaporation.

In order to avoid that the working medium is heated to temperatures above the decomposition temperature, intermediate circuits are conventionally used in ORC plants, in which the heat from the hot medium used for evaporation (flue gas) is transported via an intermediate circuit to the evaporator. For such an intermediate circuit, a thermal oil is typically used whose temperature stability is higher than that of the working medium. The single-phase heat transfer with the help of thermal oil allows a more even flow through the heat exchanger, in which the evaporation of the working medium takes place. However, this solution has the following disadvantages. First, thermal oils are typically combustible, and thus the thermal oil circuit must be pre-pressurized with nitrogen to prevent oxidation of the thermal oil, making the equipment technically complex and expensive. In addition, thermal oils age due to the high thermal load and must be replaced at regular intervals. This results in downtime for the plant and an increase in costs. In addition, the circulating pump, which transports the oil due to the high viscosity of the thermal oil to perform a large electrical power. Then, the use of the thermal oil results in a significant reduction of the heat transferable and thus the electrical power obtained in comparison to the direct evaporation of a working medium, which manages without an intermediate circuit.

It is therefore the object of the present invention to provide an improved ORC process which overcomes the abovementioned disadvantages and in particular is able to guarantee a temperature of the working medium below the decomposition temperature. In general, the task is to regulate the temperature at a heat exchanger so that excessive temperatures can be avoided.

EP 1 221 573 A1 discloses a method for recovering electrical and thermal energy from biomass boilers, where the spent combustion gases are mixed as needed by a bypass duct with cooled combustion gases prior to being fed to a heat exchanger.

US 2007/0034704 A1 shows a method for recirculation of exhaust gases, with which a desired concentration of oxygen for a stable combustion is achieved. The hot combustion gases originating from the combustion in a burner are mixed via a return line and a mixing line with a stream of fresh air to feed the mixture of combustion gases and fresh air into the supply line to the burner, so that a complete mixing of the coming from an upstream gas turbine combustion gases and the mixture of combustion gases and fresh air can take place.

DE 29 07 694 A1 discloses a mixing device for flowing liquid, gaseous or vaporous media, especially for those with large temperature differences.

Description of the invention

The above object is achieved by an Organic Rankine Cycle apparatus according to independent claim 1, inter alia, with a heat exchanger for transferring heat of a heat-supplying medium to a different working medium from this; a first supply means configured to supply a flow of the heat-supplying medium at a first temperature from a heat source to the heat exchanger; and
a second supply means, which is adapted to at least partially the heat-supplying medium after it has passed through the heat exchanger, and / or another medium each having a second temperature which is lower than the first temperature, to the flow of the heat-carrying medium with the to deliver the first temperature.

The heat exchanger is provided in the form of an evaporator, in which the working medium is evaporated. According to the invention, the temperature of the heat-supplying medium is not only given by the heat source upon exposure of the heat exchanger / evaporator, but it is governed by the return of the heat-carrying medium after passing through the heat exchanger and / or the other medium in the flow of the heat-supplying medium to the Heat exchanger is delivered, regulated. By this temperature control takes place a comparison with the prior art more homogeneous admission of the heat exchanger and excess temperatures at the heat exchanger can be avoided. As indicated above, as an alternative or in addition to recycling the heat-carrying medium after passing through the heat exchanger, another medium may be supplied to the flow of the heat-carrying medium at the second temperature. This additional medium may in particular be ambient air that is supplied from outside the device.

The heat-supplying medium may, in particular, be a hot flue gas, as arises, for example, in the combustion of fossil fuels as a heat source. The working medium is an organic material.

Said heat exchanger may be a shell and tube heat exchanger, such as a flue or water tube boiler, or a plate heat exchanger, in which the working medium is guided in a jacket of the boiler, through which the flue gas is passed in tubes. Thus, by way of example, the above device is part of a steam power plant, ie an Organic Rankine Cycle (ORC) plant. The ORC system comprises according to the invention an expansion machine, such as a turbine, a generator, and means for supplying the working fluid evaporated in the evaporator to the turbine. From the turbine, the expanded vaporized working fluid can be supplied by a conveyor (eg a pipe) for condensing to a condenser and the working fluid there liquefied can be delivered back to the heat exchanger in a cycle process by a feed pump.

A decomposition of the organic working medium is reliably prevented by appropriate regulation of the temperature of the heat-supplying medium below the decomposition temperature of the working medium to the heat exchanger.

According to a development, the second supply device comprises a fan or a vacuum device in order to return the cooled heat-supplying medium, after it has passed through the heat exchanger, and / or the further medium into the flow, which acts on the heat exchanger. A blower provides a cost effective and efficient means of recycling. Alternatively or additionally, the first feed device may comprise a vacuum device in order to suck the medium from the second feed device.

According to a further development, the second supply device is designed to supply the heat-supplying medium, after it has passed through the heat exchanger, and / or the further medium to the flow of the heat-supplying medium at the first temperature in such a way that it is distributed over the circumference of the stream becomes. Hierduch a homogeneous mixing of the components, for example, coming directly from the heat source hot flue gas and recirculated after passing through the evaporator cooled flue gas while avoiding the formation of hot gas strands achieved.

In the above-mentioned examples of the device according to the invention, the first supply means may comprise a first conduit for conducting the heat-carrying medium at the first temperature, and the second supply means a second A conduit for conducting the heat-carrying medium after it has passed through the heat exchanger and / or further comprising medium, the apparatus comprising a mixing section or a mixing section, which is for a fluid connection of the heat-supplying medium with the first temperature in the first conduit and the heat-supplying Medium, after it has passed through the heat exchanger, and / or the other medium is formed in the second line. The mixing section or the mixing section may include a portion of the first conduit having openings formed therein in the shell thereof and a portion of the second conduit surrounding the portion of the first conduit (see also detailed description below).

The present invention also provides a steam power plant with a device according to one of the above examples of the device according to the invention. The additional medium may be ambient air provided outside or inside the steam power plant.

The above object is also achieved by a method of vaporizing an organic working fluid in an Organic Rankine Cycle thermal power plant according to independent claim 8, which comprises, among other things, the steps of supplying the working fluid in a liquid state to an evaporator;
Supplying a heat-supplying medium different from the working medium at a first temperature from a heat source to the evaporator, and
Returning at least a portion of the heat-carrying medium after passing through the evaporator and at a second temperature lower than the first temperature; and / or feeding another medium (e.g., ambient air) into the flow of the heat-supplying medium supplied from the heat source to the evaporator ,

The step of returning the at least one part of the heat-supplying medium after passing through the evaporator or supplying the further medium, eg from ambient air, can be performed by means of a blower and / or a vacuum device. The at least part of the heat-supplying medium may be mixed after passing through the evaporator with the flow of the heat-supplying medium supplied from the heat source to the evaporator at the first temperature distributed over the circumference of this flow. The additional medium can also be supplied over the circumference of the flow of the heat-supplying medium supplied by the heat source to the evaporator. The working medium is or comprises an organic material and the heat-carrying medium may be or include flue gas.

In all of the above-described examples of the method according to the invention and the device according to the invention, increased flexibility is thereby provided in the adaptation of the mixing temperature of the heat-supplying medium upon entry into the heat exchanger such that the heat-carrying medium is heated or cooled as desired after exiting the heat exchanger. Thus, in the above-described process developments, the heat-supplying medium after passing through the evaporator and before supplying to the flow of the heat-supplying medium supplied from the heat source to the evaporator is heated or cooled to the second temperature. Also, the other medium, such as outside air, is heated or cooled before being supplied to the flow of the heat-supplying medium supplied from the heat source to the evaporator.

• Figur 1 stellt eine Prinzipskizze für eine herkömmliche ORC-Anlage ohne (links) und mit (rechts) einem Zwischenkreislauf dar.
• Figur 2 stellt eine Prinzipskizze für ein Beispiel einer ORC-Anlage gemäß der vorliegenden Erfindung dar.
• Figur 3 zeigt TQ - Diagramme für ein herkömmliches Verdampfungsverfahren durch Direktverdampfung (links) und das erfindungsgemäße Verfahren unter Einbezug rezirkulierten abgekühlten Rauchgases (rechts).
• Figur 4 zeigt eine Ausbildung für ein Mischstück zum Mischen heißen Rauchgases und abgekühlten rezirkulierten Rauchgases.

Further features and exemplary embodiments and advantages of the present invention will be explained in more detail with reference to the drawings. It should be understood that the embodiments are not within the scope of the present invention exhaust. It is further understood that some or all of the features described below may be combined with each other in other ways. The invention is defined by the entirety of the features of the independent claims.

• FIG. 1 represents a schematic diagram for a conventional ORC system without (left) and with (right) an intermediate circuit.
• FIG. 2 FIG. 12 illustrates a schematic diagram of an example of an ORC system according to the present invention. FIG.
• FIG. 3 shows TQ diagrams for a conventional evaporation process by direct evaporation (left) and the inventive method with the inclusion of recirculated cooled flue gas (right).
• FIG. 4 shows a design for a mixing piece for mixing hot flue gas and cooled recirculated flue gas.

FIG. 1 shows a conventional ORC system with direct evaporation (left) or with an intermediate circuit (right). An evaporator 1, which functions as a heat exchanger or heat exchanger, is supplied with heat from a heat source (not shown) by, for example, a flue gas resulting from the combustion of a fuel, as indicated by the left arrow in the left part of FIG FIG. 1 is displayed. In the evaporator 1, heat is supplied to a working medium supplied through a feed pump 2. For example, it is completely evaporated or evaporated by flash evaporation after the heat exchanger. The working medium vapor is fed via a pressure line of a turbine 3. In the turbine, the working medium vapor is released, and the turbine 3 drives an electric energy generator 4 (indicated by the right arrow in FIG. 1, respectively). The relaxed working medium vapor is condensed in a condenser 5 and the liquefied working medium is fed back to the evaporator 1 via the feed pump.

If an intermediate circuit 6 is used, as it is in the right part of FIG. 1 is shown, the heat transfer of the flue gas is not directly to the evaporator to the working fluid, but by means of a medium, such as a thermal oil, the intermediate circuit 6. The intermediate circuit 6 includes a heat exchanger 7, where the flue gas transfers heat to the medium of the intermediate circuit 6 , The heat exchanger 7, the medium of the intermediate circuit 6 is supplied by a pump 8. From the heat exchanger 7, the medium of the intermediate circuit 6 passes to the evaporator 1, where it leads to the evaporation of the working medium, which is supplied to the turbine 3.

In FIG. 2 an exemplary embodiment of the present invention is illustrated. Elements related to the in FIG. 1 have already been described, are provided with the same reference numerals. In contrast to the prior art, the medium (eg a flue gas), which evaporates the working medium is used after the evaporation of the evaporator 1 partially led to the ORC system again. Thus, part of the cooled after exposure to the evaporator 1 flue gas 10, for example by means of a (recirculation) blower 9 is added to the flow of the originating from a heat source hot flue gas.

The ORC system itself can be, for example, a geothermal or solar thermal system or also have the combustion of fossil fuels as a heat source. As working media, all "dry media" used in conventional ORC systems, such as R245fa, "wet" media, such as ethanol or "isentropic media", such as R134a, are suitable. Likewise, silicone-based synthetic working media such as GL160 can be used.

According to the above description, there is thus no risk of destruction of the working medium due to overheating due to malfunctions, such as a failure of the feed pump 5 or an inhomogeneous flow through the evaporator with the heat-supplying medium (flue gas).

This is not the only advantage of the inventive design. FIG. 3 FIG. 4 shows a comparison of the temperature-transferable heat (TQ) diagrams for a conventional evaporation process by direct evaporation (left) and the process according to the invention with the inclusion of the recirculated cooled flue gas. In comparison with the direct application of hot flue gas to the evaporator 1, recirculation of at least part of the cooled flue gas after passing through the evaporator 1 reduces the inlet temperature of the heat-transporting medium at the evaporator 1. In addition, the slope of the cooling curve decreases but not so much as it would be due to the mere decrease in the flue gas temperature, since this effect is partly compensated by the larger mass flow.

The residual heat of the recirculated cooled flue gas, which is simply lost in conventional methods, is provided for the heat transfer in the evaporator 1 again and is in the right figure of FIG. 3 marked by the hatched bar. The pinch point of the next approximation of the TQ curves of flue gas and working medium is at the end of the preheater, which is typically upstream of the evaporator 1 or can be considered as a part thereof, and thus reduces the heat transferable in the evaporator 1 at a constant held Pinch point temperature ΔT _pinch (temperature difference between heat-emitting (relatively hot) and heat-absorbing (relatively cold) mass flow, here the difference at the point of the next approximation of flue gas and working medium TQ curves).

Although the temperature gradient between the temperature of the inlet of the mixed flue gas and the temperature of the flue gas at the outlet from the evaporator 1 is lower compared to the conventional method, however, since the evaporator 1 is flowed through by a larger mass flow per unit time, the heat transfer coefficient U increases that for a same throughput of flue gas theoretically no significant increase in the area A of the evaporator is necessary. In practice, however, one will adjust the area so as not to increase the exhaust back pressure too much. In this case, the transmittable heat flow per unit time of the evaporator 1 is determined to be U · A · ΔT _M , where ΔT _{M is} the average logarithmic driving temperature difference. Typical rates for the recirculation mass flow are in the range of 10 to 60% of the flue gas mass flow for mixing temperatures when the flue gas enters the heat exchanger from 300 ° C to 200 ° C.

The additional amount of heat of the recirculated gas according to the invention leads to a mitigation of the effect of reducing the amount of heat transferable due to the lower flue gas inlet temperature.

In the simplest case, the mixture of the supplied from a heat source to the evaporator 1 hot flue gas and the cooled flue gas, the evaporator 1 has happened through a Y-piece of pipe. In such a mixture realized, however, hot streaks can arise in the mixed gas, which lead to an inhomogeneous loading of the evaporator 1. In principle, a conventional gas mixer of the prior art can be used.

A better mixing can be achieved if the cooled flue gas that has passed through the evaporator 1, distributed over the circumference of the hot flue gas flow is supplied to this. For example, the mixture may be via a mixing piece comprising a portion 21 of a first conduit for directing the hot flue gas flow having openings 22 formed therein in the shell thereof and a portion 23 of a second conduit for conducting the recirculated flue gas, the portion 23 of the second conduit surrounds the part 21 of the first conduit and is sealed with this outside by a seal 24, as in FIG. 4 is illustrated. The pressurized by a blower recirculated flue gas is forced through the openings 22 in the part of the jacket of the first line in this, so that it can mix homogeneously with the hot flue gas.

Claims (12)

1. Organic Rankine Cycle apparatus, comprising:

   a heat exchanger (1) for transferring heat of a heat-supplying medium to an organic working medium which differs from the heat-supplying medium;

   an expansion machine (3), in particular a turbine;

   a generator (4) connected with the expansion machine (3);

   a device for supplying the organic working medium evaporated in the heat exchanger (1) to the expansion machine (3);

   a first supply device adapted to supply a flow of the heat-supplying medium having a first temperature from a heat source to the heat exchanger (1);

   a second supply device adapted to supply at least partially the heat-supplying medium, after it has passed through the heat exchanger (1), and/or a further medium at a second temperature which is lower than the first temperature to the flow of the heat-supplying medium having the first temperature such, that the temperature of the heat-supplying medium at the heat exchanger (1) lies below a decomposition temperature of the organic working medium; and

   a device adapted to heat or cool the heat-supplying medium, after it has passed through the heat exchanger (1), and/or the further medium to the second temperature before it is supplied to the flow of the heat-supplying medium supplied from the heat source to the heat exchanger (1).
2. The apparatus according to claim 1, wherein the first supply device comprises a vacuum device and/or the second supply device comprises a fan (9) and/or a vacuum device.
3. The apparatus according to claim 1 or 2, wherein the second supply device is adapted to supply the heat-supplying medium, after it has passed through the heat exchanger (1), and/or the further medium to the flow of the heat-supplying medium having the first temperature such that it is supplied to same distributed over the circumference of the flow.
4. The apparatus according to claim 3, wherein the first supply device comprises a first conduit for conducting the heat-supplying medium having the first temperature, and the second supply device comprises a second conduit for conducting the heat-supplying medium, after it has passed through the heat exchanger (1), and/or for conducting the further medium, and wherein the apparatus comprises a mixing piece or a mixing section, which is designed for a fluidic connection of the heat-supplying medium having the first temperature in the first conduit and the heat-supplying medium, after it has passed through the heat exchanger (1), and/or the further medium in the second conduit.
5. The apparatus according to claim 4, wherein the mixing piece or the mixing section comprises a part (21) of the first conduit with holes (22) formed therein in the shell of same, and a part (23) of the second conduit surrounding the part (21) of the first conduit.
6. The apparatus according to one of the preceding claims, further comprising a condenser (5) adapted to condense the expanded organic working medium, after it has passed through the expansion machine (3), from the vaporous state into the liquid state.
7. Steam power plant comprising the apparatus according to one of the preceding claims.
8. Method for evaporating an organic working medium in an Organic Rankine Cycle thermal power plant, comprising the steps of:

   supplying the organic working medium in a liquid state to an evaporator (1),

   supplying a heat-supplying medium having a first temperature, which differs from the organic working medium, from a heat source to the evaporator (1),

   recirculating at least a portion of the heat-supplying medium, after it has passed through the evaporator (1), at a second temperature which is lower than the first temperature, and/or supplying a further medium into the flow of the heat-supplying medium supplied from the heat source to the evaporator (1) such, that the temperature of the heat-supplying medium at the evaporator (1) lies below a decomposition temperature of the organic working medium, and

   cooling or heating the heat-supplying medium, after it has passed through the evaporator (1), and/or the further medium to the second temperature before it is supplied to the flow of the heat-supplying medium supplied from the heat source to the evaporator (1).
9. The method according to claim 8, wherein the step of recirculating the at least a portion of the heat-supplying medium, after it has passed through the evaporator (1), and/or of supplying the further medium is accomplished by means of a fan (9) and/or a vacuum device.
10. The method according to claim 8 or 9, wherein the at least a portion of the heat-supplying medium, after it has passed through the evaporator (1), and/or the further medium is mixed with the flow of the heat-supplying medium having the first temperature and supplied from the heat source to the evaporator (1) in a manner distributed over the circumference of this flow.
11. The method according to one of claims 8 to 10, wherein the heat-supplying medium is or contains flue gas.
12. The method according to one of claims 8 to 11, further comprising:

    supplying the organic working medium evaporated in the evaporator (1) to a turbine (3) for expanding the evaporated organic working medium;

    supplying the expanded, evaporated organic working medium to a condenser (5) for liquefying the expanded, evaporated organic working medium; and

    supplying the liquefied organic working medium to the evaporator (1).

Images