Patent Application
20140007576
The invention relates to a method for conversion of energy in which a hydrocarbon-containing energy source is burned in a combustion space in an oxygen-enriched atmosphere and the generated heat is transmitted to a steam power plant circuit.
Furthermore, the invention relates to an apparatus or device for conversion of energy with a combustion space for combustion of a hydrocarbon-containing energy source in an oxygen-enriched atmosphere and a steam power plant circuit that is energy-coupled to the combustion space for use of the heat that has been generated in the combustion space.
So-called oxyfuel power plant methods are known. In them, a hydrocarbon-containing energy source is burned not in a normal air atmosphere, but rather in an oxygen-enriched atmosphere or even in almost pure oxygen. A flue gas that is formed during combustion then consists mainly of carbon dioxide (CO2) and water vapor in the ideal case.
Therefore, the method is suitable especially as an energy conversion method in combination with separation of carbon dioxide. As a result of the flue gas consisting mainly of carbon dioxide and water vapor, the carbon dioxide can be separated comparatively easily from the flue gas by first of all the water vapor being condensed and the remaining gas then being separated into a carbon dioxide portion and a residual gas portion that may be present. The separated carbon dioxide can be, for example, forced into the ground or intercalated therein (so-called “carbon capture and storage” method, CCS). Thus, it does not end up in the earth's atmosphere. Carbon dioxide is made responsible for a considerable portion of global warming.
One disadvantage of the known oxyfuel method consists in that the flue gas is present at relatively low temperatures so that the condensation of water out of the flue gas takes place at relatively low temperatures (less than 150° C.). Due to the low temperature, the energy content of this heat, therefore the usable portion of the heat, is relatively low. The condensation energy is therefore generally discarded, i.e., released to cooling water without energy use. This leads to degraded process efficiency.
For improved use of the waste heat of the flue gas, especially of the condensation energy of the water in the flue gas, an oxyfuel power plant method is also known in which both the energy source and also the oxygen are compressed and at pressures in the range of roughly 50 bar are delivered into the combustion space. Combustion then takes place at a correspondingly high pressure, and the flue gas is present at the outlet from the combustion space likewise at a high pressure.
One advantage of this method is that the entire flue gas path, i.e., the path from the outlet from the combustion space up to condensation of the flue gas, can be designed in a much more compact manner due to the reduced volume. Another advantage consists in that the flue gas dew point, i.e., the temperature at which condensation of the flue gas begins, is much higher compared to the low-pressure oxyfuel method. Consequently, the condensation energy is also present at high temperatures so that the energy content of this energy is greater.
By integration of this heat or energy into the steam power plant circuit, for example by use of the energy for preheating a working fluid of the steam power plant circuit, generally feed water, the total efficiency of the system, which can also be called a power plant, can be improved.
In a known method, the water vapor of the flue gas is condensed in a heat exchanger (flue gas condensation heat exchanger) in counterflow to the feed water of the steam power plant circuit for use of the energy of the flue gas, whereby the feed water is preheated.
Preheating the feed water makes it possible to reduce the number of conventionally undertaken taps (side streams from the steam turbine unit of the steam power plant) as well as the amount of the tapped steam from the turbines for feed-water preheating, especially in the medium-pressure and low-pressure range. The turbines can thus generate more electrical or mechanical power.
One problem in this use of the energy of the flue gas, however, consists in that in reality, the flue gas, in contrast to the idealized model, contains not only carbon dioxide and water, but also a plurality of other components, such as, for example, sulfur oxides and nitrogen oxides that are soluble in water. In addition, with rising pressure, the solubility of carbon dioxide in water rises. These above-mentioned substances constitute strong acids, dissolved in water.
Due to the high pressures, the high temperatures, a large amount of heat to be transferred, and the acid water solution, the demands on the flue gas condensation heat exchanger are high. These demands can so far be managed only with a very high technical effort that is associated with correspondingly high costs.
Another disadvantage of the known approach consists in that the available condensation heat of the flue gas is greater than the heat that is required for heating the feed water. The condensation heat can therefore not be completely integrated into the method and used so that the theoretical potential for improvement that exists cannot be completely exhausted.
The use of the condensation energy of the flue gas of an oxyfuel process for feed-water preheating is described in U.S. Pat. No. 6,918,253 B2 and U.S. Pat. No. 6,196,000 B1.
Therefore, an object of the invention is to provide a method and a device or apparatus for conversion of energy that are especially economical and that enable especially energy-efficient and cost-efficient use of the flue gas exhaust heat of an oxyfuel power plant process.
Upon further study of the specification and appended claims, other objects, aspects and advantages of the invention will become apparent.
These objects are achieved according to the invention by a method for conversion of energy, in which a hydrocarbon-containing energy source is burned in a combustion space in an oxygen-enriched atmosphere and the generated heat is transmitted to a steam power plant circuit, wherein flue gas, formed in the combustion of the hydrocarbon-containing energy source, is cooled in a direct-contact cooler in direct contact with a water-containing coolant flow. These objects are also achieved according to the invention by an apparatus with a combustion space for combustion of a hydrocarbon-containing energy source in an oxygen-enriched atmosphere and a steam power plant circuit, which is energy-coupled to the combustion space for use of heat generated in the combustion space, wherein a direct-contact cooler is connected downstream from the combustion space and in which cooler a flue gas, formed in the combustion of the hydrocarbon-containing energy source, can be cooled in direct contact with a water-containing coolant flow. Preferred configurations of the invention are given in the following description.
The method is characterized according to the invention in that the flue gas that is formed in the combustion of the hydrocarbon-containing energy source is cooled in a direct-contact cooler in direct contact with a water-containing coolant flow.
With respect to the device, it is provided according to the invention that a direct-contact cooler is connected downstream from the combustion space and in it a flue gas that is formed in the combustion of the hydrocarbon-containing energy source can be cooled in direct contact with a water-containing coolant flow.
One advantage of the method according to the invention and of the device according to the invention is that the transport of heat and mass in a direct-contact apparatus is much more intense than in a heat exchanger with flows separated by substance. The heat transfer or heat exchange therefore proceeds more efficiently so that less surface is needed; this leads to a considerable cost reduction.
Another advantage of the flue gas making direct contact with the water-containing coolant consists in that flue gas washing takes place by the liquid water, and in the washing, at least some of the water vapor is condensed and washed out of the flue gas. In the direct-contact cooler, therefore, separation of substances takes place. The cooled gas flow that is leaving the direct-contact cooler contains a smaller portion of water than the hot flue gas flow that is entering the direct-contact cooler. Preferably, the cooled gas flow already contains a relatively pure carbon dioxide, together with gaseous impurities that may be present and a preferably small portion of water vapor. In the direct-contact cooler, in one advantageous configuration of the invention, an at least partial, preferably extensive, separation of the water portion from the flue gas can be undertaken.
One basic idea of the invention can be seen in dissipating the condensation heat of the flue gas, not directly to the working fluid (feed water) of the steam power plant circuit, but rather to a coolant flow that is then used as a heat transfer medium. The heat is transferred to the coolant flow in this case in the flue gas making direct contact with the cold liquid flow, which is enriched in this connection with water from the flue gas. The usable heat of the flue gas is therefore released to a heat transfer medium that can then relay or distribute the heat to one or optionally several consumers. This enables especially efficient and flexible use of the condensation heat of the flue gas.
The energy coupling of the combustion space to the steam power plant circuit is implemented especially by routing the working fluid through the combustion space, especially in pipelines. Vaporization and optionally superheating of the working fluid take place in the pipelines.
Preferably, the water-containing coolant flow that is fed directly into the direct-contact cooler is a water-rich flow or one consisting largely of water, for example with a water portion of at least 80 or 90%. By way of simplification, the coolant flow is therefore water. The flue gas is condensed in direct contact with the water flow and optionally cooled. The coolant flow can be especially a circulated flow that contains water that has been condensed from the flue gas or at least largely consists of it. The coolant flow can therefore contain impurities or components of the flue gas that dissolve in water.
The flue gas flow is preferably fed into the direct-contact cooler in a lower region and is routed in counterflow to the coolant that is preferably fed into an upper region of the direct-contact cooler and trickles down into the direct-contact cooler. To make available intensive contact of the gas with the liquid, the direct-contact cooler contains preferably fillings or packings. With respect to the high temperatures and pressures, the use of ceramic and/or metal fillings or packings is preferred (e.g., random packings such as Raschig rings, Pall rings, and Berl saddles, and structured packings such as Koch-Sulzer packing, Intalox packing, or Mellapak, as well as combination of random and structured packings).
The energy source (fuel, propellant) can be a solid, liquid and/or gaseous feedstock. To make available the condensation heat at a temperature level that can be used technically more efficiently, it is preferred according to the invention that the combustion of the hydrocarbon-containing energy source in the combustion space, which can also be called the combustion chamber, takes place at a pressure above atmospheric pressure. The flue gas thus likewise has an elevated pressure and a corresponding dew point (dew point temperature).
A preferred pressure range for the combustion of the energy source is 5 to 100 bar (abs.), in another configuration 40 to 100 bar (abs.). In particular, it is preferred that the combustion of the hydrocarbon-containing energy source in the combustion space takes place at at least 8 bar (abs.), preferably at least 10 bar (abs.). In another configuration, it is preferred that the combustion of the hydrocarbon-containing energy source in the combustion space takes place at at least 40 bar (abs.), preferably at least 80 bar (abs.). Depending on the specific flue gas composition, the dew point of the flue gas, for example at a flue gas pressure of 80 bar, is in a range above 200° C.
Accordingly, it is preferred that a liquid flow that has been withdrawn from the direct-contact cooler be used as a heat transfer medium for energy use. The flow can be cooled especially in at least one heat exchanger for energy use. The fluid flow withdrawn from the direct-contact cooler is preferably essentially water that may contain dissolved substances such as sulfur oxides, nitrogen oxides or carbon dioxide.
To increase the efficiency of the power plant process, it is especially preferred that at least one part of the liquid flow withdrawn from the direct-contact cooler be used to preheat a working fluid of the steam power plant circuit.
The steam power plant circuit in the fundamentally known manner is a circuit with a working fluid that can be vaporized for conversion of heat into mechanical work (energy). To generate the mechanical energy, the vaporous working fluid is expanded in a steam turbine (Rankine process). The steam turbine is coupled to a generator for generating a flow. The working fluid is brought to a high pressure by means of a pump. The pressurized working fluid is then vaporized by supplying heat and superheated, and it is expanded to a low pressure in the steam turbine. After condensation in a condenser, the fluid is brought again to high pressure. For vaporization and superheating, the working fluid is conventionally routed in pipelines through the combustion space. The final temperature can be in the range from roughly 500° C. to 700° C., especially roughly 600° C., depending on the specific design. Preferably, the working fluid is water that is also called feed water.
Preferably, prior to vaporization and superheating of the working fluid, preheating takes place to increase the efficiency of energy conversion. The preheating of the working fluid that can be called especially feed-water preheating takes place by heat transfer from the liquid flow from the direct-contact cooler to the working fluid of the steam power plant circuit. The liquid flow that has been withdrawn from the direct-contact cooler is cooled in doing so and heats the working fluid (feed water).
Advantageously, the preheating of the working fluid takes place in at least one liquid-liquid heat exchanger. The liquid-liquid heat exchanger is preferably a water-water heat exchanger with feed water on one side and the water flow that has been withdrawn from the direct-contact cooler on the other side. Feed-water preheating of the steam power plant circuit can take place in this way in conventional water-water heat exchangers and thus can be implemented economically and with relatively low hardware cost. Preferably, the feed-water preheating takes place in counterflow to the liquid flow that has been withdrawn from the direct-contact cooler.
Alternatively or in addition to the heating of the working fluid, at least one part of the liquid flow withdrawn from the direct-contact cooler can be used to vaporize the working fluid of the steam power plant circuit. The vaporized and optionally (slightly) superheated working fluid can then be fed into a low-pressure turbine part of the steam turbine and thus can increase the output of the steam turbine. This steam feed can be usefully regarded as negative steam removal.
Another preferred possibility of the use of the energy of the flue gas consists in that at least one part of the liquid flow that has been withdrawn from the direct-contact cooler is used in an oxygen preheater for preheating an oxygen flow. An oxygen flow here is defined as a flow that contains at least one oxygen portion that is larger than the oxygen portion in the ambient air. For example, it can be a flow with an oxygen portion of at least 80%, preferably roughly 97%. The oxygen flow is fed into the combustion space for preparing the oxygen-enriched atmosphere in which the combustion of the energy source takes place. The preheating of the oxygen before being fed into the combustion space leads to an improvement of the efficiency of the overall process.
Within the scope of this invention, an oxygen-enriched atmosphere is defined as an atmosphere that contains a larger oxygen portion than ambient air. Preferably, the oxygen portion in an oxygen-enriched atmosphere is at least 80%, preferably roughly 97%.
The flow of oxygen can be efficiently heated or preheated in that the oxygen flow is heated in a direct-contact heat exchanger (direct-contact heater) in direct contact with the liquid flow withdrawn from the direct-contact cooler or a part of it. In this case, it can be provided in particular that the gaseous oxygen flow is fed underneath into the direct-contact heat exchanger and is routed in counterflow to the liquid that is fed preferably in an upper region and trickles down into the direct-contact heat exchanger. The direct-contact heat exchanger preferably has a packing or filling for making available an intensive gas-liquid contact. The preheating of the oxygen by direct contact with a condensed water fraction from the flue gas ensures especially efficient heat transport so that compared to a conventional heat exchanger, a smaller surface is required.
Preferably, a liquid flow withdrawn from the oxygen preheater is at least partially returned as a coolant flow to the direct-contact cooler. This flow is a water-rich flow or one consisting largely of water. The return of this water flow to the direct-contact cooler for condensing or cooling the flue gas can take place either directly or via another heat exchanger, for example a cooling water heat exchanger.
It is especially preferred according to the invention that a liquid flow that has been withdrawn from the direct-contact cooler be returned after cooling at least partially as a coolant flow to the direct-contact cooler. The coolant flow is therefore circulated, it being heated as the water portion of the flue gas is received in the direct-contact cooler, cooled with the release of heat to the heat consumer, and fed again into the direct-contact cooler. As a result of receiving water and optionally other components from the flue gas flow, a partial flow that contains essentially water is transferred out to equalize the material balance.
To protect the apparatus and lines of the water circuit, for example against corrosion, preferably the liquid flow that has been withdrawn from the direct-contact cooler is delivered to a water-treatment apparatus. In the water-treatment apparatus, the water conditioning takes place that, for example, can include the setting of a pH value and/or the addition of anti-corrosion agents.
One preferred measure for setting, especially reducing, the combustion temperature in the combustion space is the return of a part of the flue gas to the combustion space. To do this, some of the flue gas is branched off preferably upstream from the direct-contact cooler and returned to the combustion space via a fan.
Another possibility for influencing the combustion temperature in the combustion space is to return part of the liquid flow that has been withdrawn from the direct-contact cooler to the combustion space. The liquid flow that contains largely water and thus can be called a water flow can either be delivered as liquid into the combustion space or at least partially vaporized beforehand in a heat exchanger and then at least partially in vapor form delivered into the combustion space. In the case of prior vaporization, it is preferred that the liquid flow or water flow be heated or vaporized against flue gas from the combustion space. The heat exchanger that is intended for this purpose is installed in the flue gas path preferably upstream from or in front of the direct-contact cooler.
The invention as well as additional details of the invention are explained in more detail below using preferred embodiments that are shown in the attached schematic figures, wherein:
First of all, a conventional steam power process as well as a known oxyfuel method are described using
In a conventional steam power process, a working fluid 160, which is conventionally water (feed water 162), is circulated. A steam power plant circuit 60 (Rankine cycle) comprises a feed-water pump 62, a feed-water preheating part 64, a steam turbine unit 66, and a condenser 76. The steam turbine unit 66, as shown in the figures, can comprise several parts, for example a high-pressure part 68, a medium-pressure part 70, and a low-pressure part 72 that can consist of independent turbines in each case. The corresponding turbines (high-pressure turbine, medium-pressure turbine, and low-pressure turbine) can each have several expansion stages (impellers).
The working fluid 160 or feed water 162 is brought to a high pressure level by means of the feed-water pump 62 that can have several pump units with different pressure stages. Depending on the design, this can be in the range of 300 bar. The feed water 162 is preheated in the feed-water preheating part 64 and then routed in pipelines 13 through a combustion space 12, in which an energy source (fuel) is burned. In the combustion space 12, the feed water is further heated, vaporized and superheated.
The resulting high-pressure steam 168 is expanded in the steam turbine unit 66. The expansion takes place preferably in several stages, first the superheated high-pressure steam 168 being expanded in the high-pressure part 68 of the steam turbine unit 66 and afterwards again routed through the combustion space 12 and again superheated or superheated further. Afterwards, the steam as medium-pressure steam 170 is expanded in the medium-pressure part 70 and as low-pressure steam 172 in the low-pressure part 72 and then is condensed in the condenser 76.
To preheat the feed water 162, a series of heat exchangers 65 is used. The feed water 162 is heated by steam that is removed at suitable sites of the turbine unit 66. These steam removals reduce the amount of steam in the turbines so that the total output is reduced.
The energy source is burned in the combustion space 12 and the heat that forms in doing so is transferred via pipelines 13 to a steam power plant circuit 60. The feed water 162 is preheated in a first step in a counterflow heat exchanger 90 in counterflow to condensing flue gas 104. The counterflow heat exchanger 90 is exposed to especially high loads due to the prevailing temperatures and the material composition of the flue gas 104.
Further feed-water preheating takes place in heat exchangers 65 by removing steam from the steam turbine unit 66.
Before delivery of the flue gas 104, solid particles are separated in a particle separation apparatus 14 and withdrawn as ash 118. Some of the flue gas flow is returned to the combustion space 12 as a partial flow 106 by means of a fan 36.
In a flue gas cooler 92, the flue gas is further cooled. Water that has condensed out as a water product flow 136 is withdrawn from a water-separation tank 94. After liquefaction of the carbon dioxide in a CO2 condenser 96, a liquid CO2 product flow 116 and a gaseous residual gas flow 114 are withdrawn from a CO2-separation tank 98.
A first preferred embodiment of the invention is shown in
To prepare the oxygen atmosphere, an oxygen-enriched flow that is called the oxygen flow 150 is produced in an air-separation apparatus 50. The oxygen flow 150 exists at a pressure above a combustion space pressure. The pressure can be, for example, at least 80 bar. The temperature at the outlet of the air-separation apparatus 50 can be, for example, roughly the ambient temperature, i.e., roughly 20° C.
Before delivery into the combustion space 12, the oxygen flow 150 is preheated in an oxygen preheater 35 that is a direct-contact heat exchanger 34 in the illustrated embodiment. The oxygen flow 152 that has been preheated preferably to roughly 180° C. to 200° C. is delivered into the combustion space 12.
A flue gas 104 (flue gas flow) that is formed by combustion leaves the combustion space 12 and is supplied to a particle separation apparatus 14 for separation of solid particles. The separated solid particles together with a solid flow are withdrawn from the combustion space 12 as ash 118. After the particle separation apparatus 14, the flue gas flow is divided into a first partial flow 106 that is returned to the combustion space 12 and a second partial flow 108. To return the partial flow 106 to the combustion space 12, there is, for example, a fan 36.
The second partial flow 108 is routed into a direct-contact cooler 20 for cooling and partial condensation. The direct-contact cooler 20 can have a tank or a column. The tank or the column can contain fillings and/or structured packings.
The partial flow 108 of the flue gas is fed into a lower region of the direct-contact cooler 20 and rises in counterflow to a coolant that is trickling down. The coolant is a water-rich liquid flow 121 that has been withdrawn from the bottom of the direct-contact cooler 20. This liquid flow 121, which can also be called a water flow 122, flue gas condensation flow or bottom flow is fed at least partially after cooling as a coolant flow 138 into an upper region of the direct-contact cooler 20 and thus is circulated (water circuit 120).
In the direct-contact cooler 20, cooling and partial liquefaction of the flue gas 104 or of the partial flow 108 take place. Due to the direct contact with the coolant flow 138 (water flow), a predominant part of the water vapor condenses out of the flue gas 104. Therefore, the water or water vapor is depleted. The cooled flue gas flow 112 leaves the direct-contact cooler 20 and is supplied to a CO2 separation unit 40. There, the flue gas flow 112 is separated into a liquid CO2 product flow 116, which contains primarily carbon dioxide, and a gaseous residual gas flow 114. The CO2 separation unit 40 has a CO2 condenser 42 and a gas-liquid separating tank 44. Optionally, aftertreatment steps, for example further cleaning of the CO2 flow, can also take place.
The aforementioned liquid water flow 122 is withdrawn from the bottom of the direct-contact cooler 20. The temperature of the water flow 122 corresponds to the dew point of the flue gas at a given pressure and a given flue gas composition. The water flow 122 is first chemically conditioned in a water-treatment apparatus 22 and then cooled in a series of heat exchangers in order to be supplied again afterwards as a coolant flow 138 at least in part to the direct-contact cooler 20.
The circulation of the water flow 122 takes place by means of a pump 24 that can have several pump units. The water flow 122 is divided into at least two partial flows that are supplied to different heat users.
According to the configuration of
To preheat the feed water 162, the partial flow 124 is routed in one or more heat exchangers 65 of the feed-water preheating part 64 in counterflow to the feed water 162 and in doing so is cooled. The heat transfer takes place in liquid-liquid heat exchangers with flows that are separated by material. In addition, in other heat exchangers 65, the feed water can be preheated by removing steam from the turbine unit 66.
The partial flow 126 is fed into the direct-contact heat exchanger 34 in an upper region and flows down into the heat exchanger. The oxygen flow 150 (gas) to be heated is supplied to the direct-contact heat exchanger 34 in a lower region and rises into the heat exchanger.
A liquid flow 140 that can also be called a bottom flow 142 is withdrawn from the bottom of the direct-contact heat exchanger 34. This flow that contains essentially water is combined with a return flow from the heat exchangers 65 and further cooled in a water cooler 30 against cooling water. The cooled flow is delivered again as a coolant flow 138 to the direct-contact cooler 20. A water product flow 136 is withdrawn from the water circuit 120.
Another partial flow 130 is routed to a heat exchanger unit 28, in which heat is released to an external heat consumer 29, for example an adjacent power plant installation.
Instead of a return via the water cooler 30, the bottom flow 142 (water flow) that has been withdrawn from the direct-contact heat exchanger 34 can also be fed directly, i.e., without intermediate cooling, into the direct-contact cooler 20, as shown in
The version according to
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.
From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.
The entire disclosures of all applications, patents and publications, cited herein and of corresponding German patent application DE 10 2012 013 414.2, filed Jul. 5, 2012, are incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102012013414.2 | Jul 2012 | DE | national |
