MICROEMULSION-ENABLED HEAT TRANSFER

Provided are microemulsion-enabled heat transfer apparatus and/or methods, such as for condensing steam exiting a steam turbine of a power plant using.

About 99 percent of thermal-electric power plants use water in their cooling systems. These thermal-electric power plants account for about 40 percent of total freshwater withdrawals and about 3 percent of total freshwater consumption in the United States. The cooling systems of these power plants account for about 90 percent of power plant water usage in the United States.

The remaining about 1 percent of thermal-electric power plants utilize air cooled condensing (“ACC”) cooling systems, in many instances because the power plant is not near a water source. In some instances, the thermal-electric power plants which use ACCs are located in regions which experience relatively high average temperatures, such as deserts. During times of high outdoor temperatures, the ACCs are less efficient due to the higher ambient air temperature, which can result in a power production penalty of up to about 10%. Also, nuclear power plants may not be able utilize ACCs due to regulation and safety concerns. Furthermore, the footprint of an ACC may be much larger than the footprint of a water-cooled cooling system, due to the less efficient heat transfer accomplished by air as compared to water.

What is needed are apparatus and/or methods which reduce thermal-electric power plant water consumption, improve thermal cycle efficiency, and reduce cooling system size, and which may be utilized in various types of thermal-electric power plants.

Embodiments of the subject matter are disclosed with reference to the accompanying drawings and are for illustrative purposes only. The subject matter is not limited in its application to the details of construction or the arrangement of the components illustrated in the drawings. Like reference numerals are used to indicate like components, unless otherwise indicated.

FIG. 1 is a schematic diagram of an illustrative adsorption/absorption and desorption process utilizing the subject microemulsion.

FIG. 2 is a schematic diagram of an illustrative adsorption/absorption refrigeration cycle using a conventional sorption agent.

FIG. 3 is a schematic diagram of an illustrative adsorption/absorption refrigeration cycle using the subject microemulsion.

FIG. 4 is a graph depicting an illustrative Rankine cycle.

FIG. 5 is a schematic diagram of an illustrative adsorption/absorption refrigeration cycle using the subject microemulsion used in connection with a coal-fired power plant.

Provided is a heat transfer apparatus comprising: (i) an evaporation chamber in heat transfer communication with a first heat source, wherein the first heat source causes a liquid in the evaporation chamber to evaporate into a gas; (ii) an adsorption/absorption chamber in fluid communication with the evaporation chamber and in heat transfer communication with a cooling source, the adsorption/absorption chamber containing a microemulsion which adsorbs/absorbs the gas, when cooled, as droplets of the liquid sequestered within the microemulsion to form a used microemulsion; and (iii) a desorption chamber in fluid communication with the adsorption/absorption chamber and the evaporation chamber, and in heat transfer communication with a second heat source capable of desorbing the liquid droplets out of the used microemulsion as the liquid, without vaporizing the liquid, to form a regenerated microemulsion.

In certain embodiments, the first heat source may comprise steam exiting a steam turbine of a power plant, and the steam may be condensed into water as a result of said evaporation of the liquid.

In certain embodiments, the desorption chamber may comprise a separating device capable of (a) separating the liquid from the regenerated microemulsion; (b) routing the liquid to the evaporation chamber; and (c) routing the regenerated microemulsion to the adsorption/absorption chamber.

Attempts have been made to utilize sorption refrigeration systems for power plant cooling using “conventional sorption agents”. Sorption refrigeration systems are desirable because they may be driven by low-grade heat, not requiring electricity or other sources of energy or power. Conventional sorption agents are classified into two general categories: adsorbents and absorbents. Examples of absorbent/refrigerant pairs include lithium bromide/water and water/ammonia. During absorption, the refrigerant molecules are entirely dissolved or diffused in the absorbent for form a solution. Examples of adsorbent/refrigerant pairs include zeolite/water and silica/water. Adsorption is a surface-based process where a layer of refrigerant is adsorbed on the surface of the adsorbent. Both absorption and adsorption are exothermic, while desorption is endothermic. Heat is required to desorb the refrigerant out of the absorbent or off of the adsorbent.

Examples of conventional sorption agents include lithium bromide, lithium chloride, calcium chloride, zeolite and silica. A key deficiency of conventional sorption agents, however, is that they release the refrigerant (such as water) as a gas. Because the refrigerant must be released as a gas, the only way to effect desorption of the refrigerant is to impart sufficient energy to the conventional sorption agent to cause the refrigerant to undergo a phase change. Using water as an exemplary refrigerant, this would require that the heat of vaporization of water (2,360 J/g at 60° C.) be imparted to the conventional sorption agent. Furthermore, because the refrigerant is desorbed as a gas, it must be condensed before continuing the refrigeration cycle.

In contrast, the microemulsions used in the present subject matter are able to release the refrigerant as a liquid, which drastically reduces the energy required to effect desorption of the refrigerant, and also eliminates the requirement of condensing the refrigerant before continuing the refrigeration cycle. Table 1 shows the required heat of desorption (Q_d) for various exemplary sorption agents (sorbents), using water as an exemplary refrigerant.

TABLE 1

Sorbent

Microemulsion

LiBr

LiCl

CaCl₂

Zeolite

Q_d

~100 J/g

~2,500 J/g

~2,500 J/g

~2,500 J/g

~3,400 J/g

Because of the high heat of desorption required to desorb refrigerant out of the conventional sorption agents, sorption refrigerant systems utilizing the conventional sorption agents have not been proven to significantly increase the efficiency of thermal-electric power plants. In contrast, the microemulsions used in the present subject matter significantly increase the efficiency of thermal-electric power plants. One measure of the efficiency of a steam condensing refrigeration system is the Coefficient of Performance (“COP”), which is an important factor which has a significant impact on the net power output of a steam turbine cycle in a thermal-electric power plant. COP is described by the following formula:

COP

=

Q

e

Q

d

+

W

where Q_e is the heat of vaporization of the refrigerant in the evaporator, Q_d is the heat of desorption, and W is the pump power (which may be much smaller than Q_e). Assuming that Q_e and W remain constant, the drastically lower Q_d of the microemulsion as compared to conventional sorption agents will result in a significant increase in the COP.

For example, the COP of refrigeration cycles using conventional sorption agents may be from about 0.4 to about 0.7, while the COP of a refrigeration cycle using the microemulsions described herein may be about 1.8 or higher. In comparison with these illustrative COP figures, the COP of the perfectly efficient Carnot cycle is about 4. Thus, use of the present microemulsions increases the COP of the refrigerant system from about 10-18% of the Carnot cycle COP, to about 45% or more of the Carnot cycle COP.

The microemulsion used in the present subject matter comprise inverse micelles of surfactant (such as amphiphilic surfactant) in oil (such as apolar oil). When the surfactant concentration in the oil/surfactant mixture exceeds the critical micelle concentration (“CMC”), the surfactant molecules form inverse micelles via spontaneous self-assembly in the oil.

The CMC may be defined as the concentration of surfactants above which micelles or inverse micelles form. The CMC can be determined by measuring the surface tension of the oil/surfactant mixture. Before reaching the CMC, the surface tension changes strongly in relation to the concentration of surfactant in the mixture. After reaching the CMC, the surface tension remains relatively constant or changes little in relation to the concentration of surfactant in the mixture. Small angle neutron scattering (“SANS”) may also be used to measure the fluid internal structure to determine whether the CMC has been reached. The value of the CMC depends on temperature, pressure, and the presence and concentration of other surface active substances. For example, the value of CMC for sodium dodecyl sulfate in water at 25° C. and atmospheric pressure is 0.008 mol/L, without other additives or salts.

The hydrophobic tail of each surfactant molecule is in contact with the surrounding oil, sequestering the hydrophilic head of the surfactant at the center of the micelle. The hydrophilic head groups of each surfactant molecule have strong physiochemical affinity for refrigerant (such as water) molecules, and can therefore adsorb refrigerant vapor into the inner surface of the inverse micelle, forming refrigerant nanodroplets sequestered in each micelle. Because the refrigerant is adsorbed by the micelles within the microemulsion, it can also be said that the refrigerant is absorbed into the microemulsion, resulting in both adsorption and absorption.

At low temperatures (such as room temperature), the hydrophilic head groups of the surfactant molecules provide effective adsorption sites for refrigerant. As temperature increases, the inverse micelles release the refrigerant nanodroplets. As long as the temperature required to release the refrigerant nanodroplets is lower than the boiling point of the refrigerant, the refrigerant will be released as a liquid. The refrigerant nanodroplets will coalesce and separate from the oil/surfactant solution. For example, when water is the refrigerant, the water droplets will coalesce and fall out of the oil/surfactant solution.

Referring to FIG. 1, the adsorption/absorption and desorption process may be described as follows. A microemulsion 30 adsorbs 32 water vapor to form an at least partially saturated microemulsion 34. The temperature of the saturated microemulsion 34 is increased 36 to separate liquid water 42 from a first oil/surfactant mixture 38. The liquid water 42 is removed 40 to provide a second oil/surfactant mixture 44. The temperature of the second oil/surfactant mixture 44 is decreased 46 to spontaneously regenerate the surfactant micelles to provide a regenerated microemulsion 48, which can be recycled for reuse in the cyclical refrigeration process.

In certain embodiments, the microemulsion comprises at least one oil and at least one surfactant, the at least one surfactant molecules comprising a hydrophobic end and a hydrophilic end.

In certain embodiments, the at least one oil may have a boiling point greater than about 100° C. at 100 kPa, optionally wherein the at least one oil has a carbon-hydrogen atomic fraction of greater than about 70%. In certain embodiments, the at least one oil may comprise at least one polyalphaolefin.

In certain embodiments, the at least one surfactant comprises at least one of organosulfate salts, sulfonate salts or anhydride amino esters. In certain embodiments, the at least one surfactant may comprise at least one of sodium dodecyl sulfate or dioctyl sodium sulfosuccinate.

In certain embodiments, the apparatus may comprise an evaporation chamber which comprises a heat exchanger having a first side and a second side, wherein the first side comprises an inlet and an outlet, wherein the second side comprises an inlet and an outlet, wherein the first side inlet is in fluid communication with the desorption chamber to receive the liquid from the desorption chamber, wherein the first side outlet is in fluid communication with the adsorption/absorption chamber to exhaust the gas to the adsorption/absorption chamber, wherein the second side is in heat transfer communication with the first heat source. The second side inlet may be in fluid communication with a steam turbine of a power plant to receive steam exiting the steam turbine, and the second side outlet may be in fluid communication with a steam generator of a power plant to exhaust the water to the steam generator.

In certain embodiments, the apparatus may comprise a desorption chamber which comprises a heat exchanger having a first side and a second side, wherein the first side comprises an inlet and an outlet, wherein the first side inlet is in fluid communication with the adsorption/absorption chamber to receive the used microemulsion, wherein the first side outlet is in fluid communication with the separating device to exhaust the regenerated microemulsion and the liquid to the separating device, and wherein the second side is in direct or indirect heat transfer communication with a heat source supplied from a steam generator of the power plant.

Also provided is a method of condensing steam exiting a steam turbine of a power plant comprising: (i) condensing the steam in an evaporation chamber which causes a liquid in the evaporation chamber to evaporate into a gas, resulting in the steam being condensed to water; (ii) transporting the gas into an adsorption/absorption chamber containing a microemulsion; (iii) providing the adsorption/absorption chamber with a cooling source to cause the microemulsion to adsorb/absorb the gas as droplets of the liquid sequestered within the microemulsion, forming a used microemulsion; (iv) transporting the used microemulsion into a desorption chamber; (v) providing the desorption chamber with a heat source to cause the liquid droplets in the used microemulsion to be released from the used microemulsion as the liquid, forming a regenerated microemulsion; (vi) separating the liquid from the regenerated microemulsion; (vii) routing the liquid to the evaporation chamber; and (viii) routing the regenerated microemulsion to the adsorption/absorption chamber. In certain embodiments, the cooling source may be supplied from an ambient environment. In certain embodiments, the heat supplied to the desorption chamber may be directly or indirectly supplied from a waste heat source supplied from a steam generator of the power plant.

The apparatus and methods described herein may significantly reduce or eliminate water consumption in power plant steam condensation systems and/or improve the plant thermal cycle efficiency by reducing the steam condensation temperature and/or turbine back pressure.

Illustrative adsorption/absorption refrigerant cycles are shown in FIGS. 2 and 3, in order to illustrate certain benefits of the adsorption/absorption refrigerant cycle utilizing the subject microemulsion. FIG. 2 depicts an illustrative adsorption/absorption refrigeration cycle 60 using a conventional sorption agent. The evaporator 62 evaporates the refrigerant in order to provide a cooling effect (Q_e) to an associated system (not shown). The gaseous refrigerant proceeds to the adsorber/absorber 64, which utilizes a conventional sorbent agent to adsorb/absorb the gaseous refrigerant, rejecting heat (Q_a) to the environment and/or an associated system. The sorbent/refrigerant mixture proceeds to the desorber 66 via a pump 68, where the refrigerant is desorbed as a gas utilizing waste heat (Q_d) from an associated system, such as a thermal-electric power plant. The regenerated sorbent returns to the adsorber/absorber via an expansion valve 70. The gaseous refrigerant proceeds to the condenser 72, where it is condensed into a liquid, requiring a cooling source (Q_c), and returned to the evaporator 62 via a refrigerant expansion valve 74, to complete the cycle. An optional heat exchanger 76 may be placed between the adsorber/absorber 64 and the desorber 66 in order to transfer heat between the used sorbent and the regenerated sorbent, which will increase the efficiency of the system.

FIG. 3 depicts an illustrative adsorption/absorption refrigeration cycle 80 using the subject microemulsion. The evaporator 82 evaporates the refrigerant in order to provide a cooling effect (Q_e) to an associated system (not shown). The gaseous refrigerant proceeds to the adsorber/absorber 84, which utilizes the subject microemulsion to adsorb/absorb the gaseous refrigerant, rejecting heat (Q_a) to the environment and/or an associated system. The microemulsion/refrigerant mixture proceeds to the desorber 86 via a pump 88, where the refrigerant is desorbed as a liquid utilizing waste heat (Q_d) from an associated system, such as a thermal-electric power plant. The regenerated microemulsion returns to the adsorber/absorber via an expansion valve 90. The liquid refrigerant returns to the evaporator 82 via a refrigerant expansion valve 94, to complete the cycle. An optional heat exchanger 96 may be placed between the adsorber/absorber 84 and the desorber 86 in order to transfer heat between the used microemulsion and the regenerated microemulsion, which may increase the efficiency of the system. As can be seen, the refrigeration cycle 80 does not require a condenser, and therefore does not require a cooling source (Q_c), which renders the cycle 80 much more efficient than the cycle 60 of FIG. 2.

Referring to FIG. 4, an illustrative steam power plant Rankine cycle is illustrated. The condensed steam is pressurized by a pump from point 1 to point 2. The water is then boiled to become steam again from point 2 to point 3. The steam expands through a steam turbine to generate work from point 3 to point 4. The steam is then condensed to water from point 4 back to point 1. The areas bordered by the lines 5 and 6, which depict a coal-fired power plant and a nuclear power plant, respectively, represent the amount of work generated by the cycle. The present apparatus and methods, utilizing the subject microemulsion, enable lower steam condensation temperatures as compared to ACCs, which increases the area bordered by the lines 5 and 6 by moving point 4 to the right and/or down. Thus, the water condensation temperature provided by the present apparatus and methods may be lower than the ambient temperature, leading to an increase in power plant efficiency compared to power plants which utilize ACCs. Furthermore, the heat transfer rate by evaporation provided by the microemulsion refrigerant cycle may be more than ten times the heat transfer rate provided by ACCs.

FIG. 5 depicts an illustrative coal-fired power plant 100 with an illustrative refrigeration cycle 102 utilizing the subject microemulsion. Combustion air 104 is optionally passed through a first pre-heater 106 and a second pre-heater 108 before entering a boiler 110, which is heated by burning coal. Steam generated by the boiler 110 proceeds to a high-pressure steam turbine 112, then to a low-pressure steam turbine 114. The steam then proceeds to a steam condenser/refrigerant evaporator 116, where it is condensed into water utilizing the cooling effect of the refrigeration cycle 102. The water is then recycled to the boiler, optionally passing through water pre-heater 118, low-pressure feedwater heater 120, deaerator 122 and high-pressure feedwater heater 124.

Flue gas generated by the boiler 110 is utilized to heat a low-pressure by-pass steam generator 126, and may also be used to pre-heat the combustion air in the second pre-heater 108. The flue gas then proceeds through a fabric filter 128 and a desulfurization chamber 130, and is ultimately exhausted out of the power plant via stack 132.

The illustrative refrigeration cycle 102 utilizes water as the refrigerant. The water is converted to steam in the steam condenser/refrigerant evaporator 116. The steam proceeds to the adsorber/absorber 134, where it is adsorbed/absorbed by the subject microemulsion to create a used microemulsion. The adsorber/absorber 134 is supplied with a cooling source from at least one of the ambient environment, the first pre-heater 106, or the water pre-heater 118. The used microemulsion is then pumped to the desorber 136 via a pump 138. The desorber is supplied with heat from the by-pass steam generator 126, and optionally with heat from the low-pressure steam turbine 114, in order to disrupt the micelle formations in the microemulsion to release the refrigerant as liquid water to create a regenerated microemulsion. The regenerated microemulsion is recycled to the adsorber/absorber 134, while the water is returned to the steam condenser/refrigerant evaporator 116.

It is noted that the subject apparatus and methods may be associated with various types of thermal-electric power plants in arrangements similar to that depicted in FIG. 5. Furthermore, other arrangements may also be possible using the design parameters discussed herein.

In a first embodiment of the present subject matter, provided is an apparatus comprising: (i) an evaporation chamber in heat transfer communication with a first heat source, wherein the first heat source causes a liquid in the evaporation chamber to evaporate into a gas; (ii) an adsorption/absorption chamber in fluid communication with the evaporation chamber and in heat transfer communication with a cooling source, the adsorption/absorption chamber containing a microemulsion which adsorbs/absorbs the gas, when cooled, as droplets of the liquid sequestered within the microemulsion to form a used microemulsion; and (iii) a desorption chamber in fluid communication with the adsorption/absorption chamber and the evaporation chamber, and in heat transfer communication with a second heat source capable of desorbing the liquid droplets out of the used microemulsion as the liquid, without vaporizing the liquid, to form a regenerated microemulsion.

The first embodiment may further include that the first heat source comprises steam exiting a steam turbine of a power plant, wherein the steam is condensed into water as a result of said evaporation of the liquid.

Either or both of the first or subsequent embodiments may further include that the desorption chamber comprises a separating device capable of (a) separating the liquid from the regenerated microemulsion; (b) routing the liquid to the evaporation chamber; and (c) routing the regenerated microemulsion to the adsorption/absorption chamber.

A second embodiment of the present subject matter comprises the first or subsequent embodiments, further including that the microemulsion comprises at least one oil and at least one surfactant, the at least one surfactant molecules comprising a hydrophobic end and a hydrophilic end.

The second embodiment may further include that the at least one oil has a boiling point greater than about 100° C. at 100 kPa, optionally wherein the at least one oil has a carbon-hydrogen atomic fraction of greater than about 70%.

Either or both of the second or subsequent embodiments may further include that the at least one oil comprises at least one polyalphaolefin.

Any of the second or subsequent embodiments may further include that the at least one surfactant comprises at least one of organosulfate salts, sulfonate salts or anhydride amino esters. The at least one surfactant may comprise at least one of sodium dodecyl sulfate or dioctyl sodium sulfosuccinate.

The apparatus of the first, second or subsequent embodiments may further include that the evaporation chamber comprises a heat exchanger having a first side and a second side, the first side comprises an inlet and an outlet, the second side comprises an inlet and an outlet, the first side inlet is in fluid communication with the desorption chamber to receive the liquid from the desorption chamber, the first side outlet is in fluid communication with the adsorption/absorption chamber to exhaust the gas to the adsorption/absorption chamber, the second side is in heat transfer communication with the first heat source. The second side inlet may be in fluid communication with a steam turbine of a power plant to receive steam exiting the steam turbine, and the second side outlet may be in fluid communication with a steam generator of a power plant to exhaust the water to the steam generator.

The apparatus of the first, second or subsequent embodiments may further include that the desorption chamber comprises a heat exchanger having a first side and a second side, the first side comprises an inlet and an outlet, the first side inlet is in fluid communication with the adsorption/absorption chamber to receive the used microemulsion, the first side outlet is in fluid communication with the separating device to exhaust the regenerated microemulsion and the liquid to the separating device, the second side is in direct or indirect heat transfer communication with a waste heat source supplied from a steam generator of the power plant.

In a third embodiment of the present subject matter, provided is a method of condensing steam exiting a steam turbine of a power plant comprising: (i) condensing the steam in an evaporation chamber which causes a liquid in the evaporation chamber to evaporate into a gas, resulting in the steam being condensed to water; (ii) transporting the gas into an adsorption/absorption chamber containing a microemulsion; (iii) providing the adsorption/absorption chamber with a cooling source to cause the microemulsion to adsorb/absorb the gas as droplets of the liquid sequestered within the microemulsion, forming a used microemulsion; (iv) transporting the used microemulsion into a desorption chamber; (v) providing the desorption chamber with a heat source to cause the liquid droplets in the used microemulsion to be released from the used microemulsion as the liquid, forming a regenerated microemulsion; (vi) separating the liquid from the regenerated microemulsion; (vii) routing the liquid to the evaporation chamber; and (viii) routing the regenerated microemulsion to the adsorption/absorption chamber.

A fourth embodiment of the present subject matter comprises the third embodiment, further including that the microemulsion comprises at least one oil and at least one surfactant, the at least one surfactant molecules comprising a hydrophobic end and a hydrophilic end.

The fourth embodiment may further include that the at least one oil has a boiling point greater than about 100° C. at 100 kPa, optionally wherein the at least one oil has a carbon-hydrogen atomic fraction of greater than about 70%.

Either or both of the fourth or subsequent embodiments may further include the at least one oil comprises at least one polyalphaolefin.

Any of the fourth or subsequent embodiments may further include that the at least one surfactant comprises at least one of organosulfate salts, sulfonates salts or anhydride amino esters. The at least one surfactant may comprise at least one of sodium dodecyl sulfate or dioctyl sodium sulfosuccinate.

The method of the third, fourth or subsequent embodiments may further include that the water is transported to a steam generator of the power plant.

The method of the third, fourth or subsequent embodiments may further include that the cooling source is supplied from an ambient environment.

The method of the third, fourth or subsequent embodiments may further include that the heat supplied to the desorption chamber is directly or indirectly supplied from a waste heat source supplied from a steam generator of the power plant.

It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described hereinabove. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.