This invention pertains to the field of energy conversion and specifically to the conversion of heat energy to mechanical energy.
BACKGROUND OF THE INVENTION
Energy conversion engines have long been employed to recover process heat and convert it to mechanical energy as in the familiar Rankine cycle. Typical systems are in a series of patents by Alexander Kalina and various coworkers such as U.S. Pat. Nos. 5,095,708; 5,029,444; 4,982,568; 4,899,545; 4,732,005; 4,604,867; 4,586,340; 4,548,043; and 4,489,563. Scharpf, U.S. Pat. No. 5,842,345 teaches the use of two component working fluids, preferring ammonia and water, in a heat recovery method. DeVault U.S. Pat. No. 5,555,738, teaches use of an ammonia water refrigeration system to cool the inlet air of a gas turbine for improved efficiency. Lewis et al U.S. Pat. No. 6,195,997 discloses an energy recovery system using a refrigeration loop to cool the inlet air for a gas turbine wherein the working fluid is split into 2 streams. Rosenblatt U.S. Pat. No. 5,421,157 discloses an organic Rankin cycle system with a recuperator. U.S. Pat. No. 4,442,675 discloses a thermodynamic cycle wherein the work expanded fluid is compressed isentropically to its original pressure then heated at constant pressure to its initial temperature.
The art has not heretofore recognized the unexpected advantage of using a working fluid at supercritical conditions as a heat transfer medium in a waste heat recovery organic Rankin cycle with the expander mechanically coupled to a refrigeration compressor in a refrigeration cycle wherein the inlet air to a turbine is cooled by heat exchange with a cold fluid supply from the refrigeration unit while power to drive the refrigeration compressor is supplied by waste heat recovery from the turbine exhaust in the heat recovery system; while also providing additional cooling capacity. Indeed certain prior art patents suggest that the critical condition is the upper limit for heat transfer conditions. See for example U.S. Pat. No. 4,089,175. Others teach use of high boiling working fluids in order to maintain sub-critical conditions. See for example U.S. Pat. No. 4,137,965. In Linde, 1981, Reports on Science and Technology Vol. 31 pages 38 to 46, Hans-Peter Corneille and Siegfred Haaf, “Organic Rankin Cycles for the Conversion of Waste heat and Solar Heat to Mechanical Energy” the advantages of using the organic Rankin cycle is discussed and Rankin cycles converting waste heat to mechanical energy in a variety of systems are described generically, but a system wherein a coupled refrigeration system used to cool inlet air for a gas turbine was not recognized in the art reported therein.
SUMMARY OF THE INVENTION
The invention may be described in several ways as alternate embodiments of the same novel discovery.
A conventional Rankine cycle that can be used in an energy recovery system that comprises:
a. providing a first working fluid to a first pump;
b. feeding the first working fluid to a heat transfer zone to transfer heat to the first working fluid thereby heating the first working fluid to a higher temperature,
c. feeding the heated first working fluid to an expansion means;
d. expanding the heated first working fluid to a lower pressure;
e. feeding the expanded lower pressure first working fluid to a heat transfer zone where the first working fluid is cooled;
f. returning the first working fluid to the first pump and repeating the cycle as set out above.
In a preferred embodiment the invention provides:
g. in a coupled refrigeration system the steps of feeding a second working fluid. to a second heat exchanger and heating the second working fluid by extracting heat from a refrigeration source;
h. feeding the heated working fluid work to a compressor coupled to the expansion means of the energy recovery system
i. compressing the heated working fluid to a higher pressure
j. feeding the compressed heated working fluid to an expansion means and
k. expanding the working fluid to a lower pressure
l. returning the expanded working fluid to the inlet side of the second heat exchanger to remove energy from a refrigeration source
In a more preferred embodiment the invention further provides the steps of:
m. supplying from the coupled refrigeration system a cooled fluid stream to a heat exchange means in contact with an inlet air stream to a gas turbine and cooling the inlet air stream to the turbine and
n. feeding heated turbine exhaust to the first heat transfer zone.
In a preferred embodiment the method further comprises:
a. feeding the first and second working fluids through a plurality of coupled expander/compressor pairs to recover energy and provide cooling in stages. These expanders can be in series or in parallel and a single expander can drive multiple stages of compression with the use of a gear driven multi-stage compressor or similar device.
In an especially preferred embodiment the method further provides the same working fluid in both the heat recovery system and the refrigeration system eliminating the need for mechanical seals between the two fluids. The working fluid may be any hydrocarbon, or other refrigerant, pure or mixed having energy efficient properties to enable waste heat recovery in the system. Hydrocarbon working fluids are preferred and normal butane, Isobutane, isopentane, normal pentane, iso-hexane, or normal hexane are the best mode working fluids known to the inventor.
In an optional embodiment the method further comprises the steps of feeding a third working fluid to a heat exchange in the refrigeration loop after the expansion means and cooling the third working fluid. Preferably the third working fluid cools the inlet air coming to a gas turbine. In a preferred embodiment the third working fluid is water, aqueous ethylene glycol solution, alcohol brines, or other brines.
The first working fluid stream may also be fed back through multiple compressors or heat exchangers to further increase heat uptake and process efficiency and /or to produce a lower refrigerant temperature.
In an alternate embodiment, the invention is an energy recovery apparatus that comprises:
a. fluid conduit means and a working fluid the conduit means connecting all components listed below;
b. pumping means;
c. heat exchange means with a sufficient pressure rating to contain the working fluid at an operating temperature above its critical temperature;
d. an expansion means connected to the heat transfer means and configured to receive a heated working fluid and expand said working fluid to a lower pressure zone thereby extracting mechanical work from the working fluid;
e. and condensing means configured to condense the working fluid at a pressure in the working fluid above atmospheric pressure.
A preferred apparatus further provides:
f. a second working fluid contained in conduits in a refrigeration system;
g. a compressor coupled to the expansion means to compress the second working fluid in the refrigeration system , a condenser to reject heat while condensing the working fluid, a refrigeration expansion means and a heat exchange evaporation means in the refrigeration system;
An especially preferred apparatus provides:
h. a gas turbine having an inlet air stream and an exhaust stream;
i. a heat exchange means to receive a cooled working fluid from the refrigeration system and positioned to cool the inlet air to the gas turbine;
j. a heat exchange means positioned to recover heat from the turbine exhaust and supply heat to the first working fluid prior to the first working fluid entering the work expansion means and under conditions wherein the first working fluid is heated above its critical temperature.
In a preferred embodiment the invention further comprises
k. a second pump means for circulating a third working fluid between a heat exchange means downstream from the refrigeration expansion means and a second heat exchange means in contact with inlet air to the gas turbine and a separate fluid conduit containing a working fluid and linking the second pump with the two heat exchange means;
In a preferred embodiment the working fluid in the energy recovery apparatus and the refrigeration system is the same. Hydrocarbon working fluids are preferred and more preferably the working fluid in both systems is selected from the group consisting of isobutane, normal butane, propane, iso-propane, normal pentane, iso pentane, hexane or a two component mixture of any of the preceding with any other of the preceding or a three or more component mixture of any of the preceding with any others of the preceding. The working fluid in the optional third conduit system, can be any heat transfer fluid, but is preferably water, aqueous ethylene glycol solution, alcohol brines, or brines.
In an additional preferred embodiment the apparatus comprises a series of turbo-expanders coupled to multiple compressor and may also employ a flash economizer or multiple refrigeration expansions and multiple heat recovery stages to provide additional heat recovery or refrigeration capacity.
The invention in an alternative embodiment provides a method for increasing the efficiency of a gas pipeline that comprises:
a. providing a gas compression system having a gas turbine that compresses the pipeline gas and a heat recovery system having a first working fluid and a first pump;
b. feeding the first working fluid through the first pump to a first heat transfer zone to transfer heat to the working fluid stream thereby heating the stream to a higher temperature using heat from the gas turbine exhaust,
c. feeding the heated working fluid to an expansion means operative coupled to a refrigeration system compression means;
d. expanding the first working fluid to a lower temperature and pressure;
e. feeding the expanded lower temperature and pressure first working fluid to a second heat exchanger where the first working fluid is cooled by heat exchange while rejecting heat to an external medium;
f. returning the first working fluid to the first pump and repeating the cycle as set out above
g. and in a coupled refrigeration system feeding a second working fluid. to second heat exchanger and heating the second working fluid;
h. feeding the heated second working fluid work to a compressor
i. compressing the heated working fluid to a higher pressure
j. condensing the compressed working fluid by rejecting heat to an external medium
k. feeding the condensed working fluid to an expansion means and
l. expanding the working fluid to a lower pressure
m. returning the expanded working fluid to inlet side of a heat exchange means in contact with an inlet gas pipeline stream to the pipeline gas compressor and cooling the inlet gas pipeline stream to the compressor and
n. feeding the turbine exhaust to supply heat to the heat transfer zone in contact with the first working fluid, and preferably
o. feeding the first and second working fluids through a plurality of coupled expander/compressor pairs to recover additional energy.
In summary, the invention provides a system for energy recovery that combines mechanically coupled refrigeration capacity with an energy recovery system to provide cooled air to a gas turbine inlet and/or other refrigeration load. The system preferably is operated with a working fluid having a phase diagram wherein the curve passes through a maximum and wherein the working fluid absorbs heat energy above its critical temperature. For a given system, the quantity of energy, usually heat, available to be recovered, the desired product temperature in the refrigeration system and the available heat sink capacity for condensing the working fluid will define the requirements for the latent heat of vaporization, and the temperature and pressure conditions that must be met by the working fluid. The working fluid may be of any composition that will meet the required temperature, pressure and heat transfer requirements of the system. Alternatively, operating temperature and pressure ranges for the overall system may be defined by mechanical limitations of desired equipment, such as the maximum operational pressure of a preferred heat exchanger or the desired approach temperature for the product temperature against ambient conditions. When these additional considerations are imposed on the system, the working fluid composition will be adjusted to meet these preferred ranges. Preferred working fluids are those listed and discussed above. Hydrocarbon or refrigerants listed in ASHRAE, or mixtures of these working fluids are especially preferred. However, those skilled in the art will recognize that in many applications other working fluids may be used to practice the invention.
In another embodiment the invention may be viewed as an improvement in the method for designing an energy recovery system disclosed in U.S. Pat. No. 6,195,997 to provide enhanced energy recovery while at the same time providing a coupled refrigeration capacity. The improvement comprises the steps of defining a desired product temperature in the refrigeration system, defining an available heat sink, defining a quantity of energy to be recovered in an energy recovery system, defining a means for converting the quantity of energy to be recovered into a recovered energy output while also providing sufficient heat energy to provide a sufficient quantity of a volatile component of at least a portion of the working fluid which is work expanded in a system having coupled compressors which compress a separate working fluid to be expanded to provide cooling to the defined product temperature when evaporated and, defining a group of conditions to be meet by a working fluid, the working fluid in the energy recovery system being substantially vaporized by contacting the energy to be recovered thereafter driving the means for energy recovery while also providing the compression required to generate the desired cooling in the refrigeration loop and selecting a working fluid composition that permits meeting all design constraints.
The invention is illustrated by the specific examples set out below.