U.S. patent application number 12/606571 was filed with the patent office on 2011-04-28 for waste heat recovery system.
This patent application is currently assigned to General Electric Company. Invention is credited to Gabor Ast, Sebastian Freund, Thomas Frey, Pierre Huck, Herbert Kopecek.
Application Number | 20110094227 12/606571 |
Document ID | / |
Family ID | 43897208 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110094227 |
Kind Code |
A1 |
Ast; Gabor ; et al. |
April 28, 2011 |
Waste Heat Recovery System
Abstract
In one embodiment, a waste heat recovery system includes a
Rankine cycle system that circulates a working fluid that absorbs
heat from exhaust gas. The Rankine cycle system includes an
evaporator that may transfer sensible heat from the exhaust gas to
the working fluid to produce cooled exhaust gas. The Rankine cycle
system also includes an economizer that may transfer latent heat
from the exhaust gas to the working fluid. The economizer is a
carbon steel heat exchanger with a corrosion resistant coating.
Inventors: |
Ast; Gabor; (Garching,
DE) ; Kopecek; Herbert; (Hallbergmoos, DE) ;
Frey; Thomas; (Ingolstadt, DE) ; Freund;
Sebastian; (Munich, DE) ; Huck; Pierre;
(Munich, DE) |
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
43897208 |
Appl. No.: |
12/606571 |
Filed: |
October 27, 2009 |
Current U.S.
Class: |
60/671 ;
60/670 |
Current CPC
Class: |
F01K 23/065 20130101;
F01K 25/08 20130101 |
Class at
Publication: |
60/671 ;
60/670 |
International
Class: |
F01K 25/00 20060101
F01K025/00; F01K 27/00 20060101 F01K027/00 |
Claims
1. A waste heat recovery system, comprising: an exhaust system that
generates exhaust gas; and a Rankine cycle system for circulating a
working fluid and comprising: an evaporator configured to transfer
sensible heat from the exhaust gas to the working fluid to produce
cooled exhaust gas; and an economizer configured to transfer latent
heat from the exhaust gas to the working fluid, wherein the
economizer comprises a carbon steel heat exchanger with a corrosion
resistant coating.
2. The waste heat recovery system of claim 1, wherein the corrosion
resistant coating comprises a silica coating.
3. The waste heat recovery system of claim 1, wherein the corrosion
resistant coating exhibits at least one of hydrophobic, oleophobic,
or antistatic properties.
4. The waste heat recovery system of claim 1, wherein the working
fluid comprises an organic working fluid.
5. The waste heat recovery system of claim 1, wherein the Rankine
cycle system comprises an expander configured to expand the working
fluid evaporated by the evaporator to drive a generator.
6. The waste heat recovery system of claim 1, wherein the Rankine
cycle system comprises a condenser configured to condense the
working fluid.
7. The waste heat recovery system of claim 1, wherein the
evaporator is configured to at least partially evaporate and/or to
superheat the working fluid.
8. The waste heat recovery system of claim 1, comprising an exhaust
gas heat exchanger configured to transfer the sensible heat from
the exhaust gas to an intermediate fluid in heat transfer
communication with the working fluid.
9. A waste heat recovery system, comprising: an exhaust system that
generates hot exhaust gas; a first Rankine cycle system for
circulating a first working fluid and comprising: an evaporator
configured to transfer sensible heat from the hot exhaust gas to
the first working fluid to produce cooled exhaust gas; and an
economizer configured to transfer latent heat from the cooled
exhaust gas to the working fluid, wherein the economizer comprises
a carbon steel heat exchanger with a corrosion resistant coating; a
second Rankine cycle system for circulating a second working fluid
and configured to transfer heat from an engine heat source to the
second working fluid; and a shared heat exchanger common to the
first and second Rankine cycle systems and configured to transfer
heat from the first working fluid to the second working fluid to
condense the first working fluid and to evaporate the second
working fluid.
10. The waste heat recovery system of claim 9, wherein the first
and second working fluids comprise organic working fluids, and
wherein the first working fluid has a condensation temperature
above a boiling point of the second working fluid.
11. The waste heat recovery system of claim 9, wherein the engine
heat source comprises an engine cooling system.
12. The waste heat recovery system of claim 9, wherein the second
Rankine cycle system comprises a preheater configured to transfer
heat from the heat source to the second working fluid to at least
partially evaporate the second working fluid prior to directing the
second working fluid to the shared heat exchanger.
13. A waste heat recovery system, comprising: an exhaust system
that generates hot exhaust gas; and a Rankine cycle system for
circulating a working fluid and comprising: an evaporator
configured to transfer heat from the hot exhaust gas to the working
fluid to at least partially vaporize the working fluid and to
produce cooled exhaust gas; a condenser configured to receive and
to condense the vaporized working fluid; and an economizer
configured to transfer heat from the cooled exhaust gas to the
condensed working fluid to at least partially condense the cooled
exhaust gas, wherein the economizer comprises a carbon steel heat
exchanger with a silica coating.
14. The waste heat recovery system of claim 13, wherein the working
fluid comprises cyclohexane.
15. The waste heat recovery system of claim 13, wherein the silica
coating comprises silica nanoparticles disposed on surfaces of the
heat exchanger exposed to the cooled exhaust gas.
16. The waste heat recovery system of claim 13, wherein the carbon
steel heat exchanger comprises a carbon steel shell configured to
receive the cooled exhaust gas and carbon steel tubes configured to
receive the working fluid and wherein the corrosion resistant
coating is disposed on an interior surface of the carbon steel
shell and on an exterior surface of the carbon steel tubes.
17. The waste heat recovery system of claim 13, comprising a
thermal oil loop for circulating thermal oil between the evaporator
and an exhaust gas heat exchanger configured to receive the hot
exhaust gas and transfer heat from the hot exhaust gas to the
thermal oil.
18. The waste heat recovery system of claim 13, comprising an
exhaust gas heat exchanger configured to receive the hot exhaust
gas and transfer heat from the hot exhaust gas to an intermediate
fluid in thermal communication with the working fluid.
19. The waste heat recovery system of claim 13, wherein the
evaporator is configured to transfer sensible heat from the hot
exhaust gas to the working fluid, and wherein the economizer is
configured to transfer latent heat from the cooled exhaust gas to
the working fluid.
20. The waste heat recovery system of claim 13, comprising a gas
engine configured to combust biogas to generate the hot exhaust
gas.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates to waste heat
recovery systems, and more specifically, to systems for recovering
waste heat from exhaust gas.
[0002] In general, power generation systems, such as combustion
engines, may produce exhaust gas in addition to power. A bottoming
Rankine cycle may be employed to recover waste heat from the
exhaust gas as well as from other heat sources, such as the cooling
system. The power output of the bottoming Rankine cycle may
generally increase the more that the exhaust gas is cooled.
However, the temperature to which the exhaust gas may be cooled may
be limited by corrosive elements in the exhaust gas. For example,
exhaust gas may include sulfur that may mix with water upon
condensation of the exhaust gas to produce sulfuric acid.
Accordingly, to inhibit corrosion in certain bottoming Rankine
cycles, the exhaust gas may not be cooled below the dew point
and/or to temperatures that may produce condensation of the exhaust
gas.
BRIEF DESCRIPTION OF THE INVENTION
[0003] In one embodiment, a waste heat recovery system includes an
exhaust system that generates exhaust gas and a Rankine cycle
system for circulating a working fluid. The Rankine cycle system
includes an evaporator configured to transfer sensible heat from
the exhaust gas to the working fluid to produce cooled exhaust gas
and an economizer configured to transfer latent heat from the
exhaust gas to the working fluid. The economizer includes a carbon
steel heat exchanger with a corrosion resistant coating.
[0004] In another embodiment, a waste heat recovery system includes
an exhaust system that generates hot exhaust gas, a first Rankine
cycle system for circulating a first working fluid, a second
Rankine cycle system for circulating a second working fluid and
configured to transfer heat from an engine heat source to the
second working fluid, and a shared heat exchanger common to the
first and second Rankine cycle systems and configured to transfer
heat from the first working fluid to the second working fluid to
condense the first working fluid and to evaporate the second
working fluid. The first Rankine cycle system includes an
evaporator configured to transfer sensible heat from the hot
exhaust gas to the first working fluid to produce cooled exhaust
gas and an economizer configured to transfer latent heat from the
cooled exhaust gas to the working fluid. The economizer includes a
carbon steel heat exchanger with a corrosion resistant coating.
[0005] In yet another embodiment, a waste heat recovery system
includes an exhaust system that generates hot exhaust gas and a
Rankine cycle system for circulating a working fluid. The Rankine
cycle system includes an evaporator configured to transfer heat
from the hot exhaust gas to the working fluid to at least partially
vaporize the working fluid and to produce cooled exhaust gas, a
condenser configured to receive and to condense the vaporized
working fluid, and an economizer configured to transfer heat from
the cooled exhaust gas to the condensed working fluid to at least
partially condense the cooled exhaust gas. The economizer includes
a carbon steel heat exchanger with a silica coating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0007] FIG. 1 is a diagrammatical representation of an embodiment
of a waste heat recovery system; and
[0008] FIG. 2 is a cross-sectional view of a portion of the
economizer shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0009] One or more specific embodiments of the present invention
will be described below. In an effort to provide a concise
description of these embodiments, all features of an actual
implementation may not be described in the specification. It should
be appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure.
[0010] When introducing elements of various embodiments of the
present invention, the articles "a," "an," "the," and "said" are
intended to mean that there are one or more of the elements. The
terms "comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements.
[0011] The present disclosure is directed to techniques for
recovering waste heat from exhaust gas. In accordance with certain
embodiments, a waste heat recovery system may include a pair of
organic Rankine cycle (ORC) systems arranged in a cascade
configuration. The high temperature ORC system may recover waste
heat from exhaust gas, and the low temperature ORC system may
recover waste heat from another heat source, such as an engine
cooling system. The high temperature ORC system may include a
working fluid economizer designed to recover latent heat from
condensing water in the exhaust gas in addition to sensible heat.
Specifically, the economizer may allow the exhaust gas to be cooled
below the dew point of the exhaust gas, which may increase the
power output of the waste heat recovery system. To inhibit
corrosion that may occur during condensation of the exhaust gas,
the economizer may be constructed of carbon steel with a corrosion
resistant coating. The coating may facilitate decreased
manufacturing and/or capital costs by allowing low cost carbon
steel to be employed rather than more expensive stainless
steel.
[0012] FIG. 1 depicts a waste heat recovery system 10 that may
employ a carbon steel economizer with a corrosion resistant
coating. The waste heat recovery system 10 may recover heat from a
heat generation system, such as an engine 12. In certain
embodiments, the engine 12 may be part of a power generation system
and may run on fuels such as biogas, natural gas, landfill gas,
coal mine gas, sewage gas, or combustible industrial waste gases,
among others. Further, although the engine 12 is depicted as a
combustion engine, in other embodiments, any suitable heat
generation system that produces exhaust gas may be employed, such
as a gas turbine, micro-turbine, reciprocating engine, or
geothermal, solar thermal, industrial, or residential heat
sources.
[0013] The waste heat recovery system 10 includes a pair of ORC
systems 14 and 16 arranged in a cascade configuration with a shared
heat exchanger 18 that transfers heat between the ORC systems 14
and 16. Each ORC system 14 and 16 may include a closed loop that
circulates a working fluid through a Rankine cycle within the ORC
system 14 and 16. Specifically, the high temperature ORC system 14
may circulate a first working fluid, and the low temperature ORC
system 16 may circulate a second working fluid. According to
certain embodiments, the first and second working fluids may
include organic working fluids. However, in other embodiments,
steam may be employed as the first and/or second working fluid.
Further, in certain embodiments, the first working fluid may have a
condensation temperature above the boiling point of the second
working fluid. According to certain embodiments, the first working
fluid may include cyclohexane, cyclopentane, thiophene, ketones,
aromatics, or combinations thereof. The second working fluid may
include propane, butane, fluoro-propane, pentafluoro-butane,
pentafluoro-polyether, oil, or combinations thereof, among others.
Further, in certain embodiments, the first and/or second organic
working fluids may include a binary fluid such as
cyclohexane-propane, cyclohexane-butane, cyclopentane-butane, or
cyclopentane-pentafluoro propane, among others.
[0014] Each ORC system 14 and 16 may be coupled to a generator 20
and 22 that converts heat recovered from the engine 12 to
electricity. Specifically, the high temperature ORC system 14 may
recover heat from an exhaust system 24 of the engine 12, and the
low temperature ORC system 16 may recover heat from another heat
source of the engine 12, such as the engine cooling system 26.
[0015] The first ORC system 14 may recover heat from the exhaust
system 24 through a heat exchanger 28 and an economizer 30. The
heat exchanger 28 and the economizer 30 may allow the first ORC
system 14 to recover heat from the exhaust gas at two different
temperatures. Specifically, the heat exchanger 28 may transfer heat
from the hot exhaust gas existing the exhaust system 24 to the
first ORC system 14 to produce cooled exhaust gas. The cooled
exhaust gas may then be direct to the economizer 30, which
transfers heat from the cooled exhaust gas to the first ORC system
14.
[0016] In certain embodiments, the exhaust gas may exit the exhaust
system at a temperature of approximately 400 to 500.degree. C., may
be cooled to a temperature of approximately 150 to 200.degree. C.
in the heat exchanger 28, and may be cooled to a temperature of
approximately 100 to 110.degree. C. in the economizer 30. More
specifically, the exhaust gas may exit the exhaust system at a
temperature of approximately 427.degree. C., may be cooled to a
temperature of approximately 180.degree. C. by the heat exchanger
28, and may be cooled to a temperature of approximately 104.degree.
C. by the economizer 30. In yet another example, the heat exchanger
28 may reduce the temperature of the exhaust gas by approximately
200 to 300.degree. C., and the economizer 30 may reduce the
temperature of the exhaust gas by approximately 80 to 90.degree.
C.
[0017] In certain embodiments, the heat exchanger 28 may recover
primarily sensible heat from the exhaust gas, and the economizer 30
may recovery primarily latent heat from the exhaust gas. In other
words, the exhaust gas flowing through the heat exchanger 28 may be
cooled to reduce its temperature while the exhaust gas remains in
the gaseous phase, while the exhaust gas flowing through the
economizer 30 may be all or partially condensed to produce liquid
phase exhaust gas.
[0018] The heat exchanger 28 may transfer heat from the exhaust gas
to the first ORC system 14 through a thermal oil loop 32 in heat
transfer communication with the first working fluid. Specifically,
as the exhaust gas flows through the heat exchanger 28, the exhaust
gas may heat the thermal oil flowing within the thermal oil loop
32. For example, in certain embodiments, the exhaust gas may heat
the thermal oil from a temperature of approximately 160.degree. C.
to a temperature of approximately 280.degree. C. A pump 34 may
circulate the thermal oil within the thermal oil loop 32, and the
heated thermal oil exiting the heat exchanger 28 may enter an
evaporator 36 of the first ORC system 14. As the heated oil flows
through the evaporator 36, the heated thermal oil may transfer heat
to the first working fluid flowing within the first ORC system 14.
In other embodiments, the thermal oil loop 32 may be replaced by
another closed loop circulating any suitable type of heat transfer
fluid for transferring heat from the exhaust gas to the first
working fluid.
[0019] Within the evaporator 36, the first working fluid may absorb
heat from the thermal oil and may be evaporated and/or superheated.
In certain embodiments, the first working fluid may be heated to a
temperature of approximately 225.degree. C. Upon exiting the
evaporator 36, the vapor phase working fluid may then flow to an
expander 38 where the fluid may be expanded to drive the generator
20. In certain embodiments, the expander may be a radial expander,
axial expander, impulse type expander, or high temperature screw
type expander, among others. Within the expander 38, the first
working fluid may be expanded to produce a low temperature and
pressure vapor.
[0020] From the expander 38, the first working fluid may enter the
shared heat exchanger 18 as a low temperature and pressure vapor.
Within the shared heat exchanger 18, the first working fluid may
transfer heat to the second working fluid flowing through the
shared heat exchanger 18 within the second ORC system 16.
Specifically, the first working fluid may transfer heat to the
second working fluid and condense into a liquid. The liquid phase
first working fluid may then flow through a pump 40 that circulates
the first working fluid within the first ORC system 14.
[0021] From the pump 40, the first working fluid may flow through
the economizer 30 where the first working fluid may be heated by
the exhaust gas flowing through the economizer 30. As noted above,
the exhaust gas flowing through the economizer 30 may be partially
or completely condensed to transfer latent heat to the first
working fluid. Within the economizer 30, the heat from the exhaust
gas may be transferred to the first working fluid to preheat the
first working fluid before the first working fluid enters the
evaporator 36. In certain embodiments, the preheating within the
economizer 30 may improve the efficiency of the waste heat recovery
system 10 by allowing additional heat to be extracted from the
exhaust gas. The first working fluid may then return to the
evaporator 36 where the cycle may begin again.
[0022] Through the shared heat exchanger 18, the first working
fluid flowing within the first ORC system 14 may transfer heat to
the second working fluid flowing within the second ORC system 16.
Specifically, as the second working fluid flows through the shared
heat exchanger 18, the second working fluid may absorb heat from
the first working fluid and may evaporate. The vapor phase second
working fluid may then enter an expander 44 and expand to drive the
generator 22. In certain embodiments, the expander 44 may be a
radial expander, axial expander, impulse type expander, or high
temperature screw type expander, among others. The second working
fluid may exit the expander 44 as a low temperature and pressure
vapor.
[0023] From the expander 44, the vapor phase second working fluid
may flow through an air-to-liquid heat exchanger 46 where the
second working fluid may be condensed by air flowing across the
air-to-liquid heat exchanger 46. In certain embodiments, the air-to
liquid-heat exchanger may include a motor with a fan that draws
ambient air across the air-to-liquid heat exchanger. The condensed
second working fluid may then enter a pump 48 that circulates the
second working fluid within the second ORC system 16.
[0024] From the pump 48, the second working fluid may flow through
a preheater 42 that may heat the second working fluid. The
preheater 42 may circulate a fluid from a heat source within the
engine 12. For example, the preheater 42 may circulate heated
cooling fluid from the cooling system 26 of the engine 12. The
temperature of the fluid entering the preheater 42 from the engine
12 may generally be lower than the temperature of the exhaust gas
entering the heat exchanger 28 and the economizer 30. For example,
in certain embodiments, the fluid from the engine 12 may enter the
preheater 42 at a temperature of approximately 80 to 100.degree. C.
Within the preheater 42, the fluid may transfer heat to the second
working fluid to cool the fluid from the engine 12. For example, in
certain embodiments, the fluid from the engine 12 may exit the
preheater 42 at a temperature of approximately 30.degree. C. The
cooled fluid may then be returned to the engine 12. In other
embodiments, the preheater may receive fluid from one or more heat
sources within the engine 12 instead of, or in addition to, the
cooling system 26. For example, the pre-heater 42 may receive fluid
from gas turbines and/or intercoolers.
[0025] Regardless of the heat source, the preheater 42 may transfer
heat from the engine 12 to the second working fluid. In certain
embodiments, the second working fluid may partially evaporate to
form a liquid-vapor mixture. However, in other embodiments, the
second working fluid may remain in a liquid phase. Upon exiting the
preheater 42, the second working fluid may return to the shared
heat exchanger 18 where the cycle may begin again.
[0026] The cascade arrangement of the first and second ORC systems
14 and 16 may generally allow an increased heat recovery over a
larger temperature range. For example, the first ORC system 14 may
allow recovery of heat in higher temperature ranges, such as
approximately 400 to 500.degree. C. while the second ORC system 16
facilitates recovery of heat in lower temperature range, such as
approximately 50 to 100.degree. C. Further, the inclusion of the
economizer 30 in the first ORC system 14 may allow additional heat
in an intermediate temperature range, such as approximately 150 to
250.degree. C., to be recovered from the exhaust gas. For example,
rather than recovering heat solely through the heat exchanger 28,
additional heat in an intermediate temperature range also may be
recovered through the use of the economizer 30. In certain
embodiments, the additional heat percent when compared to ORC
systems without an economizer. Further, as will be discussed below
with respect to FIG. 2, the economizer 30 may be constructed of
carbon steel and coated with a corrosion resistant coating. The
coating may allow carbon steel, rather than stainless steel, to be
employed for the economizer, which may reduce manufacturing and/or
capital costs.
[0027] As may be appreciated, additional equipment such as pumps,
valves, control circuitry, pressure and/or temperature transducers
or switches, among others may be included within the waste heat
recovery system 10. Furthermore, the types of equipment included
within the waste heat recovery system 10 may vary. For example,
according to certain embodiments, the heat exchangers 18, 28, 30,
36, and 42 may include shell and tube heat exchangers, fin and tube
heat exchangers, plate heat exchangers, plate and shell heat
exchangers, or combinations thereof, among others.
[0028] FIG. 2 is a cross-sectional view taken through the
economizer 30 illustrating a surface 50 of the economizer that
includes a corrosion resistant coating 52. In general, the coating
52 may be applied to surfaces 50 of the economizer that are exposed
to the exhaust gas. For example, in a shell and tube heat exchanger
where the exhaust gas flows through the shell portion, the coating
52 may be applied to the exterior surfaces of the tubes and the
interior surface of the shell. In another example where the exhaust
gas flows across tubes circulating a working fluid within a fin and
tube heat exchanger, the coating 52 may be applied to the external
surfaces of the tubes, to the fins, and to the interior surfaces of
the enclosure surrounding the fin and tube heat exchanger. In a
further example where the exhaust gas flows through the tubes of a
shell and tube heat exchanger, the coating 52 may be applied to the
interior surfaces of the tubes.
[0029] The coating 52 may be designed to inhibit corrosion that may
occur during condensation of the exhaust gas. The coating 52 may
include a silicon dioxide (silica) coating that provides a barrier
layer to inhibit corrosion to the surface 50 of the economizer 30.
In certain embodiments, the coating 52 may inhibit corrosion by
contaminants in the exhaust gas, such as sulfur that may react with
water upon condensation to form sulfuric acid that may corrode
and/or pit the surface 50. Further, in addition to corrosion
resistant properties, the coating 52 may exhibit hydrophobic,
oleophobic, and/or antistatic properties. According to certain
embodiments, the coating 52 may include a nanoparticle coating of
colloidal silica with particles ranging in size from approximately
one to five nanometers. However, in other embodiments, the size of
the nanoparticles may vary.
[0030] The coating may be applied by any suitable manufacturing
process, such as spray coating, dipping, or flooding. For example,
in certain embodiments, the external surfaces of the tubes and/or
fins may be spray coated to apply the coating. The coating may then
be cured upon startup of the engine 12 or through a separate curing
step where the coating 52 may be exposed to high temperatures. In
another example, the heat exchanger may be flooded with the coating
and then drained to allow the coating to adhere to surfaces of the
economizer 30. Further, in other embodiments, the coating 52 also
may be applied to other heat exchangers within the waste heat
recovery system 10. For example, the coating 52 may be applied to
surfaces of the heat exchanger 28.
[0031] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *