U.S. patent application number 13/761209 was filed with the patent office on 2014-08-07 for corrugated tube regenerator for an expansion engine.
The applicant listed for this patent is Jay Stephen Kaufman. Invention is credited to Jay Stephen Kaufman.
Application Number | 20140216687 13/761209 |
Document ID | / |
Family ID | 51258288 |
Filed Date | 2014-08-07 |
United States Patent
Application |
20140216687 |
Kind Code |
A1 |
Kaufman; Jay Stephen |
August 7, 2014 |
Corrugated Tube Regenerator for an Expansion Engine
Abstract
A regenerative heat exchanger for transferring heat from the
exhaust gas to the intake working fluid of a prime mover.
Application includes gas turbines for both motor vehicles and
distributed electric generation. The heat exchanger employs a
rotating matrix, which circulates through working fluid exhaust and
intake channels while absorbing and rejecting heat between the two
channels. Features include corrugated tubes for enhanced heat
transfer, minimally welded low stress construction, quick-detach
assembly of standard components, and purge flow sealing using
recovered heat. Effectiveness exceeding 95% increases thermal
efficiency of low-pressure ratio gas turbines.
Inventors: |
Kaufman; Jay Stephen;
(Kingston, NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kaufman; Jay Stephen |
Kingston |
NH |
US |
|
|
Family ID: |
51258288 |
Appl. No.: |
13/761209 |
Filed: |
February 7, 2013 |
Current U.S.
Class: |
165/86 ; 165/157;
29/890.03 |
Current CPC
Class: |
F02C 7/105 20130101;
Y10T 29/4935 20150115; F28D 19/047 20130101; F28F 1/08 20130101;
F28D 19/042 20130101; F28F 1/40 20130101 |
Class at
Publication: |
165/86 ; 165/157;
29/890.03 |
International
Class: |
F28D 11/04 20060101
F28D011/04; B21D 53/02 20060101 B21D053/02; F28D 1/053 20060101
F28D001/053 |
Claims
1. Rotary regenerator heat recovery means of a prime mover
comprising heat transfer matrix means with corrugated heat transfer
tubes inserted longitudinally in working fluid flow cells of said
matrix means, wherein circumferential surface ridges and grooves of
said corrugated tubes provide heat transfer enhancement, while said
matrix provides transfer of exhaust gas heat of said prime mover to
the higher pressure intake working fluid of said prime mover during
rotation of said matrix about a central shaft of said regenerator
means.
2. The matrix means of claim 1 comprising a one piece array of
working fluid honeycomb cells containing said corrugated tubes for
providing compact heat transfer surface means.
3. The matrix means of claim 1 comprising a packed array of working
fluid tubular cells containing said corrugated tubes, wherein said
array is retained at the periphery by essentially circular duct
means for providing compact heat transfer surface means.
4. The matrix means of claim 3 comprising essentially line contact
between said tubular cells, wherein said tubular cells are held in
essentially hexagonal arrangement by said duct means,
5. The heat transfer cells of claim 1 comprising strip fin means
disposed longitudinally through said corrugated tubes for providing
further heat transfer enhancement of said matrix means.
6. The regenerator means of claim 1 comprising working fluid
containment means constructed of first conduit fitting means and
second conduit fitting means, wherein each said fitting means
comprises a main branch with support means for said matrix and
connection means for attachment of said first fitting means to said
second fitting means, a pressurized branch for channeling
compressed working fluid, and an exhaust branch for channeling
exhaust working fluid.
7. The support means of claim 6 comprising purge flow distribution
means, wherein pressure of purge flow to said distribution means is
provided by a purge system with compression work means selected
from the recovered energy group consisting of solar, building
amplified wind, motor vehicle momentum, motor vehicle draft loss
and motor vehicle shock.
8. The purge system of claim 7 comprising purge flow heating means
wherein purge flow temperature is increased by recovered heat
selected from the group consisting of combustor waste heat,
compressor heat, motor vehicle transmission heat and stored solar
heat.
9. A method for constructing a heat transfer matrix of a rotary
regenerator of a prime mover comprising the steps of: enclosing
said matrix within an essentially circular duct disposed in
essentially parallel relation to working fluid flow cells of said
matrix, inserting and retaining corrugated heat transfer
enhancement tubes into said cells, and inserting a matrix rotation
shaft along the area centroid of said matrix, wherein said matrix
provides transfer of exhaust gas heat of said prime mover to the
higher pressure intake working fluid of said prime mover during
rotation of said matrix about said shaft.
10. The method of claim 9 comprising the first step of sequentially
packing cell tubes in essentially line contact within an
essentially hexagonal arrangement to provide an array of tubular
working fluid flow passages of said matrix.
11. The method of claim 10 comprising the next step of inserting
filler tubes in essentially line contact with said cell tubes and
with said duct for providing an essentially circular periphery of
said matrix.
12. The method of claim 11 comprising the next step of attaching
the periphery of at least one perforated retainer disk to said duct
for retention of said corrugated tubes in said cell tubes, wherein
perforations of said disk or disks provides for essentially
unrestricted flow of working fluid through said disks.
13. The method of claim 12 comprising the next step of attaching
said cell tubes to said disk or disks by a process selected from
the group consisting of gasketing, interference fitting, welding
and brazing, for limiting leakage of working fluid between ends of
said cell tubes and said disk or disks.
14. The method of claim 10 comprising working fluid leakage
limiting means, wherein material of said cell tubes and of said
duct means are selected to limit the difference of diametral
thermal expansion between said cell tubes and said duct.
15. The method of claim 14 comprising the first step of grinding or
machining the outside diameter of said cell tubes, wherein line
contact between said cell tubes is maintained within a specified
tolerance range for limiting leakage of working fluid between said
tubular cells.
16. A rotary regenerator of a prime mover comprising: a heat
transfer matrix containment vessel, a rotating heat transfer matrix
within said vessel, p1 corrugated working fluid tubes inserted
within working fluid flow passages of said matrix, colder matrix
end support bars within said containment, hotter matrix end support
bars within said containment, and matrix shaft bearings within said
bars, wherein circumferential surface ridges and grooves of said
corrugated tubes provide enhanced transfer of exhaust gas heat from
a combustor and a turbine of said prime mover to the higher
pressure intake working fluid from a compressor of said prime
mover, during rotation of said matrix about a central shaft mounted
to said bearings.
17. The support bars of claim 16 comprising purge flow distribution
nozzles disposed radially with respect to said shaft and in direct
fluid communication with at least one end of said bars, for passage
and direction of purge flow from a purge system toward pressurized
working fluid of said prime mover.
18. The purge system of claim 17 comprising a purge flow evaporator
in contact with said compressor and a purge flow superheater in
contact with said combustor, for providing steam from said
evaporator to said colder matrix end support bars and steam from
said superheater to said hotter matrix end support bars.
19. The corrugated tubes of claim 16 comprising strip fins inserted
in said corrugated tubes for providing further heat transfer
enhancement within said matrix.
20. The corrugated tubes of claim 16 comprising corrugation
geometry, wherein the width of said grooves exceeds the width of
said ridges to provide meshing of said tubes disposed in adjacent
relation, for reducing the diameter of said matrix.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to counter flow regenerative
heat exchangers for heat recovery in low capacity prime movers.
This includes distributed electric generation and vehicle use, and
pertains particularly to an improved regenerator for small gas
turbine engines. Low capacity gas turbines are generally considered
to be impractical, especially in variable speed automotive use, due
to very high turbine speed, inefficient turn-down during
deceleration and idling, and high exhaust temperature. The rotary
regenerator of the present invention with heat transfer enhancing
features resolves these issues, enabling efficient low compression
operation with effectiveness greater than 95%. Low stress and
compact low cost metallic construction withstands high turbine
outlet temperature associated with low compression. As a result,
cycle efficiency is high within turbine stress limitations imposed
by the pressure-speed relation, wherein rotor speed is directly
proportional to working fluid flow rate and compression ratio and
indirectly proportional to turbine diameter. Additional benefits of
enhanced heat transfer in low compression application are reduced
leakage of intake air into exhaust gas, improved flow distribution
through the heat transfer surface and closer balance between intake
air and exhaust gas pressure drop. Estimated cost is 40 $/kW engine
capacity
[0002] The regenerator of the present invention employs a rotating
matrix of corrugated heat transfer tubes, which absorb heat on both
inner and outer surfaces from the lower pressure exhaust gas side
for transfer to the pressurized intake air side of the regenerator.
Heat transfer in the laminar flow range provides a compact and high
effectiveness design. Compactness is further improved using either
pre-fabricated honeycomb or packed tubular cell construction in a
hexagonal array. Each cell contains one or more corrugated tubes
with enhanced heat storage and heat transfer capability. Further
compactness is achieved in the tubular type matrix by meshing the
ridges and grooves of corrugated tubes in hexagonal groups within
the cells. This arrangement provides positive tube positioning in a
relatively low stress unconstrained matrix. Heat transfer may be
further enhanced in both matrix types by insertion of longitudinal
strip-fins within the corrugated tubes. The stainless steel or
nickel alloy matrix operates well within recommended service
temperature limits approaching normal micro-turbine inlet gas
temperature of 1150 K in this low stress application. The honeycomb
matrix may be mass produced using a relatively inexpensive
automatic welding process and the alternate cell tube matrix is
non-welded. The corrugated tubes are readily available and
installed without welding at minimal cost.
[0003] The matrix is supported on bearings at each end of a central
shaft and rotates through seals having minimal working fluid
leakage. Two factors lower seal leakage; low compression ratio of
the application and an elongated matrix due to enhanced heat
transfer. Matrix length to diameter is reduced from a ratio of
about 5 to a ratio of 1 in the regenerator of the present
invention. Seal leakage may be further reduced by a purge system,
drawing fluid from a turbine bearing air supply or a rotor cooling
water supply for distribution along matrix support bars. An
electric motor provides rotation of the matrix via a pinion and
ring gear.
[0004] Current practice for small gas turbines utilizing heat
recovery to increase thermal efficiency is to employ recuperators
with fixed surface area for stationary use and rotary regenerators
for automotive use. In the former case micro-turbines for
distributed electric generation are gaining wide acceptance, while
in the latter case gas turbine development is ongoing and limited
to constant speed proto-types. The state-of-the-art micro-turbine
heat exchanger is a counter-flow recuperator, which operates in the
laminar flow range for acceptable heat transfer and effectiveness
in a plate type matrix with numerous parallel flow passages fitted
with strip-fins. It is the most expensive component of the gas
turbine system, constructed of high temperature alloys with a large
number of closely spaced brazed joints and complex header
arrangements. Efforts are ongoing to develop a less expensive heat
exchanger. The state-of-the-art automotive heat exchanger is a more
advanced rotary regenerator, which also relies on laminar flow, but
in a ceramic disk matrix, It must withstand thermal cycling to
nearly turbine inlet gas temperature during deceleration and
idling. Both fixed and rotary heat exchangers are subject to design
compromise to limit thermal stresses. The fixed metallic
recuperator is constrained by thermal expansion and maximum service
temperature is limited to about 950 K. Estimated cost is 160 $/kW
engine capacity. The ceramic rotary regenerator matrix can
withstand elevated turbine exhaust temperature, but off-design
operating conditions may impose excessive thermal stress. In
addition, the latter is subject to erosion/corrosion due to seal
leakage and is not conducive to heat transfer enhancement geometry
and ring gear attachment. Estimated cost is 80 $/kW engine
capacity
SUMMARY AND OBJECTS OF THE INVENTION
[0005] Accordingly, objects and advantages of the rotary
regenerator of the present invention are:
[0006] (a) to provide a rotary regenerator for increasing
thermodynamic cycle efficiency of expansion engines;
[0007] (b) to provide a rotary regenerator having high
effectiveness;
[0008] (c) to provide a rotary regenerator with a low constraint
metallic heat transfer matrix to withstand thermal stresses at
highest service temperature;
[0009] (d) to provide a rotary regenerator having a compact
assembly using a hexagonal matrix;
[0010] (e) to provide a rotary regenerator having low seal leakage
or increased pressure capability;
[0011] (f) to provide a rotary regenerator having heat recovering
purge flow for matrix lubrication and low seal leakage without loss
of engine efficiency;
[0012] (g) to provide a rotary regenerator having uniform matrix
flow distribution;
[0013] (h) to provide a rotary regenerator constructed of readily
available components including enclosure and heat transfer cells;
and
[0014] (i) to provide a rotary regenerator with tube matrix
accessibility contained in a quickly detachable enclosure.
[0015] Further objects and advantages are to provide an inexpensive
and reliable regenerator, which will enable widespread application
of expansion engines including low capacity gas turbines. Still
further objects and advantages will become apparent from a
consideration of the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In the drawings, closely related figures have the same
number but different alphabetical suffixes.
[0017] FIG. 1A is a plan view illustrating working fluid channeling
and component arrangement of a preferred embodiment of the
regenerator of the present invention for prime mover application.
Dashed lines depict internal components.
[0018] FIG. 1B is an end elevation view illustrating working fluid
channeling and component arrangement of a preferred embodiment of
the regenerator of the present invention. Dashed lines depict
internal components.
[0019] FIG. 1C is a longitudinal cross-section view illustrating
component arrangement of a preferred embodiment of the heat
transfer matrix of the regenerator of the present invention.
[0020] FIG. 1D is a transverse cross-section view illustrating
component arrangement of a preferred embodiment of the of the heat
transfer matrix of the regenerator of the present invention.
[0021] FIG. 1E is a longitudinal cross-section view of a preferred
embodiment of a portion of a corrugated tube of the heat transfer
matrix of the regenerator of the present invention.
[0022] FIG. 2A is an transverse cross-section view illustrating an
alternate preferred embodiment of a heat transfer matrix of the
regenerator of the present invention.
[0023] FIG. 2B is a transverse cross-section view illustrating an
alternate preferred embodiment of a matrix cell of the regenerator
of the present invention.
[0024] FIG. 2C is a transverse cross-section view illustrating an
alternate preferred embodiment of a heat transfer matrix of the
regenerator of the present invention.
[0025] FIG. 2D is a partial longitudinal elevation view
illustrating an alternate preferred embodiment of adjacent
corrugated heat transfer tubes of the heat transfer matrix of the
regenerator of the present invention.
[0026] FIG. 3 is a longitudinal cross-section view illustrating an
alternate preferred embodiment of a heat transfer enhancement
component of the regenerator of the present invention.
[0027] FIG. 4A is a schematic illustrating a preferred embodiment
of a purge flow system of the regenerator the present invention.
Dashed lines depict purge flow distribution.
[0028] FIG. 4B is an elevation view illustrating a preferred
embodiment of a purge flow distribution component of the
regenerator the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] FIG. 1A and FIG. 1B illustrate working fluid channeling and
component arrangement of a preferred embodiment of a rotary
regenerator 100 of a prime mover of the present invention. Arrows
indicate flow direction of working fluid from a compressor
discharge line 102 through a pressurized regenerator channel 104
and discharging to a combustor intake line 106, while working fluid
exhaust from a turbine discharge line 108 continues through a
depressurized regenerator channel 110 to atmosphere. Heat is
transferred from the turbine exhaust to pressurized working fluid
within a rotating heat transfer matrix 112. The matrix is contained
and supported in a containment vessel 114 constructed of two tee
fittings 116 held together by a bolted clamp 118. Clamped stainless
steel tee fittings are available from Victaulic Company of Easton,
Pennsylvania. Semi-circular baffle plates 120, welded to the
fittings and abutted to a colder matrix end support bar 122 and to
a hotter matrix end support bar 124, divide the pressurized and
depressurized channels. Each bar is fitted with shaft bearings 126,
which support a central rotational shaft 128 of the matrix. The
matrix is driven by a geared electric motor 130 via a ring gear 132
attached to the matrix. Radial leakage of working fluid across the
ends of the matrix is limited by appropriate surfacing of the bars,
while a circumferential seal 134 limits longitudinal leakage of
working fluid past the matrix and insulation 136 limits heat loss
from the vessel.
[0030] FIG. 1C illustrates component arrangement of a preferred
embodiment of the matrix. Longitudinal cells 138 are in a hexagonal
honeycomb pattern constructed of longitudinally welded cells to
facilitate a low leakage and compact matrix. Honeycomb matrix of
stainless steel is available from Benecor, Inc. of Wichita, Kans.
The matrix is held in place in the center by shaft 128 and at the
periphery by a circular duct 140. FIG. 1D illustrates the pattern
of matrix cells. FIG. 1E illustrates a corrugated tube 142, one of
which isE inserted in each cell. The corrugated tubes are retained
in the cells by retainer plates 144 having an appropriate
perforation pattern and flow area greater than flow area through
and along the corrugated tubes. Corrugated tubing of longitudinally
welded stainless steel is available from Hose Master Inc. of
Cleveland, Ohio and in open seam form from George Risk Industries
of Kimball, Nebraska. Components in contact with the matrix are
shown including the two shaft support bars with bearings, the ring
gear and the seal.
[0031] The corrugated heat transfer tubes, with both inside and
outside active surfaces, enable low hydraulic diameter of the
matrix and high conductive heat transfer coefficient in the laminar
flow range. Heat transfer coefficient and friction factor are
comparable to that of a fixed plate type recuperator operating in
similar flow conditions, but at about one-third of the cost. This
is accomplished by elimination of headers and associated welds in
conjunction with automated honeycomb matrix production. Performance
of the exemplary regenerator is estimated at operating conditions
applicable to a compact motor vehicle at a cruising speed of 120
km/h (75 mph). Turbine inlet gas temperature is 1110 K (2000 R) and
compression ratio is 3 with exhaust and pressurized side losses
limited to 2.5% and 1%, respectively. At these conditions cycle
efficiency and regenerator effectiveness are approximately 30% and
92%, respectively. The regenerator is configured as a hexagonal
group of 7 corrugated tubes per cell, with sizing based on turbine
exhaust temperature of 900 K (1620 R) and heat duty of 460,000 kJ/h
(436,000 Btu/h). Heat duty is based on the assumption that a
portion of the exhaust is bypassed around the regenerator to avoid
surface area penalty during infrequent high power operation. The
resulting matrix geometry is; surface area per cell=300 cm.sup.2(46
in.sup.2), flow area per cell=0.65 cm.sup.2(0.10 in.sup.2), total
cells=230, hydraulic diameter=0.21 cm (.084 in.), cell and
corrugated tube length=30.5 cm (12 in.), and matrix mass per
cell=0.045 kg (0.10 lb.).
[0032] FIGS. 2A through 2D illustrate an alternate preferred
embodiment of the matrix 212 of the regenerator of the present
invention. FIG. 2A is a further cross-section of FIG. 1C and
illustrates the tubular matrix constructed of cell tubes 238 in a
hexagonal pattern. The cell arrangement forms a non-welded matrix
held in line contact by compression imposed by a duct 240. Smaller
diameter filler tubes 241 complete fitting of the hexagonal matrix
to the circular duct. FIG. 2B illustrates a hexagonal group of 7
corrugated tubes 242 inserted in a cell tube. FIG. 2C illustrates a
perforated retainer plate 244 for holding the corrugated tubes in
the matrix. Two plates are held within the duct between the matrix
support bars 224, 226 and the ends of the cell tubes. Each plate
has a flow area through the perforations greater than the flow area
through the matrix. FIG. 2D is an alternate preferred embodiment
246 of adjacent corrugated tubes illustrating meshing of annular
corrugations 248 of the corrugated tubes. Nearly full engagement of
the corrugations is expected to decrease the matrix and vessel
diameters by about 20% with little effect on hydraulic diameter and
heat transfer rate of the matrix. Overall sizing of the tubular
cell matrix is comparable to the honeycomb matrix of FIGS. 1A
through 1D, however the corrugated tubes are inserted in hexagonal
groups to reduce the number of cell tubes. Performance of the
tubular cell matrix is expected to be comparable to the honeycomb
matrix. Some additional leakage will occur between cell tubes,
however cost is estimated to be 20% as compared to a plate type
stationary recuperator operating in similar flow conditions. Cost
reduction is accomplished by elimination of headers and welds. The
resulting matrix geometry is; surface area per 7 tube cell=(317
in.sup.2), flow area per 7 tube cell=4.6 cm.sup.2(0.72 in.sup.2),
total cells=43, hydraulic diameter=2.5 cm (0.10 in.), cell and
corrugated tube length=30.5 cm (12 in.), and matrix mass per 7 tube
cell=0.20 kg (0.45 lb.).
[0033] FIG. 3 is an alternate preferred embodiment illustrating a
saw toothed strip fin 346 inserted in a corrugated tube 342. The
strip decreases hydraulic diameter of the tube by an estimated 33%
while increasing heat transfer coefficient and friction factor in
approximately the same proportion.
[0034] FIG. 4A is a schematic illustrating a preferred embodiment
of a purge flow injection system for limiting working fluid leakage
transverse to tube ends and cell ends of the matrix. An exemplary
steam purged regenerator 400 is shown in relation to prime mover
components including a compressor 450, a combustor 452 with a fuel
tank 454, and a turbine 456. Open arrows and dashed lines indicate
flow and direction of purge water and steam. Purge flow is from a
water tank 458 through a recovery evaporator 460 of the compressor
from which a portion of steam is diverted and injected into the
tips of a colder end matrix support bar 422. The remaining portion
then continues through a recovery superheater 462 of the combustor
for superheating and injection into the tips of a hotter end matrix
support bar 424. FIG. 4B illustrates a hollow support bar 422 or
424 connected to water or steam lines of the purge flow supply.
Purge flow distribution nozzles 425 are oriented to discharge
toward the pressurized channel of the matrix. A shaft bearing 426
is shown oriented at right angles to the steam discharge.
[0035] Working fluid leakage across a non-purged matrix is low
because of low compression ratio and high length to diameter ratio
of the matrix. The purge system is adaptable in high temperature
gas turbines employing a water cooled turbine rotor while reducing
surface area of the matrix. This is because of two factors; zero
working fluid leakage and enhanced heat transfer with non-luminous
water vapor radiation.
[0036] While I have illustrated and described my invention by means
of specific embodiments, it is to be understood that numerous
changes and modifications may be made therein without departing
from the spirit and scope of the invention as defined in the
appended claims. For example, prime mover heat input may include
solar, the regenerator may be oriented with downward exhaust
requiring only one tube retainer plate at the bottom, and fin
strips with various cross-section configurations may be inserted in
the corrugated tubes.
* * * * *