1. 1
Microchannel Heat
Exchangers: Applications
and Limitations
Anna Lee Tonkovich, PhD
Manager, Technology Development Center
Velocys, Inc
Plain City, OH
www.velocys.com
2
Overview
Microchannel Exchanger Definition
Advantages of Microchannel Exchangers
Implementation Challenges
Microchannel Exchanger Applications at
Velocys
2. 2
3
D ~ 0.1-0.3 mm
Characteristic
dimension
Microchannel Technology Definition
Microchannel
Tube and Shell
Plate and Frame
D ~ 3-10 mm
D ~ 10-50 mm
Size:
Small channels
(typically < 2mm) in
close proximity
4
Microchannel Definition
Manufacturing:
Shims or sheets with
microchannel features
Diffusion bonded or
welded to form
hermetically-sealed
microchannels
3. 3
5
Higher Performance
• High volumetric heat flux
• Modest pressure drop
• Compact hardware for space critical applications (e.g., off-shore
applications, transportable systems, etc.)
Robust Design
• Proven manufacturing processes
• Demonstrated mechanical integrity
Scalable Technology
• Repeatable Design
• Effective Flow Distribution
Microchannel Technology Advantages
6
d
kNu
h
×
=
Nu: Nusselt number
h: Heat transfer coefficient
d: Hydraulic diameter
k: Thermal conductivity
Performance:
Higher Heat Transfer Coefficients
Small channels provide high heat transfer
coefficient
Small diameter results in large heat
transfer coefficient in microchannels
Microchannel Heat Exchanger Conventional Heat Exchanger
High surface area/volume ratio
High heat transfer per volume
Low surface area/volume ratio
Low heat transfer per volume
4. 4
7
Micro-channel Heat Exchanger
Performance Comparison
400 – 200050 – 30020 – 100
Heat Transfer
coefficient (W/m2/K)
(Gas)
LaminarTurbulentTurbulent
Flow Regime
< 10°C~ 10°C~ 20°C
Approach
Temperature (°C)
> 70003000 – 7000
~ 5000
(tube side)
Heat Transfer
coefficient (W/m2/K)
(liquid)
> 1500850 – 150050 – 100
Surface Area Per
Unit Volume (m2/m3)
Micro-channel
Heat Exchanger
Compact Heat
Exchanger
Shell and Tube
Heat Exchanger
Parameter
75.1
V
L
P
p
∆ 75.1
V
L
P
p
∆
V
L
P
p
∆
8
Performance:
Manageable Pressure Drop
Laminar Flow
• Orderly flow – less fluctuations
•
Laminar Flow
Turbulent Flow
flowh VDf
L
P
µ)(=
∆
Turbulent Flow
• Random flow – more fluctuations
•
75.175.025.0
)( VDf
L
P
h ρµ=
∆
flow
(Blasius friction factor)
5. 5
9
Performance:
Manageable Pressure Drop
Distributed flow provide shorter flow length,
overall low pressure drop
ρ2
4
2
G
d
L
fP ××=∆
f: Friction factor
G: Mass Flux
d: Hydraulic diameter
ρ: Density
L : Length
Microchannel Exchanger Conventional Heat Exchanger
Distributed flow
Short length
Bulk flow
Long length
10
Performance:
Increased Volumetric Heat Flux
0.01
0.1
1
10
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Channel Gap (in)
VolumetricHeatFlux(W/cm3
)
Basis:
• N2 / N2 heat exchanger (gas/gas)
• Stream 1: 150°C inlet, 1.5 psig
• Stream 2: 50°C inlet, 1.5 psig
• Approach temperature: 5°C per stream
Higher Volumetric Flux Smaller Hardware
Low system pressure drop 1.5 psig
7. 7
13
Robust:
Mechanical Integrity
Validated Mechanical Strength
Stamped Diffusion Bonded Device
Pressure hammer tests
• 0 psig to 1000 psig
• 30 second cycle time
Example Results of Test Specimen
• First: 8,816 cycles at 850oC – no failure
• Then: 14,871 cycles at 900oC – no failure
• Finally, failed after 87 cycles at 950oC.
14
Scaleable:
“Numbering-up” vs Scaling-up
Reduce time and cost to commercialization
Number up Scale up
Identical channel
hydrodynamics at
all scales
8. 8
15
Scaleable:
Development Methodology
Full-scale
Reactor
C
E
L
L
Cell
• Internal channel dimensions same
as commercial chemical processor
• Number of channels increase;
size of channels does not
Multi-Cell
• Many channels
• 10-100 lb/hr
Full-Scale
• >1000 channels
• 1000-5000 lb/hr
Full-Scale Reactor is the
basic building block of a
commercial plant
Gas flow
M
U
L
T
I
C
E
L
L
16
Scaleable:
Flow Distribution Strategy
Inlet
1 2 3
max min
1
max
100%
m m
Q
m
−
= ×
2 3
Pressure Drop in flow circuits can be tailored
to achieve sufficient flow distribution
Pressure Drop in flow circuits can be tailored
to achieve sufficient flow distribution
9. 9
17
Scaleable:
Validated Flow Distribution
18
Scaleable:
Channel Flow Distribution
Sufficient flow distribution measured in test device
Irregular gasket on half of test device
Sufficient flow distribution measured in test device
Irregular gasket on half of test device
Run 16: 214.0 SLPM of air
0.0E+00
1.0E-05
2.0E-05
3.0E-05
4.0E-05
5.0E-05
6.0E-05
7.0E-05
8.0E-05
9.0E-05
1.0E-04
0 12 24 36 48 60 72
Channel number
Massflowrate(kg/s)
Model
Experiment
10. 10
Implementation Challenges
• Cost
• Reliability
20
Implementation of Microchannel
Exchangers
Overall costs determined by
• Equipment costs
• Installation costs
• Process productivity
Attractive costs for applications that
• Require expensive materials of construction, e.g.,
high nickel alloys
• Involve multiple streams
• Demand close approach temperatures
11. 11
21
Installation Costs are Lower for
Compact Equipment
0
1
2
3
4
InstallationFactor
Column Vertical
Vessels
Horizontal
Vessels
Shell &
Tube HXs
Plate HXs Pumps,
Motors
Source: Chemical Engineering, “Sharpen your
Capital Cost Estimating Skills,” Oct. 2001
Average Installation Factors for Land-based Facilities
22
Implementation of Microchannel
Exchangers
Three performance aspects impact
reliability
•Fouling/plugging
•Corrosion
•On-stream factor
12. 12
23
Reliability: Fouling
With appropriate design,
microchannels can be used in some
‘fouling’ services but not others
Fouling in microchannels depends upon
service and …
• Particulate size
• Surface chemistry
• Solids content
24
Fouling expected in some operating
services: water boiling
Vaporizer after
2000 hours operation
Significant
performance
degradation over
2000 hours
Solids at 15 ppm, 80% initial vapor quality
13. 13
25
Fouling expected in some operating
service but not detected
Solids at 1ppm, 30%vapor quality
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0:00:00 2400:00:00 4800:00:00 7200:00:00 9600:00:00
Time (hh:mm:ss)
DeltaP(psig)
0
20
40
60
80
100
120
140
160
180
200
Temperature(C),%
Steam
Delta P
SteamQuality
Outlet Air Temp (C)
Vaporizer after
9600 hours operation
No performance
degradation over
9600 hours
26
Pitted areas
Pitting observed after 100 hr of testingPitting observed after 100 hr of testing
Non-Aged Surface After 100 hrs
Reliability:
Corrosion from Unprotected Metal Surface
Coupon tested for hot corrosion at 960oC,
1 atm, 20% (O2 + steam), balance inert
Coupon tested for hot corrosion at 960oC,
1 atm, 20% (O2 + steam), balance inert
14. 14
27
Reliability:
Corrosion Resistance with Protected Surface
Non-Aged Surface After 1000 hrs
No visible difference in surface between fresh and 1000 hrs.No visible difference in surface between fresh and 1000 hrs.
Coupon tested for hot corrosion at 960oC,
1 atm, 20% (O2 + steam), balance inert
Coupon tested for hot corrosion at 960oC,
1 atm, 20% (O2 + steam), balance inert
28
Reliability: On-Stream Factor
Frequency of
Servicing
Maintenance access
Sequential service of
modules with partial
plant capacity
reduction
15. 15
Case Studies
30
• Formed in 2001 by Battelle
Memorial Institute to
commercialize microchannel
technology
• Located in a 27,000 ft2 facility
near Columbus, Ohio
• Established alliances with
engineering and manufacturing
firms
• Total S.A., Dow, ABB and other
strategic partners have invested
over $75 million
• More than 50 granted patents &
80 patent applications in process
Velocys Introduction
16. 16
31
Cryogenic Applications
Microchannel Exchanger Development
at Velocys
High temperature
reactions
Integrated phase change
Distillation
32
LNG Application
• Microchannel Heat Exchanger increases LNG process
productivity through decreased pressure drop:
• Shorter flow length
• Laminar Flow
• High surface area-to-volume
• Higher ROI for monetizing stranded natural gas
• Lower capital cost and operating cost per throughput, or
• Increase plant capacity for the same compression capacity
• Small foot-print an additional advantage of
microchannel heat exchangers
17. 17
33
Case Study: Simplified LNG Cycle
Natural gas
50,000 metric tons/year
LNG
J-T
Valve
Compressor Condenser
Three stream
main heat
exchanger
153°C
331.3 psig
29.4°C
323.3 psig
-153.9°C
318 psig -158.3°C
29.95 psig
32.2°C
635.3 psig
-153.9°C
5 psig
20.9°C
19.95 psig
322.8 psig
27.75 psig
-155.3°C
Compression Ratio
• Before 10
• After ~8
Compression
Savings = 18-22%
Compression Ratio
• Before 10
• After ~8
Compression
Savings = 18-22%
34
Heat Transfer Comparison for LNG
201Relative Length
500-1500>1500
Core Area,
m2/m3
<1>10
Core Heat Flux,
W/cm3
Conventional
Plate-fin HX
Velocys HX
Significant reduction in hardware volume
18. 18
35
Why the advantage?
Stainless steel (bonded) versus aluminum reduces
axial conduction and allows shorter lengths
Optimized multi-stream microchannel exchanger
Short lengths reduce pressure drop
Flow Flow
Benchmark
Velocys
36
Length Advantage
Alternate Material Selection Reduces Heat Exchanger Length
By Reducing Axial Conduction
L
kAc
∝λAxial Conduction Parameter
Channels
Ac
L
For same heat duty,
• Aluminum plate fin heat exchanger, L = 6.7 m
• Velocys Stainless Steel heat exchanger, L = 0.3 m
Shorter Heat Exchanger Length
• Lower thermal conductivity
• Smaller metal area
19. 19
37
Conventional Technology
Conventional Steam Reformer
20 million
standard cubic
feet hydrogen
per day
Plot ~ 30m x
~30m x ~30m
High
temperature
exchangers
required
38
Velocys® Technology Reactors
Microchannel
Steam Methane
Reformer
Identical
capacity
Plot < 10 m x
10m x 10 m
(< 10% original)
~25% reduction
in overall plant
costs
20. 20
39
Integrated Reactor and Exchanger:
Steam Reforming
Reactor
Section
Multi-stream
Heat Exchanger
Section
Internal
Manifold
Section
ReactantProduct
Fuel
Air
Exhaust
100900
Temperature (C)
Length (m)
0.9
40
30
40
50
60
70
80
0 2 4 6 8 10 12
Contact time, msec
%
CO selectivity, %
CH4 Conv, %
P = 20 atm, T = 860 C, 2:1 steam:C
Equilibrium
Steam Reformer Performance
Near equilibrium conversion and
selectivity at millisecond contact times
21. 21
41
Target Segment
Microchannel Cost Advantage
Hydrogen Production Capacity (MMSCFD)
5 5010 15 20 25 30 35 40 45
CapitalCost($/SCFD)
Velocys
Conventional
0
0
0.5
1.0
1.5
2.0
2.5
Substantial
capital cost
savings
Substantial
capital cost
savings
42
Methane Steam Reformer
Development Status
Commercial partnership
• Announced joint development project with Total S.A.
for gas-to-liquids technology
• Focused on large, land-base applications
Demonstration Facility
• Construction of industrial steam methane reforming
demonstration will begin in late 2006
• Start-up of demonstration plant expected in late 2007
• Site selection and preliminary engineering completed
22. 22
43
GTL Process:
Phase change controls FT reactor
Steam
Reforming
CO / H2
Products
Diesel
Product
Air
H2 H2O
Gas Recycle
Steam
Fischer
Tropsch
Local
Natural
Gas
Hydro-
Cracking
Natural
Gas
44
Integrated Heat Transfer
in Fischer-Tropsch Reactor
Fischer-Tropsch Synthesis (highly exothermic)
• Remove heat via integrated microchannel steam generation
• Stable partial boiling in 0.6-m microchannel demonstrated
• Excellent temperature control enables short contact time
- Conventional Fixed Bed: ~10 seconds
- Velocys reactor: < 0.4 second contact time
851210Reactor productivity, bl/te
300-5001,400-1,7001,800-2,000Reactor wt, tonnes
35,00019,00019,000Capacity, bpd
Velocys
Tubular
Fixed Bed *Slurry *
* Source: Hoek, Shell, CatCon2003
23. 23
45
Phase Change Demonstrated:
Commercial Length Microchannels
230
233
236
239
242
245
248
251
254
257
260
0 5 10 15 20 25
Distance to Inlet, inch
Walltemperature,
o
C
q"=5.8 W/cm2
q"=3.8 W/cm2
q"=1.4 W/cm2
Inlet temperature: Saturation temperature (P=522 psia)
2.5
o
C
2.9
o
C
End effect
End effect
Stable phase change in long
microchannels demonstrated
46
FT Demonstration:
Commercial Length Reactors
>0.9α number
>500 hoursTime on Stream
7.6%Methane
Selectivity
70%Conversion per
pass
330 psigPressure
< 225 °CTemperature
~ 330 msContact Time
0.9 mReaction Channel
24. 24
47
FT Reactor Assembly:
Commercial Microchannel Reactor Within Assembly
48
Impact of Compact Hardware:
Transportable Synthetic Fuel Production
Design Basis:
•350 barrels/day
•Containerized modules
A mobile fuel production plant is an application where size matters
Velocys SMR
Velocys FT
De-sulfurization
Fired Feed
Preheater
Heat
Exchangers
Steam Turbine
Generator
Boiler
Engine
Generator
Water
Treatment
Product
Storage
Sponsor: U.S. Army’s National Automotive Center
25. 25
49
Impact of Compact Hardware:
Off-shore applications
10,000 – 35,000 BPD
Land-based or ship
mounted with
conventional marine
hulls
Initial design for
floating, production,
storage and off-
loading facility
Design project
completed by external
engineering firm
Off-shore platforms cannot use autothermal reforming and
must be compact
600 ft
150 ft
Conventional Distillation
Ethane-Ethylene Fractionation
“C2 Splitter”
26. 26
Microchannel Distillation
52
Microchannel Distillation creates short
HETP
diffusion to/from
vapor-liquid interface
Vapor channel
Liquid film
Heat exchange
t: Characteristic diffusion time
d: Hydraulic diameter
D: Diffusivity
D
d
diff
2
)2(
=τ
• Liquid film flows along liquid removal structure
• Integrated heat management: Add or remove heat
near desired temperature and quantity.
• Short HETP from enhanced mass transfer
27. 27
53
Microchannel Distillation Demonstrated:
Hexane/Cyclohexane Test Separation
Liquid
Removal
Structure
Gas-Liquid
disengagement
Vapor
channel
Assembled device
54
Distillation Results:
HETP < 1 inch
Liquid In
Liquid Out
Vapor In
Vapor Out
Vapor
Liquid
Liquid In
Liquid Out
Vapor In
Vapor Out
Vapor
Liquid
1015
# Equilibrium
Stages
0.500.33HETP, inches
73%80%Vapor Out
9%7%Liquid Out
Mole % hexane
68°C69°CVapor Out
75°C76°CLiquid Out
Temperature, °C
10347-2
(2 X Base Case
Flow)
10347-1
(Base Case)
Experimental
Run
5inches
84% n-hexane
16% Cyclohexane
9% n-hexane
91% Cyclohexane
28. 28
55
Summary
Microchannel technology
• Enables process performance improvements
• Is robust and scaleable
Breadth of applications under development
• High performance heat exchangers
• Compact reactors
• Distillation units
56
Contact Information
A. Lee Tonkovich, Ph.D.
Mgr. Technology Development Center
Velocys Inc.
7950 Corporate Blvd.
Plain City, OH 43064
Phone: (614) 733-3300
Email: tonkovich@velocys.com
www.velocys.com
