annalee-1207
TRANSCRIPT
1
Microchannel Heat Exchangers: Applications and Limitations
Anna Lee Tonkovich, PhDManager, Technology Development CenterVelocys, IncPlain City, OHwww.velocys.com
2
Overview
Microchannel Exchanger Definition
Advantages of Microchannel Exchangers
Implementation Challenges
Microchannel Exchanger Applications at Velocys
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
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
dkNuh ×
=Nu: Nusselt numberh: Heat transfer coefficientd: Hydraulic diameterk: 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 ratioHigh heat transfer per volume
Low surface area/volume ratio
Low heat transfer per volume
4
7
Micro-channel Heat Exchanger Performance Comparison
400 – 200050 – 30020 – 100Heat Transfer coefficient (W/m2/K) (Gas)
LaminarTurbulentTurbulentFlow Regime
< 10°C~ 10°C~ 20°CApproach Temperature (°C)
> 70003000 – 7000~ 5000 (tube side)
Heat Transfer coefficient (W/m2/K) (liquid)
> 1500850 – 150050 – 100Surface Area Per Unit Volume (m2/m3)
Micro-channel Heat Exchanger
Compact Heat Exchanger
Shell and Tube Heat ExchangerParameter
75.1VLPp
∆ 75.1VLPp
∆ VLPp
∆
8
Performance:Manageable Pressure Drop
Laminar Flow• Orderly flow – less fluctuations
•Laminar Flow
Turbulent Flow
flowh VDfLP µ)(=
∆
Turbulent Flow• Random flow – more fluctuations
•75.175.025.0)( VDf
LP
h ρµ=∆
flow
(Blasius friction factor)
5
9
Performance:Manageable Pressure Drop
Distributed flow provide shorter flow length, overall low pressure drop
ρ24
2GdLfP ××=∆
f: Friction factorG: Mass Fluxd: Hydraulic diameterρ: DensityL : 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)
Volu
met
ric H
eat F
lux
(W/c
m3 )
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
6
11
Feature creation Stacking
Bonding Machining
Shim
Robust:Proven Manufacturing Methods
12
Robust:Mechanical Integrity
Diffusion bonded metals (stainless or high nickel alloys)
Mechanical design and validation to ASME standards
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
15
Scaleable:Development Methodology
Full-scaleReactor
CELL
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
MULTI
CELL
16
Scaleable:Flow Distribution Strategy
Inlet
1 2 3
max min1
max
100%m mQm−
= ×
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
17
Scaleable:Validated Flow Distribution
18
Scaleable:Channel Flow Distribution
Sufficient flow distribution measured in test deviceIrregular gasket on half of test device
Sufficient flow distribution measured in test deviceIrregular 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
Mas
s flo
w ra
te (k
g/s)
ModelExperiment
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
21
Installation Costs are Lower for Compact Equipment
0
1
2
3
4In
stal
latio
n Fa
ctor
Column VerticalVessels
HorizontalVessels
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
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
25
Fouling expected in some operating service but not detected
Solids at 1ppm, 30% vapor quality
00.20.40.60.8
11.21.41.61.8
2
0:00:00 2400:00:00 4800:00:00 7200:00:00 9600:00:00Time (hh:mm:ss)
Del
ta P
(psi
g)
020406080100120140160180200
Tem
pera
ture
(C) ,
%
Stea
mDelta P
Steam Quality
Outlet Air Temp (C)
Vaporizer after 9600 hours operation
No performance degradation over 9600 hours
26
Pitted areasPitting 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
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
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
31
Cryogenic Applications
Microchannel Exchanger Developmentat Velocys
High temperaturereactions
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
33
Case Study: Simplified LNG Cycle
Natural gas50,000 metric tons/year
LNG
J-TValve
Compressor Condenser
Three stream main heat exchanger
153°C331.3 psig
29.4°C323.3 psig
-153.9°C318 psig -158.3°C
29.95 psig
32.2°C635.3 psig
-153.9°C5 psig
20.9°C19.95 psig
322.8 psig
27.75 psig
-155.3°C
Compression Ratio• Before 10• After ~8
CompressionSavings = 18-22%
Compression Ratio• Before 10• After ~8
CompressionSavings = 18-22%
34
Heat Transfer Comparison for LNG
201Relative Length
500-1500>1500Core Area, m2/m3
<1>10Core Heat Flux, W/cm3
Conventional Plate-fin HXVelocys HX
Significant reduction in hardware volume
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 AdvantageAlternate Material Selection Reduces Heat Exchanger Length By Reducing Axial Conduction
LkAc∝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
37
Conventional Technology
Conventional Steam Reformer20 million standard cubic feet hydrogen per day
Plot ~ 30m x ~30m x ~30m
High temperature exchangers required
38
Velocys® Technology ReactorsMicrochannel Steam Methane Reformer
Identical capacity
Plot < 10 m x 10m x 10 m (< 10% original)
~25% reduction in overall plant costs
20
39
Integrated Reactor and Exchanger: Steam Reforming
Reactor Section
Multi-streamHeat Exchanger Section
Internal Manifold Section
ReactantProductFuel
Air
Exhaust
100900
Temperature (C)
Length (m)
0.9
40
30
40
50
60
70
80
0 2 4 6 8 10 12Contact 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
41
Target Segment
Microchannel Cost Advantage
Hydrogen Production Capacity (MMSCFD)5 5010 15 20 25 30 35 40 45
Cap
ital C
ost (
$/SC
FD)
Velocys
Conventional
00
0.5
1.0
1.5
2.0
2.5
Substantial capital cost
savings
Substantial capital cost
savings
42
Methane Steam ReformerDevelopment 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
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/te300-5001,400-1,7001,800-2,000Reactor wt, tonnes35,00019,00019,000Capacity, bpdVelocys
Tubular Fixed Bed *Slurry *
* Source: Hoek, Shell, CatCon2003
23
45
Phase Change Demonstrated: Commercial Length Microchannels
230
233
236
239
242
245
248
251
254
257
260
0 5 10 15 20 25Distance to Inle t, inch
Wal
l tem
pera
ture
, o C
q"=5.8 W/cm2q"=3.8 W/cm2q"=1.4 W/cm2Inlet temperature: Saturation temperature (P=522 psia)
2.5 oC
2.9 oC
End effectEnd 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 Time0.9 mReaction Channel
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
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
Microchannel Distillation
52
Microchannel Distillation creates short HETP
diffusion to/from vapor-liquid interface
Vapor channel
Liquid film Heat exchange
t: Characteristic diffusion timed: Hydraulic diameterD: DiffusivityD
ddiff
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
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 OutVapor In
Vapor Out
Vap
or
Liquid
Liquid In
Liquid OutVapor In
Vapor Out
Vap
or
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
5 in
ches
84% n-hexane16% Cyclohexane
9% n-hexane91% Cyclohexane
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 CenterVelocys Inc.7950 Corporate Blvd.Plain City, OH 43064Phone: (614) 733-3300Email: [email protected]
www.velocys.com