waste heat to power
TRANSCRIPT
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Waste Heat to Power
Selecting a Technology
C.B. Panchal
Argonne National Laboratory
Chemical Engineer
Phone: 443 812 5930
Houston, TX September 25, 2007
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Presentation Outline
Overview of Waste/Reject Heat in Industrial Processes
Refining
Petrochemical
Inorganic chemicals
Process Steam
Engine exhaust
Technologies for Waste Heat to Power Conversion
Commercial Technologies
Emerging Technologies
Technology Merits
Conversion efficiency and effective utilization of waste heat
Heat transfer equipment
System integration and interfacing with industrial processes
System reliability
Economic values
Selecting a Technology
Perspectives on Waste Heat Recovery and Utilization
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Energy Consumption in a Typical Refinery
Energy consumption in a typical refinery is 441,000 Btu/bbl crude, most
of which must be rejected to the atmosphere or cooling water
Process heaters and steam boilers (600F – 800F+) 87,000 Btu/bbl
Process heat (200F – 400F) 40,000 Btu/bbl
Process heat (< 200F) to cooling water Remaining
Average US Energy Use
KBtu/bbl TrillionBtu/Year
Crude distillation 205.3 880
Delayed coking 166.0 101
FCC 100.0 190
Hydrotreating/Hydrocracking 360.0 581
Reforming 284.0 373
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Crude Distillation Major Energy Consuming Process
Naphtha & Gases
Top Pump
Around E2
Kerosene
Desalter
Top Pump
Around
Heavy Gas OilLight Gas Oil
E2E3
Bottom Pump
Around
Light Gas Oil
E5
Heavy Gas Oil
Kerosene
E4
E1 F1
Bottom Pump
Around
E5 E6Process
Reduced Crude
Heater
Reduced Crude
Start
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Hydrotreating and Reforming Processes
Reactor
Process
Heater
Hydrogen
Feed/Effluent Heat Exchangers
Hydrogen
Feed
Air Cooled HX
Water Cooled HX
200 - 400 F
600-900 F
< 200 F
Recovery Boiler
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Olefin Reactor – Complex Furnace Design
Feed
Boiler Feed
Water
HP Steam
Stea
m
Stea
m
Drum
Product to
Oil Quench
and to
SeparationsTransfer
Line
Exchanger
Floor Burners
Wall
Burners
Stack
Inside of Ethylene Furnace
Burners
Tubes
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Soda Ash Process – Complex Furnace Design
NG to
Steam
Low-P
SteamNG
NG
Humid Low-
Temp d Air
High
Temp
Gases
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Steam Utilization in Process Industries
Steam is major heat carrier in refining, petrochemical, and
pulp&paper, and food processing industries
Steam optimization is an on-going effort with commercial
softwares in the market
Cost effective topping cycle provides opportunity to improve
steam economy
Effective utilization of low-pressure steam can significantly
improve the overall steam economy and plant energy efficiency
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Current Practices of Heat Recovery
Heat recovery is generally considered in the process design optimization
Feed/effluent heat exchangers to recover high-level heat
Waste heat recovery boilers for high-pressure steam generation
Fired-heater stack gas heat recovery for preheating combustion air
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Current Practices of Heat Rejection in the Process Industry
Heat rejection is generally not considered in the process design optimization
Air-cooled heat exchangers to reject medium-level (200F to 400F)
heat
Cooling water to reject low-level heat (< 200 F)
– Cooling tower (1000+ lb of water consumed per million Btu heat
rejected)
– Once through - river, seawater, and lakes (environmental
restrictions)
Regional scarcity of cooling water needs to be taken into
consideration for waste heat to power.
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Technologies for Waste Heat to Power
Commercial Technologies
– Single Fluid Rankine Cycle
• Steam cycle
• Hydrocarbons
• Ammonia
– Binary/Mixed Fluid Cycle
• Ammonia/water absorption cycle
• Mixed-hydrocarbon cycle
Emerging Technologies
– Supercritical CO2 Brayton Cycle
– Thermoelectric conversion
Combined Cycles
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Rankine Cycle
Steam Cycle
– High temperatures
– Waste heat-recovery boilers commonly used
– High-pressure steam used for large compressors and air blowers
Hydrocarbons Cycle (Organic Rankine Cycle)
– Medium to high temperatures
– Developed for geothermal applications
– Diesel engine exhaust – DOE project on ORC
Ammonia
– Low temperatures
– Developed for ocean thermal energy
– Bottoming cycle with potential dry cooling
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Ammonia/Water Absorption Power Cycle
Historical Perspectives
Ammonia/water absorption cycle is commercially used for heat-activated
refrigeration
Ammonia absorption power system proposed in 1981 by H. Sheets for
ocean thermal energy
First patented as Kalina cycle in 1982, followed by publication in 1984
In 1999-2000 first commercial scale 2.0 MW Kalina cycle plant installed at a
geothermal site in Iceland
Further developments continue:
– Cycle configuration and integration for improved thermal efficiency
– Development of heat/mass transfer equipment
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Ammonia/Water Absorption Power Cycle
Basic Cycle
Heat recuperation within the cycle is key to high thermodynamic efficiency
Phase Separator/
RectifierVapor
Generator
Absorber
Reflux Feed
Evaporative
Cooler
T/G System
Waste Heat Source
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Ammonia/Water Absorption Power Cycle
Dual-Function Cycle for Power and/or Refrigeration
Dual-function cycle concept developed at Energy Concepts Company, LLC
Power and refrigeration can be used interchangeably or simultaneously
Phase Separator/
RectifierVapor
Generator
Absorber
Reflux Feed
Evaporative
Cooler
T/G System
Waste Heat Source
Condenser
Refrigerant
Subcooler
Chiller
Cooling Water
Chilling
Load
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Mixed-Hydrocarbon Cycle
Underlying Technologies Developed
Advancement of Organic Rankine Cycle with improved thermal efficiency
Significant literature on cycle analysis
Industry is familiar with the technology
Commercially available heat transfer equipment and turbine/generator
System integration – No major technical risks
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Supercritical CO2 (SCO2) Brayton Cycle
Being Developed for Nuclear Plants
SCO2 Brayton cycle achieves high thermal
efficiency
Development of heat transfer equipment
– Internal heat recuperation crucial for achieving high
thermal efficiency
– Compact narrow flow passage heat exchangers
Turbine/Compressor
– Single-stage and two-stage centrifugal compressors
– Six-stage axial flow turbine
For waste heat to power applications, combined
cycle may have advantages
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Supercritical CO2 (SCO2) Brayton Cycle for Nuclear Reactor
T-S Diagram
Waste heat to power
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Supercritical CO2 (SCO2) Brayton Cycle for Nuclear Reactor
Flow Schematic
Na-Loop replaced with hot-oil loop
for waste heat to power cycle
100 % POWER
Efficiencies
Cyc = 39.1 % 1377 471.5 156.4 95.9
Net = 38.4 % kg/s 19.84 362.1
7.731
Na 488
176.7
250 19.96
Na 89.10 184.6
1 atm 0.8 7.516 19.96 192.1
510 323.6 7.69
19.91 173.5
27.1 19.96
355
250 0.8
32.79 31.25 84.5 90.3
7.621 7.400 20.00 7.628
355
27.9
1264 kg/s 6,000 0.3 30.0 35.8
T, C T,C kg/s 0.142 0.101
Q,MW P,MPa 71%
29%145.9
168.1
264.6
Air
ABTR TEMPERATURES AND PRESSURES
RVACS
0
1259
kg/s
333
CO2TURBINE
HTR
CORE
Na-CO2 HX
LTR
MAIN
COMP.
RECOMP.
COMP.
COOLER
Low-temp bottoming cycle or
Absorption refrigeration cycle
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Thermo-Electric Generation System
Thermo-Electric Generator (TEG) device known for some time for
TEG cooling (example – thermocouples)
Development focused on material-pair with high figure-of-merit
DOE funded project to evaluate technical/economic viability of
TEG system
Coolant
Heat Source Hot-Side Heat Exchanger
Cold-Side Heat Exchanger
TEG
Power Control
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Thermo-Electric Generation System
Figure of Merit
ZT = (a2 s / l ) T
a = the Seeback coefficient (volt/K)
s = electric conductivity (amp/volt m)
l = thermal conductivity (w/m K)
Thermal Efficiency
) )
11
112/1*
2/1*
TZ
TZ
T
TT
h
chc
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Combined Cycle
An integrated combined cycle with advantageous features of two
different cycles can be more economical than individual cycles
Combined power and refrigeration can significantly improve the
overall economics
For an example: SCO2 and ammonia/water or organic cycle
Advantages:
• Cycle configuration
• Cost-effective interfacing with heat source
• Dry cooling
• Mitigating material issue
• Refrigeration
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Technology Merits
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Criteria-1
Conversion Efficiency and Effective Utilization of Waste Heat
Cooling Media
Waste Heat Source
Single Fluid
Absorption Cycle
Binary Fluid
Enthalpy
Te
mp
era
ture
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Conversion Efficiency and Effective Utilization of Waste Heat
Understanding Cycle Efficiency – 1st Law of Thermodynamics
Commercial Power Plants
Commonly thermal efficiency is based on recovered waste heat
Thermal efficiency should be based on total recoverable waste heat
SourceHeat
Work NetcSourePrimary ofContent Heat
Work Netc
RecoveredHeat
Work NetWH
Heat eRecoverabl Total
Work NetWH
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Conversion Efficiency and Effective Utilization of Waste Heat
Understanding Cycle Efficiency – 2nd Law of Thermodynamics
Carnot Efficiency
Cornot Efficiency for Waste heat to Power
Thermal efficiency should be based on total recoverable waste heat
1
21
T
TTc
HeatSource
jectionHeatSource
WHT
TT Re
EfficiencyCarnot
RecovredHeat on Based Efficiency CycleWH
SourceHeat
Work Netc
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Conversion Efficiency and Effective Utilization of Waste Heat
Impact of Heat Transfer Performance on Cycle Efficiency
Cooling Media
Waste Heat Source
Single Fluid
Absorption Cycle
Enthalpy
Tem
pera
ture
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Waste heat source to the cycle
– Corrosion and material considerations
– Fouling: severity, mitigation, monitoring, cleaning
Internal heat transfer equipment
– Numbers and complexity
– Design constraints and impact on cycle performance
Heat rejection exchanger
– Availability of cooling water or make-up water for evaporative
coolers/condenser
– Dry cooling
Criteria-2
Heat Transfer Equipment
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Interfacing of waste heat source to the cycle: space, accessibility,
interfacing piping, impact on the process unit, need for a closed loop to
transfer waste heat to power cycle
Heat rejection: Integrated with the plant cooling system or independent
system, availability of make-up water or dry cooling
Power system integration and controls
Maintenance requirements that would impact system integration
Availability of Space for the Power System
Criteria-3
System integration and interfacing with industrial processes
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Validated performance of individual components
Validated performance of the prototype power system
Dynamic performance of the power system that may impact industrial
processes
Impact of fouling of waste heat recovery heat transfer equipment on the
system performance
Inherent safety measures for ammonia and hydrocarbon systems
Criteria-4
System reliability
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Cost of electricity (COE): present and projected COE over the life of the
waste heat to power system
Combined power and refrigeration: value of refrigeration on energy
efficiency as well as improved productivity
Productivity improvements
Environmental benefits
Criteria-5
Economic values
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Step 1: Determine incentives: Just COE or end-use benefits (refrigeration, operating
rotating equipment, expanding capacity)
Step 2: Characterize the waste heat source and evaluate technical issues of interfacing
with the power system
Step 3: Use technology merit criteria to screen different power cycles, including
combined cycles, and down select to two (may be three) options
Step 4: Perform a conceptual design to identify major technical issues, and possibly
down select to one option
Step 5: Preliminary design with planning-stage cost estimates based on budgetary
quotes of components and subsystems
Step 6: Decision to go forward with the installation of the waste heat to power system
Selecting a Technology
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Perspectives
Waste heat – a hidden source of energy
Significant loss of thermal energy from furnace/fired heater/boiler stack
gases and calciners & driers
Significant low-level (150F to 250F) energy is lost to cooling towers in the
form of latent heat from overhead condensers in distillation
Low pressure steam a major source of waste heat
Lack of incentives, such as GHG emission credits
Lack of design/economic tools to evaluate effective utilization of recovered
process waste heat in High-Value applications – power, refrigeration, heat
pumping
Process heat recovery must be applied to existing plants, with uncertain
costs of retrofitting
Major technical barriers of fouling and corrosion of waste heat sources
Scarcity of fresh water in some regions for heat rejection