Waste Heat Recovery at Compressor Stations The path towards novel and high-impact technologies and their implementation Gas Electric Partnership Houston, TX Feb 10-11 2010 Presented by Southwest Research Institute Matthew Blieske Marybeth Nored Melissa Wilcox Buddy Broerman
Presentation overview waste heat recovery (WHR) basics current technologies previous research the path forward - whr for onsite use small to medium scale large scale energy storage augmentation of other systems engineering economic analyses of selected cases organic rankine cycle co2 refrigeration Future work
WHR Basics Definition: Using the remaining heat/thermal energy to create useful energy Useful Energy Electricity Power/Torque Preheat & Refrigeration Low Grade Steam Hot Water Common Heat Losses Gas Turbine Exhaust* 72% IC Engine* Exhaust 35% Jacket Cooling 18% Lube Cooling 20% IC Engine Total 73% *McKee, R., Energy Audit Results from a Typical Natural Gas Compressor Station, Proceedings of GMC, 2001.
Current WHR Options Gas Turbine Organic Rankine Cycle ORC Common Applications: Geothermal, solar panels, biomass, and cement plants Compressor Station Average Size: 5.5 MW Power available for local use or for sale INGAA White Paper ORC Economics Station Capacity > 15,000 hp Operation at least: 5,250 hrs / 12 months Installed Cost ~ $2000 2500/kW
Current WHR Options Gas Turbine Turbine Inlet Air Cooling Current trend: Inlet Fogging (poor performance in humid and cool regions) Exhaust heat used in refrigeration cycle (applicable in most installations) Preheating Fuel Many applications require this to prevent liquid dropout Additional heater used for preheating (could use exhaust heat instead) Regeneration Preheat air going into combustor Applicable to low pressure ratio gas turbines (less than 10:1)
Current WHR Options IC Engine Turbocharger Pre-compress inlet air to engine (boost in power) New developments Preheating Fuel Inlet Air cooling Classically for GT but can provide benefits for IC engines
Turboexpanders Current WHR Options Other Generate power at pressure reduction points Applications LNG and hydrocarbon processing applications (steady flows and pressure ratio) Require either pre or post gas heating to avoid liquid dropout Waste heat from another source can supply this Average Installed cost ~ $1450/kW
commercially available products Calnetix TG-100 uses 250+ of waste liquid or gas as an input, generates electricity offshore packaging available Ormat Energy Converter (OEC) uses R245fa refrigerant in a rankine cycle sized for 2-15 MW electrical output
commercially available products Turbothermal uses a novel expander to generate electricity as part of a rankine cycle targeted for 250-750 kw voith steamdrive/steamtrac outputs shaft power to ic engine available for transportation industry, looking for application in the energy field
examples and case studies
Organic Rankine Cycle Utilize a standard Organic Rankine Cycle with a working fluid of pentane to compare pipeline transmission driver options. Purpose was to understand variations in recovered power without regard to cost of installation. Through a relative thermodynamic comparison, can identify opportunities for smaller scale, lower cost waste heat recovery: utilizing ORC or other energy conversions such as central thermal storage, thermal batteries, pre-heating solar / fuel cells. Engine drives for reciprocating compressors have other waste heat losses that could be captured these were not considered in this portion of the analysis.
Approach to Analysis Thermodynamic ORG analysis utilized to study various exhaust flow rates and energy content, for typical GT and engine drives (1-15 MW). Analysis considered primary component efficiencies, all other factors remained the same (ambient temperature, pentane cooler temperature, etc.). Compared results to INGAA survey of recoverable power vs. rated power of installation. Economic considerations were not considered, as purpose of analysis was to determine technology gaps and opportunities for recoverable power.
Cases considered in analysis Modeling utilized known driver power, exhaust flow characteristics. Combined heat energy input with basic thermodynamic analysis of pentane-based Rankine cycle.
INGAA Cases and SwRI Examples: Recovered Power Estimates
INGAA Cases + SwRI Thermo Examples: Comparison of Recoverable Power Note: Interesting trend in % return in power (recoverable power / rated power) for small GT drive applications. Additional economic considerations enter into lower power installations.
Divergence in Potential Low Side and High Side Recovery with Higher Exhaust Power
Recovered Power Estimation for ORC Recoverable Power Varies from 10-17% (somewhat independently of amount of waste heat power). Recoverable power depends on exhaust flow rate, temperature, selected ORC pressure, other optimized cycle parameters.
Inlet Cooling Several cycles suitable for inlet cooling transcritical refrigeration cycles effective for extracting low grade heat high power density emerging technology, modest commercial exposure in transportation and residential markets absorption chillers effective on medium to large scale vapor compression cycles requires mechanical/electrical work input for refrigerant compressor
Absorption chillers for inlet cooling can deliver cooling load on exhaust heat input alone org cycle requires electrical input to provide cooling eliminates the need to pump a gas (high energy process) by absorbing vapor refrigerant into hydrate solution two most common fluids are lithium-bromide-water and ammonia-water only moving part is the refrigerant pump rotor
Absorption chillers for inlet cooling two main types of construction single effect single generator COP of 0.6-0.8 commercially available double effect two generators cop of 1.0-1.2 higher capital cost some longevity and maintenance issues
Absorption chillers for inlet cooling double effect chiller
Absorption chillers for inlet cooling Prime Mover (mechanical drive) ISO rated shaft power (hp) exhaust flow (lb/hr) exhaust temperature ( o F) Cooling capacity (tons) medium gas turbine 15,000 335,560 905 4343 large gas turbine 29,500 536,400 990 8056 medium SI gas engine 1004 9756 834 109 / 92* large SI gas engine 5124 72,000 784 719 / 427* * cooling power from exhaust / engine coolant
Absorption chillers for inlet cooling Prime Mover (mechanical drive) % exhaust flow energy recovered Primer mover efficiency Combined cycle efficiency medium gas turbine 75.3 34.0 80.4 large gas turbine 78.9 36.1 82.6 medium SI gas engine 65.7 34.5 67.1 large SI gas engine 65.0 45.6 93.7
Absorption chillers for inlet cooling Performance with chilling system Prime Mover (mechanical drive) inlet temperature ( o F) primer mover efficiency shaft power (hp) efficiency improvement power increase medium gas turbine 40 34.9 16,752 2.6% 11.7% large gas turbine 40 38.2 31,451 5.8% 6.6% medium SI gas engine 40 34.5 1077 <0.5% 7.3% large SI gas engine 40 45.6 5498 <0.5% 7.3% NOTE that % improvement is relative to 77 o F 14.65 PSI standard atmosphere
Absorption chillers for inlet cooling note that more cooling is produced than what can be used by an individual prime mover Chiller can also cool pipeline gas on hot days to improve efficiency and capacity of compressors single chiller can cool multiple units inlet temperature reduction limited by the cooling water temperature of 40 o F for lithium bromide could combine medium IC engine running chiller with large gas turbine would be able to chill both engines, and pipeline gas efficiency and capacity improvements more dramatic for operating conditions above 77 o F
Past Experience Waste heat sources at compressor stations well understood SwRI GMC paper (mckee, 2001), Swri GEP presentation (2008-2009) Hoerbiger gmc paper (mathews et. al., 2008) INGAA report (Hedman, 2008) scale of economy a factor in success power export requires a utility who will play ball, and access to the grid on-site uses have received less attention
Past Experience the economics have been favorable for alliance pipeline, who continue to retrofit stations with Ormat WHR systems largely due to a favorable power purchase agreement with saskpower
Shift in Technology Development focus on electrical export leaves small to medium stations out due to economy of scale remote stations don t have access to the grid, whr for electrical export not possible few economical solutions for intermittent sources/demands i.e. gas turbine starting or stations not operating 24/7 potential to export thermal energy not addressed (could be viable for small scales)
GMRC/PRCI 2010 research plan Sources of Waste Energy Gas Turbine: Exhaust heat IC Engine: Exhaust heat Cooling fluid heat Lube oil heat Other: Pressure reducing valves Vent gas Gas cooler heat Flare heat Vibration Connection Technologies Turboexpander CO2 Refrigeration Microturbine Thermoelectrics Thermal Storage ORC Cycle Energy Harvesters New Technology End Uses at Station Heat/Pressure: Export gas temp control Heat solar panels (optimize) Human environmental control Component environmental control Energy storage Pre-heating fluids Valve actuation Electricity: Starting power Auxiliary power systems Energy storage Valve actuation Parasitic demand technology development roadmap
Gaps in Knowledge does it make sense for storage (mechanical, thermal, electrical) to be an integral part of whr strategies? what are the scenarios that make storage attractive? centralized vs. distributed are there source/end-use pairings that do not have a suitable technology to bridge them? is anyone trying to fill these gaps? what optimization is required for current technologies? tailor energy outputs (thermal vs. electrical) to on-site demands
Conclusion waste heat recovery solutions that do not export electrical power do not receive much attention currently, yet have the potential to address an under served market (small-medium stations) focused research and development in on-site use and/or export of other energy forms is needed
Questions?