Waste Heat Recovery at Compressor Stations

The path towards novel and high-impact technologies and their implementation

MatthewBlieske

Marybeth Nored

MelissaWilcox

Buddy Broerman

Presented by Southwest Research Institute

Gas Electric PartnershipHouston, TX

Feb 10-11 2010

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 BasicsDefinition: 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 OptionsGas 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

Current WHR Options Other

• Turboexpanders✴ 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

• Turbothermal✴ uses a novel expander to

generate electricity aspart of a rankine cycle

✴ targeted for 250-750 kW

• voith✴ steamdrive/steamtrac✴ outputs shaft power to

ic engine✴ available for transportation

industry, looking forapplication in the energy field

commercially available products

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.

Modeling utilized known driver power,

exhaust flow characteristics.

Combined heat energy input with basic

thermodynamic analysis of pentane-based

Rankine cycle.

Cases considered in analysis

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

• 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

Absorption chillers for inlet cooling

• two main types of construction

✴ single effect➡ single generator

➡ COP of 0.6-0.8

➡ commerciallyavailable

✴ double effect➡ two generators

➡ cop of 1.0-1.2

➡ higher capital cost

➡ some longevity and maintenance issues

Absorption chillers for inlet cooling

double effectchiller

Absorption chillers for inlet cooling

Prime Mover(mechanical drive)

ISO rated shaft power

(hp)

exhaust flow (lb/hr)

exhaust temperature

(oF)

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

(oF)

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

77oF 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 40oF 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 77oF

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)

technology development roadmap

Gas Turbine:Exhaust heat

IC Engine:Exhaust heatCooling fluid heatLube oil heat

Other:Pressure reducing valvesVent gasGas cooler heatFlare heatVibration

Sources of Waste Energy Heat/Pressure:Export gas temp controlHeat solar panels (optimize)Human environmental controlComponent environmental controlEnergy storagePre-heating fluidsValve actuation

Electricity:Starting powerAuxiliary power systemsEnergy storageValve actuationParasitic demand

End Uses at Station

Turboexpander

Connection Technologies

CO2 Refrigeration

Microturbine

Thermoelectrics

Thermal Storage

ORC Cycle

Energy Harvesters

New Technology

GMRC/PRCI 2010 research plan

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?