Waste Heat to Power (WHP) Technologies Eric Maxeiner, PhD. May 24, 2017
Presentation Outline of WHP WHP Market : Thermoelectric Steam Organic Rankine Cycle (ORC) sco 2 power cycle
Overview of WHP: Definitions WHP vs. CHP (Waste Heat-to-Power vs Combined Heat & Power) WHP converts thermal energy to electricity (often most convenient) CHP keeps the heat as heat (most efficient) Types of WHP: Combined cycle Captures exhaust heat and adds to engine output Also called bottoming cycle or exhaust heat recovery (EHR) Waste heat recovery Captures heat from unrelated process Typically industrial process such as a furnace or kiln Primary power not considered WHP but often uses the same technology Coal, biomass, landfill gas, etc. Electrical vs. mechanical output Electrical: generator, alternator, thermoelectric Mechanical: shaft work (e.g. compressor), integrated with source engine (e.g. turbocharger) Temperature determines the quality of heat High grade heat >1,000 F Low grade heat < 500 F
Combined Cycle HR Heat radiation 0.6% Lube oil 2.9% 100% Jacket water 5.2% 90% Charge air cooler 16% 80% 70% 60% 25% 26% 26% Heat radiation 1.6% Lube oil 4.6% Jacket water 4.8% Charge air cooler 17% Engine energy balance 30% 1% 62% LSD: low speed diesel, T exhaust 480 o F MSD: med speed diesel, T exhaust 650 o F GT: gas turbine, T exhaust 1000 o F 50% Other 40% 30% 20% 49% 44% 37% Exhaust Shaft Power 10% 0% Note: typical values are shown LSD MSD GT (LM2500) Engine Type
Combined Cycle HR 100% 90% 80% 70% 25% 26% Engine energy balance 1% 49% LSD: low speed diesel, T exhaust 480 o F MSD: med speed diesel, T exhaust 650 o F GT: gas turbine, T exhaust 1000 o F 60% 23% 25% 50% 40% 2% 48% 50% 4% 13% Other Exhaust EHR 30% 20% 49% 44% 37% Shaft Power 10% 0% Note: typical values are shown LSD MSD GT (LM2500) Engine Type Heat recovery can reduce efficiency differences between engine types
WHP vs. CHP cont d Q out,1 Q out,2 HX Q cap Power cycle P elec,2 Q exh Total System Efficiency Fuel in Engine Engine output CHP: η CHP = (P elec,1 + Q cap )/Q in WHP: η WHP,elec = (P elec,1 + P elec,2 )/Q in Q in P elec,1 η WHP,therm = (P elec,1 + Q cap )/Q in η therm > η elec WHP and CHP should be compared on basis of value of P elec,2 vs. Q cap
Industrial WHP Market Potential 2008 DOE report on waste heat recovery: U.S. industry consumes 32 quadrillion BTU of energy per year (30% of all U.S. energy consumption) 20-50% of this is lost as waste heat Repurposing this waste heat would save $70-150 billion/year in generation Three main energy use categories: Onsite generation of distributed power and other utilities Process energy (i.e. result of core purpose of plant) Non-process energy (e.g. HVAC, lighting) Significant emissions reduction potential Ohio grid average 1.5 lb CO 2 per kwh (US average is 1.1 lb) 1 MW of WHP offsets 6,000 ton CO 2 /year Low gas and electricity prices hurt WHP business case
Key WHP Markets Oil & Gas Gas Transmission, LNG Offshore Platform, FPSO (Gas Turbine, Gas Engine) Power Generation - - - Fossil Fuel - - - (Gas Turbine, Diesel) Marine Cruise Ship, LNG, Naval (Gas Turbine, Diesel) Oil & Gas Mechanical Drive (Gas Turbine) Power Generation Alternative/Renewable (Biomass, CSP, Nuclear, LFG) Industrial Cement, Steel, Glass (Process) 8
WHP as Renewable Energy Note: Ohio enacted 2-year freeze on clean energy standards in 2014 Source: Heat is Power, 2014 http://www.heatispower.org/about/our-efforts/
Thermoelectric WHP Solid state device that converts heat directly to electricity Utilizes Seebeck effect in which thermal gradient between two dissimilar conductors creates an electrical current Slow development since mid 1850 s, accelerated with advent of semiconductors Applications: gas pipelines, vehicle engines (<10 kw) Advantages: no moving parts, remote operation, simple, installation can be non-invasive Disadvantages: inefficient (~5%), bulky, expensive
Rankine Cycle Rankine cycle is the basis for steam, ORC and sco 2 systems 1. Liquid is fed into pump to bring up pressure 2. Heat is transferred to fluid at constant pressure to create vapor 3. Vapor expands through turbine (shaft work) 4. Fluid is cooled & condensed back to liquid
Steam WHP Applications: primary power (coal & nuclear), combined cycle, etc. Two primary components: Boiler or HRSG Water-tube boiler invented in 1876 by Babcock & Wilcox Steam turbine Modern version invented in 1884, first commercialized by Westinghouse Up to 1.75 GW output Advantages: ubiquitous, reliable, established, high specific heat Disadvantages: water chemistry, corrosion, complex auxiliary equipment, labor intensive
Steam System Diagram
Organic Rankine Cycle (ORC) WHP Uses refrigerant as working fluid instead of water Lower boiling temperature than water R134a, isobutane, pentane, naptha Requires separate thermal oil loop to separate heat source from ORC fluid (often flammable & toxic) First developed in 1883, recent proliferation due to advanced fluids Applications: applicable to smaller and cooler projects (<500F, <3 MW) than steam, geothermal, biomass, diesel engine exhaust Advantages: heat-matching fluid, established, dry working fluid Disadvantages: reduced efficiency from thermal oil loop and temperature limits, harmful fluid, scaling issues
ORC System Schematic Biomass system with district heating
WHP Technologies: sco 2 Uses supercritical carbon dioxide as working fluid Supercritical fluid has high density and compressibility No need for intermediate fluid loop Commercialization started in 2007 with Echogen. Several prototypes built including 8 MW EPS100 (1 st commercially available system). Applications: All WHP markets, >700 F, >1 MW Advantages: Clean & stable working fluid, water-free operation, compact, lower O&M costs, remote operation, made in Ohio Disadvantages: New technology, lack of supply base, relatively high operating pressure (3,400 psi)
Echogen sco 2 Cycle 2 1 3 6 5 4 Critical point of CO 2 is 1,071 psi & 88 F 1. Liquid CO 2 pumped to supercritical pressure 2. CO 2 preheated at recuperator 3. Recovered waste heat added at waste heat exchanger 4. High energy CO 2 expanded at turbine drives generator 5. Expanded CO 2 is pre-cooled at recuperator 6. CO 2 is condensed to a liquid at condenser
EPS100 pilot unit
Resources and references Heat is Power organization (www.heatispower.org) BCS, Inc. 2008, Waste Heat Recovery Technology and Opportunities in U.S. Industry, U.S. DOE Industrial Technologies Program. Eric Maxeiner, PhD Engineering Business Development 365 Water St., Akron, OH 44308 Office: 330.436.3204 E-mail: emaxeiner@echogen.com Web: echogen.com