Waste Heat Recovery Research at the Idaho National Laboratory

Transcription

1 Waste Heat Recovery Research at the Idaho National Laboratory Donna Post Guillen, PhD, PE Technology Forum: Low Temperature Waste Energy Recovery in Chemical Plants and Refineries, Houston, Texas, May 16, 2012 Sponsored by the Texas Industries of the Future and the Institute for Industrial Productivity

2 Outline Two Recent Projects; ORC Direct Evaporator Advanced Test Reactor Secondary Coolant Loop Future Directions in Low-Temperature Waste Heat Recovery Mechanisms for Partnering with the INL

3 Project #1: ORC Direct Evaporator

4 ORC Direct Evaporator Development

5 Organic Rankine Cycle Vapor power cycle that operates using the same principles as the steam Rankine cycle, except that a fluid with a lower boiling point (and higher molecular mass) is used A hydrocarbon or refrigerant working fluid is evaporated, instead of boiling water to create steam, and expanded through a turbine to generate electricity Enables the operation of the cycle at a much lower temperatures (typically 100 to 500 C) than a steam Rankine cycle Small volumetric flow rates enable use of a compact expander resulting in high turbine efficiencies T, C Functional Diagram T-s Diagram s, kj/g

6 Direct Evaporator Directly transfer heat from the waste heat source to the evaporator w/o an intermediate heat transfer loop Indirect Evaporator Direct Evaporator (DE)

7 Eliminate Intermediate Loop Disadvantages of intermediate hot oil (therminol) loop Increases cost Requires more components which increases complexity and therefore opportunity for failure Adds thermal mass (reduces rate of system start-up) Decreases conversion efficiency Elimination of loop Cost savings of ~15%

8 Efficiency Gains from DE Typical ORC efficiency 10-20% For an engine that is 35% efficient, 65% of fuel energy is turned into heat ORC can harness 10% of the wasted heat energy 10%*65%=6.5% 35%+6.5%=41.5% ~20-40% increase in efficiency!

9 Value Proposition ORC adoption driven by combination of ORC capex, current fuel cost, and ability of customer to utilize extra electricity Typical capex threshold is ~$2000/kW Most commercial ORCs are priced at approximately this threshold Direct evaporator will enable 15% cost reduction, well below the typical capex threshold

10 Project Goals and Metrics Project goals Develop a safe and reliable DE that eliminates the intermediate thermal loop and substantially reduces ORC cost Improve cost and performance by tightly integrating ORC device with primary engine Performance metrics Low flammability risk Ensure minimal working fluid decomposition (and no related fouling inside evaporator) Greater than 15% cost savings

11 Optimal HX Design Limit working fluid maximum temperature to avoid excessive working fluid degradation Ensure safety in the event of working fluid leak Observe fin surface temperature lower limit Maintaining TEG temperature above dew point temperature for nitric acid formation (otherwise, can t use carbon steel tubes) Limit backpressure from the ORC to within allowable limits to avoid choking the GT

12 Working Fluid Selection Systematic comparison of over 40 different fluids Compared on the basis of chemical stability, flammability, toxicity, performance under the boundary conditions of the gas turbine exhaust application and environmental risk in the event of a leak Other considerations include corrosiveness and tendency to foul Fluid cost not a driver, since the pressure level, component selection, operating temperature, etc. most influence cost

13 Working Fluid High stability and critical point to boil at relatively high temperature Vertical to positive slope of the vapor curve to eliminate need for superheating, increase efficiency and lower condenser cost High volatility to boil ambient temperature (condenser can be operated atmospheric pressure) retrograde dew point curve dry expansion isobutane n-butane isopentane R-245fa standard dew point curve wet expansion propane R-134a

14 Other Desirable Characteristics High thermal conductivity in the vapor phase to maximize heat transfer High AIT, preferably above TEG temperature High specific heat ratio Low environmental impact and toxicity Low overall system pressure to reduce cost Minimal reactivity with air or materials Low flammability rating and transport hazard class Low freezing point for operability in cold climates

15 Key Technical Challenges Working fluid degradation Ensure that film temperature in heat exchanger does not reach temperature limit of chemical degradation Potential for loss of performance, depending on decomposition products Potential for corrosion, depending on decomposition products and materials employed Auto-ignition temperature of working fluid well below the exhaust gas inlet temperature Leakage into the exhaust gas has the potential of starting a fire in the installation

16 Thermal Stability of Fluid Thermal stability determines the lifetime of the working fluid, affecting life-cycle cost, and has safety implications if undesirable chemical decomposition products are generated Meas. thermochemical decomposition of C 5 H 10 in a recircirculating flow loop Results in Energy & Fuels article, Thermal Stability of Cyclopentane as an ORC Working Fluid o o o o o o Decomposition increased with increasing temperature At 240 & 300 C, decomposition was minor after 12 days At 350 C, decomposition rate increased significantly Decomposition rate incr. dramatically when exposed to air Primary decomposition products in turn form other products Residues increased with reaction temperature and consisted primarily of heavy paraffinic hydrocarbons

17 Simulation of Pinhole Leak in Heat Exchanger Tube

18 Project #2: Advanced Test Reactor Waste Heat Recovery

19 Advanced Test Reactor Among the most technologically advanced nuclear test reactors in the world Irradiation of nuclear fuels and materials Experiments performed for a variety of test sponsors U.S. government, foreign governments, private researchers, and commercial companies needing neutron irradiation services Began operation on July 2, 1967 Max. operating power 250MW, nominal 110MW Primary and secondary coolant loops Waste heat rejected to a four-cell induced draft cooling tower

20 Old Waste Heat Recovery System (WHRS) Constructed in the 1980 s Used for complex-wide district heating Circulated hot water from reactor secondary coolant system (SCS)

21 Proposed Glycol WHRS Provide space heating to reactor building only Tertiary water coolant stream from 120 F, 1500 gpm Glycol in HVAC loop to prevent coil freeze-up (1700 gpm) Preheat incoming air by 45 F

22 Proposed Glycol WHRS Costs Total estimated cost $9.7M 9 mo. to construct Energy savings of ~$285K/yr

23 Future Directions in Low-Temperature Waste Heat Recovery

24 Waste Heat Temperatures With rising fuel costs, the opportunity for cost-effective waste heat recovery systems is enormous Waste heat is an abundant source of emissions-free energy Predominantly thermodynamically cold

25 Commercial Building Energy Usage U.S. commercial buildings and homes account for 40% 13.7% for space heating of commercial buildings Heat recovery most effective when heat source and sink are coincident (location & time) Use as heat most efficient, rather than suffering efficiency losses to convert to another form of energy Use as electricity suffer efficiency losses

26 Retrofitting Considerations Brownfield vs. greenfield Can invalidate equipment warranties Excessive distances for piping runs Disruptions to operations Demolition/construction/installation costs Operator buy-in

27 History of Waste Heat Recovery Lots of work done in the 1970 s and 80 s Basic thermodynamic premises have been established Costs have risen fuel, electricity, labor, equipment Key Question: What technology is available now that wasn t available then?

28 Future Directions in Low Temperature Waste Heat Recovery - Enablers Advanced thermodynamic cycles Supercritical CO 2, Kalina, trilateral flash, absorption/refrigeration, thermoelectrics New equipment designs Evaporator configurations, novel expanders, hybrid condensers New materials Nanomaterials, graphene, superalloys, etc. Computer technology Process controls and instrumentation New manufacturing processes Diffusion welding of heat exchangers Changes in regulatory environment Carbon tax, environmental, operating, etc.

29 Low-Temperature Heat Recovery Applications Borrow from geothermal technologies ORC cycles with R245fa (HDR-14) Use HVAC equipment to keep costs down

30 Thermal Energy Storage/Upgrading Store thermal energy Scenarios: Batch or semi-continuous processes produce heat for later use Store energy from continuous process to most effectively leverage time-of-use rates Technologies: Concentrating solar power systems, chemical systems Batteries, fuel cells/flow batteries, electrochemical capacitors Pumped hydro and compressed gas Boost temperature of waste heat source Scenario: Upgrade low-temperature waste heat to a higher temperature Technologies: Mechanical or chemical heat pumps

31 Mechanisms to Partner with INL Cooperative Research & Development Agreements (CRADAs) Government funded research (U.S. DOE, etc.) Direct funded research by industry (Work For Others Agreements) Contact info.: