Tanana Chiefs Conference’s goal for this project is to demonstrate the potential improved fuel efficiency of the diesel power plant in a village in the TCC region through the use of an Organic Rankine Cycle (ORC) system for heat recovery from engine jacket water and exhaust.
An ORC power system employs the same principles as a steam Rankine cycle system. The difference between these two systems is the working fluid that is used in each (organic fluid in the case of ORC). ORC systems have been installed all over the world and applied to a variety of heat sources, such as geothermal energy, water energy of stripper wells, solar energy, and biomass energy. Existing ORC systems are usually industrial in scale, with ORC technology for mid-sized engines still in the R&D development stages.
The proposal includes selection of an ORC unit and installation on a mid-sized, village diesel generator. A successful ORC application may result in a 10-15% reduction in fuel consumption for diesel power generation. Taking into account the high cost of fuel in rural Alaska, a system that improves the efficiency of village power plants represents a potentially economically viable option.
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Table of Contents
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Project Outline
Objectives
The objectives of this project are to:
- Improve the fuel efficiency of the diesel power plant of a generic TCC village by up to 10% through the use of an Organic Rankine Cycle (ORC) system to recover waste heat contained in engine jacket water and exhaust.
- Evaluate feaasibility, operation and maintenance (O/M) requirements, and payback time of applying the ORC system on the village power plant.
- Develop guidelines for ORC system selection, operation, and maintenance and evaluate the potential impact of applying waste heat ORC systems on rural Alaska economy, fuel consumption, and green house gas (GHG) reduction.
Technology
An ORC power system employs the same principle as a steam Rankine cycle system. The difference between these two systems is the working fluid that is used in each. An ORC system, which is generally used for a low-temperature heat source, uses organic fluids. Selection of the working fluid depends on heat source property, working fluid thermodynamic properties, and operating conditions. Optimal properties of the working fluid to be considered include: appropriate thermodynamic property curves, low freezing point, high stability temperature, low cost, proper working pressure, high latent heat and density, environmental sensitivity, and safety concerns. A Rankine cycle is a closed thermodynamic cycle of which the working fluid experiences at least four stages: evaporation by absorbing heat, expansion to give away work, condensation to release heat, and compression by accepting pump work to increase pressure. A variety of modifications of the basic cycle has been used in practical applications for improvement of system performance.
Due to the long development history of the steam Rankine cycle, its sibling ORC system is generally considered a mature technology. ORC systems have been installed all over the world and applied to a variety of heat sources, such as geothermal energy, water energy of stripper wells, solar energy, and biomass energy. Existing ORC systems are usually industrial in scale, however, with a capacity of more than 200 kW and many above 1 MW (the technology as applicable in small-scale rural Alaska power plants qualifies as emerging due to its largely untested nature). Examples of large-scale installations are two Sunstran operation 600 kW ORC systems on utility diesel exhaust (one is located at Beloit, Kansas, and the other at Easton, Maryland), and a Mechanical Technology 500 kW ORC unit at the diesel power house operated by the Village of Rockville Center, New York. In Alaska, ORC technology has been applied at the geothermal plant at Chena Hot Springs outside Fairbanks. The plant contains two 200 kW ORC systems, of which the energy source is 165 F underground water. The thermal efficiency of the system is 8% and estimated payback is 4 years.
Taking into account the high cost of petroleum and environmental considerations, one relatively recent research and development activity is the recovery of waste heat from mid-sized engines. Groups involved in this activity include national laboratories, power and engine industries, and private government, funding agencies. Utilized technologies include Rankine cycle, absorption cycle, Brayton cycle, and thermoelectrics. ORC and absorption cycles are commonly used and consided the most promising methods. In theory, absorption systems have been considered more efficient in recent decades; however, this hasn't been verified in practical applications. The most recent development in ORC technology is the Trilatekal Flash Cycle (TFC), in which expansion starts from saturated liquid to minimize the irreversibility. TFC is claimed to have better efficiency than conventional ORC, but no real-life TFC applications have been found by the applicant.
For waste heat recovery of mid-sized engines, the limitation in waste heat energy may represent new challenges to the practical applications of ORC technology, such as the choice of proper working fluid, the optimal design of a system for a particular operating condition, the weight of parasitic power on power generated by the system, and the effect of capital on net return. The estimated theoretical efficiency is reasonably high; however, the general consensus on the best expectation in energy efficiency is 10%. This expectation corresponds to the performance of the Chena Hot Springs power plant for the higher heat source temperature of the engine waste heat.
Work Plan
This project will include verification of the performance and reliability of a selected ORC system through laboratory testing. The testing will include an 600-hour-minimum reliability test of the ORC system under full load and a 50-hour test of the ORC system performance under controlled environmental conditions to evaluate the extent to which ORC technology is ready for application in the selected village diesel power plant and how to optimize the performance of the ORC system under varying load and weather conditions.
The work plan includes the following tasks:
- Procurement of a reliable ORC system and supporting test equipment, including a cooling system (radiator, temperature control loop components), heating system (flow rate control), thermal flow measurement devices (flow meters, digital pressure gauges, thermocouples, etc.), ORC electrical power consumption and measurement devices (resistors, heat dissipation unit, and electrical power measurement devices), and flow control system (pump, pipe, valves, thermal couple, etc.). This task includes a continuation of a previous work by UAF in searching available industrial ORC products and the selection of a reliable system with the best cost. The search will emphasize on availability, credentials of the manufacturer, cost, and lead time. This task has been completed. UAF has selected an ORC unit produced by ElectraTherm for the test.
- Installation and instrumentation of the complete testing system (ORC system, electrical power consumption system, heat source system, cooling system, instrumentation), detection and rectification, and modifications.
- Controlled testing of the selected ORC system for performance verification and optimization of the ORC system under varying engine loading and ambient conditions. Test results will also be used for formulating an operation parameter control scheme for optimal performance of the ORC system. Data from the laboratory test will also be used to establish a baseline for economic impact including projected payback time of the unit. The two testing components of this task include:
- A 600-hour-minimum reliability test under full load to verify the performance and reliability of the ORC system. All measurable data (i.e., thermal fluid data and electrical power data) will be recorded.
- A 50-hour performance test under controlled input and output conditions, which simulate variable diesel generator load and environment conditions. The data will be used for the design of an operation scheme to optimize the performance of the ORC system in a village power plant, which normally experiences varying load and environmental conditions.
Data Collection, Analysis, and Reporting
Recorded data will be used for performance analyses of critical components and the overall system. Critical components include the heat source and heat sink systems, interfaces of heating and cooling, turbine (expander), generator, and all pumps. The analyses will demonstrate the reliability for efficiency and performance consistency of the system, each of the components, and economic performance. The analysis results will show the net efficiency of the system and parasitic power consumed by the components (one of the major concerns for the application of ORC unit to mid-sized engines), effects of controlled variables (e.g., heat flow rates and temperatures of the heat source and heat sink) on system optimal performance, and the effectiveness of the design of each of the components and the direction of design improvement.
A final report will be produced, and will include test setup and data, detailed installation and O/M issues, analysis of system efficiency, GHG reduction, and fuel consumption, recommendations of how to select an ORC system, a scheme to optimize the system performance, and preliminary studies in economic impact and feasibility of applying ORC to diesel generators in rural Alaska.
Phase 2 Deployment
The original project proposal included two phases (laboratory testing followed by a field demonstration of operational and economic feasibility). Due to limited funding availability of the EETG program, the second phase was removed; this project will feature only the laboratory testing of the ORC unit. The project team is currently seeking funding from other sources for the Phase 2 field test that will take place in a village in the TCC region.
Funding Outline
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Funding Goals
This project is a Denali Commission EETG Program project. The funding goal of the EETG program is to develop emerging energy technology that has the potential of widespread deployment in Alaska and has the long-term goal of reducing energy costs for Alaskans.
Project Recipient
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Tanana Chiefs Conference (TCC) is the traditional tribal consortium of the 42 villages of Interior Alaska, based on a belief in tribal self-determination and the need for regional Native unity. TCC incorporated in 1971, representing the not only the villages but the approximately 10,000 Alaska Natives of the region. Finding opportunities for smart, clean and affordable energy solutions in rural Alaska has become a priority in order to ensure the sustainability of their cultural identity and way of life. For these villages, nestled in Interior Alaska, off the road system and far removed from the state’s electric grid, the cost of energy is typically the highest in the nation. However, this region is rich in untapped renewable resources, motivated people, and opportunities to create efficiencies in their current fossil fuel systems to decrease their dependence on expensive and unpredictably priced energy. |
Grant Management
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The Alaska Center for Energy and Power (ACEP), an energy research group housed under the Institute of Northern Engineering at the University of Alaska, Fairbanks, is serving as the program manager of the EETG solicitation. As the projects deal with emerging energy technology and by nature are high risk, high reward, ACEP’s technical knowledge and objective academic management of the projects, specifically for data collection, analysis, and reporting, is a vital component to the intent of the solicitation, i.e., providing lessons learned and recommendations. |
Project Partnerships
TCC-ACEP Joint Position
TCC recognized the need for their communities to implement smart, successful and integrated projects in a brief timeframe. They enlisted the assistance of the Alaska Center for Energy and Power through the creation of a jointly managed and funded position which is held by Ross Coen. The immediate goal is to create a region-wide plan to access available funding for projects and to link the region to existing and emerging technologies with the highest impact for their current and future energy portfolio.
The diverse energy needs and available resources for each village precludes a cookie cutter approach and requires solutions that originate within each community but are integrated and shared with the entire region. This partnership matches the community and tribal connections of TCC with the technical expertise of the ACEP to seek practical solutions that decrease high energy prices utilizing the same commitment to sustainable living that has served them well for centuries in this beautiful and often extreme climate.
Ross Coen is acting as project manager for this project, on behalf of TCC.
AEA Reimbursable Services Agreement
Due to limited funding availability, TCC had to reduce the scope and budget of their original EETG proposal to the Denali Commission. The Alaska Energy Authority awarded TCC a Reimbursable Services Agreement for the amount of $54,306 to bridge this budget shortfall, and supplement the funding needed for project equipment.
GVEA Laboratory Space
Golden Valley Electric Association (GVEA) is providing laboratory space in its building in Fairbanks, Alaska for the ORC testing.
ORC Unit Supplier
Through work plan activities, ElectraTherm has been selected by the project team to supply the ORC unit. Since selection, the project team has worked closely with ElectraTherm engineers to help design and engineer the ORC test bed.
Project Documents
Included below are quarterly reports, project photos, and supplementary documentation. Check back quarterly for updates!
Project Information
Supplementary Information
- ElectraTherm Recycled Energy White Paper
- Cost Effective Small Scale ORC Systems for Power Recovery From Low Grade Heat Sources
- Experimental Study and Modeling of a Low Temperature Rankine Cycle for Small Scale Cogeneration
Quarterly Reports
Milestone Reports
Photos
Data and Analysis
Check back quarterly for project results
