The cumulative global capacity of organic Rankine cycle (ORC) power systems for the conversion of renewable and waste thermal energy is undergoing a rapid growth and is estimated to be approx. 2000 MWe considering only installations that went into operation after 1995. The potential for the conversion of the thermal power coming from liquid-dominated geothermal reservoirs, waste heat from primary engines or industrial processes, biomass combustion, and concentrated solar radiation into electricity is arguably enormous. ORC technology is possibly the most flexible in terms of capacity and temperature level and is currently often the only applicable technology for the conversion of external thermal energy sources. In addition, ORC power systems are suitable for the cogeneration of heating and/or cooling, another advantage in the framework of distributed power generation. Related research and development is therefore very lively. These considerations motivated the effort documented in this article, aimed at providing consistent information about the evolution, state, and future of this power conversion technology. First, basic theoretical elements on the thermodynamic cycle, working fluid, and design aspects are illustrated, together with an evaluation of the advantages and disadvantages in comparison to competing technologies. An overview of the long history of the development of ORC power systems follows, in order to place the more recent evolution into perspective. Then, a compendium of the many aspects of the state of the art is illustrated: the solutions currently adopted in commercial plants and the main-stream applications, including information about exemplary installations. A classification and terminology for ORC power plants are proposed. An outlook on the many research and development activities is provided, whereby information on new high-impact applications, such as automotive heat recovery is included. Possible directions of future developments are highlighted, ranging from efforts targeting volume-produced stationary and mobile mini-ORC systems with a power output of few kWe, up to large MWe base-load ORC plants.

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Organic Rankine Cycle Power Systems: From the Concept to Current Technology, Applications, and an Outlook to the Future

Recent strategies in spray drying for the enhanced bioavailability of poorly water-soluble drugs.

Diesel engines are by far the most common means of propulsion aboard ships. It is estimated that around half of their fuel energy consumption is dissipated as low-grade heat. The organic Rankine cycle technology is a well-established solution for the energy conversion of thermal power from biomass combustion, geothermal reservoirs, and waste heat from industrial processes. However, its economic feasibility has not yet been demonstrated for marine applications. This paper aims at evaluating the potential of using organic Rankine cycle systems for waste heat recovery aboard ships. The suitable vessels and engine heat sources are identified by estimating the total recoverable energy. Different cycle architectures, working fluids, components, and control strategies are analyzed. The economic feasibility and integration on board are also evaluated. A number of research and development areas are identified in order to tackle the challenges limiting a widespread use of this technology in currently operating vessels and new-buildings. The results indicate that organic Rankine cycle units recovering heat from the exhaust gases of engines using low-sulfur fuels could yield fuel savings between 10% and 15%.

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A review of the use of organic Rankine cycle power systems for maritime applications

This article reviews bearingless motor technology for medium and high power applications. Historically, bearingless motors have resided in research settings and certain niche commercial applications. Significant literature has been dedicated to developing designs that feature highly specific geometry, restricted by applications with a unique set of needs, oftentimes with low power requirements. The first part of this article reviews existing and potentially new use-cases of magnetic levitation in transportation and industrial applications. The second part of the article reviews bearingless motor technology for these applications, presents a comprehensive literature review of prototype test results, and highlights efforts to generalize and increase the power rating of bearingless motor technology. The final part of this article derives sizing equations of different bearingless motor topologies, which are summarized as a design tool for developing industrial-scale bearingless motor technology.

Review of Bearingless Motor Technology for Significant Power Applications

The vibration controllability is an important feature in the applications of active magnetic bearings (AMBs). This paper addresses the two key challenges on the active balancing control of AMB-rotor systems: presenting a parallel-mode scheme to enhance the notch performance at high speeds, and proposing a phase-shift notch filter to ensure stable operations over the entire speed ranges. First, both the frequency characteristics of the simplified notch filter in series and in parallel mode are discussed. The analysis shows that the closed-loop system with a parallel-mode notch filter has a deeper notch depth and faster convergence. The capacities of the synchronous current elimination are also improved at high speeds. Then, an improved phase-shift notch filter connected in parallel with the controller is modeled and analyzed. In order to understand the sensibility of the proposed solution to phase-shift variations, the stability analysis of the closed-loop system in the entire operational speed range is performed using the frequency response method. Experimental results on a high-speed centrifugal air blower test rig show the effectiveness of the proposed solution.

Active Balancing Control of AMB-Rotor Systems Using a Phase-Shift Notch Filter Connected in Parallel Mode

A cryogenic gas expander system that incorporates a high-performance, high-speed permanent magnet, direct-drive generator and low loss magnetic bearings is described. Flow loop testing to 30,000 rpm was completed at the system manufacturer's facility in January 2005, and field installation is scheduled for October 2005. As part of the system testing, the rotor was dropped onto the backup bearings multiple times at an intermediate speed and at 30,000 rpm. Orbit and time-history data from a full speed drop and spin down are presented and discussed in detail. A transient, nonlinear rotordynamic analysis simulation model was developed for the machine to provide insight into the dynamic behavior. The model includes the dead band clearance, the flexible backup bearing support, and hard stop. Model predictions are discussed relative to the test data.

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Test Results and Analytical Predictions for Rotor Drop Testing of an Active Magnetic Bearing Expander/Generator

The development and testing of an integrated power module (IPM) for a waste heat recovery system is described. The IPM is part of a waste heat recovery system based on the organic Rankine cycle. The waste heat system can recover energy from a wide variety of heat sources including landfill gas, reciprocating engine exhaust, solar, geothermal, boilers, and other industrial processes. The IPM incorporates a high performance, high speed permanent magnet generator with an integrated expansion turbine and low loss magnetic bearings. The IPM operates between 20,000 rpm and 26,500 rpm depending on the energy available from the heat source. The varying frequency voltage supplied by the generator is connected to the grid using an active/active power electronics package that can deliver power at 400–480 Vac (50 Hz or 60 Hz). Active magnetic bearings (AMBs) were chosen for the application because they can operate directly in the working fluid, have low losses, and provide high reliability and remote monitoring capabilities. This system has a flow-through design and an inboard impeller layout that produces desirable rotordynamics for a simple magnetic bearing control. An extensive shop testing procedure is described, and measurements and predictions are presented, showing good correlation. Shop testing of the IPM in the waste heat system has been completed for 15 systems. The magnetic bearings and backup bearings have performed as designed. The thrust balancing system has limited the thrust load that must be reacted by the axial magnetic bearings to 25% of the design load capacity in the worst case. The first field unit was installed in April 2009 at a biogas site. DOI: 10.1115/1.4002660

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Development of a 125 kW AMB Expander/Generator for Waste Heat Recovery

A first bias magnetic flux may be communicated between a first axial pole and a first axial facing surface of the body. A second bias magnetic flux may be communicated between a second axial pole and a second axial facing surface of the body. A time-varying axial control magnetic flux may be communicated through the first and second axial facing surfaces of the body, and may be generated in a magnetic circuit including the body, the first and second axial poles, and an axial magnetic backiron. The first and second axial poles may include axial pole laminated inserts composed of electrically isolated steel laminations stacked along the body axis. The axial magnetic backiron may include laminated inserts composed of electrically isolated steel laminations stacked in the direction tangential to the body axis. The axial pole laminated inserts may be magnetically coupled to the axial magnetic backiron laminated inserts.

Combination radial/axial electromagnetic actuator with an improved axial frequency response

An electromagnetic actuator includes a body and first and second poles residing apart from the body. The first and second poles communicate magnetic flux across a gap with opposing end facing surfaces of the body. The body, the first pole, and the second pole are magnetically coupled and define an axial magnetic control circuit. A plurality of radial poles reside apart from the body, adjacent a lateral facing surface of the body, and communicate magnetic fluxes with the lateral facing surface. The body and the plurality of radial poles define a plurality of radial magnetic control circuits. The plurality of radial poles communicate magnetic fluxes with the lateral facing surface and at least one of the first pole or the second pole, and the body, the plurality of radial poles, and at least one of the first pole or the second pole define a magnetic bias circuit.

Combination radial/axial electromagnetic actuator

Qualification shock testing has been completed for a new chilled water plant developed for the US Navy. The variable speed compressor at the heart of the chiller system includes a direct drive, high-speed permanent magnet (PM) motor, PM bias active magnetic bearings, and a backup bearing system. For MIL-S-901D shock certification, the chiller was mounted on a Navy floating shock platform (barge) and subjected to a standard sequence of four different shock impacts generated from high explosive charges from varying angles and standoff distances. The chiller was fully operational during three blasts and in standby mode for the fourth blast. In the standby mode, the shaft is de levitated and stationary on the backup bearings and the chiller secured. The backup bearing system of the motor absorbed the response to the shock impacts and the magnetic bearings subsequently recovered levitation as designed. The shock testing was simulated using a transient, nonlinear rotordynamic analysis including the magnetic bearing control and saturation features, backup bearings with resilient mounts and associated clearances, and structural dynamic models of the rotor and housing. Compressor/motor housing acceleration measured during the testing was used as the driving input into the simulation. Some rotor position data recorded during shock testing, the simulation approach and comparisons are reported and discussed.

Lawrence A. Hawkins

Papers

Test Results and Analytical Predictions for Rotor Drop Testing of an Active Magnetic Bearing Expander/Generator

Development of a 125 kW AMB Expander/Generator for Waste Heat Recovery

Combination radial/axial electromagnetic actuator with an improved axial frequency response

Combination radial/axial electromagnetic actuator

Floating Shock Platform Testing of a Magnetic Bearing Supported Chiller Compressor: Measurements and Simulation Results