Solomon Davidovich Labinov

Evaluation of Different Efficiency Concepts of an Integrated Energy System (IES)

The Integrated Energy System (IES) market in the United States (US) and worldwide has been increasingly expanding over the last few years. But there is still a lot of disagreement in interpretation of one of the most important IES performance parameters – efficiency. Some organizations, for example, use higher heating value (HHV) of fuel in efficiency calculations while some use lower heating value (LHV). Some accounts for auxiliary and parasitic losses while others do not. Some adhere to the “first-law” of efficiency while some use other methods, i.e., calculations recommended by the Federal Energy Regulatory Commission or the US Combined Heat & Power Association. Different efficiency concepts based on actual performance testing from the IES Laboratory at Oak Ridge National Laboratory (ORNL) are evaluated in this paper. The equipment studied included: a 30-kW microturbine, an air-towater heat recovery unit (HRU), a 10-ton (35 kW) hot waterfired (indirect-fired) single-effect absorption chiller, and a direct-fired desiccant dehumidification unit. Efficiencies of different configurations of the above-mentioned equipment based on various approaches are compared. In addition, IES efficiency gains due to the replacement of a 1 st generation HRU (effectiveness of approximately 75%) with a 2 nd generation HRU (effectiveness of approximately 92%) for the same IES arrangement are discussed. The results showed that the difference in HHV- and LHV-based efficiencies for different IES arrangements could reach 5-8%, and that the difference in efficiency values calculated with different methods for the same arrangement could reach 27%. Therefore, it is very important to develop standard guidelines for efficiency calculations that would be acceptable and used by the majority of IES manufacturers and end-users. At the very least, every manufacturer or user should clearly indicate the basis for their efficiency calculations.

Baseline, Exhaust-Fired, and Combined Operation of Desiccant Dehumidification Unit

The performance of a commercially available direct-fired desiccant dehumidification unit (DFDD) has been studied as part of a microturbine generator (MTG)-based Integrated Energy System (IES) at Oak Ridge National Laboratory (ORNL). The IES includes a second-generation air-to-water heat recovery unit (HRU) for the MTG. The focus of these tests was to study the performance of a DFDD in baseline (direct-fired with its natural gas burner) mode and to compare it with a DFDD performance in the exhaust-fired and combined modes as part of the ORNL IES, when waste heat received from the MTG was used for desiccant regeneration. The baseline tests were performed with regeneration air heated by a natural gas burner (direct-fired). The testing of the waste-heat, or exhaust-fired DFDD as part of IES involved using the exhaust gas from the HRU for regeneration air in the DFDD after hot water production in the HRU. Hot water from the HRU was used to produce chilled water in an indirect-fired (water fired) absorption chiller. The combined DFDD was the combination of natural gas burner and exhaust-fired testing. The study investigated the impact of varying the process and regeneration conditions on the latent capacity (LC) and latent coefficient of performance (LCOP) of the DFDD, as well as overall IES efficiency. The performance tests show that LC increases with increasing dew point (humidity ratio) of the process air or the increased amount of waste heat associated with increased MTG power output. In addition, baseline LC was found to be three times higher than the LC in the exhaust-fired mode of operation. LCOP in baseline operation is also almost three times higher than that obtained in the exhaust-fired mode (55.4% compared to 19%). But, at the same time, addition of the DFDD to the IES with the MTG at maximum power output increases the overall IES efficiency by 4–5%. Results of the combined tests performed at a reduced MTG power output of 15 kW (51,182 Btu/h) and their comparison with the baseline and exhaust-fired tests show that activation of the DFDD gas burner during exhaust-fired tests increases the LC over the baseline value from 91,514.9 Btu/h (25.8 kW) to 101,835.8 Btu/h (29.8 kW). The LCOP during the combined mode is less than the “baseline” LCOP, because in addition to gas input, the low-grade MTG/HRU exhaust heat input to the DFDD are also being considered. The overall IES efficiency during the combined mode is approximately 8% higher than without the DFDD integrated into the IES.© 2004 ASME

The LAJ Cycle: A New Combined-Cycle Fossil Fuel Power System

Oak Ridge National Laboratory (ORNL) has developed a novel system for combined-cycle power generation, called the LAJ cycle. This system could serve as a basis for the development of a new generation of high-efficiency combined cycles. In one of several possible configurations of the new combined-cycle fossil fuel power system, natural gas enters the system at 4.0 MPa and about 300 K, is heated and reformed, and is transferred to a turbine at 4.0 MPa and 1200 K. The gas expands in the turbine to 0.6 MPa and 800 K, and then flows successively to heat exchangers and a condenser-separator, after which it is separated into two gas streams, one containing principally CO with some CH4 and water vapor and the other containing pure H2 . The CO and H2 flow to separate fuel cells and undergo electrochemical oxidation with the concomitant production of electricity. Separate streams of water and carbon dioxide (CO2 ) are produced, making this cycle compatible with carbon mitigation strategies based on sequestration. Model calculations indicate combined-cycle efficiencies greater than 70% based on the lower heating value of natural gas. The high efficiencies realized result from a combination of the high-pressure natural gas reformate expansion and the highly efficient CO and H2 fuel cells. Most of the power derives from the fuel cells in the system.Copyright