John Crittenden

Performance of a Novel Combined Cooling and Power Gas Turbine With Water Harvesting

A thermodynamic design-point performance analysis is performed on a novel cooling and power cycle that combines a semiclosed cycle gas turbine called the high-pressure regenerative turbine engine (HPRTE) with a vapor absorption refrigeration system (VARS). Waste heat from the recirculated combustion gas of the HPRTE is used to power the VARS. Water produced as a product of combustion is intentionally condensed and harvested. A part of the VARS cooling is used to chill the gas entering the high-pressure compressor, allowing water condensation and extraction as well as large efficiency gains. The remaining cooling capacity is provided to an external refrigeration load. The cycle is modeled using zero-dimensional steady-state thermodynamics, considering conservative values of polytropic efficiencies, a conservative model for turbine blade cooling, conservative values of pressure drops for the turbomachinery, including heat exchangers, and accurate correlations for the properties of the LiBr-H 2 O mixture and the combustion products. The cycle is shown to operate with a thermal efficiency greater than 40% for parameters appropriate to medium sized engines, while producing about 1.5 kg of water per kilogram of fuel (propane) consumed. This thermal efficiency is in addition to the large cooling effect generated in the evaporator of VARS, equivalent to 3-4% increased efficiency. The efficiency would be greater than 51% without turbine cooling bleed. The refrigeration ratio, defined as the ratio of external refrigeration load to the net work output, is found to be 0.38 for the base case. The water extracted is found to be a strong function of the recirculation ratio and low pressure compressor ratio PR c1 . Based on these and prior results, which showed that the HPRTE is very compact and has inherently low emissions, it appears that this cycle would be well suited for distributed power and some vehicle applications, especially ones with associated air conditioning loads.

Dynamic Modeling of a Novel Cooling, Heat, Power, and Water Microturbine Combined Cycle

The power, water extraction, and refrigeration (PoWER) engine has been investigated for several years as a distributed energy (DE) system among other applications for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semiclosed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, low emissions, lower air and exhaust flows (which decrease filtration and duct size), and condensation of fresh water. The present paper describes the preliminary design and its modeling of a modified version of this system as applied to DE, especially useful in regions, which are prone to major grid interruptions due to hurricanes, undercapacity, or terrorism. In such cases, the DE system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is contained in magnitude and scope. The paper describes the rather straightforward system modifications necessary for ice production. However, the primary focus of the paper is on dynamic modeling of the ice making capacity to achieve significant load-leveling via thermal energy storage during the summer utility peak, hence reducing the electrical capacity requirements for the grid.

Testing and Modeling of a Semi-Closed Gas Turbine Cycle Integrated With a Vapor Absorption Refrigeration System

A novel cooling and power cycle has been proposed that combines a semi-closed cycle gas turbine called the High Pressure Regenerative Turbine Engine (HPRTE) with a vapor absorption refrigeration system (VARS). The refrigeration cycle (VARS) interacts with the power cycle (HPRTE) solely through heat transfer in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration, in an amount which depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for three purposes: chilling the inlet air to the high pressure compressor, water extraction, and for an external cooling load. In a previous study, the combined cycle was modeled using zero-dimensional steady-state thermodynamics, with the specified values of efficiencies and pressure drops for the turbo-machinery and heat exchangers. The model predicts that the combined cycle with steam blade cooling for a medium-sized engine will have a thermal efficiency of 49%, in addition to the external refrigeration load generated in the cycle which is 13% of the net work output. It also produces about 1.4 kg of water for each kg of fuel (propane) consumed. A small experimental unit demonstrating the HPRTE/VARS combined cycle has been constructed and is currently being tested in the Energy & Gas-dynamic Systems Laboratory at the University of Florida. A 45 HP Rover 1S-60 engine is integrated with a NH3 /H2 O vapor absorption refrigeration unit having a capacity of 19 Ton Refrigeration. The engine flow-path has been significantly modified to include partial recirculation of exhaust products, turbocharging, and recuperation, thus implementing the HPRTE concept. In addition, a significant modeling effort has been undertaken to simulate the combined cycle operation under design and off-design conditions. Initial experimental results show good agreement with the model predictions, including overall efficiency and water extraction rates.Copyright

SECOND LAW ANALYSIS OF A NOVEL COMBINED COOLING AND POWER CYCLE WITH WATER HARVESTING

The first and second laws of thermodynamics were used to analyze a novel cooling and power cycle that combines a semi-closed cycle called the High Pressure Regenerative Turbine Engine (HPRTE) with a vapor absorption refrigeration system (VARS). Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration in an amount that depends on ambient conditions. The cycle is modeled using steady-state thermodynamics, with state-of-the-art polytropic efficiencies and pressure drops for the turbo-machinery and heat exchangers, and accurate correlations for the properties of the NH3-water mixture and the combustion products. Exergy analyses were performed for all the components of the cycle to examine the losses and identify critical plant devices considering different operating conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for: the inlet air to the high pressure compressor, water extraction and for an external load. The cycle is shown to operate with a thermal efficiency approaching 46 % for a turbine inlet temperature of 1400 o C while producing about 1.5 kg of water for each kg of fuel (propane) consumed. The thermal efficiency does not take into account the cooling effect produced in the evaporator of VARS. The combined cycle efficiency at the above operating condition was found to be 49%. Low emissions are also possible on liquid fuels and not just on natural gas. It should be noted that the values of efficiencies obtained are for a medium sized engine with conservative values of the design parameters. It is observed that the largest contribution to the total cycle irreversibility comes from the combustor and accounts for 85% of the total exergy loss. The generator of the vapor absorption refrigeration system is the next largest quantity, accounting for about 3.4% of the total exergy loss. The mass of water extracted from the system increases as the value of the low-pressure compressor ratio is increased. However, this rate of increase is more when the compressor ratio is increased from 1.0 to 2.0 and less as the compressor ratio is further increased. Based on these and prior results, which showed that the HPRTE is very compact and has inherently low emissions, it appears that this cycle would be ideally suited for distributed power and vehicle applications, especially ones with associated air conditioning loads.

Demonstration of a Novel Combined Cooling and Power Gas Turbine with Water Harvesting

Experiments are conducted on a novel cooling and power cycle that combines a semi-closed cycle gas turbine called the High Pressure Regenerative Turbine Engine (HPRTE) with a vapor compression refrigeration system. A fraction of the exhaust air from the combustor is recirculated back to the combustor. The recirculated air is first cooled in a heat exchanger before it is passed on to the evaporator of the vapor compression refrigeration system. The evaporator further cools the recirculated air and in this process water is condensed on the surface of the evaporator tubes. A one-ton refrigeration system was used in the experiment. A total of 1.3 liters of water was extracted for about 20 liters of fuel consumed. In the future, the vapor compression refrigeration system will be replaced with a vapor absorption refrigeration system (VARS). The generator of the VARS will first cool the recirculated air before it passes to the heat exchanger and the evaporator. The evaporator of the VARS will then provide extra cooling in addition to that required for water extraction. The cycle is also modeled using traditional one-dimensional steady-state thermodynamics, with the actual values of the efficiency and pressure drops for the turbomachinery and heat exchangers. The mixture properties of air account for the water removal rate in the evaporator. The values of temperatures and pressure at different state points obtained from the computer model are compared with the experimental values. The difference between the values is found to be within the acceptable limits. The model is then used to design the evaporator capacity for a given amount of water extraction. The evaporator should cool the recirculated gases to about 5 o C to extract about one kg of water per kg of fuel consumed with the current experimental set up. In such a case, about 35 % of the total water vapor generated in the combustor will be extracted in the evaporator.

System Design of a Novel Combined Cooling, Heat, Power, and Water Microturbine Combined Cycle

The Power, Water Extraction, and Refrigeration (PoWER) engine has been investigated for several years as a distributed energy system, among other applications, for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semi-closed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, less emissions, less air and exhaust flows (which decrease filtration and duct size) and condensation of fresh water. The current paper describes the preliminary design and modeling of a modified version of this system as applied to distributed energy, especially useful in regions which are prone to major grid interruptions due to hurricanes, under-capacity, or terrorism. In such cases, the distributed energy system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is limited in scope. The current paper describes the rather straightforward system modifications necessary for ice production. The primary focus of the paper is the use of this ice-making capacity to achieve significant load-leveling during the summer utility peak, hence reducing the electrical capacity requirements for the grid as well as load-leveling strategies.Copyright

Fischer-Tropsch Fuel Characterization via Microturbine Testing and Fundamental Combustion Measurements

Synthetic fuels such as Fischer-Tropsch (FT) fuels are of interest as a replacement for aviation, diesel, and other petroleum-based fuels, and the present paper outlines a joint program to study the combustion behavior of FT synthetic fuels. To this end, shock-tube spray and high-recirculation combustion rig experiments are being utilized to study the ignition delay times, formation of soot, and emissions of FT jet fuels. Undiluted shock tube spray experiments were conducted using a recently developed heterogeneous technique wherein the fuel is sprayed directly into the test region of a shock tube. The high recirculation combustion rig is a complete gas turbine system where Syntroleum FT jet fuel was combusted, and soot formation and emission characteristics were observed. Reduction of soot volume fraction and unchanged emissions were observed, in agreement with previous investigations. The fundamental shock tube results were found to be consistent with the observations made in the experimental engine.Copyright

Design of a Novel Quad-Generation Distributed Energy Demonstration Plant

The power water extraction and refrigeration (PoWER) — a derivative of the high pressure regenerative turbine engine (HPRTE) — has been investigated as part of the distributed energy concept. The ability of the cycle to hold efficiency nearly constant over a wide range of loads and ambient condition is a strong advantage over other concepts. Additional benefits in water extraction and auxiliary refrigeration also pose attractive possibilities. The semi-closed cycle allows for operation in the flameless combustion regime, which can yield substantial emissions reductions as well as fuel flexibility. As part of a continuing effort to illustrate this cycle’s potential, an on-grid demonstration plant is being constructed. The project is part of a collaboration among the University of Florida, Florida Turbine Technology, Energy Concepts, Inc., and Progress Energy. This new pilot plant, while not demonstrating the high efficiency of fully optimized product, is intended to validate cycle analysis codes, produce air conditioning and fresh water, and allow startup and part power operation to be assessed. Quantifying the transient performance, physics-bases multivariate control, and fundamental investigation into the flameless combustion regime — especially with bio-derived fuels — are also goals of the project. This paper describes the modeling effort for the design of the demonstration plant. The modeling proceeded in parallel with the plant development, and was used for hardware selection, integration of the various subsystems, as well as to aid in initial testing of the plant. The model has full capability to predict plant performance over a wide range of steady state conditions. The effect of different fuels and ambient can be considered. Once validated by actual performance data, this code can be used for further prediction, as well as to explore future plant modifications.© 2009 ASME

A Flexible Fuel Semi-Closed Combined Cycle for Power, Refrigeration and Water

The High Pressure Regenerative Turbine Engine (HPRTE) has been investigated since the mid 1990s as the distributed energy system, among other applications, for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when combined with a Vapor Absorption Refrigeration System (VARS) in a novel way. The benefits includes increased efficiency, high part power efficiency, small lapse rate, compactness, low emissions, low air exhaust flows (which decrease filtration and ducting) and condensation of fresh water. The current paper describes the preliminary design and modeling of a modified version of this system applied to distributed energy, especially in regions which are prone to major grid interruptions due to hurricanes, under-capacity, or terrorism. In such cases, the distributed energy system should support most or all services within an isolated “island” so that the influence of the power outage is limited in scope. In addition, the paper will describe the possible production of ice, under emergency conditions, using the fresh condensate plus other water sources.Copyright