J. R. Khan

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.

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.

Water Extraction and Performance of a Novel Pressurized CHP System

A novel cooling and power cycle is proposed that combines a semi-closed cycle gas turbine called the High Pressure Regenerative Turbine Engine (HPRTE) with a Vapor Absorption Refrigeration System (VARS). In a previous study, the combined cycle was modeled using zero-dimensional steady-state thermodynamics, with the actual values of efficiencies and pressure drops for the turbomachinery and heat exchangers. The model predicts that the combined cycle with steam blade cooling and having a medium-sized engine will have a thermal efficiency of 49 % for a turbine inlet temperature of 1400 o C. This thermal efficiency is in addition to the large cooling effect generated in the evaporator of VARS which is 13 % of the net work output. In addition it also produces about 1.4 kg of water for each kg of fuel consumed. To validate models and to demonstrate the combined cycle, experiments were conducted on a modified HPRTE using as input the measured performance values of turbomachinery efficiencies and pressure drops. The values of temperatures, pressure, mass flow rates at different state points and other overall cycle parameters obtained from the computer model are compared with the experimental values. The difference between the values is found to be within acceptable limits. The model will be used in the future for the next developmental step of the combined HPRTE/VARS cycle.

Life Cycle Cost Analysis of a Novel Cooling and Power Gas Turbine Engine

A Life cycle cost analysis (LCCA) was performed to compare life cycle costs of a novel gas turbine engine to that of a conventional microturbine with similar power capacity. This engine, called the High Pressure Regenerative Turbine Engine (HPRTE) operates on a pressurized semiclosed cycle and is integrated with a Vapor Absorption Refrigeration System (VARS). The HPRTE uses heat from its exhaust gases to power the absorption refrigeration unit which cools the high-pressure compressor inlet of the HPRTE to below ambient temperatures and also produces some external refrigeration. The life cycle cost analysis procedure is based on principles laid out in the Federal Energy Management Program (FEMP). The influence of different design and economic parameters on the life cycle costs of both technologies is analyzed. The results of this analysis are expressed in terms of the cost ratios of the two technologies. The pressurized nature of the HPRTE leads to compact components resulting in significant savings in equipment cost versus those of a microturbine. Revenue obtained from external refrigeration offsets some of the fuel costs for the HPRTE, thus proving to be a major contributor in cost savings for the HPRTE. For the base case of a high-pressure turbine (HPT) inlet temperature of 1373 K and an exit temperature of 1073 K, the HPRTE showed life cycle cost savings of 7% over a microturbine with a similar power capacity.Copyright

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