Tri-Generation Systems Optimization: Comparison of Heuristic and Mixed Integer Linear Programming Approaches

This work compares two optimization approaches for combined cooling, heating and power (CCHP or Tri-generation) energy systems scheduling. Both approaches are developed through dedicated software codes and are based on simulation models capable of evaluating of the best operating strategy (both economically and energy-wise) to run a given trigeneration plant while dealing with time-variable loads and tariffs. The simultaneous use of different prime movers operating in parallel is taken into consideration as well as their part load performance, the influence of ambient temperature and the usage of a heat storage system. Cooling may be generated through absorption chillers or electrically driven compression cycles. One of the models is heuristic and adopts an optimization strategy based on a multi-step approach: it simulates several cases according to a pre-defined number of paths, exploring the most reasonable operational modes and comparing them systematically. The other relies on a mathematical approach, based on a Mixed Integer Linear Programming (MILP) optimization model which has been developed in order to deal with more complex systems without the need of predefining a too large variety of operation paths. Results of the two models are compared against a test case based on real plant specifications, discussing their performance by the point of view of simulation capabilities, quality and accuracy of the optimization results (in terms of differences in energy and economic performance) and computational resources.

Visualization of Different Flashback Mechanisms for H2/CH4 Mixtures in a Variable-Swirl Burner

Flame flashback from the combustion chamber to the premixing section is a major operability issue when using high H2 content fuels in lean premixed combustors. Depending on the flow-field in the combustor, flashback can be triggered by different mechanisms. In this work, three flashback mechanisms of H2/CH4 mixtures were visualized in an atmospheric variable swirl burner using high speed OH* chemiluminescence imaging. The H2 mole fraction of the tested fuel mixtures varied between 0.1 and 0.9. The flow-field in the combustor was varied by changing the swirl number from 0.0 to 0.66 and the total air mass-flow rate from 75 to 200 SLPM (standard liters per minute). The following three types of flashback mechanism were observed: Flashback caused by combustion induced vortex breakdown occurred at swirl numbers ≥ 0.53 for all of the tested fuel mixtures. Flashback in the boundary layer and flashback due to autoignition were observed at low swirl numbers and low total air mass-flow rates. The temporal and spatial propagation of the flame in the optical section of the premixing tube during flashback was studied and flashback speed for different mechanisms was estimated. The flame propagation speed during flashback was significantly different for the different mechanisms.

Numerical Analysis of Gas Turbine Inlet Fogging Nozzle Manifold Pressure Drop

The air pressure drop over the nozzles manifolds of inlet fogging system and the flow resistance downstream of the nozzle array (manifold) have always been an area of concern and is the object of this paper. Fogging nozzles arrays (involving several hundred nozzles) are mounted on channels and beams, downstream of the inlet filters and affect the pressure drop. The water injection angle, nozzle injection velocities and the progressive evaporation of the water droplets evaporation all influence the inlet pressure seen at the gas turbine inlet. This paper focuses on a numerical simulation investigation of flow resistance (pressure drop) of inlet fogging systems. In this research effort, the inlet duct is meshed in order to compute the pressure drop over the nozzles frames in fogging and non-fogging conditions. First, the resistance coefficients of an air intake filter are obtained by numerical and experimental methods, and then the coefficients are used for the simulation of the inlet duct by considering the filter as a porous media. Effects of nozzle spread pattern and water injection pattern are then modeled. The results indicate that injection velocity and arrangement of nozzles could have significant effects on the pressure drop and intake distortion, which will affect compressor performance. This paper provides a comprehensive analysis of the pressure drop and evaporation of inlet fogging and will be of value to gas turbine inlet fogging system designers and users.

Evolution of Gas Turbine Intake Air Filtration in a 420 MW Cogeneration Plant

A suitable inlet air filter system is required for a gas turbine, depending on installation site and its environmental conditions, to minimize contaminants entering the compressor section in order to maintain gas turbine performance. This paper describes evolution of inlet air filter systems utilized at the 420 MW Watson Cogeneration Plant consisting of four GE 7EA gas turbines since commissioning of the plant in November 1987. Changes to the inlet air filtration system became necessary due to system limitations, a desire to reduce operational and maintenance costs, and enhance overall plant performance. Based on approximately 2 years of operational data with the latest filtration system combined with other operational experiences of more than 25 years, it is shown that implementation of the high efficiency particulate air filter system provides reduced number of crank washes, gas turbine performance improvement and significant economic benefits compared to the traditional synthetic media type filters. Reasons for improved gas turbine performance and associated economic benefits, observed via actual operational data, with use of the latest filter system are discussed in this paper.

NMHC and VOC Speciation of the Exhaust Gas From a Gas Turbine Engine Using Alternative, Renewable and Conventional Jet A-1 Aviation Fuels

This paper investigated the emissions of individual unburned hydrocarbons and carbonyl compounds from the exhaust gas of an APU (Auxiliary Power Unit) gas turbine engine burning various fuels. The engine was a single spool, two stages of turbines and one stage of centrifugal compressor gas turbine engine, and operated at idle and full power respectively. Four alternative aviation fuel blends with Jet A-1 were tested including GTL, hydrogenated renewable jet fuel and fatty acid ester. C2-C4 alkenes, benzene, toluene, xylene, trimethylbenzene, naphthalene, formaldehyde, acetaldehyde and acrolein emissions were measured. The results show at the full power condition, the concentrations for all hydrocarbons were very low (near or below the instrument detection limits). Formaldehyde was a major aldehyde species emitted with a fraction of around 60% of total measured aldehydes emissions. Formaldehydes emissions were reduced for all fuels compared to Jet A-1 especially at the idle conditions. There were no differences in acetaldehydes and acrolein emissions for all fuels; however, there was a noticeable reduction with GTL fuel. The aromatic hydrocarbon emissions including benzene and toluene are decreased for the alternative and renewable fuels.

Dynamic Analysis of Concentrated Solar Hybridised Gas Turbine

In this work the dynamic behaviour and the control strategy of a 12MWe size gas turbine hybridised with concentrated solar heat source has been investigated. Hybridised gas turbine cycles are attractive because of their high efficiency, potentially equal to combined cycle efficiency, and because of their dispatchable power capability. An existing gas turbine model has been modified into a hybrid layout to incorporate high temperature heat from a concentrated solar field, through a high pressure air-cooled receiver. The system does not involve any hot air valve and includes a ceramic thermal storage. The plant dynamic model was developed using the original TRANSEO simulation tool developed at the University of Genoa. Initially, plant steady-state performance is analysed, identifying potential issues. Then, the different dynamic operations (storage charging, discharging and bypass) are simulated, showing the feasibility of the control strategy proposed. Eventually, design recommendations are drawn to improve the flexibility and the time response of such kind of plants.

Thermodynamics Cycle Analysis, Pressure Loss and Heat Transfer Assessment of a Recuperative System for Aero Engines

Aiming in the direction of designing more efficient aero engines, various concepts have been developed in recent years, among which is the concept of an intercooled and recuperative aero engine. Particularly in the area of recuperation, MTU Aero Engines has been driving research activities in the last decade. This concept is based on the use of a system of heat exchangers mounted inside the hot-gas exhaust nozzle (recuperator). Through the operation of the system of heat exchangers, the heat from the exhaust gas, downstream the LP turbine of the jet engine is driven back to the combustion chamber. Thus, the preheated air enters the engine combustion chamber with increased enthalpy, providing improved combustion and by consequence, increased fuel economy and low-level emissions. If additionally an intercooler is placed between the compressor stages of the aero engine, the compressed air is then cooled by the intercooler thus, less compression work is required to reach the compressor target pressure. In this paper an overall assessment of the system is presented with particular focus on the recuperative system and the heat exchangers mounted into the aero engine’s exhaust nozzle. The herein presented results were based on the combined use of CFD computations, experimental measurements and thermodynamic cycle analysis. They focus on the effects of total pressure losses and heat exchanger efficiency on the aero engine performance especially the engine’s overall efficiency and the specific fuel consumption. More specifically, two different hot-gas exhaust nozzle configurations incorporating modifications in the system of heat exchangers are examined. The results show that significant improvements can be achieved in overall efficiency and specific fuel consumption hence contributing into the reduction of CO2 and NOx emissions. The design of a more sophisticated recuperation system can lead to further improvements in the aero engine efficiency in the reduction of fuel consumption. This work is part of the European funded research program LEMCOTEC (Low Emissions Core engine Technologies).

Emergency Shutdown Management in Fuel Cell Gas Turbine Hybrid Systems

A real-time dynamic model representing the pressurized fuel cell gas turbine hybrid system emulator test rig at Thermochemical Power Group (TPG) laboratories of the University of Genoa has been developed to study the fuel cell behavior during different critical operative situations like, for example, load changes (ramp and step), start-up and shut-down and, moreover, to implement an emergency shutdown strategy in order to avoid any damage to the fuel cell and to the whole system: focus has been on cathode/anode differential pressure, which model was validated against experimental data. The real emulator plant (located in Savona University campus) is composed of a 100 kW recuperated micro gas turbine, a modular cathodic vessel (4 modules of 0.8 m3 each) located between recuperator outlet and combustor inlet, and an anodic circuit (1 module of 0.8m3) based on the coupling of a single stage ejector with an anodic vessel. Different simulation tests were carried out to assess the behavior of cathode-anode pressure difference, identifying the best control strategies to minimize the pressure stress on fuel cell stack.

CCPP Performance Augmentation Using LNG Re-Gasification Cold Energy

With gas becoming a fuel of choice for clean energy, Liquefied Natural Gas (LNG) is being transported and re-gasification terminals are being set up at several locations. Re-gasification of LNG leads to availability of considerable cold-energy which can be utilized to gain power and efficiency in a Gas Turbine (GT) based Power Plant. With a number of LNG Re-gasification Terminals coming up in India & around the globe, setting up of a high efficiency CCPP adjacent to the terminal considering utilization of the cold energy to augment its performance, and also save energy towards re-gasification of LNG, provides a feasible business opportunity. Thermodynamic analysis and major applications of the LNG re-gasification cold energy in Gas Turbine based power generation cycle, are discussed in this paper. The feasibility of cooling GT inlet air by virtue of the cold energy of Liquefied LNG to increase power output of a Combined Cycle Power Plant (CCPP) for different ambient conditions is analyzed and also the effect on efficiency is discussed. The use of cold energy in condenser cooling water circulating system to improve efficiency of the CCPP is also analyzed. Air cooling capacity and power augmentation for a combined cycle power plant based on the advanced class industrial heavy duty gas turbine are demonstrated as a function of the ambient temperature and humidity. The economic feasibility of utilizing the cold energy is also deliberated.

Energetic and Environmental Analysis of Partial Repowering of a Coal Fired Power Plant Through Upstream GT Integration and Employing Waste Heated Feed Water Heaters

This paper presents a theoretical study of partial repowering scheme for an existing 210MW coal fired power plant and reports predicted performance improvement obtainable from the repowering by using Cycle Tempo software. In this method old boiler is used as it is, only modifying its air heater and forced flow sections. Out of four operating coal mills, one mill is considered to be taken out. A new natural gas fired gas turbine (GT) block is considered to be integrated with the existing plant whose exhaust is fed to the existing boiler. The GT size is selected such that its exhaust provide heat input equivalent to the replaced coal mill. The burners associated with that coal mill are assumed to be modified to handle hot exhaust gas from the GT block. It is noticed that a substantial amount of energy is available in the flue gas, coming out from the boiler, after the air preheater which can partially meet the heat loads of feed water heaters. This helps in saving of intermediate pressure (IP) and low pressure (LP) bleed steam and consequent increase in the output of the steam cycle. The partial repowering results in nearly 40% increase in capacity of the plant (from 210MW to 284MW). It also results in substantial increase in overall efficiency of the repowered plant by 28%, and consequent decrease in plant heat rate by 22%. The specific CO2 emission of the plant decreases about 31% after repowering.