Various gas turbine cycles are known where water is introduced as a liquid or as a vapor into the combustor of the gas turbine. Such cycles include the Humid Air Turbine (HAT) cycle, the Steam Injected (STIG) cycle, and the Regenerated Water Injected gas turbine cycle (RWI). The effect of water vapor is the increasing of net power output and the reduction of NOx formation within the combustor. However the net increase in power output is limited in commercial models of gas turbines, because a large addition of water vapor leads to the mismatch between the compressor and the turbine. In this paper a possible method to solve this problem is proposed: it is based on a novel concept for combining refrigeration and power production in humid gas turbine cycles. In the proposed system a fraction of the air at compressor discharge is extracted, cooled to nearly ambient temperature, dried and expanded in a turbine. At turbine outlet the air is at a very low temperature and can be used for providing refrigeration. A thermodynamic analysis has been carried out to investigate the performance of the system in HAT, STIG and RWI cycles for different operating conditions representing the state of art of commercial gas turbines. In particular the pressure ratio and the turbine inlet temperature have been respectively varied in the range 7–45 and 900–1500°C. Sensitivity analyses have been performed to assess how the amounts of extracted air and injected steam affect the net power output, the electrical efficiency and the cooling. The results show that cryogenic temperatures (lower than −100°C) for refrigeration can be achieved in combination with very high electrical efficiency (over 40%, typical of humid gas turbine cycles).

This paper presents the results of a research made by University of Perugia in collaboration with Energia Spa (now Sorgenia Spa). Various analysis have been carried out to determine the techno-economic feasibility of industrial CHP plants. Due to the particular field of application, the installation of a gas turbine has been considered and compared to the traditional internal combustion engine (ICE), both being characterized by an electrical power lower than 2 MW. The feasibility study has been made in two different way: an analytical study and a simplified approach elaborated to have a first approach formula for the installation of CHP Plant. The results confirmed that IC is more convenient, giving lower payback period for the investment for this typology of installation. We present also the sensitivity analysis to determine the minimum value over that the installation of gas turbine can become convenient.

Biomass and waste are generally considered as a very promising option for fossil fuel substitution and greenhouse effect reduction in a sustainable energy scenario. This paper examines the possible lay-out and performance of an innovative energy system based on the integration of a high temperature fuel cell with a pyrolysis reactor. The pyrolyzer converts biomass or solid waste into syngas, which is cleaned from impurities and feeds a Solid Oxide Fuel Cell (SOFC), operating at 1000°C. A combustor supplies the energy required for pyrolysis, burning the solid and liquid fraction of the pyrolysis yield, as well as the un-oxidized fuel leaving the cell anode. Literature data have been used for determining pyrolysis yield as a function of reactor temperature and evaluating its effect on the plant thermodynamic efficiency. The coupling of the system to a gas turbine using the fuel cell as its combustion chamber is also evaluated. Results show that very interesting efficiencies are obtainable in the 20%–30% range.

In this paper, a model for a solid oxide fuel cell (SOFC) system for decentralized electricity production is developed and studied. The proposed system, operated on natural gas, consists of a planar anode supported fuel cell section and a balance of plant (BoP) which includes gases supply, a fuel processor, a heat management system, an after-burner and a power conditioning system. A reference case is defined and evaluated taking into account the state of the art of the technology and the related technical constrains. Electrical and thermal efficiency of the system, for non-reference conditions are evaluated. In particular, the effect of the deviation from the reference conditions of fuel utilization, gas temperature spring in fuel cell stack, anode off-gas recirculation rate, air inlet temperature and external pre-reforming reaction extent is analyzed. The present study revealed to be a powerful tool for evaluating the SOFC system performance under a wide range of operation and paves the way for defining control strategies in order to maintain high system efficiency under part-load operations.

In the last years gasification has become an interesting option for biomass utilization, since the produced gas can be used as a gaseous fuel in different applications or burnt in a gas turbine for power generation with a high thermodynamic efficiency. In this paper a techno-economic analysis was carried out in order to evaluate performance and cost of biomass gasification systems integrated with two different types of plant, respectively for hydrogen production and for power generation. An indirectly heated fluidized bed gasifier has been chosen for gas generation in both cases and experimental data have been used to simulate the behavior of the gasifier. The hydrogen plant is characterized by the installation of a steam methane reformer and a shift reactor after the gas production and clean-up section; hydrogen is then purified in a pressure swing adsorption system. All these components have been modeled following typical operating conditions found in hydrogen plants. Simulations have been performed to optimize thermal interactions between the biomass gasification section and the gas processing. The power plant consists of a gas-steam combined cycle, with a three pressure levels bottoming cycle. A sensitivity analysis allowed to evaluate the economic convenience of the two plants as a function of the costs of the hydrogen and electrical energy.

The gasification of biomass wastes deriving from certain industrial processes is an interesting option for cogenerating heat and power. The utilization of the syngas in a high temperature fuel cell could lead to the improvement of electrical efficiency in comparison with traditional CHP plants. In this paper the performance of various Biomass Integrated Gasification Fuel Cell (BIGFC) plants are investigated. In particular an atmospheric down-draft gasifier has been considered for syngas production. The fuel cell used for power generation is a 250 kW solid oxide fuel cell, which has been simulated through a zero-dimensional steady-state model and integrated in Aspen Plus® software for evaluating the performance of the entire plant. Various system lay-outs have been investigated to analyze the effect on plant efficiency of the following parameters: (i) gasification air pre-heating; (ii) use of 90% pure oxygen for gasification; (iii) use of enriched air (55% O2) for gasification; (iv) recirculation of anodic gas flow; (v) installation of a SOFC/GT hybrid cycle for power production. BIGFC plants show an electrical efficiency in the range 20–27%, and a thermal efficiency of 39–59%. If a SOFC/GT hybrid cycle is installed electrical efficiency grows up to 39%.

Steam Methane Reformer is the commonest process for producing hydrogen in the world. It currently represents the most efficient and mature technology for this purpose. However, due to the high investment costs, this technology is convenient for large sizes only. Furthermore, the cooling of syngas and flue gas produce a great amount of excess steam, which is usually transferred outside the process, for heating purposes or industrial applications. The opportunity of using this additional steam to generate electric power has been studied in this paper. In particular different power plant schemes have been analyzed, including: (i) a Rankine cycle; (ii) a gas turbine simple cycle; (iii) a gas-steam combined cycle. These configurations have been investigated with the additional feature Of CO2 capture and sequestration. The reference plant has been modeled according to the state of art of commercial hydrogen plants: it includes a pre-reforming reactor, two shift reactors and a pressure swing adsorption unit for hydrogen purification. The plant has a conversion efficiency of approximately 75% and produces 145,000 Stm(3)/hr of hydrogen (equivalent to 435 MW on LHV basis) and 63 t/hr of superheated steam. The proposed power plants generate respectively 22 MW (i), 36 MW (ii) and 87 MW (iii) without CO2 capture. A sensitivity analysis was carried out to determine the optimum size for each configuration and to investigate the influence of some parameters, such as electricity, natural gas and steam costs.