Umberto Desideri

Performance modelling of a carbon dioxide removal system for power plants

In this paper, a carbon dioxide removal and liquefaction system, which separates carbon dioxide from the flue gases of conventional power plants, was modelled. The system is based on an amine chemical absorption stripping system, followed by a liquefaction unit to treat the removed CO2 for transportation and storage. The effect of the main parameters on the absorption and stripping columns is presented. The main constraints set for the model are a capture efficiency of 90% and the use of an aqueous solution with a maximum 30% amine content by weight. The goal of this study is to remove the CO2 with minimum energy requirements for the process when it is integrated in a fossil fuel fired power plant. Results of the simulation are compared to experimental and literature data from feasibility studies and existing plants. The power plant to which the removal system is connected is a 320 MW steam power plant with steam reheat and 8 feedwater heaters. Two different fossil fuels were considered: coal and natural gas. The effect of the modifications necessary to integrate the CO2 removal system in the power plant is also studied. The capital cost of the removal and liquefaction system is estimated, and its influence on the cost of generated electricity is calculated.

Analysis of energy consumption in the high schools of a province in central Italy

Abstract This paper presents an energy analysis of the school buildings of a province in central Italy. The analysis is aimed at calculating the main thermal and electric energy consumption indexes to determine the status of energy consumption and the possible intervention to save energy in the school sector. Two applications of energy auditing to school buildings are also presented. It is also shown that if the optimal energy consumption indexes could be valid for all the school buildings, thermal energy savings could reach 38% and electric energy consumptions could be reduced by over 46%.

Study of possible optimisation criteria for geothermal power plants

The possibility of exploiting low temperature liquid-dominated geothermal sources can considerably increase the use of this kind of renewable energy. Improvements in the performance of geothermal cycles are possible by using closed Rankine and Kalina cycles, whose working fluid may be a pure substance or a two-component mixture. In this paper three configurations of the Rankine cycle are examined and compared to conventional single and dual flash steam power plants. The Kalina cycle system no. 12 has also been studied. Results showed that there is a potential for optimisation of the performance, by modifying the main parameters, such as turbine inlet pressure and type of fluid.

Performance estimation and experimental measurements of a photovoltaic roof

The market for photovoltaic systems is rapidly expanding. Currently, there are a few large utility photovoltaic power plants, thousands of residential systems, and tens of thousands of remote power systems in use. Even if photovoltaics is a technology that has already demonstrated its effectiveness and holds great promise in electrical generation, the costs are still too high to guarantee a commercial competitivity.

Analysis and optimization of hybrid MCFC gas turbines plants

Abstract High temperature fuel cells are electricity producers that guarantee relevant energetic and environmental performances. They feature high electricity to input chemical energy ratios and availability of high temperature heat. Notwithstanding, the search for a further increase in electric efficiency, especially when applying a CHP solution is not feasible, has brought to plant integration with gas turbines (GTs) in several studies and some pilot installations. While for pressurized fuel cells the choice of internal combustion gas turbines seem to be the only one feasible, in ambient pressure fuel cells it seems useful to analyze the combination with indirect heated GT. This choice allows to optimize turbine pressure ratio and cell size. In this work, a parametric performance evaluation of a hybrid molten carbonate fuel cell (MCFC) indirect heated gas turbine has been performed by varying the fuel cell section size and the fuel utilization coefficient. The analysis of performance variation with the latter parameter shows how a cell that is optimized for stand alone operation is not necessarily optimized for the integration in a hybrid cycle. Working with reduced utilization factors, in fact can reduce irreversible losses and does not necessarily yield to less electricity production since the heat produced in the post combustor is recovered by the gas turbine section. This aspect has not been taken into sufficient consideration in literature. The analysis illustrates the methodology to define new operating conditions so to allow global output and global efficiency maximization.

CO2 capture in small size cogeneration plants: technical and economical considerations

Abstract In this study, the integration of an absorption scrubber for carbon dioxide capture in a Cheng cycle cogeneration plant with district heating is studied. Different CO 2 capture systems have been examined, and the most suitable for this type of application has been selected from both the economic and the efficiency viewpoints. The plant can be upgraded without complicated add-on systems and does not require significant redesign of the existing components. Three types of operation have been studied which are representative of winter, summer and spring–autumn conditions. It is shown that lower CO 2 emissions are possible without important reductions of efficiency and power output. The power generation costs are greatly influenced by the capital costs of the CO 2 capture system. If absorption scrubber capital costs are not going to be reduced in the future, the use of such capture systems will not be competitive with possible application of “carbon taxes”. From the viewpoint of operating costs, the increase in the cost of produced electricity will be similar to the surcharge due to application of the “carbon tax” studied by the European Union for power generation systems.

Rotary kiln slow pyrolysis for syngas and char production from biomass and waste -Part II Introducing product yields in the energy balance

A microscale electrically heated rotary kiln for slow pyrolysis of biomass and waste was designed and built at the University of Perugia. The reactor is connected to a wet scrubbing section, for tar removal, and to a monitored combustion chamber to evaluate the lower heating value of the syngas. The system allows the evaluation of gas, tar, and char yields for different pyrolysis temperature and residence time. The feeding screw conveyor and the kiln are rigidly connected; therefore a modification of the flow rate implies a modification of the inside solid motion and of residence time. Part I of the paper describes the theoretical and experimental evaluation of the working envelope of the reactor, that is, rotational speed as a function of feedstock density and humidity content, to obtain pyrolysis conditions inside the kiln. This paper describes the development and resolution of an energy balance of the reactor under pyrolysis conditions. Once the rotational speed n is fixed, the aim of the balance is to obtain the yield of wood biomass pyrolysis products such as syngas, tar, and char. Results can be used to choose the correct rotational speed of kiln and feeding screw before doing the real pyrolysis test.

Should biomass be used for power generation or hydrogen production

In the last several years, gasification has become an interesting option for biomass utilization because the produced gas can be used as a gaseous fuel in different applications or burned in a gas turbine for power generation with a high thermodynamic efficiency. In this paper, a technoeconomic 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 cleanup 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.

Rotary Kiln Slow Pyrolysis for Syngas and Char Production From Biomass and Waste—Part I: Working Envelope of the Reactor

A microscale electrically heated rotary kiln for slow pyrolysis of biomass and waste was designed and built at the University of Perugia. The reactor is connected to a wet scrubbing section, for tar removal, and to a monitored combustion chamber to evaluate the lower heating value of the syngas. The system allows the evaluation of gas, tar, and char yields for different pyrolysis temperatures and residence times. The feeding screw conveyor and the kiln are rigidly connected; therefore, a modification of the flow rate implies a modification of the inside solid motion and of residence time. The paper provides the theoretical and experimental calculation of the relationships between residence time and flow rate used to determine the working envelope of the reactor as a function of the feedstock bulk density and moisture content, given the actual heat rate of the electric heaters. The methodology is extendable to any rotary kiln reactor with a rigidly connected feeding screw conveyor, given its geometric and energetic specifications. Part II of the paper will extend the energy balance, also introducing the yields of pyrolysis products.

Analysis of Gas-Steam Combined Cycles With Natural Gas Reforming and CO2 Capture

In the last several years greenhouse gas emissions, and, in particular, carbon dioxide emissions, have become a major concern in the power generation industry and a large amount of research work has been dedicated to this subject. Among the possible technologies to reduce CO 2 emissions from power plants, the pretreatment of fossil fuels to separate carbon from hydrogen before the combustion process is one of the least energy-consuming ways to facilitate CO 2 capture and removal from the power plant. In this paper several power plant schemes with reduced CO 2 emissions were simulated. All the configurations were based on the following characteristics: (i) syngas production via natural gas reforming; (ii) two reactors for CO-shift; (iii) precombustion decarbonization of the fuel by CO 2 absorption with amine solutions; (iv) combustion of hydrogen-rich fuel in a commercially available gas turbine; and (v) combined cycle with three pressure levels, to achieve a net power output in the range of 400 MW. The base reactor employed for syngas generation is the ATR (auto thermal reformer). The attention was focused on the optimization of the main parameters of this reactor and its interaction with the power section. In particular the simulation evaluated the benefits deriving from the postcombustion of exhaust gas and from the introduction of a gas-gas heat exchanger. All the components of the plants were simulated using ASPEN PLUS software, and fixing a reduction of CO 2 emissions of at least 90%. The best configuration showed a thermal efficiency of approximately 48% and CO 2 specific emissions of 0.04 ke/kWh.