Alessandro Corradetti

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.

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.

Thermodynamic Analysis and Possible Applications of the Integrated Pyrolysis Fuel Cell Plant (IPFCP)

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.© 2007 ASME

Analysis of Biomass Integrated Gasification Fuel Cell Plants in Industrial CHP Applications

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%.Copyright

A technoeconomic analysis of different options for cogenerating power in hydrogen plants based on natural gas reforming

Steam methane reforming is the most common process for producing hydrogen in the world. It currently represents the most efficient and mature technology for this purpose. However, because of the high investment costs, this technology is only convenient for large sizes. 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, and (iii) a gas-steam combined cycle. These configurations have been investigated with the additional feature of CO 2 capture and sequestration. The reference plant has been modeled according to state-of-the-art of commercial hydrogen plants: it includes a prereforming reactor, two shift reactors, and a pressure swing adsorption unit for hydrogen purification. The plant has a conversion efficiency of ∼75% and produces 145,000 Sm 3 /hr of hydrogen (equivalent to 435 MW on the lower-heating-volume 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 CO 2 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.

A Novel Concept for Combined Heat and Cooling in Humid Gas Turbine Cycles

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).Copyright

Should Biomass Be Used for Power Generation or Hydrogen Production

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.Copyright

A Techno-Economic Analysis of Different Options for Cogenerating Power in Hydrogen Plants Based on Natural Gas Reforming

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 Stm3 /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.© 2006 ASME

Analysis of gas-steam combined cycles with natural gas reforming and CO2 capture

In the last 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 CO2 emissions from power plants, the pre-treatment of the fossil fuels to separate carbon from hydrogen before the combustion process is one of the least energy consuming way to facilitate CO2 capture and removal from the power plant. In this paper several power plant schemes with reduced CO2 emissions were simulated. All the configurations were based on the following characteristics: (1) syngas production via natural gas reforming; (2) two reactors for CO-shift; (3) “pre-combustion” decarbonization of the fuel by CO2 absorption with amine solutions; (4) combustion of hydrogen rich fuel in a commercially available gas turbine; (5) 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 post-combustion 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 CO2 emissions of at least 90%. The best configuration showed a thermal efficiency of approximately 48% and CO2 specific emissions of 0.04 kg/kWh.Copyright