In July, Enel, Italy’s largest utility, inaugurated a 16 MW hydrogen power plant in Fusina, near Venice. This is the first industrial-scale facility of its kind in the world. It generates sufficient clean electricity to meet the annual needs of 20 000 households, averting more than 17 000 tonnes of CO2 emissions a year.
The Fusina power plant, featuring a gas turbine that can use hydrogen as its main fuel along with a condensing-type heat recovery steam generator Source: Michele Gregolin
Sauro Pasini, head of research, Enel Group
Sauro Pasini, head of research, Enel Group
Sauro Pasini, Enel Group, Italy
Enel Group is strongly committed to the development and the deployment of environmentally friendly technologies. The group is investigating all the available technologies for carbon capture and storage (CCS), with the aim of identifying an effective and cost-competitive technology, as well as providing a demonstration at a pilot or industrial scale. These technologies include post-combustion, oxy-coal combustion and pre-combustion.
Post-combustion capture is considered the most mature technology for industrial application, as it is suitable for retrofitting existing coal fired plants. In this field, a 2.5 tonnes/hour of carbon dioxide (CO2) slip-stream pilot plant has been installed at Enel’s 2640 MW coal fired power plant in Brindisi.Enel is also undertaking a feasibility study for a post-combustion capture demonstration plant able to remove 1 megatonne/year of CO2 from a 660 MW coal fired unit to be installed in Porto Tolle, activity that has recently been awarded €100 million ($131 million) in funding from the European Commission through the European Energy Recovery Plan. Enel is also using this project to investigate the opportunities for geological storage of CO2
Oxy-coal combustion process, both atmospheric and pressurized, is also being investigated, with tests being carried out on experimental scale pilot plants installed in Livorno and in Gioia del Colle, near Bari.
In the field of pre-combustion capture Enel is focusing its efforts on the power island, through the installation of a hydrogen fuelled combined-cycle gas turbine (CCGT) suitable for application in integrated gasification combined-cycles (IGCC) with CCS in Fusina, near Venice.
An IGCC with CCS is based on a gasification island, where hydrogen is obtained through the gasification of coal, which produces a syngas composed of hydrogen and carbon monoxide (CO); the CO is converted into hydrogen and CO2 by means of a water shift reaction. The hydrogen is therefore burned in a combined-cycle, producing exhaust gases consisting exclusively of hot air and water vapour, with the CO2 being sent to storage.
On the gasification side, the improvement of the air separation techniques together with the enhancement in the availability are the main requirements to make IGCC plants competitive. On the gas turbine side, the development of highly efficient low-NOx combustors for hydrogen fuel is one of the main technical developments required on the way to IGCC development.
Due to the high burning velocity of hydrogen in air, premixed combustors, the standard technology for natural gas, are currently not available for hydrogen. The current technology for hydrogen combustion is based on diffusive flames, where nitrogen oxides (NOx) reduction is obtained through the injection of large amounts of nitrogen or steam.
Enel Research in hydrogen: The Fusina Project
In order to assess both technical and economic risks related to the use of IGCC plants with CCS, Enel has been investigating all aspects related to these ‘next generation’ plants from the 1990s. The production of synthetic gases from coal gasification has been extensively studied at Enel’s laboratories. Moreover, experimental characterizations of hydrogen fuelled combustors have been performed at the Sesta experimental facility at full load, full pressure conditions.
The Fusina Hydrogen Project was launched in 2004, aimed at the engineering, procurement, construction and demonstration of the world’s first industrial-scale, hydrogen fired CCGT. Rated for an overall electrical power of about 16 MW, the Fusina hydrogen plant consists of a gas turbine able to use hydrogen as the main fuel and a condensing-type heat recovery steam generator (HRSG) for maximum energy recovery.
The main goal of the Fusina project is to develop and demonstrate on an industrial-scale an innovative, hydrogen fuelled combustor with NOx emissions below 100 mg/Nm3. The first step of the development programme, started in 2006, was to modify the existing natural gas diffusive combustor of a GE10 gas turbine, featuring steam injection for NOx reduction, to allow the original machine to run with pure hydrogen with only minor modifications. The modified combustor was tested in Sesta in 2007 and then installed in the Fusina demonstration plant.
Further tests carried out in Sesta in 2009 demonstrated that an increase in primary air and an improved solution for steam injection can produce a further positive effect on NOx emissions, achieving NOx concentrations in the exhausts below 200 mg/Nm3 with acceptable steam-on-fuel ratios.
The project is also aimed at assessing the operation of a hydrogen-rich gas mixture combustion in a high-efficiency CCGT with a specific focus on the impact of long-term hydrogen operation on the turbine’s hot parts – turbine blades and combustor components. For this purpose the Fusina plant will be operated with hydrogen-rich gas mixtures for several thousand hours in the period 2010–2011. Plant operation and components will be monitored through on-line diagnostic systems and off-line inspections at different working hours.
The Fusina plant
The Fusina plant consists of a 12 MW hydrogen fuelled gas turbine – a GE10-1 supplied by GE-Nuovo Pignone, which is closely integrated with the adjacent Fusina 320 MW coal fired power plant.
The plant is fuelled by the hydrogen that is generated as a by-product from the chemical plants in the nearby Marghera industrial area in Venezia. The size of the gas turbine was chosen according to the availability of hydrogen. The turbine has a simple design with a vertical combustion chamber, particularly suitable for research purposes.
The exhaust from the gas turbine is fed to a HRSG in order to produce steam. Part of this steam is re-utilized in the gas turbine combustion chamber to reduce NOx formation and increase cycle efficiency. Residual steam is sent to the coal fired plant to increase the thermal efficiency of the coal plant.
In the second part of the HRSG, the condensate from the power station is heated before being re-sent to the plant. A considerable amount of heat is recovered from the wet gas due to the condensation of most of the water, which is re-injected after treatment into the cycle of the coal fired plant. This integration allows an additional 4 MWe to be generated from the coal fired plant.
This means that overall, the hydrogen cycle delivers in Fusina as much as 16 MW: 12 MW from the gas turbine and an extra 4 MW from the coal plant. The hydrogen is carried to the power plant by a 2.5 km long pipeline at 27 bar [g]. Its typical purity is 96 per cent in volume, with a maximum value of 100 per cent. A dedicated procedure to run and stop the pipeline was developed giving special attention to the case of an emergency stop.
Early operating experience at Fusina confirmed the results of the experimental test campaign in the combustor test rig at Sesta in 2007. The strategy selected for reducing NOx emissions has proven its effectiveness, allowing NOx emissions well below 400 mg/Nm3 with low steam consumption. While first results can be considered encouraging, additional operating experience is needed in order to draw a final conclusion.
Regarding the efficiency, the integration of the heat recovery steam generation within the thermal cycle of the existing pulverized coal power plant increases the efficiency of the plant to close to 42 per cent, an important achievement considering the relatively small scale of the plant.
Another important outcome from the integration is that, by operating the coal plant at fixed load, coal consumption can be reduced by 1.43 tonnes/h, thus obtaining a reduction in CO2 emissions in the region of 3.4 tonnes/h.
Nevertheless, the main distinctive feature of the Fusina Hydrogen Project is the achievement of low NOx emissions while burning pure hydrogen, a target that is not fully achievable with presently commercial technologies because of the high flame temperatures generated by hydrogen combustion. The stoichiometric flame temperature of hydrogen is approximately 150 °C higher than that of natural gas. This causes an increase in NOx emissions: typical values are several hundred parts per million, three times higher than for natural gas.
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