The Integrated Gasification Combined Cycle (IGCC) plant generates electricity, hydrogen and steam from the heavy hydrocarbons resulting from the refining process (tar, a substance similar to bitumen). The electricity produced is sold to the Energy Services Operator (GSE), while the steam is transferred to the refining plants together with hydrogen.
TAR – GASIFICATION – FILTER CAKE
The IGCC power plant is divided into two main sections which host the two phases of the process. The first takes place in the gasification section, where the semi-processed product from the Visbreaker plant of the refinery (tar, similar to bitumen, a heavy fraction from the bottom of the barrel) is transformed, using oxygen, into a synthesis gas called syngas. Purified of the sulphur and metals, syngas is a clean gas, similar to methane, which is then fired in the second section of the IGCC plant, i.e. in the turbines of the combined cycle section.
Meanwhile, the metals which were removed from the syngas during the gasification process are compacted and recovered as a substance visually resembling coal, "filter cake", which contains high percentages of precious metals such as vanadium and nickel. The filter cake is sent to Germany, where the metals are recovered for use in a number of sectors: in the metalworking and pharmaceutical industry, for the production of paints, etc.
The hydrogen unit of the IGCC plant
THE HISTORY OF THE IGCC PLANT
In 1991, under the new National Energy Plan, in order to deal with the growing demand for electricity in our country, which was mainly met by fossil fuel-fired plants with high emission levels, the Italian Government asked some independent producers to install power plants using renewable sources and sources classed as equivalent to renewables. It was in this context that Saras launched its project for an IGCC (Integrated Gasification Combined Cycle) power plant, able to generate electricity through the gasification of the hydrocarbons produced by crude oil refining. An innovative process ensuring that the IGCC plant is fired by a clean gas, which in environmental terms is quite similar to methane gas.
Two stages of the construction of the IGCC facilities
In 1996, the project was financed by a combination of bank financing and shareholders’ capital contributions. Construction began in 1997, under an international joint venture composed of Snamprogetti, General Electric and Nuovo Pignone. The plant, which has installed capacity of over 575 megawatt (MW) and generates over four billion kilowatt-hours (kWh) of electricity per year, became operational in December 1999. This is the most important industrial initiative in Sardinia in the last 20 years.
The IGCC plant is a highly integrated and efficient process which, in addition to generating electricity, produces hydrogen and steam for the refinery in cogeneration mode. The IGCC plant’s technology is one of the best currently available for the generation of electricity and, certainly, the cleanest among those powered by liquid hydrocarbons. Moreover, it has been recognised by the European Union as a Best Available Technique for containing the environmental impact of refineries in that it minimises atmospheric and noise emissions.
The IGCC plant uses almost solely seawater, which is processed in a desalination unit. Thanks to its particular shape, the hybrid cooling tower (wet/dry) minimises the visual impact of the plume of water vapour which can be misinterpreted by the public as being “chimney smoke”, even though it contains no chemical substances. The integration of the power plant with the refinery reduces the overall impact of the industrial site in terms of atmospheric emissions, as recognised in the “Environmental Impact Assessment”. Although the process is very complex, the IGCC power plant achieved excellent results in terms of production and operating capacity right from the first year of operation.