Italy: where industrial IGCC came of age6 May 2002
The practical engineering feasibility of full scale integrated gasification combined cycle (IGCC) power plants has been demonstrated by the first three such projects in Italy. David Smith
In IGCC, as in so many other key advances in electric power supply technology, including high head pumped storage hydropower, high solids density coal slurries, 1000 kV transmission systems, and high capacity submarine HVDC cables, Italy has led the way.
The Italian IGCC plants have been installed in association with petrochemical plants largely to meet legal requirements for the disposal of hazardous refinery waste residues.
Most of the indigenously produced electricity was generated from heavy residual oil fuel containing 3 per cent sulphur discharged from the country's large oil refineries. The European Union had to clamp down on this source of environmental pollution, and directed that the sulphur content of fuel oil must be reduced to 1 per cent.
The effect was that the domestic refiners would have to incur potentially crippling capital investment and operational costs. With remarkable perception, the Italian government came up with new legislation which yielded a very favourable economic solution. They introduced power price incentives for independent power producers that consumed indigenously produced fuels, thus killing several birds with one stone. ENEL was required to pay well over the going rate for electricity supplied from the first four IGCC's over the first eight years of the 20 year electricity contract term, paying a price equivalent to 9.0 cents/kWh, reducing to something like 5.7 cents/kWh for the remaining twelve years (based on 1995 values and $1 = 1550 lira) compared with a typical world price of around 7 cents/kWh at the time.
Four proposals for adding gasification power plants to refineries were submitted very promptly, in addition to the Sulcis coal gasification project. The one project which missed out of the first round was the Sannazzaro plant, which is now back in the running as an independently financed commercial project.
Unlike the USA, Germany and China, where early gasification projects have also been associated with chemicals and petrochemicals applications, the technology's potential for the salvation of the indigenous coal industry is a less promising prospect for Italy, in spite of its substantial commitment to ageing pulverised-coal power plants and the abandonment of nuclear power - unless the price of natural gas feedstocks goes through the roof, as some pundits predict.
Smaller demonstration projects for coal fed gasification power plants in the USA, Netherlands and Spain have been very successful in demonstrating good performance on a vast range of fuel feeds as well as the potential for separating greenhouse gas CO2 for disposal at very little cost.
But to be truly competitive in today's open markets it will probably be necessary to co-produce commercial chemical products, cogasify waste materials and cogenerate process heat and power.
IGCCs in operation
The three operating Italian IGCCs are:
• The 510 MWe ISAB Energy plant on Sicily at Priolo Gargallo, gasifying 3173 sTPD of deasphalter bottoms and using two Siemens V94.2 based integrated combined cycle units supplied by Ansaldo to produce the electricity.
• The 280 MWe API Energia project at Falconara Marittima on the Adriatic coast,
gasifying some 1470 sTPD of visbreaker bottoms with two gasifying trains fuelling a single ABB GT13E2 based combined cycle power plant with an Ansaldo steam turbine.
• The 550 MWe Sarlux project in the SARAS refinery at Sarroch in Cagliari. This is gasifying 3771 sTPD of visbreaker residues to fuel three GE S109EC single shaft combined cycle units.
These three projects all have various degrees of integration of the power generation or air separation plant functions with the gasification product stream systems, which generally yields a couple of extra points of thermal efficiency to the process.
Both the ISAB and the Sarlux plants are fully integrated systems using Texaco gasifiers but with quench coolers rather than heat recovery boilers. API Energia uses only partial integration with the air separation unit.
They are all oxygen blown units - air blown units are now considered uneconomic.
The trend in the future is likely to be non-integration to the point where syngas will be supplied to outside-the-fence power generating plants, as will products such as hydrogen, methanol and CO2, to whatever markets look most promising.
A big attraction of gasification is its adaptability to a wide range of valuable products at any stage of the project operating life, particularly if the doubtful benefits of integration are sacrificed in the name of flexibility. If and when the prices of natural and crude petroleum from politically unstable countries go through the roof, the gasification plant's ready adaptability to producing Fischer-Tropsch liquids to convert into diesel fuel and motor spirit will be an invaluable resource to any country with no indigenous deposits.
The 510 MWe ISAB Energy plant was the first Italian IGCC to go into commercial operation. It was handed over to the operator in April 2000, financing having been closed in July 1996.
The plant had been ready to commence performance tests in November 1999, but equipment failure resulted in a protracted shutdown. The plant was restarted in January 2000, and the units were aligned during the next two months before proceeding with acceptance tests.
Both the ISAB and Sarlux plants were built by a consortium of Snamprogetti and Foster Wheeler Italiana and use the ubiquitous Chevron Texaco gasifier. The two quench type gasifiers convert 132 t/h of asphalt produced from the visbroken tar at the refinery by Kellog ROSE deasphalting. A Claus desulphurisation unit removes the sulphur after MDEA separation, for sale as a high purity elemental byproduct.
As ever, among the benefits produced by these first units have been the interesting surprises from the initial operating experience.
At ISAB they found that the syngas, which consists purely of hydrogen and carbon monoxide, had an initially higher than expected H2/CO ratio on lighter feedstocks, which could be a problem for gas turbines since if hydrogen is not sufficiently diluted the combustor flames will be far too high and surge margins will be affected. Where CO is extracted for greenhouse gas separation, nitrogen has to be added from the ASU for dilution.
When processing the intended asphalt feeds the anomaly did not occur, but in any case, burner tests by Siemens showed that the gas turbine combustors could handle the variation.
The apiEnergia IGCC is possibly the most highly integrated of the three projects, using two Chevron Texaco quench gasifiers and scrubbing sections, each rated at 56 per cent of the plant throughput requirement with Arabian heavy feedstock. The GT13E2 gas turbine is an advanced high efficiency development with an ISO output of 164 MWe running on natural gas.
Operating on the syngas produced in the gasifiers, the output is increased to 189 MWe due to the extra mass of gas passing through the machine for the same amount of heat. The plant is a largely ABB (now Alstom) contract bringing together ABB Sadelmi SpA, ABB Lummus Global GmbH, and ABB Power Generation Ltd.
Contracts were signed in November 1996. Following some minor teething troubles during commissioning, turbine testing on syngas was completed in July 2000. After reaching provisional acceptance in February 2001 and final acceptance in April 2001, the project is now in full commercial operation and has been running at full output at high availability for nearly two years.
The three train low pressure quench gasification process for the Sarlux plant converts the feedstock to syngas at about 1400°C and 38 barg. The syngas, which is immediately quenched with water, consists mainly of hydrogen, carbon monoxide with small amounts of methane, hydrogen sulphide, carbonyl sulphide, and trace amounts of ammonia and hydrogen cyanide before it is scrubbed in a recirculating grey water system to remove particulates. Soot is extracted from the scrub water by naptha absorption and recycle to maximise carbon recovery.
The Sarlux IGCC was handed over to the owner after passing the MPS test in January 2001, with a net power output 535.4 MWe compared with the target of 500 MWe, and hydrogen production of 18 359 Nm3/h compared with the target output of 18 000 Nm3/h.
In addition to these three operating Italian projects, three further IGCC plants are in the planning stage:
• The Sulcis project, which aims to gasify low grade coal from deep vertical seams on the Island of Sardinia. This has not yet been funded or approved.
• The PIEMSA project, at the Repsol YPF Petronor Refinery near Bilbao in Northern Spain. This would gasify 4680 sTPD of visbreaker bottoms and produce 785 MWe for ENEL from two GE 9FA systems and a single steam turbine.
• The AGIPpetroli project at its Sannazzaro refinery in Northern Italy. This would gasify visbroken vacuum tar from two 600 t/day Shell gasifiers to produce 1000 MWe of electric power for ENIpower from a combined cycle power plant.
It is interesting that while petrochemicals giant AGIP was able to exploit the economic potential for large scale electricity production from its own refinery in Italy, former state power utility ENEL had to turn to a Spanish refinery to exploit the syngas synergy.
It is far from certain that SULCIS will ever be built. The motivation behind the project is the desire to reopen local coal mines to solve a serious unemployment problem in the area. The concept, nonetheless, is very appealing.
The coal is sub-bituminous with characteristics that make it a very suitable feedstock for gasification but very difficult for any other mode of power generation.
Being the only such source in Italy with large reserves (estimated to be over 50 million tons), the Sulcis-Iglesiente seams are an important national resource.
The concept is loosely based on two trains of the developed Shell demonstration plant at Buggenum in the Netherlands now owned NUON. The combined cycle plant would use the same Siemens gas turbine with the extra high pressure stage to increase the margin against operational instability, since known as the V92.4K, as used in the ISAB Energy plant.
The main industrial groups involved in the project are Sondel SpA, Group Protecma and Ansaldo Energia. It is difficult, however, to disassociate the costs of the project, which would have to be project financed, from the cost of reopening and operating the coal mines.
The geology and the characteristics of coal here would suggest that underground gasification would be a better proposition in terms of generating economics, particularly after the successful EU test results from a project in Spain, but this would do little for the local unemployment problems.
The PIEMSA project at the Petronor refinery near Bilbao is again based on a fully integrated gasification combined cycle plant with two Chevron Texaco quench gasifier trains and two gas turbines coupled to a single steam turbine. The planned output is some 21 500 Nm3/h of hydrogen for the refinery and gross power output of 935 MWe, with a net power output for ENEL of 785 MWe. Commercial operation is envisaged for late 2004/early 2005.
There would be no government subsidies or special electricity rates for this project, it would be a purely commercial IPP project.
Feasibility studies indicate a worthwhile ROI in a situation where an equivalent natural gas fired GTCC would produce electricity at a cost of about 0.043 $/kWh, but this does not appear to take into account the benefits to the refinery. The presence of the IGCC is said to allow an extra production of 500 000 t/y of distillates and 1 500 000 t/y of vacuum visbroken tar are processed in the IGCC, producing 6280 GWh/y with elemental sulphur as a saleable byproduct.
Like PIEMSA, the new Sannazzaro IGCC will need to be project financed without subsidies or fiscal incentives on a purely commercial basis. It will have two 600 t/day Shell gasification trains slightly larger than the three trains operating at Pernis in the Netherlands.
The vacuum flashed visbreaker residue here is run down into a common feed vessel with a feed heater which may be used if the residue is supplied from tankage rather than directly from the process.
The gasification plant is part of a project to build a new 1000 MWe power station. Again there is a degree of integration, while the gas turbines are designed to burn syngas or natural gas in any ratio.
The soot from the syngas scrubber will be filtered through membrane filter presses and passed on to a mulitple hearth furnace for drying and carbon burn off to produce a saleable nickel/vanadium containing ash. This has the dual advantages of rendering the gasification process independent of the soot/ash process and increases the operating window for the feedstock quality.
The basic and design engineering package has been prepared and the project is currently in the permitting phase.
The way ahead
The development of gasification technology in Italy has not only led to substantial increases in electricity generating capacity and spawned a degree of technology maturity that the rest of the industrialised world can now benefit from, it has yielded a substantial improvement in security of energy resources for everybody.