2.0 General Overview
2.1 Trend in the Refinery Industry
In many countries most of the refineries have been equipped with severe processes, thermal (Coking) and catalytic (Hydrocaking, Catalytic Cracking, Dewaxing), aimed to transform the heavy hydrocarbons. These are processes capable of increasing the share of light products.
Neverthless in Italy this renewal has been delayed, being preferred less severe thermal processes, like Visbreaking and thermal cracking.
These processes have in input the residue from the bottom of the Vacuum column and produce as output other distillates plus a residue, precisely named TAR. Its characteristics are the high viscosity, which hinders its displacement, and the content of polluting elements, like sulphur (it ranges between 3 and 6% depending upon the quality of the processed crude) and various metals (mainly nickel, vanadium, iron).
In Italy the choice to limit investments required to face the evolution of the demand and to upgrade the refining plant, was practicable thanks to the availability of the National Electricity Board (ENEL) to buy and to burn the oil with high sulphur content obtained from such residues.
Tar represents a considerable part of the process crude, about 12-18 wt% as average figure, depending on its quality, and has a calorific value around 9400 Kcal/Kg.
When we consider the global capacity of the Italian industry, we can estimate the considerable amount of 7.5 million tonnes of Tar produced per each year.
In the past, and nowadays as well, it was mixed with lighter products with very low sulphur content to generate an output with high sulphur content (1-3%) and good calorific value, which is still burnt in the thermal power stations.
From 1997 the environmental regulation will not allow products with sulphur content over 0.25-0.30% to be burnt in power stations. This fact forces to find out a new way to work off the residue, or better, to contrive an use economically profitable.
The existing refinery plant has substantially three alternatives to conform itself to the new environmental regulations and need of the market demand at the same time:
A. Deep Conversion: it is a deep re-design of the refinery cycle. More severe manufacturing activities based on catalytic processes are installed in order to extract a larger quantity of light products. In this case the whole plant has to be re-designed and the cost is very high;
B. Tar Desulphurisation: the second possibility is to build a desulphurisation plant in order to clean the residuals and make them adapted to the requirements of the electricity industry.
This is too a quite costly alternative as these processes involve a complex technology;
C. Tar Gasification: the last available chance consists in the gasification of the residuals. It yields a fuel gas suitable to feed gas turbines and therefore to generate electricity in a combined cycle. Whenever the electric power generated may a have a good economic value, this choice results the most interesting alternative and the investment in the gasification plant can be recovered in a reasonably short time.
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2.2 The Italian Electricity Supply Industry
Italy is extremely poor in primary energy sources. A large amount of produced energy comes from imported fuels, our country is experiencing an increasing difficulty to meet the demand for electricity in compliance with the environmental regulation.
The market for high and medium sulphur fuel oil (3.5% - 2% wt) is declining rapidly and refinery must either make a major capital investment to change their product mix or make a better use of their heavy products.
This is particular true for ISAB Refinery which was originally designed to process heavy crude oil. Different alternatives were evaluated: at the end, rather than invest in an extensive desulphurization programme, it was decided to implement a more economic alternative of gasification of its oil residues and production of electricity for sale to ENEL.
The choice of the Italian oil industry to produce electricity to be sold to ENEL has a justification in the law in force since 1991 which allots a price really attractive for the electricity produced with IGCC power stations.
The IGCC technology complies with two fundamental needs of the national energy industry:
the disposal of the refinery residual with high sulphur content and the construction of new capacity for the electricity generation.
3.0 Plant Description
Feedstock (asphalt, visbroken tar, heavy fuel oil, etc.) is introduced into the gasifiers which are operated at a temperature above 1400 °C and a pressure of about 70 barg.
Gasification takes place in the presence of oxygen and high pressure steam acting as a temperature moderator. The syngas and solids (consisting of unconverted carbon and ash) are quenched by water sprays before they exit the gasifier. The solids are trapped in the quench water, leaving the syngas clean and relatively cool. Unconverted carbon is recycled back to the gasifier to achieve 100% carbon conversion, using naphtha as the soot carrier. Quench grey water from the gasification is treated and filtered to recover a metal cake which contains large amount of nickel and vanadium. The metal cake is intended to be sold to metal reclaimers.
Thereafter the process waste water, after a further pre-treatment for ammonia removal, is sent to a municipal treatment facility.
The particulate free raw syngas is then further cooled through heat exchangers, generating medium pressure steam which is utilized to generate electric power in the steam turbines. The sulphurous compounds in the syngas (acid gas) are removed so that the sulphur emissions in the form of SO, are minimized when the syngas is burned in the combustion gas turbine.
From the acid gas removal unit, the sulphur offgas is sent to a Claus sulphur unit to convert 99.8% of sulphur offgas to elemental sulphur suitable for by-product commercial sale. The virtually sulphur-free, high pressure syngas is then sent to the gas turbines, via a gas expander that recovers the high delta-pressure of syngas through 10 MW electric power and a humidifier which saturates the syngas in order to avoid high NOx formation in the combustion chamber of gas turbines. The exhaust gas from the two gas trrbines is ducted to heat recovery steam generators which produce high pressure steam used: (i) to drive the steam turbine generators to produce additional power; and (ii) as a temperature moderator in the gasifiers.
Additional syngas is combusted in supplemental burners in the heat recovery steam generators to produce additional steam for the steam turbines.
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4.0 Technologies adopted 4.1 Texaco Gasification Process
The main licensor of the IGCC Complex is Texaco that designed gasification section. ISAB Energy gasification will be the first in the world to operate with asphalt. Texaco has tested heavier feeds in Montebello Gasification Pilot Plant.
Two gasifiers convert asphalt produced from the visbroken tar of refinery, through a Solvent deasphalting plant of Kellogg Technology, into a fuel gas for the Combined Cycle. Syngas produced from gasification reaction, at a temperature above 1400 °C , is cooled down to 250
°C using a water stream injection to control the reaction avoiding the oxidation of CO into C02.
4.2 Heavy Metal Recovery
The grey water from gasification section is processed to remove sulphides, cyanides, thiocyanates and suspended solids including all the heavy metals. Chemicals injection (caustic soda, polyelectrolite, ferrous sulphate, etc.) will favour the precipitation of dissolved salts of heavy metals and the other compounds mentioned and concetrate the precipitate in a filter press to yield a "cake" containing approximately up to 28% vanadium and up to 9% nickel which are intended to be sold for heavy metals recovery.
4.3 Acid Gas Removal
This is a conventional technology employed in the refining, petrochemical and natural gas industries. The acid gas removal system utilises a solution of Methyl-Di-ethanolamine (MDEA) solvent solution to wash the gas and concetrating H2S gas routed to Sulphur Recovery system. The process operates at relatively low temperature to improve selectivity and avoid co-absorption of C 02 into R2S gas.
The washing absorbs virtually all the H2S and a very low amount of C02 yielding a purified fuel gas of less than 15 ppm total H2S + COS and less than 10 ppm total HCN and NH3 by volume.
4.4 Sulphur Recovery
The sulphur recovery process is based on the Claus reaction in which H2S and SO2 react to form elemental sulphur. Most of the Claus plants use air for this process; however, many of the units installed over the last few years have determined it is more economical to use oxygen, especially if an oxygen plant is being installed for another purpose as is the case for ISAB Energy Project.
About 50% of conversion to sulphur takes place in the combustion chamber; the gas leaving the chamber is cooled to condense sulphur vapour. The heat removed from the gas is used to generate medium pressure steam. The remaining conversion of the sulphur gases to elemental sulphur occurs in two stages of catalytic reactors.
The liquid sulphur produced will be sent in an off-site solidification plant to produce about 190 tonnes per day of sulphur in pellets to be sold to external companies.
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4.5 Combined Cycle
The power plant design comprises two combined cycle gas turbine modules. Each module consists of one Siemens type V94.2 gas turbine modified for use with low calorific syngas from the gasification plant, one supplementary Heat Recovery Steam Generators (HRSG) and one re-heat condensing steam turbine generator unit. The proposed rating for the gas turbine is approximately 161 MW per unit and the proposed rating for the steam turbine unit is approximately 95 MW per unit. An additional 10 MW is generated in the gas expander.
4.6 Auxiliary Systems
The IGCC Complex will be equipped with all the necessary auxiliary systems including cooling water (a closed circuit with about 60.000 m3/h of circulating sea water), demi water, desalinated water (through two MED Desalination Units with a capacity of 300 m3/h each), air, fuel-oil and fuel-gas utilities, flare and blow-down system, electrical distribution, firefighting system, buildings, etc.
Herebelow a schematic block diagram is shown.
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5.0 Plant Performance . f The perfomance of the IGCC Complex in converting heavy oil into electric energy is is |
dependent on the level of load, the ambient air temperature and, to a lesser extent, on the
characteristics of the feed. Herebelow the normal operating case performance are reported: ;
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6.0 Environmental 6.1 Solid Effluents
6.1.1 Filter cake Production and Management
Filter cake is a by-product of the gasification process produced in the heavy metals recovery unit of the IGCC Complex. The composition of the filter cake, in particular the vanadium and nickel content, makes it a marketable product to the metallurgical industry. According to the current Italian legislation, the filter cake will be classified as a non-toxic hazardous material which will require special handling. The filter cake production rate will be approximately 7.5 tonnes per day (as dry material) for normal operation with asphalt.
ISAB Energy is currently developing a strategy for the management of the filter cake and is finalizing preliminary contracts with different potential reclaimers.
Taking into account the world-wide Vanadium production (about 25000 tonnes per year), ISAB Energy production will represent about 2.5 % wt.
6.1.2 Sulphur Production and Sale
Elemental sulphur is a by-product of the gasification process produced during the syngas clean-up. The sulphur is of a commercial grade suitable for sale to agricultural and chemical industry market. The sulphur production rate is approximately 60.000 tonnes per year.
6.2 Liquid Effluents
The sanitary and pre-treated process water coming from IGCC will be routed to a Municipal Treatment Plant; the blow-down from cooling tower system will be discharged to the sea after inspection in a suitable pit.
6.3 Gaseous Effluents
Due to ecological plants provided in IGCC Complex and to the final treatment of the flue gas in a SCR system (Selective Catalytic Reduction) located in the HRSG of the Combined Cycle the emissions are largely below the current environmental regulations.
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7.0 Main Commercial Agreements 7.1 Feedstock Supply Agreement
Erg Petroli and ISAB Energy have entered into a 20 years feedstock supply agreement.
Feedstock means principally asphalt but also, in case of unavailability of asphalt, other types of feedstocks either sourced from the Refinery (such as visbroken tar, vacuum residues, fuel oil) or purchased from third parties.
Erg Petroli's primary obligation is to supply asphalt, provided that where asphalt is not available for any reason, Erg Petroli will supply an equivalent alternative feedstock.
7.2 Power Purchase Agreement
The terms of the sale of electrical energy to ENEL are set forth by two agreements with ISAB Energy. These agreements, known as the Convenzione Preliminare ("Preliminary Agreement") and the Accordo Integrativo ("Integrative Agreement"), together with a series of laws and decrees which they reference, provide all the key legal and commercial terms of the agreement.
The price settlement was defined by CIP Resolution No. 6 of 29 April 1992 which sets out the tariff arrangements to be applied to independent producers of electricity.
ISAB Energy will receive a price according to CEP 92 resolution.
7.3 Oxvgen Supply Agreement
The gasification process requires large quantities of oxygen and nitrogen. Ail Liquide will supply on a long term basis "over the fence" to the Project. The oxygen plant will be located on a plot of land adjacent to the Project Site. The oxygen Supplier will guarantee a supply of more than 100.000 cubic meters per hour of 95% pure oxygen.
7.4 Operating and Maintenance Agreement
The Sponsors propose to create a Company named ISAB Energy Services who will operate and maintain the Project. The shareholders will be Erg Petroli (51%) and Edison Mission Energy (49%).
7.5 IAS Agreement
Industria Acqua Siciliana is a local service company managing waste water discharges in the area and treating them in an existing waste treatment plant located in Priolo. IAS is a public/private consortium whose shareholders are at the same time users of the plant. All private shareholders/users bear the costs of the plant on a basis proportionate to their usage.
Upon successful completion of negotiations with IAS, ISAB Energy has become a shareholder of IAS and will discharge to the Plant a maximum of 170 m3/h of pre-treated water.
7.6 SNAM Metano Agreement
In order to cope with the fuel gas consumption of IGCC Complex, normally utilized for pilots of flare and hot-oil and Claus Units furnaces pilots, an agreement for the supply of natural gas was defined with SNAM Metano Company.
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8.0 Financial Overview
The ISAB Energy IGCC Plant is financed through a limited recourse project financing scheme.
All the tasks related to the successful completion of the project financing development have been completed in July 1996 (Financial Close). This result is particularly significant because this is the first time that an IGCC Plant is completely financed without using government funds. This has been a result of intensive activities aimed from one side to finalize main contracts with ENEL, Oxygen Supplier (Air Liquide), Feedstock Supplier (Erg Petroli), and other minor Parties and from the other side to demonstrate to the Technical Advisor (Stone &
Webster) the robustness and well proven experience of the technologies involved.The Total Project Capital Costs amount to Lire 1.900 billions. Funds made available from ISAB Energy's financing arrangements will be expended over a construction period of approximately 3.5 years and repaid over a period of approximately 8.5 years. At the earlier of commercial operations the Sponsors will infuse equity in the amount of 25% of actual Project Costs.
9.0 Project Status and Schedule
The Project will be built under a lump-sum turnkey construction contract (LSTK) which will incorporate terms already agreed between ISAB Energy and the Contractor pursuant to a Memorandum of Understanding signed in March 1995. The Contractor, Consorzio SnamProgetti - Foster Wheeler - Energy, was selected after completion of a competitive international bidding process. After a six months Open Book Phase (June-December 1995) and the definition and signing of a LSTK Contract including engineering, construction and taking over of the Plant, a detailed engineering has been developing from Febraury 1996. On July 17, 1996 the notice to proceed and the official start-up of Construction activities took place. Soil consolidation works and earth movements started in September and are currently in progress. At the current date (early December 1996), engineering development was at 30% of the schedule whereas material purchase orders at 5%. Completion of engineering is foreseen by October 1997, whereas the start-up of commercial operation is scheduled by the end of
1999.
References
1. J.C. HOLDSWORTH, G.D. TOBIN: "Processing Options for Heavy Residues"; Foster Wheeler Publ., 1993.
2. A. ARIOLDI, G. BERGAMASCHI: "La gassificazione del tar in Raffineria"; La Rivista dei Combustibili, Vol. XVL, fasc. 10, 10 ottobre 1991.
3. F. BIFULCO: "La gassificazione dei residui petroliferi pesanti associata al ciclo combinato per la produzione di energia elettrica e ambiente"; Atti del Convegno ATI 1992.
4. G.BELLINA, G.CAMMARATA, M.CIANCIO, A.FICHERA, L.MARLETTA; "First and second law analysis of an IGCC with Tar Gasification"; Atti del Convegno ATI 1996 "Energy and Environment towards the Year 2000".
5. EEFE; "Assessment of the External Costs of Integrated TAR Gasification Combined Cycle"; April 1995.
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