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Report on the Labsorb regenerative SO2 scrubbing system application at the Eni SpA refinery

We know that for many years refineries in the USA have been addressing reduction of SO2 and Particulate (PM) for both new and existing sources.

Andrea Amoroso Eni S.p.A., Divisione g
Nicholas Confuorto Belco Technologies Corp
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Article Summary
In addition, several refineries in other regions of the world, such as Canada, India, the Middle East, China, Taiwan and Europe have also been addressing reduction of these pollutants for new refinery sources. In Europe, for instance, the trend will be to follow the BAT (Best Available Techniques) report recommendation to use the best possible technologies in reducing such emissions for new sources.

At the present, several European oil companies are investigating methods to reduce SO2 and PM from their refineries. Selecting a path forward with regards to reduction of these pollutants can be quite complex.

In order to select the approach that makes the most economic sense while achieving the specific refinery emission reduction goals, the refinery engineers have to evaluate the reliability, the capital costs and the operating costs of each reasonable option. Compounding the complexity of that selection is the issue of solids and/or liquid waste disposal.

Many sources are considered in order to define the one that provides the most benefit for the capital spent. Historically that source has been the FCCU because it is typically the largest single source of SO2 in a refinery. Occasionally, however, the Crude Distillation Unit Heaters or the utility boilers (both when firing heavy oils or residues) also can significantly contribute to the total refinery SO2 emissions. EDV Wet Scrubbing Systems have successfully been used by refineries worldwide for reducing SO2 and particulate from each of these sources worldwide.

In cases where the amount of SO2 is high, large quantities of reagent are required. Subsequently large amounts of byproducts are produced. Handling, transporting and landfilling sludges such as gypsum can be very expensive. Further, lime based scrubbing is not really suitable for FCCU applications due to the rigorous 5+ years continuous operation requirement. The preferred alternative for long term operations is the use of sodium based reagents. Nearly all of the FCCU scrubbers in the world use this type of reagent. However, the discharge of waste water (the purge) from such scrubbers is becoming much more difficult to permit in certain areas. All this can be avoided by using the Labsorb regenerative SO2 scrubbing process. This process nearly eliminates all waste streams.

In 2003 Eni SpA placed in commercial operation a scrubber, for their FCCU, that utilises the Labsorb process for scrubbing SO2 at their Sannazzaro refinery in Italy. A second full scale FCCU flue gas scrubber utilising the Labsorb Process is presently in the final stages of construction at a refinery in the United States. This unit is expected to be in commercial operation in October of 2004.

This paper will describe the Labsorb process and its installation at Eni’s Sannazzaro refinery in northern Italy. Due to its features and its innovative nature, since it is the first application of this technology on industrial scale in the world, the Sannazzaro project has been included in the LIFE Environmental Fund Programme, with the project acronym of REFINARS (Refinery Absorption and Recovery Sulphur).

The LIFE environment fund programme is dedicated to the implementation of the environmental policies of the European Union and promotes the sustainable development through those innovative projects suitable to be transferred to the interest sector as a whole or to other European industrial sectors.

The Labsorb Process
The history of the development of the Labsorb process The Labsorb process is a further development of the Elsorb process invented at the Norwegian Institute of Technology2, and marketed exclusively, worldwide for the oil refining industry, by Belco Technologies Corporation ( Belco Technologies Corporation (also known as Belco) is the world leader in the design and supply of systems for reduction of SOx, Particulate and NOx from refinery FCC units. Belco is headquartered in Parsippany, New Jersey (USA) and is owned by a holding company with offices in Lyon and Paris.

Because of the potential advantages expected in many applications, much effort has been directed by the industry towards the development of regenerable processes that can recover SO2. However, so far the results have been rather meager. With wet systems a main obstacle has been to find suitable aqueous buffers which fit the chemistry of the SO2 system, or suitable organic solvents. Many demands must be met, such as chemical stability, non-toxicity, low price, easy availability, acceptable energy requirement for regeneration, etc. With dry regenerative processes, deterioration of the solid reagent/adsorbent and unwanted side reactions have been major disadvantages.

Since the Labsorb process operates with instantaneous reactions and high net absorption capacity per unit volume of absorbent, this process actually profits from a higher SO2 concentrations of the flue gas: Less energy will be required per unit of SO2 removed. In addition very little waste is left for discharge, and the main byproduct, concentrated SO2 gas, is ready for transformation into commercially valuable products. This makes the Labsorb process highly preferred in cases where disposal of scrubber waste (liquid or solid) is an issue.

A general overview
In addition to FCCU regenerator flue gas scrubbing, the Labsorb process is strongly considered as an alternative for other applications such as heaters and boilers burning resides, high sulphur oils or high sulphur coal. Important advantages of the Labsorb process, are that it offers potential for maximum absorption with acceptable energy/steam expenditure and less sulphate formation through oxidation. Furthermore, absorption and regeneration can both be carried out at comparatively high temperatures. Additionally, the Labsorb process offers the possibility for selective removal of accumulated sodium sulphate with very small losses of valuable chemicals. This allows for much lower operating costs than any other alternatives.

The Labsorb process is especially suited for treating gases relatively rich in SO2, but may also be competitive on leaner gases when disposal of buffer by-products is an issue.

Figure 1 shows a simplified flow diagram of the Labsorb process. The main process units of the Labsorb system are:
(a) The pre-scrubber utilising re-circulating low pH water for removal of particulates and SO3.
(b) The absorption tower for SO2 capture.
(c) The evaporator system for the release of absorbed SO2 from the rich solvent in the regeneration of the buffer
(d) The process unit for removing accumulating sodium sulphate.
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