Heavy oil developments in the Athabasca area require large quantities of steam, and this becomes a major expense when natural gas is used in Once Through Steam Generators. This paper reports on an exploration of possible ways to reduce these costs by using alternative fuels obtained from an integrated upgrader.

Depending on the upgrader selected, associated waste streams are produced such as petcoke, asphalt or unstable vacuum residue from which little or no value can be drawn in the Athabasca area except by exploiting their heating value. Combustion of these waste streams is not technically a problem, but the cost of using an alternative fuel is strongly impacted by the specific water treatment required and the problem of sulphur oxide emissions.

Present configurations for heavy residue boilers require high-quality demineralised water, and the related water treatment represents a higher cost than for the partly softened feed water used in conventional Once Through Horizontal Steam Generators (OTHSG). Combustion of high sulphur fuels calls for an efficient desulphurisation method in order to meet the increasingly stringent statutory emission limits. Traditional methods using limestone involve injection and the problematic disposal of large quantities of solids.

This study has characterised four types of upgrading residues, namely petcoke, asphalt, unstable vacuum residue and heavy crude oil, in terms of their nature and sulphur content. It has determined for each fuel the appropriate boiler configuration, including flue gas depollution and water treatment, and compared its cost with that entailed in the common practice of producing steam with natural gas in Once Through Steam Generator (OTSG) field units. Regenerable SO2 scrubbing techniques coupled with Claus units have been investigated, as possible means of producing pure liquid or solid sulphur. By converting upgrading residues into syngas by partial oxidation, cleaning up the syngas by removing its sulphur and sending the clean syngas to OTHSG unit, both the water treatment requirements and the SO2 emission limits can be met. The cost of such a solution has been compared to that of direct combustion of residues in a boiler.

You can access this article if you purchase or spend a download.