Boilers produce the steam needed to recover bitumen located in underground reservoirs. This type of bitumen recovery is called ‘in-situ’ because the bitumen extraction occurs ‘in place’, or underground. Steam is injected through a well into the reservoir to heat the bitumen until it softens the fluid to a point where it will flow more easily. The bitumen is then brought to the surface along with the condensed steam, which has since cooled and turned back into liquid water while heating the reservoir. The water is recovered from the produced bitumen, treated and recycled through the boilers to create more steam and re-injected.
As much as 80 per cent of the water used by boilers is turned into steam. The remaining 20 per cent becomes thick with salts and silica naturally found in the water and produced from the reservoir, which are increased in concentration as the water is recycled. This stream is termed blowdown water and must be disposed of in deep underground disposal wells or trucked offsite to approved disposal facilities. Through the Boiler Blowdown Reduction Technology (BBRT) project COSIA member companies are exploring new technologies to further concentrate the undesirable components, enabling more water to be recovered and recycled instead of being entrained in the disposal stream.
Technology and Innovation
Imperial Oil and BP are spearheading the BBRT project. One of the options under investigation is the boilers-in-series configuration. Instead of putting all the boilers in a parallel configuration as they are today in most in situ operations, the boilers-in-series concept places one additional boiler downstream of the group of parallel boilers, its feed stream being the blowdown stream from the group of boilers arranged in parallel. This secondary boiler is then ‘in-series’ with the upstream boilers. Boilers-in-series allows the concentrated water slurry or blowdown from the primary, parallel boilers to be fed into the secondary boiler. This produces more steam from the same amount of water while reducing the volume of blowdown water that must be disposed of.
The BBRT technologies, boilers-in-series and rifled tubes, provide a double environmental benefit since they both increase the amount of steam produced from the same volume of water while reducing the amount of waste. Both technologies can produce a steam output of 90 per cent with only 10 per cent of waste water or blowdown.
The boiler-in-series technology has been patented by Imperial Oil, whom is co-leading the BBRT Joint Industry Project (JIP) with BP Canada Energy Group. JIP participants include Canadian Natural Resources, ConocoPhillips Canada, Devon, Nexen Energy, Statoil Canada and Suncor.