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Cleaning up high-sulphur residue
Technology for helping refiners to minimise sulphur dioxide emissions.
As refinery operators turn their attention to processing high-sulphur crudes, one of the key issues they face is how to manage the high-sulphur by-products.
Refineries that produce large volumes of low-value, high-sulphur residues may perform capital-intensive upgrading to transform them into more valuable products and/or sell the residue as bunker fuel for the marine market.
New regulations for marine fuels, however, are making it harder for refineries to sell high-sulphur residue on the open market.
In January 2012, the maximum sulphur content in ship fuel was globally reduced from 4.5 to 3.5%; from 1 January 2020, it will be cut to 0.5%.
The sulphur content allowed in emission control areas, such as the Baltic Sea, the North Sea and the English Channel, is currently 1.0% and, as of 1 January 2015, this will fall to 0.1%.
According to an International Maritime Organization study, vessel operators will largely have to abandon heavy fuel oils once the sulphur content limit falls below 1%.
Refinery operators are already planning for this eventuality, as Joe Gelder, Business Developer Oil and Gas, Shell Cansolv, explains.
“With the market for high-sulphur marine fuel shrinking, refiners need an economic alternative for disposing of residue streams, as opposed to blending it with low-sulphur distillates,” he says.
“One option is to use it as heavy fuel oil to meet the refinery’s own energy requirements. However, this option requires an approach that ensures the refinery does not breach its emission limits.”
In order to give fit-for-purpose recommendations, we need detailed information on the assets and their specific operating conditions.
The Indian Oil Corporation Ltd (IndianOil), for example, is planning a grassroots refinery and petrochemical complex at Paradip in the State of Orissa, India, with the option to use some of its residue as utility fuel in its boilers.
The refinery will be able to process high-sulphur and heavy crude oils such as Kuwait and Maya, and stay within the emission limits.
As a part of the refinery project, IndianOil intends to install two regenerative flue gas desulphurisation units downstream of the utility boilers.
SO2 from the flue gases generated in the utility boilers firing high-sulphur fuel oil will be absorbed into a proprietary CANSOLV™ solvent.
The rich CANSOLV solvent will be regenerated to recover the SO2.
Shell Cansolv has provided a process design package for the SO2 scrubbing scheme that will be used at the Paradip development.
Gelder says, “The CANSOLV SO2 Scrubbing Systems will treat the flue gas from the utility boilers to produce sulphur and lower the SO2 concentration to reach the target emission levels to atmosphere.
“The design for IndianOil has two identical parallel trains of absorbers–regenerators; each will treat half the combined flue gas from the seven utility boilers.
The trains will share a central lean solvent storage tank and a solvent purification unit.
The total flue gas flow rate from the seven boilers will be about 1,550,000 Nm3/h.
The gas will contain about 6,750-ppmv SO2 on a dry basis.
The CANSOLV system will recover about 96% of the SO2 in the flue gas and the resultant SO2 levels in the treated gas will be less than 268 ppmv on a dry basis.”
Two regenerators will strip the absorbed SO2 from the absorbent.
The SO2 from each stripper will then be compressed and cooled before passing to a sulphur recovery unit for conversion into saleable sulphur.
The stripped absorbent will also be cooled and then returned to the absorbers to treat more flue gas.
This highly efficient, closed-loop cycle is in contrast to traditional, non-regenerative methods such as alkali scrubbing, which consumes large volumes of alkali chemical and produces high volumes of environmentally unfriendly process waste for landfill or waste-water treatment.
The CANSOLV SO2 Scrubbing System is suitable for all applications burning sulphur-containing fossil fuel.
It should bring significant benefits to the Paradip refinery, as an IndianOil representative explains.
“This technology will benefit IndianOil’s Paradip refinery and enable it to use high-sulphur fuel oil in its utility boilers while still maintaining environmental norms.
We will capture most of the sulphur the fuel contains and transform it into saleable elemental sulphur.”
“There were a few challenges to be overcome while designing the Paradip installation,” says Gelder, “One of the main challenges was the design of the pre-scrubber to pretreat the flue gas before the CANSOLV absorber.
The gas flow rate at Paradip will be high and will require adequate quenching; for this, we will have two levels of spray nozzles.
The design also had to account for the potential loss of quench water; if this should happen, we have designed a set-up that enables the water coming from the cooling water system to supply a separate quench line for use in an emergency.
The pipeline between the absorbers and the regenerator areas is very long, about 3 km each way.
To reduce the cost of piping, our design combines the rich absorbent from both absorbers in a single pipe, and then splits it at the strippers. We applied the same method to the lean absorbent,” concludes Gelder.
The use of residue as a refinery fuel could become an established model for new and existing refineries seeking to become “bottom-less”.
The method is particularly useful for refineries operating in gas-constrained locations where the cost of imported gas for utility fuel is prohibitively high.
“This is the first time in IndianOil’s refineries of using this option to meet our emissions mandate,” adds the IndianOil representative.
CANSOLV is a Cansolv Technologies Inc. trademark.