New invention
removes sulphur
from coal-fired power stations
Atle Kjærvik
A process that is capable of removing as much as 99% of the sulphur dioxide (SO2) from the gases in coal-, oil-, and gas-fired power stations, has been invented by Professor Olav Erga of NTH. "With this process fully developed, environmentally friendly coal-fired power stations can become a reality in the future," says Erga.
The ELSORB plant at Esso's Slagentangen refinery.
A cleansing plant based on Erga's process is now in operation at the Esso Oil refinery at Slagentangen near Tønsberg in Norway. The process, named ELSORB, recovers sulphur from the tail gas of the refinery´s 24 ton sulphur per day Claus` plant. Thereby, the SO2 concentration is typically reduced from 10 000 to less than 200 parts per million. The recovered sulphur is a commercial product which can be utilized by a.o. the fertilizer and the cellulose pulping industries.
Patent sold
Erga developed his process with the support of the Research Council of Norway (NFR) and SINTEF/SINVENT. Patent rights to the process have been transferred to Elkem Technology, which has developed the Slagentangen plant in collaboration with Esso, the Ministry of Environment, the State Pollution Control Authority (SFT) and The Research Council's Expomil programme. SFT and NFR have contributed about NOK 9 million of the total cost NOK 25 million. The equipment costs alone are estimated at NOK 15 million. Esso has installed the scrubber at its refinery as a combined demonstration and recovery facility. The aim is to recover 99.9% of the sulphur dioxide produced by the refinery.Coal-fired future
More than 50% of the world's electricity is generated by coal-fired power stations, at the cost of huge emissions of sulphur dioxide, and thus acidification of the environment. A typical small coal-fired power station (100 MW) may produce from 20 000 up to 30 000 tons of sulphur dioxide a year, depending on the type of coal it burns. However, less than 30% of the world´s power stations are fitted with scrubbers."The world's coal reserves contain much more potential energy than oil. If we do not develop an alternative large-scale, cheap, environmentally friendly source of energy, coal is likely to be the most important source of energy in the coming century," believe Erga.
"The problem is that of finding an environmentally friendly way of exploiting our coal reserves. In the USA, for example, there are large seams of coal with such a high level of sulphur that it cannot be used to fire power stations at present. SO2 scrubbing by means of to-days technology is simply too expensive. ELSORB turns coal into an environmentally friendly fuel, in that the process becomes even more advantageous the higher the SO2 content of the flues gases," he says.
NTH's Professor Olav Erga
Competitive technology
Most coal-fired power stations that are fitted with scrubbers, utilize SO2 processes based on lime or limestone for capturing SO2. The drawback of these processes is that the product is gypsum ore sludge, most of which has to be dumped. 20,000 tons of SO2, for example, creates 50 - 60,000 tons of gypsum waste, which is costly to deposit."The ELSORB process is simple and cheap. Coal-fired power stations, boilers and oil refineries are the biggest markets. The installation and operating costs of an ELSORB plant installed at a power station will be about the same as those of a calcium-based plant, but the great advantage of our process is that it recovers SO2 regenerates the absorbent ", says project manager Paul E. Jensen of Elkem Technology. "This means that the process does not just create a new waste product that has to be dumped or thrown away. In fact, the SO2 is recovered as a marketable product, that can be used by industry in a number of production processes. The fertilizer, cellulose and chemical industries are all potential users of different types of sulphur products," says Jensen.