Sulphur recirculation: Longer lifetime and greater electrical efficiency
In the near future, the limits for steam temperatures will be closer to 500˚C. This provides completely new opportunities to utilise waste to generate electricity. The admission ticket is called sulphur recirculation.
Requirements to get more electricity out of waste are intruding. Plants in countries that cannot earmark heat for a district heating system have a growing need to increase electrical efficiency.
"If we are to increase electrical efficiency, it requires a higher pressure and temperature of the steam," says Ole Hedegaard Madsen, Director of Technology and Marketing at B&W Vølund.
Sulphur recirculation moves the limits
The challenge in this context is that the high temperatures of the steam place a strain on the boiler, because it causes corrosion. The latest plants operate with a temperature of 425 ˚C and a pressure of 55 bar. However, B&W Vølund’s proposition in the prestige project Copenhill 'Amager Bakke' in Copenhagen is to challenge the limit with the proposal of operating at 440 ˚C and a pressure of 70 bar. In addition, B&W Vølund has been asked for a proposal to operate at 480 ˚C.
"We can certainly make this proposal. It can be done, among other things, because with the purchase of Götaverken Miljö we have got the brand new patented sulphur recirculation technology in house," emphasizes Ole Hedegaard Madsen.
Sulphur recirculation removes the sulphur from the flue gas and returns the sulphur to the boiler for combustion, where it reduces the amount of the highly corrosive alkali chlorides. The addition of sulphur takes place in quantities that are closely balanced with continuous measurements of the chlorine content of the flue gas. Sulphur recirculation is based on the patent from the Karlsruhe Institute of Technology in Germany.
Doubles the lifetime of the tubes
"Sulphur recirculation halves the corrosion rate, which in turn means that the tubes in the boiler can last twice as long. This is the simple reason that we can begin to move the existing limit of the steam temperature to 480 °C. If we move the limit, we have to be able to control the sulphur-chlorine balance," says Ole Hedegaard Madsen and adds: "Furthermore, sulphur recirculation has the added bonus that it reduces the formation of dioxins."
Read more about sulphur recirculation on Götaverken Miljö’s website
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