DONG Energy owns and operates seven power stations in Denmark fueled by internationally traded bituminous coal. Since the early 1980s, competitiveness has been supported by an efficient conversion from coal to wire in super critical boilers and turbines. DONG Energy also operates a double reheat plant with ultra super critical steam parameters, and based on experience from this plant, a revised concept for the double reheat steam cycle has been developed. The revised design (named the Master Cycle or MC) solves the problems with the very strong superheating of the bleed steam from the IP turbines and paves the way for an affordable double reheat technology. The core component of the revised design is a small separate turbine (named the tuning turbine or T-turbine) driving a 100% boiler feed pump in combination with a balancing motor/generator and delivering relatively cold bleed steam for the heaters normally bleeding on the IP turbines. The T-turbine is fed with steam from the first cold reheat steam line meaning reduced steam flow through the reheaters and higher main steam flow which is advantageous for cooling of the furnace walls. Based on the Master Cycle and Ultra Super Critical (USC) steam parameters, net efficiency of a single reheat plant can be improved from 47% to 48.5% without any deterioration of availability. Many double reheat plants with elements similar to those of the Master Cycle are in operation in the USA and their operational records are excellent. Higher net efficiency of a Master Cycle plant would mean solid CO2 reductions of 4% by comparison with a new single reheat plant. Much higher reductions could be achieved by replacing an old plant.

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