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Implementation of marginal quantities in management of cogeneration units operating in liberal market environment

Miroslav Variny and Otto Mierka

Institute of Chemical and Environmental Engineering, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinsk√©ho 9, 812 37 Bratislava, Slovak Republic



Received: 2 June 2009  Revised: 4 September 2009  Accepted: 10 September 2009

Abstract: It is far more important how the cogeneration units are operated than whether they represent the latest technology progress or not. Therefore, for the management of cogeneration units it is a key issue to find optimal operating conditions bringing in the largest income. This may be achieved by combined marginal and overall performance criteria application. To prove this statement, two cogeneration units operating in the Slovak Republic, marked as A and B, were examined. Both of them use the liberal market environment and participate in provisioning ancillary services. Marginal profit values without and with ancillary services provisioning clearly indicate the most advantageous base load value, which is in both cases in the middle of the load regulation range. As shown, together with the total profit function, they are very suitable indicators of the optimal load location and a flexible tool for the market situation evaluation. Heat delivery capability of B to customers reaches its maximum at the middle of the load regulation range, again reinforcing the optimal part load operation. Being equipped with supplementary firing, the marginal steam production of B was found to be higher than 100 % which confirms that the rules for marginal quantities values are not as strict as those for overall and specific quantities.

Keywords: cogeneration unit - marginal quantity - gas turbine - heat recovery steam generator - fuel consumption

Full paper is available at

DOI: 10.2478/s11696-009-0097-4


Chemical Papers 64 (2) 163–173 (2010)

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