Modelling and dynamic simulation of the 2nd generation oxy fired power plant - oxidant fan failure case

In large and complex processes use of simulators will take place more and more in the future to avoid and learn about transients and unexpected situations. There are plenty of dynamic simulation tools in the markets but most of them have been developed and used for quite specific and limited application areas. At the moment there are just few simulation tools which are capable to handle dynamically in the same simulation case challenging process areas like combustion, distillation, chemistry and control of very large process areas. For this reason, in this study, there was a need to carry out co-simulation where two dynamic simulation tools Apros and Aspen Plus Dynamics were combined together by using Matlab Simulink as an interface. The co-simulation approach was a way to construct large dynamic process simulation environment, where typical operational transients and failure situations of an oxy fired power plant were possible to test and analyze. Under EU 7th Framework Programme (FP7) the FLEXI BURN CFB project an oxy firing concept based on circulated fluidized bed (CFB) combustion and supercritical once-through (OTU) water steam cycle was developed and successfully demonstrated [1]. This project also generated a dynamic simulation model of the 1st generation oxy firing concept, as we call it. In the EU 7th Framework Program's project O2GEN (Optimization of Oxygen-based CFBC Technology with CO2 capture), the 2nd generation concept of CFB based oxy firing was developed. The target of the project was, at first, to increase O2 content in recirculated flue gas to see what kind of effect it has to the heat exchange and corrosion in the boiler. Secondly, the target was to carry out exergy analysis to increase the whole concept efficiency by decreasing energy consumption in the boiler, Air Separation Unit (ASU) and CO2 -purification unit (CPU). Based on these steady state analysis means the refined concept was then modelled for dynamic simulations which were carried out by using Apros and Aspen Plus Dynamics dynamic modelling tools in a co-simulation mode. This paper deals with dynamic simulation of the 2nd generation 600 MW oxy fired CFB once trough boiler. In this paper we will present the dynamic model which includes oxy fired CFB boiler, turbine island, ASU and CPU with all needed equipment like heat exchangers, pipes, pumps, air and fuel feeding systems, distillation columns and sequestration vessels. Automation like measurements, controllers and actuators are included in the model. The simulation case selected for this paper presents an analysis what happens when one of the oxidant fans trips on boiler full load operation and how to handle this kind of failure by decreasing the boiler load to sufficient level of regarding the available oxidant feeding capacity. There were several items which were taken into account in the boiler, turbine island, ASU and CPU side when this kind of failure takes impact. The main findings in the failure analysis will be presented. Finally, discussion and future aspects of the simulation approach described will be given