Simulation studies on oxy-cfb boiler

Transcription

1 Simulation studies on oxy-cfb boiler dynamics and control 3 rd Oxyfuel Combustion Conference Jari Lappalainen a, Hannu Mikkonen a, Mikko Jegoroff a, Andres Sanchez-Biezma b, Jenö Kovacs c, Antti Tourunen a a VTT, Finland b Endesa, Spain c Foster Wheeler Energia Oy, Finland

2 2 Overview Background and motivation Modelling Simulation results Conclusions

3 3 EU Project: Flexi burn CFB The Flexi-Burn CFB concept: High efficiency Circulating Fluidized Bed (CFB) power plant with CCS capable of air/oxy operation with a wide range of fuels including biomass CIUDEN 3 MW

4 4 Motivation Development of a novel boiler plant concept begins with steady state modeling Dynamic modeling is the logical next step Targets To provide information on dynamic behavior of the integrated system To verify feasibility of the process concept and its control strategies from different perspectives To provide data and test bench for the development of advanced high level controls

5 5 APROS - simultaneous accuracy and comprehensiveness in dynamic modeling

6 6 Modeling principles First-principles models Pressure flow solution, realistic fluids (flue gas, water, O2, CO2) Main process units and streams modeled to provide the characteristic dynamic features of the system Realistic flow path lengths and volumes (pipes, ducts, tanks,..) Pressure increase and loss elements (pumps, p fans, pipes, pp valves,..) Heat exchangers Circulating fluidised bed (1D) Turbine sections, electrical network Control loops, ramping calculations, most important interlockings, and other supporting calculations included

7 7 Modeling scope ASU ASU-Boiler interface Boiler Circulating fluidised bed Flue gas path and recirculation Water steam path Turbine island CPU AS SU CONTRO OLS BOIL LER CPU

8 8 Model use Typical simulation studies Load changes Mode changes between air/oxy-firing Various disturbance situations Comparison and analysis of air/oxy-firing Special features of oxy-firing e.g. effect of high flue gas recirculation on boiler behavior and related control needs Development of upper level l controls

9 9 Simulation example 1: Load change Electric power 1 % 4% 1 % Ramping rates app. 3%/min Manipulated variables: Fuel feed, Pressure before HP turbine, Oxidant flows, GOX flows to oxidants, Flow from feed water tank, Feed flows to LP & HP eco

10 1 Simulation example 2: Mode change from air to oxy Constant fuel feed Manipulated variables: Air flows ramped (2 min) Oxygen flows to oxidants ramped (2 min) RFG flows ramped (2 min) Minor set point changes in Turbine pressure, Flow from feed water tank, Feed flows to LP & HP eco Flue gas O2 control OFF

11 11 Simulation example 2: Mode change from air to oxy 27 Turbine inlet Electric power 3 CO2 to storage 6 6 Flue gas O2 kg/s s; bar flow pres MW kg/s ol% m GOX to Oxidants Oxidant flows Total gas flows 3 Flue gas conc. 7 kg/s Oxdt 2Oxdt kg/s Oxdt 2Oxdt kg/s RFG Air GOX CO2 H2O

12 12 Simulation example 2: Mode change from air to oxy Concentrations of the oxidant streams Primary oxidant Secondary oxidant 6 Pi Primary oxidant gas CO2 Pi Primary oxidant gas H2O Secondary oxidant gas CO2 Secondary oxidant gas H2O Primary oxidant gas O Primary oxidant gas N Secondary oxidant gas O2 Secondary oxidant gas N

13 13 Simulation example 2: Mode change from air to oxy ASU-Boiler interface 6 Flows in the ASU-boiler interface g/s k kg/s 4 2 GOX flow from ASU Momentary O2 demand O2 flow to boiler Flows in/out of GOX buffer (kg/s) O2 from LOX tank vented GOX valve GOX header pressure MPa

14 14 Conclusions (1/2) A dynamic model of CCS capable power plant (ASU+CFB+CPU) was developed using the APROS simulation platform The model provided excellent base to study dynamic behavior of the oxyfuel CFB power plant, and to develop and optimize control strategies, upper level controls, and operational practises Control system has a central role to enable the operation of the integrate in a safe and effective way Controlling of the flue gas O2 content is more complicated in the oxy-firing mode because of the flue gas recirculation O2 content of the oxidants has strong influence to the boiler behavior. There are new risks for the boiler shut down in situations like fuel feed stop, lack of recirculation gas, etc. compared to traditional air-firing i boilers. The process islands can be only temporarily operated independently (no large buffer volumes between the process areas) Careful coordination is required to manage transients both planned operations q g p p and disturbances

15 15 Conclusions (2/2) Very tight coupling of the ASU, boiler and CPU processes (e.g. by heat integration) can make the operation more vulnerable to disturbances. Economical reasons encourage to look for agility and flexibility by control technology means. Also the future development of oxyfuel CCS concepts calls for dynamic simulation e.g. development of the second generation of oxyfuel CFB power plant concept with significantly higher efficiency FP7 project: O2GEN , coordinated by CIRCE Further development of submodels for ASU, boiler and CPU needed Integration of different simulation tools, e.g. ASPEN and APROS, provides interesting option for future dynamic studies Acknowledgements for FLEXI BURN CFB: Acknowledgements for FLEXI BURN CFB: The research leading to these results has received funding from the European Community s Seventh Framework Programme (FP7/27-213) under grant agreement n

16 16 Thank You!