Oxyfuel CFB Combustion discussion on challenges for development

Transcription

1 Oxyfuel CFB Combustion discussion on challenges for development Filip Johnsson Department of Energy and Environment, Energy Technology , Göteborg Planned and proposed CCS demos CO2 sequestration infrastructure 1

2 FI FI Dry, pressurized flue gas as carrier gas Pilot burner Cooling tube 1/4 Cylindrical furnace 800 mm Coal feed Dry, pressurized flue gas for dust control and fuel carrier gas Coal from pneumatic feed system Direct O2 injection Primary/secondary register air/o2/co2 fan SC FI TI Measurement ports R1, R2...R7 Flue gas cooler mixing point O2/flue gas pre-heater Wet flue gas recycle Fabric Filter TC TC TI FI Dry flue gas recycle Flue gas condenser Air inlet TI PIC FI SC FI Stack gas Cooling water Jan Kjärstad Oxyfuel Development strategy towards mm C3 H 8 O2 Lab scale (IVD 10 kw) Basic research Small pilot (Chalmers 100 kw) Basic research Pilot/Demo (Vattenfall 30 MW) Testing of new products (2008) Demo/full scale ( ?) 2020?) Early market introduction CO2 capture state of the art The different capture technologies proposed are similar in estimated costs but differ in complexity Different capture technologies likely to fit different markets (local conditions) rather than there will be one winner technology 1 st generation capture plants, followed by 2 nd generation plants To bring gdown cost, large units are required ed Risk for extended period before roll-out costs are reached Capture Transport and storage infrastructure CO2 sequestration infrastructure 2

3 Main oxyfuel research - Chalmers Experiments in oxyfuel units 100 kw Chalmers PC unit Vattenfall ll30ws Schwartze pumpe PC pilot plant CFB tests with VTT and in Tampere (Metso) Modeling Reaction chemistry Heat transfer CFD simulations Fluidized-bed modeling (fluid-dynamics, heat transfer and chemistry) Process simulations Chalmers 100 kw oxyfuel PC test unit 100kW Lignite flame 27% oxygen CO2 sequestration infrastructure 3

4 The basic principle of oxy-fuel combustion In PC typically 2/3 of the flue gas is recirculated (RFG) Conditions in oxy-fuel combustion Table 1. Rough overview of properties of the flue gas in an oxy-fuel power plant (see Figure 1 for stream numbers). Stream Pressure (bar) Temperature ( C) Mass Flow 1 1/3 1/3 1/3 1/4 1/4 1/25 Volume Flow 1 1/3 1/7 1/200 1/900 1/1000 1/40 Phase Gas Gas Gas Gas Liquid Fluid * Gas * Supercritical fluid. CO2 sequestration infrastructure 4

5 Why CFB for oxyfuel (rather than oxyfuel PC)? Same arguments as for air firing? Fuel flexibility In-bed sulphur capture etc Additional advantages Higher oxygen concentration compact unit The use of external heat exchangers to remove heat from the system, i.e. reducing RFG flow Retrofit possible? Oxyfuelled compared to air fired CFB Increased external solids circulation/external heat exchange Redesign of particle seal (solids residence time) Proper fluidization of particle seal for heat extraction Influence on Risk for corrosion heat balance Increased internal solids circulation Increased convection, decreased radiation: W/m2 in furnace? Risk for corrosion Local fluctuations of parameters are expected to increase in amplitude Temperature: agglomeration, NOx emissions (?), SOx emissions (?) Increased CO2 concentration Decreased sorbent calcination Increased sorbent recarbonation Fuel dispersion more critical CO2 sequestration infrastructure 5

6 A first assessment of CFB heat balance with one dimensional model Sadegh Seddighi, David Pallarès, Filip Johnsson Model 1.5 Dimensional model (based on previously developed 3D model) Fluid dynamics: Dense Bed Cluster phase Ballistic flow, strong back-mixing Dispersed phase Core-annulus flow structure Combustion Mixing controlled volatile combustion Char combustion limited by kinetics/mixing Heat transfer To heat transfer walls CO2 sequestration infrastructure 6

7 Model validation Comparison with air fired data from boilers up to 287 MW good agreement Heat extraction surfaces CO2 sequestration infrastructure 7

8 Share of heat extraction normalized by the total thermal power State of the art 278 MWth CFB boiler used, 37 m tall furnace, 15x6 m furnace cross section Summary Oxygen >29% in RFG, heat must be extracted acedfrom externally e recirculated cuaedsolids flow Oxygen > 34% in RFG, net solids flow of the boiler design is too low to provide required heat extraction, while maintaining furnace temp at 850C Up to 30kg/m2 s required CO2 sequestration infrastructure 8

9 CFB Oxyfuel combustion A large range of topics for research emerging! e g! Heat transfer Fluid dynamic Combustion Emission control CO2 sequestration infrastructure 9