Oxy Fuel Gasification in Fluidised Beds Clean Coal Technology 2009 Dresden, 18-20 May 2009 Nicolas Spiegl, Nigel Paterson, Marcos Millan, Rafael Kandiyoti (Imperial College London, Department of Chemical Engineering, Energy Engineering)
Overview 1. Introduction 2. Project Summary 3. Experimental 4. Results 5. Summary
Oxy-Fuel Gasification, IGCC and CCS
Fluidised Bed Gasification Remarks Relatively low operating temperature Suitable for coals with a high content of potentially corrosive ash typically feedstock: low ranked coals Up to 90% of S retention in the bed by adding limestone or dolomite Suitable for coals with a high S content Fuel flexible No need to grind the feedstock as fine as required for entrained processes (advantage for biomass and waste co processing) Not sensitive to load changes (high thermal capacity of the bed)
Summary: Project Motivation: Possibility for future power generation Highly efficient and flexible process Integrated CCS Challenges: Different physical properties of the fluidising gas Changed chemical environment high partial pressure of CO 2 Coal swelling and agglomerating under high partial pressure of CO 2 ==> Necessary to investigate the fundamentals of such a process Bench scale oxy-fuel fluidised bed gasifier Different gasification conditions: Temperature, pressure, O/C ratio, Fuel gas composition and operability of the gasifier
PFBR Reactor 1. Up to 1000 C and 30 bar 2. Resistance-heated reactor shell 3. Solid feed rate of up to 6 g/min 4. Possible fuels: bituminous and sub bituminous coal, lignite and olive bagasse 5. Gas flow rates of up to 15 l/min 6. Continuous operation up to 45 min Top electrode ~500 mm Counter weight Thermocouple Bubbling fluidised bed Submerged spout Coal and gas Quartz glass liner Quartz paper Spout line 7. Bubbling fluidised bed 8. 0.05-0.2 m/s superficial gas velocity ~50 mm Copper seal
[%] 100 75 50 25 0 Typical Experiment CO H2 CH4 CO2 0 10 20 30 40 Time [min] Results: Carbon conversion (solid gas): 67% Heating value of the fuel gas (LHV): 8.44 MJ/m 3 Tar free gas after 10 minutes Conditions: - 850 C - 1 bar - Feedstock: German lignite - 10% O 2, 90% CO 2 - O/C Ratio = 0.2-1.7 g/min feed rate - 60 g preheated sand bed
Effect of Temperature [%,volume] carbon conversion [%] CO CH4 H2 Carbon conversion Heating value 100 80 60 40 20 0 750 C 850 C 950 C Increasing gasification temperature: - increasing CO and H 2 concentration 10.00 5.00 0.00 - increasing heating value of the fuel gas and carbon conversion Optimal temperature: Balance between high carbon conversion, fuel costs and ash properties LHV [MJ/m3] Carbon Conversion [%] 100.00 75.00 50.00 25.00 0.00 Conditions: - 1 bar - Feedstock: German lignite - 1.7 g/min feed rate - 60 g preheated sand bed - 0.2 O/C ratio Combustion Pyrolysis Gasification 750ºC 850ºC 950ºC
Effect of O/C Ratio Carbon Converson [%] 950C 750C 850C 100.00 80.00 60.00 40.00 20.00 0.00 0 0.1 0.2 O/C Ratio Conditions: - 1 bar - Feedstock: German lignite - 1.7 g/min feed rate - 60 g preheated sand bed Pyrolysis Combustion Gasification Increasing O/C ratio: - increasing extent of combustion and decreasing extent of gasification - decrease in gasification efficiency optimal O/C ratio: defined by desired gasification temperature and heating value of the fuel CO [%, volume] 50.00 40.00 30.00 20.00 10.00 0.00 c 0 0.1 0.2 O/C Ratio
CO 2 /C Ratio Superficial Velocity Carbon Conversion [%] 100 90 80 70 60 50 40 Conditions: - 5 bar - 850ºC - O/C ratio: 0.2 - Feedstock: German lignite - 60 g preheated sand bed 30 0.16 0.14 Superficial Velocity [m/s] 0.12 0.10 0.08 0.7 1.4 2.5 3.4 4.4 5.2 CO2/C ratio - Increasing carbon conversion with increasing CO 2 /C ratio - Dilution of the fuel gas with CO 2 leads to decrease in heating value - No effect of superficial velocity under the conditions investigated
Co-Feeding of Coal and Biomass Results CO H2 CH4 Heating Value [%,volume] 70 60 50 40 30 20 10 0 0% 10% 20% 9 7 5 3 1 LHV [MJ/m3] Extent of co-feeding Reactor successfully tested for co-processing of up to 20% of biomass No operational problems observed Increase in carbon conversion due to increase in O/C ratio and reactivity of the fuel Temperature: 850 C Fuel: Olive bagasse + lignite O/C ratio (for coal only): 0.2 Carbon content coal: 57.39 [%, as res.] Carbon content biomass: 45.61 [%, as res]
Summary 1. Bench scale fluidised bed reactor capable of operating under continuous fuel feed and up to 30 bar and 1000 C. 2. Influence of gasification temperature, O/C ratio, CO 2 /C ratio and superficial velocity was investigated. Increasing temperature is increasing carbon conversion and heating value of the fuel gas O/C ratio is affecting conversion at lower temperatures Increasing CO 2 /C ratio is increasing carbon conversion (close to 100%) at 5 bar and 850ºC No influence of superficial velocity detected 3. Co-processing of coal and biomass in the reactor possible. Initial results show no operational problems for up to 20% olive bagasse.
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