Evaluation of the Slagging Behaviour of Australian and German Low Rank Coals

Transcription

1 Evaluation of the Slagging Behaviour of Australian and German Low Rank Coals Alexander Ilyushechkin, Daniel Roberts, Martin Kaiser* and David Harris *Technical University of Freiberg 6 th International Freiberg Conference on IGCC & XtL Technologies, May 214, Dresden/Radebeul, Germany CSIRO ENERGY TECHNOLOGY

2 Gasification research opportunity for lignite Driving force for research: Increasing interest in the use of low rank coals as feed stocks for the production of liquid fuels and chemicals via gasification-based processes; Oxygen-blown gasifiers are well suited to these applications; The most common oxygen-blown gasification technology is entrained-flow gasification; Very few studies of lignite behavior under entrained flow gasification conditions.

3 Mineral matter in gasification processes

4 Mineral matter transformation in gasification Volatile species (in syngas): requirements for syngas cleaning Coal mineral matter Condensed phases (slag, fly ash): Syngas cleaning Operational: slag viscosity Utilisation/handling of waste Physical & chemical properties: trace elements, leaching Condensed phases Wall slag Liquid slag Coarse slag Solid ash Fine slag Volatile species Fly ash Need to understand these processes for: Coal selection, blending, preparation Process operation Management of byproducts Approach taken: Modelling tools Experimental Pilot-scale testing Tapped slag Quench water and/ or gas cleaning

5 Slagging in entrained flow gasifiers Slag formation AFT (reducing) < operating temperatures (~16 C) Slag Viscosity Newtonian flow behaviour for continuous flow 25 Pa s is the accepted maximum viscosity at the slag tap for successful operation (@ C) Flux addition required if viscosity is too high Temperature of Critical Viscosity (Tcv) Slag becomes heterogeneous Slag tapping difficult Viscosity, Pa s Temperature, o C

6 Viscosity models development for black coals: Australian coals for entrained flow gasification: coal ash slags (lab slags) synthetic slag gasifier slag Content, wt.% Australian coals (ash) * No fluxing SiO 2 Al 2 O 3 CaO Fe 2 O 3 MgO 28 > * 32 Synthetic slag (lab) Coal Ash slag (lab) Gasifier slag Approach: determine viscosity vs temperature develop a slag viscosity database to be used for the assessment of coal applicability for entrained flow gasification synthetic slag basis for development of a semi-empirical slag viscosity model Data analysis & presentation: Viscosity-Temperature curves Viscosity contours in SiO 2 Al 2 O 3 CaO FeO diagram Tcv contours in SiO 2 Al 2 O 3 CaO FeO diagram Viscosity as function of CaO, FeO and S/A (silica/alumina) FeO CaO SiO 2 Al 2 O 3

7 Slag flow behaviour: modelling development Recent work: High iron slags model (16-21% FeO) Include anorthite, mullite and spinel regions Reviewing of other slag models performance Calculated Viscosity (Pa s) Viscosity model: Weymann model (extension of Arrhenius model): modified Urbain type: linking composition with viscosity 145 C 15 C 155 C Mullite Calculated Viscosity (Pa s) C 15 C 155 C Anorthite Compositional range of high Fe slags (16-21% FeO) Key results Measured Viscosity (Pa s) R 2 value:.993 and.997 Good fit with experimental data Measured Viscosity (Pa s) Acceptable (5-25 Pa s) viscosities in mullite region Model extension required to cover solids formation region (T cv issue)

8 Viscosity and Tcv contours SiO 2 - Brown coals CaO Al 2 O 3 Viscosity (Pa s) contours at 145 C and Tcv ( C) for SiO 2 Al 2 O 3 CaO FeO slags, indicating acceptable compositional range

9 Slag flow behaviour: Australian Brown Coal and German lignite

10 Black and Brown coal characteristics Australian Brown coals German lignite Australian Black coals Proximate analysis Moisture %, ar Ash, % db Med: 5-15 VM, % db FC, % db Ash analysis Yallourn Morwell Loy Yang German lignite SiO Al 2 O Fe 2 O CaO MgO Na 2 O K 2 O SO Major for black coals Specific for brown coals

11 Slag viscosity of Australian brown coals Viscosity, Pa s Viscosity, Pa s 5-25 Pa s Viscosity, Pa s Temperature, C Group1: AFT: C Suitable for continuous tapping S/A: Fe 2 O 3 : 2-5 wt.% CaO+MgO: wt.% Na 2 O: 2-6 wt.% Temperature, C Group2: AFT: 15 - >16 C High viscosity Newtonian S/A: >4.5 Fe 2 O 3 : 2-3 wt.% CaO+MgO: 2-3 wt.% Na 2 O: 1-4 wt.% Need fluxing or blending Temperature, C Group3: AFT: >16 C Non-Newtonian: no continuous tapping S/A: <1 (.2-.8) Fe 2 O 3 : wt.% CaO+MgO: wt% Na 2 O: 5-13 wt.% Need blending

12 Key features Australian brown coal and German lignite ashes Yallourn: Low silica, low alumina Fe 2 O 3 is very high (35-5 wt.%) MgO - high and variable (14-36wt.%) High S content (-2 wt.% as SO 3 ) Morwell: Low silica, low alumina Fe 2 O 3 high and variable (-3 wt.%) MgO - high and variable (9-24 wt.%) CaO - high and variable (15-35 wt.%) High S content (17-26 wt.% as SO 3 ) Loy Yang: S/A varies a lot (from very low to high) Na 2 O can be very high (up to 19 wt.%) S content: Variable from low to high (3-22 wt.%) Rhenish lignite: Very high S/A (>25) Very high CaO+MgO (32-35 wt.%) High Fe 2 O 3 ( wt.%) High S content (11-12 wt.% as SO 3 ) May suit slagging gasifier: S/A ratio Moderate MgO and CaO content Impact of Na 2 O? High Si content May be compensated by high CaO, MgO and Fe 2 O 3 content

13 Evaluation of slagging behaviour (brown coals and German lignite) Focus of present work: Low, med and high S/A coal ash (L1, L2 and TUF) Evaluation of the existing models Impact of Na 2 O on phase composition and viscosity (L2 and L3) Typical Ash/slag temperatures: Gasifier Temperature, C Fixed/moving bed 7-9 Fluidised bed 9-1 Entrained flow slag S/A SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO Na 2 O K 2 O TiO 2 L L L TUF 1/ Presentation title Presenter name Page 13

14 Slag viscosity: low S/A ash Newtonian Fluid Viscosity, Pa s Temperature, C L1 (low S/A): Non-Newtonian viscosity (depends on shear rates) Need blending (moving to SiO 2 corner) No good models to predict slag viscosity: Models assume Newtonian flow Underestimate η in most of the models

15 Slag viscosity: high S/A ash Viscosity, Pa s Temperature, C L1 L2 experimental Mod. Urbain Watt-Fereday Wall Viscalc Urbain Kalm-Frank Lakatos FactSage L2 (high S/A): High viscosity: T> 159 C (η< 25 Pa s) Need fluxing No good models to predict slag viscosity: Only two model gives 3 predicted values within 2% of experimental Only three models predict values within 5% of experimental Temp. C Viscalc Urbain Mod.Urbain Kal-Frank Watt Lakatos Wall % 2% 5% > 5%

16 Sodium content in high S/A slags Viscosity, Pa s % Na 2 O % Na 2 O Temperature, C L3 (high Na 2 O ): High Na 2 O incr. liquid phase Both slags are fully liquid at C (viscosity measured) Extra 5 wt% Na 2 O reduces viscosity by 12-25% Impact of Na 2 O could be different for other slag compositional ranges (eg. low viscosity slags with Nacontaining solids) Phase content, wt.% liquid olivine cordierite anorthite ilmenite spinel albite Phase content, wt.% L2(5% Na 2 O) L3(% Na 2 O) EPMA confirmed liquid olivine cordierite anorthite ilmenite spinel albite EPMA confirmed Temperature, o C Temperature, o C

17 Phase compositions: thermodynamic considerations for slagging non slagging L1composition (low S/A): L2 composition (high S/A): Phase content, wt.% (a) liquid spinel olivine anorthite clinopyroxene perovskite nepheline Phase content, wt.% (b) (c) liquid cordierite clinopyroxene anorthite ilmenite albite tridymite Temperature, o C Liquid phase expected only above C* High AFT expected Solids have impact on slag viscosityexplains non-newtonian behaviour (a) Temperature, o C At low temperatures (9-1 C), liquid phase expected (b)* Solids may have impact on slag viscosity at T<13 C (c) * EPMA in progress

18 TUF 1/4. η in Pa s Viscosity of German lignite. 1. SiO 2 Fe 2 O 3 Al 2 O 3 CaO MgO Na 2 O TiO 2 K 2 O cooling cycle Viscalc Modified Urbain (Kondratiev-Jak) Watt-Fereday Wall Temperature, C heating cycle Urbain Kalmanovitch-Frank Lakatos % 2% 5% > 5% Very low viscosity Hysteresis observed T CV 124 C (cooling cycle) Narrow operational temperature range (2 < η < 25 (in Pa s)): C Blending approach required Urbain, Mod. Urbain and Kalm.-Frank temp. in C are closest models Viscalc Very high S/A Low alumina, high CaO slag Urbain Mod.Urbai n Kalm.- Frank Watt Lakatos Wall

19 Blending approach TUF1/4 blended with CRC72 (bit) Ratio: TUF:CRC=75:25, 66:33 Reduce S/A and reduce flux (CaO) measurment75:25 measurement66:33 TUF1/4slag-cooling cycle CRC72-s2 η in Pa s Temperature, C

20 Phase compositions: thermodynamic considerations for slagging non slagging L1 composition (low S/A): L2 composition (med S/A): TUF1/4 composition: liquid 9 spinel 8 olivine 7 anorthite 6 clinopyroxene 5 perovskite 4 3 nepheline 2 (a) Temperature, o C Phase content, wt.% Phase content, wt.% Liquid phase above C High AFT expected Solids affect slag viscosity- explains non-newtonian behaviour (a) Suitable for non-slagging gasifier (b) (c) liquid cordierite Temperature, o C clinopyroxene anorthite ilmenite albite tridymite Low temperatures (9-1 C), liquid phase expected (b) Solids may affect slag viscosity at T<13 C (c) Phase content, wt.% (d) (e) liquid clinoryroxene wollastonite Temperature, o C Na2Ca3Si6O16 Liquid phase expected > C (d) Solids affect slag viscosity at T<127 C (e) Possibly OK for slagging or non slagging gasifier

21 Summary 1. Slagging behaviour: Australian brown coals have a wide range of compositions screening for specific gasification application is required; Thermodynamic modelling can be used for preliminary evaluation of slag/ash phase composition Compositions with high liquidus temperatures (and high AFT) are not suitable for slagging gasifier, likely suit fixed bed and fluidised bed conditions (like L1); Compositions with low liquidus may cause agglomeration in nonslagging gasifiers (eg fluidised bed); Low temperature mineral phase transformations must be considered where sticky ash could be a problem (eg fluid bed)

22 Summary (2) 2. Slag viscosity: Low S/A and high AFT: fluxing or coal blending are required to minimise T flow <16 C High S/A: fluxing required (high Na 2 O my help reduce viscosity) German lignite has very low viscosity due to high CaO and FeO content (despite very high S/A): need blending None of the tested models predict slag viscosity reliably Current work: grouping mineral composition for expected Newtonian and non- Newtonian flow (determine min S/A correlated with CaO, MgO and FeO content); Produce data for representative SiO 2, Al 2 O 3, CaO, MgO and FeO ranges for model development; Include sodium in the models

23 Thank you David Harris Deputy Chief CSIRO Energy Technology t e David.Harris@csiro.au w ENERGY TECHNOLOGY