SOx Sorbent Behaviour in Oxyfuel Applications Luke Morris, David Large & Colin Snape EngD Centre Efficient Fossil Energy Technologies University of Nottingham In association with Doosan Power Systems Ltd
» Background » Project Overview » Test facilities » Mineral Analysis » Air-fired vs. Oxyfuel Fired » Sorbent Behaviour » Concluding Remarks Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
» SO 2 expressed in mg/MJ is lower under oxyfuel firing than air firing and has been attributed to; ˃ Increased retention of sulphur in the fly ash; ˃ Increased conversion of SO 2 to SO 3 . » SO 3 concentrations are reported to be 2 – 4 times higher during oxyfuel combustion. » The H 2 SO 4 dew point temperature will be higher raising concerns regarding low temperature corrosion. Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
» Trials on DPS’s emission test reduction facility focussing on; ˃ Sulphur balance across the system; ˃ The formation of SO 3 under oxyfuel conditions; ˃ The SO 3 reduction potential by injection of dry pulverised sorbents. » Analysis of fly ashes using SEM-EDX and mineral liberation analysis software as developed by JKTech. » Mineral analysis focuses on; ˃ Fly ash mineral variations between air & oxyfuel firing conditions; ˃ Variations in the major sulphur bearing species. ˃ Sorbent particle behaviours; Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
Water cooled refractory lined » furnace » 5m long and 0.5m in diameter » Down fired with scaled down Mark 3 Low NO x burner » Flue-gas recycled after ESP (wet) » CO 2 /O 2 used for primary stream (coal transport) » Flue gas duct temperature controlled by air cooler Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
» Air Firing & Oxyfuel Firing; » Medium Sulphur Bituminous coal; » Two In furnace sorbents; ˃ Limestone & Dolomite. » Two Post combustion sorbents; ˃ Calcium Hydroxide & Trona. » Baseline measurements without sorbent injection; ˃ To establish SO 2 & SO 3 concentrations. » In furnace & in duct sorbent injection; ˃ To establish SO x reduction & optimise sorbent feed rate. Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
» SO 2 , O 2 , CO, CO 2 and H 2 O measurements taken at strategic points. » SO 3 measured using the controlled condensation method prior to the ESP inlet. » Solid sampling at the furnace exit and prior to the ESP inlet. Engineering Doctorate ( EngD) Centre Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies Efficient Fossil Energy Technologies
» SO 2 concentrations increased by a factor of 2.3, SO 3 concentrations by a factor of ~ 1.4 under oxyfuel conditions. » On a mg/MJ the SO 2 concentration decreased by a factor of 1.2 in agreement with past research. » The In-furnace sorbents were more effective at removing SO 2 while the post furnace sorbents showed greater SO 3 capture. » A 5 % S-balance discrepancy during air firing was found. This was approximately four times higher for the oxyfuel combustion trials. ˃ The ‘missing sulphur’ appears to be lost in the furnace. ˃ Results also indicate that the discrepancy in the sulphur balance increases as the sulphur capture potential of the system increases. Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
Actual Molar In-Furnace In-Furnace Ratio SO 2 Temperature Firing Sorbent » 22 samples analysed o C (Input S:X) ppm Air - 840 1080 for their major mineral Air - 913 1110 OF - 2630 1230 species. OF - 2636 1230 Air 0.48 1026 1110 Air 0.31 531 1070 » 4 ashes without Dolomite OF 0.36 2349 1130 OF 0.42 1834 1190 sorbent addition for Air 0.43 1933 990 Air 0.43 1837 990 variations in the Air 0.20 919 990 OF Limestone 0.20 1933 1200 air/oxyfuel ashes. OF 0.45 2017 1200 OF 0.37 2017 1200 OF 0.37 2422 1200 » Samples extracted AF 0.34 1027 - AF 0.41 1476 - Calcium prior to the ESP inlet. OF hydroxide 0.37 2627 - OF 0.43 2476 - Air 0.67 1232 - OF Trona 0.24 2487 - OF 0.30 2355 - Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
» The mineral liberation analysis utilises signals from backscattered electron and EDAX x-ray detectors on Quanta 600 SEM-EDX. » Mineral x-rays are pattern matched against a database of 200 + mineral x-rays built up around a suite of pf ash samples from various stations and coals. » > 50 000 discrete particles analysed per sample to ensure statistically realistic. » For phase classification, the pattern match with the spectra must have a reliability factor of > 0.1. ˃ This is good enough to identify the major elemental peaks; Al, Si, Ca, Fe, S, Mg, Na & K. Number of Mineral Species Criteria species Quartz Al:Si ratio 1:10 5 Si rich Al:Si ratio 1:5-10 5 Rutile - 4 Iron oxide - 7 Alumino-silicates (low fluxes) < 5 % wt. fluxes 35 Alumino-silicates (mid fluxes) 5 - 10 wt. % fluxes 38 Alumino-silicates (high fluxes) 10 - 20 wt. % fluxes 10 Ca alumino-silicates Ca > 10 wt. %, fluxes < 10 wt. % 20 Fe alumino-silicates Fe > 10 wt. %, fluxes < 10 wt. % 18 Ca/Fe alumino-silicates Ca, Fe > 10 wt. % 2 Ca/Mg oxides SO3/(CaO + MgO) < 0.1 17 Ca/Mg sulphates SO3/(CaO + MgO) > 0.1 14 Engineering Doctorate ( EngD) Centre Ca/Mg silicates - 16 Efficient Fossil Energy Technologies
» Species grouped based on their Ca, Fe, Mg, K & Na contents. » Covers the major species present in the fly ashes. » Provides a broad compositional range from which the alumino- silicate species can be accurately classified. » Calcium sulphate particles differentiated by their SO 3 :(CaO+MgO) ratio. Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
90 90 AF Limestone 0964 AF Limestone 0964 AF Limestone 0927 AF Limestone 0927 80 80 OF Limestone 0939 OF Limestone 0939 70 70 60 60 50 50 40 40 30 30 20 20 10 10 0 0 0 100 200 300 400 500 0 100 200 300 400 500 Channel Channel 90 90 AF Limestone 0964 AF Limestone 0964 AF Limestone 0927 AF Limestone 0927 80 80 OF Limestone 0939 OF Limestone 0939 70 70 60 60 50 50 40 40 30 30 20 20 10 10 0 0 0 100 200 300 400 500 0 100 200 300 400 500 Channel Channel Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
70 SiO2 Al2O3 Fe2O3 SO3 60 CaO 50 » Acceptable agreement MLA results, wt. % 40 for the major elements, 30 Si, Al, Fe, Ca & S. 20 » Poorer matches for the 10 minor alkali elements 0 0 10 20 30 40 50 60 70 6 Na, K & Mg. MgO Na2O K2O P2O5 5 » Appears to 4 MLA results, wt. % overestimate the iron 3 oxide content. 2 1 Engineering Doctorate ( EngD) Centre 0 0 1 2 3 4 5 6 Efficient Fossil Energy Technologies ICP results, wt. %
» The sulphur contents, expressed as SO 3, were 1.16 and 2.03 % respectively showing an increase in the uptake of SO x in the fly ash from air to oxyfuel fired conditions. » The weight percentages of Wt. % Species Air Oxyfuel calcium and magnesium are 54.96 55.31 SiO 2 Al 2 O 3 18.94 21.26 comparable between the two Fe 2 O 3 8.97 5.18 CaO 3.09 3.24 firing conditions. MgO 0.54 0.58 0.49 0.36 » The oxyfuel fly ashes generally TiO 2 Na 2 O 0.47 0.50 Contained slightly less iron. K 2 O 2.25 2.54 P 2 O 5 0.18 0.23 SO 3 1.16 2.03 Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
» The particle size distribution showed only minor variations between the air and oxyfuel fired conditions. ˃ The air fired and oxy-fuel fired ashes have a D 90 of 7.8 µm and 10.1 µm respectively. » The oxyfuel ashes generally contained a smaller concentration of quartz and iron oxide minerals but increased concentrations of iron alumino-silicates. ˃ This implies a higher degree of coalescence of the parent ash particle. Air Fired Oxyfuel Fired Mineral (wt. %) Ash Ash Quartz 9.66 7.15 Si rich 7.87 5.59 Rutile 0.14 0.14 Iron Oxide 5.59 1.62 3.83 5.62 Fe Alumino-silicates Ca/Fe Alumino-silicate 0.34 0.15 Alumino-silicates (low fluxes) 42.89 44.27 Alumino-silicates (mid fluxes) 24.94 29.95 Alumino-silicates (high fluxes) 0.38 0.58 1.81 1.71 Ca Alumino-silicates Calcium oxides 1.04 0.11 Ca/Mg sulphates (1) 0.99 2.57 Engineering Doctorate ( EngD) Centre Ca/Mg silicates 0.51 0.54 Efficient Fossil Energy Technologies
» ~ 75 – 80 % of the calcium in the ashes is incorporated into the alumino-silicates with little variation in firing conditions. » ~ 60 % of the sulphur is incorporated in the alumino-silicates under both firing conditions. » The additional sulphur captured in the oxyfuel ash is in the form of calcium sulphate. ˃ A slight increase in the sulphur capture of the alumino-silicates but not substantial. % of calcium sulphate particles SO 3 /(CaO+MgO) Ratio Air Fired Ash Oxyfuel Fired Ash 0-0.1 43.42 7.93 0.2-0.3 19.40 14.97 0.4-0.5 19.17 63.92 0.6-0.7 16.63 12.13 0.8-0.9 0.46 1.05 >1 0.92 0.00 Engineering Doctorate ( EngD) Centre Efficient Fossil Energy Technologies
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