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Imperial College London Measurements of the Quality of Cement Produced from Looped Limestone Charles Dean, Prof. Denis Dugwell and Dr. Paul Fennell* Department of Chemical Engineering and Chemical Technology, Imperial College London. Funded by EPSRC and Cemex. IEA GHG Solid Looping Cycles Network, Vienna 2011. *[email protected] Presentation Outline • Background to the Project • Objectives • Methods • Some Results Benefit to Cement Manufacture of Using Spent Sorbent kg / tonne clinker Assuming energy demand of 3.7GJ/tonne clinker, pet coke use at calciner and bituminous coal at kiln. Data taken from: Alsop, P. A., 2007, Cement Plant Operations Handbook Benefit to Cement Manufacture of Using Spent Sorbent kg / tonne clinker Therefore possible to mitigate ~ ¾ cement CO2 emissions by using spent sorbent from Ca-loop. Assuming energy demand of 3.7GJ/tonne clinker, pet coke use at calciner and bituminous coal at kiln. Data taken from: Alsop, P. A., 2007, Cement Plant Operations Handbook Cement Chemistry Overview CaO is used to produce calcium silicates → upon hydration these crystals form an interlocking microstructure which provide the bonding strength. KILN REACTIONS 900-1200 2CaO+SiO2 → 2CaO.SiO2 – ‘Belite’ > 1 yr strength CaO + Clay → Calcium Aluminates (‘Interstitial phases’) 1250-1500 CaO+2CaO.SiO2 → 3CaO.SiO2 – ‘Alite’ < 1 yr strength Final Proportions: ~ 60 % Alite, ~ 25 % Belite, ~ 15 % interstitials. The Role of Trace Elements in Cement Formation of calcium silicates strongly influenced by trace elements in clinker: e.g. Effect of MgO e.g. Effect of ZnO Some elements are beneficial between certain limits, detrimental outside of those limits. e.g. MgO > 2 %. Objectives of the Project • To identify chemical changes in sorbent (concentration of trace elements) upon repeated cycling under different conditions. → Repeated cycling will lead to chemical and physical changes in the sorbent. In particular combustion products and ash from fuel use in calciner will potentially be retained in the sorbent. • To relate chemical changes in sorbent to possible changes in cement quality/composition. → In this project, cement quality is being inferred from alite production (as the most prevalent phase). Objectives of the Project • To identify chemical changes in sorbent (concentration of trace elements) upon repeated cycling under different conditions. → Repeated cycling will lead to chemical and physical changes in the sorbent. In particular combustion products and ash from fuel use in calciner will potentially be retained in the sorbent. • To relate chemical changes in sorbent to possible changes in cement quality/composition. → In this project, cement quality is being inferred from alite production (as the most prevalent phase). Research Methodology 1. Produce sorbent using different fuels and numbers of cycles. 2. Analysis of sorbent (ICP). 3. Production and analysis of clinkers (XRD). Sorbent Production and Analysis Sorbent Production – 3kW Spouted Bed Reactor C) ◦ concentration 2 CO Bed Temperature ( Bed Temperature Time (s) Fluidising gas 15 % CO (balance air), 5 l/m, Longcal Fuel 2 P25 limestone, 425 – 500 µ. 2g coal / cycle – based on modeling work (essentially is amount req’d at calciner based on 30 % split fuel use). Sorbent Production – RDF Fuel Feeding System Methods: Trace Element Analysis of Fuels & Sorbent • Sorbent prepared for ICP – hot nitric acid digestion followed by filtration. • Efficacy of digestion checked using standard reference materials. SRM 1547 – Biomass (Peach Leaves) SRM 1d - Limestone 2500 2000 1500 1000 Sample Conc. (ppm) Conc. Sample 500 0 Mg Fe K S Sr Mn P Ref. Exp. [Units – ppm] Clinker Production and Analysis Clinker Production Once sorbent is removed from reactor: • Homogenised with other oxides in DI water then dried. • Pressed into a brick using 100 atm pressure. • Then fired in tube furnace at 1500°C for 2hrs. Clinker Production • The brick is then pushed directly from the furnace into an air cooled chamber – 25 l/m applied evenly across brick until ambient temp. • This is to prevent decomposition of alite to belite which can take place if clinker is allowed to cool at its own rate. Methods – Qualitative Assessment of Clinkers • First, qualitative assessment of phases present in the clinker – indicates that correct phases are present. Alite 6400 Intensity (counts) Interstitial phases 3600 Belite 1600 400 Blue – Belite Green – Alite Pink - Interstitial 0 25 30 35 40 Methods – Quantitative Assessment • % alite is achieved by mixing clinker samples with corundum (Al2O3) in 1:1 ratio. This enables changes in alite peaks to be converted to % by comparing to corundum peak (using RIR value – taken from ICDD database). 2500 Intensity (counts) 1600 900 400 100 0 26.5 27.0 27.5 Xa28.0 = (Ia/Ic)*(Irelc/Irela)*(Xc/RIR)28.5 29.0 29.5 30.0 30.5 2Theta (°) Main Results - % Alite Main Results - % Alite – No Fuel & La Jagua Coal All results average of 3 replicate experiments No Fuel 2 g / cycle 100 90 80 70 60 % Alite % 50 40 30 20 10 0 1 5 10 15 No. Cycles C. Dean, D. Dugwell, and P.S. Fennell. Energy & Environmental Science, 2011. 4(6): p. 2050-2053. Sorbent trace element levels after 5 cycles ↑ 5 cycles, La Jagua Colombian coal – 2 g / cycle ↓ Average of 3 replicate experiments La Long- 5cyc Jagua cliffe Sorbent ppm ppm ppm B 13.88 0.00 9.73 Ti 69.77 0.35 6.60 Elements Detrimental to Alite Formation Zn 6.17 0.00 5.14 Ba 80.34 12.00 27.99 * Cr 2.97 2.50 47.26 * Cu 31.50 4.50 10.64 Ni 2.89 0.35 0.30 Elements Beneficial to Alite Formation Mg 114.31 1500.00 1295.29 Mn 6.57 45.00 57.54 Sr 56.85 135.00 112.82 Increase in most elements. However largest increase is Ba and Cr. (Decrease in Mg and Sr – assume that other increases over-ride these losses). Sorbent trace element levels after 5 and 1 cycle ↑ 5 cycles, La Jagua Colombian coal – 2 g / cycle ↓ Average of 3 replicate experiments La Long- 5cyc 1cyc Jagua cliffe Sorbent Sorbent ppm ppm ppm ppm B 13.88 0.00 9.73 9.81 Ti 69.77 0.35 6.60 0.00 Zn 6.17 0.00 5.14 4.87 Ba 80.34 12.00 27.99 6.59 Cr 2.97 2.50 47.26 3.82 Cu 31.50 4.50 10.64 13.76 Ni 2.89 0.35 0.30 0.00 Mg 114.31 1500.00 1295.29 1399.19 Mn 6.57 45.00 57.54 43.98 Sr 56.85 135.00 112.82 84.23 Drop in the level of trace element concentrations after 1 cycle indicates that most elements are first lost before being replenished. This could explain drop in % alite upon repeated cycling without fuel. Conclusions on cement from cycled sorbent Repeated cycling without fuel - appears to impact negatively on alite production. Trace element results after 1 cycle indicate that this could be due to loss of impurities / trace elements. For the case of La Jagua – repeated cycling appears to improve alite formation. Trace element results after 5 cycles indicate this could be due to replenishment of impurities from fuel, esp. Ba and Cr. However further work needed – esp. producing clinker from raw materials containing a more realistic baseline of trace elements (i.e. clay) to see if repeated cycling with fuel takes trace element concentrations past any ‘tipping points’. Further Results – Trace Element Partitioning Partitioning of Trace Elements Partitioning of Trace Elements Average of 3 repeats Average % Recovered 100 150 200 250 300 350 400 450 Partitioning of Trace Elements after 5 5 after of Trace Elements cycles: RDF Partitioning 50 0 % Recovered in Solid Streams in Recovered % Ti Ti Cu B V Al Ba Cr Mn Fe Na K S Zn Sr Ni Mo • • • Contamination from Ti Cu. and Ti from Contamination More volatile elements lost. Heavier elements closer to 100 %. Mg Pb P Co Cd As Sb Partitioning: Implications for Cement Manufacture █ - Sorbent █ - Fly Ash █ - Fines █ - Lost Na K +43 % +148 % RDF Trace Element Conc. 18,000ppm! 20,000ppm! RDF S + 579 % Conclusions on RDF trace element partitioning • Heavier elements / elements with lower boiling points tend to reside in sorbent and therefore potentially also in the cement. Volatile elements tend to collect in fines / fly ash or exit as gas. • Partitioning shows that Na, K and S could cause problems in use of RDF-derived sorbent, both in cement application (i.e. aggregate/concrete) and in Ca-loop / cement plant operation. • Climafuel feeding: contamination issues need resolving before producing cement! Thankyou Questions.
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