Brown clinkerBrown cement Brown concrete Gerold Schnedl / Ingo Leth CTEC Quality Days 2003 Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE The problem: Brown concrete G. Schnedl Feb 03 2 Schnedl Feb 03 3 .Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE The reason: Brown clinker G. Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Situation ■ ■ ■ ■ Sötenich plant: ❏ Brown cored clinker caused brown cement and brownish concrete surfaces ❏ Market focus: pre-cast cement ❏ Colour of cement / concrete important ❏ Cement less competitive Problems with brown cored clinker is not new (since years. but increased in 2002) ❏ but does not always appear ❏ Sometimes problems with brown stainings (Fe2+) Distinguish between: Fuels: Colour of cement ❏ Lignite. old grate cooler G. presently animal meal Brown stainings due to Fe2+ Old burner. Schnedl Feb 03 4 . granulometry Study in CTEC-Lab ❏ ■ Higher amount of animal meal causes higher amount of Fe2+ Brown clinker cores even without animal meal Literature study.Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Study: Find levers to get “black cores” and grey cement ■ Several industrial tests: Not successful ❏ ❏ ■ September 2002: Start of systematic clinker sampling ❏ ■ G. process data. lab burned clinker granules 2003: Investment in new burner Feb 03 5 . microscopy. Schnedl Fuels. clinker chemistry. kiln conditions. Ti4+ or Si4+ Incorporation only when C4AF crystallizes: > 1250 °C Colour depending on condition in sinter zone and pre-cooling condition (crystallisation) in kiln Feb 03 6 .changes lattice parameters – semi conductive properties leads to dark colour This electrical properties can be disturbed by even small amounts of other ions.g. Schnedl C4AF is the only dark component in clinker Incorporation of Mg leads to dark C4AF . Fe2+ Mn2+ . e.Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Summary of findings Literature ■ What causes dark / light clinker ? ❏ ❏ ❏ ❏ ■ G. ) c) thermal dissociation of Fe3+ in hot sintering zone Feb 03 7 . but: a) reducing atmosphere or flame touching the lining b) fuel in clinker (too coarse material – solid fuels. Schnedl Fe2+. Ti.. Mn2+.Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE What bleaches C4AF in brown cores? ■ Fe2+ seems to be the main reason in Sötenich but: ❏ ■ No Fe2+ in clinker after cooler does not necessarily mean that no Fe2+ in liquid phase in sinter zone ❏ ❏ ■ Fe2+normally re-oxidised after sinter zone but needs time and oxygen Fe2+ appears not only due to reducing conditions: ❏ ❏ ❏ G. Si in clinker cores: no significant differences detectable. Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE What bleaches C4AF in brown cores? ■ ■ ■ ■ G.04 %) – meaning that the not incorporated FeO oxidised afterwards Feb 03 8 . resulting from literature study: Brown clinker cores seems to be caused by an diffusion effect: Balance of crystallisation speed of C4AF and re-oxidation of Fe2+ ❏ Cooling speed > 1250 °C (pre-cooling in kiln) ❏ O2 content in atmosphere / flame ❏ Porosity of clinker ❏ Liquid phase content Even when only very few FeO is detectable < 0. Schnedl Experience of plants: ❏ The core is brown and never the surface ❏ Bigger clinker granules have more often brown cores ❏ More often when kiln is operated at full capacity Hypothesis. 2 % MnO in clinker) Feb 03 9 .Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Confirmation of hypothesis Plant and lab tests ■ Analysis of plant clinker samples and process data ❏ ❏ ■ ■ Extensive microscopic investigation in CTEC-Lab Lab burned clinker with Sötenich raw material ❏ ❏ ❏ ❏ G. Schnedl Fuel mix / fuel rates burner positions Different cooling conditions over and below 1250 °C Comparison with other raw meals Impact of atmosphere Impact of Manganese (Sötenich: 0. Schnedl Feb 03 1 0 .00 60.00 61.8 1 1.4 0.00 No significant impact of animal meal on colour.2 0.00 59.2 tons / hour animal meal G.00 65.6 0.00 66.Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Analysis of plant clinker samples brightness L* clinker meal Influence on animal meal on clinker colour 68.00 62.00 64. but on FeO content 0 0.00 63.00 67. Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Analysis of plant clinker samples Brightness vs fineness 400 fineness k-value 350 300 250 (fineness) Coarse k-value clinker has brighter (browner) cores 200 150 100 58 60 62 64 66 68 Brightness L* G. Schnedl Feb 03 1 1 . 00 Brightness L* G. Schnedl Feb 03 1 2 .60 literweight 1.10 1.30 1.40 fraction 11.00 Dense clinker granules (higher liter weight) have brighter cores 70.00 60.20 1.50 1.00 55.2-16 mm fraction 4-8 mm 1.00 65.Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Analysis of plant clinker samples Brightness (L*) vs Literweight 1.70 1. Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Microscopic examination ■ ■ ■ ■ G. Schnedl Fast cooling Partly reducing conditions No difference between brown and black cores High amounts of Alkali Aluminate Fast stiffening Feb 03 1 3 . Schnedl Feb 03 1 4 .Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Lab clinker tests G. Schnedl Feb 03 1 5 .Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Different cooling conditions G. Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Lab tests to check cooling conditions Check of different cooling rates > 1250 °C in lab furnace ■ a1 G. Schnedl a2 a3 Feb 03 b c 1 6 . Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Comparison of different conditions CIZ clinker Reference 5 % MgO 1 % MnO 5 % MgO +1 % MnO Slow cooled quick cooled G. Schnedl Feb 03 1 7 . Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Results of process data an lab test study: ■ ■ Brown cores appear. even only very little FeO is detectable. nevertheless FeO is the cause Microscopy investigation – confirms lab burning tests ❏ ❏ ❏ ■ ■ G. Schnedl Partly reducing conditions due to coarse fuel (lignite + animal meal) + divergent flame + sometimes thermal overheating Too rapid cooling: No pre-cooling zone in kiln caused by burner position Rather coarse raw mix causes “overheating” High Manganese content might boost the effect Coarse clinker granules favour brown cores – due to oxygen diffusion barrier into the core Feb 03 1 8 . Schnedl Detrimental to clinker reactivity Finer fuels ❏ ■ With old burner not possible Move burner into the kiln in order to lengthen cooling zone ❏ ■ With old burner not possible No coal mill in Sötenich Finer raw mix decrease coarse Quartz content (raw mill improvement) Increase SO3 in clinker in order to improve burnability and produce smaller clinker granules (+ increase workability) Feb 03 1 9 .Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Recommendations ■ Shorter flame – shorter sinter zone ❏ ■ Convergent flame – not touching the clinker ❏ ■ ■ G. Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Industrialisation: A new burner for Sötenich ■ ■ ■ ■ Not only due to brown cores.05.2003 Shorter. convergent flame Controllable G. also to increase waste fuel rate Start: 21. Schnedl Feb 03 2 0 . Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE Other plant actions ■ Manual estimation of clinker colour ❏ ❏ ■ ❏ G. Schnedl Only black clinker for precast cement Target: Implement automatic colour measurement of press tablets in auto-lab – result triggers separation of clinker Implement FeO quick test ❏ ■ separation Separate clinker Change fuel mix (reduce animal meal) Result: No claims in 2003 Feb 03 2 1 .