Clinkering Temperature Research Articles

Effect of Phosphogypsum on the Clinkerization Temperature of Portland Cement Clincker

Phosphogypsum (PG) is a pollutant residue resulting from the production of phosphoric acid in the phosphated fertilizers industry. About 180 millions of tons of PG are generated worldwide per year, which originates storage problems because of the environmental restrictions and the high costs of storage spaces. Taking into account the mineralizer properties of PG it has been studied a way to valorize this residue as an alternative material in the production of Portland cement clinker. The PG and the raw-materials (limestone, marl, sand and iron oxide) were chemical, mineralogical and thermally characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD) and differential thermal analysis and termogravimetric analysis (DTA/TGA). After milling, the phosphogypsum was mixed with the raw-materials in different amounts up to 10% weight. The raw mixtures were submitted to two types of firing schedules, heating up to 1500°C without any holding time or heating up to 1350°C and holding for 20 minutes. After firing, the clinkers were analyzed by optical microscopy, milled and characterized in terms of chemical and mineralogical compositions. The clinkers were used to produce cement mortar according to NP EN 196-1 standard. The resultant test specimens were mechanically tested at 2 and 28 days according to the same standard. The obtained results show a reduction of about 140°C in the clinkerization temperature, when a raw mixture with 5% phosphogypsum was used. Standard clinkers, without phosphogypsum addition, which were fired at 1500°C, originated test specimens with a compressive strength of 48.1MPa at 28 days. Test specimens produced with clinker containing 5% phosphogypsum present higher compressive strength values at 28 days, being 55.1MPa for clinkers produced at 1500°C, and 49.4 MPa for clinkers produced at 1350°C.

Clinkering Reactions During Firing of Recyclable Concrete

Thermal transformations occurring during firing of recyclable concrete and hydrated Portland cement paste were monitored quantitatively by in situ and ex situ X‐ray diffraction, thermal analysis, and clinker microscopy. Reactions below 1150°C were dominated by either the decarbonation of calcium carbonates of the limestone aggregate fraction in the recyclable concrete or the low temperature decomposition of cement hydrates of the cement paste. Continued heating of the cement paste showed a rapid and extensive reaction of the free lime to form intermediate calcium silicate and aluminate phases such as belite, gehlenite, mayenite, and ye'elimite. The combination of free lime was less rapid in the dominantly limestone‐rich recyclable concrete. Similarly, subsequent melt and clinker phase formation (1250°C and higher) occurred more rapidly in the hydrated cement paste, indicating a positive contribution of cement hydrates to raw meal burnability. Reactions below typical cement clinkering temperatures were enhanced (1) by the intimate mixing of lime, silicate, and aluminate components in the hydrated cement and (2) by the elevated sulfate content that acted as flux and belite mineralizer. Lime formed in the thermal decomposition of portlandite (±450°C) was partially carbonated to calcite at temperatures below the onset of calcite decarbonation (±650°C).

Valorisation of electric arc furnace steel slag as raw material for low energy belite cements

In this paper, the valorisation of electric arc furnace steel slag (EAFS) in the production of low energy belite cements is studied. Three types of clinkers were prepared with 0 wt.% (BC), 5 wt.% (BC5) and 10 wt.% (BC10) EAFS, respectively. The design of the raw mixes was based on the compositional indices lime saturation factor (LSF), alumina ratio (AR) and silica ratio (SR). The clinkering temperature was studied for the range 1280–1400 °C; firing was performed at 1380 °C based on the results regarding free lime and the evolution of microstructure. In order to activate the belite, clinkers were cooled fast by blown air and concurrent crushing. The results demonstrate that the microstructure of the produced clinkers is dominated by belite and alite crystals, with tricalcium aluminate and tetracalcium-alumino-ferrite present as micro-crystalline interstitial phases. The prepared cements presented low early strength development as expected for belite-rich compositions; however the 28-day results were 47.5 MPa, 46.6 MPa and 42.8 MPa for BC, BC5 and BC10, respectively. These values are comparable with OPC CEMI 32.5 N (32.5–52.5 MPa) according to EN 197-1. A fast setting behaviour was also observed, particularly in the case of BC10, whereas soundness did not exceed 1 mm.

ENERGY REQUIREMENTS OF USING OIL SHALE IN THE PRODUCTION OF ORDINARY PORTLAND CLINKER

Energy balance was performed on the clinkering process when utilizing oil shale as a source of both raw materials and energy. The balance was also compared with the typical energy requirements for production of Ordinary Portland (OP) Clinker. The use of Jordanian oil shale can reduce energy requirements in production of OP clinker by 15–20%. This reduction is due to two factors: lower clinkering temperature of 1300–1350 °C and an appropriate proportion of the proposed raw materials. An additional energy of 1726 kJ/ton clinker, which represents 45% of the required energy, is needed to achieve the required clinkering temperature. This could be achieved by estimating the amounts of makeup fuel basing on the net calorific value of this fuel.

UTILIZATION OF LOKPANTA OIL SHALE IN PORTLAND CEMENT MANUFACTURING IN NIGERIA: A THERMODYNAMIC APPROACH

A thermodynamic model is applied to calculate the amount of oil shale ash (OSA), which could be used as raw material in the manufacturing of ordinary Portland cement (OPC). XRF, XRD and SEM analyses of the materials were carried out, and the thermodynamic properties for pure materials in the CaO-SiO2 system are obtained from literature, database of FACTSAGE and STGE. The main minerals and liquid phase present after blending OSA with cement raw material (employing different blending ratios) at different temperatures indicate that 15 to 20% of OSA would be suitable as clinker material. Temperatures of 1300 and 1400 degrees C can be used for such a blending ratio due to relatively high amount of C3S and C2S. The XRD and SEM of the blend at 1350 degrees C further show that C3S and C2S are the dominant species present. Addition of OSA will definitely lower the clinkering temperature by 50 to 100 degrees C. Thermomechanical analysis for the suggested blend ratio shows that the liquid is formed at temperatures higher than 1150 degrees C.

Minimizing Dioxin Emissions from Integrated MSW Thermal Treatment

The combustion of wastes has very significant benefits in reducing the volume of waste materials and producing energy. However, combustion processes produce emissions, which must be below the Best Practical Means (BPM) specified legislative limits. Several wastes, such as tires and meat meal, have been successfully combusted in cement kilns, up to 20% w/w, while retaining emission standards well below legislative limits. In the case of municipal solid waste (MSW) the introduction of large amounts of MSW into cement kilns is not practical because the additional kiln volume required is too great, the large amounts of ash generated will affect the cement clinker quality, and it would be difficult to sustain the required very high clinkering temperature of 1500 degrees C with large quantities of low calorific value MSW. A completely novel process, termed the Co-Co process, has been developed, integrating MSW combustion in a synergistic fashion with the cement production. This process is based on combining the cement "front-end" calcination reaction and incorporating it with a high temperature, at 1200 degrees C, combustion process, providing a giant acid gas scrubber. A pilot plant was designed, constructed, and operated to demonstrate the benefits of the Co-Co process. The pilot plant achieved emissions minimization: dioxins were typically 0.5-1% of the European BPM limits, HCl, SOx, NOx, and particulates were 15, 10, 20, and 25% of BPM limits, respectively. Heavy metals were typically below 25% of BPM limit values.

Influence of CuO on the formation and coexistence of 3CaO·SiO 2 and 3CaO·3Al 2O 3·CaSO 4 minerals

The influence of CuO on the formation and coexistence of 3CaO·SiO 2 and 3CaO·3Al 2O 3·CaSO 4 minerals in Portland cement containing 3CaO·3Al 2O 3·CaSO 4 mineral is reported in this paper. The results show that a suitable amount of CuO can lower the clinkering temperature and improve the burn-ability of clinkers. It can also promote the formation of 3CaO·SiO 2 and 3CaO·3Al 2O 3·CaSO 4 minerals and facilitate the coexistence of the two minerals in the clinkers. But adding 1% CuO to the raw material can cause the decomposition of 3CaO·3Al 2O 3·CaSO 4.

Investigation on minerals of Ba-bearing calcium sulpho-ferritealuminate

In this study, a series of new cement minerals, Ba-bearing calcium sulpho-ferritealuminates, were synthesized by the substitution of Fe3+ for Al3+ ions of C2·75B1·25A3S(1·75CaO·1·25BaO·1Al2O3·CaSO4). Differential thermal analysis—thermogravimetric analysis was used to determine the optimum sintering temperature and 1300°C was found to be a suitable clinkering temperature for the formation of minerals. The composition and structure of the clinker minerals were studied by X-ray diffraction and scanning electron microscopy energy dispersive X-ray spectroscopy. The results indicated that the size of the crystal was about 2 μm in diameter and the composition of Al2O3 can be substituted for Fe2O3, with a value of 0 ∼ 1·25. The development of strength was investigated and the results showed that the strength of Ba-bearing calcium sulpho-ferritealuminates was higher than C2·75B1·25A3S, and the optimal composition is 0·25.

Reduction of clinkerization temperature by using phosphogypsum

Valorization of phosphogypsum as mineralizer in the burning of Portland cement clinker was studied in our laboratory. X-ray fluorescence, optical microscope technique and powder X-ray diffraction were then used to characterize the synthesized clinker and its raw mixture in terms of chemical composition and clinker mineralogical composition. The effects of phosphogypsum on structural and morphological properties of clinker minerals and on the presence of alite were followed by scanning electron microscopy combined with microprobe analysis. The addition of phosphogypsum to the cement raw mixture shows that the burning temperature decreases and therefore improves the production process of clinker. The addition of 10% phosphogypsum permits a complete clinkerization at low burning temperature (1200°C), instead of 1470°C, which increases the cement factory efficiency by 25% and extends the service life of furnace fire brick. Structural and morphological analysis of clinker produced under the new conditions show that phosphogypsum preserve perfectly the crystalline structure of silicate phases, which leads to the improvement of physical and mechanical properties of cement.

Kinetic Consideration of Clinker Formation in Portland Cement Production Using Demolition Rubbles (Concrete,mortar and plaster) Part I : Burning Ability of Raw Mixes

Wahyudi B.S.Wahyudi B.S.In general, the main raw materials in Portland cement production are limestone, clay, and corrective materials such as iron sand and silica sand. These raw material come from natural deposits, which are very hard to find in some countries. In this research, Portland cement was made by utilizing the demolition rubble of office and housing buildings. The rubble consists of concrete wastes (mixtures of hydrated Portland cement minerals and some aggregates) and some building bricks as well as mortar/plaster of Portland cement. To meet the cement modulus, which is generally used in Portland cement industries, corrective materials such as limestone (source of CaO) and disposed building bricks are used. The term burning ability is used for Portland cement to measure the CaO free content in the cement clinker produced from specified raw material mixes at a specific operating 'condition of clinkering. The cement modulus used is Ume Saturation Factor (LSF) and Silica Modulus (SM). The minimum Cao free content was found by using LSF: 0.86, SM: 2.14, and clinkering temperature 14000C for 30 minutes. The cement modulus was made from concrete waste, limestone, and disposed red brick with a weight ratio of 1: 3.489: 0.677. Keywords: Burning ability,demolition rubble of buildings, Portland cement, and raw mixes.

Belite Portland Clinkers. Synthesis and Mineralogical Analysis

The quaternary system CaO-SiO 2 -Al 2 O 3 -Fe 2 O 3 has been taken into account to design five compositions of belite Portland clinkers with belite (Ca 2 SiO 4 ) contents ranging from 60 to 65 wt%, located in its primary phase field of crystallization. The synthesis of these belite clinkers has been studied by high temperature microscopy, dilatometry, differential thermal analysis and thermogravimetric analysis. As a result, the optimum clinkerization temperature has been established at 1360 ± 5°C The quantitative phase analyses of the clinkers were carried out by X-ray powder diffraction with the Rietveld methodology. The mineralogical composition depends on the initial dosages, on the highest temperature achieved and on the time of residence at this temperature. The reaction was completed at 1365°C during 15 min (free CaO <0.5 wt%), in those conditions the β-belite form is stabilized and the harmful transformation β→γ is avoided.

Manufacture of Eco-friendly and Energy-efficient Alinite Cements from Flyashes and other Bulk Wastes

Based on the chemistry of alinite compound, we have successfully converted a wide variety of flyashes and other mineral, industrial and municipal waste materials into a new class of hydraulic setting alinite cements. Three case studies are presented for producing good quality alinite cements from representative samples of flyash from a thermal power plant in India, tailings sands from an Indian gold processing plant and chloride rich municipal incinerator ash obtained from South Korea. The process parameters optimized include raw mix composition—represented by lime index and chloride content—clinkering temperature schedule and clinker grinding fineness.

Influence of MgO on the formation of Ca 3SiO 5 and 3CaO·3Al 2O 3·CaSO 4 minerals in alite–sulphoaluminate cement

The influence of MgO on the formation of Ca 3SiO 5 and 3CaO·3Al 2O 3·CaSO 4 minerals in alite–sulphoaluminate cement is reported in this paper. The results show that adding a suitable amount of MgO can lower the clinkering temperature, promote the formation of Ca 3SiO 5 and 3CaO·3Al 2O 3·CaSO 4 minerals, and help in the coexistence of the two minerals in the clinker. MgO may obviously decrease the formation of Ca 3Al 2O 6, and increase the SiO 2 content incorporated into the interstitial phase.

CFD predictions for cement kilns including flame modelling, heat transfer and clinker chemistry

Clinker formation in coal-fired rotary cement kilns under realistic operation conditions has been modelled with a commercial axisymmetric CFD code for the gaseous phase including a Monte Carlo method for radiation, a finite-volume code for the energy equation in the kiln walls, and a novel code for the species and energy conservation equations, including chemical reactions, for the clinker. An iterative procedure between the predictions for the temperature field of the gaseous phase, the radiative heat flux to the walls, and the kiln and clinker temperature is used to predict the distribution of the inner wall temperature explicitly, including the calculation of heat flow to the clinker. It was found that the dominant mode of heat transfer between the gas and the kiln walls is by radiation and that the heat lost through the refractories to the environment is about 10% of the heat input and a further 40% is used for charge heating and clinker formation. The predictions are consistent with trends based on experience and limited measurements in a full-scale cement kiln.

Microwave clinkering of ordinary and colored portland cements

Regular and colored cement clinkers were prepared by microwave processing at 2.45 GHz. Microwave enhancement in clinker reaction was observed. The preliminary results show that microwave processing can lower the clinkering temperature by about 100 °C compared to the samples processed in a fast-heating electric furnace.

Characterization of alinite cements through X-ray diffraction and mas 29Si NMR studies

Alinite cements have been synthesized using mining and steel plant wastes and pulverized fuel ash (fly ash) as raw materials and a clinkering temperature of 1150°C. The cements possess hydration characteristics comparable to those of portland cements. X-ray diffraction studies on these samples confirm the presence of alinite as the predominant phase. MAS 29Si NMR spectra have been used to distinguish alinite and alite cements. While both show resonances characteristic of Q° type silicate species, the portland cements exhibit three distinct peaks corresponding to three inequivalent SiO 4 units present, while alinite shows a single sharp peak corresponding to the unique Si position.

Mechanism of glass formation in portland cement clinker

In the system C 3AC 4AFSiO 2MgO, the glass formation region that is closely similar in composition to the interstitial material of portland cement clinker has been determined. The interstitial melt that exists in equilibrium with the silicates at the clinkering temperature contains a little silica. This forms clusters, which increase the viscosity of the melt and cause the latter to supercool appreciably. Crystallization of C 3A and C 4AF increases the concentration of clusters, which progressively interlock in the residual liquid, thus giving a glass on quenching. The presence of SiO 2 in the interstitial melt also enables the metastable formation of the orthorhombic aluminate and the oriented overgrowth of the ferrite on the aluminate to occur through encouraging supercooling of the melt.

The role of sulphates in cement clinkering reactions: phase formation in the system CaOAℓ 2O 3Fe 2O 3SiO 2CaSO 4K 2SO 4

The CaO-rich portions of the systems CaOAℓ 2O 3SiO 2K 2SO 4, CaOAℓ 2O 3K 2SO 4, CaOAℓ 2O 3SiO 2K 2SO 4CaSO 4 and CaOAℓ 2O 3Fe 2O 3CaSO 4K 2SO 4 have been studied experimentally. Schemes are presented showing phase assemblages compatible at subsolidus temperatures. Melting commences at about 825°C in assemblages containing K 2SO 4. Silicate, aluminate and ferrite phases are comparatively insoluble in molten alkali-rich sulphates. At clinkering temperatures, two immiscible liquids form; one is rich in K 2O and sulphate, the other is a silicate liquid. Some features of vapour-liquid-solid equilibria relevant to the S cycle in cement kilns are discussed.

Crystallization of the molten phase in portland cement clinker

Crystallization of a liquid similar to that present in Portland cement at clinkering temperatures has been studied. Its composition (in wt %) is CaO = 54.8, Aℓ 2O 3 = 22.7, Fe 2O 3 = 16.5, SiO 2 = 6.0. Prolonged crystallization or slow cooling yields the equilibrium phases: C 3A, ferrite close to C 4AF, and C 2S. With more rapid cooling or with static crystallization at lower temperatures, metastable phases form. The most important is a hitherto-unreported cubic polymorph of C 3A having a o ∼ 3.9 A ̊ . It is designated “proto-C 3A’ to distinguish it from ordinary cubic C 3A.