Energy and exergy analyses for a cement ball mill of a new generation cement plant and optimizing grinding process: A case study

Nowadays, ball mills are used widely in cement plants to grind clinker and gypsum to produce cement. In this work, the energy and exergy analyses of a cement ball mill (CBM) were performed and some measurements were carried out in an existing CBM in a cement plant to improve the efficiency of the grinding process. The first and second laws efficiency of the CBM was specified to be 80.5% and 19.9%, respectively. The electrical energy consumption of the CBM unit was specified to be 37.9 kWh/t. The effects of ball charge pattern, cement fineness and two additive materials (limestone and pozzolan) on the performance of the CBM unit and the quality of cement were investigated. The first and second laws efficiency of the CBM increased (81.8% and 20.6%) and the electrical energy consumption of CBM unit decreased (36.5 kWh/t) after modifying the ball charge pattern. Also, the results demonstrated that cement production rate increases (185–224 t/h) and the electrical consumption decreases (41.1–33.1 kWh/t) when cement fineness decreases (3250 –2820 cm²/g). However, the cement compressive strength (3, 7 and 28 days) decreases and the cement setting time (initial and final) increases by reducing the cement fineness. Besides, when the clinker was replaced by limestone or pozzolan, on the one side, the efficiency of the first and second laws of the CBM unit was increased, but on the other side the cement compressive strength was decreased and the cement setting time was increased.     

Size reduction performance evaluation of HPGR/ball mill and HPGR/stirred mill for PGE bearing chromite ore

In the present study, size reduction experiments were performed on High-Pressure Grinding Rolls (HPGR), ball mill and stirred mill of PGE bearing chromite ore. The performance of HPGR was evaluated in two stages of size reduction to reduce energy consumption. In the first stage of HPGR, the effect of operating variables such as the gap between the rolls, roll speed, and specific pressing force on product size (P₈₀) and energy consumption (E_CS) was investigated. The process to get the smallest product size was optimized within the experimental range of investigation. The crushed product of HPGR was subjected to grinding in the second stage in a ball mill and stirred mill. The effect of mill speed, grinding time, and ball size on the performance of the ball mill was investigated and the product was further investigated in the second stage. A comparative analysis of the ball mill and stirred mill performance and energy consumption at different grinding time intervals was also performed. It was found that the ball mill consumed 54.67 kWh/t energy to reduce the F₈₀ feed size of 722.2 µm to P₈₀ product size of 275.4 µm while stirred mill consumed 32.45 kWh/t of energy to produce the product size of 235.6 µm. It also showed that stirred mill produced finer product than the ball mill at around 40% lesser consumption of energy. It can be concluded that the HPGR-Stirred mill combination was a more energy-efficient grinding circuit than the HPGR-Ball mill combination for PGE bearing chromite ore.     

A cement Vertical Roller Mill modeling based on the number of breakages

This study investigated a mathematical model for an industrial-scale vertical roller mill(VRM) at the Ilam Cement Plant in Iran. The model was calibrated using the initial survey's data, and the breakage rates of clinker were then back-calculated. The modeling and validation results demonstrated that according to the bed-breakage mechanism in VRM, clinker particles only stay in the VRM for a short time. Particles in the VRM haven't a 1 to 3 times greater chance of breaking due to their brief time in the VRM. Matrix model's results model provides a more robust prediction based on the number of 2-times clinker breakage in VRMs (R² = 0.9916, MSE = 5.3526, accuracy = 94.6474). Also shown by the results of the matrix modeling, the S increased with decreasing the particle size. In contrast, the population balance model increased with increased particle size.     

Enhancing the capacity of large-scale ball mill through process and equipment optimization: An industrial test verification

The production capacity of the large-scale ball mill in the concentrator is a crucial factor affecting the subsequent separation and the economic benefits of the operation. The main aim of this study is to improve the processing capacity of the large-scale ball mill. Taking a Φ5.49 × 8.83 m ball mill as the research object, the reason for the low processing capacity of the ball mill was explored via process mineralogy, physicochemical analysis, workshop process investigation, and the power consumption method. Based on this framework, a series of laboratory grinding optimization tests were conducted and verified via industrial tests. The results show that the ore primarily contained hematite and magnetite, the disseminated particle size of magnetite was primarily a coarse-grained inlay that was easy to separate from gangue, while the disseminated particle size of hematite was primarily an uneven and medium-sized inlay, which increased the grinding difficulty. Under optimum conditions of +6.0 mm material suitable for a 100 mm ball diameter, −6.0 + 2.0 mm material suitable for an 80 mm ball diameter, −2.0 mm material suitable for a 70 mm ball diameter; medium ratio of Φ90 mm 34.62%, Φ70 mm 26.92%, Φ60 mm 23.08%, Φ40 mm 15.38%; filling ratio of 32%; material ball ratio of 1.0; rotation speed rate of 80%; and grinding concentration of 78%, the −0.074 mm content in the grinding product increased from 55.10% to 58.86% and the processing capacity of the ball mill increased from 310 to 320 t/h to 350 t/h. Scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) micrograph analysis shows that the fineness of the ore and dissociation degree of useful minerals were apparently improved by optimizing the process and equipment.     

A theoretical study on a novel solar based integrated system for simultaneous production of cooling and heating

An integrated system for simultaneous production of triple-effect cooling and single stage heating is proposed in this paper to harness low grade solar energy. The proposed system combines the heliostat field with a central receiver and the ejector-absorption cycle with the shaft power driven transcritical CO₂ cycle. A parametric study based on first and second laws of thermodynamics is carried out to ascertain the effect of varying the exit temperature of duratherm oil, turbine inlet pressure, and evaporators temperature on the energy and exergy output as well as on the energy and exergy efficiencies of the system. The results obtained indicate that major source of exergy destruction is the central receiver where 52.5% of the inlet solar heat exergy is lost followed by the heliostat where 25% of the inlet exergy is destroyed. The energy and exergy efficiencies of the integrated system vary from 32% to 39% and 2.5%–4.0%, respectively, with a rise in the hot oil outlet temperature from 160 °C–180 °C. It is further shown that increase in evaporator temperature of transcritical CO₂ cycle from −20 °C to 0 °C increases the energy efficiency from 27.45% to 43.27% and exergy efficiency from 2.51% to 2.97%, respectively. The results clearly show how the variation in the values of hot oil outlet temperature, turbine inlet pressure, and the evaporator temperature of transcritical CO2 cycle strongly influences the attainable performance of the integrated system.     

A study on the effect of process parameters in stirred ball mill

An experimental study on the fine grinding of calcite powder (d₅₀ = 62.16 μm) using a 0.75 l laboratory stirred ball mill has been carried out. The effects of various operating factors, such as grinding time (min), stirrer speed (rpm), slurry density (wt.%) and ball filling ratio on fine grinding was studied under batch wet conditions using alumina balls, 95% purity with diameters 3.5–4.0 mm. A series of laboratory experiments using 2⁴ full factorial designs was conducted to determine the optimum grinding parameters. The test results showed that the stirrer speed and grinding time have strong effects on the grinding efficiency, based on the value of specific surface area (m²/g).     

Effect of specific energy consumption on fineness of portland cement incorporating amine or glycol-based grinding aids

A comprehensive research project was undertaken to evaluate the effect of specific energy consumption (Ec) on variations of portland cement fineness measured by the Blaine test and sieve analysis. Amine and glycol-based grinding aids (GA) were incorporated at various concentrations of 0.04, 0.06, and 0.08% of the cement weight. At Ec values lower than around 20 kWh/ton, test results have shown that cement fineness increases almost linearly with the increase in grinding energy according to Rittinger’s law. Beyond 20 kWh/ton, part of the energy appears to be lost due to cement agglomeration, indicating the starting of a “non-productive” phase. The Blaine test was found to be more accurate for evaluating variations in cement fineness as compared to the sieve residue determined on 100, 80, 63, and 38 μm meshes, particularly at higher grinding energy. Compared to a reference cement mixture, the addition of 0.06% GA led to significant gains in grinding mill productivity varying from 16 to 72%, depending on the GA type and Ec used.      

Investigation of the cyanide leaching optimization for ultrafine grinding gold–silver ore

ABSTRACT

In recent years, the ultrafine grinding (UFG) process has become increasingly important for the recovery of precious metals (especially for Au and Ag) from raw ores. It is well known that cyanide leaching of gold–silver ore has been an accepted process in the world. In the current study, UFG was proposed as a pretreatment method prior to cyanide leaching of a gold–silver ore. First, the ore was crushed and ground by jaw, cone crusher, and ring mill, respectively. Particle size of ground product was 75 µm based d₈₀. Second, the fine product was subjected to the grinding process by vertical wet stirred ball mill, and the final ultrafine product was used as leach feed material. The leach feed material had about d₈₀ = 20 µm and d₅₀ = 6.02 µm particle size. Some important leaching parameters were optimized by using the ultrafine powder in the study. The final leach experiments demonstrated that the recoveries of Au and Ag were 91.92% and 82.15% under optimum leaching conditions such as 150 kg/t quicklime dosage, 25% pulp density, 85°C leach temperature, 500 g/t cyanide concentration, and 90 h leaching time.     

Degradation model of Gladstone Port Authority's coal using a twin-pendulum apparatus

Single-particle breakage tests of South Blackwater and Ensham coal were conducted by using a computer-monitored twin-pendulum device to determine a parameter which will describe the product size distribution of the breakage product. The size distribution parameter ‘t’₅₀ related to the specific comminution energy [defined as the comminution energy per unit mass which transmitted to a particle during breakage (kWh/t)] of breakage coal particles and described the breakage characteristics of two types of coal. At a specific comminution energy level, the t₅₀ parameter of South Blackwater coal was higher than the t₅₀ parameter of Ensham coal. A degradation model was developed with several parameters for the coal-handling circuits of Gladstone Port. In the degradation model, the raw data of the non-cushioned curve deviates from the model data after a few initial drops because the mass of the sample reduces in successive drops and produced more fines.     

A Spear and Shield-Inspired Ar Plasma Safeguard Few-Layer Black Phosphore with Firefighting of Epoxy Resin

Appearing as an innovative and efficient strategy, a facile strategy of a plasma ball mill is carried out to prepare few-layer black phosphorus nanosheets (BPNSs), for abating the fire risk of epoxy resin (EP). A spear and shield-inspired Ar plasma emergeed through a plasma ball mill to prevent Ar@BP nanosheets from oxidation compared with the preparation of BP nanosheets (MBPNSs) in a mechanical ball mill. The absorption coefficient in the synchrotron radiation spectrum is increased by 16.91%, indicating that BP is effectively protected by Ar proof. The Vienna ab initio simulation reveals that the combination of Ar@BP with oxygen cannot proceed spontaneously with the binding energy of 4.44 eV. With the introduction of 1.5 wt% Ar@BP, the total heat release (THR), total smoke release (TSR), total smoke production(TSP), CO, and CO₂ yield, compared with that of EP, are descended by 30.40%, 24.41%, 24.10%, 33.23%, and 37.60%, respectively, indicating excellent flame retardancy property. It is attributed to the condensed and gas phase function. Meanwhile, the tensile strength and elongation at break increase by 27.92% and 56.04%, respectively, with the incorporation of 1.5 wt% Ar@BP.     

超细硅酸锆磨矿工艺优化与节能

为扩展球磨机、搅拌磨在物料粉磨过程中的应用,通过对比球磨机与搅拌磨的特性,分析两者在硅酸锆生产中的研磨效率,发现在磨矿过程中采用球磨机与搅拌磨分段研磨、优化组合的方式能充分发挥两种设备的优点,提高研磨效率。结果表明:使用该技术能大规模地生产出中位粒径为1μm的超细硅酸锆产品,并能显著降低磨矿能耗,节约生产成本。     

Structural evolution of an Al–Te mixture during ball milling

An Al–Te mixture was mechanically alloyed with a planetary ball mill, and the structural evolution of the Al–Te mixture during ball milling was characterized by X-ray diffractiometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and thermodynamic computation. Although crystalline α-Al₂Te₃ was synthesized in the initial stage of milling, but the final product is a metastable Al₂Te_3 ? δ (Space group: Fm 3¯m) with lattice parameter a = 5.925 Å. The metastable Al₂Te_3 ? δ decomposes into Al and Te at about 140 °C.     

Effect of mill speed and slurry filling on the charge dynamics by an instrumented ball

In the ball mill, the motion of charge is a complex system, especially under wet grinding. It is difficult to measure the charge physical quantities and hard to validate the correctness of charge motion simulation. To this end, an instrumented ball which is capable of measuring the charge physical quantities was designed. The laboratory ball mill was lined with 12 pieces of trapezium lifters and filled with J_b = 25% grinding balls. An iron ore was used to prepare the slurry at 50% solid concentration by mass. A series of tests were carried out to investigate the charge dynamics at different mill speeds and slurry filling. The average rotational kinetic energy, average applied force and mill power were measured and analyzed. The results showed that the average rotational kinetic energy increases with mill speed, whereas the average applied force first increases and then decreases. The average rotational kinetic energy and applied force first increases and then decreases by the increase in slurry filling. Furthermore, there exists a slurry filling U = U^* that the mill power has a maximum value.     

Hyperfine interactions and structural features of Fe–44Co–6Mo (wt.%) nanostructured powders

Nanocrystalline Fe–44Co–6Mo (wt.%) powders have been prepared by high-energy ball milling from elemental Fe, Co and Mo pure powders in a P7 planetary ball mill. The obtained powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Mössbauer spectrometry techniques. The influence of milling process and Mo substitution for Co in equiatomic FeCo have been examined in order to study structural evolution and formation mechanism of nanostructured Fe(CoMo) solid solution. XRD results show the formation of a BCC Fe(CoMo) solid solution (a = 0.2874 nm) where unmixed nanocrystalline Mo with a BCC structure is embedded. Disordered Fe(CoMo) solid solution is characterized by a broad hyperfine magnetic field distribution with two regions centered at B₁ = 35.0 T and B₂ = 30.7 T, respectively, attributed to disordered Fe(Co) solid solution and CoMo enriched environments. Prolonged milling and Mo addition cause the decrease of average hyperfine magnetic field while the average isomer shift remains nearly constant.     

Fabrication of ultrafine powder using processing control agent,and investigation of its effect on microstructure and thermoelectric properties of p-type (Bi,Sb)2Te3 alloys

Low-dimensional materials can significantly enhance the efficiency of thermoelectric devices for power generation and cooling applications. In the present work, ultra-fine powders of p-type (Bi, Sb)₂Te₃ alloys are fabricated through high energy ball milling using stearic acid as a process control agent (PCA). The influence of the PCA addition on powder characteristics, microstructure and thermoelectric transport properties are studied. Further, the ultra-fine powder is subjected to calcination (Cal-PCA) and subsequently consolidated all powders using spark plasma sintering (SPS). The PCA, Cal-PCA, and non-PCA powder morphological effects on the microstructure and thermoelectric properties are systematically investigated and elucidated thoroughly. The electron beam scattering diffraction (EBSD) results confirmed that the PCA sample exhibited very fine grains (average grain size of ～800 nm) compared to the non-PCA (average grain size of about 2.6 µm), while the grains were distributed randomly for all samples. Formation of fine grains and partial existence of the stearic acid (carbon and oxygen phases) in the matrix were strongly inhibiting the transport of the carriers that severely decreased the carrier mobility, reflecting the severe reduction in electrical conductivity for PCA sample compared to Cal-PCA and non-PCA. The lowest thermal conductivity (κ) of 0.745 W/mK was achieved for the PCA sample, which is 19%, 12% lower than that of non-PCA, and Cal-PCA samples. The strong reduction in κ was mainly attributed to the dramatic decrease in the phonon thermal conductivity owing to phonon scattering at numerous grain boundaries and oxide phases. The obtained high electrical conductivity with balanced thermal conductivity in Cal-PCA sample is attributed to the significant improvement in ZT of 1.1, which is 27%, and 47% higher than that of the Non-PCA sample at room temperature, and 350 K, respectively.     

Effect of the milling method and particle structure on the color tone of (Cr,Fe)2O3 inorganic black masterbatch pigment

(Cr, Fe)₂O₃ pigment was milled using different techniques into the same particle sizes to investigate the influence of milling processes on its properties. The research showed that milling type resulted in significant color differences, accompanied by the pigment color changing from intense reddish-brown to dark brown. Differences in the morphology of the particles embedded in the plastic matrix led to different light scattering, which is observed as a decrease in the color saturation of the pigment. Particle size distribution (PSD) was characterized by measuring with a laser diffraction particle size analyzer. Pigments were milled down to 4 µm in all milling methods. The very small particles in the pigment affected the light scattering and the color tone. The particle size of the pigment milled by the planetary mill was D₁₀ = 0.035 μ ± 0.1. Color values of the plastic plates were measured according to CIE laboratory analysis. The pigment milled with the planetary mill was lighter, greener, and yellower (ΔL*=4.15, Da*=3.68, Db*=2.96). The pigment milled with the jet-mill was closest to the pigment color after calcination. The pigment milled with ball mill was slightly greener than the values after calcination (Da*=1).     

湿法机械球磨制备片状镍粉研究

以类球形镍粉为原料,进行了湿法机械球磨制备片状镍粉的试验,考察了乙醇体积、球料比、球磨转速、球磨时间及助剂用量等因素对镍粉形貌的影响,采用XRD、SEM等对镍粉结构形貌进行了表征分析,确定了最佳工艺条件:乙醇体积60mL、球料比30:1、球磨转速450r/min、球磨时间3.5h、助剂A用量2%。在该条件下,得到的片状镍粉径厚比89,表面光滑平整,碎片粘附少,具有良好的金属光泽;其微观结构表明,球磨过程中,镍粉的微观内应力逐渐增加,晶粒不断细化;而且产品的片状化程度与<200>择优取向度有关。     

Relation between microstructure and Charpy impact properties of an elemental and pre-alloyed 14Cr ODS ferritic steel powder after hot isostatic pressing

This article describes the microstructure and Charpy impact properties of an Fe–14Cr–2W–0.3Ti–0.3Y₂O₃ oxide dispersion strengthened (ODS)-reduced activation ferritic (RAF) steel, manufactured either from elemental powders or from an Fe–14Cr–2W–0.3Ti pre-alloyed powder. ODS RAF steels have been produced by mechanical alloying of powders with 0.3 wt% Y₂O₃ nanoparticles in either a planetary ball mill or an attritor ball mill, for 45 and 20 h, respectively, followed by hot isostatic pressing (HIPping) at 1,150 °C under a pressure of 200 MPa for 4 h and heat treatment at 850 °C for 1 h. It was found that the elemental ODS steel powder contains smaller particles with a higher specific surface area and a two times higher oxygen amount than the pre-alloyed ODS steel powder. After HIPping both materials exhibit a density higher than 99%. However, the pre-alloyed ODS steel exhibits a slightly better density than the elemental ODS steel, due to the reduced oxygen content in the former material. Charpy impact experiment revealed that the pre-alloyed ODS steel has a much larger ductile-to-brittle transition temperature (DBTT) (about 140 °C) than the elemental ODS steel (about 25 °C). However, no significant difference in the upper shelf energy (about 3.0 J) was measured. TEM and SEM–EBSD analyses revealed that the microstructure of the elemental ODS steel is composed of smaller grains with a larger fraction of high-angle grains (>15°) and a lower dislocation density than the pre-alloyed ODS steel, which explains the lower DBTT value obtained for the elemental ODS steel.     

Preparation and performance of MAX phase Ti3AlC2 by in-situ reaction of Ti-Al-C system

In order to clarify the effects of the proportion of raw powders, heating temperature and holding time on the purity and properties of MAX phase Ti₃AlC₂, powder mixtures of Ti, Al and C powder with different ratio were prepared by planetary ball mill and heated under different conditions by spark plasma sintering. The microstructures and phase structures of the as-synthesized samples were characterized, the correlation between the mechanical properties and microstructure and fracture mechanism were investigated systematically. The results show that with the proportion of raw powders Ti:Al:C = 3:1.2:2, the sample heated at 1300 °C for 60 min has the highest purity 97.23 wt% of MAX phase. It has a compact and uniform lath-like structure with the length-thickness ratios of 3–5 and excellent comprehensive mechanical properties: the Vickers hardness, bending strength and fracture toughness are 5.26 GPa, 500 MPa and 7.35 MPa∙m^1/2, respectively. The experimental results show that among the three factors, the proportion of raw powders has the greatest influence on purity of Ti₃AlC₂ phase, followed by heating temperature and holding time. The fracture morphologies of the tested samples demonstrate that under the action of external force, extrusion and kink occurred in the layered structures of Ti₃AlC₂ phase. These two forms of energy dissipation lead to the bending strength and fracture toughness of Ti₃AlC₂ are higher than that of traditional ceramics.     

Hydrogen for oil refining via biomass indirect steam gasification: energy and environmental targets

The energy and CO₂ consequences of substitution of a fossil-fuel-based hydrogen production unit with a biomass-based process in a large European refinery are studied in this study. In the base case, the biomass-based process consists in atmospheric, steam–blown indirect gasification of air-dried woody biomass followed by necessary upgrading steps. The effect of gradually substituting the current refinery hydrogen production unit with this process on global energy and CO₂ targets is estimated first. Few process concepts are studied in further detail by looking at different degrees of heat integration with the remaining refinery units and possible polygeneration opportunities. The proposed process concepts are compared in terms of energy and exergy performances and potential reduction in refinery CO₂ emission also taking into account the effect of marginal electricity. Compared to the base case, an increase by up to 8 % points in energy efficiency and 9 % points in exergy efficiency can be obtained by exploiting process integration opportunities. According to energy efficiency, steam production appears the best way to use excess heat available in the process while electricity generation through a heat recovery steam cycle appears the best option according to exergy efficiency results. All investigated cases yield to significant reduction in CO₂ emissions at the refinery. It appears in particular that maximal emission reduction is obtained by producing extra steam to cover the demand of other refinery units if high efficiency marginal electricity scenarios are considered.