Grinding Plant Research Articles

Calculation of the corporate carbon footprint of the cement industry by the application of MC3 methodology

Cement is one of the most widely used construction materials in the world. Its characteristics, physicochemical properties and manufacturing process have long been the object of study. However, at this moment in time, the production of this basic construction material still accounts for 5% of worldwide emissions of CO 2 into the atmosphere. Thus, in this age of the ongoing battle against climate change, cement alone has become a key objective to which measures must be applied to mitigate the negative impact of this material on the environment. This article evaluates the sustainability of a cement industry by using one of the most rigorous tools currently in existence – the Composed Method of Financial Accounts (MC3) in its second version V.2.0. The study is based on the analysis of three model plants: (A) a conventional integral plant, (B) a grinding plant, and (C) an integral plant which has introduced the best available techniques or BAT into the manufacturing process. Therefore, the two most common scenarios in today's market (A and B) can be compared with another plant of the same size (C) in which CO 2 emissions are reduced thanks to the application of BAT. Lastly, the results are compared in each case study, establishing a diagnosis of weaknesses and opportunities for each production system as well as specific measures for action to be applied to each link in the chain that makes up the production process. Also computed is the amount in tons of CO 2 generated in the manufacture of one ton of cement. This value is of great use in the application of other methodologies such as LCA, or in the feedback of the MC3 methodology used here.

Successive centrifugal grinding and sieving of wheat straw

Grinding plant biomass may allow the lignocellulosic assembly to become more reactive/accessible by providing energy for polymer dissociation, increasing contact surface (particle size reduction) and reducing cellulose crystallinity. Moreover lignocellulosic composition varies considerably affecting biomass processability as resource for bio-based energies, composite materials and chemicals. The aims of this work were: (i) to analyse composition of wheat anatomic parts present into wheat straw, (ii) to characterize the behaviour of major components upon successive centrifugal grinding steps (2 mm-screen cutting milling followed by 4-step centrifugal grinding) and (iii) to relate particle size distribution and component concentrations into the finest sized product (0.12 mm-screen ground). The powders from successive centrifugal grindings were sieved and their chemical compositions were determined. Ground straw powders were heterogeneous according to different particle aspects: size, shapes and roughness. In general fractions with lower particle size had higher ash and protein contents whereas cellulose contents are higher in the larger fractions. Wheat straw exhibited a non homogeneous reduction behaviour when finely ground. Fraction compositions were only slightly distinct suggesting that although sieving can constitute a preliminary fractionation step, it is necessary to reduce still more the particle size to reach more effective dissociation of macromolecules assembly.

Economic Analysis of Manufacturing Costs of Pellet Production in the Republic of Ireland Using Non-Woody Biomass~!2009-07-23~!2009-12-22~!2010-03-02~!

An economic analysis of a non-woody biomass pelleting process was performed for conditions in the Republic of Ireland. The analysis considered the establishment, harvest, storage and drying costs of the feedstock's on-farm, together with transportation costs to the processing plant and the costs associated with the pelleting process. Capital and operating costs of the pelleting process were estimated at several plant capacities - 6t / h, 8t / h and 10t / h. The pellet production cost for the base case scenario of 8t / h was � 102 / t of pellets produced. By decreasing production capacity to 6t / h an increase in the production cost of � 10 / t was experienced while increasing capacity to 10t / h resulted in a decrease of � 6 / t in the production cost of pellets. The cost of the raw material is the largest cost component (66%) of the total pellet production cost. Other major cost factors include pelleting and cooling plant (11%), straw grinding plant (10%) and personnel costs (9%). Considering current energy prices the equivalent energy cost of � 7 / GJ (excluding profit margins) the potential production of non-woody biomass pellets competes favourably with oil and gas and was found to be economically viable.

Foam Separation of Oil from Enzymatically Treated Wet‐Milled Corn Germ Dispersions

AbstractMore than 9 billion gallons of ethanol were produced in 2008, mostly from dry grind corn fermentation plants. These plants are a potential source of substantial amounts of corn oil, if an economical method of separating it can be developed. In this work, oil was separated from corn germ by aqueous enzymatic extraction (AEE). Batches of wet‐milled corn germ in water were preheated in a pressure cooker, ground in a colloid mill, and churned in a vertical column/mixing vessel system, after the addition of enzyme. Nitrogen gas was then bubbled through the column removing an overflowing foam fraction which was subsequently centrifuged to separate free oil. Using a newly commercialized enzyme complex it was found that 80% of the oil could be recovered using a w/w ratio of enzyme solution to germ of 1:80. The low dose and low price of the enzyme complex leads to a cost estimate of AEE of corn oil from germ, similar to the wet‐milled germ extracted, cost competitive with expelled oil (with the separation and drying of the foam protein), and feasible for commercialization in a dry grind plant retrofitted to separate germ.

Pilot scale fiber separation from distillers dried grains with solubles (DDGS) using sieving and air classification

Distillers dried grains with solubles (DDGS), the coproduct of fuel ethanol production from cereal grains like corn, is mainly used as cattle feed and is used at low inclusion levels in poultry and swine diets because of high fiber content. Elusieve process, the combination of sieving and air classification (elutriation), was developed in laboratory scale to separate fiber from DDGS to result in a low fiber product which would be more suitable for poultry and swine. In this pilot scale study, DDGS was sieved at a rate of 0.25 kg/s (1 ton/h) into four sieve fractions using a sifter and the three largest sieve fractions were air classified using aspirators to separate fiber on a continuous basis. Results were similar to laboratory scale. Nearly 12.4% by weight of DDGS was separated as Fiber product and resulted in two high protein products that had low fiber contents. Payback period for the Elusieve process in an existing dry grind plant processing corn at the rate of 2030 metric tonnes/day (80,000 bushels/day) would be 1.1 yr.

A Two-phase Objective Function for a Constrained MPC and Its Application to a Grinding Plant

In the paper a two-phase MPC controller is described that uses a non-quadratic terminal cost. The terminal cost is computed with respect to a predefined control strategy, and it can therefore be treated as the second phase of the method. Because the problem of optimizing the MPC objective is not a quadratic programming problem, medium-scale, gradient-based optimization methods are used for the MPC implementation. The method is efficient for problems which have a lot of soft constraints, because it avoids the introduction of slack variables. The stability of the MPC is established in the paper, and the method is compared with an unconstrained MPC in the grinding plant optimization problem.

Multivariable Model Predictive Control of a Simulated SAG plant

This work presents the dynamic simulation and a multivariable predictive control strategy for a semi-autogenous grinding (SAG) plant. Models for SAG Mill, crusher and hidrocyclones have been integrated to simulate a SAG circuit. Data obtained from an industrial cooper concentrator has been used to estimate the main parameters of the dynamical models. The control strategy considers two levels: stabilizing and optimizing levels. The stabilizing level is based on a Model Predictive Control strategy with restrictions. In order to solve the optimization problem posed by this strategy, a standard Linear Programming solver has been selected. The optimizing level maximizes Power Draw using an online gradient estimation of the non-linear function between Power Draw and mill Hold Up. The results show that is possible to operate the SAG Mill in the optimal zone, compensate unmeasurable disturbances and maximize throughput without violating operational constraints. Moreover, the proposed control strategy has a modular structure; therefore its implementation can be carried out by parts. All the work has been done using Matlab® and the simulation platform Simulink®.

A Virtual Sensor for Estimating Particle Size of Hydrocyclones Overflow

In a grinding-classification circuit product quality is ultimately qualified by the particle size of the ore fed to the flotation stage. At Codelco El Teniente Division, the Unitary Grinding Plant product size is measured using analysis equipment based on slurry samples; this, for a number or reasons, has low availability, which does not complies with advanced control strategies requirements. This work presents the results obtained on developing an estimator or virtual sensor for hydrocyclones’ overflow particle size, which exhibits excellent performance and high availability sustained over time.

Composition of corn dry-grind ethanol by-products: DDGS, wet cake, and thin stillage

DDGS and wet distillers’ grains are the major co-products of the dry grind ethanol facilities. As they are mainly used as animal feed, a typical compositional analysis of the DDGS and wet distillers’ grains mainly focuses on defining the feedstock’s nutritional characteristics. With an increasing demand for fuel ethanol, the DDGS and wet distillers’ grains are viewed as a potential bridge feedstock for ethanol production from other cellulosic biomass. The introduction of DDGS or wet distillers’ grains as an additional feed to the existing dry grind plants for increased ethanol yield requires a different approach to the compositional analysis of the material. Rather than focusing on its nutritional value, this new approach aims at determining more detailed chemical composition, especially on polymeric sugars such as cellulose, starch and xylan, which release fermentable sugars upon enzymatic hydrolysis. In this paper we present a detailed and complete compositional analysis procedure suggested for DDGS and wet distillers’ grains, as well as the resulting compositions completed by three different research groups. Polymeric sugars, crude protein, crude oil and ash contents of DDGS and wet distillers’ grains were accurately and reproducibly determined by the compositional analysis procedure described in this paper.

Adaptive soft-sensors for on-line particle size estimation in wet grinding circuits

On-line particle size soft-sensors play an important role in the efficient operation of control systems in many industrial grinding plants. To cope with disturbances and changing operating points it will be necessary to adapt the soft-sensor parameters to the new conditions. This work proposes the use of constrained parameter estimation algorithms, in order to take into account some process prior knowledge and enhance the performance of the soft-sensor. Several experiments, using data taken from an industrial grinding circuit, illustrate the benefits of the proposed approach.

Fabrication, testing and evaluation of a dust filtration system for small-scale spice grinding mills

The generation of excessive levels of spicy aroma and the airborne dust in spice grinding mills is one of the main ergonomic problems of the workers and sometimes create social problems due to environmental pollution. Although the fine dust as well as the aromatic chemicals has an economic value, collection of them is fairly a difficult task under small-scale processing plants. A technically and economically feasible low-cost dust filtration system was designed to filter and maintain the concentration of airborne dust level below the recommended level of 10 mg/m 3 for 8-hour exposure time, in a spice grinding plant. The dust filtration system was designed based on a similar principle as in the existing spry tower filter. However, the method does not require very high pressure for fluid atomization as in that system and the unit can be fabricated using locally available materials with a very high lifetime. Dust measurements were carried out using a special cloth bag-collecting device with a fixed airflow rate. Dust removal rates were determined with different concentrations of a foaming shampoo (Lifebuoy shampoo) and a non-foaming detergent (‘Rinso’ automatic washing machine powder). Results showed that the filtration unit is capable of filtering airborne dust with an efficiency of 91% with the foaming detergent while an efficiency of 78% with the non-foaming detergent. An initial dust load of 108-150mg/m 3 in the air was reduced to 9.6mg/m 3 with the foaming detergent and 32mg/m 3 with the non-foaming detergent or tap water without any detergent. Therefore, the dust filtration system is effective only with the foaming detergent. The cost of the system is about Rs.11000.00 (US $ 110) and the estimated additional cost for dust filtration per one kg of processed chilli powder is about 52 Cents (US $ 0.005).

Jaw muscle functional anatomy in northern grasshopper mouse,Onychomys leucogaster, a carnivorous murid

The jaw muscle anatomy of the northern grasshopper mouse, Onychomys leucogaster, was observed and the mechanical basis of the insectivorous/carnivorous adaptations were examined. Compared with Peromyscus maniculatus, a granivorous relative of Onychomys, there is a reduction of some aponeuroses within the masseter deep layer. This characteristic indicates that shearing meat or crushing arthropod exoskeletons requires less occlusal pressure than does grinding plant material. In Onychomys both the anterior and posterior portions of the masseter deep layer are more anterodorsally inclined, so that the line of action of the masseter lies further from the jaw joint than in Peromyscus. A strong incisal bite for killing vertebrates such as other rodents can be produced by a jaw mechanism with the high lever advantage of this muscle, which compensates for the decline in muscle mass. Our quantitative analysis suggests that the disappearance of an aponeurosis along the zygomatic plate in Onychomys decreases the stretch of the corresponding muscle, i.e., the anterior fibers of the masseter deep layer, accompanying jaw opening, and increases the maximum gape necessary for hunting large prey.

Modeling of an industrial wet grinding operation using data-driven techniques

The data-driven modeling techniques have been applied to the industrial grinding operation of a lead–zinc ore beneficiation plant to predict the output variables, the key performance indicators (KPIs) for the circuit. Many grinding plants are not adequately equipped with measuring instruments that are used only to measure some of the output parameters leading to a major hindrance towards modeling the operation through the route of first principles. To add to this, for controlling the grinding operation, system identification of the process is a must and poses a critical problem in advanced control as the grinding process behavior is highly non-linear. This necessitates applying some advanced data-driven techniques that are capable of predicting the KPIs within some acceptable limits. A total of six important KPIs considered here are throughput, three size fractions (+150 μm, +63 μm, −38 μm), percentage solids and recirculation load. These KPIs are predicted using three manipulated variables, namely, solid ore feed rate, two water feed rates to two sumps. To capture the nonparametric model for these KPIs, the data-driven techniques used here are several versions of neural networks and wavelets. While using neural network topologies, feed-forward neural networks (FNN) and recurrent neural networks (RNN) are utilized whereas for wavelet-based networks, wavelet frames are used. A well-validated hybrid model, a combination of physical and empirical methodologies, is used to approximate the actual behavior of the plant. A set of data, generated from this hybrid model is used for training the above-mentioned networks whereas another exclusive set of data is used to validate the evolved data-driven models. Merits and demerits of each of these techniques are also presented. Implementation of these techniques based on analysis to the actual plant may influence implementation of control and optimization technologies and thereby enhancing the plant performance tremendously where lack of hardware sensors does not allow them to be a right candidate to take part in systematic exercises for plant performance improvement.

A multi-input-single-output smith predictor for feeders control in SAG grinding plants

The accurate control of feeders in semiautogenous grinding(SAG) mills plays an important role for obtaining good operational results. This brief presents the design of a Smith predictor for multi-input-single-output (MISO) systems, representing a set of feeders in a SAG plant. The design considers the special characteristics of the application, as well as issues like performance and robustness of the proposed controller. Experiments carried out at an industrial plant, under several operational conditions, demonstrate the effectiveness of the proposed strategy compared to the one based on a single proportional-integral derivative (PID) controller.

Advanced control of gold ore grinding plants in South Africa

The paper presents the advanced control systems installed by the authors in two gold ore grinding circuits in South Africa, with three lines at Anglogold Ashanti Mponeng mine and six lines at Anglogold Ashanti Kopanang mine. At both plants the advanced control system is based on the OCS© software, and combines the flexibility of an expert system with fuzzy logic and the power of an on-line dynamic phenomenological model used as an advanced soft sensor of the whole process. The history and implementation methodology is described, and the results—increases in throughput and gold recovery—are analysed. The improved control of particle size makes it possible to maximise gold recovery. This is discussed and illustrated.

PARTICLE SIZE DISTRIBUTIONS OF GROUND CORN AND DDGS FROM DRY GRIND PROCESSING

Ethanol production has increased in the past decade as a result of growth in the dry grind industry. In the dry grindprocess, the first step is grinding of corn. The particle size of the resulting ground corn can affect the fermentation processand the particle size of dried distillers grains with solubles (DDGS), a coproduct of dry grind processing. Few data are availablethat characterize particle size distributions of ground corn or DDGS. The objective was to determine particle size distributionsof ground corn and DDGS. Samples of ground corn and DDGS were obtained from nine dry grind plants; particlesize distribution, geometric mean diameter (dgw) and geometric standard deviation (Sgw) were determined. The dgw of groundcorn and of DDGS were not different among processing plants. The overall mean dgw of ground corn was not different fromthat of DDGS. Most of the ground corn (80 g/100 g) and DDGS (70 g/100 g) were recovered in the three largest particle sizecategories. The particle size distributions of ground corn were not correlated (r < 0.35) to particle size distributions of DDGS.

Biotechnological processes for conversion of corn into ethanol

Ethanol has been utilized as a fuel source in the United States since the turn of the century. However, it has repeatedly faced significant commercial viability obstacles relative to petroleum. Renewed interest exists in ethanol as a fuel source today owing to its positive impact on rural America, the environment and United States energy security. Today, most fuel ethanol is produced by either the dry grind or the wet mill process. Current technologies allow for 2.5 gallons (wet mill process) to 2.8 gallons (dry grind process) of ethanol (1 gallon = 3.785 l) per bushel of corn. Valuable co-products, distillers dried grains with solubles (dry grind) and corn gluten meal and feed (wet mill), are also generated in the production of ethanol. While current supplies are generated from both processes, the majority of the growth in the industry is from dry grind plant construction in rural communities across the corn belt. While fuel ethanol production is an energy-efficient process today, additional research is occurring to improve its long-term economic viability. Three of the most significant areas of research are in the production of hybrids with a higher starch content or a higher extractable starch content, in the conversion of the corn kernel fiber fraction to ethanol, and in the identification and development of new and higher-value co-products.

Optimization of continuous ball mills used for finish-grinding of cement by varying the L/D ratio, ball charge filling ratio, ball size and residence time

During the last decade, semi-finish-grinding plants have been used more and more for the energy efficient grinding of high-quality cement. In 1999, it was found that by decreasing the ball charge filling ratio it was possible to lower the specific energy demand for grinding significantly. It was obvious, too, that the L/D ratio influences the specific energy demand and the mill throughput as well. Therefore, a huge test program was carried with a semi-industrial ball mill, which was operated in closed circuit. The mass-specific surface area of the two feed materials (intermediate product) used were quite typical for industrial semi-finish grinding plants. The values were 2200 and 3000 cm 2/g according to Blaine. The product finenesses were 3000 and 3800 cm 2/g, respectively. The L/D ratio of the ball mill was varied in four steps of 1.75, 2.1, 2.79 and 3.49, and the ball charge filling ratio was varied in three steps of 15%, 20% and 25%. The experiments clearly indicated that the optimal L/D ratio and the optimal ball charge filling ratio are different for each feed fineness. The influence of the ball charge grading on the specific energy demand, characterised by the average ball diameter, was tested by means of a discontinuous laboratory ball mill. The results showed that by using a finer ball grading the specific energy demand could be lowered considerably. The obtained results can be explained well by theoretical considerations regarding the ruling stress intensity and the number of stress events. The stress intensity expressed as the power input per ball is dependent on the ball diameter to the third power and only slightly dependent on the inner diameter of the mill. The number of stresses can be characterised by the average retention time of the ground material inside the mill if the ball charge grading remains unchanged. The optimal retention time depends not only on the feed material and the desired comminution result but also on the ball charge filling ratio and particularly on the L/D ratio. On the basis of the present results and considerations, a specific optimisation of ball mills in semi-finish-grinding plants can be done.

Adaptive Soft-Sensors for On-Line Particle Size Estimation in Wet Grinding Circuits

On-line particle size soft-sensors play an important role in the efficient operation of control systems in many industrial grinding plants. To cope with disturbances and changing operating points it will be necessary to adapt the soft-sensor parameters to the new conditions. This work proposes the use of constrained parameter estimation algorithms, in order to take into account some process prior knowledge and enhance the performance of the soft-sensor. Several experiments, using data taken from an industrial grinding circuit, illustrate the benefits of the proposed approach.

High-calcium fly ash as the fourth constituent in concrete: problems, solutions and perspectives

Even though Hellenic high-calcium fly ashes of different origin are widely used by the cement industry for the production of several CEM II types of cements according to EN 197-1, their systematic use in concrete still presents some difficulties. This inhibits the establishment of specifications for their addition. Main problems concerning the quality are focused on variations in chemical and mineralogical composition, necessity for supplementary grinding, high proportion of free-CaO and periodically high proportion of SO3 content. These problems as well as the solutions, for every day use by the concrete industry, applied during the construction of a dam, are discussed, in this paper. To overcome these problems, untreated fly ash was cheaply upgraded by grinding at a specially designed ball mill, with simultaneously hydration, for the reduction of free-CaO. Details also (i) for fly ash variations in relation to their origin, (ii) the grinding plant and (iii) the industrial production of fly ash, are given. Finally, in a separate chapter of this paper, aiming to explain the treatment of fly ashes followed during their industrial production, data of the mechanical strength of mixtures of cements incorporating fly ashes with different treatment, concerning their free-CaO and their fineness, are given. (A) Reprinted with permission from Elsevier.