Cyclone Circuit Research Articles

Coal dense medium separation dynamic and steady-state modelling for process control

Coal dense medium separation is a popular beneficiation process used for the upgrading of coal ore into power station and metallurgical coal. The control systems used in coal beneficiation are often limited to localised regulatory control of feed rate and medium density. A coal dense medium separation process can benefit substantially from process control provided that a dynamic model for this process is available as was previously developed by the authors for a fine coal dense medium cyclone (DMC) circuit. In this paper, the previous model is adapted to a coarse coal DMC circuit and validated over a wider range of operating conditions using real plant data. The model is further validated by reducing it to steady-state to form a partition curve. This curve is then compared to one derived from actual production data. The derived model is able to provide an estimate of the DMC overflow coal product that should be sufficient for process control.

Improving energy efficiency of cyclone circuits in coal beneficiation plants by pump-storage systems

A pump storage system (PSS) is introduced to the coal preparation dense medium cyclone (DMC) plants to improve their energy efficiency while maintaining the required medium supply. The DMC processes are very energy intensive and inefficient because the medium supply pumps are constantly over-pumping. The PSS presented is to reduce energy consumption and cost by introducing an addition medium circulation loop. The corresponding pump operation optimization problem in the PSS scheme under time-based electricity tariff is formulated and solved, based on which the financial benefits of the design is investigated using life cycle cost analysis. A case study based on the operation status of a South African coal mine is carried out to verify the effectiveness of the proposed approach. It is demonstrated that the energy cost can be reduced by more than 50% in the studied case by introducing a 160m3 storage tank. According to life cycle analysis, the PSS Option 1 yields an annual 38% reduction of the overall cost for the beneficiation plant with a payback period of 2.68years.

Medium Quality and DMC Performance – Composition of Plant Mediums

Detailed audits on the dense medium cyclone (DMC) circuits were conducted in an Australian Coal Association Research Project (ACARP) at a number of coal preparation plants in the NSW and Queensland coalfields of Australia. It was found that there were significant differences in the size distributions and the composition of the mediums between these plants. The amount of nonmagnetics in the medium was not constant, and this could have implications on the performance of the DMC circuit. At two of the plants involved, there were both primary and secondary DMC circuits. The results from these plants provide clear evidence that mediums are much more stable at higher densities due to the much higher volume fraction of particles in the medium leading to greater hindering of particle settling. It was found that a good quantitative description of the size distribution of the medium could be obtained by assuming that it had four constituents, clay with a mean nominal size of about 0.010 mm, magnetite with a mean nominal size of 0.040 mm, fine coal with a mean nominal size of 0.080 mm, and small coal with a mean nominal size of 0.450 mm.

Process Control for a Coal Washing Plant Using a Range Control Chart and Multidimensional Scaling Analysis

In this study, a coal washing plant dataset was evaluated by using the range control chart and multidimensional scaling analyses. These analyses were conducted on the density values of a heavy medium vessel circuit and a heavy medium cyclone circuit. The range control charts indicated that the variations in the density values for the heavy medium vessel circuit and the heavy medium cyclone circuit were significantly high. The density values for the heavy medium vessel circuit and the heavy medium cyclone circuit were examined by multidimensional scaling analysis. The results of multidimensional scaling analysis findings supported the results obtained from the range control charts. Finally, this study showed that the usefulness of statistical process control techniques, such as range control charts and multidimensional scaling analysis, in helping decision makers in coal washing plant management.

Assessment of performance of a fine coal processing plant through availability analysis and the Mann-Whitney U test for two samples

In this study, the Mann-Whitney U test for two sample and availability analysis are applied on equipments belonging to a heavy dense cyclone circuit in a fine coal processing plant. Through the results from the Mann-Whitney U test for two samples, it is determined that the coal sieves fed by the upper flow of the cyclone (S25, S26 and S27) and the coal sieves fed by the lower flow of the cyclone (S28and S29) are identical. Using availability analysis, the performances of the cyclone pump engine (CPE), the cyclone pump (CP) and the coal sieves are calculated. As the result of this analysis, it is found that the performances of these equipment ranges from 96.60 - 98.99% and that they operate with a high performance. As a result, it is determined that the performances of the equipment can be calculated using availability analysis and that the Mann-Whitney U test for two samples supports this analysis. Additionally, it is believed that these methods may help the monitoring of equipment in complex facilities and help improve fine coal processing plants. Key words: Availability analysis, the Mann-Whitney U test for two samples, fine coal processing plant, cyclone circuit.

An Analysis of Mass Balance and Fractional Particle Size Distributions of Coal and Magnetite in a Dense-Medium Cyclone Circuit

In this study, a complete mass balance of magnetite and coal in the various parts of a dense-medium cyclone (DMC) circuit was determined and fractional size distributions of magnetite and coal were analyzed for the circuit. The DMC overflow product contained 71.34% of the feed coal, whereas 88.35% of the feed magnetite reported to the DMC underflow. The majority of the magnetite (about 86%) was removed by the sieve bends in both the DMC underflow and overflow streams. Sixty-one percent of the raw coal within a size range of 0.50–20.00 mm was recovered as clean coal with an average ash content of 15.30%. About 77% of the feed magnetite having a size range of 75–600 µm was obtained from the underflow of the drain-and-rinse screen belonging to DMC underflow.

Quantifying the influence of classification with the 3 product cyclone on liberation and recovery of PGMs in UG2 ore

The UG2 ore in South Africa is exploited for its enrichment in the platinum group minerals (PGMs). Given that the PGMs are typically very fine grained, the potential for poor liberation is high, especially with conventional cyclones providing a poor split of the coarse silicates and fine chromites to the over and underflows, respectively. The 3 product cyclone has been developed as a potential solution to these problems by reducing the circulating load of chromite and providing a more liberated feed to the flotation circuit. Automated mineralogical analyses have been used to compare the differences in samples sourced from a conventional and a 3 product cyclone circuit and show that use of the latter, provides a better quality flotation feed with less coarse silicate particles, less PGMs locked in silicates and more liberated PGMs. This suggests that improving classification provides an additional means to better the theoretical grade recovery curve of the valuable mineral.

Fine coal circuitry considerations in treatment of soft coal with difficult washabilities

A typical process used in Chinese metallurgical coal preparation plants employs heavy-media separation to treat the coal coarser than 0.5 mm. The − 0.5 mm fine coal is treated with froth flotation. A major disadvantage of this process is that a large quantity of fine coal is recycled in the heavy-media cyclone circuit, which results in high magnetite losses. The − 0.5 mm fine coal in the media is a result of poor raw coal deslime screen efficiency and the continuous breakage associated with the processing of soft coal. Another disadvantage of this typical process is that some coarse clean coal particles are lost to the froth flotation tailings. This investigation focuses on the simulation of processing fine soft coal with water-only cyclone (WOC) and spirals. WOCs and spirals have become popular devices for treating fine coal. WOCs can operate at low specific gravity cut points to produce low ash clean coal while spirals tends to operate at high specific gravity cut points and act as a scavenger to rewash the underflow (refuse) from WOCs. The combination of WOCs and spirals can compete with a heavy-media cyclone with respect to both efficiency and clean coal yield when treating 1 mm × 100 Mesh fine coal. This fine coal processing circuit can subsequently increase the bottom size of the heavy-media cyclone feed from 0.5 mm to 1 mm which will reduce the loading of the heavy-media cyclone circuit. This change in circuitry thus reduces magnetite consumption without scarifying separation efficiency of the 1 mm × 0 size fraction. Furthermore, the reduction of the nominal top size of the froth flotation feed from 0.5 mm to 0.15 mm will greatly decrease or eliminate the loss of clean coal to flotation tailings.

Integrating flotation to improve the performance of an HMC circuit treating a low-rank fine coal

One reason that heavy media cyclone (HMC) circuits suffer from the inadvertent loss of magnetite and fine coal is the presence of nonmagnetic material in the magnetic separator feed. In this study, flotation was applied to the undersize fractions of the HMC drain-and-rinse screens to minimize these problems. These fractions, which contain 17.9% nonmagnetic material, are currently sent to magnetic separators and the nonmagnetic portion from the separators contains 39.1% ash. Applying flotation resulted in a clean coal product with an ash content of 8.7% and a calorific value of 6,300 kcal/kg. The refuse from flotation, which will be sent to the magnetic separators, contains 7.7% nonmagnetics.

Dense-Medium Cycloning of Fine Coal Refuse Material

Laboratory testing was carried out to evaluate the performance of a dense-medium cyclone for treating fine coal refuse. The tested material was obtained from the feed stream to a water-only cyclone circuit treating nominal −0.6 mm bituminous coal refuse material obtained from an existing waste pile. A 76.2 mm (3 in) diameter cyclone was used for all tests, which were carried out at three medium relative densities, with and without ultrasonic treatment. Fractional recovery (partition) curves were generated for several size fractions (g) from which the characteristic performance parameters (relative density of separation and probable error) were determined. In addition, the corresponding magnetite size selectivity parameters (cut size, sharpness index, and apparent bypass) were also determined. The results indicated that the dense-medium cyclone was capable of cleaning down to 0.037 mm. Ultrasonic treatment appeared to have only minimal impact on the overall separation of the coal and magnetite.

Hydrocyclone Circuits

A number of plant surveys have shown that hydrocyclones used for classification have significant problems with respect to the efficiency of size separation and the particle density effect. The issues of minimizing the amount of ultrafines and maximizing the amount of light coarse particles in the oversize flowstream require conflicting operational approaches with a single cyclone. Earlier modelling work suggested that the Three Stage Counter Current Cyclone Circuit was able to provide the best mechanism for addressing these issues compared to a single cyclone. In order to evaluate the potential of this type of circuit, a pilot-scale investigation program was initiated. This involved identifying the relationship between the key control variables and response variables in order to optimize the circuit. This circuit has been shown to achieve the following: ” A much sharper separation with a low level of ultrafines in the oversize stream due to two stages of cycloning. ” Marked reduction in the amount of misplaced coarse clean coal in the undersize flowstream. ” Reduction in the amount of ultrafine pyrite in the oversize flowstream. ” Lower separation sizes without impacting efficiency.

Appraisal and Optimisation of Dense Medium Plant Separations

An extensive plant-orientated testwork campaign was undertaken to quantify and determine the causes of significant dense medium cyclone operating inefficiencies. Comprehensive plant trials, with 20–30 people sampling up to 100 process (medium and coal) streams simultaneously for eight hour shifts permitted both magnetite media and coal processing characteristics to be simultaneously quantified. Dense medium classification and coal partition curves were principally used to show that the root cause of inefficient cyclone performance was related to incorrect magnetite particle size in the cyclone circuits. When magnetite with the correct specifications was used in the plant, the reasons for coarse magnetite in the cyclone circuits was found not to result from selective fine magnetite losses in the small coal circuits, but from a fundamental design flaw in the magnetite distribution system. The flawed system was shown to prevent correct specification magnetite entering the cyclone circuits, thereby starving t...