Process Engineering is a discipline that encompasses the study (analysis), design, operation and maintenance of material manufacturing processes. Process engineering is present in a wide range of industrial activities, including petrochemical, mineral processing, material engineering, biotechnology, food and pharmaceuticals production, and high-tech semiconductor and superconductor applications.

 In the mining and mineral processing industry, process engineering entails studying mineral and ore, developing new industrial processes for the extraction of valuable minerals, managing the development of mineral processing projects (plant design and engineering) and auditing the performance and efficiency of mineral processing projects.

Role of Process Engineer

METS has been actively involved in many mineral processing projects over the past two decades. As part of the Process Engineering services offered by METS, the role of the Process Engineer involves:

• Sample and composite selection, in conjunction with the Geologist and Mining Engineer
• Development of testplans for metallurgical testwork
• Coordination and management testwork carried out by laboratories
• Writing up metallurgical reports
• Developing process flowsheets
• Developing process descriptions
• Developing a process design criteria
• Developing a process control philosophy
• Developing Piping and Instrumentation Diagrams (P&IDs)
• Developing the project equipment list
• Development of the operating costs for the processing of each ore type
• Developing data sheets and assisting with capital cost estimation
• Assessment of concentrate against market specifications

Our Process Engineering team has accumulated considerable expertise in mineral processing and metallurgical extraction for a wide array of mineral ores. In particular, METS specialised in projects involving the following products:

Precious Metals: Gold, Platinum, Osmium, Iridium
Rare Earth Minerals: Vanadium, Niobium, Tantalum, Uranium, Thorium, Ilimenite, Zircon, Rutile, Monazite, Tin, Silicon Germanium, Arsenic, Antimony, Bismuth
Common Metals: Copper, Iron, Aluminium, Nickel, Cobalt, Lead, Zinc, Chromite
Industrial Minerals: Talc, Kaolin, Diatomite, Feldspar, Gypsum, Lime

Flowsheets

Flowsheets are the conceptual models for the processing of mineral ore. They are the foundation stones of the development of any mineral processing project. The flowsheets are derived from the initial studies and metallurgical testwork carried out on mineral samples.

Flowsheets are living documents. They are iteratively refined to ascertain that the client’s requirements are met, to ensure the operability of the project and to improve the efficiency of the processes defined. Process flowsheets incorporate the features directly related to the mineralogical properties to be exploited in the processing and the product characteristics targeted. They also take into consideration the economic, environmental and efficiency constraints specific for each project. Moreover, flowsheet development usually has features included based on the skill, experience and knowledge of the Process Engineer to improve the performance and efficiency of the processes.

Typically, a process flowsheet is the graphical representation of a process. It can portray part of a process or the whole process. However, it should comprise of the major processing units laid out in logical and innovative manner. Process flowsheet can be as simple as block flow diagrams or as complex as mass balance and P&ID diagrams. For example, the process flowsheet below illustrates the process flow for part of a typical Vanadium Oxide production plant:

A process flowsheet may also focus on one particular processing unit, providing process flow definition in even more detail. Generally, process units used in the mineral processing area are:

• Crushing
• Grinding
• Flotation
• Gravity concentration
• Thickening
• Filtering and drying
• Roasting
• Leaching
• Solvent extraction
• Adsorption of gold
• Stripping
• Smelting

 
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Metallurgical Testplan

Crucial inputs to flowsheet development are the metallurgical results obtained for the mineral/ore sample. The result of the metallurgical testwork has a defining influence on all the process units of a mineral processing plan. As part of its services, METS provides the management of metallurgical tests from beginning to end. The workflow below illustrates METS’ standard procedure for conducting the metallurgical testwork:

METS works in close collaboration with laboratories to plan and supervise the testwork programs on behalf of clients. The supervision of the program enables a proactive evaluation of the testwork results and on-the-fly adjustment to the testplan, if necessary. METS has accumulated considerable experience in planning, conducting and supervising the following types of metallurgical testwork:

• Head assay
• Abrasion Index (AI)
• Bond Ball Work Index (BWI)
• Bond Rod Work Index (RWI)
• Bond Crush Work Index (CWI)
• Unconfined Compressive Strength (UCS)
• JK Parameters/JK Drop Weight Test
• Autogenous Media Competency (AMC)
• Grind establishment - Mill sizing, Circuit selection
• Leach tests
• Fleming constant: k & n, CIP, CIL, stripping plant
• Oxygen uptake rate
• Water quality - lime consumption, elution performance
• Slurry viscosity
• Settling tests
• Filtration rates

Metallurgical testwork is necessary from the initial mineral processing plant development phase through to the end of life of the mine. This is due to the variation in the mineral ore characteristics during the lifetime of the plant, to address performance degradation or re-alignment for compliance to standards and regulations and to take advantage of advances in mineral processing technology. In the initial feasibility study stage, metallurgical testwork is required to provide an indication on the optimum mineral processing method and guide the process of equipment selection. The table provided below shows a matrix of the different types of testwork required for the different phases of processing plant project development:

Process Design Criteria

In conjunction with the GA and metallurgical testwork, the design of the process flowsheet should include carefully tuned operating parameters, called the Process Design Criteria (PDC), to achieve optimum performance. The table below gives an example of a PDC, which, together with the flowsheets, the equipment specification and plant layout, is used to determine the plant specification and performance characteristics:

 
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The Mass Balances

A mass balance is an account of mineral entering and leaving a process. It is based on the conservation of mass principle, i.e. that matter cannot disappear or be created. Mass balances are used, for example, to analyse alternative processes, in pollution dispersion models etc. A mass balance diagram, shown below, is essentially a block flow diagram representing the mass flows of all material throughout the process. In other words, input must be equal to output between all process units and for the entire process. Therefore, for any change in a process the mass balance must be updated to reflect changes of the balance in each of the process streams.

The Equipment List

The equipment list is the list of mechanical equipment that will be used in the mineral processing plant. After defining an optimum processing method, the Process Engineer needs to select the appropriate equipment and control instruments to implement the process. METS has an extensive expertise in the selection of process equipment and has a reputable track record of recommending equipment of well-known and respected brands.

Together with its proven experience in Process Engineering and the use of robust quality equipment, METS ensures that processing plant can operate safely at a high level of performance, with long equipment life, minimum maintenance cost and plant shut-down time. The following is an example of a typical equipment list:

Piping and Instrumentation Diagram (P&ID)

Process Flowsheets depict process equipment connected by the major process routes and contain basic data on the essential process control circuits or process requirements. The flowsheets are not drawn to scale and the equipment items are represented by symbols. The main equipment items and flow streams are identified and included in tables which identify process requirements in sufficient detail to enable production of the P&IDs. P&IDs are diagrams which show the interconnection of process equipment and instrumentation used to control the process. In the process industry, a standard set of symbols is used to prepare P&IDs.

P&IDs are recognised as definitive and comprehensive diagrams showing all control loops, equipment, piping, valves and instrumentation. All items in the drawing are identified and tabulated in order to maintain simplicity. Thus, process equipment, valves, instruments and pipe lines are tagged with unique identification codes, set up according to their size, material fluid contents, method of connection (screwed, flanged, etc.) and the status (Valves - Normally Closed, Normally Open). For instance, a particular pipe can be identified as following:

 
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Financial Services

Beyond the technical aspect of Process Engineering, most resource project must be demonstrably viable and even financially attractive in order to acquire the necessary funds for the project to see the light of day. To address this important aspect of resource projects, METS offers reliable and accurate financial modelling services to its client. The financial modelling encompasses the estimation of the project’s capital investment requirement and operating cost.

Capital Cost

METS has an excellent record in accurately estimating project costs and has developed a high level of expertise in developing capital cost estimation for a broad range of projects in the resource sector.

In developing a project capital cost estimate, METS will:

• review the scope of the project and the accuracy of estimation that is required
• establish a work breakdown structure based on the detailed project content
• determine pricing based on:
  • vendor quotes
  • engineer quantities
  • METS’ CAPEX database

Capital is a scarce commodity and must be allocated so that the best projects, as indicated by measures such as Return on Investment (ROI), are given priority. Some of the direct cost elements that should be included in the capital cost estimation are:

Earthworks – Allowance included for bulk earthworks for plant, infrastructure and water dam based on costs for similar plants and quotes received from contractors. In some cases, contour or geotechnical information is used to confirm the accuracy of the estimation.

Concrete – Quantities are usually estimated for the anticipated layout based on experience with similar projects. The estimated cost would normally include concrete supply, earthworks, formwork, reinforcement, placement and finishing.

Structural Steel and Platework – Quantities are estimated for the anticipated layout based on experience with similar projects. The cost estimation would normally include fabrication rates for new steel inclusive of detailing, supply, fabrication and surface treatment.

Mechanical Equipment – Cost estimates are usually based on quotes obtained from equipment suppliers. Depending on the constraints of the project, METS can research second hand refurbished equipment, which can help reduce capital cost substantially.

Equipment Installation – Cost estimates take into account labour and construction equipment for installation of the various items of mechanical equipment. The estimates can be based on similar items from similar projects or from quotes received from contractors.

Pipework and pipelines – Normally, the cost estimation is based on experience with similar process plants and quotes received from contractors.

Electrical and Instrumentation – Cost estimation is based on experience with similar process plants and quotes received for electrical supply, distribution and instrumentation.

Infrastructure Buildings – Cost estimations are based on contractor quotes for plant infrastructure buildings shown on the preliminary layout drawing.

In addition, the capital estimation will include some of the indirect capital costs incurred by resource project including engineering, management (EPCM), temporary facilities, contingency plans and other service fees.

 
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Operating Costs

All resource projects are invariably very sensitive to operating costs and, in many cases, this will be the single defining characteristic of the project. In Australia, power consumption and fuel are major costs centres in comparison with labour and other consumables' costs. In today’s tough economic environment, dictated by fierce rivalry and frequent fluctuating metal prices, there has been ever increasing emphasis on controlling operating cost in order to remain profitable. This trend is expected to continue and the potential to reduce costs by re-examining plant performance will often highlight areas where savings can be made.

Also, as part of our financial modelling methodology, METS uses Sensitivity Analysis to obtain a precise indication on the factors that influences the profitability of projects, namely: metal prices, the mill feed grade, metallurgical recovery cost and other operating costs mentioned earlier. The Sensitivity Analysis, usually prepared in graphical form to show the project’s sensitivity to the various factors, provides a measure of robustness of the project to changes in key financial parameters. A typical graph of a ±10% sensitivity analysis is shown below: