Meteng Pty Ltd

Design for Controllability

2010-12-06T20:53:00.000-08:00

Consideration of process control is an integral component of process plant design. For each key process operation objective there should be a primary method of control. Control design starts with flowsheet development and equipment selection.

All successful machines have simple controls: levers, steering wheels, pedals, buttons, or graphical pictures of these or similar control elements on display screens. The most satisfying machines to use are those where the control actions are well weighted for the process - where the response to a control action is predictable and becomes familiar quickly.

In some cases process plants are built with key controls missing or with too many controls that interact in a confusing or unpredictable manner (see Choosing the Right Controls).

An example of a primary control requirement that may be missed is a crusher in a two product screening system. If "as supplied" limestone is to be screened to supply suitable lump material for a kiln and fines for milling to limestone slurry then there should either be a way of crushing excess oversize or varying the screen aperture to achieve the required mass split to match the two user's requirements. If not, you may find you need to waste one product to make enough of the other.

Another example is the supply of lump size material as grinding (or washing) media in a once through pulper. If lump size in the feed is a requirement to be able to achieve proper pulping then a method of providing (or recycling) lump size to the pulper feed should be provided.

Both of these example problems can result from an assumption that a feed material will always meet a required specification.

These potential problems may be missed in the design when steady state conditions are considered but will become apparent from dynamic modelling, or "what if" testing of the steady state model for changing conditions.

Meteng Pty Ltd can assist with flowsheet evaluation for controllability analsysis, steady state and dynamic modelling, and much more.

Control Strategies for Multi Purpose Circuits

2010-12-06T17:10:00.000-08:00

Some process plant circuits having piping and pumping systems enabling them to be configured to do many things. The process flows, chemistry, and the interlocks required for each configuration of the circuit can be completely different. The capacities of some equipment may be exceeded in some configurations, the gain of some control loops may change drastically, and there can be unexpected results from interlocks leading to loss of process containment or equipment damage.

The first step in designing a control system for a variable configuration circuit is to identify the individual process configurations and to consider the process control requirements for each, and for combinations of configurations with the other circuits they interact with.

Then common elements of the control requirements may become apparent and some compromises in tuning can be made that work for more than one process configuration.

Finally it is most likely that some unique control strategy configurational changes will be required for specific process configurations - and a method of switching between control strategies will probably be required.

If you find many changes are being made to the control system to cope with changes in how the circuit is being run it may be time to look at the fundamentals of the circuit and the control strategy.

Meteng Pty Ltd has been involved in the development of a number of very successful process control strategies and we have also seen many of the problems you may be confronted with.

Choosing the Right Controls

2010-10-27T01:46:00.000-07:00

There are usually a number of different ways to implement a control system when there are a few measured variables to be controlled and a few manipulated variables that can be used to achieve the control.

A sub optimal control strategy may seem to work OK most of the time but will give poor performance and will possibly cause plant shutdown in upset conditions. Having an optimal control strategy can be the difference between having long steady production campaigns and having many seemingly unrelated shutdowns caused by problems with subsystems.

There are many ways to analyse control strategies such as Relative Gain Analysis, Relative Disturbance Analysis, Inverse (and Direct) Nyquist Plot Analysis. These methods can provide a sound methodology for improved control strategies and design of multi variable decouplers.

We have been involved in many basic and advanced control systems including the use of economic optimisation at a complex sequential flotation plant and the design of multi variable control for milling circuits.

Whether it is a simple system that needs to be made more reliable or a complex system that should be optimised, we can help.

Goro Nickel Achieves HPAL Milestone

2010-10-02T20:12:00.000-07:00

Goro Nickel achieved a major milestone in September 2010 by continuous operation of one train of the HPAL circuit for more than 500 hours with design availability and leach performance.

The HPAL circuit design and ease of operation sets new standards for the industry.

We wish to congratulate all involved in design, construction, commissioning, and operations. The smooth transition from commissioning to operations was achieved by close co-operation between the groups using a “one team” approach under the control of the operations group.

Meteng Pty Ltd has been involved in the Goro Nickel Project since 2003, developed the integrated METSIM model, conducted studies using the model re-define aspects of the flowsheet, generated the heat and mass balance for the entire Goro Nickel Project and conducted specific design projects including the innovative and very successful design of the HPAL circuit slurry heaters.

Meteng Pty Ltd provided support services for commissioning of the HPAL circuits and now provides engineering services for troubleshooting and production assistance for the Leaching Operations Group.

Other nickel laterite projects and studies Meteng Pty Ltd has been involved with include:

Cawse Nickel, Ravensthorpe Nickel, Coral Bay (Rio Tuba), Murrin Murrin (now Minara), San Felipe Mining.

Dynamic Process Simulation Using METSIM

2010-10-01T03:55:00.001-07:00

METSIM is an industry standard for steady state heat and mass balances in the mining, mineral processing, and metals refining processes.

In its standard mode it runs until convergence criteria are met which indicate that the changes from additional calculations are no-longer significant and then it stops as it has completed the calculations for the steady state solution.

METSIM can also be configured to run dynamically, using standard control functions (such as PID, ratio control etc) to move material between unit operations that make changes to the materials passing through and /or have surge capacity.

All the required functions for heat and mass balance calculations are available for steady state and dynamic modelling.

Traditionally dynamic models built using METSIM have been used to study the effects of changes that occur on a daily basis (such as material movements between stockpiles or leach heaps). These models are useful for providing the design data for processing plants that must be built to produce an annual production target with changing feed composition and rainfall.

There are other software programs that are written with many features specifically intended for the dynamic modelling of processes which can be used as simulators, solving continuously (or at least every few seconds) and providing values for many variables calculated with each iteration.

We have developed methods to achieve all the required functionality in METSIM for dynamic flow of liquids and gases through piping networks with all the required control elements. We have done this because METSIM provides and ideal platform for developing of any functionality required and for integration with other systems.

We are using this customised functionality and integration of METSIM with other software as the foundation for the process calculations in a dynamic simulator which can be used for operator training, control system testing, and process optimisation. We have combined the dynamic process model with a stand-alone control system and a walkthrough 3D model to provide games like environment. Live data is available in the 3D model and actions can be taken from within the 3D model such as opening and closing valves, starting and stopping pumps etc.