When I was a junior metallurgist doing shift training and familiarisation my supervisor told me that the capacity of a plant is not what the designer says it is, it is the maximum tonnage that causes the quantity of spillage the foreman can make the guys easily clean up. This sounded a reasonable way to select a ‘bottleneck’.
There are many other symptoms of a bottleneck, and most plants will have at least one as it operates as close to maximum as possible. These can include, but are not limited to things like:
- Persistent high-high level indications in bins or hoppers
- Overloaded circulating load equipment, or conveyor and pump loads
- Overflowing process tanks, especially in leaching operations
- Level control valves at 100% open (maybe overflowing slurry into flotation cell launders)
- Tails pump overloads
- Too high a pressure with all cyclones operating
- Too high a density or flow in process lines, maybe causing abnormal wear or pump overload
How to Identify a Bottleneck
If a bottleneck is not obvious then defining a bottleneck will involve performing and addressing a gap analysis. This is usually a four stage process.
1. Measure the Problem
Measuring the problem involves checking the performance of the essential parameters for the successful operation of the plant and checking that the equipment is operating to that requirement.
The requirement of some mechanical equipment may be determined from design documents like the Process Design Criteria (PDC) or vendor data. The latter will probably be in excess of the PDC value. Transporting equipment, such as pumps and conveyors, can be compared to their design requirement and then checking if the current usage reflects the design.
The important factor here is measuring the parameter and the equipment performance in an accurate and auditable manner. It is a common process rule that ‘if you cannot measure it you cannot control it’. Therefore the measurements must be accurate so they cannot be dismissed as an aberration.
2. Assess the Issues Around the Problem
The second stage of the gap analysis is to check if the ‘problem’ determined is the cause or the effect of the bottleneck. This varies with each operation so it needs an experienced eye to analyse these issues.
One point may be when a crushing section recirculation conveyor is persistently tripping on overload, without affecting the rest of the operation. A conveyor belt speed increase using a bigger drive can therefore be considered.
It may be that the crushers are not being choke-fed so they are not reducing the material to the size it needs to be to pass from the circuit.
Another symptom may be that the tails line is overloaded but the cause may be a continual operating sump pump or an underperforming thickener causing the actual problem, not the pumps.
Fixed items such as hoppers, tanks and bins need to be considered - but it should be realised that they are symptoms of a flow problem. Fitting extension pieces will not fix the problem.
3. Address the Problem
The third stage is to determine a fix and this usually requires some form of business case. Just because something is a good idea it may not be underpinned by a positive business case, so it’s important to define the benefits of the change in dollar terms.
To do this usually involves considering increased performance (usually product grade and recovery) or reduced operational costs.
Other cost inputs should also be considered, especially energy and reagents, as these are getting more expensive over time. Taking a load off the conveyor will reduce its load and save energy, which can be well defined.
4. Make the Change
The final stage is to initiate the change in a controlled, safe and well-managed manner. The changes should be documented and reported in a way that can be used to assist the next stage of the debottlenecking.
It is well known that once the plant is operating as best it can someone will look for more. This is a valued activity called ‘continuous improvement’ and it should be applied vigorously.
Is It Time for a Bottlenecking Audit?
Engenium has a team of engineers well experienced in plant design and operation that can navigate the documentation, plant readings and sampling activities that are needed for a bottlenecking audit. Engenium’s team of Process and Discipline Engineers, Project Managers and support staff welcome the opportunity to discuss how we can assess your operation and provide solutions to your plant’s bottlenecks.
Principal Process Engineer, Perth WA
Engenium Pty Ltd