Critical Control Points – The Key To Sustaining Nameplate Flow And Realising Value Chain Optimisation

Instalment 2: Setting Things Up For Success:

Getting bulk solids to flow correctly is vital for plant operations and revenue. Unlike liquids, they require careful design, as flow problems are difficult to fix after construction and tend to occur in predictable places.

In the previous instalment(1) we introduced the concept of Critical Control Points (CCPs), which are defined as physical locations in the value chain where bulk solids flow issues have the potential to damage the business (quality, productivity, optimisation); and where preventative control measures can be applied.

This instalment we look at how you can apply this approach to help ensured bulk solids flow is an integral part of your plant’s design and operation without distracting from its primary processing objectives.

Fail To Plan?, Plan To Fail!

It may be well worn, but this cliché is very applicable when it comes to bulk solids flow, where baked in FLOW problems can plague a plant for its often shortened life!

Planning for controlled flow starts with an assessment of the “health” of your foundation documents, followed by application of a FLOW Analysis at Critical Control Points (FA@CCP) methodology to help identify gaps.

Doing so encourages discussion and resolution at this critical formative stage, before it’s literally too late (Figure 1).

The first milestone to establish is your process’s Bulk Solids Flow Objective (in this series we are illustrating points through the lens of one the biggest class of bulk solid flow processing categories; Mining and Mineral Processing (M&MP)).

Figure 1: The implications of late change in FLOW value-chains

Bulk Solids Flow Objective

The cornerstone of any M&MP study is the Basis of Design (BoD); a succinct statement of performance expectations. While BoDs can, and do, change (with sponsor’s approval) during study phase in response to study findings, there is always a current-best version to guide decision making activity.

In terms of designing for FLOW, there are three important considerations viz:

• FLOW Context
• Nameplate rate,
• Instantaneous rate,

FLOW Context

– The flow behaviour of raw bulk solids like ore and its derivatives are very sensitive to context. Without knowing the geometric, compositional and environmental context of a bulk solid and its intended flow path through the entire value-chain, it is impossible to achieve flow by design.

It should be noted that ore flow behaviour is so sensitive to these values that they need to be measured for your actual material. Bulk Solids Flow characterisation encompasses elapsed time so it takes time and is a specialised activity.

The results are however a life-of-plant asset which can be reused to inform future FLOW (engineering & operational) decisions. Conversely skipping this step in an attempt to save time and money is one of the M&MP industry’s biggest false economies, and reverting to “library values” is no better than ignoring the issue of FLOW completely.

Study phase is an exercise in making the decision that shape and dictate every aspect of a M&MP operation’s existence. Cognitive biases in relation to these decisions are the root cause of many of the biggest failures in the history of M&MP development(2).

Nameplate Rate

– The operation’s capability is normally expressed in the form of the number of tonnes of ore that it can process in a calendar year (tonnes/annum), which is colloquially referred to as the operation’s “Nameplate”.

This is the foundation value of the design and is the basis of calculation for the plant’s process economics. As it is reasonable easy to quantify and is reported quarterly to investors, it is used as a primary key performance indicator.

Instantaneous Rate

– Less commonly found explicitly expressed in BoD’s, yet far more important in terms of designing for bulk solids flow, is the operation’s instantaneous flowrate. Thanks to the second law of thermodynamics, M&MP operations experience wear continuously hence they need to have their rotatable spares changed out during routine maintenance shutdowns.

The number of available operating hours in a calendar year is typically in the range of 70-90% of its absolute hours (8,766 hr/y). The instantaneous flow during actual operation of the value chain therefore needs to be proportionally higher to ensure the annual nameplate value is achieved.

Usually expressed in the form of tonnes per unit time (e.g. tonnes/hr), the instantaneous rate, should be presented in the form of ranges to cover expected surges and spikes, as well as turn-down ratios, should be the basis of calculation for the detailed design and used to inform equipment sizing and selection decisions.

As basic as this seems, historically failure to make the distinction between nameplate and instantaneous rate has led to the construction of operations with (multiple) baked-in flow constraints leading to it being physically incapable of achieving its nameplate (equipment being erroneously sized on the nameplate not instantaneous rate+surge allowance), or equally problematic, operating of the entire value chain on a knife-edge (unable operate outside a very narrow flow range (aka “sweet spot”)).

Bulk Solids Flow Narrative

This is a qualitative written description of how the ore and its derivatives are intended to flow through the pit-to-port (or other site boundary) value chain. Unfortunately, like the instantaneous rate above, this simple BoD device is an often omitted from study phase reports.

The vacuum this omission creates means there is no overarching flow intent to guide the design process. Instead, the system flow narrative evolves in an ad-hoc manner without purpose, oversight or accountability.

If it is not described in the Bankable Feasibility Study (BFS), the study team will (must) fill in the gaps, but usually on a process unit operation by unit operation basis as opposed to the required systems approach. The main issues here are that bulk solids FLOW is a complex system where everything is connected.

In this operating environment it is common for detailed designers to deliver a metaphorical elephant when the owners were expecting/needing a thoroughbred racehorse.

Most of us in M&MP development are “doers”, hard-wired to spring into action and to do something rather than thinking things (like FLOW) through. When you design your plant in writing (using a human language), there are natural prompts that promote thinking about possibilities and options which nearly always act to improve your design.

Nobody feels bad when they modify a paragraph in a working document, but once things progress to detailed design the problems of an incorrect narrative start to become baked in and very expensive to rectify (if discovered that is).

After the plant is built and constructed, most flow problems are so constrained they can never be put right and go on to plague the operation for its life (Figure 1), often resulting in operational life “truncation” as a consequence of crippling financial impacts.

The bulk solids flow narrative should cover all possible operational scenarios starting with the baseline of normal steady-state operation at the instantaneous rate, but then expands to include unsteady-state events and core design intentions like:

• Start-up (from an empty [‘clean’] condition-including pre-requisite conditions),
• Controlled shutdown (ahead of scheduled maintenance for example)
• Emergency (crash) stop,
• Restart (from both a controlled and emergency stop and long-sit initial condition)
• Extreme Conditions
  • Wetter, harder, finer, coarser… ore
  • Weather (temperature, wind, rainfall, humidity..),
• Cost trade-offs
  • Wear,
  • Dust controls,
  • Manual vs Automatic control posture.

The narrative should also describe the bulk solids flow through the entire value chain covering issues like:

• device sequencing,
• pre-requisite and interlocking events/conditions,
• what to monitor and where?
• what happens when it deviates from expectation?

Finally, the bulk solids flow narrative should also cover the future. Most plants are designed for 10-20 years of operation so:

• What might happen to the ore characteristics over that time (going below water table, grinding finer to accommodate ore texture changes for example)?

• Are there plans to increase the nameplate capacity (debottlenecking/expansion) at some point (usually a “Yes”)?

Designers need to be cognisant of the plants entire operating life so as not to create expensive bottlenecks and make future-proofing decisions up front. If the process involves reagents in bulk solid form (e.g. quicklime), have they been characterised? What happens if procurement finds a cheaper source during the life of the asset for example?

While all this does take effort, it is mainly just a matter of thinking things through with the sponsor. It is probably the most important element of a design for bulk solids flow approach, as you can’t meet the sponsors expectations if you don’t know what they are?

This aspect of the planning process ensures there are no “elephants in the design room”, so no one has to ride one in the Grand National!

Ignore the “FLOW by design” elephant in the design room? Ride it in the Life of Asset stakes!

Success Criteria

Every project should contain a formal Success Criteria table (Table 1) that brings together all the disparate elements upon which the completed project is to be objectively tested against.

Because it explicitly spells out what constitutes a success outcome in testable metrics, such a table is another common omission (a casualty of designers angling to maximise the wriggle room in the event of underperformance-human nature and failure of the sponsor to insist).

When such a table is included, it normally covers performance dimensions like capital spend, schedule, operating cost, metallurgical performance, financial returns, safety. They are nearly always silent on the one thread running through all these factors-flow (we have never seen one)!

A best practice Success Criteria table defines “Clear Failure”, “Clear Success”, with performance falling between these limits requiring outcomes to be individually judged and justified. In additional to mandatory sections covering safety and financial considerations, the Success Criteria table needs to include a dedicated section defining metrics that describe flow and its operational impacts. For example:

• Ability to satisfy the flow objective and narrative? (rates: instantaneous, peak, turn-down),

• Abrasive wear rates-spares replacement frequency,

Table 1: Best Practice Success Criteria Table Format (typical)

Risk Register

The final element of the foundation documentation set that needs to cover flow is the risk register-the living document that endures for the project’s entire life to ensures risks like those associated with FLOW, do not fall off the RADAR (especially between stages) and are run to ground.

All projects, especially M&MP based ones, involve uncertainty and risk. Having defined what success looks like in the Success Criteria table, the risk register lists the things that have potential to materially interfere with these objectives.

Once again, the risk registers found in most FS’s cover financial, schedule and metallurgical risks but seldom (never in our experience) identify element that could interfere with the FLOW objective. Given M&MP revenue is directly proportional to FLOW, this is another glaring omission.

If risks to control bulk solids flow are not on the register, they have no identity and receive not design attention. Even if flow related risks are on the minds of individuals, they usually get lost as the project moves through study phase into detailed design.

The risk register is the enduring tracking record and the main legacy document for the detailed design team which should list your project’s CCPs. If it is silent or incomplete with respect to FLOW risks, it needs to be updated at the end of the FA@CCP exercise to ensure all the outcomes are captured.

There usually a very satisfying difference between the before and after versions-you feel like you have added significant value and helped the project dodged the proverbial bullet.

Next Instalment

Having covered the concept of CCP and now the foundation documents required to set things up for success, in the next instalment we will show how you can objectively identify the CCPs in your flowsheet.

References

1. Process (2024). Process Industry Informer December 2024. [online] Processindustryinformer.com. Available here [Accessed 28 Mar. 2025].
2. Wellwood, G.A., 2017. One perfect (production) day – a bulk solids handling perspective. In Iron Ore 2017. Perth, Western Australia, Jul 24, 2017. Perth, Western Australia: Australian Institute of Mining and Metallurgy (AusIMM).

FAQs: Critical Control Points and Bulk Solids Flow

What are Critical Control Points (CCPs)?
They are key locations in the value chain where solids flow issues can impact productivity and where preventative control can be applied

Why is bulk solids flow harder to manage than liquids?
Solids behave differently depending on material properties context and geometry making flow highly sensitive and complex

What is the Bulk Solids Flow Objective?
A clear definition of what the process must achieve in terms of flow rate reliability and behaviour across all conditions

What is the difference between nameplate and instantaneous rate?
Nameplate is the annual processing capacity while instantaneous rate accounts for actual throughput during available hours

Why is a flow narrative important?
It describes how solids move through the system under all conditions helping guide purposeful and consistent design

What happens if flow isn’t planned properly?
Flow problems become baked into the plant leading to underperformance bottlenecks or early shutdowns

What should be in the Success Criteria table?
Testable metrics for safety finance and flow performance such as rates wear and spares replacement frequency

Why does the risk register need flow risks?
If flow risks aren’t recorded they’re not managed and design solutions to mitigate them will be overlooked

Can FLOW be fixed after construction?
Rarely – once built most flow issues become permanent limiting operational performance for the plant’s life

How does FA@CCP help?
It identifies flow-related gaps early so they can be addressed before they’re locked into the plant design