Crushing Circuit Simulation for Engineers and Consultants

Model open and closed circuits, simulate recirculating loads, and compare circuit configurations before committing to a plant arrangement.

Circuit configuration decisions have consequences that spreadsheets cannot fully capture

Choosing between an open and closed circuit is one of the most consequential decisions in crushing plant design. The choice affects product gradation, recirculating load, machine sizing, and the total plant throughput achievable for a given feed rate.

Most engineers work through circuit balance calculations using spreadsheets or vendor estimates. These approaches handle a single stage well, but they do not capture the interaction between all stages of the circuit simultaneously. A change to the secondary crusher CSS in a multi-stage plant affects the recirculating load at that stage, which in turn affects the total crusher feed rate, which affects conveyor and screen loads throughout the circuit.

Crushing circuit simulation solves this by calculating the full circuit mass balance in a connected model, so every change propagates through all stages simultaneously.

Open circuit and closed circuit: what they actually mean

Open circuit

In an open circuit, material passes through the crusher once. It may be screened afterwards to classify product fractions, but oversize is not returned to the same crusher. Material that does not meet the target size specification either passes to the next crushing stage or becomes a coarser product.

Open circuits are simpler to operate and require less equipment, but they produce a wider product gradation and less control over the top size of the product.

Closed circuit

Closed-circuit operation is most commonly discussed around secondary or tertiary cone crushers and screens. Screen oversize is returned to the crusher, which increases the total crusher feed above the fresh feed rate and produces a tighter product gradation.

The key relationship is: Total crusher feed = fresh feed + returned oversize (recirculating load).

This matters for machine sizing: the crusher must be capable of handling the total circuit feed rate, not just the fresh feed rate. Under-sizing the crusher against fresh feed alone is a common design error that closed-circuit simulation makes visible.

Closed-circuit jaw crusher arrangements can exist but are less common at the primary stage. Most primary jaw crushers run in open circuit, with closing occurring at the secondary or tertiary stage.

Recirculating load convention

Recirculating load may be expressed as a percentage of fresh feed or as a percentage of total crusher feed. Always state which convention is being used, because the same circuit can appear to have different percentages depending on the definition. For example, a recirculating load of 150 t/h with a fresh feed of 500 t/h is 30% of fresh feed and 23% of total crusher feed (650 t/h).

How Quorr models crushing circuits

Quorr lets you build any circuit configuration and run a steady-state mass balance across the full plant. You connect crushers and screens in whatever arrangement your circuit requires, define feed conditions, and Quorr calculates throughput, product gradation, and recirculating load at every node.

Open circuit simulation

Model single-pass circuits where crusher discharge flows directly to the next stage or product stockpile. Material may be screened, but oversize is not returned to the same crusher.

Closed circuit simulation

Connect screen oversize back to the crusher inlet. Quorr calculates the recirculating load and total crusher feed rate as part of the circuit balance, and flags where the crusher is approaching capacity.

Multi-stage circuits

Build primary, secondary, and tertiary stages in any combination of open and closed configurations, and simulate them as an integrated system.

Pre-screening and product screening

Add pre-screening to remove fines before crushing, and product screens to classify output into multiple size fractions for different stockpiles.

How this is modelled in Quorr

In Quorr, a crushing circuit is modelled as a connected flowsheet. Each crusher and screen is a node in the circuit with defined inputs and outputs. The mass balance runs through all nodes simultaneously, accounting for recirculating material at each closed-circuit stage.

Recirculating load calculation

In a closed cone circuit with a given CSS and screen aperture, the simulation calculates how much of the crusher discharge exceeds the aperture, returns to the crusher, and adds to the total feed rate. This total feed rate is what the crusher must be sized for, not just the fresh feed.

Illustrative example: if fresh feed is 500 t/h and recirculating load is 150 t/h, total crusher feed is 650 t/h. Actual values depend on feed gradation, CSS, screen aperture, screen efficiency, and material properties.

CSS and aperture sensitivity

Tightening the CSS produces finer product and reduces the proportion of material that returns as oversize, reducing the recirculating load. Increasing the screen aperture reduces carry-over but passes coarser material to the product. Quorr lets you adjust both variables and see the circuit-wide effect immediately.

Multi-stage balance

In a two-stage circuit with a primary jaw in open circuit and a secondary cone in closed circuit, the secondary recirculating load feeds back only to the secondary crusher. The primary handles only fresh feed. Quorr keeps these boundaries correct automatically, regardless of how many stages you build.

Common circuit simulation mistakes

These are the most frequent errors in crushing circuit calculations, and the ones that circuit simulation is most useful for catching:

Sizing the crusher on fresh feed only: In a closed circuit, the crusher must handle fresh feed plus recirculating oversize. Sizing on fresh feed alone underestimates the required capacity.
Ignoring screen efficiency: A screen operating at 85% efficiency passes a significant proportion of oversize to the product, affecting both product gradation and recirculating load. Assuming 100% efficiency overstates product quality.
Treating product top size as the whole PSD: A crusher set at 25 mm CSS does not produce all 25 mm product. The output is a gradation, including fines, and the screen aperture determines what stays in the product and what recirculates.
Forgetting that recirculation increases conveyor and screen loads: Conveyors and screens between the crusher and the recirculating screen carry total circuit load, not just fresh feed. This must be accounted for in equipment sizing.
Comparing scenarios without checking product gradation: Two circuits with the same throughput may produce different product PSDs. A scenario that looks better on tonnage may fail the product specification check.
Confusing recirculating load conventions: Recirculating load expressed as a percentage of fresh feed is a different number from the same load expressed as a percentage of total crusher feed. Compare circuits on the same basis.

Simulating a crushing circuit in Quorr

Choose circuit topology

Decide whether each stage will run in open or closed circuit. In Quorr, this is done by connecting screen outputs back to crusher inlets.

Add equipment

Select crushers and screens from the equipment library. Set CSS, screen aperture, and deck area for each machine.

Set feed conditions

Enter feed gradation, material density, and fresh feed rate. Quorr uses these as the starting point for the circuit mass balance.

Run the simulation

Quorr calculates total crusher feed rate (fresh plus recirculating), product gradation at each stockpile, and machine utilisation across the circuit.

Adjust and compare

Change CSS, screen aperture, or circuit topology and re-run. Share the result with colleagues or clients via a browser link.

Simulation limits and engineering judgement

Quorr is a design and scenario comparison tool. It helps users estimate mass balance, product yield, utilisation, and likely bottlenecks, but it does not replace manufacturer guarantees, detailed engineering design, site trials, pilot testing, commissioning data, or professional judgement.

Circuit simulation is most valuable when used to compare options, identify the sensitivity of a design to key parameters, and catch sizing errors before procurement. It does not predict dynamic behaviour, wear rates, liner change intervals, or the effect of operator practice on production.

Circuit configurations you can model and compare

Single-stage open circuit: jaw or cone crusher with direct discharge to product
Single-stage closed circuit: cone crusher with screen oversize recirculation
Two-stage circuit: primary jaw in open circuit, secondary cone in closed circuit
Three-stage circuit: primary, secondary, and tertiary crushing with screening between stages
Circuit with pre-screening to bypass fines around the primary crusher
Multi-product circuit with separate screen decks for each product size fraction
Comparison of different CSS settings and their effect on recirculating load and product yield

Who uses crushing circuit simulation

Process engineers

Size crushing and screening equipment correctly for the target throughput and product specification, accounting for recirculating loads at each stage.

Consultants

Compare open versus closed circuit options for a client's plant, with a rigorous mass balance showing the trade-offs in machine size, product quality, and throughput.

Plant managers

Model proposed circuit changes before making them on site. Understand how a CSS adjustment or screen aperture change will affect the full circuit balance.

Model your crushing circuit in the browser

Frequently asked questions

What is a recirculating load in a crushing circuit?

Recirculating load is the oversize material that a screen returns to the crusher rather than passing to the next stage or product stockpile. It adds to the fresh feed to give the total crusher feed rate. Always state whether recirculating load is expressed as a percentage of fresh feed or total crusher feed, because the same circuit can appear to have different percentages depending on the convention.

What is the difference between an open and closed crushing circuit?

In an open circuit, material passes through the crusher once. It may be screened afterwards, but oversize is not returned to the same crusher. In a closed circuit, screen oversize is returned to the crusher. Closed circuits produce tighter product gradations but add recirculating load to the crusher, which must be sized for the total feed rate, not just fresh feed.

How does CSS affect recirculating load?

A tighter (smaller) CSS produces more material below the screen aperture, reducing the oversize fraction and therefore reducing recirculating load. A wider CSS increases the proportion of oversize and therefore increases recirculating load. The relationship depends on the feed gradation and screen aperture settings.

Can Quorr model multi-stage circuits?

Yes. You can build circuits with primary, secondary, and tertiary crushing stages in any combination of open and closed configurations. Quorr keeps the mass balance correct across all stages simultaneously.

What is CSS?

CSS stands for closed side setting: the minimum gap between the crushing surfaces in a jaw or cone crusher. It is the primary control variable for product size in compression crushers. A smaller CSS produces a finer product with a lower throughput rate; a larger CSS produces a coarser product with a higher throughput rate.