Feeds and mass balance

What it is for

The balance calculates, for each stream, solids (t/h), water (m³/h), slurry (t/h and m³/h), slurry density, % solids by weight and by volume and solids SG. The starting points are the Feeds and the parameters of each unit.

Specify a Feed

Insert a Feed ("Feed and product" group).
In the panel, enter:
- Solids (t/h);
- Solids by weight (% solids);
- Solids SG (t/m³) — required.
If the project has particle size, enter the feed particle size distribution (see Particle size distribution). Without it the balance does not calculate.
If the project has grades, enter the assayed grades. Blank = not assayed.

A new Feed comes with 100 t/h, 50 % solids and SG 3.5.

How the balance propagates

Each unit receives the sum of what arrives at its inlets and splits it among its outlets by the rules of its model (Equipment).
Recycles (underflow returning to the mill, middlings returning to the feed) are solved by iteration. If the calculation does not converge, the result comes with a warning pointing to where the problem is.
There is a single balance for the whole project, even with several tabs.

Solids SG

On the Feed the SG is required.
An outlet with no specified SG inherits the SG of the mixture that entered the unit.
In a mixture, the resulting SG conserves the solids volume (volume-weighted average, not mass-weighted).
You can specify the SG on a stream (stream panel). It takes precedence. If only one outlet of the unit is left without SG, it is calculated to close the solids volume.
If the specified SGs do not close the solids volume of a unit, the balance accepts them and warns where and by how much.

Tip: specify the SG only where it is measured or where the mineralogy really changes (Feed, concentrates). Specifying SG on every stream, as in old spreadsheets, usually produces warnings about volume that does not close.

The stream panel

Click a stream to see its values, one per row:

% solids and SG (and, on separator outlets, the grades) are fields: when blank, the calculated value shows in grey inside the field; what you type shows in blue bold.
Solids, water, slurry and density are read-only.
On a stream leaving a Feed, everything is read-only; edit it on the Feed itself.

Target % solids on a stream

Specifying the % solids of a stream adds whatever water is missing at that point (dilution water). The balance never removes water: if the stream is already more dilute, it warns. This water enters the closure as an input.

Do not confuse this with the % solids of a product of a separator (concentrate at 50 %, underflow at 65 %): that is a unit parameter and defines how the water is split among the outlets.

Specified × calculated values

In the stream table and in the panel, what the client specified shows in blue bold. These count as specified: on Feeds, solids, % solids, SG and grades; on Water feeds, the flow rate; on streams, SG, target % solids and specified grades.

Balance closure

The summary above the table shows inputs → outputs of solids and water. The Balance closure tab gives the detail:

Inputs: Feeds and Water feeds, the water added at each unit (sprays, washing, water addition, mill dilution) and the dilution water of streams with a target % solids.
Outputs: the Products, with the streams that reach them.
Total inputs, Total outputs and Difference (inputs − outputs): green and "Balance closed" when zero; red when not.

Common warnings and limits

"The flowsheet has no feed": insert a Feed.
"No result: the balance cannot be calculated yet": something still needs to be connected or a value entered; the summary says what.
Mass split and splitters refuse values outside 0–100 %.
The balance does not handle design specifications of the type "find the water to reach 65 % in the underflow" by any route other than the unit's own parameter.