Wash plant properties

To visualise a wash plant node in the Material flow node menu the Wash Plant must be first configured and enabled.

A wash plant is a specialised process node that has two sub-processes, wash plant product and wash plant reject.

The feed to the wash plant node is processed by PO using the feed material wash table data. The PO can target qualities or cut-points, or adjust these to meet the overall material flow benefit settings. The plant yield will be driven by how the targets are met by PO and any yield adjustments.

When targeting qualities, the wash curve cut-points can be set to use the nearest wash table values or interpolated. When relative density (RD) interpolation is used, there are a number of options to control how to handle interpolated values.

The theoretical yield of the wash plant can be adjusted based on the qualities at the cut-point used by PO. When targeting cut-points, the yield can be based on average float qualities.

Assumptions

Each plant will be modelled as a single-stage plant.
Coal washability data is provided for one or more cut-points; these are assumed to be on a cumulative basis for each cut-point.
All quantities are on a single moisture basis (ROM).
All qualities are on a single moisture basis (air-dried).
Partings and dilution are treated alike as waste.
Adjustment of quantities and/or qualities for moisture are made during reporting.

Wash plant (node) configuration fields

Field	Description
Name	The name of the wash plant node.
Rate	The rate at which the plant processes input material in mass/hour.
Override per Period (General)	Option to override the wash plant Rate on a period basis.
Objective	The objective rule the PO will attempt to satisfy.
Target Type	The target type used by PO. Quantity: use one or more wash qualities for the PO target. If multiple targets are used, PO will use the lowest cut-point to meet the target. See Wash Field. Quality targets can be overridden on a period basis. Cut-point: uses the relative density as entered in the Relative Density > Default field as the PO target, or use override period values. Optimised Cut-point: allow PO to set the cut-point to meet overall material flow benefits.
Target Match	The method PO will use when attempting to optimise the Target Type. Nearest: the cut density where the absolute difference between the quality value at either bound and the target quality value is lowest. Interpolate: the exact cut-point required to meet the target is determined by using a cut-point above and below the target, then using a straight line average (assuming that all wash data is linearly related).
Change Theoretical Wash Table	Used to adjust the theoretical wash curves to achieve a practical yield to account for any misplaced material, such as material that floats but should have sunk and vice versa. No Change: no adjustment is made for the misplaced material and the New Theoretical Yield Expression row will be disabled. Use Qualities at RD Cut-point: The quality of the misplaced material will be the qualities of the material that floats at the current RD, but would have sunk at the previous RD. The wash table is then adjusted accordingly to take into account the 'good' material that will sink. Use Float Qualities: the quality of the misplaced material will be the average qualities of all coal that floats at that particular RD. The wash table is then adjusted accordingly to take into account the 'good' material that will sink.
New Theoretical Yield Expression	The yield expression to use if enabled by the Change Theoretical Wash Table setting.
Interpolation Correction	How to manage the cut-point returned by PO (the cut-point used in the wash table). No RD Connection: do not adjust the relative density value used to achieve the PO target. Clamp RD to Limit: use the nearest RD limit value (upper and lower) in the wash curve if the PO cut-point is outside these limits. Set RD to Default: use the supplied default vale if the PO cut-point is above or below the limit values.
Upper Limit	The upper RD limit to use in interpolation rules.
Default	The default RD to use in interpolation rules.
Lower Limit	The lower RD limit to use in interpolation rules.
Override Per Period (Relative Density)	Override the RD limit values on a period basis.
Wash Field	The wash quality field for PO to target. Select the field from the list and click the green + icon to add a field. To remove a field, click the red - icon.
Override Per Period (Quality Target)	Override the wash quality targets on a period basis.

Wash plant product and reject

The output of the wash plant is split into product and reject material that is represented by two sub-process nodes.

Each wash table quality of the wash plant product node can be adjusted with an expression that references the theoretical wash table qualities and the wash cut-point (as returned by PO). For example, when adjusting for practical wash values and overall plant efficiency factor.

To adjust product qualities

Click the wash plant product node to open the dialog showing theoretical product fields.
Click the fx button to open the expression builder.
Create an expression to adjust the product quality or yield.

The wash plant reject is sent to a wash plant reject node. This node represents the wash plant feed minus the wash plant product material and can be renamed for reporting purposes.

The reject node can be used as a feed for secondary or two-stage washing. The reject node wash table is automatically adjusted to reflect the qualities and quantities removed by the primary wash plant as described in the next section.

Wash plant two-stage washing

When a secondary circuit is involved, the wash table needs to be recalculated to allow for material that was separated using a cut-point in the primary circuit. This is because the original wash table had yield and product quality data on a cumulative basis and is based on the original plant feed. However, the feed to the secondary circuit is the reject (sinks) stream of the primary circuit, and is, therefore different from the plant feed.

The following assumptions are used when arriving at the wash table for the secondary circuit.

All yield and quality data for cut-points which are the same as, or lesser than, the primary circuit cut-point will be unavailable in the secondary was table.
The data for all cut-points greater than the primary circuit cut-points will be amended to allow for the primary circuit yield and product qualities.
The yield and quality data for the various cut-points of the amended wash table will also be on a cumulative basis.
The yields and product qualities at the various cut-points in the amended wash table are assumed to be theoretical.
You are able to specify a separate yield adjustment expression for the nominated cut-point of the secondary circuit.
This adjusted yield will then be used to compute the product (floats) and reject (sinks) streams of the secondary circuit.