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Data Description
| Data | Unit | Description | ||
| Set | Item | Type | Native | |
| Equipment Properties | Mat Consistency | Fraction or Percent | Fraction | Consistency of the outlet pulp stream. |
| Displacement Ratio | The fraction of Or replaced with shower water | |||
| Dilution Factor | If the Dilution Factor (DF) is non-zero the Total Flow in the shower stream is calculated. | |||
Equipment Properties
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Example of using equipment
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Method&Equations
If the Displacement Ratio (DR) is not given, the washing calculation mode defaults to the predictive mode.
Predictive mode is basically a mass balance assuming:
1) Initial split from vat to mat outlet consistency.
2) A portion of the mat liquor equal to four times the weight of the pulp (equal to the liquor in a sheet at 20.0% consistency) is "non-displaceable" in any incremental displacement.
3) The shower is divided up into the number of "displaceable units" equal to the mat displaceable liquor at the given consistency.
The displaceable mat liquor mixes with an equal portion of shower flow and comes to equilibrium. Then one-half this mixed volume is mixed with the pulp and its non-displaceable liquor and the other half continues to the next mat layer.
The outlet consistency must be positive, and must be less than 0.2 when using predictive mode.
The mass balance is calculated for every component of the shower and vat flows as follows:
Cmat = DR * Cshower + (1 - DR) * Cvat
where:
Cmat is the component concentrations (lb/ft3) in the mat
Cshower is the component concentrations (lb/ft3) in the shower
Cvat is the component concentrations (lb/ft3) in the vat.
Therefore, the component concentration of the mat should be correct for washers where entirely different shower liquor components can be present compared to the vat liquor (as in bleach plants).
Shower flow can be back-calculated by the washer (providing there is a non-zero shower flow) according to the input Dilution Factor (DF). If the shower flow is zero, the washer model acts like a 'decker' and only dewaters the pulp to outlet mat consistency. No change in liquor composition or concentration occurs.
The convention used for pressure (internally, inlet stream pressures are not changed) is that the vat and the shower operate at vat pressure, or the 1st inlet pressure. The mat and filtrate are assumed to exit at this pressure, even though a portion of the dropleg can operate under vacuum (except in pressure washers).
Gas flows are allowed in both inlet streams. Any vat inlet gas flow is sent with the filtrate flow, and any shower inlet gas flow is sent with the mat.
All solids (pulp, etc.) are assumed to leave with the mat.
Two considerations need addressing when allowing a user chosen efficiency term (independent of shower flow) which is handled as follows:
1) Higher efficiency than mat penetration at DF less than or equal to zero.
If DF is less than or equal to zero, then an expected DR is calculated by using the predictive mode. If your input DR is higher than the expected DR, then higher displacement than shower penetration is implied and is a mass balance violation. The predictive mode results override your input, and an error message is issued. If the DR is less than the predicted DR, your DR is used.
2) Low efficiency at high shower flows.
Such a condition is allowed, since in the real-world this phenomenon results from 'channeling' of shower water through the mat. The mass and energy balance are calculated with the given DR.
In the predictive mode, an outlet temperature DR is calculated from the mass and energy balance mode chosen (plug or nonplug flow). It will often be lower than solids DR.
The outlet temperature in the mat is assumed to follow the same 'efficiency' as the solids in the mat liquor. Therefore a 'Temperature DR' is defined as:
DR (temperature) = Tvat-Tmat / Tvat-Tshower = DR (dissolved solids)
The outlet enthalpy is calculated from that temperature. This method is used over an 'Enthalpy DR' since at high efficiencies the enthalpy of the shower (largely water) could be assigned to the mat which contains pulp, a lower specific heat component than water. Applying too high (or low) a specific enthalpy to this stream can cause the outlet temperature to exceed the range of the inlets.
Warnings
Errors
| Related Topics |
| Three Compound Washer Example |
| Three Vats and Washers Example |