Mass and Volume

Mass and Volume tabs

Here, you can define, both for mass and volume, the minimum and maximum flow rates, the default flow rates and the tolerances.

• Use Min/Max Constraints: This checkbox, if checked, makes the data reconciliation algorithm use the Minimum Flow rate and Maximum Flow rate as constraints. If the reconciled value of the stream after running data reconciliation in DR Solver is below the Minimum Flow rate, DR Solver sets the measured value of this stream to zero and then runs data reconciliation again. If you define the Min/Max constraints of the stream, these minimum flow rate and maximum flow rate act as boundary constraints when running data reconciliation.

• Maximum handling: If the reconciled value is above the maximum flow rate, the data reconciliation step sets the reconciled value to the maximum flow rate and then runs overall data reconciliation again.

• Minimum handling: f the reconciled value of a flow after running data reconciliation is below the minimum flow rate specified for it, the data reconciliation step sets the measured value of the stream to zero and then runs the overall data reconciliation steps again.

  Note The handling of minimum constraints is not entirely like the handling of maximum constraints, because reconciled values that fall below the minimum are not set to the minimum, but rather to zero. AVEVA™ Production Accounting does this because this approach is more likely to model reality. Normally, in processes, if the reconciled value is below the specified minimum flow rate, it means there was actually no flow, not some small amount of flow at the minimum value.

  

  It means Gross Error Detection step can detect the stream as gross error even though the reconciled value of the stream may not satisfy the Min/Max constraints but the measured value satisfies the Min/Max constraints. It is unrealistic and AVEVA Production Accounting prevents this for more accurate gross error detection. The global option set the below check box in DR Solver tab of Option dialog box. (See also Gross Error Detection With Min/Max Constraints).

  For example, GROSS_ERROR_FLOW stream is detected as gross error if there is no Min/Max constraints of this stream since other streams have good measured values to fit the material balances.

  

  We set the Min/Max constraints in GROSS_ERROR_FLOW stream as 0/10 as shown below and then reconcile again.

  

  

  The reconciled value of GROSS_ERROR_FLOW stream is set to maximum value (10) and the solvability status is Constant Redundant Flow by Maximum Constraint.

  But it is unrealistic because measured value of this stream satisfies maximum constraint and if it is not detected as gross error, the reconciled value may satisfy maximum constraint as shown below.

  

  The option of Gross Error Detection considering Min/Max Constraints gives the more realistic gross error detection.

• Use ± Min/Max: If checked, this checkbox causes the minimum and maximum to be treated as two ranges, one in the positive range and one in the negative range. For instance, if the min and max are set to 10 and one million, values between 0 and 9.99… are forced to zero. If you check the box for ± interpretation, then values between -9.99… and +9.99… will be forced to zero. In many cases, this is the behavior desired.

  Circumstances under which negative flows may be encountered:

  If reconciliation determines that there was a negative loss (that is, a gain), the reconciled flow may appear negative.AVEVA Production Accounting normally forces all negative values to zero. You may wish to preserve negative values that are of large magnitude. Enabling the Use ± Min/Max feature does that, forcing to zero only those gains which were close to zero. This is the primary use of this feature.

  Note It is not permitted to explicitly enter negative numbers into the Min and Max fields. The only way to cause them to be treated as negative is to use the ± option.

  If the checkbox Use Min/Max is not checked, the ± setting is ignored and the checkbox on the dialog box is disabled.

• Default Flow Rate: This value is defined by numeric value or equation. The numeric value is used as the default flow rate when new event data is created for this stream. For example, assume you input the value of the default mass flow rate of a stream object as 100 ton/hour. The new event data of the stream are created automatically with the mass flow rate of the stream object being 100 ton/hour initially.

  You can use the Smart Object feature to calculate mass and volume flow rates. Clicking the Calculate Function button brings up the Equation Editor dialog shown below. In this editor, you can create a mathematical expression that will assign the desired, calculated value to the FEED property of the stream. For example, assume the mass flow rate of this stream object is 0.3*(mass flow rate of Feed stream object).

  

  

  The equation (Stream (FEED;MassFlowrate)*0.3) is written in the textbox of default flow rate.

  

  The detailed functionality of Smart Object is described in Smart Objects.

  The calculated mass flow rate (=0.3*100) is updated and the text boxes containing the mass flow rate related numbers on the Results tab are disabled because they should no longer be editable.

  

• Tolerance: Tolerance governs how much of the discrepancies found during reconciliation will be distributed to the flow associated with this stream, with larger values causing larger assignments of error. This value is specified as an absolute amount plus a percentage of the actual flow. For example, assume the measured flow rate of a stream object is 100 kg/hour and its relative tolerance is 5%. The mass tolerance value of this stream object is 5 kg/hour. AVEVA Production Accounting strongly recommends the use of standard percentage values for most configurations, with zero for the absolute portion. These default values are normally configured in the DR Solver Tab of the Option dialog. For more information on fine tuning of tolerance values, refer to the information in section Data Reconciliation Algorithm.