Relationship between Composition Tracking and Data Reconciliation

In general, for composition tracking to run properly, it requires balanced volume movement data.

The question arises: Does AVEVA Production Accounting Composition Tracking require AVEVA Production Accounting Data Reconciliation to be run beforehand or afterwards?

The answer varies by industry.

For those industries that normally require a volume balance for the plant, the steps are:

• Step 1 Execute Data Reconciliation to perform a volume balance on the plant

• Step 2 Execute Composition Tracking

For those industries in which a mass balance is normally performed for the plant, the steps are:

• Step 1 Execute Composition Tracking. This automatically invokes a volume balance algorithm on the feedstock tank farm(s).

• Step 2 Execute Data Reconciliation for mass balance. The mass balance is dependent on accurate densities, which were made available by Step 1 (CT) having been run.

Mass balances are the only possibly accurate balance for operations that create products with densities radically different from the feedstocks. CT provides accurate density on feedstocks for mass balances.

AVEVA Production Accounting CT automatically calculates the composition and quality of mixtures in a set of off-site feedstock receipt and storage facilities (tank farm) based on starting tank compositions and qualities, the introduction of material of known composition and quality into the tank farm, and a knowledge of total quantities moving within the system or entering/leaving the system. It is necessary to have a material balance before a meaningful composition tracking can be performed.

AVEVA Production Accounting CT improves the accuracy of predicting and tracking the composition and quality inside the tank farm when these data cannot be explicitly measured.

AVEVA Production Accounting CT is performed in a sequential manner. Feedstock receipts are the starting point for tracking, and the composition/quality is calculated as the oil movements propagate through the tank farm. Tanks can be modeled as well-mixed, FIFO, or LIFO.

Figure: AVEVA Production Accounting CT Model Focus

Figure: AVEVA Production Accounting CT calculates the quality of each tank.

Figure: AVEVA Production Accounting CT calculates the feedstock composition of each tank.

Figure: AVEVA Production Accounting CT calculates the feedstock composition distribution and quality of the feed stream.

The function of data reconciliation is to adjust the feedstock quantity data over a finite time horizon using minimization of the sum of squares of measured values minus reconciled values so that the material balance is achieved. Data reconciliation provides more accurate, reliable and consistent feedstock quantity data for a tank farm than can normally be achieved by direct readings from measurements.

After achieving accurate feedstock quantity data by data reconciliation, the tracking simulation module can use the reconciled movement and inventory data to calculate the composition and quality of feedstock tanks and streams within the tank farm.

Normally, in a refinery, the manual calculation of quality and composition in tank farms is inaccurate or mismatched because of the following reasons.

• Wrongly specified feedstock oil movement data.

• Gross errors in gauging measurements or manual inputs.

• Inaccurate quantity data for feedstock oil movement and tank inventory.

• Calculation errors in material balance with both mass and volume.

• Inaccurate feedstock composition tracking logic.

AVEVA Production Accounting CT can easily check for these kinds of discrepancy and automatically find the most accurate composition and quality data with its state-of-the-art mathematical tracking technique, which cannot be achieved by manual calculation.

Figure: AVEVA Production Accounting CT processing steps

The first step is to get input data, as shown below, for tracking. The static input data are already configured in the AVEVA Production Accounting CT and the variable data such as feed stock receipts, tank movements and tank inventory are imported from external systems.

Figure: Input data obtained for composition tracking

AVEVA Production Accounting validates the retrieved data. AVEVA Production Accounting CT performs data reconciliation to generate reconciled values which meet the requirements of the material balance. AVEVA Production Accounting CT’s tracking simulation uses the reconciled values to calculate the compositions and qualities in each tank and stream.

In crude oil refineries, AVEVA Production Accounting CT is able to offer the only reliable means to accurately track actual and expected yields as well as the properties of each cut in the crude distillation unit. It does so by interfacing with external crude assay systems.