Identification and elimination of missing flows

AVEVA Production Accounting has a proprietary algorithm to detect and eliminate the missing flows separately from faulty measurements.

A serial search scheme is used first to isolate the candidate sources of missing flows and then simultaneous identification/elimination of missing flows is accomplished. The performance and accuracy of the detection are well proven from many applications of AVEVA Production Accounting to the needs of many different, real plants.

Real-world examples of missing flow detection

The following are real examples of missing flow detection.

Example 1

In this example, tank “20D415” is detected as a balance point with missing flows.

In the real-life situation modeled in the figure, it was ultimately proven that there was a missing movement at the tank “20D415,” just as AVEVA Production Accounting indicated.

Mathematically, the missing flow detection step uses the reduced balance matrix to detect that a balance point has missing flows, rather than using the full incidence matrix. This means it detects missing flows using the reduced set of balance envelopes, not the set of individual balance points. The two tanks shown above are part of the same balance envelope, due to the presence of the unmeasured flow between the two tanks.

The missing flow detection algorithm detects that there is a missing flow in the balance envelope and then has to assign the missing flow to one of the two tanks. The algorithm chooses the tank with the larger initial imbalance, which is tank “ 20D415.”

Figure: Example 1 of missing flow detection

Example 2

The “2103-FB” node is detected as a balance point with missing flows.

In this real-world example, it was proven that there was a shipment from this node with 2,090,000 kg at that time.

The calculated amount of the missing flow is 2,102,556 kg, as shown by the imbalance amount for the process. It is very close to the real missing amount.

Figure: Example 2 of missing flow detection

Example 3

The “120D823” and “20D103” tanks are detected as balance points with missing flows. These tanks are widely separated from each other on the flowsheet, and they both actually have outlet streams and inlet streams. (The diagram only shows streams of relevance that had flow.)

In this real-world example, it was proven that there was an oil movement from “120D823” to “20D103” of about 350,000 kl at that time. This can be deduced from the fact that the imbalance on tank “120D823” is of roughly the same magnitude as the imbalance on tank “20D103”.

The calculated imbalance in the “120D823” tank is 347,565 kl and the calculated imbalance in “20D103” is 351,179 kl. Both amounts are close to the real missing oil movement amount.

Figure: Example 3 of missing flow detection