REQUISITOS MÍNIMOS DE ESPACIOS, INSTALACIONES Y EQUIPAMIENTO

volumes are accumulated at the lifting and delivery locations in order to meet the nomi- nated volume requirements during batch operation and to account for the total lifted and delivered volumes. Since tanks can be simultaneously receiving and discharging product batches, use of tank gauging cannot provide accurate volume data. The best approach to accurately measure batch volumes is to install flow meters with volume accumulators so that accurate information can be transmitted to the control center.

In addition, an on-line batch tracking capability is required to provide the pipeline and terminal operators with up-to-date and accurate information about batch locations, batch volumes and estimated arrival times. This capability reduces the possibility of errors and allows the operators to be much more effective and efficient in dealing with batch movement and operation.

5.2.9.2 Launching and Delivery Operation

Batch launching operations can be triggered by an indication from SCADA, a change in density, a change in valve status, and/or a schedule. The batch launcher is normally automated for the control center to remotely launch the batch at the batch interface. Conversely, the procedures for launching batches can be implemented in the tank farm controller or PLC, which performs the sequence of valve operations and/or checks density changes. After completing this sequence, the controller generates the batch launch signal, which is picked up by the SCADA system and used to start tracking batches along the pipeline.

When a batch is launched, the meter should be initialized with the batch ID and the actual start date and time. The meter factor for the new batch has to be determined based on the product and meter type. The meter factor is obtained from the meter prov- ing records. The batch is injected until the metered batch size becomes the same size as the scheduled batch size. If the metered batch size is similar to the scheduled batch size within a defined tolerance, the batch lifting should be terminated and the actual batch size recorded. This actual batch size derived from an injection meter will be used to deliver the batch. The delivery will be active until the delivered batch size is the same as the actual batch size for the appropriate delivery meter.

The batch receiver at the delivery location is another set of manifold piping and valves designed to flow out of the line to the designated tank. Similar to the launch sequence, the sequence to operate the manifold has to be created to deliver the batch to the correct receiving tank.

5.2.9.3 batch Tracking

Batch tracking monitors each batch for its volume, origin, current location, destina- tion, and estimated time of arrival to the designated locations. A batch is defined as a contiguous entity of uniform fluid properties which moves through the pipeline system as a single entity. For example, a batch is assumed to have constant density, compress- ibility and viscosity.

Real-time batch tracking information helps the operators reduce unnecessary downgrading of product or contamination of product in tanks. In addition, up-to-date batch tracking information is useful in improving the accuracy of short-term batch schedules.

The batch tracking process (Figure 5-37) must be able to perform the following main functions:

Determine and update the positions of the batch interfaces with each scan. ·

Maintain batch volumes in the pipeline. ·

Calculate batch overages and shortages in the pipeline. ·

Calculate estimated time of arrival (ETA) of batch interfaces at designated ·

Pipeline Operation and Batching n 277

Estimate interface mixing lengths and volumes. ·

Detect an actual interface arrival automatically at a batch interface detector ·

such as densitometer.

Adjust batch volumes and interfaces automatically according to the specified ·

rules in the event that a batch interface is detected, and provide the opera- tor with the capability to modify batch volumes, batch positions, or batch ID manually.

Alert the operator of batch arrivals. ·

Batch volumes are updated based on injection and delivery volumes obtained from metering locations along the pipeline. The interface positions can be determined, given the order and volume changes in and out of the pipeline. Given pipeline flow rates and interface positions, estimated times of arrival (ETAs) to the designated downstream lo- cations can be determined. Upon completion of delivery and removal of the batch from the pipeline, an over/short volume is calculated and stored. The over/short volume reflects the difference between metered injections and deliveries along the pipeline as well as any manual adjustment that may have been made along the way.

If a side stream injection takes place, batch tracking is affected in two different ways: either the injected product is the same as the flowing product or the injected product is different from the flowing product. The former case maintains the same batch ID but the size is different and the flow rate downstream of the side stream injec- tion point increases by the same amount as the injection rate. However, if a different product is injected into the flowing product, then the following changes take place:

Two products are blended and the properties of the blended product should be ·

determined for modeling;

The batch size on the upstream side of the injection point reduces and eventu- ·

ally the batch disappears; and

The blended product becomes a new batch downstream of the injection point, ·

and its size grows.

The above figure displays the batch tracking information. The operator uses the batch tracking information for effective batch operations, which is normally made available to him/her through the SCADA system. The critical information for the op- erator includes the batch IDs, line fill volumes and flow rates of the lifting and deliv- ering batches, batch interface positions along the pipeline, and ETAs for each batch to the next designated locations. If a drag reducing additive (DRA) is injected, the

batches containing DRA together with their positions and the concentration of DRA and their ETAs to the next pump stations or significant facilities should be reported. Also, any contaminated batches and their positions should be tracked and reported to the operator.

Batch tracking may be integrated with a batch scheduling system, to determine an up-to-date batch schedule; this is accomplished by comparing actual batch tracking data with scheduled injection and delivery volumes and times. Current batch volumes and positions can also be used to update short-term batch schedules.

5.2.10 Multiproduct Pipeline batch Optimization

Batch sizing and sequencing/cycling have been described previously. However, it is the industry’s practice to decide the optimum batching cycle for a pipeline project based on contamination costs as a function of the cycle time as well on the basis of tankage costs for differing cycle sizes. The larger the cycle time, the larger the tankage that is required to store the cycle volume prior to injection and after delivery from the pipeline.

To determine the most economical batching cycle, the required analysis compares the costs resulting from various batching cycles by determining the net present value (NPV) of these costs, as indicated in Figure 5-38. The batch cycle with the lowest NPV is preferred as it will minimize the present value of the costs. In this example, the two- day cycle is shown as being optimum.