Working Calendars in Refinery Shipment Simulation

       A refinery shipment node represents a refinery shipment point where products leave the process through truck loading racks, rail terminals, marine berths, pipelines or other export facilities. It connects refinery production with outbound product transportation and refinery logistics, supporting realistic shipment execution under different operating conditions. They often follow defined working hours, remain closed on weekends, or suspend operations during public holidays. These operating constraints directly affect shipment scheduling, tank farm inventory and loading operations. Ignoring working calendars can produce unrealistic simulation results, allowing products to leave storage when shipment facilities should be unavailable and preventing the inventory accumulation that naturally occurs in real refinery operations. By incorporating working calendars into shipment simulation, refinery Digital Twins can accurately reproduce loading schedules, inventory dynamics and overall shipment behavior.

       A common simplification in refinery simulation is to represent shipments as a continuous average flow distributed evenly throughout the day or month. Although this approach may reproduce the planned shipment volume, it fails to capture how shipments are actually executed.
       In real refinery operations, shipment facilities are periodically unavailable due to working hours, weekends or public holidays. During these periods, products cannot leave the refinery and continue accumulating in the tank farm. Once the shipment point reopens, inventories begin to decrease as shipments resume.
       Continuous shipment removes product from storage at every simulation step, preventing this natural accumulation from occurring. As a result, tank inventory profiles become unrealistic, storage utilization is underestimated, tank farm inventory management becomes unrealistic, and refinery logistics behavior is distorted.
       By incorporating working calendars, shipment simulation reproduces these operational interruptions, resulting in more realistic inventory dynamics and more accurate refinery logistics models.

       A working calendar defines when a refinery shipment node is allowed to execute shipments. Instead of assuming continuous operation, the node follows the configured working schedule, automatically opening and closing as operating periods begin and end.
       Working calendars can include working days, weekends, public holidays and daily operating hours. When the shipment point is closed, the refinery shipment node blocks product transfer and the shipment flow immediately becomes zero. Once the operating period resumes, shipments continue automatically.
       Modeling these operating constraints is essential for realistic refinery process simulation, logistics simulation, and refinery scheduling studies. During non-working periods, products remain in the tank farm instead of being shipped continuously, reproducing the inventory accumulation observed in real refinery operations. This results in more realistic inventory profiles, improved shipment scheduling accuracy and a more faithful representation of refinery logistics.

       Working calendars are particularly important in refinery planning studies where production units operate continuously while loading facilities follow predefined operating schedules. Dynamic simulation makes it possible to reproduce the interaction between production, tank farm inventory, shipment scheduling and outbound refinery logistics under realistic operating constraints.

       Working calendar settings are configured at multiple levels of the simulation model. The configuration separates operating rules from shipment logic, making calendars easy to modify without changing the simulation model. The basic behavior is defined for each refinery shipment node, where users specify whether the node should follow a working calendar or operate continuously. This allows individual loading facilities to be configured independently.
Public holidays and other non-working days are maintained in a dedicated calendar table. Updating the calendar automatically changes the operating schedule without requiring any modifications to the refinery shipment node or the simulation model.
       Daily operating hours are configured through the class constants of each refinery shipment node instance. These parameters define the start and end of the operating day and allow different loading facilities to follow independent loading schedules and refinery operating calendars. In addition to calendar-based operation, the refinery shipment node generates events whenever it opens or closes. These events enable users to implement custom logic, synchronize other model components, or record operational events during simulation.

Working calendars are commonly applied to:
• Truck loading racks;
• Rail loading terminals;
• Marine loading berths;
• Pipeline export stations;
• Product dispatch terminals;
• Tank farm loading facilities;
• Distribution depots;
• Refinery logistics hubs;
• Multi-product loading facilities.

       Working calendars represent one aspect of refinery shipment modeling. Shipment Nodes may also execute shipments using manual dispatch orders, production-based shipment plans or predefined scheduling algorithms (shipmentScheduleType (label: Shipment algorithm)), depending on the requirements of the simulation model. The same Shipment Node can be configured to represent truck loading racks, rail terminals, marine berths or pipeline export facilities. Additional operating rules and event callbacks make it possible to model a wide range of refinery shipment scenarios while maintaining consistent simulation logic. Working calendars extend this behavior by introducing operating schedules that determine when shipments are permitted, allowing inventory accumulation and shipment execution to follow realistic refinery operating practices.

       A truck loading rack operates Monday–Friday from 08:00 to 18:00. During weekends, product continues arriving from production units, increasing tank farm inventory until the loading facility becomes available again. On Monday morning, the refinery shipment node reopens and shipments resume until the accumulated inventory returns to its normal operating level.

       Without working calendars, shipment simulation assumes that logistics infrastructure is always available, which rarely reflects refinery reality. Modeling operating schedules enables Digital Twins to reproduce realistic tank farm inventory accumulation, shipment scheduling, refinery logistics and loading operations.

1. What is a working calendar in refinery shipment simulation?
A working calendar defines when a Shipment Node is allowed to execute shipments. It can include working days, weekends, public holidays and daily operating hours.

2. Why are working calendars important for shipment simulation?
Without working calendars, shipments may continue when loading facilities should be closed, producing unrealistic inventory levels and shipment schedules.

3. Can different shipment points use different working calendars?
Yes. Each Shipment Node can be configured independently, allowing different loading racks, rail terminals or marine berths to operate according to their own schedules.

4. What happens when a Shipment Node is closed?
The Shipment Node blocks shipment flow until the next operating period begins. Products remain in storage, reproducing the inventory accumulation that occurs in real refinery operations.

5. Can Shipment Nodes generate events when their operating status changes?
Yes. Shipment Nodes generate events when they open or close, allowing users to implement custom simulation logic or synchronize other model components.

6. Do working calendars affect inventory levels?
Yes. During non-working periods, products remain in storage instead of being shipped, producing realistic inventory accumulation and more accurate tank farm simulation.