# 13.3.7 Scheduling Process Trains

### Intended learning outcomes: Differentiate between reverse flow scheduling, forward flow scheduling, and mixed flow scheduling.

Process trains were introduced in Chapter 8. A process train is a representation of the flow of materials through a process industry manufacturing system that shows equipment and inventories.

To schedule the process train, we need to know the order in which to schedule the stages of the process train. Take, for example, a process train with three consecutive stages 1, 2, 3. There are three possible scheduling techniques:

• Reverse flow scheduling (3, 2, 1) starts with the last stage and proceeds backward (countercurrent to the process flow) through the process structure. It supports demand-based planning.
• Forward flow scheduling (1, 2, 3) starts with the first stage and proceeds sequentially through the process structure until the last stage is scheduled. It supports supply-constrained planning, such as short harvest cycle in the food industry.
• Mixed flow scheduling (2, 1, 3 or 2, 3, 1) supports planning where stage 2 is the logical focus of attention for scheduling because of processing capacity or material supply constraints. In general, detailed scheduling starts at each bottleneck stage and works toward the terminal process stages or another bottleneck stage.

It is easy to see that these three scheduling techniques have much in common with backward, forward, and central point scheduling.

## Course section 13.3: Subsections and their intended learning outcomes

• ##### 13.3 Scheduling of Orders and Scheduling Algorithms

Intended learning outcomes: Describe the manufacturing calendar and the calculation of the manufacturing lead time. Differentiate between Backward Scheduling and Forward Scheduling. Explain network planning, central point scheduling, the lead-time stretching factor, and probable scheduling. Present scheduling of process trains.

• ##### 13.3.1 The Manufacturing Calendar, or Shop Calendar

Intended learning outcomes: Present characteristics of the manufacturing calendar, or shop calendar. Explain an example of a manufacturing calendar.

Intended learning outcomes: Produce an overview on lead time scheduling. Identify definitions for the elements of operation time. Present the lead time formula and the start date as a function of completion date. Differentiate between manufacturing lead time, cycle time and throughput time.

• ##### 13.3.3 Backward Scheduling and Forward Scheduling

Intended learning outcomes: Produce an overview on lead time scheduling. Explain forward scheduling and backward scheduling. Describe a simple algorithm for backward scheduling.

• ##### 13.3.4 Network Planning and CPM — Critical Path Method

Intended learning outcomes: Explain network planning and the critical path method (CPM). Present an example of a scheduled network. Describe a network algorithm for backward scheduling.

• ##### 13.3.5 Central Point Scheduling

Intended learning outcomes: Explain central point scheduling. Describe several possible solutions in a directed network of operations.

• ##### 13.3.6 Probable Scheduling

Intended learning outcomes: Produce an overview on order urgency and slack time. Differentiate between forward, backward, and probable scheduling. Explain the role of the lead-time-stretching factor in probable scheduling.

• ##### 13.3.6b Calculating the Lead-Time-Stretching Factor

Intended learning outcomes: Describe the determination of the lead-time-stretching factor. Explain the equation for recalculation of lead-time-stretching factor.

• ##### 13.3.7 Scheduling Process Trains

Intended learning outcomes: Differentiate between reverse flow scheduling, forward flow scheduling, and mixed flow scheduling.