The Problem

How Process Bottlenecks Limit Plant Throughput

Plants should be designed so that the various process units act together to produce the desired throughput rates. However, this is not always the case. We have, on occasion, witnessed plants where no amount of loop tuning increased total plant throughput. In these circumstances, the bottlenecks appear to be inherent to the equipment deployed in the plant, e.g., a compressor that cannot produce enough volume to satisfy plant demand for gas.

The Consequence

The throughput of the plant is limited to the throughput of the bottleneck. This means that the plant will not be able to produce beyond a certain limit, thus reducing the return on investment in the plant.

The Cause

There are two scenarios to consider:

x The plant was never able to produce at full capacity, even when it was newly constructed

x The plant used to produce at full capacity, but something changed, and now the plant cannot reach previous production levels.

The Solution

There are several libraries of robust thermodynamic models available that can be used to model the plant processes end-to-end. These range from high-fidelity models to inexpensive models, which, although not high-fidelity, are able to model the plant with reasonable accuracy to pinpoint causes of bottlenecks.

The thermodynamic models are run in parallel to the real plant, and data is continually compared to ascertain where and why deviations are occurring from the theoretical ideal.

Remedies often entail the addition of plant equipment or increasing equipment power and throughput. These solutions are not strictly in the realm of process control, but the approach does prove that the control system does not sit at the heart of the throughput problem.