Gas Pipe Diameter Optimisation
It is a common operating practice to use the capacity of a gas pipeline for storage - packing the pipeline up when demand is low and drawing it down again when the demand increases again. And this means that the pressure in the line will vary, almost cyclically over a 24hr period. At the same time, certain safety and operating criteria must be met - the peak pressure must not exceed the ratings set at the design stage whilst the minimum pressure must not fall below the limits nominated for delivery.
One practical example of this concept covers the design of a supply line to a Power Station. The pressure in the pipeline drops as each of the generators is started and the corresponding demand from the power station increases. And this means that, in turn, the pipeline must be able to satisfy the changing demand - if the pipeline capacity is too small (as in the case of the 24in line shown below) the pressure at the Power Station falls dangerously close to the operating limit and an automatic shutdown is imminent.
In contrast, the pressure fluctuations are significantly smaller with the 30in pipeline but of course, the initial capital expenditure is higher.
A pipeline simulation study at design stage therefore allows these conflicting demands to be rationalised. The most economical design can be adopted with the assurance that operational integrity is not being jeopardised.
Optimisation is very effective at an early or conceptual design stage.
