Speaking at Rice University, Houston last November, mathematician Henry Rachford (Advantica) explained why the modeling of gas flow in pipelines is both important and hard.
Havoc
In the US, much electricity is generated by burning gas in power stations. The demands of the electricity market are for quite rapid intra-day changes in generation capacity. Since there is no storage capacity in the electricity grid, the transients are ‘passed on’ to the gas supplier, turning the pipeline network into de facto storage. Without careful planning, this can wreak havoc on the gas transmission companies attempts to keep the pipeline supplied with gas and operating at safe conditions.
Rachford showed a simple transient scenario as flow changed from its initial state, taking some time to travel along the pipe. Controls to achieve one goal may have unexpected results elsewhere. Advantica’s modeling package helps operators evaluate pressure and power requirements at pumping stations along pipe, respecting delivery and pipeline operating constraints.
Simulation
Achieving such goals is a mixture of simulation, guesswork and experience. It turns out that subtle changes in controls can satisfy goals. Rachford’s software uses ‘smarts’ rather than brute force. Results are usually obtained within a couple of minutes of CPU time and if a task is not feasible, this is quickly flagged by the software. Further optimization includes uncertainty as to what users will take out of the system, identifying controls that ‘defensively position’ linepack to support delivery of different anticipated loads.
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