Saturday, September 19, 2009

Why the Gas is Always On

Turn the knob on a gas oven and the energy flows immediately. While the blue flame from the burning gas is obvious, the delivery system that is bringing the gas hundreds of miles to the oven isn't. That system includes not only the vast network of pipelines, but numerous pumps to maintain pressure.

A new study shows that this complex grid of gas pipes is surprisingly robust, so that even when one pipeline fails the gas generally finds an alternative way to reach its destination.

Rui Carvalho, who works at Queen Mary University in London, said that the gas grid resembles the electrical grid in some respects. In both cases, energy is added to the grid by one or more suppliers, travels over various available pathways, and then is extracted by customers. Unlike the electrical grid, where a power line can shut down, individual gas pipes go on working.

Carvalho and his colleagues studied how the gas grid in Europe functions so well. They found that the pipe network has evolved over time in two ways. The grid is partly deliberately planned by gas companies with pipes built as short as possible (to save money) and as wide as necessary to carry the expected load.

Another competing mechanism is at work, however. This is the redundancy in the grid that emerges when a lot of pipes are added over the years by different companies. The resultant grid is a bit like the vasculature system, the mesh-like system of veins reliably supplying blood to all parts of the body. Redundancy might seem like a wasteful thing, but it is the factor that allows gas to go on flowing even blockages in any one node arise.

This redundancy of nodes and possible paths helps the gas grid to survive occasional pipe breakdowns. The consequence is that it's almost impossible for the gas grid to suffer the kind of blackouts that occur on the electricity grid.

When the gas does fail to flow, it's usually something other than the pipes. In January a disagreement between Russia and the Ukraine led to the shut-off of gas to some parts of Europe.

This study of the Trans-European gas network was published recently in the journal Physical Review.

By Phillip F. Schewe
Inside Science News Service

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