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Gas - Natural Gas Pipeline PLC Project BC Gas Inc. is a leading
provider of energy and utility services in North America, serving over 750,000
customers. To provide a more secure gas supply for their customers, BC Gas constructed
the Southern Crossing Pipeline to connect their distribution system to the gas
transmission network in Alberta. Their new 303 kilometer, 24-inch, high
pressure transmission pipeline and compressor facilities have an initial design
capacity of 250 mmcfd (million cubic feet per day) with future capacity of up
to 600 mmcfd. Emerson Process Management was selected to configure the Programmable
Logic Controller's (PLC) that controlled the gas compressors. Although this project
was small by comparison to our other projects, only 3,500 person hours in total,
it required the incorporation of some unique control logic. As a crossing pipeline,
or linking pipeline, the compressor stations were required to function in both
directions. That is, the gas flow in the pipeline had to be able to flow in both
directions. This required the creation of two complete logic sequences to accommodate
the automatic switching of the nine control valves on the pipeline. Another
unique application of the control system was the automatic Purge and Loading command
sequence. To safely transport natural gas through a pipeline, any air in the pipeline
has to be purged prior to the introduction of the natural gas. By eliminating
the mixture of air and gas in the pipeline, the chance of an explosion is removed.
Usually, this would be done manually by having pipeline operators travel to each
control valve along the pipeline to open and close them in order to purge the
system. By automating this activity, it could be accomplished from the pipeline
control room in Vancouver, British Columbia. The savings for the client in labor
costs were significant. Besides being able to purge and load the system
from the main control room, operators have monitoring capabilities as well. From
the control room consoles, they can observe the pressure, flow rate, and temperature
of the gas in the pipeline. They can also monitor critical compressor statuses
such as vibration and speed. Despite the unique requirements, all programming
and testing for the project was completed on time and under budget.
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