Start-up and Filling the System with Gas
The pipeline was filled with gas in sections, between selected shut-off and relief valve systems. A nitrogen slug without separating pigs was used to push air out of the pipeline. Liquid nitrogen from a tanker was gasified in an evaporator and fed to the pipeline section through the vent column in the first shut-off and relief valve system. Next the nitrogen slug in the pipeline was moved by means of natural gas being fed through the by-pass of the closed main valve. The pipeline stretch was filled with natural gas following the nitrogen slug until gas reached the flow-stop pressure. The nitrogen slug was vented from the pipeline via the vent column of the last shut-off and relief valve system of the pipeline stretch. Having removed the nitrogen from the pipeline stretch and filled it with natural gas, the gas pressure was increased to the level of operating pressure occurring in the neighbour stretches of the pipeline.
This technique allowed for fastening the natural-gas filling operation and avoiding troublesome operations connected with launching and receiving the separating pigs.
The pipeline was filled with gas in sections, between selected shut-off and relief valve systems. A nitrogen slug without separating pigs was used to push air out of the pipeline. Liquid nitrogen from a tanker was gasified in an evaporator and fed to the pipeline section through the vent column in the first shut-off and relief valve system. Next the nitrogen slug in the pipeline was moved by means of natural gas being fed through the by-pass of the closed main valve. The pipeline stretch was filled with natural gas following the nitrogen slug until gas reached the flow-stop pressure. The nitrogen slug was vented from the pipeline via the vent column of the last shut-off and relief valve system of the pipeline stretch. Having removed the nitrogen from the pipeline stretch and filled it with natural gas, the gas pressure was increased to the level of operating pressure occurring in the neighbour stretches of the pipeline.
This technique allowed for fastening the natural-gas filling operation and avoiding troublesome operations connected with launching and receiving the separating pigs.