Abstract
The objective of this work is to conduct flow assurance analyses for optimum transportation of gas through pipelines for use in CNG vehicles in Nigeria. Port Harcourt – Owerri – Onitsha expressway is used as case. The work is for a pipeline network that would be laid from a gas treatment plant about 10km off the Port Harcourt - Owerri – Onitsha expressway to the five CNG refueling stations installed along the route for refilling the CNG vehicles. Flow assurance analyses include analyses on: condensate drop-out prevention; hydrate formation prevention; erosion prevention; slug formation tendency; and leak detection. They are performed to ensure that solids or liquids do not deposit in the pipeline. Condensate drop-out prevention analysis is conducted to determine the conditions within which hydrocarbon liquids would not form in the pipeline during the transportation of the gas. Hydrate formation is checked to establish the temperatures and pressures at which hydrate would not deposit in the pipeline. Erosion prevention analysis is performed to determine the velocity profile above which erosion cannot occur in the pipe. Slug formation tendency is evaluated to ensure that slugs do not form in the pipe. Pipeline leak is also checked by generating pressure profile that would govern the flow of gas in the pipe and help determine any possible leak of gas from the pipeline. The results of the analyses indicate that: liquid drop-out will not occur in the pipe if the temperature of the gas does not go below 65.73°F; once the temperature and pressure of the gas remain outside the hydrate curve, hydrate will not form in the pipe; the velocity profile along the pipe length is far higher than the erosional velocity therefore the possibility of erosion occurring in the pipe is highly minimal; slugs cannot form in the pipe since the fluid remains in single phase throughout the transportation in the pipe; with the pressure profile generated; leak detection is made easy by installing five pressure gauges at different lengths of the pipe and recording the expected pressures at these lengths. It is further observed from the work that these flow assurance parameters and tests are highly indispensable in gas transportation as the results of the analyses help the engineer to apply all precautionary measures to ensure that solids or liquids do not deposit in the pipeline. Recommendations are also made for the optimum operating conditions based on the flow assurance analyses.
Highlights
According to [1], natural gas can be described as a gas consisting primarily of methane
The side effects of slugs are that they create significant pressure fluctuations; cause flooding at the receiving end; induce severe mechanical vibrations in the pipeline; and increase hydrate deposition and corrosion
The optimization principles and techniques outlined in this chapter include, pipeline design to meet sales gas specifications, liquid drop-out, hydrate formation, carbon dioxide freeze-out and erosion, preventions across the pipeline
Summary
According to [1], natural gas can be described as a gas consisting primarily of methane It is found associated with other fossil fuels, in coal bed, as methane clathrates, which is a type of physical compound, and is created by methanogenic organisms in marshes, bogs and landfills. It is an important source of fuel, a major feedstock for fertilizers, and a potent greenhouse gas. Before natural gas can be used as CNG fuel energy, it must undergo extensive processing to remove almost all the incompressible components from the gas stream, meaning C4 – C7+ would be removed (considered as condensable hydrocarbons).
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