Question

200 MMscfd natural gas that contains 20vol% CO2 and no H2S is to be transported 60 miles through pipelines to a natural gas liquefaction plant where gas sweetening and dehydration will take place. Suggest:

Minimum specifications for the gas as it enters the pipeline.

Suitable processing sequence for the field facility.

Answer 1

Minimum specifications-

(1) Natural gas should be technically exempt, that is, there should be no visible traces of solid and liquid particles.

(2) Specification limits are values referred to as 293.15 K (20 ºC) and 101.325 kPa (1 atm) on a dry base, except at dew point.

(3) Combustion properties are-

Processing sequence for field facility-

Compressor Stations

As mentioned, natural gas is highly pressurized as it travels through an interstate pipeline. To ensure that the natural gas flowing through any one pipeline remains pressurized, compression of this natural gas is required periodically along the pipe

Metering Stations

In addition to compressing natural gas to reduce its volume and push it through the pipe, metering stations are placed periodically along interstate natural gas pipelines. These stations allow pipeline companies to monitor the natural gas in their pipes. Essentially, these metering stations measure the flow of gas along the pipeline, and allow pipeline companies to ‘track’ natural gas as it flows along the pipeline. These metering stations employ specialized meters to measure the natural gas as it flows through the pipeline, without impeding its movement.

Valves

Interstate pipelines include a great number of valves along their entire length. These valves work like gateways; they are usually open and allow natural gas to flow freely, or they can be used to stop gas flow along a certain section of pipe. There are many reasons why a pipeline may need to restrict gas flow in certain areas. For example, if a section of pipe requires replacement or maintenance, valves on either end of that section of pipe can be closed to allow engineers and work crews safe access. These large valves can be placed every 5 to 20 miles along the pipeline, and are subject to regulation by safety codes.

Control Stations and SCADA Systems

Natural gas pipeline companies have customers on both ends of the pipeline – the producers and processors that input gas into the pipeline, and the consumers and local gas utilities that take gas out of the pipeline. In order to manage the natural gas that enters the pipeline, and to ensure that all customers receive timely delivery of their portion of this gas, sophisticated control systems are required to monitor the gas as it travels through all sections of what could be a very lengthy pipeline network. To accomplish this task of monitoring and controlling the natural gas that is traveling through the pipeline, centralized gas control stations collect, assimilate, and manage data received from monitoring and compressor stations all along the pipe.

Pipeline Inspection and Safety

In order to ensure the efficient and safe operation of the extensive network of natural gas pipelines, pipeline companies routinely inspect their pipelines for corrosion and defects. This is done through the use of sophisticated pieces of equipment known as ‘smart pigs.’ Smart pigs are intelligent robotic devices that are propelled down pipelines to evaluate the interior of the pipe. Smart pigs can test pipe thickness, and roundness, check for signs of corrosion, detect minute leaks, and any other defect along the interior of the pipeline that may either impede the flow of gas, or pose a potential safety risk to the operation of the pipeline. Sending a smart pig down a pipeline is fittingly known as ‘pigging’ the pipeline.