Fuel Gas Monitoring in Natural Gas Compressor Station and Transmission/Distribution Lines

As gas pressure drops in the gas pipeline network, the transportation capacity is reduced. Compressor plants are used to boost gas pressure back up to optimum operating levels. Monitoring fuel gas to compressors is typically accomplished with an orifice or turbine meter. Because both of these methods are subject to fouling and failure, they require frequent skilled maintenance in order to provide an accurate measurement. Constrained piping conditions are another problem. Because long straight pipe runs are difficult to find in these installations, varying flow profiles within the pipe degrade measurement accuracy. Furthermore, both the orifice and the turbine meter measure only volumetric flow. Additional pressure, temperature, and differential pressure sensors, as well as a flow computer, are required to calculate mass flow. The installation and maintenance costs of such a compensated measurement system greatly increase instrument cost-of-ownership. Reliability, accountability and efficiency drove the requirement for direct mass flow measurement of fuel gas at a large compressor station. The natural gas distributor had been using turbine meters to measure fuel gas, but because these meters required frequent oiling and maintenance, and because the company was experiencing a personnel shortage, the meters were generally inaccurate and often not functioning at all. The process engineers were seeking a field-rangeable, low-maintenance, high-accuracy device.

MODEL 780S MEASURES FUEL GAS TO COMPRESSORS

The compressor station utilizes a portion of the natural gas in the storage facility or pipeline to power their equipment. Sierra's Model 780S smart thermal mass flowmeter has provided the following benefits in this application:

Mass flow measurement ensures accurate cost-allocation

Mass flow measurement improves combustion efficiency

No moving parts design eliminates fouling and failure

Integral flow straightener reduces straight run requirements

MODEL 780S MEASURES FUEL GAS TO REBOILER UNITS

The glycol dehydrator is used to remove water from the natural gas. The reboiler supplies the heat required to separate the glycol and water by distillation. In this operation thermal mass meters offer the following advantages:

Mass flow measurement improves burner efficiency

Built-in alarms ensure efficiency of continuous process

Built-in flow conditioning improves accuracy and facilitates installation in constrained piping environments

MODEL 780 MEASURES FUEL GAS TO LINE HEATERS

Line heaters are used at hundreds of pressure-reducing stations along the pipeline. Extreme pressure reduction causes gas temperature to drop. Critical liquid components of the gas will drop out if the line is not heated. The benefits of Sierras smart thermal mass flowmeters in this application include:

Field-adjustment capabilities improve operational reliability and flexibility

Simple, no-moving parts design reduces maintenance requirements on remote equipment