Oxygen measurement in pipeline natural gas with Panametrics
Oxygen is a contaminant in natural gas processing and pipeline transportation with the potential to create serious issues for production and storage facilities, gas plants and the associated transportation pipelines. Natural gas and methane (CH4) are terms often used interchangeably however natural gas is typically comprised of 70%-90% methane with the remainder comprising mostly of ethane (C2H6), propane (C3H8), carbon dioxide (CO2), nitrogen (N2) and oxygen (O2). The oxygen concentration in the gas stream is continuously measured to ensure that the oxygen concentration and resultant harmful effects are minimized.
Natural gas is extracted from wells where it passes to treatment plants for multistage separation. The treated natural gas is then pumped using compressors through transportation pipelines to storage facilities or end users. The presence of oxygen in the natural gas can cause a number of issues for the end product and transportation infrastructure. Combining oxygen (O2) with hydrogen sulfide (H2S) and moisture (H2O) produces highly corrosive sulfuric acid (H2SO4), detrimental to pipeline infrastructure. Pipelines are typically under pressure and, leakage due to the corrosion of components can have serious consequences. Furthermore, the presence of oxygen can reduce the efficacy of carbon dioxide (CO2) and hydrogen sulfide (H2S) removal. It also adds no specific heating value to the end product and is therefore undesirable to the end user. Oxygen can enter the gas streams for any number of reasons such inadequate vapor recovery units, failures in tank blanketing systems or leakages in compressor seals or pipeline fittings. Oxygen concentration is measured at several points along the value chain of natural gas with limits being placed based on regional requirements. Typically these measurements will be conducted at custody transfer points or metering skids. For treated pipeline natural gas in Europe, EASEE-gas stipulates that the oxygen concentration maximum limit is 0.01% or 100ppmv. The North American region is more fragmented with limits ranging from 1% oxygen down to 50ppm.
The challenge with this measurement is having a sensor technology that can measure oxygen in low ppm ranges, which is unaffected by background gases in the stream and can work with low levels of hydrogen sulfide (H2S). Coupled with this, the sampling package to support the measurement must be capable of protecting the oxygen transmitter by reducing the stream pressure, filtering out particulates or other contaminants and removing any moisture. Analyzer shelters frequently have many measurement points and therefore have associated space considerations. The sample handling requirements and the measurement itself must therefore adhere to space considerations and in a hazardous area rated package.
Benefits: • Turnkey packaged solution • Stainless steel IP66 enclosure • Background gas unaffected • Class 1 Div 1/Zone 0 option
The O2.IQ is an oxygen analyzer package specifically designed for this application. The oxy.IQ oxygen transmitter can be configured to low ppm and percent oxygen ranges and is unaffected by the background gas stream. The standard measurement cell can tolerate up to 5ppm H2S, with greater than 4ppm being classed as sour gas. The complete O2.IQ solution also comprises the sample handling system required to support an accurate and reliable measurement in a very space conscious package. Sample handling features include filtration and pressure reduction along with flow control and calibration gas inlets. The stainless-steel enclosure also ensures the integrity of the system. Sample take off configurations can also be added in cases where the O2.IQ is not installed as part of a metering skid.
- Sample gas pressure: 0 - 400psig (0 - 27.5 Bar)
- Sample gas temperature: 32 to 113°F (0 to 45°C)
- Power requirements: 24 to 28 VDC at 50 mA