SS2100 - H2O Natural Gas Product Purity (Residue Gas)

Natural Gas Processing Plants
Natural Gas Processing involves a number of different goals: Acid Gas removal, N2 Rejection, NGL recovery and fractionation to name a few. A variety of different processes are designed to achieve these goals.

Critical Control of Moisture
In most, if not all process involve some form of cryogenic processing of the gas, so water must be removed to a very low concentrations. Desiccant dryers are frequently used to reduce the moisture in the process gas to <1 ppm H2O, but in many plants, some of the water removed in regeneration is returned to the Natural Gas product, also called Residue Gas. There may be other wet streams that are combined with the Residue Gas before it leaves the plant.

Traditional Measurement Solutions
Electrochemical and vibrating quartz crystal moisture analyzers have been the traditional methods for monitoring the levels of moisture in Natural Gas Product. Unfortunately, trace hydrocarbons and other contaminants present in the stream contaminate the electrochemical probes, resulting in high maintenance costs due to the need to be constantly replaced. It’s not uncommon for moisture probes to be replaced multiple times a year. Quartz crystal moisture meters have slow wet-up and dry-down times that may distort the true moisture content during an upset.

SpectraSensors' Solution
SpectraSensors SS2100 is the ideal solution for this challenging application. Its non-contact laser and detector is impervious to damage from contaminants. Tunable Diode Laser technology means that measurement interferences from other infrared absorbing compounds are avoided. There are no wet-up or dry-down delays, resulting in fast updates even when the concentration changes dramatically. Only SpectraSensors employs Differential Spectroscopy, which incorporates a dryer using metal getter technology to subtract the spectrum of the dry gas from the wet spectrum. This allows the SS2100 to measure streams whose background gas compositions changes.

Validation
Validation of low level (<10 ppm) water measurements is essential, but also extremely difficult, as certified blends at such low levels are not readily available. Some have attempted to use permeation devises, but these require regular maintenance to prevent drying out, and there is no independent way to verify the accuracy of the permeation device. SpectraSensors employs a dilution system that dilutes a relatively high concentration certified standard of H2O in Methane using dried sample gas. Thus the validation is accurate and traceable.