To ensure that online moisture analyzers continuously provide reliable measurements of natural gas drying process, operators must frequently verify these locally with portable hygrometers. This often means the service technicians visit multiple installations spread over large areas. Where a combined water and hydrocarbon dew point measurement e.g. as described in ASTM D1142 is required, the new, chilled-mirror based Michell Instruments CDP301 Dew-Point Tester can be used.
For trace moisture measurements, the lightweight, hazardous area-certified Michell Instruments MDM300 I.S. portable hygrometer allows technicians to cover more sample locations during one shift without the need to carry heavy equipment from one sample location to another.
CDP301 is housed in a rugged explosion-proof case and has global hazardous area certification. It is able to measure at up to 100 bar operating pressure and is supplied with sample conditioning to ensure accurate and repeatable dew-point measurements in the field. The battery allows 8 hours of operation of a full charge – enough for all-day operation with the ability to swap in a spare battery if required.
The Michell MDM300 I.S. offers case-mounted compact sample systems designed for field operation including coalescing filters for liquids, membrane filters and glysorb to remove glycol.
Natural gas extracted from underground sources is saturated with water and needs several stages of processing to meet the requirements for a clean, dry gas that is suitable for transmission through pipelines and burning by end users. The most common process for drying natural gas is glycol dehydration. Here the gas flows up through a tower, where it is exposed to a mist of glycol – acting as a liquid desiccant. Such glycol contactors are specified to achieve a moisture content of less than 3 lb/MMSCF (pounds of moisture per million standard cubic feet) under normal operating conditions.
The presence of moisture vapor in concentrations above a few tens of parts per million has potentially disastrous consequences. The lifetime of a pipeline is governed by the rate at which corrosion occurs, which is directly linked to the available moisture in the gas, so the performance of glycol contactors is critical. This is typically monitored by on-line moisture analyzers, such as a Michell Instruments OptiPEAK TDL600.