Michell Condumax II Hydrocarbon Dew-Point Analyzer

Overview

The Michell Condumax II is an on-line analyzer that continuously and automatically measures the hydrocarbon dew point of natural gas, with an optional second channel for water dew point. Hydrocarbon dew point is one of the most difficult gas quality parameters to measure and control, yet it sits at the centre of custody transfer contracts, where tighter limits can lead to disputes and shut-ins. Michell uses its patented Dark Spot™ chilled-mirror technique, a direct and fundamental measurement, to give objective and highly repeatable results with a stated hydrocarbon dew-point accuracy of ±0.5 °C. The original Condumax was introduced in 1986, and the Michell Condumax II carries that proven method forward with updated electronics, sampling and communications.

Seven Star LLC supplies the Michell Condumax II, its sampling systems and its key spare assemblies to gas processing plants, pipeline operators and power producers in Oman and across the GCC, with engineering support in Muscat. We help customers specify the correct configuration from the Michell order code list, including the choice between indoor and outdoor sampling systems and the optional water dew-point channel.

Measurement Principle

Hydrocarbon condensate is almost invisible at its dew point because it has a low surface tension and no colour, which is why the manual Bureau of Mines (BOM) visual method is so subjective. The Dark Spot™ sensor turns this property into an advantage. Its optical surface is an acid-etched, semi-matt stainless steel “mirror” with a central conical depression. Collimated visible red light is focused onto the centre of the surface; when the surface is dry, the matt finish scatters the light and gives a base signal to the optical detector. As the surface is chilled and condensate forms, the film becomes reflective, an annular ring of light forms around the detector, and the scattered light inside the central dark spot falls sharply. Michell states a sensitivity of better than 1 ppm molar (1 mg/m³) of condensed hydrocarbons. When a predetermined condensate layer is detected, the temperature of the optical surface is recorded as the hydrocarbon dew point.

The Michell Condumax II also uses flow de-coupling. In each measurement cycle a fixed sample of gas is locked into the sensor cell before chilling begins, so all hydrocarbon components condense in their true proportions rather than the heaviest fractions dropping out first, as happens with a flowing sample and leads to a falsely high reading. After detection, the surface is heated, typically to +50 °C, to evaporate the condensate back into the gas, and the whole automatic cycle completes in under ten minutes. A three-stage Peltier heat pump under adaptive digital control first “range-finds” the dew point and then slows its chill rate to 0.05 °C/s as it approaches the previous value, which gives the precision and reproducibility the method is known for.

Engineering Design of the Michell Condumax II

The Main Unit of the Michell Condumax II holds every critical component in a single explosion-proof/flameproof cast enclosure with a glass viewing window, for installation in Zone 1 or Zone 2 (Class I, Division 1 and 2) areas. Inside the Michell Condumax II Main Unit are the Dark Spot™ sensor cell, the optional ceramic metal-oxide water dew-point sensor, pressure transducers, flow switches, measurement electronics and a vacuum fluorescent display operated through a touch-glass keypad, so settings can be viewed and changed safely in the hazardous area. Flame arrestors protect the gas inlet and outlet ports, the enclosure is internally heated against condensation, and the sensor cell itself is a stainless steel assembly rated to 100 barg that achieves a measurement depression of up to −55 K from the analyzer operating temperature.

The Main Unit is mounted integral to an indoor or outdoor sampling system. Both versions provide pressure regulation, flow control and microporous membrane filtration with a bypass arrangement and condensate drain, which protects the sensor from liquid hydrocarbon and glycol carry-over while keeping the response fast. The standard design conditions gas at up to 138 barg; the outdoor version is housed in an IP66, insulated stainless steel enclosure with optional thermostatic heating, and dual-channel sampling is available for combined hydrocarbon and water dew-point packages. Michell also lists a transportable version of the Michell Condumax II for field spot checks, and the photograph on this page shows the analyzer in that transportable configuration.

Key Features

The Michell Condumax II combines a fundamental measurement with fully automatic operation:

• Patented Dark Spot™ chilled-mirror detection gives a direct, fundamental hydrocarbon dew-point measurement rather than an inferred value.
• Hydrocarbon dew-point accuracy is stated as ±0.5 °C for both single and multiple condensable component analysis.
• Fixed-sample flow de-coupling prevents preferential drop-out of heavy ends and the falsely high readings this causes.
• The optical surface is heated after each cycle, so the sensor is self-cleaning and no purge or cooling gas is needed.
• An optional ceramic metal-oxide channel measures water dew point from −100 to +20 °C alongside the hydrocarbon dew point.
• Condensate Mode supports potential hydrocarbon liquid content (PHLC) work, and readings at different pressures help define the gas phase envelope.
• Two configurable 4–20 mA outputs and Modbus RTU over RS485 connect the analyzer to a DCS, PLC or computer in the safe area.
• The analyzer is suitable for natural gas containing up to 20 % hydrogen without further modification.

Industrial Applications

Michell lists natural gas processing, protection of turbo-expander plant, gas quality measurement at custody transfer, transmission pipeline monitoring, and confirmation and control of fuel gas superheat to turbine power plants as the main uses of the Michell Condumax II. In Oman these duties are found at gas processing and dew-point control plants, at custody transfer and fiscal metering points on the national gas transmission network, at LNG feed gas facilities, and at gas-turbine power and desalination plants where fuel gas must stay above its hydrocarbon dew point to protect burners and hot-gas-path parts. Because the Michell Condumax II also correlates well with laboratory gas chromatography and equation-of-state calculations, it is often used to confirm and harmonise results between producers and buyers.

Seven Star LLC supports the Michell Condumax II with engineering support in Muscat, serving operators around Muscat, Sohar, Duqm, Salalah and the interior gas fields. Alongside the complete analyzer, we supply the replacement sensor cell and the exchange and new water dew-point sensors that keep an installed Michell Condumax II in service with minimum downtime.

Technical Specifications

The following Michell Condumax II data is taken from the Michell Instruments datasheet:

How to Order

Send Seven Star LLC an RFQ with your gas pressure, expected dew-point range and whether you need the water dew-point channel and an indoor or outdoor sampling system, and our analyzer team will prepare a Michell Condumax II proposal based on the Michell order codes. The official Michell Condumax II datasheet is attached to this page for download. For installed analyzers we can also quote the Condumax II CD2-SCR-002 sensor cell, the CD2-SX-WDC-002 water dew-point sensor exchange and the CD2-WDC-002 water dew-point sensor assembly. Seven Star LLC is a trusted supplier with engineering support in Muscat for customers throughout Oman and the GCC.