Panametrics Aurora TDLAS Moisture Analyzer for Natural Gas

Overview

The Panametrics Aurora is a moisture analyzer based on tunable diode laser absorption spectroscopy (TDLAS) that measures water vapour quickly and accurately in a range of background gases, most commonly natural gas. It is built for installation in hazardous areas and for operation over a wide band of ambient conditions. Its fast response alerts operators as soon as moisture moves out of specification or a dehydration unit is upset, and, once the problem is corrected, it confirms equally quickly that the gas can be returned to the pipeline or process.

Seven Star LLC supplies the Panametrics Aurora to gas producers, pipeline operators, gas processing plants and refineries in the Sultanate of Oman and across the GCC, with engineering support in Muscat. Moisture in sales gas causes hydrate formation, corrosion with CO2 and H2S, and contract disputes at custody transfer points, so a dependable online water analyzer is a standard requirement downstream of glycol dehydration units throughout the region’s gas network.

Measurement Principle

TDLAS exploits the fact that water molecules absorb light at very specific near-infrared wavelengths. Inside the Panametrics Aurora, a semiconductor laser is tuned repeatedly across one of these narrow absorption lines while the sample gas flows through an optical cell. A detector records how much light is absorbed at the line centre compared with its edges; according to the Beer-Lambert relationship, that absorption is proportional to the number of water molecules in the beam path. Because the laser line is far narrower than the absorption feature, the measurement is highly selective for water and is little affected by the hydrocarbons that make up the background gas.

The optics never touch the gas in a way that changes the reading, so there is no sensing surface to saturate, drift or be poisoned by glycol carry-over and liquid slugs, which is a recognised weakness of contact sensors in upset conditions. The result is a Panametrics Aurora measurement with an optical response under 2 seconds; overall system response then depends mainly on sample tubing length, sample system components, flow and pressure. Panametrics Aurora calibration is traceable to NIST or equivalent national standards, with options for nitrogen, standard natural gas and three customisable curves.

Engineering Design of the Panametrics Aurora

The Panametrics Aurora is delivered as a self-contained analyzer in a stainless steel cabinet with IP66 ingress protection, measuring about 841 × 461 × 332 mm and weighing 45 kg. Electronics are housed in a flameproof compartment with increased safety terminations, certified explosion-proof for Class I, Division 1, Groups B, C and D in the USA and Canada and Ex de IIB+H2 T6 under ATEX and IECEx elsewhere, for ambient temperatures from -20 to 65 °C. An optional heater and thermostat stabilise the cabinet in cooler climates.

The sample cell operates at 69 to 172 kPa absolute with a maximum cell pressure of 1380 kPa. Process pressure up to 400 psig is accepted, or 2500 psig with the heated pressure regulator option, and a fast bypass loop at five to ten times the cell flow keeps response short. The operator interface is a backlit LCD showing three parameters, programmed through the glass with a magnetic stylus so the enclosure need not be opened in a hazardous area. Three 0/4-20 mA outputs, a loop-powered 4-20 mA input for a process pressure transmitter, RS232 and RS485 with Modbus RTU and an Ethernet port with Modbus TCP connect it to the control system.

Key Features

The Panametrics Aurora brings the following advantages to gas moisture monitoring:

• Measurement range of 0 to 5000 ppmv, or 0 to 1000 ppmv for CO2 applications.
• Accuracy of ±1% of reading or ±2 ppmv, whichever is greater, up to 1000 ppmv.
• Repeatability of ±0.2 ppmv or ±0.1%, whichever is greater.
• Optical response time below 2 seconds for rapid upset detection.
• Calculated process dew point using a 4-20 mA process pressure signal or a fixed value.
• Readings in ppmv, frost point and absolute humidity from 1.52 to 3,803 mg/m³.
• Hazardous-area certified cabinet with through-the-glass programming.
• Class 1 laser product conforming to IEC 60825-1.

Industrial Applications

The core application of the Panametrics Aurora is natural gas: monitoring the outlet of TEG dehydration units, checking gas at pipeline entry and custody transfer stations, and protecting compressor stations and LNG pre-treatment from wet gas. The Panametrics Aurora datasheet also defines performance for CO2 streams and for hydrogen recycle gas in refinery reformers and hydrotreaters, where moisture affects catalyst activity. Aurora variants such as the portable Aurora TransPort and the remote-mount Aurora RM extend the same TDLAS measurement to spot checks and different installation layouts.

In Oman, typical locations include gas processing plants in the interior concessions, the national gas transmission grid and refinery hydrogen units in Sohar and Duqm. Seven Star LLC supplies the Panametrics Aurora and can coordinate sample conditioning requirements with engineering support in Muscat. Where an aluminium oxide sensor is preferred for very dry gases, compare the Panametrics HygroPro II moisture transmitter; other analyzers on our site include the AMETEK 5100P transportable TDLAS analyzer and the BARTEC HYGROPHIL F 5674 trace moisture analyzer.

Technical Specifications

Panametrics Aurora data from datasheet PANA003DS Rev. 5:

Sampling and Installation of the Panametrics Aurora

Because the Panametrics Aurora is an extractive analyzer, overall performance depends as much on the sample system as on the optics. The sample cell runs at 69 to 172 kPa absolute, so gas taken from a high-pressure pipeline is reduced before it reaches the cell; the standard design accepts process pressure up to 400 psig, and the heated pressure regulator option raises this to 2500 psig, with higher pressures possible through extra sampling components. Panametrics specifies a cell flow of 10 to 60 standard litres per hour, 30 SLH nominal, and a fast bypass loop that carries five to ten times the cell flow, so fresh gas is always close to the analyzer and response is not lost in long tubing.

Calibration is chosen at order. Nitrogen and standard natural gas curves are available, and up to three curves can be customised for a particular composition. The background conditions for each instrument are recorded in its Certificate of Conformance. For CO2 service the range is 0 to 1000 ppmv with accuracy of ±3% of reading or ±5 ppmv and a lower detection limit of 50 ppm. For hydrogen recycle gas the accuracy is ±1% of reading or ±2 ppmv for variations of up to ±5% hydrogen and ±1% ethane from the nominal composition. Readings can also be shown as process dew point using a live 4-20 mA pressure signal, for which the Panametrics Aurora supplies 24 VDC loop power, or a fixed pressure value.

For outdoor sites, an optional heater and thermostat hold the cabinet near 20 °C in the USA and Canada or 10 °C in the EU and other regions, each within ±5 °C. The front panel has LEDs for power, laser temperature stability and keypad lockout beside the alphanumeric status and diagnostic display. Analogue outputs follow the NAMUR convention for signal levels and drive loads of up to 500 ohms, and the RS485 port supports multidrop addressing. Gas and power connections are simple, so a Panametrics Aurora can usually be commissioned quickly once its sample line is in place.

How to Order

To request a quotation for the Panametrics Aurora, send the gas composition, expected moisture range, process pressure and temperature, area classification and required outputs. Seven Star LLC will confirm the analyzer configuration, confirm availability and lead time and provide engineering support from Muscat for customers in Oman and the GCC. The technical datasheet can be downloaded from this page.