The Moisture Analyser for the Modern Process Environment
For the last thirty years, Michell Instruments has provided online moisture measurement solutions for the natural gas and petrochemical industries. All of that experience and expertise is encapsulated in Promet EExd, where the highest priorities have been given to the needs of the customer in terms of simplicity of installation, total plant communications integration, moderate cost of ownership, and highest calibration integrity.
Promet EExd offers single and dual channel moisture measurement, with integrated electronic pressure reading, within a single field-installed flameproof housing. User interface is provided through the bright vacuum fluorescent display and touch screen switches.
Comprehensive Sampling Systems of state-of-the-art design, with best practice sample filtration, pressure reduction and fl ow control, and a range of options are available to fulfill user specific installation and application requirements.
Simple Flameproof Installation
Promet EExd is flameproof certified for use in IEC Zone 1 and 2/NEC Class 1 Div. 1 and 2 hazardous areas. The Main Unit (electronics and sensing) and associated sampling system may be mounted at a convenient location next to the pipeline or process, with gas sample and vent connections. A single, low power single-phase AC supply is required for both the analyzer and sampling system. No barrier units or safety earth are required, saving the user both cost and inconvenience.
Advanced Sensor Technology
Promet EExd utilizes the Michell Ceramic Moisture Sensor, offering unrivalled reliability and performance with more than 1,000 installations in natural gas and petrochemical installations world-wide.
Thick- and thin-fi lm semiconductor technologies with metallized ceramics produce an exceedingly durable sensor, with measurement sensitivity to 10 ppbV moisture content and high pressure capability up to 206 barg (2988 psig).
Unlike older aluminium-oxide technologies, the inherent immunity to pressure shock of the Ceramic Sensor completely avoids any risk of sensor failure at commissioning or shut-down, whilst the unique inert nature of the sensor gives unrivalled long-term resistance to chemical attack, even in extremely sour gas with percentage level H2S concentrations.
The Ceramic Sensor responds to the partial pressure of water vapor in the gas being measured, which is directly related to the dew point temperature. Every Promet EExd sensor is calibrated against fundamental dew point measurement systems in Michell’s world-class laboratory, which is internationally accredited and directly traceable to both NPL (UK) and NIST (USA) base standards. Precise process moisture measurement with a class leading best accuracy of ±10% of measured value is assured.
Comprehensive Measurement Units
Promet EExd offers complete flexibility for the user to select the preferred hygrometric unit, be it dew-point temperature in °C or °F, or an exhaustive list of moisture content units. Integral pressure measurement enables unit conversions from dew point to moisture content, or dew point to dew point for different pressure conditions.
The firmware of Promet EExd incorporates conversion data for ideal gases and also specific to natural gas, using either the long established IGT Research Bulletin No. 8 or the more recently published ISO 18453, to customer order preference.
Calibration Maintenance Made Easy
Maintenance of traceable calibration is essential to the lifetime performance of all analyzers. Beware claims of “automatic calibration”. This is a non-traceable, internal field check and does not represent a true calibration of the analyzer.
For Promet EExd, true calibration maintenance is simple. The unique Michell Calibration Exchange Service offers fast delivery, world-wide, of newly calibrated replacement Ceramic Sensors certified traceable to NPL and NIST. As the calibration data for the Promet EExd Sensor is programmed into on-board nonvolatile memory, fitment of a Calibration Exchange Sensor renews the calibration with minimal downtime.
No programming or data input is required by the user to complete the calibration process. The Calibration Exchange Service facilitates a professional, scheduled user QA program at a lower cost than a traditional ‘return to manufacturer’ recalibration service.
Calibration or exchange is recommended annually for sweet gases and six-monthly for sour gases. Field calibration, using a portable dew point generator (ASTM D5454), against a calibrated reference hygrometer or against certified moisturein- gas cylinders is also possible. Promet EExd accommodates such needs within the operating fi rmware, providing userfriendly access to the calibration characterization table to allow adjustments to be made at just one point (for example using a certifi ed moisture in gas cylinder) or multiple points (using a field generator) across the measurement range.
Temperature Controlled for Best Accuracy
To ensure continuous optimum performance, the Promet EExd Main Unit is internally temperature controlled at the normal maximum local environmental temperature. This greatly reduces the effect of diurnal temperature variations that would otherwise introduce transitional adsorption and de-sorption effects in the sampling system components and result in erroneous measurements during periods of temperature change.
In addition the Promet EExd features an advanced temperature compensation algorithm that automatically maintains best possible measurement accuracy in the event of heater failure or if the prevailing climate exceeds the set temperature level.
Communication Capability for Total Plant Integration
Promet EExd offers digital and analog communications as standard.
- Modbus RTU is provided with optional Active X controls for integration to site SCADA/DCS.
- Two non-isolated 4-20 mA outputs per channel are user configurable for unit and range of measurement.
- Process alarm contacts can be set by the user.
- Instrument status alarms provide a continuous ‘health check’ through to the site control room.
- Low sample fl ow alarms are available as an option. Such individual alarm states are identifi ed through the Modbus instrument registers and appear locally on the display.
- Field cable connections are conventional instrumentation pairs for all signals and alarms.
For users that wish to have a dedicated host within their Control or Instrument Room, the optional Remote Interface (RI) provides advanced graphical display of measurement and status information, data logging and all program confi guration functions for up to 31 analyzers. Each analyzer communicates with the RI through the Modbus RTU, so transferring all the functionality of the Main Unit through into the comfort and convenience of an indoor safe area environment. Additionally, global access to all functionality is provided through any web browser into the embedded unique IP address of the RI.
Premium Sampling Systems
Good sample conditioning and handling is particularly important in the field of moisture measurement. As the moisture sensor has to be exposed directly to the process gas stream in order to detect the water vapor present, then key sampling issues such as the avoidance of particulate and liquid contamination are imperative to successful operation. Our 30 years of expertise in on-line process gas analyzers are used to optimize the design of the Promet EExd Premium Sampling Systems.
Two core configurations, both available in either single- or dual channel version, are available for key applications:
Natural Gas Processing and Transmission
The reliable solution for glycol dehydration processes offshore and onshore and for onward pipeline transmission of sales gas. The most advanced filtration techniques with micro-porous membrane and continuous by-pass fl ow remove and dispose of all liquid phase contaminants. A glycol adsorption cartridge removes residual vapor that may otherwise interfere with the moisture signal.
Trace Moisture in Hydrocarbon Gas Sampling System
An optimized design for continuous trace moisture measurement in low ppmV and ppbV ranges for molecular sieve dehydration of natural gas prior to cryogenic liquefaction. Also suitable for many other monitoring applications at trace moisture levels in refinery gases and critical petrochemical processes. A minimalist approach to the sampling system design is essential to ensure best dynamic response to process moisture variations. A particulate fi lter and isolation valve are the only components prior to the sensor. As measurements are made at pipeline conditions, no regulators or other complex upstream components are necessary so ensuring the Promet EExd remains in continuous equilibrium with the process gas condition without any significant response lag.
Custom Design Service
Custom design sampling systems are available for other specific applications such as higher pressure processes and hydrogen recycle gas moisture measurement in catalytic reformer refinery processes. Your Michell office or authorized distributor will be pleased to discuss your specific application/ installation requirements.