Real-time BTU Sensor for Natural Gas Applications
Sandia National Laboratory will conduct a market analysis to determine industrial interest in an inexpensive analytical instrument for rapid, distributed, on-line determination of natural gas heating values. In addition, micro-fabricated analytical components will be combined with electronics and software to produce a field-portable “breadboard” instrument (experimental prototype) for natural gas analysis.
A fuel-quality sensor system is under development, through collaboration between General Electric and Sandia National Laboratories. The effort is directed towards real-time monitoring of the Wobbe Index of natural gas and syn-gas fuels used in power turbines. Sandia’s micro-hotplate calorimeter forms the basis of this system. A thin catalyst layer deposited on the calorimeter catalytically combusts the fuel, premixed with air, and the heat of combustion is measured. The micro-machined calorimeter allows for very sensitive and rapid calorimetry with a heat capacity of ~10-6 J/K (joule per Kelvin), thermal resistances ~104 K/W (Kelvin per watt) and ramp rates ~104 K/sec (Kelvin per sec). The calorimeter provides a direct measure of the British Thermal Unit (BTU) content of the fuel, which, combined with a density measurement from a commercially available sensor, will yield the Wobbe Index. The calorimeter has been tested with various natural gas standards (purchased from Supelco) and pure methane, ethane and propane, and has shown the ability to distinguish between their BTU contents for optimized flow and fuel/air ratios. The sensor has yet to be tested against other natural gas sources.
To better assure the ability to handle a wide variety of natural gas mixes while still maintaining an adequately rapid response (less than five minute total analysis time), an improved system would couple the fuel calorimeter with Sandia’s microfabricated gas chromatography (GC) column. Using micromachining techniques, a meter long column is etched into silicon using only about 1 cm2 of chip area. This device has been tested extensively for separations of semivolatile compounds using a five psi air carrier, and taking about two minutes per analysis. Modified versions have been packed with solid-gas chromatography materials for separations of natural gas samples and other volatile mixtures. Coupling this device with the fuel calorimeter will greatly enhance speciation of complex fuel mixtures. Separation of a mixture of methane through pentane (C1-C5) in less than two minutes has been demonstrated. In addition, microliter injections of natural gas upstream of the detector produce a signal with a temporal response typical of chromatography detectors.
Sandia National Laboratory (SNL)
Albuquerque, New Mexico 87123
Industries involved in the production, transfer, and final use of natural gas have only limited information as to the actual heating value of each unit bought and sold. The gas monitor under development here will provide a simplified and inexpensive method of accurately measuring the BTU value and quality of natural gas currently being carried through the pipeline infrastructure.
SNL has completed a market study to gauge interest of potential consumers in a low-cost, portable, gas chromatography based BTU analyzer, and has assembled a prototype BTU monitoring instrument using existing and modified microfabricated components that can address market niches for efficient natural gas transfer at key points in the national gas distribution network. In conjunction with a commercial injection valve, the instrument uses a silicon microfabricated, packed, gas chromatography (GC) column. A microfabricated calorimeter with a reference element serves as the detector. The microcalorimeter senses combustion at its catalytic surface through monitoring the power required to keep the device at a constant, elevated temperature. Batch microfabrication techniques will allow these components to be manufactured in production quantities at a low cost in order to meet industry requirements for cost, lifetime and performance. The market study reveals that the current system may be suitable for large commercial users, as well as niche applications. An order of magnitude improvement in the sensor’s measurement capability will make it appropriate for custody transfer applications and gas turbines.
Current Status and Remaining Tasks:
All experimental work has been completed. The final report has been submitted and the project has been completed.
Project Start: September 2004
Project End: February 2005
DOE Contribution: $25,000
Performer Contribution: $0
NETL – Daniel Driscoll (firstname.lastname@example.org or 304-285-4717))
Sandia National Laboratory (SNL) – Mike Hightower (email@example.com or 505-844-5499)
Final Report - September 2005: [PDF-163KB] Sandia National Laboratory