Grantee Research Project Results
Final Report: Inexpensive Low Power Nano-Sensor Based Measurement of Fugitive Methane Emissions
EPA Contract Number: EPD17034Title: Inexpensive Low Power Nano-Sensor Based Measurement of Fugitive Methane Emissions
Investigators: Carter, Michael T.
Small Business: KWJ Engineering, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: September 1, 2017 through February 28, 2018
Project Amount: $99,989
RFA: Small Business Innovation Research (SBIR) - Phase I (2017) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air and Climate
Description:
The purpose of this Phase I SBIR program was to demonstrate that an advanced, ultralow power,
microfabricated thermal conductivity detector (TCD) could be used to accurately measure methane in air for the purpose of leak detection, cost reduction and safety. Current measurement of CH4 level is accomplished with either open path IR spectrometers, or nondispersive infrared (NDIR) sensors, which are rather costly and power-hungry to use in large numbers, e.g., leak detection or area monitoring. There are low-cost natural gas sensor based on heated metal oxide semiconducting films, but these also use significant power and are suited more for fixed site and handheld detectors than distributed networks. The goal of this project is to demonstrate that a microfabricated TCD device, which can be manufactured for a small fraction of the cost and power requirements of NDIR sensors, could be used to monitor CH4 accurately in air over ranges of temperature, atmospheric pressure and relative humidity encountered in real conditions and CH4 could be measured at concentrations and with resolution relevant to atmospheric concentrations and leak detection.
Summary/Accomplishments (Outputs/Outcomes):
MEMS thermal conductivity sensors for CH4 were fabricated by standard microfabrication methods. The sensors were characterized in CH4 monitoring over a wide range of CH4 concentrations: 0 – 10000 ppm CH4. Temperature, pressure and relative humidity were held constant as the CH4 concentration was varied. The calibration method was developed and improvements for Phase II were identified (T and RH compensation, precise small-area thin-film deposition). The detection limit and resolution of the CH4 measurement were related to the other environmental variables.
Using the bare bridge as a TCD sensor, CH4 was found to be measurable in air with about 100 ppm resolution, which - while substantially higher than the 2 ppm target range need for atmospheric measurements - is quite sufficient for applications such as leak detection in storage tanks, distribution pipelines and wells. Furthermore, we found that CH4 could be detected at concentrations as low as 2.5ppm using commercially available metal oxide sensors. We also demonstrated response to methane with our own metal oxide coated ”nanobridges”, using 2-5X lower power than the commercial sensor.
Conclusions:
The thermal conductivity sensor, in miniaturized MEMS form, is capable of extremely fast, ultra-low power and stable CH4 measurements in air. The microsecond response time of the MEMS device allows thousands of individual measurements to be performed and signal averaged, resulting in improved signal to noise, before a conventional CH4 sensor has made a single measurement. The CH4 concentration can be accurately calibrated for changes in temperature, pressure and relative humidity on a continuous basis. Future developments of thin- film metal oxide coatings will enable low-ppm sensitivity with <10µW power consumption in pulsed operation.
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.