Wednesday, September 24, 2014

Real time air monitoring system for personnel protection at a TCA cleanup site


Real time air monitoring system for personnel protection at a trichloroethane cleanup site


Remediation site aerial

1,1,1 Trichloroethane has been used as a solvent in industry, in home cleaning products and as a fumigant. We are involved in the development of a real time monitoring system for the cleanup of a closed chemical plant that had manufactured 1,1,1 trichloroethane (TCA). More precisely, we were concerned with minimizing the exposure of personnel and neighbors during this cleanup.

 Continuous Analyzer Requirements

Sensor: PID detector
Model 112
The analyzer is capable of measuring TCA down to low ppm levels, should require a minimum of maintenance, be able to run for a minimum of 50 hours/week on batteries, produce a 4-20 mA output, and be in a weather proof enclosure. The PID Analyzers Model 112 meets all those requirements. The ionization potential of TCA is 10.70 eV. As a result, we would need an 11.7 eV lamp for this application. The lifetime of the 11.7 lamp is 600-800 hours of continuous operation. If the lamp is on for 8 hours per day, the lamp would have to be changed every 3 months. In order to extend the lifetime, we modified the software so that the lamp is only switched on for 30 seconds every 5 minutes with a duty cycle of 9%. This would provide a lifetime of  6 months to a year. The 4-20 mA signal is fed into a wireless transmitter to a central PC which is connected to the internet. The PC also collects data from a weather station that provides wind speed, direction temperature, etc. This would allow an engineer to monitor the site from their desk and shut down the cleanup if the levels were above a specific level or if the wind was blowing in the direction of the nearby homes.

Sensor Technology
The technology employed is photoionization  
The ionization potential (IP) of TCA is 10.70 eV, As a result, we would need an 11.7 eV lamp for this application.
The IP’s of major components of air are:
O2=  12.08 eV
N2=15.60 eV
H2O=12.59eV
CO2=13.79eV
Data Acquisition
These sensors use an integrated, 2.4GHz - 802.11b/g, FCC/CE certified radio transmitter  that work with new and existing Wi-Fi networks. One of these transmitters is located in each of the 8 analyzers as well as the weather station.
Monnit’s MoWi sensors communicate through existing Wi-Fi networks to iMonnit, the online data monitoring system, which agrigates sensor information and sends notifications via text or email if user defined conditions are met or exceeded.
Central Computer
A PC at the site will collect the data, process it and store it locally.  The data will then be sent via the internet to a protected website. Any change in weather conditions or TCA concentrations and/or alarm levels will be immediately sent to a mobile phone.
Data Collection Schematic
Summary
•A battery operated Model 112 uses photoionization to detect low MW  chlorinated HC during remediation.
•The HW site has homes and a small town nearby so a fast responding analyzer with weather stations and wireless data logging connected to the internet is used to monitor the site at the remote location during the remediation.
•The remediation site can be shut down remotely by mobile phone if there is a combination of unacceptable levels of chlorinated HC or wind conditions that could affect the workers or residents in the local area
•This automated system will maximize safety at the plant/ fence line and the remote industrial hygienist can control the activities/problems at the plant. 

Our Model 112 analyzers are available with choice of PID or FID (flame ionization detector) sensors. Learn more by viewing the brochure here. Have an application you would like to discuss? Then email us or use the online quote request system.

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