Monitoring and control of pump and treat systems in gasoline stations

J.N.Driscoll & J. MaclachlanPID Analyzers, LLC

Sandwich, MAACS Fall Meeting San Francisco, CA

Aug. 13, 2014 6PMPaper #589

Introduction

• In the late 1980’s and 1990’s, leaking underground gasoline storage tanks from gas stations were linked to VOC’s in drinking water

• Starting in the late 1980’s states began requiring double wall tanks in new gasoline stations. In the late 1990’s & early 2000’s, EPA and states also began requiring Gas Station operators to clean up gasoline in soil & groundwater that had leaked from their stations . LA county was no exception and required the cleanup of hundreds of stations. This is the story of a number of those stations that required the cleanup and used our PID analyzers.

• It starts by pumping air (at a high pressure) into the soil & groundwater and removing VOC’s with a soil vapor recovery system via a carbon bed and monitoring VOC’s at the exhaust with our with our photoionization (PID) analyzer

Tank Removal

Typical Vapor Well

This is a well proven but long & tedious process

Pump & Treat System

• Pump & Treat System

– Air pump for sparging VOC’s from Soil/groundwater

– Vapor Extraction Well

– Vacuum Pump to remove VOC’s

– Carbon Bed for VOC removal

– PID Analyzer from monitoring VOC’s from C Bed

Carbon Bed Cleanup Systems

• VOC’s are typically absorbed on carbon beds. The process can be considered as separating the flow of VOC’s from the air flow of a pump & treat system. The VOC’s are pumped from the groundwater or soil which is contaminated.

• The pollutant is adsorbed on the surface (mostly the internal surface) of a of the carbon adsorbent material. It is not absorbed by a chemical reaction. The adsorbed material is held physically (chemisorption), and can be released (desorbed/regenerated) easily by either heat or vacuum.

Typical Carbon Bed Regeneration System

112 @ Gasoline Station P & T Remediation

Cleanup in LA County

• The cleanup at the gasoline started with pump and treat. In the initial stages, when the concentration of the exhaust was > 1,000 ppm, the exhaust was flared. Below 1,000 ppm, when it was not feasible (too costly) because of the cost of the natural gas to keep the plume burning.

• At this stage, carbon beds were added to the pump & treat system. A photoionization based monitor was added at the exit of the carbon bed. This analyzer had data logging capability and a programmable setpoint that could be used to switch off the pump when the breakthrough point of 4 ppm gasoline was exceeded. The input from the pump was then switched to the second carbon bed.

• This process ran for nearly 6 years before the hydrocarbons level in the soil were reduced to an acceptable levels.

1990’s C Beds Used to Reduce emissions of VOC’s and HAP’s

C Bed Collection System Industries

• Automotive• Aerospace• Chemical manufacturing • Degreasing• Electronics (photoresist)• Food products• Gravure printing (publications, packaging &

product)• Paper film & foil coating (magnetic media, adhesive

tape)• Pharmaceuticals (tablet coating, fluid bed drying, )• Rubber (offset printing blankets, gloves, gaskets)• Waste water treatment (Solvent removal)

• Remediation-Remediation (soil vapor extraction; air strippers)

• HAP emissions abatement

• SVC Carbon Canister

Current PID Products Model 201W and low cost Model 112 NEMA 4

Early History of the PID

• 1973- Started HNU Systems with the concept of developing photoioniztion based instrumentation for environmental monitoring

• 1974- Introduced the first portable PID for industrial hygiene at the AICHE in Miami- Model PI101. The target market was vinyl chloride where the PEL had been reduced from 500 ppm to 1 ppm over a period of < 1 year because VC had been declared a carcinogen.

• 1976-We introduced the first commercial PID for gas chromatography at Pittcon- PID was 50x more sensitive than FID for aromatics

• 1976- We introduced the Model 201 continuous PID and one of the first applications was for carbon bed monitoring

Photoionization Process

Compound Ionization Potential (eV)

Response

Benzene 9.25 High

Carbon dioxide 13.79 None

Carbon monoxide 14.01 None

Methane 12.98 None

Nitrogen 14.54 None

Oxygen 13.61 None

Trichloroethylene 9.00 High

Water 12.35 None

Ionization Potentials of Major and Minor components in Air

R + hv R+ + e -

where:R = an ionizable specieshv= a photon with sufficient energy to ionize species R

Comparison of 112 & 201 Specs for C Bed Monitors

112

• Specifications

– Single Detector- PID or FID (total VOC’s)

– Range 0.1 to 3,000 ppm

– Wall mount NEMA 4 enclosure

– 7.5” x 9” x 6”

– Weight 7.5 #

• Options

• 4-20 mA to PLC

• 1 Programmable setpoint

• Expanded logging

201

Specifications • Multiple Detectors-PID, FID, others

(to 4)• Range ppb to 5,000 ppm• Wall Mount NEMA 4• 17” x 21 x 10” D• Weight 35 #• Auto & Remote Cal• 201 FID has auto restart after flame

outOptions

• 4-20 mA, RS485• Multiple setpoints –can replace PLC• Expanded logging• Direct internet connection• Multipoint (2-8 points)

VP and BP of typical solvents

Shepard, Env.Expo, Boston, MA (2001)

What Component Should the Analyzer be set for?

• The first components to breakthrough are the most volatile like VCM in the previous slide.

• In the case of gasoline, the component to look for would be hexane so the Analyzer should be calibrated for hexane The setpoint for switching the bed can be determined and programmed into the analyzer.

• When the setpoint is reached, the contact closure can be used to turn off the pump and in a remote location a cell phone can be dialed to notify an engineer that the bed needs to be switched.

Conclusions

• Soil vapor extraction (SVE) is one of the few innovative technologies that has gained wide use worldwide.

• This process was used to successfully cleanup many gasoline stations in the US. The main drawback is the long time required for the process.

• The PID has proven to be an effective tool for monitoring VOC’s from carbon beds.