DUAL PHASE EXTRACTION

Dual-phase extraction (DPE), also known as multi-phase extraction, is a technology that uses a high vacuum system to remove both contaminated groundwater and soil vapors. A single vacuum source (vacuum pump or blower) is used to extract both liquid and gaseous phases in the same conduit or pipe. In DPE systems a high vacuum extraction well is installed (by others) with its screened section in the zone of contaminated soils and groundwater. During the Fluid/vapor extraction process, the water table is depressed and the fluids flow faster towards the extraction well. This process removes contaminants from above and below the water table. As the water table around the well is lowered exposing the unsaturated soil. This area, called the capillary fringe, is often highly contaminated. Contaminants in the newly exposed zone can now easily be removed by the vapor extraction process. Once above ground, these extracted vapors groundwater are then separated and treated. Use of dual-phase extraction can shorten the cleanup time at a site, as the capillary fringe is often the most contaminated area.

THERMAL OXIDIZERS

Basically thermal oxidizers work on the principal of promoting oxidation of the VOC's. (volatile organic compounds). By elevating the air temperature to 1400 degrees, oxidation begins to occur. This oxidation process breaks down the Hydrogen / Carbon bonds into namely Carbon Dioxide (CO2) and water vapor (H2O). This conversion depends on two things: temperature & time. The minimum dwell time the VOC’s should remain at the minimum temperature is 0.5 seconds and the minimum temperature should be 1400ºF.

 

A BTU (British thermal unit) is a measure of the heat content of a fuel and indicates the amount of energy contained in the fuel. For example, 1 gallon of gasoline contains about 125,000 Btu’s. Thermal oxidizers are rated on the amount of BTU’s they can effectively destroy during a one hour period. Our thermal oxidizers can handle over 7 Million BTU’s per hour. That is over 56 gallons of gasoline per hour!

 

ADDITIONAL BTU’s: Gasoline 125,000 Btu’s/gallon Diesel fuel 138,690 Btu’s/gallon LP gas 93,300 Btu’s/gallon Natural gas 1,030 Btu’s/cubic foot

SCFM –vs- ACFM

There is a great deal of confusion between the terms SCFM and ACFM.

 

Lets first start off with the definitions:

• SCFM - “Standard” Cubic Feet Per Minute - This is the volume of air a pump is able to move at a “standardized” pressure, temperature, and relative humidity. In most cases, the “standard” ambient conditions defined by the CAGI (the Compressed Air and Gas Institute) are 14.7 psig atmospheric pressure, 68 degrees Fahrenheit, and 0% relative humidity
• ACFM – “Actual” Cubic Feet per Minute – This is the “actual” airflow (uncorrected) that is measured at the air inlet of the pump. This is a realistic representation of the actual air flow that was moved during the pumping process.

 

So, theoretically, if you were moving air at exactly 14.7 psig, it was a perfect 68 degree day, and there was no humidity (you are in the desert) these two standards to reference a flow rate would be identical. Unfortunately, this usually is not the case as the most important change between these two definitions is the pressure. While moving air, you are either creating a pressure or a vacuum. When pressure is applied to a standard cubic foot of air, it gets smaller. When vacuum is applied, it expands. The volume of air after it is pressurized or rarified is referred to as its “actual” volume

 

As a rule of thumb, an SCFM result will be lower than an ACFM result during a vacuum application, and a SCFM result will be higher than an ACFM result during a pressure application

 

How this effects our calculations: The standard EPA formula for calculating mass removal rates for hydrocarbons requires an ACFM (Actual Cubic Feet per Minute) flow result. If you were to use an SCFM result in the EPA formula (unless you were at the exact “standard” parameters of a SCFM calculation) would provide you with an inaccurate result.

 

CONVERSION CHART - ACFM/SCFM Vacuum Vacuum Vacuum Level Conversion Level Conversion Level Conversion (Gauge) Factor (Gauge) Factor (Gauge) Factor 1" 1.03 11" 1.58 21" 3.33 2" 1.07 12" 1.67 22" 3.75 3" 1.11 13" 1.76 23" 4.28 4" 1.15 14" 1.88 24" 5.00 5" 1.20 15" 2.00 25" 6.00 6" 1.25 16" 2.14 26" 7.63 7" 1.30 17" 2.31 27" 10.00 8" 1.36 18" 2.50 28" 15.00 9" 1.43 19" 2.73 29" 30.00 10" 1.50 20" 3.00

To find ACFM - Multiply SCFM by conversion factor

 

EXAMPLE:

• 99 SCFM @ 19" Hg 99 SCFM @ 25" Hg
• 99 x 2.73 = 270.27 ACFM 99 x 6 = 594 ACFM

 

To find SCFM - Divide ACFM by conversion factor

 

EXAMPLE:

• 270.27 ACFM @ 19" Hg 594 ACFM @ 25" Hg
• 270.27 divide by 2.73 = 99 594 divide by 6 = 99

AIR ENTRAINMENT

Air entrainment (also known as entrainment technology or bioslurping) is the process of adding small air bubbles to the flow of water in a suction down tube. By adding these tiny bubbles to the down tube(stinger assembly) during a dual phase extraction event, these tiny bubbles actually creates an aerodynamic dragging action that lifts fluids up the slurping tube from depths that what would be unachievable with high vacuum alone. Typically, this allows extraction of the groundwater from depths over 100’.