SIX-PHASE HEATING™ The Rapid Remediation POWER TOOL

TABLE OF CONTENTS

1. A NEW TECHNOLOGY
2. WHAT IS SPH?
3. HOW SPH WORKS
4. WHAT SPH CAN DO
   

A NEW TECHNOLOGY

The removal of Dense Non-aqueous Phase Liquids (DNAPL) in-situ remains one of the remediation industry's toughest burdens. Numerous treatment methods have been applied in an effort to deal with this problem, most requiring many years of continued application to produce even marginally successful results. Current Environment Solutions (CES) has brought a new technology, known as Six-Phase Heating™ (SPH), to bear on this problem. This new technology is proving capable of providing rapid remediation of DNAPLs as well as fuel oils and dissolved phase contanimants from the toughest and tightest soils at reasonable costs.

WHAT IS SPH?

Developed by Battelle's Pacific Northwest National Laboratories (PNNL), Six Phase Heating (SPH) is a patented, multi-phase electrical technique that uses readily available 60 Hz electricity to resistively heat soil and groundwater. Heating between the SPH electrodes creates an in-situ source of steam to strip volatile and semi-volatile contaminants from the subsurface. Soil Vapor Extraction (SVE) is then used to capture the off-gases for above-ground treatment.

SPH operates under the principal that electrical current passing through a resistive component, such as soil, will generate heat. The amount of current which can be made to flow through a given soil type is a function of the voltage applied and the resistance of that soil. Several factors govern the resistance between adjacent SPH electrodes including; soil type, moisture content, and the distance between electrodes. Since distance and soil types are fixed components, current flow can be controlled by regulating soil moisture content and the applied voltage.

As voltage is applied to the electrodes, the current flows via the path of least electrical resistance, causing the soil in these areas to heat first. As subsurface temperatures rise to the boiling point of water, contaminants with low boiling points are volatilized and soil moisture is vaporized into steam. As contaminant vapors and steam are withdrawn by the SVE system, the subsurface in these areas begins to dry out. This drying reduces the electrical conductivity of the soil in these areas, causing an increase in soil resistance. As the resistance of the soil increases, other pathways become preferential for current flow, effectively redirecting the heating to the remaining impacted areas. This self-regulation provides for uniform heating of even heterogeneous lithologies.

SPH uses conventional single-phase transformers to convert standard three-phase electricity into six-phase electricity. This power is then delivered to an electrode array consisting of six (6) steel electrodes arranged in a hexagonal pattern, with one neutral electrode placed in the center. These electrodes are installed into the subsurface either vertically or horizontally using conventional drilling methods. Electrodes are surrounded with granular graphite to improve electrical conductivity to the soil matrix. The center electrode functions not only as the electrical neutral, but is also an SVE extraction well.

HOW SPH WORKS

SPH is a valuable tool for the treatment of DNAPL in soil and groundwater since the current flow will pass directly through the DNAPL, expediting its removal through direct boiling. In addition, this technology can be used to treat DNAPL pools or hot spots in groundwater by boiling the aquifer to produce steam. The steam is then removed via the SVE system, passed through a condenser, and the vapors and condensate are then treated using conventional abatement methods such as oxidation or adsorption.

By heating to the boiling point, an in-situ source of steam is created which strips contaminants from the soil. The steam serves two purposes. First, its physical action drives contaminants out of portions of the soil that tend to lock in the contaminants via capillary forces. Second, the steam acts as a carrier gas for the contaminants, enabling the contaminants to be swept out of the soil into the vacuum vent by increasing the permeability of the soil.

WHAT IT CAN DO

The SPH technology is not only effective in treating difficult sites with DNAPL and low permeability soil, but can also be used to heat soil to enhance biodegradation. This is accomplished by maintaining the subsurface temperature between 30°C and 40°C. The increased temperature in the subsurface has been shown to spur natural biodegradation. This technique is has been applied at a number of sites.

Additionally, SPH can be used to mobilize heavy hydrocarbons to make removal by pump and treat more viable. As resistive heating raises the temperature of the hydrocarbons, they become less viscous and more readily mobile. SPH is also extremely well suited for application in Cold Regions treatment sites, where the soil may be frozen or may contain some level of permafrost.

Since little energy is lost in transmitting the heat to the soil, resistive heating is preferential to both radio frequency (RF) and to steam injection. RF heating uses electromagnetic energy to heat soil in the subsurface. One study indicated that the RF generator/AC power conversion efficiency is 73%, with the RF applicators being designed for >95% radiation efficiency. This yields an overall efficiency of less than 70%. Standard efficiency for steam boilers is approximately 85%, with typical piping transmission losses accounting for another 3% drop in efficiency. This brings the overall efficiency of steam injection down to about 82%. SPH has a higher efficiency than either of these methods, since nearly all of the energy supplied by the source is applied to the subsurface. Less than 2% of the energy supplied by SPH is dissipated in the cables. When combined with a nominal transformer efficiency of 95% and a silicon controlled rectifier (SCR) efficiency of 97%, the SPH technology is over 90% efficient. This improved efficiency can result in reduced cleanup time, as well as reduced costs for cleanup.

The total costs for applying the SPH technology is typically between $50/yd³ and $100/yd³, including electrical usage. This cost is only one measure of the advantages of using SPH to solve a difficult remediation problem. The amount of time spent with cleanup is reduced from years to months or even to weeks. The cost savings should not be considered for the contractor alone, but also in terms of interaction time with regulatory agencies, analytical sampling and analysis, reporting, and planning. In ending the cycle of liability and enabling sites to be returned to productive use, time is money. The SPH technology enables clients to more quickly convert liabilities into profits, and does so without the disruption and spectacle of bulk soil exhumation, and without adding volume to dwindling landfills.