This project, located in Santa Ana, California, involved cleaning up an automobile service station that had suffered underground storage tank leakage. State and federal guidelines dictate that contaminated soil must be cleaned or disposed of in an acceptable manner. This site employed a method know as vapor extraction to perform the clean up operation. Water treatment was also employed since there was a slight amount of water contamination.
Vapor extraction involves installing a series of perforated pipes in the contaminated soil. A large vacuum blower is installed at the end of the perforated pipes. When the fan is started, the vacuum pulls air through the contaminated soil picking up volatile organic compounds (VOC's). The air and VOC's then travel through the fan into a vessel filled with activated carbon (carbon bed). The carbon absorbs the VOC's. As the air exits the carbon bed, it is discharged into the atmosphere. This stage of the process is called the adsorb cycle.
Eventually the carbon becomes saturated with VOC's. When the carbon is completely saturated, "break-thru" occurs. At this point, the carbon must be cleaned or disposed of. It is far more economical to clean the carbon by passing hot steam through it. The steam releases the VOC's. The steam/VOC mixture is condensed in a water jacked condenser. The condensate then enters a decanter type separator, where the water (from the condensed steam) is separated from the lighter VOC's. The liquid VOC's are then stored in a tank for proper disposal. The water is run through a carbon filter, then reused for the steam boiler feed water.
Water treatment was another process that was integrated into the vapor extraction. A series of wells are drilled around the contaminated area. The wells are drilled to a predetermined depth below the normal water table. Two pumps are lowered into the well, a pump for pumping the water, and a second pump for pumping product (gasoline, diesel, kerosene, etc.). The water pumps are started to lower the water table surrounding the well, called water table depression. The petroleum product, being lighter than water, floats on top of the water. Since water flows from high areas to low areas, the petroleum is drawn towards the well. The second pump, the product pump, is critically adjusted so as to only pump the pooled petroleum. The water that is pumped from the well is pumped up and sprayed into a large tower (stripper) filled with aerating media. As the water runs down through the tower, air is blown up from the bottom to "strip" the VOC's from the water. The water is then run through activated carbon, treated with various compounds and returned (recharged) into the ground. The air from the stripper is discharged into the vapor extraction piping for further air/VOC cleaning.
R. L. Shields Associates designed a controller and programming to run this automatic process, unattended. A trailer was fitted with the following pieces of equipment:
|2 - Carbon Beds|
|1 - Steam Boiler|
|1 - Air Compressor|
|1 - Vacuum Blower|
|1 - Cool Down Blower|
|1 - Mechanical Chiller|
|1 - Separator and Pump|
|1 - Exterior Air Stripper Tower|
|1 - Exterior Stripper Blower|
|Pumps - Water Depression and Product Pumps|
|Baseboard Heating to prevent freeze ups in cold climates|
An American Auto-Matrix STAR controller was installed to control this continuously operating process. One carbon bed is always operating in the adsorb cycle while the opposite bed is cleaned and cooled. Break-thru detection was automated, thus avoiding potential fines and penalties. This provided the maximum rate of remediation from this cleanup equipment.
Because the process involved fire hazards, the controller needed to be able to detect carbon bed fires and control a fire suppression system. Fires could start from an interrupted adsorb cycle. The controller needed to recognize the interruption and resequence the bed for cleaning.
The STAR controller provided an enormous amount of telemetry data for required reports. This included:
|Run Hours for all pieces of controller equipment.|
|Gallons of Water Treated|
The controller also provides various alarms, should an abnormal event occur, or if a tank needed to be emptied.
A key feature of using the STAR for controlling this process was that it allowed the contracted operator to call into the site from their office for off-site monitoring. This saved a substantial amount of travel time during the expected 3 to 5 year term of this remediation project. If an exception condition occurred, the operator was paged and the process shutdown for safety. The operator could then review the shutdown logs, correct the problem, and restart the process in minutes or hours, not days or weeks.
Following site closure, the equipment will be relocated to another site and the software will be customized for the next remediation project.
For more information on this project or American Auto-Matrix controls, contact:R. L. Shields Associates, Inc.
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