MCS TECHNOLOGY
SYSTEM COMPONENTS

The MCS is comprised of a heater base assembly with treatment trays, a vacuum blower system and an air emission control system.

HEAT SOURCE
The MCS system uses infrared radiation to generate the thermal energy necessary to desorb the target compounds. The energy transfer efficiency of an infrared system exceeds that of a "conventional" low temperature thermal desorption system. In general, other systems use a direct or indirect energy source to heat the air in the desorption chamber and transfer the heat to the matrix using a countercurrent flow. Heat transfer is mainly by convection. Air has relatively low thermal conductivity and specific heat values, which tend to result in lower energy transfer efficiency for the "conventional" systems compared to the MCS.

Attached to the underside of the steel base are 8 propane-fired infrared heaters. When the trays are loaded into the steel base, the heaters are approximately ten inches below the surface of the matrix. The fuel source is typically high pressure liquid (2-4 psi) propane or other suitable gas.

The propane-fired heaters heat an array of metal tubes to a temperature between 1,100° to 1,300° F. At this temperature, the metal tubes emit electromagnetic energy in the infrared spectrum. This generated infrared energy is directed upward to the bottom of the matrix. Within 10 to 15 minutes, the surface of the matrix (bottom 4 inches) is heated from 200° to 800° F). System temperature, which plateaus until 95% or more of the water is driven off, reaches 300° F within 70 minutes. Ultimately, the matrix can be heated to temperatures as high as 1,100° F. The degree of heating is primarily dependent upon the moisture content and type of matrix (i.e. amount of clay/silt/sand). Average energy generation of the MCS system is between 1.7 to 2.0 million BTU/hr.

TREATMENT TRAYS/CHAMBER
The matrix treatment trays are carbon steel containers that measure 8' x 8' x 1.5'. The trays have a screened bottom which supports the matrix and allows the air to flow through the material. The tray has two forklift pockets in its base below the screen and a dump gate at the opposite end. The base of the chamber contains 8 four-inch steel heater tubes. The capacity of each treatment tray is 2.5 cubic yards. Two trays are loaded into one heater base and a gasketed steel manifold is mechanically lowered to form a seal between the top manifold and the trays. This forms the treatment chamber.

VACUUM/CARRIER GAS
A vacuum is created in the treatment chamber using a 75 horsepower vacuum fan. The fan unit is rated to transfer 6,500 cfm of air at 95 inches of water column vacuum.

One benefit of operating the MCS under vacuum conditions is that the amount of energy required to desorb the target compounds is significantly reduced when compared to removing these contaminants at atmospheric pressure. A second benefit of operating the MCS under vacuum conditions is that the low operating temperatures of the system minimizes the potential production of thermal degradation products.

Essentially, the contaminants undergo a phase change from the liquid phase to a vapor phase and them return to the liquid phase; there are no changes in the chemical structure of the contaminants.

The MCS system uses the air flow created by the vacuum blower as a carrier gas stream to transport the desorbed water and chemicals from the treatment chamber to an emission control system consisting of a series of nondestructive devices.

The primary function of the carrier gas stream is to convey the desorbed contaminants from the treatment chamber to the emission control system and to convect heat through the mass in the treatment chamber. A second function of the carrier gas stream is to enhance the desorption of the water and contaminants from the matrix. Similar to reducing the pressure in the treatment chamber, evacuated air cascading through the matrix reduces the boiling point of both the contaminants and the water; an effect referred to as air stripping. The net result is shorter treatment times and lower energy costs.

A third function of the carrier gas stream is to enhance the transport of the infrared energy through the matrix. The upward flow of air helps to convey the thermal energy from the bottom several inches of material to overlying layers. Since this convective heat transfer will adhere to classical physical laws, the parameters regulating the rate of this transfer to the overlying layers is the temperature differential between the various mediums and the velocity of the carrier gas.

EMISSION CONTROLS
A variety of air emission control options are available, depending on the type of chemical and condition of the carrier stream. Condition refers to the temperature, pressure, volume, chemicals and moisture content. Air handling options include:

Dry Particulate Filter (DPF) – Used to minimize dust accumulation in downstream air emission control components (i.e. condenser, coalescing media, carbon units) and eliminate particulate emissions to the atmosphere. Certain types of contaminants, such as heavy fuel oils, asphalt-like substances, wood, and other combustible organic debris can generate smoke. The release of smoke is controlled by microfiltration.

Condenser and Chiller – Temperatures of the air stream exiting the treatment chamber can range from 175° to 800° F. Carbon treatment units are ineffective at these temperatures; therefore a condenser or cool down chamber is required. The condenser, which is connected to an appropriately sized chiller, reduces the air temperature to approximately 40° F. Selection of a chiller is based upon the inlet temperature, outlet temperature requirements, and airflow. The condenser is connected via a transfer pump to an appropriately sized storage vessel for the collected condensate. The condensate is treated and the products can be recycled or concentrated for proper disposal.

• Activated Carbon – The MCS system is equipped with the necessary size and number of carbon polishing units to achieve the desired result. Carbon units provide the final polishing of the air stream prior to discharge to the atmosphere.

• Coalescing Filter – This filter is incorporated within the condenser unit to consolidate small liquid particulates into larger droplets which condense on the opposite side of the centured metal media of the coalescing filter and are collected as purified product.

• Scrubber Systems – For mercury and cyanide containing matrices, a packed tower and countercurrent scrubber system is used in conjunction with an acidified or caustic fluid to absorb or dissolve residual contaminants as either a primary or polishing step (depends on the specific application).

• Air Sampling – Air samples are collected as required to monitor the proper functioning of the emission control system. Individual states have specific emissions monitoring requirements, which are normally contained in discharge permits. At a minimum, one stack test is usually performed at the start of a project. This involves a complete treatment cycle. Air samples are collected after the final carbon unit prior to discharge to atmosphere.