Texas facility treats, recycles refinery, petrochemical wastes

This computer model of a thermal desorber shows refinery wastes being vaporized in a rotating drum. The hydrocarbon vapors are removed through an extraction tube (shown at left), then condensed and recycled (Fig. 2).

A U.S. Gulf Coast environmental services company is treating refinery and petrochemical plant wastes to universal treatment standards (UTS).

DuraTherm Inc.'s recycling center uses thermal desorption to treat a variety of refinery wastes and other hazardous materials. The plant is located in San Leon, Tex., near the major Houston/Texas City refining and petrochemical center.

DuraTherm's customers include major U.S. refining companies, plus petrochemical, terminal, pipeline, tranportation, and remediation companies. Examples of typical contaminant concentrations and treatment levels for refinery wastes are shown in Table 1.

DuraTherm chose a central-facility approach because the per-unit cost of on site disposal in the petroleum industry has increased as a result of waste minimization efforts. The San Leon waste recycling plant meets Resource Conservation & Recovery Act (RCRA) Part B requirements, promulgated by the U.S. Environmental Protection Agency (EPA).

Bird Environmental Gulf Coast commissioned the plant in 1994. In 1995, GTS Duratek acquired the plant and began a $3 million expansion program to increase its storage and service capabilities. DuraTherm is a subsidiary of GTS Duratek.

Thermal desorption

Thermal desorption technology can process a variety of feedstocks including: dewatered, listed, or characteristic hazardous wastes from API separators and tanks; dissolved-air-flotation float; slop oil; and contaminated soils, such as wastes carrying the EPA designations D001, D018, K048-K052, F037, and F038.

Under RCRA regulations, these wastes must be treated to meet Universal Treatment Standards before they can be disposed of in landfills.

Process description

Fig. 1 shows a flow diagram of the DuraTherm thermal desorption process.

The process uses high temperatures to volatilize and recover the hydrocarbons. The technology centers around a rotating drum that is externally heated by a gas-fired convection air heater.

Waste is conveyed through the drum by a free-floating, rotating helix. Steel carriers pulverize the waste and help distribute heat. These mechanisms also clean the drum, prevent clumping, and homogenize the material for consistent treatment results, according to DuraTherm.

Water and hydrocarbons are vaporized in the drum's enclosed, nonoxidizing atmosphere at temperatures as high as 1,400° F. The vapors are removed through a vapor extraction line under negative pressure (Fig. 2).

A countercurrent nitrogen purge sweeps the drum, preventing combustion and aiding extraction of the volatiles through the vapor exit.

Because the waste does not come in contact with burner gases, the process does not produce large volumes of combustion gases that must be scrubbed prior to release.

Support systems for the process include: feed storage and conveyors, feed rate control, vapor condensation, phase separation, liquids recovery, solids cooling and handling, and air pollution control devices. Recovered hydrocarbons are recycled as refinery feedstock or, in some cases, used as fuel. Typically, 10-20 wt % of the feed can be recaptured, says DuraTherm.

Testing

Waste samples arrive at the recycling plant for analysis and approval. Once approved, the wastes are shipped to the facility in 15-20 ton containers. DuraTherm checks each container upon arrival, weighs it, and transfers the waste to process boxes, removing any debris during the transfer process.

Trucks pick up the empty containers, which are cleaned in acccordance with RCRA standards for backhaul. Typical turnaround time for trucks is less than 1 hr.

For large-volume shipments and major remediation programs, DuraTherm processes a sample cargo of the waste before performing full-scale modeling. With the resulting data, the company can generate precise throughput projections and costs, which it uses to guarantee performance. Typical treatment costs are $250-$500/ton. The cost of on site treatment in portable units is $100-200/ton, depending on the volume of waste and duration of treatment.

The desorbed waste res idues consistently meet RCRA UTS and EPA Hazardous Waste Identification Rule (HWIR) delisting criteria (Table 1).

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