TWO ON SITE TREATMENT METHODS REDUCE SLUDGE WASTE QUANTITIES

Ramin Abrishamian
Retec/Tetra
Concord, Mass.

Randolph Kabrick
Remediation Technologies Inc.
Austin

Geoffrey Swett
Remediation Technologies Inc.
Tucson, Ariz.

In spite of wide-spread refinery restructuring and industry calls for decreased regulation, environmental concern and regulatory pressures continue to determine how petroleum refiners must manage hazardous sludges in the 1990s.

Regulatory developments in the '90s have greatly affected sludge management. Fortunately, technological developments allow waste minimization, oil recovery, and economic on site treatment of hazardous sludges.

Two cost-effective, on site sludge treatment options available to refiners are thermal desorption and biological liquid/solids treatment.

SLUDGE GENERATION

The U.S. petroleum refining industry annually produces more than 2.5 million tons of wet, hazardous (as defined by U.S. environmental regulations) sludges. In addition, the industry produces a large quantity of nonhazardous sludges from crude, refined products, and intermediate-product tank bottoms.

The vast majority of hazardous sludges are produced in the oily sewers and wastewater treatment systems of refineries.' The following oily sludges are listed hazardous wastes under the Resource Conservation and Recovery Act (RCRA):

Leaded tank bottoms, U.S. Environmental Protection Agency (EPA) hazardous waste code K052
API separator sludge, K051
Dissolved air flotation (DAF) float, K048
Slop oil emulsions, K049
Sludges produced from cleaning heat exchanger bundles, K050
Primary/secondary sludges, F037 and F038.

SLUDGE MANAGEMENT

Historically, refinery sludges have been managed to recover hydrocarbons and minimize risk to human health and the environment. During the late 1970s, RCRA required that hazardous sludges be managed in conformance with hazardous waste regulations.

The initial effect of RCRA hazardous waste designation was to increase the cost of managing listed sludges. Sludge management facilities, such as landfills and landfarms, were modified to meet the ever-increasing EPA requirements. These initial costs, while not insignificant, were minor compared to costs imposed by land disposal restrictions (LDRs) required under the Hazardous and Solid Waste Amendments Act of 1984 (HSWA).

HSWA mandated that land disposal and/or landfarming of untreated hazardous wastes be prohibited. Further, the act required that EPA develop treatment standards for all hazardous wastes. These treatment standards would become known as Best Demonstrated Available Technology (BDAT) standards.

EPA adopted BDAT levels for K048-K052 petroleum refining oily sludges, known as K-wastes, during the late 1980s. In August of 1992, EPA adopted BDAT levels for F037 and F038 (primary/secondary impoundment sludges). Table 1 identifies BDAT levels for listed petroleum refinery wastes.

Table 2 summarizes the effective dates for treating hazardous sludges to BDAT levels prior to land disposal.

The impact of these regulations on industry has been significant. Prior to the imposition of new regulations in 1990, the refining industry was spending about $40 million/year managing hazardous oily sludges.

The refining industry is currently spending at least $150 million/year to treat hazardous oily sludges. By 1994, Remediation Technologies Inc. (Retec) estimates that cost to increase to $240 million/year as primary and secondary sludges become subject to new regulations.

INDUSTRY RESPONSE

The petroleum refining industry has pursued numerous options to reduce rapidly escalating sludge management costs. These actions include:

Pollution prevention programs to reduce the volume of sludge produced
Recycling sludge into production units such as cokers and fluid catalytic crackers
Off site thermal treatment in hazardous waste incinerators and industrial furnaces such as cement kilns
On site solvent extraction treatment
On site thermal desorption
On site biological treatment.

Others have addressed waste minimization, recycling to production units, off site thermal treatment, and solvent extraction.1-3 The remainder of this article will address recent commercial experience with on site thermal treatment and biological treatment of hazardous refinery sludges.

THERMAL DESORPTION

Thermal desorption is the moderate to high temperature treatment of sludges. The material is heated to between 600 F. and 850 F. in an oxygen-deficient atmosphere (Fig. 1). Hydrocarbons are desorbed from the solids.

The desorbed hydrocarbons are carried to an offgas treatment system by a nitrogen purge. The treated waste material is cooled and removed from the unit. (Fig. 2).

The offgas treating system condenses the hydrocarbons for recovery. The small quantity of noncondensable hydrocarbons are captured on activated carbon.

Retec entered a joint venture with Tetra Technologies Inc. to provide refiners with the dual benefits of Retec's thermal desorption and Tetra's on site service capabilities.

Retec/Tetra's thermal desorption process is based on the use of conventional, Holo-Flite, screw-type, indirect heaters which have been modified to increase their effectiveness and efficiency. These modifications increase the temperature range of the conventional heaters to 850 F.

At these higher temperatures, the process is applicable to a wide range of solid and sludge wastes. The concentration of organic compounds in these wastes is typically reduced to below detection limits.

Thermal desorption has been effective in achieving EPA's BDAT treatment standards for numerous hazardous wastes, including K048-K051 wastes from the petroleum refining industry.

Retec/Tetra has integrated sludge dewatering into the thermal desorption process. This proprietary feature allows raw sludge to be pumped directly to the unit without having to first be mechanically dewatered. This design significantly increases the operability and reliability of the technology.

DEMO UNIT EXPERIENCE

A total of four successful demonstrations of the portable demonstration unit have occurred (Fig. 3). The first two demonstrations were at a Louisiana Gulf Coast refinery and a Delaware River Valley refinery. Additional demonstrations occurred at two locations in the Great Lakes Regions, where contaminated sediments were treated.

COMMERCIAL EXPERIENCE

In the first half of 1992, the first commercial Retec/Tetra thermal desorption unit was installed at a commercial oil refinery in Port Arthur, Tex. (Fig. 4). By early September the unit had operated 3 months at an average throughput of 0.75 tons/hr.

All of the waste was treated to BDAT standards as indicated in Table 3. The refinery has saved more than $100,000/month by employing the on site thermal desorption process.

Retec/Tetra has completed designs for an additional three units and is procuring equipment for them.

BIOLOGICAL TREATMENT

Biological liquid/solids treatment is the aerobic biological degradation of organics in a controlled aqueous suspension, Organic sludges are blended and processed with an active microbial seed and appropriate nutrients in an engineered reactor. Treatment can be accomplished in either batch or continuous operating mode.

The biological liquid/solids process has been developed for tank-based applications but can be adapted for in situ impoundment treatment. This in situ approach has been used most recently at Amoco's former Sugar Creek, Mo., refinery and at the French Limited Superfund site in Texas.

Future in situ applications potentially include the treatment of primary/secondary impoundment sludges, or F037 and F038 wastes (OGJ, Nov. 11, 1991, p. 33).

Biological liquid/solids treatment promotes rapid biodegradation of the BDAT organics by providing optimal environmental conditions such as pH, mixing energy, dissolved oxygen, temperature, and nutrients, in a controlled reactor.

Most volatile organic compounds (VOCS) are biodegraded. However, a small quantity of VOCs remain in the offgas. These are easily treated by biofilters, activated carbon, or catalytic oxidizers.

Metals cannot be treated by the biological liquid/solids treatment process. Some sludges may require immobilization of chromium and/or nickel after biological treatment to meet BDAT limits for these metals.

The data in Table 4 summarize the capability of this technology to treat refinery wastes.

DEMO UNIT EXPERIENCE

A demonstration-scale biological liquid/solids treatment system was installed and operated at a Gulf Coast refinery during the first three quarters of 1992 (Fig. 5). The demonstration confirmed that biological liquid/solids treatment can achieve BDAT levels under the proper waste loading and reactor operating conditions.

The demonstration also confirmed the critical need for waste-specific biotreatability studies and an understanding of the waste matrix and variability of the waste prior to scale-up.

Key design parameters include the initial concentrations of 4, 5, and 6-ring polynuclear aromatic compounds and oil and grease. If the inlet concentrations of these constituents are within the range for a standard design, the liquid/solids treatment cost will be less than 40% of the cost of incineration.

FUTURE

Sludge management has become more complex and costly due to the advent of RCRA and subsequent HSWA land disposal restrictions. However, many opportunities exist for refiners to reduce the costs imposed by these regulations. These opportunities include the minimization of sludge formation increased recovery of recycled oil, and economical on site treatment options such as biological treatment and thermal desorption.

Combining oil recovery through recycling with cost-effective, on site treatment can significantly reduce operating costs.

ACKNOWLEDGMENT

The authors wish to thank Dale Simmons, Retec's technical editor, for his work on this article.

REFERENCES

Abrishamian, Ramin, Coover, M., Kabrick, R., Ryan, J., and Swett, G., "Petroleum Refinery Oily Sludge Management in the Nineties - Biological and Thermal Treatment Options for K & F Wastes," presented at Petro-Safe 92, January 1992, Houston.
Ryan, John, Abrishamian, R., Coover, M. and Kabrick, R., "Regulatory and Technical Considerations for Treating Petroleum Refinery Wastes," Retec, June 1991, Seattle.
de Filippi, Richard and Markiewicz, John, "Propane extraction treats refinery wastes to BDAT standards," OGJ, Sept. 9, 1991, p. 52.