RESOURCE RECOVERY OF HEAVY COAL TAR
BASED SLUDGES
Anthony DiFilippo, Project EngineerWasteChem Corporation
Ramsey, New Jersey 07446
INTRODUCTION
Since 1974, WasteChem Corporation has maintained an active program to study waste encapsulation and resource recovery in conjunction with other organizations. To date, over 50 types of hazardous wastes have been successfully tested in our twin-screw extruder process. These include liquid
wastes containing inorganic compounds, painting and refinery sludges containing heavy metals and
organics, pharmaceutical wastes, dry incinerator ash, and baghouse dust.
The stabilization and disposal of acid coal tar and other heavy petroleum based sludges and residues presents a challenging problem. WasteChem has conducted extensive pilot scale tests to establish
the feasibility of recovering usable fuels and other fractions from such sludges.
The process utilizes a twin-screw co-rotating extruder-evaporator to mix in sludge preconditioning
chemicals, drive off volatile components in the sludge, and blend fuel oil such that the final product
will be acceptable for combustion in conventional burners.
The economic benefits of recovering this troublesome waste by-product for its heat value are very
attractive. The process described allows recovery of thousands of BTU's per pound of sludge while
providing ultimate final disposal. Atomization of the fuel product in conventional process boilers has
been proven, thereby precluding the need for specialized equipment.
BACKGROUND
Numerous sites exist across the United States where the residues of coal coking, liquefaction, and
gasification have been impounded for years. Many impoundments were poorly designed, and as a
result these residues have migrated. The presence of aromatic hydrocarbons and inorganic acids
results in these materials being categorized as toxic. In addition to the hazards of physical contact, the
potential exists for these components to migrate into subsurface waters where they contaminate drinking water supplies. Contamination of the air in an area local to the impoundment during the warmer
months can also result from devolatilization of the sludge. Petroleum based sludges, including still
bottoms, can produce similar hazards; however, since the volatile content is normally lower, the overall hazard is somewhat reduced.
Regulatory pressures have recently focused a great deal of attention on the hazards of these sludge
impoundments. Remedial programs that are being considered include:
improvements in the impoundments to better contain the sludges;
incineration for complete destruction;
devolatilization of the sludge with a resulting final waste form similar to tar;
excavation and placement of sludge in engineered landfills;
recovery of heat value of sludge by conditioning and utilization as a fuel.
The most intriguing prospect above is the option which results in recovery of the heat value of the
sludge. This alternate presents the possibility of generating revenues equal to or greater than the cost
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