Grease Incineration
D. E. DREIER, Director of Engineering and Research
J. D. WALKER, President and General Manager
Walker Process Equipment, Inc.
Aurora,  Illinois
INTRODUCTION
The handling of greasy skimmings and scum, which separate from sewage as
floatable material on settling tanks, has posed a knotty problem to sewage plant
operators for many years.
Grease in sewage comes from many sources, which accounts for the great
variability in quantity and type encountered. Grease originates from the unused
fats in culinary wastes, from soaps, and from garbage fed through household
grinders. Many industrial wastes contain very large amounts of grease, particularly those from packinghouses, canneries, dairies, wool processing plants, and
refineries. Garages and auto washing facilities contribute increasing amounts of
oils and greases, as do the machine industries which all discard considerably more
than in yesteryear.
A factor contributing considerably to the increase in greasy skimmings is the
household and supermarket garbage grinder. Garbage grinders add about 0.064
lbs solids per capita per day, and, of this, about 0.02 lbs is grease. A considerable portion of this grease appears as floating material on settling tanks. Efficient
detergents and general affluence of the populace also bring an increased greasy
contributions from homes and coin laundries.
Skimmings have been disposed of by burial, by selling to grease recovery
plants (nearly extinct now), and by pumping to digesters with the sludge. Periodic efforts at open pond burning nave been reported, but are not very popular.
Anaerobic digesters have been plagued with grease and oil accumulation and
interference problems for years, but lacking other means of disposal, most treatment plants have had to live with their digester grease blanket problems. Mineral
oils and greases have a deleterious effect on digestion. All digesters are adversely
affected oy grease and oil which accumulate to interfere with normal operation,
and eventually, high rate digesters may suffer mineral oil foaming when agitated
by gas bubbles. At Greensboro, North Carolina, a circulated floating cover digester foams "all over the landscape" if the circulator is operated for more than
a couple of hrs at a time. The digestion is excellent and the offending foam
has a tar-oil odor,   it is caused by accumulated, undigestible mineral oils.
The increasing magnitude of the greasy skimmings problem, and continuing
and increasing problems with its disposal to digesters, led us to pursue intensively
the feasibility of incineration of grease and skimmings. We have been working
on this development for nearly five years.
GREASY SKIMMINGS AS A FUEL
The burning of sewage greasy skimmings is a problem defined by the presence
of four broad and overlapping components: the grease itself; fibrous trash; water,
both combined and free; andash. Unlike any ordinary fuel burning situation,
this material is truly heterogeneous,  and highly variable in composition in any
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