CARVER-GREENFIELD PROCESS
DRYING OF PULP MILL ACTIVATED SLUDGE
FOR ENERGY RECOVERY IN A HOG FUEL BOILER
D. F. Bress, Coordinating Manager
Foster Wheeler Energy Corporation
Livingston, New Jersey 07039
Charles Greenfield, President
DeHydro-Tech Corporation
East Hanover, New Jersey 07936
INTRODUCTION
One of the "Catch 22" problems which arose in the 1970s is to find a way to dispose
of the ever-increasing quantity of sludge resulting from the new water treatment facilities
put in during the decade now ending.
The catch, of course, is that while increasing the quantity of sludge to be disposed of,
the traditional method—ocean dumping-has been prohibited. We feel that the Carver-
Greenfield process is an ideal solution to this problem. With the C-G process, wet sludge
is dried in a modern, energy-efficient manner which does not adversely affect the environment. The dried sludge is completely sterile and can be used as a fertilizer supplement,
animal feed supplement, or as a fuel. Today, we will describe a plant designed to solve a
sludge disposal problem at a paper mill. The operator of one paper mill is giving the installation of this unit his serious consideration.
THE CARVER-GREENFIELD PROCESS
Before discussing the specific plant being considered, a brief description of the Carver-
Greenfield process is in order. The process was developed in the food industry and has
found wide application in dehydrating aqueous wastes from rendering plants. More recently,
it has been used on a full scale commercial basis to dry sludges derived from brewery wastes,
pharmaceutical operations and municipal sewage sludges. The process, which is covered
by many patents, is owned by the Dehydro-Tech Corporation of East Hanover, New
Jersey. Foster Wheeler Energy Corporation is an international engineering and contracting
company with headquarters in Livingston, New Jersey, a 5-min drive from Dehydro-Tech.
Foster Wheeler has the exclusive right to offer the C-G process in all nonfood industrial
and municipal applications.
The pulp mill sludge plant will be the first commercial installation of the process in the
paper industry.
The Carver-Greenfield process can accommodate any solids concentration in the sludge
feed and some of the installations are fed with as little as 3-4% solids. However, the overall
economics dictate using mechanical means such as the centrifuge, filter press or belt press
to prethicken the feed prior to drying it. Thus, depending upon the specific situation, the
sludge feed to the C-G process will range from 10-30% or even 35% solids.
The prethickened feed enters the Carver-Greenfield unit where the wet sludge is mixed
with a hydrocarbon oil and the resulting slurry fed to a multieffect evaporation system.
Keeping the terminology used in this field straight is akin to understanding the Si/notation
such as gigajoules and nanograms which are now seriously proposed as useful design and
operating units. When we get to the details of the proposed design you will note that
English units are used.
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