35    INCINERATION OF LIQUID FLAMMABLE WASTES AND
BIOLOGICAL SLUDGE IN COAL-FIRED BOILERS
Mark W. Townsend, Utilities Supervisor
Monsanto Company
Nitro, West Virginia 25143
INTRODUCTION
The Monsanto Chemical Company, an operating division of Monsanto Company, has a production
facility for the manufacture of rubber chemicals located in Nitro, West Virginia. Residues or co-
products generated from these processes are of high heating value and are considered hazardous by
RCRA definition. These co-products are reused to generate steam in the stoker-spreader coal-fired
boilers, thereby reducing costly outside disposal fees, reducing coal requirements and RCRA regulations.
Additionally, the same boilers are used to incinerate non-hazardous sludge generated from the 2
mgd activated sludge Waste Treatment Plant located on site. The waste sludge is pumped from the
holding basin, transferred to a holding tank, and fed to the boilers along with the co-products.
This paper discusses characteristics of the co-products and sludge, design of the systems that feed
these streams into the boilers, environmental factors, and cost savings associated with this process.
INCINERATION ALTERNATIVES
In 1976, the Monsanto Nitro plant sought to eliminate the biological treatment of waste residues
which caused frequent upsets in the waste treatment system. These residues averaged 15,000 BTU/lb
in heat value, therefore, incineration was a logical choice (Table I).
Five alternatives were initially investigated, the first being outside contract incineration (Figure 1).
The cost of disposal was $164,000/yr in 1975 dollars. The advantages were no maintenance or
operation concerns, no capital outlay, and the method of disposal could be initiated in a very short
time. The disadvantages were the high cost and possible liabilities.
A new incinerator with heat recovery was examined. The capital expense was $800,000 in 1975
dollars. Allowing for a ten year depreciation, estimating operating and indirect costs, and subtracting
$35,000/yr in steam value, the net cost was $161,000/yr. The advantage of the recovered heat value
was outweighed by the disadvantage of high cost, having another system to man and operate, and the
potential for refractory, slagging, and salt caking problems.
Another alternative was to modify an existing incinerator at a cost of $75,000 in 1975 dollars.
Depreciating this over a ten year period and including operating and indirect costs, the net cost was
$29,000/yr. The advantages were reasonable costs; all the residues could be burned in one location,
and the project could be operational in six to eight months. The disadvantages were numerous. The
incinerator was a high maintenance item and burning the residues had the potential to increase
maintenance due to possible refractory, slagging, and salt caking problems. Increased downtime for
maintenance would cause production downtime for a unit that required the incinerator to run. Also
the total BTU capacity of the incinerator was limiting as was allowable sulfur dioxide emissions.
The fourth alternative was to burn the waste residues in one of the existing gas boilers used to
generate process and heating steam for the plant. The capital expense was $90,000 in 1976 dollars.
Allowing for a ten year depreciation, estimating operating and indirect costs and savings due to
Table 1. Residue I
Chemical Chai
vet eristics
Residue
BTU/Pound
1o Ash
It Chlorine
-7o Sulfur
Building 42
Building 91
17000
16400
Trace
0.02
6.9
1.0
1.07
1.30
319