64    WORKING SMARTER: REDUCING NOx EMISSIONS IN
MULTIPLE HEARTH INCINERATORS BY IMPROVED
OPERATING TECHNIQUES
James P. Scisson, Jr., Operations Specialist
Felix F. Sampayo, Senior Vice President
Gary A. Goldberg, Director, Construction Services
Jones & Henry Engineers, Inc.
Toledo, Ohio 43606
Michael Heitz, Assistant Superintendent
Metropolitan Sewer District of Greater Cincinnati
Cincinnati, Ohio 45204
INTRODUCTION
Working harder, although a virtue, may not be the best way to solve a problem. Solutions to many
difficult problems are found by working smarter.
A team of engineers, programmers, and operators dramatically improved the performance of
incinerators at the Metropolitan Sewer District (MSD) of Greater Cincinnati Mill Creek Wastewater
Treatment Plant. Modifications to the original operating scheme resulted in the incinerators meeting
NOx emission limits that were not contemplated at the time of design. As a side benefit, particulate
emissions and fuel consumption were reduced significantly from previous values.
BACKGROUND
In August 1982, the MSD retained Jones & Henry Engineers, Inc. to prepare a Diagnostic Evaluations and Composite Correction Program for the 120-MGD Mill Creek Wastewater Treatment Plant.
As part of the improvements, MSD constructed two additional multiple hearth incinerators (MHIs)
and rehabilitated the four existing ones. Design began in June 1984; construction in 1986.
Each incinerator is a 22 ft, 3-in., 9-hearth unit with a capacity of 9.4 wet tons/hr (Figure 1). The
units are "typical" MHIs and have burners on the odd-numbered (out) hearths. The air pollution
control equipment for the two new units (Incinerators 5 and 6) consists of venturi scrubbers followed
by a three-tray impingement scrubber. Afterburners were provided for the new units to meet expected
future regulations. The four original units (Incinerators 1-4) have a three-tray impingement scrubber
with an air bleed inlet damper to maintain constant gas flow and differential through the scrubber. All
induced draft fans have variable frequency drives for draft control. The incinerators are controlled by
a Programmable Logic Controller (PLC) system which provides automatic operation with little need
for operator intervention
At the time of design and construction there was no limit on NOx emissions. The requirements
changed before startup.
The Mill Creek Incinerators are required to comply with emission limits of 1.1 lb/particulate per
dry ton of sludge burned and 5.0 lb NOx per dry ton of sludge burned. The NO„ limit was triggered by
the need to maintain National Ambient Air Quality Standards for NOx, and to prevent significant
deterioration of the air quality. USEPA publication AP-42 NOx emission factors were used by the
regulatory agency to estimate NOx emissions. To the best of our knowledge this is the first enforced
NOx permit limit applied to MHIs in the United States.
The two new incinerators were placed in service after a protracted construction period. The construction delays were due to the subsequent bankruptcies of two general contractors on the project.
Emission testing in August 1990 produced NOx levels 300% of permit.' The incinerators were ordered
to shut down after failing their emissions test.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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