x-xEPA
United States
Environmental Protection
Agency
EPA542-B-93-011
November 1993
Solid Waste and Emergency Response (5102W)
Innovative Site
Remediation
Technology
Thermal Desorption
Volume 6
(^y Recycled/Recyclable
r\ <0> Pnr"ed with Soy/Canola Ink on paper that
N_U (^J contains at least 50% recycled Sber
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INNOVATIVE SITE
REMEDIATION TECHNOLOGY
THERMAL DESORPTION
One of an Eight-Volume Series
Edited by
William C. Anderson, P.E., DEE
Executive Director, American Academy of Environmental Engineers
1993
Prepared by WASTECH®, a multiorganization cooperative project managed by
the American Academy of Environmental Engineers® with grant assistance from
the U.S. Environmental Protection Agency, the U.S. Department of Defense, and
the U.S. Department of Energy.
The following organizations participated in the preparation and review of this
volume:
Air & Waste Management
Association
P.O. Box 2861
Pittsburgh, PA 15230
American Society of
® Mechanical Engineers
345 East 47th Street
New York, NY 10017
American Academy of
Environmental Engineers1
130 Holiday Court, Suite 100
Annapolis, MD 21401
American Institute of
Chemical Engineers
345 East 47th Street
New York, NY 10017
, Hazardous Waste Action
Coalition
1015 15th Street, N.W., Suite 802
Washington, D.C. 20005
, Water Environment
Federation
601 Wythe Street
Alexandria, VA 22314
Published under license from the American Academy of Environmental
Engineers®. © Copyright 1993 by the American Academy of Environmental
Engineers®. ^ ^ Environmental Protection Agency
Region 5, Library f L-12J)
onn library v
West Jackson Boulevard, 12th Floor
Chicago, IL 60604-3590
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Library of Congress Cataloging-in-Publication Data
Innovative site remediation technology / edited by William C. Anderson
p. cm.
Includes bibliographic references.
Contents: 6. Thermal desorption
ISBN 1-883767-06-7 (v. 6)
1. Soil remediation. I. Anderson, William, C., 1943-
II. American Academy of Environmental Engineers.
TD878.I55 1993
628.5'5»dc20 93-20786
CIP
Copyright 1993 © by American Academy of Environmental Engineers®. All
Rights reserved. Printed in the United States of America. Except as permitted under
the United States Copyright Act of 1976, no part of this publication may be
reproduced or distributed in any form or means or stored in a database or retrieval
system without the prior written permission of the American Academy of Environ-
mental Engineers.
The material presented in this publication has been prepared in accordance with
generally recognized engineering principles and practices and is for general informa-
tion only. This information should not be used without first securing competent advice
with respect to its suitability for any general or specific application.
The contents of this publication are not intended to be and should not be construed
as a standard of the American Academy of Environmental Engineers® or of any of the
associated organizations mentioned in this publication and are not intended for use as a
reference in purchase specifications, contracts, regulations, statutes, or any other legal
document.
No reference made in this publication to any specific method, product, process, or
service constitutes or implies an endorsement, recommendation, or warranty thereof by
the American Academy of Environmental Engineers® or any such associated organiza-
tion.
Neither the American Academy of Environmental Engineers® nor any of such
associated organizations or authors makes any representation or warranty of any kind,
whether express or implied, concerning the accuracy, suitability, or utility of any
information published herein and neither the American Academy of Environmental
Engineers® nor any such associated organization or author shall be responsible for any
errors, omissions, or damages arising out of use of this information.
-------
CONTRIBUTORS
This monograph was prepared under the supervision of the WASTECH® Steering
Committee. The manuscript for the monograph was written by a task group of experts
in thermal desorption and was, in turn, subjected to two peer reviews. One review was
conducted under the auspices of the Steering Committee and the second by profes-
sional and technical organizations having substantial interest in the subject.
PRINCIPAL AUTHORS
JoAnn Lighty, Ph.D., Task Group Chair
Assistant Professor
Department of Chemical and Fuel Engineering
University of Utah
Martha Choroszy-Marshall Vic Cundy, Ph.D.
CIBA-GEIGY Professor & Chair
Program Manager Mechanical Engineering Department
Thermal Treatment Louisiana State University
Michael Cosmos Paul De Percin
Project Director Chemical Engineer
Roy F. Weston U.S. Environmental Protection Agency
In addition, Mr. Charles A. Cook is credited with substantial contributions to the
monograph manuscript. At the time of writing, Mr. Cook was a doctoral candidate in
Mechanical Engineering at Louisianna State University under the supervision of Dr.
Cundy.
REVIEWERS
The panel that reviewed the monograph under the auspices of the Project Steering
Committee was composed of:
Charles O. Velzy, P.E., DEE, Chair Carl Swanstrom
Private Consultant Senior Project Manager
Chemical Waste Management, Inc.
Joseph W. Bozzelli, Ph.D. William L. Troxler, P.E.
Distinguished Professor Vice President
New Jersey Institute of Technology Focus Environmental, Inc.
Peter J. Kroll, P.E. Walter J. Weber, Jr., Ph.D., P.E., DEE
Manager, Process Systems Engineering Earnest Boyce Distinguished Professor
ICF Kaiser Engineers, Inc. University of Michigan
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STEERING COMMITTEE
Frederick G. Pohland, Ph.D., P.E., DEE
Chair
Weidlein Professor of Environmental
Engineering
University of Pittsburgh
William C. Anderson, P.E., DEE
Project Manager
Executive Director
American Academy of Environmental
Engineers
Paul L. Busch, Ph.D., P.E., DEE
President and CEO
Malcolm Pirnie, Inc.
Representing, American Academy of
Environmental Engineers
Richard A. Conway, P.E., DEE
Senior Corporate Fellow
Union Carbide Corporation
Chair, Environmental Engineering
Committee
EPA Science Advisory Board
William D. Coins, P.E.
Deputy Director for Technology
Development
Office of the Secretary of Defense
U.S. Department of Defense
Timothy B. Holbrook, P.E.
District Engineering Manager
Groundwater Technology
Representing, Air and Waste Management
Association
Walter W. Kovalick, Jr., Ph.D.
Director, Technology Innovation Office
Office of Solid Waste and Emergency
Response
U.S. Environmental Protection Agency
Joseph F. Lagnese, Jr., P.E., DEE
Private Consultant
Representing, Water Environment Federation
Peter B. Lederman, Ph.D., P.E., DEE, P.P.
Center for Env. Engineering & Science
New Jersey Institute of Technology
Representing American Institute of Chemical
Engineers
Raymond C. Loehr, Ph.D., P.E., DEE
H.M. Alharthy Centennial Chair and
Professor
Civil Engineering Department
University of Texas
Timothy Oppelt, Ph.D.
Director, Risk Reduction Engineering
Laboratory
U.S. Environmental Protection Agency
George Pierce, Ph.D.
Editor in Chief
Journal of Microbiology
Manager, Bioremediation Technology Dev.
American Cyanamid Company
Representing the Society of Industrial
Microbiology
H. Gerard Schwartz, Jr., Ph.D., P.E.
Senior Vice President
Sverdrup
Representing, American Society of Civil
Engineers
Claire H. Sink
Acting Director
Division of Technical Innovation
Office of Technical Integration
Environmental Education Development
U.S. Department of Energy
Peter W. Tunnicliffe, P.E., DEE
Senior Vice President
Camp Dresser & McKee, Incorporated
Representing, Hazardous Waste Action
Coalition
Charles O. Velzy, P.E., DEE
Private Consultant
Representing, American Society of
Mechanical Engineers
William A. Wallace
Vice President, Hazardous Waste
Management
CH2M Hill
Representing, Hazardous Waste Action
Coalition
Walter J. Weber, Jr., Ph.D., P.E., DEE
Earnest Boyce Distinguished Professor
University of Michigan
IV
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REVIEWING ORGANIZATIONS
The following organizations contributed to the monograph's review and acceptance
by the professional community. The review process employed by each organization is
described in its acceptance statement. Individual reviewers are, or are not, listed
according to the instructions of each organization.
Air & Waste Management
Association
The Air & Waste Management Asso-
ciation is a nonprofit technical and educa-
tional organization with more than 14,000
members in more than fifty countries.
Founded in 1907, the Association pro-
vides a neutral forum where all view-
points of an environmental management
issue (technical, scientific, economic,
social, political, and public health) re-
ceive equal consideration.
This worldwide network represents
many disciplines: physical and social
sciences, health and medicine, engineer-
ing, law, and management. The Associa-
tion serves it's membership by promoting
environmental responsibility and provid-
ing technical and managerial leadership in
the fields of air and waste management.
Dedication to these objectives enables the
Association to work towards it's goal: a
cleaner environment.
Qualified reviewers were recruited
from the Technical Council Committee,
Waste Division. It was determined that
the monograph is technically sound and
publication is endorsed.
The reviewers were:
James R. Donnelly
R. Sahu, Ph.D.
Wileen Sweet Dodge
American Institute of Chemical
Engineers
The Environmental Division of the
American Institute of Chemical Engineers
has enlisted its members to review the
monograph. Based on that review the
Environmental Division endorses the
publication of the monograph.
American Society of
Mechanical Engineers
Founded in 1880, The American
Society of Mechanical Engineers
(ASME) is a nonprofit educational and
technical organization, having at the date
of publication of this document approxi-
mately 116,400 members, including
19,200 students. Members work in indus-
try, government, academia, and consult-
ing. The Society has thirty-seven techni-
cal divisions, four institutes, and three
interdisciplinary programs which conduct
more than thirty national and international
conferences each year.
This document was reviewed by vol-
unteer members of the Monograph Re-
view Committee of the Solid Waste
Processing Division and the Hazardous
Waste Committee of the Safety Engineer-
ing and Risk Assessment Division of
ASME, each with technical expertise and
interest in the field covered by the docu-
ment. Although, as indicated on the
reverse of the title page of this document,
neither ASME nor any of its Divisions or
Committees endorses or recommends, or
-------
makes any representation or warranty
with respect to, this document, those
Divisions and Committees which con-
ducted a review believe, based upon such
review, that this document and the find-
ings expressed are technically sound.
Hazardous Waste Action
Coalition
The Hazardous Waste Action Coali-
tion (HWAC) is a nonprofit association of
engineering and science firms that pro-
vide hazardous waste remediation ser-
vices for both public and private sector
clients. Coalition member firms employ
experts in over ninety technical disci-
plines, including all engineering disci-
plines.
Qualified reviewers were recruited
from HWAC's Technical Practices Com-
mittee. After consulting with HWAC's
lead reviewer, it was determined that the
monograph is technically sound and
publication is endorsed.
The reviewers were:
Kris Krishnaswami
Senior Associate
Malcolm Pirnie, Inc.
Robert G. Wilbourn
Process Development Manager
IT Corporation
Gil M. Zemansky, Ph.D., P.HGW.
Principal Hydrogeologist
Terracon Environmental, Inc.
Water Environment
Federation
The Water Environment Federation is
a nonprofit, educational organization
composed of member and affiliated asso-
ciations throughout the world. Since
1928, the Federation has represented
water quality specialists including engi-
neers, scientists, government officials,
industrial and municipal treatment plant
operators, chemists, students, academics,
and equipment manufacturers, and dis-
tributors.
Qualified reviewers were recruited
from the Federation's Industrial and Haz-
ardous Wastes Committees. It has been
determined that the monograph is techni-
cally sound and publication is endorsed.
The reviewers were:
Peter J. Cagnetta
Project Soil Scientist
R.E. Wright Associates, Inc.
Larry J. DeFlui
Project Environmental Engineer
R.E. Wright Associates, Inc.
Gomes Ganapathi
Section Manager
Waste Management Technologies
Section
Science Application International
Corporation
Stephen Gelnian
District Operations Manager
CH2M Hill, Inc.
S. Bijoy Ghosh, P.E.*
Principal Engineer
Engineering-Science, Inc.
Michael Joyce
Director of Engineering Sales
R.E. Wright Associates, Inc.
Les Porterfield
Assistant Vice President
BCM Engineers, Inc.
Delmar H. Prah
Project Engineer
Argonne National Laboratory
Robert C. Williams, P.E., DEE
Director of the Division of Health
Assessment and Consultation
Agency for Toxic Substances and
Disease Registry
* WEF lead reviewer
VI
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ACKNOWLEDGMENTS
The WASTECH® project was conducted under a cooperative agreement
between the American Academy of Environmental Engineers® and the Office of
Solid Waste and Emergency Response,U.S. Environmental Protection Agency. The
substantial assistance of the staff of the Technology Innovation Office was
invaluable.
Financial support was provided by the U.S. Environmental Protection Agency,
Department of Defense, Department of Energy, and the American Academy of
Environmental Engineers®.
This multiorganization effort involving a large number of diverse professionals
and substantial effort in coordinating meetings, facilitating communications, and
editing and preparing multiple drafts was made possible by a dedicated staff
provided by the American Academy of Environmental Engineers® consisting of:
Paul F. Peters
Assistant Project Manager & Managing Editor
Susan C. Richards
Project Staff Assistant
J. Sammi Olmo
Project Administrative Manager
Yolanda Y. Moulden
Staff Assistant
I. Patricia Violette
Staff Assistant
VII
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Table of Contents
TABLE OF CONTENTS
Contributors iii
Acknowledgments vii
List of Tables xiii
List of Figures xiv
1.0 Introduction 1.1
1,1 Thermal Desorption 1.1
1.2 Development of the Monograph 1.2
1.2.1 Background 1.2
1.2.2 Process 1.3
1.3 Purpose 1.4
1.4 Objectives 1.4
1.5 Scope 1.5
1.6 Limitations 1.5
1.7 Organization 1.6
2.0 Process Summary 2.1
2.1 Process Identification and Description 2.1
2.2 Potential Applications 2.6
2.3 Process Evaluation 2.6
2.4 Limitations 2.7
2.5 Technology Prognosis 2.8
VIII
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Table of Contents
3.0 Process Identification and Description 3.1
3.1 Description 3.1
3.2 Scientific Basis 3.2
3.3 Waste Characterization 3.5
3.4 Rotary Desorber — Direct Fired 3.11
3.4.1 Description 3.11
3.4.2 Status of Development 3.13
3.4.3 Pretreatment Requirements 3.14
3.4.4 Design Data and Unit Sizing 3.15
3.4.5 Posttreatment Requirements 3.17
3.4.6 Special Health and Safety Considerations 3.22
3.4.7 Operational Requirements and Considerations 3.23
3.4.8 Process Variations per Vendors 3.25
3.5 Rotary Desorber — Indirect Fired 3.27
3.5.1 Description 3.27
3.5.2 Status of Development 3.28
3.5.3 Pretreatment Requirements 3.29
3.5.4 Design Data and Unit Sizing 3.29
3.5.5 Posttreatment Requirements 3.30
3.5.6 Special Health and Safety Considerations 3.32
3.5.7 Operational Requirements and Considerations 3.32
3.5.8 Process Variations per Vendors 3.33
3.6 Heated Conveyors — Indirect and Direct 3.33
3.6.1 Description 3.33
3.6.2 Status of Development 3.34
3.6.3 Pretreatment Requirements 3.35
3.6.4 Design Data and Unit Sizing 3.37
IX
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Table of Contents
3.6.5 Posttreatment Requirements 3.38
3.6.6 Special Health and Safety Considerations 3.39
3.6.7 Operational Requirements and Considerations 3.39
3.6.8 Process Variations per Vendors 3.39
3.7 SoilTech System 3.39
3.7.1 Description of Process 3.39
3.7.2 Status of Development 3.41
3.7.3 Pretreatment Requirements 3.41
3.7.4 Design Data and Unit Sizing 3.42
3.7.5 Posttreatment Requirements 3.42
3.7.6 Special Health and Safety Considerations 3.42
3.7.7 Operational Requirements and Considerations 3.42
3.8 Environmental Impacts 3.42
3.9 Costs 3.44
3.9.1 Fixed Cost Elements 3.44
3.9.2 Unit Cost Elements 3.46
3.9.3 Cost Comparison 3.47
4.0 Potential Applications 4.1
4.1 Determining Applicability — Treatability Testing 4.1
4.1.1 Remedy Screening 4.2
4.1.2 Remedy Selection 4.3
4.1.3 Remedy Design 4.4
4.2 Quality of Residuals 4.5
4.2.1 Solid Residuals 4.5
4.2.2 Liquid Residuals 4.5
4.2.3 Gaseous Residuals 4.6
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Table of Contents
5.0 Process Evaluation 5.1
5.1 Full-Scale Systems 5.1
5.1.1 McKin Site (Gray, Me.) — Direct-Fired Desorber 5.1
5.1.2 Ottati and Goss Site (Kingston, N.H.) — Direct-Fired
Desorber 5.3
5.1.3 Cannon Bridgewater Site (Bridgewater, Mass.) —
Direct-Fired Desorber 5.3
5.1.4 Caltrans Maintenance Station Site (Kingvale, Cal.) —
Direct-Fired Desorber 5.4
5.1.5 Coke-Oven Plant Soils — Indirect-Fired Desorber 5.5
5.1.6 Wide Beach Superfund Site (Buffalo, N.Y.) — SoilTech 5.6
5.1.7 Waukegan Harbor Superfund Site (Waukegan, 111.)—
SoilTech 5.7
5.1.8 Anderson Development Site (Adrian, Mich.) — Indirect-
Heated Screw Conveyor 5.7
5.1.9 Gasoline and Diesel Soil — Direct-Heated Conveyor 5.8
5.2 Pilot-Scale Systems 5.9
5.2.1 Petroleum Refinery Waste Sludge — Indirect-Heated
Desorber 5.9
5.2.2 PAH Contaminated Soils — Indirect-Fired Desorber 5.11
5.3 Bench-Scale Systems 5.11
5.3.1 PAH Contaminated Soils 5.13
6.0 Limitations 6.1
6.1 Waste Matrix 6.1
6.2 Process Needs 6.2
6.3 Risk Considerations 6.2
6.4 Site Considerations 6.2
6.5 Reliability of Performance 6.3
6.6 Process Residues 6.3
XI
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Table of Contents
6.7 Quality of Treated Material 6.3
6.8 Regulatory Requirements 6.4
7.0 Technology Prognosis 7.1
7.1 Development and Demonstration Needs 7.1
Appendices
A. Other Treatment Alternatives A. 1
B. Engineering Bulletin: Thermal Desorption Treatment B. 1
C. Thermal Desorption of PCB Contaminated Waste at the Waukegan
Harbor Superfund Site: A Case Study (Excerpt) C. 1
D. List Of Vendors and Consultants D. 1
E. Table Of Acronyms and Abbreviations E. 1
F. List Of References F. 1
XII
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LIST OF TABLES
Table Title
2.1 Design and operating characteristics 2.3
2.2 Pretreatment requirements 2.4
2.3 Posttreatment requirements 2.5
3.1 Waste characterization analyses 3.7
3.2 Summary of the status of heated conveyor systems,
August 1992 3.36
3.3 Screw conveyor size versus maximum particle size 3.37
3.4 Rounded costs for excavation based on hazard level 3.45
3.5 Cost data from the literature 3.48
3.6 Costs for petroleum-contaminated soil as a function of
desorber type and site size 3.49
4.1 Status of thermal desorption, April 1992 4.2
5.1 Direct-fired thermal desorber case studies 5.2
5.2 Results of the DBA pyrolysis full-scale plant —
Konigsborn coke-oven plant 5.6
5.3 Chemical Waste Management pilot-scale plant —
petroleum refinery waste 5.10
5.4 IT rotary thermal apparatus — PAH contaminated soils 5.12
XIII
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LIST OF FIGURES
Figure Title Page
2.1 Treatment system schematic 2.2
3.1 Schematic of the transport phenomena occurring during
thermal treatment of a solid bed 3.3
3.2 Relationship of contaminant removal time for increasing
temperatures 3.5
3.3 Summary of waste characteristics and related concerns 3.6
3.4 Model predictions showing the effect of the initial weight
fraction of moisture in the solid feed on bed temperature
profile 3.8
3.5 Components of a direct-fired rotary desorber system 3.11
3.6 (a) Cocurrent desorber — offgas posttreatment process 3.17
(b) Countercurrent desorber — offgas posttreatment process 3.18
3.7 Components of the indirect-fired rotary desorber system 3.27
3.8 (a) Components of a direct-heated conveyor system 3.34
(b) Components of an indirect-heated conveyor system 3.35
3.9 Schematic of the SoilTech ATP process illustrating the
four zone heating approach 3.40
3.10 Moisture effect on heat requirement assuming 7.5 ton/hr
facility 3.46
7.1 Fill-fraction predictions for full-scale and pilot-scale rotary
kilns 7.2
xiv
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Chapter 1
INTRODUCTION
This monograph on thermal desorption is one of a series of eight on innova-
tive site and waste remediation technologies that are the culmination of a
multiorganization effort involving more than 100 experts over a two-year pe-
riod. It provides the experienced, practicing professional guidance on the appli-
cation of innovative processes considered ready for full-scale application.
Other monographs in this series address bioremediation, chemical treatment,
soil washing/soil flushing, solvent/chemical extraction, stabilization/solidifica-
tion, thermal destruction, and vacuum vapor extraction.
/. 7 Thermal Desorption
The thermal desorption processes addressed in this monograph use heat,
either direct or indirect, ex situ, as the principal means to physically separate
and transfer contaminants from soils, sediments, sludges, filter cakes, or other
media. Thermal desorption is part of a treatment train; some pre- and
postprocessing is necessary. Thermal desorbers are physical separation facili-
ties and are not specifically designed to decompose organics (organic denotes
compounds, including volatiles, semivolatiles, PCBs, and pesticides); depend-
ing on the organics present, and the temperature of the system, however, some
decomposition may occur.
The separated contaminants, water vapor, and particulates must be collected
and treated. This is typically accomplished using conventional methods of
condensation, adsorption, incineration, filtration, and the like. The methods
selected depend on the nature and concentration of contaminants, regulations,
and the economics of the systems employed. It may be possible to reuse the
treated material, and, in some cases, the recovered contaminants may have
commercial value. Regulations that govern thermal destruction processes may
apply in some cases to some thermal desorption processes.
1.1
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Introduction
The effectiveness of the desorber is generally measured by comparing the
contamination levels in the media pre- and posttreatment.
/ .2 Development of the Monograph
1.2.1 Background
Acting upon its commitment to develop innovative treatment technologies
for the remediation of hazardous waste sites and contaminated soils and ground
water, the U.S. Environmental Protection Agency (EPA) established the Tech-
nology Innovation Office (TIO) in the Office of Solid Waste and Emergency
Response in March, 1990. The mission assigned TIO was to foster greater use
of innovative technologies.
In October of that same year, TIO, in conjunction with the National Advi-
sory Council on Environmental Policy and Technology (NACEPT), convened a
workshop for representatives of consulting engineering firms, professional
societies, research organizations, and state agencies involved in remediation.
The workshop focused on defining the barriers that were impeding the applica-
tion of innovative technologies in site remediation projects. One of the major
impediments identified was the lack of reliable data on the performance, design
parameters, and costs of innovative processes.
The need for reliable information led TIO to approach the American Acad-
emy of Environmental Engineers. The Academy is a long-standing,
multidisciplinary environmental engineering professional society with wide-
ranging affiliations with the remediation and waste treatment professional com-
munities. By June 1991, an agreement in principle (later formalized as a Coop-
erative Agreement) was reached. The Academy would manage a project to
develop monographs describing the state of available innovative remediation
technologies. Financial support would be provided by the EPA, U.S. Depart-
ment of Defense (DOD), U.S. Department of Energy (DOE), and the Academy.
The goal of both TIO and the Academy was to develop monographs providing
reliable data that would be broadly recognized and accepted by the professional
community, thereby, eliminating or, at least, minimizing this impediment to the
use of innovative technologies.
1.2
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Chapter 1
The Academy's strategy for achieving the goal was founded on a
multiorganization effort, WASTECH® (pronounced Waste Tech), which joined
in partnership the Air and Waste Management Association, the American Insti-
tute of Chemical Engineers, the American Society of Civil Engineers, the
American Society of Mechanical Engineers, the Hazardous Waste Action Coa-
lition, the Society for Industrial Microbiology, and the Water Environment
Federation, together with the Academy, EPA, DOD, and DOE. A Steering
Committee composed of highly respected representatives of these organizations
having expertise in remediation technology formulated the specific project
objectives and process for developing the monographs (See page iv. for a listing
of Steering Committee members).
By the end of 1991, the Steering Committee had organized the Project.
Preparation of the monograph began in earnest in January, 1992.
1.2.2 Process
The Steering Committee decided upon the technologies, or technological
areas, to be covered by each monograph, the monographs' general scope, and
the process for their development and appointed a task group composed of five
or more experts to write a manuscript for each monograph. The task groups
were appointed with a view to balancing the interests of the groups principally
concerned with the application of innovative site and waste remediation tech-
nologies — industry, consulting engineers, research, academe, and government
(see page iii for a listing of members of the Thermal Desorption Task Group).
The Steering Committee called upon the task groups to examine and analyze
all pertinent information available, within the Project's financial and time con-
straints. This included, but was not limited to, the comprehensive data on
remediation technologies compiled by EPA, the store of information possessed
by the task groups' members, that of other experts willing to voluntarily contrib-
ute their knowledge, and information supplied by process vendors.
To develop broad, consensus-based monographs, the Steering Committee
prescribed a twofold peer review of the first drafts. One review was conducted
by the Steering Committee itself, employing panels consisting of two members
of the Committee supplemented by at least four other experts (See Reviewers,
page iii, for the panel that reviewed this monograph). Simultaneous with the
Steering Committee's review, each of the professional and technical organiza-
1.3
-------
Introduction
tions represented in the Project reviewed those monographs addressing tech-
nologies in which it has substantial interest and competence. Aided by a Sym-
posium sponsored by the Academy in October 1992, persons having interest in
the technologies were encouraged to participate in the organizations' review.
Comments resulting from both reviews were considered by the Task Group,
appropriate adjustments were made, and a second draft published. The second
draft was accepted by the Steering committee and participating organizations.
The statements of the organizations that formally reviewed this monograph are
presented under Reviewing Organizations on page v.
1.3 Purpose
The purpose of this monograph is to further the use of innovative thermal
desorption site remediation and waste processing technologies, that is, technolo-
gies not commonly applied, where their use can provide better, more cost-effec-
tive performance than conventional methods. To this end, the monograph
documents the current state of a number of innovative thermal desorption tech-
nologies.
1.4 Objectives
The monograph's principal objective is to furnish guidance for experienced,
practicing professionals and users' project managers. The monograph is in-
tended, therefore, not to be prescriptive, but supportive. It is intended to aid
experienced professionals in applying their judgment in deciding whether and
how to apply the technologies addressed under the particular circumstances
confronted.
In addition, the monograph is intended to inform regulatory agency person-
nel and the public about the conditions under which the processes it addresses
are potentially applicable.
1.4
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Chapter 1
7.5 Scope
The monograph addresses innovative thermal desorption technologies which
are not yet conventional, that is, not commonly applied, that have been suffi-
ciently developed so that they can be used in full-scale applications. It ad-
dresses all such technologies for which sufficient data was available to the
Thermal Desorption Task Group to describe and explain the technology and
assess its effectiveness, limitations, and potential applications. Laboratory- and
pilot-scale technologies were addressed, as appropriate.
The monograph's primary focus is site remediation and waste treatment. To
the extent the information provided can also be applied to production waste
streams, it will provide the profession and users this additional benefit. The
monograph considers all waste matrices to which thermal desorption processes
can be reasonably applied, such as, soils, sludges, filter cakes, and other solid
media.
Application of site remediation and waste treatment technology is site spe-
cific and involves consideration of a number of matters besides alternative
technologies. Among them are the following that are addressed only to the
extent essential to understand the applications and limitations of the technolo-
gies described:
• site investigations and assessments;
• planning, management, specifications, and procurement;
• regulatory requirements; and
• community acceptance of the technology.
1.6 Limitations
The information presented in this monograph has been prepared in accor-
dance with generally recognized engineering principles and practices and is for
general information only. This information should not be used without first
securing competent advice with respect to its suitability for any general or spe-
cific application.
1.5
-------
Introduction
Readers are cautioned that the information presented is that which was gen-
erally available during the period when the monograph was prepared. Develop-
ment of innovative site remediation and waste treatment technologies is ongo-
ing. Accordingly, postpublication information may amplify, alter, or render
obsolete the information about the processes addressed.
This monograph is not intended to be and should not be construed as a stan-
dard of any of the organizations associated with the WASTECH® Project; nor
does reference in this publication to any specific method, product, process, or
service constitute or imply an endorsement, recommendation, or warranty
thereof.
7.7 Organization
This monograph and others in the series are organized under a uniform out-
line intended to facilitate cross reference among them and comparison of the
technologies they address. Chapter 2.0, Process Summary, provides an over-
view of all material presented. Chapter 3.0, Process Identification and Descrip-
tion, provides comprehensive information on the processes addressed. Each
process is fully analyzed in turn. The analysis includes a description of the
process (what it does and how it does it), its scientific basis, status of develop-
ment, environmental effects, pre- and posttreatment requirements, health and
safety considerations, design data, operational considerations, and comparative
cost data to the extent available. Also addressed are process unique planning
and management requirements and process variations.
Chapter 4.0, Potential Applications, Chapter 5.0, Process Evaluation, and
Chapter 6.0, Limitations, provide a synthesis of available information and in-
formed judgments on the processes. Each of these chapters addresses the pro-
cesses in the same order as they are described in Chapter 3.0. Technology
Prognosis, Chapter 7.0, identifies other processes or elements of processes that
require further research and demonstration before full-scale application can be
considered.
1.6
-------
Chapter 2
PROCESS SUMMARY1
2.1 Process Identification and Description
Thermal desorption is an ex situ means for physically separating organics
from soils, sediments, sludges, filter cakes, and other solid media. Thermal
desorbers are not specifically designed to effect decomposition. Desorber per-
formance is generally measured by comparing the contaminant levels in the
untreated medium with the contamination levels remaining in the processed
medium.
The contaminated material is excavated and delivered to the thermal
desorber. Typically, large objects are screened from the medium and rejected.
Rejected material can sometimes be sized and recycled to the desorber feed.
The medium is then delivered by gravity to the desorber inlet or conveyed by
augers to a feed hopper from which it is mechanically conveyed to the desorber.
There are two approaches to thermal desorption remediation: stationary
facilities to which the contaminated media is transported and mobile systems
that operate on site. Both kinds of facilities are available for treating petroleum-
contaminated wastes; however, only mobile systems are available for treating
Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) wastes.
There are significant variations in the desorption step reflected in the follow-
ing classification of thermal desorption systems:
• direct-fired rotary desorbers;
• indirect-fired rotary desorbers;
1. This chapter is a summary of Chapters 3.0 through 7.0. Sources are cited, where appro-
priate, in those chapters — Ed.
2.1
-------
Process Summary
• direct- or indirect-heated conveyor systems; and
• SoilTech System.
Limited data are available on fluidized beds and one other desorption system
that cannot be placed in any of the above classes, the Texarome Process.
Therefore, these systems are not addressed in the monograph proper but are
described in Appendix A. See figure 2.1 for a schematic of an example of a
thermal desorption system. See also tables 2.1 (on page 2.3), 2.2 (on page 2.4),
and 2.3 (on page 2.5) for summary lists of the key features of the equipment of
each of the three major classes of thermal desorption systems (the first three
listed above) to facilitate a general comparison.
In a desorption unit, heat is transferred to the solid media. The contaminated
material is heated, and water and the contaminants are devolatilized. An inert
gas, such as nitrogen or oxygen-deficient (less than 4%) combustion offgas,
may be injected as a sweep stream. Organics in the offgas may be collected and
recovered by condensation and adsorption or burned in an afterburner. Particu-
Figure2.1
Treatment System Schematic
a Direct-fired rotary
desorber
b Indirect- fired rotary a Organic collection/
desorber destruction
c. Conveyor b Particulate collection
d. Others c. Acid gas remova
Pre-
treatment
^
W
Thermal
Desorber
^
W
Gas Post-
treatment
a Excavation
b. Storage
c Sizing
d. Crashing, dewatenng,
neutralization
e. Blending
f. Feeding systems
„
f w
i
\
c
(
Solid Post-
treatment
Discharge mater
handling system
t Cooling
Dust control
1 Stabilization
2.2
-------
Chapter 2
late matter is removed by conventional air pollution control (APC) methods.
The selection of the gas treatment system will depend on the concentrations of
the contaminants, cleanup standards and regulations, and the economics of the
offgas treatment system(s) employed.
Operation of thermal desorption systems can create a number of process
residual streams: treated media; untreated, oversized rejects; condensed con-
taminants and water; paniculate control-system dust; clean offgas; and spent
Table 2.1
Design and Operating Characteristics
System
Rotary Drum —
Direct fired
Rotary Drum —
Indirect fired
Heated Conveyers
SoilTech ATP
Heat
• Duties from 7-100 •
MM Btu/hr
• 25,000 Btu/hr per ft ' •
internal volume •
* Propane, natural gas.
or fuel oil
* Kiln materials
Carbon Steel" up to •
315°C
Alloy Steel, up to
650'C
• Propane or natural gas •
• Kiln materials
Carbon Steel- up to •
3I5°C •
Alloy Steel' up to
600"C
• 40% of input heat is
transferred to waste
material
• Discharge temperature •
dependent on heating
media, up to 370'C •
maximum
• Indirect or directly
heated
• Natural gas or propane •
• Up to 590'C
Operating
Parameters
Rotational speeds 0.25 •
to 1 0 rpm
UD- 2.1 to 101 •
Soil residence time
to 1 0 mm for •
petroleum, 20 to 30
for SVOC •
Feed rates up to 40
ton/hrl •
Rotational speeds up •
to 2 5 rpm
L/D: 5:1 to 10.1 •
Feed rate up to 10
ton/hr
•
Soil residence time up •
to 90 mm
Feed rate up to 10
ton/hr
Feed rate 1 0 ton/hr •
(25 ton/hr in design)
Other
Co- or countercurrent
gas flow
Negative pressure in
the dryer
Variations in gas clean
up
Need to be careful not
to exceed LEL
Fire hazards
(baghouse) and
explosion (storage
building)
Negative pressure in
the dryer
Variations in gas
cleanup (usually
smaller volume)
Same hazards as
above
Same hazards as
above
4 zones of physical
processes
All units are available, either stationary or mobile
Treatability studies are required
2.3
-------
Process Summary
carbon, if used. Treated media, debris, and oversized rejects may be suitable
for return on site.
Treated condensed water and/or treated scrubber purge water (blowdown)
can be purified and returned to the site wastewater treatment facility (if avail-
able), disposed to a sewer system, or used for rehumidification and cooling of
the hot dusty media. If produced, concentrated, condensed organic contami-
nants are stored for shipment to recycling centers or off-site treatment facilities,
such as incinerators.
Table 2.2
Pretreatment Requirements
Storage Required
Size Distribution:
- Generally less than 2 to 2.5 in. (see text)
- Crush and/or screen large solids
- May need to remove magnetic materials
- Special requirements for asphalt production
Contaminant Characterization
- Define contaminants and cleanup criteria for system
- For direct-fired units operation, Btu content must be below limits
- May require blending for homogeneity
- Generally pH should be above 5 (and less than 11)
Moisture Content
- Dewater to 20 to 50% before feeding
- Thaw frozen soils if necessary
Dust collected from paniculate control devices may be combined with the
treated medium or, depending on the results of contaminant analyses, recycled
through the desorption unit.
Clean offgas is usually released to the atmosphere, although systems that use
inert gas, for example, nitrogen, recycle the gas to the desorber after treatment.
Activated carbon can also be used to treat both the gases and condensed water,
and both on and off-site regeneration of activated carbon could be used.
Environmental impacts associated with all thermal desorbers, aside from
process emissions, are attributable to excavation of contaminated solids, man-
2.4
-------
Chapter 2
agement of treated solids, and equipment noise. Appropriate material handling
measures are needed to control fugitive emissions of dust and highly volatile
contaminants following excavation and before processing. Treated solids
should be cooled and stored while testing takes place, which can take several
days. Accordingly, dust, runoff, and runon controls are needed.
It is not possible to differentiate among the thermal desorbers based on cost.
The costs are scale dependent, ranging from $90-130/ton for a 1,000 ton site to
$40-70/ton for a 10,000 ton site for mobile systems treating petroleum-contami-
nated soils and from $300-600/ton for a 1,000 ton site to $150-200/ton for a
10,000 ton site mobile system operating at a CERCLA site. Matrix moisture
and contaminant type are critical parameters in analyzing desorption costs.
Cost for treating petroleum-contaminated soils in stationary facilities may be as
low as $35 per ton.
Table 2.3
Posttreatment Requirements
System
Treated Soil
Gas
Treatment
Liquid
Treatment
Rotary Drum —
Direct fired
Water quench
Stabilization for heavy
metals
Disposal
Rotary Drum —
Indirect fired
Same as above
Heated Conveyers
Same as above
Direct fired require
larger capacity
Organic control.
afterburner, catalytic
oxidizer, carbon
adsorption
Acid gas and
paniculate removal
ventun scrubber, acid
neutralization,
cyclone, baghouse
Indirect lower gas
volume
Organic control.
afterburner,
condenser, carbon
adsorption
Acid gas and
paniculate removal.
same as above, but not
required in all units
Same as above
depending on direct or
indirect fired
Treat water for
orgamcs using carbon
adsorption
Filter to remove solids
NPDES or POTW
requirements apply
If there are organic
liquids, dispose
Same as above
Same as above
2.5
-------
Process Summary
22 Potential Applications
Thermal desorption technology appears to be applicable to many types of
waste streams. As of February 1992, thermal desorption had been chosen for
28 remedial actions whose projects were in various stages from predesign
through completion (US EPA 1992e). Effective removal of a number of con-
taminants has been demonstrated, including those in petroleum-contaminated
and PCB-contaminated soils, volatile and semi-volatile organics, pesticides, and
manufactured gas plant soils containing hydrocarbons. The process generates
some residual streams that must disposed of either off or on site.
Thermal desorption is generally not effective in separating inorganics from
the contaminated medium. Very volatile metals, such as, mercury, however,
can be removed by these processes.
2.3 Process Evaluation
Thermal desorption has been proven effective in removing organics to levels
in established cleanup standards from contaminated soils, sludges, sediments,
and filter cakes. Chemical contaminants for which bench-scale through full-
scale treatment data exist include volatile organic compounds (VOCs),
semivolatile organic compounds (SVOCs), polynuclear aromatic hydrocarbons
(PAHs or PNAs), polychlorinated biphenyls (PCBs), pesticides, and dioxins
and furans. Volatile organic compounds have been commonly targeted at
CERCLA sites where thermal desorption was selected; VOCs were targeted at
19 sites. Polychlorinated biphenyls were targeted at five sites, other SVOCs at
five sites, and pesticides at three sites (US EPA 1992e). While some mixed
wastes (radioactive and hazardous) have also been treated using thermal desorp-
tion, this application of the technology will not be addressed in this monograph.
There are more than 150 full-scale thermal desorbers available in the U.S.
(Troxler et al. 1992) and in operation. This number includes asphalt aggregate
dryers for remediating petroleum-contaminated soils. Although most of these
units treat only petroleum-contaminated soils, the use of this approach for
Superfund site remediation is increasing. The number of times that thermal
desorption has been selected in a Record of Decision (ROD) as the remediation
2.6
-------
Chapter 2
method for Superfund sites has grown from one in 1985 to ten in 1991 (US
EPA 1992e). Thermal desorption appears in the RODs for 28 Superfund sites
as of February 1992 (US EPA 1992e).
The cost of thermal desorption treatment is principally a function of the solid
moisture content, solid characteristics, contaminant volatility, contaminant
concentration, vendor equipment limitations, and cleanup standards. Regula-
tory requirements may be a key contributor to the cost of treatment and those
that govern thermal destruction processes may apply to certain thermal desorp-
tion systems.
2.4 Limitations
The primary technical factor affecting thermal desorption performance is the
maximum bed temperature effected in the solid media. Since the basis of the
process is physical removal of contaminants from the medium by volatilization,
bed temperature largely determines the type of organics that will be removed
and the effectiveness of removal.
Material handling of soils that are tightly aggregated, such as clays, certain
rock fragments, or particles greater than 2.5 to 5.0 cm (1 to 2 in.), can result in
poor processing performance because of caking. Caking occurs if soil moisture
is above the plastic limit. Also, if a high fraction of fine silt or clay exists in the
matrix, fugitive dusts will be generated and a greater dust loading will be placed
on the downstream air pollution control equipment. The treated medium will
typically contain less than 1% moisture. Dust can easily form in the transfer of
the treated medium from the desorption unit, but can be mitigated by water
sprays. Desorption systems that produce a condensed water stream normally
use it for wetting the treated material.
There is evidence that with some system configurations some materials, such
as tars, may foul and/or plug heat transfer surfaces. Both laboratory and field
tests have documented the deposition of insoluble brown tars on internal system
components.
There are also limitations as to the concentration of organic contaminants
that can be thermally treated in any one process. First, with regard to excava-
tion of the site, as with any ex situ technology, concentrations must be such that
2.7
-------
Process Summary
fugitive emissions are not excessive. In addition, vapor organic concentrations
within the thermal desorber must be kept below 25% of the lower explosive
limits (LEL) if the desorber is operated with excess oxygen.
2.5 Technology Prognosis
This technology continues to evolve, particularly as applied in hazardous
waste site remediation. More information is needed concerning the scaling of
laboratory results with full-scale systems, the fate of metals in desorbers, and
the formation of dioxins. The emission of metals, especially volatile metals,
such as mercury, needs to be understood. In addition, the degree of leachability
of metals in the ash needs to be determined for purposes of ultimate disposal.
2.8
-------
Chapter 3
PROCESS IDENTIFICATION AND
DESCRIPTION
Of the 76 demonstrations being conducted under the United States Environ-
mental Protection Agency (US EPA) Superfund Innovative Technology Evalu-
ation (SITE) Program, 17% of the technologies being evaluated are thermal
desorption processes (US EPA 199la). Through fiscal year 1991, of 498 reme-
dial actions, thermal desorption was selected as the alternative technology for
28. Alternative technology accounted for 210 (42%) of the treatment technolo-
gies selected (US EPA 1992e).
3.1 Description
The thermal desorber is one part of the total system used in the remediation
of contaminated solid media (see figure 2.1 on page 2.2). Before thermal des-
orption, excavation and pretreatment — material handling, material sizing, and
removal of large objects — will be required. There are significant variations in
the desorption step reflected in distinct classes of thermal desorber systems. In
this monograph, the systems are classified and addressed as:
• direct-fired rotary desorbers;
• indirect-fired rotary desorbers; and
• direct or indirect-heated conveyor systems.
Another rotary desorber system, the SoilTech process, could not be classified
exclusively as indirect or direct and, therefore, is addressed here as a separate
class. Two other systems, fluidized beds and the Texarome Process, were iden-
tified, but insufficient data were available to enable the authors to address them
at the time of this writing (August 1992). They are briefly described in Appen-
dix A.
3.1
-------
Process Identification and Description
Following the thermal desorption step, posttreatment is usually necessary.
Posttreatment consists of: gas treatment (through condensation units, afterburn-
ers, carbon adsorption units), solids' treatment (quenching, stabilization, dis-
posal), and liquid treatment (water treatment, organic liquid treatment, and
disposal in the case of condensing system). The objectives of the overall treat-
ment system are clean solids, environmentally acceptable stack gases and water,
and complete disposal of all other residuals.
See also the US EPA Superfund Engineering Bulletin: Thermal Desorption
Treatment, of April 1993, appended hereto as Appendix B.
3.2 Scientific Basis
In any thermal desorption system, heat must be transferred to the solid par-
ticles to vaporize the contaminants from particles; in turn, the vaporized con-
taminants must be transferred from the particles to the gas phase. The specific
modes of heat and mass transfer vary with the type of thermal desorption sys-
tem employed. Figure 3.1 (on page 3.3) depicts the transport mechanisms to
be considered. As explained in Owens et al. (1991), system temperature will
determine the importance of radiative heat transfer. Interparticle phenomena
refer to heat and mass transfer within the bed. Heat and mass transfer processes
at the interparticle level are distinct, depending on the thermal desorption sys-
tem used. For example, in a rotary desorber, heat must be transferred to the bed
of solids by radiative, convective, and conductive heat transfer with the wall
and gas, while mass must be transferred through the bed of solids. At the gas/
solid interface, mass must then move into the free stream gas.
Intraparticle processes, referring to transfer of heat and mass between the
particle and the bulk environment within the bed, are also important. These
processes are not dependent on the system, since they are fundamental to the
contaminant and type of media being treated. The work of Keyes (1992)
showed that in toluene desorption from montmorillonite clay, local equilibrium
exists within pores and that the effective rate of desorption from individual
particles is controlled by intraparticle diffusion. Bozzelli and coworkers (Wu,
Dong, and Bozzelli 1992; Wu and Bozzelli 1992) found that, when assuming
linear equilibrium (where the concentration in the soil is directly proportional to
the gas-phase concentration) within the pores, the equilibrium constants were
3.2
-------
Chapter 3
Figure 3.1
Schematic of the Transport Phenomena Occurring During Thermal
Treatment of a Solid Bed
Desorption
Radiation (importance depends on the temperature)
and convection fiom the gas
Radiation (importance depends on temperature)
from walls or heating elements
- GAS
Conduction
from the
hot wall
Mass transfer to the
gas stream
V SOLID
" Conduction throu
ugh the bed
Interparticle mass transfer
through the bed
^- Represents heat
^" Represents mass
Mass transfer out of particle to the
bulk gas
Single
Particle
Local desorption kinetics
at the gas/solid interface
Heat transfer
through
the particle
Included are heat transfer (conduction, radiation) and mass transfer (from particle, from bed
processes.
strongly dependent upon temperature for their soil/contaminant systems. In
addition, they found no effect of particle size on the equilibrium constants.
Keyes showed also, however, that when these particles constitute a sorbent bed
in a rotary kiln, mass-transport resistances associated with the sorbent bed con-
trol the overall desorption rate and that equilibrium exists between the adsorbed
3.3
-------
Process Identification and Description
contaminant and the interparticle gas phase. The concept of local equilibrium
within pores is supported by the work of Gorte (1982), Herz, Kiela, and Marin
(1982), and Jones and Griffin (1983).
Researchers have identified several important variables that need to be con-
sidered in the equilibrium between contaminants and soil particles. They have
demonstrated that contaminant removal is highly dependent on the following
parameters:
• Temperature — modest increases in temperature greatly decrease
residual concentrations; for example, Helsel and Groen (1988)
found that at 300°C (570°F) the Pyrene residual was 1.2% of the
original. At 400°C (750°F), this dropped to 0.01%. The tests were
bench-scale at an initial concentration of 1,400 ppm;
• Soil matrix — coarse particles such as sands will desorb contami-
nants easier than fine grained clays and silts;
• Contaminant — some contaminants will bind strongly to soils while
others will not; and
• Moisture content — increased moisture reduces the capacity of the
contaminant to adsorb on soils with high mineral contents (silts and
clays).
(Varuntanya et al. 1989; Flytzani-Stephanopoulos et al. 1991; Lighty et al.
1988; Lighty, Silcox et al. 1990; Helsel and Groen 1988; Rogers, Holsen, and
Anderson 1990; and Gilot et al. 1992.)
Researchers have found that, while the initial 90% of a contaminant might be
easily removed, the final 10% will take much longer, especially if the cleanup
criteria is in the parts per billion range. See figure 3.2 (on page 3.5). This phe-
nomena is due to the adsorptive properties of the soil, which may have a ten-
dency to strongly "hold" monolayers (single molecules) of contaminant to its
surface. Lighty, Silcox et al. (1990), Locke, Arozarena, and Chambers (1991),
and Borkent-Verhage et al. (1986) found that the relationship between tempera-
ture and removal of contaminant is nonlinear, confirming the possibility of a
monolayer effect.
Limited performance data for thermal desorption systems will be presented
in the subsequent chapters. For each remediation, however, treatability studies
should be conducted, and data reviewed to determine the applicability of the
technology (US EPA 1992d). Specifically, it is important to determine the solid
3.4
-------
Chapter 3
Figure 3.2
Relationship of Contaminant Removal Time for Increasing Temperatures
o.o
residence time and temperature required to meet the cleanup criteria. The stud-
ies should be conducted such that interparticle heat and mass transfer phenom-
ena are minimized, since these processes are system specific.
3.3 Waste Characterization
See figure 3.3 (on page 3.6) for a summary of waste characteristics and re-
lated concerns. Waste characterization must be performed relative to cleanup
criteria. It is important to understand not only the nature of the contaminants
but also, where a solid is to be treated, the structure of the solid and the binding
of the waste to the solid. See table 3.1 (on page 3.7) for analyses of the chemi-
cal and physical properties of the solid and contaminant that may need to be
performed. Laboratories performing these analyses should meet US EPA ac-
3.5
-------
Process Identification and Description
Figure 3.3
Summary of Waste Characteristics and Related Concerns
Ultimate, Proximate, and Chemical
Analysis
TCLP
Potential || Considerations
Fugitive
Emissions
Offgas
Treatment
Requirements
Coarse-Grained Soils
have little material
handling problems,
good heat transfer
Fine-Gramed Soils may
have material handling
& entramment problems
3.6
-------
Chapter 3
creditation requirements. Their quality assurance programs should meet pre-
scribed standards, a priority requirement.
Sulfur and nitrogen are analyzed to determine whether there is potential for
production of the pollutants sulfur dioxide and nitrogen oxides. Moisture con-
tent is important because of the energy required to heat and vaporize the water
in the solid. Moisture is a major heat sink in the thermal desorber. See figure
3.4 (on page 3.8). Under the conditions specified therein, high-moisture content
solids never rise above the vaporization temperature of the water because of the
given heat input. In this case, it would be necessary to change the feed rate or
firing rate in order to bring the material to the temperature.
Table 3.1
Waste Characterization Analyses
CHEMICAL
Ultimate. c, H, O, N, P and S (if waste has greater than 17c sulfur, then
analyze for pyntic, SO4, and ovgamc sulfur)
Proximate moisture, ash, fixed carbon, volatiles
Hahdes ci (total and ionic), F, I, Br
Orgamcs Pesticides, dioxm, semivolatiles, volatiles, and PCBs
Metals Ag, As, Cd. Cr, Ba, Be, Hg, Pb, Se, Ni, Sb, Tl
PHYSICAL
Bulk density
Heating value
Specific heat
Ash Fusion Temperatures initial deformation, softening, hemispherical,
fluid (if the ash fusion initial deformation
temperature is less than 2,000°F then also
perform Na, K, and Ca)
pH (for corrosion considerations)
Flash point
Liquid limit
Plasticity index
Soil gram si/e
Depending upon the site history, specific chemical evaluations and analyses
of compounds such as dioxins, Polychlorinated Biphenyls (PCBs), pesticides,
volatiles, and semivolatiles should be performed to determine the nature and
3.7
-------
Process Identification and Description
concentration of contaminants in the waste. Knowledge of the initial concentra-
tion of contaminants is important for the following reasons:
n During excavation, fugitive emissions must be considered. To
ensure safe operation, 25% of the lower explosion limit (LEL)
should not be exceeded within a thermal desorber operating in an
oxygen atmosphere;
n The types and amounts of organics that are being removed are fac-
tors in an engineering analysis of the offgas treatment systems;
Figure 3.4
Model Predictions Showing the Effect of the Initial Weight Fraction of
Moisture in the Solid Feed on Bed Temperature Profile
1200
1000 -
^
8
2
I
"8
800 '
600 •
400 •
200
02
04 0.6
Fractional Distance
08
I 0
The dry solid feed rate is constant at 2.55 kg/sec.
Repnnted by permission of the Air and Waste Management Association from "The Effects of Rotary-Kiln Operating
Conditions and Design on Burden Heating Rates as Determined by a Mathematical Model of Rotary Kiln Heat Transfer" b)
G D Silcox and D.W Pershmg, Journal of Air and Waste Management Association, Volume 40, March, 1990 Copyright
1990 by the Air and Waste Management Association
3.8
-------
Chapter 3
• Heat release is the critical parameter for the design of an after-
burner; and
• The composition of the organics is critical to the design of a con-
denser recovery system.
The residual material should be analyzed to verify that treatment standards
have been met.
Analysis of concentrations of metals must be performed where volatile met-
als are present and might exit the stack. In assessments of hazardous waste
incinerators, risk is almost always driven by the metals and dioxin emitted from
the stack when indirect pathways are considered. Metals emissions from some
incinerators, along with those from all boilers and industrial furnaces, are regu-
lated under the Boiler and Industrial Furnace (BIF) Regulations (Appendix VIII
of 40 CFR Part 261). Following are the metals whose emissions are regulated:
• Arsenic (As);
• Beryllium (Be);
• Cadmium (Cd);
• Chromium (Cr);
• Antimony (Sb);
• Barium (Ba);
• Mercury (Hg);
• Silver (Ag);
• Thallium (Tl); and
• Lead(Pb).
The first four are identified as carcinogens. The Resource Conservation
Recovery Act (RCRA) lists, in addition, nickel (Ni), selenium (Se), and os-
mium (Os). Regulations under the RCRA and BIF, as well as state regulations,
may govern emissions from thermal desorbers, depending on the regulatory
status of the overall system (see also Section 6.8). The treatability test (see
Subsection 4.1.2) will help determine the amount of vaporization that might
occur at the desorber solid temperature.
The Toxic Characteristic Leachate Procedure (TCLP) metals analysis should
be performed on the solid residuals to determine the proper disposal procedure.
Residue that fails the TCLP test is precluded from land disposal under 40 CFR
3.9
-------
Process Identification and Description
Part 268 and, therefore, must be processed further. If the waste was classified
as hazardous under the RCRA before being treated and passes the TCLP test, it
may be placed in a RCRA landvault. If waste that was being remediated under
the Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) passes the TCLP test, the treated waste may be placed back in the
excavation hole, if allowed under the consent decree governing the remediation
(see Section 6.8).
The physical properties of the solid must also be considered (US EPA
1992g). Knowledge of the particle size distribution of the solids to be
remediated is important for proper selection of the type of thermal desorber and
pretreatment scheme that will be used. Large boulders and cobbles (materials
with equivalent diameters between 7.5 and 30 cm (3.0 and 12 in)) will need to
be crushed or removed. Coarse-grained soils (gravels and sand that have more
than 50% material retained on a 7.7-cm sieve) are generally free flowing and do
not agglomerate into large particles. These solids have low moisture adsorption
capacities and relatively good heat transfer characteristics. Silts, clays, organic
soils, and peat are fine-grained and absorptive. Moisture content greatly affects
the material handling of these soils. With fine-grained soils, entrained panicu-
late can cause problems. Since the degree of paniculate entrainment is directly
related to gas-flow rate and particle size, different types of thermal desorber
units will entrain varying quantities of solid.
The plasticity of the material is also important, because this characteristic
will determine whether the material likely to stick to screening, sizing, convey-
ing, and desorber equipment. Thermal treatment of a fine-grained soil with a
moisture content above the plastic limit is extremely difficult (US EPA 1992g).
Bulk density relates the volume of solid that needs to be remediated (the num-
ber usually given in the remedial investigation report) to the mass of solid that
will be treated (a performance characteristic of a specific desorber system). The
specific heat of the solid must be known to determine the amount of heat re-
quired to raise the temperature of the material. The ash-fusion temperatures are
important in higher temperature environments, where the solid residue might
form a slag. It is unlikely that desorbers will operate above 650°C (1,200°F);
therefore, the ash-fusion temperature will not likely be exceeded. In systems
with afterburners, however, slagging may present a problem because of the
higher temperature environment.
3.10
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Chapter 3
3.4 Rotary Desorber—Direct Fired
3.4.1 Description
Direct-fired rotary desorber systems may be mobile or stationary. The typi-
cal system (see figure 3.5) consists of three components: the pretreatment and
material handling systems, the desorption unit, and the posttreatment systems
for both the gas and the solid.
3.4.1.1 Pretreatment
If storage of solids is required after excavation, the pretreatment process
begins with proper fugitive emissions control and/or ventilation. The pretreat-
ment process continues with screening to remove large material (to be crushed
or manually cleaned) and foreign debris. If the medium contains an excessive
Figure 3.5
Components of the Direct-Fired Rotary Desorber System
\
a. Storage
b. Screening
c. De watering
d. Neutralization
e. Blending
f. Feeding Syster
Pre-Treated
Solids, Sludges, etc
n
Desorption
Unit
a Direct-Fired
Rotary Desorb
a. Particulate Removal
b Organic Treatment
c. Acid Gas Treatment
a. Discharge Material
Handling Systems
b. Cooling
c. Dust Control
d. Stabilization
3.11
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Process Identification and Description
amount of contaminant or moisture, it is usually blended to effect uniform con-
taminant and moisture levels. Blending can be quite difficult. Excessively wet
media can be dewatered by such methods as filter presses and adsorbent addi-
tion to 30 to 50% by weight moisture, improving material handling and reduc-
ing energy costs. In addition, dry treated solids are sometimes added to effect
uniform moisture conditions. In northern climates, the medium may be tempo-
rarily stored in a building to preclude freezing. Highly acidic media may also
be pretreated (i.e., neutralized) to mitigate corrosion of materials handling,
thermal desorption, and treated solids handling equipment.
3.4.1.2 Desorber
The function of the desorption unit, the rotary desorber, is to heat the me-
dium to a sufficient temperature and maintain it for a sufficient period to desorb
the moisture and the contaminants from the medium. A rotary desorber con-
sists of a rotating cylindrical metal drum that is inclined slightly with respect to
the horizontal axis. Material is passed through the rotating cylinder and is
heated by direct exchange with a support flame and/or combustion products.
The burner is usually fired with natural gas, propane, or fuel oil. The direction
of solids flow through the unit can be either cocurrent or countercurrent with
respect to the gas flow direction. Typically, lifters are attached to the inside
surface of the cylinder to enhance gas/solid contact; hence, heat and mass-
transfer limitations are reduced within the unit. The residence time of the mate-
rial in the desorber is controlled by cylinder length/diameter ratio, rotation rate,
the angle of inclination, and the design of the lifters.
3.4.1.3 Posttreatment
Posttreatment entails the addition of water to cool the treated media and to
control fugitive dust emissions. Mixing is usually accomplished in a pug mill
or similar unit. Depending upon the nature of the original contamination, the
treated material may be redeposited on the site or used in landfills. If the media
contains high levels of heavy metals, a stabilizer, such as lime, can be added to
the soil in the pug mill. Stabilization processes are discussed in detail in an-
other monograph in this series.1
1 . See Innovative Site Remediation Technology: Stabilization/Solidification — Ed.
3.12
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Chapter 3
The objective of the gas posttreatment system is to remove pollutants from
the purge gas stream before it is discharged to the atmosphere. These pollutants
consist of the original contaminants and any by-products. Special measures
may be needed to handle heavy metals, sulfur dioxide (SO2), oxides of nitrogen
(NOx), hydrochloric acid (HC1), and other acids depending on waste, fuel fired,
and emission requirements. In some cases, National Ambient Air Quality Stan-
dards (NAAQS) will need to be considered. Entrained particles must also be
removed before discharge. Typical gas posttreatment equipment includes cy-
clone separators, a secondary oxidizer (typically an afterburner or catalytic
oxidizer), a baghouse (filtration system), a scrubber, and an evaporative cooler.
Carbon adsorption filters are less common. Depending upon the application,
applicable air quality regulations, and chemical constituents and their concen-
trations, some or all of these posttreatment components may be used.
3.4.2 Status of Development
The direct-fired rotary desorber technology is based on techniques used in
such processes as asphalt and cement production, calcination, and common
industrial drying processes. The use of either mobile or stationary systems
utilizing rotating drums to process granular materials is well established, and
direct-fired rotary desorbers are similar to conventional industrial units. As-
phalt aggregate dryers have been directly applied in treating petroleum-con-
taminated soils; where the properties of the soil were suitable, the treated soil
has been incorporated into the asphalt product. Because many direct-fired ro-
tary desorbers are adaptations of existing equipment, there is a general unifor-
mity in design and operation.
The principal application of direct-fired thermal desorption units is the treat-
ment of petroleum-contaminated soils. The contamination has often resulted
from leaking underground storage tanks (UST). Most of these petroleum-con-
taminated soils are exempt from regulations under federal hazardous waste
laws. The most common exception is soil contaminated with lead from leaded
gasoline. Soil is not exempt in any event if it exhibits toxicity characteristic
under RCRA waste codes D004 through D017 (Troxler et al. 1992), and treat-
ment of petroleum-contaminated soils must comply with state regulations.
Troxler et al. (1992) and the US EPA (1992g) report that one-half to three-
fourths of existing rotary dryers used to remediate petroleum-contaminated
soils are of the asphalt aggregate dryer design. These asphalt aggregate dryers
are not usually designed with afterburner systems. Because of the requirement
3.13
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Process Identification and Description
to meet regional air quality standards, specifically with regard to potential hy-
drocarbon emissions, some states are requiring that asphalt kilns treating petro-
leum-contaminated soils be equipped with an afterburner (US EPA 1992g).
Thus, while existing technologies have been directly applied to treat petroleum-
contaminated soils, the technology is evolving in response to regulatory con-
cerns.
Direct-fired thermal desorbers have been successfully used also to treat
wastes regulated under the Comprehensive Environmental Response, Compen-
sation, and Liability Act (CERCLA), Superfund Amendment Reauthorization
Act (SARA), and RCRA. Although the systems employed have some of the
characteristics of conventional rotary desorbers, they have been specifically
designed to treat material contaminated with hazardous wastes. Because of
more stringent regulatory criteria, they must have the capability to destroy haz-
ardous compounds desorbed from the solids. Therefore, systems designed to
treat hazardous wastes are typically equipped with a gas posttreatment system,
such as, an afterburner, carbon adsorption system, or catalytic oxidizer.
3.4.3 Pretreotment Requirements
The pretreatment processes are those used in storing the excavated media,
conditioning the material to meet the feed specifications of the desorber, and
delivering the material to the desorber.
3.4.3.1 Storage
The contaminated media may need to be stored after excavation. For ex-
ample, an operation might involve excavation only during the dayshift. Exca-
vated material is often stockpiled to provide an adequate feed supply for con-
tinuous operation of the treatment facility. The material should be stored under
a canopy to prevent addition of moisture from rainfall. If the contaminated
material is stored in a confined location, consideration must be given fugitive
emission control and/or ventilation. Frozen media should be warmed before it
is fed to the desorber. The storage area should be designed to control runon and
runoff precipitation.
3.4.3.2 Solid Particle Size Distribution
The maximum range of particle size that can be treated in most rotary
desorbers is 5 to 6.5 cm (2 to 2.5 in.), primarily because of materials handling
3.14
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Chapter 3
limitations. Large particles are either screened and/or crushed before treatment,
removed and manually cleaned, or returned to the site, if this is permitted.
Magnetic objects are usually removed by a magnet suspended over the belt
feeder.
3.4.3.3 Contaminant Characterization
In treating contaminated solids, the type and concentration of contaminants
in the feed matrix is a key consideration. The LEL of the combustible material
in the desorber must be considered, since oxygen is present in the gas. In good
practice, concentrations are limited to 25% of the LEL. In addition, materials
handling limitations must be considered for wastes containing heavier, tar-like
contaminants. Lower explosive limits can be found in the literature for ex-
ample, in NFPA Standard 325, Sax 1989; Turner and McCreery 1981; and Lide
1990.
The material is generally not uniformly contaminated. In some cases, mate-
rial with higher levels of contamination can be blended with other less contami-
nated material in order to make the feed more uniform. But blending is difficult
and a uniform feed can not always be produced.
In order to limit equipment corrosion, highly acidic media can be treated
with lime in order to maintain a pH greater than 5.
3.4.3.4 Moisture Content
Moisture affects the amount of energy required to heat the medium as well
as the handling characteristics of fine-grained soils. Pretreatment methods
include filter presses, air drying, blending with drier material, and mixing with
treated fines.
3.4.4 Design Data and Unit Sizing
Direct-fired rotary desorbers are increasingly used because of their flexibility
and versatility, enabling them to handle the wide variation in conditions en-
countered among and within sites.
A site is initially characterized by analyzing many solid core samples to
develop maps of the type and concentration of contamination, the matrix, and
the moisture levels. The maps are used to determine process equipment re-
quirements. Treatability studies are normally conducted in laboratory-scale
3.15
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Process Identification and Description
equipment, in parallel with the mapping. These studies are described in Sub-
section 4.1.2.
Based upon information provided by the maps and treatability studies, oper-
ating conditions can be determined. Combustion gases provide heat to effect
the solid temperature required. Direct-fired thermal desorber heat duties com-
monly range from 7 to 100 MM Btu/hr (Cudahy and Troxler 1992). As a rule
of thumb, a heat input of 25,000 Btu/hr is the maximum required for each cubic
foot of internal kiln (desorber) volume. Residence time is varied by adjusting
the horizontal inclination and rotational speed of the desorber. Typical rotation
speeds range from 0.25 to 10 rev/min. Length-to-diameter ratios vary from 2:1
to 10:1.
Another important design factor is the direction of flow of the combustion
gas relative to the flow of the solid in the desorber. The flow configuration of
the desorber (cocurrent or countercurrent) will affect the arrangement and size
of components used in the gas treatment process. In the cocurrent configura-
tion, the gases exiting the desorber are relatively hot. The larger entrained par-
ticles can be removed by a cyclone, but the gases are too hot to enter the
baghouse. Therefore, the most common design with the cocurrent configura-
tion places the cyclone after the desorber, followed by an afterburner, a gas
cooler, a baghouse, an induction fan, and the stack (see figure 3.6a on page
3.17). Since the afterburner is upstream of the baghouse, the particles collected
in the baghouse should be essentially free of contaminants in this configuration.
If acid neutralization is required, a scrubber may also be included. Venturi
scrubbers followed by carbon adsorption units can be used in place of after-
burner/baghouse systems.
Alternatively, if the countercurrent flow configuration is used, the gases
leaving the desorber will generally be cool enough to flow directly from the
cyclone into the baghouse. Thus, the arrangement of the gas posttreatment
equipment with the countercurrent desorber configuration is as follows:
desorber, cyclone, baghouse, induced draft fan, afterburner, and stack (see fig-
ure 3.6b on page 3.18). Since the afterburner is near the end of the pollution
control train, the flow rates through the other components are reduced lower
than those of the cocurrent configuration. The lower flow rates permit the use
of smaller gas posttreatment equipment.
Because of the cooler temperatures in the baghouse of the countercurrent
configuration, it is possible that heavier organics will condense in the baghouse
and pose a fire hazard or blind the bags. Therefore, heavier organics are not
3.16
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Chapter 3
usually treated with this arrangement. In addition, since the afterburner is lo-
cated downstream of the baghouse, the particles collected in the baghouse may
not yet be fully decontaminated and, therefore, are typically recycled back to
the desorber.
Figure 3.6(a)
Cocurrent Desorber — Offgas Posttreatment Process
Combustion
Air — ^>
Fuel— ^-
Solids,
Desorber
Filter Treated X
Cake, Soil Solid T
Cyclone
^-
Combustion
Air — ^
Fuel —**
Afterburner
Gas Cooler
Stack
3.4.5 Posttreatment Requirements
Posttreatment of both the treated solids and the gas stream leaving the
desorber is required. In addition, posttreatment of liquids is required in systems
utilizing a wet scrubber.
3,4.5.1 Solid Posttreatment
Posttreatment of solids typically entails water quenching to cool the solid
and control dust. The solid leaves the desorber and usually drops onto a screw
conveyor. Water may be added in either the screw conveyor or pug mill. Other
3.17
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Process Identification and Description
Figure 3.6(b)
Countercurrent Desorber — Offgas Posttreatment Process
Combustion
Air
Fuel
Treated
Solids
Desorber
^
Solids ^
Sludges, ' Cyclone
Filter
Cake, Soil
Afterburner
Combustion
Air Induced
Draft Fan
Fuel
Stack
treatments, such as stabilization, may also be necessary if heavy metals are
present. Where water, nitrogen, phosphorus, organic material, or other nutrient
is absent from the treated matrix, it must be added to solids that will be used as
a final cover in order for them to sustain viable plant growth.
3.4.5.2 Gas Posttreatment
The gas posttreatment system removes pollutants from the gas stream before
it is discharged. These gases may consist of the original contaminants, the
combustion gas products, products of incomplete combustion (PICs), and par-
ticulate matter. The gas posttreatment system for a direct-fired rotary desorber
requires a larger capacity air pollution control (APC) train than those of indi-
rectly heated thermal desorption treatment systems because of increased gas
volume. Equipment used in the gas posttreatment process includes cyclone
separators, secondary oxidizers (an afterburner or catalytic oxidizer), baghouses
(filtration systems), scrubbers, evaporative coolers, carbon adsorption filters,
and condensers. Some of these components are described below.
3.18
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Chapter 3
Organics Control. In systems requiring organics control, a conventional
afterburner is the most commonly used oxidizer. Catalytic oxidizers have been
used for secondary oxidation to a lesser extent. Carbon adsorption systems
have also been used in place of an oxidizer.
The gas treatment train may or may not include an afterburner, depending on
the particular application and the regulatory status of the effluents. Most as-
phalt dryers currently processing petroleum-contaminated soil are not equipped
with afterburners (US EPA 1992g) although, unsatisfactory levels of organics
were emitted without gas treatment. The likelihood is increasing that gas post-
treatment will be required in rotary desorbers processing all kinds of wastes.
Conventional afterburners are currently the equipment of choice primarily be-
cause of their robustness and relative low cost.
Typically, the afterburner is a refractory-lined shell providing enough resi-
dence time at a sufficiently high temperature to destroy organic compounds that
have been desorbed from the media. Afterburners typically operate between
760 to 980°C (1,400 to 1,800°F), with a 0.5 to 2.0 second gas-phase residence
time. Afterburners can be used before or after particulate control.
Several contractors currently make use of a catalytic oxidizer in place of an
afterburner. The catalysts normally used are noble metal compounds, such as
platinum or rhodium, used in small quantities and deposited on a support mate-
rial, such as alumina. In addition to controlling organics, catalytic oxidation can
be very effective in eliminating odors.
According to Tarmac Equipment Company, one disadvantage of catalytic
oxidizers is that a high-moisture content will adversely affect the operation of a
catalytic bed. Furthermore, chlorine and sulfur compounds may poison the bed,
resulting in inefficient conversion. The catalytic oxidizer, therefore, must be
located downstream from the particulate control and acid gas removal systems.
Gases entering the catalytic oxidizer should not have concentrations of organics
greater than 25% of the LEL. Catalytic oxidization is addressed in another
monograph in the series.2
Carbon adsorption has been used to remove low concentrations of organic
compounds from the gas phase. The temperature of the process gas should be
less than 60°C (140°F). Above this temperature, efficiency may fall. The spei
carbon must be periodically regenerated or disposed of. Carbon collection
2 . See Innovative Site Remediation Technology: Thermal Destruction — Ed.
3.19
spent
-------
Process Identification and Description
efficiency varies with the chemicals of the gases, and selection of carbon ad-
sorption, therefore, depends on the contaminants in the media.
Two important design parameters for carbon adsorption units are the empty
bed contact time and superficial gas velocity. The empty bed contact time is the
ratio of empty bed volume to the volumetric gas-flow rate through the bed. The
superficial gas velocity (or empty bed velocity) is the ratio of the volumetric
gas-flow rate to the cross-sectional area of the bed. These parameters are used
in estimating the operating period before breakthrough. One report (PRC Envi-
ronmental Management, Inc., Versar, Inc., and Radian Corporation 1991) sug-
gests a typical empty bed contact time of 4.2 seconds and a superficial gas ve-
locity of 0.3 m/sec (0.9 ft/sec). In reports of other satisfactory applications of
carbon absorption used as a tail gas scrubber, the contact time is as low as 2 sec
and superficial gas velocities are as high as up to 0.46 m/sec (1.5 ft/sec). Before
a specific application is undertaken, however, a trial test to acquire engineering
data is recommended.
Removal of Acid Gas and Particles. In addition to organics, acid gases, such
as, hydrogen chloride and sulfur dioxide, may also have to be removed, depend-
ing on the waste, fuel fired, and system. Particulate removal is almost always
necessary.
Conventional venturi scrubbers have been used to remove sulfur dioxide and
hydrogen chloride. An added benefit of the venturi scrubber is its capability to
remove particles larger than 5 |jg in the gas stream (Wark and Warner 1981);
however, the resultant water stream and/or sludge must be handled. A signifi-
cant problem associated with the venturi scrubber is the erosive effect of the
gas/liquid mixture passing through the throat section, which is heightened by
the high turbulence in this section.
The heart of the venturi scrubber is a venturi throat where gases pass through
a reduced area reaching velocities in the range of 60 to 180 m/sec (200 to 600
ft/sec), enhancing mixing. Typically 8 to 45 L (2 to 12 gal) of water per 28
standard m3 (1,000 standard ft3) of gas is required in the throat section. High
efficiency venturi scrubbers have a pressure drop of 10"-30" w.g.
As the high-velocity gas stream removes gases, particles, and droplets from
stack gases, a large number of fine water droplets are formed and entrained.
Manufacturers usually provide devices to remove the entrained liquid droplets.
Most thermal desorption systems do not produce significant quantities of
acid gases. Acid neutralization may be required, however, to prevent corrosive
3.20
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Chapter 3
attack on steel and other materials throughout the system, including the stack.
A few systems employ wet scrubbers. The scrubbers are designed to use an
alkali reagent to acid gas stoichiometric ratio of slightly over one. Sodium
hydroxide is typically used for pH adjustment. Normally, the scrubbers operate
within a pH range of 5 to 7. At higher pH levels, insoluble forms of calcium
carbonate and sodium bicarbonate can form and may foul scrubber internals. If
heat is being recovered from the stack gas, the gas should not be cooled below
its dew point. Stacks can be lined with refractory or fiberglass-reinforced plas-
tic (FRP) to prevent corrosion.
The cyclone separator is designed to remove the largest of the entrained
particles from the gas stream. Since it is usually located directly downstream
from the primary desorber, the particles collected may still have high concentra-
tions of adsorbed organics and may need to be recycled through the system.
There are wet and dry cyclone separators, but only the dry are presently in
thermal desorption systems. The dry cyclone separator is a true inertial separa-
tor. Particles entrained in the gas stream enter the cyclone, are directed into a
vortex flow pattern, collect on the wall of the separator because of inertial ef-
fects, and eventually drop to the receiver part of the unit. Wet cyclone separa-
tors operate on the same principle, but use water to assist in gas cleanup and
particle entrainment.
Cyclone separators are most efficient in removing larger particles (>15 |Jm).
Agglomeration may occur if the dust is fibrous, sticky, or hygroscopic or if the
gas stream contains excessive paniculate matter.
Collection efficiencies usually increase with increases in inlet velocities,
which is limited, however, by the allowable pressure drop of the separator. A
typical inlet velocity is approximately 25 m/sec (80 ft/sec) (PRC Environmental
Management, Inc., Versar, Inc., and Radian Corporation 1991).
The baghouse contains cloth filters that collect finer entrained particles.
Baghouses contain a series of permeable bags that allow the passage of gas but
not paniculate matter. Depending on the location of the baghouse relative to
the afterburner, the particles collected in the baghouse may be contaminated
with organic compounds.
Baghouses are normally used to remove particles <10 jjm and are highly
efficient in removing particles <1 )jm. There are a number of design factors to
consider when selecting a baghouse, including the degree of filtration, bag life,
ability to clean the bags, ability to provide adequate gas and dust distribution,
3.21
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Process Identification and Description
and dust removal. Typical filter fabrics and suggested operating exposure tem-
peratures are as follows (Bruner 1985):
• nomex (220 to 260°C) (425 to 500°F); '
• fiberglass (290 to 315°C) (550 to 600T); and
• Teflon (230 to 260°C) (450 to SOOT).
The collected particles must be removed from the bags periodically to avoid
high-pressure drops. A number of methods have been developed to discharge
collected particulate matter on a regular basis, including shakers, compressed
air jets, sonic cleaners, and reverse air flow.
3.4.5.3 Liquids Posttreatment
For systems utilizing wet scrubbers, blowdown must be filtered or treated
before release. Granular filters are used to reduce total suspended solids. Liq-
uid-phase carbon is used to remove organics from the blowdown. If the
blowdown is to be released through a National Pollutant Discharge Elimination
System (NPDES) or publicly owned treatment work (POTW), other cleanup
parameters may apply.
3.4.6 Special Health and Safety Considerations
In pretreatment, potential safety concerns include explosion hazards in im-
properly ventilated storage buildings and exposure to fugitive emissions. In the
desorber, which is usually operated with excess air, the concentration of con-
taminants in the feed must be low enough so that 25% of the LEL is not ex-
ceeded. Further, in order to control fugitive emissions, most direct-fired rotary
desorbers are operated under slight negative pressure. In gas posttreatment, a
potential fire hazard exists in the baghouse if hydrocarbons or other combus-
tible materials are allowed to collect on the filters. This presents a potential
problem especially in the countercurrent rotary desorber configuration when
used to treat material contaminated with heavier organics. The usual precau-
tions relating to hot operating equipment, such as, warning signs, barriers, and
safety shields, must be implemented.
3.22
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Chapter 3
3.4.7 Operational Requirements and Considerations
3.4.7.1 Temperature Requirements and Limitations
The temperature required to heat the solids to a temperature sufficiently high
to evaporate contaminants from the media depends on the contaminant vapor
pressure, initial contaminant concentration, intended cleanup level, and the
material matrix. Contaminated materials will vary, exhibiting different desorp-
tion characteristics at each site. Laboratory-scale and/or pilot-scale treatability
studies addressing the specific solid/contaminant/moisture matrix are usually
needed to determine the temperature required.
Controlling the solid temperature is very important in most desorption pro-
cesses. The temperature is usually directly measured by a thermocouple imbed-
ded at the discharge end of the rotary desorber. Where it is not possible to mea-
sure the temperature directly, the retention time and the exiting gas temperature
are used as alternative indicators.
The materials of construction chosen for the desorber determine the maxi-
mum temperature to which the solid can be heated. Most rotary desorbers are
constructed from metal cylinders. According to Troxler et al. (1992), the maxi-
mum solids' operating temperature of a desorber made of carbon steel, is 315 to
340°C (600 to 650°F), while those made of alloy steels are up to 650°C
(1,200°F).
3.4.7.2 Solid Residence Time
The complexities of contaminated solids require that laboratory and pilot-
scale treatability studies be conducted to determine not only the required tem-
perature, but also the length of time for which the solid must be maintained at
this temperature.
Troxler and coworkers (1992) report that residence times of petroleum-
contaminated soils, in directly-fired thermal desorption devices are usually less
than 10 minutes. The residence time of semivolatile organic compounds
(SVOCs), can be as long as 20-30 minutes.
The solid residence time may be controlled by adjusting the rotation rate and
angle of inclination of the desorber and varying feed rate, although the angle of
3.23
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Process Identification and Description
inclination is usually fixed by the vendor. Residence time of the solid material
in minutes is:
0.19L,
t = :-L-
(rpm)(D)(S)
where:
LT is length of the kiln in meters
rpm is revolutions per minute
D is the ID in meters
S is the slope in m/m
3.4.7.3 Solid Particle Size Distribution
When clay and silt-type soils are treated, "dusting" may increase; that is,
particles may become entrained in the gas phase and be carried over to the gas-
treating equipment. This is of particular concern because these particles may
not be fully decontaminated. Entrainment of particles will also increase the
pressure drop through the gas-treatment system which includes a baghouse, and
thus increase the power required by the induced draft fan.
The characteristics of the solid can affect also the amount of contaminant
that is adsorbed on the solid. For example, smaller particles have greater sur-
face area on which contaminants can adsorb. In addition, some organic com-
pounds adsorb preferentially to solids with high organic contents.
When soil is being decontaminated as part of an asphalt production process,
the particle size distribution is very important, because this distribution greatly
affects the characteristics of the asphalt. In general, silts and clays are not suit-
able for mixing with asphalt. The high surface area of these particles degrades
the quality of the asphalt (Troxler et al. 1992). Usually materials in the asphalt
product must be less than 6% by weight of 74 ^.m (200 mesh). Soils with a
high organic content (peat) are also unsuitable for asphalt (US EPA 1992f).
3.4.7.4 Contaminant Characterization
Since direct-fired thermal desorbers are operated with excess air, the concen-
tration of contaminants must be sufficiently low to the point that 25% of the
LEL in the unit is not exceeded. Combustible gas monitors are recommended
3.24
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Chapter 3
for monitoring the desorber gases. Blending of solids may be required to stay
below the LEL.
The type of contaminant may dictate the selection of the gas posttreatment
system. For highly regulated wastes, a more detailed characterization of con-
taminants and evaluation of the potential for formation of PICs in the thermal
desorption process may be required.
3.4.7.5 Moisture Content
Energy required to evaporate moisture in the media increases greatly directly
with the amount of moisture. In addition, high moisture levels may cause oper-
ating difficulties. For example, moisture may cause the soil's plasticity limit to
be exceeded, which may in turn cause the soil to stick to surfaces of the dryer
(US EPA 1992g). Moisture may also cause fine particles to form larger clumps
with low surface area-to-volume ratios, making the material more difficult to
heat (Troxler et al. 1992).
3.4.7.6 Gas Flow Rate
Direct-fired thermal desorbers produce the largest volume of offgas per ton
of material of any of the thermal desorbers. This is due to the presence of com-
bustion products from the field used to provide heat for the process. Excessive
flow rates should be avoided in order to allow for the use of smaller APC
equipment and to minimize dust problems.
3.4.7.7 Desorber Rotational Speed
Solids residence time and the degree of mixing effected are directly related
to the rotational speed of the rotary drum. Both of these may affect heat and
mass transfer within the desorber. Increased rotational speed may increase
paniculate entrainment.
3.4.8 Process Variations per Vendors
Since direct-fired rotary desorbers are based upon existing rotary dryer tech-
nology, many units on the market have common characteristics. Although
some systems have unique features, all have the main components discussed
here: pretreatment system, desorption system, and posttreatment systems for
both the solid and the gases. Uniformity in design is particularly evident in the
asphalt aggregate dryers used to treat petroleum-contaminated soils.
3.25
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Process Identification and Description
As explained in Subsection 3.4.7, however, variations in design are needed
to accommodate different solid/contaminant matrices and to meet varying regu-
latory requirements. Many vendors offer a variety of designs to suit specific
applications. The common design variations and their applications are summa-
rized below.
3.4.8.1 Stationary vs. Mobile Units
Both stationary and mobile units are currently in use. A number of both
mobile and stationary facilities are available for treating petroleum-contami-
nated soils; however, all thermal desorption systems that are currently treating
CERCLA wastes are mobile.
3.4.8.2 Secondary Oxidizer
Many asphalt plant aggregate dryers converted to treat petroleum-contami-
nated soils do not have afterburners or other oxidizer systems. Although this
apparently has been common practice in treating petroleum-contaminated soils,
some state regulatory agencies are beginning to disallow this practice (US EPA
1992g). Alternatives to conventional afterburners include catalytic oxidizers
and activated carbon adsorption units. Use of these alternatives has been lim-
ited.
The location of the secondary oxidizer where used, typically depends on
whether the desorber is operating in a cocurrent or countercurrent mode. For
cocurrent operation, the secondary oxidizer is usually located upstream from
the baghouse. This arrangement allows the treatment of heavier organic com-
pounds. For countercurrent operation, the secondary oxidizer is located down-
stream from the baghouse, and heavier hydrocarbons are not usually treated
with this arrangement.
3.4.8.3 Use of Carbon Adsorption
Carbon adsorption filters have been used to treat the offgases prior to dis-
charge. This design does not require an afterburner or other secondary oxidizer.
The adsorption bed must be periodically regenerated. If the carbon becomes
contaminated with PCBs, it may have to be sent off site for incineration at a
Toxic Substance Control Act (TSCA)-permitted facility.
3.26
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Chapter 3
3.5 Rotary Desorber—Indirect Fired
3.5.1 Description
The indirect-fired rotary desorber consists of three subsystems, discussed in
Subsection 3.4.1: pretreatment and material handling, the desorption unit, and
posttreatment, including offgas treatment and treated solid handling. Figure 3.7
illustrates a typical indirect-fired rotary system with possible variations.
3.5.1.1 Pretreatment
The pretreatment considerations are basically the same as those for direct-
fired desorbers, discussed in Subsection 3.4.1.1.
Figure 3.7
Components of the Indirect-Fired Rotary Desorber System
Combustion
Products
(Some treatment
1 may be required)
Pretreatment
a. Storage
b Screening
c Blending
d Dewatenng
e Neutralization
f Feeding Systems
r
i
Pre-Treated
Solids ^ 1
1
1_
_ J_ _0ffgases/
Desorption
Unit
~f "
Fuel and
Combustion
/
a. Indirect-fired rotary desorber
a. Discharge Material
Handling
Systems
b Cooling
c. Dust Control
d. Stabilization
3.27
-------
Process Identification and Description
3.5.1.2 Desorber
The desorber unit of indirect-fired rotary systems is different from direct-
heated rotary desorbers in one major way — the combustion gases do not come
in contact with the solid media. The metal rotary shell is heated on the outside
by the combustion of natural gas or propane. The hot shell indirectly heats the
solids tumbling on the inside via conduction through the metal shell. As ex-
plained by Owens et al. (1991), at higher temperatures radiation may control the
heat transfer. Refractory lining is not used because it would impede the heat
transfer to the solids and it is not needed for low temperature operation. A
sweep gas is used to transfer the volatized organics and water to the offgas
treatment system. The thermal desorber is under negative pressure that is in-
duced by a fan downstream of the desorber. Cocurrent flow of the solids and
gases is used, normally with lifters inside the desorber enhancing the solid-gas
contact. Residence time is controlled by varying rotation speed, the angle of
inclination, the lifter design, and the feed rate.
3.5.1.3 Posttreatment
The posttreatment for organics involves one of two general control ap-
proaches: destruction or recovery. The destruction processes are discussed in
Subsection 3.4.1.3, above; they are not normally used with indirect-fired units.
The recovery system uses condensation and refrigeration units, substantially
reducing the volume of gases that must be subsequently treated.
Gases of combustion of auxiliary fuel used to heat the desorber shell do not
usually require treatment through APC systems; however, depending on the
fuel used, NOx and acid gases may need to be treated. The gases do not require
treatment because they do not come in contact with the contaminated medium,
as they are isolated from the offgases containing volatilized organics.
3.5.2 Status of Development
Indirect-fired rotary desorbers were developed from existing materials dry-
ing techniques. Removal of volatile materials from solids by indirect heating is
a well established approach to avoid contamination of the heated material by
the combustion gases or avoid problems with explosive gases. Currently, (Au-
gust 1992), there is one US full-scale design of indirect-heated rotary desorber
and a number of European processes. There are also several pilot plant systems
available for treatability studies and possible scale up (see Section 5.3). There
3.28
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Chapter 3
are considerable amounts of treatability data for both full-scale and pilot-scale
systems. The full-scale US unit has been demonstrated at a CERCLA site.
3.5.3 Pretreotment Requirements
The pretreatment steps consist of storing the excavated material, condition-
ing the material to meet the feed specifications of the rotary dryer, and deliver-
ing the media to the desorber. Most of the requirements are similar to those
discussed in Subsection 3.4.3 and they are not repeated here. Only differences
are addressed.
3.5.3.1 Storage
See Subsection 3.4.3.1.
3.5.3.2 Solid Size Distribution
See Subsection 3.4.3.2.
3.5.3.3 Contaminant Characterization
Acidic wastes must be neutralized before being fed to the system because
indirect desorbers are typically made of mild steel. High levels (>10%) of very
heavy organics, such as tars and polymeric materials, can interfere with the
materials handling systems by plugging and sticking to surfaces.
3.5.3.4 Moisture Content
Typically, less than 40% moisture is desired, 20% is considered ideal, and
5% is too low because of prehandling dusting.
3.5.4 Design Data and Unit Sizing
There are no large variations in the primary unit design of the two full-scale
indirectly-heated rotary desorber systems studied (the US system and one Euro-
pean system). The rotary desorbers are less than =2.4 m (8.0 ft) in diameter and
have heated lengths less than 14 m (45 ft). The systems presently in use are
cocurrent flow units wherein solids and inert material flow in the same direc-
tion. Solids retention time is determined by the desorber volume, rotation
speed, angle of inclination, and lifter design. Thirty to 120 minutes is a typical
range of retention times. Rotation speeds can be as high as 2.5 rev/min. Angle
3.29
-------
Process Identification and Description
of inclination can vary from 1° to 2° downward, moving the solids toward the
exit end of the desorber.
Feed rates vary depending on the waste characteristics and the contaminant
residual levels required. Nominal feed rates for the process vary from 1.3 kg/
sec (5 ton/hr) to 2 kg/sec (8 ton/hr). Where moisture is high, the feed rate is
limited because of heat duty in the desorber.
Propane or natural gas is used to heat the shell via conduction. Full-scale
systems heat the shell using zones of independently fired burners to control the
rate of volatilization. Energy studies performed on soil containing 14% mois-
ture found that 60% of the total heat fired was exhausted to the atmosphere and
the remaining 40% was transferred through the shell to heat the solid material.
Of the heat transferred through the shell, 60% was used in evaporating water,
0.8% in volatilizing organics and almost 40% in heating the solids (Lehmann
1991).
3.5.4.1 Gas Flows
Full-scale systems operate with the rotary desorber under negative pressure
to ensure no leakage or fugitive emissions. The European system has a high
gas-flow rate (6,000 to 10,000 normal m3/hr (200,000 to 350,000 normal ftVhr))
because the offgases flow to a destructive, that is, afterburner APC device
(Schneider and Beckstrom 1990). The US system has a very low flow rate
because a recovery APC system is used. In this system, a nitrogen blanket
reduces the necessity of maintaining the organic vapor concentration below the
LEL by keeping the oxygen concentration below 4%. Since the majority of the
nitrogen is recycled, only 5 to 10% of the carrier gas is vented to the atmo-
sphere, at approximately 34 to 85 mYhr (1,200 to 3,000 ftYhr).
3.5.5 Posttreatment Requirements
Posttreatment of both the treated solids and the offgases is required. Re-
quirements are similar to those of the direct-fired system addressed in Subsec-
tion 3.4.5, above; only differences are discussed here.
3.5.5.1 Solid Posttreatment
See Subsection 3.4.5.1
3.30
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Chapter 3
3.5.5.2 Gas Posttreatment
One important difference between direct-fired systems and indirect-fired
systems is the volume of exhaust gases. The indirect-fired system has a much
lower volume of exhaust gases. Harwood (1992) states that the differences
between a low temperature desorber with no combustion products entering the
afterburner (indirect fired) versus a high temperature desorber with combustion
gases entering the afterburner is a factor of 3 to 5 times depending on cocurrent
or countercurrent flow of the gas and solid.
3.5.5.3 Organics Control
There are two types of organics control — afterburners (destruction) and
condenser systems (recovery). There are regulatory advantages, however, in
having a recovery system. Regulations under the RCRA generally do not apply
to recovery systems, unless they have been specifically cited as the ARAR for
the cleanup. Resource Conservation and Recovery Act Regulations usually are
the ARAR for destruction systems. They require that the system be proven to
effect a 99.99% destruction and removal efficiency (DRE) and to emit less than
100 ppm rolling hour average CO.
Afterburner. See Subsection 3.4.5.2
Condenser. The recovery system uses an eductor scrubber, primary and
secondary condensers, and a mist eliminator to recover the organics and water
from the nitrogen gas stream. Most of the nitrogen is reheated and recycled
through the desorber. About 5 to 10% of the nitrogen is bled to the atmosphere.
This purge stream passes through a 2 um filter and two carbon adsorption beds
in series. This system employs a high-energy scrubber, using direct contact
with water, to cool the gas to its saturation temperature. Particulates and an
estimated 30% of the organics and considerable water are removed from the
nitrogen stream by this device. The primary condenser is air cooled and re-
duces the nitrogen stream temperature to about 5°C (10°F) over ambient tem-
perature, producing the bulk of the liquid condensate. Refrigeration in the sec-
ond condenser reduces the nitrogen stream temperature to about 4.5 °C (40°F).
3.5.5.4 Acid Gas and Particulate Control
Acid gas removal does not present a problem when a recovery system is
used because of the low-production levels of the process. When a destruction
system is used for organic control, however, depending on the fuel used and on
3.31
-------
Process Identification and Description
the fuel used for the combustion offgas from the desorber, some consideration
of acid gas removal might be in order. Paniculate removal in the recovery
system is effected by a cyclone and/or scrubber.
3.5.5.5 Liquids Posttreatment
A considerable quantity of liquids can be recovered by the recovery treat-
ment system. For example, water will be recovered at the rate of about 0.3kg/
sec (1 ton/hr) from material that is 20% moisture and is fed at 1.3 kg/sec (5 ton/
hr). This water must be treated. The condensed organics and water are physi-
cally separated. After carbon treatment, the water is used to wet the solids, and
the organics are shipped off for incineration or to recycling facilities. Solids in
the organic phase can be a problem. Flocculation and filtration can be used to
separate the organic from the solid phases. The scrubber blowdown from the
recovery system is filtered and the filtered water is returned to the scrubber.
The dewatered solids are reprocessed through the desorber.
3.5.6 Special Health and Safety Considerations
Indirect-fired rotary desorbers present no special health and safety consider-
ations. The condenser systems pose the same kind of concern as may any other
system that generates a concentrated, hazardous liquid. These materials must
be handled as any other hazardous or toxic substance. The unit must be kept
rotating at all times to avoid hot spots and resulting equipment failure.
3.5.7 Operational Requirements and Considerations
Many of the operational requirements and considerations appertaining to the
indirect-fired rotary desorber are similar to those of the direct-fired rotary
desorber, discussed in Subsection 3.4.7; only differences are discussed below.
3.5.7.1 Temperature Requirements and Limitations
See Subsection 3.4.7.1. The mild steel used in the construction of the
present systems will limit the operating temperatures of the units to 315°C
(600°F).
3.5.7.2 Solid Particle Residence Time
See Subsection 3.4.7.2.
3.32
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Chapter 3
3.5.7.3 Solid Size Distribution
See Subsection 3.4.7.3.
3.5.7.4 Contaminant Characterization
See Subsection 3.4.7.4.
3.5.7.5 Moisture
See Subsection 3.4.7.5. High moisture levels (>40%) require more fuel and
larger residual liquid handling systems (recovery approach) and present addi-
tional materials handling problems. In addition, processing rates are lowered.
3.5.8 Process Variations per Vendors
The primary variation is in the treatment of the off gases: destruction versus
recovery. The condenser/recovery system is usually transportable on about 10
trailers. The destruction system is a stationary facility. These offgas treatment
systems are described in Subsection 3.5.5.2.
3.6 Heated Conveyors— Indirect and
Direct
3.6.1 Description
Conveyors used in thermal desorption applications consist of screw convey-
ors, paddle or mixing conveyors, and belt conveyors. Direct or indirect heat is
applied to the contaminated media while it is transported or moved in a process
conveyor. See figures 3.8(a) (on page 3.34) and 3.8(b) (on page 3.35).
In direct-heated conveyor systems, heat is transferred from a source in direct
contact with the material being treated. Sources of heat consist of electric resis-
tance heaters imbedded in the conveyor or a source located in the open space
above the contaminated media in the conveyor (fuel combustion or radiant
heaters). When electric heating is used, offgases generated during processing
are greatly reduced.
3.33
-------
Process Identification and Description
Figure 3.8(a)
Components of a Direct-Heated Conveyor System
a. Storage
b. Screening
c Blending
d. Dewatermg
e Neutralization
f Feeding Systems
a Discharge Material
Handling
Systems
b Cooling
c Dust Control
d Stabilization
In indirect-heated conveyor systems, the heat is generated outside of the
main process desorber in a separate, secondary process unit and is conducted by
a media in contact with the desorber conveyor. The source of heat can be the
combustion of a common fuel or waste process heat from another process sys-
tem. Indirect systems employ various media to transfer the heat to the con-
veyor: steam, special heat transfer fluids (e.g., Dowtherm or Therminol), and
eutectic salts. Indirect processes minimize the volume of offgases generated by
the thermal desorption system.
3.6.2 Status of Development
Heated conveyors technology is based upon techniques used in mineral
processing industries and in bulk solid chemical processing. Many vendors
offer services and equipment using heated conveyors. The systems are in vari-
ous stages of development depending on the specific conveyor and heating
3.34
-------
Chapter 3
Figure 3.8(b)
Components of an Indirect-Heated Conveyor System
Offgas
a Participate Removal
b. Organic Treatment
c. Acid Gas Treatment,
if necessary
Decontaminated Solid
a.
b.
d.
e.
f.
Storage A 1 \
Screening ^~ W \
Blending * \^
Dewatenng ^^
Neutralization Heating
Feeding Systems System
Soil
Posttreatment
a. Discharge Matenal
Handling
Systems
b Cooling
c. Dust Control
d Stabilization
method. Heated conveyors have been used on a full-scale basis to treat petro-
leum-contaminated soils, sludge from CERCLA sites, and RCRA-regulated
hazardous waste. Bench- and pilot-scale units are available to provide demon-
stration of the full-scale systems. See also table 3.2 (on page 3.36).
3.6.3 Pretreotment Requirements
The pretreatment steps for conveyor desorbers are the storage of the con-
taminated material, conditioning of the solid to meet the specifications of the
desorber conveyor, and delivering the solid to the desorber. Most of the pre-
treatment requirements are similar to those discussed in Subsection 3.4.3 and
are not repeated here. Differences only are addressed.
3.35
-------
Process Identification and Description
Table 3.2
Summary of the Status of Heated Conveyor Systems, August, 1992
Conveyor
Type
Direct-heated system
Heat Source
Fuel Radiant*
Combust Heating
Resistance
Heating
Indirect-heated system
Heating Media
Steam Hot
Oil
Salts
Screw - Full scale
Belt Full scale Full scale
Paddle
Full scale
Full scale Full scale Full scale
Pilot scale Pilot scale
' Both electric and fuel combustion
3.6.3.1 Storage
See Subsection 3.4.3.1.
3.6.3.2 Solid Particle Size Distribution
In general, it is recommended that particle size be limited to a maximum of 5
to 7.6 cm (2 to 3 in.). But the maximum size of particles that can be treated by
a heated conveyor varies with the type of conveyor. For screw conveyors,
maximum particle diameters are based upon the screw diameter and size distri-
bution of the particles. See table 3.3 (on page 3.37). Similar limitations apper-
tain to disc or paddle-type conveyors. Belt-type conveyors, are limited to treat-
ing the minimum size of particle required to prevent excessive sieving through
the belt. Pretreatment steps to reduce particle size include screening, crushing,
and shredding.
3.6.3.3 Contaminant Characterization
See Subsection 3.4.3.3
3.6.3.4 Moisture Content
See Subsection 3.4.3.4
3.36
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Chapter 3
Table 3.3
Screw Conveyor Size Versus Maximum Particle Size
Conveyor Size
(inches)
4
6
9
10
12
14
16
18
20
24
Maximum Size (inches)
25% of Lumps
0.5
0.75
1 5
1.5
20
2.5
30
30
3.5
4.0
Note: Lumps are materials such as rocks, non-fire material
Excerpt from Materials Handling Handbook, edited by R A Kulwiec, John Wiley & Sons, Publisher Copyright
1985 by John Wiley & Sons, Inc By permission
3.6.4 Design Data and Unit Sizing
The design and sizing of a heated conveyor thermal desorber is keyed to the
basic design parameters for treatment systems which have been discussed pre-
viously, namely:
• discharge temperature of the solid;
• retention time (maximum of 90 minutes); and
• sweep gas requirements.
The discharge temperature is a critical parameter in the selection and appli-
cation of a heated conveyor. A conveyor's physical construction should be such
that it can operate at the required maximum temperature plus a safety factor for
over-temperature excursions. Indirect-heated conveyors should be designed to
accommodate the maximum temperature of the conducting media. Typical
maximum solid discharge temperatures are (Troxler, et al. 1992):
• Hot oil 150-260°C(300-500°F)
• Molten salt 315-480°C (600-900°F)
• Steam-heated 120-180°C (250-350T)
3.37
-------
Process Identification and Description
The retention time of the conveyor system is determined by the volumetric
feed rate of the media and the system's conveying velocity. The retention time
of belt conveyor systems, is based upon bed depth because of volatilization
limitations and belt speed. Throughput of screw conveyors can be varied with
rotational speed, diameter, and flight pitch.
Direct-heated systems generate a greater volume of sweep gas than do indi-
rect-heated systems. By maintaining low-sweep gas velocities, high dust gen-
eration and entrainment of particulate from the conveyor can be avoided.
Sizing of a heated conveyor is dependent upon heat transfer calculations,
factoring in the overall heat-transfer coefficient from the heat source to the
media, which are used to determine discharge temperature. Balancing of oper-
ating temperatures, retention times, and conveyor size depends upon the type of
conveyor and the heating method. The selection of these parameters is left to
the treatment services supplier.
3.6.5 Posttreatment Requirements
Posttreatment of both the treated solid and the offgases is required. Similari-
ties exist between this system and the systems discussed previously. Differ-
ences only are discussed below. Where direct-heated systems are used, the
gases will include the products of combustion of the fuel source. Indirect-
heated systems and electrically heated conveyor systems are sometimes pre-
ferred, since they generate a smaller quantity of offgas requiring posttreatment
than do other direct-heated systems.
3.6.5.1 Solid Posttreatment
See Subsection 3.4.5.1
3.6.5.2 Gas Posttreatment
The control of emissions of organics from heated conveyor systems will
typically be through either thermal destruction in an afterburner or collection of
the organics by condensation followed by activated carbon treatment. These
methods are discussed in Subsection 3.4.5.2. Particulate removal and liquid
posttreatment are discussed in Subsections 3.4.5.2 and 3.4.5.3.
3.38
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Chapter 3
3.6.6 Special Health and Safety Considerations
The heated conveyor systems must be designed to minimize fugitive emis-
sions, which can contain elevated concentrations of toxic gases and chemicals.
Conveyors must have adequate safety mechanisms to prevent inadvertent op-
eration during maintenance.
Special attention to containment of the heating media in indirect-heated
systems is required to avoid fires and personnel injury. Adequate control of
pressure is required where heated media, such as steam and other heat-transfer
fluids, are circulated at elevated pressure. Where electrically heated fluids are
employed, special attention to high voltage electrical safety precautions is re-
quired.
3.6.7 Operational Requirements and Considerations
Operational requirements and considerations are similar to those of direct-
and indirect-fired rotary desorbers, discussed in Subsections 3.4.7 and 3.5.7.
Systems using electrical resistance heaters have special hardware requirements,
such as silicon controlled rectifiers (SCR). The maximum solid temperature
will be dependent on the heat transfer media used in the system.
3.6.8 Process Variations per Vendors
A number of units are presently available as explained in Subsection 3.6.2.
The conveyor types include belt, screw, or paddle. In addition, a number of
offgas treatment systems are available.
3.7 SoilTech System3
3.7.1 Description of Process
The SoilTech Anaerobic Thermal Processor (ATP) heats and mixes con-
taminated soils, sludges, and liquids in a special, indirect-heated rotary dryer.
3 . See the monograph in this series Innovative Site Remediation Technology: Chemical
Treatment wherein this process is addressed as a chemical treatment process — Ed.
3.39
-------
Process Identification and Description
The unit desorbs, collects, and recondenses hydrocarbons from solids. See
figure 3.9. The unit can also be used in conjunction with a dehalogenation
system to destroy halogenated hydrocarbons through a combined thermal/
chemical process.
Figure 3.9
Schematic of the SoilTech ATP Process Illustrating
The Four Zone Heating Approach
ATP
PROCESSOR
FLUE GAS
TREATMENT
T
Flue Gas
Vapor to
Condensers
y
Feed
Preheat
Zone
Cooling Zone
Combustion Zone
l
r
Retort
Zone
'//
%
Distilled
Vapors
\ ^-
CONDENSATION,
SEPARATION
Solids to
cooling and
disposal
\uxiliary 4 A Combustion
Fuel I I Air
The dryer portion of the system contains four separate internal thermal
zones: preheat, retort, combustion, and cooling. In the preheat zone, water and
volatile organic compounds (VOCs) are vaporized (temperature, 260°C
(500°F)). The vaporized contaminants and water are removed by vacuum to a
preheat vapor cooling system consisting of a cyclone to remove solids and a
heat exchanger and separator to condense liquids and separate the condensate
from the noncondensable gases. Condensed water is usually treated on site, and
organics usually require off-site treatment.
From the preheat zone, the hot granular solids and unvaporized contaminants
pass through a sand seal to the retort zone (temperature, 510-620°C (950-
3.40
-------
Chapter 3
1,150°F)). Heavy oils vaporize in the retort zone, and thermal cracking of hy-
drocarbons forms coke and low molecular weight organics. The vaporized
contaminants are removed by vacuum to a retort gas handling system. After
cyclones remove dust from the gases, the gases are cooled, and condensed oil is
separated into its various fractions. Organics and water are treated off site and
on site respectively. The coked solid passes through a second sand seal to the
combustion zone, where the coke is burned off the solid and is then either re-
cycled to the retort zone or sent to the cooling zone.
Flue gases from the combustion zone are extensively treated prior to dis-
charge. Treatment is by (1) cyclone and baghouse for particle removal, (2) wet
scrubber for removal of acid gases, and (3) carbon adsorption bed for removal
of trace compounds.
The treated solid that enters the cooling zone is cooled in the annular space
between the outside of the preheat and retort zones and the outer shell of the
kiln. Here, the heat from the solid is transferred to the solid in the preheat and
retort zones. The cooled treated solid is quenched with water and then trans-
ported by conveyor to a storage area.
3.7.2 Status of Development
SoilTech's ATP is a transportable full-scale 3 kg/sec (10 ton/hr) system that
has been used twice to successfully remediate Superfund sites with PCB-con-
taminated soils and sediments. A transportable, pilot-scale system capable of
treating 1.5 kg/sec (5 ton/hr) is available as well as bench-scale treatability
equipment. Design is complete for a 6.5 kg/sec (25 ton/hr) unit, as of early
1993.
3.7.3 Pretreotment Requirements
Feed with less than 20% moisture is ideal for the SoilTech process; however,
less than 5% moisture may cause excessive entrained dust.
Screening to a particle size of less than 5.0 cm (2 in.) is required, and if the
solid is mostly fine grained (clay), some sand must be added to the waste to
maintain seal integrity with the unit.
3,41
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Process Identification and Description
3.7.4 Design Data and Unit Sizing
The full-scale SoilTech system, with a nominal rating of 2.5 kg/sec (10 ton/
hr), can operate up to a 590°C (1,100°F) solid discharge temperature. The pilot-
scale SoilTech system can operate up to 1.5 kg/sec (5 ton/hr) depending on the
solid type and sizing. Both systems are transportable on a series of trailers and
skids.
3.7.5 Posttreotment Requirements
The residuals generated by the systems consist of the treated solids, con-
densed water and organics, and offgases. The treated solids, of course, are
routinely tested, since it is the object of the remediation. All streams must be
handled as described in Subsection 3.4.5.
3.7.6 Special Health and Safety Considerations
In addition to the considerations already discussed, the seals between the
preheat and retort zones in the SoilTech system need to be maintained to pre-
vent oxygen from entering the system and creating an explosion potential.
3.7.7 Operational Requirements and Considerations
After several successful site remediations, the SoilTech system is considered
mechanically reliable and proven effective. Burning of the noncondensable
organics in the combustion zone of the SoilTech ATP may be considered incin-
eration of hazardous waste. The US EPA Regions II and V and state regulatory
agencies (New York and Illinois) permitted operation of the SoilTech system as
a thermal desorber, as of 1992.
3.8 Environmental Impacts
Air emissions from the excavation, handling, and operation of the thermal
desorption system have the potential of impacting the air. The typical on-site
remediation, however, is of short duration (less than one year) and thermal
desorption systems have extensive air pollution control systems. Therefore, the
National Ambient Air Quality Standard (NAAQS) should not be significantly
3.42
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Chapter 3
exceeded. The suggestions and approaches discussed in this section can miti-
gate the short-term, local air impacts.
Excavation of contaminated media for thermal desorption necessarily ex-
poses new material to the atmosphere. Highly volatile contaminants can readily
evaporate into the air, presenting potentially dangerous hazards to workers and
people living near the contaminated site. A wind screen may need to be con-
structed around the excavation area to minimize fugitive emissions, or, in more
severely contaminated sites, foams, water sprays, organic/inorganic control
agents, or portable enclosures may be used to prevent the release of potentially
harmful substances. Real-time air monitoring may be used to protect workers
at the site and to guard against off-site migration.
It is often necessary to store excavated material, and care must be taken to
store it so as to prevent migration of hazardous compounds or objectionable
odors from the work area. Physical enclosures with independent dust/vapor
control or covers can be used to minimize air impacts.
Equipment used in decontaminating material may develop leaks over time.
Every effort must be made to promptly repair leaks and to contain all spills.
Wastewater from low temperature thermal desorption units must be treated and
tested before being discharged into Publicly-Owned Treatment Plants (POTW)
or navigable waterways.
The transfer and handling of residuals can also present difficulties. Treated
material exiting the desorber may need to be cooled before transport to its final
disposal area. Since the residual matter from the desorption unit must be tested
before final disposal, and analyses can take up to several days to complete,
treated material may require temporary storage. Dusting can be a problem if
the treated material is stored in an open area. Rainwater runoff from ash piles
of treated solids can also present problems. Treated material awaiting fixation
before final disposal may leach potentially hazardous compounds when it
comes into contact with rainwater.
One of the most common complaints from persons residing or working near
a remediation site is about the noise. Earth-moving equipment is equipped with
warning beepers that sound whenever the machine is backing up. Other noise
from large motors or fans may also be bothersome, and noise abatement steps
may be necessary.
3.43
-------
Process Identification and Description
3.9 Costs
Low-temperature thermal desorption of a site contaminated with CERCLA
regulated waste is typically conducted by contractors who operate equipment as
an on-site service. Contractors provide operating labor and equipment as well
as the ancillary services, such as material excavation and waste disposal. Both
on- and off-site treatment services are available for treating petroleum-contami-
nated soils.
3.9.1 Fixed Cost Elements
Fixed costs for operations at a remediation project consist of:
• Planning and Permitting —
Project team;
Training;
Regulatory permit applications;
Health and safety plans;
Performance testing;
• Mobilization —
Site preparation;
Installation of utilities;
Transportation to site;
Excavation, blending, and feed storage pad;
Containment;
Storm water control;
On-site analytical area;
Land vault; and
• Demobilization —
Decontamination of equipment;
Disconnection of utilities;
Transportation from site; and
Site restoration.
Planning and preparation costs are those involved in obtaining federal, state,
and/or local permits to operate the thermal desorption system. The regulatory
environment of projects can vary widely. The cost of applying for air permits
can range from a few thousand to many hundreds of thousands of dollars.
3.44
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Chapter 3
Projects being conducted on hazardous waste material must comply with the
Occupational Safety and Health Administration (OSHA) regulation
29CFR1910.120, and will require preparation of a proper Health and Safety
Plan. Where site-specific permits are needed and hazardous wastes are being
treated, emissions testing is often required. One of the author's experience has
shown that the cost of emissions testing can range from $15,000, for simple
particulate emissions, to over $500,000, for complete stack analysis, which is
comparable to incineration trial burn requirements.
Mobilization costs are incurred in transporting the thermal desorption system
to the site, assembling it, and connecting utilities. The costs of mobilization
depend on the size of the thermal desorption system, condition of the site, and
location of the system before mobilization. Thermal desorption systems are
highly mobile systems. Many vendors offer systems that can be transported by
a few trucks or only one vehicle. Site conditions greatly affect the cost of mobi-
lization. To adequately estimate cost of mobilization, the location of the site
and nearest utilities and availability of rights-of way must be ascertained.
The costs of excavation vary with the level of personal protective equipment
required (US EPA 1992a). See table 3.4. See US EPA 1992a for several ex-
amples of estimated costs for excavation, including Rocky Mountain Arsenal.
If the soil is to be transported to a fixed facility for posttreatment, these costs
must also be considered. Estimated costs range from $0.08-$0.15 per ton per
mile for petroleum-contaminated soils to $2.00-$4.00 per ton per mile for haz-
ardous wastes (US EPA 1992a).
Table 3.4
Rounded Costs for Excavation Based on Hazard Level
Hazard
No Hazard
Level D
Level C
Level B
Level A
Cost (note, Sl/m 3 = $ 1 30/yd3 )
$22.00 ±$18 80 perm3
$75 00 ± $56.00 per m 3
$90.00 ± $84.00 per m 3
$120.00 ±$86.00 perm3
$130.00 ±$96.00 perm3
(USEPA1992a)
3.45
-------
Process Identification and Description
3.9.2 Unit Cost Elements
The unit costs consist of variable operating costs, semivariable operating
costs, and fixed charges. The variable operating costs include fuel, electric
power, process water, and if necessary, neutralization chemicals, nitrogen, and
residual disposal (McCormick et al. 1985). The variable costs will depend on
the thermal desorption system design and will vary directly with the quantity of
material to be treated. They will vary also with the physical and chemical char-
acteristics of the solid. During the thermal desorption process, the inherent
matrix moisture will evaporate; the process heat consumption will be a function
of the quantity of moisture in the solid. See figure 3.10. Moisture is a critical
parameter in an analyses of desorption costs.
Semivariable costs consist of costs of operating labor, administration, main-
tenance, pre- and posttreatment analyses. They are affected by the thermal
desorption system size, regulatory requirements, and local labor costs.
Figure 3.10
Moisture Effect on Heat Requirement Assuming 7.5 ton/hr Facility
> —
si
"§•3
•3.S
s"o
84 -
82
80
78
76
74*
20 25 30 35 40 45
Moisture Content of Feed (%)
50
55
3.46
-------
Chapter 3
Fixed charges for the operation of a thermal desorption process consist of
annualized capitalized cost for equipment and costs of support facilities, insur-
ance, and taxes.
3.9.3 Cost Comparison
To obtain cost information, a search was made of the Vendor Information
System for Innovative Treatment Technologies (VISITT) program (US EPA
1992h). The factors that were listed as important in price consideration in-
cluded moisture (see Subsection 3.9.2), initial concentration and type of con-
taminant (for example, gasoline, PCBs), contaminant concentration, and the
quantity of material to be remediated. The search price range for full-scale
systems was $25-$ 1,000 per ton. These values cited in the literature, are quite
different from others probably because of the broad range of applications that
are considered.
Because of the large variation in cost and little knowledge of the cost effect
of moisture, site size, etc., vendors were surveyed for budgetary costs of ex-
ample thermal desorption projects. The example project sites were divided into
two classes, petroleum-contaminated sites and CERCLA or Superfund sites.
Both sets of sites had 20% moisture, and the petroleum-contaminanted sites
contained 1,000 ppm of total petroleum hydrocarbons contamination, while the
Superfund sites had 1,000 ppm of chlorinated VOCs. The vendors were asked
to provide costs for 1,000 ton, 10,000 ton, and 100,000 ton sites. The response
to the survey was limited and only mobile vendors replied; therefore, the full
results are not presented here. The results did show, however, that the size of
the site is extremely important. The costs at larger sites are less affected by the
initial mobilization and fixed costs, since these costs are distributed over a
larger volume of process material. The greater efficiency of larger equipment
also helps reduce the unit costs for large sites. In addition, as expected,
remediation of petroleum-contaminated sites is less costly than remediation of
the Superfund sites.
The four vendors who replied offer different types of thermal desorption
equipment. In general, fixed costs were broken down for the Superfund site as
follows:
• Mobilization 35-50%
• Demobilization 20-35%
3.47
-------
Process Identification and Description
• Plans and Permits 15-40%
(dependent on site size)
• Other 0-10%
The unit costs were (% of unit cost, $/ton):
• Fuel 2-20%
• Other utilities 2-10%
• Residual disposal 1-10%
• Operating labor 10-50%
(decreasing with increasing size)
• Supervision laboratory 3-10%
• Pre-and posttreatment analyses 5-10%
• Capital equipment 15-30%
• Insurance taxes 2-10%
• Other 5-30%
See US EPA 1992g as an excellent and detailed source for cost estimates for
petroleum-contaminated soils.
Costs of operating the SoilTech system were provided by Hutton and Shanks
(1993). Fixed costs were $500,000, $1.5 million, and $3.5 million for the three
units offered by SoilTech, 1.3 kg/sec (5 ton/hr), 2.5 kg/sec (10 ton/hr), and 6.5
Table 3.5
Cost Data From the Literature
Size of Waste Site
(Tons)
1,000
10,000
100,000
All
Application Petroleum-Contaminated Soil
($/Ton)
Mobile/Transportable
Mobile/Transportable
Mobile/Transportable
Stationary
$90-130
$40-70
$35-50
$35-75
Hazardous
($/Ton)
$300-600
$200-$30()
$150-200
Not available
Costs represent total turnkey bid prices.
Sources of Data Cudahy and Troxler 1992, Troxler et al 1992
3.48
-------
Chapter 3
kg/sec (25 ton/hr). Respectively, the unit costs were $300, $200, and $100 per
ton. Moisture, particle size, hydrocarbon content, material handling characteris-
tics, and chemical characteristics all affected the costs of remediation. The
quoted costs did not include the disposal of generated organic liquid, which in
this case contained PCBs.
Costs of operating heated conveyers ranged from $100 to $150 per ton not
including excavation, permits, and residual treatment (US EPA, 1992h).
See also table 3.5 (on page 3.48). Again, the size of the site and type of
containment are quite important. Troxler et al. (1992) includes data for several
different types of desorbers remediating a 20% moisture, silty soil contaminated
with 0.3% no. 2 fuel oil. See table 3.6 for excerpts of these data; costs include
both operating and fixed costs. Excavation costs, remedial investigation (RI),
and project management costs are not included.
Cost information is also provided in some of the case studies presented in
Chapter 5.0.
Table 3.6
Costs for Petroleum-Contaminated Soil as a Function of Desorber
Type and Site Size
Size
(tons)
2,000
6,000
10,000
Large Mobile
Rotary Drum
(40 MM Btu/hr)
110
60
50
Cost ($/ton)
Small Mobile
Rotary Drum
(10 MM Btu/hr)
70
60
55
Mobile Thermal
Screw
(12 MM Btu/hr)
80
60
55
Source Troxler et al 1992
3.49
-------
-------
Chapter 4
POTENTIAL APPLICATIONS
Thermal desorption has been widely used in treating petroleum-contami-
nated wastes and is finding increasing use in remediation of Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) sites.
The United States Environmental Protection Agency (US EPA 1992e) states
that treatment of volatile organic compounds (VOCs) by thermal desorption is
ongoing, planned, or completed at 19 sites, embracing 8 polychlorinated biphe-
nyls (PCBs), 5 semivolatile organic compounds (SVOCs), and 3 pesticides.
See table 4.1 (on page 4.2) for the status of thermal desorption projects. Chap-
ter 5.0 presents case studies that also demonstrate the applicability of thermal
desorption. See also the draft US EPA Engineering Bulletin: Thermal Desorp-
tion Technologies, appended as Appendix B (US EPA 1993).
4.1 Determining Applicability— Treatability
Testing
The highly variable nature of contaminated material often makes it difficult
to determine whether thermal desorption will be effective. Treatability testing
of contaminated materials is done to establish process viability and establish
design and operating parameters for the optimization of the selected technol-
ogy. Treatability testing should be conducted as early as possible during the
remedial investigation feasibility studies (RI/FS) in order to evaluate the tech-
nology and provide a sound basis for the Record of Decision (ROD).
Treatability testing must be carefully planned and executed in order to en-
sure that sufficient data are generated for use in evaluating the performance (US
EPA 1992d). It is typically divided into three phases: (1) remedy screening,
(2) remedy selection, and (3) remedy design. Details are given in US EPA
1992d.
4.1
-------
Potential Applications
Table 4.1
Status of Thermal Desorption, April 1992
Region
Project
Status
Key Contaminants
2
2
2
2
2
2
2
2
2
2
3
3
4
4
4
4
4
5
5
5
5
5
8
Cannon Engineering, Mass
Re-solve, Mass
McKm, Maine
Union Chemical Co., Maine
Ottati and Goss, N H
Caldwell Trucking, N.J
Metal tech/Aerosystems, N.J
Reich Farms, N.J.
Waldick Aerospace Devices, N.J.
American Thermostat, N Y.
Claremont Polychemical, N.Y
Fulton Terminals, N Y
Sarney Farm, N Y.
Solvent Savers, N.Y.
GE Wiring Devices, P R
U.S.A. Letterkenny, Pa.
Saunders Supply Co , Va
CIBA-GEIGY (Macintosh), Ala
Aberdeen Pesticide Dumps, N C
Sangamo/Twelve Mile/Harwell,
S.C
Wamchem, S C
Arlington Blending & Packaging
Co. Tenn
Acme Solvent Reclaiming, 111
Waukegan Harbor, 111
Anderson Development, Mich.
Carter Industries, Mich
Umv of Minnesota, Minn
Martin Marietta, Colo.
Completed
Predesign
Completed
In design
Completed
In design
Design Complete/Installation not begun
In design
Design Complete/Installation not begun
In design
In design
In design
In design
Predesign
In design
Predesign
Predesign
Predesign
Predesign
Predesign
In design
Predesign
Predesign
Operational
Operational
Predesign
In design
Predesign
VOCs
PCBs
VOCs
VOCs
VOCs
VOCs
VOCs
VOCs, SVOCs
VOCs
VOCs
VOCs
VOCs
VOCs, SVOCs
VOCs, PCBs
Metals
VOCs
SVOCs, Metals
(As)
Pesticides
Pesticides
VOCs, PCBs
VOCs
VOCs, SVOCs.
Pesticides,
Metals
VOCs, SVOCs,
PCBs
PCBs
Orgamcs
PCBs
PCBs
PCBs(As)
(US EPA 1992e)
4.1.1 Remedy Screening
The purpose of remedy screening is to determine whether thermal desorption
will remove the contaminants of interest. Samples used in testing should be
representative of site conditions for the range of concentrations of contami-
nants. If solids are expected to be blended in full-scale operation, blending
should be done before testing. If solids will not be blended, and the character of
the material changes drastically from location to location or at various depths,
multiple test runs should be conducted to assure that samples from areas of both
high- and low-contaminant concentration are tested and that the contaminants
are reliably removed from the media.
4.2
-------
Chapter 4
The particle size distribution of the solids being tested should be consistent
with the particle size distribution that will be treated on a full scale.
A test is normally conducted in order to make a rough determination of tech-
nical feasibility for low-temperature thermal desorption. In the test, care should
be taken to minimize the temperature and concentration gradients so that the
solid is at a constant temperature and mass transfer of contaminants to the sur-
face is not limited.
Thermocouples must be used so that the true solid temperature can be re-
corded. Time-at-temperature data should be recorded, and concentrations of the
target contaminants should be measured in the solid both before and after the
tests. If a number of contaminants are present, the least volatile contaminant
should be monitored. Several test runs should be done to assure that the data
are reproducible. The primary criterion used to evaluate a test is the degree to
which the target compounds have been desorbed from the contaminated media.
If the tests indicate that thermal desorption may be effective in cleaning the
media, then further testing should be done to define the operating characteristics
of the thermal desorption device.
4.1.2 Remedy Selection
The primary objective of the remedy selection phase is to determine which
system will best serve the needs of the job at hand. Materials handling con-
straints or other constraints may dictate which system should be used. If so,
one would proceed directly to the remedy design testing phase.
Remedy selection should be systematic. The work done must satisfy both
the site owner and the regulatory agencies. A significant amount of attention
must be directed toward establishing data quality objectives and implementing
appropriate quality assurance/quality control (QA/QC) programs in data collec-
tion and analysis.
Systems typically tested in the remedy selection phase of treatability work
include the following:
• rotary desorber — direct or indirect;
• conveyor;
• other technologies; and
• offgas treatment system.
4.3
-------
Potential Applications
Many equipment vendors, as well as independent outside testing companies,
have bench- and pilot-scale thermal desorption units that can be used in
treatability testing. Once a particular device (e.g., rotary desorber) has been
selected, remedy design testing should begin.
4.1.3 Remedy Design
The main objective of the remedy design phase of treatability testing is to
obtain all information necessary to ensure the success of the full-scale treatment
unit. Target treatment levels must be established for all compounds of interest
and all applicable, relevant, and appropriate regulations (ARARs) must be iden-
tified for the specific site before testing so that complete criteria for evaluation
can be developed.
Criteria for process evaluation should include not only the cleanup standard
for the media requiring remediation, but also the requirements of all federal,
state, and local regulations that are expected to apply to any liquid, gaseous, or
fugitive emissions from the unit.
In general, sufficient testing should be done to develop and confirm a heat
and material balance around the unit. Concentrations of all contaminants of
regulatory concern should be measured in the feed material. All streams exiting
the desorber should be characterized and analyzed for not only the target com-
pounds of interest, but also for potential intermediates and compounds of regu-
latory concern, such as dioxins, furans, acid gases, carbon monoxide, heavy
metals, and polynuclear aromatic hydrocarbons (PAHs).
Paniculate matter exiting the unit should be characterized both in terms of
loading and particle size distribution. Gases leaving the unit should be analyzed
to determine the content and concentration of compounds that must be removed
before discharge into the atmosphere. Any condensed liquids from the offgas
treatment system should be analyzed for target and other potentially hazardous
intermediate compounds.
Treated solid residue should be analyzed for target compounds and should
undergo any necessary further physical and chemical testing to ensure that it
can be disposed of appropriately. Baghouse dust or other fines from the unit
must be similarly analyzed. To aid in the identification of any problems that
might arise in the processing of the contaminated media with respect to the
quality of the treated material, these streams should be analyzed separately,
even if they will be combined in the full-scale unit.
4.4
-------
Chapter 4
If carbon adsorption is to be used to treat the offgas, a complete mass bal-
ance should be done around the carbon adsorption unit. The issue of disposal
or regeneration of the carbon should be addressed during the treatability testing
phase to preclude problems in the disposal, regeneration, and usage of activated
carbon.
4.2 Quality of Residuals
All thermal desorption units create a number of residual streams that must be
properly managed. Both destruction and recovery offgas APC systems create
residual streams, such as particulate, scrubber water, condensed water, con-
densed organic liquids, and stack gases, discussed in Subsections 3.4.5, 3.5.5,
and 3.6.5. These residuals can be divided into three types: solids, liquids, and
gases.
4.2.1 Solid Residuals
Solid residuals include the treated solids, particulate from the scrubbers,
baghouse and micron filters, and used carbon from both gas- and aqueous-
phase carbon adsorption beds. Treated solids must meet the cleanup require-
ments set by the regulatory agencies, but the material may also need wetting
and stabilization before disposal. Posttreatment use of the material is a consid-
eration in determining the need for further treatment. Chapter 5.0 discusses in
detail the soil residual levels of various contaminants that have been effected by
thermal desorption.
The chemical constituents of the particulate collected in the scrubber,
baghouse, and micron filter will determine the fate of the residual. Residuals
may frequently be considered a hazardous waste requiring further treatment or
regulated disposal. With proper collection or destruction of contaminants in the
offgas, used gas-phase carbon can be regenerated on site. But generally, it is
shipped off site for regeneration, as is the aqueous-phase carbon.
4.2.2 Liquid Residuals
Liquid residuals from thermal desorption include the scrubber waters, con-
densed water, and condensed organics. When the destruction approach to air
4.5
-------
Potential Applications
pollution control (APC) is employed, the scrubber waters will have paniculate,
neutralized salts, and possibly organic constituents. Particulates should be
handled as explained immediately above.
When the recovery approach to APC is employed, the condensed water is
separated from the condensed organics by a phase separator. The liquid organ-
ics must be shipped to an incinerator or recycling facility. Aqueous liquids
from the phase separator usually contain some level of organics (0.01 to 10
ppm) that must be removed. Following treatment, discharge to an on-site water
treatment plant or the local municipal waste treatment plant is possible. In most
cases, the thermal desorption vendors treat the recovered water and then use it
to wet the treated solids.
4.2.3 Gaseous Residuals
Depending on the type of system used, there are a number of possible gas
streams that require further treatment, including:
• purge gas ladened with organics; and
• combustion gas that has been used as purge gas (direct-fired units).
The purge gas and combustion gas that has been used as a purge gas are
major emission sources requiring employment of extensive APC systems.
These systems are discussed in detail in Chapter 3.0. If any organics are stored
in tanks, the tanks should be vented to an appropriate APC system.
4.6
-------
Chapter 5
PROCESS EVALUATION
When considering application of a technology, it is instructive to review past
experiences. To this end, this Chapter presents case studies of operations of
full-scale systems and reports of operations of pilot- and bench-scale systems.
5.7 Full-Scale Systems
There is growing literature concerning the operation of full-scale desorbers,
both open and through vendors. The detail and completeness of data provided,
however, varies considerably among sources. In reviewing the literature, infor-
mation should be sought in the following areas: site description and specifica-
tions, contaminant types, process performance, process by-products, cost, and
operational considerations.
See table 5.1 (on page 5.2) listing case studies of direct-fired rotary desorber
operations. In addition, the following subsections present case studies of opera-
tions of direct-fired and other systems upon sites for which relatively complete
information is available.
5.1.1 McKin Site (Gray, Me.) — Direct-Fired Desorber
The McKin site had previously been used as a liquid waste storage treatment
and disposal facility. As a result of these operations, soil at this site was con-
taminated with volatile organic compounds (VOCs) and heavy oils (Bell and
Giese 1991; US EPA 1991a, 1992e; Canonic Environmental Services, Corp.
1991). A drinking water aquifer had also become contaminated. The soil was
contaminated with trichloroethene (TCE), tetrachloroethene (PCE), and 1,1,1
trichloroethane (TCA). The contaminant concentrations were >3,000 ppm for
TCE, >120 ppm for PCE, and >19 ppm for TCA.
5.1
-------
Process Evaluation
Table 5.1
Direct-Fired Thermal Desorber Case Studies
Available Information as of August 1992.
Source/Reference
Site Contam -
Descnp- inant
tion Type
Perfor-
mance
By-
products Cost
Opera-
tional
Consid- Number
erations of Cases
USEPA 199 Ib No
Operator — Weston Services,
Inc.
USEPA 1991b No
Operator — Canonic
Environmental Services, Corp.
Canome 1991 Yes
Marketing Literature
Bell and Giese 1991 Yes
Operator — Canome
Environmental Services, Corp.
Soil Purification Inc 1991 No
Marketing Literature
USEPA 1992h Limited
Operator — Soil Purification
Inc
Halliburton NUS No
Environmental Corp 1991
Marketing Literature
California Dept. of Health Yes
Services 1990a
Operator — Earth Purification
Engr. Inc.
Yes Yes No
Yes Yes No
Yes, Limited No
Yes Yes No
Yes Yes No
Yes Yes No
Yes Yes No
Yes Yes Yes
No No 1
No No
Yes Limned 4
No No
No No
10
No No 10
Yes No
Fuel Yes
USEPA 1992g
Operators — Various
USEPA 1992h
Operators — Various
No
No
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
25
5
Over 8,800 m3 (11,500 yd3) of soil was excavated and treated using Canonie
Environmental Services Corporation's Low Temperature Thermal Aeration
(LTTA) process. The principal components of this process are a feed system, a
direct-fired desorber, a pugmill, cyclonic separators, a baghouse, a venturi
scrubber, and a carbon filter system. The soil was treated in a continuous op-
eration with a soil retention time of 6 to 8 min. During processing, the soil was
heated to approximately 150°C (300°F).
5.2
-------
Chapter 5
The treated soil contained VOC concentrations of less than 0.04 ppm (0.04
for TCE, 0.02 for PCE, and 0.02 for TCA) and concentrations of polynuclear
aromatic hydrocarbons (PAHs) below 10 ppm. The treated soil was solidified
and disposed of on site.
During excavation, VOC emissions were controlled so as not to exceed 2
ppmv at the site boundaries. In addition, fugitive dusting was controlled to
remain below 150 mg/m3 at the site boundaries.
The total cost for treatment of this site was $6,500,000.
5.1.2 Ottati and Goss Site (Kingston, N.H.) — Direct-Fired
Desorber
The Ottati and Goss site had previously been used as a facility to treat or-
ganic solvents (Bell and Giese 1991; US EPA 1991b, 1992e; Canonic Environ-
mental Services Corp. 1991). The soil and groundwater at the site were con-
taminated with VOCs and other chemicals. Soils contaminated with polychlori-
nated biphenyl (PCB) levels above 20 ppm were to be incinerated, according to
the Record of Decision (ROD) (US EPA 1987). The original contaminant
concentrations were PCE, 1,200 ppm; TCA, 470 ppm; and TCE, 460 ppm.
Contaminants such as toluene (3,000 ppm) and ethylbenzene (440 ppm) were
also found. Approximately 3,400 m3 (4,500 yd3) of soil were excavated and
treated. The Canonie Environmental Services Corporation LTTA process was
used to treat the contaminated soils at this site. During processing, the soils
were heated to approximately 150 to 200°C (300 to 400°F).
This treatment process reduced the contaminant concentrations to the follow-
ing levels: PCE, TCA, and TCE, <0.025 ppm; toluene, 0.11 ppm; and
ethylbenzene, 0.025 ppm. The cleanup criteria was 1 ppm (US EPA 1987).
The total cost for the treatment of this site was $1,470,000.
5.1.3 Cannon Bridgewater Site (Bridgewater, Mass.) — Direct-
Fired Desorber
The Cannon Bridgewater Site, formerly a chemical waste storage and incin-
eration facility, was remediated using the LTTA system (Bell and Giese 1991;
US EPA 1991b, 1991c, 1992e; Canonie Environmental Services Corp. 1991).
Between 1974 and 1980, this seven-acre site was used to handle, store, and
incinerate chemical wastes. After operations were halted by state regulatory
5.3
-------
Process Evaluation
agencies, 590 m3 (155,000 gal) of sludge and liquid waste stored in tanks and
drums were removed from the site.
A remedial investigation was performed between 1982 and 1987 to deter-
mine the level of contamination. The soil was found to be contaminated with
VOCs, such as, TCE, vinyl chloride, benzene, and toluene. Pretreatment con-
taminant concentrations were as follows: PCE, 4 ppm; toluene, 78 ppm; xy-
lene, 29 ppm; chlorobenzene, 57 ppm; and total VOCs, 461.3 ppm. The soil
moisture content varied from 5 to 25%.
Approximately 8,400 m3 (11,000 yd3) of soil were treated in a continuous
operation. Pretreatment included screening, mixing, and dewatering. The
maximum particle size of the feed was limited to 5 cm (2 in.). The solids feed
rate to the kiln was about 10 kg/sec (40 ton/hr). The LTTA process was used to
heat the soils to approximately 230 to 260°C (450 to SOOT). This process re-
duced total VOCs concentrations to less than 0.025 ppm.
Both the residuals from the air pollution control (APC) equipment and the
generated wastewater were treated on site and were disposed of off site. No
costs were given for this operation.
Approximately 150 m3 (200 yd3) of PCB-contaminated soil were also exca-
vated and incinerated off site. No costs were given.
5.1.4 Caltrans Maintenance Station Site (Kingvale, Cal.) —
Direct-Fired Desorber
Soil at this site was contaminated with diesel fuel that leaked from an under-
ground fuel tank (California Department of Health Services 1990a). The diesel
concentrations ranged from 440 to 5,200 ppm, with approximately 5% moisture
content. Approximately 153 m3 (200 yd3) of soil were excavated and treated
using Earth Purification Engineering Inc.'s Soil Cleanup System, a direct-fired
desorber. The California State Department of Health Services assisted in the
treatment and monitored it. During the treatment, several tests were made to
evaluate the performance of the system. The treatment system consisted of a
reciprocating pan feeder, an asphalt recycling rotary desorber, dual cyclones, an
exhaust cooler, a baghouse, and an exhaust fan. It should be noted that this unit
was not equipped with an organic emissions control device.
During part of the processing period, stack gases were sampled to estimate
emissions. The exhaust gas and soil exit temperatures were 425 and 413°C
(796 and 775 °F) for this period, and the feed rate to the desorber was 1.4 mVhr.
5.4
-------
Chapter 5
(1.8 ydVhr.). Under these conditions, the soil contaminant concentration was
reduced from an average 1,875 ppm to less than 1 ppm. Stack gas samples
revealed, however, a nonmethane VOC concentration of 268 ppmv and a CO
concentration of 1,373 ppmv. Destruction and removal efficiency was esti-
mated to be between 71 and 89%. The concentration of total particulates was
4.56 gr/dry standard cubic meter (dscm) (0.1278 gr/dscf). Even when the
desorber was fed decontaminated soil, the nonmethane VOC and CO concen-
trations were 67 and 545 ppmv, respectively.
During these tests, the reciprocating pan feeder did not deliver a continuous
feed to the desorber. This resulted in fluctuations in the heat input to the system
and offgas generation, and made it difficult to maintain a vacuum in the
desorber.
The total cost of the site cleanup was not reported. The following amounts
of fuel were consumed during the processing: 4,350 L of propane (1,150 gal),
200 L of gasoline (52 gal), and 280 L of diesel (75 gal).
5.1.5 Coke-Oven Plant Soils — Indirect-Fired Desorber
Deutsche Babcock Anlagen (DBA) has presented some data on the cleanup
of a former coke oven site (Schneider and Beckstrom 1990). The system used
was a 2.2 m (7.2 ft) in diameter by 21 m (69 ft) indirect-heated rotary desorber.
Capacity of the system was 2 kg/sec (8 ton/hr) for a moisture content of 20%.
Temperatures range from 500 to 750°C (930 to 1,380"F) in the desorber, with a
secondary combustion chamber for gas destruction operating at temperatures of
1,000-1,300°C (1,830-2,400°F). The wall temperature of the desorber during
normal operation is 600-650°C (1,100-1,200°F). Following their passage
through the secondary chamber, the gases are cooled, limestone is injected for
neutralizing acid gases, and the gases then pass through a baghouse filter. The
desorber is heated with hot flue gas produced by 18 natural gas burners installed
in the heating jacket.
The soils fed contained various PAHs, 17 of which were directly measured.
The soil results are shown in table 5.2 (on page 5.6). Data exist for two tests
but only one set of results is presented. As shown in the table, concentrations of
most PAHs were below 1 ppm with the exception of phenathrene, fluoranthene,
benzo(b)fluoranthene, and benzo(e)pyrene. No information was given about
organics in the exhaust gas.
5.5
-------
Process Evaluation
The capital cost of the plant was approximately $5.5MM(US), and operating
costs were estimated at $65-80 per ton of soil. It was noted that the cost of
excavation, prefeed treatment, and backfilling are dependent on the conditions
in the area and can vary over a wide range.
Table 5.2
Results of the DBA Pyrolysis Full-Scale Plant
Konigsborn Coke-Oven Plant
Constituents
Feed
Discharge
Naphthalene
2-methyl-naphthalene
1 -methyl-naphthalene
Dimethyl naphthalene
Acenaphthylene
Acenaphthene
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benzo[ajanthracene
Chrysene
Benzo[b]fluoranthene
Benzo[k]fluoranthene
Benzo[e]pyrene
Benzo[a]pyrene
Indeno[ 1 ,2,3-cd]pyrene
Dibenzo[a,h]anthracene
Benzo[g,h,i]perylene
161 6 ppm
738
42.9
932
68.2
423
238.0
1055.3
226.0
6886
3982
22592
1346
1685
81.9
111.5
138.1
69.5
232
602
05 ppm
01
01
03
0 1
0 1
0.1
1 4
0.3
1.3
0.6
0.3
0.9
52
03
1 1
0.4
0.1
0.1
0.1
Total
6134.8 ppm
13.4 ppm
Source Schneider and Beckstrom 1990
5.1.6 Wide Beach Superfund Site (Buffalo, N.Y.) — SoilTech
The SoilTech anaerobic thermal processor (ATP) system was used in the
cleanup of PCBs from the Wide Beach Superfund Site (Vorum and Ritcey
1991; Vorum 1991, 1992). The site was contaminated through the use of oil
containing PCBs on the roads of the Wide Beach residential development to
reduce dust. As described in Subsection 3.7.1, the SoilTech ATP system is an
indirect-heater desorber with zones of heating and cooling. Total solids resi-
dence time in the unit is under one hour (30 to 45 min), and application oftem-
5.6
-------
Chapter 5
peratures up to approximately 510 to 620°C (950 to 1,1 SOT) are cited. Feed
rates were approximately 2 to 2.3 kg/sec (8 to 9 ton/hr). The added effect of
chemical dechlorination of PCBs was applied at the Wide Beach site to process
38,000 kg (42,000 ton) of PCB-contaminated soil.
The average feed concentration of PCBs in the soil was approximately 25
ppm (the range was 10 to 5,000 ppm), and the treatment was shown to reduce
the residual PCBs to less than 70 ppb. Stack PCB concentrations were less than
25% of the allowable rate (target was 1.5 g/hr (3.33 x 10~5 lb/hr)) and dioxins
and furans were within the state target value of 0.2 ng/dscm. Vorum (1991)
states that no PCB-bearing residuals needed to be treated off site, with the ex-
ception of process wastewater which had PCB concentrations =1 ppb.
No costs are given for the project; however, the authors state that a range of
$150-$300/ton, not including costs of excavation and delivery of feed materials
or pickup and disposal of treated solids and oil product, can be expected. Costs
depend upon volume of material to be treated, material handling considerations,
moisture level, hydrocarbon content and the potential for recycling, acidity,
particle-size distribution, water disposal options, and regulatory impacts. Site
remediation was completed in June, 1993.
5.1.7 Waukegan Harbor Superfund Site (Waukegan, III.)—
SoilTech
The SoilTech ATP system was used also to treat 11,500 tonne (12,700 ton)
of PCB contaminated sediments using the 2.6 kg/sec (10 ton/hr) ATP transport-
able system. An excerpt of the report of Hutton and Shanks (1993) on this
project is appended as Appendix C, since the information it provides is quite
complete.
5.1.8 Anderson Development Site (Adrian, Mich.) — Indirect-
Heated Screw Conveyor
A wastewater lagoon at the Anderson Development Company site was con-
taminated with VOCs, semivolatile organic compounds (SVOCs), and 4,4'
methylene bis (2-chloroaniline)(MBOCA C13H12C12N2). A remediation was
conducted using the Roy F. Weston, Inc. (WESTON^) Low Temperature Ther-
mal Treatment System, which utilizes an indirect-heated screw desorber. The
screw was heated by circulating heat transfer oil. The feed rate was 0.54 kg/sec
(2.0 ton/hr). The soil discharges at 270°C (515T) after approximately 90 min-
5.7
-------
Process Evaluation
utes of thermal treatment. The desorber offgases were vented through a
baghouse dust collector, an air cooled condenser, a refrigerated condenser, and
carbon adsorption bed before discharge.
The chemical of primary concern was MBOCA, a semivolatile compound
with a low solubility and extremely low vapor pressure. During a Site Demon-
stration Test treatment of lagoon sludge, MBOCA removal efficiencies greater
than 88% for sludge containing from 10 to 800 ppm of MBOCA were
achieved. Treated sludge ranged in concentration from 3 to 9.6 mg/kg (US
EPA, 1993). During processing, volatile organics were removed to below de-
tection limits (approximately 60 ppb). Semivolatile compounds generally de-
creased during treatment; however, some compounds did increase as a result of
chemical transformation specifically, chrysene and phenol. Polychlorodibenzo-
dioxins (PCDDs) and polychlorodibenzofurans (PCDFs) were formed, but were
removed from the exhaust by the vapor-phase treatment system. During opera-
tion, by-products included fabric filter dust, condenser water, and activated
carbon from vapor and liquid phase treatment systems. The total cost for treat-
ment of the 3,000 ton of lagoon sludge was $1,700,000 (US EPA 1992c).
5.1.9 Gasoline and Diesel Soil — Direct-Heated Conveyor
A full-scale demonstration of a U.S. Waste Thermal Processing direct-fired
belt conveyor system was conducted using a synthetic contaminated soil and
reported by the California Department of Health Services (1990b). Natural soil
was contaminated with diesel fuel and gasoline for the demonstration. The
system operates at temperatures from 150-340°C (300-650T) using eight burn-
ers that are located in the primary furnace. A 2.5-cm (1 in.) layer of soil is
moved through the furnace and soil throughput is controlled to maintain the
desired soil temperature. The throughput ranges from 3 to 6.9 m3/hr (4 to 9 yd3/
hr). The offgases are vented to an afterburner for control of emissions of organ-
ics and to a venturi scrubber for particulate control. The liquid blowdown from
the scrubber is used to cool and wet the treated soil.
During testing, the feed soil was spiked to contain 5,000 ppm of diesel or
gasoline. The moisture content of the soil varied from 5.2 to 8.9% by weight.
During the gasoline test, stack emission analyses showed no dioxins, furans, or
PCBs, with the exception of dichlorobiphenyl, present at 0.073 [ig/dscm; the
report states that this measurement is questionable. Phenanthrene, anthracene,
fluoranthene, and pyrene were also detected. Lead and chromium concentra-
tions were 10.6 and 14.4 (ig/dscm, respectively. Some cadmium was also de-
5.8
-------
Chapter 5
tected. The diesel run stack analyses showed no dioxins, furans, or PCBs. The
analyses showed 6.6 (ig/dscm of naphthalene; 13 (ig/dscm of phenathrene; and
0.25 pg/dscm of anthracene. Some carbon disulfide and methylene chloride
were also measured, but these data were questionable. Lead, chromium, and
cadmium levels were slightly lower than in the gasoline test. Lead emissions
for both tests were below the regulatory standard. During the gasoline tests
chlorinated volatiles, fuel hydrocarbons, and aromatic hydrocarbons were not
detected in the treated soil. Metals were detected, but at concentrations below
20 ppm, except for barium (76 ppm). During the diesel tests, fuel hydrocarbons
or aromatic volatiles were not detected in the treated soil. A semivolatile analy-
sis of treated soil found approximately 30 ppm of unknown alkanes, benzoic
acid, and other constituents. The results of metals analyses were similar to
those of analysis of gasoline treated soils. Scrubber blowdown analyses re-
vealed only a few compounds above detection limits, but none was at such a
high level that would cause concern.
5.2 Pilot-Scale Systems
5.2.1 Petroleum Refinery Waste Sludge — Indirect-Heated
Desorber
The Chemical Waste Management pilot-scale X*TRAX™ has been used to
process a variety of petroleum wastes (Ayen and Swanstrom 1992). The pro-
cess is an indirect-fired rotary desorber with inert gas passing through at a tem-
perature of 315°C (600°F). The pilot-scale system is a 61 cm (24 in) in diam-
eter by 6.4 m (21 ft) long desorber with a capacity of 0.05 kg/sec (0.20 ton/hr)
for a feed with 30% moisture (Swanstrom and Palmer 1990). The inert purge
gas passes through a series of condensers prior to recycle; a small portion of the
gas is passed through a carbon filter and vented (=5%). Waste codes K048,
Dissolved Air Flotation Sludge, K049, Slop Oil Emulsion Solids, and Heat
Exchanger Bundle Sludge, K050, were treated. The moisture content was 49%
by weight and the oil and grease content was 23%. Soil exit temperatures were
in the 290-360°C (554-680°F) range. Table 5.3 (on page 5.10) lists the results
of the pilot-plant study. As shown in this table, most of the treated product met
the best demonstrated available control technology (BOAT) for K048-50. The
BOAT standards for metals, namely chromium and nickel, were not met since
5.9
-------
Process Evaluation
the materials exceeded TCLP Leachate concentrations, as shown in the table.
Further treatment of the residual stream would be necessary. The authors state
that the condensed oil recovered could feasibly be recycled.
Table 5.3
Chemical Waste Management Pilot-Scale Plant
Petroleum Refinery Waste
Constituent
Total Constituent Analysis (ppm)
Feed Treated Prod. BOAT for K048 - 50
Anthracene
Benzene
Benzo[a]pyrene
Chrysene
Di-n-butylphalate
Ethylbenzene
Naphthalene
Phenanthrene
Phenol
Pyrene
Toluene
Xylene(s)
Cyanide
9.2
BDL (5)
BDL(100)[1]
BDL(100)[11
69.0
400
19.0
44.0
BDL(100)t1]
570
29.0
203.0
05
0.37
BDL (0.5)
BDL (2)
1.3
BDL (2)
BDL (0.5)
14
1 9
046
1.3
8.7
BDL (0.50)
28.0
140
120
15.0
3.6
14.0
42.0
34.0
3.6
360
140
22.0
1.8
Note: [1] BOAT standards are lower than method detection level (BDL)
TCLP Leachate Concentration (mg/L)
(2 samples shown)
Component
Feed
Treated Prod. BOAT for K048 - 50
Chromium
Nickel
028
0.25
2.7, 0.24
0 55, 0 26
1.7
020
Reprinted by permission of the American Institute of Chemical Engineers from "Low Temperature Thermal Treatment
for Petroleum Refinery Waste Sludges" by R J Ayen and C.P. Swanstrom, Environmental Progress, Volume 11,
Number 2. Copynght 1992 by Amencan Institute of Chemical Engineers.
The authors also conducted laboratory-scale tests for the same materials;
these tests yielded similar results. Additional contaminated soils have also been
tested and results are discussed in Swanstrom 1991; Swanstrom and Palmer
1990, 1991; and Romzick and Swanstrom 1991.
5.10
-------
Chapter 5
5.2.2 PAH Contaminated Soils — Indirect-Fired Desorber
International Technology (IT) Corporation's Rotary Thermal Apparatus was
used to treat soils contaminated with waste materials, including coal tar, which
resulted from manufactured gas plant (MGP) operations (Alperin, Groen, and
Helsel 1992; Fox, Alperin, and Huls 1991; Helsel, Alperin, and Groen 1989).
Coal tar contains numerous PAHs. Three soils were tested with moisture con-
tents from 4% (Soil A) to 9% (Soil C). In addition, material from a creosote
and coal tar-based wood treater site was studied (Alperin, Groen, and Helsel
1992; Lauch et al. 1991). This soil contained 11% moisture.
The IT facility has a 16.5-cm (6.5 in.) internal diameter and a 2-m (6.7 ft)
heated length. A nitrogen purge is used at a rate of 0.06 mVmin (2 ftVmin).
The purge gas is cooled and passed through a high-efficiency particulate filter
and an activated-carbon adsorber.
See table 5.4 (on page 5.12) for the results of several tests of the MGP soils
and of a test creosote-contaminated soil. The MGP soil results show that an
increase in temperature decreased the residual concentration; however, there did
not appear to be a strong correlation with residence time. The heat up in the
facility is quite rapid; therefore, the effect of residence time would be difficult
to determine. The variability in final PAH concentration for different residence
times is probably a result of inhomogeneity in the feed material. The creosote-
contaminated soil test was conducted at 550°C (1,020°F) for 10 minutes. All
concentrations were below detection limits.
For the creosote soil, the offgases were also analyzed. The PAHs and aro-
matic compounds were found as well as some phenolics and volatiles which
were not in the parent soils. All PAHs that were in the parent soil were detected
in the offgas. Phenanthrene and fluoranthene were used to determine a material
balance, since these constituents were present in largest quantity (see table 5.4
on page 5.12). The material balance closure was 63% and 68% for phenan-
threne and fluoranthene, respectively.
5.3 Bench-Scale Systems
Many of the case studies discussed above reported numerous tests on the
bench scale. Studies of other wastes can also be found in the documents cited.
5.11
-------
Process Evaluation
In many cases, the bench-scale studies were conducted prior to the pilot- and/or
full-scale studies.
International Technology Corporation also conducted numerous tests with a
bench-scale tray test apparatus. See the above sources for details.
Table 5.4
IT Rotary Thermal Apparatus
PAH Contaminated Soils
Part A
Creosote
Concentration mg/kg
Feed Product
Naphthalene
2-Methylnaphthalene
Acenaphthalene
Acenaphthene
Dibenzoturan
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benzo[a]anthracene
Chrysene
Benzo[b]tluoranthene
Benzo[a]pyrene
Indeno[ 1 ,2,3-cdjpyrene
Dibenzo[a,h]anthracene
Benzo[g,h,i]perylene
1430
1800
380
3420
237.0
3880
1 ,028 0
4150
6680
580.0
170
1580
1580
770
250
<1 0
260
<0016
<0 190
<0007
<0210
<0.081
<0.020
<0 034
<0073
<001()
<0 052
<0023
<() 120
<0047
<0 110
<0 035
<0016
<0 320
Total Identified PAHs
4629
-------
Chapter 5
5.3.1 PAH Contaminated Soils
The University of Utah has completed bench-scale studies on the same MGP
soils that were run in the IT pilot-scale system (Lighty, Eddings et al. 1990).
The studies were conducted with IT Corporation in an attempt to scale the
bench-scale results to the pilot-scale facility using computer modeling. The
data from these systems showed that PAHs were reduced below 0.1 ppm at a
temperature of 400°C (750°F), consistent with the pilot scale data. The source
cited above also details exhaust gas measurements conducted with a gas chro-
matograph/mass spectrometry technique. Attempts were made to use the re-
sults of attempts to use the bench-scale data to predict the full-scale data by
scaling with a computer model; these results are reported in Lighty, Silcox, and
Pershing (1990). The results were inconclusive because of the difficulty in
measuring of the hydrocarbons and the differences in reporting the concentra-
tions between the bench-scale and pilot-scale data. The bench-scale data were
given in terms of total hydrocarbons, whereas the pilot-scale data were constitu-
ent specific. It was found that the specific constituents accounted for only a
fraction of the total hydrocarbons present.
5.13
-------
-------
Chapter 6
LIMITATIONS
6.1 Waste Matrix
Several factors must be considered when deciding whether a waste can be
treated by thermal desorption, including:
• Type of Contaminant and solid — treatability testing will help in
determining the necessary temperature and time at temperature to
achieve cleanup standards. Volatility of contaminant might be
important;
• Contamination level — explosive limits must not be exceeded
within systems operating with excess oxygen, and fugitive emis-
sions must be controlled in an ex situ process;
• Moisture content — the energy required to remove moisture is a
significant portion of the energy required to operate the system.
Moisture also affects the desorption kinetics of the solid/contami-
nant matrix;
• Particle size distribution — important when considering material
handling of the feed and the residual material;
• Environmental impacts of residuals — a material balance approach
must be applied to the whole treatment system, not only the thermal
desorber. The ultimate fate of all streams must be addressed and
determined in the treatment decision; and
• Metals — the fate of the metals in the system must be determined.
Metals must be captured before discharge from the stack and immo-
bilized in residuals before replacement or disposal.
6.1
-------
Limitations
6.2 Process Needs
The system must be able to provide the necessary time-at-temperature to
achieve the cleanup criteria. Fuel, electricity, and process water sources must
be available. In addition, the process design must provide for complete, envi-
ronmentally-sound disposal or elimination of all residuals.
6.3 Risk Considerations
Since the thermal desorption process is ex situ, fugitive emissions must be
controlled. In addition, procedures must be implemented to preclude cross
contamination. Cross contamination occurs when clean media is placed by a
pile of contaminated media. As with any high temperature process involving
potential contact with hot surfaces or the potential for explosion, careful consid-
eration must be given worker safety. General industrial safety considerations
apply; rotating equipment, conveyers, etc., require safety conscious operation.
Exposure of personnel to hazardous materials must be minimized, and proper
protection provided.
6.4 Site Considerations
Utility requirements and the space available for the remediation are basic
considerations. Space requirements vary among the processes. If the facility is
to be located in a residential area, these considerations are particularly impor-
tant, especially as they affect public acceptance. Getting permits is an issue,
especially for stationary facilities. For both mobile and stationary systems,
permit acquisition is dependent on the physical location and specific character-
istics of the site. Topography and meteorology are also important consider-
ations.
6,2
-------
Chapter 6
6.5 Reliability of Performance
The systems addressed in this monograph have demonstrated reliability in
the field tests reported; however, limited data are available on long-term opera-
tions. Most reliability problems occur not within the desorption system, but in
material handling. Feeds and ash must be sized, screened, and conveyed; these
processes often represent a considerable challenge, depending upon the material
and type of equipment employed.
6.6 Process Residues
The process design must account for all residues of the thermal desorption
process — gas, liquids, and solids. The cleanup and/or disposal of these
streams must be planned. For example, if dioxins are present or are formed,
and if heavy metals are present and/or enriched in the fly ash, their disposition
must be provided for in the treatment program, since the disposal of these
streams will affect the cost of treatment.
6.7 Quality of Treated Material
The quality of the treated material must be such that the residue can be dis-
posed of or returned to the ground. If the requirements for cleanup are stringent
for a particular contaminant, a treatability test might show that low-temperature
thermal desorption will not meet the requirements and that higher temperatures
are warranted. In addition, if the material is to be used as a final cover that must
support plant growth, nutrients may have to be added.
6.3
-------
Limitations
6.8 Regulatory Requirements
Remediation of hazardous contaminated media is highly regulated (see also
the discussion of regulatory requirements in Section 3.3). Resource Conserva-
tion Recovery Act (RCRA) Subpart X and, possibly, Subpart O may apply if
the medium is classified as a hazardous waste under the Act or if the
remediation is carried out under RCRA corrective action. If the cleanup is
regulated under the Comprehensive Environmental Response, Compensation,
and Liability Act (CERCLA), regulations under the RCRA may be applied as
the applicable or relevant and appropriate regulations (ARAR). Applicable or
relevant and appropriate regulations are determined on a case-by-case basis.
The process of selecting a remedy for a site under CERCLA is well delin-
eated. After a remedial investigation/ feasibility study (RI/FS), a record of
decision (ROD) is written by the Regional EPA Remedial Project Manager,
specifying a selected remedy. The ROD becomes the basis for the consent
decree or administrative (106) order or is included in an attached statement of
work.
Although low-temperature thermal desorbers may not generally be as highly
regulated as incineration systems, there is an exception. The US EPA's regula-
tion on treatment of debris notes that a thermal desorber is regulated under the
RCRA "either as an incinerator (if the device is direct-fired or if the off-gas is
burned in an afterburner) under subpart O of part 264 or 265, or as a thermal
treatment unit under subpart X, part 264 or subpart P, part 265."' Thus, regula-
tions governing thermal desorption processes may vary depending upon the
location of the site, contaminants, waste matrix, and system being employed.
Therefore, it behooves practitioners to work closely and early with regulatory
personnel to ascertain regulatory requirements.
1. Federal Register, August 18, 1992, page 37,194, footnote 24
6.4
-------
Chapter 7
w
TECHNOLOGY PROGNOSIS
Properly designed and operated thermal desorption units offer a viable
means for the remediation of contaminated soils, sludges, and sediments. The
technology can be used to treat a variety of wastes. A large volume of data has
been generated concerning its use in treating petroleum-contaminated wastes.
Thermal desorption itself is but part of the total remediation process; pre-
and postprocessing requirements are equally important when considering ther-
mal desorption. As explained in Chapter 6.0, the technology has limitations
that need to be addressed.
A number of vendors are available to provide the systems discussed in this
monograph. A list of vendors and consultants who replied to a request for in-
formation in 1992 is set forth in Appendix D.
7.1 Development and Demonstration Needs
The following aspects of the technology have been identified as needing
further development and demonstration:
• scaling of pilot or bench data to a full-scale system;
• fate of metals; and
• dioxin formation.
Figure 7.1 (on page 7.2) illustrates the importance of effectively scaling the
system using computer modeling. The temperature history in a small, pilot-
scale kiln might be completely different than that in a full-scale unit for the
same fill fractions and wall temperatures. As shown in the figure, the bed
reaches temperature within 500 seconds for 5% fill fraction in the pilot-scale
unit. In the full-scale unit, the bed reaches temperature in 1,800 seconds for the
7.1
-------
Technology Prognosis
Figure 7.1
Fill-Fraction Predictions for Full-Scale (1.5 kg/sec feed rate) and
Pilot-Scale (0.044 kg/sec feed rate) Rotary Kilns at Constant
Revolution Rate of 0.2 rpm and Kiln Wall temperature of 800°C
1000
800
£ 600
1
8.
I 400
200
5% fill, pilot scale
5% fill, full scale
300 600 900 1200 1500 1800
Time (Seconds)
Reprinted by permission of the Combustion Institute From "Thermal Analysis of Rotary Kiln Incineration Comparison
of Theory and Expenment" by WD Owens, G D Silcox, J S Lighty, X X Deng, D W Pershing, VA Curdy, C B
Ledger, andA.L Jackway, Combustion and Flame, Volume 86, 1991 Copyright 1991 by the Combustion Institute
same fill fraction. This difference is due to the heat transfer in the units. In
fact, the pilot-scale unit would have to have a fill fraction of 25% to fully repre-
sent the same thermal profile as the full-scale unit. Lester and coworkers
(1991) demonstrated some relation between full- and pilot-scale data even with
a limited amount of full-scale data.
There is evidence that even at moderate temperatures, metals can be volatil-
ized, especially volatile metals such as mercury. In the presence of chlorine,
some chlorinated metal species could be formed that exhibit a more volatile
nature than the parent oxide (Lighty, Eddings et al. 1990). In addition, metals
can be volatilized and subsequently condensed on particles or condensed homo-
geneously to form small particulate which is enriched in metals (Barton, Clark,
7.2
-------
Chapter 7
and Seeker 1990). This paniculate could be difficult to capture in conventional
air pollution control (APC) devices. If the metals are captured, disposal may be
quite difficult, since they will probably not pass the Toxicity Characteristic
Leachate Procedure (TCLP). Sorbent materials have been shown to capture
some metals, and the metals react to form insoluble species (Uberoi and
Shadman 1990, 1991; Scotto, Peterson, and Wendt 1992).
Two United States Environmental Protection Agency (US EPA) Superfund
Innovative Technology Evaluation (SITE) demonstrations have produced evi-
dence of dioxin/furan formation when solids contaminated with chlorinated
aromatic organics were treated. These dioxins/furans are found in the interme-
diate liquid and gaseous treatment residuals, and are rarely detected in the
treated soils/sediments. The mechanisms for the formation of dioxins and
furans in these systems needs to be investigated further.
There is greater emphasis by US EPA regional offices and state regulatory
personnel on the alternate uses of soils and sediments after thermal desorption
treatment. Two factors affect the posttreatment usage: geophysical characteris-
tics (e.g., strength), and toxicity. The geophysical characteristics are relatively
easy to determine. Toxicity, however, is a very complex matter. Factors in-
clude not only carcinogenic, mutagenic, and lethal dose considerations, but also
flora and fauna viability considerations. Procedures need to be developed for
assuring that treated soil/sediment can meet minimum biological requirements
for reuse.
7.3
-------
-------
Appendix A
APPENDIX A
Other Treatment Alternatives
Two other treatment systems were identified — fluidized beds and the
Texarome Process — for which limited data is available relating to their appli-
cation in thermal desorption as of August 1992. Therefore, they are addressed
here rather than in the monograph proper.
The fluidized bed is a large refractor-lined vessel that can be divided into
two sections: a plenum and a bed section. In the plenum section, air or hot gases
pass through a distribution plate or tuyeres. The air rises up through the tuyeres
and into the bed section. This air fluidizes a sand or granular-like material that
constitutes the "bed." The bed serves as a heat transfer media. Extremely
heavy fuel oils are lanced into the bed and are combusted directly as a source of
auxiliary fuel. Natural gas and light oils are combusted in conventional burners,
and the hot exhaust flows directly into the fluid bed to provide any required
auxiliary heat. Particle diameters must be such that the medium can be fluid-
ized. Also, the feed must not contain elements that form low-melting eutectics
that would cause the bed to slag and defluidize. (See Roenzweig 1991, 9.)
The Texarome thermal desorption system is a continuous process using
superheated steam as a conveying and stripping gas for treating contaminated
materials. During the conveying process, the organic contaminants are sepa-
rated from solid particles. An elaborate arrangement of piping within the con-
veying system allows for a countercurrent flow, as well as multistage dispersion
and separation of the gas and solid phases. The last stage of the Texarome
process is used as a quenching stage and a reactor loop to provide a chemical
breakdown of the chemical residuals in the solids (US EPA 1992b). A SITE
demonstration is being developed for a 6 kg/sec (25 ton/hr) unit. Presently a 3
kg/sec (12 ton/hr) pilot scale system is removing cedarwood oils from cedar-
wood chips. Steam temperatures vary from 150 to 480°C (350 to 900°F), de-
pending on the contaminants. The system is to be transportable on three or four
trailers or skids.
A.1
-------
-------
Appendix B
APPENDIX B
Engineering Bulletin:
Thermal Desorption Treatment1
Purpose
Section 121(b) of the Comprehensive Environmental Response, Compensa-
tion, and Liability Act (CERCLA) mandates the Environmental Protection
Agency (EPA) to select remedies that "utilize permanent solutions and alterna-
tive treatment technologies or resource recovery technologies to the maximum
extend practicable" and to prefer remedial actions in which treatment "perma-
nently and significantly reduces the volume, toxicity, or mobility of hazardous
substances, pollutants and contaminants as a principal element." The Engineer-
ing Bulletins are a series of documents that summarize the latest information
available on selected treatment and site remediation technologies and related
issues. They provide summaries of and references for the latest information to
help remedial project managers, on-scene coordinators, contractors, and other
site cleanup managers understand the type of data and site characteristics
needed to evaluate a technology for potential applicability to their Superfund or
other hazardous waste site. Those documents that describe individual treatment
technologies focus on remedial investigation scoping needs. This document is
an update of the original bulletin published in May 1991 [1].
1. US EPA. 1993. Engineering Bulletin-Thermal Desorption on Treatment. Vol. 2. EPA/
540/0-00/000. OERR, Washington, D.C., and ORD, Cincinnati. In review.
B.I
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Engineering Bulletin: Thermal Desorption Treatment
Abstract
Thermal desorption is an ex situ means to physically separate volatile and
some semivolatile contaminants from soil, sediments, sludges, and filter cakes
by heating them at temperatures high enough to volatilize the organic contami-
nants. For wastes containing up to 10 percent organics or less, thermal desorp-
tion can be used in conjunction with offgas treatment for site remediation. It
also may find applications in conjunction with other technologies or be appro-
priate to specific operable units at a site.
Thermal desorption is applicable to organic wastes and generally is not used
for treating metals and other inorganics. The technology thermally heats con-
taminated media, generally between 200°F to 1000°F, thus driving off the water
and volatile contaminants from the contaminated solid stream and transferring
them to a gas stream. The contaminated gas stream is then treated by being
burned in an afterburner, condensed to reduce the volume to be disposed, or
captured by carbon adsorption beds.
The use of this well-established technology is a site-specific determination.
Thermal desorption technologies are the selected remedies for one or more
operable units at 31 Superfund sites [2J. Geophysical investigations and other
engineering studies need to be performed to identify the appropriate measure or
combination of measures to be implemented based on the site conditions and
constituents of concern at the site. Site-specific treatability studies may be
necessary to document the applicability and performance of a thermal desorp-
tion system. The EPA contact indicated at the end of this bulletin can assist in
the definition of other contacts and sources of information necessary for such
treatability studies.
This bulletin discusses various aspects of the thermal desorption technology
including applicability, limitations of its use, residuals produced, performance
data, site requirements, the status of the technology, and sources of further in-
formation.
Technology Applicability
Thermal desorption has been proven effective in treating organic-contami-
nated soils, sediments, sludges, and various filter cakes. Chemical contami-
B.2
-------
Appendix B
nants for which bench-scale through full-scale treatment data exist include
primarily volatile organic compounds (VOCs), semivolatile organic compounds
(SVOCs), polychlorinated biphenyls (PCBs), pentachlorophenols (PCPs), pesti-
cides, and herbicides [1][3][4][5][6][7]. The technology is not effective in
separating inorganics from the contaminated medium.
Extremely volatile metals may be removed by higher temperature thermal
desorption systems. However, the temperature of the medium produced by the
process generally does not oxidize the metals present in the contaminated me-
dium [8, p. 85]. The presence of chlorine in the waste can also significantly
affect the volatilization of some metals, such as lead.
The technology is also applicable for the separation of organics from refin-
ery wastes, coal tar wastes, wood-treating wastes, creosote-contaminated soils,
hydrocarbon-contaminated soils, mixed (radioactive and hazardous) wastes,
synthetic rubber processing wastes, paint wastes [4] [9, p. 2] [10].
Performance data presented in this bulletin should not be considered directly
applicable to other Superfund sites. A number of variables, such as concentra-
tion and distribution of contaminants, soil particle size, and moisture content,
can all affect system performance. A thorough characterization of the site and a
well-designed and conducted treatability study are highly recommended.
Table 1 lists the codes for the specific Resource Conservation and Recovery
Act (RCRA) wastes that have been treated by this technology [4] [9, p.7][10].
The indicated codes were derived from vendor data where the objective was to
determine thermal desorption effectiveness for these specific industrial wastes.
The effectiveness of thermal desorption on general contaminant groups for
various matrices is shown in Table 2. Examples of constituents within contami-
nant groups are provided in "Technology Screening Guide for Treatment of
CERCLA Soils and Sludges" [8, p. 10]. This table is based on the current avail-
able information or professional judgement where no information was avail-
able. The proven effectiveness of the technology for a particular site or waste
does not ensure that it will be effective at all sites or that the treatment efficien-
cies achieved will be acceptable at other sites. For the ratings used for this
table, demonstrated effectiveness means that, at some scale, treatability was
tested to show the technology was effective for that particular contaminant and
medium. The ratings of potential effectiveness or no expected effectiveness are
both based upon expert judgement. Where potential effectiveness is indicated,
the technology is believed capable of successfully treating the contaminant
B.3
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Engineering Bulletin: Thermal Desorption Treatment
group in a particular medium. When the technology is not applicable or will
likely not work for a particular combination of contaminant group and medium,
a no expected effectiveness rating is given.
Another source of general observations and average removal efficiencies for
different treatability groups is contained in the Superfund Land Disposal Re-
strictions (LDR) Guide #6A, "Obtaining a Soil and Debris Treatability Variance
for Remedial Actions," (OSWER Derective 9347.3-06FS, September 1990)[11]
and Superfund LDR Guide #6B, "Obtaining a Soil and Debris Treatability
Variance for Removal Actions," (OSWER Derective 9347.3-06BFS, Septem-
ber 1990)[12].
A further source of information is the U.S. EPA's Risk Reduction Engineer-
ing Laboratory Treatability Database (accessible via ATTIC).
Technology Limitations
Inorganics constituents and/or metals that are not particularly volatile will
likely not be effectively removed by thermal desorption. If there is a need to
remove a portion of them, a vendor process with a very high bed temperature is
recommended; due to the fact that a higher bed temperature will generally result
in a greater volatilization of contaminants. If chlorine or another chlorinated
compound is present, some volatilization or inorganic constituents in the waste
may also occur [13, p.8].
Table 1
RCRA Codes for Wastes Treated
by Thermal Desorption
Wood Treating Wastes K041
Dissolved Air Flotation K048
Stop Oil Emulsion Solids K049
Heat Exchanger Bundles Cleaning Sludge K050
American Petroleum Institute (API) Separator Sludge K051
Tank Bottoms (leaded) K052
B.4
-------
Appendix B
Table 2
Effectiveness of Thermal Desorpfion on General Contaminated
Groups for Soil, Sludge, Sediments, and Filter Cakes
Contaminants Groups
Organic
Inorganic
Reactive
Halogenated volatiles
Halogenated semivolatiles
Nonhalogenated volatiles
Nonhalogenated semivolatiles
PCBs
Pesticides
Dioxms/Furans
Organic cyanides
Organic corrosives
Volatile metals
Non volatile metals
Asbestos
Radioactive materials
Inorganic corrosives
Inorganic cyanides
Oxidizers
Reducers
Soil
•
•
•
•
T
V
T
T
Q
T
Q
Q
Q
a
Q
Q
Q
Effectiveness
Sedi-
Sludge ments
T
T
T
T
T
T
V
T
Q
T
Q
Q
Q
Q
Q
Q
Q
T
T
T
T
V
T
T
T
Q
V
Q
Q
Q
Q
Q
Q
Q
Filter
cakes
•
•
•
•
V
T
T
T
Q
V
Q
Q
Q
Q
Q
Q
Q
Demonstrated Effectiveness. Successful treatabihty test at some scale completed
Potential Effectiveness: Expert opinion that technology will work
No Expected Effectiveness: Expert opinion that technology will not work
The contaminated medium must contain at least 20 percent solids to facili-
tate placement of the waste material into the desorption equipment [3, p.9].
Some systems specify a minimum of 30 percent solids [14 p.6].
As the medium is heated and passes through the kiln or desorber, energy is
lost in heating moisture contained in the contaminated soil. A very high mois-
ture content may result in low contaminant volatilization a need to recycle the
soil through the desorber, or a need to dewater the material prior to treatment to
B.5
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Engineering Bulletin: Thermal Desorption Treatment
reduce the energy required to volatilize the water. High moisture content, there-
fore, causes increased treatment costs.
Material handling of soils that are tightly aggregated or largely clay, or that
contain rock fragments or particles greater than 1-1.5 inches can result in poor
processing performance due to caking. The solids may have to be prepared by
being crushed, screened, or shredded in order to meet the minimum treatment
size. However, one advantage to soil preparation is that it the contaminated
media is mixed and exhibits a more uniform moisture and BTU content.
If a high fraction of fine silt or clay exists in the matrix, fugitive dusts will be
generated [8, p. 83] and a greater dust loading will be placed on the downstream
air pollution control equipment [14, p.6].
The treated medium will typically contain less that 1 percent moisture. Dust
can easily form in the transfer of the treated medium from the desorption unit,
but can be mitigated by water sprays. Normally, clean water from air pollution
control devices can be used for this purpose. Some type of enclosure may be
required to control fugitive dust if water sprays are not effective.
Although volatile and semivolatile organics are the primary target of the
thermal desorption technology, the total organic loading is limited by some
systems to up to 10 percent or less [15, p. 11-30]. As in most systems that use a
reactor or other equipment or process wastes, a medium exhibiting a very high
pH (greater than 11) or very low pH (less than 5) may corrode the system com-
ponents [8, p. 85].
There is evidence with some system configurations that polymers may foul
and/or plug heat transfer surfaces [3, p.9]. Laboratory/field tests of thermal
desorption systems have documented the deposition of insoluble brown tars
(presumably phenolic tars) on internal system components [15, p. 76].
Caution should be taken regarding the disposition of the treatment material,
since treatment processes may alter the physical properties of the material. For
example, this material could be susceptible to such destabilizing forces as lique-
faction, where pore pressures are able to weaken the material on sloped areas or
places where materials must support a load (i.e., roads for vehicles, subsurfaces
of structures, etc.). To achieve or increase the required stability of the treated
material, it may have to be mixed with other stabilizing materials and/or com-
pacted in multiple lifts. A thorough geotechnical evaluation of the treated prod-
uct can provide the necessary design characteristics needed in order to achieve
post-treatment soil stabilization [13, p.8].
B.6
-------
Appendix B
There is also a concern that during the cleanup process dioxins and furans
may form and be released from the exhaust stack and into the environment.
Therefore, the system must be frequently monitored in order to ensure the unit
is not releasing pollutants that may be harmful to the public and environment.
Technology Description
Thermal desorption is a process that uses either an indirect or direct heat
exchange to heat organic contaminants to a temperature high enough to volatil-
ize and separate them from a contaminated solid medium. Air, combustion gas,
or an inert gas is used as the transfer medium for the vaporized components.
Thermal desorption systems are physical separation processes, that transfer
contaminants from one phase to another, and are not designed to provide high
levels of organic destruction, although the higher temperatures of some systems
will result in localized oxidation and/or pyrolysis. Thermal desorption is not
incineration, since the destruction or organic contaminants is not the desired
result. The bed temperatures achieved and residence times designed into ther-
mal desorption systems will volatilize selected contaminants, but typically not
oxidize or destroy them. System performance is typically measured by the
comparison of untreated solid contaminant levels with those of the processed
solids. The contaminated media is typically heated to 200°F to 1000°F, based
on the thermal desorption system selected.
Figure 1 is a general schematic of the thermal desorption process.
Material handling (1) requires excavation of the contaminated solids or de-
livery of filter cake to the system. Typically, large objects greater than 1.5
inches are screened, crushed, or shredded and, if still too large, rejected. The
medium is then delivered by gravity to the desorber inlet or conveyed by augers
to a feed hopper [6, p. 1].
Volatilization of contaminants can be effected by use of a rotary dryer, ther-
mal screw, vapor extractor (fluidized bed), or distillation chamber [14].
As the waste is heated, the contaminants reach their respective boiling
points, vaporize, and then become part of the gas stream. An inert gas, such as
nitrogen, may be injected in a countercurrent sweep stream to prevent contami-
nant combustion and to aid in vaporizing and removing the contaminants [4] [9,
B.7
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Engineering Bulletin: Thermal Desorption Treatment
Figure 1
Schematic Diagram of Thermal Desorption
Clean Offgas
Excavate
Material
Handling (1)
1
Paniculate
Removal/Gas
Treatment System (3)
Participates
Desorption (2)
Oversized
Rejects
Spent Carbon
Concentrated
Contaminants
Water
p. 1]. Other systems simply direct the hot gas stream from the desorption unit
[3,p.5][5].
The actual bed temperature and residence time are primarily factors affecting
performance in the desorption stage. These factors are controlled in the desorp-
tion unit by using a series of increasing temperature zones [9, p. 1], multiple
passes of the medium through the desorber where the operating temperature is
sequentially increased, separate compartments where the heat transfer fluid
temperature is higher, or sequential processing into higher temperature zones
[16] [17]. Heat transfer fluids used include hot combustion gases, hot oil, steam,
and molten salts.
Offgas from desorption is typically processed (3) to remove particulates that
remained in the gas stream after the desorption step. Volatiles in the offgas
may be burned in an afterburner, collected on activated carbon, or recovered in
condensation equipment. The selection of the gas treatment system will depend
on the concentrations of the contaminants, cleanup standards, and the econom-
ics of the offgas treatment system(s) employed. Some methods commonly used
to remove the particulates from the gas stream are a cyclone furnace, a quench
B.8
-------
Appendix B
water tower, and a baghouse. In a cyclone, particulates are removed by cen-
trifugal force. In the quench tower, particulates are passed through a highly
atomized water mist, causing them to discharge through the bottom of the
tower. In a baghouse, particulates are caught by bags and discharged out of the
system.
Process Residuals
Operation of the thermal desorption systems typically creates up to six pro-
cess residual streams: treated medium oversized medium and debris rejects,
condensed contaminants and water, paniculate control system dust, clean
offgas, and spent carbon (if used). Treated medium, debris, and oversized re-
jects may be suitable for return onsite.
Offgas from a thermal desorption unit will contain entrained dust (particu-
lates) from the medium, vaporized contaminants, and water vapor. Particulates
are removed by conventional equipment such as cyclone dust collectors, fabric
filters, or wet scrubbers. Collected particulates may be recycled through the
thermal desorption unit or blended with the treated medium, depending on the
amount of carryover contamination present. Very small particles (<1 micron)
can cause a visible plume from the stack [13, p.5].
The vaporized organic contaminants can be captured by condensing the
offgas and then passing it through a carbon adsorption bed or other treatment
system. Emissions may also be destroyed by use of an offgas combustion
chamber or a catalytic oxidation unit [13, p.5].
When offgas is condensed, the resulting water stream may contain signifi-
cant contamination depending on the boiling points and solubility of the con-
taminants and may require further treatment (i.e., carbon adsorption). If the
condensed water is relatively clean, it may be used to suppress the dust from the
treated medium. If carbon adsorption is used to remove contaminants from the
offgas or condensed water, spent carbon will be generated, which is either re-
turned to the supplier for reactivation/incineration or regenerated onsite [13,
p.5].
When offgas is destroyed by a combustion process, compliance with incin-
eration emission standards may be required. Obtaining the necessary permits
B.9
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Engineering Bulletin: Thermal Desorption Treatment
and demonstrating compliance may be advantageous, however, since the incin-
eration process would not leave residuals requiring further treatment. If incin-
eration is used, the heat from the incineration process may be used in the des-
orption process unit [13, p.5].
Site Requirements
Thermal desorption systems are transported typically on specifically adapted
flatbed semitrailers. Since most systems consist of three components (desorber,
particulate control, and gas treatment), space requirements on site are typically
less than 50 feet by 150 feet, exclusive of materials handling and decontamina-
tion areas.
Standard 440V, three-phase electrical service is needed. Water must be
available at the site. The quantity of water needed is vendor and site specific.
Treatment of contaminated soils or other waste materials require that a site
safety plan be developed to provide for personnel protection and special han-
dling measures. Storage should be provided to hold the process product
streams until they have been tested to determine their acceptability for disposal
or release. Depending upon the site, a method to store waste that has been
prepared for treatment may also be necessary. Storage capacity will depend on
waste volume. Onsite analytical equipment capable of determining site-specific
organic compounds for performance assessment make the operation more effi-
cient and provide better information for process control.
Performance Data
Performance data in this bulletin are included as a general guideline to the
performance of the thermal desorption technology and may not always be di-
rectly transferable to other Superfund sites. Thorough site characterization and
treatability studies are essential in determining the potential effectiveness of the
technology at a particular site. Most of the data on thermal desorption come
from studies conducted for EPA's Risk Reduction Engineering Laboratory
under the Superfund Innovative Technology Evaluation (SITE) Program.
B.10
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Appendix B
Seaview Thermal Systems (formerly T.D.I. Services, Inc.) conducted a pilot-
scale test of their HT-5 thermal desorption system at the U.S. DOE, Oak Ridge,
Tennessee, Y-12 plant. The test was run in order to evaluate the capability of
the unit to remove and recover mercury from a soil matrix. Initial mercury
concentrations in the soil were 1140 mg/kg. The mercury was removed to
concentrations of 0.19mg/kg with a detection limit of 0.03 mg/kg. A full-scale
cleanup (80 tons per day) using the HT-5 system, was conducted for Chevron
U.S.A. at their El Segundo Refinery. The final primary contaminants and their
initial and final concentrations are indicated in Table 3 [19].
Table 3
Full-Scale Cleanup Results of the H-T-5 System
Contaminant
Tolune
Benzene
Ethlybenzene
Xylenes
Naphthalene
2-Methylnaphthalene
Acenaphthlene
Phenanthrene
Anthracene
Pyrene
Benzo(a) Anthracene
Chrysene
Styrene
Feed Soil
Concentration
(mg/kg)
30
38
93
290
550
1400
57
320
320
38
36
45
13
Treated Soil
Concentration
(ug/kg)
<620
<620
<620
<620
<620
<330
<330
<330
<330
<330
<330
<330
<620
Removal
Efficiency '
(%)
< 97.93
< 98.36
<9979
<9978
< 99.89
<9998
< 99.42
<9990
<9990
<99 13
<9908
<9927
<9923
1. SIC Re: <
In September 1992, a pilot-scale (35 ton per hour capacity) EPA Superfund
Innovative Technology Evaluation (SITE) demonstration was performed at a
confidential Arizona pesticide site using Canonie Environmental's Low Tem-
perature Thermal Aeration (LTTA®) system. Approximately 1,180 tons of
pesticide-contaminated soil was treated during the demonstration over three 10-
hour replicate runs. Pesticide-contaminated soils ranged in concentration from
7,080 ug/kg to 1,540,000 ug/kg. The LTTA® system obtained removal effi-
B.ll
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Engineering Bulletin; Thermal Desorption Treatment
ciencies ranging from 82.4 to greater than 99.9 percent. All pesticides with the
exception of dichlorodipheyltrichloroethane (DDE), were removed to near or
below method detection limits in the soil. Trace amounts of polycholorinated
dibenzo(p)dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) were
formed in the LTTA® system but at concentrations too low to quantify. No
Class I or Class II dioxin precursors were found above detection limits. Total
chloride concentrations in the treated soil were approximately three times the
total chloride concentrations in the feed soil. This increase was likely due to the
dechlorination of the pesticides in the feed soil. Table 4 Presents a summary of
four case studies involving full-scale applications of the LTTA® process [17].
Table 4
Full-Scale Cleanup Results of the LTTA® System
Site
South Kearney
McKm
Ottati and Goss
Cannon Bndgewater
Former Spencer
Kellogg Facility
Volume/Mass
Treated
16,000 tons
1 1 ,500 cubic yards
4,500 cubic yards
11, 300 tons
6,500 tons
Primary
Contaminant(s)
Total VOCs
SVOCs
VOCs
SVOCs
U.1TCA
TCE
Tetrachloroethene
Toluene
Ethylbenzene
Total Xylenes
VOCs
Total VOCs
SVOCs
Feed Soil
Concentration
(mg/kg)
308.2
0.7-15
27-3,310
0.44- 1 .2
12-470
6.5-460
4.9-1200
>87-3,000
>50-440
>170->1100
5.3*
5.42
0.15-47
Treated Soil
Concentration
(mg/kg)
051
ND-1.0
<0.05a
<0.33-051
<0.025
<0025
<0025
<0 025-0 Oil
<0.025
<0 025-0 014
<0025
045
0 042-<0 39
a Average concentration
b Maximum concentration
A pilot-scale (2.1 tons per hour capacity) SITE demonstration was per-
formed at the Anderson Development Company (ADC) Superfund site in
Adrian, Michigan using Roy F. Weston's Low Temperature Thermal Treatment
(LT3®) system. Approximately 80 tons of contaminated sludge was treated
during the demonstration over a period of six 6-hour replicate tests. The lagoon
sludge was primarily contaminated with VOCs and SVOCs, including 4,4'-
B.12
-------
Appendix B
methylenebis (2-chloroanilinine) (MBOCA). Initial VOC concentrations ranged
from 35 to 25,000 ug/kg. In the treated sludge VOC concentrations were below
method detection limits (less than 60 ug/kg) for most compounds. MBOCA
concentrations in the untreated sludge ranged from 43.6 to 960 mg/kg. The
treated sludge ranged in concentration from 3 to 9.6 mg/kg. The LT3® system
also decreased the concentrations of all SVOCs present in the sludge, with two
exceptions: chrysene and phenol. The increase of chrysene concentration
likely was caused by a minor leak of heat transfer fluid. Chemical transforma-
tions during heating likely caused the phenol concentrations to increase.
PCDDs and PCDFs were formed in the system, but were removed from the
exhaust gas by the unit's vapor-phase carbon column with removal efficiencies,
varying with congener, from 20 to 100 percent. Paniculate concentrations
ranged from less than 8.5 x 10"4 to 6.6 x 10"3 grains per dry standard cubic meter
(gr/dscm). Chloride concentrations were below the average method detection
limit of 2.8 x 10~2 milligrams per dry standard cubic meter (mg/dscm). Chloride
emissions were less than 6.0 x 10'5 Ib/hr. Table 5 presents a summary of three
case studies involving pilot- and full-scale applications of the LT3® system
[21].
Table 5
Full-Scale Cleanup Results of the LT 3 ® System
Site
Confidential
Tinker AFB,
OK
Letterkenny
Army Depot
Volume/Mass Primary
Treated Contaminants )
1,000 cubic feet Benzene
Toluene
Xylene
Ethylbenzene
Napthalene
PAHs
3,000 cubic yards TCE
Chlorinated Orgamcs
JP4 Aviation Fuel
7.5 tons Benzene
Trichloroethene
Tetrachloroethene
Xylene
Other VOCs
Feed Soil
Concentration
1,000 ppb
24,000 ppb
1 10,000 ppb
20,000 ppb
4,900 ppb
890-<6,000 ppb
6,100 ppma
586, 106 ppb
2,678,536 ppb
1,422,031 ppb
27,197,367 ppb
39, 127 ppb
Treated Soil
Concentration
5.2 ppb
5.2 ppb
<1 0 ppb
4 8 ppb
<330
<330 - 590 ppb
All contaminants were
reduced to
concentrations below the
goal cleanup levels and
in most cases, to less
than detection limits
730 ppb
1,800 ppb
1,400 ppb
550 ppb
BDL
a Maximum concentration
BDL Below Detection Limits
B.13
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Engineering Bulletin: Thermal Desorption Treatment
In May 1991 a pilot-scale SITE demonstration was performed at the Wide
Beach Development site in Brand, New York using Soil Tech's Anaerobic
Thermal Processor (ATP) system. Approximately 104 tons of contaminated
soil were treated during three replicate test runs. The soil and sediment at the
site was primarily contaminated with PCBs, along with VOC's and SVOCs.
The average total PCB concentration was reduced from 28.2 mg/kg, in the
contaminated soil and sediment, to 0.043 mg/kg in the treated soil (a 99.8 per-
cent removal efficiency). The test indicated that an average of 23.1 ug/dscm of
PCBs were discharged from the unit's stack to the atmosphere. The high PCB
concentrations in the emissions may have been caused by low removal efficien-
cies in the unit's vapor phase carbon system, high paniculate loadings (0.467 g/
dscm) in the stack or a combination of the two. Low levels of dioxins and
furans were present in the feed soil, but none were detected in the treated soils,
baghouse fines, or the cyclone's flue gas. The toxicity equivalents (TEQ) of the
stack gas ranged from 0.0106 to 0.0953 mg/dscm. The total VOC concentra-
tion was reduced from 0.085 mg/kg in the contaminated soil to 0.0008 mg/kg in
the treated soil. The total SVOC concentration was reduced from 61.8 mg/kg in
the contaminated soil to 0.24 mg/kg in the treated soil [22].
In June 1991 a SITE demonstration test was performed at the Waukegan
Harbor Superfund site in Waukegan Harbor, IL. The site was primarily con-
taminated with PCBs, along with VOCs, SVOCs, and metals. Approximately
253 tons of contaminated soil were treated over a period of four runs using Soil
Tech's ATP thermal desorption system. The average PCV concentration in the
feed soil was 9,173 mg/kg; the average final concentration was 2 mg/kg, which
is a 99.98 percent removal efficiency. PCB's were discharged out of the stack
at 0.834 ug/dscm (a 99.999987 percent removal efficiency). Tetrachlorinated
dibenzofurans were the only dioxins and furans detected in the stack gas at an
average concentration of 0.0787 ng/dscm. Low concentrations of SVOCs (total
of 16.99 mg/kg) in the feed soil were detected. In the treated soils SVOC con-
centrations totaled only 0.031 mg/kg with only two contaminats detected below
the concentration limit. In the contaminated soil, VOC concentrations totaled
17 mg/kg, while in the treated soil the total was only 0.03 mg/kg. Metal con-
centrations were approximately the same in both the contaminated and treated
soil. This was due to the fact that the unit does not operate at temperatures high
enough to significantly remove metals. The pH of the soil rose from 8.59 in the
contaminated soil to 11.35 in the treated soil. This was likely to the addition of
sodium bicarbonate in order to reduce PCB emissions [22].
B.14
-------
Appendix B
In May 1992 a pilot-scale (4.9 tons per hour) SITE demonstration was per-
formed at the RE-Solve Superfund site in North Dartsmouth, Massachusetts
using Chemical Waste Management X*TRAX™ system. Approximately 215
tons of contaminated soil were treated over a period of three duplicate six-hour
tests. The soil is primarily contaminated with PCBs, along with some oil and
grease, and metals. Initial PCB concentrations ranged from 181 to 515 mg/kg.
PCS concentrations in the treated soil were less than 1.0 mg/kg with the aver-
age concentrations being 0.25 mg/kg (a 99.9 percent removal efficiency).
PCDDs and PCDFs were not formed during the demonstration. Concentrations
of oil and grease, total recoverable petroleum hydrocarbons, and
tetrachloroethane were reduced to below detectable levels. Metal concentra-
tions were not reduced during the test. This was expected since the unit does
not operate at temperatures high enough to significantly remove metals [23].
RCRA LDRs that require treatment of wastes to best demonstrated available
technology (BOAT) levels prior to land disposal may sometimes be determined
to be applicable or relevant and appropriate requirements for CERCLA re-
sponse actions. Thermal desorption can produce a treated waste that meets
treatment levels set by BDAT but may not reach these treatment levels in all
cases. The ability to meet required treatment levels is dependent upon the spe-
cific waste constituents and the waste matrix. In cases where thermal desorp-
tion does not meet these levels, it still may, in certain situations, be selected for
use at the site if a treatability variance establishing alternative treatment levels is
obtained. Treatability variances are justified for handling complex soil and
debris matrices. The following guides describe when and how to seek a
treatability variance for soil and debris: Superfund LDR Guide #6 "Obtaining a
Soil and Debris Treatability Variance for Remedial Actions" (OSWER Direc-
tive 9347.3-06FS) [11], and Superfund LDR Guide #6B, "Obtaining a Soil and
Debris Treatability Variance for Removal Actions" (OSWER Directive 9347.3-
06BFS)[12].
Technology Status
Several firms have experienced in implementing this technology. Therefore,
there should not be significant problems of availablity. The engineering and
configuration of the systems are similarly refined, such that once a system is
designed full-scale, little or no prototyping or redesign is required.
B.15
-------
Engineering Bulletin: Thermal Desorption Treatment
A SITE demonstration is scheduled to take place in June 1993 at the Niagara
Mohawk Power Corporation site in Utica, New York. The facility is a former
gas manufacturing plant and contains 425,000 cubic yards of manufactured gas
plant soil. The soil is primarily contaminated with polyaromatic hydrocarbons
(PAHs), benzene, toluene, ethylbenzene, xylene (BTEXs), lead, arsenic, cya-
nide. EPA Technology Evaluation and Application Analysis Reports will be
developed in order to evaluate the performance of and the cost to implement the
system.
Thermal desorption technologies are the selected remedies for one or more
operable units at 31 Superfund sites. Table 6 presents the status of selected
Superfund sites employing the thermal desorption technology [2].
Table 6
Superfund Sites Specifying Thermal Desorption as the Remedial
Action
Site
Cannon Engineering
(Bridgewater Site)
McKm
Ottati & Goss
Wide Beach Development
Metaltec/Aerosystems
Caldwell Trucking
Outboard Marine/Waukegan
Harbor
Reich Farms
Re-Solve
Waldick Aerospace Devices
Waumchem
Fulton Terminals
Anderson Development
Company
Location (Region)
Bndgewater, MA (1)
McKm, ME(1)
New Hampshire (1)
Brandt, NY (2)
Franklin Borough, NJ
(2)
Fail-field, NJ (2)
Waukegan Harbor, IL (5)
Dover Township, NJ (2)
North Dartmouth, MA (1)
New Jersey, (2)
Burton, SC (4)
Fulton, NJ (2)
Adrian, MI (5)
Primary
Contaminants)
VOCs (Benzene, TCE,
Toluene, Vinyl Chloride)
VOCs, (TCE, BTX)
VOCs, (TCE, PCE,
1,2-DCE, Benzene)
PCBs
VOCs (TCE)
VOCs (TCE, PCE, TCA)
PCBs
VOCs (TCE, PCE,
TCA), SVOCs
PCBs
VOCs (TCE, PCE),
Metals (Cadium,
Chromium)
VOCs (BTX)
VOCs, (Xylene, TCE,
Benzene, DCE)
VOCs, SVOCs
Status
Project completed 10/90
Project completed 2/87
Project completed 9/89
Pilot study completed
5/91
Design completed
Design completed
Pilot study completed
6/92
Pre-design
Pilot study completed
5/92
Design completed
In design
In design
Pilot study completed
12/91
NOTE: The two Stauffer Chemical sites in Table 10 of the first version are not
included in this table due to the fact that EPA's ROD Annual Report FY 1990
indicates that thermal desorption will no longer be implemented.
B.16
-------
Appendix B
Several vendors have experience in the construction of this technology and
have documented processing costs per ton of feed processed. The overall range
varies from approximately $50 to $400 (1993 dollars) per ton processed [22].
Caution is recommended in using costs out of context because the base year of
the estimates vary. Costs also are highly variable due to the quantity of waste to
be processed, term of the remediation contract, moisture, content, organic con-
stituency of the contaminated medium, and cleanup standards to be achieved.
Similarly, cost estimates should include such items as preparation of Work
Plans, permitting, excavation, processing itself, QA/QC verification of treat-
ment performance, and reporting of data.
EPA Contacts
Technology-specific questions regarding thermal desorption may be directed
to:
Paul dePercin
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 W. Martin Luther King Drive
Cincinnati, Ohio 45268
(513)569-7797
James Yezzi
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Releases Control Branch
2890 Woodbridge Avenue
Building 10 (MS-104)
Edison, NJ 08837
(908)321-6703
B.17
-------
Engineering Bulletin: Thermal Desorption Treatment
Acknowledgments
This updated bulletin was prepared for the U.S. Environmental Protection
Agency, Office of Research and Development (ORD), Risk Reduction Engi-
neering Laboratory (RREL), Cincinnati, Ohio, by Science Applications Interna-
tional Corporation (SAIC) under Contract No. 68-CO-0048. Mr. Eugene Harris
served as the EPA Technical Project Monitor. Mr. Jim Rawe (SAIC) was the
Work Assignment Manager. He and Mr. Eric Saylor (SAIC) co-authored the
revised bulletin. The authors are especially grateful to Mr. Paul dePercin of
EPA RREL, who contributed significantly by serving as a technical consultant
during the development of this document.
The following other Agency and contractor personnel have contributed their
time and comments by participating in the expert review meetings and/or peer
reviewing the document:
Dr. James Cudahy Focus Environmental, Inc.
Dr. Steven Lanier Energy and Environmental Research Corp.
References
1. Thermal Desorption Treatment. Engineering Bulletin. U.S. Environmen-
tal Protection Agency, EPA/540/2-91-008. May 1991.
2. Innovative Treatment Technologies. Semi-Annual Status Report (Fourth
Edition), U.S. Environmental Protection Agency. EPA/542/R-92/011.
3. Abrishamian, Ramin. Thermal Treatment of Refinery Sludges and Con-
taminated Solids. Presented at American Petroleum Institute, Orlando,
Florida, 1990.
4. Swanstrom, C, C. Palmer. X*TRAX® Transportable Thermal Separator
for Organic Contaminated Solids. Presented at Second Forum on Innova-
tive Hazardous Waste Treatment Technologies: Domestic and Interna-
tional, Philadelphia, Pennsylvania, 1990.
5. Canonic Environmental Services Corp., Low Temperature Thermal Aera-
tion (LTTASM) Marketing Brochures, circa 1990.
6. VISITT Database, 1993.
B.18
-------
Appendix B
7. Nielson, R., and M. Cosmos. Low Temperature Thermal Treatment (LT3)
of Volatile Organic Compounds from Soil: A Technology Demonstrated.
Presented at the American Institute of Chemical Engineers Meeting, Den-
ver, Colorado, 1988.
8. Technology Screening Guide for Treatment of CERCLA Soils and Slud-
ges. EPA/540/2-88/004, U.S. Environmental Protection Agency, 1988.
9. T.D.I. Services, Marketing Brochures, circa 1990.
10. Cudahy, J., W. Troxler. 1990. Thermal Remediation Industry Update - II.
Presented at Air and Waste Management Association Symposium on
Treatment of Contaminated Soils, Cincinnati, Ohio, 1990.
11. Superfund LDR Guide #6A: (2nd Edition) Obtaining a Soil and Debris
Treatability Variance for Remedial Actions. Superfund Publications
9347.3-06FS, U.S. Environmental Protection Agency, 1990.
12. Superfund LDR Guide #6B: Obtaining a Soil and Debris Treatability
Variance for Remedial Actions. Superfund Publications 9347.3-06FS.
U.S. Environmental Protection Agency, 1990.
13. Guide for Conduction Treatability Studies under CERCLA Thermal Des-
orption Remedy Selection, Interim Guidance, U.S. Environmental Protec-
tion Agency. EPA/540/R-92-074A.
14. Recycling Sciences International, Inc., DAVES Marketing Brochures,
circa 1990.
15. The Superfund Innovative Technology Evaluation Program - Progress and
Accomplishments Fiscal Year 1989. A Third Report to Congress, EPA/
540/5-90/001, U.S. Environmental Protection Agency, 1990.
16. Superfund Treatability Clearinghouse Abstracts. EPA/540/2-89/001, U.S.
Environmental Protection Agency, 1989.
17. Soil Tech, Inc., AOSTRA - Tuciuk Processor Marketing Brochure, circa
1990.
18. Ritcey, R., and F. Schwarz, Anaerobic Pyrolysis of Waste Solids and
Sludges - The AOSTRA Taciuk Process System. Presented at Environ-
mental Hazardous Conference and Exposition, Seattle, Washington, 1990.
19. Seaview Thermal Systems, Marketing Brochures, circa 1993.
20. Low Temperature Thermal Treatment Aeration (LTTA) Technology.
B.19
-------
Engineering Bulletin: Thermal Desorption Treatment
Canonie Environmental Services Corporation. Applications Analysis
Report, U.S. Environmental Protection Agency (Draft).
21. Roy F. Weston, Inc. Low Temperature Thermal Treatment (LT3®) Sys-
tem. Applications Analysis Report. Anderson Development Company
Site, U.S. Environmental Protection Agency (Draft).
22. Soil Tech ATP Systems, Inc. Anaerobic Thermal Processor. Applications
Analysis Report. Wide Beach Development Site and Outboard Marine
Corporation Site. U.S. Environmental Protection Agency (Preliminary
Draft).
23. X*TRAX Model 200 Thermal Desorption System. Chemical Waste Man-
agement, Inc. Demonstration Bulletin. U.S. Environmental Protection
Agency (Draft).
B.20
-------
Appendix C
APPENDIX C
THERMAL DESORPTION
OF PCB CONTAMINATED WASTE AT THE
WAUKEGAN HARBOR SUPERFUND SITE
A CASE STUDY (Excerpt)!
Abstract
In June 1992, SoilTech ATP Systems, Inc. (SoilTech) completed the soil
treatment phase of the Waukegan Harbor Superfund Project in Waukegan,
Illinois, after approximately five months of operation. SoilTech successfully
treated 12,700 tons of polychlorinated biphenyl (PCB) contaminated sediments
using a transportable SoilTech Anaerobic Thermal Processor (ATP) System
nominally rated at 10 tons-per-hour throughput capacity. The SoilTech ATP
Technology anaerobically desorbs contaminants such as PCBs from solids and
sludges at temperatures over 1,000 degrees Fahrenheit (°F). Principal products
of the process are clean treated solids and an oil condensate containing the hy-
drocarbon contaminants.
At the Waukegan Harbor Superfund Site, PCB concentrations in the sedi-
ments excavated and dredged from a ditch, lagoon and harbor slip averaged
1. Excerpted from "Thermal Desorption of PCB Contaminated Waste at The Waukegan
Harbor Superfund Site - A Case Study" by J.H. Hutton and R. Shanks presented at Innova-
tive Treatment Technologies - Uses and Applications for Site Remediation, Thermal I -
Thermally Enhanced Volatilization, Satellite Seminar, February 18, 1993. Reprinted by
permission of the Air & Waste Management Association. Copyright 1993 by the Air &
Waste Management Association.
C.I
-------
Thermal Desorption of PCB Contaminated Waste
10,400 parts per million (ppm) (1.04 percent) and were as high as 23,000 ppm
(2.3 percent). Treated soil contained less than 2 ppm PCBs and was backfilled
in an on-site containment cell. The removal efficiency of PCBs from the soil
averaged 99.98 percent, relative to the project performance specification of 97
percent. Approximately 30,000 gallons of PCB oil, desorbed from the feed
material, were returned to the potentially responsible party (PRP) trust for sub-
sequent off-site disposal. After modifications to the emissions control equip-
ment, compliance with the 99.9999 percent destruction and removal efficiency
(DRE) for PCBs in stack emissions required by the United States Environmen-
tal Protection Agency was achieved. In fact, SoilTech demonstrated compli-
ance with the DRE requirement in eleven consecutive stack sampling events.
Feed rate averaged 8 tons-per-hour at a mechanical availability of 85 percent.
SoilTech revenues for the project were $700,000 in fixed costs and $185 per ton
of soil processed.
1.0 INTRODUCTION
This technical paper outlines SoilTech's role in the Waukegan Harbor
Superfund Project. SoilTech was responsible for the soils processing phase of
the project using their unique rotary kiln known as the SoilTech Anaerobic
Thermal Processor (ATP) Technology to remediate the PCB contaminated soils
and sediments. The Waukegan Harbor Project is the second commercial appli-
cation of the SoilTech ATP Technology. 42,000 tons of PCB contaminated
soils were successfully treated to nondetect levels at the Wide Beach Superfund
site in western New York in 1990 and 1991. The ATP distills organics con-
taminants out of a solid matrix in an oxygen free environment. Oxidative deg-
radation of contaminants such as PCBs into more harmful reaction products is
therefore prevented. Contaminants are collected in an oily condensate, which
can then be economically disposed of.
C.2
-------
Appendix C
4.0 WAUKEGAN HARBOR SUPERFUND
PROJECT DESCRIPTION
The Waukegan Harbor Superfund site was listed on the EPA's Superfund
Priority List. Contamination resulted from leakage of PCBs - used as an alumi-
num casting lubricant and machine tool lubricant - through floor drains from a
major manufacturing facility into an adjacent stream and Waukegan Harbor.
PCB concentrations in excess of 20,000 ppm were found in the harbor sedi-
ments and stream bed. Remediation of the site was complicated by the fact that
the harbor was being used for both commercial and recreational boating activi-
ties and was adjacent to a public beach. The client was insistent that operations
not impact the day-to-day activities of the local community. It was, therefore,
necessary for Canonie, the prime contractor, to build a new boat slip prior to
isolating the old one. Sediments with PCB concentrations greater than 500 ppm
were hydraulically dredged from the old slip and pumped to a containment cell
where dewatering was achieved before they were blended with soils from the
contaminated stream bed.
The 1984 Record of Decision called for stabilization of these soils and sedi-
ments. SoilTech and the PRPs were, however, able to convince the EPA that
the use of SoilTech's ATP Technology offered a more environmentally accept-
able and cost-effective solution. The EPA accepted that the SoilTech ATP
System was an innovative treatment technology that provided a significant and
permanent reduction in the toxicity and volume of PCB wastes at the
Waukegan Harbor Site. SoilTech's approach fulfilled the requirements of the
Superfund Amendments and Re-authorization Act (SARA). Under the 1984
ROD, there would have been a potential future liability posed by stabilized
stored wastes.
SoilTech was contracted by Canonie to process the soils and sediments for
$700,000 in fixed costs and $185 per ton of material processed. SoilTech was
not responsible for providing utilities (water, gas, and electricity). Site prepara-
tion and excavation of contaminated material were carried out by Canonie. The
PRP's took full responsibility for disposing of the PCB condensate produced.
Had SoilTech been responsible for any or all of these additional activities, the
unit price for soils processing would have been correspondingly higher.
The project clean-up criteria called for a treated soil residual PCB level of
500 ppm, or 97 percent removal efficiency from the soils, whichever was more
stringent. The average target clean-up level turned out to be approximately 310
C.3
-------
Thermal Desorption of PCB Contaminated Waste
ppm. Total soils requiring treatment amounted to about 12,700 tons. Treated
soils were to be placed in one of two containment cells along with untreated
soils containing less than 500 ppm PCBs before being closed with a TSCA
approved impermeable cap. PCB contaminated oils extracted from the soils
were returned to the PRP for subsequent disposal.
Since no applicable air emissions standard exists for thermal desorption, the
EPA required that SoilTech meet the 99.9999 percent (6 nines) destruction and
removal efficiency (DRE). SoilTech was also required to meet the municipal
waste incineration standard of 30 ng/m3 total dioxins and furans applied to
incineration of PCB contaminated wastes. Discharged water was to be less than
1 part-per-billion (ppb) PCBs.
4.1 Sequence of Events
SoilTech arrived at the Waukegan Harbor Superfund site in the last week of
November 1991. Modification and repair of key process components continued
at a shop in Indiana while the site was prepared, and support equipment as-
sembled and erected. Shakedown and troubleshooting of the SoilTech ATP
System was conducted in mid-January. SoilTech began treating contaminated
soils and sediments on January 22, 1992. This date also marked the start of the
30-day proof-of-process period.
Between startup and March 6, 1992 the SoilTech ATP System averaged a
feed rate of 10 tph outperforming initial projections of 9 tph. Net plant avail-
ability was over 85 percent. PCB concentrations in the feed averaged 14,000
ppm and treated soil concentrations less than 2 ppm PCBs were attained. The
average removal efficiency from the treated soil was 99.96 percent.
During this time period, SoilTech performed seven stack tests. Although the
emissions criteria for dioxins and furans were met, SoilTech was unable to meet
the 6 nines DRE for PCBs and consequently stopped operations at the direction
of the EPA.
During the next two months, SoilTech operated the ATP System intermit-
tently to test various modifications to the ATP and to the emission control sys-
tem. Specific modifications included:
• Increased volume of carbon in flue gas carbon bed;
• Removal of the wet scrubber from the flue gas handling system;
• Addition of carbon beds to internal gas recycle streams;
C.4
-------
Appendix C
• Testing of continuous addition of powdered activated carbon up-
stream of the baghouses to facilitate adsorption of PCBs;
• Reduction of flue gas carbon bed temperature; and
• Testing of continuous addition of sodium bicarbonate in the com-
bustion zone of the ATP in an attempt to induce catalytic destruc-
tion of residual PCBs.
In the latter phase of this period of intermittent operation and testing,
SoilTech discovered a gap in the flue gas carbon bed seal which was allowing
70 percent of the flue gas stream to bypass the carbon bed. SoilTech corrected
the poor seal before stack testing on May 12, 13, and 14, 1992.
Each of four stack tests conducted on those three consecutive days demon-
strated performance superior to the 6 nines DRE required. A summary of the
stack testing conducted throughout the project is given in Table 1.
It appeared that the final three tests, using powdered activated carbon in the
baghouse and then soda ash in the combustion zone, produced slightly better
Table 1
Stack Test Summary
Waukegan Harbor
Date
01-28-92
02-04-92
02-11-92
02-18-92
03-04-92
03-05-92
03-05-92
03-18-92
04-09-92
04-10-92
05-12-92
05-13-92
05-13-92
05-14-92
06-02-92
06-02-92
06-09-92
06-16-92
Feed PCBs
(#/hr)
192.50
215.50
213.40
155.70
105.60
100.80
100.80
174.90
148.60
298.50
230.40
264.60
183.00
205.70
167.40
213.60
159.15
140.80
Stack PCBs
(#/hr)
0.0144000
0 0932000
0.0690000
0.0087600
0.0039700
00012700
0.0007720
0 0009890
0.0034500
0 0009430
00002000
0.0000735
0.0000464
00000448
0.0000942
0.0001850
0.0000432
0.0000050
PCB DRE '
(%)
99.9925195
999567517
99 9676664
99 9943738
99 9962405
999987401
99.999234!
99.9994345
99.9976783
99.9996841
99.9999132
99.9999722
99 9999746
99.9999782
99 9999437
999999134
99 9999729
99.9999964
Note:
1. PCB Destruction Removal Efficiency (DRE) criterion is 99.9999 percent.
C.5
-------
Thermal Desorption of PCB Contaminated Waste
results than the test conducted without these additives. The results are, how-
ever, statistically inconclusive.
With EPAs approval SoilTech was then able to resume processing the con-
taminated soils and sediments having met all of the project performance crite-
ria.
To insure that this performance was maintained, SoilTech instituted several
new procedures and operating conditions.
• Soda ash fed to combustion zone at 200 Ibs/hour;
• Stack temperature maintained at 170°F with automatic waste feed
shutoffat!90°F;
• Sample the stack gas carbon bed on a daily basis. Shut down plant
and change the carbon bed when the PCB concentration exceeds 10
ppm;
• Weekly stack testing to be performed by Clean Air Engineering.
Failure to meet 6-nines DRE would necessitate immediate shut-
down until the cause had been identified and remedied; and
• Monitor pressure drop across stack carbon bed. Inspect bed if it
drops below 5-inches water column.
4.2 EPA Site Demonstration
On June 16, 1992 the EPA began a Superfund Innovative Technology
Evaluation (SITE) demonstration of the SoilTech ATP System. This involved
three days of rigorous sampling and testing. The test runs were conducted at
typical operating conditions. The fourth and final test was, however, run with-
out the addition of soda ash to the combustion zone. The other three tests were
run while 200 Ibs/hr or soda ash was added to the combustion zone. Each test
run consisted of 8.5 hours of solids and liquids sampling and 8 hours of stack
sampling. During the site demonstration, 224 tons of PCB contaminated soils
and sediments were processed. In addition to sampling, critical operating pa-
rameters were collected during each test.
Based on the preliminary results at the site demonstration, the EPA con-
cluded the following:
• PCB concentrations were reduced from an average of 9,761 parts
per million (ppm) in the untreated soil and sediment to an average
concentration of 2 ppm in the treated soil and sediment.
C.6
-------
Appendix C
• Approximately 0.12 milligrams (mg) of PCBs were discharged
from the ATP System's stack per kilogram of PCBs fed to the ATP.
• The majority of PCBs removed from the untreated soil and sedi-
ment were accumulated in the waste oil discharge from the vapor
cooling system.
• No dioxins, other than a low concentration [0.1 nanograms (ng) per
dry standard cubic meter (dscm)] of octachlorinated dibenzo-p-
dioxin in one stack gas sample, were detected in the stack gas from
the ATP System. Tetrachlorinated dibenzofurans were found in
both the untreated soil and sediment (88 ng/g) and treated soil and
sediment (5ng/g) and the stack gas (0.07 ng/dscm).
• Leachable VOCs, SVOCs, and metals in the treated soil and sedi-
ment were below Resource Conservation and Recovery Act
(RCRA) toxicity characteristic standards.
• No operational problems affecting the ATPs ability to treat the
contaminated soil and sediment were observed.
Selected results provided by the EPA are presented in Table 2 (on page C.8).
As expected, the results confirm that SoilTech met all of the project perfor-
mance criteria. Removal efficiency for PCBs in the treated soil averaged 99.98
percent. DRE for the stack emissions exceeded the 6 nines criteria in each test
and bettered 7 nines in two of the tests.
The results also demonstrated that dioxins and furans are not produced in the
ATP. Trace amounts detected in the waste oil, the treated soil and stack gas can
be traced back to the untreated soils and sediments.
The highest DRE for PCBs in the stack was achieved for the test in which no
soda ash was added to the combustion zone of the ATP. This indicates that the
addition of soda ash provides no reduction in the flue gas emissions produced
by the SoilTech ATP System. Further bench testing might, however, provide a
more statistically conclusive evaluation.
Processing of soils and sediments at the Waukegan Harbor Site continued
without further incident and was successfully completed on June 23, 1992 when
a total of 12,700 tons had been processed. A summary of production data is
provided in Table 3 (o page 3.9). Approximately 30,000 gallons of PCB con-
C.7
-------
Thermal Desorption of PCB Contaminated Waste
Table 2
EPA Superfund Innovative Technology Evaluation Draft Results
Waste Feed
Contaminant Concentrations
Contaminant Average Concentration
Total PCBs 9231 ppm
Dioxin/Furan:
TCDF 86 ppb
PeCDF 16 ppb
Treated Soils
Contaminant Concentrations
Contaminant Average Concentration
Total PCBs 1.972 ppm
Dioxin/Furan:
TCDF 5 4 ppb
Waste Discharge Oil
Contaminant Concentrations
Contaminant Average Concentration
Total PCBs 32 %
Dioxin/Furan:
TCDF 136 ppb
PeCDF 14 ppb
Stack Gas
Contaminant Concentrations
Average Output
Contaminant Concentration (Ibs/hr)
Particulates 0.0039 ug/dscm 0.071
Total PCBs 0.8330 ug/dscm 1 7 E-5
Total TCDF 0 0790 ng/dscm 1 .4E-9
HCL Gas 23.000 ug/dscm 0 00042
Total Hydrocarbons ND 0
Emissions
Criteria
8.7 Ib/hr
30ng/m3
0.2 Ib/hr
Stack Gas Emissions
Destruction and Removal Efficiences
PCBs Fed to ATP PCBs Exiting Stack
Test Run No. (Ib/hr) db/hr)
1 140.60 18.9E-6
2 13687 1427E-6
3 15373 17 15E-6
4 181.71 8.09E-6
ORE1
(%)
99 999987
99 999990
99 999989
99 999996
Note:
1. Project emissions criteria for PCBs is 99.9999% ORE.
C.8
-------
Appendix C
Table 3
Production Data
Waukegan Harbor
Week
Ending
1-25-92
2-01-92
2-08-92
2-15-92
2-22-92
2-29-92
3-07-92
3-21-92
4-11-92
4-18-92
5-16-92
5-30-92
6-06-92
6-13-92
6-20-92
6-27-92
Productions
(Tons)
561
1,476
1,202
1,205
1,493
606
841
245
483
592
377
46
1,284
1,000
887
402
Average PCB in
Feed Soil
(ppm)
15,500
9,243
11,657
13,143
9,571
7,025
7,060
9,950
8,350
13,740
8,800
12,000
10,486
9,450
9,917
9,300
Average PCB
Removal Efficiency '
(%)
99.97
9995
99.98
99.98
99.98
99.98
9999
99.97
9997
99.99
9999
99.99
99.98
99.98
9999
9995
TOTAL
12,700
10,400
9998
Note:
1. Soil treatment criterion is 97 percent removal efficiency.
laminated oil was desorbed from the soils and sediments and returned to the
PRPs for subsequent off-site disposal. An average plant throughput of 8 tph
had been achieved with a mechanical availability of 85 percent.
Process water generated during operations was discharged to Canonie's wa-
ter treatment system at approximately 5 gallons-per-minute (gpm) and released
to the sewer at a PCB concentration of less than 1 ppb PCBs.
C.9
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Appendix D
APPENDIX D
List Of Vendors and Consultants
Chemical Waste Management
1950 South Batavia Ave.
Geneva, IL 60134-9838
(708)513-4578
Progressive Recovery, Inc.
700 Industrial Dr.
Dupo, IL 62239
(618)286-5000
Soil Purification, Inc
P.O. Box 72515
Chattanooga, TN 37407
(404) 861-0069
Texarome, Inc.
P. O. Box 157
Leakey, TX 78873
(210)232-6079
Westinghouse Environmental &
Geotechnical Services Inc.
111 Kelsey Lane, Suite B, #11
Edwinslack, FL 33619
(813)620-1432
Roy F. Weston Inc.
1 Weston Way
West Chester, PA 19380-1499
(215) 430-7428 FAX (215) 430-3126
Site Reclamation System, Inc.
P.O. Box 11
Howey-In-The-Hills, FL 34737
(904)324-3651
Nevada Hydrocarbon, Inc.
P.O. Box 9927
Reno.NV 89507
(702) 342-0200
Encore Environmental
344 West Henderson Road
Columbus, OH 43214
(614)263-9287
Thermotech Systems Corporation
5201 North Orange Blossom Trail
Orlando, FL 32810
(407) 290-6000
Four Nines, Inc.
125 E. Trinity PL, Suite 305
Decatur, GA 30030
(404) 370-0490
Tarmac Equipment
North 7 Highway
Blue Springs, MO 64014
(800) 833-4383
Focus Environmental, Inc.
9050 Executive Park Drive
Suite A-202
Knoxville.TN 37923
(615)694-7517
Waste-Tech Services, Inc.
800 Jefferson County Parkway
Golden, CO 80401
(303)279-9712
D.I
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List of Vendors and Consultants
FB&D Technologies, Inc.
P.O. Box 58009
375 Chipeta Way
Salt Lake City, UT 84158-0009
(801) 583-3773
Ariel Industries
P.O. Box 9298
403 Spring Creek Road
Chattanooga, TN 37412
(615) 894-1957
International Technology (IT) Corp.
304 Directors Drive
Knoxville, TN 37923
(615)690-3211
Canonic Environmental Services
800 Canonic Drive
Porter, IN 46304
(219)926-8651
Separation and Recovery Sys., Inc.
1762McGawAve.
Irvine, CA 92714-4962
(714) 261-8860
SoilTech, Inc.
94 Inverness Terrace East, Suite 100
Englewood, CO 80112
(303) 790-1410
ABB Environmental Services, Inc.
261 Commercial Street
P.O. Box 7050
Portland, ME 04112
(207) 775-5400
AAA Consulting Services Inc.
P.O. Box 5067
Novato, CA 94948
(415) 883-6380
Halliburton NUS
Environmental Corp.
5950 North Course Drive
P.O. Box 721110
Houston, TX 77272
(713)561-1556
Soil Remediation Co.
P.O. Box 6217
Denver, CO 80206
(303) 756-2441
(800)441-1968
Williams Environmental Services, Inc.
2076 West Park Place
Stone Mountain, GA 30087
(404) 498-2020
U.S. Waste Thermal Processing
3419 DiaLido, Suite 308
Newport Beach, CA 92663
(714) 509-7783
GDC Engineering
822 Neosho Avenue
Baton Rouge, LA 70802
Remedquip International Manufacturing
102B-267 West Esplanade
North Vancouver, BC V7M1A5
Remediation Technologies, Inc.
9 Pond Lane
Concord, MA 01742
(508)371-1422
Southdown Thermal Dynamics
12235 FM 529
Houston, TX 77041
(800) 364-2402
D.2
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Appendix E
APPENDIX E
Table Of Acronyms and Abbreviations
APC Air Pollution Control
ARAR Applicable or Relevant and Appropriate Regulations
ATP Anaerobic Thermal Processor
BOAT Best Demonstrated Available Technology
BIF Boiler and Industrial Furnace
CERCLA Comprehensive Environmental Response, Compensation, and
Liability Act
DBA Deutsche Babcock Anlagen
FRP Fiberglass Reinforced Plastic
HC1 Hydrochloric Acid
LEL Lower Explosion Limit
LTTA Low Temperature Thermal Aeration Process
MGP Manufactured Gas Plant
NOx Oxides of Nitrogen
NPDES National Pollutant Discharge Elimination System
OSHA Occupational Safety and Health Administration
PAH Polynuclear Aromatic Hydrocarbon
PCB Polychlorinated Biphenyls
PCE Tetrachloroethene
PIC Product of Incomplete Combustion
E.I
-------
Table of Acronyms and Abbreviations
PNA Polynuclear Aromatic Hydrocarbon
POTW Publicly Owned Treatment Works
QA/QC Quality Assurance / Quality Control
RCRA Resource Conservation and Recovery Act
RI/FS Remedial Investigation / Feasibility Study
ROD Record of Decision
SARA Superfund Amendments and Reauthorization Act
SCR Silicon Controlled Rectifier
SITE Superfund Innovative Technology Evaluation Program
SOx Oxides of Sulfur
SO2 Sulfur Dioxide
SVOC Semi-Volatile Organic Compound
TCA 1,1,1 Trichloroethane
TCDD Tetrachlorodibenzo-p-dioxin
TCDF Tetrachlorodibenzofuran
TCE Trichloroethene
TCLP Toxicity Characteristic Leachate Procedure
TSCA Toxic Substance Control Act
USA United States of America
US EPA United States Environmental Protection Agency
UST Underground Storage Tank
VOC Volatile Organic Compound
E.2
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Appendix F
APPENDIX F
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Appendix F
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F.6
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