CEN/TR 15473:2007

SLOVENSKI STANDARD
01-julij-2008
Karakterizacija blata - Dobra praksa pri sušenju blata
Characterization of sludges - Good practice for sludges drying
Charakterisierung von Schlämmen - Gute fachliche Praxis zur Schlammtrocknung
Caractérisation des boues - Bonne pratique pour le séchage des boues
Ta slovenski standard je istoveten z: CEN/TR 15473:2007
ICS:
13.030.20 7HNRþLRGSDGNL%ODWR Liquid wastes. Sludge
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 15473
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
March 2007
ICS 13.030.20
English Version
Characterization of sludges - Good practice for sludges drying
Caractérisation des boues - Bonne pratique pour le Charakterisierung von Schlämmen - Gute fachliche Praxis
séchage des boues zur Schlammtrocknung
This Technical Report was approved by CEN on 27 August 2006. It has been drawn up by the Technical Committee CEN/TC 308.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2007 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 15473:2007: E
worldwide for CEN national Members.

Contents Page
Foreword.3
Introduction .4
1 Scope .5
2 Normative references .5
3 Terms , definitions and abbreviated terms .5
4 General.7
5 Treatment process description .9
6 Drying plant ancillaries .35
7 Operation .38
8 Safety considerations .42
9 Characteristics of dried sludge products .47
10 Outlets available .51
Bibliography .56

Foreword
This document (CEN/TR 15473:2007) has been prepared by Technical Committee CEN/TC 308
“Characterization of sludges”, the secretariat of which is held by AFNOR.
The status of this document as CEN/TR has been chosen because much of its content is not completely in
line with practice and regulations in each member state. This document gives recommendations for good
practice concerning the drying of sludges, but existing national regulations remain in force.
Introduction
All the information of this CEN Technical report constitutes a framework for the process of drying sludges.
Various Directives will apply to thermally dried sludge products depending on the use to which they are to be
put. These Directives include Directive 86/278/EEC(see [1]) for recycling to land, Directive1999/31/EC (see
[2]) for disposal to landfill and Directive 2000/76/EC (see [3]) for incineration and energy recovery and
Directive 94/9 for equipment intended for use in potentially explosive atmospheres (see [4]).
This document should be read in the context of the requirements of these Directives and any other relevant
regulations, standards and codes of practice, which may prevail locally within Member States.
1 Scope
This CEN Technical report describes good practices for sludge drying and it is one of a series on sludge
management options. It gives guidance on
- drying processes;
- characteristics of dried sludge products;
- recycling or disposal of dried sludge products.
from urban wastewater treatment plants.
Sludges of other origin, like sludge from water supply or industrial treatment plants are not in the exact scope
of this CEN Technical Report, however the handling of most of these sludges will comply to a large extent with
the leads given in this CEN Technical Report.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 1085, Wastewater treatment – Vocabulary
EN 12832, Characterisation of sludges – Utilisation and disposal of sludges –Vocabulary
CR 13714, Characterisation of sludges – Sludge management in relation to use or disposal
CEN/TR 13767, Characterisation of sludges – Good practice for sludges incineration with and without grease
and screenings
CEN/TR 13768, Characterisation of sludges – Good practice for combined incineration of sludges and
household wastes
CEN/TR 15126, Characterisation of sludges – Good practice for landfilling of sludges and sludge treatment
residues
3 Terms , definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document the terms and definitions given in EN 1085, EN 12832 and CR 13714
apply and also those given in:
Directive 91/271/EC (see [5]) concerning urban wastewater treatment;
Directive 75/442/EC (see [6]) the waste framework directive as amended by Directive 91/156/EC (see [7]);
Directive 99/31/EC (see [2]) on the landfill of waste;
Directive 86/278/EEC (see [1]) on the protection of the environment, and in particular the soil, when
sewage sludge is used in agriculture;
Directive 2000/76/EC (see [3]) on incineration;
Directive 94/9 (see [4]) for equipment intended for use in potentially explosive atmospheres;
Directive 99/92/EC (see [8]) on minimum requirements for improving the safety and health protection of
workers potentially at risk from explosive atmospheres;
and the following terms and definitions apply:
3.1.1
adhesion or shearing phase
phase, which exists in a range of some 40 % to 60% dry residue content, where the sewage sludge changes
its rheological behaviour. Within this phase there is a "sticky mass" whose treatment and transportation is to
be given special attention. Above the adhesion phase the sewage sludge has, in many cases, depending on
the drying equipment, a more crumbly/lumpy structure that makes it easier to handle
3.1.2
fully dried / partly dried sludge
sludge dried above 85% dry residue content is defined as “fully dried” and sludge of dry residue content
below 85% as “partly dried”
3.1.3
convection dryer
drying system where the heat is transferred to the product by a gaseous medium which is in intimate and
direct contact with the product
NOTE The evaporated water is thus mixed with the drying medium and the exhaust gases from the dryer consist of
the drying gas including leakage air plus the evaporated water. Convection dryer can operate with direct or indirect heating.
3.1.4
conduction dryer
drying system where the heat is transferred through an intermediate heat transfer surface to the product
NOTE The medium, which supplies the heat to the product, is never in direct contact with it. The total exhaust gas
amount leaving the dryer is the evaporated water plus some leakage air. Therefore a conduction dryer is always operated
with indirect heating.
3.1.5
solar dryer
drying system where the heat is transferred to the product by solar radiation
3.1.6
combined drying system
system, which uses both principles, convection and conduction in the same dryer
3.1.7
hybrid drying system
system that consists of a combination of a conduction dryer and a convection dryer
3.1.8
direct heating
off gas from the burner is in contact with the drying product
3.1.9
indirect heating
heating loop is crossing a heat exchanger
3.2 Abbreviated terms
BOD Biological Oxygen Demand
COD Chemical Oxygen Demand
HAZOP Hazard and Operability Studies
LCV Lower Calorific Value
LIT Layer Ignition Temperature
LOC Limiting Oxygen Concentration
MEC Minimum Explosion Concentration
MIE Minimum Ignition Energy
MIT Minimum Ignition Temperature
MPOC Maximum Permissible Oxygen Concentration
PLC Programmable Logic Controller
RTO Regenerative Thermal Oxydizer
SCADA System Control, Alarm and Data Acquisition
VOC Volatile Organic Carbon
WWTP Waste Water Treatment Plant
4 General
The drying of sewage sludge is a complex process but it can contribute to the need for increased disposal
security for sewage sludge. With dried sewage sludge, a wider potential customer market can be approached
than for liquid or dewatered products. It can be recorded that the range of those willing to accept sewage
sludge can be expanded if one offers dried sewage sludge. In any case, the opportunity for marketing sewage
sludge can be extended considerably which, in turn, represents an additional security for disposal and/or
utilisation. The overview of thermal dryer types is given in Figure 1.
Dryers
Convection Solar dryers Conduction
dryers dryers
with direct with indirect with indirect
heating heating heating
Hybrid drying systems
+
Convection dryer Conduction dryer
Combined drying systems:
The principles of convection and conduction are applied in one dryer

Figure 1: Overview on thermal dryer types
Thermal drying of sludge can result in the following advantages for almost all outlet routes:
• Substantial minimisation of the bulk of sludge for disposal. Thus 1 t dry residue of sludge at 90%
represents 1,1 t actual or wet mass of sludge for disposal, but 1 t dry residue of sludge at 5% represents
20 t wet mass of sludge for disposal. Minimisation of sludge mass and volume by thermal drying results
in savings in transport costs, which can be a major component of disposal costs.
• The removal of water leaves a thermally dried sludge product with a lower calorific value (LCV) (about 10
MJ/kg to 15 MJ/kg, depending e.g. upon the extent of pre-treatment), which can be used for thermal
recycling.
• The thermally dried sludge product has favourable properties, as it is usually handable and storable,
which lends flexibility to operations.
• For recycling to agriculture, in particular, there is the advantage that thermal drying is an ‘advanced
treatment process whereby the dried sludge product gets sanitised and effectively free of pathogens at
the end of the process.
Whilst the thermally dried product has definite advantages over other types of sewage sludge, there are some
reservations (Brown and Jacobs, 2001 (see [9])) about the thermal drying process as follows:
• High capital cost (see 7.2.1);
• High operating cost, mainly energy consumption (see 7.2.1);
• Safety issues, particularly risk of fire and explosion (see clause 8);
• Technology can be complex and needs some well trained operators (see 7.3);
• The thermally dried product can be re-infected by micro-organisms and as a result of rewetting odour
can be released after storage dependent upon the conditions of storage.
The thermally dried sludge product can reach a dry residue content up to about 95% mass fraction. In most
instances thermal drying of sludge will aim to achieve a dry residue content of more than 50% in order to
avoid the adhesion or shearing phase.
5 Treatment process description
5.1 General
There are numerous designs of thermal drying equipment available on the market and many of these have
been adapted from other industries and used for sewage sludge drying. Few have been designed specifically
for sewage sludge.
The equipment can be classified into four main groups defined by the drying process:
• Conduction dryers;
• Convection dryers;
• Combined or hybrid drying system;
• Solar dryers (radiation dryers).
5.2 Conduction dryers
5.2.1 General
A conduction dryer is a drying system where the heat is transferred through an intermediate heat transfer
surface to the product.
The medium, which supplies the heat to the product, is never in direct contact with it. The total exhaust gas
volume leaving the dryer is the evaporated water plus some leakage air. Therefore conduction dryers are
always operated with indirect heating.
5.2.2 Disc dryers
Disc drying plants are - dependent on their shape - in a position to dry sewage sludge, both partially and
completely. With this, complete drying is made possible using a mixing machine placed before the dryer. Here,
a part of the already dried product is mixed with the dewatered sludge and thus overcoming of the adhesion
phase is achieved outside the dryer. Plants for full drying, as special structures, are also used by which the
return admixture takes place in the input area of the dryer.
Wear problems and dried sludge behaviour (fines and dust) have contributed to the decline in use of disc
dryers for full drying. In the majority of cases
...