Comments to Cement kilns firing hazardous waste
see also comments made directly in the text
General comments:
In an introductionally statement it should be mentioned, that although in the Stockholm
Convention cement kilns are only considered a part II source when they fire hazardous waste
there is also the potential to release POPs when firing non hazardous waste. This is the case
because conditions which may favour the formation of POPs are under some circumstances
less dependent from the waste characteristic but more dependent from the combustion
conditions.
Cement kiln are regarded as Annex C part 2 sources with the potential for high releases of
POPs. Therefore the wording used in this section has to be consistent with that finding and a
more “precautionary” approach should be followed. That means that this sections should give
a very clear picture of the circumstances, process and operating parameters which lead to a
reduction of POP releases. Reading the curent draft version one may get the impression that
cement kilns are just providing the service of hazardous waste disposal.
In particular, the term “alternativ fuels” should be replaced by the term “waste”; expressions,
such as “recovery of energy” and “destruction” should be replaced by “incineration” or “coincineration”.
It should also be made clear in this document, that the potential for POP releases is not
restricted to the co-incineration of hazardous waste, but to the process itself and to coincineration of waste in general.
The summary for the source category cement kilns is very vaguely and does not well reflect
the outcome of the respective section. Statements such as “if necessary” and “if properly
operated” are not appropriate to give the reader a clear picture of how to operate a cement kiln
in an environmental sound manner.
Therefore it is suggested to improve the paragraphs dealing with the following issues:
o Firing of waste and of hazardous waste
o Introduction of waste into the kiln
o Operating conditions which leads to destruction of POPs
o Operating conditions which prevent formation of POPs
In addition the influence of co-incineration of waste on product quality (clinker) should be
discussed, since it is common practice in many cement kilns to recirculate precipitated filter
dust back into the product.
Ad 1.1. cement industry in general
The cement consumption was estimated to be 260 kg/capita in 2004. Is this a mean value for
Europe, the EU or cement producing countries?
Ad 1.2. recovery of energy from waste in cement kilns
Plesae change the title into: “co-incineration of waste in cement kilns”.
It is said that a cement plant consumes 3000-6500MJ/t clinker. The maximum value for
energy demand given in the BAT document is 6000 MJ/t clinker for the wet process in long
kilns. This large range of energy demand covers all kinds of cement kilns. Maybe a splitting
for the most used kilns would be effective (e.g. about 3000MJ/tclinker for dry process,
multistage cyclone preheater and precalciner kilns, 3100-4200 for dry process rotary kilns
equipped with cyclone preheaters.... [these are values of the BAT Document])
According to the paragraph in the European cement industry 12% wastes are used by the
cement industry. Please add the information whether this is related to the energy or mass
input.
Ad 1.3. hazardous waste destruction in cement kilns
Please change the title accordingly.
For inserting hazardous waste the fact that it is a service to the public or industry is not
relevant (the cement industry earns a great deal of money for that kind of disposal).
Co-incineration of hazardous waste can only be done if certain requirements with respect to
input control (heavy metal content, heating value, ash content, chlorine content etc.), process
control and emission control (and monitoring and reporting requirements) are met. These
factors should also be integrated in this chapter.
Ad 2.1 general waste management
This chapter should be generally in line with the waste management section.
Comment to the wording: it should not be named resource coprocessing or resource
destruction but waste co incineration and waste incineration.
Ad 3.1. in the rotary kiln
In this chapter coal or petroleum coke are named as primary fuel. In practise at the hot end of
the kiln not only coal and pet coke are added, but different kinds of fossil fuels and wastes as
well. Please add a description where waste feeding may occur and also include a short
description of the consequences with regard to operating and emission behaviour.
Ad 3.3.1. the dry processes
It should be included that also the energy efficiency of a kiln is higher, if the raw meal is
preheated before it enters the kiln.
If relevant differences between the different processes with respect to POP formation and
releases should be explained. Also the distribution of these techniques within different regions
of the world should be given.
Ad 3.4. emission control
It is correct that acid gas control devices are usually not used at cement kilns. Wet scrubbers
are used in a few kilns, if the sulphur content of the raw meal is high. Devices for
minimisation of NOx are used more and more, and in Europa denox plants will be installed in
most plants until October 2007, because until then the limit value of the waste incineration
directive is valid. For most cement plants it is not possible to reach 500mg/Nm³, that are
prescribed by primary measures.
Ad 4.1. operation with conventional fuels
Conventional fuels used in cement plants are fossil fuels like coal, lignite, fuel oil or natural
gas. These fuels can be used as singular fuel or in combination, whereby a minimum quality
(heating value, heavy metal content etc.) must be ensured. Some of the fossil fuels are ground
before they are inserted e.g. lignite. But mixing with other fuels, as said in this chapter is not
required for clinker burning.
It is said that a cement plant consumes 3000-6500MJ/t clinker. The maximum value for
energy demand given in the BAT document is 6000 MJ/t clinker for the wet process in long
kilns.
Ad 4.2 operation with possible alternative fuels
In the title of the chapter, alternative fuels should be replaced by wastes.
In this chapter general considerations for inserting wastes in a cement kiln are missing and
must be included. It is relevant to check if the wastes are suitable for being incinerated in a
cement kiln. Relevant parameters are the heating value, water content, heavy metal content,
ash content, S content, Cl content etc. Also the impact on the kiln operation and additional
investments (e.g. for measuring all these parameters) must be checked beforehand.
Ad 4.2.1 examples of alternative fuels
In the title of the chapter, alternative fuels should be replaced by wastes.
Ad 4.2.2. negative waste list
It should be mentioned that this list can not be exhaustive.
Also wastes with a low heating value and a very high heavy metal content are not suitable for
being inserted into a cement kiln. Please mention that municipal solid waste should not be coincinerated in cement kilns due to its unpredictable composition and its characteristics.
Ad 4.2.3. selection
Selection of wastes for a cement plant IS (not can be) a complex process, because many
parameters of the waste, and the impact to the environment and the clinker must be taken
under consideration. Of all these influences the formation of POP is only one parameter!
Kiln operation: For kiln operation also the stability of operation (e.g. CO peaks) and the state
(liquid, solid..), preparation (shreddered, milled..), and homogeneity of the waste is relevant.
Emissions: For S emissions not only the raw material, but also the inserted fuels and wastes
are relevant.
In this chapter many emissions e.g. PCDD/F, HCl .. are missing.
Ad 4.2.4. anaylsis of the input material
It should be made clear that a legal framework has to be established for sampling and analysis
of waste fractions (esp. hazardous waste) prior to co-incineration (see for example the
European Waste Incineration Directive 2000/76/EC). Leaving that issue to the operator alone
will lead to unequal requirements for waste sampling and analysis within a region/country.
Please list required specifications: name and adress of the deliverer, origin of the waste,
volume, water and ash content, calorific value, concentration of chlorides, fluorides, sulfur
and heavy metals.
Ad 4.2.5 pretreatment and storage for use of wastes
Please change the title accordingly.
It is not clear here, if common practice (e.g. …is generally stored…) or if BAT/BEP (e.g.
…have to be protected….) is decsribed in this section. This should be clarified.
It should be made clear in this section – and also in the BAT/BEP section – that mixing of
waste with the aim of meeting certain requirements is prohibited by law in many countries
and therefore not BAT/BEP.
In this chapter the pretreated wastes are named as product, but they are still wastes. This
should be clarified.
Ad 4.2.6. destruction efficiency
Paragraph 2: The relevant European BREF states, that at the secondary burner it is not
ensured in all cases, that the temperatures are high enough to decompose halogenated organic
compounds. Therefore it is suggested to add a sentence, that the operator must prove prior to
waste feeding, that the temperature in the feeding zone is high enough to warrant complete
destruction of pollutants.
Ad 5.2. energy use
It is said that energy efficiency will be increased by most types of end of pipe abatement. End
of pipe abatement can be fabric filters, ESP, SNCR etc., but all these devices need energy. It
is not clear, how they increase the energy efficiency. The given example of process control is
no end of pipe technique, but a primary measure.
Ad 5.3.3. studies on emissions of PCDD/F into air
The Guidebook version from December 2004 contained a table with emission data from
cement kilns worldwide (Karstensen 2004). It is suggested to include these data again, since
this table gave a very good overview of emissions. Furthermore it could be seen, that
emissions varied very much depending on technology, waste quality, waste feeding and other
operating parameters, including sampling and analysis. Therefore it will be clear for the
reader, that it is necessary to carefully consider and control important operating and process
parameters to achieve low emissions. see also range of Austrian emission measurement given
above.
Comparing the data presented in table 1 (page 17) and in the former Guidebook (version dated
Dec. 2004) one may get the impression that only the lowest emissions are presented here. This
should be another argument for including the whole table of the previous version of the
guidebook.
Ad 5.3.4
The concentrations are given either as ng/g (paragraph 2) or as ng/kg (other paragraphs).
Please check if the correct units are used. In every case PCDD/F should be given in I-TEQ.
This is not the case in paragraph 2.
Ad 6.1. General measures for management
This chapter should give an overview of what is BAT/BEP. Therefore all references to legal
framework and laws should be deleted, since laws should be based on BAT/BEP. Reading
this chapter one may get the impression that BAT/BEP should be based on laws!!
Since in many countries stringent legal requirements do simply not exist every reference to
existing regulatory requirements would weaken the spirit of the whole Guidebook.
Please see changes made directly in the text.