Polystyrene packing waste might well be described as the most common waste, besides paper sludge, used in brick manufacturing.
In Table 28 a general overview is given.
Table 28: Summary of utilization of surface treatment and packaging waste
Source
Sector Material Potential benefits Potential Issues
Surface treatment Powder coatings Body fuel, green strength, brick body density reducing agent Some issues with heavy metal content. Emissions into air.
Packaging Polystyrene Body fuel, brick body density reducing agent
Some issues with compressive non proportional reduction in compressive strength
Emissions into air.
Including the Poroton1 polystyrene process, patented by the Swedish engineer Sven
Fernhof in 1958 (227), in this literature review might appear at first sight a bit far fetched. Poroton is the first patented density reduction process in brick making and has gained wide acceptance. In most cases today the expanded polystyrene used is sourced from waste streams and hence the inclusion of the Poroton process has been deemed appro- priate. A very good overview of the technical effects of the addition of polystyrene to bricks is given by Veiseh and Yousefi in (228) without making any direct reference to the original patent. Krcmar in (85) has investigated the effects of various brick body density reducing agent agents on the mechanical properties of brick. He found substantial differ- ences in compressive strength of the brick when using recycled and freshly foamed poly- styrene.
Given their calorific potential powder coating waste could be very interesting but their classification as “dangerous” (EC waste code 080112) makes them unattractive.
A number of tests with powder coatings have been carried out at Ziegel Gasser Mattoni GmbH S.r.l., Baustoffwerke Hüning GmbH and JUWÖ Poroton Werke Ernst Jungk und Sohn GmbH. The problem that emerged was, that the chemical composition and heavy metals content varied considerably with the color of the powder coatings waste. A patent by Park (229) describes the use of this waste as a “catalyst” but does not offer any ex- planation about the catalytic reaction. The effect of using such material as an odor inhib- iting agent has been undertaken at the Baustoffwerke Hüning GmbH brick plant in Ger- many in 1991 (230) by mixing the waste powder coatings with sewage sludge. The inhib- iting effect might be most probably due to the pH value of the powder of 10 to 11 in an aqueous solution hence creating an alkaline environment.
Preliminary tests with powder coatings added to a standard brick feed at Ziegel Gasser Mattoni GmbH S.r.l. resulted in some very interesting results that, due to legislation in Italy classifying such wastes as hazardous, did not find any practical application. Powder coatings are thermosetting at temperatures in the range of 80°C to 200°C. Calorific val- ues and combustion behavior are similar to finely ground coal. The tests have been car-
ried out with a carboxyl group terminated polyester resin with primid, a hydroxamylkyl- amid, as bonding agent1. The density is to be found between 1.4 and 1.5 kg/l. In Table
29 a general overview is given.
Table 29: Analysis of powder coatings
Impact category Unit Concentration measured
pH in water 7,5 – 9 Incombustibles at 99°C % 99,20 Incombustibles at 600°C 27,90 Benzene mg/kg 3,9 Toluene 48,00 Ethylbenzene 12,00 Xylene 19,00 Styrene < 10,00
Ethanol and ethanol compounds < 10,00 Propanol and propanol compounds < 10,00 Butanol and butanol compounds < 10,00 Acetate and acetonic compounds < 10,00 Phenol and phenolic compounds < 0,1
Σ Cadmium < 1,00
Σ Chromium < 50,00
Lead < 650,00
Copper < 130,00
Arsenic < 100,00
Emission tests have been carried out with an addition of 10 to 12% in volume. The tests have been carried out at temperature of 391 °C, the peak energy release temperature, see the DTA's Fig. 28: and Fig. 29: on page 31, for substances with a high concentration of volatile compounds. The tests suggest, when compared to the standard emission val- ues of Ziegel Gasser Mattoni GmbH S.r.l., kiln equipped with an internal post combustion system, that an use of these substances would have been feasible and certainly, from a financial and technical point of view, interesting. The average grain size dimension of the powder coatings is by far inferior to the average grain size of saw dust and hence a far higher compressive strength values for a same density would have had to be expected (but these have not been tested for). Brick densities achieved have been more or less similar to the densities achieved with the use of saw dust. No chemical analysis has been made on the finished brick.
Table 30: Flue gas concentrations at 391°C
Impact category Unit Raw gas concentra-tion measured Raw gas concentra-tion standardized to 18% O
Gasser values (after post combustion)
Oxygen % 19.4
Carbon monoxide mg/Nm3 67,00 42.43 8
Σ C 34,00 21.53 Not measurable
HCl 3,50 2.21 < 50
Vinyl chloride μg/Nm3 < 30,0 19.00 No data
Formaldehyde mg/Nm3 < 2 1.26 < 0.01
Acrolein < 1 0.63 No data
Plasticizers of various types μg/Nm3 < 100 < 63.33 No data
Benzene 616 390.13 < 100 Toluene 221 139.96 No data Ethylbenzene 52 32.93 No data Xylole 174 110.20 No data Styrene 54 34.20 No data Naphthalene 54 34.20 No data n-Alkane 332 210.26 No data Methlyacetate < 10 < 6.33 No data Ethlyacetate 112 70.93 No data Butylacetate < 10 < 6.33 No data 2-Butanone 169 107.03 No data
Olefines / Paraffin e(C1-C5) mg/Nm3 < 0,05 < 0.03 < 1
Methane < 10 < 6.33 No data Ethane / Ethene < 10 < 6.33 No data
The analytical flue gas concentration data certainly suggest that with an appropriate post combustion system, such as the one installed at Ziegel Gasser Mattoni GmbH S.r.l., the use of such additives would be possible without any harm to the environment as the val- ues would certainly result much lower than the allowed emissions.