Abstract Archive

Taiwan: dioxin emission factors during start-up and normal operations of MSW incinerator

Chen et al., 2008. Polychlorinated dibenzo-p-dioxins/dibenzofuran mass distribution in both start-up and normal condition in the whole municipal solid waste incinerator. Journal of Hazardous Materials. Article in Press. doi: 10.1016/j.jhazmat.2008.02.077

Abstract: Although many researches focused on the polychlorinated dibenzo-p-dioxins/ dibenzofuran (PCDD/F) emissions from stack, in the bottom ash and in the surrounding environment, researches focused on PCDD/F mass distributions in the whole incineration plant have seldom been addressed. This study determined PCDD/F emissions in the whole plant. A high-resolution gas chromatograph/high-resolution mass spectrometer was utilized for analyzing 17 PCDD/F species. Experimental results displayed that PCDD/Fs were formed during fly ash from super heater (SH), economizer (EC), semi-dryer absorber (SDA) and fabric filter (FF) was transferred to fly ash pit. Mass distribution ratios of PCDD/Fs in g I-TEQ (Toxicity Equivalency Quantity) per week from stack, SH, EC, SDA, FF, generation and bottom residue (BR) in start-up operations were 14.6%, 0.1%, 8.3%, 1.0%, 41.7%, 33.4% and 0.9%, respectively. Above results indicated that main PCDD/F source in the MSWI was from fly ash. However, the fly ash is easily controlled and PCDD/F emitted from stack flue gases will be difficult to be handled. Therefore, we should pay more attention on PCDD/F emission from flue gases especially from start-up procedure. Besides, fly ash should be controlled by sodium hypophosphite before being landfilled. MSWI did require further detoxification treatments for the solid residues and flue gases.

[from body of text]: The stack samples and ash samples were collected from KS MSWI, located in southern Taiwan. There are four incinerators, each of which includes own heat recovery systems (350 degrees C), selective non-catalytic reduction, dry scrubber (250–230 degrees C), activated carbon injection, fabric filter (180–160 degrees C) and stack. The treatment processes are the most common ones in Taiwan, which are recognized as the most effective technique for PCDD/F emission control.

Operation of the KS MSWI began in 2000 and its total capacity is 1800 ton/day with lower heating value of 2500 kcal/kg-waste

Experimental results displayed that the averaged PCDD/F equivalent concentration was 0.0511 ng I-TEQNm-3. The averaged PCDD/F contents for ash samples from the bottom residue, super heater, economizer, semi-dryer absorber, fabric filter and fly ash pit were measured to be: 17.2, 37.9, 4180, 620, 5020 and 6410 ng I-TEQ kg-1, respectively. The total PCDD/Fs emission factors were stack (8.47mg ton-waste-1; 0.454mg I-TEQ ton waste-1), BR (58.2 mg ton-waste-1; 3.54 mg I-TEQ ton-waste-1), SH (4.40 mg ton-waste-1; 0.306 mg I- TEQ ton-waste-1), EC (961 mg ton-waste-1; 31.9 mg I-TEQ ton-waste-1), SDA (100 mg ton- waste-1; 3.66 mg I-TEQ ton-waste-1), FF (1870 mg ton-waste-1; 160 mg I-TEQ ton-waste-1) and FAP (3610 mg ton-waste-1; 323 mg I-TEQ ton-waste-1), respectively. Theoretically the PCDD/F emission factor in FAP should be equal to summation of that in SH, EC, SDA and FF because fly ash from SH, EC, SDA and FF were transferred to fly ash pit. In other words, the PCDD/Fs might be formed (674 mg ton-waste-1; 128 mg I-TEQ ton-waste-1). As a result, the temperature of transmission system should be maintained at a level of 105–110 degrees C to prevent formation of PCDD/Fs and save energy as well. Recently, several studies have focused on the high PCDD/F emission during the start-up of incinerators. Therefore, the total emission amount of PCDD/Fs from stack, BR, SH, EC, SDA, FF and generation were 0.596, 0.0377, 0.00326, 0.340, 0.0390, 1.70 and 1.36 g I-TEQ week-1 with considering the start-up operations, respectively. Mass distribution ratios of PCDD/Fs in g I-TEQ week-1 from stack, SH, EC, SDA, FF, generation and BR in start-up operations were 14.6%, 0.1%, 8.3%, 1.0%, 41.7%, 33.4% and 0.9%, respectively. It could be seen that the main PCDD/F source in the MSWI was from fly ash although start-up procedure can generate 60% of the PCDD/F emissions from stacks for one whole year of normal operations.

Specific emergy of cement & concrete

Pulselli et al., 2008. Specific emergy of cement and concrete: An energy-based appraisal of building materials and their transport. Ecological Indicators 8: 647 – 656.

Abstract: Use and production of building materials, such as cement and concrete, is a major cause of global ecological problems with special reference to the overexploitation of non-renewable natural resources due to high temperature production processes, fossil fuels combustion, extraction of raw materials and non-recycling. In this paper, an environmental accounting method was applied to the production of cement and concrete in order to evaluate its dependence on natural resources even non-renewable and heavily relied on external inflows. The main steps of the production process (1) cement production, (2) transport of materials and (3) concrete mixing, were assessed by the emergy analysis (spelled with an ‘‘m’’). This was performed to measure the amount of environmental resource use in terms of equivalent solar energy, extending the energy hierarchy principle to building materials. The resulting unit emergy values of cement and concrete were compared with previous emergy assessments in order to highlight how emergy analysis is sensitive to local context and reference system’s boundaries. An Emergy Investment Ratio (EIR) was assessed and presented as a synthetic indicator of sustainability. Results showed a high dependence of cement and concrete production on external resource flows. Furthermore, the high value of EIR suggested a weak competitive capacity due to a high sensitivity to external instabilities.

[from body of text]: In this paper, an evaluation of building materials sustainability was presented through an emergy evaluation. The specific emergy of cement and concrete are 3.04 x 10 to the 9 sej/g and 1.81 x 10 to the 9 sej/g, respectively, in the Italian context. The emergy analysis of cement and concrete production takes into account various steps in the process. More than procedures for materials production, the results highlight the impact of the use of quarry materials. These are seen as mineral resources with high specific emergy provided by natural sedimentary cycles and accounted in sej. In the case of cement, materials (limestone, chalk, shale, clay and sand) are about 84% of the total emergy, while emergy for the blast furnace is about 15%. In the case of concrete, materials (sand, gravel, crushed stone, cement) are about 97% of the total emergy. Thus emergy highlights the critical role of overuse of non-renewable resources in the building industry, since it accounts for the work of nature (sedimentary cycle), not only human work for quarrying (the only process accounted in economic analysis). The dominant contribution of mineral resources underlines the un-sustainability of the building industry. Non-renewable and non-recyclable materials such as cement and concrete are undergoing depletion.

Burning RDF in cement kilns

Genon, G., Brizio, E., 2008. Perspectives and limits for cement kilns as a destination for RDF. Waste Management. Article in Press.
a: Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
b: A.R.P.A. Piemonte, Via Vecchia di Borgo 11, 12100 Cuneo, Italy

Abstract: RDF, the high calorific value fraction of MSW obtained by conventional separation systems, can be employed in technological plants (mainly cement kilns) in order to obtain a useful energy recovery. It is interesting and important to evaluate this possibility within the general framework of waste-to-energy solutions. The solution must be assessed on the basis of different aspects, namely: technological features and clinker characteristics; local atmospheric pollution; the effects of RDF used in cement kilns on the generation of greenhouse gases; the economics of conventional solid fuels substitution and planning perspectives, from the point of view of the destination of RDF and optimal cement kiln policy. The different experiences of this issue throughout Europe are reviewed, and some applications within Italy are also been considered. The main findings of the study are that the use of RDF in cement kilns instead of coal or coke offers environmental benefits in terms of greenhouse gases, while the formation of conventional gaseous pollutants is not a critical aspect. Indeed, the generation of nitrogen oxides can probably be lower because of lower flame temperatures or lower air excess. The presence of chlorinated micro-pollutants is not influenced by the presence of RDF in fuel, whereas depending on the quality of the RDF, some problems could arise compared to the substituted fuel as far as heavy metals are concerned, chiefly the more volatile ones.

[from body of text]: Some studies reported 1.8 million t/y of secondary fuels co-incinerated in cement kilns in Europe in 1997, which is expected to increase by 15% by 2003. The related strategy for the cement industry is to rely on alternative fuels to reduce its high energy bill (energy costs typically represent 30–40% of manufacturing costs of Portland cement), as well as for sustainable development. This is also an important consideration from the point of view of carbon dioxide emissions and the consequent possibility to benefit from carbon emission credits.

Hazardous wastes (1 million t/y) and tyres (550,000 t/y) are the most frequently used secondary fuels. However, future attention should be switched to biomass-based fuels including wastepaper and sewage sludge for carbon emission credits.
On the contrary, an increase in chlorine (0.3–0.5% in RDF, very low values less than 0.1% in coke) can lead to some problems arising from reactions between alkali and chlorine, the volatilisation of chlorides and recycling with dust, and the necessity to operate a bypass (extraction of part of the flue-gas) in order to limit the chlorides in the final clinker ( Kurdowski, 1983 ).

The presence of heavy metals in secondary fuels can lead to a transfer in the produced clinker

… A final important aspect for the proposed substitution of secondary fuels is the low density of this material in comparison with conventional fuels. Taking into account the transport and storage costs, the cost of substituted fuels per unit of heat produced is higher than the cost of coke or coal.

… The use of RDF in cement manufacturing kilns seems to be positive, as the combustion of RDF allows for a reduction of about 1.61 kg of CO2 per kg of utilised RDF compared to conventional combustible materials (coal). This is due to the chemical composition of the combustible material. When RDF is used in specifically set up combustion systems with energetic recovery, taking into consideration the energetic mix for the production of electric energy and the efficiency of the electric production, the substitution of the combustible material involves an increase in the production of CO2 of about 0.15 kg per kg of RDF.

… The negative impact of the emission of atmospheric pollutants from the raw composition of burned RDF consists of the possible transfer of substances contained in the waste to the atmosphere or the produced clinker.


In any case, it is evident that the use of RDF instead of traditional fuels in a cement kiln could be dangerous in terms of the presence of larger amounts of heavy metals in the waste gas, so the quality and the quantity of RDF

… It is important to underscore that the transfer factors can change according to the composition of the fuel (for example, which molecules mercury forms around), to the presence of halogens (for example, Pb, Ag, Ni are much more volatile as chlorides) and to the occurrence of a reducing or oxidising atmosphere.

… As far as the possible formation of dioxin is concerned, a complete study has been conducted on the emissions from the co-combustion system ( SINTEF, 2004 ). The main results of this study are as follows:

• there is no correlation between dioxin emissions and the type of alternative combustible material used ( Fig. 4 );
• the formation of dioxins can occur in a thermal window between 200 and 450 _C, zones that are encountered in fume cooling systems before the final separator of the fumes;
• potential precursors released by combustible material introduced into the pre-calcination zone can react with the chlorine not retained by the alkaline matrix of the clinker, in the presence of metallic catalysts present in the transported powders, giving rise to emissions of dioxin where de-novo synthesis occurs;
• while the dioxin concentrations are, in most cases, lower than 0.1 ng/Nm3, concentrations of PCB at least a thousand times higher are possible. In this sense, they constitute a significant source of precursors that are able to generate micro-pollutants where the aforementioned kinetic conditions allow this to happen.

… Based on our experience, some problems can arise for cement kilns when using secondary raw materials containing micro pollutants or precursors (PCB, PAH).

Abstract:

Abstract:

This section last checked or updated: 23 May 2008