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Teixeira, Paula, Helena Lopes, Ibrahim Gulyurtlu, Nuno Lapa, and Pedro Abelha. "Evaluation of slagging and fouling tendency during biomass co-firing with coal in a fluidized bed." Biomass & Bioenergy. 39 (2012): 192-203. AbstractWebsite

Over the last decades, several indices based on ash chemistry and ash fusibility have been used to predict the ash behaviour during coal combustion, namely, its tendency for slagging and fouling. However, due to the physical–chemical differences between coals and biomass, in this work only the applicability of an ash fusibility index (AFI) to the combustion and co-combustion of three types of biomass (straw pellets, olive cake and wood pellets) with coals was evaluated. The AFI values were compared with the behaviour of ash during combustion in a pilot fluidized bed and a close agreement was observed between them. For a better understanding of the mechanisms associated with bed ash sintering, they were evaluated by SEM/EDS and the elements present on the melted ash were identified. Evidences of different sintering mechanisms were found out for the fruit biomass and herbaceous biomass tested, depending on the relative proportions of problematic elements. The particles deposited on a fouling probe inserted in the FBC were analyzed by XRD and the differences between the compounds identified allowed concluding that the studied biomasses present different tendencies for fouling. Identification of KCl and K2SO4 in the deposits confirmed the higher tendency for fouling of fruit biomass tested rather than wood pellets.

Teixeira, Paula, Helena Lopes, Ibrahim Gulyurtlu, and Nuno Lapa. "Uncertainty estimation to evaluate mass balances on a combustion system." Accreditation and Quality Assurance. 17.2 (2012): 159-166. AbstractWebsite

Mass balances of ash and potassium for a fluidized bed combustor were performed incorporating measurement uncertainties. The total output mass of ash or a chemical element should be equal to the mass in the input fuel; however, this is not often achieved. A realistic estimation of recovery uncertainty can support the reliability of a mass balance. Estimation of uncertainty helps to establish a reliable evaluation of the recovery ratio of ash mass and elemental mass. This may clarify whether any apparent lack in closing the mass balance can be attributed to uncertainties. The evaluation of measurement uncertainty for different matrices, namely coal, biomass, sand and ashes from different streams was based on internal quality control data and external quality control data, namely analysis of samples from proficiency tests or use of a certified reference material. The evaluation of intermediate precision and trueness allowed the estimation of measurement uncertainty. Due to the different physic and chemical characteristics of the studied matrices, the uncertainty of precision was evaluated using R-charts of data obtained from the analysis of duplicates for the majority of samples. This allowed evaluating sample heterogeneity effects. The instrumental acceptance criterion was also considered and included in the combined uncertainty. The trueness was evaluated using data from several proficiency tests and from analysis of a certified reference material or sample spiking. Statistically significant bias was included.

Teixeira, P., H. Lopes, I. Gulyurtlu, and N. Lapa. "Use of chemical fractionation to understand partitioning of biomass ash constituents during co-firing in fluidized bed combustion." Fuel. 101 (2012): 215-227. AbstractWebsite

Three species of biomass origin (straw pellets, olive cake and wood pellets) and two coals from different countries (Coal Polish and Coal Colombian) have been studied to understand the fate of their ash forming matter during the combustion process and to investigate the influence of co-firing biomass with coal. Three different approaches to investigate the ash behaviour were employed: (1) chemical fractionation analysis to evaluate the association/reactivity of ash forming elements in the fuels as a prediction tool, (2) establishment of elements partitioning in ash streams produced in the combustion and co-combustion trials, and (3) evaluation of enrichment factors of elements in the ash streams. The chemical fractionation analysis was applied to all fuels used to evaluate how the association/reactivity of elements making up ash may influence their behaviour during combustion. Combustion tests were carried out on a pilot scale fluidized bed combustor (FBC). Four ash streams were obtained at different locations. The uncertainty of measurements was estimated allowing a critical evaluation of mass balances over the combustion system and the partitioning of elements in the ash streams. The enrichment factors of elements in the several ash streams were estimated, incorporating uncertainties associated with analytical measurements. Results obtained showed that for FBC the relation between the chemical fractionation and the experimental partitioning is strongly affected by elutriation of particles. The element enrichment factor estimated for each ash stream, using Al as a reference element, revealed better correlations with the elements reactivity obtained by chemical fractionation because it overcomes particles elutriation effects. Nevertheless, it was observed that the reactivity estimated by chemical fractionation could not be solely interpreted as tendency of the elements to volatilize on FBC system, as reaction in bed zone of boiler may also occur retaining reactive elements.

Lapa, N., J. Morais, C. Borges, B. Mendes, and J. F. Santos Oliveira. "An integrated approach to assess the biodegradability of a wastewater containing chromium by using chemical and biological methods." Global Symposium on Recycling, Waste Treatment and Clean Technology, REWAS’2004. Eds. I. Gaballah, B. Mishra, R. Solozabal, and M. Tanaka. San Sebastián: TMS/INASMET, 2004. 1351-1362. Abstractrewas04_lapa_et_al.pdf

The Water Company of the North Alentejo (Águas do Norte Alentejano) (Portugal) has decided to implement a treatment plant to treat an urban wastewater with a significant influence of tannery effluents. The design of the wastewater treatment plant was attributed to a consortium coordinated by Sisaqua Company. Since the levels of the biodegradability and toxicity of the wastewater to be treated were unknown, Sisaqua Company asked the New University of Lisboa to develop and execute a monitoring plan to define the chemical composition and the levels of the biodegradability and toxicity of the wastewater.
A composite sampling procedure of the wastewater was performed during a daily working cycle of the tanneries. The composite sample was characterized for 19 chemical parameters. Five of these parameters were total Cr, Cr (VI), Zn, Cu and Al, which were determined in the dissolved and suspended fractions. The composite sample was also submitted to a biological test to assess its biodegradability degree. This assay was performed according to the methodology indicated in the test 301E of OECD [1], taking into account the amendment of 1992. A respirometric assay was carried out, to assess the toxic effect of the composite sample on the biological populations involved in the biological stabilization of organic compounds. This assay followed the “Sapromat” methodology developed by Brabander and Vandeputte [2]. Finally, the composite sample was submitted to a coagulation-flocculation process according to the methodologies proposed by Eckenfelder [3, 4] and Pereira [5]. The supernatants were characterized for the same chemical and biological parameters as it was described for the composite sample.
It was possible to conclude that the high levels of Cr present in the composite wastewater were mainly in the trivalent oxidation state. Since this oxidation state is less toxic for biological populations than the Cr (VI) and this metal was mainly in the suspended fraction, it was possible to obtain a biodegradability of the organic compounds quite similar to those observed for domestic wastewaters. The toxicity determined by the “Sapromat” method was slightly higher than those determined for domestic wastewaters. Nevertheless, this toxicity did not affect significantly the wastewater biodegradability. The Cr (III) was easily removed by a chemical coagulation-flocculation process.