Accreditation and Quality Assurance

, Volume 17, Issue 2, pp 159–166 | Cite as

Uncertainty estimation to evaluate mass balances on a combustion system

  • Paula TeixeiraEmail author
  • Helena Lopes
  • Ibrahim Gulyurtlu
  • Nuno Lapa
Practitioner's Report


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.


Uncertainty budget Precision Trueness Mass balance 



Financial support through a PhD grant (SFRH/BD/30076/2006) given by the Portuguese Foundation for Science and Technology (Fundação para a Ciência e a Tecnologia) is gratefully acknowledged.


  1. 1.
    ISO/IEC 17025 (2005) General requirements for the competence of testing and calibration laboratoriesGoogle Scholar
  2. 2.
    Method EPA 29 (1996) Determination of metals emissions from stationary sourcesGoogle Scholar
  3. 3.
    Ohman M, Nordin B, Skrifvars B, Backman R, Hupa M (2000) Bed agglomeration characteristics during fluidized bed combustion of biomass fuels. Energy Fuels 14:169–178CrossRefGoogle Scholar
  4. 4.
    Thy P, Lesher C, Jenkins B (2000) Experimental determination of high-temperature elemental losses from biomass slag. Fuel 79:693–700CrossRefGoogle Scholar
  5. 5.
    Eurachem/CITAC Guide (2000) Quantifying uncertainty in analytical measurement, 2nd ednGoogle Scholar
  6. 6.
    Evaluation of measurement data—guide to the expression of uncertainty in measurement, JCGM 100 (2008)Google Scholar
  7. 7.
    Measurement uncertainty in testing, EURALAB technical report no. 1/2002Google Scholar
  8. 8.
    ISO 8258 (1991) Shewhart control chartsGoogle Scholar
  9. 9.
    Thompson M, Ellison S, Fajgelj A, Willetts P, Wood R (2000) Harmonised guidelines for the use of recovery information in analytical measurement. IUPAC/ISO/AOAC International/EurachemGoogle Scholar
  10. 10.
    Nordtest Tr 537 (2004) Handbook for calculation of measurement uncertainty in environment laboratories, 2nd ednGoogle Scholar
  11. 11.
    ASTM D3682-01 (reapproved 2006) Standard test method for major and minor elements in combustion residues from coal utilization processesGoogle Scholar
  12. 12.
    CEN EN 13656 (2002) Characterization of waste—microwave assisted digestion with hydrofluoric (HF), nitric (HNO3), and hydrochloric (HCl) acid mixture for subsequent determination of elementsGoogle Scholar

Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Paula Teixeira
    • 1
    Email author
  • Helena Lopes
    • 1
  • Ibrahim Gulyurtlu
    • 1
  • Nuno Lapa
    • 2
  1. 1.LNEGLisbonPortugal
  2. 2.UNL-FCT-DCTB-UBiACaparicaPortugal

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