Estimation and modelling of black liquor heat content

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School of Engineering | Master's thesis
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Date

2013

Department

Energiatekniikan laitos

Major/Subject

Energiatekniikka

Mcode

Ene-47

Degree programme

Language

en

Pages

(9) + 85

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Abstract

Black liquor, a by-product of kraft pulping, is combusted in a recovery boiler to reclaim spent pulping chemicals and the evolved heat is used to generate process steam and electricity. Black liquor's heating value is a function of its elemental composition. It influences the dimensioning of the recovery boiler heat transfer surfaces and is an important parameter in material and energy balance calculations. It is determined experimentally using bomb calorimetry (a time consuming process) and experimental results have been used to derive generic empirical formula for ease of estimation. This thesis presents a third, semi-empirical, programmable, structural property based approach to determine the heating value of a given black liquor flow in the Virtual Chemical Pulping (VIC) model developed as a part of the EfFibre programme. The VIC model split black liquor into its constituent compounds and the standard enthalpy of combustion of eleven lignin and two polysaccharide VIC model compounds was determined using two structural property based methods: Benson Group Increment Theory and Cardozo's method. Additionally, bomb calorimetry experiments were carried out in order to understand the variations in the heating value of different lignin compounds and compare the heating value of selected compounds with those obtained using structural property based methods. Both Cardozo's method and BGIT yielded results comparable to the values in the literature and, under certain circumstances, with the experimentally calculated values. The VIC model compound enthalpy values ranged between 24 MJ/kg and 28 MJ/kg. The results of lignin bomb calorimetric experiments showed Alcell (organosolv) lignin as the compound with the largest enthalpy of combustion (28.9 MJ/kg) followed by Milox lignin (21.0 MJ/kg). The results identified the sensitivity of group additivity methods to structural simplifications and intermolecular effects. These include non-nearest neighbour and rain strain interactions which may be compound specific and were not taken into account in the modelling. The agreement between experimental and modelling approaches appeared to diminish when the compound in question had an unverifiable or a complicated molecular structure.

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Supervisor

Järvinen, Mika

Thesis advisor

Kuitunen, Susanna
Salmenoja, Keijo

Keywords

black liquor heating value, BGIT, group additivity, lignin enthalpy of combustion, Cardozo's method

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https://urn.fi/URN:NBN:fi:aalto-2020122859747

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[dipl] Insinööritieteiden korkeakoulu / ENG