Advanced chemical and thermodynamic simulation of Kraft Recovery Boilers

Abstract

This doctoral thesis describes advanced chemical and thermodynamic modeling of modernKraft Recovery Boilers in pulp industry. In this work a complete Boiler was validatedand modeled using commercial engineering software such as AspenPlus, PPSDand FactSage. Purpose of the boiler model is visualization of non or difficultly measurablequantities to form a strong basis for optimization and monitoring. In total thisthesis comprises three main parts. Firstly, one basic calculation chapter is dedicated toessential equations for Kraft Recovery Boilers. Special quantities such as effective heatingvalue and combustion air demand are derived and defined based on internationalstandards. In the second part the modeling of Black Liquor as pseudo component is explained.Since Black Liquor contains numerous chemical compounds, which can not allbe handled by standard engineering software, an intermediate step called pseudo componentis required. The pseudo component comprises same information about mass andenergy content but has chemically defined compounds. In the third part, the hearth ofthe thesis, the simulation and its interfaces are explained. The first simulated element isa complete furnace model including chemical reactions and radiation phenomena. Radiationcalculation is assumed to be one-dimensional and without back radiation. Resultsof the furnace models are heat flux density, temperature and composition profiles dependingon furnace height. Further outcomes are ash melting temperatures. The secondsimulated element is the upper boiler including all heating surfaces and a natural calculationstudy. This element comprises simulation of all elements such as pipes in naturalcirculation, water and flue gas side. Chemical compositions of flue gas and ash in theupper boiler are also an outcome of this model. Furthermore, total mass, energy balanceand efficiency analysis are executed linking all outputs from used simulation softwaretools. Part three concludes with validation of the developed model based on comparisonof three realistic simulation cases. In total the obtained results are very convincing andthe developed boiler model is able to perform live simulation.i