Om rökgasåterföringens påverkan på NOx-utsläpp och verkningsgrad
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
This report is a sum of a master thesis carried out at Lulekraft AB, with the purpose to size a flue gas recirculation (FGR) system. The goals were to decrease the amount of NO$_x$ in the flue gases, to minimize the fluctations of the temperature of the steam in the super heaters and to investigate how the efficiency changes with implemented FGR.There are numerous methods for reduction of NOx emissions well described in the litterature, both from modifications of the burners and from methods reagarding the flue gas path. Modifications in the flue gas path can be e.g. FGR or SCR (selective catalytic reduction). Burner modifications can be e.g. flame less combustion or staging combustion.When air is used as heat carrier the temperature fluctuates when the operator is switching fuel. With implemented FGR the fluctations can be minimized with respect to the specific heat capacity. That is higher for the flue gases as a heat carrier than that for air. This leads to higher power output with shorter time for heating up the steam as a result, compared to air as heat carrier.Results show that the adiabatic flame temperature decreases with higher flow of FGR, but also with higher flow of the extra supplied air. The difference can be explained as follows: For FGR the O2 concentration in the flue gases is constant, while for the extra supplied air the O2 concentration increases. With a decreased flame temperature the emissions of thermal NOx will be reduced, due to the fact that thermal NOx is approximately exponentially dependent of the flame temperature.Results also show that the efficiency increases with implemented FGR. This is because that it is possible to increase the power input in the water/steam cycle. The flue gas temperature difference, along the flue gas path, between FGR and supplied extra air can be neglected. This justifies the increased power input in the water/steam-cycle. The efficiency when extra air is supplied is 76.3 %, and with FGR the efficiency is 82.5 %.
Place, publisher, year, edition, pages
2015. , 59 p.
Teknik, NOx, rökgasåterföring, FGR, Stökiometri, stoichiometry, förbränning, combustion
IdentifiersURN: urn:nbn:se:ltu:diva-46886Local ID: 47e56f05-c7b9-4669-8ca0-61a29e2be2b5OAI: oai:DiVA.org:ltu-46886DiVA: diva2:1020201
Subject / course
Student thesis, at least 30 credits
Mechanical Engineering, master's level
Validerat; 20150216 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved