The function of a flue-gas quench is to remove additional contaminants from flue-gas and to reduce the wastewater from a waste incineration plant. The aim of this degree project is to find how the system is affected by using a quench and what factors limits the performance. This is done by modelling and simulating a waste incineration plant in Aspen Plus. Data and plant schematics were obtained by a study visit to Mälarenergi Plant 6 situated in Västerås, Sweden, which were used as model input and for model validation. The results have shown that the amount of wastewater can be reduced by more than half compared to a plant without a quench. The heat produced in the condenser, when discharging water to the boiler, would be lowered by up to 20%. For systems with a quench present when more water was discharged to the boiler both the heat production and the pollutant capturing became better. However, the system has limits regarding the amount that could be recirculated, in the form of temperature limits in different parts of the system. In addition, if the heat load is low there is an insufficient amount of wastewater generated in the condenser to run the quench. In that situation, clean (fresh) water needs to be used instead. Using clean water is unwanted since the plant will then consume more resources while still producing less heat than a plant without a quench would.

The aim of this thesis is to design the condensation heat exchanger for stationary engine running on natural gas. Flue gas condenser is designed for universal use of refrigerants (i.e. water or 35% fusion ethylene-glycol in water) and their working temperatures. The work includes theoretical, computational and design part. In the attachment is located the drawing documentation to flue gas condenser.

Syftet med undersökningen var att klargöra om en rökgaskondensor är en bra investering för Nybro Energi AB. Saxlund Bioenergy AB kontaktades för sammanställning av offert. Med hjälp av parametrar från Nybro Energi AB och offerten från Saxlund Bioenergy AB, gjordes beräkningar för att avgöra om en investering är lönsam. Resultatet av undersökningen visade att en investering av sådant slag som behandlats i detta arbete var intjänad efter mindre än sju år i drift och effekten som är möjlig att utvinna uppgår till 2,8 MW, förutsatt att panneffekten utgjordes av minst 15 MW.  Slutsatserna var att investeringen inte var betald efter sju år med underlag av att kostnader som utgjordes av eventuell ombyggnation inte var behandlade i undersökningen, detta innebar dock inte att en investering ärr olönsam då dessa kostnader uppskattades som små i förhållande till den totala besparingen efter att den ekonomiska livslängden på 15 år har löpt ut. / The purpose of this investigation was to clarify whether a flue gas condenser was a good investment for Nybro Energi AB. Saxlund Bioenergy AB was contacted for the compilation of quotation. Using parameters from Nybro Energi AB and the quote from Saxlund Bioenergy AB, calculations were made to determine whether an investment was suitable. The results of the study showed that the investment of the kind dealt with in this work was earned after less than seven years of operation, and the output that was possible to recover amounted to 2,8 MW, provided that the boiler output consisted of at least 15 MW. The conclusions were that the investment was not paid after seven years because of the costs consisted of possible reconstructions were not considered in the survey, this does not mean that an investment was unprofitable since these costs were estimated as small relative to the total savings after the economic life of 15 years, has expired.

Thesis is focused on calculation of the condenser of flue gas, which is created by burning of natural gas. In the first part is theoretical overview of equations describing film condensation and physical properties of the flue gas. The second part deals with practical thermal calculation of the specified condenser. In third part parametric study is done in which a tempature of cooling water at inlet and the coefficient of excess air are changed. The last part of the thesis is dedicated to geometric design of the flue gas condenser whose required power is 8 MW.