This research proposes a novel Retrofit Design Approach based on process simulation and the Response Surface Methodology (RSM).Retrofit Design Approach comprises: 1) a diagnosis stage in which the variables are screened and promising variables to improve system performance are identified through a sensitivity analysis, 2) an evaluation stage in which RSM is applied to assess the impact of those promising variables and the most important factors are determined by building a reduced model from the process response behaviour, and 3) an optimisation stage to identify optimal conditions and performance of the system, subject to objective function and model constraints. All these stages are simulation-supported. The main advantages of the proposed Retrofit Design Approach using RSM are that the design method is able to handle a large industrial-scale design problem within a reasonable computational effort, to obtain valuable conceptual insights of design interactions and economic trade-off existed in the system, as well as to systematically identify cost-effective solutions by optimizing the reduced model based on the most important factors. This simplifies the pathway to achieve pseudo-optimal solutions, and simultaneously to understand techno-economic and system-wide impacts of key design variables and parameters. In order to demonstrate the applicability and robustness of the proposed design method, the proposed Retrofit Design Approach has been applied to two case studies which are based on existing gas processing processes. Steady-state process simulation using Aspen Plus TM® has been carried out and the simulation results agree well with the plant data. Reduced models for both cases studies have been obtained to represent the techno-economic behaviour of plants. Both the continuous and discrete design options are considered in the retrofitting of the plant, and the results showed that the Retrofit Design Approach is effective to provide reliable, cost-effective retrofit solutions which yield to improvements in the studied processes, not only economically (i.e. cost and product recovery), but also environmentally linked (i.e. CO₂ emissions and energy efficiency). The main retrofitting solutions identified are, for the first case, column pressure change, pump-around arrangement and additional turbo-expansion capacity, while for the second case, columns pressure change, trays efficiency, HEN retrofit arrangements (re-piping) and onsite utility generation schemes are considered. These promising sets of retrofit design options were further investigated to reflect implications of capital investment for the retrofit scenarios, and this portfolio of opportunities can be very useful for supporting decision-making procedure in practice. It is important to note that in some cases a cost-effective retrofit does not always require structural modifications. In conclusion, the proposed Retrofit Design Approach has been found to be a reliable approach to address the retrofit problem in the context of industrial applications.

Införandet av byggnadsstadgan 1874 medförde ett förbud mot byggande av flerbostadshus i trä om högre än två våningar på grund av omfattande bränder. Detta hämmande utvecklingen av trä då de större företagen byggde flervåningshus högre än två våningar vilket ledde till byggande av annat material än trä. I dagsläget är byggnadsmaterialet betong det dominerande materialet inom byggbranschen, speciellt inom byggandet av flerbostadshus. De senaste 15 åren har andelen byggda flerbostadshus med en stomme av betong varierat mellan 80 och 91 procent. Byggnad- och fastighetsbranschen står idag för cirka 21 % av Sveriges totala utsläpp av växthusgaser, en totalsiffra på cirka 21 miljoner ton koldioxidekvivalenter. Under de senaste åren har både företag och privatpersoner i både Sverige och länder runt om i världen fått upp ögonen för de miljöproblem som världen står inför och har blivit mer miljömedvetna och letar oavbrutet efter lösningar på hur samhället kan minska koldioxidutsläppen. Resultaten i detta examensarbete för de tillhandahållna projekten som detta arbete utgått från är att byggnaden konstruerad i korslimmat trä är det material som är att föredra ur ett miljö- och kostnadsperspektiv. Dock har detta arbete enbart avhandlat bärande inner- och ytterväggar samt bjälklag. / With the introduction of the 1874 building code, a prohibation against multi-storey apartment buildings built in wood was implemented, mainly because of the widespread fires throughout the years. Since most of the bigger companies built their apartment complexes in levels higher than two, it meant they had to build in construction material other than wood - thus hampering woods’ development in the field of construction. As of today, concrete is still the dominating material within construction industry, especielly when it comes to building apartment complexes. Theamount of partment buildings built with its framework consisting mostly of concrete has varied between 80 to 91 percent the past 15 years. The building industry and real estate industry represent approximately 21 % of Swedens greenhouse gas emissions, a total figure of about 21-million-ton carbon dioxide equivalents. In recent years, people and companies in Sweden and countries around the globe have become more aware of the environmental issues and its consequences that we’ll soon face and are therefore working on finding solutions on how society can reduce carbon dioxide emissions. The results presented in this thesis, which represents the projects that were provided, shows that the building built with its framing in CLT is the more sustainable material from an environmental perspective and more profitable economically. It should however be mentioned that calculations were only done for the load-bearing inner and outer walls and the floor joist.