Biomass combustion can be seen as CO2 neutral, thereby biomass combustion plants can have negative CO2 emissions if retrofitted with post combustion capture (PCC) technology using liquid absorbents. Monoethanolamine (MEA) has been used for carbon capture in coal combustion plants but are not suitable for use in biomass combustion plants due to corrosion and high solvent regeneration cost. Instead, the hot potassium carbonate (HPC) process using potassium carbonate (K2CO3) as absorbent show better attributes in these aspects. Although, K2CO3 has slow reaction kinetics with CO2 which need to be improved using promoters. Piperazine is the most tested promoter but are hazardous to humans. Recent research has revealed promising alternatives, among these different amino acid salts such as glycine, proline, and isonipecotic acid which are chemically benign. Biomass flue gas composition vary depending on the biomass fuel characteristics. How this affects the degradation and potential formation of hazardous substances need to be studied further. Biomass combustion plants are generally equipped with flue gas condensation systems, making retrofitting more feasible due to increased system flexibility and energy recovery options. The operation costs of carbon capture and sequestration (CCS) in biomass combustion plants need to be monitored to optimize the plant revenue. To make implementation of HPC in biomass combustion plants a reality, piperazine should be used as promoter. Meanwhile, research should focus on improving the absorption rate in HPC process with more chemically safe promoters.

Bioenergy is extracted from biomass. What counts as biomass is generally quite diverse, but broadly speaking, it is material that previously lived. Today, energy extracted from biofuels make up around 23% of Stockholm city's total energy consumption. Stockholm city has set a goal to be a fossil-free city by 2040, i.e. zero emissions from energy use. Two sectors have been identified where emissions occur and these are the transport sector and the electricity and heating sector. This thesis will only address the electricity and heating sector. This includes all energy consumption within Stockholm city municipality. When Stockholm is developing towards a fossil fuel free city, it’s interesting to look at how important bioenergy will be as an energy source in the future. This thesis has scrutinized the role of bioenergy in reaching a fossil fuel free city. Three major policies have been investigated. The carbon dioxide tax and the emission rights system have promoted the bioenergy and its deployment in a positive way. The system of electricity certificates has shown to indirectly affect the bio energy in a negative way. The key finding is that bioenergy will have a great impact in reaching the goal mainly through its contributions with negative emissions, but it is also an important substitute to fossil fuels. / Bioenergi utvinns ur biomassa eller biobränslen. Biomassa och biobränslen är ganska diffusa begrepp då definitionen varierar runt om i världen, men generellt sett är det material som tidigare levt. Idag utgör energi från biobränslen cirka 23% av Stockholms stads totala energiförbrukning. Stockholms stad har satt upp ett mål att vara en fossilfri stad år 2040, det vill säga inga utsläpp från stadens energiförbrukning. Det finns två huvudsakliga sektorer där koldioxidutsläpp förekommer, dessa är transportsektorn och eloch värmesektorn. Detta inkluderar all energiförbrukning inom Stockholms kommuns gränser, till exempel uppvärmning av hushåll och energin de fordon som körs i staden förbrukar. När Stockholm utveckling går mot att bli en fossilbränslefri stad är det intressant att se hur viktig bioenergi kommer att vara som energikälla i framtiden. Denna rapport granskar bioenergins roll i att nå klimatmålet till 2040. De huvudsakliga slutsaterna är att bioenergi kommer ha en stor och viktig roll i att nå målet och att dess största inverkan kommer vara de negativa utsläppen. Vissa lagar har främjat bioenergin medans vissa indirekt har påverkat dess utveckling negativt. Bioenergin har en ljus framtid i Stockholm.

Det ständigt växande behovet av att minska CO2-utsläpp har lett till en ökad tonvikt på teknik för avskiljning av koldioxid från rökgas. MEA (monoetanolamin) anses vara riktmärket för lösningsmedel för att fånga in koldioxid på grund av dess höga absorptionshastighet. MEA är dock benäget att brytas ner, bilda giftiga biprodukter och dess regenerering har ett högt energibehov. Ett annat lösningsmedel med liknande teknisk mognad är vattenlösning med kaliumkarbonat (K2CO3) som används i den så kallade hot-potash carbonate (HPC)-processen. Emellertid är absorptionshastigheten i K2CO3-lösningen låg i jämförelse med MEA, vilket kräver tillsats av hastighetspromotorer för att öka absorptionshastigheten. Denna avhandling undersöker effekten av olika hastighetspromotorer på absorptionshastigheten av kaliumkarbonat. För detta utfördes absorptionsexperiment i laboratorieskala i en autoklavreaktor av rostfritt stål under kontrollerade förhållanden. Olika promotorer har undersökts, nämligen de organiska promotorerna glycin, piperazin och MEA, och de oorganiska promotorerna borsyra och vanadinpentoxid. Promotorkoncentrationen varierades mellan 3 vikt% till 7 vikt% samtidigt som koncentrationen av K2CO3 hölls konstant vid 25 vikt%. Driftförhållandena såsom det initiala partialtrycket av CO2 och temperaturen var respektiva 5 bar och 50 °C. De oorganiska promotorerna studerades enskilt såväl som i blandningar med K2CO3 för att studera effekten av varje promotor. De organiska promotorerna visade en signifikant förbättring av absorptionshastigheten jämfört med icke promoterad K2CO3. När det gäller de oorganiska promotorerna visade vanadinpentoxid jämförbara resultat med organiska promotorer med endast 3 vikt%. Ökad tillsatts av borsyra minskade absorptionshastigheten av lösningen promoterad av vanadin. Den experimentellt uppmätta absorptionshastigheten är anpassad till en enkel absorptionsmodell från vilken en skenbar absorptionshastighet för de främjade lösningsmedlen härleddes / The ever-growing need to reduce CO2 emissions has led to an increased emphasis on carbon capture technologies. MEA (monoethanolamine) is considered the benchmark solvent for CO2 capture due to its high rate of absorption. However, MEA is prone to degradation, forms toxic side products and its regeneration has a high energy demand. Another solvent with similar technological maturity is aqueous potassium carbonate (K2CO3) that is used in the so-called hot-potash carbonate (HPC) process. However, the rate of absorption in aqueous K2CO3 is low in comparison to MEA calling for the addition of rate promoters to enhance the absorption rate.  This thesis investigates the effect of different rate promoters on the absorption rate of potassium carbonate. For this, absorption experiments on the laboratory scale were conducted in a stainless-steel autoclave reactor under controlled conditions. Various promoters have been explored, namely the organic promoters glycine, piperazine, and MEA, and the inorganic promoters boric acid and vanadium pentoxide. The promoter concentration was varied between 3 wt% to 7 wt% while keeping the concentration of K2CO3 constant at 25 wt%. The operating conditions, such as the initial partial pressure of CO2 and the temperature were 5 bar and 50°C, respectively. The inorganic promoters were studied alone as well as in blends with K2CO3 to understand the effect of each promoter. The organic promoters demonstrated a significant enhancement of the absorption rate compared to unpromoted K2CO3. Regarding the inorganic promoters, vanadium pentoxide showed comparable results to organic promoters with only 3 wt%. When looking at the results of vanadium and boric acid, increasing concentration of boric acid resulted in a decrease in the absorption rate. The experimentally measured absorption rate are fitted to a simple absorption model from which an apparent absorption rate for the promoted solvents was derived.