With increasing oil prices and attention towards the reduction of anthropogenic CO2, the use of supercritical carbon dioxide for Fischer Tropsch Synthesis (FTS) is showing promise in fulfilling the demand of clean liquid fuels. The evidence of consumption of carbon dioxide means that it need not to be removed from the syngas feed to the Fischer Tropsch reactor after the gasification process. Over the last five years, research at SIUC have shown that FTS in supercritical CO2 reduces the selectivities for methane, enhances conversion, reduces the net CO2 produces in the coal to liquid fuels process and increase the life of the catalyst. The research has already evaluated the impact of various operating and feed conditions on the FTS for the once through process. We believe that the integration of unreacted feed recycle would enhance conversion, increase the yield and throughput of liquid fuels for the same reactor size. The proposed research aims at evaluating the impact of recycle of the unreacted feed gas along with associated product gases on the performance of supercritical CO2 FTS. The previously identified conditions will be utilized and various recycle ratios will be evaluated in this research once the recycle pump and associated fittings have been integrated to the supercritical CO2 FTS. In this research two different catalysts (Fe-Zn-K, Fe-Co-Zn-K) were analyzed under SC-FTS in different recycle rate at 350oC and 1200 psi. The use of recycle was found to improve conversion from 80% to close to 100% with both catalysts. The experiment recycle rate at 4.32 and 4.91 was clearly surpassing theoretical recycle curve. The steady state reaction rate constant was increased to 0.65 and 0.8 min-1 for recycle rate of 4.32 and 4.91 respectively. Carbon dioxide selectivity was decreased for both catalyst as it was converting to carbon monoxide. Carbon dioxide consumption was increased from 0.014 to 0.034 mole fraction. This concluded that CO2 is being used in the system and converting which created the concentration of the feed gas higher inside the reactor. The research has provided the best conditions for the enhanced conversion while minimizing CO2 formation. Though this research was not able to provide the optimal recycle rate it have created the path for the future research to proceed in the right direction. This reduction and utilization of CO2 will help to reduce the cost of carbon dioxide removal and saves the environment from carbon dioxide emission.

Margretelund wastewater treatment plant (WWTP) operated by the water utility Roslagsvatten AB, wasbuilt in 1956 and is located in Åkersberga town, Stockholm County, Sweden. Margretelund WWTP waslast renovated in 1999, and has been operated with the same physical, chemical, and biological processessince then. Due to issues with increased phosphorus emissions connected to increased concentration ofeffluent total suspended solids (TSS), Roslagsvatten would like to optimize the operation of their dissolvedair flotation (DAF) process and the author was tasked to conduct a study about the subject. The specificaim of the study was to propose one method for optimization with available means to reduce effluentTSS concentration during high flow rates for the present DAF process at Margretelund WWTP.Achieving the aim required an historical analysis of Margretelund WWTP’s DAF process and aninvestigation of the effect influent flow rate and effluent recycle rate (ERR) had on effluent TSSconcentration. The increase of effluent TSS was believed to be caused by increased flow rates frominfiltration and inflow (recorded to 32% of total volume the year 2020) affecting the dissolved air flotation(DAF) process.The literature study design parameters for a dissolved air flotation process, specifically the recycle flowpressurization configuration, generated information about which parameters to take into considerationwhen optimizing a DAF unit. Analysis of historic effluent measurements at Margretelund showed that42% of all samples analysed between January 2015 – January 2021 were below 10 mg/l TSS. Eachhistorical increase of surface load has brought a decreased effluent recycle rate (ERR) and consequentlyan increasing percentage of samples exceeding 10 mg/l. A Pearson correlation presented a negativecorrelation with both ERR and surface load in relation to effluent TSS concentration. This resulted inthe selection of the experimental factors ERR and surface load to be investigated in this study.Margretelunds WWTP’s DAF design of ERR being 10-15% and the design surface load of 4 m/h wasthe base values for the experimental runs. Increases of ERR percentage was done during the experimentfor four different surface loads (2.5, 4, 5 and 6 m/h), with five steps between 15% up to 35% ERR inone of the three parallel DAF units in Margretelund WWTP. TSS in the effluent was constantlymonitored using a TSS sensor. Influent TSS was measured at Roslagsvatten’s accredited laboratory in a24h composite sample with 1 hour for each sub-sample.The results showed that both the highest and the lowest ERR settings tested provided the lowest averageeffluent TSS concentrations. However, a decreased surface load was found to lower effluent TSSconcentration and ERR providing only minor differences within each surface load. Largest surface loadpossible was found to be 5 m/h, for an ERR of 15 or 35%. Surface load less than 5 m/h provided aconcentration under 10 mg/l for all ERR setting. / Margretelund avloppsreningsverk (ARV) placerat i Åkersberga, Stockholms län, byggdes 1956 och drivs av Roslagsvatten AB. Margretelund ARV har sedan 1956 renoverats vid två tillfällen senast 1999. Samma reningsprocess för fysisk, kemisk och biologisk rening har använts sedan senaste renoveringen. Roslagsvatten har haft problem med oönskat tillskottsvatten (motsvarade 32% av total volym 2020) som har påverkat deras flotationsprocess negativt gällande rening av suspenderat material. Detta har till slut lett till förhöjda utsläppsvärden av fosfor som finns bundet i det suspenderade materialet. Denna studie har utförts av författaren på efterfrågan av Roslagsvatten, med syfte att presentera optimeringsåtgärder till styrning av flotationsprocessen vid höga flöden. För att uppnå målet med studien gjordes en historisk analys av Margretelunds flotationsprocess samt undersökningar om hur variationer i inkommande flöde samt recirkuleringsgrad har påverkat koncentration av utgående suspenderat material.Teori undersöktes och information insamlades angående designparametrar gällande optimering av flotationsprocesser, mer specifikt en flotationsprocess med recirkulerat trycksatt flöde för avskiljning av susp. Analys av historiska utsläppsvärden från Margretelund ARV’s flotationsprocess visade på att 42% av proverna analyserade mellan januari 2015-januari 2021 låg under 10 mg/l för utgående suspenderat material. Varje historisk ökning av ytbelastning påvisade en minskande recirkuleringsgrad samt en ökande andel prover som översteg koncentrationen 10 mg/l. Utifrån en Pearson korrelation visades en negativ korrelationen för både ytbelastning och recirkulationsgrad gentemot koncentration av utgående suspenderat material. Både recirkuleringsgrad och ytbelastning valdes därför till denna studies experimentella faktorer. Flotationsprocessen på Margretelund ARV’s var designad för en recirkuleringsgrad på 10–15% vid ytbelastning på 4 m/h, och valdes som basvärde för experimentet. Fem olika grader av recirkulation testades för fyra olika ytbelastningar (2.5, 4, 5 och 6 m/h) i intervallet 15–35% i en av tre parallella flotations bassänger på Margretelund ARV. Koncentration utgående suspenderat material mättes kontinuerligt med en sensor. Inkommande koncentration bestämdes genom ett dygnsprov som analyserades av Roslagsvattens ackrediterade laboratorium.Ett resultat från experimenten var att både den högsta och lägsta inställningen av recirkuleringsgrad visade de lägsta medelvärdena för utgående koncentration av suspenderat material. Dock, visade resultaten att en minskande ytbelastning resulterade i lägre koncentrationer av utgående suspenderat material. Vidare sågs att recirkuleringsgraden enbart hade en låg påverkan på koncentrationerna för varje ytbelastning. Den högsta möjliga ytbelastningen utan att överstiga 10 mg/l visades vara 5 m/h med recirkuleringsgraderna 15% och 35%.