This thesis is a part of a collaboration between Höganäs AB and Luleå University of Technology, aiming at replacing fossil process coal with bio-coal in their sponge iron process. The difference in gasification reactivity, i.e. reaction rate, between fossil coals and bio-coals is the major challenge in the endeavor to decrease the climate impact of the existing process. The goal of this thesis is to develop a model of reaction rate for bio-coals in relation to particle size distribution. Different particle size distributions were combined and tested to see how that affects the effective reaction rate. Within the scope of this work, gasification reactivities of different materials, including coal, cokes, and bio-coals, were determined. Three bio-coals were selected to study the effect of particle size distribution on reactivity. Kinetic parameters were determined by using thermogravimetric analysis in the temperature range of 770-850 °C while varying CO2 partial pressure between 0.1-0.4 atm. The effect of particle size on the reaction rate was investigated by using particles with diameter between 0.18 and 6.3 mm. The effect of particle size distribution on the reactivity of bio-coal in a packed bed was carried out in a macro thermogravimetric reactor with a constant bed volume of 6.5 cm3 at 980 °C and 40% (vol.) of CO2. The experimental investigation in three different rate-limiting steps was done for one bio-coal sample, i.e. Cortus Bark bio-coal. The activation energy of the bio-coal was 187 kJ mol-1, and the reaction order was 0.365. For the internal diffusion control regime, an increase in particle size resulted in low reaction rate. The effective diffusivity calculated from the Thiele modulus model was 1.41*10-5 m2 s-1. For the external diffusion control regime, an increase in particle size increased the reaction rate up to a certain point where it plateaued at >1 mm. By choosing two discrete particle size distributions, where a smaller average distribution can fit into a larger average distribution the reaction rate was lowered by 30% compared to only using a single narrow particle size distribution. This solution decreased the difference of apparent reaction rate in a packed bed between the bio-coal and anthracite from 6.5 times to 4.5 times. At the moment the model is not generalized for all bio-coals. However, the developed methodology can be routinely applied to assess the different bio-coal samples. One possible error can be that pyrolysis influences the gasification rate for bio-coal that is pyrolyzed below the temperature of the gasification test. There is a clear correlation between particle size distributions, bulk density, and apparent reactivity. By mixing two distributions the reaction rate of Cortus Bark was reduced from 6.5 times the reaction rate of anthracite to 4.5.

The steel industry is aiming to reduce CO2 emissions by different means; in the short-term, by replacing fossil coal with highly reactive carbonaceous material like bio-coal (pretreated biomass) and, in the longer term, by using hydrogen. The use of bio-coal as part of top charged briquettes also containing iron oxide has the potential to lower the thermal reserve zone temperature of the Blast furnace (BF) and, due to improved gas efficiency, thereby give a high replacement ratio to coke. In order to select a suitable bio-coal to be contained in agglomerates with iron oxide, the current study aims at investigating the devolatilization behavior and related kinetics of different types of bio-coals. In addition, the aim is to investigate the self-reduction behavior of bio-coal-containing iron ore composite under inert condition and simulated blast furnace thermal profile. In the BF the temperature of the top-charged material will increase rather quickly during the descent in the upper part. Ideally, all the carbon and hydrogen contained in the top-charged bio-coal should contribute to the reduction. The devolatilization of bio-coal is thus important to understand and to compare between different types of bio-coal. To explore the devolatilization behavior for different materials, a thermogravimetric analyzer equipped with a quadrupole mass spectrometer was used to monitor the weight loss and off-gases during non-isothermal tests for bio-coals having different contents of volatile matter. The samples were heated in an inert atmosphere up to 1200°C at three different heating rates: 5, 10 and 15°C/min. The thermogravimetric data were evaluated by using the Kissinger–Akahira–Sonuse (KAS) iso-conversational model and the activation energy was determined as a function of the conversion degree. Bio-coals with both low and high content of volatile matter can produce reducing gases that can contribute to the reduction of iron oxide in bio-agglomerates. Bio-coals containing a higher content of catalyzing components such as CaO and K2O will enhance the devolatilization and release of volatile matter at a lower temperature.  The self–reduction of composites was investigated by thermogravimetric analyses in argon atmosphere up to 1100°C and evolved gases were monitored by means of quadrupole mass spectroscopy. Composites with and without 10% bio-coal and sufficient coke breeze to keep the C/O molar ratio equal to one were mixed and Portland cement was used as a binder. To explore the effect of added bio-coals, interrupted vertical tube furnace tests were conducted in a nitrogen atmosphere at temperatures selected based on thermogravimetric results, using a similar thermal profile as for the thermogravimetric analyzer. The variation between fixed carbon, volatile matter contents and ash composition for different types of bio-coal influences the reduction of iron oxide. The results showed that the self-reduction proceeds more rapidly in the bio-coal-containing composite and that the volatile matter could have contributed to the reduction. The self-reduction of bio-coal-containing composites started at 500°C, while it started at 740°C with coke as the only carbon source. The hematite was successfully reduced to metallic iron at 850°C with bio-coal present as a reducing agent, but not until 1100°C when using coke. Use of bio-coal with high content of volatile matter but low content of catalyzing elements as potassium, sodium and calcium in bio-agglomerates for the BF can be recommended because it enhances the self-reduction of iron oxide, e.g., wustite was detected by XRD analysis in samples treated up to 680°C. Bio-coal with low content of volatile matter, low alkalis, low phosphorous and high content of fixed carbon will also be suitable to use in the BF.

In recent years, the consequences of global warming have increased the discussion about the climate impact caused by humans and the fossil emissions. Sweden has decided to reduce the negative climate impact with a zero vision for the fossil carbon dioxide emissions in year 2045. In order to achieve this, great efforts and changes are needed both in the inhabitants' way of living but primarily in the base industry. The major cause is the use of fossil coal, which generates fossil carbon dioxide in the steel industry in particular. The fossil coal is added to the blast furnace in the steel process in forms of coke and coal, which reduces the iron and emits heat. The quality of the coke is important as it functions reducing agent, provides a mechanical support to the bed and enables the gas flow up through the blast furnace and enables dissolution of carbon in hot metal. Also, coke supplies energy from exothermic reactions between carbon and carbon dioxide that takes part in the blast furnace and the energy are further used for the heating and melting of the cold iron pellets. Due to these factors, the blast furnace process is dependent on coke for its function, which means that the entire process must be replaced if the steel production should work without fossil coal. However, there are many studies that have been done on how to replace some of the fossil coal with bio-coal, which is produced from biomass. If some of the fossil coal could be replaced by some bio-coal, this would mean that fossil carbon dioxide emissions would decrease and lead to a reduced climate impact. The process would still generate carbon dioxide, but on the other hand, a cycle would be formed because when biomass is grown, carbon dioxide is taken up, e.g. by the trees grown for this purpose. However, bio-coal does not have the same properties as fossil coal, which in turn affects the quality of the coke. Bio-coke is more reactive and more porous than fossil coke. In order to be able to replace fossil coke with bio-coke, it is likely necessary to pre-treat the biocoal before it replaces part of the fossil coal in the coke production. Bio-coal contains ash that acts as an internal catalyst. One theory is that if it is possible to produce a bio-coal with ash-free carbon structure, it can be used in the production of coke without having such a great effect on the coke quality. In this project, the ash's impact on the properties of bio-coal in coke was studied. Previous studies have shown that leaching is an effective method for removing ash from bio-coal. It can be leached in three different ways, either with water, weak acid or acid. However, it has been found that acid leaching has a certain impact on the carbon structure itself. For this reason, two types of bio-coal, torrefied Grot (forest residue) and torrefied sawdust were selected, which were leached both with water but also with weak acid in order to achieve an ash-reduced carbon structure. The acid selected was acetic acid, as it has been tested for similar purposes in previous studies. The leaching efficiency was evaluated by analysing the leachate with ICP-OES after leaching. According to the result, a significant part of the ash had been leached out, but the leaching with weak acid was much more effective than water leaching. To ensure that the carbon structure was not altered, light-optical microscopy was made which showed that the structure was intact. However, it was not possible to determine whether the pore sizes were changed after leaching and it is therefore relevant to investigate this further. Moreover, the leached II bio-coal replaced 5% of the fossil coal in the coal mixture for coke making. In addition to this, coke was also made with only the ash from the two bio-coals to see what effect the ash has on the coke quality. The result that was obtained from the TGA showed that the ash had a low impact on the reactivity of the coke. However, the coal structure of the coke had a great impact on the reactivity behaviour. Keywords: Bio-coke, bio-coal, leaching, ash, coke quality, carbon structures, torrefied sawdust

Carbon dioxide emissions to the atmosphere today cause problems around the world. In Sweden, the steel production contributes significantly to carbon dioxide emissions. The steel industry challenge is to improve the metallurgical processes to decrease the carbon dioxide emissions. One way to reduce the emissions is to use renewable carbon sources. The blast furnace process is a counter current reduction process for ironmaking. Raw materials such as iron ore agglomerates, coke and slag formers are charged at the top of the furnace while oxygen-rich blast air and powdered coal are injected in the bottom. The gases produced by combustion rise through the burden on the top of the furnace. The combustion of carbon produces carbon monoxide which is the reducing gas used for the reduction of iron oxides to pig iron. The process is the highest producer of CO2 emissions in Sweden; biomass can partially replace fossil carbon in coal blends for cokemaking, coal powder for coal injection and coke in self-reducing briquettes.  The purpose of this project was to maximize the addition of biomass in coal blends for cokemaking and the addition in briquettes produced for the recovery of iron bearing rest products. The challenge with biomass in cokemaking is its low density and high reactivity which decrease the coke yield and coke strength at the same time that it increases the coke reactivity. The coke quality has to be kept at sufficient quality in order to avoid effects on productivity and process stability in the blast furnace. The addition of biomass in briquettes is limited due to the low density of the biomass which may affect the strength of the briquettes. The effect of the addition of sawdust in coke and briquettes has been studied to understand the effect on reaction behaviour of bio-coal. Heat-treatment of sawdust with high volatile coal was performed in order to achieve a coating of coal on the sawdust surface and get less reactive sawdust. Torrefied sawdust contained 23 wt. % fixed carbon while the pre-treatment of sawdust with high volatile coal increased the content to about 60 wt. %. Pre-treated sawdust was added to coal blend for coke making and briquettes containing iron oxide. The pre-treated sawdust was added to five coal blends for coke production, the contents were 5, 10 and 20 wt. %, and a base blend was used as reference. Coke reactivity, chemical composition and cold compression strength in coke were studied. This work resulted in an improved bulk density; up to 20 wt. % pre-treated sawdust could be added to the coal blend and still keep a bulk density of 800 kg/m3. The coke yields in cokes with pre-treated sawdust were comparable to the coke reference. The temperature at which carbon in coke began to be consumed was slightly higher in coke containing sawdust treated with 50 wt. % high volatile coal. It was estimated that the CO2 emission from fossil coal could be reduced with 8.6 % per ton hot metal (THM) with the addition of 10 wt. % pre-treated sawdust to coal blends for cokemaking. The addition of 20 wt. % pre-treated sawdust could reduce the CO2 emission with 10% per THM. In addition, two different mixes of briquettes were produced, one with torrefied sawdust and one with pre-treated sawdust. The chemical composition and reduction of iron oxides in briquettes was also studied and evaluated. Briquettes with treated sawdust were more compact, i.e. had a higher density than briquettes containing torrefied sawdust. The amount of hematite that could be added to the briquette mixes was 0.107 moles in briquettes with torrefied sawdust and 0.112 moles in briquettes with pre-treated torrefied sawdust. / Koldioxidutsläppet till atmosfären orsakar idag problem runt om i världen. I Sverige bidrar stålproduktionen avsevärt till koldioxidutsläppet. Stålindustrin har som en utmaning att förbättra de metallurgiska processerna för att sänka utsläppet av koldioxid. Ett sätt att sänka koldioxidutsläppen är att minska påverkan genom att använda förnybara kolkällor. Masugnsprocessen är en kontinuerlig reduktionsprocess för råjärnframställning och en av processerna där det används reduktionsmedel från fossila kolkällor. Råmaterial som järnmalm, koks och slaggformare chargeras på toppen av ugnen medan syrgasberikad blästerluft och pulveriserat kol injiceras i botten av ugnen genom masugnens formor. De gaser som produceras vid förbränning stiger upp genom beskickningen upp till ugnens topp. Vid förgasning av kol bildas kolmonoxid som är den reducerande gasen, den möjliggör reduktionen av järnoxider vid framställning av råjärn. Torrefierad biomassa kan delvis ersätta fossilt kol i kolblandningarna för kokstillverkning, i kolinjektionen och i briketter. Syftet med detta projekt var att maximera mängden tillsatt biomassa i kolblandningarna för kokstillverkning och i briketter för återvinning av järnbärande restprodukter. Utmaningen med biomassa i kokstillverkningen är den höga reaktiviteten och den låga densiteten av kol, vilket resulterar i låg koksutbyte när den tillsätts i kolblandningar. Biomassa innehåller också en högt halt flyktiga ämnen vilket resulterar i koks med låg hållfasthet och hög reaktivitet. Kokskvalitén måste behållas för att undvika processvariationer i masugnen. Tillsatsen av biomassa i briketter, är begränsat då biomassa kan påverka briketternas hållfasthet. Effekten av tillsatsen av biomassa i koks och briketter har studerats för att kunna förstå reaktionsbeteendet i dessa när torrefied sågspån och förbehandlat sågspån med hög fluiditetskol har tillsatts till blandningarna. Värmebehandling av torrifierat sågspån med en hög fluiditeteskol gjordes för att uppnå en mindre reaktiv biomassa. Torrifierat sågspån innehöll 22.9 viktsprocent kol, förbehandlingen av sågspån med hög fluiditetskol ökade halten till cirka 60 viktsprocent. Den behandlade sågspånen tillsattes till fem kolblandningar för koksframställning, 5, 10 och 20 viktprocent tillsattes till en bas blandning som användes referens. Koksreaktiviteten, kemisk sammansättning och hållfasthet i koks studerades. Arbetet resulterade i en förbättrad bulkdensitet då upp till 20 viktprocent förbehandlad biomassa kunde tillsättas i kolblandningen och fortfarande behålla en bulkdensitet på 800 kg/m3. Koksutbytet i alla koks med förbehandlat sågspån var jämförbart med koksreferensen. Temperaturen där kemisk kol i koks började förbrukas, var något högre i koks som innehöll sågspån med 50 viktsprocent hög fluiditetskol. Koldioxidutsläppen från fossilt kol per ton råjärn (THM) uppskattades att vara 8,6 % lägre med tillsatsen av 10 viktprocent förbehandlat sågspån i kolblandningar för kokstillverkning. Tillsatsen av 20 viktprocent skulle innebära en minskning på 10 % per ton råjärn. Briketter med två olika blandningar framställdes, en blandning med torrifierat sågspån och en blandning med behandlat sågspån. Briketterna karakteriserades genom att analysera den kemiska sammansättningen och reduktionen av järnoxider i termisk reducerade briketter. Briketter med behandlat sågspån var mer kompakta, d.v.s. hade en högre densitet än briketter som innehöll torrifierad sågspån. Mängden hematit som kunde tillsättas i mixen med torrifierad sågspån var 0.107 mol, medan i mixen med förbehandlat sågspån 0.112 mol kunde tillsättas. / Bio4metals / CAMM

Steel is one of the most essential metals in the world, and it plays a vital role in various industries. The growing demand for steel has resulted in increased CO2 emissions, with the steel industry contributing to approximately 7% of global emissions of carbon dioxide. Among the different production methods, the electric arc furnace (EAF) has emerged as a promising option, and its market share is expected to double in the future. While the EAF exhibits high efficiency and a reduced carbon footprint in comparison to alternative production routes, there is still considerable room for improvement. In the EAF, a significant amount of input energy, ranging from 15% to 30%, is wasted through off-gas, along with a substantial amount of CO2. To better understand the current state and ongoing research in off-gas handling, a literature review and a preliminary analysis were conducted which revealed that the waste heat from the off-gas can be effectively recovered using an evaporative cooling system, yielding approximately 105 kg of steam per ton of liquid steel. This emphasizes the importance of waste heat recovery in conjunction with CO2 capture. Calcium looping stands out as a promising carbon capture technology among the available options, primarily because of its lower environmental impacts and energy penalty. Furthermore, with its operation at elevated temperatures and dependence on limestone, calcium looping presents a potential solution to reduce the emissions from steel industry. Therefore, this study focuses on the analysis of a waste heat recovery system integrated with calcium looping technology, aiming to capture CO2 and utilize waste heat from the EAF off-gas. Additionally, the potential of coal substitution with bio-coal in the EAF for achieving negative emissions is also investigated. Through a steady state analysis and by employing semi-empirical mass and energy balance equations, it was determined that capturing 90% of the CO2 emissions from a 145-ton EAF requires 12 MW of heat and 16 kg of fresh limestone per ton of liquid steel. Although the average off-gas temperature is high, it cannot be considered as a reliable heat source. Therefore, the heat demand is met by burning biomass inside the calciner. Despite the increased heat demand, the waste heat recovery system integrated with calcium looping has the potential to generate approximately 11 MW of electricity using a supercritical steam cycle. This significant output can be attributed to the elevated temperature of the off-gas and the exothermic carbonation process. The economic analysis reveals that the levelized cost for capturing and storing CO2 is 1165 SEK per ton of CO2 with a negative Net Present Value (NPV). It was noted that, a higher carbon tax could significantly enhance the economic viability of the system. Moreover, the study found that by introducing bio-coal in the EAF with a fossil coal share below 69%, it has the potential to achieve negative emissions. Furthermore, recent studies have shown an increase in the CO2 content in the off-gas when introducing bio-coal into the EAF which further enhances the efficiency and economic feasibility of carbon capture. / Stål är en av de viktigaske metallerna i världen, och det spelar en avgörande roll i olika branscher. Den ökade efterfrågan på stål har lett till ökade koldikoxidutsläpp, och stålindustrin står för cirka 7% av de globala koldioxidutsläppen. Bland de olika produktionsmetoderna har ljusbågsugnen (EAF) framstått som ett lovande alternativ, och dess marknadsandel förväntas fördubblas i framtiden. Även om EAF uppvisar hög effektivitet och ett minskat koldioxidavtryck jämfört med alternativa produktionsvägar, finns det fortfarande stort utrymme för förbättringar.  I EAF går en betydande mängd tillförd energi, mellan 15 och 30%, till spillo genom avgaserna, tillsammans med en betydande mängd CO2. För att bättre förstå det aktuella läget och pågående forskning inom hantering av avgaserna genomfördes en litteraturstudie och en preliminär analys som visade att spillvärmen från avgaserna effektivt kan återvinnas med hjälp av ett evaporativt kylsystem, vilket ger cirka 105kg ånga per ton flytande stål. Dettta understryker vikten av att återvinna spillvärme i samband med CO2-avskiljning.  Kalciumlooping framstår som en lovande teknik för koldioxidavskiljning bland de tillgängliga alternativen, främst på grund av dess lägre miljöpåverkan och energiåtgång. Eftersom kalciumlooping används vid förhöjda temperaturer och är beroende av kalksten, utgör den dessutom en potentiell lösning för att minska utsläppen från stålindustrin. Därför fokuserar denna studie på analysen av ett system för återvinning av spillvärme integrerat med kalciumlooping-teknik, i syfte att fånga in CO2 och utnyttja spillvärme från EAF-avgaserna. Dessutom undersöks potentialen för att ersätta kol med biokol i EAF för att uppnå negativa utsläpp.  Genom en steady state-analys och med hjälp av semi-empiriska mass- och energibalansekvationer fastställdes att det krävs 12 MW värme och 16 kg färsk kalksten per ton flytande stål för att fånga 90% av CO2-utsläppen från en 145-tons EAF. Även om den genomsnittliga avgastemperaturen är hög kan den inte betraktas som en tillförlitlig värmekälla. Därför tillgodoses värmebehovet genom förbränning av biomassa i kalcinatorn. Trots det ökade värmebehovet har systemet för återvinning av spillvärme integrerat med kalciumlooping potential att generera cirka 11 MW el med hjälp av en superkritisk ångcykel. Denna betydande produktion kan hänföras till den förhöjda temperaturen i avgaserna och den exoterna karbonatiseringsprocessen. Den ekonomiska analysen visar att den nivellerade kostnaden för avskiljning och lagring av CO2 är 1165 SEK per ton CO2 med ett negativt nettonuvärde (NPV). Det konstaterades att en högre koldioxidskatt skulle kunna förbättra systemets ekonomiska lönsamhet avsevärt. Dessutom visade studien att genom att introducera biokol i EAF med en andel fossilt kol under 69%, har det potential att uppnå negativa utsläpp. Nya studier har dessutom visat en ökning av koldioxidhalten i avgaserna när biokol införs i EAF, vilket ytterligare förbättrar effektiviteten och den ekonomiska genomförbarheten för koldioxidavskiljning.