Spray towers have proven to be efficient in capturing gases and vapours, finding widespread use across various applications including CO₂ capture. As there is scarce reference material regarding spray tower performances with different flow configurations other than the conventional counter-current flow, as well as the use of substitute solvents to MEA, there is a need to study different configurations and setup designs, including different placements of gas and liquid inlets in the absorber tower, to find the optimal configuration. In this study, the capture of CO₂ from a CO₂/N₂ mixture using unpromoted potassium carbonate as the absorbent in a lab-scale spray tower was experimentally measured in four different flow configurations over a wide range of operating conditions, including gas and liquid flow rates, CO₂ concentration, K₂CO₃ concentration and solvent temperature. Among four different configurations, the two sides co-current configuration, with gas nozzles positioned on opposite sides of the column and liquid coming from above, was found to be the most effective setup for enhancing CO₂ capture efficiency by promoting better mixing and contact between gas and liquid.

 To reduce carbon emissions in heavy-duty transportation, renewable fuels like biodiesel and hydrotreated vegetable oil are increasingly blended with fossil fuels as drop-in alternatives. However, these blends can lead to issues such as the formation of insoluble materials, or soft particles, within the fuel system. These precipitates, composed of inorganic salts and organic aggregates, cause filter clogging, nozzle fouling, and internal injector deposits, negatively impacting engine performance, increasing fuel consumption, and causing drivability issues. This study investigates internal injector deposits through an accelerated laboratory thermal test, replicating the deposits observed in injectors from heavy-duty vehicles. The goal is to understand the chemistry behind these deposits and explore the formation of inorganic salts, such as calcium crystals, and soft particle deposits. Temperature plays a critical role in deposit formation, influencing both morphology and composition. FTIR-ATR and SEM-EDX analyses reveal that metal carboxylates form between 100 ◦C and 170 ◦C, while calcium sulfate crystals form above 170 ◦C. The test successfully replicates the characteristics of real-world deposits, with findings suggesting that calcium sulfate deposits primarily form in the presence of engine oil contaminants. This points to engine oil leakage as a significant factor in the formation of internal diesel injector deposits (IDIDs). This research highlights the value of laboratory testing as a cost-effective alternative to engine tests for studying deposit formation in drop-in fuel systems. 

Low-temperature soot oxidation in catalytic diesel particulate filters (DPF) is important for maintaining high efficiency of heavy-duty vehicles. This can be achieved by coating DPFs with an oxidation catalyst. In this work, catalytic DPFs have been collected from real-world operating heavy-duty vehicles for assessment of their catalytic activity and subsequent characterization. Testing of catalytic activity revealed the diminishing nitric oxide (NO) oxidation of the aged catalysts. The apparent reaction rates showed that the number of available catalytic sites decreased with mileage explaining the loss in activity. Characterization of the samples showed a decreasing surface area as well as an accumulation of metals and poisonous elements. An important finding from SEM-EDS analysis is the evident accumulation of phosphorus and sulfur in the washcoat in the absence of other ash-related elements, potentially explaining the decreased activity.

 In recent years, deposit formation in fuel systems for heavy-duty engines, using drop-in fuels, have become increasingly common. Drop-in fuels are particularly appealing because they are compatible with existing engines, allowing for higher proportions of alternative fuels to be blended with conventional fuels. However, the precipitation of insoluble substances from drop-in fuels can result in fuel filter clogging and the formation of internal injector deposits, leading to higher fuel consumption and issues with engine drivability. The precise reasons behind the formation of these deposits in the fuel system remain unclear, with factors such as operating conditions, fuel quality, and fuel contamination all suggested as potential contributors. In order to reproduce and study the formation of internal injector deposits, for heavy-duty engines under controlled conditions and to facilitate a more precise comparison to field trials, a novel injector test rig has been developed. This newly constructed, non-firing rig includes the main components of heavy-duty vehicle engines and uses an electric motor to simulate the revolutions per minute of an engine. A tailored run cycle has been developed to enable the continuous monitoring of injector performance during the deposit formation process, as well as to meticulously mimic the actual operations of a real engine. The deposits formed on injectors during the rig tests were analyzed using scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and pyrolysis connected to gas chromatography-mass spectroscopy (Py GC-MS). This work presents the outcome of the analysis of injector deposits using the test rig, and compares these findings with deposits gathered from field operations. The deposits obtained from the injector test rig were found to be similar in terms of deposit location, composition, and microstructure, with both sets of deposits containing metal carboxylates and derivatives of engine oil additives. These similarities demonstrate that the test rig effectively reproduces the formation of injector deposits observed in real-world conditions. 

 The formation of deposits in the fuel systems of heavy- duty engines, using drop-in fuels, has been reported in recent years. Drop-in fuels are of interest because they allow higher levels of alternative fuels to be blended with conventional fuels that are ompatible with today’s engines. The precipitation of insolubles in the drop-in fuel can lead to clogging of fuel filters and internal injector deposits, resulting in increased fuel consumption and engine drivability problems. The possible mechanisms for the formation of the deposits in the fuel system are not yet fully understood. Several explanations such as operating conditions, fuel quality and contamination have been reported. To investigate injector deposit formation, several screening laboratory test methods have been developed to avoid the use of more costly and complex engine testing. To further evaluate and understand the formation of internal injector deposits in heavy-duty engines, a thermal laboratory test method has been developed. The test method is called Thermal Deposits Test (TDT) and it is inspired by Jet Fuel Thermal Oxidation Test (JFTOT) method. This test unit can be used to study in applications where a fluid is in contact with a hot surface. The method uses common laboratory hardware and readily available off-the-shelf parts, making it inexpensive to build and very flexible to operate. Deposits are collected on a metal foil, which makes it easier to analyze. This paper describes the construction of the apparatus and its performance. Experimental tests with diesel fuel, doped with soap-type soft particles, which contain typical particles that can form deposits, are performed, and compared with JFTOT results. Analytical techniques, such as Scanning Electron Microscopy with Energy Dispersive X-Ray, Fouriertransform Infrared Spectroscopy, and Pyrolysis coupled with Gas Chromatography-Mass Spectroscopy and Ellipsometry were used. Conclusions about the performance of the doped fuel are drawn from the test. Future plans are to study the mechanisms behind the formation of internal diesel injector deposits. 

Heavy-duty transportation is one of the sectors that contributes to greenhouse gas emissions. One way to reduce CO2 emissions is to use drop-in fuels. However, when drop-in fuels are used, i.e., higher blends of alternative fuels are added to conventional fuels, solubility problems and precipitation in the fuel can occur. As a result, insolubles in the fuel can clog the fuel filters and interfere with the proper functioning of the injectors. This adversely affects engine performance and increases fuel consumption. These problems are expected to increase with the development of more advanced fuel systems to meet upcoming environmental regulations. This work investigates the composition of the deposits formed inside the injectors of the heavy-duty diesel engine and discusses their formation mechanism. Injectors with internal deposits were collected from field trucks throughout Europe. Similar content, location and structure were found for all the deposits in the studied injectors. The physical structure was analyzed using a Scanning Electron Microscope with an Energy Dispersive X-Ray (SEM-EDX). Pyrolysis coupled with Gas Chromatography Mass Spectrometry (Py GC-MS) and Fourier-transform Infrared Spectroscopy (FTIR) were also used to determine the composition of the injector deposits. The deposits consist of a mixture of organic and inorganic compounds, indicating that they originate from fuel and engine oil. To further analyze the origin of the formed deposits, samples were collected from various parts of the fuel system. The analysis suggests that the deposits were formed exclusively in the injectors, and by comparing and describing the composition and structure of the deposits from different parts of the injector, a mechanism is proposed.

Increasing concern for air pollution together with the introduction of new types of fuels pose new challenges to the exhaust aftertreatment system for heavy-duty (HD) vehicles. For diesel-powered engines, emissions of particulate matter (PM) is one of the main drawbacks due to its effect on health. To mitigate the tailpipe emissions of PM, heavy-duty vehicles are since Euro V equipped with a diesel particulate filter (DPF). The accumulation of particles causes flow restriction resulting in fuel penalties and decreased vehicle performance. Understanding the properties of PM produced during engine operation is important for the development and optimized control of the DPF. This study has focused on assessing the reactivity of the PM by measuring the oxidation kinetics of the carbonaceous fraction. PM was sampled from two different heavy-duty engines during various test cycles. The heavy-duty engines were 6- and 8-cylinder direct injection diesel engines rated at 550 and 650 hp respectively. Reaction kinetics of the samples and characteristic oxidation temperatures were assessed by the non-isothermal thermogravimetric analysis (TGA) employing a multiple-ramp rates method in a 10% oxygen atmosphere. The oxidation of the diesel soot was compared with a model soot, Printex-U, and values were compared with the existing literature. The calculated activation energies range between 114.8 and 155.8 kJ/mol for diesel soot as well as the Printex-U samples indicating similar reactivity despite differences in engine configuration, fuel chemistry or, aging.

While extensive research has been done on improving diesel engines, much less has been done on auxiliary heaters, which have their own design challenges. The study analyzes how to optimize the combustion performance of an auxiliary heater, a 6 kW diesel burner, by investigating key parameters affecting diesel combustion and their properties. A model of a small diesel heater, including a simulation of fuel injection and combustion process, was developed step-wise and verified against experimental results that can be used for scaling up to 25 kW heaters. The model was successfully applied to the burner, predicting the burner performance in comparison with experimental results. Three main variables were identified as important for the design. First, it was concluded that the distance from the ring cone to the nozzle is essential for the fluid dynamics and flame location, and that the ring cone should be moved closer to the nozzle for optimal performance. Second, the design of the swirl co-flow is important, and the swirl number of the inlet air should be kept above 0.6 to stabilize the flame location for the present burner design. Finally, the importance of the nozzle diameter to avoid divergent particle vaporization was pointed out.

It is not easy to replace fossil-based fuels in the transport sector, however, an appealing solution is to use biomass and waste for the production of renewable alternatives. Thermochemical conversion of biomass for production of synthetic transport fuels by the use of gasification is a promising way to meet these goals.

One of the key challenges in using gasification systems with biomass and waste as feedstock is the upgrading of the raw gas produced in the gasifier. These materials replacing oil and coal contain large amounts of demanding impurities, such as alkali, inorganic compounds, sulphur and chlorine compounds. Therefore, as for all multi-step processes, the heat management and hence the total efficiency depend on the different clean-up units. Unfortunately, the available conventional gas filtering units for removing particulates and impurities, and also subsequent catalytic conversion steps have lower optimum working temperatures than the operating temperature in the gasification units.

This report focuses on on-going research and development to find new technology solutions and on the key critical technology challenges concerning the purification and upgrading of the raw gas to synthesis gas and the subsequent different fuel synthesis processes, such as hot gas filtration, clever heating solutions and a higher degree of process integration as well as catalysts more resistant towards deactivation. This means that the temperature should be as high as possible for any particular upgrading unit in the refining system. Nevertheless, the temperature and pressure of the cleaned synthesis gas must meet the requirements of the downstream application, i.e. Fischer-Tropsch diesel or methanol.

Before using the gas produced in the gasifier a number of impurities needs to be removed. These include particles, tars, sulphur and ammonia. Particles are formed in gasification, irrespective of the type of gasifier design used. A first, coarse separation is performed in one or several cyclone filters at high temperature. Thereafter bag-house filters (e.g. ceramic or textile) maybe used to separate the finer particles. A problem is, however, tar condensation in the filters and there is much work performed on trying to achieve filtration at as high a temperature as possible.

The far most stressed technical barriers regarding cleaning of the gases are tars. To remove the tar from the product gas there is a number of alternatives, but most important is that the gasifier is operated at optimal conditions for minimising initial tar formation. In fluid bed and entrained flow gasification a first step may be catalytic tar cracking after particle removal. In fluid bed gasification a catalyst, active in tar cracking, may be added to the fluidising bed to further remove any tar formed in the bed. In this kind of tar removal, natural minerals such as dolomite and olivine, are normally used, or catalysts normally used in hydrocarbon reforming or cracking. The tar can be reformed to CO and hydrogen by thermal reforming as well, when the temperature is increased to 1300ºC and the tar decomposes. Another method for removing tar from the gas is to scrub it by using hot oil (200-300ºC). The tar dissolves in the hot oil, which can be partly regenerated and the remaining tar-containing part is either burned or sent back to the gasifier for regasification.

Other important aspects are that the sulphur content of the gas depends on the type of biomass used, the gasification agent used etc., but a level at or above 100 ppm is not unusual. Sulphur levels this high are not acceptable if there are catalytic processes down-stream, or if the emissions of e.g. SO₂ are to be kept down. The sulphur may be separated by adsorbing it in ZnO, an irreversible process, or a commercially available reversible adsorbent can be used. There is also the possibility of scrubbing the gas with an amine solution. If a reversible alternative is chosen, elementary sulphur may be produced using the Claus process.

Furthermore, the levels of ammonia formed in gasification (3,000 ppm is not uncommon) are normally not considered a problem. When combusting the gas, nitrogen or in the worst case NO_x (so-called fuel NO_x) is formed; there are, however, indications that there could be problems. Especially when the gasification is followed by down-stream catalytic processes, steam reforming in particular, where the catalyst might suffer from deactivation by long-term exposure to ammonia.

The composition of the product gas depends very much on the gasification technology, the gasifying agent and the biomass feedstock. Of particular significance is the choice of gasifying agent, i.e. air, oxygen, water, since it has a huge impact on the composition and quality of the gas, The gasifying agent also affects the choice of cleaning and upgrading processes to syngas and its suitability for different end-use applications as fuels or green chemicals.

The ideal upgraded syngas consists of H₂ and CO at a correct ratio with very low water and CO₂ content allowed. This means that the tars, particulates, alkali salts and inorganic compounds mentioned earlier have to be removed for most of the applications. By using oxygen as the gasifying agent, instead of air, the content of nitrogen may be minimised without expensive nitrogen separation.

In summary, there are a number of uses with respect to produced synthesis gas. The major applications will be discussed, starting with the production of hydrogen and then followed by the synthesis of synthetic natural gas, methanol, dimethyl ether, Fischer-Tropsch diesel and higher alcohol synthesis, and describing alternatives combining these methods. The SNG and methanol synthesis are equilibrium constrained, while the synthesis of DME (one-step route), FT diesel and alcohols are not. All of the reactions are exothermal (with the exception of steam reforming of methane and tars) and therefore handling the temperature increase in the reactors is essential. In addition, the synthesis of methanol has to be performed at high pressure (50-100 bar) to be industrially viable.

There will be a compromise between the capital cost of the whole cleaning unit and the system efficiency, since solid waste, e.g. ash, sorbents, bed material and waste water all involve handling costs. Consequently, installing very effective catalysts, results in unnecessary costs because of expensive gas cleaning; however the synthesis units further down-stream, especially for Fischer-Tropsch diesel, and DME/methanol will profit from an effective gas cleaning which extends the catalysts life-time. The catalyst materials in the upgrading processes essentially need to be more stable and resistant to different kinds of deactivation.

Finally, process intensification is an important development throughout chemical industries, which includes simultaneous integration of both synthesis steps and separation, other examples are advanced heat exchangers with heat integration in order to increase the heat transfer rates. Another example is to combine exothermic and endothermic reactions to support reforming reactions by using the intrinsic energy content. For cost-effective solutions and efficient application, new solutions for cleaning and up-grading of the gases are necessary.

Det är en stor utmaning att ersätta fossila bränslen inom transportsektorn, en tilltalande lösning är att använda biomassa och avfall för produktion av förnyelsebara drivmedel. Termokemisk omvandling av biomassa är ett lovande sätt för att producera olika sorters syntetiska drivmedel, då främst genom förgasningsteknik. En av de främsta utmaningarna i att använda termokemisk omvandling av biomassa och avfall är en rening och uppgradering av rågasen som produceras i förgasaren. Dessa material som är tänkta att ersätta olja och kol innehåller betydande mängder av alkaliska-, oorganiska-, svavel- och klor-föreningar.

De olika renings- och uppgraderingsstegen påverkar den totala verkningsgraden på hela processen, därför blir hanteringen av värme i de olika process strömmarna viktiga, som för alla processer i flera steg. Dessvärre, har de tillgängliga konventionella gas filtreringsenheterna för att ta bort partiklar och orenheter, och även efterföljande katalytiska omvandlingssteg, lägre optimala arbetstemperaturer än driftstemperaturen hos förgasningsenheterna.

Denna rapport fokuserar på pågående forskning och utveckling för att hitta ny teknik och lösningar när det gäller rening och uppgradering av rågas till syntesgas, samt efterföljande bränslesyntesprocesser, såsom hetgas-filtrering, smarta uppvärmnings lösningar och högre grad av integrationsprocess, samt katalysatorer som är mer tåliga mot deaktivering. Detta innebär att temperaturen bör vara så hög som möjligt för varje enskild renings- och en uppgraderingsenhet, likväl måste temperaturen och trycket hos den renade syntesgasen uppfylla kraven för nedströms bränslesyntes, d.v.s. Fischer-Tropsch-diesel eller metanol.

Ett antal orenheter behöver tas bort innan gasen som producerats i förgasaren kan användas, dessa inkluderar partiklar, tjäror, svavelföreningar och ammoniak. Partiklar bildas alltid vid förgasning, oberoende av vilken typ av förgasningsteknik som används, en första grovseparation utförs i en eller flera cyklonfilter vid höga temperaturer. För att separera de finare partiklarna används därefter olika keramiska- eller textilfilter, ett problem är dock kondensation av tjära i filtren, mycket arbete utförs på att försöka uppnå filtrering vid så hög temperatur som möjligt, så att man slipper tjärproblemen.

Det största hindret när det gäller rening och uppgradering av gaserna är tjära. För att bli av med tjäran från produktgasen finns ett antal olika alternativ, men det väsentligaste är att själva förgasaren drivs vid optimala förhållanden för att minimera att tjära bildas överhuvudtaget.

För förgasning med fluidiserad bädd och entrained flowförgasning skulle det första steget kunna vara katalytisk tjärkrackning efter att ha avlägsnat alla partiklar. Vid förgasning i fluidiserad bädd kan aktiva katalysatorer tillsättas till den fluidiserande bädden som kan kracka tjäran redan i bädden och hindra att ytterligare eventuell tjära bildas. Katalysatorer som används är främst naturliga mineraler, såsom dolomit och olivin, dessa användes normalt vid reformering eller krackning av kolväten.

Tjäran kan reformeras till vätgas och kolmonoxid genom termisk reformering såsom när temperaturen höjs till 1300ºC och tjäran sönderfaller. En annan metod för att avlägsna tjära från gasen är att tvätta gasen med hjälp av het olja (200-300ºC). Tjäran löser sig i den heta oljan, som delvis kan vara regenererad och den återstående tjärhaltiga delen kan antingen brännas eller återföras till förgasaren för förgasning.

Svavelföreningar är en annan viktig kontaminering som behöver tas bort ur gasen, svavelhalten i gasen beror främst på vilken typ av biomassa som används. Nivåer över 100 ppm inte är ovanligt och är inte acceptabelt för efterföljande nedströms katalytiska processer, eller om utsläppen av t.ex. SO₂ ska hållas nere.

Svavel kan separeras genom adsorption med ZnO som är en irreversibel process, eller genom kommersiellt tillgängliga reversibla adsorbenter som kan användas. Ytterligare alternativ är att tvätta/skrubba gasen med en aminlösning. Om ett reversibelt alternativ används kan elementärt svavel framställas med hjälp av Claus-processen.

Ammoniak bildas vid förgasning och nivåer runt 3000 ppm är inte ovanligt, men anses vanligtvis inte ett problem efterföljande nedströms processer. Om gasen förbränns, kan dock kväve eller i värsta fall NOx (så kallad bränsle NOx) bildas. Det finns dock indikationer på att problem kan uppstå, speciellt när förgasning följs av nedströms katalytiska processer, exempelvis vid ångreformering där katalysatorn kan deaktiveras vid långvarig exponering för ammoniak

Sammansättningen på produktgasen beror framförallt på valet av förgasningsteknik, vilket förgasningsmedel som används, samt viken sorts biomassa sam används. Valet av förgasningsmedel, dvs. luft, syre, vatten, är extra viktigt eftersom det har en direkt inverkan på sammansättningen och kvaliteten hos gasen. Valet av förgasningsmedel påverkar också vilka renings- och uppgraderingsprocesser som kan användas och lämpar sig bäst för olika slutanvändningstillämpningar som t.ex. drivmedel eller för gröna kemikalier.

Idealt består en syntesgas som är uppgraderad av vätgas och kolmonoxid i korrekt förhållande, med mycket låga halter vatten och koldioxid. Detta innebär att tjäror, partiklar, alkalisalter och oorganiska föreningar, som nämnts tidigare, måste avlägsnas för de flesta tillämpningarna. Genom att använda syre som förgasningsmedel, i stället för luft, kan innehållet av kväve i gasen minimeras, så man undviker efterföljande dyrbar separation av kväve.

Sammanfattningsvis finns det ett antal olika användningsområden för olika producerade syntesgaser. De olika tillämpningarna kommer att diskuteras i rapporten med början med produktion av vätgas, följt av framställning av syntetisk naturgas (SNG), metanol, dimetyleter, Fischer-Tropsch-diesel och syntes av högre alkoholer, samt beskrivningar av metoder som kombinerar dessa. Processystemen är olika där syntes av SNG och metanol begränsas jämvikt, medan syntes av dimetyleter, (DME), FT-diesel och alkoholer inte är jämviktsberoende. Samtliga reaktioner är exoterma, med undantag för ångreformering av metan och tjäror, vilket medför att det är viktigt att kontrollera temperaturökningen i reaktorerna. Dessutom måste syntes av metanol utföras vid högt tryck (50-100 bar) för att vara industriellt gångbar.

För att hålla nere kapitalkostnaderna för hela reningssystemet och systemets effektivitet behöver man kompromissa, eftersom hanteringen av fast avfall, t.ex. aska, absorberande medel, bäddmaterial och avloppsvatten alla innebär kostnader.

Att installera väldigt effektiva katalysatorer resulterar i dyrare gasrening på grund av onödiga kostnader, men nedströms syntesprocesser kommer att dra nytta av effektiv gasrening som förlänger katalysatorernas livstid, särskilt för Fischer-Tropsch-diesel, och DME/metanol syntes. Generellt måste katalysatorerna i de olika uppgraderingsprocesserna vara mer stabila och motståndskraftiga mot olika typer av deaktivering.

Slutligen är process-intensifiering ett viktigt område för utveckling inom hela kemiindustrin som bland annat omfattar integration av både syntes och separationssteg, med olika former av avancerad värmeväxling med värmeintegration för att öka värmeöverföringshastigheten, och att kombinera exoterma och endoterma reaktioner. Därför är det nödvändigt med nya innovativa lösningar för rening och uppgradering av gaserna för att få fram kostnadseffektiva och effektiva tillämpningar.

Transportation fuels such as ethanol can be obtained through thermochemical processing of biomass. Interest in the development of more selective catalysts for the conversion of biomass-derived syngas (H2 + CO) to ethanol is increasing in both academia and industry. In this work, we have evaluated the performances of K and Fe as metal promoters of a mesoporous Cu/MCM-41 catalyst and their effects on the product selectivity and especially on ethanol formation. The metal loading was 29 wt.% Cu, 2 wt.% Fe and 1.6 wt.% K. The catalysts were tested at 300 °C, 20 bar and gas-hourly-space-velocities in the range of 1500–30000 mlsyngas/gcat h; under these conditions the syngas conversion level was between 2 and 11%. The non-promoted Cu/MCM-41 catalyst showed interesting selectivity toward oxygenated compounds, mostly methanol. The addition of K as promoter increases the selectivity toward methanol even more, while the addition of Fe as promoter favors the formation of hydrocarbon compounds. When both K and Fe as promoters are incorporated into the Cu/MCM-41 catalyst, the reaction rate to oxygenated compounds is notably increased, especially for ethanol. The space time yield for ethanol for the Cu/MCM-41 catalyst is 0.3 × 10−5 carbon-mol/gcath which increases to 165.5 × 10−5 carbon-mol/gcath for the Cu-Fe-K/MCM-41 catalyst. From XPS analysis, the Cu-Fe-K/MCM-41 catalyst was found to have the following atomic composition: Cu0.34Fe0.08K0.08Si1.00. The promoting effect of both K and Fe, may be related to an increased reaction rate toward CO non-dissociation and CO-dissociation paths, respectively, which is beneficial for the ethanol formation. Further catalytic results, catalyst characterization and discussion of results are presented in this work.