A study of combustion phenomena in circulating fluidized beds by developing and applying experimental and modelling methods for laboratory-scale reactors

The results shown in this thesis are based on selected publications of the 2000s decade. The work was carried out in several national and EC funded public research projects and in close cooperation with industrial partners. The main objective of the thesis was to study and quantify the most important phenomena of circulating fluidized bed combustors by developing and applying proper experimental and modelling methods using laboratory scale equipments. An understanding of the phenomena plays an essential role in the development of combustion and emission performance, and the availability and controls of CFB boilers. Experimental procedures to study fuel combustion behaviour under CFB conditions are presented in the thesis. Steady state and dynamic measurements under well controlled conditions were carried out to produce the data needed for the development of high efficiency, utility scale CFB technology. The importance of combustion control and furnace dynamics is emphasized when CFB boilers are scaled up with a once through steam cycle. Qualitative information on fuel combustion characteristics was obtained directly by comparing flue gas oxygen responses during the impulse change experiments with fuel feed. A one-dimensional, time dependent model was developed to analyse the measurement data Emission formation was studied combined with fuel combustion behaviour. Correlations were developed for NO, N2O, CO and char loading, as a function of temperature and oxygen concentration in the bed area. An online method to characterize char loading under CFB conditions was developed and validated with the pilot scale CFB tests. Finally, a new method to control air and fuel feeds in CFB combustion was introduced. The method is based on models and an analysis of the fluctuation of the flue gas oxygen concentration. The effect of high oxygen concentrations on fuel combustion behaviour was also studied to evaluate the potential of CFB boilers to apply oxygenfiring technology to CCS. In future studies, it will be necessary to go through the whole scale up chain from laboratory phenomena devices through pilot scale test rigs to large scale, commercial boilers in order to validate the applicability and scalability of the, results. This thesis shows the chain between the laboratory scale phenomena test rig (bench scale) and the CFB process test rig (pilot). CFB technology has been scaled up successfully from an industrial scale to a utility scale during the last decade. The work shown in the thesis, for its part, has supported the development by producing new detailed information on combustion under CFB conditions.

Studies on Neuromuscular Blocking Agents and Their Antagonists During Anaesthesia

Neuromuscular blocking agents (NMBAs) are widely used in clinical anaesthesia and emergency medicine. Main objectives are to facilitate endotracheal intubation and to allow surgery by reducing muscle tone and eliminating sudden movements, which may otherwise lead to trauma and complications. The most commonly used NMBAs are non-depolarizing agents with a medium duration of action, such as rocuronium and cisatracurium. They bind to the acetylcholine receptors in the neuromuscular junction, thus inhibiting the depolarization of the postsynaptic (muscular) membrane, which is a prerequisite for muscle contraction to take place. Previously, it has been assumed that nitrous oxide (N2O), which is commonly used in combination with volatile or intravenous anaesthetics during general anaesthesia, has no effect on NMBAs. Several studies have since claimed that N2O in fact does increase the effect of NMBAs when using bolus administration of the relaxant. The effect of N2O on the infusion requirements of two NMBAs (rocuronium and cisatracurium) with completely different molecular structure and pharmacological properties was assessed. A closed-loop feedback controlled infusion of NMBA with duration of at least 90 minutes at a 90% level of neuromuscular block was used. All patients received total intravenous anaesthesia (TIVA) with propofol and remifentanil. In both studies the study group (n=35) received N2O/Oxygen and the control group (n=35) Air/Oxygen. There were no significant differences in the mean steady state infusion requirements of NMBA (rocuronium in Study I; cisatracurium in Study II) between the groups in either study. In Study III the duration of the unsafe period of recovery after reversal of rocuronium-induced neuromuscular block by using neostigmine or sugammadex as a reversal agent was analyzed. The unsafe period of recovery was defined as the time elapsed from the moment of no clinical (visual) fade in the train-of-four (TOF) sequence until an objectively measured TOF-ratio of 0.90 was achieved. The duration of these periods were 10.3 ± 5.5 and 0.3 ± 0.3 min after neostigmine and sugammadex, respectively (P < 0.001). Study IV investigated the possible effect of reversal of a rocuronium NMB by sugammadex on depth of anaesthesia as indicated by the bispectral index and entropy levels in thirty patients. Sugammadex did not affect the level of anaesthesia as determined by EEG-derived indices of anaesthetic depth such as the bispectral index and entropy.

Etelä- ja Pohjois-Savon maakuntien kasvihuonekaasutaseet 2010

Kasvihuonekaasutaselaskennassa selvitettiin Etelä- ja Pohjois-Savon maakuntien kasvihuonekaasupäästöjen ja nielujen suuruudet vuodelta 2010. Päästölaskenta suoritettiin Etelä- ja Pohjois-Savon alueilta kunta- ja maakuntakohtaisesti kuntaliiton Kasvener-ohjelmalla. Etelä-Savon kulutusperäiset kasvihuonekaasupäästöt olivat vuonna 2010 yhteensä 1492 tuhatta tonnia (kt) CO2-ekv, joka oli noin 2% koko Suomen kasvihuone-kaasupäästöistä. Asukasta kohti laskettuna päästöt olivat 9,6 t CO2-ekv. Maankäyttösektorin nettonielu oli 1300 kt CO2-ekv vuonna 2010. Päästöt olivat siten 192 kt CO2-ekv suuremmat kuin nieluvaikutukset. Pohjois-Savon kulutusperäiset kasvihuonekaasupäästöt olivat vuonna 2010 yhteensä 3148 kt CO2-ekv. Asukasta kohden päästö oli 12,7 t CO2-ekv. Koko Suomen vuoden 2010 päästöistä Pohjois-Savon osuus oli 4%. Pohjois-Savon maankäyttösektorin nettonielu oli 2600 kt CO2-ekv vuonna 2010. Yhteen laskettuna päästöt olivat 548 kt CO2-ekv suuremmat kuin nieluvaikutukset. Suomen vuoden 2010 laskennassa kulutusperusteiset kasvihuonekaasujen kokonaispäästöt olivat 74600 kt CO2-ekv, joka oli 13,9 tonnia CO2-ekv asukasta kohden. Etelä-Savossa suurimmat kasvihuonepäästöjä tuottavat sektorit vuonna 2010 olivat liikenne (tie-, laiva, lento- ja raideliikenne) ja rakennusten lämmitys. Molempien sektoreiden osuudet olivat 30% maakunnan kasvihuonekaasupäästöistä. Muun sähkönkäyttösektorin osuus oli 19%, joka sisältää mm. teollisuuden ja kotitalouksien sähkönkulutuksen lukuun ottamatta kotitalouksien sähkölämmitystä. Maatalouden osuus päästöistä oli 13% sisältäen sekä karjankasvatuksen että peltoviljelyn päästöt. Muiden polttoaineiden osuus oli 6%, joka sisältää teollisuuden käyttämien polttoaineiden ja työkoneiden polttoaineiden käytöstä syntyvät kasvihuonekaasupäästöt. Jätehuollon osuus oli 1%. Teollisuuden prosessiperäisiä päästöjä syntyi vain hyvin vähäisiä määriä poltetun kalkin tuotannosta Kerimäellä. Pohjois-Savossa suurin kasvihuonepäästöjä tuottava sektori vuonna 2010 oli rakennusten lämmitys, joka tuotti 29% alueen kasvihuonekaasupäästöistä. Muun sähkönkäyttösektorin osuus oli 22%, mikä sisältää mm. teollisuuden ja kotitalouksien sähkönkulutuksen lukuun ottamatta kotitalouksien sähkölämmitystä. Muiden polttoaineiden osuus oli 13%, joka sisältää teollisuusprosessien käyttämien polttoaineiden ja työkoneiden polttoaineiden käytöstä syntyvät kasvihuonekaasupäästöt. Liikenteen (tie-, laiva, lento- ja raideliikenne) päästöt olivat 19% ja maatalouden osuus sisältäen sekä karjankasvatuksen että peltoviljelyn päästöt oli 15%. Teollisuuden prosessiperäisiä päästöjä (N2O) syntyi Siilinjärvellä typpihapon tuotannossa. Prosessiperäisten päästöjen ja jätehuollon osuus kokonaispäästöistä oli molemmista 1%.

Biogas production in regional integrated biodegradable waste treatment – Possibilities for improving energy performance and reducing GHG emissions

The greatest threat that the biodegradable waste causes on the environment is the methane produced in landfills by the decomposition of this waste. The Landfill Directive (1999/31/EC) aims to reduce the landfilling of biodegradable waste. In Finland, 31% of biodegradable municipal waste ended up into landfills in 2012. The pressure of reducing disposing into landfills is greatly increased by the forthcoming landfill ban on biodegradable waste in Finland. There is a need to discuss the need for increasing the utilization of biodegradable waste in regional renewable energy production to utilize the waste in a way that allows the best possibilities to reduce GHG emissions. The objectives of the thesis are: (1) to find important factors affecting renewable energy recovery possibilities from biodegradable waste, (2) to determine the main factors affecting the GHG balance of biogas production system and how to improve it and (3) to find ways to define energy performance of biogas production systems and what affects it. According to the thesis, the most important factors affecting the regional renewable energy possibilities from biodegradable waste are: the amount of available feedstock, properties of feedstock, selected utilization technologies, demand of energy and material products and the economic situation of utilizing the feedstocks. The biogas production by anaerobic digestion was seen as the main technology for utilizing biodegradable waste in agriculturally dense areas. The main reason for this is that manure was seen as the main feedstock, and it can be best utilized with anaerobic digestion, which can produce renewable energy while maintaining the spreading of nutrients on arable land. Biogas plants should be located close to the heat demand that would be enough to receive the produced heat also in the summer months and located close to the agricultural area where the digestate could be utilized. Another option for biogas use is to upgrade it to biomethane, which would require a location close to the natural gas grid. The most attractive masses for biogas production are municipal and industrial biodegradable waste because of gate fees the plant receives from them can provide over 80% of the income. On the other hand, directing gate fee masses for small-scale biogas plants could make dispersed biogas production more economical. In addition, the combustion of dry agricultural waste such as straw would provide a greater energy amount than utilizing them by anaerobic digestion. The complete energy performance assessment of biogas production system requires the use of more than one system boundary. These can then be used in calculating output–input ratios of biogas production, biogas plant, biogas utilization and biogas production system, which can be used to analyze different parts of the biogas production chain. At the moment, it is difficult to compare different biogas plants since there is a wide variation of definitions for energy performance of biogas production. A more consistent way of analyzing energy performance would allow comparing biogas plants with each other and other recovery systems and finding possible locations for further improvement. Both from the GHG emission balance and energy performance point of view, the energy consumption at the biogas plant was the most significant factor. Renewable energy use to fulfil the parasitic energy demand at the plant would be the most efficient way to reduce the GHG emissions at the plant. The GHG emission reductions could be increased by upgrading biogas to biomethane and displacing natural gas or petrol use in cars when compared to biogas CHP production. The emission reductions from displacing mineral fertilizers with digestate were seen less significant, and the greater N2O emissions from spreading digestate might surpass the emission reductions from displacing mineral fertilizers.

Excavation-drier method of energy-peat extraction reduces long-term climatic impact

Climatic impacts of energy-peat extraction are of increasing concern due to EU emissions trading requirements. A new excavation-drier peat extraction method has been developed to reduce the climatic impact and increase the efficiency of peat extraction. To quantify and compare the soil GHG fluxes of the excavation drier and the traditional milling methods, as well as the areas from which the energy peat is planned to be extracted in the future (extraction reserve area types), soil CO2, CH4 and N2O fluxes were measured during 2006–2007 at three sites in Finland. Within each site, fluxes were measured from drained extraction reserve areas, extraction fields and stockpiles of both methods and additionally from the biomass driers of the excavation-drier method. The Life Cycle Assessment (LCA), described at a principal level in ISO Standards 14040:2006 and 14044:2006, was used to assess the long-term (100 years) climatic impact from peatland utilisation with respect to land use and energy production chains where utilisation of coal was replaced with peat. Coal was used as a reference since in many cases peat and coal can replace each other in same power plants. According to this study, the peat extraction method used was of lesser significance than the extraction reserve area type in regards to the climatic impact. However, the excavation-drier method seems to cause a slightly reduced climatic impact as compared with the prevailing milling method.