Numerical modelling of thermochemical processes inside a cement calciner for a cleaner cement production

Trenutna proizvodnja cementa suočena je s dva značajna problema. Prvi je proizvodnja velike količine stakleničkih plinova, oko 5 % ukupnih globalnih CO2 emisija ljudskog podrijetla, a drugi je visoka cijena goriva, uglavnom ugljena. Proizvođači cementa su stoga pod sve većim pritiskom da smanje potrošnju fosilnih goriva i s njima povezanim emisijama stakleničkih plinova. Utvrđeno je da je djelomična zamjena ugljena alternativnim gorivima, poput biomase i goriva dobivenih obradom otpada, može imati važnu ulogu u smanjenju CO2 emisija. Kako je zbrinjavanje otpada na odlagalištima zadnja opcija u strategiji upravljanja otpadom, energetska oporaba goriva dobivenog obradom otpada, poznatijeg kao kruto gorivo iz otpada (engl. solid recovered fuel - SRF), ima veliki potencijal u cementnoj industriji. Spaljivanje visokog udjela SRF-a u cementnim kalcinatorima još se uvijek suočava sa značajnim izazovima, poglavito jer je dobro poznato da upotreba alternativnih goriva u postojećim plamenicima mijenja oblik plamena, profil temperatura unutar peći, te izgorenost samog goriva koje se koristi. Korištenjem računalne dinamike fluida (engl. computational fluid dynamics - CFD) moguće je prethodno ispitivati i kontrolirati proces izgaranja različitih vrsta goriva. CFD simulacije su se tokom godina pokazale kao moćan alat za razvoj i optimizaciju kemijskih procesa te samih uređaja unutar kojih se te kemijske reakcije odvijaju. One mogu pokazati neke važne karakteristike strujanja fluida i miješanja više faza koje je teško eksperimentalno istražiti i stoga je CFD, zajedno sa eksperimentima i teorijom, postao sastavni dio istraživanja procesa izgaranja goriva. Glavna tema ovog rada bila je postizanje fizički točne i numerički učinkovite metode za simuliranje termo-kemijskih procesa koji se odvijaju unutar cementnog kalcinatora. To je podrazumijevalo dobro poznavanje najmodernijih modela izgaranja krutih goriva kao što su modeli za izgaranje ugljena, biomase i goriva iz čvrstog otpada, kao i pravilno definiranje endotermnog procesa kalcinacije. Kako bi se ispravno numerički proučavala uloga i interakcija izgaranja krutih goriva i termičkog raspadanja vapnenca unutar cementnog kalcinatora, upotrijebljeni su novi i poboljšani fizikalni i kemijski modeli. Nadalje, kako bi se provjerila točnost numeričkog modeliranja, novi modeli su se opsežno analizirali, a numerički dobiveni rezultati svakog novog modela su bili uspoređeni s dostupnim eksperimentalnim podacima. Primjenjivost razvijenog numeričkog modeliranja prikazana je na tri različite trodimenzionalne geometrije realnih industrijskih cementnih kalcinatora, koje su se koristile za detaljne numeričke simulacije.The present cement production is facing two main problems. The first one is the production of large amount of greenhouse gases, around 5 % of world’s anthropogenic CO2 emissions, and second one is the high fuel prices, mainly coal. The cement producers are therefore under increasing pressure to reduce their fossil fuel consumption and associated greenhouse gases emissions. It was found that partial substitution of coal by alternative fuels like waste derived fuels and biomass may play a major role in the reduction of CO2 emissions. As waste disposal at landfills is the last option in the waste management strategy, energy recovery of waste derived fuels, commonly known as solid recovered fuels – SRF, in the cement industry has a high potential. Incineration of high share of SRF in cement calciners still faces significant challenges, mainly because it is well known that the use of alternative fuels in existing pulverized burners alters the flame shape, the temperature profile inside the furnace, and the burnout of the fuels used. A possibility for the ex-ante control and investigation of the incineration process are computational fluid dynamics - CFD simulations. CFD simulations have shown to be a powerful tool during the development and optimisation of chemical engineering processes and involved apparatuses. They can show some important flow characteristics and mixing phenomena, which cannot be experimentally investigated, and because of that CFD together with experiments and theory, has become an integral component of combustion research. The main focus of this work was to achieve a physically accurate and numerically efficient method for simulation of thermo-chemical processes occurring inside a cement calciner. This implied good knowledge of state-of-the-art solid fuel combustion models, such as coal, biomass and solid recovered fuel combustion model, as well as proper definition of the endothermic calcination process. In order to correctly numerically study the role and interaction of solid fuel combustion and limestone calcination within cement calciner, new and improved physical and chemical models were introduced. To verify the accuracy of the modelling approach, the new models were extensively analysed, and the numerical predictions of each new model was compared with experimental data. To represent the applicability of the modelling approach, three different three dimensional geometries of real industrial cement calciners were used for the numerical simulations

Steel and Aluminum Energy Conservation and Technology Competitiveness Act of 1988: Annual report of the metals initiative for fiscal year 1996

This annual report has been prepared for the President and Congress describing the activities carried out under the Steel and Aluminum Energy Conservation and Technology Competitiveness Act of 1988, commonly referred to as the Metals Initiative. The Act has the following purposes: (1) increase energy efficiency and enhance the competitiveness of the American steel, aluminum, and copper industries; and (2) continue research and development efforts begun under the U.S. Department of Energy (DOE) program known as the Steel Initiative. These activities are detailed in a subsequent section. Other sections describe the appropriation history, the distribution of funds through fiscal year 1996, and the estimated funds necessary to continue projects through fiscal year 1997. The Metals Initiative supported four research and development projects with the U.S. Steel industry: (1) steel plant waste oxide recycling and resource recovery by smelting, (2) electrochemical dezincing of steel scrap, (3) rapid analysis of molten metals using laser-produced plasmas, and (4) advanced process control. There are three Metals Initiative projects with the aluminum industry: (1) evaluation of TiB2-G cathode components, (2) energy efficient pressure calciner, and (3) spray forming of aluminum. 1 tab

CO2 Capture and Renewable Energy

The urgently needed carbon neutral economy requires a portfolio of strategies, among which, CO2 capture and renewable energy will need to play a decisive role. Dispatchable renewables, such as bioenergy, will play an increasing role in maintaining electricity security, in producing heat in the industry and residential sectors, and in reducing the emissions from the transport sector. Biomethane, also known as a renewable natural gas, can be directly blended with or fully replace natural gas in existing pipelines and end-user equipment, with the added advantage of being carbon neutral. CO2 capture and storage (CCS) will also be of paramount importance in abating CO2 emissions from existing infrastructure in the power and industrial sectors. There are many industries that will be difficult or impossible to decarbonize in the short term, such as the cement sector, in which CO2 emissions are intrinsic to the production process. In such cases, CCS will be mandatory to achieve the goal of net zero emissions. Permanent CO2 removal technologies, such as bioenergy with carbon capture and storage (BECCS) and direct air capture and storage (DACS), will also be necessary in the medium term to compensate for emissions from the hard-to-abate sectors, and in the long term, even to remove atmospheric CO2 from past emissions. This book consists of six peer-reviewed scientific articles that cover a range of high-interest subjects related to the aforementioned hot topics

High temperature processing of kaolinitic materials

Calcination, is the process of heating a substance, to a temperature below its fusing point, with a resultant loss of water. It is one of the most important techniques currently used to enhance the properties, and therefore value, of kaolin. The overall aim of this project was to provide a better understanding of the principles of the kaolin calcination reaction in order to enhance the efficiency, quality and sustainability of the Imerys calcining operations. This research has shown a strong correlation between the chemistry of kaolin and the colour of the calcined product. This is due to the influence of contaminant materials on the colour of the hydrous kaolin, which in turn affects the calcined material. The strongest colour influencing factor is the presence of iron, particularly if it is present on the surface of the kaolin. Surface iron is currently reduced using a reductive bleaching process. This has an improving influence on even the most contaminated kaolins, however there can be quite a lot of interbatch variability. Despite its effect on colour the chemistry of kaolin has little influence on post calcination reactivity. Reactivity is due to physical factors such as particle and agglomerate size and the penetration of heat into the material. Any kaolin will calcine to produce a low reactivity product; provided the heat is able to penetrate into the bed and that the material is able to remain at temperature for sufficient time for the calcination reaction to occur. Another outcome of the research was the discovery that a higher temperature and shorter time period has little on the end calcined product but has implications for lower energy usage