The deposition of mineral phases on the heat transfer surfaces of brown coal power plants may have a negative effect on power plant boilers. The paragenesis of these deposits contains information about the actual temp...The deposition of mineral phases on the heat transfer surfaces of brown coal power plants may have a negative effect on power plant boilers. The paragenesis of these deposits contains information about the actual temperature prevailed during the combustion of lignite, if the temperature-dependences of distinct mineral transformations or reactions are known. Here, we report results of a sintering study (to ?1100℃) with samples containing anhydrite, quartz, and gehlenite, which are typical components of Rhenish lignite ashes. Thermal decompositions and solid-state reactions were analyzed (1) in situ and (2) both in situ and after quenching using confocal hyperspectral Raman imaging. This novel application of confocal Raman spectroscopy provides temperature-and time-resolved, 2-dimensional information about sintering processes with a micrometer-scale resolution. In the course of the sintering experiments with anhydrite and quartz with a weight ratio of 2:1 both polymorphs wollastonite and pseudowollastonite were identified in situ at about 920 and 1000℃, respectively. The formation of pseudowollastonite was thus observed about 120℃ below the phase transition temperature, demonstrating that it can form metastably. In addition,α′L-Ca2SiO4 was identified at about 1100℃. In samples containing equal weight fractions of anhydrite and quartz that were quenched after firing for 9h at about 1100℃,β-Ca2SiO4 (larnite) crystallized as rims around anhydrite grains and in direct contact to wollastonite. We furthermore observed that, depending on the ratio between quartz and anhydrite, wollastonite replaced quartz grains between 920 and 1100℃., i.e., the higher the quartz content, the lower the formation temperature of wollastonite.展开更多
Hard coal and lignite—also referred to here jointly as coal—play a central role in the worldwide supply of humanity with primary energy. As a fossil energy carrier, coal is one of the finite natural resources. The r...Hard coal and lignite—also referred to here jointly as coal—play a central role in the worldwide supply of humanity with primary energy. As a fossil energy carrier, coal is one of the finite natural resources. The reach of the world’s coal reserves is significant, and coal has the potential to cover some of the global energy and raw-material needs at least into the 22nd century. Precondition for this is a sustainable energy policy, i.e. an equal-ranking view of the goals of environmental and climate compatibility (sustainability), security of supply and competitiveness (affordability). The focus of developments is on resource efficiency and energy savings to obtain more modern and more efficient coal-based power plants. Greater use of coal translates into higher CO2 emissions. So if we are to achieve the climate-protection goals of limiting the rise in temperatures and reducing the CO2 content in the Earth’s atmosphere, the launch of CCS technology is recommended. Within the scope of the climate-protection debate, a discussion is also underway about an alleged drying up of coal availability in the short term (under the heading of “peak coal”). This discussion is an example of how, from the limited perspective of particular interests, a swathe of facts can be ignored. Hence, this article sets out to take a fact-based, sober look at the subject of the “reach of global coal reserves”. How much coal do we really have? And to what extent will coal be available tomorrow to guarantee secure and affordable energy supplies in the future as well? These issues will be investigated here.展开更多
文摘The deposition of mineral phases on the heat transfer surfaces of brown coal power plants may have a negative effect on power plant boilers. The paragenesis of these deposits contains information about the actual temperature prevailed during the combustion of lignite, if the temperature-dependences of distinct mineral transformations or reactions are known. Here, we report results of a sintering study (to ?1100℃) with samples containing anhydrite, quartz, and gehlenite, which are typical components of Rhenish lignite ashes. Thermal decompositions and solid-state reactions were analyzed (1) in situ and (2) both in situ and after quenching using confocal hyperspectral Raman imaging. This novel application of confocal Raman spectroscopy provides temperature-and time-resolved, 2-dimensional information about sintering processes with a micrometer-scale resolution. In the course of the sintering experiments with anhydrite and quartz with a weight ratio of 2:1 both polymorphs wollastonite and pseudowollastonite were identified in situ at about 920 and 1000℃, respectively. The formation of pseudowollastonite was thus observed about 120℃ below the phase transition temperature, demonstrating that it can form metastably. In addition,α′L-Ca2SiO4 was identified at about 1100℃. In samples containing equal weight fractions of anhydrite and quartz that were quenched after firing for 9h at about 1100℃,β-Ca2SiO4 (larnite) crystallized as rims around anhydrite grains and in direct contact to wollastonite. We furthermore observed that, depending on the ratio between quartz and anhydrite, wollastonite replaced quartz grains between 920 and 1100℃., i.e., the higher the quartz content, the lower the formation temperature of wollastonite.
文摘Hard coal and lignite—also referred to here jointly as coal—play a central role in the worldwide supply of humanity with primary energy. As a fossil energy carrier, coal is one of the finite natural resources. The reach of the world’s coal reserves is significant, and coal has the potential to cover some of the global energy and raw-material needs at least into the 22nd century. Precondition for this is a sustainable energy policy, i.e. an equal-ranking view of the goals of environmental and climate compatibility (sustainability), security of supply and competitiveness (affordability). The focus of developments is on resource efficiency and energy savings to obtain more modern and more efficient coal-based power plants. Greater use of coal translates into higher CO2 emissions. So if we are to achieve the climate-protection goals of limiting the rise in temperatures and reducing the CO2 content in the Earth’s atmosphere, the launch of CCS technology is recommended. Within the scope of the climate-protection debate, a discussion is also underway about an alleged drying up of coal availability in the short term (under the heading of “peak coal”). This discussion is an example of how, from the limited perspective of particular interests, a swathe of facts can be ignored. Hence, this article sets out to take a fact-based, sober look at the subject of the “reach of global coal reserves”. How much coal do we really have? And to what extent will coal be available tomorrow to guarantee secure and affordable energy supplies in the future as well? These issues will be investigated here.
