Ignition and combustion characteristics of coal- water fuels based on coal & semi-coke

Annotation: The article presents the results of experimental and theoretical studies of the ignition processes of coal-water fuel (CWF) drops made from coals of various degrees of metamorphism and coal semi-coke of these coals. It is shown that the preliminary torrefaction of coal leads to a significant improvement in environmental performance (50-60% reduction in flue gas concentrations of the main anthropogenic coal combustion products: nitrogen oxides NOx and sulfur SOx) of coal-water fuel combustion processes. This effect is most pronounced during the combustion of CWF based on lignite. Also, according to the results of the experiments, the ignition delay times of typical droplets (in the initial state), and then particles (after drying the near-surface fuel layer) of coal-water fuel s based on coals and coal semi-coke were established. It has been established that the igni-tion delay times of coal-water fuel particles based on pre-torrefied coals at relatively low ambient temperatures (Tg <= 873 K) are on average 20% higher than when igniting CWF droplets based on natural coal. Under conditions of high-temperature heating, the ignition delay times of CWF particles made from natural coal and semi-coke differ insignificantly (no more than 2%).Based on the results of the experimental studies, a mathematical model of the ignition process of a coal-water fuel drop based on semi-coke was developed, which differs from the known ones in a relatively simple description of the most significant processes of thermal preparation and ignition, but at the same time retains a fairly high predictive potential. Using the previously developed method of quasi-stationary "thermal approximation" with the selection of an asymptotic estimate, an analytical solution is derived for the essentially nonlinear problem of coal -water fuel droplet ignition.Colloquium: An analysis of modern political discourse shows that the information entropy associated with the problem of the anthropogenic impact of mankind on the planet's atmosphere as a result of the operation of en-ergy facilities is constantly growing. At the same time, the constant growth of energy consumption in the world makes it necessary to introduce more and more new heat and power generating capacities. For a long time (the last 30 years) it was believed that the solution to all energy problems is the large-scale introduction of non-traditional renewable energy sources (solar batteries and wind power generators -RES) into the overall balance of energy generation. However, recent events in North America and Western Europe show that the potential for using renew-able energy sources is significantly limited, and electricity generation from these renewable energy sources is still significantly unstable. In this regard, a new impetus for development is acquiring coal energy. However, the main problem of coal power engineering, the anthropogenic impact of thermal power plants on the planet's atmosphere, remains unresolved. This situation creates prerequisites for the development of new "clean" coal technologies with complete sequestration of anthropogenic emissions generated during coal combustion. This article presents the re-sults of experimental and theoretical studies of the combustion processes of coal-water suspensions prepared from pre-torrefied coals. As a result of preliminary thermal (pyrolysis under conditions of high-temperature heating in an inert environment) preparation of coal, gaseous pyrolysis products are formed and removed into the external environment, a large proportion of which are hydrogen sulfide (the main source of sulfur oxides) and hydrocyanic acid (the main source of nitrogen oxides). After the preliminary pyrolysis of coal, a mixture of coke carbon and the mineral part of coal remains. When burning a coal-water suspension based on torrefied coal, only carbon dioxide and water vapor are formed. The latter can be relatively easily condensed and returned back to the power genera-tion cycle (or disposed of). Accordingly, the combustion of CWF based on torrefied coal creates the prerequisites for the fundamental justification of the technology for environmentally friendly combustion of coal in the combustion chambers of gas turbine plants operating on the Allam cycle.(c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.