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Evaluation of thermal calculation method for natural gas-fired steam boilers
Published in Evgeny Rybnov, Pavel Akimov, Merab Khalvashi, Eghiazar Vardanyan, Contemporary Problems of Architecture and Construction, 2021
V.A. Yakovlev, V.N. Yurchenko, N.S. Ponomarev
DKVr boiler units serially produced by the boiler-building industry of the Russian Federation are time-tested and have proven themselves excellently at municipal and industrial energy facilities. These devices are capable of operating in both steam and hot-water modes, thereby confirming their versatility in the production of two different types of heat-carrying agents, both hot and superheated water, as well as saturated and superheated steam.
Microwaves and Green Chemistry of Biofuels
Published in Veera Gnaneswar Gude, Microwave-Mediated Biofuel Production, 2017
Water is considered a green solvent especially in microwave mediated chemical synthesis due to its high dielectric properties. It is considered a non-toxic and non-corrosive and abundant solvent available at low costs. Reactions involving water as a solvent have matched the rates, yields and selectivities observed for many reactions in other solvents, or in many cases, surpass those in organic solvents. In contrast to many other solvents, water not only provides a medium for solution chemistry but often participates in elementary chemical events on a molecular scale. Water also offers practical advantages over organic solvents. It is cheap, readily available, non-toxic and non-flammable. In addition to using water for chemistry at ambient pressure in open vessels, there has been a growth of interest in the use of high-temperature water, superheated water and supercritical water. High temperature water is broadly defined as liquid water above 200°C, superheated water as water between 200-300°C and supercritical water as that above 374°C and 218 atm. At these temperatures the water approaches properties more like those of polar organic solvents at room temperature, and can act as an acidic or basic catalyst. The use of water as a solvent for metal-mediated synthesis has attracted considerable research interest since it can be used to implement approaches combining the advantages of homogeneous and heterogeneous catalysis by distributing the reagents, products and catalysts between different phases, pseudo-phases or interface regions. Three distinct types of approaches can be taken based on phase transfer, phase separation or solubilization although most processes involve a combination of two or all three of these. Due to its properties, water is an excellent solvent for microwave-promoted synthesis. Although it has a dielectric loss factor which puts it into the category of only a medium absorber, even in the absence of any additives it heats up rapidly upon microwave irradiation. Using a sealed vessel it is possible to heat water to well above its boiling point. At these elevated temperatures organic substrates become increasingly soluble and, even if they are not, addition of a phase-transfer agent can be used to facilitate solvation. Of course water cannot be used as a replacement for organic solvents for every class of reaction and, at the high temperatures used in microwave reactions, competitive decomposition of starting materials or products can become an issue (Leadbeater 2005). However, the major difficulty in using water as a solvent is its insolubility in most of the organic reactants which makes reactions heterogeneous. The major difficulty with using water as a solvent is the insolubility of most of organic reactants, making reaction mixtures heterogeneous. One way to overcome this is by using phase-transfer catalysts, but their expensive nature means that the resulting method is not economical. Product isolation from aqueous reaction mixture is another critical issue. Usually, evaporation of water is an option, but this is not an energy-efficient technique. Interestingly, these challenges can be tackled successfully by using the microwave heating technique for reactions in aqueous medium.
Engineering practice of underground heat injection-enhanced gas extraction in low-permeability coal seams
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Linjie Hu, Zengchao Feng, Dong Zhou, Xing Wang, Dong Zhao
The left side of Figure 1(a) shows the connection scheme of the underground heat injection system. The tunnel water supply pipe acts as the source of water. The water flows through the water tank, is pressurized by the high-pressure water pump, and is then fed into the electric heating boiler for conversion into superheated water (liquid water with a temperature greater than 100°C without boiling). The superheated water from the electric heating boiler is fed into the heat injection borehole via the heat transfer pipe, and this water is used to heat the coal seam. Finally, the extraction pipeline transports the low-temperature water discharged from the nearby boreholes to the highway sump. Notably, the wastewater discharged from the extraction system will have certain impact on the environment, and it should be recycled (Xue et al. 2022a). Therefore, the wastewater first passes through a settling and filtering device and is then converted into superheated water that is finally reinjected into the coal seam for recycling.