The use of a storage tank to regulate the loads of the mini-CHP plant improves the technical and economic indicators of its operation. However, the results of studies of the use of a storage tank in heating systems, in contrast to hot water supply systems, are poorly represented. The purpose of the study is to determine the conditions and indicators under which the use of a storage tank to regulate the heating load of a mini-CHPP is economically viable. The study of the heat grid is based on solving the standard heat balance and heat transfer equations. Modeling of heat transfer in the heat recovery circuit of a cogeneration unit is carried out by approximating the passport specification of the equipment in the range of operating loads from 50 to 100 %. Modeling the standing time of the outside air temperatures is carried out in accordance with the method of B. Shifrinson and V.Ya. Khasilev. The conditions of the numerical study are quite typical for the heating network of Donetsk. For the first time, to satisfy the conditions of a numerical study, the dependence of the available and used thermal capacity of the storage tank on the outside air temperature has been established for different values of the design volume of the tank. The quantitative characteristics of the influence of the design volume of the storage tank on electricity generation during peak, half-peak and minimum power system loads are investigated. The reliability of the results obtained is determined by the correct use of proven methods for calculating the operation parameters of water heating system and heat devices. The study shows that the use of a storage tank to regulate the heating load of a mini-CHPP is technically and economically feasible. With the design volume of the storage tank in the range of 65–126 m3 per 1 MW of the connected heating load, the simple payback period of the mini-CHPP varies insignificantly and can be considered acceptable. The presence of a storage tank allows realizing the maneuverable capabilities of cogeneration units, while maintaining a high share of energy generation in combined mode. The district heating coefficient, equal to one, allows achieving high efficiency of fuel utilization for generation of both electrical and thermal energy. The research results can be used in municipal heat supply systems when introducing gas piston cogeneration units.
There are a number of technical solutions to utilize the waste gases of electric arc furnaces (EAF) for scrap preheating thus returning back the heat into the technological process. The waste gases can be utilized also for steam or hot water production. The preliminary scrap heating before charging it into EAF is more perspective. Technical features of various types scrap heaters considered, including conveyer and shaft scrap heating technologies with continuous (Contiarc, Consteel, Comelt, BBC-Brusa) and periodic charging (Fuchs Systemtechnik, COSS, backet). It was shown that application of scrap heaters for EAF ensures saving of electric energy, increase of metal yield, decrease of dust and gases level in the shop, decrease of negative impact on environment. The disadvantages include frequent and costly repairs of the facilities, impossibility to control some factors having effect on the process of scrap heating. It was shown that when designing new EAFs with a charge exceeding 100 t, horizontal facilities are more preferrable, while for EAFs of small volumes shaft heaters suit better. At EAF modernizing it is recommended to use shaft heaters and backet-thermos, since it is easier to construct a vertical furnace than a horizontal one with minimal length of 100 m. It was noted that horizontal heaters operate better in terms of technology, since ensure continuous charging by scrap, but at that occupy a considerable space in the shop. When comparing vertical heaters and backet by all the characteristics including heat-engineering and designingones, vertical shaft heaters prevail.
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