Известия Томского политехнического университета: Инжиниринг георесурсов (Apr 2018)
Development of mathematical model of the system of high-temperature ceramic heat exchangers of periodic action
Abstract
The relevance of research is conditioned by the need to create and develop heat power plants, in which the processes of electric power generation are combined with the processes of coal gasification. Interest in this direction is explained by large natural reserves of coal and minimal harmful emissions into the atmosphere during the combustion of gas obtained during gasification. As a rule, to improve the quality of gasification, air enrichment with oxygen is used, which is very expensive. An alternative way to increase the calorific value of the generator gas is to supply air heated to a high temperature (more than 1500 °C) into the gasifier. Heating to this temperature in the tubular recuperative heat exchangers is not possible. The only real way to heat the air to the specified temperature level is to heat it in the regenerative heat exchangers of batch operation with ceramic backfilling. The aim of the study is to develop a mathematical model of a system of periodic ceramic heat exchangers for obtaining high-temperature air and suitable for use in optimization calculations of combined-cycle gas turbines with coal gasification. Methods. The authors applied the approach based on the use of the stationarity condition. The latter consists in the fact that the temperatures of the ceramic ball layers at the beginning of the heating stage should be equal to these temperatures at the end of the cooling stage. This approach allows us to take into account the dependence of heat capacity and heat transfer coefficient on temperature without significant expenditure of computing resources. Results. The authors developed the mathematical model of a system of regenerative batch heat exchangers with a ceramic ball filling, which allows simulating air heating to high temperatures. With the help of the developed mathematical model, calculations were made. It is determined that increase in the number of pairs of heat exchangers in the system from two to six leads to decrease in the temperature variations of the coolant by 6,25 times. It is shown that, with the initial data considered, the increase in the number of pairs of heat exchangers above 10 does not lead to a significant decrease in temperature fluctuations at the outlet.
