Improving the efficiency of plant based on furnace heating and intermediate heating media

Abstract

An important task for the designers of new plant is the economic enhancement of equipment based on fumace heating and intermediate heating media.Basic geometrical and other parameters have been given [1--4] for two plants having furnace heating, which differed in the disposition of the heat-uptake tube bundles: in the old design, they were contained in a rectangular box above a cylindrical body, while in the new one, they were placed between the gas tubes (the rectangular box was eliminated, and consequently the hot outer surface was substantially reduced).The technological efficiency is a basic parameter governing the economic operation, and it can be defined by the foliowing if the fuel is gaseous: 1"1 a = 100 -(q2 + q3 + q5), (i) in which q2, q3, and q5 are the heat losses with the stack gases, due to incomplete combustion, and from the hot components into the surrounding space, respectively.It has been found [1, 2] that if the excess air factor in the fire tubes is c~ > 1.5, then q3 = 0, and (1) simplifies to qa = 100 -(q2 + qs)"The heat lost with the stack gases q2 is substantially dependent on the gas temperature ts:Vscsts-aV~176 100, q2-Qtp.in which V s = VRO 2 + V~ 2 + VI_t20 + (c~-I)V ~ is the stack gas volume; VRO 2, V~ VH20, V 0 are the volumes, respectively, of the triatomic gases, the nitrogen (theoretical), the water vapor, and the air (theoretical); c s is the average specific heat of the outgoing combustion products; (Ct)o is the product of the specific heat and temperature for the surrounding air; and Q~ is the available heat from the fuel.We compared q2 for the old and new plants in relation to the energy produced BQ~. = 20, 50, 100, 140 kW (where B is the fuel flow rate).