2.3 Performance furnaces
Each tube furnace is characterized by three main indicators:
- performance;
- useful heat load;
- efficiency.
Kiln expressed by the number of raw materials, in tube coils heated per unit time (typically in tons / day). It determines the capacity of the furnace, i.e. the amount of the heated raw material, which is pumped through the coils at a set operating parameters (temperature of raw material to the furnace inlet and outlet thereof, feed properties, etc).
Thus, for each furnace performance it is rhe most complete characterization.
Useful thermal load – the amount of heat transferred raw materials in a furnace (MW Gcal / h). It depends on the thermal capacity and the size of the furnace. Thermal load most exploited ovens 8-16 MW.
Perspectives are more powerful furnace with a heat load of 40-100 MW and more.
Factor furnace efficiency characterizes the efficiency of its operation, and is expressed by the ratio of useful heat used Qfull to the total amount of heat Qtotal that is released by the complete combustion of fuel.
It is considered useful to use the heat sensed by all heated products (streams) feedstock, steam superheated in the furnace and in some cases the air heated in the recuperator (air heaters).
The coefficient of efficiency depends on the completeness of fuel combustion, as well as the heat losses through the furnace bricking, and with the gases leaving the stack.
Tubular furnace currently in operation at the refineries, have efficiency within 0,65-0,87.
Increasing the efficiency of the furnace action coefficient by making fuller use of flue gas heat possible to a value determined by its minimum temperature. Typically, the temperature of the flue gases leaving the convection chamber must be higher than the initial temperature of the heated feedstock is not less than 120 ... 180 °C.
The performance properties of each of the furnace along with the above indicators are characterized by:
- Calorific heating surface;
- Thermal stress of the furnace volume;
- Hydraulic regime in the pipe coil at steady work.
The complexes of these parameters depend on the efficiency of the kilns and their service life.