Электронная библиотека магистра ДонНТУ Горнилиной А.М.

 

Bytkin V.N. Preparing the row materials for blast furnace process (sintering). Summary of lectures. - 160 p.

 

HEAT BALANCE OF SINTERING PROCESS

 

Compiling the overall heat balance of the sintering process proceeds from the initial and final states of the system. Table 1 represents an exemplary composition of the overall balance and shows the ranges of variation of the values of its individual items. The balance gives an idea of the overall fuel consumption for 1 ton of sintered cake. Examining the income items is of interest in sintering ores high in sulfur and with a combined heating of the sintering mixture. Redistribution of heat among the main income items makes it possible to outline the ways for cutting down the consumption of solid fuel and to quantitatively evaluate its economy. When examining the expenditure part of the heat balance, the overall heat consumtion is divided into "losses" and an 'useful" heat consumption. The "losses" include the heat of exit gases and the external heat losses:

 

Process efficiency = Q - (Q8 + Q10) *100%
Q

 

where: Q - overall heat consumption, kJ/kg of sinter cake;

Q8 - heat of exit gases, kJ/kg of sinter cake;

Q10 - external heat losses, kJ/kg of sinter cake.

 

Table - Heat Balance of Sintering Process

 

Balance item

 Proportion in overall heat consumption*, %

Income

  

Combustion of carbon

 50 - 90

Combustion of sulfur

 1 - 40

Physical heat of ignition

1 - 15

Physical heat of sintering mixture

1 - 4

Physical heat of air

 0.5 - 1.5

Heat of exothermal reactions of new chemical compounds formation

 1 - 3

Expenditure

Heat of finished sinter

30 - 60

Heat of exit gases

 30 - 60

Heat consumption for endothermal processes

30 - 60

External heat losses

 7 - 10

*Overal heat consumption is 1470 - 2940 kJ/kg.

 

The overall heat balance fails to reflect the specific features of the processes of heat transfer, heat development and absorption in the course of sintering. However, it is these features of the sintering process that to a great extent determine its high economy. The set of all the zonal heat balances compiled for individual horizontal layers for the time from the beginning of the process till cooling of the sinter obtained demonstrates that up to a certain moment the entire heat obtained is usefully utilized within the bed as a whole (except the external radiation losses). Heat losses with exit gases begin only after the drying zone has reached the underlayer ("bed") level, when the heat previously utilized for heating the underlying layers of the sintering mixture now leaves the bed with exit gases.

The zonal balances take account of three principal items which constitute the production-process basis of sintering:

1. Heating and melting the sintering mixture.

2. Heating the air by overlying layers of sinter before the air enters the combustion zone.

3. Utilizing the gases leaving the combustion zone for heating the underlying layers of sintering mixture.

Measurements of the temperature in the fuel combustion zone demonstrate that, with a normal run of the process, the whole sintering mixture bulk is sequentially, layer by layer, heated up to plus 1100 — plus 1600°C. The simplest calculations indicate that the heat of combustion of solid fuel in any sintering mixture bed is insufficient to maintain so high a temperature therein. The high temperatures in bad stem from regeneration of heat in the course of agglomerating the materials being sintered. In the bottom layers of the sintering mixture the proportion of regenerated heat in the heat balance of combustion zone often exceeds 55-60%.

Fuel combustion in the topmost layers proceeds without air heating, and the lack of heat is made up by the sintering mixture ignition heat.