Environmental Engineering Reference
In-Depth Information
radiation heat from the furnace body. This latter model uses the furnace temperature
and the heating surface, plus the heat loss by cooling water.
The required heat volume and steel temperature are calculated based on the heat
balance obtainable by combination of the above, the combustion heat, and the
sensible heat of the exhaust gas. The difference between the continuous reheating
furnace model with regenerative heat exchangers from the conventional continuous
reheating furnace model is the difference depending on whether the combustion air
to be heated goes through regenerative heat exchangers or recuperators. Furthermore,
regarding the high performance model, the program is also applicable to the non-
combustion zone at the furnace tail.
5.2.2.1 Estimation Method of Fuel Flow Volume and Exhaust
Gas Temperatures Using Heat Balance
The method to calculate the volume of fuel flow and exhaust gas temperature to obtain
the heat balance in each divided zone is shown in
Figure 5.29
.
The heat inputs related
to the combustion gas are the sensible heat of the semifinished steel coming into the
zone from the steel charging side, as well as the sensible heat of preheated air and
exhaust gas coming into the zone from the steel discharging side. Scale-forming heat
and fuel combustion heat are also heat inputs, even though sensible heat of preheated
air and scale-forming heat do not exist in the noncombustion zone.
Heat outputs are sensible heat of a semifinished steel going out of the zone on
the discharge side and of the exhaust gas flowing to the zones on the steel charging
side (downstream), as well as the sensible heat of exhaust gas going out to the
regenerative heating exchangers (no heat exchangers in the noncombustion zone),
heat loss by zone cooling water, and heat radiation loss from the furnace wall.
The way to obtain the heat balance between these heat inputs and outputs is to
calculate the temperature and the fuel necessary. The zones are split into two groups
and the calculation is carried out for each group. For the noncombustion zone, the
foregoing heat input and output values of items, a semifinished steel, exhaust gas into
the zone, scale forming, cooling water heat loss, and heat radiation loss are given (or
hypothetically determined) and the sensible heat of exhaust gas from the zones on the
steel charging side (downstream) is calculated. For the preheating zone, heating zone,
and soaking zone, the foregoing heat input and output values (which are sensible heat
of exhaust gas flowing out to the zones on the steel charging side) are given, in addition
to the case of calculation for the noncombustion zone. By using these data input, the
fuel combustion heat and its associated airflow rate are calculated. Both calculation
methods assume that the temperature of the semifinished steel and its heat input are
known, and the calculation required here is a convergence calculation involving a heat
balance and a steel-temperature calculation.
5.2.2.2
Calculation Method of the Internal Temperature of the
Semifinished Steel
The semifinished steel is approximated to one of the following three forms to
calculate the temperature. The forms are one-dimensional infinite plate (slabs),
Search WWH ::
Custom Search