Heating – Having condition responsive control – Of or by pressure of fluid work or work chamber atmosphere
Reexamination Certificate
2002-09-04
2003-11-11
Lu, Jiping (Department: 3743)
Heating
Having condition responsive control
Of or by pressure of fluid work or work chamber atmosphere
C432S128000, C432S146000, C432S152000, C432S153000
Reexamination Certificate
active
06644962
ABSTRACT:
TECHNICAL FIELD
This invention concerns a method of optimally controlling the furnace pressure of a heating furnace. This invention relates to a method of controlling the atmosphere in a heating furnace and, particularly, a method of suppressing increase of an oxygen concentration in the atmosphere. This invention relates to an operation method of a heating furnace having heat regenerating burners and a heating furnace, particularly, to an operation method for conducting alternate combustion of paired burners in heat regenerating burners advantageously and a heating furnace used directly for the operation. This invention concerns a method of measuring the concentration of an atmospheric gas in a heating furnace and a heating furnace.
BACKGROUND ART
A heating furnace for steel materials is used with an aim of re-heating steel pieces roughly rolled in a blooming factory or continuously rolling cast pieces into final products to a predetermined temperature suitable to rolling. The heating furnace is generally classified into a batch type and continuous type. Since they have respective advantages and drawbacks, they are used selectively depending on the purposes. Since the continuous heating furnace is suitable to mass production in recent years, they have been often been used, for example, in iron making plants.
FIG. 1
shows a typical example of a cross sectional view for a continuous heating furnace. It generally comprises a preheating zone
1
, a heating zone
2
and a soaking zone
3
successively from the side of charging steel materials. At least the heating zone
2
and the soaking zone
3
are heated to and kept at a predetermined temperature by burners
4
. Steel material
5
introduced from a charging door
1
a
into the preheating zone
1
are moved on a transportation path
6
and heated to a predetermined temperature by way of the heating zone
2
and the soaking zone
3
and then delivered to the outside of the furnace from an extraction door
3
a
on the exit side of the soaking zone
3
. Exhaust gases formed by combustion of the burners
4
are discharged from a stack
7
disposed on the entrance of the preheating zone
1
to the outside of the furnace.
7
a
denotes a recuperator for heat exchange of the sensible heat of an exhaust gas in the stack
7
to the sensible heat of a burner combustion gas and
7
b
denotes a damper for furnace pressure control. Then, in the continuous heating furnace, it is necessary to heat the steel materials to a temperature suitable to a subsequent rolling step. When the temperature of the steel materials heated in the continuous heating furnace is lower than the lower limit of a predetermined temperature suitable to rolling, it results in undesired effects on the rolling operation and product quality. On the other hand, when the temperature of the steel materials extracted from the heating furnace is unnecessarily higher, heat loss increases in the continuous steel material heating furnace. Therefore, it is important in the continuous heating furnace to heat the steel materials up to the temperature suitable to rolling with necessary minimum of fuels. Further, in the heating furnace, it is also required to control the heating time such that heated steel materials are supplied successively from the heating furnace corresponding to the rolling pitch in the rolling step.
In the continuous heating furnace, heat loss, particularly, radiation energy loss from the heating zone is large. The heat loss is suppressed by providing a preheating zone and a soaking zone at the inlet and the exit of the heating zone to partition the inside of the furnace into three parts.
Steel materials to be charged in the continuous heating furnace includes, for example, cast pieces cooled to a normal temperature and hot charged materials sent directly after continuous casting to the rolling step, and the temperature on the inlet of the heating furnace is various. The heating temperature is varied and the processing amount of steel materials to be heated in the heating furnace also varies. The temperature in the heating furnace has to be controlled in according with such various conditions. The heating temperature is adjusted by increasing or decreasing the combustion amount of burners. The pressure in the furnace fluctuates in this case depending on the change of the combustion amount of the burners.
When the pressure in the furnace is lowered compared with the pressure outside the furnace, external air intrudes into the furnace through the charging door and the extraction door as openings of the heating furnace. When air intrudes into the furnace, since the temperature in the furnace lowers, the combustion amount of the burners is increased. This increases the fuel consumption ratio to increase the cost. When air intrudes into the furnace, since concentration of oxygen in the furnace atmosphere increases, oxidation, nitridation or decarbonization on the surface of steel materials charged in the furnace are promoted. As a result, it results in deteriorates the surface quality of the steel materials.
Accordingly, it is necessary to properly control the pressure in the heating furnace. Various proposals have been made for the control of the furnace pressure. For example, JP-A-61-119987 discloses prevention of air intrusion from a charging door and an extraction door by controlling the furnace pressure set in the soaking zone of a heating furnace to a positive pressure relative to the pressure outside of the furnace (hereinafter simply referred to as positive pressure) in accordance with the amount of exhaust gases generated in the furnace. According to this method, it is possible to control the furnace pressure in an upper region of the furnace with the transportation path as a boundary (hereinafter referred to as an upper zone) to a positive pressure. However, when the combustion load on the entire heating furnace is small, the furnace pressure in the lower region of the furnace with the transportation path as the boundary (hereinafter referred to as a lower zone) becomes negative relative to the pressure outside the furnace (hereinafter referred to as a negative pressure). It has been difficult to reliably prevent intrusion of air through gaps below the charging door and the extraction door. It has been difficult to reliably prevent intrusion of air through so-called extra fork openings in which the doors are closed while being engaged to each other in a comb teeth shape. Comb-shaped extract fork opening is shown at
3
C in FIG.
14
.
Further, JP-A-9-209032 discloses optimum control for a furnace pressure in accordance with the amount of combustion load on a heating furnace by a furnace pressure damper disposed in a stack through which exhaust gases from the heating furnace are passed in the upper region of the soaking zone. However, when the amount combustion load is small, draft in the stack increases compared with the pressure loss due to the flow of exhaust gases from the inside of the furnace to the stack. The draft means that gases heated in the stack or in the furnace cause buoyancy to form a negative pressure. In this case, it is difficult to form a positive pressure as far as the lower zone by the furnace pressure damper. It has been difficult to reliably prevent intrusion of air from the charging door and the extraction door.
JP-A-7-316645 discloses a method of connecting a gas supply pipeline system to a stack on the exit of a recuperator and blowing a gas such as air into the stack thereby controlling the furnace pressure. This method requires to additionally provide a blower, various pipelines and a control system for controlling the furnace pressure. It involves a problem in that the installation cost is high and the maintenance is troublesome. In addition, since ducts or accessory equipments are incorporated in a complicate manner at the periphery of the heating furnace, there is no room for installation space and additional prevision of the control system is difficult.
Prevention of air intrusion into the heating furnace is extremely importa
Andachi Kazunari
Furukawa Masahiro
Karube Kenta
Sugimoto Ichiro
Kawasaki Steel Corporation
Lu Jiping
Oliff & Berridg,e PLC
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