SE1200505A1 - Heating furnace for the metal industry and ways to heat one - Google Patents

Abstract

The furnace burners (16-21,28,29) in a step beam furnace (11) are jointly connected to two-ball bed generators (22,23) for regenerative preheating of the combustion air. Each ball bed generator is assigned to an auxiliary burner (50,50 ') whose exhaust line is connected to the inlet of the ball bed generator, which satisfies the temperature of the incoming furnace exhaust gases to the generators. The combustion air to the furnace burners maintains a temperature of over 1000 degrees Celsius and the burners work with lös amless combustion.

Description

Figure 1 shows a step beam furnace 11 with four zones, Zones 13,14,15 each have two burners 16-21. Conventionally, the first zone 12 has no burners, but in this example it also has two burners 28,29. Two ball bed generators 22,23 are cylindrical and have a central cylindrical space 25,25 'and an outer annular space 26,26' and between them there are an annular bed 27,27 'of ceramic balls.

The outlet 30 from the furnace is connected to the central space 25,25 'of the two ball bed generators 22,23' via lines 31,31 'and valves 32,32'. The annular space 26,26 'of the ball bed generators is connected to an exhaust outlet 33 via lines 34,34' with valves 35,35 '. A suction fan is connected to the exhaust emission 33.

The burners 16-21 are jointly connected to a line 40 for supplying combustion air.

This common line 40 is connected via lines 41,41 'and valves 42,42' to the central space 25,25 'of the ball bed generators. A fresh air intake 43 is connected via lines 44,44 'and valves 45,45' to the annular space 26,26 'of the ball bed generators. A pressure fan is connected to the fresh air intake.

When the valves 32,35 are open and the valves 32 ', 35' are closed, the exhaust gases from the furnace flow radially out through the hot ball bed 27 as shown to the exhaust outlet 33.

The exhaust gases are then cooled at the same time as the ball bed is heated. At the same time the valves 45 ', 42' are open and combustion air to the burners 16-21 is preheated in the ball bed 27 '. After a certain time, normally 15-20 minutes, the valves are switched so that the ball bed 27 'is preheated and the ball bed 27 gives off its stored heat.

During the switching moment, a valve 47 opens in the exhaust line 30, but since the cycle times are long and the changeover is fast, the switching losses are much smaller than when using regenerative burners.

Two auxiliary burners 50,50 'are connected to the lines 31,31' to raise the temperature of the hot gases which are led from the furnace to the ball bed generators 22,23. You raise the temperature so that you then get a preheated combustion air with a temperature of over 950 degrees Celsius and preferably above 1000 degrees or above 1100 degrees. With as high a temperature as can be achieved by using the auxiliary burners 50,51 ', the burners 16-21 can be burners for flamless combustion. Flameless combustion gives a high temperature without giving hot spots and you can thus reduce the NOX content while you can increase production and reduce the energy cost per tonne of steel. You want a temperature of the combustion air that is not so much lower than the oven temperature and you therefore use a temperature of 1100-1200 degrees Celsius.

Conventionally, furnace burners are not used in the first zone 12 because they want to use the furnace exhaust gases for a first heating of the steel blanks. When using the invention, you want to make the most of the exhaust heat in the regenerators instead of directly using part of the exhaust heat to preheat the steel blanks and it is advantageous to have burners 28,29 also in the first zone, ie. zone 12. The oven capacity is then increased by about 20%.

Figure 2 shows an example of a burner for flameless combustion that can be used as a furnace burner. The hot combustion air 55 enters the central and the fuel, e.g. propane, is injected through two nozzles 56 which are directed obliquely towards the flameless heat 57 which expands conically. Arrows 58.59 show how furnace gases are drawn into the heat 57.

Claims (7)

Patent claims 1. 2. A method of heating a heating furnace for the metal industry with a number of furnace burners (16-21, 28,29) which are supplied with combustion air via two regenerators (22,23) which are alternately connected to furnace exhaust gases and to inlet air, characterized by connecting the furnace burners ( 16-21,28,29) jointly to two ball bed regenerators (22,23 ') and mixes the exhaust gases from an auxiliary burner (50,50') into the incoming exhaust gases to the regenerator which is heating and controls the process so that the combustion air to the furnace burners 950 degrees C. 3.. A method according to claim 1, characterized in that the combustion air to the furnace burners (16-21) is kept at a temperature of at least 1000 degrees. A method according to claim 2, characterized in that the combustion air is kept at a temperature of over 1100 degrees Celsius. A method according to claim 2 or 3, characterized in that flameless combustion is used for the furnace burners (16-21). Heating furnace for the metal industry, comprising a plurality of furnace burners (16-21,28,29) and a device (22,23) for regenerative preheating of the combustion air, characterized in that the device for preheating comprises two ball bed regenerators (22,23) connected to all the furnace burners (22,23) together and each of the ball bed generators is assigned an auxiliary burner (50,50 ') whose exhaust line is connected to the inlet of the ball bed generator. Heating furnace according to Claim 5, characterized in that the furnace burners (16-21) are flameless burners. 5 Heating furnace according to Claim 5 or 6, characterized in that it is a step beam furnace which has a furnace burner in all zones.