FIELD OF THE INVENTION

The present invention relates to a method for tundish preheating and a system thereof involving preheating of air used for combustion using flue gases at tundish preheating station. More particularly, the present invention is directed to providing a method and system for preheating combustion air for tundish preheating burner utilizing the heat of flue gases escaping through the tundish spout, carrying large amount of heat, which is being wasted to atmosphere. Importantly, the method and system of the invention is adapted to extract large portion of the thermal energy in the flue gases and transfer it to the incoming combustion air by recovering the sensible heat energy in the exhaust flue gas at elevated temperatures which otherwise leaves through the tundish spout opening and is usually wasted. The air preheating system for tundish preheating burner according to the invention thus would favour recovery of waste heat of flue gases and ensure saving of fuel consumption.

BACKGROUND OF THE INVENTION

It is well known in the field of steel production that tundish used for steel processing are pre-heated in tundish pre-heating station before start of casting and also during the waiting time when the tundish is not in use. Most of the modern steel making plant, tundish is needed to be heated to a range of temperature of 1150°-1250°C.

During continuous casting, tundish heating system is practiced to prevent temperature drop of molten metal. In tundish pre-heating station, tundish (used for steel processing) are pre-heated to 1150° - 1250°C before start of casting. Tundish preheater is used for heating the covered tundish. Heating is carried out using oil/gas-fired burners. These burners are connected to air blowers and fuel pumping system. Tundish is placed on tundish car facing the burner hood and is heated for about one and a half hours before taken for casting.

Heating is conventionally carried out using oil/gas fired burners, which requires air for combustion. Burners are mounted on burner hoods with refractory lining. In this arrangement, almost 50-60% of the heat energy is lost with flue. However, efficient tundish heating systems should aim to improve heating rates, provide uniform temperature so that higher pouring temperature may not be required.

It is presently well known to heat tundish such as involving three burners, which are situated on top of the tundish. Tundish is covered entirely by tundish cover except tundish spout. Such tundish pre-heaters presently consume large quantity of fuel. In the existing system of utilization of heat, tundish pre-heaters consume large amount of fuel oil due to inefficient heating.

OBJECTS OF THE INVENTION

It is thus the basic object of the present invention to provide a method and system for tundish preheating directed to utilisation of the heat value of the flue gases lost through the tundish spout and thereby reducing the fuel consumed at the tundish heating station so as to ensure recovery of substantial amount of waste heat from flue gases and utilize the same for preheating of combustion air.

A further object of the present invention is directed to providing a method for tundish preheating involving preheating of air used for combustion using flue gases at tundish preheating station and a system thereof which would be adapted to extract large portion of the thermal energy in the flue gases and transfer it to the incoming combustion air.

A still further object of the present invention is thus directed to providing a method and system for tundish preheating involving preheating of air used for combustion using flue gases at tundish preheating station, which would be adapted to reduce fuel consumption by using preheated air.

A still further object of the present invention is directed to a cost effective and faster method of preheating of tundish involving tundish preheating system which would enable preheating of air for combustion using available heat of flue gas for faster heating and enhanced tundish availability and productivity.
Yet another object of the present invention is directed to providing a higher flame temperature of tundish heating burners and thus heating the tundish to a higher temperature than is otherwise possible.

A still further object of the present invention is thus directed to providing a method and system for tundish preheating which would ensure reduction in emission of C02 and other volatiles to the environment.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided a method of preheating air used as combustion air going into the burner for tundish pre-heating comprising:

directing the incoming combustion air though heat exchanger exposed to the hot flue gases escaping through the tundish spout and the burner hood whereby the combustion air gets heated up during its travel through the heat exchanger, and injecting the thus heated combustion air from the heat exchanger into the burner for tundish preheating.

A further aspect of the present invention is directed to said method of preheating air wherein said incoming combustion air is directed into the heat exchanger through inlet hood and the heated combustion air is exited through an outlet hood which is injected into the burner.

A still further aspect of the present invention is directed to said method of preheating air wherein the recycling of the heat from the hot flue gas again into the combustion air for pre heating of the combustion air is carried out to reduce the amount of fuel needed for heating leading to saving of fuel by about 15-20%.

Yet another aspect of the present invention is directed to said method of preheating air wherein the inlet air temperature is raised from ambient to about 300°C and above.

Advantageously, also said method of preheating air adapted for reduction in emission of C02 and other volatiles to the environment.

A further aspect of the present invention is directed to a system for tundish preheating for carrying out the method as described above comprising:

a heat exchanger means adapted and placed on the circumference of the tundish spout on the path of the escaping flue gases such as to extract the thermal energy in the flue gases means to direct the incoming combustion air to said burner via said heat exchanger means to thereby transfer the thermal heat to the said combustion air and thereby pre heat the combustion air before reaching the burner for its combustion.

A still further aspect of the present invention is directed to a system for tundish preheating comprising:
tundish with tundish cover having a spout portion placed on tundish preheating station;

a recuperative burner including supply of combustion air mounted on burner hoods;

said tundish disposed such that the tundish spout faces the burner hood at top;

a heat exchanger means mounted below the tundish preheater arm disposed with respect to said tundish spout to cover the gap pathway of said tundish spout such as to arrest maximum heat energy of escaping flue gas and utilize the same for preheating said combustion air supplied to said burner.

Another aspect of the present invention is directed to said system for tundish preheating wherein said heat exchanger means comprise substantially circular shaped atleast one steel pipe having respective two end portions connected with hoods/ headers disposed surrounding the tundish spout.

A still further aspect of the present invention is directed to a system for tundish preheating wherein said heat exchanger comprises assembly of plurality of circular shaped pipelines obtained of layered steel pipes with hood/header at each end, which acts as inlet and outlet, adapted for conveying combustion air exposed to flue gases.

A still further aspect of the present invention is directed to said system for tundish preheating wherein the said heat exchanger is adapted to extract a large portion of the thermal energy in the flue gases and transfer the same to the incoming combustion air.

A still further aspect of the present invention is directed to said system for tundish preheating wherein said heat exchanger comprises an assembly of plurality of tubes selectively disposed in concentric circles of variable diameter which are gradually reducing upward placed one above another connected to hood at each end portion which act as inlet and outlet, air blown to the burner is first directed to the inlet hood from where it passes along said plurality of pipelines assembly which is directly exposed to the hot flue gas, air introduced into the inlet thus getting heated up during its travel through the assembly of pipelines and finally injected into the burner through said outlet hood thereby enabling continuous beneficial recycling of the heat.

Yet another aspect of the present invention is directed said system for tundish preheating wherein said plurality of heat exchanger pipes are arranged in a manner to enable maximum heat exchange surface area of tubes exposed to hot flue gases escaping through tundish spout.

A still further aspect of the present invention is directed to said system for tundish preheating wherein said heat exchanger tubes material is selected from any one of mild steel pipes, or any weldable metals such as Copper & alloys, Aluminium & alloys and stainless steel pipes.

The various other objects and advantages of the present invention is described in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMAPNYING FIGURES

Figure 1: is the schematic illustration of the conventional tundish preheating system without using any heat exchanger.

Figure 2: is the schematic illustration of the modified and improved tundish preheating system according to the present invention involving a heat exchanger with multiple concentric circular layered tube configuration mounted on tundish spout to recover waste heat of flue gas for preheating of combustion air.

Figure 3: is the schematic illustration of the heat exchanger used in the tundish preheating system of Figure 2, showing the details of the layered multiple concentric circular steel tubes configuration.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES

The present invention is directed to providing a system for tundish preheating involving preheating of air used for combustion using flue gases at tundish preheating station wherein a multiple circular steel pipe based heat exchanger is placed on the circumference of the tundish spout exactly on the path of the escaping flue gases to recover the waste heat of flue gas leaving the burner for preheating of combustion air.

Accompanying Figure 1 schematically illustrates the conventional tundish preheating system without using any heat exchanger. In the existing system, tundish is heated with three burners, which are situated on top of the tundish. Tundish is covered entirely by tundish cover except tundish spout. During the heating process, flue gases escape through tundish spout and the burner hood, carrying large amount of heat, which is being wasted to atmosphere. It was observed that, the escaping flue gases have temperatures up to 700°C. This large amount of heat is released to the atmosphere un-utilized. Hence, due to the non-utilisation of heat, tundish pre-heaters consume large quantity of fuel.

However, for fuel-fired industrial heating processes, one of the most potent ways to improve efficiency and productivity is to preheat the combustion air going to the burners. Pre-heated air helps in increasing the adiabatic flame temperature and thereby rendering higher heat at lower fuel consumption. This principle is utilized in the present invention by providing a heat exchanger in the path of exhaust flue gas used for heating combustion air.

The present invention is thus an attempt to provide for an improved tundish preheating system directed to utilisation of the heat value of the flue gases lost through the tundish spout by providing a heat exchanger assembly for preheating air (used for combustion) and thereby reducing the fuel consumed at the tundish heating station.

Accompanying Figure 2 schematically illustrates the modified and improved tundish preheating system according to the present invention involving a heat exchanger with multiple concentric circular layered tube configuration mounted below the tundish preheater arm to cover tundish spout to recover waste heat of flue gas for preheating of combustion air. When tundish is placed on tundish heating station for preheating and the tundish preheater arm is swung down to rest on the tundish cover, the heat exchanger fixed below the arm comes in position of spout and covers the opening of the tundish spout. It is apparent from Figure 2 that a heat exchanger has been placed on the circumference of the tundish spout exactly on the path of the escaping flue gases, so that, it extracts a large portion of the thermal energy in the flue gases and transfer it to the incoming combustion air.

Accompanying Figure 3 is the schematic illustration of the heat exchanger used in the tundish preheating system of Figure 2 showing that the heat exchanger is having a configuration with 11 number concentric circular tubes (each having a diameter of one and half inch) assembly with hood at each end, which acts as inlet and outlet for combustion air from blower. The diameter of concentric circular orientation of the steel tubes is arranged in a selective manner with the diameters of circles increasing from bottom to top in a stack. The largest diameter of annular tube at bottom is 1000mm and the smallest diameter of circle at top is 450mm. This particular configuration of the heat exchanger enable maximum heat exchange surface area of the circular tubes to be exposed to hot flue gas escaping through tundish spout. Air, which is directly connected to the burner, is directed to the inlet hood, from where it passes along the 11 tubes heat exchanger assembly, which is directly exposed to the hot flue gases. Air gets heated-up during its travel (due to heat exchange) and is injected into the burner through the outlet hood. Recycling heat, this way, reduces the amount of fuel needed for heating. Furthermore, this modification helps in improving the inlet air temperature from ambient to 300°C and above. Selective Multiple layered pipes configuration of the heat exchanger has been developed to increase and maximize the surface area of contact between steel pipes and out going hot flue gases. These hot flue gases heats up the steel pipes in heat exchanger. This sensible heat is utilized to heat up inlet air meant for combustion. Thus use of multiple layered pipes increases the effectiveness of heat exchange between the pipes and inlet combustion air.

The number of pipes in the heat exchanger depends on the capacity of the burner. Depending upon the maximum temperature of the preheating air for burner, the number of tubes for the heat exchanger means may be determined. As the maximum temperature of preheating air for burner according to the embodiment tried under the present invention is approximately 300°C, all tube heat exchanger was involved. In order to further emphasize the benefits including in particular the fuel efficiency in the heat exchanger system for tundish preheating in accordance with the present invention vis-a-vis conventional tundish heating without the involvement of heat exchanger means was further studied and the results of trials conducted to assess such performance of the heat exchanger on the consumption of fuel based on parameters recorded during the preheating of tundish are presented in the following Table 1.

Table -1: Comparative table showing the benefits achieved by the modified system

It can be observed from the Table that, due to the installation of air preheater system, the temperature of burner inlet air obtained is much higher than temperature of burner inlet air obtained before preheater installation. Higher initial temperature of preheated air leads to a decrease in oil consumption, heating time and improves the efficiency of burner and intensity of flame.

The method of tundish preheating involving the system for preheating of combustion air as per the present invention is adapted to achieve the following advantages:

1. Savings in fuel due to use of pre-heated air to the tune of 15-20%.

2. Reduction in the consumption of fuel.

3. A reduction in the emission of C02 and other volatiles to the environment.

It is thus possible by way of the present invention to providing a method and system for tundish preheating involving preheating of air used for combustion using flue gases at tundish preheating station wherein a multiple layered circular steel pipe based heat exchanger comprising a plurality of concentric circular arrangement of steel tubes is used to recover the waste heat of flue gas leaving through the tundish spout for preheating of combustion air. The heat exchanger can be simply mounted surrounding the tundish spout with the circular steel tubes connected to inlet and outlet hoods/headers at two ends for air inlet and outlet. Advantageously, the tundish preheating system according to the present invention involving the air preheating heat exchanger recover substantial amount of the waste heat of flue gas and thereby reduces fuel consumption significantly, making the system useful for application in steel industry.

We Claim:

1. A method of preheating air used as combustion air going into the burner for tundish pre-heating comprising:

directing the incoming combustion air though heat exchanger exposed to the hot flue gases escaping through the tundish spout and the burner hood whereby the combustion air gets heated up during its travel through the heat exchanger, and

injecting the thus heated combustion air from the heat exchanger into the burner for tundish preheating.

2. A method of preheating air as claimed in claim 1 wherein said incoming combustion air is directed into the heat exchanger through inlet hood and the heated combustion air is exited through an outlet hood which is injected into the burner.

3. A method of preheating air as claimed in anyone of claims 1 or 2 wherein the recycling of the heat from the hot flue gas again into the combustion air for pre heating of the combustion air is carried out to reduce the amount of fuel needed for heating leading to saving of fuel by about 15-20%.

4. A method of preheating air as claimed in anyone of claims 1 to 3 wherein the inlet air temperature is raised from ambient to about 300°C and above.

5. A method of preheating air as claimed in anyone of claims 1 to 4 adapted for reduction in emission of C02 and other volatiles to the environment.

6. A system for tundish preheating for carrying out the method as claimed in anyone of claims 1 to 5 comprising:

a heat exchanger means adapted and placed on the circumference of the tundish spout on the path of the escaping flue gases such as to extract the thermal energy in the flue gases means to direct the incoming combustion air to said burner via said heat exchanger means to thereby transfer the thermal heat to the said combustion air and thereby pre heat the combustion air before reaching the burner for its combustion.

7. A system for tundish preheating as claimed in claim 6 comprising:

tundish with tundish cover having a spout portion placed on tundish preheating station;

a recuperative burner including supply of combustion air mounted on burner hoods;

said tundish disposed such that the tundish spout faces the burner hood at top;

a heat exchanger means mounted below the tundish preheater arm disposed with respect to said tundish spout to cover the gap pathway of said tundish spout such as to arrest maximum heat energy of escaping flue gas and utilize the same for preheating said combustion air supplied to said burner.

8. A system for tundish preheating as claimed in anyone of claims 6 or 7 wherein said heat exchanger means comprise substantially circular shaped atleast one steel pipe having respective two end portions connected with hoods/ headers disposed surrounding the tundish spout.

9. A system for tundish preheating as claimed in anyone of claims 6 to 8 wherein said heat exchanger comprises assembly of plurality of circular shaped pipelines obtained of layered steel pipes with hood/header at each end, which acts as inlet and outlet, adapted for conveying combustion air exposed to flue gases.

10. A system for tundish preheating as claimed in anyone of claims 6 to 9 wherein the said heat exchanger is adapted to extract a large portion of the thermal energy in the flue gases and transfer the same to the incoming combustion air.

11. A system for tundish preheating as claimed in anyone of claims 6 to 10 wherein said heat exchanger comprises an assembly of plurality of tubes selectively disposed in concentric circles of variable diameter which are gradually reducing upward placed one above other connected to hood at each end portion which act as inlet and outlet, air blown to the burner is first directed to the inlet hood from where it passes along said plurality of pipelines assembly which is directly exposed to the hot flue gas, air introduced into the inlet thus getting heated up during its travel through the assembly of pipelines and finally injected into the burner through said outlet hood thereby enabling continuous beneficial recycling of the heat

12. A system for tundish preheating as claimed in anyone of claims 6 to 11 wherein said plurality of heat exchanger pipes are arranged in a manner to enable maximum heat exachange surface area of tubes exposed to hot flue gases escaping through tundish spout.

13. A system for tundish preheating as claimed in any one of claims 6 to 12 wherein said heat exchanger tubes material is selected from any one of mild steel pipes, or any weldable metals such as Copper & alloys, Aluminium & alloys and stainless steel pipes.