FIELD OF THE INVENTION

The present invention relates to a system for ladle preheating involving preheating of air used for combustion using flue gases at ladle preheating station. more particularly, the present invention is directed to providing a system for preheating combustion air for ladle preheating burner utilizing the heat of flue gases leaving the burner. Importantly, the air preheating system for the ladle preheating involve heat exchanger made up of layered steel pipes and junction headers mounted on the burner hood used for heating combustion air by recovering the sensible heat energy in the exhaust flue gas at elevated temperatures which otherwise leaves through the gap between ladle mouth and burner hood. The air preheating system for ladle preheating burner according to the invention thus 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 steel ladles (used for steel processing) are pre-heated in ladle pre-heating station after every new refractory lining and also during the waiting time when the ladles are not in use. Most of the modern steel making ladles is needed to be heated to temperature of 1150-1200°C.

Heating is conventionally carried out using oil / gas fried burners, which requires air for combustion. Burners are mounted on burner hoods with refractory lining. Ladle mouth is placed facing the burner hood with 50mm gap to avoid sticking of hood to the ladle. Newly lined ladles are usually heated for 8-10 hrs before being put in circulation. Also while in circulation, ladles are preheated for 20-30 minutes before each heat cycle. In this arrangement, almost 50-60% of the heat energy is lost with flue. However, efficient ladle heating systems should aim to improve heating rates, provide uniform temperature and reduce furnace tap temperatures.

In the existing preheating process of steel ladles, flue gases escape through the gap between the ladle and the burner hood, carrying large amount of heat, which is being wasted to atmosphere. It has been observed that flue gases escaping from the gap have temperatures up to 1000°C. This large amount of heat is released to the atmosphere un-utilized. In the existing system of utilization of heat, ladle pre-heaters consume large amount of fuel oil inefficiently.

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.

Preheated air helps in increasing the adiabatic flame temperature and thereby rendering higher heat at lower fuel consumption.

There has been therefore a need in the area of ladle preheating in steel plant to develop a system and method for ladle preheating to on one hand ensure recovery of the waste heat of flue gases escaping from burners through gap between burner hood and the ladle mouth and on the other hand utilize the available heat of flue gas for preheating of combustion air to thereby achieve fuel economy and improved thermal efficiency of burner enabling cost effective and efficient ladle heating.

OBJECTS OF THE INVENTION

Thus according to a basic object of the present invention there is provided for a system for ladle preheating involving preheating of air used for combustion using flue gases at ladle preheating 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 thus directed to providing a system for ladle preheating involving preheating of air used for combustion using flue gases at ladle preheating station wherein a circumferential configuration of heat exchanger comprising layered steel pipes mounted on the burner hood for conveying air exposed to flue gases covering partly the gap between burner hood and the ladle mouth.

A still further object of the present invention is thus directed to providing a ladle preheating system involving preheating of air used for combustion using flue gases at ladle 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 ladle using an improved ladle preheating system involving preheating of air for combustion using available heat of flue gas which would enhance ladle availability and productivity.

Yet another object of the present invention is directed to providing a higher flame temperature and thus heating the ladle to a higher temperature than is otherwise possible.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided a system
for ladle preheating comprising:

ladle having a ladle opening /mouth portion;

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

said ladle disposed such that the ladle mouth faces the burner hood with an intermediate gap therebetween;

a heat exchanger means disposed with respect to said intermediate gap therebetween said ladle mouth and burner hood in the said gap pathway of the escaping flue gas such as to direct the escaping flue gas heat energy and utilize the same for preheating said combustion air supplied to said burner.

A further aspect of the present invention is directed to a system for ladle preheating wherein said heat exchanger means comprise substantially circular shaped atleast one steel pipe having respective two end portions with junction headers mounted along the circumference of the burner hood.

A still further aspect of the present invention is directed to a system for ladle preheating wherein said heat exchanger comprises assembly of plurality of circular shaped pipelines obtained of layered steel pipes and end junction headers adapted for conveying air exposed to flue gases.

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

Yet another aspect of the present invention is directed to a system for ladle preheating wherein said heat exchanger comprises an assembly of plurality of circular tubes with junction headers at end portion which act as inlet and outlet, air blown to the burner is first directed to the inlet junction from where is 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 junction box thereby enabling continuous beneficial recycling of the heat.

A still further aspect of the present invention is directed to said heat exchanger system which comprises plurality of circular shaped heat exchanger pipelines assembly adapted to be directly exposed to hot flue gas/heat energy emanating from any gaps in the assembly of pipelines and the like.

A still further aspect of the present invention is directed to an improved method of ladle preheating adapted to reduce fuel consumption using the system for ladle preheating as described above comprising:

preheating air received from blower in said heat exchanger by passing first through inlet junction header whereby air gets heated-up during its travel through plurality of layered steel tubes due to heat exchange with flue gas coming out from burner and resulting hot air is subsequently injected into the burner through the outlet junction box, to thereby increasing the adiabatic flame temperature and thus rendering higher heat at lower fuel consumption.

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

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Figure 1: is the schematic illustration of the existing ladle preheating arrangement showing the gap between the burner hood and the ladle mouth placed in ladle preheating station.

Figure 2: is the schematic illustration of ladle preheating system according to the present invention involving the air preheating provision showing the heat exchanger coil mounted on the burner hood located in between ladle mouth and burner hood, for preheating air with flue gas.

Figure 3: shows the schematic illustration of the fabricated heat exchanger coil of the air preheating system according to the present invention comprising layered steel pipes in circumferential orientation connected with inlet and outlet air headers.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES

The present invention is directed to providing a system for ladle preheating involving preheating of air used for combustion using flue gases at ladle preheating station wherein a layered circular steel pipe based heat exchanger is used to recover the waste heat of flue gas leaving the burner for preheating of combustion air.

Reference is first invited to the accompanying Figure 1 that illustrates the existing ladle preheating arrangement showing the gap between the burner hood and the ladle mouth placed in ladle preheating station. Heating is carried out using oil/gas fired burners, which uses air for combustion. Burners are mounted on burner hoods with refractory lining. The air for combustion is supplied from a blower without preheating. In this arrangement, ladle mouth is placed facing the burner hood with 50mm gap to avoid sticking of hood to the ladle. During the heating process, flue gases escape through the gap between the ladle and the burner hood, carrying large amount of heat, which is being wasted to atmosphere. It was observed that flue gases escaping from the gap have temperatures up to 1000°C. This large amount of heat is released to the atmosphere un-utilized. Due to the present inefficient utilization of the heat, ladle pre-heaters consume large amount of fuel.

Reference is now invited to the accompanying Figure 2 that illustrates the air preheating system for ladle preheating according to the present invention showing the heat exchanger coil mounted on the burner hood located in between ladle mouth and burner hood, for preheating air with flue gas. It is apparent from the figure that the system involves a heat exchanger having layered steel pipes having circumferential configuration with inlet and outlet headers, mounted on the burner hood for preheating of combustion air with flue gas generated in the burner. In the present case, the heat energy in the exhaust flue gas (which leaves from the gap between ladle mouth and burner hood at elevated temperatures) is used for heating combustion air. The heat exchanger is placed on the circumference of the burner hood, 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 illustrates the fabricated heat exchanger coil of the air preheating system according to an embodiment of the present invention comprising layered steel pipes in circumferential orientation connected with inlet and outlet air headers. Apart from mild steel pipes, any weldable metals such as Cu & alloys, Al & alloys and stainless steel pipes can also be used as heat exchanger pipes. The heat exchanger of the air preheating system according to an embodiment of the present invention is a circular 12 tubes (each 2 inch diameter) assembly with junction headers at each end, which acts as inlet and outlet. 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 prehearing 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, a 12 tube heat exchanger was involved. Alternatively, for higher temperature the number of tubes may be varied as per the burner design restriction.

The tubes are arranged in concentric circular shapes in two rows, wherein each row having six such tubes providing a layered configuration for effective heat exchange surface. The hot flue gas coming out from the burner passes through the layered tube stack favouring desired heat exchange with inlet air through tubes enabling preheating of the combustion air. Air from blower is directed to the inlet junction/header, from where it passes along the 12 tubes heat exchanger assembly, which is directly exposed
to the hot flue gases. Air gets heated-up during its travel (due to heat exchange) through tubes and is injected into the burner through the outlet junction box/header. Recycling heat, this way, reduces the consumption of fuel needed for heating.

To further ascertain the benefits including in particular the fuel efficiency in the heat exchanger system for ladle preheating in accordance with the present invention vis-a-vis conventional ladle 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 ladles are presented in the following Table 1.

The above results clearly and sufficiently reveal the substantive fuel saving achieved by the system in accordance with the present invention which not only efficiently performs ladle preheating but also achieves substantial savings in fuel costs vis-a-vis the conventional system of ladle preheating.

It is thus possible by way of the present invention to providing a system for ladle preheating with preheating of air used for combustion using flue gases at ladle preheating station involving a layered steel pipe based heat exchanger comprising a plurality of multilayered circumferential arrangement of steel tubes used to recover the waste heat of flue gas leaving the burner for preheating of combustion air. The heat exchanger can be simply mounted on the burner hood covering the gap between the ladle mouth and the burner hood. Advantageously, the ladle preheating system according to the present invention involving the air preheating heat exchanger utilizes the waste heat of flue gas and thereby reduces fuel consumption significantly, making the system useful for steel producing industry.

We Claim:

1. A system for ladle preheating comprising:

Ladle having a ladle opening /mouth portion;

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

said ladle disposed such that the ladle mouth faces the burner hood with an intermediate gap therebetween;

a heat exchanger means disposed with respect to said intermediate gap therebetween said ladle mouth and burner hood in the said gap pathway of the escaping flue gas such as to arrest the escaping flue gas heat energy and utilize the same for preheating said combustion air supplied to said burner.

2. A system for ladle preheating as claimed in claim 1 wherein said heat exchanger means comprise substantially circular shaped atleast one steel pipe having respective two end portions with junction headers mounted along the circumference of the burner hood.

3. A system for ladle preheating as claimed in anyone of claims 1 or 2 wherein said heat exchanger comprises assembly of plurality of circular shaped pipelines obtained of layered steel pipes and end junction headers adapted for conveying air exposed to flue gases.

4. A system for ladle preheating as claimed in anyone of claims 1 to 3 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.

5. A system for ladle preheating as claimed in claim 4 wherein said heat exchanger comprises an assembly of plurality of circular tubes with junction headers at end portion which act as inlet and outlet, air blown to the burner is first directed to the inlet junction from where is 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 junction box thereby enabling continuous beneficial recycling of the heat.

6. A system for ladle preheating as claimed in any one of claims 1 to 5 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.

7. An improved method of ladle preheating adapted to reduce fuel consumption using the system for ladle preheating as claimed in anyone of claims 1 to 6 comprising preheating air received from blower in said heat exchanger by passing first through inlet junction box whereby air gets heated-up during its travel through plurality of layered steel tubes due to heat exchange with flue gas coming out from burner and resulting hot air is subsequently injected into the burner through the outlet junction box, to thereby increasing the adiabatic flame temperature and thus rendering higher heat at lower fuel consumption.