Description:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to the sinter production and more particularly a comprehensive waste heat transfer and distribution system for improvement in green mix temperature and life enhancement of Combustion and Hot air fan.

BACKGROUND OF THE INVENTION
In the process of sinter making, base mix (raw materials) is blended with water for preparing green mix to feed onto sinter machine. For sintering of fines in continuous endless conveyor type sintering machines, it is necessary to nodulize or pelletize the fines before charging onto sinter strand. To ensure good sinter bed permeability a mixing and nodulizing drum (MND) is used for preparation of green mix. While preparing green mix it is ensured that the mix should have around 8% moisture content. In green mix preparation process base mix which contains iron ore fines (< 8mm), coke breeze (<3 mm), lime stone fines (<3 mm), dolomite fines (<3 mm), calcined lime, mill scale and other plant wastes are also used.

The major attributor for the cost of sinter production is coke breeze. Therefore, the idea conceived for addition of hot water in the base mix to reduce the specific consumption of coke rate to reduce the cost of sinter produced.

Sinter plant process is dependent upon permeability of sinter bed. Permeability depends upon granulometry of material and the temperature of the green mix. Temperature of the green mix can be increased by raising the temperature of the input mixing water inside mixing and nodulizing drum (MND). With this view, a comprehensive system was designed to raise the temperature of inlet water by utilizing the unutilized heat / energy. It is found that circular cooler is the area at sinter plant where energy is underutilized and also nearer to the mixing and nodulizing drum.

At IISCO Steel Plant, there are two sintering machines, each sinter machine is having one sinter cooler where input sinter temperature is 600oC to 800oC and the air leaving after receiving area of sinter cooler is having temperature approx. 370oC to 400oC. This particular mentioned heat energy was being utilized via combustion air fan and hot air fan. In the combustion air fan system, uplifting hot air from cooler inlet was passing through fan to deliver at ignition furnace which requires hot air with maximum temperature of 250oC. This particular line is designed with bleeder to captures atmospheric air in case temperature rises beyond 250oC, which was the process to devalue the energy utilization by mixing with air.
Hot air fan extract the heat from cooler inlet receiving and delivers to annealing hood for preventing the sinter bed from thermal shock just after ignition furnace. Minimum temperature requirement is 350oC whereas practically average temperature was 380oC-400oC.

Limitations of existing system:
i) Frequent bearing damage of combustion air fan due to high temperature (more than 350oC) of hot air.
ii) Frequent bearing damage of hot air fan due to high temperature (more than 400oC) of hot air results lubrication oil of Plummer block to burnout.
iii) Underutilization of heat of circular cooler leads to excess heat at cooler area causing inspection problem.
iv) Sinter process was not stable as water temperature was totally dependent upon atmospheric temperature.
v) Burn through point temperature fluctuation due to re condensation of water at lower area of sinter bed due to low temperature of green mix.

SUMMARY OF THE INVENTION
The following disclosure presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

An object of the present invention is to utilize the extra heat from cooler and increase the temperature of Mixing and Nodulizing Drum (MND) inlet water.

An object of the present invention is to control the hot air fan and combustion air fan inlet temperature in order to avoid tripping of both the fans due to high temperature.

An object of the present invention is the reduction of coke to save input material cost and hence sinter production cost.

An object of the present invention is to resolve the problem of frequent tripping of hot air fan and combustion air fan due to high temperature.

An object of the present invention is to provide a comprehensive waste heat transfer and distribution system for heating the water entering the mixing drum for green mix preparation.

Coke is the major contributor in cost sheet of sinter making among all input material in sintering process. Coke consumption is the leading sinter cost defining factor. Extra energy in terms of heat in green mix will reduce the coke consumption. With this thought process, idea arises to increase the green mix temperature through hot water addition.

Still, the objective is to improve the permeability of sinter bed by adding hot water as it will increase the reaction speed of calcined lime which will help in better nodulizing in MND and hence balling index will improve which will increase the permeability of the sinter bed and increase production of sinter plant.

By utilizing this hot air, the raw water temperature of inlet of MND increased from 34oC to 70oC. By increasing the temperature, balling index of raw mix has improved; hence permeability of sinter bed increased which in turn has increased the sinter machine speed and decreased the coke rate.

The basic aspect of the present invention is directed to design a comprehensive waste heat transfer and distribution system (i.e. heat exchanger & preheating coil) comprising of preheating coil having small tubes, main water carrying pipeline with input & output water pipeline and it is placed at the open area (hood) of circular cooler adjacent to designed comprehensive system.

At first, cold water from feeding pump enters into preheating coil and the same entering water is heated by natural conduction, convection & radiation of hot air coming from circular cooler, after that preheated water go to the designed comprehensive system inlet box.

The basic aspect of the present invention is directed to a comprehensive waste heat transfer and distribution system comprising of hollow box, having inside small tubes, fins, water chambers, input & output water line and installed in between hot duct & combustion air duct of circular cooler.

Hot air coming from circular cooler hood enters into the bottom of designed comprehensive system. Through conduction and convection process hot air releases its heat to the incoming water inside the tubes and chambers and finally the air is diverted through hot air fan and combustion air fan inlet ducts.

Pre heated water enters into the bottom of comprehensive waste heat transfer and distribution system where a chamber is designed to hold this water and later it passes through tubes and get heated by hot air via convection and radiation. This heated water gets collected inside another chamber at other end of tubes. As per flow rate and pressure heated water rises to the up side and enters into the tubes in upper chamber. In the upper chamber, water tubes again are in contact with hot air which further increases the temperature of water via conduction, convection & radiation. Finally hot water discharges into outlet water carrying pipeline.

After installation of comprehensive waste heat transfer and distribution system: The temperature difference between inlet & outlet water T = 40 to 45 Deg c

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description,
which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 illustrates the schematic front view of comprehensive waste heat transfer and distribution system consisting of preheater, inlet & outlet water pipeline, water chambers of both sides, air inlet & outlet box at bottom side & top side along with safety systems.

Figure 2a illustrates the schematic front view of comprehensive waste heat transfer and distribution system having tubes of calculated dimension in calculated number of zigzag rows for each inlet & outlet water line.

Figure 2b illustrates the schematic top view of comprehensive waste heat transfer and distribution system having fronts & back side water chamber. Water chambers of both sides with water pipelines are shown.

Figure 3 illustrates the schematic top view of comprehensive waste heat transfer and distribution system having tube and fins between inlet and outlet water chamber.

Figure 4 illustrates the schematic top view of comprehensive waste heat transfer and distribution system having wall fins with back side water chamber.

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE PRESENT INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure.

The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown.

In the process of sinter making, base mix (raw materials) is blended with water for preparing green mix to feed onto sinter machine. For sintering of fines in continuous endless conveyor type sintering machines, it is necessary to nodulize or pelletize the fines before charging onto sinter strand. To ensure good sinter bed permeability a mixing and nodulizing drum (MND) is used for preparation of green mix. While preparing green mix it is ensured that the mix should have around 8% moisture content. In green mix preparation process base mix which contains iron ore fines (< 8mm), coke breeze (<3 mm), lime stone fines(<3 mm), dolomite fines (<3 mm), calcined lime, mill scale and other plant wastes are also used.

The major attributor for the cost of sinter production is coke breeze. Therefore, the idea conceived for addition of hot water in the base mix to reduce the specific consumption of coke rate to reduce the cost of sinter produced.

A comprehensive waste heat transfer and distribution system was designed, fabricated and installed on the circular cooler hot flue gas venting area for heating the water entering the mixing drum for green mix preparation. The designed comprehensive system is based on conduction, convection and radiation type heat transfer. The water which normally enters directly into the mixing drum is being diverted through the designed comprehensive system and the waste hot air from circular cooler. Hot air of circular cooler is used for combustion air in ignition furnace as well as in the annealing hood to prevent top layer sinter bed just after the ignition furnace from thermal shock. The input water line for MND in the process is being routed through the designed comprehensive system for heat transfer and preheating the water. Thus, air leaving from the comprehensive system has a temperature of approx. 350oC. This hot air is used by combustion air fan (1/3rd) and hot air fan (2/3rd) to utilize in ignition furnace and annealing hood respectively.

Utilization of waste heat is the prime objective of this invention. With this objective of heat utilization it is found that circular cooler is the one area where excess heat is there which can be utilized. The inlet temperature of hot air fan at circular cooler was having in the range of 400oC whereas the required temperature was 300oC to 350oC. This excess temperature can be used to heat up other substance like water via comprehensive waste heat transfer and distribution system, and this heated water can be used in the process to reduce the total energy required for sinter making.

With this view a comprehensive waste heat transfer and distribution system is designed and fabricated as per site area and practical conditions. Detailed drawing is mentioned below.

Figure 1 explains the overall layout of comprehensive waste heat transfer and distribution system. This layout is divided into five parts, viz.; Part A, Part B, Part C, Part D and Part E.
Part A= Air inlet system
Part B= Heat exchange system
Part C= Air outlet system
Part D= Pre heater coil
Part E= Safety system shown as P, Q and R.

Details about Part A:
As per the air flow requirement, the calculation was done from which opening of bottom and top of Part A was calculated. On this basis, an opening was fabricated and installed on the top of circular cooler inlet. Inlet box was designed from the calculated value. The total height of the inlet box was also calculated. The whole inlet box is made with the calculated thickness of mild steel plate. Reference of Part A is given in Figure 1.

Details about Part B:
Part B is referred to accompanying Figure 1, 2a, 2b, 3 and 4. Figure 1 shows the schematic front view of comprehensive waste heat transfer and distribution system in which part B comes in the middle of Part A and Part C. Figure 2a shows the arrangement of tubes in calculated number of zigzag rows for each inlet & outlet water pipeline.

Figure 1 shows of comprehensive waste heat transfer and distribution system arrangement according to the present invention comprising of

i. Body of calculated size shown in Figure 2 b. Body consisting of water tubes, fins, inlet water chamber, outlet water chamber, Back water chamber, inspection door, and wall fins.
ii. Water tubes of calculated size and number shown in Figure 2 a and 3. These tubes are placed in zigzag mode in horizontal direction.

iii. Inlet water chamber with water pipeline of calculated size shown in Figure 2 b. Role of this chamber is to collect the inlet water from preheater.
iv. Outlet water chamber with water pipeline of calculated size shown in Figure 2 b. Role of this chamber is to collect the hot water and keep it in heated condition by providing heat from wall fins as shown in Figure 4. Again this water passes through water tubes as shown in Figure 2 a and 3.
v. Back water chamber of calculated size shown in Figure 2 b. Role of this chamber is to store the hot water and keep it in heated condition with wall fins shown in Figure 4.
vi. Inspection door of calculated size shown in Figure 2 b. This door is very much required for regular inspection of the tubes and fins.
vii. Tube fins of calculated size shown in Figure 3. Role of this tube fins are to collect the heat from heated air and to transfer it to the water tubes.
viii. Wall fins of calculated size shown in Figure 4. Role of these wall fins are to collect the heat from heated air to keep water in both inlet and outlet chamber in hot condition.

Details about Part C: As per the air flow requirement, the calculation was done from which opening of bottom and top of Part C was calculated. On this basis, an opening was fabricated and installed on the top of Part B. Inlet box was designed from the calculated value. The total height of the inlet box was also calculated. One of the outlets is connected to inlet of combustion air fan and the other side of the outlet box is connected with inlet of hot air fan with a controlled damper to adjust the airflow. The whole inlet box is made with the calculated thickness of mild steel plate. Reference of Part C is given in Figure 1.

Details about Part D: Preheater consists of four sets of water tubes and individual set have a calculated number of tubes with calculated dimension. All the sets are connected in series with inlet water pipeline. At first row water enters inside preheater and passes via all four sets and finally exits and become inlet water for comprehensive waste heat transfer and distribution system. Overall temperature increase across preheater was also calculated. Reference of Part D is given in Figure 1.

Details about Part E:
Safety of the system is ensured by adapting the following safety precautions. Three safety points have been provided as per Figure 1. Safety points are designated as point P, Q & R.
Point P: Additional water supply arrangement was made during supply pump trip or breakdown condition. An additional water pipeline was connected with inlet water pipeline with a shutoff valve. If regular water supply pump is tripped then comprehensive waste heat transfer and distribution system may become empty and its tubes may deform so external water arrangement has been done.
Point Q: Safety valve has been provided for release of extra pressure inside comprehensive waste heat transfer and distribution system.
Point R: By-pass shutoff valve was fixed as per Figure 1. Purpose of this valve is to maintain water flow inside comprehensive waste heat transfer and distribution system in case outlet pipeline is close.

Salient features of the comprehensive waste heat transfer and distribution system are: preheater as mentioned in part D, wall fins, tube fins, water collecting chamber as mentioned in Part B, safety features as mentioned in part E.

Advantages of the system are:
1. Compact design: The body of the comprehensive waste heat transfer and distribution system is a very compact design and quiet successful to increase the water temperature as per requirement with required water flow in Mixing and Nodulizing Drum (MND) and required air flow in combustion and annealing hood with required air temperature as 250oC and 350oC respectively.
2. Life enhancement of bearing of Hot air fan & Combustion Air fan.
3. Dust filter is not required with this system, as designed, from Part A.
4. Minimum Cost: The comprehensive waste heat transfer and distribution system can be installed in very small area without using any additional electrical equipment and the existing system was modified to get the desired result; thus the system can be built with minimum cost of approx. 3.5-4.00 lakhs. The fabrication material used to design the system is MS plates, SS tubes with flow control devices.
5. Low maintenance: The system designed with ease of cleaning and tube changing facility. As the tubes have been designed as straight lines which gives minimum jamming of water pipelines.
6. Preheater is one of the innovative segments for this heat exchanger. This facility provides additional heat to inlet incoming water to comprehensive waste heat transfer and distribution system.
7. Safety features (explained in Part E) are the unique features which will save the comprehensive waste heat transfer and distribution system from any kind of damage.
8. Temperature control has been provided to regulate desired temperature. Individual flow control valves have been given in inlet and outlet water line for temperature and flow control.
9. When not in use, the comprehensive waste heat transfer and distribution system can be easily isolated from the existing unit.

Those skilled in the art will recognize other use cases, improvements, and modification to the embodiments of the present disclosure. All such improvements and other use-cases are considered within the scope of the concepts disclosed herein.
, Claims:
1. A comprehensive waste heat transfer and distribution system, the system comprising:
an air inlet system (A);
a heat exchange system (B);
an air outlet system (C);
a pre heater coil (D); and
a safety system (E),
wherein preheater consists of four sets of water tubes and the individual set has a calculated number of tubes with calculated dimensions.

2. The system as claimed in claim 1, wherein an inlet box is made with the calculated thickness of mild steel plate.

3. The system as claimed in claim 1, wherein an opening is fabricated and installed on the top of circular cooler inlet.

4. The system as claimed in claim 1, wherein the heat exchange system comprises wall fins, tube fins, and a water collecting chamber.

5. The system as claimed in claim 4, wherein the water collecting chamber comprises an inlet water chamber, an outlet water chamber, and a back water chamber.

6. The system as claimed in claim 4, wherein wall fins are used to collect the heat from heated air to keep water in both inlet and outlet chamber in hot condition.

7. The system as claimed in claim 4, wherein tube fins are used to collect the heat from heated air and to transfer it to the water tubes.

8. The system as claimed in claim 1, wherein the fabrication material used to design the system is MS plates, SS tubes with flow control devices.

9. The system as claimed in claim 4, wherein tubes have been designed as straight lines which gives minimum jamming of water pipelines.

10. The system as claimed in claim 1, wherein three safety points (P, Q & R) are provided in the safety system (E).

11. The system as claimed in claim 1, wherein the safety system (E) protects the system from any kind of damage.

12. The system as claimed in claim 1, wherein temperature control is provided to regulate desired temperature.

13. The system as claimed in claim 1, wherein the comprehensive waste heat transfer and distribution system can be easily isolated from the existing unit, when not in use.