FIELD OF THE INVENTION
The present invention relates to a process of maximizing production of different types of cokes in a coke oven plant with multiple blast furnaces of dissimilar capacity.
BACKGROUND OF THE INVENTION
Coke is one of the most important raw materials fed in Blast Furnace corresponding to the operating conditions of the Blast Furnace including hot metal quality. It is a major input factor in Blast Furnace which accounts for around 60% of hot metal cost. Coke strength after reaction (CSR) and Coke Reducibility Index (CRI) are two important properties of coke that influence the performance of Blast Furnace. A good CSR value increases PCI Injection rate which reduces the coke rate and hence reduces the operation cost of the Blast Furnace.
To produce a better quality coke, prior art shows blast furnaces operating with Non Recovery / Heat Recovery coke making technology with at least 176 ovens (2 blocks of 8 batteries) each assigned for every 11 ovens.
Blending of Coal:
Although raw coals produce an acceptable standard of coke product, it has however become a normal practice to use blends of a variety of coals to meet both technical and economic objectives of coal making process. The basic requirement of an efficient technology is to reduce cost of coke produced including conservation of coal. In order to improve the coke quality, it is important to firstly identify the coal quality parameters which control the coke properties, develop a technique for selection of coals from multiple sources and

their optimum blending proportions to ensure that the coke produced from the blend meets desired quality indicators at a minimum cost.
Carbonization:
Carbonization of coal is known as the enrichment of carbon in coal. It is achieved by heating the coal up to a specified temperature range under prefixed oven conditions. The resulting solid residue is obtained after removing the volatile matters (VM) is called coke.
The entire coke formation process is generally guided by three factors i.e.
1. Softens
2. Swells
3. Stick (resolidify)
It is known that the coking coal is composed of mainly two groups of constituents, i.e. fusible (Reactive) and inerts.
The first group is a substance that softens or melts during coking process and produces a cementing material needed for obtaining a coherent mass of carbon in the carbonized product. The second group consisting of multiple constituents which do not undergo a change to a liquid phase during carbonization.
In many of the known coke oven plants, multiple blast furnaces of different capacities are used. Although the Coke oven of the plant produce a single quality of Coke, the requirement of both the furnaces being different, an optimized coal blending is normally used to suit both the Blast furnaces. For example, in a coke oven plant having a main blast furnace (MF) and an auxiliary blast furnace (AF)

having 30% capacity of the (MF), and when a coke product is produced in the plant with the optimized coal blending to achieve a targeted value of CSR and CRI such as 64 and 26, the MF exhibits operational constraints due to low CSR wherein the AF shows high coke consumption due to high CSR leading to less PCI injection. Such a finding asserts that coke product having different targeted values of CSR and CRI, need to be separately produced in a coke oven plant for furnaces of dissimilar capacities. Accordingly, the total production from a coke oven plant will be divided as per coke quantity requirements of MF and AF.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose an improved process of . maximizing production of different types of cokes in a coke oven plant with multiple blast furnaces of dissimilar capacity.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a process flow chart in a prior art coke oven plant.
Figure 2 - shows an arrangement of coal storage silos with Weigh feeders.
Figure 3 - schematically shows transportation of coal from silos to hammer mill and then to coal hoppers through conveyor belts.
Figure 4 - shows a quenching tower and wharf in a coke oven plant.
Figure 5 - shows dispatch of coke through conveyors to coke yard through emptying the equipments to start a next production cycle.

SUMMARY OF THE INVENTION
Accordingly, there is provided an improved process of maximizing production of different types of cokes in a coke oven plant with multiple blast furnaces of dissimilar capacity, the coke oven plant having one each single coal feeding conveyor and coke discharging conveyor, a plurality of a coal hoppers, a hammer mill, the multiple blast furnaces, comprises main furnaces and auxiliary furnaces with different capacities but producing a single quality of coke which requires an optimized coal blending to suit the multiple types of furnaces, wherein an optimization of coal blending achieves the desired coke properties such as coke strength after reaction (CSR) including coke reducibility index (CRI), leading to opposing operational constraints of the multiple types of furnaces, wherein a first type of furnaces (AF) exhibits high coke consumption due to high CSR, wherein a second type of furnaces (MF) indicates operational constraints, the process comprising the steps of setting hard coal ratio and soft coal ratio in weigh feeders assigned for main blast furnaces (MF) and auxiliary blast furnace (AF), the ratio of the number of furnace ovens (MF, AF) being maintained around 1:3; blending the coals for the MFS and AFS conveyed from coal silos via the coal feeding system, transporting the blended coal for the AFS in a hammer mill; charging the ovens (MFS, AFS) with MF and AF coal blends for about 60 - 70 hours for carbonization to produce MF and AF cokes, wherein the MF grade coal blend is charged in the MF ovens, and wherein the charging of AF grade coal blend is commenced upon discontinuation of charging the MF coal blend to avoid mixing of both grades of coal blends (MF, AF).

DETAIL DESCRIPTION OF THE INVENTION
After various experimentations, the present inventors noted that CSR value should be 60 to 64 and CRI should be 27 to 31 for smooth operation of an auxiliary furnace. For the main furnace, CSR value should be between 65 to 67 and CRI value should be 23 to 25. To address these issues and to fulfill these
requirements, the existing coke building process need modifications, particularly due to the following constraints:
• Most of the known plants have a single coal feeding conveyor system and a single coke discharging conveyor system;
• A pre-defined Charging of ovens are done, 50-52 No. of ovens with MF Coal blend and 16-18 ovens with AF Coal blend every day after 64-66 hrs of carbonization these MF and AF coke are separately pushed and dispatched to both furnace.
• For suitable blending of coals for the MF and AF from the silos, the Weigh feeders ratio are to be set for different blends, for example more hard coal ratio for preparation of MF coal and less for AF.
This blended coal for the AF is then sent for crushing in a Hammer mill then charged in a coal hopper having hoppers after making one hopper empty and ensuring that the coal route is kept clean for the next cycle. When one hopper gets full with AF grade coal, changing of MF grade coal in the ovens is discontinued and AF grade coal is then charged in 8-9 ovens of each block.

Approx 800 MT coal is charged in 18 ovens every day and after about 64-66 hrs of carbonization wherein the coke is pushed from both the blocks.
Pushing of Coke
Before Pushing the AF grade coke, the wharf, Conveyors, hoppers of coke cutter sizing building is made empty to. avoid mixing of MF grade coal with AF grade coal. This AF grade coal is dropped in a separate place in the coke yard for dispatch to the AF as per requirements.

TABLE 1 - shows Average CSR and CRIfor both MF-grade coal and and AF-grade coal during a particular time period.

TABLE 2 - shows data on charging of AF-blend coal in the furnace for a specified time period with the charge results.
TABLE 3 - shows data on charging of MF-blend coal.

WE CLAIM :
An improved process of maximizing production of different types of cokes in a coke oven plant with multiple blast furnaces of dissimilar capacity, the coke oven plant having one each single coal feeding conveyor and coke discharging conveyor, a plurality of a coal hoppers, a hammer mill, the multiple blast furnaces, comprises main furnaces and auxiliary furnaces with different capacities but producing a single quality of coke which requires an optimized coal blending to suit the multiple types of furnaces, wherein an optimization of coal blending achieves the desired coke properties such as coke strength after reaction (CSR) including coke reducibility index (CRI), leading to opposing operational constraints of the multiple types of furnaces, wherein a first type of furnaces (AF) exhibits high coke consumption due to high CSR, wherein a second type of furnaces (MF) indicates operational constraints, the process comprising
the steps of
- setting hard coal ratio and soft coal ratio in weigh feeders assigned for main blast furnaces (MF) and auxiliary blast furnace (AF), the ratio of the number of furnace ovens (MF, AF) being maintained around 1:3;
- blending the coals for the MFS and AFS conveyed from coal silos via the coal feeding system, transporting the blended coal for the AFS in a hammer mill;

- charging the ovens (MFS, AFS) with MF and AF coal blends for about 60 -70 hours for carbonization to produce MF and AF cokes,
- wherein the MF grade coal blend is charged in the MF ovens, and wherein the charging of AF grade coal blend is commenced upon discontinuation of charging the MF coal blend to avoid mixing of both grades of coal blends (MF, AF).