FIELD OF THE INVENTION
The present invention relates to a technique of producing highly reactive catalysed coke from medium and non-coking coal using low grade iron ore fines as a catalyst and petroleum pitch as a binder through carbonization in stamp charge coke oven. More particularly, the invention relates to a process for producing reactive catalysed coke in a stamp charge coke oven.
BACKGROUND OF THE INVENTION
Metallurgical coke plays an important role in blast furnace as fuel, reducing agent and permeable burden support at high temperature region. A good quality coke for blast furnace application requires high mechanical strength as well as high reactivity with CO2. However, these two properties such as strength and reactivity of coke are contrary to each other as increase in reactivity decreases the strength. This happens mainly because coke with high reactivity involves more intense solution loss reaction with CO2 and subsequently results in more porous structure with less mechanical strength. On one side the high reactivity of coke helps in increasing the indirect reduction of iron ore at the stack region through gasification reaction. However, on the other side, it decreases the permeability due to the formation of fines resulted from coke with less strength.
The standard testing indices for measuring coke quality are Coke Strength after Reaction (CSR) with CO2 and Coke Reactivity Index (CRI). In general, coke CSR is inversely proportional to coke CRI. The challenge is to produce the coke of high CSR with reasonably a good CRI as well. Further, increase in reactivity of coke decreases the temperature of thermal reserve zone and thereby improving the reaction efficiency of blast furnace. This phenomena reduces the coke rate of blast furnace and reduces the cost of production of hot metal.

The reactivity of coke is enhanced by the addition of iron ore as reported in the patent literatures (Patent number EP2233548A1, EP2450419A1, EP2543716A1, EP2554632A1 & EP2460869A1).
According to patent # EP2543716A1, ferro-coke is manufactured by
briquetting a mixture of carbonaceous material and iron ore and subsequently
carbonization of briquette in a vertical shaft furnace, wherein a temperature
of carbonization is maintained in the range of 800° C to 900° C. Ferro-coke
manufactured through this process route is a two stage process that involves
briquetting of carbonaceous material and iron ore in first stage and
subsequently carbonisation in shaft furnace in second stage. Implementation of this methodology in the existing steel plant requires fresh capital investment for installing briquetting and shaft furnace equipment facility. Moreover, it demands additional space requirement for the said facility when considering the brownfield steel plant which already suffers space constraints. Hence, the idea is to manufacture the highly reactive catalysed coke in the conventional stamp-charged coke ovens which are already under operations without any requirement for additional capital investment and space.
Moreover, the reason cited in the patent # EP 2233548A1 for not manufacturing ferro-coke using conventional chamber oven commercially is that the chamber oven is lined with silica brick and the iron ore charged reacts with silica to form low-melting fayalite ( 2FeO SiO2) which leads to the failure of refractory.
OBJECTS OF THE INVENTION
In view of the foregoing limitations inherent in the prior-art, it is an object of the invention to propose a process for producing reactive catalysed coke in a stamp charge coke oven.

SUMMARY OF THE INVENTION
Accordingly, there is provided a process for producing reactive catalysed coke in a stamp charge coke oven. Thus, the invention provides a process to produce highly reactive catalysed-coke by means of carbonisation in stamp charge coke oven lined with alumina refractory after mixing the raw materials coal and iron ore along with addition of petroleum pitch as binder. By using alumina refractory as a lining material for oven wall, fayalite formation can be avoided when using iron ore added coal blend for carbonization.
The invention process comprising steps of grinding of coal blend to less than 500 micron size, grinding of iron ore to the size range of 75 -210 micron, mixing the raw materials coal and iron ore along with addition of petroleum pitch as binder, addition of water to maintain the moisture content with in the range of 8-10 %, stamping of mixture to make up the bulk density at 1100-1350 kg/m3, preheating the oven to 800°C, charging of stamped cake into the carbonization oven lined with alumina refractory lining, heating the oven to reach the centre mass temperature to around 850 to 950°C, pushing of hot coke from oven and wet quenching of hot coke with the help of water.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 illustrates a schematic diagram of steps for production of catalyzed-coke through stamp charge coke oven.
FIG. 2 illustrates a optimization scheme of process parameters influencing the properties of Catalysed-coke.
FIG. 3 illustrates a scheme for selection of binder and optimization of quantity of binder.
FIG. 4 illustrates a scheme for optimization of iron ore content in mixture.

FIG. 5 Petrographic image of: a) conventional coke and b) catalyzed coke after carbonization; c) conventional coke and d) catalyzed coke after reaction with CO2
FIG. 6 SEM image of: a) conventional coke and b) catalyzed coke after carbonization; c) conventional coke and d) catalyzed coke after reaction with
CO2
DETAILED DESCRIPTION OF THE INVENTION
Coal used in this process included a medium caking grade (Coal A) and the non-coking PCI coal (coal B). Proximate analysis of these coals is given in table 2.1. The chemical analysis of iron ore is given in table 2.2.
Table 2.1: Proximate analysis of coal

Sample Water % VM Ash FC
Coal A 1.25 23.21 15.81 59.73
Coal B 2.12 16.36 8.87 72.65
Table 2.2: Chemical analysis of iron ore

Sample Fe(T) SiO2 Al2O3 P LOI
Iron ore 61.01 3.97 3.35 0.08 3.4
The schematic of process steps involved in manufacturing of catalysed coke is illustrated in Fig.1. Coals of desired proportion are blended together and ground to less than 500 micron size using a ball mill. Subsequently iron ore is ground to the size range of 75 to 210 micron. Further coal, iron ore and binder blended together manually before addition of water to maintain the moisture level between 8-10%. The raw mix obtained is stamped inside the

box having dimensions of length 340 mm, width 90 mm and height 270 mm. The bulk density of coal cake is maintained between 1100 to 1350 kg/m3.
The dimensions and operation of an electrically heated carbonization oven are selected based on the standards of the British Carbonisation Research Association (BCRA). For experimentation purpose a 7 kg capacity oven was selected. The internal chamber dimensions are, length 370 mm, width 115 mm and height 305 mm. The oven is heated by twelve equally spaced vertical silicon carbide heating elements (rod type), which are 0.98 m long, 0.019 m diameter with a heating zone length of 0.355 m. The refractory lining of oven is made up of alumina.
The stamped coal (coal + iron ore) cake is charged into the carbonization oven when its temperature is around 800°C and the heating rate is maintained at 3°C/min. Carbonization cycle is continued for 4-6 hours till the temperature at center mass reached to 900°C. At the end of carbonization cycle, hot catalysed coke pushed out from the coke oven and subsequently wet quenched using water.
The key process parameters those are identified as critical to influence the property of catalysed coke are binder type, binder quantity and the ratio of coal to iron ore. Petroleum pitch and phenolic resin are the two different binders used for experiments. The quantity of binder varied between 0.5 to 2.0%. Further, the iron ore content in blend varied from 0 to 20 %. The schematic representation of optimization scheme is illustrated in Fig.2. A stepwise procedure is followed to obtain the optimum conditions required for production of the catalysed coke. At each stage, one parameter is varied while the others are kept constant. Once the coke is prepared, tests are conducted to determine its strength or reactivity. Based on the best results, the parameter is fixed. In the next step, the next parameter is varied,

keeping other parameters fixed at average values and previous parameters fixed at their already determined optimum values.
The effect of binder and its quantity on the mechanical strength of coke is illustrated in Fig.3. The strength of coke is measured in terms of cold compressive strength (CCS). It is observed that the petroleum pitch yields higher mechanical strength than phenolic resin in all the cases. Further, it is observed that petroleum pitch with 0.5% gives adequate strength to withstand the stress inside blast furnace. Even though there is significant increase in strength from 0.5 to 1% (for petroleum pitch), there is no further raise in strength after 1%. The optimum amount of petroleum pitch for producing catalysed coke is fixed as 0.5% as this proportion is considered to be economic in addition to providing the adequate strength.
Reactivity of coke is measured as the weight loss of coke when exposed to CO2 in tube furnace at 1000°C temperature for the duration of 60 min. The CO2 flow rate is maintained at 5 L/min. Figure 4 reveals the influence of iron ore content on the reactivity of coke. It is observed that the iron ore content of 10% in coal blend gives the maximum reactivity. It is also observed from fig.4 that the reactivity of catalysed coke is 30% greater than conventional coke (i.e. with 0% iron ore content).
Through a petrography analysis the pore structure of coke is analysed. Here, Fig.5 (a) & (b) shows the petrographic image of conventional coke and catalysed coke after carbonization, respectively. The size of pores in catalysed coke is greater than that of conventional coke, suggesting greater reactivity. Further, Fig.5 (c) & (d) shows the petrographic image of conventional coke and catalysed coke after reaction with CO2, respectively. The pore size is even greater after reaction in case of catalysed coke when compared to the conventional one. Similar observations also witnessed from SEM images as shown in Fig.6.

Advantages
a) The catalyzed coke produced through this methodology exhibits reactivity higher than the conventional coke.
b) The developed process for catalyzed coke gives flexibility to accommodate more proportion of non-coking coal in the coal blend.
c) The developed process does not need any major capital investment for implementation as the existing facilities can be utilized with minor modification.
d) Replacing small portion of conventional coke with catalyzed coke would result in the reduction of coke consumption in blast furnace.

WE CLAIM :
1. A process for producing reactive catalysed coke in a stamp charge
coke oven, the process comprising the steps of:
- grinding a coal blend to a crushing fineness of 90% less than 500 micron size, grinding iron ore to a size range of 75-210 micron, mixing the ground coal and iron ore, and adding petroleum pitch as binder, adding water to maintain the moisture content of the mixture within a range of 8-10%; stamping of mixture to make up the bulk density at 1100-1350 kg/m3;
- preheating the stamp charged carbonization oven to 800°C through electrical power supply;
- charging the stamped cake into the carbonization oven lined with alumina refractory lining;
- heating the oven to reach the centre mass temperature to about 850 to 950°C; and
- pushing the hot coke from the oven and subsequent wet quenching of the hot coke with of water.

2. The process as claimed in claim 1, wherein 7 kg electrically heated carbonization slit type oven is used.
3. The process as claimed in claim 1, wherein the refractory lining of coke oven is made up of Alumina.
4. The process as claimed in claim 1, wherein the average size of the coal blend is 0.2 - 0.5mm.
5. The process as claimed in claim 1, wherein the average size of the iron ore is in the range of 75 to 210 micron.
6. The process as claimed in claim 1, wherein the optimum value of coal : iron ore is 90 : 10 (weight %).

7. The process as claimed in claim 1, wherein the composition of coal blend is maintained as medium coking coal : non-coking coal is 60 : 40 (weight %).
8. The process as claimed in claim 1, wherein petroleum pitch is used as the binder.
9. The process as claimed in claim 1, wherein the quantity of binder used is 0.5 to 1.0 % (weight basis) of total mixture (coal + Iron ore).
10. The process as claimed in claim 1, wherein the moisture content of feed mixture is 8-10%.
11. The process as claimed in claim 1, wherein the bulk density of stamped coal cake is maintained between 1100 and 1350 kg/m3.
12. The process as claimed in claim 1, wherein the carbonization temperature is maintained in the range of 850 C to 950 C.
13. The process as claimed in claim 1, wherein the catalyzed coke produced exhibits 30% higher reactivity than the conventional coke.
14. The process as claimed in claim 1, the catalyzed coke produced is characterized with CRI of 35%, CSR of 47% and porosity of 40%