FIELD OF THE INVENTION

The present invention relates to a process for producing coke with improved CRI and CSR and with reduced porosity. The invention is also directed to catalytic early devolatilisation of coals, which is an advancement in the manufacture of coke with improved CRI and CSR even involving coal blends containing non-coking coals. The advancement provides for a variety of devolatilisation catalysts including divalent and multivalent metal oxides (metals capable of exhibiting multiple oxidation states) which can be reduced at temperatures within the fluidity range of coking coals favouring a cost effective process for producing coke from coal blends containing even non coking coals and reduced quantity of costly and scarce hard coking coals. Importantly, the process of catalytic early devolatilisation of coal/coal blend is adopted to provide on one hand superior quality coke with decrease in CRI to an extent of 1.0-3.5% and an increase in CSR to an extent of 1.0-3.5 % (depending on the nature of coals used in the blend) at less cost and on the other hand reduce the carbonization completion time by 3% and thus improving the coke oven productivity by about 3%, making the process useful for industrial application.

BACKGROUND OF THE INVENTION

It is well known that manufacture of coke from coal is always important in the art of iron and steel making since the quality of coke plays a crucial role in the required generation of products in the iron and steel industry.

GB746,697 discloses that addition of specific metal oxides, including copper and manganese oxides to coal prior to coking leads to reduction of ammonia formation during the coking process, by superficial wetting of the oven charge by contact mass consisting of metal oxides such as oxides of iron, aluminium, zinc, magnesium, manganese, copper and nickel. Wetting is done by a suspension of metal oxide. The contact mass is applied to destroy or prevent the formation of ammonia during the coking of coal in coke or like ovens.

Moreover, experiments under this prior work suggest that destroying or preventing ammonia generation during coking, metal oxides and in particular ferric oxides performs in a superior manner than other metal salts.

GB 28941- A.D. 1913 discloses a process for the production of a metallurgical coke without materially increasing the contents of slag to render harmless all sulphur compounds of the coal by replacing in the coking process part of the usual lime addition by a compound of phosphorous which favourably aids in the manufacture of pig iron. The addition is so calculated that the lime contained therein just suffices to bind the sulphur. Phosphorous compound for addition include phosphorite, phosphate chalk, apatite, vivianite and the like. A further addition apart from phosphorous compound to mixture of coal to be coked is made of manganese ore such as manganese di-oxide for the purpose of oxidizing the sulphur compounds by the oxygen and causing them to be carried away with the gases. The process increases the rigidity of the coke by increasing the phosphide of iron and avoiding formation of sulphides of iron detrimental to properties of coke.

GB963,435 disclosed a process for the carbonization of poorly-coking coals to obtain metallurgical coke of high quality comprising drying ground coals or mixtures of ground coals at a temperature greater than 100°C but less than the pyrolysis temperature of the coal, adding a hydrocarbon binder in a liquid or viscous state to the coals before or after drying the coals. This prior art disclosed an improved method for obtaining metallurgical coke form poorly-coking coals by adding a hydrocarbon binder to increase the charge density of coal cake. The resulting coke was found to exhibit improved M40 and M10 indices (cold strength properties).

WO2009/047682 A2 disclosed a method of making coke that included feeding an admixture of coking coal and non-coke fines susceptible to microwave volumetric heating and/or induction heating into a coke oven and heating the admixture in the substantial absence of air to drive off volatile compounds from the coal thereby producing coke. The heating is at least partially by microwave irradiation and/or induction heating. The coking coal may be soft coking coal or may be an admixture of hard coking coal and soft coking coal. The admixture may also include non-coking coal. The non-coke fines is selected from the group consisting of a ferro alloy, a ferro alloy ore, a chromium compound, a chromium ore, a nickel compound, a nickel ore, a manganese compound, a manganese ore, a titanium containing material and mixture of two or more of these.

It is well known an the field of iron and steel making that the quality of coke, especially, CRI and CSR of coke are important parameters for the smooth operation of the blast furnace. It is experienced from past performance of blast furnace that coke having a maximum of 25% CRI and a minimum of 64% CSR are found to be generally suitable for blast furnace operation (though this might differ from furnace to furnace). Charging an inferior coke inside the blast furnace poses problems such as high dust generation, poor permeability, hanging, slips, high fuel rate, reduction in the quantity of coal injection, low productivity etc. To avoid this, the coke produced is tested for CRI & CSR before charging in the blast furnace. Only that coke, which meets the set specification in terms of CRI and CSR are charged into the furnace.

It is also well known in the art of coke production in coke oven to feed coal cake prepared by blending various types of coals viz. hard coking coal, semi-hard coking coal and non-coking coal in various proportions to minimize the use of scarce resource (hard coking coal), to minimize the.cost of coke produced as there is a direct dependence of cost of coke to profitability of a steel industry and also to maintain the required coke quality. However, the quality of coke produced from such coal blend must have the required CRI and CSR values for use in blast furnace (the values are selected by each iron maker, which suits his blast furnace). This is thus a challenging task in coke oven plant operation to adopt newer technology to produce improved quality of coke at less cost reducing the use of scarce hard coking coal and increasing the use of non-coking coal in the blend.

OBJECTS OF THE INVENTION

It is thus the basic object of the present invention to develop processes whereby the values of CRI and CSR which usually depend directly on the quality of coals or coal blend used for bulk production of coke can be modulated such that an improvement in CRI and CSR values could be obtained which facilitates the use of increased percentage of non-coking coal in the blend.

Another object of the present invention is directed to explore the possibility of developing a process, whereby it could be possible to involve a coal blend even consisting of minimum of hard coking coal and maximum of semi-hard and non-coking coal, produces coke with required CRI and CSR suitable for blast furnace operation, at reduced cost per ton of coke.

Another object is directed to developing a process for coke production with improved quality whereby the furnace temperature in coke ovens could rise quickly favouring reduced carbonization time in the case of self heated non-recovery coke ovens and improved coke oven productivity.

A further object of the present invention is directed to use of selective devolatilisation catalysts mixed in micro proportion with coal blend for coke production in coke ovens, catalyzing early devolatilisation of coal blend, leading to reduced porosity in coke.

A still further object of the present invention is directed to use of devolatilisation catalysts, which could initiate volatilization of hydrocarbons and volatile matter in coal at lower temperatures.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is thus directed to a process for the manufacture of coke from coal with improved CRI and CSR values comprising:

subjecting the coal to heating in absence of air to its fluidity range temperatures (comprising initial softening stage ,maximum fluidity stage and final resolidification stage) whereby, the coal initially softens and gradually becomes fluid and finally resolidifies to form hard mass of coke involving early devolatilisation of most volatiles during fluid stage (in presence of catalysts) before resolidification, such that the resultant coke possesses improved CRI and CSR properties.

A further aspect of the present invention is directed to said process wherein said step of early devolatilisation is carried out involving devolatilisation catalysts consisting of elements which are good oxygen carriers, which readily undergo redox reactions.

A still further aspect of the present invention is directed to said process wherein said devolatilization catalyst comprise of selective oxides of divalent and multivalent metals which can be reduced at temperatures within the fluidity range and noble metal oxides which can easily part with oxygen.

Yet another aspect of the present invention is directed to a process wherein said devolatilisation catalysts are metal oxides including copper oxide, manganese oxide, vanadium oxide, cobalt oxide, nickel oxide, silver oxide, chromium (III) oxide, chromium (VI) oxide and copper chromite. But, oxides of iron, sodium, potassium and calcium are detrimental to the final properties of coke and hence not to be used as devolatilisation catalysts.

A further aspect of the present invention is directed to said process wherein said devolatilization catalyst are finely divided and powdered to at least minus 200 mesh (75 microns) preferably minus 70 mesh (212 microns).

A still further aspect of the present invention is directed to said process wherein said devolatilisation catalyst preferably contains lower levels of iron oxide and alkali metal oxides for producing coke with improved CRI and CSR properties.

Importantly, in said process for the manufacture of coke wherein involvement of said devolatilisation catalyst would favour apart from improving CRI and CSR of coke, improve productivity of coke ovens by decreasing carbonization time and increasing output.

A further aspect of the present invention is directed to a process for the manufacture of coke wherein said catalyst is in finely divided form and uniformly distributed in coal cake.

According to a further aspect of the present invention directed to a process for the manufacture of coke, which comprises either manual application of catalysts in 3 layers during the preparation of coal cake or application of catalysts by mechanical means (by means of a feeder) such that the catalyst is uniformly distributed in coal blend.

A still further aspect of the present invention is directed to a process, wherein the fluidity range temperatures is in the range of 375-550°C and said catalyst promote early devolatilisation predominantly within said fluidity range temperatures such as to release most of the volatiles (devolatilisation) at this fluid range and before resolidification, whereby the resulting coke is less porous and exhibit improved CRI & CSR properties.

A still further aspect of the present invention is directed to a process for the manufacture of coke comprising the steps of:

providing coal blend and crushing to desired size;

adding the said devolatilization catalyst to the thus blended coal before sizing of the blend by crushing ;

subjecting the coal blend with said devolatilization catalyst to carbonization such as to favour said devolatilisation at the maximum fluidity of coal blend and favour producing coke with reduced porosity. Also in said process, said devolatilization catalyst is mixed in two stages to ensure homogeneous mixing whereby in the first stage, the catalyst and coal/coal blend is premixed in a ratio preferably 1: 10-12 and thereafter the pre-mixed material is blended with the main coal in the ratio of 12-15 part of catalyst to million parts of coal particles.

Yet another aspect of the present invention is directed to said process for the manufacture of coke, which comprises the addition of catalysts as follows:

Initially the catalysts are powdered to minus 70 mesh (212 microns). The finer the size of the catalysts, better is their performance. The total quantity of catalyst added per oven remains same irrespective of the nature of catalyst used.

Stage I: About 555 grams of finely divided catalyst is mixed manually with 6445 grams of any coal / coal blend / inert coal / non-coking coal, so that, the total quantity becomes 7 kg.

Stage II: This 7 kg of material containing the catalyst is mixed with 50 tons of coal blend. This can be done in two ways.

a) Initially 7 kg of material is mixed with 50 tons of coal blend in three layers in stamping station.

Coal cake is prepared by compacting about 50 tons of coal blend. The coal blend is stored in overhead bunkers (coal tower). In stamping station, coal blend is discharged three times (to make the coal cake in three layers) from the coal tower onto the charging plate, which is then stamped by "cam operated mechanical hammers". After each discharge, the catalyst is added on top of each layer (after it is stamped by hammers) by manually spreading over the surface of coal cake. In this way, catalyst is applied on top of all the three layers of coal cake and the coal cake is then charged inside the ovens for carbonization as per normal procedure.

b) In the other method, the addition is mechanized whereby, the blended material is added by means of feeder such that, the same ratio of catalyst gets mixed with coal blend, which is then stored in coal towers for the subsequent preparation of coal cake.
Trials experiments showed that, both the methods of application of catalysts yield almost same results.

A still further aspect of the present invention is directed to a process for the manufacture of coke providing for improved CRI by 1.0-3.5% and CSR by 1.0-3.5% at less cost and reduce the carbonization completion time by about 3% and thereby improving the coke oven productivity by about 3%.

A further aspect of the present invention is directed to said use of devolatilization catalyst comprise finely divided powdered to atleast minus 200 mesh (75 microns) preferably minus 70 mesh (212 microns) preferably selected from metal oxides including copper oxide, manganese oxide, vanadium oxide, cobalt oxide, nickel oxide, silver oxide, chromium (III) oxide, chromium (VI) oxide and copper chromite having high purity containing preferably lower levels of iron oxides and alkali metal oxides, for early devolatilization of coal/coal blend enabling producing coke with improved CRI and CSR values.

The metal oxide catalysts mentioned above are readily available in the market. No pretreatment or preparation stage is required for these catalysts barring copper chromite, which was prepared as follows:

Copper chromite is prepared by mixing copper (II) oxide and chromium (III) oxide at two ratios namely Cu/Cr = 1 and Cu/Cr = 2. The mixtures of oxides were homogenized with acetone followed by subsequent calcination at 900°C for 6 hours. It is a solid state reaction and proceeds according to the following equation

CuO(solid) + Cr203 (solid) -» CuCr204 (solid)

With regard to purity levels, it was found that the metal oxide catalysts required to be of high purity with lower the iron and alkalies in the metal oxide, better was their performance.

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

BRIEF DECSRIPTION OF THE ACCOMPANYING FIGURES

Figure 1: is the flow chart showing the steps involved in the production of coke by carbonization of various coal blends using catalysts according to the present invention.

Figure 2: shows the three-dimensional schematic view of the coal cake preparation by stamping of coal blend in three layers with a layer of catalyst uniformly sprayed on each of the coal blend layers.

Figure 3: is the schematic diagram showing the apparatus used for the determination of devolatilisation of coals.

Figure 4: is the graphical representation to illustrate the phenomenon of early devolatilisation vis-a-vis the fluidity temperature range of any coal blend sample.

Figure 5: graphically illustrates the phenomenon of early devolatilisation of Goonyella coal in presence of catalyst as compared to conventional process of heating of Goonyella coal in absence of catalyst.

Figure 6: graphically illustrates the phenomenon of early devolatilisation of Hail creek coal in presence of catalyst as compared to conventional process of heating of hail creek coal in absence of catalyst.

Figure 7: is the graphical presentation showing devolatilisation curve of Illawara coal (i) without catalyst & (ii) with silver oxide as devolatilisation catalyst.

Figure 8: is the graphical presentation showing quantum of devolatilisation curve for Illawara coal- without catalyst & (ii) with silver oxide as devolatilisation catalyst.

Figure 9: is the graphical presentation showing devolatilisation curve of Illawara coal - (i) without catalyst & (ii) with V205 as catalyst.

Figure 10: is the graphical presentation showing quantum of devolatilisation curve for Illawara coal - (i) without catalyst & (ii) with V2Os as catalyst.

Figure 11: is the graphical presentation showing devolatilisation curve of Poitrel coal-(i) without catalyst & (ii) with Cr03 as catalyst.

Figure 12: is the graphical presentation showing quantum of devolatilisation curve for Poitrel coal- (i) without catalyst & (ii) with Cr03 as catalyst.

Figure 13: is the graphical presentation showing devolatilisation curve of Chippanga Mozambique coal- (i) without catalyst & (ii) with Co203 as catalyst.

Figure 14: is the graphical presentation showing Quantum of devolatilisation curve for Chippanga Mozambique coal - (i) without catalyst & (ii) with Co203 as catalyst.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES

As discussed hereinbefore the present advancement is based on the study of devolatilisation behavior of coal/coal blend to produce coke with improved CRI and CSR values suitable for use in blast furnace. A series of trials were carried out to find out the role of devolatilization on the quality of coke produced from coal/coal blend.

Experimental work:
Various properties of different types of coals used for the experiments such as proximate analysis, crucible swelling number, fluidity etc. are presented in Table 1. Table 1: Table showing various properties of coals:

Coals used for the experiments included those mixed in definite proportions to obtain the desired coal blend. Coal blend is designed to minimize the use of scarce resources, to minimize cost per ton of coke produced while producing coke of required quality.

Experimental Series -1:
Initial studies were carried out to ascertain the behavior of various metal oxides on devolatilisation of a variety of coal blends and the CRI and CSR values w.r.t. same coal variety being devolatalised with and without such metal oxides including (CuO/Mn02) under varying environments as per the following protocol and conditions and the results are provided hereunder in Table 2:

CRI and CSR of coke is carried out as per ASTM D-5341-99 (Reapproved 2004), (Standarad test method for measuring Coke Reactivity Index (CRI) and Coke Strength after Reaction (CSR)).

The above results showed that the metal oxides CuO and Mn02 were able to achieve the desired devolatilization maintaining the desired CRI and CSR values of the coke. The Lower the iron oxide and alkali metal oxide levels, the better is the results as these oxides have been found to deteriorate the coke quality with respect to CRI & CSR.

It has also been found that, the CRI and CSR values of coke produced by using these metal oxides CuO and Mn02 are better than the coke obtained without the addition of such metal oxides and involving other oxides.

The metal oxides having shown favourable contributions towards effective devolatilization, further studies on the effect on CRI and CSR of coke prepared from a wide variety of coal blend and the purity level of such metal oxides involved as given below:

Copper oxide (specification: preferably CuO- 90% minimum and preferably containing lower levels of iron and alkali metal oxides and Manganese dioxide (specification: preferably Mn02- 90% minimum and preferably containing lower levels of iron and alkali metal oxides).

Experimental Series -2:
Different sets of experiments were subsequently conducted with metal oxides in combination to achieve the best possible values of CRI and CSR of coke obtained with different coal blend samples when compared with performance of normal conventional coke making process without the use of any metal oxide.

The test protocol followed for the purpose is represented under accompanying Figure 1, which is self -explanatory.

The metal oxides are added during stamping of coal in stamping station (step 4 of Annexure 1). The blended coal is filled on the charging plate in 3 layers and the coal cake is prepared by stamping, such that, its bulk density (BD) is approximately 1.10 tons/m3. The metal oxide are added to the regular coal blend (after stamping each layer), by spreading the catalysts over the coal cake, approximately at 500 mm, 800 mm and 970 mm height of coal cake. The stamped coal cake is then charged into coke ovens for carbonization as per normal procedure.

The results of the various options tried with metal oxides such as CuO and Mn02 in various ratios are illustrated hereunder in Tables 3-6.

Table 3 (Box Tests):

Table 4:

Table 5:

It could be seen from the above results that, these metal oxides generally improve CRI & CSR of coke when used alone or in combinations. But, certain combination, such as 4:1 (CuO:Mn02), in this case, the improvement has been found to be much better.

As would be apparent from Tables 3-6 above, the best CRI and CSR values for the coke produced were obtained involving the 4:1 blend of CuO: Mn02 metal oxide combination. Thus the above confirm that though all these combinations yielded coke with improved CRI & CSR properties, the metal oxide in the weight ratio of 4:1 yields coke with much better CRI & CSR values.

Accompanying Figure 2 schematically illustrates a three dimensional view of coal cake prepared by stamping of coal blend in three layers in accordance with a preferred embodiment with a layer of metal oxide on each layer of coal blend according to an embodiment of the present invention following the above stated process.

Importantly it is found that the application of the metal oxides in layers is advantageous. Hence, during the application of metal oxide in layers, it needs to be ensured that, the metal oxide is uniformly distributed over the entire surface of the coal blend (which is very critical) and failing to adhere to this practice may not yield the desired results.

Devolatilisation studies have been conducted with all the available coals by adapting an instrument normally used for the analysis of RDI & RI of sinter. Accompanying Figure 3 shows the schematic diagram showing the apparatus for the determination of devolatilisation of coals.

Having found the advantages achieved in terms of the desired CRI and CSR values of coke produced involving the metal oxides as above, further studies were carried out to determine the technical advance, which facilitates such improvement in CRI and CSR values of coke involving such metal oxide based devolatilization. It was observed that when a coking coal is heated in absence of air, it not only devolatilises but also softens and resolidifies. A coal is characterized byr its fluidity range temperature, which involves three distinct temperatures namely Initial softening temperature (1ST), Maximum fluidity temperature (MFT) and final resolidification temperature (FST). Thus the coal initially softens and gradually becomes fluid (semi molten) and resolidifies to form a hard mass called coke. But, for most coking coals, the fluidity range lies between 375-550°C and devolatilisation predominantly starts after 450°C (and is maximum mainly at the temperature range of 550 -700°C). It was thus identified that the addition of metal oxides to coals promoted early devolatilisation at this fluid range (and before resolidification), whereby the resulting coke was less porous and exhibited improved CRI & CSR properties. The metal oxides were thus identified by way of the present invention for the first time have been found to do exactly this, by promoting early devolatilisation of coals and improve CRI & CSR of the resultant coke.

Accompanying Figure 4 is an illustration by way of graphical representation of the phenomenon of early devolatilisation in general in relation to the fluidity temperature range for any coal blend sample attained under the present advancement.

Experimental Series -3:

Under this example further comparative studies were conducted (i) clearly identifying the coal blends tried and working the same as per conventional processes (without the use of the metal oxide) and noting their CRI and CSR values and (ii) trying the same coal blends with the use of the metal oxides and determining their CRI and CSR values.

The results of above experiments conducted with different specified coal blend samples are presented in following Table 7.

Table 7:

The results showed that metal oxides significantly improved CRI and CSR of the resulting coke.

Experimental Series - 4:

Under this example how porosity of coke is reduced with the presence of selective metal oxide with coal blend during coke making process facilitating early devolatilisation was further studied. Importantly it was found that porosity is reduced by devolatilisation at the maximum fluidity of coal. Metal oxides promoted this activity and performed as catalyst for such purposes. It was also noted that such metal oxide based catalytic achievement of early devolatilisation for the purposes of the present advancement should be such as not to also catalyse oxidation of coke in the blast furnace and thus increase CRI and decrease CSR. Such ineffective metal oxides include oxides of iron and alkali metals such as Calcium, Sodium and Potassium.

Porosity in coke arises as a result of the path left by the escaping gases (volatiles) during resolidification. The metal oxides being very good devolatalising agents are selected to drive out volatile matter from coal blend. The addition of these metal oxides (catalysts) to coal blend, drives out faster the volatile components present in the coal cake, when the coal blend is highly fluid. In the absence of these metal oxides, the volatile components are driven out, when the coal blend (coke) is pasty and during the period of its resolidification. But, in the presence of metal oxides, the gases escape faster (than in their absence) much before the coke resolidifies and thus making the coke less porous. A hard and less porous coke tends to exhibit better CRI & CSR property than the soft and porous coke. The coke obtained from these tests are analysed for porosity. Porosity measurements revealed that, use of catalysts^ as additives during carbonization yield coke with improved porosity (by making coke more hard and less porous). In this way, the selected catalysts, serve to improve CRI and CSR of coke by reducing porosity. The porosity of coke obtained with and without the addition of catalyst is presented in the following Table 8.

Table 8:

It could be seen from the above table that porosity of coke obtained with metal oxides are better than that of coke obtained without metal oxides. Experimental Series -5;

Devolatilisation (removal of hydrocarbons and other volatiles) studies have been conducted with all the available coals by adapting an instrument normally used for the analysis of RDI & RI of sinter. In this experiment, 500 gms of coal was taken in the retort and heated gradually under inert atmosphere of nitrogen (to avoid oxidation) from room temperature to 950 deg C. The coal is soaked for two hour at the following temperature intervals viz. 300, 350, 400, 450, 500, 550, 600, 700, 800, 900 and 950°C and the loss in weight is recorded at all these intervals. The loss in weight corresponds to the amount of volatiles removed. Experiments were repeated with all available coals.

In another series of experiments, devolatilisation was conducted with all these coals with 2 hours soaking time for comparison.

The following observations were made from devolatilisation experiments:

1. Early devolatilisation such as in presence of metal oxide could be achieved in almost all the coals analysed and the same facilitated in improving the CRI and CSR of coke obtained.

2. Even though the amount of volatiles removed with and without metal oxide remained the samd, early devolatilisation such as in presence of metal oxide was observed indicating the catalytic action (speedy devolatilisation) of the metal oxide.

3. In some coals, for eg. Hailcreek, it is observed that, the percentage of devolatilisation is more in presence of metal oxide than in its absence.

The devolatilisation behavior of Goonyella and Hailcreek coals with and without metal oxide achieved is presented in following Table 9 and 10 respectively.

Table 9:

In the above tables, the difference in weights indicate the early devolatilisation of Goonyella coal (at the temperature of higher fluidity) and Hail creek coals in presence of catalyst, which is an indirect evidence for improvement in porosity and better quality of coke obtained.

Accompanying Figure 5 and Figure 6 illustrate graphically the nature of early devolatilisation of Goonyella and Hailcreek coals respectively in presence of catalyst.

Experimental Series -6:

Under this example, the various coals were subjected to devolatilisation experiments separately in presence and in absence of catalysts and the weight loss during each interval were recorded. When coals were mixed with catalysts and subjected to devolatilisation, it was found that, coals devolatalised faster and at low temperatures when compared to the same coals, which were devolatalised in the absence of catalysts. Experiments also revealed that, addition of small quantities of catalysts to coal blends was found to be sufficient for significant results. Furthermore, it was observed that, in some cases, the percentage of devolatilisation was found to be slightly more, when they were mixed with catalysts.

Results of devolatilisation experiments:

A plot of temperature versus percent cumulative weight losses recorded for each coal, yielded "S" type curves (Devolatilisation curve). The initial weight loss corresponds to moisture content and amount of gas occluded in coal sample, which is followed by a very rapid devolatilisation, until the weight loss gradually decreased. Furthermore quantum of devolatilisation curves was also obtained by plotting temperature versus percent loss in weight. For illustration, the results of devolatilisation study of Illawara, Chippanga Mozambique (hard coking coals) and Poitrel (semi-hard coking coal) with and without catalysts is presented through Tables 11-14.

Table 11: Devolatilisation behavior of Illawara coal- With silver oxide as catalyst and without catalyst

Table 12: Devolatilisation behavior of Poitrel coal-with CrOs as catalyst and without catalyst

Table 13: Devolatilisation behavior of Illawara coal -with V2Os as catalyst & without catalyst

Table 14: Devolatilisation behavior of Chippanga Mozambique coal: With Co203 as catalyst and without catalyst

The graphical plot of devolatilisation curve/"s" curve and the quantum devolatilisation curves based on the above data are presented in the accompanying Figures 7-14.

The following observations were made from devolatilisation experiments:

1. Devolatilisation study revealed that, almost all the coals exhibited early devolatilisation behavior and in some cases the influence was more prominent than others.

2. In some coals, it is observed that, the percentage of devolatilisation is more in presence of catalyst than in its absence.

3. In some cases, though the amount of volatiles removed with and without catalyst remains the same, early devolatilisation in presence of catalyst observed with most coals indicate the catalytic action of chemical compounds in promoting early devolatilisation of coals.

It could be observed from the Tables 11-14 that, difference in weight is a direct measure of early devolatilisation of coals in presence of catalysts. The devolatilisation curves clearly indicate the early devolatilisation of these coals in presence of catalysts.

Quantum of devolatilisation curves reveals that, peaks corresponding to coal with catalysts shift towards low temperatures, indicating early devolatilisation at lower temperatures. It clearly indicates that, the presence of catalysts in coals promotes the rate of devolatilisation (as indicated by peak height) and early devolatilisation (as indicated by peak shift towards the temperature of maximum fluidity). Thus, the addition of catalysts to coals, aids in promoting speedy devolatilisation at lower temperatures closer to the fluid range. It was also observed that, most of devolatilisation in presence of catalysts occurs in the temperature range of 350-550°C, which is exactly the temperature range at which maximum fluidity occurs in coals. Based on this, it was expected that, when these catalysts were added to the coal blend and carbonized, the catalysts would promote maximum devolatilisation in the temperature of fluidity range. If such a thing happens, most of the gases in coal blend would devolatalise before it resolidifies, which in turn would produce coke with minimum porosity. Porosity in coke is due to the path left by the escaping gases during resolidification. Hence, if all/most of the gases devolatalise before resolidification temperature, then the volume of gases escapes during resolidification would be very minimal and hence the porosity in coke would also be minimal. It is known that, coke with lesser porosity will have higher strength than a highly porous coke. Thus carbonisation of coal blend with catalyst would lead to the production of coke superior to the one it would have produced in its absence. In order to verify this phenomenon, the catalysts were mixed with various coal blends and carbonized by means of box tests. After carbonization, the coke were removed, crushed, screened and analysed for CRI & CSR. Table 15, presents the hot strength properties (CRI & CSR) of coke produced from box tests.

Procedure for Box test

Box tests for carbonization of coal samples under the experiments are carried out as per procedure involving (applicants copending patent application no. 811/CHE/2012 dated 27.02.2012) a cost effective method for evaluating suitability of different coal blend samples for coke manufacture involving box test by filling coal blend of desired size fraction, duly moisturized and homogenized, in a cubic box of desired size made of mild steel / stainless steel preferably stainless steel, stamped to desired bulk density, carbonized and then carrying out CRI(Coke Reactivity Index) and CSR(Coke Strength after Reactivity) analysis of the coke sample obtained to thereby determine the suitability of the coal blend for coke for use in blast furnace. After carbonisation, the box is removed and the contents are analysed for CRI and CSR properties.

Table 15 - CRIv& CSR of coke produced from box tests

It could be seen from the Table 16 that, addition of catalysts to coal blends produced coke with improved CRI and CSR properties. A decrease in CRI to an extent of 1.0-3.5% and an increase in CSR to an extent of 1.0-3.5 % were observed in most of the cases.

It was observed in a number of trial experiments that box test results and oven test results match very closely. Still, oven tests were conducted with Cr03 catalyst (as it is cheaper than other catalysts) and the results are presented in Table 18. Initially, the trials were conducted in selected ovens. Based on the results of oven test, it was decided to implement catalyst addition in all ovens and hence the addition of catalyst was mechanized, whereby, the required quantity of catalyst was added through belt and premixed with coal blend before it reaches the stamping station. At stamping station, the coal cake is prepared as per normal procedure and carbonized.

During the trial experiments conducted with catalysts in coke ovens, it was observed that, temperature inside the coke ovens picks-up faster (due to early devolatilisation of coals in presence of catalysts) and because of this, the time taken for completion of carbonization reduces by 3%. The coke thus obtained after carbonization were analysed for CRI and CSR and the results are presented in Table 16.

Table 17 reveals that, the addition of catalysts to coal blends improves both CRI & CSR properties of coke. It was also observed that, the coke produced exhibited a better micum indices (cold strength properties) with an increase in M40 value of 0.6-1.6 % and decrease in M10 value of 0.4-0.8 %, the related data are given in following Table 17.

Table 17 - Micum index of coke (obtained by bulk production)

The above results indicate that, similar to chromium (VI) oxide, the other catalysts such as oxides of silver, vanadium, cobalt, nickel, chromium (III) oxide and copper chromite also would yield coke with improved properties when used for the mass production of coke.

It is thus possible by way of the present invention to achieve improvement of CRI and CSR values of coke by catalytic early devolatilisation of coals. The advancement also identifies possible varieties of metal oxide based catalysts for providing a process for producing coke by early and faster devolatilisation of coal/coal blend involving selective devolatilisation catalysts comprising oxides of divalent and multivalent metals such as chromium (VI) oxide, chromium (III) oxide, oxides of vanadium, cobalt, nickel and also copper chromite, which can be reduced at lower temperatures (and noble oxides (eg. silver oxide), which can easily part with oxygen) for use in producing coke with reduced porosity and improved CRI(Coke Reactivity Indexp and CSR(Coke Strength after Reaction). Importantly, the process would favour faster carbonization of coal blend due to early devolatilisation in the lower temperature range closer to maximum fluidity of coals, which in turn would produce coke with minimum porosity in presence of such devolatilisation catalyst. The present invention is thus directed to providing a cost effective process for producing coke from blend of coal varieties including even non-coking coal and reduced quantity of costly and scarce hard coking coal. The* catalytic devolatilisation of coal blend according to the present invention improve coke quality by decreasing CRI to an extent of 1.0-3.5% and increasing CSR to an extent of 1.0-3.5% and corresponding improvement in micum indices (cold strength properties) with an increase in M40 value of 0.6-1.6 % and decrease in M10 value of 0.4-0.8 % achieved at less cost. Furthermore, the process reduces the carbonization time by 3% by the catalytic action of these catalysts in coke making.

We Claim:-

1. A process for the manufacture of coke from coal with improved CRI and CSR values comprising:

subjecting the coal to early devolatilisation coincident with fluidity range temperatures by using suitable catalysts, whereby the coal initially softens and gradually becomes fluid and finally resolidifies to form hard mass of coke involving early devolatilization of volatiles with devolatilization predominantly being carried out early prior to the stage of resolidification such that the resultant coke possesses improved CRI and CSR properties and lower porosity.

2. A process as claimed in claim 1 wherein said step of early devolatilization is carried out involving devolatilization catalysts containing elements which are good oxygen carriers and readily undergo redox reactions.

3. A process as claimed in anyone of claims 1 to 2 wherein said devolatilization catalyst comprise selectively oxides of divalent and multivalent metals (i.e, metals exhibiting variable oxidation states) which can be reduced at lower temperatures and noble oxides which can easily part with oxygen.

4. A process as claimed in anyone of claims 1 to 3 wherein said devolatilization catalyst comprising, metal oxides (either alone or in combinations) preferably selected from metal oxides including copper oxide, manganese oxide, vanadium oxide, cobalt oxide, nickel oxide, chromium (III) oxide, chromium (VI) oxide, copper chromite and noble metal oxides (eg. silver oxide) which can easily part with oxygen.

5. A process as claimed in anyone of claims 1 to 4 wherein the said devolatilisation catalysts could be used either alone or in combinations to promote early devolatilisation of coals at lower temperatures and to produce coke with improved CRI and CSR properties.

6. A process as claimed in anyone of claims 1 to 5 wherein said devolatilization catalysts preferably containing lower levels of iron oxide and alkali metal oxides (such as oxides of calcium, sodium and potassium) as they weaken the coke inside the blast furnace and hence can not be used as devolatilisation catalysts for producing coke with improved CRI and CSR properties.

7. A process as claimed in anyone of calims 1 to 6 wherein said coal blend used even includes higher percentages of non-coking coals and yet achieve required CRI and CSR properties suitable for blast furnace operation.

8. A process for the manufacture of coke as claimed in anyone of claims 1 to 7 wherein involvement of said devolatilization catalyst would favour apart from improving CRI and CSR of coke, improve productivity of coke ovens by decreasing carbonization time and increasing output in the case of self heated non-recovery coke ovens.

9. A process as claimed in anyone of claims 1 to 8 wherein the said catalysts promote early devolatilisation predominantly in the fluid range of coals before resolidification, whereby the resulting coke is less porous and exhibit improved CRI & CSR properties.

10. A process as claimed in anyone of claims 1 to 9 wherein said the catalyst is added in two stages to ensure homogeneous mixing whereby in the first stage, the catalyst and coal/coal blend is premixed preferably in the ratio of 1: 10-12 and in the second stage, the pre-mixed material is blended with the main coal blend in the ratio of 12-15 parts of catalyst to million parts of coal particles (to ensure uniform distribution with coal blend) feeding conveyor for crushing, preparation of coal cake and subsequent carbonization.