It is further noticed that during coal carbonization for coke making, apart from the combustion of hydrocarbons, a part of carbon present on the surface of the coal cake also reacts with oxygen inside coke oven and gets oxidized and lost due to availability of oxygen at high temperature. The loss of carbon due to surface oxidation of coal cake inside the coke ovens is called burning loss. In non-recovery coke making, such a burning loss is unavoidable and it varies from 2-5%, with a corresponding reduction in coke yield, depending on the design and operating conditions of the coke oven.

There has been thus a persistent need in the art to developing a process for producing coke by carbonization of coal whereby the loss of carbon due to surface oxidation of coal cake inside the coke ovens known as the burning loss would be reduced / minimized and thereby improving the coke yield.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture by carbonization of coal blend by reducing surface oxidation losses of coal cake.

A further object of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture involving a sacrificial barrier layer on coal cake prior to carbonization in coke oven.

A still further object of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture by involving fly ash with high loss on ignition which is otherwise considered as a waste.

A still further object of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture favouring conservation of natural resource such as coal by preventing burning losses.

A still further object of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture by involving new and alternate material such as fly ash for providing sacrificing barrier layer on coal cake in coke making.

Yet another object of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture to achieve reduction in cost per ton of coke through improvement in coke productivity.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided a process for improving coke yield in non-recovery coke manufacture comprising:

i) preparation of coal cake by compaction of coal blend;

ii) providing a sacrificial barrier layer of low carbon content on the compacted coal cake;

iii) subjecting the compacted cake with said sacrificial layer on top thereof to carbonization whereby the carbon in the coke is beneficially prevented from oxidation and thereby reducing burning loss and improving coke yield.

A further aspect of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture wherein said sacrificial barrier layer has low carbon content in the range of 6 to 12%.

A still further aspect of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture wherein said sacrificial barrier layer comprises of fly ash of thickness in the range of 15-25 mm such that loss on ignition is of about 6-12 % carbon.

A still further aspect of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture wherein said sacrificial barrier layer is provided on compacted coal cake manually and/or through automatized means.

A still further aspect of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture comprises the steps of preparing coal cake involving storing coal blend in bunkers/coal tower and charging therefrom on plates for stamping and compaction; followed by application of said sacrificial barrier layer on the compacted coal and finally carrying out the carbonization of the compacted coal with said top covering of the sacrificial barrier layer in a oven.

Yet another aspect of the present invention is directed to said process for improving coke yield in non-recovery coke manufacture comprising the steps of:

(i) Filling bunkers with variety of coals after crushing to below 3.35 mm size (90 +/- 2%) at 9-11% moisture,
(ii) Filling these coals in required proportions as per coal blend in coal towers,
(iii) Discharging the coal blend preferably thrice from coal towers on charging plate , compacting the coal after each discharge to make a layer of coal blend and adding water to maintain the moisture level between 9-11%., thus compacting three layers of coal blend to prepare a coal cake such that its Bulk Density is above 1.10.
(iv) (iv) Spreading fly ash manually over the compacted and prepared coal cake such that the thickness of fly ash layer is 15-25mm to make the coal cake ready for carbonization,
(v) (v) Charging the coal cake as prepared in step
(vi) (iv) inside the oven and increasing the top and sole temperature to 1325°C by means of primary and secondary air opening and flue duct suction and sending the flue gas to boiler operation for power generation, (vi) Allowing completion of carbonization time (65-70 hrs), and soaking the cake for about 30-60 minutes, pushing the coke into quenching car, subjecting the Hot coke to quenching in quenching station and discharging the quenched coke in wharf,
(vii) (vii) Discharging the Coke for screening after cooling whereby higher sized coke is sent to coke cutter and after cutting, the coke is segregated into three size fractions by using double deck screen,
(viii) (viii) Sending Hard coke and nut coke for use in blast furnace and Coke breeze to sinter plant.

A still further aspect of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture wherein said fly ash based sacrificial barrier layer involve said lower level of carbon which get oxidized by reacting with oxygen available inside the ovens during carbonization, and thereby, preventing carbon in coke from getting oxidized.

Yet another aspect of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture wherein said Fly ash with high loss on ignition in barrier layer contains about 6-12% of carbon, said carbon in fly ash burns at high temperature inside the oven so that fly ash softens, fuses and subsequently forms an impervious layer covering the coal cake preventing oxidation of carbon present in coke.
A still further aspect of the present invention is directed to a process for improving coke yield in non-recovery coke manufacture involving significant reduction in the burning loss which is loss of carbon due to surface oxidation of coal cake inside the coke ovens, resulting in a corresponding improvement in coke yield from 33.83 tons/oven to 35.66 tons / oven.

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

BRIEF DESCRIPTION OF THE ACCOMPNYING DRAWINGS

Figure 1: is the flow diagram to illustrate the main steps involved in non-recovery coke making with improved coke yield according to the present invention.

Figure 2: is the schematic diagram showing fly ash as the sacrificial barrier layer on top of coal cake to reduce surface oxidation for coke making with improve yield according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention thus provides a process a process for improving coke yield in non-recovery coke manufacture by providing a barrier layer to reduce surface oxidation losses of coal cake.

It has already been described that in non-recovery coke making process, volatiles evolved during coal carbonization are not recovered as by-products but are combusted completely in presence of controlled quantity of air. The heat energy of the evolving gases is utilized for coking the coal mass into coke and thus no external heating is required.

It has been found that during coal carbonization, apart from the combustion of hydrocarbons, a part of carbon present on the surface of the coal cake also reacts with oxygen inside coke oven and gets oxidized and lost due to availability of oxygen at high temperature. The loss of carbon due to such surface oxidation of coal cake during conventional coke making process inside the coke ovens is known as burning loss. In non-recovery coke making, such a burning loss is unavoidable and it varies from 2-5%, with a corresponding reduction in coke yield, depending on the design and operating conditions of the coke oven.

The present invention thus provides for a process for improving coke yield in non-recovery coke manufacture by avoiding burning loss by providing for the first time a sacrificing fly ash barrier layer with high loss on ignition (LOI) on top of coal cake before carbonization.

Reference is now invited to the accompanying Figure 1 which is the flow diagram to illustrate the main steps involved in non-recovery coke making process according to the present invention involving a sacrificial barrier layer of fly ash on top of coal cake. The process of coke making according to the present invention thus having the following sequential steps:

(i) Filling the main bunkers with various coals (after crushing to below 3.35 mm size
(90 +/- 2%) at 9-11% moisture,
(ii) Filling these coals in required proportions as per coal blend in coal towers. .
(iii) Discharging the coal blend thrice from coal towers on charging plate , compacting the coal after each discharge to make a layer of coal blend and adding water to maintain the moisture level between 9-11%., thus compacting three layers of coal blend to prepare a coal cake such that its Bulk Density is above 1.10.
(iv) Spreading fly ash manually over the compacted and prepared coal cake such
that the thickness of fly ash layer is 15-25mm to make the coal cake ready for carbonization,
(v) Charging the coal cake as prepared in step(iv) inside the oven and increasing the top and sole temperature to 1325°C by means of primary and secondary air opening and flue duct suction and sending the flue gas to boiler operation for power generation,
(vi) Allowing completion of carbonization time (65-70 hrs), and soaking the cake for
about 30-60 minutes , pushing the coke into quenching car, subjecting the Hot coke to quenching in quenching station and discharging the quenched coke in wharf,
(vii) Discharging the Coke for screening after cooling whereby higher sized coke is sent to coke cutter and after cutting, the coke is segregated into three size fractions by using double deck screen,
(viii) Sending Hard coke and nut coke for use in blast furnace and Coke breeze to
sinter plant.

In the above process, to minimize the burning loss and improve coke yield, a step of providing a sacrificial layer of fly ash (having high loss on ignition) of thickness 15mm to 25 mm and preferably about 20mm spread on top of the coal cake ,has been introduced as a technical advancement to arrest burning loss. Presently, the addition is effected either by manually spreading the fly ash over the compacted coal cake, but, however, provision could be made for its mechanization. Fly ash with high loss on ignition normally contains about 6-12% of carbon. Inside the oven, at high temperature, carbon in fly ash burns; fly ash softens, fuses.and subsequently forms an impervious layer covering the coal cake. This layer acts as a barrier, preventing the coke beneath from being oxidized by acting as a sacrificial layer and whereby reducing oxidation of carbon present in coke. Thus, applying a barrier layer of fly ash onto the coal cake is a clear technical advancement leading to a significant reduction in the burning loss with a corresponding improvement in coke yield in non recovery type coke making process.

Reference is now invited to the accompanying Figure 2 which is the schematic diagram showing fly ash as the sacrificial barrier layer on top of coal cake to reduce surface oxidation for coke making with improved yield according to the present invention. Application of fly ash on top of coal cake (after compacting in stamping station) as barrier layer to prevent / minimize the oxidation of carbon in coke, was implemented in coke ovens for regular production. During carbonization, the carbon present in the fly ash layer gets oxidized by reacting with oxygen available inside the ovens (hence the term "sacrificial layer") and thereby, preventing carbon in coke from getting oxidized. Hence, as a result of such a sacrificial oxidation, a drastic reduction in burning loss and improvement in yield could be observed in coke making. A number of trial experiments involving differing coal blends with and without fly ash barrier layer were carried out. Various operating parameters such as temperature, pressure etc, monitored and maintained during these trials were recorded. A comparative data on the productivity of coke and coke yield per oven during the trial period during which coke was produced with fly ash barrier layer according to the present invention, against data of previous period during which the coke was made as per convention process without fly ash layer, is presented in the following Table 1.

Table 1:

It would be clearly apparent from the above table of comparative data that there is an increase in coke productivity and yield from average 33.83 tons/oven by conventional coke making process to 35.66 tons / oven by adopting the process using sacrificial barrier layer of fly ash on top of coal cake according to the present invention. The increase in coke yield is a direct evidence for reduction in burning loss.

We Claim:

1. A process for improving coke yield in non-recovery coke manufacture comprising:

(i) preparation of coal cake by compaction of coal blend;

(ii) providing a sacrificial barrier layer of low carbon content on the compacted coal cake;

(iii) subjecting the compacted coal cake with said sacrificial layer on top thereof to carbonization whereby the carbon in the coke is beneficially prevented from oxidation and thereby reducing burning loss and improving coke yield.

2. A process for improving coke yield in non-recovery coke manufacture as claimed in claim 1 wherein said sacrificial barrier layer has low carbon content in the range of 6% to 12%.

3. A process for improving coke yield in non-recovery coke manufacture as claimed in anyone of claims 1 or 2 wherein said sacrificial barrier layer comprises of fly ash of thickness in the range of 15-25 mm such that loss on ignition is of about 6-12 % carbon.

4. A process for improving coke yield in non-recovery coke manufacture as claimed in anyone of claims 1 to 3 wherein said sacrificial barrier layer is provided on compacted coal cake manually and/or through automatized means.

5. A process for improving coke yield in non-recovery coke manufacture as claimed in anyone of claims 1 to 4 comprising steps of preparing coal cake involving storing coal blend in bunkers/coal tower and charging therefrom on plates for stamping and compaction;followed by application of said sacrificial barrier layer on the compacted coal and finally carrying out the carbonization of the compacted coal with said top covering of the sacrificial barrier layer in a oven.

6. A process for improving coke yield in non-recovery coke manufacture as claimed in anyone of claims 1 to 5 wherein said fly ash based sacrificial barrier layer involve said lower level of carbon which gets oxidized by reacting with oxygen available inside the ovens during carbonization, and thereby, preventing carbon in coke from getting oxidized.

7. A process for improving coke yield in non-recovery coke manufacture as claimed in anyone of claims 2 to 6 wherein said Fly ash with high loss on ignition in barrier layer contains about 6-12% of carbon, said carbon in fly ash burns at high temperature inside the oven so that fly ash softens, fuses and subsequently forms an impervious layer covering the coal cake preventing oxidation of carbon present in coke.

8. A process for improving coke yield in non-recovery coke manufacture as claimed in anyone of claims 1 to 7 involving significant reduction in the burning loss which is loss of carbon due to surface oxidation of coal cake inside the coke ovens, resulting in a corresponding improvement in coke yield from 33.83 tons/oven to 35.66 tons / oven.