CLIAMS:1. A process for making the briquettes from coke dust fines generated in CDQ process during cooling of coke produced in coke oven, the process comprising the following steps -
- air drying the coke dust fines collected
- mixing the binders consisting of Pitch and wash oil in the proportion of 2:1-2:1.5 ratio wherein, the Pitch is mixed with coke dust fines in dry conditions followed by mixing with preheated wash oil to form a homogeneous mixture
- forming the briquettes by compressing the mixture in a sand rammer by free dropping the fixed weight number of times from fixed height to achieve the desired compression strength
- drying the briquette produced after compression at room temperature for a day in an open atmosphere
- curing the briquettes thus obtained at 150-250 °c temperature.

2. A process as claimed in claim 1, wherein the average particle size of coke dust fines used is less than 1mm.

3. A process as claimed in claim1, wherein Pitch and wash oils are generated as by-products during fractional distillation of crude tar and added for increasing the strength of the briquette produced.

4. A process as claimed in claim 1, wherein the mixture of coke dust fines, Pitch and wash oil are mixed in Muller mixer for 30-40 minutes.

5. A process as claimed in claim 1, wherein 16-20% w/w of Pitch is mixed to the coke dust fines for 10-20 minutes.
6. A process as claimed in claim 1, wherein 8-12% w/w of wash oil is mixed to the coke dust fines and Pitch mixture for 10-20 minutes.

7. A process as claimed in claim 1, wherein the wash oil used is preheated to 70-80°c.

8. A process as claimed in claim 1, wherein the distillation range of wash oil used is 220-270°c for better adhesion with surface of coke dust fines.

9. A process as claimed in claim 1, wherein the solubility of pitch with wash oil is due to high softening point of Pitch in the range of 170-175°c.

10. A process as claimed in claim 1, wherein the pitch obtained from tar distillation plant is crushed using toothed two roll crusher to a size of 0.7-1.2mm.

11. A process as claimed in claim 1, wherein Pitch contains 19-25% w/w of Quinolene insoluble; 54-59% w/w of Toluene insoluble; 30-36% w/w of Beta resin; 0.15-0.20% w/w of Ash; 63-66% w/w of coking value (Conradson) respectively.

12. A process as claimed in claim1, wherein wash oil contains the 4-5%w/w of naphthalene; 0-4-0.7%w/w of moisture.

13. A process as claimed in claim1, wherein coke dust fines consists of the 81-84%w/w of fixed carbon; 17-18%w/w of ash; 2-3%w/w of total moisture; 0.5-0.8%w/w of volatile mixture.
14. The briquettes as claimed in claim 1, wherein the briquettes produced are cylindrical in shape having thickness of 45-55mm in diameter and 27-35mm in height.

15. The briquettes as claimed in claim 14, whenever used in replacement of coke in Blast Furnace process.

16. The briquettes as claimed in claim 14, wherein the briquette produced are cured at 150-200°c for 50-60minutes.

17. The briquette as claimed in claim 14, wherein the briquettes produced are having fuel value (CV) of 7900-8000Kcal/kg.

18. The briquettes as claimed in claim1 and 14, wherein the briquette comprises of 1.15-1.35%w/w of moisture; 1.05-1.55%w/w of volatile mixture; 15.75-16.25%w/w of ash; 80.87-82.08%w/w of fixed carbon respectively.
,TagSPECI:Field of Invention

The invention relates to a process for making the briquettes from the coke dust fines generated during the cooling of coke produced in coke oven by coke dry quenching(CDQ) and the briquettes made thereof. These briquettes are to be used as a partial replacement of the coke in the Blast Furnace process thus reducing the storage problem, thereby reducing the environmental pollution to a great extent.

Background
A Briquette is a block of compacted material made up of fines. Common types of briquette, used as fuel, are made of charcoal and bio- mass. Coke dust fines are a byproduct generated during the cooling of coke produced in coke oven, by coke dry quenching (CDQ) process. If not evacuated in time, the coke dust fines can cause serious damage to equipment and environment. These coke dust fines mixed with pitch and wash oil are used to make briquettes which can be used in blast furnaces as a fuel in partial replacement to coke.

Coking Coal is converted into coke by heating the prepared coal blend in coke ovens in absence of air at a temperature of 1000-1050 oC for a period of 16-19 hours. This process is called carbonization. The coke is pushed out of the oven by pusher car through a guide into the coke bucket. The red hot coke which is around 1000 0C is further cooled by either conventional wet quenching or by Coke dry quenching (CDQ) process. The CDQ process uses circulating gas to cool the coke in a closed cycle. The circulating gas absorb the sensible heat of hot coke and is used in producing steam for power generation. The cooled coke from CDQ plant is separated into three fractions in coke sorting plant - BF coke (25-80 mm) which is sent to Blast Furnaces, Coke Breeze (+0-10 mm) which is sent for Sinter making and nut coke (10-25 mm) which is also used in Blast Furnace. During cooling of coke a lot of coke dust fines (<1 mm) are generated. This dust has a detrimental effect on equipment and environment if not evacuated in time. Appropriate use is the need of the day instead of selling the coke dust fines in the market, thus creating environmental hazards.

Timely evacuation of generated coke dust fines plays a key role in CDQ productivity and disposal of these fines have an environment impact.

The volatile matter of coal liberated during carbonization is collected in a gas collecting mains in the form of raw coke oven gas after passing through stand pipes and is directly cooled with ammonia liquor spray. The gas cooled by means of an Exhauster from 800 oC to 80 oC is carried to Coal Chemical Plant.

The main by-product in the process of coke making is crude coke oven (CO) gas and this has a lot of valuable chemicals. The primary By-products from crude CO gas are Ammonium Sulphate (NH4)2SO4, Crude Tar, Crude Benzol and cleaned CO Gas. Pitch and Wash Oil are produced as by-products from the fractional distillation of crude tar.

Prior Art

There is a substantial need for the pollution control in India as well as in whole world. During cooling of coke a lot of coke dust fines (<1 mm) are generated. This dust has a detrimental effect on equipment and environment if not evacuated in time. An appropriate use has to be found for these coke dust fines avoiding the sale in the market.

Various practices are suggested time to time which have been tried to utilize and recycle the coke dust fines.

The German Patent Application no. DE3742817A1 teaches about the prevention, by controlling the process in a suitable manner, the coke briquettes from disintegrating during coking. This object is achieved by dressed pit-wet raw lignite (1) being predried (2) to approximately half its natural water content, the predried lignite (3) being pressed into briquettes (4) the briquettes (5) optionally being re-dried (6) to a lower water content and then being coked in a continuous process, passing through a hearth furnace (8) at temperatures between 700 and 1000@ 0C. Predrying (2) of the raw lignite (1) is carried out to give water contents between 20 and 60% by weight. Redrying (6) of the briquettes (5) is carried out to give water contents between 10 and 20% by weight. The briquettes (5) have a diameter of approximately from 0.5 cm to 1.3 cm and a length of 1 to 2 cm.

The European Patent No. EP0155439B1 teaches about a process for the preparation of briquettes, suitable for use as an additional combustible in shaft furnaces for melting of mineral material in the manufacture of mineral wool, and comprising particles of coke and/or coal or both and a hydraulic binder, wherein the hydraulic binder is present in an amount of at least 8% based on the dry weight of the briquette and characterized in that fine grain particles of the coke and/or coal of a size of below 2 mm are removed before forming the briquettes, and in that the briquettes further comprise a fine grain oxidic, mineral component of a size below 2 mm.

The Indian Patent No. 234272 teaches about a coal briquette for a smelting reduction process comprising: 50% by weight or less of dust, mixture of sludge and dust, the balance of fine coal, as major components, the sludge having iron (Fe) or iron compounds, carbon (C), Ca compounds and Mg compounds; and 5-20 parts by weight of a binder, based on 100 parts by weight of the major components.

Object of the Invention
The object of the present invention is to produce briquettes by utilization of coke dust fines produced during the cooling of coke in coke dry quenching process, thereby reducing the storage problem of coke dust fines and thus environmental pollution to a great extent.

The another object of the present invention is to produce low cost, useful briquettes having improved properties in a recycling system. The briquettes produced are environment friendly and utilized in most economical way.

The another object of the invention is to partially substitute the coke in the Blast furnace process with coke dust fines briquettes due to its high carbon content (81-84%).

Detailed Description

A Briquette is a block of compacted material made up of fines. Common types of briquettes, used as fuel, are charcoal briquettes and bio- mass briquettes. Coke dust Briquettes are made with coke dust fines by compaction using pitch and wash oil as a suitable binder. The aim of compaction is to bring the fines particles into sufficiently close contact to produce briquettes having adequate strength to withstand subsequent handling and processing.

According to an embodiment of the invention, coke dust fines produced as a by-products have the typical composition of the coke dust fines with its size analysis as given below .

Typical composition of Coke Dust Fines (wt. %)
Fixed Carbon Ash Total Moisture VM
81-84 17-18 2-3 0.5-0.8

Typical size analysis of Coke Dust Fines
Size (mm) +6.3 -6.3
+3.35 -3.35
+2 -2
+1 -1
+0.5 -0.5
+0.25 -0.25
+0.106 -0.106
% of coke dust 0.16 0.25 0.45 1.36 6.41 58.56 21.5 11.31

The binders are by-products generated during Fractional Distillation of Crude Tar in coke ovens. These binders are Pitch and Wash oil. The residual content of toluene insoluble after taking out quinolene insoluble is called beta resin, which is used to assess pitch quality in relation to its binding behaviour. The beta resin content along with the higher softening point (>170oC) in pitch is believed to be a strong factor in giving better bonding properties.

Typical Pitch Composition (wt. %)
Softening point (Ring & Ball method) Quinolene Insoluble % Toluene Insoluble % Beta resin content % Coking value % (Conradson) Ash content % Size(mm)
170-175 oC 19-25 54-59 30-36 63-66 0.15 -0.20 -1 mm(60 % minimum)

Typical Wash Oil Composition (wt. %)

Naphthalene % Specific gravity at 20 oC Moisture Distillation range at 220-270 oC
4-5 1-1.15 0.4 – 0.7 80% min.
According to another embodiment of the invention, the coke dust is mixed with binders in the required percentage for 25-30 minutes. The mixed material is briquetted. The briquettes are of a cylinder shape. The briquettes are allowed to air dry for a day at room temperature and later cured at 150-200 oC for 50-60 minutes to attain required strength.
The coke dust briquettes were manufactured experimentally in ½ kg
batches using pitch (16-20%) and wash oil (8-12%) as binders with remaining being coke dust fines. It was seen that with increase in binder content, the strength of briquette increases. However, beyond a certain percentage of binder addition, the strength does not increase appreciably.
A typical flow sheet of the Briquette making process is given under:

Dust collection from CDQ (<1mm)

Dry Mixing of coke dust fines with pitch (16-20 wt. %)10-15 minutes

Wet mixing with wash oil (8-12 %) for 10-15 minutes

Briquetting using sand rammer

Curing (at room temp.) for 22-24 hrs

Curing (150-200 °C) for 50-60 minutes

Briquettes for use

The briquettes were manufactured by mixing the raw materials like coke dust fines and Pitch in Muller mixer slowly adding wash oil. While conventional (blender type mixer) mixing is usually sufficient for the blending of easy to handle solids, a more intensive form of mixing in Muller mixer produces total uniformity in a mix of materials having disproportionate mass, particle size, liquidity, viscosity or density. Intensive mixing is required to produce even distribution of individual particles throughout the mix. A Muller type mixer provides additional mixing forces ass compare to the conventional mixers to assure that the total mixture prepared is of uniform consistency.

Unlike conventional mixing, mulling provides forces that incorporate kneading, shearing, smearing, and blending of materials for total uniform consistency. This process produces just enough pressure to move, intermingle and push particles into place without crushing, grinding, or distorting the ingredients. The result is a final mixture of truly uniform consistency in both physical and chemical structure.

According to further embodiment of the invention, the coke dust fines generated in CDQ process were collected and air dried for briquette making. As the average particle size of coke dust is less than 1 mm, it does not require further grinding. Pitch received from Tar distillation plant of specific composition is crushed using toothed two roll crusher to a size - 1 mm (min.60 %).

The coke dust fines and Pitch are slowly mixed in dry condition for 10-15 minutes in a Muller mixer. Blending and mixing is continued with addition of wash oil preheated to 70-80 oC for another 10-15 minutes. A homogeneous mixture is prepared using the minimum amount of energy and time to get desired properties for briquetting.

The solubility of pitch is more with wash oil due to high softening point (170-175 oC) of pitch. It was found that solubility of pitch in the wash oil will be better when oil of 220-270 oC distillation range is used. This
favours better adhesion property with the surface of coke fines.

The mixed material is compressed in a sand rammer to produce cylindrical briquettes (50 mm dia. x 30 mm height). A sand rammer is an equipment used in the foundry for sand testing to make test specimen of moulding sand.

According to further embodiment of the invention, the briquettes made are taken out of the mould and stored in a specified area at room temperature in open atmosphere. The briquettes are then allowed to dry for a day at ambient temperature in an open atmosphere and later cured at 150-200 °C for 50-60 minutes to attain required strength.

Typical characteristic of briquettes produced in laboratory (in weight %)
AM VM Ash Fixed Carbon Green strength CCS (Kg/cm2) strength of Briquette cured at 150-200°C
CCS(kg/cm2)
Bulk Density
(gm./cm3) Calorific Value CV (Kcal/kg)
1.15-1.35 1.05-1.55 15.75-16.25 80.87-82.08
3.6-4.4
30.0-32.0 1.0-1.1.4 7900-8000

The table indicates the various physical and metallurgical properties of Briquette manufactured in laboratory. High fixed carbon, low volatile matter and low ash in briquette is comparable to the required chemical properties of BF coke. Bulk Density value (1.0-1.14 gm./cm3) is higher in comparison with coke lump (0.7-0.9 gm./cm3) and may have the advantage of higher volume utilization in the furnace. The briquettes can be charged in Blast Furnace process as a partial replacement for coke.

The invention will be described with reference to following example without restricting the scope of the invention.

Example:
A process for making the briquettes from the coke dust fines generated during cooling of coke produced in coke oven, the process comprising-
- Cooling the hot coke by coke dry quenching process to generate coke dust fines
- - air drying the coke dust fines collected after cooling the hot coke produced in coke oven.
- Adding the binders(Pitch and wash oil) to the coke dust fines for increasing the strength of the briquette produced
- Mixing the 16% of Pitch slowly with coke dust fines in dry conditions for 10minutes in a mixer followed by mixing 8% of wash oil preheated to 70 °c with the coke dust fines and pitch mixture for 10 minutes to form a homogenous mixture
- Allowing the mixture for briquetting by pressing the mixture in a sand rammer to produce the briquettes.
- Drying the briquette at room temperature for a day in open atmosphere
- curing the briquettes to attain the desired strength at 150°c temperature for 1 hr to attain the required strength
- transporting the cured briquette to weighing bunker and adding
it to the BF process.
Use of briquettes formed by the above process is advantageous due to the following reasons:
• Due to high carbon content (81-84%) in coke dust fines generated in the CDQ process, they can be used to form coke dust briquettes which can be used as a replacement for Blast Furnace coke.
• Coke can be partially substituted by Coke dust fines briquettes in performing the following three roles.
- As a fuel, it provide thermal energy for chemical reactions and melting of slag and metal
- As a reducing agent, for the reduction of iron oxides
- As a permeable support, it is the only solid material in the furnace that supports the iron bearing burden.
Such a substitution brings down the coke rate for the blast furnace.
• Briquetting of the coke dust fines can provide a way of utilization of coke dust fines and help to reduce the storage problem, thereby reducing the environmental pollution to a great extent.
The briquettes formed by above process are of low cost, mainly use of in-house produced by-products. The present invention is an industrial process for making use of coke dust fines to produce useful briquettes having improved properties in a recycling system. The briquettes made by the above process are environment friendly and utilized in most economical way.

While the invention has been described in detail with the help of a preferred embodiment, the invention is not limited to the disclosed examples. Other variations can be deducted by those skilled in the art without leaving the scope of protection of the claimed invention.