Title of Invention

A METHOD OF MAKING STABLE STAMPED COAL CAKE AND COAL CAKE PRODUCED THEREOF TO PRODUCE COKE

Abstract

This invention relates to a method of making stable stamped coal cake to produce coke comprising the steps of preparing a coal blend on crushing coal to fines of 0.0032 m and adding heated coal tar of 0.25 to 6% by weight with the fines and mixed thoroughly, the coal blend then compacted by ramming in a ramming unit to result coal cake of improved wet bulk density, shear and compressive strength than coal cake without any binder excepting moisture which properties being determined through test results followed by characterization tests of coke produced in an oven for ash content, CSR and CRI

Full Text

FIELD OF INVENTION This invention relates to a method of making stamped coal cake with improved stability and coal cake produced thereof which is treated in oven to produce coke. More precisely the present invention relates to cost effective and production line encouraging development of stamped coal cake with improved coal cake stability by addition of coal tar as a binder in the coal blend to improve the rheoiogical properties of coal blend to pave the way to form stamped coai cake with improved stability on process treatment according to the proposed invention. BACKGROUND OF THE INVENTION Stamp charging has been established as a versatile technology which not only improves the coke properties that can be obtained from a given coal blend, but also broadens the coal base for coke making, permitting the use of inferior coals without impairing the coke quality. To derive the maximum benefit from this technology it is important to achieve the requisite dry bulk density and stability of the stamped coal cake. Compared to the conventional top charging, stamp charging is a more energy intensive process as the extra quantity of water (3-4%), added intentionally to the coal blend to impart the requisite coal cake strength. This calls for additional thermal energy and also causes delay in the process. Besides, the extra water prohibits desired amount of coal from being charged into the oven thus causing less production of coke. Hence, another alternative for increasing the productivity of stamp charged batteries is trialled by addition of a suitable organic binder to the coal charge. Addition of organic binders like tar to the coal blend prior to stamping though reduce the consumption of thermal energy but improve the productivity and would impart the requisite strength and stability at lower moisture levels. Moreoever, tar addition improves the strength characteristics of the resultant coke made from coals having pool rheological properties. In the mid-twenties H. Brosche extracted so called coal bitumen from high grade coking coal and showed that, when the extracted bitumen coal added to a low-rank coal type, it proved possible to produce usable blast furnace coke. These experiments were the basis for later technical developments to produce coke from low rank coal by the addition of binders. Since then, different types of additives have been tried to alter the basic coking propensity. Coal tar is a resinous materia! containing a and ß types of resins. ß resins, indicated by the difference between Quinoline Insoluble (Q.I) and Benzene/Toluene Insoluble (B.I/T.I) contribute significantly to the binding of coal particles. Moreover, the imported semi soft coals, presently being used in the stamp charging coal blend in Tata Steel, although have low ash and low volatile matter (V.M.) lack in rheological properties. Additives such as coal tar, commonly referred to as fluidity enhancers, can piay a more direct role in improving the strength characteristics of the resultant coke. It is reported that addition of coal tar to coal blends improves the fluidity of the blends, favours wetting of non-softening grains, effects the homogenization of coal mass and facilitates moving and binding of the structure elements. Tar penetrating into the porous structure of coal, retards the thermal decomposition of the group components of the blend at plastic temperatures and promotes the re-arrangements of the structure. Coal tar has an advantageous influence on the formation of homogeneous optically anisotropic coke structures with high mechanical strength. There are numerous binders like coal tar, pitch, bentonite, sodium lingo sulphanate, latex phenolic resins, molasses, sodium silicate etc.; but coal tar, being coal derivatives were selected for the trials. Most of the other binders do not help in improving the strength of the resuitant coke, on the other hand add harmful constituents to the coal blend. Although elaborate studies in the laboratory as well as in the plant have been carried out earlier on the use of pitch as a part replacement of moisture as binder, it could not be implemented on a continuous basis due to non-availability and higher cost of pitch. Hence, it was decided to replace pitch with alternative binders like coal tar. According to one objective of the invention coal tar has been used as a binder to improve the rheological properties of coal blend prior to stamping. According to another objective of the invention tests were carried out to determine bulk density of coal blend and strength of stamped coal cake and prevent coal cake breakages. According to still another objective of the invention any low graded coal is aimed to be used as starting material of coal blend. According to yet another objective of the invention the stability of coal cake is enhanced with low moisture level of the coal blend. According to still further objective of the invention the thermal energy in production of stamped coal cake is minimised, According to yet further objective of the invention the cycle time in production of coal cake is reduced. According to still another objective of the invention enhancement of nominal yield of coke and gas is proposed by adding coal tar as a binder of coal blend. DESCRIPTION OF THE INVENTION In the conventional stamp charging, water is used as a binder for achieving proper coal cake stability. It calls for addition of 3-4% extra water to the coal blend to maintain the requisite limit of coal moisture prescribed for proper coal cake stability. Such addition of water leads to reduction in net dry coal throughput to the oven and requires more heat to drive out the moisture. Inspite of many positive attributes of stamp charging technology, this is considered to be main drawback of prior art. Coal tar which is obtained as a by-product during coal carbonisation is very rich in resinous matter and has a good binding property. Even with low dosage (2-3%) of coal tar addition to the coal charge, it is possible to obtain the desired coal cake stability. This tar addition also contributes to nominal enhancement in the coke yield and gas yield. In addition, the application of the proposed binder also improves the rheological properties of coal blend which contributes to the improvement in the quality of coke. According to the invention there is provided a method of making stable stamped coal cake to produce coke comprising the steps of preparing a coal blend on crushing coal to fines of 0.0032 m and adding heated coal tar of 0.25 to 6% by weight with the fines and mixed thoroughly, the coal blend then compacted by ramming in a ramming unit to result coal cake of improved wet bulk density, shear and compressive strength than coal cake without any binder excepting moisture which properties being determined through test results followed by characterization tests of coke produced in an oven for ash content, CSR and CRI By carrying out the following experimentations, the positive effects of tar as a binder for improving coal cake stability and resultant coke quality has been established. A. The effect of addition of binders on the stability of coal cake B. The effect of addition of binder on the quality of resultant coke produced A. The effect of addition of binder on the stability of coat cake Two different equipment were used for the determination of stability of coal cake. One for making test coal cake by ramming and the other for determining their compressive and shear strengths. The coal was compacted by the drop hammer principle in accordance with the operating parameters followed in large scale stamping units. The coal cake was produced in a mould into which the charge is fed and compacted with a rammer to a cylindrical shape of 50x50 mm. The kinetic energy required to accomplish ramming was converted from the potential energy of the rammer whose weight and height were adjusted. The test cake was made after determination of the number of drops required to produce cake with specified stamping energy The coal cakes, thus made, were subjected to testing in the other equipment for the determination of compressive and shear strengths. For adequate stability fo the coal cake, the minimum shear and compressive strength required are 150 g cm and 1600 g/cm2 respectively A series of tests were conducted to find out the optimum level for the moisture content of the coai blend to achieve maximum possible strength and stability under the conditions being followed presently in the plant (10% moisture without any binder addition). Keeping these strength values as the base, a second series of trials were carried out to determine the compressive and shear strengths of the coal cakes made under different dosages of addition of tar to the coal blend at two different levels of moistute contents (7% & 8%). These moisture levels were chosen mainly because of the fact that the moisture contents of the as received coals in the coke plant remain at an average level of 7-8% during non-monsoon seasons. During monsoon, the moisture is usually at a much higher level and addition of binder will neither be needed for improving the coal cake stability nor will be economical. The coal blend used in all these tests was the sarne for ait to have a comparative evaluation. Coal tar from by-product plant of Tata Steel was used as the binder. The crushing fineness of coal samples used was maintained at 90 ± 1% (through 0.0032 m) and the wet bulk density of the coal cake remained between 1140 1160 kg/m3. The test cakes were made after determination of the numbes of drops required to produce cake with specified stamping energy of about 450 Nm/kg. Before mixing to the coal blend, the tar sample was heated up to 70-80 deg. C. Tests were conducted with different dosages of tar addition (0.25-6%) at two different moisture levels (7% & 8%) to find out the maximum achievable coal cake strength and the optimum amount of tar addition required for adequate stability. Improved physical properties achieved through the test cakes are illustrated in the following table 1. An improvement in compressive and shear strengths of the coal cakes made under different dosages of tar addition up 10 nearly 3.5% was observed for both the levels of moisture contlents (7% & 8%). It is possible to get the requisite coal cake strength {as that of coal cake made from base blend containing 10% moisture and without binder) even at lower moisture levels of 7% and 8% with only 2.0% and 1.25% tar addition respectively. Hence, since coal tar which is obtained as a by-product during coal carbonisation is very rich in resinous matter and has a good binding property, even with low dosage (2-3%) of coal tar addition to the coal charge, it is possible to obtain the desired coal cake stability. B. The effect of addition of tar on the quality of resultant coke produced A series of carbonisation tests were carried out in the 7-kg. Carboiite oven to study the influence of different levels of tar addition to the base blend under stamp charging conditions. All the above test results were analysed to derive the optimum level of tar addition to the coal blend at 7% moisture level that couid ensure coal cake stability. For a comparative study, the carbonisation tests were also carried out suing the base blend generally being used in the coke plant. In all the Carboiite oven tests, the maximum lateral expansions of the coal mass during carbonisation were also measured. The resultant coke was tested for ash contents, CSR (Coke Strength After Reaction) and CRI (Coke Reactivity Index) The flue temperatures in the Carboiite oven are maintained at 1050 °C. However, it is always ensured that, before charging the coal cake into the oven, the empty oven temperature is ~ 900°C. At the time of pushing, the center mass temperature of the coke inside the oven is kept at 1000 °C. The test results of carbonisation test are enumerated in the following Table - 2. The addition of coat tar to base blend to produce marginal improved result of coal cake strength are best understood from the following comparative test datas. Maximum amount of coal cake strength achieved with tar as a binder: Compressive Strength: At 7% Moisture and 4% tar Addition: 1753 gm/cm2 At 8% Moisture and 4% tar Addition: 1788 gm/cm2 Shear Strength: At 7% Moisture and 4% tar Addition: 243 gm/cm2 At 8°/o Moisture and 4% tar Addition: 263 gm/cm2 Maximum amount of coal cake strength achieved without any binder (only water): Compressive Strength: At 9% Moisture: 1733 gm/cm2 At 10% Moisture: 1675 gm/cm2 Shear Strength: At 9% Moisture: 215 gm/cm2 At 10% Moisture: 198 gm/cm2 The lateral expansion also increases marginally when tar is used as a binder. From the above test results carried out in carbolite oven it has been verified that Safe max lateral expansion, % is +8.2 max. Acceptable minimum coke CSR is 54 (Equivalent to CSR of 64-65 in existing commercial oven) As expected, addition of coal tar to the base blend marginally increased the CSR of the resultant coke. Such improvement in coke quality is attributed basically due to effective homogenisation of coal mass accompanied with formation of more optically anisotropic coke, as a result of tar addition. Also, addition of binder like tar permits more use of weakly coking and non-coking coals that are poor in rheological properties. This would in turn facilitate partial teplacement of imported blended semi-soft coal in the stamp charging blend without deterioration in coke CSR. The invention as described hereinabove and illustrated should not be read in a restrictive manner as various adaptations, modification and changes are possible as encampused within the scope of the appended claims. WE CLAIM 1. A method of making stable stamped coal cake to produce coke comprising the steps of preparing a coal blend on crushing coal to fines of 0.0032 m and adding heated coal tar of 0.25 to 6% by weight with the fines and mixed thoroughly, the coal blend then compacted by ramming in a ramming unit to result coal cake of improved wet bulk density, shear and compressive strength than coal cake without any binder excepting moisture which properties being determined through test results followed by characterization tests of coke produced in an oven for ash content, CSR and CRL 2. A method as claimed in claim 1 wherein the coal used for preparation of coal blend contains 7 to 8% by weight of moisture in as received conditions in a plant. 3. A method as claimed in claim 1 wherein the tar before mixing with coal fines is heated at 70°C to 80°C. 4. A method as claimed in the preceeding claims wherein coal tar as a binder is added to the coal fines in an amount of 2 to 3% by weight. 5. A method as claimed in the preceeding claims wherein safe maximum lateral expansion during carbonisation in % is 8.2 and acceptable minimum coke CSR is 54 equivalent to 64-65 in existing commercial oven. 6. A method as claimed in the preceeding claims wherein the maximum shear and compressive strength of the coal cake achieved with tar as a binder are 243-263 gm/cm2 and 1753-1788 gm/crrr and minimum shear and compressive strength are 160-180 gm/cm2 and 1550-1603 gm/cm2 respectively. 7. A method as claimed in the preceeding claims wherein the wet bulk density of the coal cake is maintained at 1140-1160 kg/m3 8. A method as claimed in the preceeding claims wherein the resultant coke has improved CRS and CRI though with higher ash contents as high as 13% 9. Stable stamped coal cake to produce coke in an oven as prepared according to the method claimed in the proceeding claims. 10. A method of making stable stamped coai cake to produce coke as herein described and illustrated. This invention relates to a method of making stable stamped coal cake to produce coke comprising the steps of preparing a coal blend on crushing coal to fines of 0.0032 m and adding heated coal tar of 0.25 to 6% by weight with the fines and mixed thoroughly, the coal blend then compacted by ramming in a ramming unit to result coal cake of improved wet bulk density, shear and compressive strength than coal cake without any binder excepting moisture which properties being determined through test results followed by characterization tests of coke produced in an oven for ash content, CSR and CRI

Documents:

00601-kol-2006-abstract.pdf

00601-kol-2006-asignment.pdf

00601-kol-2006-claims.pdf

00601-kol-2006-correspondence other.pdf

00601-kol-2006-description (complete).pdf

00601-kol-2006-form-1.pdf

00601-kol-2006-form-2.pdf

00601-kol-2006-form-3.pdf

601-KOL-2006-FORM 1-1.1.pdf

601-KOL-2006-FORM 2-1.1.pdf

601-kol-2006-granted-abstract.pdf

601-kol-2006-granted-claims.pdf

601-kol-2006-granted-correspondence.pdf

601-kol-2006-granted-description (complete).pdf

601-kol-2006-granted-examination report.pdf

601-kol-2006-granted-form 1.pdf

601-kol-2006-granted-form 18.pdf

601-kol-2006-granted-form 2.pdf

601-kol-2006-granted-form 3.pdf

601-kol-2006-granted-gpa.pdf

601-kol-2006-granted-reply to examination report.pdf

601-kol-2006-granted-specification.pdf

601-KOL-2006-REPLY TO EXAMINATION REPORT.pdf