FIELD OF THE INVENTION
The present invention relates to evaluating of chemical and mineralogical compositions of coal ash and their effect on environment. More particularly, the present invention relates to a coal blend used in coke making, which contain significantly lower level of trace elements of major environmental concern.
BACKGROUND OF THE INVENTION
The coke oven is a major source of fugitive air emissions. The coking process emits particulate matter (PM); volatile organic compounds (VOCs); polynuclear aromatic hydrocarbons etc.Blending of coals is necessary from economical point of view by reducing the percentage of high cost, prime or hard coking coals and replacing it with medium or soft coking coals. In some coke oven plants, even a small percentage of non-coking or steam coals have also been used in the blend. For obvious reason, this exercise is without sacrificing coke quality and battery health.
Coal ash composition and its characteristics play a vital role in selection of coal for coke making. The chemical compositions of coal ash retain the mineral matter composition of original coal which effects the meso-phase formation during carbonization process.
Production of iron through BF route is still a dominant route and coke is a major raw material and energy source for the blast furnaces. Coke production remains an inseparable part of the steel production and coke making process is a well-documented source of pollution in terms of gaseous and particulate emissions. Emission of SO2, NOX, CO, H2S, particulate matter, Pb, Ni, As, Cd, Cr, Cu, Zn, Se, Hg, organic compounds and other pollutants originate from several operations in the coking plants. The emissions from the coke ovens at an integrated steel plant can be attributed to two components; operation of a coke oven (technology, operational practices etc) and the coal being used (coal chemistry).

Coal without mineral matter is impossible to achieve, these minerals take predominant role in carbonization process. Coal ash consists of fine particles, which contain a mixture of minerals such as clays, quartz, iron oxides, alumino-silicate formed by melting of mineral matter at the high temperatures of combustion, and unburned carbon remaining after the combustion process. Major chemical constituents of coal ash typically include Si, Al, Fe, Ca, Mg, K, S, Ti and P in various proportion from coal to coal and seam to seam. Coal ash also contains minor amounts of trace elements, including Cr, Ni, Zn, As, Se, Cd, Sb, Hg and Pb. A number of studies have focused on coal ash fusibility. Previous studies on fusibility and flow behavior proved a correlation between the ash fusion temperature and chemical composition of coal ash samples.
WO200246100 describes an improved process for removing mercury and other trace elements from coal containing pyrite by forming a slurry of finely divided coal in a liquid solvent capable of forming ions or radicals having a tendency to react with constituents of pyrite or to attack the bond between pyrite and coal and/or to react with mercury to form mercury vapors, and heating the slurry in a closed container to a temperature of at least about 50 Deg.C to produce vapors of the solvent and withdrawing vapors including solvent and mercury-containing vapors from the closed container, then separating mercury from the vapors withdrawn.
Indian patent application 01891/DEL/2013 teaches that environmentally sensitive trace elements like Cd, Cu, Cr, Ni, Pb and Zn from coal samples can be successfully removed with the help of mixed-bacterial consortium comprising of Ralstoniasp and Pseudo xanthomonas sp. The bacterial consortium could remove 85.744 % Ni, 87.656 % Zn, 85.226 % Cd, 83.176 % Cu and 71.618 % Cr, while the removal of Pb was 44.748 %. The present work is a major breakthrough in this field.

JP5153144 provides a method for efficiently suppressing the elution of harmful trace elements, particularly, hexavalent chromium, from coal combustion residue. The solution to the prior art problem as provided herein is that an elution inhibitor added to coal is added to fuel coal, and further an elution inhibitor added to ash is added to coal ash to suppress the elution of the harmful trace elements from the coal combustion residue. An elution inhibitor mainly containing at least one kind selected from the group consisting of lime stone, hydrated lime, and burnt lime is used as the elution inhibitor added to coal. An elution inhibitor essentially containing hydrated lime is added as the elution inhibitor added to ash.
CN202989088U discloses a continuously-treating type device for rapidly treating total sulfur in raw coal to generate clean coal, comprising low-temperature and negative-pressure treating the total sulfur in raw coal by a method of vacuum negative pressure combined to microwave heating. The device comprises a feeding device, a treating device and a discharging device. The device can rapidly remove vaporizable hazardous substances in raw coal, and simultaneously can rapidly convert pyrite in raw coal into magnetic pyrite and troilite with stronger paramagnetic by a microwave irradiation method, in order to more effectively remove the sulfur-containing substances in followed magnetic separation. The product is also used for drying by heating and removing vaporizable hazardous substances in the fields of weaving, printing and dyeing, printing, foodstuff, medicine, chemical industry, mining, papermaking, etc. The device can be used for rapidly removing hazardous substances such as formaldehyde in textiles and clothes, and xylene in wood-based plates.
WO200448623 teaches a method for the recovery of one or more trace elements including gold and one or more platinum group elements from coal.
CN101839900Bprovides a detection method of mercury content in burning coal, which adopts various of reagents and a common instrument to detect without expensive precise instruments or gold amalgamation to adsorb, so that the detection method is convenient to detect, has low cost, can detect mercury content in burning coal, and can

detect the content of mercury of various forms by extracting step by stepso as to solve the defect that trace element mercury in coal is difficult to detect. The detection of the mercury content in coal of various forms is favorable for judging the type of mercury pollutant in smoke and the migration rule and can guide to select the best desorption means to purify burning coal smoke.
EP2269714 describes an air pollution control system which includes a de-nitration apparatus, that reduces nitrogen oxide in flue gas discharged from a coal combustion boiler, and that sprays hydrogen chloride into the gas to oxidize mercury, an air heater that recovers heat in gas, a dust collector that reduces dust in gas, a desulfurization apparatus that reduces sulfur oxide in gas from which the dust has been reduced, a stack from which gas thus desulfurized is discharged to the outside, a hydrogen chloride vaporizer that evaporates concentrated hydrochloric acid to obtain the hydrogen chloride, and a hydrochloric acid neutralization tank where dilute hydrochloric acid discharged from the hydrogen chloride vaporizer or the concentrated hydrochloric acid is neutralized with an alkali agent.
Neutralized chloride is supplied to a fuel feeder, mixed with a fuel, i.e., coal, and then burned as a fuel F in a boiler, to produce hydrogen chloride in flue gas.
Then, together with sprayed hydrogen chloride derived from the hydrogen chloride vaporizer, the mercury is reduced.
• C-N and C-S coals contain significantly lower level of trace elements of major
environmental concern.
• Other experimental coal eg. C-J, C-W, C-T and C-I have the comparativelyhigher
level of trace elements.
• Specifically the average values of the key environmental elements like As, Hg,
Si, Al, Fe, B and Ca were noticeably lower in C-N and C-S and C-T than C-J, C-
W and C-I.

• Melting temperature of C-N and C-S coals are much lower than the other coals
under study.
• Suggested coals for blend of coke is C-N, C-S and C-T.
• C-I and C-J are not recommended to use in coke making because of the
hazardous air pollutant present in them.
• Though CW and CJ are captive coal and used for economic purpose. CI being
an imported coal can be suitably replaced.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose a coal blend used in coke making, which contain significantly lower level of trace elements of major environmental concern.
SUMMARY OF THE INVENTION
Accordingly, there is provided a coal blend used in coke making, which contain significantly lower level of trace elements of major environmental concern, the coal blend comprising at least three coal compositions, the first coal having composition of Na: 0.534-0.536, K-BDL, Al: 8.19-8.21, Si: 8.07-8.09, Ca: 1.95-1.97, V-BDL, Cr: 0.031-0.033, Mn: 0.056-0.058, Mg: 0.591-0.593, Fe-5.553-5.555, Co: 0.003-0.005, Ni: 0.090-0.092, Cu-BDL, Zn: 0.037-0.039, Cd- BDL, Sb-BDL, Hg: 3.82-3.84, Ba: 0.01-0.013, Pb: 0.099-0.092, Bi-BDL, Se-BDL, As-BDL, Ti: 0.369-0.371, B: 0.22;7-0.229 (all in wt.%); the second coal having composition of Na: 0.360-0.370, K-BDL, Al: 4.40-4.50, Si: 3.50-3.59, Ca: 0.20-0.27, V-BDL, Cr: 0.020-0.029, Mn: 0.002-0.006, Mg: 0.042-0.048, Fe-1.930-1.940, Co: 0.002-0.008, Ni: 0.035-0.045, Cu-BDL, Zn: 0.020-0.029, Cd-BDL, Sb-BDL, Hg: 0.82-0.89, Ba: 0.005-0.01, Pb: 0.091-0.096, Bi-BDL, Se-BDL, As-BDL, Ti: 0.301-0.309, B: 0.032-0.039 (all in wt.%); the third coal having composition of Na: 0.317-0.325, K-BDL, Al: 10.48-10.68, Si: 9.20-9.30, Ca: 1.92-1.99, V-0.004 approx., Cr: 0.030-0.037, Mn: 0.022-0.029, Mg: 0.190-0.199, Fe-2.42-2.43, Co: 0.012 approx, Ni: 0.150-0.159, Cu-BDL, Zn: 0.033-0.039, Cd- 0.015-0.023, Sb-BDL, Hg: 2.31-2.38, Ba:

0.05-0.10, Pb: 0.090-0.099, Bi-BDL, Se-BDL, As-BDL, Ti: 0.615-0.626, B: BDL (all in wt.%); and the first coal, the second coal and the thirdcoal blended in a ratio of 15-20:7-12:7-12.
According to the preferred embodiment of the invention, the first coal has following components

In another aspect of the invention, the second coal has following components

In a further aspect of the invention, the third coal has following components

The present invention specify parameters for the selection of coal for combustion, the parameters for combustion of the pre-selected coal, the parameters for the preparation and mixing of a charge for a furnace including ash from the combustion of the coal with an inquartand a fluxing agent, the parameters for the heating of the charge and casting of a dore bar and the parameters for the production of an anode slime from the dore bar.

The method of the present invention may also specify parameters for the recovery of silver, gold and one or more trace platinum group elements from the anode slimes.
The method of the invention is especially suitable for detecting mercury content in power plant burning coal.
However, the present invention has been implemented at laboratory scale and needs to be scaled up to the Pilot scale and ultimately to the commercial scale to solve the problem of environmental pollution. It is pertinent to mention here that since the removal of hazardous trace metals have so far not been attempted, especially through bacterial process as done in this work, there appears to be no competition in terms of cost, performance and reliability.
DETAIL DESCRIPTION OF THE INVENTION
The present invention aims to evaluate the chemical composition of coal ash samples to identify the hazardous pollutant present in the coal and the coal blend and their role on environmental pollution. This may help in making the coal blend with right choice of coal to avoid environmental pollution.
Both proximate and ultimate analysis have been done according to the invention, of all the coal samples. To evaluate trace element emissions from the plant to the atmosphere, proportions of trace elements in coal were studied. Tests on ash fusion temperature and has been conducted a good correlation between the melting temperature has been found including presence of trace element in the coals.
It is seen that the C-N and C-S coal ash show the medium melting temperature, whereas other experimental coals show the high melting temperature. Melting temperature is increased with the increase in the proportion of Hg, Al and Ca in coal. The coal C-W, C-J, C-T, C-I is having comparatively higher melting temperature with

high proportion of Si, Al, Hg, Fe and Ca. So the recommended blend may be done with the coals C-N, C-S and C-T to avoid environmental pollution.
Methodology: adapted by the inventors
Coal analysis involves the following steps:
1. Sample preparation
2. Chemical characterization (Proximate and ultimate analysis, CSN value)
3. Experimentations (Ash fusion temperature)
4. Conclusion.
Sample Preparation:
Six typical coal samples, designated as C-S, C-W, C-J, C-N, C-T, C-I were considered for this study. For each coal 5 different samples were collected on different dates and all the samples were pulverized and passed through 72 mesh sieve. The method of sampling and sample preparation for coal was done according to standard (IS-436, 1964) and ash preparation done following ASTM-D 3683-11. Coal and coke samples were ashes by heating the samples at 500oC in air for 4 hours in a muffle furnace. The coal samples used for this study represent a blend consists of six different indigenous and abroad sources.
Chemical Characterization:
The samples were analyzedfollowing the ASTM and ISO. The methods are based on modern instrumental techniques. Total six coal samples were analyzed for the trace element present in it. The proximate analysis was conducted using TGA-701 (Leco) following ASTM-D 7582/2015. Fixed carbon is calculated by taking the difference between 100 and the sum of the present moisture, ash and volatile matter. Ultimate analysis was conducted using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES-MERCK)), the most versatile methods of inorganic analysis (Table 1). Chemical analysis for major inorganic elements present in the coal and its ash was also done by using the same ICP-OES (MERCK).

Ash Fusion Temperature:
The ash fusion temperature (AFT) consists of four temperatures, namely initial deformation temperature (IDT), softening temperature (ST), hemispherical temperature (HT) and melting temperature (MT). In AFT analysis, the softening and flow behaviour of ash was measured by the Heating Microscope with Automatic Image Analysis (Hesse Instrument, Germany).
Results and Discussion:
Trace elements of major concern:
The presence of trace elements in coal does not imply a health risk. Rather it takes into account the potential for these elements to impact on the environment through their distribution in the waste products from combustion.
Elements of major concern are arsenic, boron, cadmium, chromium (VI), mercury, lead and selenium. These elements have known adverse health effects at high levels of exposure. The compounds of these elements are mostly volatile and may be released to the atmosphere through gaseous emissions and in stack particulates. Their presence in aqueous process streams is also of concern.
The trace elements analysed in the coal ash were As, Sb, Se, Ti, V, Si, Al, B, Na, Ni, Ba, Bi, Ca, Hg, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Pb,Zn. These were chosen because they represent a significant environmental burden. The results of trace elements concentrations from this study are presented in Table-2, which is the average of five test results.
Here Cu, Cd, Sb, Bi, Se, As, V and K were the least present elements in the ash, whereas Hg, Al, Si, Fe and Ca are showed highest level. For the coal C-N the average value of Hg, Si, Ca, Mn, Mg, Fe and Ti was much lower than the coal C-I and C-J. It is thus found that significantly higher level of Hg, Fe, Al and Si were present in both C-I and C-J and thus the major contributor of hazardous trace elements to the blend of coke. The average value of As, Se and B were similar for all the coals selected for the present study. These elements are volatile and contribute to air emission.

Ash fusion temperature (AFT):
Ash fusion temperatures give an indication of the softening and melting behaviour of fuel ash. During the process of AFT measurement, the initial deformation temperature (IDT), softening temperature (ST), hemispherical temperature (HT) and melting temperature (MT) was recorded according to the specific shape of the ash cone. This investigation done under oxygen atmosphere to visualise the change in contact angle during heating.The dried sample placed in the system, where it forms a soldering tablet, which is then applied to the substrate material. The substrate was positioned in the middle of the tube furnace where the external thermos-element is located. All the samples were tested following DIN 51730-2007. All the changes were captured through high temperature sharp image. Any changes in swelling behavior was observed by change in area of the images. A good correlation was found between the MT and the trace element present in different coals.
The measurement of AFT is an important preliminary factor to explain the combustion and gasification behavior of coals. For that an intense study has been conducted to relate AFT with chemical composition and some relationship have been established to predict the melting behavior of the ash. Measurement of AFTs of all the selected coals are listed in Table 3. The coal ashes are normally classified as low melting (< 1300 oC), medium melting (1300-1450 oC) and high melting (>1450 oC). Figure 1 shows the image of the ash button at different temperature. It shows the four temperatures include ST, DT, HT, MT. these temperaturesvary from coal to coal. Ash composition plays a major role in that case. We have found si, al, si/al ratio, ca content varies the AFT of coal ash. The phases of ash minerals can be realized based on those results. Coking coal not necessary exhibit good relationship with AFT. Some cases some coking coal exhibits good response in terms of AFT. Lower the AFT means lower energy consumption in blast furnaces which may incurs a substantial benefit to the company.
It is seen that the C-N and C-S coal ash show the medium melting temperature. Whereas other experimental coals show the high melting temperature. It is seen that there is a strong relationship between the presence of Hg, Al and Ca with melting

temperature. Melting temperature has increased with increase in the proportion of Hg, Al and Ca in coal ash (Figure2 to 6). The medium melting ash of C-N has lower proportion of Hg, Fe, Cr, Ca, Si and Al, next of which is C-S. Both the coal ashes are having much lower melting temperature than the other experimental coal ashes. The coal C-W, C-J, C-T, C-I is having comparatively higher melting temperature with high proportion of Si, Al, Hg, Fe and Ca. So, the recommended blend may be done with the coals C-N, C-S and C-T to avoid environmental pollution.

WE CLAIM
1. A coal blend used in coke making, which contain significantly lower level of trace
elements of major environmental concern, the coal blend comprising at least
three coal compositions, characterized in that:
the first coal having composition of Na: 0.534-0.536, K-BDL, Al: 8.19-8.21, Si: 8.07-8.09, Ca: 1.95-1.97, V-BDL, Cr: 0.031-0.033, Mn: 0.056-0.058, Mg: 0.591-0.593, Fe-5.553-5.555, Co: 0.003-0.005, Ni: 0.090-0.092, Cu-BDL, Zn: 0.037-0.039, Cd- BDL, Sb-BDL, Hg: 3.82-3.84, Ba: 0.01-0.013, Pb: 0.099-0.092, Bi-BDL, Se-BDL, As-BDL, Ti: 0.369-0.371, B: 0.22;7-0.229 (all in wt.%);
the second coal having composition of Na: 0.360-0.370, K-BDL, Al: 4.40-4.50, Si: 3.50-3.59, Ca: 0.20-0.27, V-BDL, Cr: 0.020-0.029, Mn: 0.002-0.006, Mg: 0.042-0.048, Fe-1.930-1.940, Co: 0.002-0.008, Ni: 0.035-0.045, Cu-BDL, Zn: 0.020-0.029, Cd- BDL, Sb-BDL, Hg: 0.82-0.89, Ba: 0.005-0.01, Pb: 0.091-0.096, Bi-BDL, Se-BDL, As-BDL, Ti: 0.301-0.309, B: 0.032-0.039 (all in wt.%);
the third coal having composition of Na: 0.317-0.325, K-BDL, Al: 10.48-10.68, Si: 9.20-9.30, Ca: 1.92-1.99, V-0.004 approx., Cr: 0.030-0.037, Mn: 0.022-0.029, Mg: 0.190-0.199, Fe-2.42-2.43, Co: 0.012 approx, Ni: 0.150-0.159, Cu-BDL, Zn: 0.033-0.039, Cd- 0.015-0.023, Sb-BDL, Hg: 2.31-2.38, Ba: 0.05-0.10, Pb: 0.090-0.099, Bi-BDL, Se-BDL, As-BDL, Ti: 0.615-0.626, B: BDL (all in wt.%); and in that
the first coal, the second coal and the thirdcoal blended in a ratio of 15-20:7-12:7-12.
2. The coal blend as claimed in claim 1, wherein the first coal has following
components


3. The coal blend as claimed in claim 1, wherein the second coal has following
components

4. The coal blend as claimed in claim 1, wherein the third coal has following
components