FORM 2
THE PATENTS ACT 1970
(39 of 1970)
AND
PATENT RULES
COMPLETE SPECIFICATION
(See Section 10 rule 13)
(In respect of Provisional Application No. 1221/MUM/2011
dated 13th April 2011)
TITLE OF THE INVENTION
ECO-FRIENDLY AND ECONOMICAL PROCESS
FOR BENEFICIATION OF COAL
APPLICANT
Name : PRADEEP METALS LTD.
(A Company Incorporated under the Companies Act, 1956)
Nationality : Indian
Address : R - 205, TTC Industrial Area,
M.I.D.C., Rabale,
Navi Mumbai-400 701
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF INVENTION
This invention relates to improvement in the quality of coal.
This invention particularly relates to the enhancement the combustion properties of coal by using electro-magnetic radiations such as microwaves under controlled conditions.
This invention more particularly relates to the development of environment friendly and energy saving, efficient process for improving the quality of coal by converting some adverse mineral matter constituents present in the coal, into friendly (catalytic) ones due to their selective and differential interactions with the microwaves thereby improving the ash characteristics.
DESCRIPTION OF RELATED ART
Coal has many important uses worldwide. The most significant uses are in electricity generation, steel production, cement manufacturing and as a liquid fuel. In coal-fired power stations lignite (brown coal), bituminous coal (black coal) and anthracite is used for producing electricity. The gradation of Indian coal based on its calorific value is as follows:

Grade Calorific Value R
(in kCal/kg)
A Exceeding 6200
B 5600 - 6200
C 4940 - 5600
D 4200 - 4940
E 3360 - 4200
F 2400 - 3360
G 1300-2400
Usually D, E and F coal grades are used by the Indian Industries, The average Gross Calorific Value (GCV) value of the Indian coal is about 4000 kCal/kg, while that of the Indonesian coal is around 5500 kCal/kg and South African coal is 6000 kCal/kg. A good quality coal with less ash but higher GCV is widely used in power plants.

Apart from GCV, other important properties of coal are defined and explained below with their importance in the commercial use of coal for different applications.
"Gross Calorific Value" (GCV) also known as heating value of coal is the amount of potential energy available in coal that can be converted into heat.
"Moisture content" is an important property of coal, as all mined coal is purified by washing it with water in collieries. Moisture occurs in four possible forms within coal which are (i) surface moisture which is water held on the surface of coal particles, (ii) hydroscopic moisture which is water held by capillary action within the microfractures of the coal, (iii) decomposition moisture which is water held within the coal's decomposed organic compounds and (iv) mineral moisture which is water which comprises part of the crystal structure of hydrous silicates such as clays. The typical moisture content in bituminous coal is in the range of 2.2 to 15.9 % by weight. In lignite coal the same is almost 39 % by weight.
"Hardgrove Grindability Index" (HGI) was developed as an empirical test to indicate how difficult it would be to grind a specific coal to the particle size necessary for effective combustion in a pulverized coal fired boiler.
"Volatile matter" (VM) in coal refers to the components of coal, except for moisture, which are liberated at high temperature in the absence of air. This is usually a mixture of short and long chain hydrocarbons, aromatic hydrocarbons and some sulphur. The volatile matter of coal is determined under rigidly controlled standards.
"Ash content" of coal is the non-combustible residue left after coal is burnt. It represents the bulk mineral matter after carbon, oxygen, sulphur and water (including from clays) has been driven off during combustion.
"Ash fusion temperature" gives an indication of the softening and melting behavior of coal ash. These temperatures are widely cited in fuel specifications for boilers

despite mere being a relatively poor record of correlating with slagging or fouling behavior of heat exchanger tubes.
"Fixed carbon" (FC) content of the coal is the carbon found in the material which is left after volatile materials are driven off. This differs from the ultimate carbon content of the coal because some carbon is lost in hydrocarbons with the volatiles.
An "electrostatic precipitator (ESP)" is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge.
"Colliery" is a workplace consisting of a coal mine plus all the buildings and equipment connected with it.
The chemical composition of coal has a strong influence on its combustibility. The properties of coal are broadly classified based on its above described physical properties and chemical properties. Although, one of the important physical properties of coal is GCV, which indicates its heating value, coal has another set of physical properties which are mostly controlled by moisture, volatile matter (VM) and carbon content. These properties of the coal viz. GCV, moisture content, Nitrogen(N) content, Sulphur(S) content and Ash percentage is essential while optimizing the combustion process at coal fired power plants. The economics of the plant is also defined by the particle size range of the coal so that it can react effectively with the oxygen present in the gas stream which is controlled by HGI and is more recently included as one of the key properties in the specifications for the supply of coal.
The major limitations in the existing quality of coal is that it is hard to grind in presence of high and thoroughly disseminated mineral matter present in it. This creates multiple problems in its use for the intended purpose. It is desirable that such available coal is so treated that it is converted into a usable form with optimum energy input. Conventional practices using different grinding systems are not able to provide this solution.

Physical and chemical processes and even biological organisms are used for cleaning of coal. Coal washing is widely used to remove higher specific gravity ash and pyritic sulphur but typically results in the loss of upto 20% coal in the process. The burning or combustion of coal, in presence of moisture, ash, sulphur and other constituents in varied amounts, even of higher ranks such as anthracite and bituminous generates significant emissions of undesirable gases and is of increasing concern due to environmental and global warming considerations.
Also, ash deposition from the combustion of the coal creates problems in the boilers due to ash deposition on the walls of the furnace and heat exchanger tubes. Two basic forms of ash deposits in the boiler, the first is molten ash and the second is alkali salts which gets deposited and buildup on the furnace walls which reduce the efficiency of the boiler. The ash fusion temperature of Indian coal is generally in the region of 1200 to 1500°C, whereas in case of imported coals it ranges from 1150 to 1300°C. It is advisable to operate boilers with coals of high ash fusion temperatures for better efficiency and avoid operational problems.
Numerous attempts have been made oyer the years to remove or otherwise reduce the amounts of moisture, ash and sulphur in coal and thereby reduce the various forms of contaminants present in coal and improving the quality and combustion characteristics of coals. Unfortunately, such attempts have limited scope and some are even too complex to be used practicably.
Attempts have also been made to utilize the addition of one or more catalysts to the coal, in an effort to reduce the amount of unwanted by-products created in the combustion of the coal. For example, certain types of catalysts added to coal can reduce the amount of sulphur emitted during the combustion of the coal. These attempts are also aimed at improving the combustion characteristics, such as using less excess air and increasing the calorific value (kCal/kg), of the coal to be burned. However, these attempts can create a different set of by-products that can be hazardous and expensive to dispose of or to store.

Much of the effort for improving coal properties are attempted by using electromagnetic radiations viz. use of ultraviolet, infrared, radio, microwave, x-ray and even gamma ray frequencies and combinations thereof. Microwave technology is being tried out for drying and sulphur reduction with addition of several other components. References of few patents can be seen in this regard. However, these are not sufficient to effect overall improvement in the quality of coal which will make the process very economical and/or environment friendly.
US19770835276 discloses a process for drying a conductive material, particularly coal, by subjecting the material to microwave energy. A conductive aggregate is directed through a region where microwave energy excites absorbed water molecules and the conductive material causing the water to evaporate, leaving behind a drier material.
DE19762657472 discloses a process for desulphurization of coal as well as petroleum products using microwave. During this process, initially material is treated with a solvent containing oxidizing agent for oxidizing Sulphur compounds followed by alkali treatment and the mixture is further treated by microwave radiations to about 150°C where S-O bond breaks to release Sulphur in gaseous form.
US19750642900 discloses a process for desulphurization of coal for which the coal is pulverized to about 4 cm and exposed to low power microwave at one or less than one atmosphere for less than 60 seconds. During this exposure the chemical bonds between sulphur and other elements rearrange thereby converting sulphur into gaseous form such as H2S, COS and SO2.
CN200910023192 discloses a process for rapid production of coke using microwave heating. Coal is heated at the temperature of 900-1100°C to perform high-temperature carbonization and to produce coke, coal tar and coal gas.
GB19630024316 discloses a process and apparatus for pre-treating coal fines using microwave technology. In this process, coal fines are heated to a minimum of 400°C

to drive out moisture and volatiles. The hot gases are used for pre-heating the incoming coal.
DE19792903982 discloses a process for Sulphur removal by chemical treatment followed by Microwave treatment. The alkali compound reacts with the sulphur within the coal to form water soluble or separated compounds of sulphur which can easily be removed by washing the treated coal with water and/or to form compounds which do not convert into sulphur oxides during combustion of the coal.
Hence, there is a need for creation of such technology for overall improvement in the coal combustion properties apart from just sulphur or moisture removal with minimum inputs thereby according economic and environmental advantages as well.
OBJECT OF THE INVENTION
It is a primary object of the invention to develop a process for improvement in the coal properties using a single step pretreatment process by selective and differential heating of adverse constituents present in the coal.
It is another object of the invention to develop an eco-friendly process for beneficiation of coal by using electromagnetic radiations such as microwaves and does not require the use of any additives to the coal.
It is yet another object of the invention to develop a process for beneficiation of coal, which is less complicated as well as economical and can be carried out as a batch process or continuous process.
It is yet another object of the invention to convert adverse constituents of mineral matter present in the coal to friendly ones including sintering of mineral matter by the selective and differential interaction of the microwaves thereby enhancing the combustion efficiency of coal and also increasing the ash fusion temperature thereby enhancing the boiler efficiency.

SUMMARY OF THE INVENTION
Accordingly, an eco-friendly, single step process for improving the combustion efficiency of coal and increasing the fusion temperature of coal ash, the process comprising of providing the coal in the form of lumps; placing the coal lumps in a microwave cavity/tunnel of the microwave system; exposing the coal lumps to electromagnetic radiations such as microwaves and maintaining the temperature between 70 to 100°C in a non-oxidizing atmosphere; soaking the coal lumps at the same temperature until the moisture content of coal drops down below 10% taking the coal lumps out of the microwave system to obtain beneficiated coal. The coal used can lignite, bituminous or anthracite or pet coke.
The electromagnetic radiations such as microwave can be used in pulse or in continuous mode, or a combination of both, without adding any other additives to the coal. The beneficiated coal has improved properties such as grindability, calorific value and combustion properties. The ash formed in the process has higher fusion temperature.
The invented process is a single step pretreatment process for coal leading to multi-benefits. It selectively and differentially acts on the coal constituents. Microwave radiation processing is through 'Homogeneous/Heterogeneous Energy Activation Treatment' (H E A T). It affects the material homogeneously or heterogeneously depending on whether the material has a single constituent or a composite of multi constituents like coal, ore, polymer etc.
The valuable coaly portion is significantly transparent to microwaves and remains practically unaffected while the moisture and mineral matter as well as occluded gases undergo changes and are removed depending on their polar nature and, the dielectric properties. Moisture, sulphur forms like pyrite and some mineral matter constituents

have significant dielectric property to absorb microwave and decompose differentially to varying degrees.
According to one aspect of the invention, a process for beneficiation of coal to achieve coal with improved quality like reduced moisture content, increase in GCV and ash fusion temperature, etc. is provided. The process comprises loading the coal sample in the microwave cavity, and exposing to microwaves thereby heating selectively the moisture and mineral matter present in the sample and soaking the said sample at the desired temperature.
According to another aspect of the invention, the reactivity of coal increases thereby releasing large amount of heat due to opening of the pores in the coaly portion as well as the activation of the mineral matters by microwave decomposition which, in turn, acts catalytically and enhances combustion.
According to yet another aspect of the invention, a microwave treatment of the coal is done continuously using a continuous microwave system. The continuous microwave system contains a tunnel installed with a variable speed conveyor belt. The process comprises continuously loading the coal sample in the microwave cavity, irradiating the microwave cavity with microwaves where the coal is treated under controlled conditions. The microwave energy is absorbed selectively by the mineral matter constituents and moisture based on their specific dielectric properties. This short exposure to microwaves changes their properties favourably to promote combustion.
This process does not require any addition of the additives to the coal and is performed only by using electromagnetic radiations such as microwave under controlled conditions, thereby evolving a more eco-friendly process.
The said process can be used in treating coal in any form available, and at any site such as the collieries or the user end such as power plants etc.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1/5
Effect of moisture removal at different temperatures with the same soaking time (During batch processing)
FIG. 2/5
Determination of soaking time at different temperature for coal during batch
processing
FIG. 3/5
Batch process for beneficration of coal (Schematic diagram)
FIG. 4/5
Continuous process for beneficiation of coal (Schematic diagram)
FIG. 5/5
Differential Scanning Calorimetry (DSC) analysts of untreated and microwave treated
coal
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to the controlled microwave treatment of low, medium and high ash coals intended to be used particularly in power plants. The invented process is applicable for the coals used in other industries such as cement, steel, coke and other end-users of similar coal.
The coal fraction used in this invention is in the size range of 1 mm to 75 mm and more particularly 3 to 50 mm. The coal is exposed for 1 to 15 min more particularly 1 to 5 min using either continuous or pulse frequency or their combination in different orders of exposure. The microwave frequency used is in the range of 800 to 5000 MHz, preferably between 890 and 2450 MHz. and more preferably 2450±50 MHz.

The enhancement in the final quality of the coal is further achieved by controlled maintenance of non-oxidizing atmosphere during the processing of coal. The non-oxidizing atmosphere comprises of gases such as nitrogen, carbon dioxide or dust free and moisture free flue gases without any contaminants.
In an embodiment of the present invention, the beneficiation of coal is carried out in a batch process as shown in Fig. 3/5. According to this embodiment, a thermally insulated ceramic cylinder 6 made of ceramic fibers made from high purity alumina and silica fibers placed on the ceramic board 5. This cylinder 6 is made of the materials which are transparent to microwaves and allow microwave to enter but prevents heat radiating from sample to relatively cold atmosphere outside the cylinder and achieving high energy efficiency. The said ceramic cylinder 6 is placed on a ceramic fiber board 5 which is placed over a turn table 3 and its height is configured for uniform exposure of microwaves entering through a horn 10 using a ceramic cylinder 4. Coal sample 8 placed in the ceramic cylinder 6, Coal fraction used in this invention in the range of 1 mm to 75 mm and more particularly 3 to 50 mm. A temperature sensor 7 inserted from the top lid ensuring that it is located in the middle portion of the coal sample 8. A special type of temperature sensor 7 used in this invention consists of a grounded, mineral insulated and shielded chromel-alumel, 'K' type thermocouple. The grounding and shielding makes thermocouple more stable and its signal do not get affected by microwaves during exposure of coal sample. The reactor is closed by placing the water cooled top lid 2. The microwaves are generated in a water cooled magnetron 12. These microwaves pass through a circulator 11 in the microwave cavity 1 through a horn 10. For safety of the magnetron, a dead load 13 is installed to absorb the reflected microwaves if any. The non-oxidizing gas is continuously flown through an inlet valve 15. The non-oxidizing gas such as nitrogen or carbon dioxide is used during the process. The non-oxidizing gas minimizes the oxidation of microwave treated coal sample surface 8 placed in ceramic container cylinder 6 placed in the microwave cavity 1. The exhaust gases removed through outlet 14 by applying a vacuum and condensing the moisture through glass condensers. The gas is then released in the atmosphere.

In a particularly advantageous embodiment of the present invention, the beneficiation of coal is carried out in a batch process as shown in Fig. 3/5. The coal sample 8 is loaded into the microwave cavity 1. The interior of the microwave cavity 1 is irradiated with microwaves via circulator 11 from magnetron 12. Microwaves irradiate the interior of the space of the microwave cavity 1. The moisture and mineral matters present in the coal sample 8 placed in the ceramic cylinder 6 absorb the microwaves selectively. By exposing to the electromagnetic radiations such as microwaves, the temperature of the coal sample 8 increases. The temperature is maintained within the specific limit and soaking of the said sample is carried out at the same temperature. The coal temperature is preferably maintained in the range of 70 to 100°C and more preferably between 80 and 90°C. The unwanted/adverse components such as mineral matter and moisture present in the coal sample 8 get heated and selectively driven out of the coal matrix. To prevent microwaves from leaking to the outside of the microwave system, the cavity is water-cooled and lid opening is sealed. The microwaves emitted from magnetron 12 entering in the microwave cavity 1 through a circulator 11 and a horn 10 are not blocked by ceramic cylinder 6 because it is made from materials that are transparent to microwave radiations. Microwaves directly couple with the mineral matter and moisture present in the coal sample 8 placed inside the ceramic cylinder 6 which act as insulator and do not allow heat to radiate outside thereby increasing the energy efficiency of the process.
In another embodiment of the present invention, the beneficiation of coal is carried out in a continuous process as shown in Fig. 4/5. According to this embodiment, the continuous microwave system contains a tunnel 1 installed with a variable speed conveyor belt 5. The belt 5 is made of microwave transparent material such as Polytetrafluoroethylene (PTFE) coated glass cloth with excellent physical and chemical properties and can withstand relatively higher temperatures upto 250°C. The conveyor belt 5 is driven by a variable frequency drive capable of adjusting the speed by adjusting the frequency of the driving motor thereby enabling the control of the coal exposure to electromagnetic radiations such as microwaves during processing. The microwave tunnel 1 is installed with three 1.5 kW air cooled magnetrons 4. The

microwaves are introduced from the bottom of the tunnel. For uniform distribution of the microwave field and modes formed in the tunnel, a mode stirrer 2 is installed in the top portion of the microwave tunnel 1, just above the inlet of the microwaves entry point in the tunnel. Three infrared temperature sensors 6 are installed just adjacent to the mode stirrers for monitoring and controlling the temperature of the coal sample travelling inside the tunnel over the conveyor belt 5. The three sensors are located at the three different locations close to the microwave entry points of each magnetron. The signal from all three IR sensors 6 is given to programmable logic controller (PLC) which controls the power of microwave generation in the magnetron thereby controlling the temperature of the coal travelling in the tunnel over the conveyor belt 5. The coal sample 8 is continuously feed through a hopper installed with a vibrator 7 in the microwave tunnel. The openings of the hopper controlled with the flaps for controlling and ensuring the uniform feeding of the coal sample 8 on the conveyor belt 5. For minimizing the oxidation of the microwave treated coal surface, a non-oxidizing gas such as nitrogen or carbon dioxide is purged continuously through gas inlet 3, The gas along with the water vapour and other gases are collected through exhaust port 9. The exhaust gases are further treated by passing through condenser or through heat exchanger to recover the heat and use for different applications including the pre-heating of the incoming coal thereby achieving still better energy savings and improved economics. It is possible to also recover and recirculate the non-oxidizing gas after moisture removal for further economic efficiency. The microwave treated coal collected from the outlet of the microwave tunnel 1 through port 10. Sample is immediately weighed and sampling is done by employing a standard procedure.
In a particularly advantageous embodiment of the present invention, the beneficiation of coal is carried out in a continuous process as shown in Fig. 4/5. The coal sample 8 is loaded continuously into the microwave tunnel 1. The interior of the microwave cavity 1 is irradiated with microwaves and uniform field is maintained within the tunnel by three mode stirrers located just above the entry points of the microwaves in the tunnel 1. Microwaves irradiate the interior of the microwave tunnel 1. The moisture and mineral matters present in the coal sample 8 moving over the conveyer

belt 5 absorbs the microwaves selectively throughout its travel time in the tunnel 1. Thereby the temperature of the coal sample 8 is increased by exposing to the electromagnetic radiations such as microwaves. The temperature of the said coal sample travelling over conveyor is maintained preferably in the temperature range of 70 to 100°C and more preferably at between 80 and 90°C. The coal sample 8 thereby gets heated due to mineral matter and moisture present in it and the unwanted/adverse components present in the coal are partially driven out of the coal matrix. The microwave exposure time is decided by the speed of the conveyor belt 5 through VFD. The coal is exposed for 1 to 15 min more particularly 1 to 5 min using continuous (2.45 GHz) or pulse either single or in the combination in different orders of exposure.
Microwaves directly couple with the moisture and mineral matter present in the coal sample travelling over the microv/ave transparent PTFE coated glass fiber conveyor belt inside the tunnel 1. The enhancement in the final quality of the coal is further achieved by controlled maintenance of non-oxidizing atmosphere during the processing of coal.
In the invented process it is preferred to maintain a non-oxidizing atmosphere by passing any gas such as nitrogen or carbon dioxide or their mixture or flue gases without any contaminant over the coal surface during controlled microwave exposure for short durations thereby minimizing the surface oxidation of the treated coal. After which the volatile constituents are retained in the coal matrix and their % is increased thereby improving its fuel property. Apart from this, by rapid interaction of the constituents present in the coal matrix such as moisture, occluded gases, mineral matters, with microwaves, the coal temperature rises rapidly creating very high internal pressure in the matrix resulting in to generation of the internal cracks. This improves the grindability of the coal by improvement in the HGI. Another reason for improving the grinding efficiency after processing of the coal using the invented process, the eroding alpha silica component of the mineral matter which is hard to grind otherwise, is also reduced and converted partially into beta silica form which is soft to grind. By processing coal for a short duration using microwave and under

controlled conditions, the coal becomes mors reactive releasing a large amount of heat compared to the untreated sample (Fig. 5/5). This is, obviously due to the opening of the pores in the coaly portion as well as the activation of the mineral matters by microwave decomposition which, in turn, acts catalytically and enhances combustion releasing a higher amount of energy.
Apart from this, the controlled exposure of microwaves to coal under ambient conditions or under controlled atmosphere using the invented process also increases the ash fusion temperature of the ash from 1300 to 1490°C (Table 1). This impact the boiler efficiency, as boiler working life increases with decrease in the maintenance frequency due to decrease in blockage of boiler tubes. Microwave treatment of coal, reduces the ash resistivity which in turn, enhances the conductivity of fly ash and heat transfer from hot gas to the water inside the heat exchanger tube. Sticking nature of ash on heat transfer surface is reduced. This facilitates easy removal of ash deposits on the heat transfer surface which is deterrent to heat transfer. The magnetic characteristics as well as sintering of mineral matter present in the microwave treated ash enhance the performance of Electrostatic precipitator (ESP) in thermal power plants and reduce the fly ash pollution released in the air around the plant as well.
Thus, the features of this invented novel process can be seen as:
- Single pre-treatment processing of coal and converting the unfriendly matters in to friendly resulting in enhancement of performance of coal including its combustibility.
- Preferably, intermediate size coal is brought under the influence of electromagnetic radiations such as microwaves for the short duration under controlled conditions.
- Electromagnetic waves such as microwaves can be continuous or pulsed or their combination
- Frequency used in this invention 2.45 GHz and 0.915 GHz.
- Process is amenable for batch and continuous operations for commercial exploitation.

EXAMPLES
Apart from GCV, there are two other analytical aspects used for determination of coal properties are 'ultimate analysis' and 'proximate analysis'. The ultimate analysis determines all coal component elements such as carbon, nitrogen, hydrogen and sulphur while the proximate analysis determines only the fixed carbon (FC), volatile matter (VM), moisture and ash percentages. All tests results reported in the following examples are done by using standard ASTM or IS process and number of each specification following which the test performed is fisted in Table 1. The results reported in Table 1 are obtained after conducting microwave trials on the imported coal samples.
Table 2 illustrates the effect of microwave exposure on Indian coal (lignite) with respect to moisture content and GCV (as received coal fraction 3 to 50 mm was used).
Table 3 illustrates the effect of microwave exposure on coal moisture and GCV in the
continuous microwave system.
The examples given below are illustrative of the invention.
A. Batch processing
The process is carried out in Microwave Batch System as mentioned earlier, the cross section view of which is shown in Fig 3/5. Effect of moisture removal at different temperatures with the same soaking time is illustrated in Fig. 1/5. The determination of soaking time at different temperature on the coal is depicted in Fig 2/5.
EXAMPLE 1
During batch trials 1 kg imported coal with total moisture 15.80 %, GCV 5575 kCal/kg and ash content 1.07 % having size fraction of 3 to 50 mm was weighed and placed in the microwave cavity and temperature sensor was inserted in the cavity. CO2 was passed in the microwave cavity. Microwaves at the frequency of 2.45 GHz

are passed in the cavity. The maximum temperature of the coal maintained around 80°C. After reaching this temperature, the sample was soaked for 15 min (till the total moisture is reduced to 5.2%). Then microwave was stopped and sample was removed from cavity. After quarter conning technique the representative sample was drawn and analyzed for other coal properties reported in Table 1.
EXAMPLE 2
During batch trials 1 kg imported coal with total moisture 15.80 %, GCV 5575 kCal/kg and ash content 1.07 % sample in size fraction of 3 to 50 mm was weighed and placed in the microwave cavity and temperature sensor was inserted in the cavity. Microwaves at the frequency of 2.45 GHz are passed in the cavity. The maximum temperature of the coal maintained around 80°C under ambient conditions i.e. without passing any inert gas such as CO2. After reaching this temperature, the sample was soaked for 15 min (till the total moisture is reduced to 7.7%). Then microwave was stopped and sample was removed from cavity. After quarter conning technique the representative sample was drawn and analyzed for other coal properties reported in Table 1.
EXAMPLE 3
During batch trials 1 kg Indian lignite coal sample with initial moisture about 38 to 40 % and GCV 3860 kCal/kg in the fraction of 3 mm to 50 mm was weighed and placed in the microwave cavity and temperature sensor was inserted in the cavity. Microwaves at the frequency of 2.45 GHz are passed in the cavity. The sample generated heat due to interaction of microwaves. The maximum temperature of the coal was maintained at around 90°C to 100°C. After reaching this temperature, the sample was soaked for different durations varying from 5 to 13 min (till the total moisture is reduced to 9.7 %). Then microwave was stopped and sample was removed from cavity. After quarter conning technique, the representative sample was drawn and analyzed for GCV and moisture content and are reported in Table 2.

B. Continuous process
The process is carried out in Continuous Microwave System, the cross section view of which is shown in Fig 4/5. Effect of moisture removal at different temperatures with the same soaking time is illustrated in Fig. 1/5.
EXAMPLE 4
During continuous trials about 15 kg imported coal with total moisture 14.3 % and GCV 5475 kCal/kg sample having size fraction of 3 to 50 mm was conveyed in the microwave cavity through hopper and vibrator. The flow of coal was controlled through the openings of the hopper flaps. The belt speed was set at 12 Hz at which microwave exposure time for coal lumps was 5 min until the moisture content drops below 10 %. However, the bed height of coal maintained almost the same at around 25 to 35 mm. The microwave frequency used was 2.45 GHz. An inert gas such as CO2 with flow rate around 1 nrVh was introduced in the microwave tunnel through a gas inlet port provided near sample inlet point in the tunnel. The coal temperature was monitored with the non-contact type infrared pyrometers. The coal temperature was controlled between 80 to 90°C. The temperature controlling done through PLC based program. The sampling of 15 kg coal after microwave trial was done by quarter conning technique manually and the same analyzed for other coal properties as reported in Table 3 the moisture content was reduced to 7.5 %.
Differential Scanning Calorimetry (DSC)
The thermal analysis i.e. Differential Scanning Calorimetry (DSC) was done on coal samples using a standard instrument and the DSC plot is presented in Fig 5/5. DSC was carried out using 4 mg sample, each, of untreated (as-received) and microwave treated coal. The scanning was done at the heating rate of 10°C /min under ambient conditions. The moisture contents of untreated and microwave treated (at 80°C for an exposure time of 5 min) coals were 16% and 10% respectively. The DSC plot presented in Fig 5/5 shows the rate of heat flow remains almost the same for both the samples up to 360°C. About 360°C, the microwave treated coal heats-up faster and

takes off at a steeper rate covering a much higher exothermic region and higher peak intensity at 430.5°C compared to a fairly small exothermic region with a smaller peak intensity at 389.3°C, followed by an higher intensity endothermic peak about 420°C. This thermogram indicates that the microwave treated coal becomes more reactive and releasing a large amount of heat compared to the untreated sample (see the area under the peak). This is, obviously due to the opening of the pores in the coaly portion as well as the activation of the mineral matters by microwave decomposition which, in turn, acts catalytically and enhances combustion releasing a higher amount of energy.

Table 1: Effect of microwave exposure on coal moisture and other fuel properties (3 to 50mm fraction of imported coal)

Analysis Standard Method/Technique no. As received 80°C -15 min (with inert gas) 80°C -15,
under
ambient
condition
Total Moisture ASTM D 3302 - 09 15.80% 5.24% 7.71%
GCV (kCal/Kg) ASTM D 5865 - 07 5575 6242 6065
Proximate Analysis
ASH ASTM D 3174-04 1.07% 1.17% 1.14%)
Volatile Matters (VM) ASTM D 3175-07 42.75% 51.60% 50.78%
Fixed Carbon (FC) ASTM D 3172-07 40.37% 41.99%) 40.37%
Ultimate Analysis
C ASTM D 5373-08 62.70% 70.00% 68.30%
H ASTM D 5373 - 08 5.83% 5.72 5.68%
N ASTM D 5373 - 08 0.89% 0.86 0.77%
S ASTM D 5016-08 0.39%) 0.3 0.32%
Grindability Index
Hard Grove Index (HGI) IS:4433-1979 48 50 50
Ash Fusion Temperature
Initial
Deformation
temp. (°C) ASTM D 1857-04 1100 1160 1220
Softening temp. (°C) ASTM D 1857-04 1160 1230 1310
Hemispherical temp. (°C) ASTM D 1857 -04 1240 1400 1390
Fusion temp. (°C) ASTM D 1857-04 1300 1490 1480
*A
*IS STM : American Soci : Bureau of Indian Sta ety for Testing & ndard c Materials

Table 2: Effect of microwave exposure on Indian coal (lignite) with respect to
moisture content and GCV

Sample Description GCV (kCal/kg) % Moisture
Lignite Coal (3 to 50 mm fraction) 3860 38-40
Lignite 5 Minutes MW treated at 100oC 3959 31
Lignite 7 Minutes MW treated at 100°C 4448 25
Lignite 10 Minutes MW treated at 100°C 4708 16.8
Lignite 13 Minutes MW treated at 100°C 4873 9.7
Table 3: Effect of microwave exposure on coal moisture and GCV in the continuous microwave system

Coal type Processing temperature
range (°C) Microwave
exposure
(min) % moisture Gross calorific value (Kcal/Kg)
As received MW treated As received MW treated
Imported
(3 to
50mm
fraction) 80-90 5 14.3 7.5 5475 5759
ADVANTAGES OF THE INVENTION
i. The process of the present invention leads to improvement in properties of coal like decrease in the moisture content and increase in the gross calorific value (GCV) of the coal.
ii. By processing coal using the process of present invention, the reactivity of coal leads to more efficient combustion due to which carryover of carbon particles in exhaust along with fly ash is also reduced,

iii. The invented process is less complicated and economical that can be used in the power plant or at the collieries for reducing the transportation cost.
iv. The invented process also reduces the production of fines and the associated fines recovery problem.
v. The increase in the ash fusion temperature will considerably ease the problem of deposition of molten ash on burner tips facilitating smooth and better combustion.
vi. The reactivity of the coal is enhanced due to the catalytic activity of the mineral matter after short microwave exposure in batch or continuous operations.
vii. The reduction in moisture content increases the calorific value proportionately without any losses.
viii. Not bound to the theory we believe that the alpha silica content in the coal which is hard to grind is reduced and converted partially into beta silica form which is soft to grind.
ix. The process of the present invention is eco-friendly as the magnetic characteristics as well as the sintering of mineral matter enhances the performance of ESP in thermal power plant and results in reduction of fly ash pollution in the air around the plant as well.
x. The process of the present invention reduces the ash resistivity which in turn, enhances the conductivity and heat transfer from hot gas to the water inside the heat exchanger tubes (in a boiler). Sticking nature of ash on heat transfer surface is reduced that facilitates easy removal of ash deposits on the heat transfer surface which is deterrent to heat transfer.

We Claim,
1. An eco-friendly, single step process for improving the combustion efficiency of
coal and increasing the fusion temperature of coal ash, the process comprising:
i. providing the coal in the form of lumps;
ii. placing the coal lumps in a microwave cavity/tunnel of the microwave system; iii. exposing the coal lumps to electromagnetic radiations such as microwaves and
maintaining the temperature ' between 70 to 100°C in a non-oxidizing
atmosphere; iv. soaking the coal lumps at the same temperature until the moisture content of
coal drops down below 10% v. taking the coal lumps out of the microwave system to obtain beneficiated coal.
2. A process as defined in claim 1, wherein the coal is lignite, bituminous or anthracite or pet coke.
3. A process as defined in claim 1, wherein the size of coal lumps is 1 mm to 75 mm
and particularly 3 to 50 mm.
4. A process as defined in claim 1, wherein the electromagnetic radiations such as microwaves are either continuous or pulsed or a combination of both.
5. A process as defined in claim 1, wherein the microwave energy used is in the frequency range of 800 to 5000 MHz, preferably between 890 and 2450 MHz and more preferably 2450±50 MHz.
6. A process as defined in claim 1, wherein coal lumps temperature is maintained between 80 to 100°C during microwave exposure.
7. A process as defined in claim 1, wherein the non-oxidizing atmosphere comprises of gases such as nitrogen, carbon dioxide or dust free and moisture free flue gases without any contaminants.

8. A process as defined in claim I, wherein coal lumps with total moisture content of 15.80 %, GCV 5575 kCal/kg and ash fusion temperature 1300°C having size fraction between 3-50mm are placed in the microwave cavity and exposed to electromagnetic radiations such as microwaves in the presence of CO2 and the maximum temperature is maintained at 80°C and then soaked for 15 min till the total moisture is reduced to 5.2% to obtain beneficiated coal having coal ash fusion temperature 1490°C.
9. A process as defined in claim 1, wherein coal lumps with total moisture 14.30 % and GCV 5475 kCal/kg having size fraction of 3 to 50 mm are placed on conveyor belt in the microwave tunnel and exposed to microwaves frequency of 2.45 GHz in the presence of CO2 and the temperature is maintained between 80 to 90°C and then soaked for 5 min till the total moisture is reduced to 7.5% to obtain beneficiated coal.
10. An eco-friendly, single step process for improving the combustion efficiency of coal and increasing the fusion temperature of coal ash substantially as described in the text and examples.