This confirms that the thesis entitled "DRY COMBINERATION OF HIGH ASH NON-COKING COAL USING AIR-DENSE MEDIUM FIXED BEDS" submitted by Sri Asish Kumar Sahoo partially fulfilled the requirements for the degree of Bachelor of Technologist in Chemical Engineering. at National Institute of Technology, Rourkela (Deemed University) is an authentic work done under my supervision and guidance. Despite the many quotations provided, the author assumes full responsibility for the content that follows. 1 Forces acting on a spherical coal particle in an ADMFB 9 2 Schematic representation of an experimental air-dense medium 13.
In this project, dry beneficiation of high-ash non-coking coal was carried out using an air-dense medium fluidized bed. The dynamic stability of the bed, which plays an important role in the sharpness of separation, was also investigated. Key words: air compacted medium fluidized bed, dry coal beneficiation, dynamic stability of the bed, coal beneficiation.
The benefits of non-coking coal in India did not gain due importance until the past decade due to its low value or inability to cover the cost of the process. The demand for water and pollution have opened up the space for research into the development of the coal dry cleaning process. Hand-picking gangue minerals or coarse-sized shales is one of the simplest, oldest, and labor-intensive techniques of dry-cleaning processes.
Airtight medium fluid bed separation is one of the dry beneficiation processes that would provide advantages compared to other dry beneficiation processes. The results of economic evaluation for various processes are given in Table-2.
AIR DENSE MEDIUM FLUIDIZED BED BENEFICIATION (SEPARATION) PROCESS--(ADMFB PROCESS)
PRINCIPLE OF AIR DENSE MEDIUM FLUIDIZED BED SEPARATOR
An airtight medium fluid bed separator was designed and tested at the Institute of Minerals and Material Testing lab, (CSIR) Bhubaneswar, India in 2003 for high ash Indian non-coking coal in the -25+6 mm size range. In the optimal condition, the ash percentage of the feed could be reduced from 40 to 34% with 70% product yield. It has been reported that adding fine particles to a bed of small particles improves fluidization quality by increasing the minimum bubble velocity and the extent of particle expansion.
Between minimum fluidization and minimum bubble velocity, a fluidized bed of fine powder may exhibit particle expansion to a large extent. The current state of progress in determining the theoretical criteria for the transition from particle fluidization to aggregate fluidization has been described by various mathematical forms amp; 6. In this investigation, an experiment was made on fluidized bed stability using magnetite fine powder with air in a fluidized bed separator with a dense medium in particle behavior.
The concept of this was later applied to the beneficiation of non-coking coal in the dry process.
MATHEMATICAL EQUATIONS FOR CHECKING DYNAMIC STABILITY OF ADMFB
The quality of the particle fluidization can be predicted using the following expression (Froude number) (Reynolds number) (bed aspect ratio) (density ratio) <100. The plot of є3/1- є against superficial air velocity gives a straight line on a logarithmic plot which will determine the dynamic stability of the bed.
SEPARATION MECHANISM WITH AIR DENSE MEDIUM FLUIDIZED BED
It is the liquid-like properties of the airtight medium fluidized bed that separates the heavy and light particles. The pressure drop between two points in the bed is almost equal to the difference between the hydrostatic heads of head of the same points, .. c) The bed exhibits pseudo-liquid flow characteristics. Pseudo-liquid characteristics in an airtight fluidized bed separator form a stable and uniform gas-solid suspension with a certain bulk density in which light particles float and heavy particles sink in the suspension medium.
The Archimedes principle is generally referred to to explain the mechanism of separation of coal particles in ADMFBS. Therefore, movement of the medium solids should be considered to study the separation mechanism in ADMFBS. Fb= effective buoyancy force exerted on the coal particle, Newton Fgd= frictional resistance force from gas exerted on the coal particle, Newton Fsd= air resistance force of airtight medium exerted on the coal particle, Newton ρc= density of the coal particle, kg /m3.
Ur= relative velocity between coal particles and dense medium particles, m/s Since the diameter of a coal particle is much larger than that of the medium solid, the friction drag of the gas exerted on coal particles can be neglected. Ut is the terminal velocity of coal particles in a fluidized bed when there is no relative motion between the coal particle and the medium. When Ur is 0, i.e. there is no relative velocity between coal particle and liquid medium, acceleration a=(ρb −ρc)g/ρc the coal particles can be perfectly separated according to the bed density,.
The position of the coal particles in the bed depends on the relative velocity between the coal particles and the medium solids. Separation efficiency is generally determined by the movement of coal particles (ie, viscosity misalignment effect) and the average solids velocity (movement misalignment effect). At very low gas velocities, the activity of the medium solids is weak, which results in a higher misalignment viscosity effect.
Furthermore, when the medium of solids is not well dispersed and gas cannot be distributed uniformly in the bed, the misplaced effect of movement is also greater in some areas of the bed. At too high a gas velocity, back-mixing of the medium solids caused by gas bubbles is enhanced and the misplaced effect of movement will also be enhanced. As coal size decreases, the specific surface area increases and the terminal velocity of coal particles decreases, resulting in an increase in the ratio of resistance to gravity exerted on the coal particle and increasing the misplacement effect of both viscosity and movement.
MATERIALS AND UTILITIES
EXPERIMENTAL SET UP
Bed expansion was studied at different air flow rates until minimal bubbling in the bed started. Bed density at different air flow rates and corresponding voidage were determined using the measurement parameters of expansion bed height, true solidification density, and sample weight. Table-4 Bed height vs air flow rate for different amounts of 100µm magnet powder in 50mm configuration.
Table-5 Bed expansion vs bed density for varying amounts of 100µm magnetite powder in 50mm setup. After a uniform and stable ADMFB was formed, the coal of given size was put into the fluidized bed. After the separation of magnetite, the ash of the coal samples from four equal bed heights.
This was repeated varying the airflow rate and the size and amount of coal and magnetite. In the primary design (Fig. 4), during sample collection, a significant amount of fine dust entered the suction line connected to the vacuum pump, clogging the pump. So to rectify this, the collection design was modified (as shown in Fig. 5) so that instead of entering the suction line, the fines were held back above the cotton wrapper.
INTERPRETATION OF EXPERIMENTAL DATA
- STUDY OF DISTRIBUTOR BEHAVIOUR
- BED STABILITY ANALYSIS IN 50 MM DIA SETUP
- BED STABILITY ANALYSIS IN 100 MM DIA SETUP
- COAL ENRICHMENT ANALYSIS
Fig-9(a) Bed expansion versus bed density for Fig-9(b) Bed expansion versus bed density for 100µm magnet 80µm magnet. Further for the 100µm magnetite, more uniform curves (straight lines) are obtained when bed extent is plotted against bed density (fig. 9(a)). It shows that the expansion of the bed is linear at different amounts of magnetite powder, therefore the system is in a bubble-free state.
Fig-10(a) Fluidization characteristics for 100 µm Fig-10(b) Fluidization characteristics for 80µm magnetite in 50 mm dia setup magnetite in 50 mm setup. Again, the properties of the fluidized bed were investigated using equation (6) and the plot of є3/1- є against superficial air velocity gives a straight line on a logarithmic plot. c).For 100µm magnetite, the converging trend indicates that the Fig- 10(c) Fluidization characteristics for 60µm system operates in non-bubble. To see the effect of diameter on bed stability and subsequently on refinement, the larger dia (100mm) fluidized bed was used for a mixture of coal and 100µm magnetite powder in different amounts.
As can be observed for 100 mm dia setup almost constant bed heights are obtained for air flow rates in the range 25-50 lpm. Furthermore for 100µm magnetite powder the bed expansion vs bed density plot (Fig-12) and Fluidization characteristics plot (ln(є3/1- є) vs. Similarly the minimum fluidization velocity for the bed (coal + magnetite) was calculated as Umf =0.784 cm /sec =0.923 lpm and checked for particle fluidization.
The different coal samples were taken by varying Wc/Wm, dpc/Dt, dpc/dpm and (Gf-Gmf)/Gmf. The magnetite particles of the samples were separated by magnetic separation and the coal samples were subjected to ash analysis. The ash content of the above coal samples after dry enrichment is given in Table 7 from which the percent enrichments were calculated using equation (16).
RESULTS AND DISCUSSIONS
DEVELOPMENT OF CORRELATION
From the dimensional analysis approach, the above equation can be represented in terms of dimensionless sets as. Where a, b, c, and d are the individual group exponents calculated from log-log plots of E vs. Now, the rest of the experimental enrichment data (besides the use for the correlation calculation) was used to verify the above correlation.
The enrichment values calculated from the above correlation were compared with the experimental values of enrichment (fig.19) and fairly good agreement was found.
DISCUSSION ON RESULTS AND CONCLUSION
Based on the above considerations, coal and magnetite particles of sizes 1 mm and 100 µm respectively in the volume ratio of 2:1 with 30 times the minimum fluidization rate have been found to be effective for enrichment in a fluidized bed with a diameter of 50 mm, which reduces the ash content of the coals of Mahanadi coal fields ltd, Ib Valley, Brajrajnagar from 43.9%.
POTENTIAL APPLICATION OF THE PRESENT PROJECT WORK