370 each component can be adjusted to reflect actual performance under plant conditions. After establishing the efficiencies for each component of CPP, the LIMN model can simulate beneficiated products. Once each CPP component is added in sequential order, the LIMN model simulates how a coal feed will beneficiate through the set design. LIMN model uses the principal of incremental quality, which is defined as - clean coal yield for parallel operations is highest when all circuits are operated at the same incremental ash. This concept, which has been long recognised in coal preparation. There is ash controllers in the LIMN model to control the RD within design ranges to achieve a specified ash percentage per product stream. LIMN model uses process design criteria (PDC) assumptions as input parameters. LIMN models are robust as component(s) can be added or removed from the flowsheet to test design configurations or possible modifications [8]. The data that feeds into a LIMN model is the washability data (i.e. float & sink data) of raw coal for different size range to be fed to the CPP. The LIMN model can generate the washability data of the size fractions as per the flowsheet, even if the actual washability available is for different size fractions [8]. Figure 3- Process flowsheet of New Bhojudih Washery In the proposed flowsheet, screening of -50 mm coal is done at 10 mm and deshaling of 50 + 10 mm coal is done to in Jig to remove the shale before feeding to washery; re-crushing of Jig floats to 10 mm and mixing of natural -10 mm; Classify the crushed coal into coarse, fine and ultra-fine fractions as -10.0 +1.0 mm, -1.0 + 0.25 mm and -0.25 mm sizes; beneficiation of -10.0 +1.0 mm coal fraction in Dense Media Cyclone (DMC) in two stage due to high NGM value for sharp separation; in first stage beneficiation is done at lower gravity to obtain float (clean coal ~18% ash) & sink ; rewashing of sink in second stage at higher gravity to obtain middlings (ash < 40%) and rejects; beneficiation of -1.0 +0.25 mm in Reflux Classifier is obtain fine clean coal & middlings; beneficiation of -0.25 mm in Column flotation cell to obtain clean coal & rejects. The top size of feed is selected as 10 mm size for improving the liberation and washability as finer crushing helps in distribution of NGM to higher gravity section. The variation of NGM with cut density for coal of top size as 13 mm (plot-1) and 10 mm (plot-2) is shown in Figure 4. It can be seen that NGM decreases from 49% to 38% (for 18.0% ash), shows that liberation characteristics has improved on crushing to 10 mm size instead of 13 mm.
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