Study On High Voltage Pulse Underwater Discharge Enabled Raw Coal Desulfurization And De-ashing Technology

Coal is the “ballast stone” of China’s energy supply and an important industrial raw material.Despite the great progress of renewable energy,coal remains irreplaceable.However,the environmental pollution and climate change caused by the combustion and processing of low-grade coal without desulfurization and deashing have become increasingly severe.Mineral matter in raw coal account for the bulk of sulfur and ash in coal.Therefore,the key to efficient desulfurization and deashing is the efficient liberation of mineral matter from coal.Raw coal usually requires to be comminuted to finer particle size to achieve a high degree of mineral liberation from coal in conventional methods because of the growing intensity of China’s coal mining and the general reduction of coal washability in recent years,which further gives the rise to deterioration of coal processability,the increase in energy consumption and aggravation of dust pollution during the crushing process.This paper proposes a novel technique for desulfurization and deashing of raw coal based on high voltage pulse underwater discharge followed by size-based separation by introducing the selective breakdown method.The feasibility and effectiveness of the novel technique are validated.The major research contents and innovations of this paper are as follows:An experimental platform based on a high voltage pulse generator and a processing vessel with discharge electrodes is established.The synthetic samples are used in preliminary tests to simulate raw coal.The preliminary tests validate the capability of the experimental platform to implement selective breakdown of mineral-rich particles.It is verified the designed annular-plate electrode has advantages in aspects of reinforcing operational efficiency,improving selective breakdown precision,eliminating the state differences of feed particles,decreasing the pulse energy consumption by producing a more uniform electric field.This paper utilized pre-separated high-grade and low-grade coal particles as experimental samples,the high voltage pulse selective breakdown characteristics are investigated.The paired-particle tests accomplish ≥75% selective breakdown probability of mineral-rich low-grade coal particles.In addition,both de-ionized water and tap water are used as the liquid medium.The universality of the selective breakdown of low-grade coal particles is validated by the experiments of raw coal from three origins with different feed sizes,which provides a crucial fundamental for the desulfurization and deashing technique of raw coal based on high voltage pulse selective breakdown.The general mass distribution patterns of raw coal particles after selective breakdown are obtained and the corresponding factors of high voltage pulse experimental conditions by studying the experimental conditions and product characteristics of paired-particle tests.The Back Propagation Artificial Neural Network(BPANN)algorithm is introduced to fit the paired-particle tests data,which studied the influence of generator specific energy and average electric field on breakage outcome.The optimization of the high voltage pulse experimental conditions by the BPANN on the selective breakdown of low-grade coal particles lays the foundation for the multi-particle method.The finite element method models of electrostatic field and electro-quasistatic field are established according to paired-particle tests scenario.The contributions of the electrode structure,permittivity,and conductivity of mineral matter on electric field distribution are studied,which provides the theoretical elucidation of selective breakdown.Furthermore,the decisive factors that affect the extent of electric field distortion inside the raw coal particles are analyzed,which uncovers the connection between ash content and selective breakdown effectiveness.Moreover,a Finite Difference Method(FDM)based Dielectric Breakdown Model(DBM)is constructed to simulate the breakdown process of three origins of coal particles during the tests,the obtained breakdown selective probability shows great agreement with experimental results.The multi-particle tests proved the feasibility and effectiveness of the proposed technique in this paper: 70% of desulfurization and deashing can be achieved with the rejection of 45.9% and 50.7% undersize mass,separately.It has significant effects on energy saving,emission reduction,and efficiency enhancement.Besides,the trait of better sulfur pre-concentration performance than ash in coal by high voltage pulse is discovered.The comparative study explains the function of improved carbon recovery rate and washability in the multi-stage method compared with the single-stage method.It is found that tap water will not significantly decrease the operational efficacy by the tests that repeated three times of three coal origins,which paves the way for industrial uptake of the technique.The average generator specific energy of multi-particle tests is 3.0 k Wh/t,which is close to a typical toothed roller crusher,but evidently lower than comminution.The relation between coal particle features and operational efficacy is found by the experimental study: The pyrite content plays a pivotal role in desulfurization and deashing efficacy.