| Municipal sludge(sludge) is consisted by floc matrix with abundant filamentous bacteria, zooglea, extracellular polymeric substances(EPS) and plenty water in it, which presents gel-like. Moreover, a lot of inorganic and organic substances including toxic and harmful chemicals are also the components of sludge. Due to the development of wastewater treatment industry, the output of sludge is increasing year by year. In order to avoid the secondary pollution from sludge components, such as difficult degradational organic pollutants, heavy metals, pathogenic microorganism and parasites, the environmental and efficient treatments and disposals of sludge are needed. For the sake of heat value and water content in sludge, coal sludge slurry(CSS) based on coal water slurry(CWS), is developed. As a potential fluid fuel, the CSS can be used in existing boilers and gasification equipment of CWS. Meanwhile, the recycling of sludge as energy environmental friendly can be achieved.SEM with modified pretreatment, FTIR and TG-DSC were used to test the characteristics of three kinds of sludge from different regions. The influences of heat drying and mechanical force on the water content of sludge were comprehensively studied. An orthogonal experiment about co-slurrying was carried out to deeply systematic study the slurryability, heat value and rheology of CSSs. To avoid the collapse and destroy of floc structure in sludge after water running out by traditional pretreatment, the modified pretreatment of sludge can keep the origin micromorphology as much as possible without the influences of temperature and drying process. Dried basis samples and raw wet samples were selected to test the different water contents' effects on sludge combustion. Sludge inhibited high fix-viscosity concentration(CFV), more sludge in slurry system led to lower CFV. When sludge mixing proportions were increased from 5% to 20%, the CFV of FSWN CSSs were decreased from 50.78% to 46.55% and that of XZWN CSSs were decreased from 50.35% to 44.40%. The CFV of dry sludge did not show the same trend and the range of CFV were 53.35% to 52.42% and 53.33% to 51.51% for FSGWN and XZGWN, respectively. Water content and its occurrences were the prominent factor for low CFV,which were beyond the influences of differences between sludges from two regions. CSSs shown shear-shinning behaviors with unclear fluid pattern in shear rate going up state and Bingham plastic fluid pattern in shear rate going down state. In the research, all CSSs achieved or were closed to the heat requirement of commercial CWS and the highest heat value was 14.169MJ/kg. And after shearing, CSSs had bigger yield stress than CWSs and nearly the same plastic viscosities. Based on the steric stabilization theory and fractal theory of colloid chemistry, the concept- “combined sludge coal particles(CSCP)” and its formations and properties, were proposed to analyze the effect of sludge in CSS.Single factor parallel experiments were adopted to research on the mechanism of CSCP detailedly. When sludge mixing proportion was 5%, 10%, 15% and 20%, the corresponding highest CFV was 67.73%, 65.80%, 64.00% and 61.05%, respectively. Dense dispersion theory and DLVO theory were used to analyze the characteristics of slurry. The influences of detrimental impurities in slurry system were studied by the tests or calculations based on solid-fluid chemistry, adsorption process, kinetics of adsorption and interfacial energy between particles. After the adsorption of dispersant, the electronegativity on the surface of sludges and detrimental impurities were strengthened by increasing pH value, and the biggest decreasing value of isoelectric point was 0.551 of FSWN. Isothermal adsorption of dispersant on sludges surfaces followed the Langmuir adsorption model with S pattern, and the extent of saturated adsorptions were 7.61, 7.98 and 8.63mg/g for FSWN, XZWN, LCWN, respectively. The extent of saturated adsorption of quartz was 20.38mg/g, but the other two minerals did not achieve the saturated adsorption state in experiment condition. The adsorption of dispersant by sludges were belong to different kinetic adsorption patterns associated directly with the dispersant properties and loose structures of sludge particles. The calculation of interfacial energy of detrimental impurities shown that due to smaller particle size they were inlaid in the interspace of coal-dispersant frameworks. The Van der Waals' force repelled impurities and coal particles, where also had energy barrier and critical distance caused by electrostatic potential energy. The proof tests shown that adding more dispersant can weaken the influences of detrimental impurities on co-slurrying to a certain extent to increase the slurryability.To understand the influences of chemical disintegration on water content and CSS, sludges were modified by different alkalis. The analysis of orthogonal experiment shown that the biggest CFV of coal modified-sludge slurry(CMSS) is 66.95% and the modified effect of NaOH was the best one. All the CMSSs had good rheological behaviors. Comparing the differences of CMSSs modified by Ca(OH)2 and CaO to NaOH and KOH, the CMSSs with Ca2+ had no yield stress. The characteristics of modified sludge were measured through TG-DTG-DSC, FTIR and Zeta potential. SEM-EDX was used to test the fixed point of organic substances in order to check the migration of carbon elements before/after modifying. The temperature of water escaping from sludge was increased after modifying, but the rate of escaping was decreased with the amount of hydroxyl reducing and Zeta potential enhancing. The alkalis destroyed the cells of organism and plenty of water coming into the slurry system with carbon element uniformly distribution. The modification of sludges by alkalis changed the ability to form CSCP, which was the main reason for different characteristics of slurrying between CMSSs and CSSs.CSSs and corresponding CWSs were made by wet-grinding process of ball mill to study the slurryability, rheology and particle size distribution(PSD) deeply and analyzed the mechanism of CSCP. The influences of sludge on particle size were systematic calculated and analyzed. And the results shown that sludge can increase the amount of fine particles. To CSSs, the time of wet-grinding played more effects than dispersant amount, conversely to CWSs. The research on median diameter(D50) of particles shown the same law too. The smallest D50 of CSSs was 17.67?m, while the number in CWSs was 26.21?m. The calculation shown that the PSD of CSSs were up to Alfred model, but the accumulations were lower than sphere particles'. Additionally, CSCP theory can roundly explained the stability of CSSs from three aspects, for example, organic substances as EPS, inorganic electrolyte and minerals particles. |
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