| The sugar cane factories in Guangxi produce more than one million tons of filter mud per year,which is a large byproduct of the sugar industry.The most common way to dispose the sludge from sugar mills is to sell it to farmers as basic fertilizers at a low price.The comprehensive utilization rate of filter mud is not high and the economic efficiency is low.However,the filter mud has actually good applied value and development potential,which has wide processing applications in many fields and in many ways.The high water content of the filter mud limits its processing and comprehensive utilization,wasting the full use of resources while imposing a burden on the sugar industry and the environment.Deep dewatering and drying of mud,on the one hand,can further recover the sugar containing in the mud and reduce the loss of sucrose.On the other hand,it prevents the mud from fermenting and polluting the environment while facilitating storage and long-distance transportation.It provides possibilities for the development and utilization of the mud.The thermal press filtration dehydration technology combines mechanical dehydration with thermal dehydration,which has advantages over traditional mechanical dehydration and requires less energy consumption than thermal dehydration.The current project combines thermal press filtration and high pressure expression using fly ash as filter aid to dewater the filter mud,developing a new way of deep dewatering of filter mud.Experimental investigation is carried out to study the characteristics and mechanism of the dehydration and the process conditions.The experimental research content and results are as follows:1.As the existing membrane filter press has the deficiency of operating temperature under 80 ? and low diaphragm expression pressure,a novel filter press with high pressure expression is developed which can withstand the temperature as high as 100? and have the expression pressure as high as 40 MPa.An experimental rig based on the filter press was established.2.The influence of the dilution factor of filter mud on the dewatering effect was studied.The filter mud was diluted at multiple times with hot water and constant pressure filtration experiments were conducted.The experimental results show that the filtration constant K of the filter mud increases with the increase of the dilution factor.After the sludge was diluted,it was press-filtered and then expressed.The water content was greatly reduced,and the dewatering effect was significant.The moisture content of the filter cake was under 47.68%and the lowest was 38.32%.When the minimum dilution of filter mud was 3 times dilution,the filter cake had the highest moisture content.The filter cake had the lowest moisture content when the sludge dilution factor was 6 times.When the dilution ranged between 3 times and 6 times,the water content of the filter cake decreased with the increase of the filter dilution factors.When the dilution ratio increased over 6 times,the water content of the filter cake showed a slight increase and became stable.3.The effect of temperature on the dewatering characteristics of the filter mud was studied.By setting the temperature gradient,the filtration characteristic curve of the filter mud at different temperatures and the moisture content of the filter cake were determined.The variation of filter mud compressibility index with filtration temperature and the relationship between the dehydration effect and temperature were studied.The experiment shows that the compressibility index of the filter mud decreased with the increase of temperature,and the compressibility index decreased greatly from 80? to 90?.From 90? to 95?,the compressibility index decreased insignificantly.The compressibility index of the sludge was about 0.36,which is referred to as the medium compressive material.The moisture content of the filter cake was measured.It was found that as the temperature increased,the moisture content of the filter cake gradually decreased,and the minimum moisture content reached 37.79%.4.Based on the determined the optimal dilution factor and filtration temperature,experiments of filtration with fly ash as the filter aid were performed to study the effects of addition ratios of 3.33%,6.67%,10%,13.33%and 16.67%on the dewatering.The water content of the filter cake decreased more obviously when the mortar of fly ash was used.When the ratio is between 10%and 16.67%,the moisture content shows a slight upward trend.It shows that proper addition of filter aids can effectively improve the filtration efficiency,and excessive addition of filter aids will have adverse effects.The experiment of filtration characteristics of different addition ratios showed that the addition of fly ash can effectively change the filter cake structure and compressibility index and improved the filtration efficiency.The compressibility indexes of the cakes were 3.396,0.2838,0.2528,0.2312,and 0.2014 when the addition ratios were 3.33%,6.67%,10%,13.33%,and 16.67%,respectively.The compressibility index of sludge decreased with the increase of additon ratio.Scanning electron microscopy was performed on cross-sections of filter cakes with different additon ratios.The fly ash particles were microporous,irregular mass,flake-like or strip-shaped small particles,and the fly ash particles were irregularly distributed in various sizes.The holes made the fly ash light and loose.Therefore,the fly ash has a certain supporting structure and at the same time has both physical and chemical adsorption,showing good filter aid characteristics.When the addition ratio is between 0 and 10%,the internal structure of the filter cake was changed by the characteristics of large particles,strong adhesiveness,few filtrate channels,and small particles,orderly arrangement,and multiple and wide filtrate channels.The filter cake is loose and porous,the compressibility index is reduced,and the filtration and dehydration efficiency was increased.After the addition ratio was more than 10%,the solid particles were fine and the filter cake structure gradually becomes dense.The filtrate channel was fine,which was not conducive to filtration and dehydration.5.A mathematic model was established to describe the expression dewatering rate of the mud.Based on Darcy's theory,a macro one-dimensional mathematic model for expresion dewatering rate was established.The model reflected the expression process,and the variation of moisture content on the dry basis of the sludge over time was:(1+?r/X?)2 ln Xo(X-X?)/X(X0-X?)+2?r(?r+2X?)/X0X?X0-X/X+3?r/X02X02-X2/X2=X?KS2(P-P0)/?(X0+X?)tThe comparison between the experimental data and the predicted values of the model shows that the calculated values of the model is in a good agreement with the experiment data,the average error between the calculated values of the model and the experimental data is 8.5%. |
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