Experimental Study On The Mechanical Compression Dewatering Of Bagasse Pith

Bagasse is one of the main by-products of cane sugar production, and a kind of renewable resource which is rich in fiber. Its production is huge, cost is low, and source is centralized, having a wide range of application. Most of the bagasse of sugar mills in China is delivered to the boiler for burning as fuel. The rest is packaged for sale, mostly used for papermaking. So the bagasse depithing process is adopted by most of sugar mills. The bagasse pith acting as fuel is delivered to boiler, and the shortage can be compensated by the undepithing bagasse. The depithed bagasse is packaged for sale. With the energy-saving and emission reduction technology of sugar mill in China, the standard coal consumption of sugar production has been reduced to below 4%, accordingly, the package rate of bagasse has reached more than 11%. So the sugar mills only need to burn the bagasse pith, which can meet the demand of sugar production. The moisture content of bagasse is about 50%, after bagasse depithing, the bagasse pith still contain high moisture, which will affect the thermal efficiency of boiler and is also adverse to its long-term preservation. Therefore, the dewatering of bagasse pith is very necessary.Dewatering methods include thermal drying and mechanical dewatering. For a long time, the technology of using flue gas has been deeply investigated, which has also achieved certain achievements. But the mechanical dewatering of bagasse has little been studied yet. Mechanical compression dewatering is the process that forcing the water contain in the bagasse pith to drain away in liquid state through mechanical c ompression at normal temperature. The dewatering process can basically keep the natural of the material itself, the result of dewatering is good, and the energy consumption is relatively low.In the paper, the dewatering of bagasse pith by compression dewatering was investigated. Firstly, in order to evaluate the feasibility of the compression dewatering of bagasse pith, the particle properties, the compression characteristics, and the characteristics of permeate flow resistance of bagasse pith were studied. Secondly, compression dewatering experiments of bagasse pith were carried out to investigate the compression dewatering process, so that it could provide a valuable reference for technical schemes and process methods, laying the foundation for its industrial application. The research contents and results are detailed as follows:1. The industrial analysis of the bagasse and pith was carried out. It was found that the air-dried moisture of bagasse pith was two point four times higher than that of depithing bagasse, the ash content was two times higher than that of depithing bagasse, but the content of volatiles and fixed carbon were slightly lower. The analysis of the particular properties of the bagasse and pith showed that the particles of bagasse and pith had all sizes and shapes, while most of them were in spindly slabs. The pith particle was much smaller than the bagasse. The particle size between 1.5 cm and 4.0cm was 71.9% in the bagasse. The particle size of pith between 0.3mm and 3.2mm was in the majority, being more than 84%. The mass percentage of the particle with the size over 3.2mm was only 5.3% in the bagasse pith.2. In order to study the effects of pressure and particle size on the compression density of bagasse pith and investigate the compression characteristic of it, compression experiments on bagasse pith for boiler and pith in different particle size were carried out, using a compression device. The results showed that within the pressure range of the experiment, the compression density of bagasse pith increased exponentially with the increase of pressure. The compression density of bagasse pith decreased with the increase of particle size under the same pressure. The compression density of bagase pith for boiler varying with the pressure could be described as:For different particle size, the compression density of bagasse pith varying with the pressure could be described by:3. Experiments were carried out on a self-designed and installed device for measurement of flow resistance to investigate the seepage resistance characteristics of bagasse pith, through measuring the flow velocity of fluid flowing through the bagasse pith in the different particle size and void rate. The results showed that when other conditions were constant, the flow velocity of fluid flowing through the bagasse pith increased with the water pressure. Under the same pressure and the void rate of bagasse pith, the smaller the particle size of bagasse pith, the lower the flow velocity of fluid, namely, the flow resistance was greater. When the water pressure and the particle size of bagasse pith was constant. The bigger the void rate, the greater the flow resistance, and the flow velocity was faster. A simplified model based on the Darcy law was developed, through the regression of the experimental data, a model describing the fluid flow through the bagasse pith in different particle sizes and void rates under different water pressures was established as:4. Experiments were carried out to investigate the effects of pressure and particle sizes on dewatering the bagasse pith, including the final moisture content and the dewatering velocity. The results showed that within the pressure scope of the experiment, the final moisture content of bagasse pith decreased with the increase of pressure, falling rapidly when the pressure was less than 6MPa, the decreasing trend slowed down from 6MPa to 10MPa, and the moisture content decreased obviously again after 10MPa. When the pressure was constant, the final moisture content of bagasse pith increased with the particle size of it, increasing rapidly when its particle size was less than 1.125mm, and slowing down after the particle size was more than 1.125mm. In the process of compression dewatering, the fitting equation of the final moisture content of bagasse pith in different particle size varying with the pressure was as follow:On the other hand, when the pressure was constant, the dewatering velocity of bagasse pith decreased with the increase of time, which fell rapidly at first, then slowed down. Namely, the process could be divided into two stages. And the boundary was around 50 seconds. The dewatering velocity nearly dropped vertically before the 50 seconds, the decreasing trend gradually became smooth after 50 seconds, and close to horizontal after 200 seconds. At the same time, the higher the pressure, the faster the dewatering velocity, and the gap was narrowed over time. And the smaller the particle size of bagasse pith, the faster the dewatering velocity in the same time.