Analysis And Experimental Study On Process Chain Of Rice Husk Carbonization In Cross-flow Packed Bed

As a typical agricultural product residue in China,rice husk has many ways of utilization.The current utilization of rice husk is mainly as fuel and to provide heat energy.Rice husk is a kind of biomass fuel with high ash content and rich in chlorine and potassium.The main component of ash is silica.It is easy to form silicon carbon complex under high temperature conditions which makes the rice husk hard to burn out.Chlorine and potassium are easy to induce corrosion and clogging of the heating surface of the boiler during the combustion process.Potassium easily forms slag in the bed,resulting in instability of the bed structure.Carbonization-combustion method can effectively solve a series of problems such as hard-to-burn,blocked ash on heating surface and slagging in the bed.Rice husk char is a valuable biochar product.In this paper,the experimental study on the carbonization process of rice husk in the cross-flow packed bed was carried out.The carbonization process was analyzed according to the experimental results.The main work contents and conclusions are as follows:(1)Experimental study on carbonization of rice husk under inert atmosphereA laboratory bench was set up to study the carbonization products of original rice husk granules and the migration of potassium and chlorine under inert atmosphere.The experimental variable were temperature and time.The results showed that potassium and chlorine in rice husk gradually precipitated into gas phase products during carbonization.Most of chlorine had been precipitated at 400 ℃,and the release amount increased rapidly with the increase of temperature.The amount of chlorine precipitation was positively correlated with the amount of volatile precipitation.The precipitation of potassium elements was concentrated in the two ranges below 400 ° C and above 700 ° C,and the total release rate was lower than that of chlorine.The precipitation characteristics of potassium were consistent with the trend of using rice husk powder as material in the existing literature,but the precipitation data had obvious differences,which confirms that the particle morphology had a significant effect on potassium precipitation.(2)Experimental study on carbonization of rice husk in internal combustion fixed bedA laboratory bench was set up to determine the flame spread speed of rice husk fixed bed under different air flow.The results showed that the flame spread speed was proportional to the air flow.The tested rice husk sample obeyed the relationship: v=0.722 Q’-0.0118(unit:mm/s).The carbonation products of rice husk fixed bed were determined,and the retention rate of potassium and chloride in the rice husk char under different air flow conditions was obtained.The results showed that the oxygen-containing atmosphere promoted the release of potassium and chloride to some extent during carbonization process.The retention rate of potassium and chloride was significantly different in the height direction of the bed,which proved that the potassium and chloride released under the bed may be trapped in the upper area of the bed.(3)Numerical calculation of temperature field of rice husk carbonization process inside the cross-flow packed bed.Based on the measured data of the flame spread speed of the rice husk fixed bed,a calculation model was established for the carbonization process of the cross-flow packed bed,and the temperature in the bed under different working conditions was calculated.The calculation results showed that the inner part of the bed of the cross-flow packed bed was mainly divided into three parts: the unreacted area,the ignition area and the carbonized area.The temperature of the unreacted area and the carbonized area was basically balanced,and the ignition area was very thin and had a very high temperature gradient.The calculation results showed for the first time that the cross-flow bed of rice husk carbonization had a different inner bed structure from the classical chain grate fire bed.(4)Sampling and analysis of rice husk carbonization process in cross-flow packed bedFor the actual industrial operation of the rice husk cross-flow packed bed carbonization furnace,the cross section of the tail of the bed was sampled by grid and the sample was tested.The results showed that the internal carbonization process of the bed was not balanced,and the potassium retention rate in the bed fluctuated greatly in the horizontal direction.The average potassium retention rate at the same height can reflect the enrichment of the bed.Especially,the enrichment effect was obvious under slow air flow,which indicated that the lateral air distribution uniformity of the bed had a decisive influence on the practical application of the rice husk carbonization process in the cross-flow packed bed.