The Effects Of Pretreatment To Straw Ash Characteristics And Straw Combustion Characteristics

Biomass fuels,a renewable energy,have earn more and more focus worldwide.Biomass fuels have the characteristics of resources widely distributed,CO2 zero emission,low sulfur,low pollution,easy to ignite and so on.As an agricultural country,our country is rich in biomass fuel,so the development and utilization of biomass play an important role in China's energy strategy and environmental protection.However,plenty of alkali metal elements contained in the biomass fuels,such as potassium,sodium,silicon and mineral elements,chlorine,sulphur,etc..These elements produce a complex physical and chemical reaction in the process of biomass combustion,generate low melting point compound or eutectic,and then lead to serious slagging,deposition,agglomeration,and high temperature corrosion of combustion equipment,which seriously hinder the large-scale use of biomass.Therefore,choosing the right way of removing ash pretreatment,will improve melting ash properties of the biomass fuels,inhibit the slagging of the biomass fuels,which have an important significance to promote the scale utilization of biomass fuels.In this experiment,two typical crop straws,wheat straw and rice straw,were chosen as research objects.And XRF fluorescence analyzer,XRD diffraction analyzer,ash melting analyzer,etc.were used to explore the composition and melting characteristics of the oxide in the two kinds of straw ash,and to prejudge of slagging.It was found that the alkaline oxide in the two kinds of straw ash was about 36% and 30%,alkali metal element K was mainly existed in the form of KCl,and the results of prejudgement both have serious slagging tendency.As straw ash has the problems of high alkali content,easy slagging and so on,washing and pickling were adopted to reduce certain elements content in straw ash,then to study the ash fusion characteristics and to prejudge of the slagging results.Through different liquid-solid ratio washed,it was found that,under the condition that liquid-solid radios of wheat straw and rice straw were 30,the straw ash melting temperatures were both more than 1260?and the prejudgement results of slagging were all mild.With the increase of liquid-solid radio,the ash melting point of the two kinds of straw changed slightly,and the prejudgement results of slagging were mild as well.Taken washing temperatures,ash melting point and prejudgement results of slagging into consideration,it was conformed that the optimal washing temperature of wheat straw and rice straw was 70?.Pickling can remove the alkaline metal of the ash effectively,improve the ash melting point the two kinds of straw.However,the concentration of hydrochloric acid has little impact on the ash melting point of the two kinds of straw and prejudgement results of slagging.Single heating rate method was adopted to thermogravimetry experiment of the two kinds of straw and the samples of pretreatment,and to investigate the combustible characteristics,comprehensive combustion characteristics,then to calculate the kinetics of combustion.It was showed that activity energy in wheat and rice straw fixed carbon combustion phase was higher than that in volatile component combustion phase.Meanwhile,activity energy of rice straw was less than that of wheat straw in both phases.After washing,activity energy of the two kinds of straw both increased in two phases.After 70? hot water washing,the activity energy of both kinds of straw increased in volatile component combustion phase,while decreased in fixed carbon combustion phase,less than in fixed carbon combustion phase.Pickling reduced activity energy of wheat straw in both phases.To rice straw,activity energy decreased in fixed carbon combustion phase,and increased in volatile combustion phase after pickling.