Experimental Study On The Occurrence And Heat Release Of Alkali Metals In Biomass

As a renewable and clean energy source,biomass will occupy an increasingly important position in China's energy structure.It contains more alkali metals,causing problems such as ash accumulation,slagging and corrosion,and inhibits the promotion and application of biomass energy.It will increase the complexity of the power generation system and the cost of power generation.Therefore,this paper focuses on the occurrence of biomass alkali metal and the release rule and mechanism of alkali metal elements during heat treatment,which provides strong theoretical support for the clean and efficient use of biomass in China,and has good socioeconomic and academic Significance.The experimental methods used in this paper are chemical fractionation experiment,microwave digestion experiment and pyrolysis combustion experiment.The detection methods were:inductively coupled ion mass spectrometer?ICP-AES?,scanning electron microscope and energy spectrometer?SEM-EDS?and X-ray diffraction?XRD?,and the law of CO₂ and HCl precipitation in pyrolysis combustion test flue gas was measured by flue gas analyzer.Taking wheat straw and rice husk as research objects,the occurrence patterns of alkali metals K and Na and the factors affecting the removal of water soluble K were studied.Taking wheat straw as the research object,through biomass pyrolysis combustion experiment,the alkali metal content of ash sample or ash residue was analyzed,and the release law of alkali metal was obtained.At the same time,the element content,microstructure and alkali metal form on the surface of ash sample or slag were analyzed experimentally.The chemical flotation experiments were carried out to analyze the occurrence of wheat straw and rice husk alkali?earth?metal.The conclusion is that wheat straw and rice hull have similarities in alkali?earth?metal occurrence;alkali metal is mainly K The elements are mainly composed of water-soluble K;the alkaline earth metals Ca and Mg are mainly dissolved in ammonium acetate and water-soluble.The cations of wheat straw and rice husk filtrate are mainly K+and Ca2+,and the anions are mainly Cl^-and NO₃^-.The water-soluble K is mainly composed of hydrated ions or crystals such as KCl,KNO₃,K₂SO₄ and K₃PO₄.By analyzing the cation and anion concentrations of the wheat straw water washing filtrate,the water solubility K in the solution is about 80%,wherein KCl is about 80%,KNO₃ is about 13%,K₂SO₄ is about 4%,and K₃PO₄ is about 2%.The main order of factors influencing the removal of water-soluble K:washing temperature>washing time>particle size>stirring rate.By wheat straw pyrolysis combustion experiment alkali metal release characteristics,the conclusion is:200?⁶00?as the main stage of thermal decomposition weightlessness,600?¹000?high temperature carbonization stage.Most alkali metals K and Na are easy to volatilize and to be discharged with flue gas.Alkali metal K is the main component released by alkali metal.Surface enrichment of alkali metal elements of K in ash situation analysis:200?⁶00?temperature period mainly for samples of KCl,SiO₂ and moisture binding reaction to form silicate and HCl,and KNO₃ in gaseous form;Above 600?temperature period mainly KCl released in gaseous form.In the combustion experiment,Na is more easily released than K with the increase of combustion temperature.The release amount of Ca and Mg in alkaline earth metals is small.According to the analysis of the enrichme nt of alkali metal K on the surface of ash and slag,the surface contents of K and Cl change synchronously.Temperature is less than 600?,ash surface K and Cl element content increased synchronously;Surface temperature greater than 600?,K and Cl element content decreased,mainly for KCl react with SiO₂,or KCl release in gaseous form.