Study On Improving The Performance Of Biomass Briquettes With Loaded Additives

The rapid development of science and technology in the world is also accompanied by problems such as short-term energy and environmental pollution.Renewable energy has attracted more and more attention because of its cleanliness and sustainability.Its energy consumption will surpass traditional fossil energy sources such as coal and oil in 2050.Our country is a large agricultural country with abundant biomass energy,and the development of biomass briquettes conforms to my country's national conditions.As a renewable alternative fuel,biomass briquettes have the advantages of low cost,low pollutant emissions,and convenient transportation and storage.However,there are some shortcomings,such as low calorific value and high alkali metal content leading to fuel ash melting and slagging.Additives are usually used to modify biomass briquettes,and the development of multifunctional additives to reduce the cost of additives and improve their effects has become a research topic.This article uses loaded additive technology.Calcium formate and ammonium dihydrogen phosphate are prepared into a solution according to a certain ratio,and unburned carbon(biomass boiler fly ash with a particle size greater than 0.3mm)is used as a carrier.The carrier is mixed with biomass raw materials after being impregnated and loaded with additives to prepare biomass briquette.This article carried out the following work:(1)The selected biomass raw materials are WS(Wood Sawdust)and CS(corn stalk).The two biomasses have the typical characteristics of woody biomass and herbaceous biomass,respectively.The physical characteristics of the biomass briquette under the three blending ratios were tested,and it was concluded that the mass ratio of wood chips and corn stalks maintained good mechanical durability under the conditions of 3/7,4/6,and 5/5.Using TG-DSC to analyze the biomass raw materials,it is found that the combustion of biomass briquettes is mainly divided into five stages,namely dehydration stage(<200?),volatile combustion stage(about 200?-350?),and transition stage(about 350??400?),fixed carbon oxidation stage(about 400??500?)and burnout stage(>500?).According to the TG?DTG image,the thermodynamic parameters are obtained.The ignition temperature of corn stalk is 270?,and the wood chips are 294?.CS are obviously easier to ignite than WS.When the mass ratio of the two blends is 5/5,the comprehensive combustion index is the best.According to the Coats-Redfern method,the thermogravimetric curve is kinetic fitting.The fitting linear correlation coefficient R2 in the volatile combustion stage and the fixed carbon oxidation stage is basically above 0.99,and the fitting effect is good.Activation energy E and index factor A which are calculated show that the blending of WS and CS at 4/6 and 5/5 can effectively improve the reaction efficiency in the middle and late stages of combustion.The NO and SO₂ emission characteristics of biomass under fixed bed at 900?were tested,and it was concluded that when WS and CS were blended at a mass ratio of 5/5,the amount of NO and SO₂ precipitation were the lowest.Combining physical characteristics,thermodynamic parameters and kinetic parameters,It is concluded that the optimal blending ratio of wood chips and corn stalks is 5/5,and this ratio will be used as the biomass raw material for subsequent experimental research.(2)The influence of loading additives on pollutant emissions from biomass briquettes was explored.The precipitation of SO₂ is greatly affected by temperature.Briquettes at 900? have higher self-sulphur fixation characteristics under unloaded conditions,realizing near zero SO₂ emissions;the sulfur fixation rate at 1000?decreases slightly,but remains above 93%,the real time concentration is also controlled below 10mg/Nm3.XRD characterization shows that the sulfur element in the ash below 1000? exists in the form of CaSO₄Na₂SO₄,K₂Ca₂(SO₄)₃,etc;The sulfur fixation rate at 1100? is significantly reduced,and the sulfur fixation component of biomass alone cannot satisfy the better sulfur fixation effect.The higher the temperature,the lower the nitrogen precipitation rate of the forming fuel,and the 20wt%carrier has less NO emission compared with 10wt%.Calcium formate loaded in biomass briquette can effectively increase the sulfur fixation rate at high temperature.Under 10wt%carrier,the sulfur fixation rate increases 7.09%?13.73%,20wt%carrier increases 14.54%?16.42%,The loading effect of 20wt%carrier is more stable than that of 10wt%.For the nitrogen release rate of the fuel,the higher calcium formate loading has little effect on it.Continue to load ammonium dihydrogen phosphate with a fixed load of calcium formate with a calcium-sulfur ratio of 2.The results show that as the load of ammonium dihydrogen phosphate increases,the precipitation of nitrogen and sulfur does not change much.The addition of ammonium dihydrogen phosphate only slightly promotes the precipitation of nitrogen and sulfur.Considering that excessive loading will lead to a decrease in fuel calorific value,the optimal loading condition for suppressing pollution emissions is 20wt%carrier loaded with calcium formate with a calcium-sulfur ratio of 2.(3)The alkali to acid ratio,contamination index and silicon ratio show that the ash melting of biomass is severe slagging.Loaded additives can improve the above problems.The morphology of combustion ash shows that the morphology of combustion ash without loading has a large range of pores in the morphology,and the polycondensation is obvious.The loading of calcium groups can make the large pores disappear.The addition of ammonium dihydrogen phosphate The fuel ash is looser and the melting and slagging phenomenon is improved.A single load of calcium formate can increase the ash melting temperature of the biomass briquette fuel.When the load is Ca/S=8,the effect is the best.The fuel DT is increased by 114?,and the ST is increased by 75?,but the load is too large;The loading of calcium formate and ammonium dihydrogen phosphate not only has a significant increase in the melting temperature of the ash,but the loading is also within a controllable range.Therefore,it is concluded that the optimal loading condition for improving ash melting is that the 20wt%carrier supports calcium formate with a calcium-sulfur ratio of 2 and ammonium dihydrogen phosphate with a phosphorus-to-potassium ratio of 1.The mechanism of loading additives to improve the melting of fuel ash is explained.Calcium formate can combine with the components in the ash at a specific temperature to form composite metal salts such as Ca₂Mg(Si₂O₇)and CaMgSi₂O₆.The addition of ammonium dihydrogen phosphate can also fix metal elements such as K and Na in the bottom ash with the form of K-Ca,Na-Ca phosphate.The above-mentioned complex salts all have a melting temperature of over 1500?,which greatly improves the ash meltability of the fuel.