| Energy is the foundment for the human civilization and the improvement. Now with the decreasing of the fossil energy, renewable energy begin to attract human’s focus. Biomass fuel is the fourth largest enery as a renewable energy just follow the petro, coal and natural gas. Biomass energy have some advancements such as little pollution, wide spreading and carbon natural. And compare with the coal, biomass has a lower ash, S and N content and a lower amount of combustion pollutant. And when using biomass fuel as energy supplier, we can get a reduction on energy comsuption and carbon dioxide emission. The direct combustion of biomass is the basic and the most important way to using biomass energy. However, due to the higher potassium, content, the boiler can always get slag, deposition, erosion and some other problems.This thesis present a research based on 5 typical biomass samples and their ADP modification samples which are Rice Straw (RS), Maize Straw (MS), Cotton Straw (CS), Poplar Wood (PW), Pine Sawdust (PS) respectively in order to research the ADP’s potassium capturing characteristics during the biomass combustion.(1) This thesis using the thrmoequilibrium calculation software FactSage to simulating the effect of KCl reduction by ADP in the biomass flue gas atmosphere. It is include the researching on the influence of ADP’s amount and the reaction temperature on the reduction of KCl. The results of the simulation shows that, the main product of the reduction reaction is dipotassium hydrogen phosphate (DKP). The KCl’s conversion rate increases with the P/K ratio and the DKP’s conversation rate also increases with the reaction temperature. This reduction reaction has an optimal P/K ratio (a=0.5) when reacting at a specific temperature. The reaction window of that reaction is wide which covers 700 ℃ to 1000 ℃. When the reaction temperature is lower than 900 ℃, the conversion rate of the reduction reaction is over 80% which indicate the reaction of KCl capturing by ADP works well during 700～900 ℃. But when the reaction temperature is over 950 ℃, the conversion rate of KCl is dropping obviously.(2) This thesis using drop tube furnace system to research the influce of reaction time, reaction temperature and P/K ratio on the reaction characteristics of the reduction reaction. The experimental results shows that the reaction between ADP and KCl can produce polyphosphorate, potassium hydrogen phosphate and potassium dihydrogen phosphate which include some potassium metaphosphate and potassium pyrophosphate with a higher melt point. When the amount of ADP is less than the KCl, the products of their reaction mainly are phosphate, metaphosphate, polyphosphate and multi-polyphosphate. When ADP is overdosing, the products of their reaction are mainly hydrogen phosphate, ammonium hydrogen phosphate and some unreacted ADP which indicates that the amount of ADP has a higher affect than the reaction time to the types of final products. When the reaction time is 1 s, the KCl is detected both in the two groups while in 2s condition there is no KCl detected. That case indicates the reaction time has a greater affect than the ADP amount to the KCl reaction degree. What’s more, increasing the reaction time and P/K ratio can increase the reaction degeree of the reduction reaction.(3) This thesis using RS and ADP combustion in the air atmosphere at different temperature to research the ADP’s influence on potassium capturing characteristics during biomass combustion. The experimental results shows that potassium capturing rates at P/K ratio 1 are 23.1% and 21.0% respectively when the reaction temperature is 700 ℃ and 900 ℃. They have an enhancement of 55.1% and 63.1% compare to the original RS sample. But the potassium capturing rate of the ADP modificated sample has an insignificant enhancemet compare to the original one at 500 ℃. The potassium capturing growth rate(β) is small at 500 ℃, but very large at 700 ℃ and 900 ℃. That means the effect of the ADP in capturing potassium during biomass combustion is significant. Experimental results shows that there’re some black spots like substance produced during the combustion of ADP and biomass at high temperature. A high melting point compound K2CaP2O7 detected by XRD in those substance, which means that compound would be a help for increasing the ash melting point of the biomass.(4) This thesis uses ash melting point measurement system to research the ADP’s influence on 5 typical biomass ash fusion characteristics. The experimental results shows that the ash fusion characteristics of those 5 typical biomass have different degrees of improvements after adding ADP. For the herbaceous plants (MS, CS, RS) which has a high content of potassium, the addition of ADP could make a large enhancement to the melting point of the ash. When the reaction P/K=1, the floating temperature for MS, CS,RS are 1475 ℃,1380 ℃,1500 ℃ respectively. For the woody plants which has a plain content of potassium, the addition of ADP helps a little to improve the characteristic temperature. SEM for microscopic view of the ash surfaces shows that ADP could help inhibiting the surface melting and enhancing the ash melting characteristics. What’s more important, the potassium retention ability of ADP will increase as the temperature increasing. As a conclusion, ADP is a good additive for capturing the potassium in the biomass. ADP can effectively improve the biomass ash fusion characteristics and the effect of potassium capturing by ADP is positively correlated with the content of potassium.(5) This thesis uses TG/DTG system to analysis the influence of ADP on 5 typical biomass combustion characteristics, and the results show that those 5 typical biomass have similar combustion characteristics. That is those 5 typical biomass combustion can be devided into three stage, the moisture evaperation stage, the volatiles evaporation and combustion stage, the fix carbon combustion and burnout stage. The biomass’s DTG curve becomes less steep and stable after adding ADP which indicates ADP could make the biomass combustion gentler. The biomass’s ignation point decreaing as the adding of ADP which indicates ADP could make the biomass becomes easily ignation. However, the ADP is a retardant, the retardant effect of ADP is showing on enhancing the biomass burnout temperature and dropping the biomass combustion integration index.(6) The dynamics analysis for the combustion of original biomass samples and the ADP addition biomass samples shows that, the addition of ADP could reduce the activation energy of the low temperature section of the combustion progress, making the ignition easily. However, the flame retardant properties of ADP could make the number of effective collisions between reactant molecules droping significantly, and reduce the reactive in high temperature section of biomass combustion.This thesis provide a theoretical and experimental basis of potassium capturing for the process of combustion pollutant integrated synergistic removal of KCl, NOx, HCl, SOx. And it is significant for solving the problems related to the alkali metal during using biomass energy, such as slag, deposition and erosion. |
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