Investigation On Chemical Looping Combustion Using Iron Ore Decorated By Plant Ash As Oxygen Carrier

The global warming due to the increasing amounts of CO2 relaesed to the atmosphere has caused huge disaster and economic loss.The reduction of CO2 from fossil fuel burning is an effective way to tackle global warming issues.Chemical looping combustion(CLC)is an innovative combustion technology with inherent separation of CO2 without energy penalty.Oxygen carriers play an important role in the CLC process as carrier of oxygen and heat by oxidation-reduction reaction.Natural iron ore is an attractive oxygen carrier,because it is inexpensive and environmentally benign.But the reactivity of iron ore is relatively low.The reaction reactivity of iron ore decorated by K-Na double alkali metal and plant ash with high content of K,Na and Ca was studied.Experiments on chemical looping combustion were conducted in a fluidized bed reactor with iron ore decorated by K-Na by the wet impregnation method.The effects of K-Na ratio and reaction temperature on reduction reactivity of oxygen carriers were examined,and cycle characteristics were also researched.The results indicate that the CO cumulative conversion of iron ore decorated by K-Na is obviously higher than that using natural iron ore.With the increase of the reaction temperature from 850? to 950?,the CO cumulative conversion of 5Na1K-Fe and 3Na3K-Fe increases rapidly,and the CO cumulative conversion of 3Na3K-Fe is higher than that of 5Na1K-Fe at 850?,but on the contrary at 950?.The CO cumulative conversion of 1Na5K-Fe has an increase during 850?900?,and subsequent remain unchanged during 900?950?.In the 10 cycles at 900?,the CO cumulative conversion of 5Na1K-Fe and 3Na3K-Fe increases firstly,and then tends to be stable after 4 and 8 cycles respectively,while that of 1Na5K-Fe is still higher than 99%.The alkali metals K-Na have a lasting positive effect on iron ore.And the reaction rate of 5Na1K-Fe and 1Na5K-Fe is obviously higher than that using 3Na3K-Fe,which indicates that the effect of improving iron ore reactivity of the equal ratio of K and Na is lower than that using predominantly K or Na.Experiments on chemical looping combustion were conducted in a fluidized bed reactor with iron ore decorated by rape stalk ash(RSA),wheat stalk ash(WSA),bamboo stem ash(BSA)and corn cob ash(CCA)by dry calcination method based on that K and Na of plant ash would migrate at high temperatures.The effects of ash type and ash ratio on reduction process of iron ore were investigated,and cycle characteristics were also researched.Characterizations of iron ore decorated by plant ash through XRD,BET,XRF and SEM-EDS were carried out.The results show that the K,Na and Ca can migrate from ash to iron ore efficiently during calcination process.The reactivity of iron ore decorated by ash is obviously higher than that using pure iron ore.Ash type and ash ratio have obvious effects on the reactivity of iron ore due to the content of K,Na,Ca and Si migrating from ash to iron ore.The reactivity of iron ore decorated by RSA depends on the content of K,Na and Ca.The reactivity of iron ore decorated by WSA and CCA depends on the content of K and Si,and that of iron ore decorated by BSA depends on the content of K.In the 10 cycles,the iron ore decorated by RSA and WSA maintain the enhanced reactivity.SEM shows that they have a porous structure on their surface.There are no obvious loss of K,Na and Ca of the decorated iron ore during cycles.The reaction reactivity of iron ore decorated by rape stalk ash and wheat stalk ash by wet impregnation method were studied in a fluidized bed reactor based on that K and Na of plant ash are soluble in water.The effects of ash type,ash ratio and ash type on the reaction reactivity of iron ore were investigated,and cycle characteristics were also researched.The results show that K in wheat stalk ash,K and Na in rape stalk ash can migrate from ash to iron ore efficiently during wet impregnation method.The rape stalk ash and wheat stalk ash enhance the reaction reactivity of iron ore greatly.Ash type and ash ratio have obvious effects on the reactivity of iron ore.The reaction reactivity of iron ore decorated by wheat stalk ash depends on the content of K.When ash ratio is 20%,the CO cumulative conversion of iron ore decorated by wheat stalk ash is 86.05%.The reaction reactivity of iron ore decorated by rape stalk ash depends on the content of K and Na.When ash ratio is 20%,that of iron ore decorated by rape stalk ash is 84.4%.And that of pure iron ore is just 72.5%.The cycle experiments indicate that the iron ore decorated by rape stalk ash and wheat stalk ash keep a lasting high redox reactivity.After 10 redox cycles,there is a certain loss of K and Na of iron ore decorated by rape stalk ash,but a less loss of K of iron ore decorated by wheat stalk ash.And the pure iron ore shows severe sintering on the oxygen carrier particles with no porous structure on their surface,while the iron ore decorated by rape stalk ash and wheat stalk ash still have a porous structure on their surface.Chemical looping combustion of coal was experimentally carried out in a fluidized bed reactor using iron ore decorated by wheat stalk ash based on dry calcination method and wet impregnation method.Effects of reaction temperatures and cycle number were studied.Under the same temperaturecondition,the carbon conversion rate and the reaction rate of coal gasification of iron ore decorated by wheat stalk ash based on two methods are higher than those of pure iron ore.Both the carbon conversion rate and CO2 gas fraction of pure iron ore increase with the increase of the reaction temperature from 850? to 950?,while those of iron ore decorated by wheat stalk ash based on two methods have a increase and subsequent reduce.After 10 redox cycles,CO2 gas fraction of iron ore decorated by wheat stalk ash based on two methods is still higher than that of pure iron ore.And the reactivity of iron ore decorated by wheat stalk ash based on two methods remain stable during 10 redox cycles.