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Mechanism of Low-NOx Emission for Circulating Fluidized Bed Decoupling Combustion of N-rich Industrial Biomass Waste

Author: YangWu
Tutor: LiuYueJin
School: Xiangtan University
Course: Chemical Engineering and Technology
Keywords: distilled spirit lees decoupling combustion pyrolysis reburning NOreduction
CLC: TK6
Type: Master's thesis
Year: 2013
Downloads: 28
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Abstract


Distilled spirit lees, which is rich in cellulose, moisture as well as nitrogen, is alight industry biomass byproduct from the unique solid-state fermentation of distilledspirit in China. Distilled spirit lees has already considered as one of the importantpollutions. Based on this background, IPE, CAS proposed and developed a circulatingfluidized bed decoupling combustion technology(CFBDC), which was demonstratedto effectively treat spirit lees with large scale, clean and low NOx emission. However,the mechanism of low-NOx emission in CFBDC is not clear. Based on the CFBDCtechnology dividing combustion into the pyrolysis of distilled spirit Lees andreburning of distilled spirit lees pyrolysis products, we carried out this study frompyrolysis and reburning.A series of experiences were carried out in a laboratory fixed bed at theatmosphere of N2for the purpose of better understanding the pyrolysis behavior ofdistilled spirit lees. The results showed that increasing the pyrolysis temperature from500℃to850℃, caused the yield of char to decrease, to increase for pyrolysis gasand a parabola variation with increase first and then decrease for tar. At thetemperature of700℃, the yield of tar was highest. At the temperature of500℃,there is no H2detected in the pyrolysis gas. With the temperature increasing further,the content of H2in the pyrolysis gas was increasing. At the temperature of850℃, H2was the main composition in the pyrolysis gas. For the compositions of CO and CO2,increasing the pyrolysis temperature caused their contents declining. A parabolavariation with increase first and then decrease for CH4. At the temperature of600℃,the content of CH4was highest among the pyrolysis gas and reached20%.GC-MS instrument is used to detect the tar compositions, which are produced inpyrolysis reaction, because of the complex compositions of tar. The compounds whichis toluene, phenol, naphthalene and1-hydroxy-naphthalene were chosen as the maincompositions of tar. A so–called micro-fluidized bed reactor analyzer (MFBRA) wasused to investigate the NO reduction characteristic of these four compounds and tar.The results showed that all of the four compounds and tar had strong NO reductionefficiency. With the temperature increasing, the efficiency was increasing. Among thefour compounds, the benzene ring substituents played an important role on NOreduction. The radical released by cracking the substituents of-CH3played a moreimportant role on NO reduction compared with that released by cracking the substituents of-OH.A continuous drop-tube furnace was employed to simulate the combustionconditions in the reburning zone of circulating fluidized bed decoupling combustion,and a series of experiments were conducted to study the NO reduction characteristicsof pyrolysis products of distilled spirit lees, which are char, tar and pyrolysis, in termsof the specific NO reduction efficiency (ηE) defined against the unit-mass flowreductant. The results indicated that with increasing the reaction temperature from800℃to1050℃, increasedηEof char, tar and pyrolysis gas. The optimal residence timefor the possibly highest ηEwas found to be3.4s for the tar and char reductants.Increasing the NO concentration from400ppm to1000ppm in the reactant gas, theηEdecreased but the reduced absolute NO amount increased for all the pyrolysisproducts. Increasing the O2concentration in the reactant gas caused ηEto decrease forchar, to increase for pyrolysis gas and a parabola variation with increase first and thendecrease for tar. At an O2concentration of1.63vol.%, the ηEfor tar was highest andreached60.1%. The study demonstrated that unit-mass flow reactant tar enabled thehighest NO reduction in comparison with char and pyrolysis gas.

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