Desulfurizing absorbent for flue gas and its absorption mechanism

Journal of Entiratental Sciences Vul. 15, No. 1. pp 92-96. 2003Article D:10O10742(203)01409205CLC number: X511 Document code: ADesulfurizing absorbent for flue gas and its absorption mechanismLI Hua", CHEN Wan-ren, LIU Da-zhuang(I Chemical Engineering College, Zhengzhou University, Zhenghou 450002, China. E- mail: Lihua e zzu, edu. en; li husa(e wohu.con:Abstract: A new desulfurizing absorbent for flue gassmall amount of chemical solvent( Mn2.)was studiedabsorbent was improved. And its absorption and reaction mechanism are discussedKeywords: liquid absorption; desulfurization: nue gasIntroductionRemoval of SO,, CO, and other acidic gas from nue gas is one of very important research pnthe world. In order to find effective method, various desulfurization technique( Zhu, 1998; Li, 1996Lin, 1992; Chen, 1997; Tai, 1999; Yeh, 1992; Tan, 1999 ), such as activated carbon, molecularsieve,the electron-beam radiation technique, chemical method, physical solvents etc. are all attemptedompared with these methods, organic solvent absorption has some advantages as low investment, high SO,absorption efficiency and desorption efficiency and worth to further research. In this paper, we study andselect a liquid organic absorbent with a high absorption and desorption efficiency for high selectivity to SOwith low toxicity and low price, And this absorbent will be used to remove SO, from nue gas to solveindustrial problem for flue gas purification1 EThe experiment includes two sections: (1)the solubility experiments and the optimum absorbentlection;(2)technological conditio1.1 Experimental apparatusThe apparatus for So, solubility and regeneration(Li, 1987). The technological process is shown in Fig.A1「掉Theahsrinoapraasotctrolgalcondtionisana l tAs absorption lube with sandglass. The sulfur dioxide with anole fraction purity x(S02)>0. 997, pure nitrogenwith a purity×(N2)≥0.9999 are both frumcylinders. The sulfur dioxide and nitrogen are mixed by agas mixer with static agitation unil lo simulate the fluegas. A flowrator is used to control the flow. The S0analyzer with SO2 sensor( type NTS 100, Nanjing. ChinaFig. I The technological proress of sow器sused for the SO2 analysis ofCI: $0,cylinder:C2:N,cylinder:B1-B2: walve: A1-feed gas and the tail gas. The SO, concentralion in the gas1. a gas mixer with statie agitation unit: 2, absorption tube;phase before and after3. constant temperature bath: 4. inlet gas to $ 2 analyser; analyzer, then the purification efficiency is calculated5, outletFoundation item: The Key Project of Science and Technology of Henan Province, China(No. 001200420)中国煤化工CNMHGDesulfurizing absorbent for flue gas and its absorption mechanismC-CThe purification efficiency(n)is: nCo 100%, where, Co is the SO, concentration beforebsorption:C is the SO, concentration after absorption. All the chemical reagents used are AR grade. Thewater is purified and deionized with a conductivity <0. 06 js/em1. 2 Determination method0, solubility deternination: The whole apparatus is evacuated and flushed several times with nitrogento ensure complete exclusion of oxygen and carbon dioxide, then it is evacuated again, A known amount ofdegassed absorbent is sucked into the absorption tube the weight of which is initial weight W,. Put it inthe thermostatic bath, and let SO, go through the absorption lube al a rate of 25 ml/ min at differenttemperatures till its saturation( constant weight is W,)SO, solubility(gS02 /g solvent)sWhere, W, is the initial weight(g)= solvent absorption tube: W, is the end weigh(g)= solventabsorption tube+ $02: V is the solvent volume( ml ); d is the solvent density(g/ml)Desorption capacity determination: The above-mentioned saturated sulfur dioxide absorption tube( theweight is W2) is regenerated by heating at 60C and bubbling nitrogen at a rate of 25 ml/ min till a constantweight occurs( the weight is W,)W=HSo, desorption efficiency( %W2-W,X100%1.3 Test of apparatusIn ordler to ensure proper operation of Table I Comparison between experimental data for Sot solubility inthe apparatus, the solubility of so, in waterater and literature datais measured and compared with the values Temperaturereported in the literature( John, 1999)g100gl20g/100gHO Leviation,%The experimental measurements agreed with0.12the reporled values with a mean deviation of0. 67%. The measured result is listed in30Table I6,51322 Result and discussion2.1 The selection of absorbents2.1.1 Solubility and desorption of So, in difTerent solventsThe experiment results in Fig. 2 and Table 2 show that the solubilities of SO, in different solvents insequence are: DMSO> DMF DMA>SuHinol >PEG400 TBP>DEA. Thus there are goodsolubility and good regeneration for SO2 in DMSO. Therefore DMSO is fit for as a desulfurizing absorbentfor flue gas purification, and worth further studies2.1.2 The effect of additive on the removal of SO,In order to increase purification efficiency, some additives such as Fe,Mnand thiophene wereadded to liquid absorbents to test the effect of additives on SO, removalExperiment conditions: temperature: 24C, gas now rate: 80 ml/min, inlet SO,concentration0. 1798%.The experiment result is shown in Fig. 3The result mentioned above showed that the addition of Mn in DMSO can increase purificationfficiency: the addition of Fe'increases removing efficiency only at the beginning of absorption, butdecreases as the time goes: the addition of thiophene to DMSO showed negative effect on the removing中国煤化工CNMHG1. I Hua et alefficiency compared with pure DMSO. The addition of Mn"in DMSO can increase purification efficiencyTable2 SO, solubility and desorption in different solventsDMSODMAurinalPEC40020551.14200.960.40180.30250.1%.22920.【8700.87900,990,8750.13730.7890000.61220.18870.16670.1250Desorption efficieneyof so., %Notes: DMF:N. N-dimethyformamide: DMSO: dimethyl sulfoxide: DMA: N N-dimethyl acetamide: PEG400: polyethyleneglycol: TBPtributyl phosphate; DEA: diethanolamineNDMSO+MDMSO4101520SO, solubility in different slventsFig. 3 The effeet of additives on the reiwa of sl2.1.3 The effect of Mn concentration on purification efficiencyThe experiment conditions: I =30C, inlet S0, concentration8MMS2-g403MMnso40. 1806%, gas now rate: 80 ml/min, Mnconcentration: 0. 03-0. 1 8 98From the above experiment re, is found that the remo、momol/L. The result is shown in Fig. 4efficiency of SO, of mixed absorbents is better than pure DMSO, and 2 94optimum Mn: concentration is about 0.03 mol/DMSO2.1. 4 The desulfurizing effect of Mn and DMSO5101520253035404550The desulfurizing effect of 0.03 mol/L Mn and DMSO are listed inTable 3Fig 4 Results of the remval of SO,Determination conditions: absorption temperature: 30C, the gas under differe2.1.5 Desorption determination of Mn" and DMso desulfurization at different temperaturesThe ideal absorbent shouldTable 3 The desxhave a good SO, removal efficientInlet scOutlet S(),Purifieationnd a good regeneration. SoLiquid absorbentration of D)MS0 MnSO(v/34V=1:0. 03) absorbentMns)a98.56determined. The results are listedn Table 4 and Fig. 5中国煤化工CNMHGNo. IDesulfurizing absorbent for flue gas and its absorption mechanism95respectivelyFig. 5 shows that the desorption of DMSO+ MnSO, is influenced by the lemperature. The higher themperature, the higher the desorption efficiency. When the regeneration time is near 60 minutes, theneration efficiencies at different temperatures are all over 99, so the absorbent of DMSO+MnS0),hasdesorption efficiency al a lower lemperatureTable 4 The desorption result of DMSO MnSOI, min Desorption temperatur, 60T.Desorption temperature. 70)TSO,concen-DesorptionS, concentrationDesorptionronc entration, Desorptionefficienlymol/I%0.970067.01200.04,00180.0020w Solution concentration before desorption2.2 The effect of technological conditions on the removalefficiency of SO,This experiment mainly lesl the effect of absorbent concertemperature and gas flow on SO, purification eff2. 2.1 The effect of absorbent concentration on the removalefficiencies of soExperiment condition: temperature: 24C, gas flow: 60 ml/min,a ri oni soinlet SO, concentration: 0. 1792 % The results are shown6Fig. 6 shows that DMSO has a good purification efficiency for lowSO, and SO, purification efficiency increases with DMSO concentration Fig. 5 The desoption rure of DMso)+Increase2.2.2 The effect of absorbent temperature on purificationSOExperiment conditions: gas now: 80 ml/ min, inlet SO, concentration: 0.1783%.Thehown in Fig. 7De DMSO020406080100120Fig. 6 The fect of absortent concentration on theFig. 7 The effect of absorbent temperature neremoval efficieney of SoFig. 7 shows that the temperature influences purification efficiencies. And the sulfur dioxidepurification efficiency decreases when the temperature increases中国煤化工CNMHG11 ilua et al3 Mechanism analysisDMSO is a polar organic solvent with a rather large dipole matrix, while SO, is also a polar gasmolecule. DMSO has a strong solubility for SO, The absorption model of SO, in DMSO is shown in Fig8( Huang,1991)After adding MnSO2+102+H2OH2,.DMSO has a rather large solubility forSO,. After adding Mn" to DMSO, SO,oxidized to H: SO4 catalyzed by MnS(4. Themixed absorbent has a good removal efficiencyof SO, and a good regeneration. Therefore theFig 8 The absorption model of SO2 in DMsselected absorbent has a good future in SO, removal3 ConclusionsDMSO is a colorless, non-loxic, polar organie liquid solvent, and has a large solubility for polar gasAfter adding additives of Mn, desulfurizing efficiency is increased, and the amount of MnsO, has notchanged before and after chemical reactions. It is a cheap method for regeneration of sulfur. ' Thereforedesulfurization of DMSO and Mn" will have a good futureIt is a new idea to use organic solvent mixed with a relatively small amount of chemical solvent(Mn)as sulfur dioxide absorbents. It has not only strong desulfurizing efficiency, but also goodselectivity for SO, and CO2, solving the problem that the present liquid inorganic compound absorbingsulfur dioxide can not be regenerated or the regeneration temperature is high. And this solvent can beregenerated at 60C and has high regeneralion efficiencyThe major advantages of selected mixed solvents are that the method of regeneration is simple, and theperation is easy, compared with the absorption and regeneration of activated carbon, molecular sieve; itdoes not need too much power consumption compared with the electron-beam radiation techniques; it hasstronger regeneration in compared with the traditional alkali methods. Therefore, the development andapplication of above solvents will have a great influence on the removal of So, from flue gasReferencesCai WJ, LJW, 1999. Initial probe into surface-active agential Mn''solution removal SO, in gasl J].Environ(hen L, 1997. Recent development in flue gas desulfurization and DENOX processes abroad I J Environmental Protection nf Chemicalustry,17(3):145Huang H, liZ Y, Sun P S. 1991. Studies on low S() absorbed by DMSO and produring S[J). Yunnan Chemical Industry.4:2-4John A D, 1999. Lange', handbook of chermistry, 5.6( 15th edition )[ M Beijing: Beijing World Publishing CorporationliZY, 1996. Oversea technologies for removal of sO) from flue gas[ J]. Sulfuric Industry, 22(4): 1-3Li T C, Zhang D Y. 1987. Fficient absorption of sulfur dioxide by some polar non-proton solvents[ JJ. Envimnmental Chemistry. 6(6):1.315Lin Z T, 1992. New method for removal of SO, from flue gas[ J. Word Chemical Trend.(3-4):43-47Pasiuk-Broniknwska W. Bmnikowski T, 1980. The rate equation for SO, autoxidation in aqueous MnSn4 solutions containing H2S( 4[Jemical Enginerring Science, 36(3):Tai B H, 1999. Purfication for industrialtallurgiralPressTan t E, ShiY, Wu ZB ef al., 199for FDI JJ.Cor7:1-4.Yeh J T, 1942. Integrated testing of tbr NoXS( proeess-simultaneous removal of so2 and NOx from flue gas( 3]. Chem Eng Comm,114:65-88hu Y R. 1998. Contmt techniques of environmental pollution M]. Beijing: China Environmental SciencePressReceived for review November 19, 2001, Acceped December 13. 2001)中国煤化工CNMHG