Performance And Theory Of Removal Black Carbon From Black Smoke Based On Surfactant Theory

In China, there is serious air pollution which mainly results from atmosphericparticles. The particles are mainly emitted by stationary sources, such as power plantboilers, industrial boilers, ceramic kilns which are fueled by coal, oil, natural gas andbiomass-fueled, and mobile sources, such as vehicles fueled with gasoline, diesel andcompressed natural gas. The air pollution contributed by atmospheric particles canalso influence local and global climate. It is notable that the atmospheric particles aremainly contributed by soot particles of black smoke, especially in the developingcountry. Because coal and other fossil fuel are still world widely used with a largeamount, the emitted soot particles are huge per year. In China, the amount of sootparticles emitted in2001was about1.1Tg, and in2006it was about1.8Tg, whichwas increased about63.64%. However, there is still no suitable technology whichcould be used to efficiently remove soot particles from black smoke due to its specialphysical and chemical characterization.Therefore, the physical and chemical characterizations of soot particles were firstlystudied in this paper. After that, the properties of surfactant solution and theflocculation efficiency of soot particles in surfactant solution or mixed surfactantsolution were studied in a new type umbrella plate scrubber. Meanwhile, the theoryrelated to surfactant solution studied in this paper was also studied. Finally, thedistribution characteristics of soot particles in dust collector were simulated by Fluent.The experimental results showed that the bulk density, true density and rest angleof soot were0.33g/cm³,1.85g/cm³and48°, respectively. The soot particles weremainly nanoparticles with less than100nm particle size and similar to spherical style.However, the particles could be aggregated into larger ones, and their mediandiameter was3.66μm. Meanwhile, the nanometer pores were also detected in the sootand the pore diameters were mainly distributed from2nm to4nm. Due to its largesurface area and pore volume, the soot could adsorb other pollutants from thesurrounding and then become more hazardous. In addition, though several elements,such as C, O, Pb, were detected in the soot, only a small amount of crystallites wereobserved in the soot contributed from the fact that most of the detected carbon andmetals/metal oxides/metal salts were in amorphous status. Furthermore, there wereabout90kinds of organic pollutants detected in the soot including aromatic compounds and other hydrocarbons. Because of the carcinogenesis of aromaticcompounds and the photochemical effect of hydrocarbons, the soot could causeseriously healthy and environmental damages. Due to its characterizations, soot wassuggested to be purified from the flue gas by a wet dedusting method.After that, the surface-active properties of sodium dodecylbenzene sulfonate（SDBS, C18H29NaO3S）, hexadecyl trimethyl ammonium Bromide （CTAB,C16H33（CH3）3NBr）, fatty alcohol polyoxyethylene ether-9（AEO-9, RO（CH2CH2O）3H,R=C12H25） and polyoxy ethrlene nonyl phinyl ether-10（TX-10） was studied. Theinfluence of pH and temperature on surface tension of the four studied surfactants wasalso studied. Meanwhile, the removal ratio of soot particles from experimental blacksmoke by the4studied surfactants under several experimental conditions in theumbrella plate scrubber was studied. The experimental results showed that the surfacetension of AEO-9was the lowest one in the four studied surfactants, and the surfacetension was hardly influenced by pH and temperature. When the surfactants of SDBS,CTAB, AEO-9and TX-10was used to remove soot particles from experimental blacksmoke, the removal ratio had obvious relation to their surface tension while theconcentration of the surfactants was various. The soot removal ratio of AEO-9onlyslightly decreased when the soot particles concentration was increasing. The similarphenomenon was found when the experimental velocity was various. When theliquid-gas（L/G） ratio was different, the soot particles removal ratios of SDBS, CTAB,AEO-9and TX-10was mostly influenced by their surface tension when thesurfactants concentration was low than critical micelle concentration （CMC）, and theremoval ratio of the surfactant with the lowest surface tension could yielded thehighest soot particles removal ratio. With the increasing of L/G the soot particlesremoval ratio was all increased, and the removal ratio of SDBS was higher than thatof CTAB when the L/G was0.55L/m³. Meanwhile, the soot removal ratios of SDBSand CTAB were greatly affected by the change of their concentration, especially forthat of SDBS, which its soot particles removal ratio could be decreased from99.50%to98.07%when its concentration was increased from2mmol/L to8mmol/L.However the decrease of soot particles removal ratio of CTAB was mainly due to itsstrong foaming properties. When the concentration of surfactants was various, thesoot particles removal ratio was not only significantly higher than that of SDBS andCTAB, but also the ratios could be slightly increased with their concentrationincreasing. Moreover, the highest soot particles removal ratio of the four studiedsurfactants could be found when the concentration of AEO-9was4.00mmol/L, which was about99.65%.Furthermore, in order to find the most suitable mixing ratio, the characterizationsof AEO-9-SDBS, AEO-9-CTAB, AEO-9-TX-10and SDBS-CTAB mixed surfactantsolution were also studied under different experimental conditions. The surfacetension of the mixture, the best mixing ratio, the change trend of the mixture underdifferent mole ratio, the mole ratio of surfactant1in the mixed monolayer of mixedsolution surface （x₁） and he molecular interaction parameters （β） between thesurfactant molecules was all included. Base on the experimental results, the sootparticles removal ratios of the mixtures were studied under their CMC. Furthermore,the mathematical correlation between the soot particles removal ratio and the mixtureswas studied and analyzed. The experimental result indicated that when the molar ratiobetween AEO-9and SDBS was1:1, the surface tension of the mixed solution was theminimum. The surface tension was about35mN/m under the CMC （0.2mmol/L）. Thesoot particle removal ratio of AEO-9-SDBS mixed solution was closely related to thesurface tension which was at the concentration of CMC. The mixed solution ofAEO-9-SDBS yielded the highest removal ratio of soot particles as high as99.81%,which was also related to its lower β and higher x₁. However, in the study ofmathematical correlation betweenΔG_m⁰of the solution and the correspondingparticle removal efficiency of carbon black, the mathematical correlation was not well.Its R²was only0.889.When the molar ratio between AEO-9-CTAB and SDBS was1:1the surface tensionof the mixed solution was the minimum one. The surface tension was38.48mN/munder the concentration of CMC （1.00mmol/L）. The removal ratio of soot particleswas decreased with the increasing of the CTAB concentration in the mixed solution.Meanwhile, the mathematical correlation betweenΔG_m⁰of the solution and thecorresponding particle removal ratio of soot particles was relatively well, its R²was0.947.When AEO-9and TX-10were mixed, the series mixed solution had the highest βand lowest x₁. The surface tension of the mixed solution was36.5mN/m when themole ratio between AEO-9and TX-10was1:2, and its CMC was0.18mmol/L. Thesoot particles removal ratio was closely related to the surface tension of the mixedsolution. The removal efficiency of carbon black particles was about99.20%at thelowest surface tension position. Simultaneously, the mathematical correlation betweenΔG_m⁰of the type of surfactant mixed solution and the corresponding removalefficiency of soot particles was very well, and its R²was0.989, which indicated that the formula of the mathematical correlation could be used directly to the calculationand inference in the experimental research and engineering applications.The removal ability of soot particles by the mixture solution of SDBS and CTABwas the lowest though the β value of the mixed solution was the smallest, which wasdue to the fact that the value of x₁was relatively small and CTAB was the majorcomponent in the monolayer, moreover, the surface tension of the mixture was higherthan that of TX-10and AEO-9, and the strong foam ability of CTAB was also aimportant influence factor. The smallest surface tension was achieved when the molarratio of SDBS and CTAB was1:1, which was about38.20mN/m, and the CMC of themixed solution was0.6mmol/L. The removal ability of soot particles wasunsatisfactory, about98.32%, which was similar with that of the mixture of AEO-9and CTAB. However, the correlation ofΔG_m⁰and removal efficiency of carbon blackwas the best, and the correlation coefficient was about0.997, which could be used inthe correlation calculation and inference of the experimental study and engineeringapplication.The influence of the inorganic salt included NaCl, Na₂SO₄, Na₃PO₄was alsostudied in this paper. The results showed that the inorganic salt had a certain influenceon the solution of CTAB, displaying certain regularity. The concentration of theinorganic salt was bigger, and the effect of which on the surface tension of CTABsolution was larger while the surface tension was getting smaller with the increaseconcentration of CTAB solution. Moreover, NaCl was the most influential inorganicsalt on the surface activity of CTAB solution. Therefore, the influence of NaCl on thesurface property of AEO-9and SDBS solution was specially studied. The resultsshowed that the influence of NaCl on AEO-9solution was few, and the change of thesurface activity was not dramatic. The surface tension was decreased with NaClconcentration increasing, which was due to the fact that SDBS was anionic surfactantand its surface tension was getting smaller with the increase of NaCl concentration,however, the downdraght was getting slowly with the increase concentration of NaClin the solution.The influence of NaCl on the mixed solution of AEO-9and TX-10was also few.However, the surface tension was decreased when NaCl was added into the mixturesolution of SDBS-CTAB and AEO-9-SDBS which was due to the presence of SDBS.In especial, the fall in surface tension of the mixed solution of SDBS-CTAB waslarger than that of AEO-9-SDBS.Moreover, the surface tension was changed when the flocculants such as polyaluminum chloride （PAC） and polyacrylamide （PAM） were dissolved in thesurfactant solutions. When the PAC and PAM was dissolved in AEO-9, SDBS, CTAB,AEO-9-TX-10and SDBS-CTAB solutions, it was clearly that the surface tension ofall of the surfactant solutions were slightly decreased because there was Al3+in thesolution except that of AEO-9and SDBS, while the surface tension of the surfactantsolutions was slightly increased when PAM was dissolved except that of AEO-9.However, both of the amounts of the increase and decrease were few. When the PACwas dissolved in SDBS-CTAB solution which0.1000g soot particles was suspendedin the solution, the precipitation rate of soot particles, about94%, could be get.Therefore, the soot particles suspended in the absorption surfactant solution could beefficiently removed from the solution, which was beneficial to the recycling ofabsorbing solution. When5mmol/L NaCl was involved in the solution, theprecipitation rate of soot particles could be increased to about95%. While PAM wasadded into the solutions, the highest precipitation rate of soot particles was only about87.6%. In the flocculation and precipitation process of soot particles from thesurfactant solutions, the particles with higher diameter could be more easilyflocculated and precipitated, and the soot particle average diameters were decreasedwith the precipitation increasing.The results of the Fluent simulation about soot particles concentration distributionin the dedusting umbrella plate scrubber showed that the particles concentration ofsoot was tended to decrease at the axial position of canopy dust catcher. Thedistribution of the particles concentration in both sides of the wall wasnon-axisymmetric, and with the increasing of particles at inlet, the concentration wasradically distributed into low-concentration in the middle areas andhigh-concentration near the wall. The particles concentration distribution at Radialdirection reduced by the enhancing inlet velocity, and it also decreased withincreasing particle diameter. It could also be found that the voltage drop withincanopy dust catcher increased with the raising of inlet velocity and inlet dust loading.The pressure drop in canopy dust catcher vary at240⁵90Pa with deferent inletvelocity （10¹2m/s） and deferent inlet particles concentration （1000⁷000mg/m3）,which had less than6%agreement with that of the experimental results. It was under350Pa when the inlet velocity was12m/s. The result showed that dedusting efficiencyin the canopy dust catcher increased with the raising of inlet velocity and inlet dustloading. The dedusting efficiency of the simulation was from69%to74%, which wasin good agreement with the experimental results with less than10%of the error.