Cyclones as PM 10 and PM 2.5 emission measurement classifiers

Transcription

1 Air Pollution XVIII 395 Cyclones as PM 10 and PM.5 eission easureent classifiers J. Heerka, M. Braniš & P.Vybíral Faculty of Mechanical Engineering, Czech Technical University in Prague, Czech Republic Abstract Two cyclone classifiers D = 78 and 3 for eission easureent of particle fractions PM 10 and PM.5 were developed at our departent as a part of R&D activities. Verification tests of the cyclones were generalized in the for of criteria relations Stk = f(re). These relations tell us how the cyclone classification ability given by the value of Stokes nuber Stk for the aerodynaic cut size a 1, changes in dependence on the saple volue flow rate V of the gas generalized by Reynolds nuber Re. By a subsequent analysis of both non-diensional criteria relations the dependances of the saple volue flow rate on the gas teperature V = f(t), where cyclones classify as PM 10 and PM.5 classifiers, were derived for both dry air and flue gases fro cobustion of lignite and hard coal in the usual range of excess cobustion air coefficients and vapour contents. Fro the individual dependences V = f(t) for both cyclones it follows that : The dependance of V ( 3 /h) on gas teperature t ( C) is significant. Dependances V = f(t) for dry air and cobustion flue gases significantly differ (fro 1 to 13%). For coal cobustion the differences of the corresponding volue flow rates depend on the flue gas coposition and differ in the range of several percent. Differences between volue flow rates for hard coal and lignite cobustion are not very significant. In all entioned cases, the corresponding volue flow rates for gas teperature up to 00 C change in the range fro to 6 3 /h (usual saple volue flow rates in eission easureents) and the cyclones D = 78 and 3 can be thus used as PM 10 and PM,5 eission classifiers. Keywords: eission easureent, PM 10 and PM,5 fraction, cyclone separator. WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press doi:10.495/air100351

2 396 Air Pollution XVIII 1 Introduction Concentrations of fine dust particles in abient air in the Czech Republic and on a global scale are given in the for of PM 10 and PM.5 particle fractions. Containation of abient air with fine dust particles, which represents a serious health hazard for the population and its established relation with sources of solid state pollutants, calls for the introduction of easureent of eissions with graded sapling easureent of PM 10 and PM..5 fractions into practical use. Present Czech legislature on eission control is concerned only with the eission liits of total solid state pollutants (TSP), i.e. concentration of all solid state particles without considering their grain size. The present paper brings inforation on the research of cyclone classifiers for eission easureent, which classify particles at usual saple gas flow rates fro to 6 3 /h and a current teperature range up to 00 C in copliance with requireents defined by the PM 10 and PM.5 fraction. Design of cyclone classifiers for eission easureent During sapling of solid state particles fro a carrier gas a particle classifier is inserted between the sapling probe and the final filter. The task of the classifier is to separate particle fractions of particular sizes fro the saple. The basic characteristic of every classifier is the dependance of grade efficiency E on the aerodynaic particle size a 1 function E(a 1 ). The level at which a particle is captured with grade efficiency E = 0.5 is designated as the cut size a 1,. PM 10 and PM.5 classifiers are classifiers, where a 1, = 10 and a 1, =.5 and the dependance E(a 1 ) is in the for of a sharp S curve..1 Design of PM 10 cyclone classifier Assessent of the ain diensions of the cyclone separator was based on an assuption that for geoetrically siilar cyclones the separating ability E can be described by function E = f(stk), where Stk is Stokes criterion which is a decisive paraeter for particle separation in cyclones. Stokes criterion for the agnitude of cut size a 1, is defined as Stk a1, 1000 vd (1) 18 D where v D (/s) is the characteristic velocity in the cylindrical chaber of a cyclone with diaeter D expressed by v D 4 V () D WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

3 Air Pollution XVIII 397 The concept of the cyclone was based on the value of Stk = given by Sith et al [1] for a SRI-I type cyclone. The cyclone was originally designed at our departent according to a requireent fro industry to design a preseparator of coarse fractions a 0 (a 1 30 ) in saples of eissions in an assued range of volue flow rates fro 3 to 6 3 /h and gas teperatures up to 00 C. Fro the viewpoint of separation the cyclone was designed for the ost unfavourable case in the range of the above saple flow rates and gas teperatures. The ain diension of the cyclone - cylinder diaeter D = 78 - was deterined by calculation fro equation (1), where a 1, = , V = 3 3 /h = /s and = Pa.s (corresponds to dry air teperature 00 C). The reaining diensions were derived by geoetrical siilarity fro the original diensions of the SRI-I type cyclone and are apparent fro fig. 1. Our preliinary laboratory tests indicated that the cyclone D = 78 could serve in current conditions of eission easureents as a PM 10 classifier and this was the reason why the cyclone was subjected to other ore detailed tests. Figure 1: Main diensions of the cyclone D = 78.. Design of PM.5 cyclone classifier Based on equations (1) and () and experients with the cyclone D = 78, a cyclone D = 35, geoetrically siilar to the cyclone D = 78, was first designed as a PM.5 classifier. However laboratory tests with this type of a cyclone did not give satisfactory results. For this reason a URG type of cyclone was chosen for further design. The URG type has a tangential inlet with a rectangular cross-section and a longer cylindrical part and thus has higher grade efficiencies copared with the SRI type cyclone. Preliinary experients with WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

4 398 Air Pollution XVIII coercial URG type cyclones D = 18 and D = together with findings of our previous experients with the SRI type cyclone D = 35 led to an original design of the cyclone with a D = 3 diaeter of the cylindrical part. The ain diensions of the cyclone are shown in fig.. Figure : Main diensions of the cyclone D = 3. 3 Verification tests Changes of the separating ability of the cyclone with varying flow rate V perfored in laboratory conditions can be generalized in the for of the dependence of Stokes criterion Stk (related to the aerodynaic cut size a 1, ) on Reynolds nuber Re []. According to (1) and () the value of Stk can be expressed as Stk and Reynolds nuber Re is defined as a1, V (3) 3 18 D v D D 4V 4V Re (4) D D In equations (3) and (4) (kg/ 3 ) is the gas density and (Pa.s) is the dynaic viscosity of the gas. WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

5 Air Pollution XVIII 399 Cyclone perforance tests were perfored in the laboratory dust rig in the range of saple flow rates V = 6 3 /h for cyclone D = 78 and V = /h for cyclone D = 3. Dependances of grade efficiency E on the aerodynaic particle size a 1 (functions E(a 1 )) were deterined by the standard capture outlet ethod, where dust saples for deterination of corresponding oversize cuulative distribution curves were taken fro the discharge hopper of the cyclone and fro the end filter. Particle size analyses of the dust saples were perfored by a Fritsch Analysette laser analyzer which classifies particles into 6 size intervals ranging fro 0.3 to 300 and the found nuber distribution of particle sizes is recalculated to the required distribution according to ass. Due to the fact that in the range of sall particles, where values of grade efficiency E should theoretically approach zero but the found dependances E(a 1 ) did not reach zero values, the functions E(a 1 ) were corrected in the range of sall particles into the for of an S curve - E (a 1 ). Hence for further calculations of Stk corrected values of the aerodynaic cut size a 1, are used. 3.1 Results of verification tests with cyclone D = 78 Results of 14 laboratory tests with the cyclone D = 78 in the range of saple flow rates V = 6 3 /h are expressed in the for of criteria dependance Stk and Re in fig. 3. 0,001 0,001 0,0008 Stk [-] 0,0006 0,0004 0, Re [-] Figure 3: Dependance of Stk on Re for cyclone D = 78. The found dependance of Stk on Re can be best expressed in the for 1.91 Stk Re (5) WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

6 400 Air Pollution XVIII 0,005 0,00 0,0015 0,001 0, Stk [-] 5000 Re [-] Figure 4: Dependance of Stk on Re for cyclone D = Results of verification tests with cyclone D = 3 Siilarly, results of 14 laboratory tests with the cyclone D = 3 in the range of saple flow rates V = /h are expressed in the for of criteria dependance Stk and Re in fig. 4. The dependance of Stk on Re can be best expressed in the for 1.81 Stk 559.Re (6) 4 Use of cyclone D = 78 as a PM 10 classifier Verification tests of a cyclone D = 78 generalized in the for given by relation (6) akes it possible to deterine for what teperatures and for what flow rates the cyclone D = 78 can be used as a PM 10 eission classifier (condition a 1, = 10 ). If criteria Stk and Re in eqn. (6) are substituted with their definitions (3) and (4) respectively we obtain V a1, V (7) D D In this relation the quantities and depend on the gas coposition. The gas density furtherore depends on state quantities teperature and pressure and dynaic viscosity is a function of teperature. 4.1 Cyclone D = 78 as PM 10 classifier for dry air In further processing of results it is assued that the gas is dry air and current relations are used for functions = f(p,t) and = f(t). The calculation is WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

7 Air Pollution XVIII 401 perfored for standard pressure 98 kpa in such a way that a 1, is set equal to and by iterating a dependance of the volue flow rate of air V ( 3 /s) on the teperature of air t ( C) for which the cyclone can be used at 98 kpa as a PM 10 eission classifier is obtained. The found dependance V = f(t) can be expressed by a polynoial of the nd degree in the for 6 V 7.10 t t,35 (8) where V is for practical reasons expressed in 3 /h. According to this relation the required flow rate through the cyclone V increases fro.35 3 /h at 0 C to /h at 00 C. 4. Cyclone D = 78 as PM 10 classifier for flue gases fro coal cobustion processes For a different gas than dry air the use of the cyclone as a PM 10 classifier differs fro (8) and a siilar relation V = f(t) can be derived fro (7) by the sae procedure as for dry air by eans of relevant values of = f(p,t) and = f(t) for the particular gas. In the Czech Republic a cyclone can be used as a PM 10 eission classifier ainly for flue gases fro coal cobustion processes. In calculations designers of boilers prefer to use kineatic viscosity ( /s) rather than dynaic viscosity (Pa.s) and therefore equation (7) can be rewritten using relation =. in the for V a1, V (9) D D Deterination of the flue gas density (kg/ 3 ) follows fro the expression of the density of wet flue gas at standard conditions N (kg/ 3 ) and fro state equation N d, N d w, N (10) w p TN N (11) p T In eqn. (10) d,n (kg/ 3 ) and w,n (kg/ 3 ) are densities of dry flue gas and water vapour under standard conditions and d (1) and w (1) are volue ratios of dry flue gas and water vapour in wet flue gas. The value of the density of dry flue gas d,n (kg/ 3 ) depends on the fuel coposition and can be accurately deterined by eans of stoichioetric calculations of cobustion equations or by calculation fro the known dry flue gas coposition. In a siplified way d,n (kg/ 3 ) can be deterined according N WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

8 40 Air Pollution XVIII to the fact that the density of dry flue gases depends above all on an excess of cobustion air, expressed by an excess cobustion air coefficient (1) which influences the actual value of CO in flue gas and depends less on the fuel coposition. According to [3] for the deterination of d,n (kg/ 3 ) it is possible for lignite cobustion to derive the expression d, N CO, act (1) where CO,act (1) gives the actual volue ratio of CO in flue gas. Siilarly, for the hard coal cobustion the expression can be derived for d,n (kg/ 3 ) d, N CO, (13) act The siplified calculation of the actual flue gas density (kg/ 3 ) consists of steps as follows: choice of used coal, hard coal or lignite, which deterines the axiu value of CO in flue gas, CO,ax = for lignite or CO,ax = for hard coal [3], choice of the value of the excess cobustion air coefficient (1) or the volue ratio of O in flue gas and calculation of as = 0.1/(0.1 O ), deterination of CO,act (1) fro the equation for ideal cobustion CO,act = CO,ax /, calculation of d, N (kg/ 3 ) by eans of equation (1) or (13), choice of the value of water vapour in wet flue gas w (1) and atospheric pressure p (Pa), calculation of N and (kg/ 3 ) by eans of equations (10) and (11). The flue gas kineatic viscosity ( /s) can be according to [4] deterined as M ean (14) where ean ( /s) is the kineatic viscosity of the flue gas with ean gas coposition ( w = 0.11and CO,ean = 0.13) and M (1) is the correction factor which depends on the actual value of w (1) in wet flue gas and gas teperature. The value of ean ( /s) is a function of the gas teperature and fro data in [4] can be expressed as t t (15) ean The value of correction factor M (1) lies in a narrow range [4]. Deterination of the dependence of the saple volue flow rate on the gas teperature V = f(t), where the cyclone at the pressure p (Pa) classifies as a PM 10 classifier, is perfored by an authorized software [5]. WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

9 Air Pollution XVIII 403 Analysis of equation (9) by eans of software [5] was perfored for a real range of the excess cobustion air coefficient (1) and the content of water vapour in wet flue gas w (1) for lignite and hard coal cobustion. For lignite cobustion (1) ranged fro 1. to and w (1) fro 0.10 to 0.5 and for hard coal cobustion (1) ranged again fro 1. to and w (1) fro 0.08 to In figures 5 and 6 are plotted as exaples dependances V = f(t) for cobinations of (1) and w (1) for lignite and hard coal cobustion which lead to axiu ( w = 0.10, = 1.) and iniu ( w = 0.5, =.0) values of the volue flow rate of the saple. In figures 5 and 6 the dependences V = f(t) for dry air are added for coparison. 6 5 V ( 3 /h) ω(w)=0,10; α=1, ω(w)=0,5; α=,0 dry air t ( C) Figure 5: Range of dependances of V = f (t), where the cyclone D = 78 for lignite cobustion serves as a PM 10 classifier. V ( 3 /h) ω(w)=0,08; α=1, ω(w)=0,15; α=,0 dry air t ( C) Figure 6: Range of dependances of V = f (t), where the cyclone D = 78 for hard coal cobustion serves as a PM 10 classifier. WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

10 404 Air Pollution XVIII Fro both diagras it follows that the cyclone D = 78 can serve as a PM 10 classifier in cobustion processes at flue gas teperatures up to 00 C in the real range of saple volue flow rates fro to 6 3 /h. 5 Use of cyclone D = 3 as a PM.5 classifier Results of easureent with the cyclone D = 3, expressed by equation (6), were processed by the siilar way as results with the cyclone D = Cyclone D = 3 as PM.5 classifier for dry air Processing equation (6) for dry air, where the cyclone D = 3 classifies as a PM.5 classifier, leads to dependance of V ( 3 /h) on teperature t ( C) in the for 6 V 8.10 t t.575 (16) According to this relation the required flow rate through the cyclone V increases fro the value.58 3 /h at 0 C to /h at 00 C. 5. Cyclone D = 3 as a PM.5 classifier for flue gases fro coal cobustion processes For flue gases fro coal cobustion processes the Eq. (6) was rewritten into the for V a1, V (17) D D The processing of eqn. (17) by eans of software siilar to [5] was perfored in the sae range of values of the excess cobustion air coefficient (1) and the content of water vapour in wet flue gas w (1) as in the case of the cyclone D = 78. The results are presented in figures 7 and 8. In figure 7 dependances of V = f (t) are plotted for lignite cobustion and cobination of the excess cobustion air coefficient (1) and the content of water vapour in wet flue gas w (1) which leads to the axiu ( w = 0.10, = 1.) and iniu values ( w = 0.5, =.0) of the saple flow rate V ( 3 /h). In figure 8 siilar dependances of V = f (t) are plotted for hard coal cobustion. Again, for coparison the dependence V = f (t) for dry air is plotted in figures 7 and 8. Fro diagras in figures 7 and 8 it follows again that cyclone D = 3 can serve as a PM.5 classifier in cobustion processes at flue gas teperatures up to 00 C in the real range of saple volue flow rates fro to 6 3 /h. WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

11 Air Pollution XVIII 405 V ( 3 /h) ω(w)=0,10; α=1, ω(w)=0,5; α=,0 dry air Figure 7: t ( C) Range of dependances of V = f (t), where the cyclone D = 3 for lignite cobustion serves as a PM.5 classifier. V ( 3 /h) ω(w)=0,08; α=1, ω(w)=0,15; α=,0 dry air Figure 8: Conclusion t ( C) Range of dependances of V = f (t), where the cyclone D = 3 for hard coal cobustion serves as a PM.5 classifier. Two cyclones D = 78 and 3 for eission easureent of particle fractions PM 10 and PM.5 were developed at our departent. Verification tests of the cyclones were generalized in the for of criteria relations Stk = f(re). By a subsequent analysis of the criteria relations dependances of the saple volue flow rate on gas teperature V = f(t), where cyclones classify as PM 10 and PM.5 classifiers, were derived for dry air and flue gases fro cobustion of lignite and hard coal in the current range of the excess air cobustion coefficient and vapour content. Fro the individual dependences V = f(t) for both cyclone follows: In the given case the dependence of V ( 3 /h) on the gas teperature t ( C) is significant. WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press

12 406 Air Pollution XVIII Dependances V = f(t) for dry air and cobustion flue gases differ significantly (fro1 to 13%). For coal cobustion the differences of the corresponding volue flow rates depend on the flue gas coposition and differ in the range of several percents. Differences between volue flow rates for hard coal and lignite cobustion are not very significant. For both cyclones and in all analysed cases the corresponding volue flow rates for gas teperatures up to 00 C change in the range fro to 6 3 /h, usual for eission easureents, and the cyclones D = 78 and 3 can be thus used as PM 10 and PM,5 eission classifiers. Acknowledgeent The above research is an ite of the Czech Research Plan MSM Environental Technology. References [1] Sith, W.B., Parsons, C.T., Wilson Jr., R.R., Harris, D.B., A Five-Stage Cyclone Syste for Measuring Particle Size and Concentration in Process Streas. Journal of Aerosol Science, 13(3), pp , 198. [] Büttner H., Investigation on Particle Collection in Sall Cyclones. Journal of Aerosol Science, 17(3), pp , [3] Jelínek, V., Vanko, R., Chiney Technique (in Czech), KOMTEC and ROKA, pp [4] Dlouhý, T., Design of Boilers and Flue Gases Heat Exchangers (in Czech), Vydavatelství ČVUT, Praha, pp , [5] Heerka, J., Braniš, M., Vybíral, P., Hruška, A., Cyclone as PM 10 Classifier at Solid Particle Eission Measureent fro Coal Cobustion Deterination of the Saple Volue Flow Rate (in Czech), Authorised Software Ú1116 ASW PM10, FS ČVUT v Praze, 009. WIT Transactions on Ecology and the Environent, Vol 136, 010 WIT Press