Point Pollution Sources Dimensioning

Transcription

1 Point Pollution Sources Diensioning Georgeta CUCULEANU 1 ABSTRACT In tis paper a etod for deterining te ain pysical caracteristics of te point pollution sources is presented. It can be used to find te ain pysical caracteristics of te. Te ain pysical caracteristics of tese sources are top inside source diaeter and pysical eigt. Te top inside source diaeter is calculated fro gas flow-rate. For reckoning te pysical eigt of te source one takes into account te relation given by te proportionality factor, defined as ratio between te plue rise and pysical eigt of te source. Te plue rise depends on te gas exit velocity and gas teperature. Tat relation is necessary for diinising te environental pollution wen te production capacity of te plant varies, in coparison wit te noinal one. KEYWORDS: point pollution source, source diaeter, pysical eigt, proportionality factor. JEL Classification: O14, Q53 Introduction Tere are any types of pollution sources: point, linear, of surface and volue, as for; low, ean and ig, as eigt; continuous, interittent and instantaneous, as tie of eission. Te point sources ave a large use in industry for evacuating te gases resulting fro te tecnological processes. Tey are of stack type and are et in power plants, etallurgy, ceical industry, paper industry, petroceistry etc. Teir ain pysical caracteristics are te top inside diaeter of te source, d, and te pysical eigt of te source,. Tese caracteristics ust be deterined so tat to assure a iniu ipact on environent, even wen te production capacity of plant varies. 1. Teoretical Base Te data necessary for calculating te two source caracteristics entioned above are: gas flow rate, V g, evacuated fro te source, coputed fro te production capacity of te plant; stack gas exit velocity, ν, and stack gas teperature, T g, cosen in suc way tat buoyancy flux to assure an appropriate plue rise. 1 Georgeta CUCULEANU P.D. Eng, Te Bucarest Acadey of Econoic Studies, Roania E-ail cuculeanu@gail.co

2 Econoia. Seria Manageent Volue 14, Issue 1, 2011 Te top inside diaeter of te stack, d, is deterined fro te gas flow rate and is equal to: 4 V g d (1) were V g is in [ 3 /s] and ν in [/s]. Te pysical eigt of te stack,, is calculated by using te proportionality factor, R, given by te following forula (Cuculeanu, 2010): were Δ is te plue rise. R (2) In te industrial activity tere are periods of tie wen, for different reasons, te plants function at a saller production capacity tan te noinal one. For decreasing te environental pollution in tese periods, te proportionality factor ust fulfil te condition (Cuculeanu, 2010): p q O R 1/ 1 k (3) q were: p, q are dispersion paraeters, depending on te atosperic stability class and te dispersion scee ,,,,,1 according to te atosperic stability k 1 (Cuculeanu, 2010) Te plue rise is calculated wit te general forula: F C (4) n u were: F is buoyancy flux, 4 /s 3 u wind at te source eigt, /s. Te coefficient C and exponents and n depend on stability class, being (Turner, 1994): for unstable and neutral conditions: o C = 21,425, = 3/4, n = 1, wen F < 55; o C = 38,71, = 3/5, n = 1, wen F > 55; for stable conditions: o C = 2,6/s 1/3, = n = 1/3; for cal conditions: o C = 4/s 3/8, = 1/4, n =

3 Georgeta CUCULEANU In te forulae of te C, s represents te stability paraeter (Turner, 1994) and is given by: were: 1 dt s g (5) T dz T is air teperature, 0 K g acceleration of gravity, 9,8 /s2 Γ adiabatic lapse rate, 0, K/. Te buoyancy flux is calculated using eiter te forula (Turner, 1994): 2 T F 9,8d (6) 4Tg were: ΔT is stack gas teperature inus abient air teperature, 0 K or te forula depending on te gas volue evacuated fro te source: V T g F 9,8 (7) Tg Te wind at te pysical eigt of te source, u, is coputed wit te forula (Roanof, 1983; Turner, 1994): wen: a r u ua (8) u a is te wind at aneoeter eigt, /s a aneoeter eigt above ground, r exponent dependent on atosperic stability and surrounding area. Taking into account te relations (2) and (8), Δ given by (4) can be written as: 1/ 1 nr nr F R C a (9) n ua were R fulfil te condition (3). It is recoended tat te R value to be cosen round te average of te interval defined above. Te values near te axiu liit of te interval results in low pysical eigt of te stack, wat does not assure an appropriate dispersion. Te values of R near te iniu liit of te interval deterine great values of te stack eigt, difficult to be built. Te pysical eigt of te stack,, is calculated by eans of te relation (2). Te effective eigt of te plue,, is obtained by adding te pysical eigt and plue rise. 186

4 Econoia. Seria Manageent Volue 14, Issue 1, 2011 Te axiu ground level concentration is equal to (Arya, 1999): were: p q / 2q 2 Q b p q C ax (10) abu 2 q Q is pollutant eission rate, g/s a, b dispersion paraeters depending on te atosperic stability class. Te environental protection is assured wen te axiu ground level concentration is equal or less tan te adissible axiu concentration (CMA); te pollutant eission rate is deterined under tis condition. Te difference between te pollutant quantity per unit tie, occurring fro te tecnological process and te pollutant eission rate will be retained in gas cleaning equipent before te gas evacuation in te atospere. Wen te production capacity of plant varies up to a percentage l, te effective eigt of te plue will be calculated wit te forula (Cuculeanu, 2010): l = + k l Δ (11) In te sae condition te axiu ground level concentration will be (Cuculeanu, 2010): p q / q C ax l l Cax (12) l were C ax is te axiu ground level concentration, wen plant works wit wole production capacity and equal wit CMA. In order to calculate te pysical caracteristics of te stack one ay use tis etod, wic supposes te following steps to be acieved. 1. Calculation of te top inside diaeter, d, of te stack. Tis is done by eans of te forula (1), for any atosperic stability class. 2. Calculation of te pysical eigt,, of te source. Te pysical eigt of te source is coputed following te procedure: establising te atosperic stability classes for te annual ean wind (Turner, 1994) of te area were te plant will be built; coosing te dispersion scee, tat is necessary for te values of te dispersion paraeters, a, b, p, and q; coosing te value of r, depending on te atosperic stability class and area were plant will be built (Roanof, 1983; Turner, 1994); calculating te buoyancy flux; establising te variation interval of R, fro te condition (3) and coosing its value tat is to used; calculating te plue rise for cosen R; calculating te pysical eigt of te source. 187

5 Georgeta CUCULEANU 3. Calculation of te pollutant eission rate. Te pollutant eission rate is calculated fro te forula (10) using te effective eigt of te plue,, wic as been previously coputed. Tis calculation supposes tat te axiu ground level concentration in equal to CMA. In order to take into account te wind variability during te year, te axiu ground level concentration is verified for different wind s. For eac considered wind one calculates: te plue rise; te effective eigt of plue, by keeping te sae value of te pysical eigt of te stack previously calculated; te axiu ground level concentration; te pollutant eission rate for te wind wic deterines te greatest value of te axiu ground level concentration, under te condition tat tis concentration to be equal to CMA. Te dispersion paraeters used in te verification are tose of te atosperic stability class corresponding to te wind interval in wic te considered wind belongs to (Turner, 1994). Te verification as resulted in te fact tat te pollutant eission rate, wen plant works at te noinal production capacity, as te sallest value. Wen te wind as saller value tan te annual ean one, te axiu ground level concentration is saller tan CMA, because te plue rise increases. 2. Nuerical Application Let s suppose tat a plant eitting sulpur dioxide in te atospere is to be built in one of two urban areas: first, were te annual ean wind at te aneoeter eigt ( a = 10 ) is 2 /s; second, were te annual ean wind at te sae eigt is 4 /s. One as to calculate te pysical eigt and top inside diaeter of te stack using te following data: stack gas flow rate, V g = /s; stack gas exist velocity, ν = 15 /s; stack gas teperature, T s = K. Te axiu ground level concentration, wen te production capacity of te plant will decrease till 70% of te noinal one, is to be deterined. 1. Te top inside diaeter of te stack, for any atosperic stability class is calculated wit te forula (1) and te result is 5, According to te Pasquill atosperic stability, te possible classes are: A, B, C, E and F, wen te wind is 2,5 /s; B, C and D, wen te wind is 4 /s. Te dispersion scee used in tese calculations is tat given in ASME (Seinfeld, 1986), wic as not dispersion paraeters for te classes C and E. 188

6 Econoia. Seria Manageent Volue 14, Issue 1, 2011 In table 1 te dispersion paraeters used in te present calculation are given: Table 1. Dispersion paraeters (after Seinfeld, 1986) Atosperic stability class a p b q A 0,4 0,91 0,4 0,91 B 0,36 0,86 0,33 0,86 D 0,32 0,78 0,22 0,78 F 0,31 0,71 0,06 0,71 Te values of te r for te four atosperic stability classes are (Roanof, 1983): r = 0,15 for classes A and B; r = 0,25 for class D: r = 0,6, for class F. Te buoyancy flux, coputed wit te forula (7), is 256,69 4 /s 3, for all atosperic stability classes. According to te condition (3) te factor R is in te interval (0,5), because = 3/5 and k 1 (Turner, 1994; Cuculeanu, 2010). In accordance wit wat was previous entioned, te value of R as been considered 2,35. For te annual ean wind of 2,5 /s te values of te pysical eigt of te stack and plue rise for te class A are equal wit te corresponding values for te class B. Tese values are = 125,8 and Δ = 295,6. In case of SO 2 for te sae value of te wind and axiu ground level concentration equal wit CMA ( g/ 3 ) te pollutant eission rate is 69,04 g/s, for te class A, and 75,32 g/s, for te class B. For te class A te wind ranges in te interval (0,3) and te class B te wind in interval (0,5) depending of insolation (Turner, 1994). Terefore, te verification of te axiu ground level concentration was perfored for ore values of te wind. On te base of te results presented in table 2, te following conclusions can be drawn: te axiu ground level concentration as te sae value for te bot atosperic stability classes toug te pollutant eission rate is different. te axiu ground level concentration is saller tan CMA wen te wind is saller tan its annual ean value and greater tan CMA wen te wind rises above its annual ean value (2,5 /s). Wen te wind rises above its annual ean value te environental pollution increases. Consequently, te pollutant eission rate ust ave te value corresponding to te class A for te axiu wind used for verifications. Fro te table 2 one can notice tat tis is 4 /s. Te corresponding pollutant eission rate is 58 g/s. /s Table 2. Pysical and eission caracteristics for te classes A and B wen u a = 2,5 /s (C ) Δ Q, g/s C ax A B g/ 3 ax 70 g/ ,72 125,8 864,52 14, , ,4 125,8 495,2 22, , ,5 295,6 125,8 421,4 69,04 75, , ,24 125, , , ,64 125,8 310,44 28, ,

7 Georgeta CUCULEANU Concerning te class E, only verifications ave been ade for soe wind s, because its probability of occurrence is very sall. Te results of te verifications find in te table 3; tey sow tat at te ground level te pollution is very sall, even for te greatest pollutant eission rate (75,32 g/s). /s Table 3. Pysical and eission caracteristics for te class F wen u a = 2,5 /s Δ Q g/s 1 236,38 125,8 362,2 5, ,2 125, , ,5 94,56 125,8 220,36 75,36 6, ,8 125,8 204,6 5, C ax (C ax ) 70 g/ 3 g/ 3 Wen te annual ean wind is 4 /s and class is B, te pysical eigt of te source and te plue rise are 83,6 and 196,4 respectively. For te sae wind, but te class D, te two caracteristics are 70,51 and 145,7 respectively. Te pollutant eission rate is 50,036 g/s for te class B and 56,28 g/s, for te class D. For tese atosperic stability classes te verifications were ade for ore values of te wind s and teir results are given in te table 4. Te analysis of te table 4 sows tat te sae conclusions can be drawn, as in te case of te wind of 2,5 /s. For protection te environent, te pollutant eission rate ust be saller tan te value resulted fro te annual ean wind. Tus, for te class B it ust be 44 g/s and for class te D it ust be 49 g/s, values corresponding to te wind of 6 /s. Taking into account tat te difference between te classes B and D consists in te insolation degree and day tie (Turner, 1994) te dispersion paraeters of one class were verified on te pysical eigt of te oter class. Te results are presented in te tables 5 and 6. /s Table 4. Pysical and eission caracteristics for te classes B and D wen u a = 4 /s Δ Q g/s C ax (C ax ) 70 g/ 3 g/ 3 class B 2 392,74 83,6 476,34 17, , ,82 83,6 345,42 21, , ,4 83, , , ,1 83,6 240,7 27, , ,6 214,6 28, , class D 2 331,29 70,51 401,8 17, , ,86 70,51 291,37 21, ,

8 Econoia. Seria Manageent Volue 14, Issue 1, 2011 /s Δ Q g/s C ax (C ax ) 70 g/ 3 g/ ,7 70,51 236,21 56, , ,52 70, , , ,44 70, , , Te verification of te stack pysical eigt for te class B wit te dispersion paraeters of te class D sows tat pollution decreases for te pollutant eission rate of 56,28 g/s, even for te wind ore tan 4 /s (table 5). /s Table 5. Verification of te class B diensions for u a = 4 /s, wit te class D dispersion paraeters Δ Q g/s C ax g/ 3 (C ax ) 70 g/ ,65 83,6 401,25 16, , ,77 83,6 295,37 20, , ,83 83,6 242,43 56,25 22, , ,34 83, , , ,6 189,6 24, , ,76 83,6 174,36 25, , Te verification of te stack pysical eigt for te class B wit te dispersion paraeters of te class B sows tat pollution increases even fro te wind of 4 /s for te pollutant eission rate saller tan in te precedent case (table 6). Fro te results one infers tat te pysical eigt corresponding to te instable conditions deterines a saller pollution at te ground level. /s Table 6. Verification of te class D diensions for u a = 4 /s, wit te class B dispersion paraeters Δ Q g/s C ax (C ax ) 70 g/ 3 g/ ,51 473,51 17, , ,7 70,51 339,21 23, , ,5 70, ,036 27, , ,2 70,51 231,71 29, , ,33 70,51 204,84 31, , ,14 70,51 185,65 33, ,

9 Georgeta CUCULEANU Conclusions Te etod presented in tis paper for deterining te pysical eigt of te point pollution source, at teir designing, as te following advantages: it akes a connection between te pysical eigt of te source and functional caracteristics of te plant by eans of te proportionality factor; it is assuring te ground level concentration under te adissible axiu liit; it is assuring a precise deterination of te pollutant quantity tat as to be retained by purification equipent; it is leading to te reducing of te environental pollution were te production capacity of plant was decreased. References Arya, S. Pal, (1991). Air pollution eteorology and dispersion, Oxford University Press, Inc. Cuculeanu, G., (2010). Effects of te production capacity variation on te pollutant eission caracteristics, Metalurgia International, vol. XV, no. 4, p. 71. Roanof, N., (1983). Dispersia poluanţilor în atosferă şi diensionarea coşurilor de fu, IM, Bucureşti. Seinfeld, J., (1986). Atosperic ceistry and pysics of air pollution, Wiley Interscience Publication, USA. Turner, D. B., (1994). Atosperic dispersion estiates, CRC Press, Inc., USA. 192