API 931 Chapter 6 Dispersion of Gases

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MANUAL ON DISPOSAL OF REFINERY WASTES VOLUME ON ATMOSPHERIC EMISSIONS

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CHAPTER 6-DISPERSION OF GASES

AMERICAN PETROLEUM INSTITUTE Division of Refining 1801 K Street, N.W. Washington, D.C. 20006

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Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use in connection with any method, apparatus, or product covered by letters patent, nor as insuring anyone against liability for infringement of letters patent. API publications may be used by anyone desiring to do so, and every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them. However, the Institute makes no representation, warranty, or guarantee in connection with API publications and hereby expressly disclaims any liability or responsibility for loss or damage resulting from their use; for any violation of any federal, state, or municipal regulation with which an API publication may conflict; or for the infringement of any patent resulting from the use of an API publication.

Copyright © 1974 American Petroleum Institute

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FOREWORD

This chapter describes environmental conditions at the probable site of refinery construction and the effects of these conditions on plume rise, atmospheric dispersions, and ground level concentrations. Meteorological aspects are discussed at some length. Ground level concentrations of pollutants should be determined from the most accurate existing predictive techniques prior to actual construction. This will ensure that specific requirements are not exceeded. In evaluating plume rise and atmospheric dispersion, an eclectic approach is used. The result is one formula for the determination of plume rise and one set of formulas for the determination of ground level concentrations. For refineries located where abnormal conditions are not encountered, these equations represent a suitable tool for the design engineer to use in estimating ground level concentrations and thereby determining the required stack heights. (High-velocity vents are not covered by these equations.) The predictive techniques presented herein are applicable to estimating atmospheric dispersion at a single source of emission over uncomplicated terrain, when mean wind speed and direction can be determined. The equations enable determination of ground level concentrations for an elevated source and for a ground level source. Predictive techniques for estimating atmospheric dispersions of emissions from multiple sources are also included. Dispersion coefficients are most applicable to ground level releases, but they have been applied to stack releases as well. Within the layer in which diffusion occurs, it is assumed that stability characteristics remain constant. When designing a refinery facility, neither this approach nor any textbook approach is sufficient in cases of unusual atmospheric conditions or irregular topography. Handling these conditions requires a high degree of expertise and may involve the use of other predictive aids, such as wind tunnels .

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iii

CONTENTS

CHAPTER 6-DISPERSION OF GASES PAGE

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6. J Typical Regulatory Requirements .... 6.2 Environmental Conditions at Construction Site ................. . 6.2.1 Temperature ..... 6.2.2 Wind Motion and Turbulence .. 6.2.3 Lapse Rate....... ..................... . 6.2.4 Stable and Unstable Air ..... 6.2.5 Inversions ... 6.2.6 Influence of Local Terrain .. 6.3 Behavior of Plumes .. 6.3.1 Plume Types and Characteristics ... 6.3.2 Influence of Wind Fluctuation .... 6.3.3 Plume Dilution and Diffusion .. 6.3.4 Effects of Obstructions, Eddies, and Downwash ... . 6.3.5 Plume Rise and Plume Rise Formulas ................... . 6.3.6 Limitations and Reliability of Predictive Techniques .............. . . ............ . 6.3.7 Behavior of Flare Plumes .. 6.4 Atmospheric Dispersion Theories 6.4.1 Background ... 6.4.2 Basic Formulas .................................. . 6.4.3 Parameters and Dispersion Coefficients ..... 6.4.4 Influence of Atmospheric Conditions ... 6.4.5 Dispersion of Aerosols and Particulate Matter ... 6.4.6 Multiple Sources.......... ...... ...... ........ . 6.4.7 Wind Tunnel and Other Studies ...... .... . 6.4.8 Limitations and Reliability of Predictive Techniques ... 6.5 Cooling Tower Plume Rise.. ............... . 6.5.1 B a c k g r o u n d . . . ............ ... 6.5.2 Analysis of Plume Rise and Plume Behavior... 6.5.3 Plume Condensation and Precipitation. 6.5.4 Minimizing Visible Plumes... ......... . 6.6 Sample Calculations .... 6.6. J Refinery Boiler Stack ... 6.6.2 Process Heaters and Stacks .... 6.6.3 Catalytic Cracking Units ... 6.6.4 Flares...... .... . 6.6.5 Storage Tanks .... . 6.6.6 Product Loading .. . 6.6.7 Roof Vents .... REFERENCES ... APPENDIX-ABBREVIA nONS AND SYMBOLS ..

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6-1 6-1 6-1 6-2 6-3 6-3

6-4 6-4 6-5 6-5

6-6 6-6 6-7 6-7 6-8

6-9 6-11 6-11 6-11 6-13 6-13

6-14 6-16 6-16 6-17 6-\8

6-18 6-18 6-20 6-21

6-24 6-24 6-24 6-27

6-28 6-29 6-30 6-33

6-33 6-35

',1ANUAL ON DISPOSAL OF REFINERY WASTES VOLUME ON ATMOSPHERIC EMISSIONS CHAPTER 6-DISPERSION OF GASES Typical Regulatory Requirements 1':

These publications define the contaminants and describe their properties and their effects on human health and welfare, animals, and vegetation. The human health category includes toxicology data and effects on the respiratory and nervous systems. Standard test methods are also included.

i,'c!cr~d

Air Quality Standards, or the current are outlined in the Federal Register. I * .1."C standards appear in tabular form in the Air " r \ ('irS of May 3,1971, and are reproduced in i ,doic 6-1 also gives the levels at which the ""'1,111 contaminants affect human health and

_,::1"011[\, ',,'

.\

..

6.2 Environmental Conditions at Construction Site

"

Department of Health, Education and ,,",,: .• :,' '.1' ",ued a series of six publications on the ."If',,[ " \ i r l)uality Criteria, t The subject of each ".~, "';:"1 I', olle of the six common contaminants: . !!\

The three most important factors of weather in all parts of the world are temperature, wind, and precipitation. For our purpose, however, the primary concerns are temperature and wind.

ilks.

:1 ,']l)Jl0xide.

"!;lil'al

i

Oxidants,

6.2.1 TEMPERATURE

Temperature can vary widely because it is influenced by geographical location and seasonal change. The lowest and highest recorded readings in the United States are - 66 F and + 134 F at Yellowstone Park and

',(IS on pages 6-33 and 6-34,

rI, 'Tl1 :)'Jperintendent of Documents. U.S. Washington, D,C, 20402.

Govern~

: ';lIi,':,

I able 6-1 ~Federal Air Quality Standards and levels at Which Effects Show in Humans Federal Air Quality Standards ~~~--------"-~-

Primaryt

Levels at Which Effects Show'

.. ---~-

Secondaryt

Human Health

Welfare§

80 200

60 150

115 300

85 285

fIn);.:uIJIt:\ .

Annu~l~ ~~llJl1t:tric

'h., ... ·Ilr Cl)nc,

mean, [J.g per ell m :1.g per ell mt

75 260

60 150

. s.uur (h,des:

Annu.d ,lfIth aver. f.Lg per ell m 'h, ~-~-hr (llne, ag per ell mil \f,l, ;-hr cune. tJ.g per ell m!1 C.l.t~·n \1t1no\l-l .' \ . ut::. ~':lr ('{me, mg per ell ml! J\ I'il[ ":unc, mg per ell mil "x"'h,hcmical Oxidants' 0:' . t'·nr l11ax. :1.g rer ell mi i

80 (0.03 ppm) 365 (0.14 ppm)

,:,,u

If • ..!r".Jrthln~'

10 (9 ppm) 40 (35 ppm)

10 40

12 58

160 (0.08 ppm)

160

130

160 (0.24 ppm)

160

100

100 (0.05 ppm)

100

117 118

100

-'·hr ('!.)·nc 6-9 am,

"..1.\

. ..:. per cu m

", -,

60 (0.20 ppm) 260 (0.1 ppm) 1,300 (0.5 ppm)

'''cn (hides: ,d .trith aver, iJ.g per eu m 1\ ~l\'l'r, 'J..g per ell m

• '"

~

Fnkral criteria. hv June I, 1975. enforcement.

l'lllit un

.lnd crops. h 4/8 Cloudiness' Cloudiness * E

D D D

F E D

D

"'The degree of cloudiness is that fraction of the sky above the local apparent horizon that is covered by clouds. The neutral class (D) should be assumed for heavy overcast conditions, day Of night.

6.2.5 INVERSIONS

Temperature inversions occur when the temperature of the air increases with altitude. A common cause of inversion is rapid cooling of the ground at night by radiation. The surface air is then cooled by convection so that the air temperature some distance from the ground is higher than the air temperature at or near ground surface. Inversion can also be caused by air masses, or fronts, and occasionally by turbulence. In Los Angeles it is caused by cool marine air forcing its way under warmer continental air. Both masses of air are then trapped by the adjacent coastal mountains. When an inversion occurs, the existing lapse rate is negative, and therefore always less than the adiabatic

lapse rate. This results in extreme air stability. Under these conditions plumes generally tend to disperse downward, thus decreasing effective stack height. Since most elevated inversions are higher than 500 feet, this would apply to most stacks. If a stack is designed for a location with a condition favorable to inverSIOn, two design possibilities should be considered:

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I. Design the stack with sufficient height so that the stack exit will be above most inversion layers. 2. Design the stack exit gas velocity and exit gas temperature so that the plume will rise above inversion, or will at least provide good penetration. Frequently the inversion layer is sufficiently high so that neither of these alternatives is possible. With most stacks a critical wind velocity causes maximum ground level concentrations of pollutants at moderate wind speeds. Under these conditions, increasing the physical stack height further elevates the plume, thus reducing ground level concentrations. Increasing stack gas velocity or temperature has no significant effect on these ground level concentrations. 6.2.6 INFLUENCE OF LOCAL TERRAIN

Local terrain can have a pronounced influence on weather and weather characteristics such as air stability. A wind proceeding over a level area changes direction on reaching hills, high structures, or mountains so that the obstruction can usually be cleared. Air that is forced to rise to pass over such obstructions mayor may not become unstable depending upon the speed of ascent, humidity conditions, and contrast between the cooling rate of the rising air and the lapse rate of the surrounding air. In the Los Angeles area the incoming cool marine air does not have sufficient momentum to clear the mountains, resulting in inversion and very stable air. As discussed previously, the type of terrain-rocky, sandy, or wooded-influences the magnitude of daily temperature variations. The smaller the daily temperature variation, the greater the tendency toward stable air. Areas of strong topographic relief also experience air currents (breezes). These breezes are usually upward during the day when the valley floor is relatively warm, and downward at night when the obstruction cools faster than the sheltered valley below. The major effect of local terrain on weather is the extent to which it introduces instability into air movements or promotes turbulence and eddy currents. These in turn directly affect gas dispersion.

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DISPERSION OF GASES

6-5

plume alternately ascends and descends or descends and ascends after leaving the stack. TYPlability. Generally, the equations are ,,'lW[[C in low to moderate wind velocities-that ,:',1 lllPh (2.3 to 9.1 m/sec). The accuracy tends cI ':11 'e somewhat for lower or higher wind veloci!" is not generally important because t1H is a "I" Ilii'h figure for low wind velocities, thus '" II" '! !!round concentrations. At high wind :', dilution effects preclude high concentrations, 1 "line of the plume is occasionally swept to ,l:lnd.

III,' rl'asoning with reference to wind velocities IIp[llleS to unstable air except that the factor I ".,jiIV usually produces an increase in average '. !'!'I~ilt. This is reflected in equation (4) by use of :111' ;'1 1,1 or 1.2 applied to t1H. Unfortunately, ., ,':I;,rl\, with strong instability, the higher stack 'I ""'1' 'lot overcome the effect of looping, which "'[lei uce undesirable ground concentrations at I',ilort distances downwind from the stack. It a I reg uent occurrence. ,',:[I"t deviation from these equations is ", '1',','0 wilen there is an inversion above the stack , :.ilion) where the most precise results should ""hlC, 1' a protective shield.

",II

63.7 BEHAVIOR OF FLARE PLUMES

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I,.: Illalor potential contaminant from a flare is ''':iur dio\idc (SO,), and this contaminant is related to "'t ;'I,)rngen sulfide (H,S) content of the flared gas. I'H[I"ulllk matter (smoke), odor, and plume visibility ,i,,) contribute to pollution. These pollutants can 1,1111 he eliminated to a large extent by proper .. """ion techniques and by the use of steam to effect ""'k",e combustion. Infrequently heavier hydror "IIlh. ,uch as phenolics, and alkylation residues "l,lllllll~ hydrofluoric acids may also be present.

6-9

It should be noted that under normal flare operation, sulfur dioxide emission is negligible when compared with emissions from refinery stacks in which sulfurcontaining residual fuel oils have been used. Sulfur dioxide assumes serious proportions only when there is an emergency condition such as the loss of a compressor or the shutdown of the sulfur pidnt. This discussion is concerned with lighted flare operation under design conditions. If the flare is unlighted, dispersion is governed by the criteria discussed in this section and in the subsequent section (see Paragraphs 6.4. I through 6.4.8). The calculations of plume rise and atmospheric dispersion from stack effluents are relatively complicated. These calculations are even more complex for flared gas, in which case the stack effluent gas is burned prior to final dispersion and heat release is external to the flare stack. An empirical approach to the problem of plume rise is given in the following equation: H

= Hs

Where:

+ t1FL + t1H

(5)

H

effective height of plume rise. Hs = actual stack height. t1FL = vertical component of flare length. t1H = plume rise after burning is complete. The following paragraphs show that the accuracy of determination of t1FL and t1H is su bject to question. Practically, the flare length can be assumed to be 120 times the flare stack diameter, as indicated in API RP 521. 14 This figure is directly applicable at 0.2 sonic velocity, which is the usual basis of design. The flare length varies with velocity and flame temperature, which is related to the material being burned. The flare length also varies with the value of Cp/C, the ratio of specific heats. It is apparent that the true flare length may be greater than or less than the value shown. To determine the vertical component of flare length (t1FL) a correction must be made for the horizontal component, which is related to the angle of incidence of the flare to the horizontal. This angle is influenced by the relation of wind velocity to exit gas velocity. Two methods are presented in API RP 521,14 and the recommended method involves the use of the graph shown in Figure 6-6, from which ~t1 Y (vertical component) can be obtained. The second determination is that for t1H, the burned flare gas plume rise. This is calculated by using Holland's formula: 12

t1H = :d

[1.5 +

2.68 (IO-ap )

(T.:';:-, T}/J

(6)

This formula is applicable at the theoretical or imagi-

6-10

DRW

MANUAL-ATMOSPHERIC EMISSIONS

f

1.0

.--

0.9

/

0.8

--l

101

b

A - E~trernely unstable B _ Mod.rately unstable

e-

J " ~ ~

• 2

>-

~

1i 0

E

ci;

cT

~

..,; "

E

a "-

0

c

~v c

"

LL

0

,..;i «

~

0

~.

:i.

'"

E

.;" x

0

..,~c 0

c

.g 0

l: c 41

v 0

c:

U

E

.;" x

0

~ ~

0 41 v

c:

E 15 I ~

co

I

I 1 .I i

I

-0

"" ~

i.!. •

'.,

~

'xew x

I

6-25 1

'"

i.i: w~

6-26

DRW

MANUAL-ATMOSPHERIC EMISSIONS

large boilers use forced draft. Also, many refinery boilers burn gas as well as fuel oil, while process heaters are more often gas-fired and generally use a higher percentage of gas. To allow for greater variation in the combustion value of gas, more air is used in process heaters; excess air may be as high as 40 percent. Finally, process heater stacks are usually lower than boiler stacks because the lower height provides a chimney effect and a slightly negative combustion box pressure. The concentration of nitrogen oxides (NO x ) is usually higher in a process heater stack because higher temperatures enable the conversion of nitrogen to oxides. Combustion box temperatures and stack temperatures are higher in process heaters than in boilers. Heater stacks range in temperature from 700 to 1,000 F. Sulfur dioxide and carbon dioxide concentrations are lower in process heaters primarily because of the dilution supplied by additional excess air. In the case of carbon dioxide, an additional factor is the carbon: hydrogen ratio of gas, which is lower than that of fuel oil. Consider a process heater with a stack height of 164 feet and a stack exit diameter of 8 feet. The stack emits 150,000 cubic feet per minute of gas at 800 F and the gas analysis shows 0.25 percent NO x (as NO,)*, 2.9 percent 0" 77.5 percent N 2 ; the balance is water vapor. The average wind speed is 15 mph (6.7 m/sec). On a sunny day, the ambient temperature is 68 F. Thus the stability category is C. Calculate the critical wind speed (problem I). For a wind speed of 15 mph, calculate the maximum ground level concentration of NO x and the point of maximum concentration (problem 2). Calculate the ground level concentration of NO x 1.25 miles downwind from the stack (problem 3).

6.6.2.1 Assumptions I. Stack height is 164 fcet (50 meters).

2. Stack temperature is 800 F (427 C) (700 K). 3. Ambient temperature is 68 F (20 C) (293 K). 4. Molecular weight of NO, is 46 grams per gram mole and weight is 0.129 pounds per cubic foot at N.T.P. 5. Atmospheric pressure is 10 13 millibars. *Jt is assumed that all oxides of nitrogen are included in the 0.25 percent NO" analysis. The primary components of NO" are NO and NO, and are usually updated as NO" which has a molecular weight of 46. To the extent that the average molecular weight of NO, differs from that of NO-, the solutions in Problems I. 2, and 3 would require modification.

Q _ (\50,000) (0.25%) (0.129Ib/cu ft) (454 g/Ib) (29~\ 60 sec/min 700)

= (375L~8~) (0419) 60'

(375) (2~.6) 60

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= 154 g/sec 6,6,2,2 Problem I Holland's equation is used to determine effective stack heights, which can be calculated for various wind speeds as follows (see Table 6-3):

~H

=

1'/ [1.5 +

2.68 (lO-'p)

C'~, Ta) d J

Where: 150,000

)', = stack exit velocity

2980 ft· mm

50.3

15.1 m/sec Substituting,

~H =

15.1

~2.44)[1.5 + 2.68G~~~)eO~~0293)2.44J

3~8 [1.5 + 2.71 (~~) 2.44J 36.~ (5.3) [1.

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195 [1.

Table 6-3-Effective Stack Heights j.H

i'

h

(01)

(m/sec)

1.0

3 5 6.7 8 10

j.H

(m)

195 98 65 39 29 24 20

2

+

245 148 115

89 79 74 70

It is apparent that the critical wind speed is approximately 5 m/ sec, or 11 mph. A more precise critical wind speed can be obtained by plotting maximum concentration vs. wind speed (see also Turner B). The critical wind speed corresponds to the highest maximum concentration on the curve. (See Table 6-4.) Table 6-4-Maximum Concentration as a Function of Wind Speed at Stability Condition C .... (m/sec) 1.0 2 3 5 6.7 8 10

H

(m) 245 148 115 89 79 74 70

Z'tJ./Qrnax

(m2)

2.4 6.4 1.0 1.8 2.3 2.7 2.9

X X X X X X X

10-" 10-" 10-" 10-" 10-:' 10- 5 10-"

QI . .

(g/m) 154 77 51 31 23 19 15

ZIlH\X

(g/m:l) 3.7 X 10-' 4.9 X 10-' 5.1 X 10-' 5.6 X 10-' 5.3 X 10-' 5.1 X 10-' 4.4 X 10-'

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6-27

DISPERSION OF GASES

6.6.2.3 Problem 2

6.6.3.1 Assumptions

At a wind speed of 15 mph (6.7 m/sec), the maximum concentration of NO x is 5.6 X 10-4 g/ml and will be found at a downwind distance of 0.9 km (Figure 6-18).

I. Stack height is 200 feet (61 meters).

2. Stack temperature is 800 F (427 C) (700 K). 3. Ambient temperature is 68 F (20 C) (293 K).

6.6.2.4 Problem 3

4. Wind speed is 4 m/sec (8.9 mph).

To determine the NO x concentration at a distance of 2.0 kilometers (1.25 miles) downwind of the source at the centerline of the plume and at ground level, the equation is:

Z(x,O,O;H)

=

Q

7C'cr y cr z [J.

exp [ - 2!

(H)'J z IJ

~ C~~),J

Where:

x

=

~ II

= 200 meters

2000 meters at stability condition C

cr. = 115 meters

z(2000, 0,0;79)

z

=

154 (4.84)(10=5) exp

[I - 2 (0.69) 2J

=

(3.2 X 10-4) (7.88 X 10-')

=

2.5 X 10-4 gicu m

6. Stack diameter is 12 feet (3.66 meters). 7. Gas discharge is 600,000 cubic feet per minute (actual). 8. SO, in exit gas is 1,000 parts per million (0.1 percent by volume).

154 Z(2000, 0,0 ;H) = (3.1416) (200) (lIS) (6.7) exp [ -

5. Atmospheric pressure is 10\3 millibars (N.P).

This is equivalent to 250 micrograms per cubic meter.

9. S02 emitted is 0.1827 pound per cubic foot (N.T.P.) 10. Particulate emission with no precipitator is 154 grains (10 g) per SCF. II. Particulate emission with an electrostatic precipitator is 15.4 grains (1.0 g) per SCF.

6.6.3.2 Problem 1

Calculate maximum downwind concentration of SO, and the point of maximum downwind concentration. Use Holland's formula to obtain the effective stack height.

6.6.3 CATALYTIC CRACKING UNITS

j,H =

I II j

i

In a catalytic cracking unit, the catalyst regulator is equipped with two stages of internal cyclones in the regenerator, and the catalytic off-gases are then processed in a carbon monoxide (CO) boiler. In general, for all catalytic cracking units having CO boilers, the CO content in the tail gas will be essentially zero. The CO boiler inlet gas will contain an average of 9.5 percent CO for a fluid bed and 6.0 percent CO for an hourly bed. 28 Under the following conditions, assumed for a fluid bed unit during a 50,000-barrel day, calculate the maximum ground level concentration of S02 at a wind speed of 4 m/sec (8.9 mph) and determine the location. (See Problem I.) The day is bright and sunny, stability category B. Under the same conditions, calculate the particulate concentration at ground level at distances of 0.5 mile and 2.0 miles, and displaced horizontally 0.25 mile (0.25 mile from x-axis). Calculate these concentrations for emissions if no electrostatic precipitator is present (see problem 2) and if an electrostatic precipitator is connected to the CO boiler (see problem 3).

v~d [1.5 + 2.68 (10-'p)

C-'-j.,Ia)

dJ

Where: v., = stack exit velocity = 60,0.000 X __ L_ 113.1 60 X 3.28 =

26.9 m 'sec

Substituting, j,H= =

~6.9~3.66)[1.5 + 2.68 (1.013)C()().ffit93 )3.66J 24.6 [1.5

+ 2.71(0.581) (3.66)]

178.6 X 1.10

H = H, =

196 meters (at stability condition B)

=

Thus,

= 24.6 (7.26)

+

j,H = 61

+

196

257 meters (effective stack height)

Determine Q, quantity of S02 emitted in g/sec.

Q = ((>OQ.000)(O·20Il(0.1:~7 Ib/cuftl (4}_~lll)G~~) 600

~~.95) (0.419

829.5 (0.419)

347 g/sec

DRW

6--28

Xm.x = (QX:J (;) = 2.7 X = 2.39

10-'

MANUAL-ATMOSPHERIC EMISSIONS

e:

7

)

x (2000,400,0;257)

= 0.049 exp [ -

1/2 (1.38)'J

X 10- 4 glcu m

exp [ -

Where:

~ Qmax

=

6.6.3.3 Problem 2

Determine the particulate concentrations if no precipitator is present. To calculate downwind concentrations, the effective stack height, H, and the total quantity emitted, Q, must be known. H has been calculated as 257 meters. _ (600,000 cu ft/min)(10 g/cu ft) (?93) Q 60 sec/min 700 100,000 (0.419)

=

TO

_Q- exp [ - I (l')'J

cr"O',1L

2

cry

exp [ -

~ (~YJ

For stability condition B, at 0.8 km downwind, cry = 130 m and crz = 85 m. For 2 km, cry = 290 m and cr, = 235 m. x(800,400; 257) =

7:

41,900 [ I (400)2J (130) (85r (4) exp - 2 130 exp [

=

1.1 X 10-2 g/cu m (at 2.0 km

downwind and 0.25 km from x-axis) 6.6.3.4 Problem 3

As indicated in the preceding data, the precipitator generally reduces particulates by approximately 90 percent overall, the reduction being greater for larger size particles. The effective stack height, H, is still 257 meters and Q is only 10 percent of its former value (i.e., 4190 g/sec). Therefore, z(800,400,0; 257) = 2.74 X 10- 1 g/Cll m x(2000,400,0; 257)

41,900 glsec

The eq uation to determine particulate concentration at a finite distance is: X(x,y,O;H) =

•

= 0.049 (3.86 X 10-1) (5.52 X 10-1)

2.7 X 10-'sqm

The location of maximum downwind concentration of SO, at ground level, for stability condition Band an effective stack height of 257 meters, is 1.7 kilometers (Figure 6-18).

=

1/2 (1.09)'J

-1 e;n'J

0.30 exp [ - 1/2 (3.08)'J exp [ - 1/2 (30.2)2J

=

1.1 X 10-3 g Icu m

In the preceding examples, it is assumed that particulates behave as gases. This is substantially true after the particulates pass through a precipitator because the remaining particles are primarily small (under lOlL); although some medium-sized particles (lOlL to 60IL) are present. If no precipitator is present, more particles are in the medium range, and possibly some in the large range (over 60IL). The large particles, and to some extent the medium particles, suffer fallout resulting in the so-called "tilted pI ume." Thus, downwind readings without a precipitator are higher than the values shown, especially for X(800,400,0 ;257), which is now shown as 2.74 X 10- 5 g/Cll m

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6.6.4 FLARES

Calculate the total effective height of a flare plume under the following conditions: I. Stack height is 150 feet (45.7 meters).

2. Stack diameter is 2 feet (0.61 meters).

= 0.30 (8 71) (l0- 3) (1.05) (10- 2) 2.74 X 10-' g leu m (at 0.5 km downwind and 0.25 km from x-axis) Z(2000,400,0 ;257) =

7:

41,900 4) exp (290)(235f(

[I - 2 (400)'J 290

exp [

-1 G~~YJ

3. Wind velocity is 15 mph (22 ft/sec) (6.7 m/sec). 4. Stack exit velocity is 0.2 sonic velocity or 1000 X 0.2 = 200 ft/sec (61 m/sec). The total effective height of the plume, H, is determined by: H

= Hs

+ J.FL + J.H

•

6-29

DISPERSION OF GASES

! Is = stack height. '... fL vertical component of flare length (to .~

f!

yield imaginary stack height). = plume rise above imaginary stack height using Holland's equation.

;, has been shown that j.FL can be determined with degree of accuracy, but j.H is an approximation .;t hcst. regardless of the formula used. There is reason ;. helieve that j.His a relatively low figure, numerically. ',)Ille

lis 1"' . L

J.FL

obtain

i ,0 . il

= 45.7 meters. = constant X stack diameter (API RP 52 I) 120 X 2 = 240 feet (73.2 meters). =

FL

(~~l). velocity (IL".) to stack

~'W = ~ = 0.110 200

,d from Figure 6-6, =

044 .

.1FL = 240 (0.44) = 105.6 feet (32.3 meters)

,'" obtain .1H from the Holland equation, the [,)llowing data were assumed for the imaginary stack height:

T. (temperature of total gases) is 600 F (589 K).

3. Tn (ambient temperature is 40 F (278 K).

6. Flare velocity (vertical component) is 22 X 0.44 =

9.7 ft/sec (2.96 m/sec).

I

=

C' t,J'n)

dJ

26.'1 [l.~ + 2.68 (\.013) G~~) 2. \3 ] + 2.72 (0.53) (2.13)1 0.94 (1.5 + 3.1) = 4.3 meters 45.7 + 32.2 + 4.3 = 82.2 meters (270 feet)

= 0.94 [1.5

•

=

H =

NOTE: The sources of loss and the formulas for tankage loss are described in some detail in the API Manual on Evaporation Loss, specifically Bulletins 2517 29 and 2518. 30 These bulletins discuss evaporation loss from floating-roof and fixed-roof tanks, respectively and also include relatively simple nomographs that can be used in lieu of the equations. The method for determining true vapor pressure (TVP) from Reid Vapor Pressure (RVP) for any given temperature is given in API Bulletin 2513. 2

6.6.5.2 Problem 1: Evaporation Losses of Fixed-Roof Tanks

L!/ = 0.024

C4./~P)'"" (D)'73 (H)051 (T)O '0 (FpHC)

breathing loss, in barrels per year. vapor pressure of liquid at bulk temperature, in psia. D = tank diameter, in feet. H = average outage, in feet. T = average daily ambient temperature change, in degrees Fahrenheit . Fp = paint factor: \.39 for aluminum. \.00 for white. C = adjustment factor for small diameter tanks. L" P

5. Flare velocity is 22 ft/sec.

V~d[1.5 + 2.68 (lO-"p)

3. Annual average wind velocity is 10 miles per hour.

Where:

4. p (pressure) is 1013 millibars.

.1H =

6.6.5.1 Assumptions

a. BREATHING Loss

I. Flare diameter is 7 feet (2.13 meters).

,

Calculate total annual storage loss for regular (or premium) grade gasoline at I \.0 pounds Reid Vapor Pressure when stored in a 125-foot by 48-foot tank (97,700 barrels), comparing fixed-roof tanks (Problem I) with floating-roof tanks (Problem 2).

2. Annual throughput is 2,000,000 barrels.

velocity ([.I.,,) must be calculated:

'E..1y L

6.6.5 STORAGE TANKS

I. Annual average temperature is 52 F.

;::;~~, the ratio of wind

[.1.0

inaccurate, there is an indication that plume rise, after burning is complete, is of a low order of magnitude. To compute sulfur dioxide concentration, use the example given in Paragraph 6.6.3, substituting 82.2 meters as the effective height of flare plume rise.

Although some of the preceding assumptions may be

=

Assuming: P = 5.0 pounds. D H

= 125 feet.

24 feet. T 16 F. Fp = 1.15 for white paint in poor condition. C = 1.0.

f DRW MANUAL-ATMOSPHERIC EMISSIONS

6-3.0

Thus,

Then, L!I

= 0.024 (9\)"'8 (125)173(24)0.51(16)050(1.15)(1.0) 1495 bbl/yr

=

b.

FILLING

W =

(0.OOO448)e'0~~5000)

Total loss of floating-roof tank is: 200

Loss F

t,

7 bbl/yr

=

0.OOO3PVK,

+7

= 207 bbl/yr

6.6.5.4 Conclusions

Where:

filling loss, in barrels per year. vapor pressure of light at bulk temperature, in psia. V = volume of liquid pumped into tank, in barrels per year. K, turnover factor (t = throughput in turnovers per year, V/tank capacity). F

The fixed-roof loss will be 4495 barrels per year. The floating-roof loss will be only 207 barrels per year.

P

Then, F

= (0.0003)(5.0)(2,000,000)(1.0) = (0.0015)(2,000,000) = 3,000 bbl/yr

Total loss of fixed-roof tank is: 1495

+ 3000

=

6.6.6 PRODUCT LOADING

Determine the loading loss experienced when loading a tank truck with 10,000 gallons of 1l.0-pound RVP gasoline at temperatures of 40 F and 60 F by splash loading, subsurface loading, and vapor recovery. Assume average saturation of truck vapor space of 30 percent. Volumetric loading losses with relation to gasoline TVP are shown graphically in Figure 6-19. 31

4495 bbl/yr 0.4

6.6.5.3 Problem 2: Evaporation Losses of FloatingRoof Tanks 0.3

a. STANDING-STORAGE Loss

L" = K f (D)15 (

P

14.7 _

)O.7( VW)0.7 P