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t10TEXTRACTED SATURATED

GAS STEAM 0APPROX.

900'F......

z0a::u..

2 3 -- + ETC. ZONES

SECTION "A- A"

PROCESS GAS OUTOF Tt11RD PASS

(APPROX. 70% OF TOTAL)

a::

IIIIIIIL -

..--- >1IIII

II

I" 'I

>

(START)

+SELECT

TRIAL FLAMETEMPERATURE

+HEAT BALANCE

BETWEEN REACTANTSAN D PRODUCTS

-------RRIVE ATCORRECT FLAMETEMPERATURE

ELECT TUNNELFURNACEDIAMETER

ELECT TUNNELFURNACE

LENGTH

+HEAT BALANCEAT ZONE I

OF TUNNEL

+ARRIVE AT

TEMPERATURE ATTUNNEL OUTLET

S ~ L E C TSECONDASS TUBEDIAMETER

~SELEC T

TRIAL MASSVELOCITY

ALCULATEll Pz THRU

SECOND PASSI II 1..

I

-------+IIIIII '

' IIIIIIIIIIIIL - -

ARRIVE AT

A SATISFACTORYMASS VELOCITY

+HEAT BALANCE

AROUND ZONE AOF SECOND PASS

+DETERMINE

LENGTH OFSECOND PASS

- -----RRIVE ATTEMPERATURE OUT OFSECOND PASS TUBES

ct

I + -

1+-

I

cpSELECT TUBE

r--> DIAMETER FORI THIRD PASSI

J.

..->SELECT

I TRIALI MASS VELOCITYI J.I

CALCULATE liP3I THRUI THIRD PASSIL----- -- -

ARRIVE ATI A SATISFACTORYII MASS VELOCITYI +I

HEAT BALANCEI AROUND ZONE III OF THIRD PASSI +I DETERMINE

I LENGTH OFI THIRD PASS TUBESI

L----------ONE COMPLETE CYCL

OF CALCS. COMPLETErAT THIS POINT

4r. D(

FINAL PRINT OUTOF POSSIBLE

REACTOR DESIGNSI

+SELECTION OFDESIGN SPECS .FOR FABRICATION

J.c END

'

Il

Fig. 2-This guide will help you set up a computer progr; 1.

27. Calculate: M (Cp) 1 (T 1 - T R )28. Look up h129. Calculate: W , ( h p - h 1 )30 . Look up the emissivity of the wetted surface of the tum I,

ea.

31. Calculate the ari'thmetic ave rage temperature in Zone

TF ,t = ( T p + Tl)/2 .32. Look up sl at temperature T F ,l for each of the gase IS

components.33. Look up the sulfur dew point temperature, T Dp34. Look up s. at temper at ure T Dp for each of the gaseous c1 1-

ponents.'

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lEW WAY TO DESIGN FIRETUBE REACTORS

l= m

5. Calculate 2: e, (S 1 - S8 ) (For sulfur plants, m will al-1=1

ways be assumed to be 5 , corresponding to C 0 2 , H 2S, N 2 ,HzO and S0 2 )

36. Look up the temperature corresponding to the saturatedsteam temperature at the design pressure, T sT

37 . Calculate (MTD).

38. Look up: h 839. Look up: r 1g40 . Look up: r 841. Look up: rm42. Calculate: l/ h 143 . Look up first choice of tunnel diameter: D44 . Calculate: '1702/445. Look up molecular weight of the gas mixture, M.W.46 . Calculate the mass velocity, G:

M (M .W.)G = 90077'0 2

47 . Calculate: [(Cp )p + C p ) 1 ]/ 2

48 . Calculate : h ~= 8.3 [ ~ ~ ; : . - : ][ ( C p ) ~+ (Cp) 1J49. Calculate: 1/ h g50. Add the following steps: 39 , 40, 41, 42, and 49 , and store

the sum.51. Calculate U 1~ U 1 = / ( Step 50)52. Calculate: U 1 (MTD) 1

Step 2 5 - Step 27 + Step 2953. Calculate A1 : A 1 = - - 5: : : - t - e p - - - : : -3 5: : - - ; + - : : : - S t _ e _ p ~5: : : -2 - -

54. Calculate th e length of Zone 1, Lz 1 :

12A 1Lzt = 7r D

Ill. DETERMINATION OF THE REQUIRED AREA ANDLENGTH OF ZONE 2 OF TH E TUNNEL FURNACE

(Using Equation (10))

55 . Look up T 2 , which determines the lower temperature limitof Zone 2.

56. Repeat Steps 24 through 54 inclusive, noting the followingrequirements:1) T 1 replaces T t'2) T 2 replaces T 13) (Cp) 1 replaces (Cp)F4) Physical properties of the gas components based on T F

must be replaced by the corresponding ones at T 1 5) Physical properties of th e gas components based on T 1

must be replaced by the corresponding ones at T 2 6) Th e following units are no t temperature dependent and

will remain constant in all calculations required forZone 2 and additional zones of the tunnel furnace:(a ) Constants a, b, c, & d (d) Ta = 525 R (g) TDp(b ) (m.f . ) 1 (e ) W 8 (h) S,(c ) M (f ) e, (i ) m(j ) TsT (n) rm

(k) h 8 (o ) G(I ) r ~ r ( p) D

(m) r 8 (q) M.W.[Note: At this point, repetition of Steps 24 to 54

inclusive will add 31 steps to the numberingsystem, so the next step will be Step 88)

88 . Add the areas of Zone 1 and Zone 2 and store the sum(Ste p 5 3 + Step 86 ) .

8!1. Aelel tne 1 ~1 1! 1 ' " v. - - -.(Step 54 + Step 87)

90. Look up the value of L91. Find the absolute value of ((Step 89) -L )92. Look up the value of fJ (also arbitrarily pre-assigned)93. If the result of Step 91 < 11, it shall be assumed that a pos

sible tunnel design has been achieved, and the followingvalues shall be printed out:a) The total length of the tunnel (Step 89)b) The tunnel diameter, D, (Step 43)c) Total heat transfer area in the tunnel (Step 88)d) The gas temperature out of the tunnel (Step 55)

94. If the results of Step 91 > 3, calculate (Step 89) - L95. I f (Step 89) - L > 0, a possible tunnel design has also beenachieved, bu t some final interpolation will be requir ed . Print

out the following values:a) The total length of the tunnel (Step 90)b) The tunnel diameter (Step 43)c) Total heat transfer area in the tunnel:

AT= A1 + A2 [ (L - L 1 ) /L 2 ]d) The gas temperature ou t of the tunnel :

T x = T 1 - ( T 1 - T 2 ) [ ( L - L 1 )/ L 2 ]

IV. DETERMINATION OF TH E REQUIRED AREA ANDLENGTH OF ADDITIONAL ZONES OF TH E TUNNELFURNACE

96 . If (Step 89) - L < 0, additional zones must be determined .Look up T 8 , which determines the lower temperature limitof Zone 3.

97. Carry out Step 56, making all the necessary and corresponding replacement of values between Zone 3 and Zone 2 thatwere required previously between Zone 2 and Zone 1.

98 . Repeat steps corresponding to Step 88 through Step 95 inelusive.

99. I f a final tunnel furnace length is not obtained by executingthe steps outlin ed by Step 98, Step 96 will have to be carriedou t as will a whole sequence of steps corresponding to Step56 thru Step 95 inclusive until either conditional St ep 93 or

Step 95 has be en satisfied.

V. SELECTING A MASS VELOCITY AND DETERMININGTHE NUMBER OF TUBES IN THE SECOND PASS OFTHE W. H. BOILER

[Using Equation ( 11 ) ]

1. Look up a tube diameter, d 12. Look up a mass v elocity, GT3. Look up N14. Look up p5. Look up z .. (based on a mean tube wall temperature corre

sponding to saturated steam temperatur e plus 20 F)6. Look up the final temperature out of the tunnel furnace , T .7. Calculate the mean gas temperature in th e second pass of

the boiler, tm2 : tm 2 = (1/2) (Tx+900) = 1/2)Tx+4508. Look up Z at a temperature corresponding to tm29. Calcula te= (Z/Z.,)O .H

10. Calculate the Reynolds No. from Equation (12) .11. Look up the friction factor f1 corresponding to Re value cal-

culated in Step 10.12 . Calculate AP from Equation ( 11).'13. Look up the value of;. , (also arbitrarily assigned)14. I f the absolute va lue of ( . iP -1 .00 ) < ;., the va lu e of G.r

selected is satisfactory .15. If (AP - 1 . 0 0 ) > ., calculate ( A P - 1.00)16. If the result of Step 15 > 0, select a lower mass velocity and

repeat Step 2 thru Step 14 inclusive.17. I f the result of Step 15 < 0, select a h igher mass velocity andrepeat Step 2 thru Step 14 inclusive .

18. Look up a 1

HYDROCARBON PROCESSING

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19. Determin e th e required number of tubes, N 2, by Equation( 13 ) .

VI . DETERMINATION OF THE REQUIRED AREA AND

LENGTH OF ZONE A OF THE SECOND PASS OF

THE W. H. BOILER

20 . Look up T A which determines the lower temperature limitof Zone A.

21. From storage, take the last value calculated for M(Cp)x(T . - Ta l. i.e., the heat content of the gases entering these ond p ass above the reference temperature T a

22. Determine (Cp)A by carrying out Steps !.7. and 1.8. butbased on TA .

23 . Calculate; M(Cp)A ( TA - T R )24. Look up: hA25. Calculate W 8 (hx - hA)26. Look up the emissivity of the wetted surface of the tubes, e 8 .27 . Calculat e the arithmetic average temperature in Zone A:

Tx,A = (Tx+TA) /228 . Look up SA at temperature T x. A for each and every one of

the gaseous components.l = m

29. Calculate: 1:,e. ( S A - S8 )I = 1

30 . Calculat e ; ( 1 1TD) A

T x - TA

( MTD ) A= ( )T x - Ts TIn T rA - ST

31. L ook up first choice of tube diameter: d 132. C alculate; 7Td 12/4

(GT)O.a33. Calculate; h ~ ;2 = 13.3 ~ ((Cp)x + (Cr)A]

I 1 I34 . Calculate: U = h + r ~ ;1 2+ rm2 + .r82 + h

A g 2 s 2

(Note: Here, the subscript " 2" is used to indicate "2nd pass"so as not to confuse these values with the previousones employed in the tunnel furnace. However, sincevalues do not change for h 6 , rgr r 8, rm; the followingrelation below can be used to simplify the nomenclature.)

1 1 1U = h + r gr+rm+r.+h

A g2 s

35. Calcul a te: U A36. Cal culate: U A (MTD) A37 . Calculate AA:

(Step V I . 2 1 . ) - (Step VI.23.) +(Step VI.25.)A" = (Step Vl.29.) + (Step VI.35.)

38 . Ca l ulat e the length of Zone A, LzA from Equation ( 14).

VII. DETERMINATION OF THE REQUIRED AREA AN D

LENGTH OF ZONE B OF THE SECOND PASS OF

THE W . H. BOILER

It should be clear without going into a stepwise outline howZone B and additiona l zones of the second pass can be dealtwith . The procedure here is similar to that outlined in SectionII I and Section IV .

VIII. SELECTING A MASS VELOCITY AND DlTERMIN-

IN G THE NUMBER OF TUBES IN THE THIRD PASSOF THE W . H. BOILER

The sequence of steps involved here is similar to those outlinedin Section V. The only difference arises in the selection of num-

May 1965, Vol. 44, No. s

her of tubes, (Step V. 19), where M must now be reduced bythe amount of hot gases extracted out of the second pass. Th i samount depends on the process design and is known at the time

of designing the W. H. Boiler.

IX . DmRMINATION OF THE REQUIRED AREA ANDLENGTH OF ZONE I OF THE THIRD PASS OF THE

W . H. BOILER

The sequence of steps involved in this section is similar tothose outlined in Section VI. The outlet temperature of the third

pass is arbitrarily fixed , and in general is not critical for theW. H . Boiler is usually followed by a su lfur cendenser in whichthe process gas is cooled further . Th e selection of the outlet temperature should be made, however, judiciously . The question ofwhether a square foot of heat transfer surface in theW. H . Boilervs. that in the Sulfur Condenser is more or less expensive is notthe sole consideration. Differ ent levels of steam pressure in thesetwo units will also influence the selection.

Since radiant heat transfer is not significant below 900 F, thefollowing corresponding steps can be omitted: VI. 26, 27, 28,and 29. The calculation of the heat transfer area in Zone I ofthe third pass corresponds to a step similar to Step VI. 36, butmodified as follow s:

(Step Vl:21 ) - ( Step VI.23) +(Step VI.25)Ar = (Step VI.35)

X. QETERMINATION OF THE REQUIRED AREA ANDLENGTH OF ZONE II OF THE THIRD PASS OF THEW. H. BOILER

The sequence of steps required for these determinations hav1been previously outlined in Sections II , III, and IV . Here againthose steps pertaining to radiant heat transfer may be omittedThe method of determining the total area of the third pass awell as the number of tubes should b e apparent .

At this point, one complete cycle of a ll necessary calcul a tio rhas been performed. As shown on the preliminary flow charFigure 2, it is now necessary to repeat the entire cycle by makina second selection for a tunnel furnace length . Specifically, thmeans going back to Step III.90. After a second complete eyeof calculations from Step III.90 to the last step in Section )the entire sequence is repeated for all tunnel furnace lengtincluded in the data. From experience we can lim it the numbof different tunnel lengths to approx imately 10 to 12 differcva lues.

To complete the design, different furnace tunnel diamct(must now be investigated . A second tunnel diameter mustselected an d the entire cycle of calculations must be repeated

each tunnel len gth selecte d. Specifically, this means repeati 5Steps 11.43 through the last step in Section X. Here again , fr nexperience, a list of approximate ly 6 to 8 possible diameters ra specific design is all that is required in the data .

This completes the entire program for the genera lized des nof firetube boilers. I t should be self-evident that the use o acomputer will permit one to design the unit rigorously , and aff dthe designer the opportunity of specify ing two or three poss lemechanical and structural designs and arrive at the most econo .leal arrangement.

LITERATURE CITED'McAdams , William H ., Heat Transmission, Third Edition, McGraw- ill,

pp. 99-10!>, New York (1954). Trinks , Willibald, Indunrial Furnaces , Vol. 1, Filth Edition, Wiley , ~ P pendix II , New York (1961).

I McAdaw, William H. , Heat Transmission, Second Edition, McGraw :ill,p. 71, New York (1942).

Clarke , Loyal, Manual Fo r Process En gineering Calculation.s, First Ed on ,McGraw-Hill, p. 103, New York (1947) .

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