Page 46 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10B 5/30/2001 4:17 PM Page 36

36 Applied Process Design for Chemical and Petrochemical Plants

Errors in tube count can cause recalculation in expected Figures 10-25A—E are for U-bundle tubes and require a
exchanger performances. 125 wide blank space across the center of the tubesheet to rec-
ognize the U-bend requirement at the far end of the tube
Number of tubes>shell: bundle, see Figures 10-1E, 10-1A item U, and 10-1K. Figures
112 Triangular pitch 10-25F—K are for fixed tubesheet layouts.
2
31D s K 1 2 >4 K 2 4 p 1D s K 1 23K 3 1n2 K 4 4 Before fabrication, an exact layout of the tubes, clear-
N t
1.2231p2 2 ances, etc., must be made; however, for most design pur-
(10-2) poses, the tube counts for fixed tubesheets and floating
heads as given in Tables 10-9 and 10-10 are quite accurate. A
122 Square pitch
2
31D s K 1 2 >4 K 2 4 p 1D s K 1 23K 3 1n2 K 4 4 comparison with tube counts in other references (19, 70)
N t indicates an agreement of 3% in the small diameters up
1p2 2 1
to about 23 / 4 -in. I.D. shell and graduating up to about
(10-3) 10% for the larger shells. The counts as presented have
checked manufacturers’ shop layouts one tube for 8-in. to
where
1
1
17 / 4 -in. I.D. shell; 5 tubes for 21 / 4 -in. to 27-in. I.D.;
N t Number tubes in shell
and 10—20 tubes for the larger shells. No allowances for
D s Inside diameter of shell, in.
p Tube pitch, in. impingement baffles are made in these layouts, although
n Number of tube passes channel and head baffle lanes have been considered. A stan-
3
K 1 , K 2 , K 3 , K 4 Constants depending on the tube size and layout. dard manufacturing tolerance of / 8 in. has been main-
Use the following table. tained between the specified inside diameter of the shell to
the nearest point on any tube (tube clearance).
Table of K Values
Tube spacing arrangements are shown in Figure 10-26
Tube for the usual designs. Countless special configurations exist
Size Pitch for special purposes, such as wide pitch dimensions to give
In. Arrangement In. K 1 K 2 K 3 K 4 larger ligaments to provide access for cleaning tools to
clean scale and fouling films from the outside of tubes by
3 Triangular 15 1.080 0.900 0.690 0.800
/ 4 / 16
3 Triangular 1 1.080 0.900 0.690 0.800 mechanical means. Often chemical cleaning is satisfactory,
/ 4
3 Square 1 1.040 0.100 0.430 0.250 and wide lanes are not justified. Wide spaces also give low
/ 4
1
1 Triangular 1 / 4 1.080 0.900 0.690 0.800 pressure drops but require special care to avoid low trans-
1
1 Square 1 / 4 1.040 0.100 0.430 0.250 fer coefficients, or at least these conditions should be rec-
ognized. Special directional tube lanes, as in steam surface
The tube layouts given in Figures 10-25A—K are samples of condensers for power plants, allow the fluid to penetrate
the convenient form for modifying standard layouts to fit the large bundle and, thereby, give good access to the sur-
special needs, such as the removal of certain tubes. face.
Method of Figuring Tube Counts—Use with Table 10-9
A. Fixed Tubes: All pitches and tube sizes
Pass: One: Straight through
1 1 1 1 1 1 1
Two: Half-circle per pass – – – – – – –
Four: 15 / 4 in. shell I.D. and smaller, used 6 6 6 8 8 8 8
1
pie shape baffle layout 1 1 1 1 1 1 1
–
–
–
–
–
–
–
1
17 / 4 in. shell I.D. and larger, used 6 6 6 8 8 8 8
ribbon baffle layout
Six: Ribbon baffle layout for all shell I.D.
Eight: Ribbon baffle layout for all shell I.D. Six Pass Eight Pass
1
B. U-Tubes: Radius of Bend 2 / 2 times tube
O.D. for all pitches and tube sizes C. Allowances: For tie rods:
Pass: Two: Pie shape layout 8—13 / 4 in. shell I.D., removed 4 tubes
1
1
Four: Pie shape layout 15 / 4 —29 in. shell I.D., removed 6
Six: Vertical baffle layout tubes
Eight: Vertical baffle layout 31—37 in. shell I.D., removed 8 tubes