Book - School of Science and Technology

254 Piping design for indirect heating systemsTable 9.6 Values of Z for use with Figure 9.14 (P = absolute pressure in kPa)P Z P Z P Z P Z100 100 240 541 460 1899 740 4751110 120 250 586 480 2061 760 5001120 142 260 632 500 2230 780 5258130 166 270 679 520 2405 800 5522140 191 280 729 540 2587 820 5791150 219 290 780 560 2775 840 6066160 248 300 832 580 2969 860 6348170 278 320 943 600 3170 880 6636180 311 340 1060 620 3377 900 6930190 345 360 1183 640 3590 920 7230200 381 380 1313 660 3810 940 7536210 418 400 1450 680 4036 960 7849220 458 420 1593 700 4268 980 8167230 499 440 1743 720 4506 1000 8492Notefor convenience in using whole numbers, the values given are actually (100Z). Figure 9.14 has been adjusted similarly.Initial steam pressure ˆ 600 kPaPressure loss, say 10% ˆ 60 kPaFinal steam pressure ˆ 540 kPaEnergy to be transmitted ˆ 1000 kWLatent heat, final (Table 6.6) ˆ 2099 kJ/kgSteam flow thus is 10 6 /2099 ˆ 476 g/sZ for 600 kPa (Table 9.6) ˆ 3170Z for 540 kPa (Table 9.6) ˆ 2587Length including single resistances ˆ 55 mThus(Z 1 Z 2 )/L ˆ (3170 2587)/55 ˆ 10.6Reading this last value on the base scale of Figure 9.14, against 476 g/s on the verticalscale, it will be seen that a 65 mm pipe will carry about 510 g/s. By reference to Tables 6.6and 9.4, the velocity of flow will be 0:476 0:349/0:003 53 ˆ 47 m/s and if drainage of themain presents any problem, it would be better to select an 80 mm pipe since the 10%pressure drop assumed is near the top of the preferred range of velocities.Condensate pipe sizesPipes carrying condensate fall into three classes as far as selection of size is concerned:. Pump discharges following condensate collection in a receiver which is so vented toatmosphere that the majority of the air and flash steam has been removed. These maybe considered as flowing full and may be sized using the water flow data of Figures 9.1and 9.2, plus a 25% margin on the pressure drop read therefrom.. Gravity flow at low pressure where extraneous means have provided that the majorityof the air and flash steam has been discharged. A pressure drop three times that due towater flow alone may be anticipated.