Читать книгу Petroleum Refining Design and Applications Handbook - A. Kayode Coker - Страница 29

1 1. For conservative estimate set F = 0.9 for shell and tube exchangers with no phase changes, q = UAF∆Tlm. When ∆T at exchanger ends differ greatly then check F, reconfigure if F is less than 0.85.

2 2. Take true countercurrent flow in a shell-and-tube exchanger as a basis.

3 3. Standard tubes are 19.0 mm (3/4 in.) outer diameter (OD), 25.4 mm (1 in.) triangular spacing, 4.9 m (16 ft) long.A shell of 300 mm (1 ft) diameter accommodates 9.3 m2 (100 ft2);600 mm (2 ft) diameter accommodates 37.2 m2 (400 ft2);900 mm (3 ft) diameter accommodates 102 m2 (1100 ft2).

4 4. Tube side is for corrosive, fouling, scaling, and high-pressure fluids.

5 5. Shell side is for viscous and condensing fluids.

6 6. Pressure drops are 0.1 bar (1.5 psi) for boiling and 0.2–0.62 bar (3–9 psi) for other services.

7 7. Minimum temperature approach is 10°C (20°F) for fluids and 5°C (10°F) for refrigerants.

8 8. Cooling water inlet temperature is 30°C (90°F), maximum outlet temperature 49°C (120°F).

9 9. Heat-transfer coefficients for estimating purposes, W/m2°C (Btu/h-ft2-°F): water to liquid, 850 (150); condensers, 850 (150); liquid to liquid, 280 (50); liquid to gas, 60 (10); gas to gas, 30 (5); and reboiler 1140 (200). Maximum flux in reboiler is 31.5 kW/m2 (10,000 Btu/h-ft2). When phase changes occur, use a zoned analysis with appropriate coefficient for each zone.

10 10. Double-pipe exchanger is competitive at duties requiring 9.3–18.6 m2 (100–200 ft2).

11 11. Compact (plate and fin) exchangers have 1150 m2/m3 (350 ft2/ft3), and about four times the heat transfer per cut of shell-and-tube units.

12 12. Plate and frame exchangers are suited to high sanitation services and are 25–50% cheaper in stainless steel construction than shell-and-tube units.

13 13. Air coolers: Tubes are 0.75–1.00 in. OD., total finned surface 15–20 ft2/ft2 bare surface, U = 450–570 W/m2°C (80–100 Btu/h-ft2 (bare surface)-°F). Minimum approach temperature = 22°C (40°F). Fan input power = 1.4–3.6 kW/(MJ/h) [2–5 hp/(1000 Btu/h)].

14 14. Fired heaters: radiant rate, 37.6 kW/m2 (12,000 Btu/h-ft2), convection rate, 12.5 kW/m2 (4000 Btu/h-ft2); cold oil tube velocity = 1.8 m/s (6 ft/s); approximately equal heat transfer in the two sections; thermal efficiency, 70–75%; flue gas temperature, 140–195°C (250–350°F) above feed inlet; and stack gas temperature, 345–510°C (650–950°F).