Petroleum Refining Design and Applications Handbook. A. Kayode Coker

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      1 1. Line velocities (υ) and pressure drops (∆P): (a) For a liquid pump discharge, υ = (5 + D/3) ft/s and ∆P = 0.45 bar/100 m (2.0 psi/100 ft); (b) For liquid pump suction, υ = (1.3 + D/6) ft/s, ∆P = 0.09 bar/100 m (0.4 psi/100 ft); (c) for steam or gas flow: υ = 20D ft/s and ∆P = 0.113 bar/100m (0.5 psi/100 ft), D = diameter of pipe in inches.

      2 2. Gas/steam line velocities = 61 m/s (200 ft/s) and pressure drop = 0.1 bar/100 m (0.5 psi/100 ft).

      3 3. In preliminary estimates set line pressure drops for an equivalent length of 30.5 m (100 ft) of pipe between each of piece of equipment.

      4 4. Control valves require at least 0.69 bar (10 psi) pressure drop for good control.

      5 5. Globe valves are used for gases, control and wherever tight shut-off is required. Gate valves are for most other services.

      6 6. Screwed fittings are used only on sizes 38 mm (1.5 in) or less, flanges or welding used otherwise.

      7 7. Flanges and fittings are rated for 10, 20, 40, 103, 175 bar (150, 300, 600, 900, 1500, or 2500 psig).

      8 8. Approximate schedule number required = 1000 P/S, where P is the internal pressure psig and S is the allowable working stress [about 690 bar (10,000 psi)] for A120 carbon steel at 260°C (500°F). Schedule (Sch.) 40 is most common.

      1 1. Power for pumping liquids: kW = (1.67) [Flow (m3/min)] [∆P(bar)]/ε[hp = Flow (gpm) ∆P (psi)/(1, 714)(ε)]. (ε = fractional efficiency).

      2 2. Net positive suction head (NPSH) of a pump must be in excess of a certain number, depending upon the kind of pumps and the conditions, if damage is to be avoided. NPSH = (pressure at the eye of the impeller-vapor pressure)/(ρg). Common range is 1.2–6.1 m (4–20 ft) of liquid.

      3 3. Specific speed Ns = (rpm)(gpm)0.5/(head in ft)0.75. Pump may be damaged if certain limits of Ns are exceeded, and efficiency is best in some ranges.

      4 4. Centrifugal pumps: Single stage for 0.057–18.9 m3/min (15–5000 gpm), 152 m (500 ft) maximum head; multistage for 0.076–41.6 m3/min (20–11,000 gpm), 1675 m (5500 ft) maximum head. Efficiency: 45% at 0.378 m3/min (100 gpm), 70% at 1.89 m3/min (500 gpm), and 80% at 37.8 m3/min (10,000 gpm).

      5 5. Axial pumps for 0.076–378 m3/min (20–100,000 gpm), 12 m (40 ft) head, 65–85% efficiency.

      6 6. Rotary pumps for 0.00378–18.9 m3/min (1–5000 gpm), 15,200 m (50,000 ft) head, 50–80% efficiency.

      7 7. Reciprocating pumps for 0.0378–37.8 m3/min (10–10,000 gpm), 300 km (1,000,000 ft) maximum head. Efficiency: 70% at 7.46 kW (10 hp), 85% at 37.3 kW (50 hp), and 90% at 373 kW (500 hp).

      1 1. The rate of reaction in every instance must be established in the laboratory, and the residence time or space velocity and product distribution eventually must be found from a pilot plant.

      2 2. Dimensions of catalyst particles are 0.1 mm (0.004 in.) in fluidized beds, 1 mm in slurry beds, and 2–5 mm (0.078–0.197 in.) in fixed beds.

      3 3. The optimum proportions of stirred tank reactors are with liquid level equal to the tank diameter, but at high pressures slimmer proportions are economical.

      4 4. Power input to a homogeneous reaction stirred tank is 0.1–0.3 kw/m3 (0.5–1.5 hp/1000 gal.) but three times this amount when heat is to be transferred.

      5 5. Ideal CSTR (continuous stirred tank reactor) behavior is approached when the mean residence time is 5–10 times the length needed to achieve homogeneity, which is accomplished with 500–2000 revolutions of a properly designed stirrer.

      6 6. Batch reactions are conducted in stirred tanks for small daily production rates or when the reaction times are long or when some condition such as feed rate or temperature must be programed in some way.

      7 7. Relatively slow reactions of liquids and slurries are conducted in continuous stirred tanks. A battery of four or five in series is most economical.

      8 8. Tubular flow reactors are suited to high production rates at short residence times (seconds or minutes) and when substantial heat transfer is needed. Embedded tubes or shell-and-tube constructions then are used.

      9 9. In granular catalyst packed reactors, the residence time distribution is often no better than that of a five-stage CSTR battery.

      10 10. For conversions under about 95% of equilibrium, the performance of a five-stage CSTR battery approaches plug flow.

      11 11. The effect of temperature on chemical reaction rate is to double the rate every 10°C.

      12 12. The rate of reaction in a heterogeneous system is more often controlled by the rate of heat or mass transfer than by the chemical reaction kinetics.

      13 13. The value of a catalyst may be to improve selectivity more than to improve the overall reaction rate.

      1 1. A ton of refrigeration is the removal of 12,700 kJ/h (12,000 Btu/h) of heat.

      2 2. At various temperature levels: −18°C to −10°C (0–50°F), chilled brine and glycol solutions; −45 to −10°C (−50 to −40°F), ammonia, Freon, and butane; −100 to −45°C (−150 to −50°F), ethane or propane.

      3 3. Compression refrigeration with 38°C (100°F) condenser requires kW/tonne (hp/ton) at various temperature levels; 0.93 (1.24) at −7°C (20°F), 1.31 (1.75) at −18°C (0°F); 2.3 (3.1) at −40°C (−40°F); 3.9 (5.2) at −62°C (−80°F).

      4 4. Below −62°C (−80°F), cascades of two or three refrigerants are used.

      5 5. In single-stage compression, the compression ratio is limited to 4.

      6 6. In multistage compression, economy is improved with interstage flashing and recycling, the so-called “economizer operation.”

      7 7. Absorption refrigeration: ammonia to −34°C (−30°F) and lithium bromide to 7°C (45°F) is economical when waste steam is available at 0.9 barg (12 psig).

      1 1. Grizzlies that are constructed of parallel bars at appropriate spacings are used to remove products larger than 50 mm in diameter.

      2 2. Revolving cylindrical screens rotate at 15–20 rpm and below the critical velocity; they are suitable for wet or dry screening in the range of 10–60 mm.

      3 3. Flat screens are vibrated, shaken, or impacted with bouncing balls. Inclined screens vibrated at 600–7000 strokes/min and are used for down to 38 µm, although capacity drops off sharply below 200 µm. Reciprocating screens operate in the range СКАЧАТЬ