Petroleum Refining Design and Applications Handbook. A. Kayode Coker

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).

      REACTORS

      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.

      REFRIGERATION

      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).

      SIZE SEPARATION OF PARTICLES

      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 of 30–1000 strokes/min and handle sizes to 0.25 mm at the higher speeds.

      4 4. Rotary sifters operate at 500–600 rpm and are suited to a range of 12 mm–50 µm.

      5 5. Air classification is preferred for fine sizes because screens of 150 mesh and finer are fragile and slow.

      6 6. Wet classifiers mostly are used to make two product size ranges, oversize and undersize, with a break commonly in the range between 28 and 200 mesh. A rake classifier operates at about 9 strokes/min when making separation at 200 mesh and 32 strokes/min at 28 mesh. Solids content is not critical, and that of the overflow may be 2–20% or more.

      7 7. Hydrocyclones handle up to 600 ft3/min and can remove particles in the range of 300–5 µm from dilute suspensions. In one case, a 20-in. diameter unit had a capacity of 1000 gpm with a pressure drop of 5 psi and a cutoff between 50 and 150 µm.

      UTILITIES, COMMON SPECIFICATIONS

      1 1. Steam: 1–2 bar (15–30 psig), 121–135°C (250–275°F); 10 barg (150 psig), 186°C (366°F); 27.6 barg (400 psig), 231°C (448°F); 41.3 barg (600 psig), 252°C (488°F) or with 55–85°C (100–150°F) superheat.

      2 2. Cooling water: For design of cooling tower use, supply at 27–32°C (80–90°F); from cooling tower, return at 45–52°C (115–125°F); return seawater at 43°C (110°F); return tempered water or steam condensate above 52°C (125°F).

      3 3. Cooling air supply at 29–35°C (85–95°F); temperature approach to process, 22°C (40°F).

      4 4. Compressed air at 3.1 (45), 10.3 (150), 20.6 (300), or 30.9 barg (450 psig) levels.

      5 5. Instrument air at 3.1 barg (45 psig), −18°C (0°F) dew point.

      6 6. Fuels: gas of 37,200 kJ/m3 (1000 Btu/SCF) at 0.35–0.69 barg (5–10 psig), or up to 1.73 barg (25 psig) for some types of burners; liquid at 39.8 GJ/m3 (6 million British Thermal unit per barrel).

      7 7. Heat-transfer fluids: petroleum oils below 315°C (600°F) Dowtherms below 400°C (750°F), fused salts below 600°C (1100°F), and direct fire or electricity above 232°C (450°F).

      8 8. Electricity: 0.75–74.7 kW (1–100 hp), 220–550 V; 149–1864 kW (200–2500 hp), 2300–4000 V.

      VESSELS (DRUMS)

      1 1. Drums are relatively small vessels to provide surge capacity or separation of entrained phases.

      2 2. Liquid drums are usually horizontal.

      3 3. Gas/liquid phase separators are usually vertical.

      4 4. Optimum length/diameter = 3, but the range 2.5–5.0 is common.

      5 5. Holdup time is 5 min half-full for reflux drums and gas/liquid separators, 5–10 min for a product feeding another tower.

      6 6. In drums feeding a furnace, 30 min half-full drum is allowed.

      7 7. Knockout drums placed ahead of compressors should hold no less than 10 times the liquid