Process Engineering Equipment Handbook Episode 3 Part 3 potx

Pulp and Paper P-213 FIG. P-224 Steam production for different scenarios. (Source: Ahlroth and Svedberg.) FIG. P-223 Power output for different scenarios. (Source: Ahlroth and Svedberg.) TABLE P-25 Simulation Results for the Hybrid System and the Tomlinson Boiler Power Output Thermal Efficiency Power Production (MW) (%) Gas turbine Steam turbine Reference case 11.8 13.8 33.1 Low heat demand case 11.8 17.8 38.2 Biomass gasifier malfunction 2.1 7.0 Black liquor gasifier malfunction 13.5 8.1 45.6 Tomlinson boiler 35.6 Steam Production Saturated Steam Produced in t/h Pressure in bar 3 5 12 Reference case 3.4 28.3 10.5 Low heat demand case 1.6 3.9 Biomass gasifier malfunction 1.6 16.4 10.5 Black liquor gasifier malfunction 1.4 Tomlinson boiler 24.6 206.7 76.5 Steam demand 28 235 87 Production Minus Demand (t/h) “+” is surplus and “-” is deficit Reference case Balance Balance Balance Low heat demand case +1.6 +3.9 Balance Biomass gasifier malfunction -1.8 -11.9 Balance Black liquor gasifier malfunction Balance 1 +1.4 Balance 1 1. Steam demand is lower in this case. P-214 Pulsation Dampeners It is therefore noticeable that in all studied cases with a hybrid energy system instead of a conventional one, the process steam demand for the pulp mill is satisfied at all points of operation, except when the biomass gasifier suffers a malfunction. The introduction of the hybrid-energy system, with black liquor gasification as a unit operation, enables an increase in pulp production as planned. The thermal efficiency of the hybrid system is 33 percent for the reference case based on the LHV for the gasified fuels shown in Table P-24. Compared to modern gas turbine combined cycle plants, with efficiencies up to nearly 60 percent this might seem as mediocre performance. It should be kept in mind, however, that the fuel used is difficult to refine to such a degree that it can be used in a gas turbine and that it has a low heating value. Secondly, comparing the efficiency of the Tomlinson boiler and the steam turbine cycle to the efficiency of the hybrid-energy system, the potential of the gas turbine in the pulp and paper industry is demonstrated. For a 12 percent increase in fuel input to the pulp mill, the conventional Tomlinson boiler with a steam cycle can deliver only 6.8 MW more power, whereas the hybrid-energy system, thanks to its gas turbine, can deliver 13.3 MW more power. This will make gas turbines an interesting option for pulp mills when biomass and black liquor gasification reaches full-scale commercial breakthrough. The hybrid energy system is restricted in many ways, since it has to fit in an existing energy system with certain demands. The decision not to use black liquor synthesis gas in the gas turbine also limits the power output of the system. Still, it performs well. In order to significantly increase the power output of a pulp mill, gasification of all the black liquor in an IGCC is needed. For a pulp mill with equal flow of black liquor, 108 t DS/h, a power output of 96.6 MW is reported. This does not include gasification of biomass, as in this study. The total power output for such a combined system would be 122.2 MW. Reference and Additional Reading 1. Bloch, H., and Soares, C. M., Process Plant Machinery, 2d ed., Butterworth-Heinemann, 1998. Pulsation Dampeners Flow irregularities in fluid flow can cause pulsation in flow that is audible and causes vibration in process machinery. These irregularities can be corrected with pulsation dampeners, which essentially are vessels that provide the fluid (usually this problem is most common with gases) with enough residence time to steady the flow. A description of typical pulsation dampeners follows.* Preferable manufacturing facilities are ASME-certified and are registered with the National Board of Boiler and Pressure Vessel Inspectors, with fully accredited “U” and “R” stamps. Specialty services include fabrication with a wide range of materials to pressures in excess of 10,000 psi. Multicylinder dampeners can be built with tolerances of ± 1 / 32 in. See Table P-26 and Figs. P-225 through P-232. Pumps Pumps are the most common piece of equipment in any plant or process. They vary considerably in operating parameter ranges and scope. Manufacturers can customize a design for any operation with specific requirements, but, for the most * Source: Peerless, USA. Pumps P-215 TABLE P-26 Improved Efficiency Means Lower Costs Problem/Solution Discussion Equipment Benefits Pulsation/ Waves of compression (pulsation) set in motion ᭿ Reduce or eliminate equipment vibration by the periodic intake and discharge of gas or downtime/failure. liquid from reciprocating compressors or ᭿ Increase safety: Reduce/ pumps can couple with resonant equipment eliminate possibility of rupture frequencies and produce damaging vibrations, caused by equipment vibration resulting in safety hazards, shortened fatigue. equipment life, and increased downtime and ᭿ Lengthen equipment life by maintenance/replacement costs. Pulsation eliminating rapidly cycling pressures. Solution The installation of pulsation dampeners Dampeners ᭿ Lower compressor piping costs. or combination units eliminates these ᭿ Increase the accuracy of in-line problems. Pulsation dampeners measurement equipment attenuate harmful pulsations and reduce without vibrations. damaging vibrations by introducing a series ᭿ Save fuel: Less horsepower of choking and expansion volumes. required to run nonvibrating systems. Dynamic Fluctuating flow due to acoustic resonance can ᭿ Simplify and reduce frequency pressure drop cause significant additional pressure drop and/ of maintenance. or meter error. ᭿ Protect equipment from liquid Solution The use of proven acoustic control techniques Pulsation condensate. diminishes excessive pulsation by effectively dampeners ᭿ Protect machinery from solids. decoupling cylinder excitation from the resonant response of the piping. Solid/liquid Formation of condensate and the presence of entrainment solid particles may cause exchanger fouling and/or compressor cylinder damage. Combination Solution The combination dampener/separator effectively dampener/ removes both solids and liquids in a singgle separators vessel, providing maximum protection at minimum cost. FIG. P-225 Natural gas transmission compressor station is typical of facilities where pulsation dampening equipment provides reliable long-term service. (Source: Peerless.) P-216 Pumps FIG. P-226 General finite-element software is used to analyze structures such as this crosshead guide. (Source: Peerless.) FIG. P-227 Specialized finite-element software is used to perform mechanical analysis of manifolds and complex piping systems. (Source: Peerless.) FIG. P-228 Welding certified to the highest standards to the use of specified materials is prudent. (Source: Peerless.) FIG. P-229 Analog simulators have been utilized to perform hundreds of pulsation studies resulting in thousands of successful structural piping designs. (Source: Peerless.) FIG. P-230 An acoustical and mechanical engineer performs a field survey using state-of-the-art signal analyzers. The company is known for its field service and works closely with customers to identify, solve, and correct vibration problems in compressor and pump installations (Source: Peerless.) FIG. P-231 Pulsation dampeners in low-pressure hydrogen service. These dampeners, installed in a fluid catalytic cracker (FCC) unit, ensure low refinery maintenance costs. (Source: Peerless.) P-217 P-218 Pumps part, picking a pump out of a catalogue will be possible. After that, one has to choose between manufacturers, based on previous experience with items such as after- sales service, longevity of components, time between overhauls, and so forth. There are various types of pumps such as centrifugal, piston, reciprocating, rotary, gear, lobe, and several others. To help illustrate how varied features and types can be, information on common pump types in the process sector is included. The sources in this section are primarily three different manufacturers, so contrasting operational/design philosophies can be observed. Pump Theory* Centrifugal pumps The centrifugal pump is one of the most versatile types of machinery for industry. Every plant has in operation a multitude of pumps of this type, and modern civilization could not be visualized without this equipment. Compared with other types of pumps, e.g., reciprocating and rotary pumps, centrifugal pumps operate at relatively high speeds and consequently are smaller and lighter when designed for comparable capacity and head. Required floor space, weight, initial cost, and building costs are therefore reduced. Owing to their relatively high speed, centrifugal pumps are usually direct- connected to the driver, the majority being electric-motor driven. Having no reciprocating parts, centrifugal pumps are inherently balanced. There are no internal rubbing parts, and because running clearances are relatively large, wear is minimized. The liquid is delivered in a steady stream so that no receiver is needed to even out pulsations. In contrast to positive-type displacement pumps, centrifugal pumps develop a limited head at constant speed over the operating range from zero to rated capacity, and excessively high pressures cannot occur. They can therefore be started against FIG. P-232 The pulsation dampeners are configured for dual nozzle suction manifolds. Installed in a natural gas reciprocating compressor transmission station in the northeastern United States, they reduce damaging vibrations and provide many years of trouble-free service at reduced costs. (Source: Peerless.) * Source: Demag Delaval, USA. Pumps P-219 a closed discharge valve but should be operated at this condition for a minimum period (see subsection “Minimum Flow-Through Pump”). Generally, the bearings are located outside the casing, so that the liquid does not come in contact with the lubricating oil and is not contaminated by it. Classification. There are three general classes of pumps, depending on the configuration of the pump impellers: ᭿ Centrifugal or radial-flow pump ᭿ Mixed-flow pump ᭿ Axial-flow pump Those classes can be subclassified according to ᭿ Number of stages: single-stage pump, multistage pump ᭿ Arrangement of liquid inlet: single-suction pump, double-suction pump ᭿ Position of shaft: horizontal pump, vertical pump (dry-pit type), vertical pump (submerged type) Specific speed. Specific speed is a correlation of pump capacity, head, and speed at optimum efficiency, which classifies pump impellers with respect to their geometric similarity corresponding to the classification mentioned above (see also Fig. P-233). Specific speed is a number usually expressed as* where N s = specific speed N = rotative speed, rpm Q = flow, gal/min, at or near optimum efficiency H = head, ft per stage The specific speed of an impeller is defined as the revolutions per minute at which a geometrically similar impeller would run if it were of such a size as to discharge one gallon per minute against one foot head. Specific speed orN N Q H N N Q H H s S == 34 14 FIG. P-233 Profile of several pump-impeller designs, ranging from the low-specific-speed radial flow on the left to the high-specific-speed impeller design on the right, placed according to where each design fits on the specific-speed scale. (Source: Hydraulic Institute.) * The value of H 3/4 may be found in Table P-28. Specific speed is indicative of the shape and characteristics of an impeller, and it has been found that the ratios of major dimensions vary uniformly with specific speed. Specific speed is useful to the designer in predicting required proportions and to the application engineer in checking the suction limitation of pumps. Impeller form and proportions vary with specific speed, as shown in Fig. P-233. Pumps are traditionally divided into three classes: the centrifugal or radial-flow, the mixed-flow, and the axial-flow, but it can be seen from Fig. P-233 that there is a continuous change from the radial-flow impeller, which develops pressure principally by the action of centrifugal force, to the axial-flow impeller, which develops most of its head by the propelling or lifting action of the vanes on the liquid. In the specific-speed range of approximately 1000 to 4000, double-suction impellers are used as frequently as single-suction impellers. Figure P-233 gives values of H 3/4 for the accurate determination of the specific speed N s . Figure P-234 may be used to find specific speed with sufficient accuracy for practical purposes without calculating the head to the three-fourths power. The point located by plotting the total head and capacity in gallons per minute at the P-220 Pumps FIG. P-234 Diagram for determination of specific speed. Using the diagram, plot the head-capacity point; move from this point parallel to heavy lines to correct speed; from there move horizontally to the left and read specific speed. Example (dashed lines): H = 1,000 ft; Q = 10,000 gal/min; N = 3575 rpm; N s = 2015. (Source: Demag Delaval.) Pumps P-221 design point is moved parallel to the sloping lines to the correct speed in revolutions per minute. The specific speed is read at the left of the diagram. The procedure is illustrated by the heavy dashed lines. For double-suction impellers, total flow is used in the calculation, although historically there has been considerable use of half of the flow in the equation. For multistage pumps, the head per stage is used in the specific-speed equation. Generally, this is the total head of the pump divided by the number of stages. Impeller performance curves are intimately related to their types or specific speeds. Higher-specific-speed impellers operating at partial loads have higher heads, require more horsepower, and have lower efficiency. This is illustrated in Fig. P-235 on a percentage basis for the three general types mentioned above. Hydraulics Definition of static, pressure, and velocity heads. One of the most useful relationships of hydraulics is the continuity equation, which is based upon the principle that after steady conditions in any system have been established, the weight flow of fluid per unit of time passing any point is constant. Since most liquids are practically incompressible, this may be put in equation form as Q = AV, where Q = flow, ft 3 /s; A = cross-sectional area, ft 2 ; and V = velocity, ft/s. This equation may be rewritten in the form V = 0.321Q/a, where V = velocity, ft/s; Q = volume flow, gal/min; and a = area of pipe, in 2 . This equation is of importance in determining the velocity of the fluid at various points in either the piping or the pump itself. FIG. P-235 Comparison of performance curves for various types of impellers: (1) propeller; (2) mixed-flow; (3) Francis; (4) radial. (Source: Demag Delaval.) [...]... P-2 23 TABLE P-27 Values of H3/4 Head H3/4 Head H3/4 Head H3/4 Head H3/4 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 0 1.00 1.68 2.28 2. 83 3 .34 3. 83 4 .30 4.75 5.20 5.62 6. 03 6.45 6.85 7.24 7.62 8.00 8 .38 8. 73 9.09 9.45 9.80 10.2 10.5 10.8 11.2 11.5 11.8 12.2 12.5 12.8 13. 1 13. 5 13. 8 14.1 14.4 14.7 15.0 15 .3. .. 2 ,30 0 2,400 2,500 2,600 2,700 2,800 2,900 3, 000 3, 100 3, 200 3, 300 3, 400 3, 500 3, 600 3, 700 3, 800 3, 900 4,000 4,100 4,200 4 ,30 0 4,400 4,500 4,600 4,700 4,800 4,900 5,000 184.4 191.0 197.4 2 03. 8 210.2 216.4 222.7 228.8 234 .9 241.0 247.0 252.9 258.8 264.7 270.5 276 .3 282.0 287.7 2 93. 4 299.0 31 0.2 32 1.2 33 2.1 34 2.8 35 3.5 36 4.1 37 4.5 38 4.9 39 5.1 405 .3 415.4 425.4 435 .3 445.2 455.0 464.7 474.4 4 83. 9 4 93. 5... 125 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 18.8 19.4 19.9 20.5 21.0 21.6 22.1 22.6 23. 2 23. 7 24.2 24.7 25.2 25.7 26.2 26.8 27 .3 27.7 28.2 28.7 29.2 29.7 30 .2 30 .7 31 .1 31 .6 32 .8 33 .9 35 .0 36 .2 37 .4 38 .5 39 .6 40.6 41.8 42.8 43. 9 45.0 46.0 47.1 48.1 49.2 50.2 51.2 52.2 53. 2 54.2 55.1 56.2 57.1 225 230 235 240 245 250 260 270 280 290 30 0 31 0 32 0 33 0 34 0 35 0 36 0 37 0 38 0... 37 0 38 0 39 0 400 410 420 430 440 450 460 470 480 490 500 520 540 560 580 600 620 640 660 680 700 720 740 760 780 800 850 900 950 1,000 58.1 59.0 60.0 61.0 62.0 62.9 64.8 66.6 68.4 70.2 72.0 73. 9 75.7 77.4 79.2 80.9 82.6 84.4 86.1 87.8 89.1 91.1 92.8 94.4 96.1 97.7 99 .3 101 1 03 104 106 109 112 115 118 121 124 127 130 133 136 139 141 145 148 150 157 164 171 178 1,050 1,100 1,150 1,200 1,250 1 ,30 0 1 ,35 0 1,400... impeller is 131 /2 in What would the performance be if the impeller diameter were reduced to 13 in and the pump speeded up to 1800 rpm? Qb = Q nb Db 1, 800 13 = 2, 500 = 2, 460 gal min na Da 1, 760 13. 5 2 Hb = H a 2 1, 800 ˆ 2 Ê 13 ˆ 2 Ê nb ˆ Ê Db ˆ = 150 Ê = 146.7 ft Ë 1, 760 ¯ Ë 13. 5 ¯ Ë na ¯ Ë Da ¯ 3 hp b = hp a 3 Ê nb ˆ Ê Db ˆ = 117 Ë na ¯ Ë Da ¯ 3 3 Ê 1, 800 ˆ Ê 13 ˆ = 112 hp Ë 1, 760 ¯ Ë 13. 5 ¯ hb... up to 30 0 ft or higher, single-stage pumps are used, while for higher heads two or more units are arranged in series Figure P-2 53 shows an installation of two motor-driven units arranged in series P-242 Pumps TABLE P-28 Summary of Material Selections and National Society Standards Designations* ASTM† ACI AISI A48, Classes 20, 25, 30 , 35 , 40, and 50 A 339 , A395, and A396 B1 43, 1B and 2A; B144, 3A; B145,... vapor pressure is 0.5069 psia Hp = 2 .31 p 2 .31 ¥ 14.27 = = 32 .97 ft sg 0.9984 H z = -7 ft (negative since it is a lift) Hvp = 2 .31 p 2 .31 ¥ 0.5069 = = 1.17 ft sg 0.9984 H f = 1 ft NPSH = H p + H z - Hvp - H f = 32 .97 - 7 - 1.17 - 1 = 23. 80 ft Determine the available NPSH of a condensate pump drawing water from a condenser in which a 28-in vacuum, referred to a 30 -in barometer, is maintained The friction... condenser is 30 - 28 = 2 inHg, or 0.982 lb/in2 The corresponding specific gravity is 0.9945 H p = Hvp = 2 .31 p 2 .31 ¥ 0.982 = = 2.28 ft sg 0.9945 H f = 1 ft H z = 5 ft NPSH = H p + H z - Hvp - H f = 2.28 + 5 - 2.28 - 2 = 3 ft A third example is that of a deaerating heater having a water level 180 ft above the pump centerline The water temperature is 35 0°F The pipe friction loss is P- 234 Pumps FIG P-2 43 Upper... pressure will be 2.889 0.596 = 2.2 93 lb/in2, and the correction for altitude will be 14.69 - 13. 66 = 1. 03 lb/in2 The corresponding head change will be 2 .31 (2.2 93 + 1. 03) /0.9850 = 7.8 ft For the double-suction pump the maximum suction lift would be 12.0 - 7.8 = 4.2 ft, and for the single-suction pump the positive suction head would have to be 1.0 + 7.8 = 8.8 ft P- 236 Pumps FIG P-245 Upper limits of... gauge, +18 in Therefore, Pg = 50 hsg = Vd = 12.8 ft s 11 or 0.916 ft 12 Vd2 = 2.55 2g zd = 1.5 ft zs = Vs = 8.17 ft s 7 or 0.5 83 ft 12 Vs2 = 1. 03 2g Substituting in the formula, H = 2 .31 07 ¥ 50 + 13. 57 ¥ 0.916 + 1.5 + 0.5 83 + (2.55 - 1. 03) = 115.5 + 12.4 + 1.5 + 0.6 + 1.5 = 131 .5 ft Determination of power required The work required for pumping depends on the total head and the weight or volume of the . 109 3, 200 425.4 32 13. 5 135 39 .6 540 112 3, 300 435 .3 33 13. 8 140 40.6 560 115 3, 400 445.2 34 14.1 145 41.8 580 118 3, 500 455.0 35 14.4 150 42.8 600 121 3, 600 464.7 36 14.7 155 43. 9 620 124 3, 700. 105 32 .8 460 99 .3 2,700 37 4.5 27 11.8 110 33 .9 470 101 2,800 38 4.9 28 12.2 115 35 .0 480 1 03 2,900 39 5.1 29 12.5 120 36 .2 490 104 3, 000 405 .3 30 12.8 125 37 .4 500 106 3, 100 415.4 31 13. 1 130 38 .5. 2,100 31 0.2 21 9.80 92 29.7 410 91.1 2,200 32 1.2 22 10.2 94 30 .2 420 92.8 2 ,30 0 33 2.1 23 10.5 96 30 .7 430 94.4 2,400 34 2.8 24 10.8 98 31 .1 440 96.1 2,500 35 3.5 25 11.2 100 31 .6 450 97.7 2,600 36 4.1 26