Document RjoLoQ5LV432VZkpN09V6OB47

SUPERPRESSURE PUMPS , Design o( Pumps for High Pressures Requires Careful Study of Different Schemes (le-casing design running at 6500 rpm. Capacity selected was about 1000 gpm of 350-F water. Using a double-sucticm -- ;.:v- ^ v. first-stage impeller, we chose a 9-stage pump. Our calculations show it should : f?;;$Vi -,',nfVir be possible to obtain reasonably good f, efficiently with' this pump by driving It -, V' ' ' V A -i f -js V^ *v ` *]?v *CC9*UiVtpr.\ J. ' ' . V*_'v I -1 through a hydraulic coupling and gear, Fig. IA. Specific speed of unit will be in line with that of other successful installations. Further studies of this arrangement show that application of the feed sys tem's high-pressure ;componenls (such as healers) make it impractical for eco nomic and design rdifsons. It is not now rVW- ... */" t "\\CfQt ' feasible to place high-pressure heaters between pump discharge and boiler. Second Study, tlext approach. Fig. "" 1 I - 1 _<V LpJ ;>M*w^jy.l PMflV ' . - , iW y;, coupling t Htattn' ,J ' ` I ^ ' *>Al ' '- ;'>;rv IB, used a similar, pump, but it was fitted with re-entry features. First half of the unit would deliver to the heaters at 2500 psi the relatively' cold water coming from the-deaerator. After pas sage through the healers, the water would return to the pump at about 500 ------------ - ---- - WUWB.'M unsuitable. Using two cotings, C and O, is more contetvotWe -V '7&'. Seal test arrangement developed to insure adequate Investigation of conditions : at the teal during actual operation of the pump of pressures obove the crlticol F. Second half of pump would dis charge the weier at the rated design i/V* pressure. 1 Because half of tho pump must han I ) As niroirnm in July Power, p ISO, ond Sept, pp 80-85, we're at the atart of a great stride forward in power-plant design--a move into the region far above the critical pressure of steam. This necessitates development of boiler-feed pumps having discharge pressures of 5000 psi or more. Superpressures are today's answer to the need for higher over-oil thermal efficiency in large plants. Present Practice. Today's central sta tions need boiler feed pumps suitsble for maximum pressures in the 2600-psi range. A few of the latest stations use pumps discharging at 2000 psi. In many plants it is standard practice I it, * Sharge pressure of 5000 psi, or more, [^jl'sbout twice this number of stages would to use s single-casing barrel-type pump, Fig. 3, below, running at 3550 rpm (or $t! ;^.lbe; required if pump ran at the same Js/jtjpeed, 3550 rpm. This presents a most this job. ai many This as 12 type of unit or 13-stages. must -here For a dls- '`&I ', j'djficolt design problem l;'r new approach. and requires Our firm has done much work on this problem, investigating several potal* bitkies. It appeared evident from the start that for the high pressures insolved, speeds higher than 3600 rpm must be considered to reduce the number of stages needed in the pump. First Study. We started with a sin- dle water with a specific gravity of 0.786 as against a gravity of 0.892 for 350-F water, the horsepower of the sec ond half of the pump will be increased about 13%, assuming the efficiency of both halves is about the same. Studies of the design and economics of arrangement 1A and IB show a more conservative hookup is preferable. 1 Third Study. Arrangement worked ] out resembles the setup that some utili ties are now using. One pump feeds the heaters, its discharge going to a second unit after passage through beaters. Sec ond pump discharges to boiler. Fig. ID. In effect, this design splits the pump into two casings, the first consisting of a standard up-to-date barrel-type feed pump, designed for a dischnge pressure of about 2100 psi and operating at 3550 rpm. Second pump handles the re mainder of the work in eight stages, turns at 6500 rpm. Both pumps can be driven from the same motor, the discharge pump being driven through o variable-speed hydrau lic coupling and a speed-increasing gear. Second pump handles 500-F water if,hooked up as in ID. With hookup 1C, second pump handles 350-F water but heaters are uneconomical!, as in M. Two-casing arrangement has some additional operational advantages. Hy draulic coupling size Is smaller and its full-speed loss is less than for the ar rangements in Fig. 1A and IB. Part of 3 Cross section through a typical modern barrel-type teed The pump consists of o single-suction rocfially-split diaphragm* pump designed for high-temparoture high-pressure service, type multistage pumping unit running In the forged-steel barrel viow of o borrel-type feed pump In a largo utility station. The piping ond ke connections to hlgh-temporaiurs hlgk-presture units are Important this advantage it retained when the dis charge pump runs at reduced speed. It it interesting to note here thot 71 EN0INEEIIN0 AND MANAGEMENT SECTION POWII 1953 CNOINEERtNO AND MANAOEMENI SECTION 71