Document jBoEpNLROnYK8zOVDEBqgXRnZ

smnmsm pumps ww better coil* are reflected in the type of pumping echeme chosen. This is neces sary because excessive heater costs would reduce some ol the savings that result from using superpressures. DESIGN PROBLEMS Performance. Feed pumps for su perpressure plants require considerably more input horsepower per pound of team delivered to main turbine than is required at lower pressures. It is, there fore, imperative that optimum pump efficiency be obtained in order not to jeopardise the advantages ol the superpressure, cycle. Design of the high-apeed pump (or the various arrangements in Fig. 1A-1D requires new approaches to determine performance of the individual impellers and the correet shape of the dischsrge volutes. Tip speed is about $0% greater than that ordinarily used in modern pump practice. Our firm is developing basic design information by tests that check the performance of a complete stage operating at high tip speeds. Test rig is arranged to handle hot water so actus) field inlet conditions can be ob tained and the necessary net positive suction head for various capacities meas ured. Compressibility. Some Interesting problems present themselves when we make performance calculations for high-pressure pumps. We ordinarily think of water as being Incompressible at the pressures encountered in usual boiler feed-pump practice. Actually, of course, water is compressible, and for pressures of SQOQ psi this U definitely a factor to be considered. Fig. 6A shows the rectangular pres sure-volume diagram for an incompres sible fluid. Diagram area indicates the amount ol work in foot-pounds per pound that must be done to compress the fluid trom suction to discharge pres sure. If the real properties of water are considered, (he pressure-volume diagram changes lo the shape in Fig. 60. This shows that the theoretical work required is reduced somewhat by the volume change, Fj to Vt. To illustrate the mag nitude of the compressibility, assume that water at 500 F is compressed from 2000 lo 5000 psi. Under these condi tions the specific'volume will be reduced 1.7%, assuming isenlropic compression. Decause work is done on the water between points 1 and 2, Fig. 6B, the water temperature increases, even though pump efficiency Is assumed to be 100%. For the 3000-psi pressure rise discussed above, water temperature will increase 10 F. Actual temperature rise will be still greater, depending on the interne! losses In Die pump. It is evident that it is necesary to consider compressibility during design of these pumps. Shaft seal will be an extremely im portant port of a successful installation of a superpreasure pump. Ordinary watercooied packing, as used in many present designs, will not be suitable for the pressures and speeds involved. This Is particularly true cl the secondary unit in Fig. 1C and ID, where seal is exposed to 2)00 pal and ahher 350- or 500-F water. Design of the pump incorporates a packingless shaft seal. While this will require some leakage front tl* pgoJL design is being developed that wUIL'tI this leakage to a minimum. Wsdr fl progressing on a test rig, Fig. 2, u, seal performance under actual operJv fog conditions and to Investigate thJl best materials combination suitable forf the seal. Materials. Research studies over number of years have developed the' proper chemical analysis of latteA*^ for feed pumps. Temperatures involved' in superpressure applications are width the range of previous practice, requiring the use of chrome steels throughout tW pump Interior. .< Physical-analysis studies indicate Out well thickness and stresses are well within safe limits and present no mu- ufacturing problems. Some partkaUr care will have to .be taken to assure s good joint at the flange of the outer 0 barrel ol the high-pressure pump. Pro Umlnary investigations show that a tu- j isfoctorily tight joint can be obtained? with bolted construction, thus retaining | ease of maintenance. Our design Includes provisions (or' bringing the inside and outside of ths barrel up to operating temperature si uniformly as possible- Also, therms! expansion is provided for to mlolmisa thermal stresses. Particular care mult be given to expansion problems la high- pressure pumps for superpreuure serv ice. Maintenance. Reliability Is of prime importance in superprcssuTe plants- The barrel-type feed pump has proven Itself to be well suited (or this service. Main tenance, when needed. Is aimpM. un be performed quickly. Fig. 5. t Barrel-type feed pumps require little molntemmee, but when work must be done si ow a unit it Is important that disassembly bo eosy. "A"* frame hero Is big help EHOINEISINO AMO MANAGEMENT SECTION 6 Pressure-volume dlaproms for A, 0,1 Incompressible fluid; 0 compressible PQWtt ; MUNICIPAL power-plant building hot expanded twice to provide spoce for more capacity [Grand Haven Thrives With More Diesels islotllng ttlow-ipood heavy- [ftta^oil diesels successively is :eeping this Michigan munici- il plant out front In today's lively operating competition * By j gBYAN SIMS, Superlnte/tdeet, 'taerd at Public Worfcj, Grand Horen, Mrch. From t*i inccptio* of the munici'pel diesel power plant in 1931, we have eooiincmly used large ilow-jpced die- Engines, burning straight-run resi dual fuel. Thia policy has paid off In fuel economy, low operating and main tenance coats. In 23 years, plant capacity has grown Iran 1600 to 16,430 kw, keeping pace with load growth of the community. Grand Heven, which now baa a popula. lion of 10,000 to 12,000, aupporta 51 In< dnatriea that make a wide range of prod* ecu, Like many other municipal plants, we 1*1*6 with reciprocating ateara engines, tdded turbines, and later turned to InNnul-combusiion engines aa a more efficient source of power. Ol*tl Inatollotlona. The first two diesels Installed In 1931 were DeLaVergne 4-eycle 200-rpm 1160-bbp 800kw 6-cyl units. A similar unit was in stalled (n 1934. In 1937, when the plant was expanded for two additional en gines, a Nordberg 2250-bhp 225-rpm mechanicai-in}eetion 1600-kw 2-cycJe 6-cyl unit was put on the tine. In 1942, we added the.fifth engine, e Nordberg 2cycle 225-rpm air-injection diesel, rated ot 3B50 hhp, 2715 kw, 225 rpm. In 1946, management, recognising the need for additional power, studied the feasibility of extending and modernizing the 150-psi steam plant that had been retained for standby service. Coal could be purchased for $8 or $9 a ton- But the nature end size of the load was againat economical steam operation, es pecially In view of the wide variance in load demand. Besides, operating both steam and diesel planta would have re quired additional personnel, since the team plant la in a separate building. So the diesel plant was extended a second time. The sixth engine to go on the line, another Nordberg 3850-bhp air-injection unit, started operation in June 1948. Total plant capacity rose to 943(1 kw, but with peak loads zooming past the 7000-kw mark, the plont Mill did not have sufficient firm capocity. The 1947-48 expansion had provided additional space for 4000 to 5000 kw in diesel power, or 5000 to 6000 kw in gaiturbine power. We took bids on both types of prime movers and made aa in vestigation and analysis. Advantage* appeared for both types of prime movers. But over-all evidence Indicated that the diesel engine was more advantageous for Grand Haven, and a 2-eycle, 9-cyl, 29x40-in- mechani cal-injection diesel, rated 7000 hhp, 5000 kw net at 171 -S rpm, was ordered from Nordberg Manufacturing Co. Before this unit could be built and installed, an anticipated power emer gency required extra capacity at the earliest possible date. In addition, man agement wanted to save banking costs for fuel burned under the boiler in the team plant. In June 1951, we Installed two 1000-kw General Motors' surplus engines in the powerhouse basement. These engines operate at 720 rpm, burn ing o gas oil or No. 3 distillate. They supply standby and peaking power. We also orderod a Nordberg 3000-fcw 10-cyl 4300-bhp 225-rpm 2lVtx3l-ln. 2cycle mechanical-injection unit, .which will replace the No. 3 DeLaVergne en gine when It it Installed in late 1953. The 5000-kw unit was placed in serv. iee April 11, 1952, giving the plant a total capacity ol 16,430 kw. All the engines, except the two General Motors units, use residual oil (or (uel. Auxiliary Equipment. Table bottom of page 77 lists auxiliary equipment for the new 5000-kw engine. One of the interesting features of the installation HOVlMitB 1933 ENGINEERING ANO MANAGEMENT SECTION r in I I i.