Document Rp3aJDJ39n9k5zBx29L01azMa

/2-a, '10 v? ffh Temperature Water Heating System Supplies Doveir Air Force Needs !"J; Water has long proved to be an excellent heat transfer fluid and the recent in creased attention to high temperature water for heating and process reflects the development of system designs which make it possible to utilize the relatively high specific heats of water in and around 300 psig. Here is a description of a large scale high temperature installation at a U. S. Air Force Base. By M. W. WILLIAMS Combustion Engineerinq, Inc. HE U. S. Air Force Base, Dover, Del., employs a the Dover Air Force Base are (_-n jla M.ont controller Tdistrict heating system for the various buildings, circulation hot water boilers designed for 400 psig pres warehouses and hangars on the base with a central sure but operated at 275 psig (415 F equivalent). The heating plant serving as the heat source. High temsp- ecified rated output is 50,000,000 Btu per hr, maximum : perature water was selected as the most economical continuous, when using No. 6 fuel oil of a calorific value ; medium for distributing the heat. of 18,500 Btu per lb, as fired. Each generator is of the In essence, high temperature water heating systems watertube type with the boiler tube assembly divided are a further development oil a larger scale of principles into radiant and convection sections. Each tube cir i used in countless heating systems for homes, schools and cuit is l'/rin. O.D. tubing with an orifice located at the other small buildings. To effect economies on heat inlet end for metering the water in accordance with the transfer apparatus and hot water distribution equip heat absorbing capacity of that tube. ment higher temperatures and necessarily higher pres Water from the distribution system enters the boilers sures are used. Higher pressures were used as early as through the inlet header at the bottom of the boiler in the 1920's when pressures up to 235 psig (400 F equiva the rear, Fig. 4. The side wall tube platens and the wF!f lent) were adopted. Since very high temperatures, that front wall tubes have connecting headers so that the is above 380 F, are not often required, except for process water parallels the gas flow, due to the single pass boiler heating, the more practical and general range is from 330 design, with water leaving the boiler through the front ;F to 370 F. Temperatures above 400 F do not prove top header and entering the expansion drum that serves economical for district heating service. more than one boiler. Water from the expansion drum High Temperature 11 'atcr Boilers enters the distribution system circulating pumps which discharge it into the system at 375 psig. Fig. 4 does not Tlie three hot water generators, Figs. 3, 4, selected for show the single separate!}' installed expansion drum. Fig. 1--Exterior view of the boiler plant at the Dover. Del.. Air Force Base which can supply with three C-E La Mont controlled circulation boilers a heat load distributed in 98 buildings around the Base ^COMBUSTIO N--March 1955 Fig. 2--Heat exchangers have been located in each of the 98 buildings for local building heating needs. Where steam is needed separate heat exchangers are provided. About 14: . miles of interconnecting piping are employed RS-000242 1/17/02 NUECES 53 OUTLCT ht!,,*`:` / '- C 1c o: st :ii Je n :ei e 10 :ui Am ze in m] vh I___i i___i Fig. 3--Compact, fully enclosed design of the controlled circulation boilers, above, permits high degree of shop as sembly as well as a conservative use of building space Fig. 4--Sectional view of the C-E La Mont controlled cir culation boiler demonstrates its single pass design, freedo from baffles, absence of a boiler drum Heating Load Hall--30 psig, Refrigerator Storage--20 psig, Hospital 45 psig, Airmen's Mess Halls--30 psig, Boiler plant--6 At Dover Air Force Base there are 9$ buildings re psig. Maintenance Shops--30 psig, and the total stear^rS{ quiring heat. Some of these buildings, such as the ware flow amounts to 16,810 lb per hr. houses, are heated directly with high temperature water If there were no heat exchangers, a separate boil at the full pressure in the distribution system, whereas would be necessary' in each building, requiring a license* tea, the living quarters, mess halls, and others are heated with low pressure, hot water. These individual heat loads, together with the steam requirements they impose, are listed below: operator or boiler room attendant. Since heat ex o. changers are classified as unfired pressure vessels, the equ can be, and are, of course, left unattended except :o 6. periodic inspections and servicing visits. This is one c ;ySt{ (a) High temperature water at 3S5 F is distributed directly to the unit heaters installed in the warehouses, hangars and shops. the greatest advantages of a district heating system enai With high temperature water, "there are other advanta ^yste such as the elimination of steam traps; no grading cTatcl ([b) Low pressure hot water heats the living quarters through baseboard convectors, the mess halls by means of supply and return lines, no condensate receivers or cor 7. densate pumps and a complete return of all unused hea 0nd* unit heaters, the medical buildings with fin tube radiators, the operational buildings also with fin tube radiators and unit heaters, and the special services buildings with fin tube radiators and unit heaters. to the central heating plant. Distribution System ider; ure, This low pressure hot water is produced - through in At the Dover Air Force Base, there are three mal: direct heat exchangers. Fig. 2. located one to each utility zones; Zone 1--19.S90 ft of piping, Zone 2--35,350 room. Each of the 9$ buildings has its own utility room. of piping, Zone 3--20,850 ft of piping. The total lens The high temperature (3S5 FI water from the main dis tribution system passes through the primary' coils of the heat exchanger. The low pressure hot water is pumped from the secondary side to the local heating units. The medical and operational buildings will have air condition ing and will be connected into the low pressure heating lines serving the fin-tube type radiators. of these heating lines, excluding internal distribute Fol within the 98 buildings, amounts The main supply and return lines to almost alone total 3144,'3/240mfeile;1Issotht( the balance being external branches or sub-main circuit' einpi In steam distribution systems, the system pressu ge drop is the deciding factor and one which has a direct r lOUSl lation to the diameter of pipe used. With high temper's nu[t[, Where steam is required, whether it be for cooking, ture water, however, it is the design temperature dm ^ ^ sterilizers or other purposes, a separate high-temperature- which is the governing factor. In low pressure hot watt - ctor water-to-steani heat exchanger has been installed in the systems for internal hot water space heating, it is usui -pj building s utilitv room. The steam requirements are as follows: Officers Mess to design* drop of 20 the distribution piping degrees F, but with high fotermapertaetmurpeerwatatitren.b.r -.VK 54 RS-000243 1/17/02 riMarch 1955--C OMBUSTIOJ O M NUECES he design temperature drop may be as high as 200 de 1. Controlled circulation such that water is distributed crees F, although the most commonly used and more to the various tubes in accordance with the heat ab economical design drop ranges from 150 degrees to 160 sorbing capacities of the tubes. With this arrangement, Legrees F. a minimum amount of water need be circulated through Another great advantage of high temperature water the boiler with a corresponding minimum pressure loss. or heat distribution is its "thermal-flywheel" character- With a small increase in head, the system circulation stic. This feature develops from the fact that the en- pumps can therefore provide for circulation through the ire piping system, always maintained full of high tem- boilers. The need for a separate boiler circulation pump oerature water, constitutes a vast reserve heat storage. is thereby eliminated thus affecting a saving in initial This reserve effect represents approximately a 20 per and operating costs. :ent cushion or safety factor in boiler capacity. As a 2. No drums are required on individual boilers. A esult boilers can and are designed for the average 24 single expansion drum common to all boilers can be used. lour temperature rather than the peak load tempera- This results in a simplification of the control system and :ure. eliminates the necessity of providing balance pipes be The reserve of heat in the entire system at the Dover tween the various boilers in multi-boiler installations. kir Force Base may be better understood when you real- 3. Special tube arrangement is provided so that: ze the total water in the complete system, including the (a) Boiler tubes are ventable to the outlet header (and hree operating boilers, is about 700,000 lbs. This is an thence to the expansion drum) under all operating con mportant asset in an emergency and one of great value ditions. Vapor binding will not occur. Even though a rhen changes or extensions are contemplated. small amount of steam may be formed in the tubes under some operating conditions, it will remain entrained until it separates in the expansion drum. System Economies (b) Boiler tubes are completely drainable, and there are no reverse vertical tube circuits. (c) The boiler has a single pass design with no baffles, Economies to be affected by using hot water instead and tube arrangement gives parallel flow of gas and rTodort ^ steam are as follows: water. Low metal temperatures are avoided in zones of 1. No high pressure steam traps required, resulting low gas temperature thus minimizing the possibilities of n substantial saving in first cost and a further saving by corrosion resulting from high sulfur fuels. liminating steam losses likely in normal trap operation (d) Maximum furnace water cooling and the most is well as attendant maintenance. effective utilization of heating surface occurs. This 2. Elimination of blowdown, normally a three per pital-- :ent operational loss. nt--6' 3. No pressure reducing valves needed, producing a stean irst saving in valve cost, a second in maintenance and a markedly lengthens refractory life. (e) Maximum cleanability is obtained with minimum fouling in operation. 4. Miscellaneous advantages include: hird in steam losses from improper regulation. boile 4. No safety valve vent losses such as exist with a censer ;team boiler, it ex No condensate pumps, tanks, controls and vents (a) Maximum degree of shop assembly thus greatly reducing field erection costs. [b) Complete steel casing suitable for pressurized operation with oil or gas fuels thus eliminating the nec the! equired, avoiding their inherent steam losses. pt fo 6. Elimination of expensive feedwater treatment one o: ;ystem, with its continuous chemical cost and main/stem ;enance. Water makeup for a high temperature water itage ,ystem is negligible and this can be handled with a small inS >atch treatment storage system. r con 7. No investment outlays for corrosion protection in 1 hea ondensate return lines, representing an essential con- ideration for a steam system but not for a high tempera- essity of induced draft equipment. c) Bottom-supported design thereby reducing struc tural steel. d) Adequate access panels for cleaning, inspection and maintenance of convection bank heating surface. e) Minimum space required saving in building costs. R8-0002*4 1117/02 NUECES ure, water system. man ^ engt Boiler Advantages 'Utio Following the decision to use high temperature water ml es s the heat distributing medium instead of steam, it was ) fee1 Iso decided to use boilers especially designed for high cmt: emperature water, Figs. 3, 4, rather than units designed ssur G generate steam but modified for hot water. Prect re iously, the conventional watertube steam boiler with Peranultiplc water passes had been adapted for high tem<^ro ierature water with _ mixed and not altogether satiswate lctory results. usuc 'Tire C-E La Mont controlled circulation boiler, Figs. atur , 4, especially designed for use m hot water systems vatejrovides the following features: I O OMBUSTIO N--March 1955 COMBUSTION ENGINEERING A Reference Book on Fuel Burning and Steam Generation Edited by orro de LORENZt COMBUSTION ENGINEERING is probably the most comprehensive technical book aver published by an equipment manufacturer, lb 30-odd chapters end appendix run to well over a thousand pages and Include more *fan 400 Illustrations end ebout 80 tables. It is designed for the use of both engineering studenb and practicing engineers. Among the subfeeb covered in this book are: all types of stokers/ pulver ised fuel burning equipment/ burners for liquid end gaseous fuels/ furnaces for wood refuse and bagasse; ail types of stationary bolters/ marine boittrs/ forced circulation boilers; electric boilers; superheaters and desuperheaters; Seat recovery equipment; the origin and production of coal; fuels for steam- i-"3 purposes; fluid cycles; steam purification; feedwater; performance calculations; drafts, fans and chimneys; selection of equipment; testing of steam generating unita; and operation and maintenance of equipment. A full chapter is devoted to the A.S.M.E. Boiler Construction Code. The Append/* includes complete steam tables, and a Moilier Diagram is tipped i-. to the back cover. Profusely Illustrated 1041 Pages Size 6'/< X J'/i Price $7.50 Book Dept., COMBUSTION PUBLISHING COMPANY, INC. 100 Madison Avenue, New York 16, N. Y. A guide to better flow metering Here's a new fact-filled, technical booklet that tells you feature for feature how the new Hays electronic flow meter excels. Electronic operation -- provides maximum accuracy (14% of full scale differential), and speed (4 seconds for full scale pen travel). Mercuryless transmitters -- rupture-proof metallic bellows for differential pressure measurement. Continuous integration--motor-driven, continuous mechanical integrator is extremely accurate even on rapid load changes. Other features include powerful motor, easy readability, accuracy unaffected by normal temperature changes, optional explosion and weather-proof transmitter. Write for bulletin 54-1074-222 and get the important facts. 56 RS40024S 1/17/02 NUECE8 Automatic Combuttion Control Coder Paneti COt Recorders Veriflow MeteM and Veritrol Cot Anolyiert * Draft Coget Convbvition Te Setv Electronic 0*ygen Recorders i i March 1955--C OMBUSTION