Ralph Johnson design engineer for Baldwin Locomotive Works offers a differing opinion concerning the feed water heater designs,
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"The preheating of boiler feed water by means of waste exhaust steam is a highly important economy without which no heavy-duty locomotive can be considered efficient. The reasons, summarized briefly are:
1. On any boiler it increases the maximum evaporative capacity, no matter how efficient the boiler may be in itself.
2. For equivalent evaporative capacities it decreases the weight of the boiler.
3. The effective tender capacity is increased.
4. Boiler maintenance is decreased because a percentage of the feed water is returned in the form of condensed steam or distilled water.
5. Produces an increase in the general over-all efficiency of the locomotive.
Feed water heating reduces the amount of heat which must be supplied by the fuel for the generation of steam, and for a given locomotive there will be either a decrease in coal consumption for a given evaporation, or the total evaporation of the boiler will be increased if the same quantity of fuel is burned. In either case a pound of fuel will evaporate a greater amount of water than would be the case if cold feed water were used. Also, as exhaust steam in the form of condensate is returned to either the boiler or the tender tank, it follows that a smaller amount of cold water will be required and in this way there will be a reduction of cold feed water used per horsepower developed. The cylinder performance, however, is not affected by feed water heating except that there is some reduction in back pressure, as less steam is passing through the nozzle when the heater is in use...
Theoretically the feed water heater can add up to 18 per cent to the maximum evaporative capacity of the boiler, depending upon the temperature of the water in the tender and the exhaust steam....
In the case of a locomotive the feed water heater and its pump should be compared to the injector which they replace; therefore, from the heat recovered from the exhaust steam and returned to the boiler, should be deducted the heat in the steam required to operate the feed pump in order to find the net heat recovery by the installation. As the feed pump requires about 2.5% of the total heat for its operation the net or useful recovery of heat will be 9.53% in the above example.
An approximate rule is that a saving of 1 per cent is made by each increase of 10* in the temperature of the feed water. This corresponds to 0.10 per cent per degree of temperature rise...
The heat recovered by the heater is a direct addition to the heat output of the boiler proper and the maximum steaming capacity of the locomotive is therefore increased in the same proportion.
Feed water heaters condense more steam and show a greater percentage effect in winter when the tender water is cold than in summer."
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Considering the low overall efficiency of the external combustion steam locomotive all efforts to increase this efficiency were and are extremely important compared to the high efficiency of the internal combustion diesel engine.
Ross Rolland and CO 614 being the play toy of a millionare aside, that engine needed its feed water system!
Doc
Dr D Water temperature into the boiler without feed water heat could be almost freezing,
For example, the temperature of unsaturated steam (which the injector uses) at 300 psi is 421.7 degrees F (water tempurature varies, plus or minus, according to the pressure). For all intents and purposes, all of this heat is transfered to the feedwater going into the boiler. So, there is absolutely no "almost freezing" water going into the boiler. Somewhere in the 200+ degree range may be more like it.
Hot water supplied from the feedwater heater is in about the same temperature range, varying according to how hard the locomotive is being worked.
The idea that using the injector for putting cold* water into the boiler and knocking down the boiler pressure is pure myth also. The reason the boiler pressure lowers is because boiler pressure is being used to inject the water into the boiler.
* "Cold" is a relative term. As we have just seen, the feedwater isn't cold at all. The water in the tender is "Cold". The feedwater going into the boiler, whether it be by use of the injector or the feedwater heater is very hot compared to the tender water, yet, colder (200+ degrees) than the water at boiler pressure (420 degrees).
Use the following links (wait for them to load) to learn about:
Injectors: http://www.icsarchive.org/icsarchive-org/bb/ics_bb_508d_section_5236_locomotive_injectors.pdf
Feedwater Heaters: http://www.icsarchive.org/icsarchive-org/bb/ics_bb_508d_section_2517_locomotive_feedwater_heating_equipments.pdf
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Dr DWater temperature into the boiler without feed water heat could be almost freezing, however, with the feed water system the water went into the locomotive boiler with heat at 200-250 degrees temperature.
The idea that feedwater is admitted 'cold' might have been true in the mid-Nineteenth Century, in the days of rod-driven pumps, but a moment's reflection will show that any locomotive using an injector will have hot feedwater. The concern is that, because of the way an injector operates, it cannot use feedwater that is hot enough to 'flash' to steam during injection. A FWH system with a hot-water pump does not have this limitation.
Note that a delivered-water temperature in the range quoted (200-250 deg.F) is still well shy of the actual equilibrium temperature of water in a typical large Super-Power locomotive, particularly one that uses "modern" high pressure of 300 psi or higher. Part of the importance of FWH on such locomotives is to reduce thermal cycling of parts of the boiler structure. Do you not mean the rise in temperature through the heater, starting with water at whatever temperature the cold-water pump delivers?
During the 'age of steam' the use of FWH was driven by economics -- the substantial first cost and mintenance costs of the system being balanced against the financial results of the benefits. It is interesting to note that one of the most sophisticated modern locomotives, C&O 614, had her (admittedly poor) FWH system removed early in her life, and never replaced even during the 614T testing. On a 'preserved' locomotive, the advantages of good FWH may take on more importance, more for the preservation of boiler integrity than for any supposed improvement in fuel economy (which saving is a minuscule part of the overall cost of running big steam) or nominal water rate.
Might be a good idea to discuss heat recovery in the Rankine cycle, an important consideration in steam power design, as part of the context of this thread.
I believe Coffin was the first design followed by Elesco and finally the Worthington was the latest and probably most effective and modern design.
Elesco was the least efficient but easiest to identify because of the famous cylinder bundle mounted just ahead of the locomotive stack.
Elesco was a "closed design" because it kept exhaust steam and boiler feed water separate from each other in order to prevent cylinder lubrication oil which was in the exhaust steam out of the boiler intake water.
The very successful Worthington was a "open design" because it mixed exhaust steam into the feed water. Worthington had developed a separator design to extract the oil.
Worthington is usually seen as a small tank or box just ahead of the locomotive smoke stack but is really a large tank sunk into the front end design of the locomotive smoke box.
Feed water heaters were not widely added to steam locomotives in the United States until the 1920's. They were one of the truely modern locomotive appliances that increased the performance and efficiency of the engine.
Early 1920s designs almost overtook the locomotive with all of the external plumbing and large clumbsy pumps they used. For example the Elesco "closed design" heater tube bundle was a large beadle brow mounted on the boiler top. The Coffin design was sometimes mounted externally and appeared as a large "horse shoe" tank mounted over the smoke box door.
In the 1920's you will notice most all of the plumbing necessary to effect the feed water systems was hung along the outside of the boiler giving a sometimes ugly mess appearance to the locomotive with a huge pump often carried on the left side of the engine.
As the 1930's progressed the systems were perfected and the piping and pumps became almost invisible. New York Central Hudsom 4-6-4 sunk the Elesco "closed design" bundle down into the boiler top so only the ends protruded. Other builders did this also. By the time the Wortington "open design" was perfected you could hardly notice the feed water system at all such as on the New York Central famed Niagara 4-8-4. Don't be fooled this large efficient system was hidden inside the boiler front.
The idea that the feed water system was just an "accessory" is misleading because it became a "necessity" for modern efficient steam locomotive design. Water temperature into the boiler without feed water heat could be cold, however, with the feed water system the water went into the locomotive boiler with heat at 200-250 degrees temperature. Not only was this was less thermal shock to the hot boiler but secondly the hot water went to steam quickly and easily.
We are all familiar with energy conservation in Americal today. If you buy and new American sink faucet or shower head it will have a small "restrictor" inside to prevent water flow - the so called Al Gore restrictor. This is to cut down on excessive use of water and particularly hot water which conserves precious natural resources. Imagine if the hot water going down the laundry drain or shower drain could have its heat extracted and used to heat the water used for laundry or bathing use. Many home owners and businesses would be shocked to have reduction in utility bills.
The steam railroads were glad to recoup the waste heat going out the locomotive stack and put it to use heating the cold boiler water. Locomotive boiler evaporation rate was increased 8-10 percent. About 15 to 20 percent of the exhaust steam was used in the heating process.
The "feed water heater" and the locomotive "superheater" were responsible for the "super power era" and they truely were responsible for making the steam locomotive of the mid Twentieth Century competative to the internal combustion diesel engine.
Although the Elesco's were the most appealing in my opinion, what feedwater heater (and valve gear) was the most efficient and why? If a new "classic" steam locomotive were to be built today which would it utilize?
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