US1974288A - Steam boiler - Google Patents

Description

P 13, 9 G. w. NIGH -1,974,28

STEAM BOILER Filed Nov. 24. 1933 FIGURE. B

WITNESSES INVENTOR heads; 3 is the furnace; 4 is the refractory lining,

Patented Sept. 18, 1934 STEAM BOILER 7 George W. Nigh, Middletown, Pa. Application November 24, 1933, Serial No. 699,505

3 Claims. (01'. 122-149) My invention relates to improvements to steam or. hot waterboilers such as those used to supply steam or hot water for heating purposes, or' to supply steam for any other purpose.

In general, the usual boiler of the firetube type, in which the hot products of combustion pass through the inside of the boiler tubes, is made to operate with all water inside the boiler at approximately the same temperature. Hence, the heat transfer from the hot gases passing through the tubes to the water surrounding the tubes is that of heat passing from a non-condensable gas, falling in temperature, to a liquid at a constant temperature.

t is well known in physics that the rate of heat transfer by counterflow is much greater, measured in heat units per second per unit of area per degree temperature difference. This is demonstrated by the efficiency of boiler units of the water tube type in which the counterflow principle is used, either by an extra pass to heat the feed water in the boiler itself, or by the use of an integral economizer. But such boilers are feasible only in the very large sizes.

Now, therefore, I have invented a new and novel boiler of the firetube type, in which the counterfiow principle of heat transfer is incorporated. In other words, the low temperature feed water enters the boiler adjacent to where the hot gases leave the boiler. Thus, it is possible to lower the temperature of the exit gases down many degrees below that possible without this invention. This is of value because of the fuel saving due to the use of this invention.

The boiler is illustrated in Figure A, which is a longitudinal vertical section on the center line; and in Figure B, which is a transverse vertical section on the center line. 1 is the shell which may be oval as shown, or round when high steam pressures are to be carried; 2 shows the used when the boiler is fired with an oil burner as at 5. Feed water enters at 6 from either side, and steam or hot water is discharged from the boiler at 7. At 8 is shown the large tubes which connect to the rear of the furnace 3, and carry the hot gases forward into the front smokebox 9, which should be insulated as shown. From here the gases pass to the rear through the bank of tubes 10, into the rear smokebox 11, and out into the smokepipe through the collar 12. In order to effect the counterfiow, a baflie 13, is located as shown.

This assembly comprising the shell, heads, furnace, and tubes forms a pressure tight container wherein water, or other liquid, is heated to hot water, or hot liquid, or boiled to form steam or other vapor. Construction details should conform to the requirements of the Boiler Construc tion Code of the American Society of Mechanical Engineers, or to any code in effect in the locality where the boiler is to be used. 1

In operation, the water is fed through 6 from either side into the chamber wherein the bank of tubes 10 is located. At the same time, fuel combustion takes place within the furnace 3. The gases from the burning fuel either partly or entirely burned, leave the furnace at the rear end and enter the tubes 8, of which there are one or more to suit the size of the boiler. It is in Z tended that the connection between furnace 3 and tubes 8, also tubes 8 themselves, shall be large, comparatively, so that incompletely burned gases entering from the furnace 3 will not be quenched, but that combustion can continue into 1 the front smokebox 9. However, before entering tubes 10, combustion must be complete because tubes are to be small in diameter, limited only by the draft available to pull the gases through them. 0

The gases enter the tubes 10 at a comparatively high temperature, passing to the rear; and at the same time cold feed Water surrounds these tubes, passing forward to get around the front end of the baffle 13, to enter the normal circulation of the water in the remainder of the boiler.

To illustrate the effectiveness of this counterflow, two of a series of tests are cited. One for four hours duration at 119.5% of rating according to the Standards of the Steel Heating Boiler Institute, shows an average temperature in the front smokebox 9 of 1200 deg. F. At the same time the exit gas temperature in the rear smokeboX 11 was 429 deg. F. The heat release in the combustion volume was 57,500 B. t. u. per cubic .95 foot. The temperature of the feed water at 6 was 7'7 deg. F. Thus, the measured temperature drop of the gases passing through the tubes 10 was 771 deg. F. From the Orsat readings, the analysis of the gases is known, the rate of the fuel feed is carefully measured, so the quantity of gases entering the tubes 10 is known exactly. By formulae, according to Fessenden, the calculated temperature drop through these tubes, assuming that the water surrounding the tubes 10 is at the average boiler water temperature corre- L sponding to 24 gauge pressure of steam, which is the standard adopted for such tests, should be 594 deg. F. Thus, due to counterfiow, there is a saving of 165 deg. F, in the temperature of the.

exit gases. Similarly, at a rating of 81.7%, the observed average exit temperature was 247 deg. F., while the calculated temperature was 518 deg. R, which was a saving of 271 deg. F. in the temperature of the chimney gases. These tests were on a boiler in which the tubes 10 were 1 /2 diameter, so that it was possible to have normal operation with natural draft. v

Another feature is that of precipitating the temporary hardness out of the feed water when first heated by the tubes 10, and settling out the precipitate below the tubes in the space 14, onto boiler surfaces not heated by the products of cornbustion. Under these conditons the precipitate will not be burned to a hard scale.

I am aware that there are built today a multi tude of varieties of boilers, but none to my knowledge, include the following which I claim as new and novel:

1. An internally fired boiler made up of shell, heads, furnace, tubes, so arranged that the gases ofcombustion make three approximately horizontal passes before leaving the boiler; that each pass isflower than the preceding one; that the second pass is through tube or tubes large enough to not quench the flames and thus providing additional combustion volume over that in the furnace; that the third pass is through comparati'v'ely small diameter tubes; substantially as shown.

2. An internally fired boiler made up of shell, heads, furnace, tubes, so arranged that the gases of combustion make three approximately horizontal passes before leaving the boiler; that each pass is lower than the preceding one; that each pass is through smaller diameter tubes than the preceding one, the second pass being through comparatively large tubes which will not quench flames passing through, thus providing additional combustion volume over that in the furnace; that the feed water is delivered by a cross connection in the bottom part of the shell near the rear, the water entering through an opening that is long transversely to the boiler shell and narrow longitudinally to the shell so that the feed water is delivered at a low velocity spreading to cover a majority of the tubes in the last or third pass, arranged so the pipe connection is made horizontally from either side of the boiler; substantially as shown.

3. An internally fired boiler made up of shell, heads, furnace, tubes, so arranged that the gases of combustion make three approximately horizontal passes before leaving the boiler; that each pass is lower than the preceding one; that the second pass is through comparatively large diameter tubes which will not quench the flames passing through, thus providing additional combustion volume throughout the second pass; that the third pass is through tubes of small diame-- ter, thus providing a large heating surface in a small space; which has a feed water connection so located as to discharge the water into the boiler near the last end of the third pass of the tubes; and which also has a baflle in the water space, covering the tops of the tubes in the third pass, made tight or approximately so to the rear head and providing a space at the front for the feed water to leave the lower part of the boiler, thus entering the normal boiler water circulation after cooling the gases passing through the last pass of the tubes; substantially as shown.

GEORGE W. NIGH.

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