US1941365A

US1941365A - Art of heat transfer

Info

Publication number: US1941365A
Application number: US564298A
Authority: US
Inventors: Ward S Patterson; Rosencrants Fay Harry
Original assignee: Int Comb Eng Corp
Current assignee: International Combustion Engineering Corp
Priority date: 1931-09-22
Filing date: 1931-09-22
Publication date: 1933-12-26
Anticipated expiration: 1950-12-26

Description

2 Sheets-Sheet l 0/15 OUTLET ART OF HEAT TRANSFER Filed Sept. 22. 1931 jfiJNVENTOKS By "7 W v Mn A TTORNEYS.

7.9. d V'- s" W W. 5. PATTERSON ET AL Dec. 26, 1933.

Dec. 26, 1933. w. s. PATTERSON ET AL 1,941,365

ART OF HEAT TRANSFER Filed Sept. 22. 1931 2 Sheets-Sheet 2 G I70 I301 216 k HA Te; m M

IN V EN TORS W /mm?- V A TTORNEYS.

UNITED STATES PATENT OFFICE ART or HEAT TRANSFER Ward S. Patterson, Cranford, N. J., and 'Fay Harry Rosencrants, Scarsdale, N. Y., assignors to International Combustion Engineering Corporation, New York, N. Y., a corporation of Delaware I Application September 22, 1931 Serial No. 564,298

22.0laims. (Cl. 257-245) This invention relates to the art of heat transof heating surface in the heater, depending upon fer, and particularly to certain novel and adthe variation in operating rate. This, of course, vantageous methods and apparatus for transferinvolves complications in the heat exchanger, or, ring heat from flue or furnace gases to air which as an alternative, the expensive necessity of is to be preheated for admission into a furnace maintaining a plurality of exchangers of differfor us i n pu p s s. ent capacity, one or more of which must stand The invention primarily contemplates the idle while another is in use. Our invention, transfer of heat from furnace gases to a combroadly considered, involves the obviation of the bustion air stream, whereby the temperature of various -difliculties above outlined, by the cm- D the discharged gases is lowered and the temployment of certain novel methods and forms 6 perature of the air raised, for economical power of apparatus for regulating or controlling thep a p a sp ial y by an i pr ved oounfluid flow to accomplish the desired ends. e flOW d, in Such manner that While a high More specifically, the preferred operation acd ee of efl y s Obtained. y the p cording to the present invention involves the ature of h flue a es j n h discharge controlling of the flow of the heating fluid, as

Point thereof from the Z0116 of heat transfer is having certain desirable advantages over the conmaintained at such a level, regardless of the rate t l of th h ted fluid of operation of the furnace or furnaces, that As 111 appear in more d t il hereinafter, substantial condensation of condensibles carried several methods are cof templated, d v r l by the gases, and consequent clogging as Well forms of apparatus have been devised, all inas corrosion of the heat transfer mechanism or vowing basically certain general advantages, but apparatus are Preventedeach involving specifically certain advantages of For a clear understanding of the invention its w V and of the advantages thereof it should here be one method f carrying out the invention stated that in the preheating of air for boiler valves the by passing of least a portion of 80 furnaces or other furnaces, where the furnace or the stream, and th method involves flue-gases are used as the heating medium soot the recirculating of a part of the air stream in and dust and gummy deposits are aptto be lodged a certain manner; at the cold or gas outlet end of the air Other, and more preferred methods, involve heater, especially when the boiler is operating at the diversion of a portion of the gas stream in 85 10w loads' It is further quite dimcult various novel ways, the recirculation of a porvide means for cleaning frequently and wlthout tion of the gas stream, or the dilution of at leastshutdown, the heat transfer plates or elements a portion of the stream by at least a portion of the heater and the installation of nozzle 9 of the gas stream. These various features and jet devices for blowing the soot and other deposit advantages of the invention will be more fully 90 out of the heater from title gas exit end thereof appreciated from the following description, taken is disadvantageous, particularly because of the together with the accompanying drawings in necessity of blowing against tttllie l cllirezction ofthe which u gas stream passing through e ea er. e

40 I In heat exchangers of the counterflowtype, gg f g zfig g g gz gfi gg g f gl 95 which are desirablefor their general efllciency, heater w one form ,of our invention applied and especially at times when a boilerdfumace 1S thereto operating v atlow loads, clogging an corrosion ecfi th line frequently take, lace adjacent the air inlet end jg $;rg g fl of 1 of the heater where the cold air on one side of I I c t,

h lateorl ates and comparatively cool gas ti re Q QBF a; V .En the other g idejthereof result causing'the --,l.1gure 2a is a. seicfitioltif sum lg kfiq a g'z gf fi temperatureiof tne'gas m adjacent the plate s at a m d 9% on0 t; v or plates. to fallb low the 'dew-p'oin This'de- F re ir men rr i an me ieee n pends, oi coursefongthef two fluid temperatures, vatitonal wew anfl her m difieation pf the in- 105 cleanness or the surface, and the composi- V .1; r p 3:31 of the 'flue gas, especially-with reference to .Figure 3,,1 s a;,diagrammat cview of a modules; its contentofwater vapors and sulphuntrioxide. t on'bfthwmvention, showing a heat exchanger We are aware that it has been'proposedto mini- '01 am heaterm =1t relation to the gas a k mize this difficulty by using a variable amount ducts and the induced draft and forced draft no a power plant or 'boiler furviews of still other modifications.

By reference first to- Figures 1 and 2, it will be seen that we have illustrated an air preheater which includes a conduit-like casing 2, having a fluid or gas inlet 3, a fluid or gas outlet 4, a fiuid or air inlet 5, and a fiuid or air outlet 6.

In accordance with known practice, groups of heat transfer elements or partition walls '7-'l--7 are disposed in 'the casing 2, extending lengthwise thereof, the air inlet and outlet communicating with alternate passageways 8 formed by the walls '7, and the gas inlet and outlet communicating with the alternate intermediatepassages 9. Spacer strips or angle members 10 are provided in the gas and air passageways to position the plates 7 and to insure the proper distribution of gas and air over the entire heat transmitting surface or area. The spacer strips 10 shown in Figure 1 are strips in the gas passageways, which, in accordance with the usual practice, are broken away at zones indicated at 1111, to permit of inspection and lancing when necessary, through the apertures or doorways covered by the doors 12. i

'While we have preferred to illustrate a heat exchanger of the so-called plate type, it is to be understood that the invention may be equally well applied to heat exchangers of the so-called tubulartype.

In accordance with the present invention, we provide a diverting or by-pass passageway or channel 13, leading from the gas inlet 3 to 'an advance point or zone in the gas passageways of the heater proper, where the said by-pass communicates, at the area indicated by the numeral 14 with the said gas passageways; break away the spacer elements 10 at the points marked 15 and 16, in the gas passageways, which provides, in each gas passageway, a substantially triangular zone adjacent the gas outlet and air inlet end of the heater, as clearly shown in Figure 1; and provide control means for the gas by-pass,- such as the movable damper 17, which may be manually controlled by means of its shaft 18, or which may be controlled by a thermostat 18a of any desired type located preferably adjacent the gas outlet 4.

In Figure 2 the gas by-pass 13 is formed by angle members 10a which are attached to plates 7, the flanges 10b of the angle members being in alinement to form the inside wall of the by-pass. Thus a very simple arrangement is provided whereby a heater may be manufactured with the by-pass arrangement applied at practically the same cost as a heater not equipped with the improvement. In some instances, however, it-may be desirable to form the gas by-pass 13 by employing a casing plate 'or wall 10c as illustrated in Figure 2a.

According to the construction just described, hot flue gas at the temperature available as it enters the heater is diverted or by-passed directly to the area or zone adjacent the gas exit end of the heater thereby increasing the heat transferred to the air immediately as the latter enters the heater, and'thereby raising the plate temperature of this area near the air inlet. It is obvious that the changes necessary in the ordinary heater to carry out this invention are very easily accomplished. The gas by-pass may be entirely self-contained within the air heater casing and the fiow of gas through the by-pass may easily be thermostatically controlled by means of the damper 1'7. The use of the inspection, access or lancing openings above referred to, for hand lancing, is not interfered with in any way.

Referring, now, to Figure 3, we have diagrammatically illustrated an air preheater 2a, the fiue gas side of which is indicated at 2b, and the air side of which is indicated at 20, the forced draft fan for the furnace being indicated at FD, and the induced draft fan for the furnace being indicated at ID. The reference character G indicates the fiue gas line or conduit, the reference characters CA indicate the cold air line, and the reference characters HA indicate the hot air line to the furnace. In this formof construction, as in the form shown in Figures 1 and 2, a portion of the gas is by-passed through the by-pass 13a, into the heater at point 14a, controlled by the valve device indicated at 17a, but we have also provided an additional valve 19 in the 'gas line, between the point of takeoff of the by-pass 13a and the main point of entry of the gas into the heater. By proper manipulation of the 1 valves 17a and 19, both of which may be controlled by a single thermostat adjacent the gas outlet, any desired portion or all of the gas may be passed through the by-pass or through the gas passages 2b. The advantage of this arrange- 1 ment over that shown in Figures 1 and 2 chiefly resides in the fact that positive control, as to any proportion, is assured, without having to depend upon pressure differences due to the resistance of the gas passages in the heater. 1

Reverting now to Figure 1, it will be seen that in addition to the damper means 17 above described, we also contemplate the provision of dampers 3a mounted on shafts 3b, by means of which the gas quantity passing through the by- 1 passducts 13 may be controlled without depending entirely on the difference in resistance to flow between the passages through the preheater and the bypass ductsu Thus an arrangement is provided the operation of which is positive and fiex- 1 ible and similar to that of the form illustrated in Figure 3. In some instances, however, the form illustrated in Figure 1 may be advantageously employed without the dampers 3a.

In Figure 4, we illustrate a construction in which a passage 20 communicates between the discharge line of the fiue gas fan and the intake line of the combustion air fan, so that a mixture of hot gas and cold air, indicated at WA, is delivered into the fan FD and thus to the heater. Suitable valves 21 in the gas line and 22 in the diluting line afford control of the system. This arrangement is advantageous in installations where a certain proportion of flue gas in the combustion air, especially at low rates of operation of the boiler furnace, will do no harm, or is desired. Admission of fiue gas into the preheated air is sometimes desirable for controlling combustion in the furnace.

In the modification shown in Figure 5, somewhat similar parts are employed, but the air diluting passage 20a in this instance leadsv from the hot or inletend of the gas line, and itscontrol is effected by an auxiliary blower AB. The principal advantages of this arrangement over the arrangement shown in Figure 4 are: That the positive delivery of the flue gas into the forced draft blower or fan is controllable quite independently of the action of the induced draft fan ID, and that the gas delivered through the conduit 1 20a into the air line need be only'about 10% of the quantity of air handled as compared with about 25% of the quantity of air handled in the construction shown in Figure 4. This comparison assumes a temperature of gas entering the heater of approximately 600 F. and a gas leaving temperature of about 300 F. A valve 20b is provided in the line 20a, preferably at a point near the line G, for controlling the fan delivery and preventing air infiltration backward when the fan is not operating.

In the construction shown in Figure 6, any desired proportion of the exit gases may be recirculated or redelivered, by the diverting line 23, back to the gas inlet line. By the provision of a valve 24 in line 23 and a valve 25 in the line leading from the induced draft fan ID tothe stack, any desirable recirculation pressure is available, even at the most reduced furnace loads, at which times it is generally most necessary to effect the recirculation.

While the invention contemplates, if desired, the by-passing of a certain amount of the cold air, for example, directly from blower FD in Figure 3 to line HA; or a recirculation of hot air from line-HA into the intake side of blower FD, we prefer to control, divert or vary the flow of the gas or heating medium, since this causes little or no interference with the desired, independentcontrol of the air feed to the boiler furnace.

In the modification illustrated in Figure 2b, we have shown a novel arrangement of additional and easily replaceable heat absorbing surface over which the by-pass portion of the hot gas may be passed to effect initial preheating of the air before it enters the heater proper.

This surface may consist of readily replaceable heater elements of either the tubularor plate type, although we prefer to employ tubular elements with extended surface on the gas or air side. Through this arrangement the air may be positively preheated to a pre-determined and controllable temperature before it enters the main part of the heat exchanger. Dampers such as the dampers 3a and 17 described in connection with the form illustrated in Figure 1 may be employed to control the flow of the gas, making it possible to vary the amount of gas bypassed to suit the requirements which will depend on the ambient air temperature, the gas temperature leaving the heater, the amount of condensibles in the gas, and the amount of solid foreign matter in the gas which tends to cause clogging when such matter is moistened due to the condensation of the condensibles.

In any of ire arrangements, the valves or blowers will be so adjusted, or the thermostat or thermostats contriolling them will be so set that the relative flow of the heated and heating media will be suitably controlled or varied to prevent the exit gases from falling in temperature below the dew-point of condensibles carried thereby. It will be readily seen that the controlling of .the problem involved, in counter-flow heat exchanging, by suitably varying the gas flow, has decided advantages over prior practices involving the employment of complicated apparatus or a plurality of heat exchangers for vary-' ing the heat-transfer surface.

While we have referred .to the device as an air preheater and to its application to a' boiler furnace or other furnace, it is to be understood that we contemplate its use as a heat exchanger receiving hot gas from any source and utilizing it to heat air or other gaseous fluids such as gaseous fuel, or for use in connection with various types of furnaces, or in connection wit various other processes or apparatus. I

What we claim is:

1. The improved method of transferring heat between two flowing gas streams which includes counterfiowing the streams in generally separated but heat-transferrent proximity through a given zone whereby the coldest portion of the stream to be heated is adjacent the coolest portion of the heating stream, and controlling the flow of at least a part of the heating stream in such manner as to maintain the coolest portion of the heating stream in said zone above the dew-point of condensibles carried thereby without affecting the entering state of the gas stream to be heated.

2. The improved method of transferring heat between two flowing gas streams which includes counterflowing the streams in generally separated but he'at-transferrent proximity through a given zone whereby the coolest portion of the stream to be heated is adjacentthe coolest portion of the heating stream, and diverting the flow of at least a part of the heating'stream in such manner as to maintain the coolest portion of. the heating stream in said zone above the dew-point of condensibles carried thereby without affecting the entering state of the gas stream to be heated.

3. The improved method of transferring heat from a stream of hot furnace gases to a stream of air for combustion which includes counterfiowing the streams in generally separated but heat-transferren't proximity through a given zone whereby the coldest portion of the air stream is adjacent the coolest portion of the gas stream, and controlling the flow of at least a part of the gas stream in such manner as to maintain the coolest portion of the gas stream in said zone above the dew-point of condensibles carried thereby without affecting the entering state of the stream of air for combustion.

4. The improved method of transferring heat from a stream of hot furnace gases to a stream of air for combustion which includes counterfiowing the streams in generally separated but heat-transferrent proximity through a given zone whereby the coldest portion of the air stream is adjacent the coolest portion of the gas stream, and bypassing the flow of at least a part of the gas stream in such manner as to maintain the coolest portion of the gas stream in said zone above the dew-point of condensibles carried thereby without affecting the entering state of the stream of air for combustion.

5. The improved method of transferring heat from a stream of hotfurnace gases to a stream of air for combustion which includes counterfiowing the streams in generally separated but heat-transferrent proximity through a given zone whereby the coldest portion of the air stream is adjacent the coolest portion of the gas stream, and recirculating the flow of at least a part of the gas stream in such manner as to maintainthe coolest portion of the gas stream in said zone above the dew-point of condensibles carried thereby without affecting the entering state of the stream of air for combustion.

6. In a heat exchanger, associated passageways respectively for hot gas and gas to be heated, inlet and outlet means for the respective gas passageways, and controllable supplemental gas passage means for the hot gas adapted to vary its normal flow for controlling he temperature gas to be heated.

7. In a heat exchanger, associated passageways respectively for hot gas and gas to be heated, in-

let and outlet means for the respective gas passageways, and controllable supplemental gas passage means for the hot gas adapted to vary its normal flow for maintaining the temperature of the passageway walls adjacent the hot gas outlet in a range above the dew-point of condensibles carried in thegas without afiecting the entering state of the gas to be heated.

8. In a heat exchanger, associated main passageways respectively for hot gas and gas to be heated, inlet and outlet means for the respective gas passageways, and means for controlling the temperature of the passageway walls adjacent the hot gas outlet comprising a controllable by-passfor -by-passing hot gas from the main hot gas passageway adjacent its inlet and for returning it thereto adjacent its outlet.

9. In a heat exchanger, associated main pas-' passageways, and means for controlling the tem-- perature of the passageway walls adjacent the hot gas outlet comprising means for by-passinghot gas into the exit zone of the hot gas passages.

11. In a heat exchanger, associated-passageways respectively for hot gas and gas to be heated, inlet and outlet meansfior the respective gas passageways, and means for controlling the temperature of the passageway walls adjacent the hot gas outlet comprising means for controllably re-circulating through the hot gas passages a portionpfthe heating gas.

' 12. In an air-preheater apparatus, a flue-gas line, a combustion-air line, a counterflow heat exchanger through'which said lines run, means for setting up a flowing. stream of fine gasesthrough the gas line, means for setting up a flowing stream of air through the air line, .and a bypass for the flue gas line leading therefrom at the gas entering end portion of the exchanger and returning thereto at the gas exit end portion of the exchanger whereby a portion of the flue gas stream is by-passed to efiect the maintenance of the temperature of the flue gas stream adjacent its exit from the exchanger above a predetermined point.

13. In a heat exchanger, a casing having air and" gas inlets and outlets arranged for counterflow of gas and air through the exchanger, heat exchanging elements in said casing, and a by: pass for by-passing gas from the gas inlet to the gas outlet over heat exchanging surface which is adjacent the air inlet.

14. In a heat exchanger, a casingh'aving air and gas inlets and outlets arranged for counterflow of gas and air through the exchanger, heat exchanging elements in said casing providing pas,- sages for the air and gas, and means providing a passage independent of the heat exchanging unit adapted to be removed as such from the element passages for leading gas directly from the gas inlet to the gas outlet over heat exchanging surface which is adjacent the air inlet.

15. In a heat exchanger, a casing having air and gas inlets and outlets arranged for counterfiow of gas and air through the exchanger, heat exchanging elements in said casing, and a by-pass for by-passing gas from the gas inlet over heat exchanging surface which is adjacent the air inlet, said by-pass being formed in part by the casing and in part by the heat exchanging elements.

16. In a heat exchanger, a casing having air and gas inlets and outlets arranged for counterllow of gas and air through the exchanger, heat exchanging elements in said casing, and a bypass for by-passing gas from the gas inlet over heat exchanging surface which is adjacent the air inlet, said by-pass being formed in part by the casing and in part by means carried by the heat exchanging elements.

17. In a heat exchanger, a casing having air and gas inlets and outlets'arranged' for counterflow of gas and air through the exchanger, main heat exchanging elements in said casing, supplemental heat exchanging elements located in said casing adjacent the air inlet for subjecting the stream of air to heat as it enters the exchanger, and means for diverting gas from the gas inlet to the supplemental heat exchanging elements.

18 In a heat exchanger, a casing having air and gas inlets and outlets arranged for counterflow of gas and air through the exchanger, main heat exchanging elements in said casing, supplemental heat exchanging elements located in said 110 casing adjacent the air inlet, and means for diverting gas from the gas inlet to the supplemental heat exchanging elements, said supplemental heat exchanging elements comprising a.

heat exchanger. 1

19. In a heat exchanger of the counterfiow type having the usual heat exchanging elements, the inclusion of supplemental heat exchanging elements located between the point of admission of the gas to be heated and the usual heat exchanging elements and over which all said gas must fiow on entering the exchanger.

20. In a heat exchanger of the counterflow type having the usual heat exchanging elements, the inclusion of supplemental heat exchanging elements located between the point of admission of the gas to be heated and the usual heat exchanging elements and over which all said gas must flow on entering-the exchanger, and means for leading heating gas directly to said supplemental heat exchanging elements.

21. Ina heat exchanger, associated passageways respectively for hot gas and gas to be heated, inlet and outlet means for the respective gas passageways, and means for controlling the temperature of passageway walls comprising means for re-circulating through the hot gaspassageature of passageway walls comprising means for re-circulating hot gas from its outlet back into its passageway and over passageway walls.

WARD S. PATTERSON. FAY HARRY ROSENCRAN'I'S.