US2065850A

US2065850A - Heat exchange apparatus

Info

Publication number: US2065850A
Application number: US9798A
Authority: US
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1935-03-07
Filing date: 1935-03-07
Publication date: 1936-12-29
Anticipated expiration: 1953-12-29

Description

Dec. 29, 1936. J. E. BLACK ET AL HEAT EXCHANGE APPARATU S Filed March 7, 1955 John E. Black, Deceased BY Gerlrune M Black, Z'xeruznk 3 f2. W

ATTORNEY Patented Dec. 29, 1936 UNITED STATES Parser HEAT EXCHANGE APPARATUS Application March '1, 1935, Serial No. 9,793

4 Claims.

This invention relates to a heat exchange apparatus and has for one of its objects the utilization of heated gases from independent sources, and which may have radically different charac- 5 teristics requiring that, in their passage over the heat exchange surfaces, they shall be maintained in independent paths until the temperature of one or the other, or all, of said heated gases, as the case may be, shall have reached the point where they may be advantageously combined for passage over the remainder of the heat exchange surface without producing results which might contribute to short life of the heat exchange surfaces, or to a cumulative reduction in efficiency over the operating period.

In numerous industries of the present day an unutiiized by-product of a process or operation maybe highly heated gases containing a large percentage of solid material which, if combined with other highly heated gases of combustion entering the heat exchange passes of, for instance, a steam generator, would result in a temperature at which fusion of the solids would occur with large cumulative deposits on the heat exchange surfaces with consequent reduced efficiency and short life of the surfaces, and it is for these reasons that such highly heated gaseous by-products in the industry have often remained unutilized.

A particular instance in industry where the present invention is applicable resides in reclaiming. the heat from gases incident to the burning of so called black liquor. This liquor is the result of the digesting processes of the wood pulp and paper industry and contains valuable chemicals which may be recovered by burning the liquor, but the hot gases from this recovery process are heavily laden with solids which are slag forming when raised to the fusion temperature,

as would be the case if they were admitted to a steam generator at the customary location and allowed to mingle with the higher temperature combustion gases from another source of supply r such, for instance, as oil or pulverized fuel burners furnishing the principal heat for the generator. Such a slag forming characteristic is particularly apt to interfere with superheater operation. Therefore, this present invention has as an especial object a steam generator and superheater arrangement wherein the gas passes over the boiler and superheater surfaces are so related to the main source of heated gas supply that the gases from any other independent source of heated gases Will travel in a separate pass until the temperature, at combination, of the multiple gases is adjusted to prevent fusion of solids, either by the temperature of the gases, or as a result of any exothermic reaction which might take place under special circumstances.

A further object of the invention is to provide a superhcater the heating surfaces of which are exposed to gases from such an independent source and also from the other source of supply.

Other objects of the invention will appear as the accompanying description proceeds.

In the accompanying drawing there is indicated a modification of the invention as applied to a multiple pass boiler of the Babcock and Wilcox type. Here, the gases from a directly fired furnace are caused topass across boiler tubes before they come into contact with the dust laden gases from the burning of black liquor. The surfaces over which the gases of combustion from the direct firing are passing are so proportioned with respect to the heat in the gases passing thereover that the gases from direct firing are reduced in temperature to a point precluding fusion of the solids in the dustladen gases from the black liquor when thegases from the two independent sources mentioned are combined.

In the drawing there is illustrated a cross drum boiler of the Babcock and Wilcox type. This boiler involves the bank of steam generating tubes l0 connected so as to discharge steam and water into the drum l2. Uptake headers it are arranged at one end of this bank of tubes, and downtake headers H5 at its other end.

The illustrative boiler is heated by heated gases derived from a plurality of independent sources. One source is the directly fired furnace l8 shown as having firing means 20 such as an oil or pulverized fuel burner. A flue 22 and passage 24 are provided for highly heated gases proceeding from another source, such for instance as a black liquor furnace of any suitable design (not shown).

In the illustrated apparatus there is a first gas pass defined on one side by the uptake headers i4 and on the other side by a. bafiie 26. A baffle 28 intermediate the sides of this gas pass subdivides the same into separate passes for the combustion gases from the furnace l8 and the solid laden hot gases of the black liquor.

Supported by the bafiie 26 is a superheater. 30 having tubes providing heating surfaces extend;- ing across the gas outlet of the furnace 18. In the present instance, the supcrheater is shown as having a plurality of return bend tubes 32 some of which extend only across the outlet or first pass of the directly fired furnace. Others extend across the outlets of both furnaces and thereby proportion the superhcating surface to the heating capacities of the two furnaces. These tubes receive steam from an inlet header 36 directly connected by tubes 39 with the steam and water drum E2. The superheater outlet header 38 may be connected to a consumer in any suitable manner.

The drawing shows steam generating tubes lll extending across the first gas passes and acting as a screen for the superheater. These screen tubes are connected into boiler circulation through uptake headers 42 and downtake headers 44. These headersare, in turn, connected to the superposed headers l4 and N5 of the main boiler tube bank by rows of

nipples

46 and 48.

Hot gases from an independent source such asthe gases from the burning of black liquor contain excessive amounts of solid materials which are carried over in the hot gases and may deposit on fluid carrying tubes extending across the path of the gases. Excessive deposits of such solids may collect upon the closely spaced boiler tubes andcause these tubes to become ineffective. This undesirable excess is prevented in the illustrative apparatus by the provision of different temperatures.

additional screen tubes

50 and 52 connected at their-upper ends to the lower ends of the uptake headers l4. These tubes are shown as extending three times across the passage 22 and flue 24 carrying the heated gases from the black liquor. They are connected at their lower ends to a header 54 suitably connected by a downcomer 55 into the boiler circulation so that the header 54 will remain submerged.

Furnace wall cooling tubes 59 extend from the header 54 through the wall 58 and thence up wardly along that wall. Their upper portions extend across the top of the passage 24 and are connected to the headers 42.

The illustrative boiler is shown as having three gas passes. The gases from the top of the subdivided first gas pass join at temperatures preventing fusion of any-solids carried therein and pass downwardly towards the superheater headers between the bafile 26 and the baffle 57. In the third gas pass, the gases pass upwardly along the downtake headers Hi to a flue which leads the gases from the boiler through the uptake nipples 41.

As to superheat, it remains substantially constant at a given rate of steam output whether the superheater is contacted by the gases from either one, or both sources of heat. In the present instance, there must be a larger superheating surface subjected to contact with the gases from the direct fired furnace in order to obtain a given total steam temperature (or degrees of superheat). That is, the superheating surface must be larger than that contacted by the waste heat gas. In the illustrated apparatus the superheating surface is preferably so proportioned that if waste heat gas alone is used, the superheat will be substantially the same as it would be with direct firing at the same steam output.

The apparatus of the drawing is illustrative offluid heat exchange apparatus contacted by hot gases from different and independent sources, the gases being of different heat values and at The gases from the black liquor furnace, as before stated, carry a high percentage of solids in suspension and are maintained in a separate path across the heat exchange tubes until enough heat has been absorbed from the initially higher temperature gases of the direct firing to prevent the fusion of the dust particles in the gases from the burning of the black liquor. The tubes of the heat exchanger are thus protected against excessive accumulations.

While the invention has been described with reference to the particular diagrammatic steam generator indicated in the drawing, it is to be understood that it is not limited thereto but is of a scope commensurate with the scope of tin subjoined claims. For instance, while the invention has been illustrated in connection Witt a water tube steam boiler, it comprehends a fire tube boiler, or a combined steam generator which is awater tube boiler in part with the remaining steam generating surface provided by a fire tube boiler.

What is claimed is:

1. In a water tube steam boiler, a bank of stean generating tubes extending across a heating gar chamber, a steam and water drum connected t( the tubes, a plurality of sources of heating gase: of different combustion characteristics, wall: forming passages separately conducting burning gases from said sources to the heating gas chamber where gases from both sources are mixed before the fiow over said generating tubes, and a superheater receiving saturated steam from the drum and having parts extending across both of the passages, one of said sources being a directly fired furnace discharging its gases across the super heater.

2. In a steam boiler and furnace organization, a steam and water drum, a bank of water tubes extending across a heating gas chamber and connected to the drum, a directly fired furnace having an outlet communicating with the chamber, a source of waste heat gases, means conducting burning gases from said source to the chamber, a superheater exposed in separate gas passes tc the burning gases from the directly fired furnace and the burning waste heat gases, the gases from said separate passes being mixed before the pass over said bank of tubes, means connecting the superheater to the steam space of the drum, and additional steam generating tubes acting as a slag screen connected into boiler circulation and extending in front of the superheater relative to gas flow, there being unequal slag screen surfaces exposed to the heating gases from the furnace and from said source, the slag screen surfaces being proportioned between the separate heating gases in accordance with their slagging and other combustion characteristics.

3. In combination, a direct fired furnace, a waste heat furnace, tubes presenting steam generating surface exposed to heat from said furnaces, and a unitary superheater having surfaces separately subjected to gases from said separate furnaces and proportioned in accordancewith the superheating capacity of said gases, the superheating surfaces being also so arranged that substantially the same superheat is attained whether the superheater is subjected only to the gases from the waste heat furnace or only to the gases from the direct fired furnace, a substantial part of said generating surface exposed to the gases from both furnaces after they have joined beyond the superheater.

4. In fluid heat exchange apparatus, a plurality of spaced apart banks of steam generating tubes, a waste heat furance, a direct fired furnace, a superhcater, and means whereby only a part of said superheater and said tubes are separately exposed to hot gases from one of said furnaces while other parts are exposed only to gases from the other furnace, said means being so constructed and arranged that the gases from said separate furnaces are joined before they contact with the remainder of said generating tubes.

GERTRUDE M. BLACK, Executriac of John E. Black, Deceased.

CHARLES S. Sll/E'IH.