US2243913A - Divided economizer and control - Google Patents

Description

June 3, 1941. L.'J. MARSHALL 2,243,913

DIVIDED ECONOMIZER AND CONTROL Filed June 3, 1939 INVENTOR 'LEO/VARD J. MARSH/ILL.

Patented June 3, 1941 DIVIDED ECONOMIZER AND CONTRGL -LeonardJ. Marshall, Tenafly, N. J., assignor to Combustion Engineering Company, Inc., New

York, N. Y.

Application June 3, 1939, Serial No. 277,141

7 Claims.

This invention relates to heat exchange apparatus and particularly to the arrangement of an economizer in a steam generating unit.

It is an object of this invention to so relate the parts of the heat exchanging apparatus of a high pressure and high temperature steam generating unit that improved operating conditions of the component parts result as well as an improved use of the space occupied by said apparatus. The invention will be'more clearly understood from the following description of a preferred embodi ment of the apparatus illustrated on the accompanying drawing in which:

Fig. 1 is a sectional elevation of a boiler embodying the invention, the heat exchange apparatus including a boiler, superheater, economizer and air heater; and Fig.2 illustrates another embodiment, the apparatus including a boiler, superheater and reheater or a primary and secondary superheater, economizer and air heater.

In Fig. l the boiler I located over a furnace 2 consists of a front tube bank 3, a rear tube bank 4 and spaced tube rows 5 and 6 which serve to support bafiies l and 8 defining sides of a gas pass for the economizer. All these tubes are connected for fluid circulation into drums 9 l and l I in the usual manner. Between the tube banks 3 and 4 a superheater I2 is located. In the offtake l3 from the boiler is an air heater 14.

At the rear of the tube bank 3 is a baflle i5 extending upwardly from the bottom drum H and terminating short of the upper drum 9. At the front of the rear tube bank 4 is a bafiie l6 extending downwardly from the top drum 9 with its lower end spaced from the lower drum ll. At the rear of tube bank 4 is a baiile I! which extends for a substantial distance along the length of the tubes with its two ends spaced respectively from the upper drum l0 and lower drum ll. At the rear of the tube row 6 is a bafile 8 which extends from the top drum ID to the top of the offtake l3 and at the bottom of the same tube row is a baiile 8a which extends from the bottom of the offtake downwardly to the hopper l8, which hopper forms the remaining seal between the rear bafile 8a and boiler drum II. A baffle l9 extends across the economizer chamber formed between the tube rows 5 and 6 from baffle I! to the middle of the oiitake [3. The economizer chamber is thereby divided into top and bottom portions in which are located respectively an economizer section 20 and an economizer section 2|.

Thefeed water is delivered to the bottom of the lower economizer 2| flows upward through this economizer to the bottom of the upper economizer 20 and through the latter to the boiler drum I0. Thus, in the lower economizer section 2| there is a parallel flow of gases and water whereas in the upper economizer section 2i! there is a counterflow of gases and water. Since the heat head is relatively large in the lower economizer section 2 I, there is no material loss in heat exchange between water and gases involved below that which would occur should counterflow prevail. The combined arrangement of upper and lower economizers when using the divided flow of gases as proposed, is therefore substantially as effective in heat exchange as would be in a single economizer arranged for all counterflow and over which all gases would pass.

The gases rise from furnace 2 and enter the boiler I over the front tube bank 3, passing downwardly over superheater l2 and thence divide, a portion passing under the lower end of bailie l6 and upwardly to the second tube bank 4 and downwardly over economizer section 29 to the offtake [3. The remaining gases pass over the lower portions of tubes in bank 4 and thence under baiile l and upwardly over economizer section 2! to the ofl'take. From the offtake l3 all the gases pass through air heater l4. In offtake l3 there are located dampers 22 and 23 controlling, respectively, the gas flow leaving the top and bottom economizer sections 20, 2|. By means of these dampers control is had of the proportional amounts of gas which flow over the upper half of the superheater I2 and thence over the upper economizer section 253 and the amounts which flow over the full length of the superheater 20 and thence over the lower economizer section 2!. Accordingly, by causing more or less gas to pass over the full length of the superheater l2 the temperature of the superheated steam may be controlled.

In operating the boiler at low loads it is proposed tohave all of the gases flow over the full length of the superheater l2 and pass out through thelower economizer section 2| to offtake 13. This is efiected by closing damper 22.

At higher loads (say approximately above half full load) when the superheater 12 would deliver increasing superheat with increasing load, damper 22 is opened so that part of the gases are bypassed from flowing the full length of the superheater l2.' Theby-passed gases then flow up through the second bank 4 and through the top economizer 20 and thence to the oiftake I3.

At about half and lower ratings of the boiler only about half of the economizer surface, in this instance the lower half 21, is exposed to the flow of the gases but has all of the boiler feed water flowing through it. This ratio of water to gas avoids undesirable steaming of the water which may occur at said low ratings in single pass economizers where all of the economizer surface is exposed to the flow of gases. Such steaming at low ratings occurs in an economizer which heats the feed water to nearly steaming temperature when the full economizer surface absorbs heat from a substantially constant quantity of gas flow and delivers it to a relatively reduced quantity of feed water. The lower economizer is contacted by a substantially uniform quantity of gas from about half boiler load upwards to full load so that the resistance to gas flow therethrough would be substantially the same and always higher, except at possibly full load, than through the upper economizer. Control of the gas flow toboth upper and lower economizers may therefore be maintained by the top damper '22 alone. The continuous upward flow of water through both economizers 29, 21 avoids possible water hammer in the economizers should any steaming occur because both the Water and steam will be flowing upwardly. V

It should also be noted that because substantially only half of the gases will ordinarily pass through one of the economizer sections 20, 2| the economizers will have but about half the depth of a single economizer such as would accommodate all of the heating gases. This arrange ment materially decreases the overall depth of the boiler and eco-nomizer by an amount substantially half of the usual single economizer when placed in the same location with respect to the boiler. As a consequence of this divided flow of the gases through the economizer sections, the

' convection gas pass where bank 4 is located also maintained relatively high at the lower ratings which has the advantage of maintaining the average gas temperature through the air heater I" relatively high and thereby avoids undesirable cooling of the cold end of the air heater metal below the dew point of the gases. When at normal ratings flue gases are cooled by an air heater to a low exit temperature, the lower flue gas temperature at low ratings may cause the metal'temperature at the cold end to fall below the dew point of the gas with resultant undesirable moisture and ash deposits and corrosion. Heretofore to avoid this condition some of the air was by-passed around the heater thereby reducing the amount of heat absorbed by the gases and raising the metal temperature at the coldend, or, some of the. gases were recirculated thereby increasing their velocity and consequently their transfer and raising the metal temperature at the cold end. lhus, these earlier methods required additional conduits and apparatus which may be eliminated by applican'ts improved economizer arrangement.

In Fig. 2 parts corresponding to those inFig. l are marked with 'like'numbers. In Fig. 2 some of the tube rows in the second boiler bank are omitted and in their locationis placed a reheater 22 or a primary superheater, in which last case superheater I 2 becomes the secondary superheater connected for steam flow in series m'th the primary superheater. In case of reheater 22 the steam temperature from the reheater is controlled by the proportional amount of gas flowing through the upper and lower economizers, that which flows to the upper econom-izer 20 passing over the reheater and that to the lower economizer 2i by-passing the reheater. In case the reheater is replaced by a primary superheater 22, the control of temperature leaving the secondary superheater will be by control of gas flow over the primary superheater just as in the case recited for the reheater.

What I claim is:

1. In a boiler having a superheater located in a gas pass between the furnace and offtake; baffle means forming two separate gas passes leading from said superheater pass to the ofitake so arranged that gases entering one of said passes havecontacted only part of the superheater surface and gases entering the other of said two passes have contacted all of the superheater surface; an economizer having portions of its heat absorbing surface located in each of said two gas passes; and damper means for regulating the proportional distribution of gases flowing through c said two passes from said superheater pass to the oiftake.

2. In a steam generating unit having a furnace, an ofitake and heat absorbing elements located between said furnace and offtake including steam generating tubes and an economizer divided into two superimposed sections serially connected for water flow in an upward direction therethrough,

the distribution of heat absorbing surfaces being such that at high ratings the heat remaining in the gases passing to both sections of the economizer raises the feed water temperature to near the boiling point; baffie means forming two separate gas paths between the steam generating tubes and offtake in each of which one section of the economizer is located; and damper means so controlling gas flow through said passes that at high loads gases'may be directed to the offtake through each economizer section and directed to flow over only one economizer section at low loads.

3. A steam generating unit comprising a furnace, a boiler, an economizer divided into several sections which are serially connected for water 7 flow therethrough, and an air heatenall so located that gases from the furnace pass. through the boiler, thence through the economizer and to the air heater; baffles associated with the boiler and the economizer so disposed as to divide the gas flow from the boiler to the economizer into several parts equal in'number to said'several economizersections and to deliver each part to one each of the sections of the economizer at high ratings of the'steam generator; and damper means controlling said gas passes and'operable to direct all of the gases at low loads to less than all of the sections of theeconomizer so that the gases leaving the economizer and passing to the air heater are at a relatively high temperature whereby a too great cooling of elements of the air heater maybe avoided at low ratings.

7 4. A boiler of the bent tube type having upper drums and a lower drum connected by substantially vertical banks of tubes and containing within its limits asuperheater and an economizer; a furnace below said'boiler and connected there with for the flow of furnace gases therethrough; a substantially vertical superheater gas pass in said-f boiler; adjacent bafiles forming said pass arranged to direct the gases leaving the furnace over said superheater; two gas outlets from said superheater pass, one arranged for the flow of gases over the full superheater surface and the other for the flow of a portion of the gases over only a portion of the superheater surface; substantially vertically superposed economizer gas passes in said boiler horizontally adjacent said superheater gas pass; adjacent baffles forming said passes arranged to direct the gases leaving said superheater pass either through one or both of said economizer passes in controlled amounts, one of said passes being connected to one of said superheater pass outlets and the other of said passes being connected to the other of said superheater pass outlets; damper means for controlling the flow of gasesthrough said respective economizer gas passes, and an economizer having two vertically superposed portions connected for serial upward flow of feed water to the boiler therethrough, one economizer portion being arranged in each of said economizer gas passes.

5. A boiler of the bent tube type having upper drums and a lower drum connected by substantially vertical banks of tubes and containing within its limits a superheater and an economizer; a furnace below said boiler and connected therewith for the flow of furnace gases therethrough; a substantially vertical superheater gas pass in said boiler; adjacent bafiles forming said pass arranged to direct the gases leaving the furnace over said superheater; two gas outlets from said superheater pass, one arranged for the flow of gases over the full superheater surface and the other for the flow of a portion of the gases over 7 only a portion of the superheater surface; substantially vertically superposed economizer gas passes in said boiler horizontally adjacent said superheater gas pass; adjacent bafiles forming said passes arranged to direct the gases leaving said superheater pass either through one or both of said economizer passes in controlled amounts,

one of said passes being connected to one of said superheater pass outlets and the other of said passes being connected to the other of said superheater pass outlets; damper means for controlling the flow of gases through said respective economizer gas passes, and an economizer having two vertically superposed portions connected for serial upward flow of feed water to the boiler therethrough, one economizer portion being arranged in each of said economizer gas passes, said passes being arranged so that the lower of said economizer portions will have the gases flowing parallel to the flow of water and the upper of said economizer portions will have the gases flowing counter to the flow of water.

6. A steam generating unit comprising a furnace, a boiler, a superheater and an economizer divided into two sections, all so located that gases from the furnace pass through the boiler and superheater to the economizer; bafile means associated with the economizer and superheater so arranged as to form two separate gas passes, one including one economizer section and all of the superheater surface, and the other pass including the other economizer section and only a portion of the superheater surface; and damper means for regulating the proportional distribution of gases flowing through said passes.

7. In a boiler having a superheater located in a gas pass between the furnace and ofiftake; baflle means forming one gas pass leading to said 01T- take from said superheater pass at a point between its inlet and outlet and a second separate gas pass leading from the outlet of said superheater pass to said offtake; an economizer divided into two sections each located entirely within in only one of said last mentioned passes at points in advance of said ofitake; and damper means for regulating the proportional distribution of gases flowing through said two passes.

LEONARD J. MARSHALL.

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