US3203478A

US3203478A - Heat exchange unit

Info

Publication number: US3203478A
Application number: US166200A
Authority: US
Inventors: Bauder Marshall
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-01-15
Filing date: 1962-01-15
Publication date: 1965-08-31
Anticipated expiration: 1982-08-31

Description

Aug. 31, 1965 M. BAUDER HEAT EXCHANGE UNIT Filed Jan. 15, 1962 I I 37A l9 [9 0: J m 2 g es 7 o m 2 4 2 5 5 P INVENTOR I 34 l MARSHALL BAUDER -4. 5 By a United States Patent M 3,203,478 HEAT EXCHANGE UNIT Marshall Bauder, 6436 E. Broadway, Burnaby 2, British Columbia, Canada Filed Jan. 15, 1962, Ser. No. 166,200 10 Claims. (Cl. 165-406) My invention relates to improvements in effecting gas to gas heat exchange, and has particular application to heat exchangers for use in gas turbine and similar installations.

To be effective, tube and plate heat exchangers are large and costly, compact exchangers with high heat transfer coefficients are subject to fouling by the products of combustion in the hot gases, and are difficult to clean. In most pebble heat exchangers, the drop in pressure through the exchanger offsets the gain in thermal efficiency.

One object of my invention is to provide a low cost heat exchanger, adapted for example for use with gas turbines, which shall recover some 90% of the available heat and, moreover, accomplish this with pressure drop as low as two tenths pound per square inch. A further object is to provide a unit having the above advantages and characteristics, but such that there are no fouling and cleaning problems.

Taking advantage of the high performance unit of my invention, it becomes possible to design a gas turbine plant having up to 50% thermal eiiiciency. This approaches, and in some cases will exceed, the performance now obtainable from the better steam plants. In contrast, the overall thermal efficiency of gas turbine plants, according to the best design heretofore available, seldom exceeds 25% or 30%.

The nature of my invention, and the manner in which I attain these, and other objects and advantages, will be apparent to those skilled in the art from the following description, illustrated by the drawings of which:

FIGURE 1 is a small scale schematic representation of the invention in sectional elevation,

FIGURE 2 shows the distribution head of one chamber,

FIGURE 3 is a section on 33 of FIGURE 2,

FIGURE 4 is a partly sectioned fragmented view of the air intake end of the distribution head of FIGURE 2, showing only one transverse member, a still larger scale,

FIGURE 5 is a sect-ion on 5-5 of FIGURE 4.

Like characters of reference refer to the same parts throughout.

The following notation is used in the formulae and throughout the disclosure, units are f.p.s., temperatures are in degrees Farenheit:

A, flow cross-sectional area of a chamber at height h,

B, a dimensionless constant, see Equation 1 and Table I below,

CP, specific heat of gas at constant pressure and at temperature tg,

Cs, specific heat of shot at ts,

dp, diameter (mean) of shot particle,

F, weight rate of flow of gas,

g, acceleration of gravity,

H, height of a chamber,

h, height of a chamber flow cross-section above the base,

K, a dimensionless constant, see Equation 1 and Table I below,

kg, thermal conductivity of the gas at film temperature P, pressure of the gas,

rg, density of the gas at temperature tg,

rs, density of the shot,

S, particle size range index,

tg, temperature of the gas,

3,203,478 Patented Aug. 31, 1965 is, temperature of the shot,

u, viscosity of the gas at film temperature,

V, terminal velocity of shot falling in free air at the temperature and pressure of Equation 5,

Vg, velocity of the gas at Equation 5 temperature and pressure, Vg=F/rg.a, w, weight rate of flow of the shot, y, dimensionless design parameter indicating degree of shot suspension, y=(V Vg) V, Z, a dimensionless function, see Equation 1 below.

TABLE I Values of B and K for certain values of Z, where:

Z=g. rs. (dpWu (1) ,800 23,100 8, 020 4, 070 2, 820 1, 350 765 307 13x10- 63 74 98 113 12s 158 186 246 K .70 .76 .90 98 1.06 1. 23 1.38 1.75

Referring to FIGURE 1, the numeral 11 indicates a tall hollow chamber, disposed substantially vertically, to

which I refer as the extraction chamber, 12 indicates a second tall hollow substantially vertical chamber, the

transfer chamber. A conveyor 13, suitably of the Redler type, runs from the bottom of the extraction chamber to the top of the transfer chamber. A second similar conveyor 14 runs from the bottom of the transfer chamber to the top of the extraction chamber.

The extraction chamber 11 has a large inlet port 15 to which is attached suitable pipe means, not shown, carrying hot gases from which heat is to be extracted, and the said chamber 11 terminates at its upper end in an exhaust port 16 which, as shown, is smaller than the inlet port 15. The gases, now cooled, are discharged from the extraction chamber through the port 15. The flow of gases through the extraction chamber 11 is indicated generally by the

arrows

17, 18, 19.

The transfer chamber 12 is provided with the intake port 20 at the lower end thereof, and the outlet port 21 at the upper end of said chamber, the inlet port 20 being smaller in cross-sectional area than the outlet port 21, as shown. Cool gases enter at 20 to pass out, now heated, through the outlet port 21, thence by suitable pipe means, not shown, to the combustion chamber. The ilow of gases through the transfer chamber 12 is indicated generally by the

arrows

22, 23, 24.

The extraction chamber 11 reduces in cross-sectional area in the direction of the gas flow being smaller at the top, transfer chamber 12 increases in area in the direction of gas flow thus being larger adjacent the outlet port 21.

The heat transfer element consists of small particles, later described and specified in detail, hereinafter referred to as shot.

Near the top of extraction chamber 11 is a distribution head 25, and a similar but larger distribution head 26 is located near the top of the transfer chamber 12.

At the lowest part of each of the chambers 11, 12 is a shot discharge port indicated respectively by the numerals 2'7, 28. The conveyor 14 carries shot in the direction of the arrow 14A from 28 to the extraction chamber distribution head 25, and the conveyor 13 similarly carries shot from 27 to the transfer distribution head 26 in the direction shown by the arrow 13A. This completes the cycle.

Typically the hot gases entering port 15 would be at 1000 and at or near atmospheric pressure. The cool air entering port 20 would typically be from a compressor, and might be at 400 and pounds per square inch.

In operation, shot enters the extraction chamber distribution head 25 from the conveyor 14 and falls by gravity against the

hot gas stream

19, 18 to discharge at 27 to the conveyor 13. As will later be apparent, the temperature of the shot discharging from the distribution head 25, at the top of the extraction chamber, is lower than that of the entering hot gases 17. Consequently, the temperature of the shot increases throughout the fall to reach a maximum at discharge. The entering gases are hottest at 17, losing heat by transfer to the falling shot and attaining lower temperature upon discharge through 16.

The hot shot discharging at 27 to the conveyor 13 is carried to the transfer chamber distribution head 26, to fall by gravity against the

cool gas stream

23, 22.

As the shot, heated by passage through the extraction chamber, falls against the transfer chamber air stream, heat is transferred from the falling shot to the air, so heating it. The heated air 24, has been explained, passes out of the transfer chamber at 21, thence to a gas turbine.

The transfer chamber shot, now cooled by passage against the

air stream

24, 23, 22, discharges at 28 to the conveyor 14 to be moved in the direction 14A to the extraction chamber distribution head 25, thus completing the cycle.

It is seen then that heat is extracted from the hot exhaust gases 17 in the extraction chamber 11, which heat now appears in the shot. In a similar, but reversed, action the heat of the shot is transferred in chamber 12 to the

airstream

22, 23, 24 so heating it.

The foregoing explanation broadly describes the operation of the heat exchanger of my invention. To attain the stated objects it is however necessary to take into consideration a number of factors related to one another in a complex manner.

The percentage of available heat recovered may be taken as a measure of the effectiveness of the heat exchanger. Below are listed factors which influence effectiveness.

Shot-Size and upper and lower limits of tolerance in size, specific gravity, specific heat, weight rate of flow.

Gases in extraction chamber.Weight'rate of How, initial temperature at entry.

Transfer chamber gas (air).Weight rate of flow, initial temperature at entry.

Chambers.Height, cross sectional area in relation to height, dA/dH is negative for the extraction chamber, positive for the transfer chamber.

In this disclosure, where heat passes from the hot gas to shot at a lower temperature heating the shot, I refer to extraction. When the heat passes from hot shot to gas at a lower temperature so heating it, I refer to transfer.

Referring to the extraction chamber 11, I have found that-the weight rate of flow of shot the specific heat of the shotzweight rate of flow of gas the specific heat of the gasis a requirement for optimum effectiveness. If the shot flow is too low, the shot will attain its proper temperature but the quantity of heat extracted will reduce. If the rate is too high, the shot will not attain the required temperature.

The effect of size of shot particle alone, other factors being fixed, is generally as follows: For shot of a particular material the terminal velocity will be a function of particle size. If the shot particles are large, as for example in pebble exchangers where half inch to one inch substantially spherical pebbles may be used, then the fall is comparatively rapid and, in consequence, the particles are in contact with the air for but a short time. This limits the quantity of heat which will be extracted, or transferred, as the case may be.

Where the particle size becomes much smaller, to approach a dust, the rate of fall approaches zero. In such case, while (as has been explained) the temperature of the particles and that of the gases will tend to equalize, in this limiting condition the exchanger would become inoperative. For a particular set of conditions there is thus an optimum shot size.

Consider now the case of a body of shot wherein there is non-uniformity of particle size. Those particles which are too heavy will fall too rapidly, and the smaller particles either will remain suspended, or will fall too slowly. Thus it is required that the individual particles comprising the body of the shot shall be within certain limits of maximum and minimum size.

An individual particle of shot falling in free air will attain a particular maximum velocity, called the terminal velocity. The terminal velocity will be greater the greater the diameter of the particle. Let S be the ratio of the terminal velocity of the largest particle in the body to that of the smallest. I have found that S should not exceed 1.2 in ordinary cases in practice, and it will be understood that when I assign a particular value to S, I have established the limits of maximum and minimum particle size the symbol dp herein refers to the average particle size regardless of S.

Conventional air elutriation means are capable of providing suitable gradation.

The shot may be nickel chrome steel, providing high resistance to abrasion and having other suitable physical properties. Other alloys may be used.

The following equations are now given:

%s Cp.F.dtg dh C's.w.dh

B.kg.rg(tstg) 1 rs.C's.u.dp 1-y 1+S (2) rg.0p 2 2y+S-1 dh C's s-1 2 +1-s (3) A=KF/(g.rg.rs.dp) .(ly) (4) V: (g.rg.rs.dp) /rg.K (5) These empirical relations hold for substantially spherical particles between one and two hundredths of an inch mean diameter where S is not greater than 1 l.6y, where the shot distribution and gas velocities are substantially uniform at any section, and where the distribution of shot by size is substantially uniform within the particle size range.

Some general considerations will now be stated, after which I shall explain the application of the above equations to a particular example.

(1) Throughout the working sections of each chamber, the velocity of the gas should approach the terminal velocity of the smallest particles of the body of shot. I have found that the gas velocity should not exceed about 0.95 times the terminal velocity. That is, the said terminal velocity is slightly (about 5%) greater than the gas velocity. When this limit is exceeded the gas velocity approaches too closely that of the smallest particles and pressure drop increases rapidly because 2y-S+1:0, see Equation 3.

(2) Shot of a nominal size will contain particles larger than, and smaller than, that size. The tolerable range of size, as indicated by the range of terminal velocities, should be narrow. S places a lower limit upon the value of y. In practice, S will rarely exceed 1.2, reducing S will improve performance.

(3) When the range of terminal velocities has been determined, and this range should be narrow, y can be established according to economic considerations of space art/d2 size, y here referred to being the value at mid-section H (4) y having been established, this value is held, within limits later to be explained, throughout the working sections of the chambers by varying the cross sectional area. This results in a configuration such as FIGURE 1. The values of rg vary materially with temperature--accordingly if A is not varied to maintain y within those limits, performance reduces significantly.

(5) The gas velocity should be uniform across a flow section, the tolerable variation limit is somewhat less than the difference between the average gas velocity and the terminal velocity of the smallest particle.

(6) Particle size is desirably between one and two hundredths of an inch. Particles larger than 0.02 inch will ordinarily necessitate excessive chamber heights, or alternatively require gas velocity to be so close to the terminal velocity that an impractically restricted particle size range is required, and under these conditions very close regulation of gas flow would be required. With particles smaller than 0.01 inch, flow cross-section area becomes excessive.

It will be apparent to those skilled in the mathematical art that solution of the foregoing empirical equations will require reiterative, or tabular, procedures. The actual procedure to provide physical embodiment of the foregoing principles in a heat exchange unit according to my invention will be understood from the following explanation.

Where it is desired to keep y constant throughout, a step by step calculation of: d.tg/dh, d.ts/dh, ts, tg, A, etc., will be required working both ways from the mid-point H 2. In such case, the value of H will differ somewhat from that obtained above, and the taper will be a curve.

It has been explained that the distribution of shot across a flow cross-section is to be substantially uniform. In FIGURES 2 through 5, are shown details of the distributor head to effect this.

As best seen in FIGURE 2, the head 25, comprises a plurality of parallel hollow members and 31 transverse of the chamber, said bars at an angle to the horizontal say 5 greater than the angle of repose of the shot so that the same may flow by gravity. A slope of 20 or 30 is satisfactory, the angle is not critical. These bars are suitably in two rows the upper row members between the spaces of the lower row members as shown in FIGURE 3.

FIGURE 5 shows an enlarged section of a single bar, pear shaped the large end downwards, facing the air flow. Said section is divided by the members 32 into two hollow

longitudinal spaces

33 and 34, member 32 having a plurality of holes 35 communicating between 33 and 34. At the bottom of the bar are a number of TABLE II Particular solutions to Equations 2, 3, and 4 B X10 (see Table I) 29 63 74 98 113 129 158 186 246 398 467 K 56 61 .76 98 1. 06 1. 23 1.38 1. 75 2. 79 3. 31 dp (feet) 0098 0052 .0032 0026 0018 .0015 .0013 0010 0008 0006 0004 0003 (11) (inches 12 062 .038 .031 022 .018 015 .012 010 007 005 004 V 114 76 53 43 31 26 22 17 14 9. 2 4. 2 3. 5 H 932 316 96 51 37 27 17 12 6. 8 2. 78 1. 88 A 27 41 59 71 1.00 1. 19 1. 40 1. 84 2. 28 3. 36 7. 35 8. 83

NoTE.-A is section at h=H/2, for unit flow of gas.

dp, V, H, A, above are calculated for:

rg=0.036, u=2 10- K =0.276 B.t.u. per hour per foot per degree Farenheit.

The gas flow rate, mean temperature and pressure in each chamber, and the desired effectiveness of the exchanger are known. The required results may be attained with different combinations of particle diameter and design parametry. Each combination will have a particular associated value of chamber height H, midpoint flow cross-sectional area (area at h=H/2), and pressure drop. These values can be computed from the equations using known values Cp, Cs, rg, w, kg for the mean gas temperature and upon the assumption that d.tg/d.h is constant.

Table II following has been computed from the equations and may be used for preliminary calculations or for check purposes. Tables may obviously be calculated for smaller increments of the independent variables. Table II extends beyond the practical range, clearly to show the effect of particle size. For example, with large particles of about an eighth of an inch, to attain optimum effectiveness chambers nearly a thousand feet high are required. Practical panticle size lies between .007 and 0.03 inch, normal range is between .01 and .02 inch.

Obtaining values of height, mid-point area, and pressure drop for several combinations aforesaid will permit choice of dp and 3 that will result in height, mid-section area, and pressure drop suitable for the remaining design conditions, which conditions may be physical such as a height limitation, and physical and economic relating to area.

When particle diameter and y for the mid-section have been decided upon, the areas for values of h from O to H can be determined for the case where d.tg/dh is constant by the following procedure.

From the values of Cp, kg, Vg, and u, associated with the temperature at the subject section, the value of y necessary to hold d.tg/dh constant can be calculated, whence the gas velocity at that section, and the area of the section, are established. Normally it is sufficient to calculate A for the top, bottom, and quarter points. In such case y might, for example, vary from 0.10 to 0.13 which variation is ordinarily acceptable.

shot discharge apertures 36. The holes 35 and the holes 36 extend the full length of each bar encompassed within the chamber.

Adjacent the discharge end of the conveyor 14, on the outside of the chamber, is the shot reservoir 37. The hollow spaces 34 of the

members

30, 31, communicate with said reservoir at their upper ends, and the hollow spaces 33 of each

member

30, 31, are closed off at their upper ends adjacent the interior wall of the chamber.

The arrangement at the lower end is shown in FIG- URE 4. The lower hollow space 34 of each transverse member is closed adjacent the inner wall of the chamber as shown at 34a. The upper hollow portions 33 of each transverse hollow member communicate with an air supply fitting 37A by means of the apertures 38. Supply of air is controlled by the valve 39, the pipe 40 leading to an air supply (not shown). The action of the distribution head 25 is as follows:

As previously explained, shot from the conveyor 14 discharges to the reservoir 37, FIGURE 2, and flows by gravity to the lower hollow sections of the

members

30, 31. Reliance is not placed upon gravity discharge through the shot discharge apertures 36 FIGURE 5, air under pressure enters the upper portions 33, passes through the holes 35, and so forces the shot outwards to discharge through the apertures 36. The valve 39 FIGURE 13 serves to adjust the air so that proper discharge of the shot is attained. I have discovered that the discharge of shot from the head (W) is independent of the hydraulic head of the shot (considering it as a fluid) but substantially is a function only of the air pressure. Thus the flow of shot to make W=Cp/Cs may be effected simply by the valve 39.

The distribution head 26 FIGURE 1 is similar to the head 25. The gas entering the transfer chamber may be at several atmospheres, as for example when my heat exchange unit is used with a gas turbine, then conventional airlocks are provided in conjunction with the transfer chamber shot introducing means.

My invention is not intended to be limited to the embodiment described and illustrated, but is intended to cover such modifications and alternate constructions as are within the spirit and scope of the invention as above described and illustratde, and as set forth in the claims hereto.

Iclaim:

1. In a heat exchange unit of the class having: a vertical extraction chamber adapted for the upwards passage therethrough of gas from which heat is to be extracted, a vertical transfer chamber adapted for the up wards passage therethrough of a gas to which heat is to be added, a body of shot, means to introduce the shot at the top of the extraction chamber constructed and arranged so that the shot shall fall by gravity against the upwards passage of the gas, whereby heat is extracted from the gas to heat the shot, means to convey the heated shot from the bottom of the extraction chamber to the top of the transfer chamber, means to introduce the body of shot at the top of the transfer chamber constructed and arranged so that the heated shot shall fall by gravity against the upward passage of the gas whereby heat is extracted from the shot to heat the gas; in combination with the foregoing.

(a) a body of shot composed of metallic particles the arithmetic mean diameter of which shall be within the range of about 0.01 inch to 0.02 inch, the shot being selected so that a particular body within the range aforesaid shall be so nearly uniform that the range of terminal velocities of the largest and smallest particles thereof shall be narrow,

(b) means to control the rate of flow of the gases with respect to the rate of fall of the aforesaid body of shot.

2. A combination as described in claim 1 wherein the means to control the rate of flow of the gases with respect to the rate of fall of the body includes; an extraction chamber wherein the cross sectional area decreases upwards, a transfer chamber wherein the cross sectional area decreases downwards, constructed and arranged so that the ratio of the gas velocity to the terminal velocity of the smallest particles of the body of shot is sensibly constant at any cross section, and an up wards flow of gas to retard the rate of fall of the body.

3. A combination as described in claim 2, wherein the narrow range of terminal velocities aforesaid is restricted to have a particle size index, S, less than about 1.2.

4. A combination as described in claim 3, and means to introduce the body of shot to the chambers at a weight rate such that the weight rate times the specific heat of the shot is substantially equal to the weight rate of flow of the gas times the specific heat of the gas.

5. A combination as described in claim 3, and an upward flow of gas at a velocity about 5% greater than the terminal velocity of the smallest particles of aforesaid body of shot.

6. A combination as described in claim 5 further characterized by shot introduction means including a plurality of hollow transverse bars each having; an upper end and a sidewall, a longitudinal partition defining with the sidewall an upper and a lower compartment, means to introduce shot at the upper end of the upper compartment, the partition being perforated, the sidewall portion defining the lower chamber being provided with apertures, each bar sloping downwards from the upper end, the foregoing constructed and arranged so that when 'shot is introduced as aforesaid it passes through the several transverse bars and is introduced to the tops of the chambers, and air pressure means to regulate the rate of introduction to and discharge from the hollow transverse bars.

7. A combination as described in claim 2, wherein the individual particles of the metallic body of shot are of material providing high resistance to abrasion.

8. A combination as described in claim 7, wherein the material is nickel chrome steel.

9. A combination as described in claim 5, wherein the individual particles of the metallic body of shot are of material providing high resistance to abrasion.

10. A combination as described in claim 9, wherein the material is nickel chrome steel.

References Cited by the Examiner UNITED STATES PATENTS 2,656,007 10/53 Arnold et a] 34-167 2,813,352 11/57 Payle et a1. 3410 2,846,422 8/58 Green 165-107 2,866,625 12/58 Sylvest 34-10 2,901,837 9/59 Nierns 34167 2,967,693 1/ 61 Cunningham et al l65-107 CHARLES SUKALO, Primary Examiner.

ALDEN D. STEWART, Examiner.

Claims

1. IN A HEAT EXCHANGE UNIT OF THE CLASS HAVING: A VERTICAL EXTRACTION CHAMBER ADAPTED FOR THE UPWARDS PASSAGE THERETHROUGH OF GAS FROM WHICH HEAT IS TO BE EXTRACTED, A VERTICAL TRANSFER CHAMBER ADAPTED FOR THE UPWARDS PASSAGE THERETHROUGH OF A GAS TO WHICH HEAT IS TO BE ADDED, A BODY OF SHOT, MEANS TO INTRODUCE THE SHOT AT THE TOP OF THE EXTRACTION CHAMBER CONSTRUCTED AND ARRANGED SO THAT THE SHOT SHALL FALL BY GRAVITY AGAINST THE UPWARDS PASSAGE OF THE GAS, WHEREBY HEAT IS EXTRACTED FROM THE GAS TO HEAT THE SHOT, MEANS TO CONVEY THE HEATED SHOT FROM THE BOTTOM OF THE EXTRACTION CHAMBER TO THE TOP OF THE TRANSFER CHAMBER, MEANS TO INTRODUCE THE BODY OF SHOT AT THE TOP OF THE TRANSFER CHAMBER CONSTRUCTED AND ARRANGED SO THAT THE HEATED SHOT SHALL FALL BY