US2893697A - Heat exchangers - Google Patents

Description

July 7, 1959 Fgled Dec, 25, 1952 ,IJ jyjj w. HRYNlszAK 2,893,697

HEAT EXCHANGERS 2 Sheets-Sheet 1 /fyZ WHLDEMHR HRy/v/SZAK By July 7, 1959 Filed Dec. 25, 1952 w. HRYNlszAK l 2,893,697

HEAT EXCHANGERS 2 Sheets-Sheet 2 Wnwemfm -HRf//v/SZAK l #ir /vfys l ,i li

HEAT EXCHAN GERS Application December 23, 1952, Serial No. 327,628

Claims priority, application Great Britain June v19, 1952 9 Claims. (Cl. 257-.-1)

This invention ,relates to heat exchangers and more .specifically to recuperative heat exchangers wherein the vliow ,paths are of vsmall hydraulic diameter and particular care has to be taken that they do not `become clogged. v'The object of the present invention is to provide Icleaning means particularly suitable for cleaning such heat exchangers.

There are two known ways of preventing clogging ot a matrix, namely:

(1) By preventing the dust'from reaching the matrix;

(2') By cleaning the matrix to remove dust and other particles adhering thereto.

It is Anever quite possible to prevent all dust and the like particles from reaching the matrix.

Where heat exchangers as referred to above are used in gas turbine plant clogging is liable to occur on both the air and the gas sides of each element.

If the air is properly tiltered at the compressor inlet the main .danger of fouling will be on the gas side. This being the low pressure side of the preheater it is sensitive to pressure losses at all loads.

'This fact limits the use of method 1, because extracting dust from the gas increases the pressure loss.

As for method 2. when applied to a gas turbine plant, much depends on `the kind of fuel used and the form of dust obtained.

Method No. 2 may be suicient for certain, for example, high grade, fuels, which give only small particles of dust and few of them, but in other cases to apply this method to deal with the full amount of dirt or dust and other particles would mean that comparatively large equipment would be required or undue strain shown on the cleaning apparatus.

Referring to the accompanying drawings:

Figure 1 is a plan of a cell of a heat exchange element the cell being in plan and of circular form;

Figure 2 is a section on the line A-A of Figure 1 looking in the direction of the arrows;

Figure 3 shows in plan two cells arranged in a heat exchanger;

Figure 4 is a section on the line B--B of Figure 3 looking in the direction of the arrows;

Figure 5 illustrates a diagrammatic arrangement of heat exchanger and cleaning device according to one form of the present invention.

Figures 6 and 7 are detailed diagrammatic views of part of Figure 5 to a larger scale for the purpose more fully of illustrating the corrugated sheet arrangements and divisions or slits or spaces associated therewith, Figure. 6 showing corrugated sheets divided into two parts leaving a space with parallel sides and Figure 7 a space converging on each side towards the centre of the corrugated strip.

In carrying the invention into effect in one form by way of example but irst describing a heat exchanger of the kind to which the invention particularly applies, a heat exchanger cell as shown in Figures 1 to 4 comprises United States Patent O 2,893,697 Patented July 7, 1959 ICC a flat base sheet in the vform of a circular metal disc 1 .in which are `stamped two circular `locating holes 2.

Side walls 3 of the form shown in Figures l and 2 are aixed to disc 1 by brazing or similar means locating holes 4 in these sidewalls coinciding with the locating holes 2 of the metal disc 1.

In the space enclosed by the side wall 3 and metal disc 1 is fixed the matrix integer which consists of corrugated strip 5 as shown in Figure 2. Cut in this strip are slits 6 which allow for expansion of the integer at high temperature and they also enable the temperature gradient per strip to be small. A cell is now complete and from it the heat exchange element is assembled or built up. A disc 7 of the next cell identical with the disc 1 vis atlixed to the side walls and matrix by brazing or similar means. The flow path is contained between the discs of adjacent cells, side walls and the corrugated strip.

In Figure 3 the gas inlet is at 7a, the gas outlet at 7b, the air inlet at 7c and the air outlet at 7d.

In Figure 4 the gas passages are identied by the reference 7e and the air passages by 7f.

Further side walls 8 identical with side walls 3 are inverted and then attached to disc 7 as shown, in a similar manner as before. In this way the inlet and outlet channels for the gas flowing through this cell are displaced in an angular direction from the inlet and outlet of the iirst cell.

Another matrix of corrugated strip 9 identical with matrix 5 of cell 1 is fixed by brazing in the space enclosed by side walls 8 and disc 7, this completing a second cell. Disc 10 is then fitted over the matrix to commence a third cell.

The corrugated strip S divides the air stream into two parts 7f and the corrugated strip 9 divides the gas stream into two parts 7e; the disc 7 divides the air stream from the gas stream.

The discs, side Walls and corrugated strip are punched out to the appropriate size and assembled until a complete element is built up. It is then usual to assemble a number of such elements in a casing to form a heat exchanger.

Two such elements indicated by the reference number 11 are assembled in openings 12 of a casting 13 as shown in Figure 5, forming part of or used in conjunction with a gas turbine plant.

In that gure compressed air enters the heat exchanger through opening 13a, passes through alternate cells of each heat exchange element, that is to say through cells equivalent to those denoted by 7f in Fig. 4, and leaves in a preheated state through outlets 14 whence it is led to the combustion chamber. Hot exhaust gas from the turbine is conveyed to the heat exchanger by duct 15. On leaving duct 15 it passes through a lter 16 which removes any large particles contained in the gas and then enters the heat exchange elements by openings 17 passes through alternate cells equivalent to cells 7e in Fig. 4, where it gives up its heat to the corrugated strip and adjacent metal discs and then leaves to exhaust by exit openings 18.

For the purpose of eiecting cleaning, the corrugated sheets are divided into two parts leaving a space 19 in between. This can be explained with reference to Figure 6. The spaces or passages 19 are formed by virtue of the fact that instead of being made as one piece as shown in the drawing of our British equivalent application referred to above, the corrugated sheet insert is made in two separate pieces which, when inserted in the space formed by the side wall, are of such a size that a gap or space exists between them and this gap is marked with the reference number 19. In the case illustrated in Figure 6 the gap is parallel sided and the two gaps of the corrugated sheet are marked 19a and 19b with expansion slits 19e and 19d, respectively.

Referring now to Figure 7 the corrugated sheets may be in two halves, are so shaped as toleave a converging slit between them. The corrugated sheets are here marked 19e and 191, the openings which converge on each side toward the centre of the corrugated strip being marked 19g. Figure 7 also has arrows 19h applied illustrating the direction of gas ow between the two halves 19e and 19j. The locating holes 4 of the side walls are made to accommodate tubes 20 (Figure 4) to provide passages for the cleaning air. Cut in the side walls are slits 21 which put the tubes into communication with the openings or space 19 in the corrugated strip. Slits 21a are also cut in the tubes 20 to put the slits 21 into communication with passages or spaces 19 or 19g, the slits 21 being cut in the side walls as previously stated. For a gas turbine it is suicient generally for these slits to be cut only in side walls on the hot gas side but depending on the circumstances all the side walls may have slits cut in them to allow cleaning of each cell as opposed to the cells on the hot gas side only.

Cleaning air is forced through tubes 20 through slits 21 and through openings V19 where it spreads and flows in opposite directions through each half of the corrugated strip. In this way dust or the like accumulating in the flow passages of the cells is removed together with the dust which accumulates at the entrances and exists respectively.

Por this purpose compressed air may be tapped from a compressor or, as is preferred, supplied in short sharp blasts by means of a pump 22 (Figure 5).

A valve 23 synchronized to operate in conjunction with the pump is arranged so that one of the two heat exchange elements 11, namely that shown on the right hand side, working on the same hot gas side inlet 17 can be cut olf from the flow of hot gases for the very brief period during which cleaning takes place. The valve is working in a low pressure medium and is not subject to any pressures difference so that a tight seal is not required.

When cleaning is about to take place the valve 23 is moved into the shut position thus preventing the hot gas from entering the element 11, namely that shown on the right hand side of the drawing, through inlet channel 17 The other element, however, is still operating so that cleaning does not interrupt the functioning of the heat exchanger. By closing the inlet in this way the gas collecting at entrance 17 is put into communication with the suction ot pump 22 by `means of suction pipe 24.

Movement of pump plunger 25 forces cleaning air or other iluid through pipe 26 through tubes 20 of element 11 and hence into the channels of the cells of the element. Part of the air carries with it all the dust and other particles in the channels out to exhaust through duct 18.

The other part of the cleaning air leaves the inlet opening 17 now closed by valve 23 and is conducted away to the suction side of the pump through opening 27 connected to suction pipe 24 on the return'stroke of the pump, carrying any dust collected with it.

The pump which is driven by a motor 28 but may be driven hydraulically or by other electrical means for example a solenoid, consists of the piston or plunger 25 and a liner or cylinder 29.

On the upstroke of the plunger air is drawn in through filter Si) and inlet valve 31 whilst at the same time the dust-laden air collected on the suction stroke is forced out to atmosphere through outlet valve 32. During this stroke valves 33 and 34 are closed.

On the downstroke valve 32 is closed and dust-laden air is drawn through valve 33 in connection with suction line 24. At the same time air is forced out through valve 34 into pipe 26 and hence to tubes 20 in the element, the valve 31 being closed.

Thus air is forced through the tubes at regular intervals and hence through the slit in the side walls and through the channel between the two halves of the corrugated strip matrix and thence through the oW paths of the matrix. In this way the dust accumulating in the ow passages of the gas side is removed with dust or other particles adhering to the inlet and outlet of the cell.

Cleaning of the element on the left hand side is elected when the valve 23 is switched over to the opposite position, shown dotted. In this position, the supply of cleaning uid to the element on the right hand side would be cut ott, and the iluid supplied by ducts (not shown) but similar to 24 and 26 to the element on the left hand side of the drawing. This switching of the cleaning uid from one element to the other can be effected by any suitable means such as a rotary valve which would allow cleaning iluid to be supplied and withdrawn by the pump from only one element at a time.

The pump intake air can be cleaned to a high degree since only small amounts of cleaning air are needed at one time. The pump delivery valve maybe spring loaded to enable the pressure to be varied. If a by-pass is provided the amount of cleaning air as well as the delivery pressure can be selected to suit the particular conditions and the same applies to the frequency of the air deliveries.

Cleaning of the element may be improved by providing certain adjustments to suit the working Vconditions such as:

(a) Proper location of the slits 19 to obtain maximum possible amount of cleaning for example by placing the slits closer to the inlet 17 of the elements and the matrix, the cleaning air due to decreased path resistance will travel to a greater extent in a direction opposite to that of the gas ow provided that the influence-of the dynamic pressure be allowed for.

(b) Altering the resistance to ow of the corrugated strip by using diierent sizes of corrugations for the strip at the inlet and outlet of the cell. For example, we could make corrugations`19d larger than corrugations 19e to help induce the cleaning fluid to llow more easily toward inlet 17. Y

(c) Avoiding sharp edges and corners in the inlet and outlet ducts 13a and 17, 14 and 18 and the inlet and outlet edges of the corrugated strip so as to give the dust as much chance as possible to escape with the cleaning air.

In the case of round cells, the corners o'f the corrugated strips may be cut off so as to allow the dust to escape freely where these edges touch the side walls. The round cells have a rather more pronounced deflection because of the difference in the extent of the inlet and outlet openings compared withthe matrix opening.

When the matrix is cleaned by blowing air through the channels of its hot gas side 'as described above, one part of the dust-laden cleaning air passes through the exhaust system to the open. The other part travels in the opposite direction against the flow of the hot gases, so that the dust removed by this portion of the air tends to remain in or near the hot gas side inlet of the cell and continuously adds to the dust content of the hot gas unless the dust is removed by suitable means. Such removal is of importance, as the bulk of the dust will collect at the hot gas side inlet of the element in general, and at the inlet of its matrix in particular.

In heat exchangers of the type described the elements can be arranged in any suitable form preferably so that their hot gas sides can be fed from a common inlet-duct. A filter is preferably arranged in the inlet duct of the hot gas to prevent any -large particles entering the matrices of the cells comprising each heat exchanger element.

The cleaning mechanism is automatic and continuous and has the advantage that in a heat exchanger consisting of a number of elements a very small percentage of the total number of elements are being cleaned for a very short period and the eiiciency of the heat exchanger is not adversely impaired.

The system can apply to heat exchangers of both the counter ow and cross flow'types and canbe used in plants other than the gas turbine. The cleaning uid need not be air but may depend upon the nature of the particles adhering to the ma `trix for any given reason.

The pump may be replaced by using air from the compressor in a gas turbine plant.

What is claimed is:

l. A method of maintaining clean heat exchanger surfaces in a recuperative heat exchanger, havi-ng relatively stationary heat exchange passages and inlet and outlet passages, which comprises filtering a gas to remove at least part of any dust therein, and passing the filtered gas through a heat exchanger matrix, and intermittently introducing air into the said matrix intermediate its inlet and outlet ends and blowing the air through the matrix toward both the inlet and exhaust passages to remove any unfiltered dust and other particles adhering thereto.

2. A method according to claim 1 in which the prevention of the dust from reaching the matrix is elected by filtering the gas at the inlet of the gas side of the heat exchanger.

3. A method according to claim 1 in which the blowing of air through the matrix is effected periodically and automatically whilst the heat exchanger is in operation and in timed relation to a gas turbine, through which gas from the heat exchanger is passed and from which exhaust gas is passed through the heat exchanger.

4. A method according to claim 3 in which only the gas side of the heat exchanger matrix is periodically and automatically cleaned.

5. A method according to claim 1 in which the cleaning air is introduced into a space dividing the ilow paths of the matrix into two parts.

6. A method according to claim 5 in which at least part of the dust-laden cleaning air is drawn off by suction.

7. A method according to claim 6 in which at least one opening of the gas side of the matrix is closed whilst the matrix is being cleaned.

8. A method according to claim l in which the cleaning air is mixed with an additional cleaning iluid.

9. A recuperative heat exchanger having relatively stationary heat exchange passages and inlet and outlet passages, said heat exchanger comprising one or more heat exchange elements, each element consisting of a number of cells arranged in the form of a column or stack, each cell consisting `of a llat base sheet and side walls which deiine a lloW channel, said ow channel being further subdivided into a number of ilow passages by two corrugated strips spaced apart from each other in the direc# tion of flow therethrough, cells containing hot iluid alterntating with cells containing cold iluid, means for ltering the heat exchanging uids prior to their entry into the flow passages and means for introducing a cleaning ilud into the space separating said corrugated strips causing said fluid to ow in opposite directions through each strip towards the inlet and outlet ends of said passages to remove any unfiltered dust or other particles adhering thereto.

References Cited in the le of this patent UNITED STATES PATENTS 1,558,445 Ljungstrom Oct. 20, 1925 1,680,145 Forssblad Aug. 7, 1928 1,858,508 Kignell May 17, 1932 1,903,650 Snow et al Apr. 11, 1933 1,970,127 Colby et al Aug. 14, 1934 2,288,061 Arnold June 30, 1942 2,673,446 De Salardi Mar. 30, 1954 l. FOREIGN PATENTS 462,857 Great Britain Mar. 17, 1937

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