(19)
(11) EP 0 295 967 A2

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
21.12.1988 Bulletin 1988/51

(21) Application number: 88305611.1

(22) Date of filing: 20.06.1988
(51) International Patent Classification (IPC)4F24H 1/20, F24H 9/12
(84) Designated Contracting States:
BE DE FR IT NL

(30) Priority: 19.06.1987 GB 8714419

(71) Applicant: Finney, Geoffrey Lund
Dunchurch Near Rugby Warwickshire (GB)

(72) Inventor:
  • Finney, Geoffrey Lund
    Dunchurch Near Rugby Warwickshire (GB)

(74) Representative: Dearing-Lambert, Peter Richard 
DEARING LAMBERT & CO. P.O. Box 8 109 High Street
Ibstock Leicestershire LE6 1LJ
Ibstock Leicestershire LE6 1LJ (GB)


(56) References cited: : 
   
       


    (54) Indirect liquid heating system


    (57) An indirect liquid heating system comprises a water tank (20) having an inlet (5) and outlet (7). A fuel gas burner (1) below the tank discharges products of combustion through heat exchanger tubes (2) to a smoke box (10) above the tank, from whence they are vented from a flue( 8).
    According to the invention the part (3) of the tank bottom (21) immediately above the burner (1) is conical or pyramidal, its tip or apex (24) projecting into the orifice of the inlet (5) so as to restrict the same and cause local increase in the speed and pressure of incoming liquid. In the case of raw water this will inhibit scale formation. Scale which does form on the cone or pyramid (3) is shed by differential contraction and expansion and falls down the sloping surface(s) of the cone or pyramid (3) to collect at the bottom (21) of the tank at a position laterally offset from the burner (1), thus avoiding overheating of the tank bottom and inefficiency due to scale accumulation.




    Description


    [0001] This invention relates to an indirect liquid heating system and particularly, although not exclusively, to such a system used for the heating of raw water.

    [0002] The indirect heating of raw water, for example by a gas burner, is effected by locating the heat source in a combustion chamber in or under the tank or reservoir into which cold water is introduced and from which heated water is withdrawn. To optimise heat utilisation the products of combustion of the heat source are preferably taken through the water in the tank or reservoir, through one or more vertical tubes which extend from a generally flat area of the bottom of the tank or reservoir to a smoke box above it, and from thence to a flue or chimney. Turbulators may be included in the tube or tubes to break up laminar flow of the combustion gases and enhance heat transfer to the ambient water.

    [0003] One of the major problems affecting this type of equipment, especially in areas where the water supply is hard, is the formation of scale, particularly lime scale, on the wetted sides of the heat exchanger. On the surface of a tube itself scale formation is not a serious problem as expansion and contraction of the metal, especially on start-up and close-down, tends to break the scale off. However the broken scale falls to and collects on the bottom of the tank or reservoir, usually where it is directly subjected to the heat of the burner. This inhibits heat transfer to the water in the tank or reservoir and causes excessive heating of the bottom. The system becomes progressively less efficient and eventually the bottom of the tank or reservoir may fail through over heating.

    [0004] Various proposals have been made to overcome this problem. In one of them a secondary, horizontal plate or "false bottom" is located in the tank or reservoir above its bottom to catch the falling scale particles. In another water is introduced through one or more approximately tangential jets immediately above the bottom of the tank or reservoir so as to agitate theprecipitated scale particles and, as far as possible, prevent them from settling and solidifying.

    [0005] A principal object of the present invention is to provide an improved solution to the problem of the deposition of scale, or like precipitate, on the part of a heat exchanger directly subjected to the heat e.g. of a fuel gas burner.

    [0006] In accordance with the invention there is provided an indirect liquid heating system comprising a tank or reservoir having liquid inlet and outlet means and heating means isolated by a combustion chamber from the interior of the tank or reservoir, wherein an upper region of the combustion chamber vertically above the heating means slopes upwardly toward the liquid inlet, the arrangement being such that solids such as scale precipitated from the liquid and shed from said sloping region will fall to a position laterally offset with respect to the heating means, and wherein said inlet means extends downwardly within the tank or reservoir to open in proximity with said sloping region such that the inlet is restricted locally to increase the speed and pressure of liquid entering the tank or reservoir.

    [0007] A system in accordance with the invention thus combines two features which respectively inhibit the formation of scale, by locally accelerating the incoming liquid and increasing its pressure, and ensure that scale or other precipitate which is formed will not accumulate directly above the heating means.

    [0008] In a preferred construction the said sloping region forms part of the bottom of the tank or reservoir.

    [0009] The said sloping region is preferably constituted by a central region of the bottom of the tank or reservoir, which central region is downwardly concave and reduces in cross-sectional area upwardly to a top aligned with the orifice of the liquid inlet, whereby inflowing liquid is distributed substantially over the whole surface of said central region presented inwardly of the tank or reservoir.

    [0010] This central region may be dome-shaped, generally conical or pyramidal.

    [0011] The mean angular relation to the horizontal of any side of said central region is preferably an acute angle in excess of 50 degrees. If the central region is pyramidal, the apex of the pyramid may divide the orifice into a plurality of separate, approximately D-shaped openings.

    [0012] The heating means may be a gas burner and there may extend upwardly from said sloping region within the tank or reservoir at least one outlet for combustion gases which extends to a smoke box above the tank or reservoir. An annular array of circumferentially spaced combustion gas outlet tubes may extend upwardly from said central region from a horizontal plane intermediate its top and bottom.

    [0013] The flow of combustion gases through each outlet tube therefor may be obstructed by formations on or in the tubes so as to promote heat transfer to the surrounding water.

    [0014] A preferred embodiment of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which:

    Figure 1 is a side sectional elevation of a liquid heating system in accordance with the invention taken generally on the line I-I of Figure 2, and

    Figure 2 is a cross sectional view taken on the line II-II of Figure 1.



    [0015] The water heating system illustrated comprises a tank or reservoir 20 having a peripheral wall 9 closed at its bottom end by a bottom plate 21 and at its top of a top plate 22. The tank has a hot water outlet 7 and cold water is introduced through a generally central inlet pipe 5 which extends downwardly into the tank 20 from an inlet connection 6 on one side of a smoke box 10 above the tank.

    [0016] Beneath the bottom plate 21 of the tank is a combustion chamber 23 in which a burner 1 for a mixture of fuel gas and air is located. Gas burners are well known per se so that the burner 1 will not be particularly described except to say that it is preferably of the naturally-aspirated type, i.e. that air to be mixed with the burning fuel gas is not supplied under pressure. Flame from the burner 1 plays on the bottom of the tank 20 and the products of combustion are taken through an array of heat exchanger tubes 2 to the smoke box 10 above the tank, and thence vented through a flue 8. The tubes 2 transfer heat to the ambient water and to promote this the flow of combustion gases through each tube 2 is preferably interrupted or obstructed either by the provision in each tube 2 of a turbulator (not shown) or by giving each tube 2 a dimpled configuration through the provision of alternately inwardly and outwardly projecting areas 4.

    [0017] As so far described the system is conventional. In accordance with the invention, however, a central region 3 of top plate 21 of the combustion chamber 23, also constituting the bottom plate of the tank 20, is not flat but generally conical. This downwardly concave formation 3 is immediately above the burner 1 and tapers to an apex or point 24 which extends into the orifice of the inlet pipe 5 with a small clearance. The coaxial alignment of the cone 3 and the pipe 5 ensures that the incoming water flow is distributed generally uniformly over the wet side of the cone, while the projection of the tip 24 into the orifice of the pipe 5 accelerates the incoming water flow as well as increasing its pressure which inhibits local scale deposition. As will be apparant, the bottom ends of the array of heat exchanger tubes 2 extend from the cone 3 in a horizontal plane intermediate its tip 24 and its bottom integral with the flat part of the plate 21.

    [0018] The angle A formed by the side of the cone to the horizontal is an acute angle in excess of 50 degrees. If the cone is replaced by a pryramid, then each side of the pyramid forms such an angle with the horizontal.

    [0019] With heat variation, especially on start-up and shut down, the cone 3 along with the tubes 2 is subject to differential expansion and contraction which has the effect of shedding scale which has adhered. The scale particles sink through water in the tank 20, and on striking the sloping surface of the cone 3 are directed by it to the annular area represented by the flat part of the plate 21 beneath the base of the cone 3. This area, however, is not immediately above the burner 1 but laterally offset from it. Consequently, during the continued use of the system there is no scale accumulation immediately above the burner 1 which will impair the efficiency of the system or cause overheating of the bottom of the tank 20.

    [0020] In an alternative construction (not shown) the formation 3 is pyramidal rather than cone-shaped so that its apex, projecting into the orifice of the inlet pipe 5, forms an approximately D-shaped, restricted opening above each side of the pyramid.


    Claims

    1. An indirect liquid heating system comprising a tank or reservoir (20) having liquid inlet (5) and outlet (7) means and heating means (1) isolated by a combustion chamber (23) from the interior of the tank or reservoir (20), an upper region (3) of the combustion chamber (23) vertically above the heating means (1) sloping upwardly toward the liquid inlet (5), the arrangement being such that solids such as scale precipitated from the liquid and shed from said sloping region (3) will fall to a position laterally offset with respect to the heating means (1), characterised in that said liquid inlet means (5) extends downwardly within the tank or reservoir (20) to open in proximity with said sloping region (3) such that the inlet (5) is restricted locally to increase the speed and pressure of liquid entering the tank or reservoir (20).
     
    2. A system as claimed in claim 1, characterised in that said sloping region (3) forms part of the bottom (21) of the tank or reservoir (20).
     
    3. A system as claimed in either preceding claim, characterised in that said sloping region (3) is constituted by a central region of the bottom (21) of the tank or reservoir (20), which central region (3) is downwardly concave and reduces in cross-sectional area upwardly to a top aligned with the orifice of the liquid inlet (5), whereby inflowing liquid is distributed substantially over the whole surface of said central region (3) presented inwardly of the tank or reservoir (20).
     
    4. A system as claimed in claim 3, characterised in that said central region (3) is dome-shaped.
     
    5. A system as claimed in claim 3, characterised in that said central region (3) is generally conical.
     
    6. A system as claimed in claim 3, characterised in that said central region (3) is pyramidal.
     
    7. A system as claimed in any one of claims 3 - 6, characterised in that the mean angular relation to the horizontal of any side of said central region (3) is an acute angle in excess of 50 degrees.
     
    8. A system as claimed in claim 6, or claim 7 as appendant to claim 6, characterised in that the apex (24) of the pyramid (3) divides the orifice (5) into a plurality of approximately D-shaped openings.
     
    9. A system as claimed in any one of the preceding claims, characterised in that the heating means (1) is a gas burner and there extends upwardly from said sloping region (3) within the tank or reservoir (20) at least one outlet (2) for combustion gases which extends to a smoke box (10) above the tank or reservoir (20).
     
    10. A system as claimed in claim 9 as appendant to any one of claims 3 - 8, characterised in that an annular array of circumferentially spaced combustion gas outlet tubes (2) extends upwardly from said central region (3) form a horizontal plane intermediate its top and bottom.
     




    Drawing