GB2233077A - Fluids heaters such as boilers - Google Patents

Abstract

Means for heating a fluid such as water comprises a burner (4) and at least two heat-exchange units (12 and 11) arranged one after the other in the direction of flow of the combustion fuel. The first heat-exchange unit (12), which is disposed nearest to the burner (4) downstream of the fuel outlet opening and immediately in a flame region, withdraws heat from the flame region, the flow rate of heat thus withdrawn amounting to between 5 and 50% of the total heat flow. This direct withdrawal of heat flow from the flame region improves the combustion process. The position of the heat-exchange unit (12) and/or the quantity of fluid flowing therethrough may be adjustable. The heat-exchange units do not necessarily contain the same fluid, the first (12) for example containing air rather than water. <IMAGE>

Description

Means for heating a fluid The present invention relates to means for

heating a f luid, comprising a burner and at least two heat-exchange units arranged one after the other in the direction or intended direction of f low of the combusted fuel, in which the first heat-exchange unit, which is disposed nearer to the burner than the other, downstream of the fuel outlet opening and immediately in a flame region, withdraws heat from the flame region when the heater is in use and at least when the fuel is burning at a predetermined rate.

S uch a heater is described in EP-A 315 579. In that specification, a cooling pipe is provided in an atmospherically operated water-heater gas burner, in order to cool it. In this case the fuel outlet openings and the f lame region are particularly cooled, and cooling pipe sections extend between spaced-apart groups of fuel outlet openings, so that there is no obstacle to the burner flames but so that the cooling pipes are very near the hot central region of the flames.

It has been shown in practice that this does not improve the combustion process to an extent which is desirable.

A safety device has already been proposed which in an emergency, for example if the temperature exceeds a predetermined threshold or., the flow rate falls below a limiting value in the cooling pipe, switches of f the burner and the fuel supply to prevent damage through overheating.

An aim of the present invention is to withdraw the flow of heat necessary for optimizing the combustion process from the flame region of a water heater via the first heat-exchange unit, preferably in an active and controlled and energy-saving manner, and simultaneously to stabilize the flame and intensify the combustion process so as to reduce the formation of nitrogen oxides and carbon monoxide to a desired level.

Accordingly, the present invention is directed to means f or heating a f luid as set out in the opening paragraph of the present specification in which the flow- rate of heat thus withdrawn amounts to between 5 and 50% of the total f low of heat generated by the burner, so as to improve the combustion process.

Such a construction may result in a very marked reduction in the f lame temperature, which may practically stop the thermal formation of nitrogen oxides. If part of the heat- exchanger is positioned directly in the f laine, that part of the exchanger can be surrounded by the flames so that it acts as a baf f le and stabilizes the f lanes. Furthermore, combustion in the flame zone can continue until complete, since combustion can continue over the elements of that part of the heat-exchanger. This can greatly reduce the production of carbon monoxide, which is normally produced by cooling elements. In addition, the combustion gases are completely burnt.

Advantageously, devices monitor and/or control the operating state of the water heater.

other advantageous features are set out in the subordinate claims and the description of the present specification.

Examples of means for heating a fluid made in accordance with the present invention are illustrated in the accompanying drawings, in which; Figure 1 is a diagrammatic elevational view of such a water heater; Figure 2 is a diagrammatic elevational view of a modified water heater; Figure 2a shows a perspective view of parts of the heater shown in Figure 2; Figure 3 is a diagram of a boiler for a water heater made in accordance with the present invention; Figure 4 is a diagram of parts of the boiler shown in Figure 3, viewing them in the direction of the arrows IV; Figures 3a and 4a are diagrams illustrating respective heat-exchange element arrangements for any one of the illustrated boilers, Figure 4a showing a connection between a heat-exchange element and water compartments of the heating section; Figure 5 is a diagram of a further burner or 4 - boiler for a water heater made in accordance with the present invention; Figure 6 is a diagrammatic elevational view of a further water heater made in accordance with the present 5 invention, provided with a water reservoir; Figures 7 to 19 show respective water-flow circuits for any one of the water heaters; Figures 20a, 20b, 21 and 22 show respective diagrams of means to adjust the spacing between a heat- exchange element and a burner, or the positioning of the heat exdhange elements relative to the burner flames, in any one of the water heaters illustrated in the accompanying drawings; Figures 23a to d show respective diagrams of heat-flow monitoring and/or regulating means for any one of the water heaters illustrated in the accompanying drawings; Figure 24 shows a circuit diagram of direct flame cooling monitored in conjunction with a microprocessor for use in any one of the water heaters illustrated in the accompanying drawings; Figures 25 to 33 show respective diagrams of coolant control or regulation means; and Figures 34a and 34b are respective diagrams illustrating flame contours of burning gas issuing from a curved combustion-gas supply duct, with different respective flow-rates of gas.

A circulating-water heater 1 has a sheet-metal or other casing 2 in which a combustion chamber 3 is disposed. Chamber 3 contains an atmospheric gas burner 4 supplied with natural gas via a gas supply line 6 fitted with a proportional control valve 5. Alternatively the supply can be of liquefied petroleum gas or town gas. The valve 5 is controlled by a servomotor 7 connected by a control line 8 to a regulator 9. A heat- exchanger 10 is disposed above the burner 4 and comprises two elements 11 and 12. The two heat-exchanger elements can be ribbed core heat exchangers with copper tubes and copper ribs or steel tubes and steel ribs or mixtures of both. Aluminium or alloys thereof are also suitable materials. When used in a boiler, the heat-exchange element 11 may comprise cast members or steel sheets, whereas the other heatexchange element 12 may comprise tubes, ribbed required, and may have cooling water flowing through The heat-exchange element or elements can be made aluminium in cast, drawn or moulded form, especially use in a boiler. The combustion chamber 3 has an inlet 13 at the bottom and a waste-gas outlet 14 at top.

The circulating-water heater 1 is for supplying a room-heating system 15 and/or an industrial water reservoir (not shown). A return line 17 comprising a circulating pump 16 leads from the heating installation 15 to the heat-exchange element 11. A flow line 19 if it.

of for air the incorporating a f low temperature sensor 18 extends f rom the heat- exchange element 11 to the heating installation 15. The flow temperature sensor 18 is connected by instrument leads 20 to the regulator 9. The circulating pump 16 is driven by a drive motor 21 connected to receive an electricity supply from regulator 9 via a control line 22. An external temperature sensor 23 is provided and supplies measurements to the regulator 9 via instrument leads 24. A branch point 25 in the return line 17 is provided between the high-pressure side of the circulating pump 16 and the inlet of the return line 17 into the heatexchange element 11, and a branch pipe 26 extends from the return line 17 at the branch point 25 to a connection to the heat-exchange element 12 on the return side. A return temperature sensor 27 is disposed in the branch pipe 26 and is connected by instrument leads 28 to the regulator 9. The flow side of the heat-exchange element 12 is connected by a continuation of pipe 26 to a second branch point 29, which is situated in the flow line 19 between the flow temperature sensor 18 and the outlet of the heat- exchange element 11. A flow temperature sensor 30 and a flowmeter 31 are disposed in the last-mentioned part of the branch pipe and are both connected to the regulator 9 via respective instrument leads 32 and 33.

During operation, a number of flames 34 form at burner 4, which can also be a forced-air burner. The flames 34 are either in the form of individual flames of 1 varying height, or in the f orm of a continuous tongue of f lame. If the burner 4 is constructed as a number of adjacent individual tubes, there are individual flames of varying size, whereas if the burner is for example a ceramic plate, the result is a flame region which cannot be separated into individual flames.

In every case, the tube, tubes or network of tubes of the heat-exchange element 12 is disposed so as to be situated in the region of the flames 34 or in heat- withdrawing contact with a burner plate or the like. Preferabiy the heat- exchange element 12 is disposed so that the pipes extend through the core zones of the flames, so that the individual flames completely surround the tubular elements.

The cross-sections of lines 26 and/or lines 17 and/or 19 through the heatexchange element 11 are dimensioned so that 5 to 50-% of the total heat f low converted by the two heat-exchange elements is withdrawn from the f lame region in the heat-exchange element 12.

Means may be provided for adjusting the heat flow, for example a separate circulating pump and/or an adjustable restrictor can be provided in the branch pipe 26. This will be further described in the text relating to Figures 23a to d. If required, the cross-section of the restrictor can also be regulated. The two temperature sensors 27 and 30 are disposed in conjunction with the flowmeter 31 so as to detect the heat flow withdrawn by 1 8 - the heat-exchange element 12.

Figure 2 shows an embodiment of a gas-heated continuous water heater 40. As in the Figure 1 construction, it has a sheet-metal casing 2 containing a combustion chamber 3. An atmospheric gas burner 4 is disposed in the combustion chamber 3 and is supplied with gas from a gas pipe 6 through a gas valve 5. The gas valve 5 is controlled by a hydroblast switch 7 which is disposed in a tap water line 41 and which acts as a servomotor for the gas valve. The hydroblast switch 7 operates so that the gas valve 5 is opened in proportion to the flow rate of incoming water. As an alternative, the extent of opening of the gas valve can be additionally controlled in dependence upon the tap outflow temperature.

is The incoming water tap line 41 leads first to a height-adjusting device 42, then to the heat exchange element 12 and finally to a second height-adjusting device.43 and a temperature sensor 44, which is constructed as a capillary tube temperature sensor and, via its capillaries and instruments leads 45, is connected to an actuator 46 for varying the vertical height of the adjusting devices 42 and 43. The other heat exchange element 11 is connected to the element 12 by means of a connecting line 47.

In Figure 1 the two heat-exchange elements 11 and 12 are disposed in parallel with respect to the water circuit, whereas in the present water heater they are in 9 - series. The heat-exchange element 12 associated with the flame region is supplied with the cold return flow in the Figure 1 construction, or cold tap water in the Figure 2 construction. A tap line 49 incorporates a tap valve 48 and extends from the heat-exchange element 11. With regard to the positioning and effect of the heat-exchange element 12 on the flames of the gas burner 4, the situation is basically the same as described for the construction in Figure 1. In addition however there is the following effect:

1 The positioning of the heat-exchange element 12 can be varied in dependence upon the temperature of the tap water in the tap line 49. The positioning is in accordance with the dimensioning rule, such that the distance of the heat-exchange element 12 from the burner 4 is increased when the flames become higher, for instance when the burner output increases.

As shown in Figures 20a and b, bimetallic elements 102 are provided and are acted upon by the flames and thus adjust the position of the heat-exchange element 12 depending upon the load. The bimetallic element 102 can be in strip form, which is one of a number of possibilities, or alternatively the bimetallic element can be helical.

As shown in Figure 22, the heat-exchange element 12 can be positioned by an electromagnetic control drive 103, which is supplied with a command variable, for example a signal from a temperature sensor 104.

Alternatively the positioning of the heat exchange element 12 can be controlled in dependence upon the gas flow rate. For this purpose the instrument leads 45 are connected instead to the hydroblast switch 7. Alternatively, the extent of opening of the gas valve 5 may be scanned. In this construction, the heat-exchange element 12 preferably follows an increase in the size of the gas flames by moving away from the burner 4, in order to cool the hottest core region of the flame.

If the apparatus load of the continuous -water heater in Figure 2 is fixed, it is sufficient for the distance between the heat-exchange element 12 and the burner 4 to be adjusted once to an optimum value and left at this value.

An example of how this may be ef fected is shown in Figure 2a. The heat-exchange element 12 is vertically adjustably secured to the burner 4 by setscrews 101. In this manner the optimum height can be obtained manually.

The heat-exchange element 12 is secured as follows:

Firstly the heat-exchange element 12 can be secured both in relation to the combustion chamber and to the burner 4 and finally to the heat-exchange element 11, the combustion chamber being defined by the casing 2.

This is shown in the constructions in Figures 3a and 4a.

It is thereby possible to give the heat-exchange element 12 a particularly secure and rigid attachment, so that it can serve as a mounting part or support for the burner 4. As before, the distance between the burner and the heatexchange element 12 is preferably adjustable, or variably controllable if required.

When the distance between the heat exchange element 12 and the burner 4 is variably controllable, the drive means to effect the relative movement can be controlled in dependance upon signals issued by bimetallic sensors., spacing detectors, capillary-tube temperature sensors, detectors or expansible-material elements.

A preferred construction enabling the position of the element 12 to be varied in dependance upon gas flow rate is shown in Figure 21. In this case the lower heat- exchange part elliptical or the elements def ined, and relative to comprises a pair of elements 12 has an elongate cross-section. The spacing between 12 and the burner 4 is preferably fixedly the elements 12 are adjustable in position the flames 34 by being pivoted around respective axes 105. The heat-exchange elements can be pivoted for example by bimetallic elements 102, or by setscrews. Alternatively, components filled with expansible material are provided which react to temperature changes by changing their length and thus pivot the heat- exchange elements 12 into the required position, via pistons or linkages.

In another construction, the gas pressure, the water flow rate or the outflow temperature can instead or in addition be used as a command variable for adjusting the spacing. Pneumatic adjustment using the gas pressure regulated for the burner is another possibility. The tap water pressure or the pump pressure could also be used for hydraulic adjustment of the spacing.

In the construction shown in Figures 3 and 4, a cast-iron boiler 50 supplies a heating installation and is equipped with a cooling system. The cast-iron boiler 50 shown in Figure 3 has a casing 51, two heat-exchange elements 11 and 12, a burner 4 underneath them, an air inlet 13 and a waste-gas outlet 14. The heat-exchanger 10, comprising the elements 11 and 124r is connected to a return line 17 and a flow line 19. The special feature of this heater is that the heat-exchange element 12 has a comb-like construction, so that individual heat-conducting tubes 52 extend like tines from a casing 53 of a water compartment 54 into a flame space 55 above the burner 4. The heat-conducting tubes 52 can but need not be filled with a coolant, they may for example be solid metal rods, or they may be "heat-pipes". The heat-conducting pipes 52 can be made of ceramics, for example special ceramics with high thermal conductivity. Preferably the ends of the pipes 52 are embedded in the water compartment 54. This construction is particularly suitable for water heaters in which water is circulated without auxiliary mechanical energy, that is without circulating pumps. it is essential to withdraw a heat f low f rom the f lame region equal to 5 to 50% of the total heat absorbed by the heat exchanger 10, or generated by the burner. The heat is supplied to the water in the compartment 54. From there, the heat travels towards the heat-exchange element 11 or to the region of the water flowing through the lines 17 and 19, which can extend through the water compartment 54. The heat-conducting tubes 52 may alternatively be in the form of a screen or network, and may have either a hollow or solid cross-section, or may be in the form of a net, mesh or screen. It will be appreciated that heat conducting members such as fluid-heat dissipating members or heating tubes, may be used in any of the constructions shown in Figures 1 to 6. In general, components disclosed in one Figure for positioning, maintaining flow rate, monitoring, achieving a particular design, vertically adjusting and controlling, are equally possible in constructions illustrated in the other Figures. 20 In order to withdraw a constant heat flow, the heatconducting tubes 52 are provided with a temperature sensor, for example a thermo-element, temperaturedependent resistor or expansion sensor. More particularly the thermal expansion of the heat-conducting tubes themselves can be measured and, if the value falls below or exceeds a set limit, the positioning of the heatexchange element 12, or the gas or fuel f low rate can be changed accordingly. The same criterion could also be used for shut-down in an emergency.

Figure 5 shows another construction of the heatexchange element 12 for a continuous water heater or a boiler. The heat-exchange element 12 comprises an inlet pipe 60 and an outlet pipe 61, both connected to a return collector 62 and a flow collector 63. A number of first pipe portions 64 disposed in parallel, from the point of view of the water-flow circuit, and having relatively large cross-sections are disposed between the two collectors, and a second form of pipe portion 65 having a smaller cross-section than the first form are associated with the hottest region of the two burners 4 shown. if there are a number of burners 4 it may also be sufficient to allocate a narrow pipe portion 65 per burner. The effect is as follows:

The flow rate through the pipe portion or portions 65 having the narrowest cross-section is monitored, for example by sensing the pressure difference, or by using a separate flowmeter or by measuring the temperature increase. If the flow of coolant through this narrowest portion of pipe 65 is insufficient, then the burner power is reduced or the burner is switched off entirely, as the burner flame region is no longer sufficiently cooled. This is also a method of detecting incipient clogging through lime encrustation, to be counteracted by suitable servicing. In the case of - parallel connection, the flow rate of one or more tubular portions can be monitored by monitoring the f low rate in one or more tubular portions. If the cooling pipes of the heat-exchange element 12 are connected in series, from the point of view of the water-flow circuitry, it is possible or advantageous to monitor the total f low at one place. As before, the flow can be monitored by monitoring a pressure difference, monitoring a temperature increase or monitoring the f low rate. Measurement of expansion in length, already mentioned in one construction, can be used to actuate a microswitch. If the pressure is hydraulically monitored, and if the monitored pressure differences are relatively small, it may be advantageous to use a diaphragm switch to dissipate the differential pressure. If the f low rate is detected by monitoring a temperature difference, the temperature sensors should advantageously be temperature-dependent resistors with NTC or n-type, or PTC or p-type characteristics and should be incorporated in an electronic circuit.

Irrespective of whether the heater is continuous or circulating, a boiler or a reservoir, it is necessary to decide where the heat flow withdrawn by the heat exchage element is to be delivered.

As already described, the heat flow withdrawn by the heat-exchange element 12 from the flame region can be delivered to the water, which has to be heated in any case. Alternatively the tubes or rods of the heat- 1 exchange element 12 can be connected f or heating purposes to the casing 2, so that the heat is delivered to the combustion-chamber j acket. From there. the heat can be transferred via the other heat-exchange element 11 to the water. Another possibility would be to heat the burner 4 instead of the heat-exchange element 12.

A further possibility is to have another heat transfer medium, for example room air, flowing through the heat-exchange element 12 as well as water to be heated.

In a construction in which a water reservoir is provided, for example, the heat-exchange element 11 'may be used to heat the reservoir water, whereas the heatexchange element 12 could be used to heat the air of a room. In addition, the gas or air supplied to the burner could be preheated via the heat-exchange element 12. A further possibility would be for some or all the waste gas at the outlet 14 to be conveyed through the heat-exchange element 12 in order to increase the temperature of the waste gas and prevent sooting of the chimney. Another possibility would be to mix air with the flow of the waste gas at the outlet 14, after preheating the air through the heat-exchange element 12.

Figure 6 shows another construction, having a reservoir water heater 70 with a cylindrical casing 71 comprising a jacket 72, a cover 73 and a base 74. A flame tube 75 extends through the interior of the reservoir water heater and extends upwardly from a combustion - 17 chamber 76 surrounded on nearly all sides by the reservoir water, and leads via a draught diverter 77 to the wastegas outlet 14. A pipe 6 leading to an atmospheric gas burner 4 is disposed in the air inlet 13. As before, the heat-exchange element 12 is in a flame zone of the burner 4, and the flame tube 75 is equivalent to the heatexchange element 11. The heat-exchange element 12 is connected by pipes 78 and 79 in a natural convection circuit to an air heater 80, and room'air can enter at the bottom and be heated and delivered at 81 to an installation room. If the natural circulation is insufficient, a pump can be inserted in one of the lines 78 or 79. This construction operates without flow monitoring, as regards the heat-exchange element 12. The air heating element 80 can be a component of the water reservoir 70 or of a continuous water-supply heater, similar to that illustrated in Figure 2. For this purpose, for example, the jacket, rear wall or other components of the device could be used as a heat-exchange unit. The air heating element could also be incorporated in a closed- circuit water-circulating heater or boiler.

If for example an oil-fired forced-air burner is provided f or a boiler, the oil can be preheated by the heat-exchange element 12 before being supplied to the forced-air burner.

Alternatively a liquid other than the fuel-oil or the water f or heating could be conveyed through the heat-exchange element 12. The liquid could for example be coolant used in a heat pump circuit. Another possibility, therefore, would be to design the heat-exchange element 12 as the evaporator of a heat pump.

In the case of a closed-circuit water-circulating heater or boiler, the heating circuits of the two heat exchange elements 11 and 12 could be separated and connected to separate loads. Different heat transfer media could also be used for this purpose. Another general possibility, irrespective of the application, would be to connect the heat-exchange element 12 in a separate heat-exchange circuit and heat the water via an intermediate heat-exchanger, which could also use a heat transfer medium other than water. To this end, in the construction shown in Figure 1, the pipes 26 from the connecting points 25 and 29 would have to be separated and connected to a separate heat- exchanger exchanging heat with the flow of service water. Another possibility is to boil the cooling medium circulating in the heat-exchange element 12 or to use a vapour as the cooling medium.

To assist the natural circulation of the cooling medium, the tubes of the heat-exchange element 12 can be on a slope.

Figures 7 to 19 show various possible water-flow circuits, with different connections between the two heat-exchange elements 11 and 12. The circuits in Figures 7 to 11 relate either to a continuous flow heater, such as the one illustrated in Figure 2, or a boiler with natural circulation, such as one illustrated in Figures 3 to 5. An important feature of this group of constructions is that no special drive element is disposed in the path of 5 the water.

In the construction in Figure 7 a restrictor 90 is provided on the return side in line 17 or on the cooling-water inlet side, and branch points are provided upstream and downstream of the restrictor at 91 and 92 and are connected by lines to the heat-exchange element 12.

In this manner, a varying partial flow of water can be branched through the heat-exchange element 12 by varying the restrictor 90. The partial flow can be flow-monitored or temperature-monitored as already described.

Figure 8 shows a modification of Figure 7, in which the restrictor 90 and the branch points 91, 92 are disposed in the flow line 19 and in the tap-water line.

This circuit avoids condensation or condensate formation on the heatexchange element 12.

The circuit in Figure 9 is substantially that used in the Figure 1 construction, but for a continuous water-supply heater or a boiler-operated gravity heating system. The main feature is that the two heat-exchange elements 11 and 12 are disposed in pipes arranged in parallel from the point of view of the water-flow circuit. Note that line 6 can be a gas pipe only, or alternatively can convey gas and primary air. The same applies to all the illustrated constructions.

In the circuit shown in Figure 10, the heat exchange elements 11 and 12 are arranged in series from the point of view of the water f low, so that the entire flow of service water is guided through both heat-exchange elements.

The circuits shown in Figures 12 to 19 relate to closed-circuit watercirculating heaters or boilers provided with a circulating pump. The circuit shown in Figure 12 corresponds to the circuit shown in Figure 1, but without flow or temperature monitoring.

The circuit shown in Figure 13 comprises a restrictor 90 as before, in series with branch points 91 and 92. In Figure 13, a partial stream of water is branched through the heat-exchange element 12.

In the circuit shown in Figure 14, the restrictor and the branch points are shifted to the f low line 19, whereas in the circuit shown in Figure 13 they are disposed in the return line 17.

In the circuit shown in Figure 15, two waterf low circuits are f ormed. A pressure connection of the circulating pump 16 is moved to a branch point 93, whereas the pump return connection extends from a second branch point 94. The heat-exchange element 12 is connected through lines via the two branch points 93 and 94, and the heat-exchange element 11 is connected parallel thereto via the heating installation 15. The advantage of this 1 1 i circuit is that the entire pressure difference built up by the pump occurs at the heat-exchange element 12, so that a relatively large heat flow can be withdrawn from the flame region.

In the circuit shown in Figure 16, the circulating pump 16 is connected in a f irst water-f low circuit 95 comprising the heat-exchange elements 11 and 12 and connecting lines 95 and 97. The flow line 19 and the returnline 17, which extend from branch points 98 and 99, lead to the heating installation 15. As a result of this feature, the water supplied to the heat-exchange element 12 is brought on the inlet side to an elevated temperature level, thus reducing condensation thereon.

The circuit shown in Figure 17 is similar to that shown in Figure 13 except that here the narrow point 90 and the two branch points 91 and 92 are disposed on the return side of the pump instead of the flow side as in the circuit shown in Figure 13.

In the circuit shown in Figure 18, the two heatexchange elements 11 and 12 are connected in series from the point of view of water f low. They are in a series circuit with the heating installation 15. Cooled water coming from the heating members of the installation 15 first travels through the heat-exchange element 12 in the flame region, and is then heated in a second stage by the heat-exchange element 11.

In the circuit shown in Figure 19 the water-flow - 22 sequence of the heat-exchange elements 11 and 12 is reversed, so that the cooled water returning from the heating system is first heated to a first temperature level in the heat-exchange element 11, before entering the 5 heat-exchange element 12 for cooling the flame region.

A common feature of all the circuits shown in Figures 7 to 19 is that the f low rate through the heatexchange element 12 is not monitored. However, monitoring is possible, as in any one of the constructions shown in Figures 1 to 5.

In the case particularly of continuous-flow heaters where the heatexchange element 12 is continuously supplied with fresh water containing lime, there is a serious risk of incrustation of the tubular components of the heat-exchange element 12. Clogging of the tubular components may also occur in closed-circuit watercirculating heaters or boilers. It is therefore necessary to ensure that the tubular components or heatexchange parts of the heat-exchange element 12 can be taken out, cleaned or replaced without having to drain of f all the water or heat- transfer medium in the circuit. To this end, for example in Figure 1, it is advantageous to dispose shut-off valves in both parts of lines 26. In the construction shown in Figure 2 also, valves can be provided at the vertical adjustments 42, 43 in lines 41 and 47 respectively. In the case of the boiler shown in Figure 5 this is possible and advisable in line 60 or 61 or, in the construction shown in Figure 6, in the neighbourhood of lines 78 and 79 as near as possible to the casing 71. Instead of valvesf self- closing plug-in couplings which automatically close when the connecting 5 lines are pulled apart may be used.

If the flow-rate through the heat-exchange element 12 is controlled, the control may be manual (by adjustment of the cross-section of a restrictor) or hydraulic or thermal or electric.

If required, the continuous hot water supply heater can be hydraulically controlled. In that case the tap-water flow rate is scanned, for example via the hydroblast switch 7, and the flow rate through the heatexchange element 12 is controlled in dependance upon the tap-water flow rate.

In the case of thermal flow control, the flow temperature or the tapwater temperature can be monitored by a sensor and the flow rate through the heat-exchange element 12 can be increased when the flow temperature or tap-water temperature increases. If an electric sensor is used, the adjustment can be electrical, for example by electrically variable actuation of the pump motor 21 in the case of a closed circuit watercirculating heater. The same is possible in the case of a boiler.

Figures 23a to d shown examples of controlling the flow rate of cooling water through the heat-exchange element 12 to obtain the optimum value of flow rate.

- 24 In Figure 23a a temperature sensor 104 sends a signal through control lines 106 to a solenoid valve 107 and thus controls the flow rate of coolant through the heat-exchange element 12 in dependance upon the heating flow temperature.

In Figure 23b the variable supplied to the solenoid valve 107 is the combustion-chamber temperature, measured by sensor 104.

Another arrangement is shown in Figure 23c, where the flame temperature detected by sensor 104 is the command variable-for the solenoid valve 107.

Figure 23d shows another modification. Here the flow rate through the heat-exchange element 12 is controlled not by a solenoid valve but by the speed of a pump 109; as before the pump motor can be supplied with the previously-mentioned control variable. As before, by way of example only, the combustionchamber temperature is measured by the sensor 104.

It will be evident that combinations of parts shown in the various Figures are possible without the need to describe them individually in detail. in all of these constructions, means may be provided which serve the purpose of adjusting the flow rate of cooling water through the heat-exchange element 12 by means of a characteristic command variable and thus divert the heat flow required for optimizing the process.

In the arrangement shown in Figure 24, a - 25 microprocessor 110 can be supplied with signals by temperature sensors 104. The temperatures, f or example, can be measured in the heating f low or heating return and/or in the combustion chamber and/or at the heat- exchange element 12, disposed directly in the flame region. The microprocessor 110 compares some of these temperatures or temperature differences or the time gradients of the temperatures or gradients of the temperature differences with corresponding set values which are previously determined and stored as optimum values in a data store, which can be part of the microprocessor 110. The deviations can be used for adjusting the amount of gas (the heat load) or for adjusting the flow rate through the heat-exchange element 12 for flame cooling, or as a signal for safety monitoring against overheating or overcooling (for example for safety shut-down).

An advantage of this arrangement is that a highspeed control circuit f or guiding the entire combustion process can be built up by processing the temperatures or gradients recorded directly in the flame region.

In Figure 3, a gas nozzle 56 is disposed in the path of the gas upstream, of the heat-exchange element 12 and sucks in primary air 57 and blows gas from a gas pipe 6 into a mixing tube 58 of the burner 4. The pressure and momentum of the gas may thus be used f or increasing the f low rate of cooling medium (in this case the mixture of gas and primary air) through the tubes of the heatexchange element 12, in a modification in which the fuel mixture is used to cool the flame region.

In the construction shown in Figure 4, the thermal conducting members 52 can be chosen so that the heat withdrawn from the flame region can be automatically varied by a temperature-dependent change in the thermal conductivity of the components of the heat-exchange element 12. As regards the position of the rods, tubes or other components of the heat-exchange element 12 relative to the individual f lames of the burner 4, the components are preferably disposed centrally in the f lame or main flame or in the f lame tongue so that they are surrounded by the f lame on all sides. Alternatively, the cooling elements 52 can be positioned on the sides of the inner cones of pre- mixed burner flames or near the f lames or above partial flames.

In the case of continuous hot water supply heaters, closed circuit watercirculating heaters, reservoirs and boilers, a wide variety of burner constructions can be used. Two main classes of burners are forced-air burners and atmospheric gas burners. Forced-air burners can also be supplied with oil and/or gas. Gas burners can also be diffusion burners. In addition to tubular or ribbed tubular gas burners, usually supplied by an injector under atmospheric pressure, there are large-area metal, metalfibre and ceramic plate ' - 27 - burners. Tubular burners have a round or elongate overall contour, and there are also "grate" burners made up of a number of parallel burner tubes. A number of fuel-mixture outlet openings, in the form of holes or slots or both, are usually disposed on the top surface of the burner tubes.

In the case for example of a tubular gas burner with a number of gasmixture outlet nozzles, there is little difficulty in positioning the parts of the heat- exchange elements 12 relative to the flames. If the burner is operated under partial load, modulating the burner output, the f lames become shorter, resulting in a change in the position of the hottest zones of the burner flame. To obtain the same cooling effect, the components of the heat-exchange element 12 must be re-positioned, as already mentioned with reference to Figure 2. In order to improve the flame stabilization as well as the cooling, as an alternative to varying the position of the heatexchange elements, it is possible to close some of the gas-mixture outlet openings so that the remaining partial f low goes through fewer gas-mixture outlet openings than before, to alter the number of f lames, without altering the shape of the f lames. Since the f lane conf iguration remains unchanged, the components of the heat- exchange element 12 can be left in the same position. Individual gas- mixture outlet openings can be opened and closed by thermal or mechanical or electromagnetic means or by electric motors. the gas flow rate.

For the purpose of stabilizing and cooling, it is desirable to keep the components of the heat-exchange element 12 in a defined position relative to the flame. Accordingly, adjustable flow directors for the emerging gas or gas-air mixture can be disposed on the fuel-mixture outlet openings of the burner 4.

As an alternative to individually closable outlet openings, partial regions of the burners or partial burners 4 can be blocked under partial load, so as to expose or block the burner surface in stages.

As already mentioned, the cooling components of the heat-exchanger can have a very wide variety of shapes.

In general, these components can comprise rods, tubes, gratings or screens with widely varying cross-sections. The cross-sections can be round, conical, prismatic or elliptic.

If the burner 4 is made up of individual partial 26 burners, the partial burners can have varying loads and consequently varying flame heights. Accordingly the components of the heat-exchange elements 12 can be adjusted to the flame heights by choosing the crosssection shapes and dimensions so that the stabilizing and cooling components are varied to match the flame heights and flame sections of the partial burners. The components of the heat-exchange element 12 can be rotatable or A command variable which can be used is 1 29 - pivotable or vertically adjustable members, so that the heat withdrawal and consequently the stabilization and acceleration of the flame reaction can be varied under varying conditions. Rotary, pivoting and vertical adjustments can be controlled by thermal expansion sensors, expansible- material elements, or by electromagnets or electric motors or manually.

If the cooling medium is taken directly from the water circuit (assuming appropriate operating conditions of the water heater with regard to the pressure and temperature in the water circuit) the requirement for interf erence- free operation of flame cooling may lead to additional control requirements or necessitate particular modifications to the construction of the flame cooling system. This is particularly so if there is a risk of condensate forming on the outer wall of the heat-exchange element 12 or evaporation or boiling of the cooling water. Possible arrangements are shown in Figures 25 to 33.

In a first modification shown in Figure 25, the cooling water for cooling the flames is branched off downstream of part of the heat-exchanger 11, intermediate to two ends. The water flowing into this branch has already passed part of the heat-exchanger 11 and is therefore somewhat heated, so that the branched-off water has an intermediate temperature for flame cooling.

Figure 26 shows another modification for adjusting the flame-cooling heat flow. A connection is 1 1 provided between the cooling circuit and the heating flow and heating return, in order to keep the cooling water at a constant temperature when there are variations in the heating flow or heating return temperature. Preferably a three-way valve 111 is provided and, via a comparison between the actual and the set temperature, comprises a motor-driven mixer controlf so that incoming flow and return water are mixed until the amount of outflowing cooling water and the temperature thereof reach a given level. An alternative to the three-way valve 111 is a thermally controlling expansible-inaterial element for controlling the mixture or a thermally controlled priority reversing valve.

Figure 26a shows diagrammatically one form of 15 construction of a threeway valve ill with a built-in control device for keeping the temperature of the cooling water constant. An expansible-material regulator D disposed in the input region of a cooling coil acts on an opening plunger S1 between the flow VL and a mixing chamber M and an opening plunger S2 between the return RL and the mixing chamber M. When the temperature in the mixing chamber M increases, there is an increase in the volume of an element D, thus automatically closing the plunger Si and additionally opening the plunger S2. This results in a reduction in already-heated flow water through the plunger S1 into the mixing chamber M, and a simultaneous increase in cold return water, so that the - 31 cooling water in the mixing chamber M is cooled to a temperature level preset by the regulator D. Figure 26b shows another example of temperature regulating by means of an expansible-material regulator D. 5 Alternatively the cooling process can be controlled by a thermostat or similar valve 112 incorporated in the cooling-medium circuit, as shown in Figure 27. Valve 112 throttles the flow of coolant if the temperature falls below a set value, thus increasing the average temperature of the coolant in the heatexchange element 12.

Figure 27a shows the basic construction of one form of a valve 112. As can be seen, the coolant flow rate is adjusted by an expansible-material element D. In addition'to a free opening F, which ensures a basic flow, there is a temperature-controlled closable opening V connected to a closure element E which is spring-mounted and disposed in force equilibrium with the likewise spring-mounted element D. If the temperature of the inflowing water increases there is an increase in the volume of element D, with the result that the closure element E is pushed out of the closure opening V up to a position in which the element E meets an abutment A. There is thus an increase in the flow rate of coolant and in the cooling effect.

one possibility of reducing the maximum temperatures of the cooling medium flowing through the heat-exchange element 12 is shown in Figures 28 and 28a. Here, the heat- exchange element 12 is divided into two separate strands 113 and 114. In this construction, accordingly, a meandershaped cooling coil comprising n (preferably fourteen) parallel tube portions comprised of two separate cooling coils 113 and 114 each with n/2, preferably seven, tube portions.

Figure 29 shows an embodiment with a separate cooling circuit. The cooling circuit is coupled by a heat-exchange element 115 to the heating return flow, and also comprises a circulating pump 116 and a vent 117. A modification of the cooling system shown in Figure 29 is shown in Figure 30. In Figure 30, a coolingcircuit pump 1161 is coupled to the circulating pump 16 of the heating circuit. Units 16 and 116,1 have a common shaft or are connected by a magnetic clutch. In addition, as shown in Figure 31, a compensating line 118 for balancing the pressure level can be provided between the two water circuits. 20 Figure 32 shows an embodiment in which a branch 119 is provided downstream of the heat-exchange element 11 and supplies part of the flow water from the heating circuit to the heat-exchange element 12. Element 12 comprises a meander-shaped coiled tube 120 for the cooling water and a single coil of tube 121, which crosses the tube 120 substantially at right angles and conveys return water. The tube 120 opens into a connecting portion 122 - 33 between the coil 121 and the heat-exchange element 11. The intersection region between the tube 120 and the coil 121 are shown in Figure 32a in plan view and Figure 32b in section. As can be seen, at the intersections the meander-shaped coiled pipe 120 is connected so as to exchange heat with the tube 121 which conveys heating water.

Figure 33 shows a cooling circuit likewise comprising a meander tube 1201, which extends through a coil 121 identical with that in Figure 22. In contrast to Figure 32, however, the tube 1201 constitutes a separate is cooling-water circuit comprising a circulating pump 116 as in Figure 29. 1 Thus, the heat-exchange element associated with the flame may be any one of a wide variety of constructions for any one of a wide variety of applications for various constructions of water heater, and a number of different water-flow circuits are possible for connecting the heatexchange element associated with the flame, together with a number of positioning, monitoring and control elements and devices for regulating the coolant circuit. In general, any illustrated construction of water heater can be combined with any illustrated hydraulic connecting, monitoring and control means and any illustrated cooling control system. The actual combination selected for optimum results will depend upon the application.

Figures 34a and 34b show the position of a fixed heat-exchange element 12 relative to the flame contour in the case of a burner having a variable power and consequently variable f lame length, the passageways 123 conveying the fuel/air mixture being curved, f or example in the form of a sickle shape. When the burner output changes, there is a change in equilibrium between the outlet momentum and the thermal buoyancy of the flame. An increase in burner output, that is in the velocity of the outflowing mixture, results in an excess outlet momentum, so that the flame in the bent pipe is correspondingly aligned and consequently flows more intensively round the heat-exchange element 12 disposed in this region. If the burner output increases, therefore, the cooling effect increases also.

Oil may be used as a fuel instead of the previously-referred to gaseous fuel.

The heat-conducting tubes or the cooling tubes through which coolant flows can be made from a wide variety of metal materials or ceramics or glass.

1 claims 1. Means for heating a fluid comprising a burner and at least two heat-exchange units arranged one after the other in the direction or intended direction of flow of the combusted fuel, in which the first heat-exchange unit, which is disposed nearer to the burner than the other, downstream of the fuel outlet opening and immediately in a flame region, withdraws heat from the f lame region when the heater is in use and at least when the fuel is burning at a predetermined rate, and in which the flow-rate of heat thus withdrawn amounts to between 5 and 50% of the total flow of heat generated by the burner, so as to improve the combustion process.

2. Means according to claim 1, in which the said first heat-exchange unit is shaped, dimensioned and/or positioned so that it acts as a baf f le and improves the stability of the flame of the burner and intensifies the combustion reaction.

3. Means according to claim 1 or claim 2, in which the two heat-exchange units have a commonoperation- monitoring device.

4. Means according to claim 1 or claim 2, in which the said first heat-exchange unit is provided with an operation-monitoring device.

5. Means according to claim 3 or claim 4, in which the operationmonitoring device is a device for monitoring 36 - the flow of coolant.

6. Means according to claim 5, in which the operation-monitoring device is atemperature-difference sensor, a f low meter, a longitudinal expansion device, a device in which a medium flows through an expansible element, or a pressure difference monitor.

7. Means according to any preceding claim, in which the said first heatexchange unit comprises a heatconducting member in the f orm of a tube, rod, lattice, 10 mesh or screen.

8. Means according to any of claims 1 to 6, in which the said first heat-exchange unit comprises a member through which a coolant floTs, the heat from which is removed by convection.

9. Means according to any preceding claim, in which the said first heat-exchange unit is adjustable in position.

10. Means according to any one of claims 1 to 8, in which the said first heat-exchange unit is secured in an 20 optimum position.

11. Means according to claim 10, in which the said first heat-exchange unit is brought manually into the said optimum position and secured therein.

12. Means according to claim 9, in which the said first heat-exchange unit is maintained in anoptimum position in controlled manner by a suitable device, for example a bimetallic element.

13. Means according to any preceding claim, in which the heat f low withdrawn from the f lames by the said f irst heat-exchange element is controlled by a suitable device.

14. Means according to claim 5, in which the time 5 gradients of the temperature differences are supplied to the device for monitoring the flow rate of coolant.

15. Means according to any preceding claim, in which a coolant supply comprises a control or regulating device for maintaining the coolant at a desired temperature level.

16. Means according to claim manually, hydraulically, thermally operated control or regulating device is 17. Means according to claim 15 15 which the control or regulating device 15, in which a or electrically provided.

or claim 16, in is constructed so that the control or regulating range of the coolant temperature lies between a lower limit set according to incipient condensation on the outer wall of the said first heat-exchange unit and an upper limit set according to incipient evaporation of coolant.

18. Means according to any of claims 15 to 17, in which the control device is adapted for controlling the flow of coolant through the said first heat-exchange unit.

19. Means according to any of claims 15 to 18 1 in which a return line and a flow line of an industrial water supply each have a branch which, via a mixing valve comprising a thermal mixer control, opens into a coolant pipe containing the said f irst heat-exchange unit, the other end of the coolant pipe being connected to the return line.

20. Means according to claim 19, in which the mixer 5 control comprises a thermally regulating expansible- material element or a thermally controlled priorityreversing valve.

21. Means according to any of claims 15 to 18, in which a coolant circuit branching off a return line comprise's a thermostat or similar valve which controls the flow of coolant so that, the flow speed of the coolant is reduced when the temperature falls below a set value.

22. Means according to any of claims 15 to 18, in which a separate coolant circuit is provided.

23. Means according to claim 22, in which the said separate coolant circuit is coupled bya heat-exchange element to a return line of an industrial water circuit.

24. Means according to claim 22 or claim 23, in which an industrial water circuit and the said separate coolant circuit each comprise a circulating pump, the pumps being interconnected by a common shaft or magnetic clutch.

25. Means according to any of claims 22 to 24, in which a pressure equalizing line is provided and connects an industrial water circuit to the said separate coolant circuit.

26. Means according to any preceding claim, in which an end portion of the fuel/air mixture outlet pipe near the opening region is curved.

27. Means for heating a fluid, substantially as described herein with reference to and as shown in any one or more of the accompanying drawings.

Published 1990 at The Patent Office. State House, 66 71 High Holborn, London WC1R4TP. Further copies maybe obtained from The Patent Office Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by MultipI ex techniques ltd, St Mary Cray. Kent. Con 1'87