GB2226115A - Gas-fired water heater - Google Patents

Abstract

A gas fired direct contact water heater 10 includes a reservoir 24 carrying and communicating with an inner casing 14. The inner casing 14 encloses a gas distribution plate 34, heat transfer media 40 supported thereover and a water distribution plate 42. An outer casing 12 is provided around inner casing 14 so as to define an annular gap 16 which is supplied with cold water via water inlet 20. Thus the cold water will be heated by contact with the inner casing's wall, by direct contact with the gaseous combustion products as the water passes down through the heat transfer media 40 and finally by contact with an immersion tube 26 in the reservoir 24. In this way the efficiency of heat transfer from the gaseous products to the water is increased over prior known arrangements. <IMAGE>

Description

GAS-FIRED WATER HEATERS This invention relates to gas-fired water heaters especially of that type including heat exchange by direct contact of the gas burner combustion products with the water to be heated.

Known gas-fired water heaters comprise a reservoir of water which is heated indirectly by a gas-fired burner in the form of an immersion tube and also heated directly by contact between the hot flue gases from the immersion tube and feed water droplets which are allowed to contact via water distribution means such as a packing media or a plurality of perforated plates. Such apparatus is described in British Patent No. 2129916.

Whilst the arrangement described in this patent is fairly effecient as regards heat transfer there are several ways in which heat from the flue gases is lost to the surroundings. Firstly the flue gases are in direct contact with the outer casing of the water heater which leads to a heat loss both in the heating up of this structure and to the surrounding atmosphere.

Secondly, the water distribution means which is either a series of plates or a known packing media has or is supported on one lower plate which is in direct contact with the flue gases at their hotest.

It is an object of the present invention therefore to provide an improved gas fired direct contact water heater having a higher operating efficiency than previously known heaters.

With this object in view the present invention provides a gas-fired direct contact water heater comprising a reservoir for collecting water discharged from a gas distribution plate disposed over the reservoir, an immersion tube located within the reservoir for receiving hot gaseous products of combustion for heat exchange with water collected in the reservoir, an outlet from the immersion tube for the discharge of the gaseous combustion products towards the gas distribution plate, a heat transfer media supported over the gas distribution plate and below a water distribution plate for providing heat transfer between the gaseous combustion products and water issuing from the water distribution plate, the inner casing being surrounded by an outer casing defining an annular gap between said inner and outer casing, the outer casing being provided with a water inlet communicating with said gap and the outer casing being arranged such that the annular gap communicates with the water distribution plate at the gap's upper end, the outer casing also being provided with a waste gas outlet disposed over the water distribution plate.

It will be understood that cold water is supplied to the water inlet, and hence into the annular gap, filling the gap between the inner and outer casing until allowed to flow onto the water distribution plate. From the water distribution plate the water is allowed to flow downwardly through the transfer media where it contacts the upwardly flowing hot combustion gases and thence onto the gas distribution plate which allows the water to empty into the reservoir. Thus the cold water will receive any heat present in the wall of the inner casing due to its contact with the gaseous combustion products and will then be heated up due to direct contact within the heat transfer media and indirect contact in the reservoir with the immersion tube. In this way the efficiency of the heat removal from the gaseous combustion products is increased over that previously known.

Preferably the gas distribution plate is provided with a plurality of upwardly projecting tubes, some of the tubes being taller than other tubes of the plurality.

In this way the tall tubes will serve to permit gas to pass through the distribution plate and into the packing media whereas the smaller tubes will permit the drainage of water from the distribution plate into the reservoir below.

The invention will be described further by way of example with reference to the accompanying drawing in which the single figure is a diagrammatic sectional view of a direct contact water heater in accordance with the invention.

In the single figure a water heater 10 comprises a cylindrical outer casing 12 surrounding a cylindrical inner casing 14 and defining an annular gap 16 therebetween. The annular gap 16 is closed at its lower end 18 and open at its upper end where it communicates with the inner casing's interior. A water inlet 20 is provided on the outer casing 12 communicating with the annular gap 16.

The outer and inner casings 12, 14 are supported on a box 22 defining a reservoir 24 which is in communication with the inner casing's interior. Within the reservoir 24 is an immersion tube 26 connected to a burner 28 located outside the box 22. The immersion tube 26 receives hot gaseous combustion products from the burner 28 which are then discharged from the immersion tube 26 via a gas outlet 30. The height of the gas outlet is determined so as to be above the maximum level of water contained in the reservoir 24. A hot water outlet 32 is also provided to drain water from the reservoir for any desired use.

The gas outlet 30 is disposed on the immersion tube 26 so as to communicate with the inner casing's interior.

A gas distribution plate 34 is located within the inner casing 14 over the gas outlet 30. The gas distribution plate 34 is circular and is provided with a gas tight seal at its peripheral edges with the inner casing 14.

A plurality of tubes 36, 38 are provided on the gas distribution plate 34 projecting generally upwardly therefrom. Some of the plurality of tubes 36 are taller than the remaining tubes 38 and each tube provides communication between the spaces above and below the gas distribution plate 34. A heat transfer media 40 for example, a packing material or a plurality of perforated plates is supported within the inner casing 14 and directly over the gas distribution plate 34. The heat transfer media 40 serves to permit a liquid for example, water, to flow downwardly onto the gas distribution plate 34 whilst permitting the hot gaseous combustion products to permeate in an upward direction towards the inner casing's upper end.

A water distribution plate 42, of generally circular configuration, is located within the inner casing in a similar manner to the gas distribution plate 34 and over the heat transfer media 40. This water distribution plate 42 is also provided with a plurality of tubes 44 each tube being of a similar overall height. Also provided in the water distribution plate are a number of holes 46 located around and between the plurality oftubes 44. The holes 46 are substantially evenly distributed over the water distribution plate 42 so as to ensure an even distribution of water through the heat transfer media 40.

In operation the gas burner 28, which is of known designr fires hot gaseous combustion products into the immersion tube 26. Heat transfer takes place between the immersion tube 26 and the water contained in the reservoir 24 which surrounds the tube 26. The gaseous products now leave the immersion tube 26 via the outlet 30 and enter the inner cylindrical casing 14. The gaseous combustion products contact directly the gas distribution plate which by virtue of the tubes 38 supports thereon a predetermined volume of water collected from the heat transfer media 40. Thus any heat transmitted to the gas distribution plate 34 is also transmitted to that water.

The gaseous combustion products now rise further up the casing via the taller set of tubes 36 and thence into the heat transfer media 40. In the preferred example the heat transfer media 40 is a packing material supported over the gas distribution plate 34 by means of, for example, a grid or other similar arrangement.

The packing media to be used can be any of the conventional types, for example, broken solids or shaped packing material such as rings or saddle type packings chosen according to the desired operating characteristics such as the pressure drop per unit height of packing etc. Alternatively the heat transfer media 40 can be provided by a series of perforated plates or a series of grids or any combination thereof.

The gaseous combustion products travel up through the packing material passing through the voids or spaces therebetween so as to contact directly water droplets or streams flowing down through the packing material from the water distribution plate 42. The direct contact between the gaseous combustion products and the water streams allows for further hear transfer between the gas and the liquid.

After passing through the heat transfer media 40 the gaseous combustion products reach the water distribution plate 42 through which the gases pass via the plurality of gas tubes 44 located therein. The gaseous products then exit the casing 12, 14 via a waste gas outlet 48 located at the upper end thereof. During its passage through the inner casing 14 some of the heat contained in the gaseous combustion products will be transmitted directly to the material of which the inner casing is formed. In order that such heat is not lost to the process the annular gap 16 defined between the inner casing 14 and outer casing 12 is supplied with a constant flow of water via the water inlet 20. This water flows around the annular gap and rises upwardly, that is cocurrently with the gaseous products to reach the top of the inner casing 14.At this point the water flows over the inner casing and onto the water distribution plate 42. The water passes through the distribution plate 42 via the perforate holes 46 which serve to brake the waterflow into a series of streams or droplets flowing down onto the heat transfer media 40 located directly beneath the distribution plate 42.

It will be appreciated that heat transfer between the hot gaseous products and the water fed into the direct contact water heater occurs firstly indirectly between the water and the inner casing 14. The water then contacts the gaseous products directly within the heat transfer media 40 leading to further heat transfer and then water accumulated on the gas distribution plate is heated indirectly by the hot gases present below.

Finally the water collected in the reservoir 24 is heated indirectly by contact with the immersion tube 26. Thus the direct contact water heater as described in this application is capable of greater overall efficiencies than previously known designs where the primary heat transfer is limited to direct contact within a heat transfer media, for example perforate plates or a packing material.

It will be understood that the foregoing is intended to be illustrative and not limitative of the scope of the invention and variations may be made thereto. For example, the heat transfer media can be any conventionally known and suitable type and need not be those types described. Furthermore, although the casing is described as being cylindrical any configuration could be used which will of necessity alter the shape of -the distribution plates. The burner 28 may again be of any conventionally known type and need not be a gasfired burner but could use some other form of fuel, for example, oil.

Claims (5)

1. A gas-fired direct contact water heater comprising a reservoir for collecting water discharged from a gas distribution plate disposed over the reservoir, an immersion tube located within the reservoir for receiving hot gaseous products of combustion for heat exchange with water collected in the reservoir, an outlet from the immersion tube for the discharge of the gaseous combustion products towards the gas distribution plate, a heat transfer media supported over the gas distribution plate and below a water distribution plate for heat transfer between the gaseous combustion products and water issuing from the water distribution plate, the gas distribution plate, the heat transfer media and the water distribution plate being at least partially enclosed by an inner casing, the inner casing being surrounded by an outer casing defining an annular gap therebetween, the outer casing being provided with a water inlet communicating with said gap and the outer casing being arranged such that the annular gap communicates with the water distribution plate at the gap's upper end, the outer casing also being provided with a waste gas outlet disposed over the water distribution plate.

2. A water heater as claimed in claim 1 in which the water inlet is provided at the outer casing's lower end.

3. A water heater as claimed in claim 1 or claim 2 in which the gas distribution plate is provided with a plurality of upwardly projecting tubes open at each end to permit gaseous combination products to pass therethrough.

4. A water heater as claimed in claim 3 in which a predetermined proportion of the tubes project through the plate to a larger extent than the remaining tubes, which thereby are operative to drain water from the distribution plate into the reservoir below.

5. A gas fired direct contact water heater substantially as hereinbefore described with referennce to and as illustrated in the accompanying drawings.