IES960711A2 - Method of converting a cooker or stove from solid fuel to oil or gas - Google Patents

Abstract

A solid fuel cooker is converted to oil or gas, and the conversion includes not only installation of an oil or gas burner but also the addition of surface irregularities in the combustion chamber to improve heat transfer characteristics.

Description

The present invention relates to a method of converting a cooker or stove from solid fuel to oil or gas. Such devices burn fuel so as to generate heat for cooking, space heating or water heating purposes.

The invention relates particularly although not exclusively to a method of converting a domestic solid fuel cooker to oil or gas.

Prior Art A domestic solid fuel cooker is installed in the kitchen of a private dwelling. The cooker consists of a number of chambers including a combustion chamber, an ash pit chamber below the combustion chamber and one or more oven chambers. The cooker may also include a water boiler adjacent the combustion chamber for heating water to provide a supply of domestic hot water and/or for central heating purposes. The cooker also includes dampers and baffles for directing the flow of heated air.

IE 960711 - 2 In recent years it has become commonplace to convert such cookers from solid fuel to gas or oil. The principal reason for such conversion is because of a change in the relative prices of solid fuels on the one hand and oil or gas on the other hand. Whereas formerly it was less expensive to use solid fuel, it may now be less expensive to use oil or gas. Also, oil and gas are easier to use. Solid fuel must be transported to the home, stored, loaded into the cooker, and the ashes must be cleared out, whereas oil and gas may be simply piped into the home. Furthermore, oil and gas are also generally cleaner. When using solid fuel it is necessary to carry the solid fuel through the kitchen and carry the ashes out of the kitchen, whereas with oil and gas the incoming oil or gas is confined to the pipes and the combustion residues are exhausted to atmosphere.

The possible difficulties arising in conversion will be readily apparent. Cookers of the type described are very heavy and bulky and are usually installed in such a manner that movement of the cooker might cause damage to the surroundings. It is therefore desirable that conversion be carried out in situ.

There is a widely used method of carrying out conversion. An oil or gas burner is installed in the ash pit and the flame is directed into the combustion chamber directly above. Baffles or shields are usually added to assist heat distribution, to prevent local overheating and to reduce noise.

Conversion carried out in the above manner has been found to be effective and satisfactory.

Object and Summary of the Invention An object of the present invention is to further improve the above described method of conversion.

The invention provides a method of converting heating apparatus from solid fuel to oil or gas comprising installing an oil or gas burner so that oil or gas is burnt within the solid fuel combustion chamber, characterised by adding heat conducting irregularities to the IE 960711 - 3 combustion chamber in thermal contact with a wall or walls thereof so as to increase heat transfer to said wall or walls.

The invention is based on an appreciation of the different combustion characteristics of solid fuel on the one hand and oil or gas on the other hand, and a consequent appreciation that a combustion chamber designed so as to optimise heat transfer from solid fuel, while satisfactory for oil or gas, is nevertheless not optimum. More particularly, a typical solid fuel burns at about 950°C. Heat transfer takes place primarily by radiation (approximately 65%) and to a lesser extent by convection (approximately 35%). Oil burns at about 675°C and heat transfer takes place by both radiation (approximately 45%) and convection (approximately 55%). Gas burns at about 500°C and heat transfer takes place primarily by convection (approximately 80%) and to a much lesser extent by radiation (approximately 20%).

Tests have shown that the additional step of adding heat conducting irregularities significantly improves the heat transfer.

Preferably the irregularities are added with the apparatus in situ.

In the case of a heating apparatus including a boiler in thermal contact with the combustion chamber through a common wall, irregularities are preferably added to the common wall.

Preferably the addition of the irregularities is carried out by electrically welding metal studs to the wall or walls of the combustion chamber.

Preferably the studs are of a diameter or average thickness between 5 mm and 10 mm and of length between 20 mm and 50 mm.

The invention also provides heating apparatus which has been converted by the method of the invention.

Other features and advantages of the invention will become apparent from the description which follows.

IE 960711 - 4 Brief Description of the Drawings The invention will now be described more particularly with reference to the accompanying drawings which show, by way of example only, a prior art heater-cooker before conversion and the same heater-cooker after conversion by the method of the invention. In the drawings: Figure 1 shows, in simplified form, a front sectional elevation of a prior art solid fuel heater-cooker; Figure 2 shows, again in simplified form, a front sectional elevation of the heater-cooker of Figure 1 after conversion; and Figure 3 is a plan view of the heater-cooker either before or after conversion and shows the section line X-X relating to the sectional elevations of Figures 1 and 2.

Detailed Description of the Preferred Embodiment Referring now to Figure 1, there is shown a typical prior art heater-cooker 1 for installation in the kitchen of a private dwelling. The heater-cooker 1 includes a combustion chamber 2 provided with a grate 3 on which rests solid fuel 4. Ashes arising from combustion of the solid fuel 4 may fall into the ash pit chamber 5. The combustion chamber 2 includes a wrap around boiler the rear of which is indicated by reference numeral 6 and the sides of which are indicated by reference numeral 7. The common wall which separates the boiler from the combustion chamber is indicated by reference numeral 8. The heater-cooker 1 further comprises a hot plate 9, a top oven 10, a bottom oven 11 and a passage 12 leading to a flue 13.

Referring now to Figure 2, the heater-cooker 1 is shown after conversion in accordance with the traditional conversion method as further improved by the method of the invention. In accordance with the traditional conversion method, the grate 3 has been removed and a pressure jet oil burner 14 has been installed in the ash pit chamber 5 and directs a mixture of air and finely divided oil into the combustion /e 9β0777 - 5 chamber 2, where combustion takes place as indicated by flame 15. In accordance with the present invention, conversion includes the further step of welding metal studs 16 to the inside face of the combustion chamber, and in particular to the common wall 8 so as to ensure efficient heat transfer from the combustion chamber to the water in the boiler 6, 7.

The surface of the combustion chamber 2 is prepared for the studs 16 by removing all deposits and scale and leveling the surface by suitable grinding means such as an electrically powered grinding machine. Conventional studs and stud welding equipment may then be used to affix an array of studs to the prepared surface, although a shorter than standard stud gun length will usually be necessitated by the relatively confined space. Stud guns can be modified to such shorter lengths with little difficulty. The individual studs are positioned by means of an insulated template temporarily affixed to the surface and comprising positioning holes for the shroud or positioning legs of the stud welding gun, with the hole centres at the desired positions of the studs. Alternatively the studs can be positioned by means of a spacer piece fixed to the gun and set against previously welded studs.

It will be appreciated that both the traditional conversion method and the additional method step of the invention can be carried out on site and that there is no need to move or disassemble the heater-cooker 1.

One advantage of the improved fuel efficiency offered by the additional conversion step of the invention is that it is possible to reduce fuel consumption while maintaining heat output.

A further advantage of the additional method step of the invention is that the heater-cooker 1 produces a higher output than one converted by the method of the prior art. For example, if the heater-cooker is used to provide hot water to central heating radiators, then it would be possible to heat additional radiators in the system while maintaining the same temperature, all as a result of the additional method step of the invention. - 6 IE 960711 A still further advantage is that apparatus which has been converted in accordance with the invention more closely matches the originally designed balance and proportions between heat transferred to the different parts of the apparatus.

The precise number, configuration and specification of the irregularities will of course depend on the particular apparatus being converted, will depend on whether the conversion is to oil or gas, and will depend on the particular model of oil or gas burner installed.

It has been found that plain cylindrical metal studs 16 having a diameter of between 5 mm and 10 mm and a length of between 20 mm and 50 mm give good results in many situations, but other shapes and sizes may also be used.

Smaller diameter studs result in a higher heat transfer coefficient in proportion to their size and can be applied with smaller and less expensive welding equipment. On the other hand, larger diameter studs can be applied with less labour for a given surface area and are more robust in service. Shorter length studs result in higher heat transfers in proportion to their size and cost and are more robust in service. On the other hand, longer studs can be applied with less labour for a given surface area. The optimum will be a balance between these factors.

All of the stud related operations can be readily carried out on site without disturbing the installation of the cooker or boiler. Convenient access is provided through the top of the combustion chamber by removing the hot plate. The stud welding and grinding equipment can be powered from an ordinary domestic electric supply.

It is not necessary to drain the boiler 6, 7 before welding the studs to the common wall 8.

In a further embodiment of the invention, (not shown) the irregularities need not comprise studs, but might comprise appropriate shaped castings or pressings, which each comprise groups or arrays of irregularities, and which are in thermal contact with the walls of the IE 960711 - 7 combustion chamber or boiler, the contact being effected by mechanical means or by welding or soldering.

The invention is not to be construed as limited to the specific embodiment(s) described herein which are given by way of example only, but instead encompasses all subject matter falling within the scope of the appended claims.

Claims (5)

1. A method of converting a cooker or stove from solid fuel to oil or gas comprising installing an oil or gas burner so that oil or gas is burnt within the solid fuel combustion chamber, characterised by adding heat conducting irregularities to the combustion chamber in thermal contact with a wall or walls thereof so as to increase heat transfer to said wall or walls.

2. A method according to claim 1 in which the irregularities are added with the apparatus in situ.

3. A method according to claim 1 or 2 for converting a cooker or stove including a boiler in thermal contact with the combustion chamber through a common wall, in which irregularities are added to the common wal 1.

4. A method according to any of the preceding claims in which the addition of the irregularities is carried out by electrically welding metal studs to the wall or walls of the combustion chamber.

5. Apparatus converted by the method of any of claims 1 to 4