GB2090386A - Boiler for a central heating system - Google Patents

Abstract

A boiler for a central heating system or for producing steam, in which the combustion is carried out in the fire tube 5, or first stage, the heat transporting fluid being heated by the fire tube and at least one cluster of smoke tubes is provided, wherein the last cluster of smoke tubes 13 constitutes a heat exchanger for the pre-heating of the heat transporting fluid entering the furnace at 18. <IMAGE>

Description

SPECIFICATION Furnace for central heating system The invention relates to furnaces for central heating systems or for the production of steam. It provides an important improvement of the furnaces that comprise a tubular fire chamber and two clusters of smoke tubes.

In this type of conventional furnaces the combustionis carried out in afirsttubularcombustion chamber, or first stage. Approximately half the heat removed comes from this fire chamber and the temperature of the combustion gazes at the outlet thereof is still of the order of about 1000"C. The second stage consists of a cluster of smoke tubes from which the combustion gazes leave at a temperature of more or less 400"C. The third stage consists also of a cluster of smoke tubes. The gazes leave it to enter the chimney at a temperature of between 1800C and 200"C.

It is evident that a large portion of the available heat is not transmitted to the fluid heat carrier, generally water.

It is an object of the present invention to provide a furnace in which a more substantial portion of the generated heat is recovered, increasing thus essentially its output.

The purpose of the invention is attained by the fact that the combustion gazes, when leaving the third stage and before entering the chimney, have been cooled down to a temperature which is much lower than that mentioned above.

According to the present invention only the first stage corresponds to that of the conventional furnaces.

With regard to the second stage it is constituted also of a cluster of smoke tubes but the heat exchange surface is increased on the order of 20"C and by providing so-called retarders the combustion gazes leave this stage at a temperature which does not exceed 200"C. Another characteristic feature of the invention is the last stage which is separated and insulated from the main portion of the furnace. The heat transporting fluid does not come into contact with the smoke tubes of the cluster; all the heat is transmitted to the return water. In this way it is possible to cool the combustion gazes to a temperature lower than the condensation temperature.In order to avoid the risks of corrosion it is intended according to the invention to utilize a tubular cluster whose tubes are coated with a non-oxidizing material, or tubes made of a marterial such as stainless steel.

The features and the advantages of the furnaces according to the present invention in respect of the known furnaces are illustrated in Figures 1 and 2.

Figure lisa diagrammatic illustration of a known furnace.

Figure 2 is a diagrammatic illustration of a furnace according to the present invention.

According to Figure 1 the heat is produced by a flame (2) of the burner (1 ) placed in the fire tube (5).

This fire tube is located in the boiler (3) which is filled with a heat transporting liquid (4). The combustion gazes (7) traverse the collector (6) and enterthe second stage constituted of a cluster of smoke tubes (8). Through the collector (9) the gazes (10) pass into the third stage constituted of the second cluster of smoke tubes (12) and leave the furnace by the collector (15) before entering the chimney. As mentioned above the temperature of the gazes is at that point on the order of 200"C. The return of the liquid into the furnace is carried out through conduit (11) and the heat is thereafter transferred to the heat transporting liquid (13) through the fire tube (5), the collector (6), the cluster of smoke tubes (8), the collector (9) and the cluster of tubes (12). The liquid leaves the furnace through the tubing (14).

According to the invention and as indicated in Figure 2 the heat transporting liquid is heated by the elements (5), (6), (8) and (9).

In this embodiment the third stage constituted of the second cluster of tubes (13) is surrounded by an insulating enclosure (12). In this way the heat transporting liquid does not come into contact with the tubes of the cluster (13). The return of the liquid (14) is carried out through the tubing (18), it circulates thereafter on the inside of the enclosure (12) between the cluster (13) in countercurrent with the combustion gazes. The pre-heated liquid enters then through the orifice (11) into the furnace and leaves it through the tubing (17) at a temperature which is on the average about 90"C.

As upon its return into the furnace the liquid is at a generally lower temperature than 75"C and circulates in a countercurrent with the combustion gazes passing through the cluster (13), the gazes are cooled to a temperature which does not exceed by 5 C that of of the return liquid.

In this manner it is possible to realize an economy of 8 % on the fuel.

As a consequence of the low temperature of the combustion gazes the dew point is reached and in order to avoid the corrosion phenomena, the tubes ofthe cluster (13) are made of stainless steel, or they may be covered on the inside by a protective coating. The condensation water that is formed there is discharged through the orifice (20).

1. Furnace for a central heating system or for producing steam, in which the combustion is carried out in the fire tube, or first stage, the heat transporting fluid being heated by the fire tube and at least one cluster of smoke tubes, characterized in that the last cluster of smoke tubes (13) constitutes a heat exchanger (12) for the pre-heating of the heat transporting fluid (14) returning to the furnace.

2. Furnace according to claim 1 wherein the last cluster of smoke tube (13) is surrounded by an insulating enclosure (12) placed in the furnace and which insulates the fluid (14) entering the furnace.

3. Furnace according to claims 1 or 2 wherein the last cluster of tubes (13) is constituted of an oxidizing material.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Furnace for central heating system The invention relates to furnaces for central heating systems or for the production of steam. It provides an important improvement of the furnaces that comprise a tubular fire chamber and two clusters of smoke tubes. In this type of conventional furnaces the combustionis carried out in afirsttubularcombustion chamber, or first stage. Approximately half the heat removed comes from this fire chamber and the temperature of the combustion gazes at the outlet thereof is still of the order of about 1000"C. The second stage consists of a cluster of smoke tubes from which the combustion gazes leave at a temperature of more or less 400"C. The third stage consists also of a cluster of smoke tubes. The gazes leave it to enter the chimney at a temperature of between 1800C and 200"C. It is evident that a large portion of the available heat is not transmitted to the fluid heat carrier, generally water. It is an object of the present invention to provide a furnace in which a more substantial portion of the generated heat is recovered, increasing thus essentially its output. The purpose of the invention is attained by the fact that the combustion gazes, when leaving the third stage and before entering the chimney, have been cooled down to a temperature which is much lower than that mentioned above. According to the present invention only the first stage corresponds to that of the conventional furnaces. With regard to the second stage it is constituted also of a cluster of smoke tubes but the heat exchange surface is increased on the order of 20"C and by providing so-called retarders the combustion gazes leave this stage at a temperature which does not exceed 200"C. Another characteristic feature of the invention is the last stage which is separated and insulated from the main portion of the furnace. The heat transporting fluid does not come into contact with the smoke tubes of the cluster; all the heat is transmitted to the return water. In this way it is possible to cool the combustion gazes to a temperature lower than the condensation temperature.In order to avoid the risks of corrosion it is intended according to the invention to utilize a tubular cluster whose tubes are coated with a non-oxidizing material, or tubes made of a marterial such as stainless steel. The features and the advantages of the furnaces according to the present invention in respect of the known furnaces are illustrated in Figures 1 and 2. Figure lisa diagrammatic illustration of a known furnace. Figure 2 is a diagrammatic illustration of a furnace according to the present invention. According to Figure 1 the heat is produced by a flame (2) of the burner (1 ) placed in the fire tube (5). This fire tube is located in the boiler (3) which is filled with a heat transporting liquid (4). The combustion gazes (7) traverse the collector (6) and enterthe second stage constituted of a cluster of smoke tubes (8). Through the collector (9) the gazes (10) pass into the third stage constituted of the second cluster of smoke tubes (12) and leave the furnace by the collector (15) before entering the chimney. As mentioned above the temperature of the gazes is at that point on the order of 200"C. The return of the liquid into the furnace is carried out through conduit (11) and the heat is thereafter transferred to the heat transporting liquid (13) through the fire tube (5), the collector (6), the cluster of smoke tubes (8), the collector (9) and the cluster of tubes (12). The liquid leaves the furnace through the tubing (14). According to the invention and as indicated in Figure 2 the heat transporting liquid is heated by the elements (5), (6), (8) and (9). In this embodiment the third stage constituted of the second cluster of tubes (13) is surrounded by an insulating enclosure (12). In this way the heat transporting liquid does not come into contact with the tubes of the cluster (13). The return of the liquid (14) is carried out through the tubing (18), it circulates thereafter on the inside of the enclosure (12) between the cluster (13) in countercurrent with the combustion gazes. The pre-heated liquid enters then through the orifice (11) into the furnace and leaves it through the tubing (17) at a temperature which is on the average about 90"C. As upon its return into the furnace the liquid is at a generally lower temperature than 75"C and circulates in a countercurrent with the combustion gazes passing through the cluster (13), the gazes are cooled to a temperature which does not exceed by 5 C that of of the return liquid. In this manner it is possible to realize an economy of 8 % on the fuel. As a consequence of the low temperature of the combustion gazes the dew point is reached and in order to avoid the corrosion phenomena, the tubes ofthe cluster (13) are made of stainless steel, or they may be covered on the inside by a protective coating. The condensation water that is formed there is discharged through the orifice (20). CLAIMS

1. Furnace for a central heating system or for producing steam, in which the combustion is carried out in the fire tube, or first stage, the heat transporting fluid being heated by the fire tube and at least one cluster of smoke tubes, characterized in that the last cluster of smoke tubes (13) constitutes a heat exchanger (12) for the pre-heating of the heat transporting fluid (14) returning to the furnace.

2. Furnace according to claim 1 wherein the last cluster of smoke tube (13) is surrounded by an insulating enclosure (12) placed in the furnace and which insulates the fluid (14) entering the furnace.

3. Furnace according to claims 1 or 2 wherein the last cluster of tubes (13) is constituted of an oxidizing material.

4. Furnace according to claims 1 or 2 wherein the cluster of tubes (13) is coated with a material resisting to corrosion.