GB1604637A - Flue gas ducting - Google Patents

Description

(54) FLUE GAS DUCTING (71) We, J. B. HYND (SITE SERVICES) LIMITED, a British Company of 327 Linthaugh Road, Glasgow, G53 5QZ, Great Britain do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to flue gas ducting.

In operating a boiler having flue gas ducting in the form of a- conduit (for example, a chimney, flue or the like) it is best to remove as much heat as possible from the flue gases in order to obtain maximum boiler efficiency. A problem associated with this, however, is that the flue gases may fall below the acid dew point as they travel along the conduit, producing sulphuric acid which corrodes the inner surface of the conduit. The sulphuric acid results from the content of sulphur- containing gases in the flue gas.

Modern chimneys, flues and the like are insulated to prevent heat loss by the flue gases, but particularly in high chimneys the acid dew point problem still exists.

An object of the present invention is to obviate or mitigate this problem.

According to the present invention there is provided flue gas ducting comprising a conduit having an inlet and an outlet for flue gas, and means associated with the conduit for heating flue gas within the conduit, wherein the heating means is disposed in the conduit on a side of the inlet remote from the outlet.

Preferably, the means for heating gas in the conduit is in the form of a gas burner or electric heater. In one alternative, the means for heating the gas comprises a flow of hot gas which is introduced into the conduit through an additional inlet.

The means for heating flue gas is disposed in the conduit on a side of the inlet remote from the outlet in order to minimise the possibility of corrosion of the means by contact with the flue gases passing through the conduit.

The burner may be fed with gas, liquid or solid fuel. Gas, for example propane, is preferred.

It is preferable to provide temperature sensing means in the conduit to signal the need for more or less heat to be applied in the conduit. The temperature sensing means is preferably located a short distance beyond the point at which corrosion is most likely to occur.

A time switch may be included to allow the conduit to be pre-heated prior to flow of the flue gases so as to avoid an initial temperature drop below the acid dew point.

An embodiment of the present invention will now be described by wa of example.

A boiler I has ducting for flue gas, in the form of a flue 2 leading into a lower portion of an upright conduit in the form of a chimney 3 which is designed in accordance with BS 4076. The chimney 3 is insulated with 50 mm. thick Rocksil (R.T.M.) along its length, and is topped by a weather seal 4.

Below the junction 5 of the flue 2 with the chimney 3 is a door (not shown) providing access into the bottom of the chimney 3 for cleaning out accumulated solid waste.

Between the bottom of the chimney 3 and the flue/chimney junction 5 is a gas ring 6 which is connected to a propane gas supply 7 external of the chimney 3. The gas ring 6 is at a level above that of the accumulated waste but is low enough to be accessible through the door. The ring 6 has an output which is capable of producing and retaining a temperature of between 270 and 350"F at the top of the chimney 3.

A thermostat 8 is located at a point around two-thirds of the distance up the chimney 3 and is connected to the gas ring 6. The thermostat 8 is set to switch the gas ring 6 on when the temperature which it senses falls below 2700F and to switch the ring 6 off when the temperature exceeds 350"F.

In operation, the boiler I produces flue gases which pass along the flue 2 into the chimney 3. If as they pass up through the chimney 3 the temperature falls below the acid dew point the thermostat 8 actuates the gas ring 6 which then heats up the interior of the chimney 3, raising the temperature of the flue gases above the acid dew point and preventing the formation of sulphuric acid droplets. If the temperature becomes excessive the thermostat shuts off the gas ring 6 thereby keeping the operation as economical as possible.

Access to the gas ring 6 for servicing is easily gained through the door at the bottom of the chimney 3.

In other embodiments, more than one thermostat may be provided along the length of the chimney 3.

The system described in the above embodiment allows the boiler I to run efficiently by permitting the flue gases to be emitted into the chimney 3 at a low temperature without the concomitant danger of corrosion of the chimney 3 by acid droplets forming therein, and the system can be applied to single skin, double skin or multi-flue chimneys.

WHAT WE CLAIM IS: 1. Flue gas ducting comprising a conduit having an inlet and an outlet for flue gas, and means associated with the conduit for heating flue gas within the conduit, wherein the heating means is disposed in the conduit on a side of the inlet remote from the outlet.

2. Ducting according to claim 1 wherein the heating means is selected from a fuel burner, an electric heater and a flow of supplementary hot gas introduced into the conduit through a second inlet.

3. Ducting according to claim 2, wherein the fuel burner is fed by gas.

4. Ducting according to any one of the preceding claims, wherein temperature sensing means is provided in the ducting.

5. Flue gas ducting substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. acid dew point the thermostat 8 actuates the gas ring 6 which then heats up the interior of the chimney 3, raising the temperature of the flue gases above the acid dew point and preventing the formation of sulphuric acid droplets. If the temperature becomes excessive the thermostat shuts off the gas ring 6 thereby keeping the operation as economical as possible. Access to the gas ring 6 for servicing is easily gained through the door at the bottom of the chimney 3. In other embodiments, more than one thermostat may be provided along the length of the chimney 3. The system described in the above embodiment allows the boiler I to run efficiently by permitting the flue gases to be emitted into the chimney 3 at a low temperature without the concomitant danger of corrosion of the chimney 3 by acid droplets forming therein, and the system can be applied to single skin, double skin or multi-flue chimneys. WHAT WE CLAIM IS:

1. Flue gas ducting comprising a conduit having an inlet and an outlet for flue gas, and means associated with the conduit for heating flue gas within the conduit, wherein the heating means is disposed in the conduit on a side of the inlet remote from the outlet.

2. Ducting according to claim 1 wherein the heating means is selected from a fuel burner, an electric heater and a flow of supplementary hot gas introduced into the conduit through a second inlet.

3. Ducting according to claim 2, wherein the fuel burner is fed by gas.

4. Ducting according to any one of the preceding claims, wherein temperature sensing means is provided in the ducting.

5. Flue gas ducting substantially as hereinbefore described with reference to and as shown in the accompanying drawings.