Technical Field

The invention relates to a fire tube boiler employing hot water as heat medium and for gas firing.

Background Art

Hot water boilers are known whereby the flue and the smoke tubes are situated in a common water chamber. At the temp¬ erature of the return water below the dew point temperature of the smoke tubes it must be ensured by adding supply water that the water entering the water chamber of the boiler is of a temperature being higher than the dew point temperature of the smoke in order to avoid formation of aggressive condensate on the heating surfaces of the boil¬ er, said condensate reducing the life of the boiler. The addition of supply water to the return water is carried out by means of a shunt circuit.

The known hot water boilers are encumbered with the draw¬ back that the boiler must be kept hot during idle periods such as at night and during week-ends, i.e. the shunt-pump must be running all the time and the burner must be activ¬ ated according to requirements in order to ensure the required minimum boiler water temperature. By many plants such a procedure causes an annual increase of the energy consumption by up to 10%. When the shunt-pump is not run- ning during the idle period the water temperature within the water chamber may drop below the dew point temperature of the smoke which implies that condensate appears on the heating surface ^' s of the smoke tubes during the succeeding long start-up period.

Description of the Invention

The object of the invention is to provide a boiler of the above type which involves a minimum consumption and loss of energy during idle periods, and which stands up to a start-up involving all possible water temperatures after the idle periods.

The boiler according to the invention is characterised in that it is divided into two water chambers, whereby the flue is situated in the first water chamber and the smoke tubes are situated in the second, water chamber, and that the water chambers are interconnected by means of a con¬ necting channel provided with a temperature sensor con¬ trolling a valve situated in the connecting channel or preferably on the return stub of the boiler in such a manner that the water leaving the connecting channel and. entering the second water chamber is of a temperature higher than or equal to the dew point temperature of the smoke. As a result the boiler can operate without the addition of supply water to the return water irrespective of the temperature of said return water, i.e. without a shunt-pump. The correct temperatures of the heating sur¬ faces are obtained solely by a control of the water flow through the boiler and by the boiler being closed automat¬ ically from the plant during the idle periods. In this manner the burner of the boiler need not be activated during the idle periods for keeping the boiler hot.

According to the invention the division of the boiler into two water chambers may be provided by means of a preferably plane partition extending within the boiler and substantially parallel to the smoke tubes and the flue, respectively. In practice such an embodiment turned out to be particularly advantageous because it can be utilized for a modification of existing boilers.

Finally according to the invention the connecting channel

may be situated on the outside of the boiler and preferably be a pipe. Such an embodiment is also particularly simple and suitable for modification of existing boilers.

Brief Description of the Drawing

5 The invention will be described below with reference to the accompanying drawing, in which a preferred embodiment of the boiler according to the invention is illustrated.

Description of the Preferred Embodiments of the Invention

The fire tube boiler 1 of the Figure is divided into two 10 water chambers 2, 3, whereby the flue 4 is situated in the first water chamber 2, and the smoke tubes 5 are si¬ tuated in the second water chamber 3. Within the boiler the water chambers 2, 3 are separated by means of a partition 6 extending transverse to the interior of the boiler and τ_5 substantially parallel to the smoke tubes 5 and the flue 4. The water chambers 2 , 3 are furthermore interconnected by means of a channel in the form of an outer tube 7 si¬ tuated on the outside of the boiler.

The tube 7 includes a temperature sensor 8 which through 20 ^a control circuit not shown controls a regulating valve 10 situated on the return stub 9 of the boiler in such a manner that the water leaving the connecting channel in order to run from the first water chamber 2 and into the second water chamber 3 is of a temperature higher than or 25 equal to the dew point temperature of the smoke. The boiler 1 is furthermore provided with a supply stub 11.

When the boiler is to be connected to a plant A, the re¬ gulating valve 10 of the boiler is connected to the return pipe RL of the plant as well as to a distribution pipe VL 30 communicating with the supply pipe FL of the plant, said supply pipe in turn being connected to the supply stub 11

of the boiler 1. A plant pump AP. circulates both the water in the plant and the water in the boiler.

The boiler operates usually as follows:

The return water flows from the plant A through the return 5 pipe RL to the regulating valve 10. Controlled by the temperature sensor 8 in the outer connecting channel 7 between the first water chamber 2 and the second water chamber 3, the regulating valve allows supply of such an amount of return water into the first chamber 2 that the ^" lO temperature of the water entering the second water chamber 3 is higher than or equal to the dew point temperature of the smoke tubes. In this connection please note that even though the return water entering the first water chamber is of a temperature below the dew point temperature of

]_5 the smoke, no damaging condensate arises within this cham¬ ber because it turned out that down to the minimum load of the burner burners adapted to natural gas ensure heat¬ ing surface- and combustion temperatures in the flue which prevents condensate from arising on the heating

20 surfaces of the flue even though the temperature of the water chamber surrounding the fire tube is very low, i.e. down to 0°C. When the water has entered the second water chamber it is gradually heated by the smoke tubes 5. Subse¬ quently the water leaves through the supply stub 1 _. 1 of

25 the boiler, and. immediately thereafter it is admixed with return water flowing through the distribution pipe VL in order to achieve the desired supply temperature.

During idle periods, i.e. when the plant A need not sup¬ ply heating, the burner of the boiler 1 is closed which 30 implies that the distribution valve 10 is forcedly closed in such a manner that return water is not circulated to the boiler 1.. In this manner the boiler 1 is closed with respect to circulation from the outer pipe system of the plant, and consequently no loss of heat occurs from the

boiler 1 through said plant. As a result, the boiler can remain hot for long periods . After the idle periods the boiler can be restarted irrespective of the temperature of the return water of the plant, and in short time the plant can be provided with the desired running temperature. During the latter start-up period the regulation of the water flow between the two water chambers 2 and 3 ensures too that no condensate arises on the boiler heating sur¬ faces .

The ^invention may be varied in many ways without thereby deviating from the scope thereof. Thus the connecting channel 7 may be situated inside the boiler, cf. the dotted indication at 7a.