EP0040226A1 - Exhaust gas system in a combustion apparatus for pulsating combustion - Google Patents

Abstract

In an exhaust gas system for a pulse burner, a cyclone chamber (17) is connected between the combustion chamber (14) of the pulse burner and a silencer (19). The cyclone chamber is constructed to form a one-way pressure barrier for pressure waves in the exhaust gas system, so that the outlet line after the silencer can be of varying length, desired in the atmosphere . At the same time the cyclone chamber is adapted to prevent that the condensate inside does not cause variations in gas flow resistance with the operational troubles that this would cause.

Description

Exhaust gas system in a combustion apparatus for pulsating combustion

The present invention relates to an exhaust gas syte in a combustion apparatus operating with pulsating combus¬ tion and is of the kind disclosed in the preamble to the accompanying main claim.

The invention primarily relates to so-called pulsating burners of the kind described and shown in the U.S. patent specifications 3 267 986 and 3 853 453. In order to be used practically, e.g. as a heat source in a dwelling, the exhaust gas system must have an effective silencer. The exhaust gas system and parts incorporated therein such as silencers must therefore be of such a nature that they do not provide any substantial disturbing action on the flow sequence in the exhuast gas system, which would result in disturbances in the pulsating combustion sequence in the combustion chamber. The pulsating burners in question are namely sensitive to variations in flow conditions. In order to maintain substantially constant flow conditions, the exhaust gas system should be formed such that combustion residues such as soot, sulphur dioxide and above all condensed water vapor as far as possible will not be able to collect and remain in the exhaust gas system. With regard to the silencer itself, this can be formed as illustrated in the U.S. patent 3 608 666. If such a silencer is connected into the exhaust gas conduit from a pulsating burner of the kind in question, the conduit between the pulsating burner and the silencer or the conduit after the silencer must have a length within predetermined limits for the pulsating burner to operate with stability, i.e. with a substantially constant frequency. The length of the conduit between the pulsating burner and the silencer can be selected with a correct value relatively easily, whereas the length of the exhaust gas conduit between the silencer and the free atmosphere will in practice be depend¬ ent on the place where the pulsating burner is to be mounted, e.g. in the basement of a dwelling. The length of the exhaust gas conduit from the silencer to the free atmosphere will thus vary from case to case, and if the length is not the right one for the pulsating burner in question, variations of the pulsating frequency will be obtained within a greater or less range, which in turn re¬ sults in deteriorated silencing and deteriorated- efficiency. The object of the present invention is first of all to provide an exhaust gas system which to a substantial degree, or practically entirely, eliminates dependence on the length of the exhaust gas conduit from the silencer to the free atmosphere, but the invention also has the object of providing an exhaust gas system having advantageous proper¬ ties with regard to the requirements mentioned by way of introduction. This is achieved with an exhaust gas system which in accordance with the invention has the distinguishing fea¬ tures disclosed in the following patent claims. In the inventive exhaust gas system, a specially formed cyclone chamber is connected between the combustion chamber and the silencer, which can be of known construction, e.g. according to the U.S. patent 3 608 666, i.e. a silencer giving good silencing and relatively free through-flow with small risk of deposits in the silencer. By combining, in accordance with the invention, the silencer with the special cyclone chamber, it has been found that the length of the exhaust gas conduit from the silencer to the free atmosphere can be selected optionally according to requirements without this affecting the pulsating frequency, i.e. the frequency will keep to a substantially constant value. The reason for this is that the cyclone chamber is constructed such that it functions as a kind of one-way pressure barrier, which allows the pressure waves to go through the cyclone chamber and the silencer relatively freely, while it dampens their tendency to back up in the conduit between the cyclone chamber and the combustion chamber.

The cyclone-like whirling flow in the cyclone chamber is initiated by the gas flowing in tangentially in the vertical cyclone chamber and sweeping in a spiral path alon __ the walls of the chamber, entraining possible soot particles, sulphur dioxide and condensed water vapor which can have collected in the cyclone chamber during the starting period. The soot particles and sulphur dioxide normally occur 5 in such small amounts that they do not affect operating conditions. On the other hand, the amount of condensed water vapor can vary considerably depending on the temperature in the cyclone chamber. In turn this is dependent, inter alia, on the temperature of the medium surrounding the cyclone 0 chamber, which can be air or another gas, or a liquid medium which is usually water. Especially when the combustion chamber, cyclone chamber and silencer are arranged in a i hot-water boiler, the temperature in the latter can be i relatively low on starting under certain conditions. If the

15 temperature of the incoming water during operation is also relatively low, e.g. about 20° or lower, cooling of the cyclone chamber is obtained which can result ^'in considerable problems in known exhaust gas systems for pulsating burners, due to the exhaust gases coming into a relatively cold

20 cyclone chamber, especially during the starting period. This results in a heavy collection of condensate in the cyclone chamber, since heating the cyclone chamber in the known exhaust gas systems takes place relatively slowly. If a cyclone chamber, known per se and with a horizontal central

•*-•*- axis, is thereby used, e.g. in accordance with the French patent specification 2 532 514, a rotating gas flow together with the condensate is obtained about a horizontal axis at the central area of the chamber, where the end of the outlet pipe to the silencer is situated. The gas velocity and there-

30 by the centrifugal force striving to keep the condensate against the wall of the chamber diminishes along the length of the cyclone chamber however, and in a certain area where the gas velocity is- relatively low, the condensate will fall down in the central area. In certain cases, the condensate

35 can form a heavy spray which meets the end of the outlet pipe during a certain time, in turn resulting in that the flow conditions at the outlet pipe end will vary and thereby cause greater or less operational disturbances, which in some

OMPI can lead to breakdown.

With the exhaust gas system in accordance with the invention, these problems are avoided by the cyclone chamber being substantially vertical and by the exhaust gas pipe from the combustion chamber to the cyclone chamber being taken into the cyclone chamber to form a heat spiral therein. The condensate will namely remain on the wall of the cyclone chamber also in the area where the gas velocity is relatively low. At most, the condensate can run back again along the chamber wall, but the condensate will then meet inflowing hot gas which arrests the movement of the water downwards on the wall. However, the heat spiral results in that the temperature in the cyclone chamber rises relatively rapidly during starting to a temperature resulting in that the condensate on the wall is vaporized correspondingly rapidly, so that the water vapor formed can depart through the outlet pipe without causing operational disturbances.

A suitable embodiment of the exhaust gas system in accordance with the invention is illustrated as an example in the accompanying drawings.

Fig. 1 is a schematic axial section through a hot-water boiler with a pulsating burner provided with an exhaust gas system in accordance with the invention, and Fig. 2 is a section along the line 2-2 in Fig. 1.

The hot-water boiler 10 has an inlet 11 and and outlet 12. In certain cases the incoming water can have a relatively low temperature, e.g. about 20°C or lower.

In the boiler, there is a pulsating burner with a combustion chamber 14, to which a fuel-air mixture can be supplied via an inlet 15.

In the exhaust gas conduit from the combustion chamber

14 there is incorporated an exhaust gas pipe 16 between the combustion chamber and a cyclone chamber 17, an outlet pipe 18 from the cyclone chamber to a silencer 19, and an outlet conduit 20 from the silencer to the free atmosphere.

The cyclone chamber 17 consists of a cylinder 21 with its central axis substantially vertical. The cyclone rbaπihPT- O can also have some other form known per se, with the central axis arranged vertically. At its upper and lower ends., respectively, the chamber is closed by dished end walls 21a, 21b. The pipe 16 is taken in through the upper end wall 21a and is thereafter formed into a heat spiral 22 with a plural¬ ity of turns situated in the vicinity of the chamber wall. In the lower half of the chamber, the spiral terminates in an outlet end 23. This is situated in the vicinity of the chamber wall and is directed tangentially, as is apparent from Fig. 2. The gas flowing into the cyclone chamber is' therefore guided into the chamber such that at least a portion of the gas flow after the first turn in the chamber will come back again to the outlet end 23 and flow past it from behind. A kind of one-way pressure barrier is provided hereby, which counteracts the tendency of the pressure waves to migrate back again from the silencer and cyclone chamber up in the pipe 16 and to the combustion chamber 14. The length of the outlet conduit 20 will therefore not noticeably affect the operational conditions in the combus¬ tion chamber, and this length can therefore be selected optionally to the length required for coming out into the free atmosphere from the place where the hot-water boiler is situated, e.g. in a dwelling. An inlet opening in the form of the end 34 of the pipe 18 is arranged at approximately the same height above the lower end wall 21b or bottom of the chamber as the outlet end 23, i.e. in the lower half of the chamber. This inlet end 34 is situated in the central area of the chamber, where the gas velocity has decreased and the flow is relatively quiet. By disposing the pipe end 34 in this quiet central area, the action of said pressure barrier is increased while there is simultaneously attained a certain amount of silencing as a supplement to the silencing obtained with the silencer 19.

By the pipe end 34 being situated in the central area, it is free from condensate which collects on the chamber walls under certain conditions. The condensate is circulated round under the influence of the gas flow which executes a spiral-shaped rotational movement in the chamber. Centri¬ fugal force thereby keeps the condensate against the ver¬ tical wall of the chamber. When there are greater quantities of condensate, the water will run down along the chamber walls in a direction towards the bottom of the chamber, al¬ though without reaching the inlet end 34.

When starting the pulsating burner under such condi¬ tions/when the cyclone chamber is more or less cooled by relatively cold water flowing into the chamber, or has a relatively low temperature for some other reason, the hot gas flow will rapidly heat up the pipe coil 22, resulting in rapid heating of the cyclone chamber and a corresponding rapid vaporization of condensate possibly to be found therein. The water vapor formed departs without disturbances of the flow conditions via the pipe 18 and further out through the silencer 19 and the conduit 20.

The exhaust gas system in accordance with the invention thus signifies a considerable improvement, since the cyclone chamber with its one-way pressure barrier allows an optional required length of the conduit 20 to the free atmosphere without affecting the functions of the pulsating burner, simultaneously as the cyclone chamber is disposed such that it guides possible condensate so that it does not cause operational disturbances, and so that the chamber enables rapid vaporization of the condensate and removal of the water vapor formed.

Claims

1. An exhaust gas system for a combustion apparatus for pulsating combustion of an air-fuel mixture in a combustion chamber, comprising an exhaust gas conduit from the outlet side of the combustion chamber to free atmosphere with a silencer incorporated in the exhaust gas conduit, characterized in that a cyclone chamber (17) is connected in the exhaust gas conduit between the combustion chamber (14) and the silencer (19) ; that the cyclone chamber is disposed with its central axis in a substantially vertical position; that the exhaust gas conduit between the combustion chamber and the cyclone chamber consists of an exhaust gas pipe (16) taken into the cyclone chamber and formed into a heat spiral (22) situated in the vicinity of the chamber wall for .giving off heat to the surroundings in the chamber; that the outlet end (23) of the spiral is in the vicinity of the chamber wall and is directed substantially tangentially relative thereto (Fig. 2) for providing a rotational flow which, during its first revolution, passes from behind and over the outlet end (23) , thereby forming a single-acting pressure barrier for the pressure waves in the exhaust gas system; and that one end (34) of an outlet pipe (18) is disposed in the central area of the cyclone chamber, the other end of said pipe being connected to the silencer (19) from which an outlet conduit (20) is taken which has optional, required length to free atmosphere.

2. An exhaust gas system as claimed in claim 1, characterized in that the outlet end (23) of the spiral as well as the inlet end (34) of the outlet pipe in the central area of the cyclone is situated in the lower half of the cyclone chamber (17) .

3. An exhaust gas system as claimed in claim 1 or 2, characterized in that the cyclone chamber (17) is cylindric- al in a manner known per se.

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