PULSE COMBUSTION BOILER

Abstract: The object of the invention is a pulse combustion boiler, which includes an essentially vertical combustion tube (1), a compensation chamber (2) at its lower end, a grate (7) in the lower part of the combustion tube, fuel feed devices (12, 13, 14) for feeding fuel to the grate (7), combustion air feed devices (21, 25), and one or more heat exchange surfaces (23) for recovering the heat produced by the boiler. The boiler includes an upper compensation chamber (1) at its upper end and after this in the direction of flow a separator (15) for separating the unburnt particles. The solid particle outlet connection (16) is connected by means of a return line (19) to above the grate (7) of the combustion tube (1) in order to burn the unburnt residue and thus to reduce losses.

Description: PULSE COMBUSTION BOILER The object of the invention is a pulse combustion boiler, which includes an essentially vertical combustion tube, a compensation chamber at its lower end, a grate in the lower part of the combustion tube, fuel feed devices for feeding fuel to the grate, combustion air feed devices, and one or more heat ex¬ change surfaces for recovering the head produced by the boiler. A pulse combustion boiler of the type referred to in the intro¬ duction is presented in the congress publication ENCIT 90 VOL II, Itapema 10. - 12.12.1990, pp. 761 - 766; Ferreira et al.. Advantages of a pulse combustion boiler that can be mentioned are a very high grate loading (4,2 - 5,1 M /m 2 ) and a small excess amount of air, both of which advantages are principally due to acoustic vibration material and heat transfer, as well as to the improved gas mixing effect. There are still further advantages in using the pulse combustion system. This type of boiler is especially suitable for solid fuels. In the original Rijke type of pulse combustion boiler a compen¬ sation chamber, through which air too is fed to the combustion tube, is used at the base of the combustion tube. This type of channel construction naturally gives rise to a vibrating flame front, with a typical frequency of 50 - 100 Hz. The grate is located in the lower part of the combustion tube and fuel is fed from a connection above the grate. Despite effective mixing unburnt material also leaves with the flue gases, which weakens the efficiency of the boiler. The intention of this invention is to improve the efficiency of present pulse combustion boilers. The characteristics of a boiler in accordance with the invention are presented in the accompanying Patent Claims. The invention is, to a great extent, based on the observation that it is also possible to arrange a compensation chamber with possible heat surfaces at the upper end of the combustion tube, from which the flue gases are directed to a separator in order to remove unburnt particles and return them along a suitable return line to the combustion tube. The pressure los caused by this arrangement has not been shown to disturb the pulsing of the combustion. The efficiency of the boiler can be made very high and is required normal ash can be separated by means of a flue gas cleaner, e.g. a multicyclone, connected to the flue gas line after a separate rotation sepa¬ rator, especially to separate fly ash. Other advantages and forms of application of the invention appear from the examples of application presented later. In what follows the invention is illustrated by reference to the accompanying Figure, which shows one circulating pulse combus¬ tion boiler in accordance with the invention. In accordance with the known technique the pulse combustion boiler includes first of all a combustion tube 1, a compensation chamber at the foot of this, fuel feed devices 12, 13, and 14, a grate, and air feed devices 21 and 25. In addition to these, the boiler includes an upper compensation chamber 3, a separator 15 in the form of a cyclone connected to this by channel 24, and a return line 19 from this leading the unburnt particles back to the combustion tube. Here the combustion tube 1 is covered with a water jacket 4, which includes water inlet and outlet connections 5 and 6. When burning fuel with a low thermal value the combustion tube can be surrounded by masonry. Fuel is poured into silo 11, which leads to tube 12, from which feed device 13 regulates the fuel to be led through pipe 14 to the combustion tube above grate 7. Grate 7 is formed by a perforated surface and above it additional mixing wings 8 are used, which are rotated by motor 9 located in compensation chamber 2. Cone 10 is used as protection for the motor. Naturally, it is possible to locate the motor elsewhere as well. The fan 25 pushes air through channel 21 to the compen- sation chamber 2, through which the air is led to the combustion tube 1. It is advantageous to install heat surfaces 23 in the upper compensation chamber 3, by means of which the heat produced by the boiler can be led out, together with any possible heat that has transferred to the water jacket 4 of the combustion tube 1. Channel 24 leads from the compensation chamber 3 and forms a small pressure loss in order to stabilize conditions in the system formed by compensation chambers 2 and 3 and combustion tube 1, as well as to increase the velocity of flow when par¬ ticles are led to cyclone 15. A conventional flue gas cleaner, e.g. a multicylone or any suitable separator whatever for fly ash and other emissions, can be connected to flue gas connection 17. Return line 19 is connected to the solid particle outlet connec¬ tion 16. The return channel includes a sampling and rotating mass removal device 20, which in normal operation is switched off and permits a free flow of particles along the return line 19 to the combustion tube 1. At the beginning of return line 19 it is possible to use air blowing with the aid of blow tube 18, which by means of an ejector effect creates the necessary pressure in the return line 19 in relation to combustion tube 1. It is advantageous to use e.g. a shut-off feed in the return line 19 after separator 15, with the aid of which it is easier to create a pressure equilibrium. A shut-off feed of this kind is shown schematically in Figure 1 by the reference number 29. In the example in Figure 1 the upper compensation chamber is equipped with heat exchange surfaces. In certain cases the operation is more stable when separate intermediate chambers are used, in which the heat exchange surfaces are installed.

Claims: Patent Claims 1. A pulse combustion boiler, which includes an essen¬ tially vertical combustion tube (1) , a compensation chamber (2) at its lower end, a grate (7) in the lower part of the combus¬ tion tube, fuel feed devices (12, 13, 14) for feeding fuel to the grate (7) , combustion air feed devices (21, 25) , and one or more heat exchange surfaces (23) for recovering the head pro¬ duced by the boiler, characterized in that the boiler includes an upper compensation chamber (1) at its upper end and after this in the direction of flow a separator (15) for separating the unburnt particles and the solid particle outlet connection (16) of which is connected by means of a return line (19) to above the grate (7) of the combustion tube (1) in order to burn the unburnt residue and thus to reduce losses. 2. A pulse combustion boiler in accordance with Patent Claim 1, characterized in that the combustion tube (1) is circular in cross-section. 3. A pulse combustion boiler in accordance with Patent Claim 1, characterized in that the separator (15) is a cyclone. 4. A pulse combustion boiler in accordance with Patent Claim 1, characterized in that the return line (19) of the separator (15) includes an auxilliary separator (20) for the taking of occasional samples and/or the removal of circulating material. 5. A pulse combustion boiler in accordance with any of Patent Claims 1 - 4, characterized in that at least one heat exchange surface (23) is located in the upper compensation chamber (3) . 6. A pulse combustion boiler in accordance with any of Patent Claims 1 - 5, characterized in that it includes rotatable mixing wings (8) above the grate (7) . 7. A pulse combustion boiler in accordance with any of Patent Claims 1 - 6, characterized in that the inner surface of the combustion tube is of masonry. 8. A pulse combustion boiler in accordance with any of Patent Claims 1 - 6, characterized in that there is a cooling jacket (4) around the combustion tube (1) . 9. A pulse combustion boiler in accordance with any of Patent Claims 1 - 4, characterized in that there is an inter¬ mediate chamber equipped with a heat exchange surface between the upper compensation chamber and the separator. 10. A pulse combustion boiler in accordance with any of Patent Claims 1 - 4, characterized in that after the cir¬ culation separator (15) the flue gas line includes an ash separator, for example a cyclone, for removing solid matter from the flue gases. 11. A pulse combustion boiler in accordance with any of Patent Claims 1 - 4, characterized in that in the return line (19) after the circulation separator (15) there is a shut-off feed to maintain the pressure equilibrium.

Inventors: BRESSAN CLAUDIO, DE CARVALHO JOAO ANDRADE JR, FERREIRA MARCO AURELIO, HEISKANEN VELI-PEKKA, ORJALA MARKKU, BRESSAN, CLAUDIO, DE CARVALHO, JOAO, ANDRADE, JR., FERREIRA, MARCO, AURELIO, HEISKANEN, VELI-PEKKA, ORJALA, MARKKU
Applicants: BRESSAN CLAUDIO, CARVALHO JOAO ANDRADE JR DE, FERREIRA MARCO AURELIO, HEISKANEN VELI PEKKA, ORJALA MARKKU, VALTION TEKNILLINEN, BRESSAN, CLAUDIO, DE CARVALHO, JOAO, ANDRADE, JR., FERREIRA, MARCO, AURELIO, HEISKANEN, VELI-PEKKA, ORJALA, MARKKU, VALTION TEKNILLINEN TUTKIMUSKESKUS/PLT
Application year: 1993
Main classification: F23B7