IE45602B1 - Process and pre-combustion installation for the burning of milled peat or similar materials - Google Patents

Abstract

A method and apparatus is disclosed for burning of fuel such as milled peat or the like. The peat and the combustion air are fed into a combustion chamber via tangential channels. The combustion cyclone also includes a liquid or gas nozzle for producing an auxiliary flame. According to the invention only the fastest-burning, dust-like and gaseous parts of the peat are burned in the combustion cyclone, at a temperature below the melting point of the ash. The flames from the cyclone are directed through a flame opening into a boiler furnace. The coarser parts of the peat are directed into a second combustion chamber wherein they are burned and from which the flames are directed through another flame opening into the boiler furnace. The advantage of the invention is in that the removal of the ash be controlled even when the dampness of the peat varies and in that the necessary pre-combustion installation is relatively inexpensive.

Description

The present invention relates to a process for burning milled peat or similar material in a pre-combustion installation in which a combustion cyclone is connected to the furnace of the boiler by a flame opening, the peat and the combustion air being fed into the combustion cyclone through tangential channels; in addition the combustion cyclone has a liquid or gas nozzle for an auxiliary flame. The invention also relates to a precombustion installation for carrying out the process, the installation comprising two combustion chambers of which the first one is a combustion cyclone connected to the furnace of the boiler.by a flame opening and, linked tangentially to the combustion cyclone, a feeding channel for the peat to be burned, a channel for the combustion air, as well as oil or gas nozzles for the auxiliary flame, and a channel for the looser parts of the fuel to be fed into the second combustion chamber.

It is a known method to burn milled peat, at a temperature above the melting point of the ashes, in the combustion cyclone of a pre-combustion installation operating in connection with a boiler installation and to remove the ash in a molten state.

It is also a known method to burn milled peat in a combustion cyclone of a pre-combustion installation operating in connection with a boiler installation, keeping the temperature so low that the ash can be withdrawn in a dry state.

The disadvantage of these known processes is the difficulty in controlling the temperature, owing to large variations in the dampness bf milled peat. When peat is burned at a high - 2 45603 temperature, occasional excessive dampness of the peat will cause a decrease in the temperature, solidification of the molten ash, and clogging of the cyclone. Also, a large-sized combustion cyclone must be constructed to tolerate these high temperatures, which makes it expensive. When peat is burned at a low temperature, occasional extreme dryness of the peat will cause an increase in the temperature, partial melting of the ash, and its solidification on the cyclone walls.

The object of the present invention is to develop further the process for burning milled peat or similar materials in precombustion installations so that the removal of the ash can be controlled even when the dampness of the peat varies, and that the necessary pre-combustion installation is moderately priced.

The invention therefore provides a process for burning milled peat or a similar material in a pre-combustion installation which comprises two combustion chambers in which the first chamber is a cyclone which is connected to the furnace of a boiler through a flame opening, the peat and the combustion air are fed into the combustion cyclone through tangential channels, and the combustion cyclone also has a liquid or gas nozzle for an auxiliary flame, wherein only the fastestburning dust-like and gaseous parts of the peat are burned in the combustion cyclone at a temperature below the melting point of the ash, and the flames are directed through the flame opening into the boiler furnace, and the coarser parts of the peat are directed into the second combustion chamber, in which they are burned and from which the flames are directed through another flame opening into the boiler furnace.

In the process according to the invention, under all conditions the temperature of the combustion cyclone can be kept so low that the ash will not melt. Such a combustion cyclone is moderately priced.

The second combustion chamber can be a combustion cyclone in which the temperature is kept above the melting point of the ash and the ash is removed in a molten state. The second combustion chamber can be provided with cooling pipes also, in which case .the combustion is not adiabatic, and.the ; temperature can be kept below the melting point of the ash and the ash is withdrawn in a dry state.

The attached drawing illustrates one. embodiment of the precombustion installation invented.for carrying out the process according to the invention; however, the invention is not limited to it, j- Fig,. 1 shows'a vertical'cross section of the pre-combustion 1 installation. Fig. 2 shows a cross section of the precombustion installation along A-A in Fig, 1, seen in the direction indicated by the arrows. Fig. 3 shows a cross section of the pre-combustion installation along 3-B in Fig. 1, seen in the direction indicated by the arrows.

The pre-combustion installation depicted has two combustion chambers, the first one of which is a first combustion cyclone 1 with a horizontal axis and below it a second combustion cyclone 2 which also has a horizontal axis. The first combustion cyclone 1 has an aperture 3, to which is linked - tangentially a feed channel 4, and an aperture 5,. to which is linked tangentially a branch 7 of the air channel 6. The first combustion cyclone 1 has an inner mantle 8 and an outer mantle 9, both made from steel plate. The second branch 12 of the air channel 6 is linked tangentially to the space 10 between the mantles. Between the branches 7 and 12 of the air channel there Is a regulating flap 13. The inner mantle 8 of the first combustion cyclone 1 has ah aperture IS, and a connecting channel 17 starting from this aperture IS leads through the. space lo and the outer mantle 9 to the second combustion cyclone 2, passing through its steel mantle 18 and its internal protective masonry 19 and joining it tangentially at the point 20. The connecting channel 22 starts from the space 10 between the mantles of the first combustion cyclone 1 and joins the - 4 45602 second combustion cyclone 2, also tangentially, at the point 23. The first combustion cyclone 1 has a flame opening 26, which leads through the boiler wall 27 to the furnace 28 of the boiler. Part of the mantle of the first combustion cyclone 1 consists of a secondary air channel 30, in which there is an opening 31 at the flame opening 26. The second combustion cyclone 2 has a flame opening 33 which leads to the boiler furnace 28. At the lowest point of the second combustion cyclone 2 there is an outlet 35 for the flow of molten ash.

The first combustion cyclone 1 has oil nozzles 40 and around them an air channel 41. The entire inner surface of the second combustion cyclone 2 is protected by masonry 19.

In a pre-combustion installation of the type described above, milled peat is burned by the process according to the invention as follows: Into the first combustion cyclone 1, which is pre-heated by the oil flame at the nozzle 40, peat is fed, carried by flue gas, through the channel 4, and combustion air is fed from the channel 6 through its branch 7, whereby the peat and the gases rotate in the first combustion cyclone 1, the peat heats up and dries, and its dust-like and gaseous parts ignite. The flame of the first combustion cyclone 1 passes through the flame opening 26 into the boiler furnace 28 and receives secondary air through the opening 31.

In the first combustion cyclone 1, the coarser parts of the peat are separated by centrifugal force to the periphery, while the gaseous and dust-like parts pass to the centre, carried by heating and expanding gases. The coarser parts of the peat pass, partly unburned, through the connecting channel 17 into the second combustion cyclone 2. Air flows from the air channel 6 through its branch 12 into the space between the mantles 8 and 9 of the first combustion cyclone 1, where it cools the inner mantle 8 of the first combustion cyclone 1 and itself is heated. The heated air flows along the connecting channel 22 tangentially into the second combustion cyclone 2 as - 5 45603 combustion air. In the second combustion cyclone 2 the coarser particles of the peat burn owing to the heated combustion ait at so high a temperature that the ash melts, flows through the outlet 35 and drips fown the vertical pipe 36 into cooling water, from where it is removed in a cooled state. The flame of the second combustion cyclone 2 passes through the flame opening 33 into the boiler furnace 28.

The burning of the peat is regulated so as to keep the temperature of the first combustion cyclone 1 always below the melting point of the ash and the temperature of the second combustion cyclone 2 above the melting point of the ash. The combustion is regulated by means of the total quantity of air, the quantity of secondary air, the regulating flap 13, and the auxiliary flame Of the oil nozzle 40.

A liquid or gas nozzle for an auxiliary flame can be added to the second combustion chamber 2 of the pre-combustion installation according to the invention and/or a secondary air channel can be fitted in connection with the flame opening 33.

The second combustion chamber need not necessarily be a second combustion cyclone but may be a combustion chamber with a fire bottom or. a so-called fluidized bed chamber.

Claims (9)

1. A process for burning milled peat or a similar material in a pre-combustion installation which comprises two combustion chambers in which the first chamber is a combustion cyclone which is connected to the furnace of a boiler through a flame opening, the peat and the combustion air are fed into the combustion cyclone through tangential channels, and the combustion cyclone also has a liquid or gas nozzle for an auxiliary flame, wherein only the fastest-burning dust-like and gaseous parts of the peat are burned in the conbustion cyclone at a temperature below the melting point of the ash, and the flames are directed through the flame opening into the boiler fornace, and the coarser parts of the peat are directed into the second combustion chamber, in which they are burned and from which the flames are directed through another flame opening into the boiler furnace.

2. A process as claimed in Claim 1, in. which the combustion air of the second combustion chamber is pre-heated in the space between an inner and outer mantle of the combustion cyclone, whereby this combustion air at the same time cools the inner mantle.

3. A process as claimed in Claim 1 or 2, in which through an aperture in the combustion cyclone, the coarser parts of the peat, forced to the periphery of the cyclone by centrifugal force, are separated from the expanding gases and dusts of the centripetal flow, which are directed in a burning state through the flame opening into the boiler furnace.

4. A process as claimed in any one of Claims 1 to 3 in which the coarser parts of the peat are burned in the second combustion chamber at a temperature above the melting point of the ash.

5. A pre“combustion installation intended for carrying out the process as claimed in any one of Claims 1 to 4 comprising - 7 45603 two combustion chambers, the first one of which is a' combustion cyclone connected to a boiler furnace by means of a flame opening, a feed channel for the peat to be burned and a combustion air channel, both linked tangentially to 5 the combustion cyclone, and oil or gas nozzles for an auxiliary flame, and the second combustion chamber, which is connected to the combustion cyclone by means of peat-feeding and combustion air channels, and to the boiler furnace by means of a second flame opening, has an ash outlet pipe. 10

6. A pre-combustion installation as claimed in Claim 5, in which the combustion cyclone has an inner and outer mantle having a space therebetween, and part of the combustion air has been arranged to be fed into the space between the mantles in order to cool the inner mantle and at the same time to 15 heat the combustion air that is to be fed into the second combustion chamber.

7. A pre-combustion installation as claimed in Claims 5 or 6 in which the second combustion chamber is a second combustion cyclone which has been provided with protective 20 masonry on the inside and the lowest point of which has an outlet for the flow of molten ash.

8. A process for burning milled peat as claimed in any of Claims 1 to 4 substantially herein described.

9. A pre-combustion installation as claimed in Claim 5 25 substantially as herein described with reference to or as illustrated in the accompanying drawings.