Method and apparatus for feeding fuel into a pressurized space

Abstract: The invention relates to a method and apparatus for feeding solid material into a pressurized combustion or gasification plant in stages. The feed apparatus (l0) is provided with an inlet (l8), sluice chamber (30), and outlet (20). In a loading stage, solid material is conveyed through the inlet into the sluice chamber. The loaded sluice chamber is transferred to an unloading stage. During the transfer stage, the inlet (l8) is closed, whereas during the unloading stage, solid material is conveyed through the outlet (20) into a pressurized space (26). The volume of the sluice chamber (30) is adjustable so that the volume is enlarged during the loading stage and reduced during the unloading stage. The volume is adjusted, for example, by a piston (38).

Description: The present invention relates to a method of feeding solid material into a pressurized space in a pressurized combustion or gasification plant according to the preamble of claim 1. The invention is especially suitable for feeding bio-fuel, such as bark and peat, into a pressurized space. It may also be employed in feeding of moist fuel. The invention also relates to an apparatus for feeding solid material in a pressurized combustion or gasification plant from an inlet channel into a pressurized channel according to the preamble of claim 12. A method and an apparatus respectively according to the preambles of claims 1 and 12 is known from US-A-4 037 736. This document describes a solids feeder having feed cylinders respectively provided with pistons. The feed cylinders are filled from either of two feed chutes arranged on both sides of a solids upflow vessel which is to be fed with the solids material. The feed cylinders are arranged on a reciprocating carriage positioned below the solids upflow vessel. In pressurized combustion or gasification plants, fuel and other material to be possibly introduced into the combustion chamber have to be fed from atmospheric pressure of a storage container to a state of high pressure. The pressure of the combustion chamber varies from 5 to 100 bar. Conventional feeding means fail in such feeding. Fuel may be introduced into a pressurized space by means of a briquette press. However, the briquettes have to be crushed, for example, with a grinder before they reach the combustion or gasification stage. The briquettes easily become too hard, which impedes the grinding. Furthermore, the electric power consumption of the briquette press is high. The best-known and most common way of feeding fuel into a pressurized space is feeding with a pressurized rotary feeder. The rotary feeders, however, involve certain problems; namely poor tightness, risk of arching, and restrictions on the pressure to be achieved with the feeders. In rotary feeders, the sluice chamber is alternately connected to a fuel storage container and a pressurized fuel chamber. The pressurized space is supplied with fuel and the fuel amount dosed at a time corresponds to the volume of the sluice chamber. To secure the fuel feed, the sluice chamber has to be relatively large, which raises the cost of the equipment. In rotary feeders, e.g. pocket feeders, the infeed material easily arches. In such cases, poor emptying of the pocket constitutes a problem when the feeder moves to a discharge position. Similar problems with arching and uneven emptying of the silo have been experienced with storage silos. Empty pockets of rotary feeders always convey some pressurized gas out of the system, handling of such gas being difficult. Furthermore, as the loss of pressurized gas easily becomes great, this leads to an increase in the cost of pressurization. It is important that the feeders are tight. Feeding of fuel into a pressurized space has to be facilitated without any pressure being released or harmful gases being leaked out through the feeder. Light or loose fuel, e.g. in screw feeders, is not capable of forming a tight barrier against hot gases escaping from a pressurized space. Thus, such gases possibly flowing back may ignite the fuel already in the fuel silo. By plug screw feeders, fuel may be compressed to some extent so as to facilitate feeding of fuel to a pressure of about 4 bar. In plug screw feeders, the fuel may, however, form a plug which partly or completely clogs the feeding means. If the material to be fed is e.g. peat, the moisture content of which is higher than 65 %, no plug is formed, but the material is decomposed and the feeding fails. Feeding to a pressure in excess of 10 bar by means of a plug screw is unsuccessful even though the fuel is dryer. If the moisture of, for example, milled peat is about 50 to 75 %, feeding thereof to a pressurized combustion or gasification chamber by earlier known means is unsuccessful. The electric power consumption of the plug screw is also high. Finnish patent application 864545 teaches a pneumatic transport system for feeding fuel into a pressurized space. The feeding means comprises an enclosed vessel with a rotor and at least one funnel-shaped material chamber disposed in said vessel. The rotor is movable with a drive means. The upper section of the vessel and rotor is provided with a fuel inlet and the lower section with a fuel outlet. Fuel is discharged from the material chamber by means of pressurized gas. For that purpose, pressurized gas is supplied to the outlet duct of the material chamber. Fuel easily arches in funnel-shaped material chambers. Arching prevents complete emptying of the material chamber, thereby causing uneven fuel feed. Some pressurized gas remains in the material chamber after the fuel has been discharged therefrom. Even though the pressurized gas is discharged, some of this gas remains in the material chamber and, in refilling, such gas is harmful as it may prevent even distribution of the fuel in the material chamber. An object of the present invention is to provide an improved method and apparatus for feeding solid material into a pressurized space. Another object of the invention is to provide a method and apparatus for feeding solid material into a pressurized space also when the pressure difference is great. An object is to provide a method of feeding also moist solids. A further object of the invention is to provide a method and apparatus for introducing also loose fuel, such as peat or other bio-fuel, into a pressurized space. A still further object of the invention is to provide an improved feed apparatus where feed-disturbing arching phenomenon has been eliminated or minimized. These objects are solved according to the present invention by a method and an apparatus respectively having the features of claim 1 and claim 12. In accordance with a preferred embodiment of the invention, the feed apparatus comprises two cylindrical sluice chambers disposed in a cylindrical vessel. Both cylindrical sluice chambers are disposed at equal distances from the center of the vessel encasing the sluice chamber. As the vessel rotates around its center, both sluice chambers thus move at equal distances from the center of the vessel. The invention is also suitable for a feed apparatus in which more than two sluice chambers are disposed in a vessel. However, the number of sluice chambers is preferably even, said sluice chambers being disposed in pairs at equal distances from the axis of the vessel. When one sluice chamber is being filled, the other is being emptied at the same time, the opening of the sluice chamber alternately communicating with an inlet and an outlet. In accordance with a preferred embodiment of the invention, the piston having substantially the same diameter as the inner diameter of the cylinder is in the beginning of the loading stage pushed in the cylinder in its utmost position so that the volume of the sluice chamber is at its minimum and practically nonexistent. During the loading stage, the piston moves in the cylinder so as to enlarge the volume of the sluice chamber. The piston contributes to the filling of the sluice chamber with solid material by causing a suction effect from the inlet channel to the sluice chamber. Preferably, the sluice chambers are disposed vertically within the vessel so that gravity also contributes to the filling of the sluice chamber with solid material. As soon as the sluice chamber has been filled with a suitable amount of solid material, the vessel moves around its axis, for example 180°. A smaller or larger movement is also possible, depending on the ratio of the cross surface of the sluice chamber to the cross surface of the vessel. The rotational movement is preferably so long that during that movement, the pressure in the sluice chamber may be raised by pressure feeding means substantially to the level of or higher than the pressure of the pressure channel. During the rotational movement, the sluice chamber opening is closed, sliding tightly along the covering plate. The sluice chamber opening has to be closed so as to prevent gas or solid material from escaping from the sluice chamber. The rotational movement of the vessel ends as soon as the sluice chamber opening reaches the outlet in the covering plate. During the unloading of the sluice chamber, the piston moves within the cylinder towards the outlet, the solid material simultaneously being conveyed from the sluice chamber to the pressure channel. Transfer of the solid material may be brought about by either the piston effect or by raising the pressure in the sluice chamber higher than that in the pressure channel, or by their mutual effect. A great advantage of the method and apparatus according to the invention is that either peat or some other light bio-fuel may be fed into a pressurized, fluidized bed gasifier or combustion plant. Feeding is undisturbed even if the pressure difference is high, i.e. over 4 bar or even over 20 bar. The method according to the invention is suitable e.g. when feeding fuel to a pressurized combustion plant or a gasifier. In the feeding method in accordance with the invention, the risk of arching of the fuel is eliminated or minimized because the volume of the sluice chamber is changed, thus bringing about movement of the fuel. In the feeding method and apparatus, caking of the fuel does not occur, which is important as to further treatment of the fuel. It is, of course, important that the covering plate secures the tightness of the sluice chamber during the feed. Solid material cannot escape from the feed system. Neither hot nor poisonous gases leak backwards from the pressurized space, for example, to the space filled with fuel. In conventional pressurizing systems for solid fuels, such as Lock-hopper equipment and rotary feeders, it is typical that gas leaks from the pressure side to such an extent that it affects the process yield. The leak has to be compensated by feeding a corresponding amount of gas to the pressurized space by a gas compressor. If the gas to be replaced is, for example, nitrogen, as is usual in connection with gasifying processes, the cost incurred may be considerable. In connection with an apparatus according to the invention, such leak is very small because gas leaks occur practically through sealing means only. The invention will be described below in more detail, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a schematic sectional view of a feed apparatus according to the invention during the loading and unloading stage, and Fig. 2 is a schematic sectional view of the same feed apparatus during the transfer stage. A feed apparatus 10 disclosed in Fig. 1 comprises a movable section 12 and a stationary section 14. The stationary section includes a covering plate 16 provided with an inlet 18 and an outlet 20. The inlet is connected to a feeding section, i.e. an inlet channel 22 for solid material. The feeding section is supplied with solid material by means of fuel feeders, for example, a screw 24. The outlet is connected with a pressure channel 26 at the discharge side of the feed apparatus, said pressure channel being in communication with a fuel silo, which is not disclosed. The movable section comprises a cylindrical vessel 28 wherein two cylindrical sluice chambers 30 and 32 are disposed. Other embodiments may include more than two sluice chambers. The upper sections of the sluice chambers are provided with openings 34 and 36. The movable section also includes pistons 38 and 40 and drive cylinders 42 for the pistons. The covering plate 16 serves as an end plate for the vessel 28. In the feeding stage, as shown in Fig. 1, the opening 34 of the sluice chamber 30 is in communication with the inlet 18 in the covering plate. The opening 36 of the sluice chamber 32 is in communication with the outlet 20. The sluice chambers are provided with pistons 38 and 40. In chamber 30, which is filled with fuel, such as peat, the piston 38 lies in its lowest position. In the chamber 32, which has been emptied, the piston 40 lies in its topmost position. The pistons are moved by hydraulic cylinders 42. As soon as the sluice chamber 30 has been filled and the sluice chamber 32 has been emptied, the movable section is rotated around its axis so as to shift the opening 34 of the sluice chamber from the inlet 18 to the outlet 20. Correspondingly, the opening 36 of the sluice chamber is shifted to the inlet 18. The movement of the movable section is brought about by drive means 44. The drive means is connected to the upper section of the vessel through the covering plate by section 46 comprising bearing, clamping and lubrication means. Fig. 2 illustrates a sluice chamber moving from the loading stage from the inlet to the outlet. In that stage, both sluice chamber openings 34 and 36 are closed. The covering plate is tightly positioned on the vessel so as to completely close the openings of the sluice chambers, which openings slide when the vessel moves along the surface of the covering plate. In the embodiment of the example, the loading and unloading of the sluice chamber may be arranged so as to take place in appr. 5 seconds and the shifting of the sluice chamber from one stage to another in appr. 2 seconds. During the transfer stage, pressure is raised in the sluice chamber 30, for example, by compressed air or nitrogen by opening the valves 48, 50 and 52. The pressure valves, e.g. solenoid valves, may be arranged in the feed apparatus so as to raise the pressure in the sluice chamber merely during the transfer stage when the opening of the sluice chamber is closed. The pressure valves may also be so disposed as not to effect the final pressurization over the pressure of the pressure channel until the sluice chamber is in communication with the pressure channel. However, the pressure prevailing in the sluice chamber has to be high enough at the outlet so as to prevent gases from flowing backwards from the pressure channel to the sluice chamber to such an extent that it would be harmful. In the embodiment of the Figs, the vessel rotates 180° during the loading and unloading stages. Thus, the cylindrical chambers 30 and 32 change places with respect to the inlet and the outlet. When the vessel has rotated 180° and reached an end position, the pistons will move simultaneously in different directions. In one sluice chamber, the piston moves downwards and the chamber becomes filled with fuel. In the other chamber, the piston moves upwards and the chamber becomes unloaded. When the drive means 44 restarts the 180° movement, the solenoid valves 48-52 will open allowing some air or other gas flow into the chamber which has been filled with fuel. The solenoid valves are not opened until the sluice'chamber no longer is in connection with the fuel feeding means, i.e. the inlet channel 22. By means of the gas flowing through the solenoid valve, the cylinder is pressurized to the same pressure as prevails in the pressure channel 26. This prevents pressure strokes when the rotating movement causes the sluice chamber 30, loaded with fuel, to come into contact with the pressure duct 26. The gas flows into the sluice chamber through one or more valves. If the number of sluice chambers is greater than 2, the rotary movement of the vessel correspondingly changes so that each loaded sluice chamber is shifted to come into contact with the outlet and each unloaded chamber is correspondingly shifted to come into contact with the inlet. During the transfer stage, the pressure of the fuel-loaded sluice chambers has to be raised to a suitable level. The Figs 1 and 2 illustrate a preferred embodiment, in which the feed apparatus is vertical. The position of the feed apparatus may also be inclined, whereby the gravity causes the fuel to flow onto the bottom of the cylindrical chambers. In some cases, the chambers may be even horizontal, in which case e.g. forced feed has to be used for loading thereof. Vessel 28 is preferably in the shape of a large cylinder, but it may as well be in some other shape. It is essential that the sluice chambers disposed in the vessel are capable of moving with respect to the inlets and outlets. It is essential that the filled sluice chamber is in connection with the outlet and the empty sluice chamber in connection with the inlet. In the embodiment shown in the Figs, the sluice chambers are cylindrical. They may, of course, be in some other shape as well. It is essential that a piston or some other means adjusting the volume of the sluice chamber can be used in loading or unloading thereof. In accordance with the invention, the volume of the sluice chamber is kept small as the loading stage starts and is gradually increased during the filling of the sluice chamber. This prevents excess air from entering the sluice chamber. The excess air flows from the sluice chamber to the process. Uncontrollable excess air is disadvantageous in view of further processing. The invention is not intended to be limited to the embodiments described above, but it can be modified and applied within the inventive scope as defined in the accompanying claims.

Claims: A method of feeding solid material into a pressurized space in a combustion or gasification plant in stages and by means of a feed apparatus comprising an inlet, at least two sluice chambers and an outlet in such a manner that in the loading stage solid material is conveyed from an inlet channel via the inlet into one of the at least two sluice chambers, in a first transfer stage, the at least two sluice chambers are shifted with respect to the inlet and the outlet, in an unloading stage, solid material is conveyed from the one of the at least two sluice chambers via the outlet into a pressure channel, in a second transfer stage, the at least two sluice chambers are shifted with respect to the inlet and the outlet, and the chamber volume of the one of the at least two sluice chambers is enlarged during the loading stage and reduced during the unloading stage, characterized in that the at least two sluice chambers are shifted by rotating these about an axis during the transfer stages. A method as claimed in claim 1, characterized in that the chamber volume of at least the one of the at least two sluice chambers is enlarged and reduced by moving a piston therein. A method as claimed in claim 1, characterized in that one sluice chamber of the at least two sluice chambers is being emptied simultaneously with the filling of another of the at least two sluice chambers in the feed apparatus. A method as claimed in claim 2, characterized in that fuel is drawn into a sluice chamber from the inlet channel by moving the piston towards the bottom of the sluice chamber. A method as claimed in claim 2, characterized in that fuel is discharged from a sluice chamber through the outlet by pushing the piston towards an opening at the end of the sluice chamber. A method as claimed in claim 1, characterized in that pressure is raised in at least the one of the at least two sluice chambers during the first transfer stage by means of pressurized gas, for example, air or nitrogen. A method as claimed in claim 6, characterized in that fuel is both fed into and discharged from at least the one of the at least two sluice chambers through the upper section thereof. A method as claimed in claim 1, characterized in that fuel is both fed into and discharged from the one of the at least two sluice chambers through the upper section thereof. A method as claimed in claim 1, characterized in that fuel is introduced into a pressurized fluidized bed reactor by the feed apparatus. A method as claimed in claim 1, characterized in that peat or other bio-fuel is introduced into a pressurized gasifier or combustion plant by the feed apparatus. A method as claimed in claim 1, characterized in that a vessel comprising two sluice chambers is rotated 180° around its axis during the transfer stages. A feed apparatus in a pressurized combustion or gasification plant for introducing solid material from an inlet channel into a pressurized channel, said feed apparatus comprising a vessel, a stationary covering plate, positioned on an end wall of the vessel and having at least one inlet communicating with the inlet channel, and/or one outlet communicating with the pressure channel, at least two sluice chambers disposed in the vessel, wherein a tight connection is provided between an opening of the respective sluice chamber and the covering. plate, and a piston respectively associated with each of the at least two sluice chambers to adjust the chamber volume of the associated sluice chamber, characterized in that the vessel is rotatable about its axis. A feed apparatus as claimed in claim 12, characterized in that during the loading stage of a sluice chamber, the opening thereof is in tight connection with the inlet of the covering plate. A feed apparatus as claimed in claim 12, characterized in that during the unloading stage of a sluice chamber, the opening thereof is in tight connection with the outlet of the covering plate. A feed apparatus as claimed in claim 13, characterized in that during rotation of the vessel the opening of a sluice chamber is in tight connection with the covering plate in such a manner that the loaded sluice chamber is closed. A feed apparatus as claimed in claim 12, characterized in that the covering plate is provided with both an inlet and an outlet and that the at least two sluice chambers are so disposed in the vessel that, when one sluice chamber is in contact with the inlet, another sluice chamber is in contact with the outlet. A feed apparatus as claimed in claim 13, characterized in that the vessel is arranged with feeding means for pressurized gas, said feeding means being capable of raising the pressure of the loaded sluice chamber. A feed apparatus as claimed in claim 12, charactered in that the vessel is in the shape of a vertical cylinder and that the at least two sluice chambers are cylindrical in shape and vertically disposed in the vessel.

Inventors: ARPALAHTI OLLI, NIEMINEN JORMA, ARPALAHTI, OLLI, NIEMINEN, JORMA
Applicants: AHLSTROEM OY, A. AHLSTROM CORPORATION
Application year: 1990
Main classification: B01J3
IPC codes: B01J3, F23K3, F23B90, F23B99, B65G47, C10J3, B01J8, B65G49, C10B53