Method and Device for Feeding Particulate Material Into a Pressurized Container

The present invention relates to a method and equipment for feeding particulate material into a pressurized container. Preferably, the particulate material is fed from a container which is arranged at a lower pressure, for example from a container at atmospheric pressure, into a pressurized container. The invention primarily relates to the feeding of particulate fuel and/or particulate bed material to a combustor arranged in the form of a fluidized bed.

The feeding and handling of particulate material, in the form of bed material and fuel, which is supplied to a combustor, in the form of a pressurized fluidized bed, present difficult problems and are achieved with present-day technique by mixing the particulate material with water and pumping in the material in the form of a paste, or by pneumatic transport of particulate material. In the latter case, according to known technique, a feeding system in the form of a locking system is used, which comprises valves and intermediate containers, a so-called lock-hopper system.

In a PFBC (Pressurized Fluidized Bed Combustion) power plant the fluidized bed may operate at a pressure of the order of magnitude of 20 bar, and therefore a feeding system comprising valves is exposed to great stresses resulting in a rapid deterioration of the sealing capacity of the valves. The service life becomes short and the maintenance costs become high.

One object of the invention is to provide a simplified feeding system without valves and with low service requirement for feeding of particulate material into a pressurized container. One further object of the invention is to provide a feeding system with an even flow of material.

Accordingly, the invention relates to a method and a device for feeding particulate material into a pressurized container wherein the material is adapted to be transferred from a container arranged at a lower pressure to a pressurized container. According to the invention, this is achieved in a simplified way by feeding the particulate material into the pressurized container via a preferably vertical pipe with a large length/diameter ratio. This pipe is adapted to interconnect the containers and the length/diameter ratio of the pipe is adapted according to the invention such that a material column is built up in the pipe, whereby the pressure drop across the material column maintains the pressure difference between the containers while at the same time a leakage flow of gas flows through the material column. The leakage flow is adapted such that the transport of particulate material is directed downwards into the pressurized container.

In one embodiment of the invention, the length/diameter ratio of the above-mentioned pipe is adapted to be between 50 and 100.

To avoid fluidization of the particulate material in the container arranged at a lower pressure, in a further embodiment of this invention the lower part of this container is arranged with a downwardly decreasing cross-section area. Preferably, the lower part of this container is arranged in the form of one or more cone-shaped sections with intermediate cylindrical sections. To avoid dusting when filling this container, a fan is arranged to create a sub-atmospheric pressure in the container in relation to the surroundings, this fan suitably being combined with a filtering device.

According to a further embodiment of the invention, the pressurized container is adapted to comprise

at least one dispensing device, preferably in the form of a rotary feeder, the dispensing device being adapted to supply a pressurized combustor with particulate material through at least one feed conduit, and

an inlet part adapted to distribute particulate material to the dispensing device.

The invention will be described in more detail in the following with reference to the accompanying figures in which FIG. 1 shows the feeding of particulate material into a pressurized container according to the present invention, and

FIG. 2 shows the invention applied to the feeding of particulate fuel and/or bed material in a plant for combustion in a pressurized fluidized bed.

The feeding of particulate material into a pressurized container according to the invention is shown in FIG. 1. Particulate material is transferred from a container 1, arranged at a lower pressure, to the pressurized container 2 by feeding particulate material into the pressurized container 2 via a preferably vertical pipe 3 with a large length/diameter ratio. The containers 1, 2 are inter-connected by the vertical pipe 3 which is arranged with a length/diameter ratio adapted such that a column 4 of material is built up in the pipe 3. The pressure drop which then arises across the material column 4 maintains the pressure difference between the containers 1, 2 while at the same time a leakage flow of gas flows through the material column 4. The leakage flow is adapted so as not to fluidize the particulate material in the container 1 while at the same time the transport of particulate material into the pressurized container 2 is maintained through the pipe 3. The leakage flow of gas through the material column 4 is adapted by varying the grain size distribution of the particulate material as well as the length/diameter ratio of the pipe 3, and the like.

To avoid fluidization of the particulate material in the container 1 arranged at a lower pressure, the lower part of the container 1 is formed with a downwardly-decreasing cross-section area. Preferably, the lower part of the container 1 is arranged in the form of one or more cone-shaped sections with intermediate cylindrical sections. To avoid dusting when filling the container 1, as shown in FIG. 2 a fan 105 can be arranged to create a sub-atmospheric pressure in the container in relation to the surroundings. The fan is suitably supplemented by a filtering device 111. Particulate material is supplied to the container 1 arranged at a lower pressure by means of known technique, in FIG. 2 exemplified by a conveyor belt 106. Particulate material can be continuously supplied to the container 1 arranged at a lower pressure, or be controlled by means of a level relay provided in the container to prevent the container 1 from being emptied of material.

FIG. 2 schematically shows the present invention as applied to the feeding of particulate fuel and/or bed material into a combustor included in a PFBC (Pressurized Fluidized Bed Combustion) power plant, where the combustion takes place at a pressure considerably exceeding the atmospheric pressure, preferably at a pressure of 10-20 bar. In FIG. 2, a combustor 110 is placed inside a pressure vessel 112. The space 113 is supplied with compressed combustion air from a compressor (not shown) via the conduit 114. The combustor 110 contains a fluidizable bed of particulate material 116, in which a fuel is burnt. The combustor 110 also includes tubes 118 for generating steam for a steam turbine (not shown) and for cooling the bed 116. Combustion gases leaving the bed 116 are collected in the freeboard 120, are passed in the conduit 122 to a cleaning plant 124, symbolized by a cyclone 124, where dust is separated. The combustion gases are passed further from the cyclone 124 via a conduit 126 to a gas turbine (not shown). Separated dust is discharged from the cyclone 124 via the conduit 128 to an ash discharge and pressure-reducing system. The combustor 110 is supplied with air from the space 113 via nozzles 138 for fluidization of the material in the bed 116 and combustion of fuel supplied to the bed. Particulate fuel and bed material, which are supplied to the combustor 110 through pneumatic transport conduits 130 and nozzles 131, are fed into the plant while utilizing the present invention, whereby particulate material is supplied to the container 101, arranged at atmospheric pressure, by means of known technique, in the figure exemplified by a conveyor belt 106. Particulate material can be continuously supplied to the atmospheric container 101 or be controlled by means of a level monitor, provided in the container 101, to prevent the container 101 from being emptied of material. To prevent dusting when filling the container 101, a fan 105 is arranged to create a sub-atmospheric pressure in the container relative to the environment. The fan is suitably supplemented by a filtering device 111. The particulate material is transferred from the atmospheric container 101 to a pressurized container 102 via a long, preferably vertical pipe 103 with a length/diameter ratio of between 50 and 100. The pipe 103 interconnects the containers 101, 102 and the length/diameter ratio is adapted such that a material column 104 is built up. The pressure drop thus arising across the material column 104 maintains the pressure difference between the containers 101, 102 while at the same time a leakage flow of gas flows upwards through the material column 104. The leakage flow is adapted such that the transport of particulate material through the pipe 103 is directed downwards into the pressurized container 102. The pressurized container 102 is designed to distribute particulate material between rotary feeders 107, which are adapted to control the supply of particulate material to the pressurized combustor 110 through the pneumatic feed conduits 130. The pneumatic transport conduits 130 are supplied with transport gas which is extracted from the space 113, is pressurized further in the compressor 108, and is distributed individually between the transport conduits 130 through the throttle means 109. The transport gas in the feed conduits 130 may also be pressurized air, which is used for combustion in the fluidized bed of supplied fuel, but may also be other gases or gas mixtures. Inert transport gas is required for feeding reaction-prone, for example easily ignited, powder materials.