Method and device for feeding particulate material into a pressurized container

A method of feeding particulate material into a pressurized fluidized bed combustor including the steps of: feeding the particulate material from a source which is at a substantially lower pressure than that existing in the pressurized fluidized bed combustor into the upper end of an elongate, generally vertical gravity feed conduit constructed to have an inner bore which is substantially smaller at its lower end than at its upper end, and selecting the vertical height of the feed conduit and the extent of reduction in its bore over its length to ensure that the particulate material will move by gravity between the open input end of the conduit and the pressurized fluidized bed combustor notwithstanding the difference in pressure between the pressurized combustor and at the input end of the conduit.

TECHNICAL FIELD 
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. 
BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
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.