Dry mechanical conveyor plant for pyrites and coal dust

The present invention is about a conveyor plant for pyrites, other foreign materials like metal parts and occasionally ground solid fossil fuel, coming from the grinding mills of the solid fossil fuel, substantially comprising an open or enclosed metal container (1) inside which a metal conveyor belt (6) is disposed. The conveyor receives the material to be conveyed from the pyrites storage tanks (2) of each mill, through interception valves (3) and vibrating feeders (4) or directly from gravity discharge channels. Any spontaneous ignition of the conveyed material is controlled by a putting out system with water nozzles (17) or inert gas or steam admission nozzles (18) according to the plant configurations. The pyrites and the ground solid fossil fuel are collected in a stockage silo (16), it too provided with an inert gas or steam putting out system. For the storage tanks (2) a gas or steam inertization system is provided as well.

The present invention is about a conveyor plant for pyrites, mixed with other foreign materials and occasionally with coal dust coming from the mills for pulverizing solid fossil fuel, able to safely convey these hot materials flammable by spontaneous ignition.

Steam generators fed with solid fossil fuel, such as coal or lignite, require the fuel to be reduced at a predetermined fineness with the purpose to optimize the combustion in the boiler and to increase the energetic efficiency. The pulverization takes place in grinding plants where, by impacts, compression and friction of the mechanical members belonging to the mill grinding assembly, the coal is reduced to the desired granulometry. Then, the so obtained coal dust is conveyed to the boiler through pneumatic conveyors and burners.

In the prior art technique, the foreign and heavier materials present in the coal, such as pyrites, are ejected by centrifugal force from the mill grinding path and they are conveyed, together with a variable quantity of coal dust, to a storage area using hydraulic conveyor systems, in order to avoid the risk of fire or explosions for spontaneous ignition of the coal dust. The amount of coal dust is dependent from the kind of used mills, from the wear of the mechanical members forming the grinding assembly and from any malfunctioning.

The hydraulic systems, as well as uselessly consuming water and polluting it with the coal, have some limits in the conveyance of foreign metal pieces, normally present in the coal, and with the material size. To overcome these limits, grids at the entrance of the system for riddling the material are used, with consequent obstructions due to the need to manually clean said grids.

At present, vacuum pneumatic conveyors are also used, but they have a considerable limit consisting of the material size and the presence of iron pieces, which cause frequent obstructions.

Open rubber conveyor belts have been seldom used, collecting the pyrites from the mills, but, in case of spontaneous ignition of the coal, they can catch fire with flame spreading and catastrophic consequences.

The conveyor plant being object of the present invention removes the previously illustrated problems, since it provides for the use of a high temperature resistant metal conveyor belt able to convey the pyrites and the coal dust mixture with a minimum dust dispersion in the environment. The plant is provided with sensors able to detect any combustion and to activate a proper putting out system. The conveyor plant consists of an open or enclosed metal container in which a metal belt conveyor is installed, storage tanks positioned under the coal pulverization mills and a final stockage silo. The storage tanks which feed the metal belt conveyor have the purpose to isolate the coal pulverization mill from the downstream metal conveyor, during the loading and unloading operations. This separation is performed through a pair of valves upstream and downstream each storage tank.

The whole conveyor plant is provided with a fire prevention system to put out any combustion of the coal dust both on the metal conveyor belt and in the closed tanks. The combustion detection is performed through properly positioned sensors, which control the gas inertization for the closed areas and the water inertization for the conveyor belt. In case the conveyor belt is completely enclosed, the inertization can be performed with inert gas or steam.

The water fire prevention system is preferably positioned near the conveyor unloading point, in order to affect all the material conveyed to the stockage silo.

In case the conveyor is open, the metal belt is provided with restraining side boards to avoid the dust dispersion in the environment; the bottom of the metal conveyor is provided with openings, and a proper collecting channel of the putting out water is disposed beneath said conveyor.

In particular configurations of the conveyor plant, the metal conveyor can be provided with a fines recovery system, it too optionally provided with inertization nozzles, with water that can be conveyed to a proper collecting point by said recovery system.

The layout of the plant could provide, downstream the metal conveyor, for a pneumatic conveyor of the pyrite mixture to the stockage silo. In this embodiment an iron removal system, to eliminate the ferrous material present in the pyrites mixture, and a grinding system, to reduce the size of the pyrite mixture and to make it suitable for being pneumatically conveyed, are placed downstream the metal conveyor.

It should be pointed out that the same reference numbers in the different Figures indicate the same or equivalent parts.

The present invention is related to a conveyor plant for pyrites, foreign materials like metal parts and occasionally ground coal, all coming from the fuel grinding mills used by power plants.

The metal belt handling element, made of steel and inserted into an open or enclosed metal container1, essentially consists of a belt conveyor6comprising a belt7woven with a special steel, to which a set of mutually partially overlapping steel plates10is fastened through screws8, forming a tight conveyor channel for the material. Said conveyor is supported by upper smooth rollers10and lower bearing rollers11. The torque is transmitted by friction through a traction drum12and an opposite return drum13, provided with a tensioning device14.

Upon the application of the force exerted by the tensioning system14, a pressure increase is obtained in the overlapping area of the plates9, causing a better tight between the plates9which avoids losses of material, even of small size.

Alternatively, the steel conveyor suitable for conveying hot materials can also be of supporting plates type, with traction chains driven by sprockets.

The metal belt conveyor6receives the pyrites15, coming from the storage tanks2downstream the mills (not shown in the drawings), when the interception valve3is opened and the interception valve21is closed. When the position of the two valves is inverted, the storage of the material in the tank2takes place.

The pyrites15collected in the storage tanks2, outgoing from the interception valve3, are loaded on the metal conveyor belt6through a proportioner4.

The conveyor can have two different configurations:“a” configuration—the metal container inside which the metal conveyor is installed is provided with openings that put in communication the interior of the container with the external environment;“b” configuration—the metal container inside which the metal conveyor is installed is completely closed.

Subsequently, the material15is conveyed to the predetermined stockage area16, and this operation can be performed with a mechanical (FIG. 1) or a mechanical and pneumatic (FIG. 1b) conveyor.

In case of mechanical and pneumatic conveyor, an iron removal system25, to eliminate the ferrous material present in the pyrites mixture15, and a grinding system25, to reduce the material size in order to make it suitable for being pneumatically conveyed, are provided downstream the metal conveyor6.

In “a” configuration, the metal belt is provided with restraining side boards23, to avoid the dust dispersion in the environment. In this configuration, in order to put out any combustion of the coal dust conveyed on the metal belt6together with the pyrites15, temperature control sensors19are installed into the metal container1, controlling a putting out system consisting of water injection nozzles17.

To discharge the putting out water, the conveyor bottom can be provided with openings beneath which a proper collecting channel is disposed.

In “b” configuration, the admission of inert gas or steam in the metal container1through proper injection gates18, driven by properly positioned sensors19, is provided for putting out the combustion.

The inertization with inert gas or steam is also provided for the storage tanks2and the stockage silo16in any plant configuration.

In “b” configuration, the metal container1is provided with proper safety doors20, with automatic opening in case of explosion, in order to assure the structure protection from the pressure increase due to an explosion.

In particular embodiments of the conveyor plant, the metal belt conveyor6can be provided with a recovery system24of the fines from the metal conveyor bottom. Such recovery system24is positioned in the area underlying the return stretch of the metal conveyor belt6and it can be provided with water nozzles17.

The water used during the putting out phase can be conveyed by the same recovery system to the collecting channel.

It is evident that several modifications, adjustments, additions, variations and replacements of elements with functionally equivalent others could be made to the embodiments described hereinbefore with illustrative and not limiting purpose, without falling outside the scope of protection defined in the appended claims.