HK1109652B - Dry mechanical conveyor plant for pyrites and coal dust - Google Patents

Description

Mechanical conveyor apparatus for drying pyrite and coal fines

Technical Field

The present invention relates to a conveyor device for pyrites mixed with other impurities and occasionally with coal fines coming from mills for crushing solid fossil fuels, capable of safely conveying these hot materials which are inflammable due to spontaneous combustion.

Background

Steam generators fed with solid fossil fuels such as coal or lignite require that the fuel be reduced to a predetermined fineness in order to optimize combustion in the boiler and to improve energy efficiency. Comminution occurs in a milling apparatus where coal is reduced to a desired particle size by impact, compression and friction of mechanical elements of the mill's milling assembly. The obtained pulverized coal is then transferred to a boiler and a burner by a pneumatic conveyor.

In the prior art, impurities and heavier materials present in the coal, such as pyrite, are ejected from the milling path of the mill by means of centrifugal force and they are conveyed to a storage area with a hydraulic conveyor system together with a variable amount of coal dust, in order to avoid fires or explosions due to spontaneous combustion of the coal dust. The amount of coal fines depends on the type of mill used, the wear of the mechanical elements forming the milling assembly and any malfunctions.

Hydraulic systems that both uselessly consume water and contaminate it with coal have some limitations in terms of the transport of impurity metal pieces that are typically present in coal, as well as the size of the material. To overcome these limitations, grates are used at the inlet of the system for screening the material, which results in interruptions due to the need to manually clean said grates.

Vacuum pneumatic conveyors are also currently used, but they have considerable limitations in terms of material size and the presence of iron lumps, leading to frequent interruptions.

Open rubber conveyor belts are not commonly used, which collect pyrites from the mill, but in the case of coal spontaneous combustion they can catch fire, leading to flame propagation and catastrophic consequences.

Disclosure of Invention

The conveyor apparatus object of the present invention eliminates the aforementioned problems, since it uses a high temperature resistant metal conveyor belt, which is capable of conveying a mixture of pyrite and coal fines with minimal dust spreading to the environment. The device is provided with sensors able to detect any combustion and to activate a suitable extinguishing system. The conveyor apparatus consists of an open or closed metal container in which a metal belt conveyor is mounted, a storage tank positioned below the coal pulverizer mill, and a final storage bin. The storage tank feeding the metal belt conveyor has the purpose of isolating the coal pulverizer from the downstream metal conveyor during loading and unloading operations. This isolation is effected by a pair of valves upstream and downstream of each storage tank.

The entire conveyor apparatus is provided with a fire protection system to extinguish any combustion of the coal fines on the metal conveyor belt and in the containment tank. The detection of combustion is carried out by means of suitably positioned sensors which control the inerting of the gas (gas inerting) for the closed zones and the inerting of the water for the conveyor belts. In the case of a completely closed conveyor belt, the inerting can be carried out with an inert gas or gas flow.

The fire protection system is preferably positioned near the conveyor discharge point to react all of the material being conveyed to the storage bin.

In the case of an open conveyor, the metal belt is provided with limiting side plates to avoid dust spreading into the environment; the bottom of the metal conveyor is provided with an opening, and a suitable collection tank for the water used for extinguishing the fire is arranged below said conveyor.

In a special configuration of the conveyor apparatus, the metal conveyor may be provided with a pulverized coal recovery system, which is optionally also provided with inerting nozzles, wherein water may be conveyed to a suitable collection point through said recovery system.

The layout of the plant makes it possible to arrange a pneumatic conveyor of the pyrite mixture to the storage silos downstream of the metal conveyor. In this embodiment, an iron removal system to remove iron-containing material present in the pyrite mixture and a milling system to reduce the size of the pyrite mixture and make it suitable for pneumatic conveyance are arranged downstream of the metal conveyor.

Drawings

The innovative features, objects and advantages of the invention will be better highlighted in the following description, as well as in the appended drawings, which show a given embodiment in a non-limiting manner, in which:

fig. 1 is a schematic side view of a conveyor apparatus in which the transfer to the storage bins is only done mechanically;

FIG. 1b is a schematic side view of a conveyor apparatus in which the transfer to the storage bins is achieved by mechanical and pneumatic means;

fig. 2 is a schematic view of a metal conveyor belt provided with a plate 9, screws 8, steel woven belt 7 and a support roller 10;

FIG. 3 is a schematic view of a metal conveyor belt showing the traction drum 12 and return drum 13 and the upper 10 and lower 11 support rollers;

FIG. 4 is a cross-sectional view of the conveyor assembly with the machine not fully closed ("a" configuration);

FIG. 5 is a cross-sectional view of the conveyor assembly with the machine fully closed ("b" configuration);

FIG. 6 is a schematic view of the arrangement of nozzles 17 and sensors 19 of the fire protection system for controlling the temperature and/or concentration of combustible gas on the conveyor belt 16 in the "a" configuration;

FIG. 7 is a schematic view of the arrangement of the nozzle 18 and sensor 19 of the inert gas or gas flow introduction system for controlling the temperature and/or concentration of combustible gas within the metal container 1 in the "b" configuration;

FIG. 8 is a cross-sectional view of a conveyor having a pulverized coal recovery system in a "b" configuration; and

fig. 9 is a schematic view of explosion-proof safety door 20 in the case of a "b" configuration metal conveyor.

It should be noted that the same reference numerals in different drawings represent the same or equivalent parts.

Detailed Description

The present invention relates to conveyor equipment for pyrite, impurities such as metal parts and occasionally ground coal, both from fuel mills used in power plants.

The metal belt treatment element made of steel and inserted into the open or closed metal container 1 is substantially constituted by a belt conveyor 6, the belt conveyor 6 comprising a belt 7 woven of special steel, onto which belt 7 a set of steel plates 10 partially overlapping each other is screwed by means of screws 8, so as to form a compact conveyor channel for the material. The conveyor is supported by an upper smooth roller 10 and a lower supporting roller 11. Torque is transmitted by means of friction through the traction drum 12 and the opposite return drum 13, which return drum 13 is provided with a tensioning device 14.

Upon application of the force exerted by the tensioning system 14, an increase in pressure is obtained on the overlapping areas of the plates 9, so as to make the space between the plates 9 more compact, thus avoiding the loss of material even of small dimensions.

Alternatively, the steel conveyor adapted to convey hot material may also be of the support plate type, wherein the traction chain is driven by a sprocket wheel.

The metal belt conveyor 6 receives pyrite 15 from the storage tank 2 downstream of the mill (not shown in the figures) when the interception valve 3 is open and the interception valve 12 is closed. When the positions of the two valves are reversed, material is stored in the tank 2.

The pyrite 15 collected in the storage tank 2 is loaded on the metal conveyor 6 by the batching device 4 while flowing out of the interception valve 3.

The conveyor may have two different configurations:

"a" configuration-the metal container in which the metal conveyor is installed is provided with an opening that puts the interior of the container in communication with the outside environment;

"b" configuration-the metal container in which the metal conveyor is installed is completely closed.

Subsequently, the material 15 is transferred to a predetermined storage area 16, which operation can be carried out with a mechanical (fig. 1) or mechanical and pneumatic (fig. 1b) conveyor.

In the case of mechanical and pneumatic conveyors, an iron removal system 25 to eliminate the iron-containing substances present in the pyrite mixture 15 and a grinding system 25 to reduce the size of the material so as to make it suitable for pneumatic conveyance are provided downstream of the metal conveyor 6.

In the "a" configuration, the metal strip is provided with restraining side plates 23 to avoid dust spreading into the environment. In this configuration, in order to extinguish any combustion of the pulverized coal conveyed on the metal belt 6 together with the pyrite, a temperature control sensor 19 is installed into the metal container 1, thereby controlling the extinguishing system constituted by the water injection nozzles 17.

For discharging the water used for extinguishing the fire, the conveyor bottom may be provided with openings below which suitable collecting tanks are provided.

In the "b" configuration, an inert gas or gas flow is supplied into the metal container 1 through a suitable injection shutter 18 driven by a suitably positioned sensor 19 for extinguishing the combustion.

Inertization is also carried out with inert gas or gas flow for the storage tanks 2 and silos 16 in any plant configuration.

In the "b" configuration, the metal container 1 is provided with a suitable safety door 20 which opens automatically in case of an explosion to ensure that the structure is not harmed by the pressure increase caused by the explosion.

In a special embodiment of the conveyor apparatus, the metal belt conveyor 6 may be provided with a pulverized coal recovery system 24 at the bottom of the metal conveyor. Such a recovery system 24 is positioned in the area below the return stroke of the metal conveyor belt 6 and may be provided with water nozzles 17.

The water used in the extinguishing phase can be conveyed to the collecting tank by the same recovery system.

It is clear that various modifications, adaptations, additions, variations and substitutions of parts with other functionally equivalent parts may be made to the embodiment described for the purposes of illustration and not limitation, without departing from the scope of protection defined by the accompanying claims.

Claims (6)

1. A conveyor apparatus consisting of a conveyor for safely handling pyrite, coal fines and other impurities (15) from mills for grinding solid fossil fuels, comprising: a set of storage tanks (2), one for each mill; a closed or open metal container (1) inside which a refractory metal conveyor belt (6) is arranged that does not allow any flame propagation; and a storage bin (16), characterized in that the storage tank (2), the metal container (1) and the storage bin (16) are provided with a combustion detection sensor system which controls the input of inert gas or water according to the plant configuration.

2. Conveyor plant according to claim 1, characterized in that the conveyance of pyrite, coal dust and other impurities (15) coming from mills for crushing solid fossil fuels to the storage silos (16) is carried out by means of unique mechanical conveyors or by means of mechanical and pneumatic conveyors, on the basis of the removal of iron-containing material by an iron removal system (25) and the size reduction by a grinding system (26), said iron removal system (25) and grinding system (26) being arranged downstream of said metal conveyor belt (6).

3. Conveyor installation according to claim 1, characterized in that the metal container (1) is provided with a quenching system constituted by a water inlet nozzle (17) activated by a sensor (19) in case the metal container (1) is in communication with the outside environment, or in that the metal container (1) is provided with a quenching system constituted by an inert gas or gas flow inlet nozzle (18) activated by a sensor (19) in case the metal container (1) is closed.

4. Conveyor installation according to claim 3, characterized in that, in the case of a metal container (1) in communication with the outside environment, it is provided with side plates (23) for confining the material along the entire length of the conveyor, in order to reduce the dust spreading into the surrounding environment.

5. Conveyor installation according to claim 1, characterized in that a pulverized coal recovery system (24) is installed inside the metal container (1) to keep the bottom of the container (1) free from deposited material dust and to convey it to the unloading area.

6. A conveyor apparatus according to claim 5, characterized in that the pulverized coal recovery system (24) is provided with water inlet nozzles (17) actuated by suitable sensors (19) to extinguish any combustion of the pulverized coal.