WO2007104827A1

WO2007104827A1 - Apparatus and method for measuring of mass flow of fine grained material, especially coal fuel

Info

Publication number: WO2007104827A1
Application number: PCT/FI2007/000039
Authority: WO
Inventors: Tapani MÄKILÄ
Original assignee: Raumaster Oy
Priority date: 2006-02-17
Filing date: 2007-02-16
Publication date: 2007-09-20
Also published as: FI119706B; FI20060156A0; FI20060156A; JP4922313B2; JP2009526981A

Abstract

The object of the invention is an apparatus and a method for measuring mass flow of a fine-grained material, especially coal fuel, in a chain conveyor or chain feeder (1 ). According to the invention, a belt conveyor (6) equipped with a weighing element (13) has been arranged inside the housing (18) of the chain conveyor or chain feeder, via which belt conveyor (6) the mass flow has been arranged to pass.

Description

APPARATUS AND METHOD FOR MEASURING OF MASS FLOW OF FINEGRAINED MATERIAL, ESPECIALLY COAL FUEL

TECHNICAL FIELD OF THE INVENTION

The object of the invention is an apparatus and a method as described in the preambles to the independent claims presented below for measuring the mass flow of a fine-grained material, especially coal fuel.

PRIOR ART

In coal-fired power plants, it is important to control the mass flow of the fuel in order to regulate the combustion process and to maintain the desired power level. The volume flow of the fuel must also be controlled, since large variations in the volume may cause, among others, blockages and other mechanical problems in the conveyors and in the boiler.

Coal fuel is not homogeneous in terms of its properties. There are many different coal grades, the volume weight of which may vary greatly. In addition, the volume weight is influenced by moisture and grain size, among other things. Therefore, a sufficiently accurate regulation result is not achieved by merely controlling the volume flow.

In existing installations, mass flow is most frequently controlled indirectly by controlling only the fuel volume flow in the chain conveyor or chain feeder between the silo and the boiler. The controlling may be carried out for example by regulating the speed of the feeder conveyor and/or by adjusting the thickness of the material layer on the conveyor by means of a mechanical adjusting/limiting plate. This control method is hence indirect and inaccurate as such.

Due to the enclosed steel structure of the chain conveyor or chain feeder, it has not been possible to use known techniques based on weighing, such as belt scales, for mass flow measurement. Weighing the entire conveyor is not feasible either, as the weight of the conveyed material is very low compared to the dead weight of the heavily constructed conveyor. PURPOSE AND BRIEF DESCRIPTION OF THE INVENTION

One of the purposes of the present invention is to reduce or even eliminate some of the above-mentioned problems found in the prior art.

One of the purposes of the present invention is, in particular, to provide a solution that enables accurate mass flow measurement of the fuel flow in addition to volume flow control.

One of the purposes of the invention is to provide a measuring method that is suited not only to mass flow measurement in the desired units (kg/s, t/h, t/a) but also to cumulative measurement of the entire material flow.

One of the purposes of the present invention is to provide a solution that enables accurate mass flow measurement of the fuel flow by a method based on gravity.

To realise the above-mentioned purposes, among others, the present invention is characterised by what is presented in the characterising parts of the attached independent claims.

The examples of embodiments and the advantages referred to in this text concern, as applicable, both the apparatus and method according to the invention, even though this is not always explicitly mentioned.

A typical apparatus according to the invention for measuring the mass flow of a fine-grained material in a chain conveyor or chain feeder comprises a belt conveyor arranged inside a housing of the chain conveyor or chain feeder. The material to be conveyed has been arranged to pass through the belt conveyor. According to the invention, a weighing element has been arranged in the belt conveyor. Chain conveyors, chain feeders and belt conveyors are known techniques as such, and their functions or structure are therefore not described in more detail in this text.

The invention is excellently suited to the measurement of coal fuel in power plants and similar installations. The invention is applicable to the measurement of any bulk material conveyed on a chain conveyor. The invention is especially suited for all fine-grained solid fuels, such as wood chips, shredded wood, sawdust, bark, peat.

It has now surprisingly been discovered that by installing a belt conveyor inside the chain conveyor housing and by furnishing the belt conveyor with weighing means, the mass flow of the material moving in the chain conveyor or the chain feeder can be easily measured.

One of the greatest advantages of the invention is that the data that can be obtained with the invention on the real-time mass flow and the possibility to control the mass flow improve the controllability of the combustion process.

In one embodiment of the invention, the belt conveyor is located between the top surface and the bottom surface of the chain conveyor or chain feeder so that the material flow falling from the top surface toward the bottom surface falls onto the belt conveyor. A structure of this kind is simple and easy to realise.

In one embodiment of the invention, one or several weighing sensors, such as a strain-gauge or semiconductor weighing sensor, have been arranged in the belt conveyor frame. Weighing sensors of this type are reliable.

In one embodiment of the invention, the belt conveyor has a head pulley and a tail pulley but no support rollers between them. This is a simple structure. This kind of structure is usually only feasible in relatively short belt conveyors. In one embodiment of the invention, the belt conveyor pulleys and the conveyor belt are located inside the housing of the chain conveyor or chain feeder, but the pulley shafts and the belt conveyor frame are arranged, at least partially, outside the housing. In one embodiment, the pulley bearings and the weighing element according to the invention are located outside the housing. The advantage of this kind of structure is that the sensitive parts of the apparatus, such as bearings and weighing elements, are located so that they are not exposed to coal dust. The parts located outside the housing are easy to service.

In one embodiment of the invention, the belt conveyor frame has been articulated so that its pivot point is essentially in the same vertical line with that point on the belt conveyor onto which the material flow falls from the top surface. This minimises or even completely eliminates the impulse effect exerted on the measurement according to the invention by the coal falling onto the belt conveyor.

In one embodiment of the invention, the weighing element has been arranged near the belt conveyor end located furthest away from the pivot point. At this point, the movement or deflection of the belt conveyor caused by the mass flow is greatest, so that the measurement result is as accurate as possible.

BRIEF DESCRIPTION OF THE FIGURES

In the following, the invention is described in more detail with reference to the attached schematic drawing, wherein

Fig. 1 shows a chain feeder according to the invention below a coal silo,

Fig. 2a is an end view of a belt conveyor according to the invention,

Fig. 2b is a side view of a belt conveyor according to the invention,

Fig. 2c is an end view of an apparatus according to the invention and

Fig. 2d is a side view of an apparatus according to the invention.

DETAILED DESCRIPTION OF THE EXAMPLES PRESENTED IN THE FIGURES The same reference numbers are used for parts that correspond to each other in the different figures. The coal flow through the apparatus is marked with arrows in the figures. The layer formed by the coal is illustrated with dots. Fig. 1 shows a feeder conveyor 1 installed below a coal storage silo 14. The feeder conveyor 1 according to the invention comprises a chain conveyor for transferring coal in a controlled manner from the storage silo 14 into the power plant's boiler (not shown). Transferring coal from the silo to the conveyor 1 and from the conveyor to the power plant's boiler is a known technique per se and is therefore not presented in more detail here.

Figs 2c-2d show a chain feeder 1 , in which a belt conveyor 6, shown alone in Figs. 2a and 2b, has been placed. The chain feeder 1 is enclosed in a steel housing 18. The specially constructed belt conveyor 6, adapted particularly to the weighing of a fine-grained material, such as coal fuel, is located at the leading end 15 of the chain feeder 1 so that the entire mass flow passes through it. The coal coming from the silo 14 or from the preceding conveyor falls first onto the chain conveyor's or chain feeder's top surface 3 into the space 16. From the space 16, a conveyor chain i.e. a scraper chain 2 transports the coal under a mechanical limiting element 4. The limiting element 4 limits the height of the coal layer and spreads the coal layer evenly on the scraper chain 2. The chain 2 transfers the coal layer on past an edge 17 of the top surface 3, from where the coal falls onto the belt conveyor 6 located on a bottom surface 5. The belt conveyor 6 is located at the point onto which the coal falls from the top surface. The dimensions of the belt conveyor 6 have been chosen so that essentially all the falling coal remains on the conveyor belt 7. The belt conveyor 6 transfers the coal layer further over its edge onto the bottom surface 5. On the bottom surface 5, the scraper chain 2 transfers the coal on to the next conveyor or to the power plant's boiler.

The belt conveyor 6 is mounted on a torsion-resistant frame 11 in such a way that the belt conveyor's pulleys 8, 9 and conveyor belt 7 are located inside the feeder conveyor housing 18. The pulley bearings 10 and the weighing sensor 13 are located outside the housing 18. The frame 11 is articulated in relation to the floor 19 and the rest of the chain feeder so that the pivot point 12 is essentially in the same vertical line with the point of the belt conveyor 6 onto which the coal falls. This eliminates the impulse effect of the coal falling on the belt 7. The head pulley 8 of the belt conveyor is driven by an electric motor 21. The belt conveyor 6 has a head pulley 8 and a tail pulley 9 but no support rollers between them.

A weighing sensor 13, which may, for example, be a strain-gauge or semiconductor weighing sensor, is located on that side 20 where the lever arm is longer in relation to the pivot point 12 of the frame 11. The geometry of the structure is such that the mass of the material on the belt 7 is directly seen in the output of the weighing sensor 13. The speed of the belt 7 is measured in a known manner, for example on the shaft of the head pulley 8, and the electronic component (not shown) of the apparatus converts the signal of the weighing sensor 13 to the desired mass flow quantity (e.g. kg/s or t/h). There may also be a current signal output for the quantities in question, in which case the data obtained can be transmitted to the point in the process where it is needed, such as the control room and process control. This enables real-time monitoring of the amount of coal conveyed to the boiler using regulating devices according to the prior art. The amount of coal can be controlled by controlling, for example, the electric motor 21 of the belt conveyor, the position of the mechanical limiter 4 or the drive mechanism (not shown) of the scraper chain 2.

The belt conveyor's pulley shafts 8, 9, which go through the housing walls 18 of the feeder conveyor 1 , have specially constructed bearing-mounted 10 sealers, which do not transmit forces from the housing walls 18 and thus do not distort the result of the measurement.

The figures show only one preferred embodiment according to the invention. The figures do not explicitly show some aspects inessential for the main idea of the invention, which are known per se or obvious per se to those skilled in the art. It is obvious to one skilled in the art that the invention is not limited only to the examples presented above, but that the invention may vary within the scope of the claims presented below. The dependent claims present some possible embodiments of the invention, and they should not be considered as such to restrict the protection scope of the invention.

Claims

1. Apparatus for measuring mass flow of a fine-grained material, especially coal fuel, in a chain conveyor or chain feeder (1 ), characterised in that a belt conveyor (6) equipped with a weighing element (13) has been arranged inside a housing (18) of the chain conveyor or chain feeder, via which belt conveyor (6) the material to be conveyed has been arranged to pass.

2. Apparatus according to claim 1 , characterised in that the belt conveyor (6) is located between a top surface (3) and a bottom surface (5) of the chain conveyor or chain feeder so that the material flow falling from the top surface toward the bottom surface falls onto the belt conveyor (6).

3. Apparatus according to claim 1 or 2, characterised in that one or several weighing sensors (13) have been arranged on the belt conveyor frame (11 ).

4. Apparatus according to claim 1 , 2 or 3, characterised in that the belt conveyor has a head pulley (8) and a tail pulley (9) but no support rollers.

5. Apparatus according to claim 1 , 2, 3 or 4, characterised in that the belt conveyor's pulleys (8, 9) and conveyor belt (7) are located inside the housing (18) of the chain conveyor or chain feeder, but the pulley shafts and the belt conveyor frame (11 ) have been arranged at least partially outside the housing (18) in such a way that the pulley bearings (10) and the weighing element (13) are also outside the housing (18).

6. Apparatus according to any one of the above claims, characterised in that the belt conveyor frame (11 ) is articulated so that the pivot point (12) is essentially in the same vertical line with the point of the belt conveyor (6) onto which the material flow falls.

7. Apparatus according to claim 6, characterised in that the weighing element (13) has been arranged near that belt conveyor end (20) which is located furthest away from the pivot point (12)

8. Method for measuring mass flow of a fine-grained material, especially coal fuel, in a chain conveyor or chain feeder (1 ), characterised in that the mass flow is measured while the material is on a belt conveyor (6) located inside a housing (18) of the chain conveyor or chain feeder.

9. Method according to claim 8, characterised in that the mass flow is measured after the material has fallen from a top surface (3) of the chain conveyor or chain feeder, but before the material has reached a bottom surface (5) of the chain conveyor or chain feeder.

10. Method according to any one of claims 8-9, characterised in that the mass flow is measured by means of one or more weighing sensors (13) measuring the movement (11 ) of the belt conveyor frame.

11. Method according to any one of claims 8-10, characterised in that the belt conveyor frame (11 ) is articulated at a pivot point (12) and the weighing element (13) measures the mass flow near that belt conveyor end (20) which is located furthest away from the pivot point (12).