WO2007087861A1

WO2007087861A1 - Device for continuous feeding and dosage of refuse-derived fuel to non-pressurized user devices

Info

Publication number: WO2007087861A1
Application number: PCT/EP2006/011926
Authority: WO
Inventors: Roberto Di Salvo; Italo Romanoni; Giuseppe Natta
Original assignee: Ecodeco S.R.L.
Priority date: 2006-02-02
Filing date: 2006-12-12
Publication date: 2007-08-09
Also published as: ITMI20060176A1

Abstract

A device for continuous dosed feeding of refuse-derived fuels (RDF) to user devices at ambient pressure, constituted by a pusher screw feeder (5) driven by a variable-rpm motor (13), in which the RDF is fed by means of a feed hopper (4), by a measurement and control section (10), which is connected to the rest of the apparatus by flexible tubular membranes (12) and is supported by a weighing cell (9) and is provided with a system (7) for measuring the speed of the solids. In this way, the flow-rate by weight of the solids is determined and the rotation rate of the motor (13) and of the screw feeder (5) is adjusted so as to maintain the flow-rate at the preset value.

Description

DEVICE FOR CONTINUOUS FEEDING AND DOSAGE OF REFUSE-DERIVED FUEL TO NON-PRESSURIZED USER DEVICES

The present invention relates to a device for continuous feeding and dosage of refuse-derived fuels (RDF) to non-pressurized user devices. More particularly, the present invention relates to a device for the dosed feeding of refuse-derived fuels, RDF, to various non-pressurized user devices, such as for example hoppers of pneumatic conveyors, containers and combustion systems which operate at atmospheric pressure or under light pressure or light vacuum.

The RDFs to which the device can be applied are typically fuels obtained from municipal solid waste (MSW) by means of milling, mechanical sorting, biodrying and refining methods, but also other fuels derived from biomasses or from the processing of animal waste.

More generally, the device can be applied to feed low-density refuse with controlled particle size in energy-using systems such as incinerators or kilns for producing cement. The feeding of solid fuels in combustion systems is one of the most important factors in ensuring regular operation of combustion systems.

Among the various techniques that are used, feeding and dosage by means of screw feeders of the fuel and subsequent transfer by pneumatic conveyance with air to the burner or to the combustion chamber is one of the most widely used techniques if solids suitable for pneumatic conveyance are available and this is required by the combustor.

Typical examples are the feeding of coal to power stations, to cement kilns but also the combustion of unconventional fuels, such as sawdust, finely ground biomasses, animal flours or fuels derived from municipal solid waste (MSW).

The latter can be obtained by means of biodrying, fine milling and demetallization techniques, with procedures such as the one disclosed in EP-A-706839 in the name of this same applicant.

The result is a material with a particle size of approximately a few centimeters and a poured density of approximately 75-200 kg/m³, with a high heating value, which can be easily conveyed pneumatically and therefore can be used in incinerators, in combustors and especially in cement kilns as a replacement of, or complement to, fossil fuels. The use of screw feeders combined with subsequent pneumatic transfer under pressure of the fuel to the combustor requires separation between the screw feeder and the transfer system in order to avoid the bleeding of air under pressure toward the part of the machine where the RDF enters and the irregular operation of the feeder. The method that is normally used, even in the absence of subsequent pneumatic conveyance, is to provide a plug of compacted material which isolates the screw feeder from the rest of the apparatus.

US-4996930, for example, discloses a system for feeding contaminated soil to an incinerator which is at a different pressure and in particular at a slight negative pressure with respect to the environment.

EP-A-0967438, in the name of this same applicant, discloses a pusher screw feeder followed by a frustum-shaped converging pipe so as to act as a plug for the air pressure. Italian Patent application No. MI2005A000036, in the name of this same applicant, discloses a divergent tube which is inclined with respect to the horizontal. EP-0953525 discloses the use of a standard screw feeder, but the compaction system is constituted by a cylindrical membrane which is actuated by compressed air instead of a diverging frustum-shaped tube.

US-4473327 relates to a machine which is constituted by a screw feeder, a diverging frustum-shaped chamber and a check valve constituted by a disk which opens in the direction of outflow of the solids, leaving free an annular region as an output cross- section.

US-4138162 discloses a complete device for conveying powdered cement or cement with metallic or plastic fibers, which is constituted by a conveyance screw feeder, a diverging frustum-shaped compaction chamber, a converging frustum-shaped region in which atomization air is introduced and which is connected to a conveyance tube which ends with an atomization nozzle.

DE-3228468 discloses a station for distributing coal in powder form to burners by means of screw feeders and pneumatic conveyance.

US-4881862 discloses a hermetic device for transferring solids of various kinds to containers at pressures other than ambient pressure. US-4803836 discloses a system for feeding an extrudable material to a pressurized combustion chamber, typically powdered coal to the high-pressure combustor of a gas turbine.

All the prior art devices mentioned above relate to the transfer of solids from an environment at atmospheric pressure to environments as higher pressures, be they pneumatic conveyance systems or pressurized combustors, with the purpose of reducing the bleeding of air or loss of pressure or oscillations in the fed flow-rates.

Moreover, all those systems entrust the dosage of the material to be fed to the screw feeder alone, and this, as is known, ensures a certain uniformity of flow depending on the material to be transferred but does not ensure precise control over the mass flow- rate of the transferred material.

Moreover, RDF is a material which, when subjected to compression, considerably reduces its volume and expands when the pressure ceases, and therefore the control of the flow rate with a volumetric machine such as the screw feeder alone is a problem. In some cases, the dosage screw feeder is positioned on load cells. This application allows weight dosage, but it is applicable only to materials that have a high specific weight.

The above described dosage devices, of this same applicant, ensure a controlled flow-rate of the solids but do not ensure tightness. Since the dust released by dried RDF is explosive in cloud form and inflammable in layer form, any leak of dust is unacceptable.

Furthermore, the powder, by depositing on the rollers of the belt, causes frequent loss of calibration of the machine and therefore requires frequent cleaning actions.

Accordingly, the devices of the cited prior art are unsuitable to ensure dosed feeding of a material such as RDF by pneumatic conveyance or have the same drawbacks mentioned above.

The aim of the present invention is to provide a device which overcomes the drawbacks of the cited prior art.

A particular object of the present invention is to provide a device for feeding RDF which allows to combine the advantages of precision, which is typical of dosage belts, and tightness, which is typical of dosage screw feeders.

A further object of the present invention is to provide a device which is capable of ensuring measurement of the fed flow-rate, which is an important measurement for controlled management of combustion and for certification of the amount of waste burned.

This aim and these and other objects, which will become better apparent hereinafter, are achieved by a device for continuous feeding and dosage of refuse-derived fuels (RDF) to non-pressurized user devices, comprising a screw-feeder means for feeding combustible material, a means for weighing said combustible material, and a means for detecting the advancement speed of said combustible material, said weighing means and said speed detection means cooperating to determine the flow-rate of said advancing combustible material, a means for controlling said screw-feeder means which cooperates with said weighing means and said speed sensing means in order to vary said flow-rate. Further characteristics and advantages will become better apparent from the description of preferred but not exclusive embodiments of the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a schematic perspective view of the device according to the invention; Figure 2 is a schematic side view of the device according to the invention; Figure 3 is a schematic side view of the device according to a further aspect of the invention.

With reference to the cited figures, a device according to the invention, generally designated by the reference numeral 1 , comprises a base 2 having a metal structure, which supports a hopper 4 and a screw feeder 5 which is actuated by means of a gearmotor 13.

An accumulation cylinder or cone 6 is arranged between the screw feeder 5 and a weighing cylinder or cone 10 which is connected to a discharge duct 8.

The weighing cone 10 is connected to the rest of the machine by virtue of flexible joints 12. The device also has a centering system 3, a speed measurement wheel 7 which is functionally connected to an encoder 11 , and a load cell 9.

The material enters the hopper 4 and is pushed by the screw feeder 5 toward the discharge duct 8.

During movement, the material passes through the weighing cone 10, where it is weighed by means of the load cell 9 and its feed speed is detected by means of the speed measurement wheel 7 and the encoder 11.

These two items of information are processed by a PLC so as to obtain the flow-rate.

At this point, the PLC changes the speed of the gearmotor 13, and therefore of the screw feeder 5, in order to have the same flow-rate set in the PLC. The weighing cone is arranged inside the structure of the centering system 3, where there are bearings that contrast the thrust and torsion components which are transmitted by the screw.

The only movement allowed to the weighing cone is the vertical movement, thus allowing the load cell 9 to detect the weight correctly. The vertical movement of the cone is allowed by two connecting members, which are constituted for example by a rubber membrane 12 on the two sides between the cone and the accumulation cylinder 6 and the discharge duct 8.

The material is discharged into the discharge duct 8, from which it falls by gravity toward the user device, which can be a tank, a duct for transfer to an incinerator or a hopper of a subsequent machine such as the ones described in the patents mentioned earlier.

The apparatus includes, as mentioned, a rigid frame 2 on which all the components are mounted.

According to an example of practical embodiment, the device according to the invention can supply 2000 kg/h of RDF having an average particle diameter of 2.5 centimeters, a poured density of 75 kg/m³, a moisture content of 17% by weight and a heating value of approximately 4000 kcal/kg.

The device is constituted by a screw feeder 5, which has a length of 1000 mm and a diameter of 300 mm and is driven by a 15-kilowatt electric motor 13, which turns at the rate of 50 rpm and is provided with a loading hopper 4. The measurement cell 10 has a length of 300 mm and the same diameter as the screw feeder 5.

2000 kg/h of RDF are fed and in a few seconds fill completely the tube 6 and the measurement cell 10. In a typical test, performed on an industrial solid waste combustor with a rotating drum, it was possible to feed as auxiliary process fuel 2000 kg/h of RDF without problems, with flow-rate oscillations of less than 5%.

In practice it has been found that the invention achieves the intended aim and objects, a device having been provided for feeding RDF or similar fuels to combustion systems with high precision.

To do this, the operating principles of the devices cited in the prior art have been completely changed by entrusting the task of dosing the material not to the screw feeder but rather to the inline control system.

Figure 3 illustrates a device according to another aspect of the invention, generally designated by the reference numeral 101 , comprising, in a manner similar to the device described earlier, a base having a metal structure 102, which supports a hopper 104 and a screw feeder 105 which is actuated by means of a gearmotor.

An accumulation cylinder 106 is arranged between the screw feeder 105 and a weighing cylinder 1 10, which is connected to a discharge duct 108. The material enters the hopper 104 and is pushed by the screw feeder 105 toward the discharge duct 108.

During movement, the material passes through the weighing cylinder 1 10, where it is weighed by means of a load cell 109.

The advancement rate of the material is detected by means of an encoder 1 1 1 which is applied to the slow shaft of the gearmotor.

These two items of information, weight and speed, are processed by a PLC so as to obtain the flow-rate.

At this point, the PLC changes the speed of the gearmotor, and therefore of the screw feeder 105, in order to have the same flow rate set in the PLC. The only movement allowed to the weighing cylinder 1 10 is the vertical movement, thus allowing the load cell 109 used to detect the weight correctly.

Containment of the material within the device is ensured by chutes 1 12 provided on the initial part of cylinder 110 and duct 108.

The material is discharged into the discharge duct 108, from which it falls by gravity toward the user device, which can be a tank, a duct for transfer to an incinerator or a hopper of a subsequent machine such as the ones described in the patents cited above.

In practice it has been found that the invention achieves the intended aim and objects, a device having been provided which is capable of feeding RDF continuously and combines the advantages of precision, which is typical of dosage belts, and tightness, which is typical of dosage screw feeders.

This application claims the priority of Italian Patent Application No. MI2006A000176, filed on 2 February 2006, the subject matter of which is incorporated herein by reference.

The device for continuos feeding and dosage of refuse-derived fuel to non-pressurized user devices is susceptible of numerous modifications and variations, within the scope of the appended claims. All the details may be replaced with technically equivalent elements.

The materials used, as well as the dimensions, may of course be any according to the requirements and the state of the art.

Claims

1. A device for continuous feeding and dosage of refuse-derived fuels (RDF) to non- pressurized user devices, comprising a screw-feeder means for feeding combustible material, a means for weighing said combustible material, and a means for detecting the advancement speed of said combustible material, said weighing means and said speed detection means cooperating to determine the flow-rate of said advancing combustible material, a means for controlling said screw-feeder means which cooperates with said weighing means and said speed sensing means in order to vary said flow-rate.

2. The device according to claim 1 , characterized in that it comprises a base having a metal structure and supporting a hopper, a screw feeder actuated by means of a gearmotor, an accumulation cylinder or cone, a weighing cylinder or cone, and a discharge duct.

3. The device according to claim 1 or 2, characterized in that said accumulation cylinder or cone is arranged between said screw feeder and said weighing cylinder or cone.

4. The device according to one or more of the preceding claims, characterized in that said weighing cylinder is connected to said discharge duct.

5. The device according to one or more of the preceding claims, characterized in that said weighing cone is connected to the rest of the machine by flexible joints.

6. The device according to one or more of the preceding claims, characterized in that it comprises a centering system.

7. The device according to one or more of the preceding claims, characterized in that it comprises a speed measurement wheel which is functionally connected to an encoder.

8. The device according to one or more of the preceding claims, characterized in that it comprises a load cell.

9. The device according to one or more of the preceding claims, characterized in that said material enters said hopper and is pushed by said screw feeder toward said discharge.

10. The device according to one or more of the preceding claims, characterized in that, during movement, the material passes through said weighing cone, where it is weighed by means of said load cell and where its advancement speed is detected by means of said speed measurement wheel and said encoder.

11. The device according to one or more of the preceding claims, characterized in that the material weight and speed data are processed by a data processing device so as to obtain the flow-rate.

12. The device according to one or more of the preceding claims, characterized in that said data processing device controls said gearmotor so that it changes its rotation rate in order to change the rotation rate of said screw feeder so as to vary the flow-rate.

13. The device according to one or more of the preceding claims, characterized in that said weighing cone is arranged within the structure of the centering system, which comprises bearings that contrast the thrust and torque components transmitted by said screw feeder.

14. The device according to one or more of the preceding claims, characterized in that said weighing cone can move only in a vertical direction in order to allow said load cell to correctly detect the weight of said material.

15. The device according to one or more of the preceding claims, characterized in that said vertical movement of the cone is allowed by connecting portions.

16. The device according to one or more of the preceding claims, characterized in that said connecting portions are constituted by a rubber membrane on the two sides between said cone and the accumulation cylinder and the discharge duct.

17. The device according to one or more of the preceding claims, characterized in that it comprises an encoder which is applied to the slow shaft of the gearmotor and is suitable to provide an indication of the advancement speed of the material.

18. The device according to one or more of the preceding claims, characterized in that it comprises chutes which are present on the initial part of the weighing cylinder and of the discharge cylinder in order to contain the material within the device.