|Title of Invention||
"AN APPARATUS FOR FEEDING OF BULK SOLIDS TO PULVERISERS"
|Abstract||An apparatus for feeding of bulk solids to pulverisers comprising of a VFD Controller (1), a reactor (5) and a tacho generator (4) said VFD controller (1) being housed in a cabinet (8) which is provided with a PCB (2), characterized by said reactor (5) which receives power from a power source and being connected to tacho generator (4) through a 3 phase induction motor (3),|
|Full Text||FIELD OF INVENTION
This invention relates to an apparatus for regulating feeding of bulk solids to pulverisers. At present majority of bulk solids feeding apparatus are supplied with eddy current clutch to regulate the speed of the feeding mechanism. An eddy current clutch consists of a three phase squirrel cage induction motor which rotates the input side of the coupling at constant speed. The eddy current coupling transmits torque from the driving shaft (motor side) to the driven equipment based on magnetic coupling, in proportion to the excitation voltage given to the clutch coil of the eddy current clutch. As part of the invention, a variable seed regulating module is integrated with the bulk solids feer drive (AC motor) control which regulates bulk solids feeding to pulverisers.
DESCRIPTION OF PRIOR ART:
Currently majority of bulk solids feeding apparatus are supplied with eddy current clutch to regulate the speed of the feeding mechanism. The drive member of the eddy current clutch is a Ferro-magnetic drum coupled to the induction motor. A multi pole induction made from special alloy steel rotates freely within the drum, maintaining a close and constant air-gap. This forms the driven member of the clutch. A magnetic yoke of horseshoe section houses an annular excitation coil. Energizing the coil causes the
magnetic lines of force to link the drive with the driven member. The relative motion between the drive and driven member of the clutch causes the flux concentration to sweep the surface of the drum. This results in flow of eddy currents in the drum material, which causes a torque transmission from the prime mover (induction motor) to the variable speed member of the clutch. The torque transmitted is a function of the DC excitation voltage given to the excitation coil. Adjustment of the output speed is achieved by controlling the excitation current of the eddy current coupling.
In the eddy current clutch method of speed control, the motor runs at a fixed RPM and the speed variation is done through varying the excitation voltage given to the clutch coil. As the motor always runs at the full rated speed, there is no benefit of energy conservation or less wear and tear of the motor. Moreover there is a limitation on the accuracy of speed regulation that can be achieved.
DRAWBACKS OF PRIOR ARTs
The clutch type speed regulating mechanism requires a minimum of around 10% of loading to prevent hunting at low speed and also the method is less energy efficient.
COMPARISON OF PRIOR ART AND THE INVENTION:
To find out the details of existing state of art, a search was conducted through US Patent & Trademark office - Patent full text and image database portal using the search strings "(Control methods for coal feeders)". "(Raw coal feeding methods / controls)", "(Variable coal feeding techniques)", "(State of art feeder controls)", "(Methods for enhancing feeder controls)", and Bulk solids weighing systems have been generally disclosed in the following patents.
In United States Patent 5,747,747 relating to "Continuing belt-type conveyor and means for weighing contents transported thereon" there is provided a conveyor system having a converyor belt for continuously transporting materials from a feed hopper to an end feed mechanism and a means for continuously.
The description given in the above referred patent is for a method and system for continuously transporting materials from a feed hopper as they pass through a conveyor belt. The invented design covered in this specification is different from the instant invention since it pertains to an apparatus for regulating bulk solids feeding to pulverisers.
In United States Patent : 4,895,081 relating to "Gravimetric feeder, especially adapted for use in a calorimetry system
describes a calorimetry system for measurement of the heating value of coal, having a combustor and a mixing unit wherein heat from combustion gases is transferred to air. The system has a gravimetric feeder for providing coal at a meausred mass feed rate; the coal including any moisture present therein.
The description given in this US patent is for a method and system for computation of heating value of coal. The invented design covered in this specification is different from the above patent since it pertains to an apparatus for regulating bulk solids feeding to pulverisers.
In United States Patent : 5,784,974 relating to "System for improving fuel feed control of volumetric coal feeders" discloses at feeder system for measuring and controlling the massed feed rate of particulate fuel material, such as coal particles, made up of a group of volumetric feeders and a gravimetric feeder coupled to the group of volumetric feeders. The system controls the fuel feed rate of the volumetric feeders based upon data communicated from the gravimetric feeder.
The description given in the above referred patent is for a system for measuring and controlling the mass feed rate of coal particles, made up of a group of volumetric feeders. The invented design covered in this specification is different from the above patent since it pertains to an apparatus for regulating bulk solids feeding to pulverisers.
SUMMARY OF INVENTION
The innovative aspect of the invention is the integration of a variable speed regulating module with the bulk solids feeder drive. To deliver the required torque even at low speed, the ratio of voltage and frequency of the power supply fed to the motor is maintained constant. The hunting of feeder drive at low loads is totally eliminated. Also the apparatus provide a user friendly interface and higher overall efficiency. Additionally feedback signal from the drive motor is taken for fine-tuning of the regulated speed.
OBJECTIVES OF THE INVENTION:
The present invention is directed towards integration of a variable speed regulating module with the bulk solids feeder drive. The apparatus provides controlled acceleration and deceleration, soft staring and stopping. Based on the current operation, the apparatus also provides guidance message to the operator in a user friendly format.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS
The apparatus essentially comprises a variable frequency drive
(VFD) controller , an
induction motor (3), a tacho-generator control cables (6) and power cables (7).
In a three phase AC induction motor (3), the synchronous speed N is given as
N = 120 >; F/P
where F is the frequency of the input power supply fed to the motor and P is the number of poles.
While the number of poles cannot be altered for a selected motor, by feeding the motor with variable frequency supply, the speed varies in direct proportion to the frequency. The torque developed by an induction motor depends on V/F ratio, where V is the applied voltage to the motor. If frequency alone is changed keeping voltage constant, there will be loss of torque. To deliver the required torque even at low speed, it is necessary to maintain the V/F ratio constant.
The variable frequency drive (VFD) controller (1) consists of a rectifier stage and an inverter stage. The input power supply fed to the VFD controller is first rectified to DC and then inverted to generate variable voltage, variable frequency supply and fed to the motor, maintaining V/F ratio constant. The output of the inverter stage generates a series of pulses of constant amplitude with the pulse width and the pulse quantity varying as required by the desired voltage and frequency. The output section control the parameters - frequency and voltage.
A tacho-generator mounted on the non-drive end shaft of the induction motor provides feedback signal corresponding to the speed of the motor to the VFD controller- The PCB is used as an interface to convert the AC feedback signal from tacho-generator into a 0-5 V DC signal compatible with the VFD controller. The signal from the tacho-generator is fed to the PCE-i through control cables (6). The VFD controller and the PCB are mounted inside a cabinet (8) located in control room. A reactor Salient features / advantages of VFD controls:
High overall efficiency and low operating cost. Controlled linear acceleration and deceleration provide soft starting and stopping and smooth speed changes.
Current limit provision for quick and accurate control. Boosting of torque.
1. An apparatus for feeding of bulk solids to pulverisers comprising of a VFD Controller (1), a reactor (5) and a tacho generator (4) said VFD controller (1) being housed in a cabinet (8) which is provided with a PCB (2), characterized by said reactor (5) which receives power from a power source and being connected to tacho generator (4) through a 3 phase induction motor (3),
2. An apparatus as claimed in claim 1, wherein said bulk solids are all types of coal, biomass and bagasse.
3. A apparatus as claimed in claim 1, wherein speed regulation is done without hunting at lower loads.
4. An apparatus as claimed in claim 2, wherein said controller (1) provides diagnostic features for quick trouble shooting.
|Indian Patent Application Number||1200/DEL/2004|
|PG Journal Number||41/2013|
|Date of Filing||29-Jun-2004|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LIMITED|
|Applicant Address||BHEL HOUSE, SIRI FORT, NEW DELHI-110 049, INDIA.|
|PCT International Classification Number||B02C 53/09|
|PCT International Application Number||N/A|
|PCT International Filing date|