Title of Invention

A SYSTEM FOR ONLINE COMPUTATION AND CONTROL OF BULK SOLIDS FEED-RATE TO PULVERIZERS ADAPTED IN COAL-FIRED BOILERS .

Abstract

The invention relates to a system for online computation and control of bulk solids feed rate to pulverizers adapted in coal-fired boilers, comprising a feeding device having a motor (10) driving an eddy current clutch (11) which drives a conveyor belt of the pulverizers, the feeding device comprising a signal conditioning module (3), and additionally having an integral cabinet (5), a remote power cabinet (1) having a man-machine interface (2), and a card rack (1), the interconnections between the remote power cabinet (4) and the integral cabinet (5) being established via a screened cable (6), a plant-control desk (7) storing and displaying data relating to coal integration and feed rate for operator's control; and a calibration probe (9) operable to perform calibration by using test- weights attached to the feeding device. The card rack (1) comprises atleast one microprocessor/microcontroller module, a power-supply and motor speed control, and a plurality of interface electronic modules, and in that the microprocessor/ microcontroller module determines the actual feed rate based on a speed factor and a weight factor estimated during the calibration of the feeding device, the actual feed rate being compared with a fuel-demand feed rate signaled by the signal conditioning module (3) to determine a motor-speed set-point by means of the power supply and motor speed control module which regulates the eddy current clutch (11) thereby regulating the speed of the conveyor belt of the pulverizers.

Full Text

FIELD OF INVENTION The present invention relates to the field of bulk solids feeding device used for feeding bulk solids (coal) to pulverizers envisaged in coal-fired boilers. More particularly, the invention relates to a retrofit kit system for online computation and control of bulk solids feeding to pulverizers envisaged in coal-fired boilers. BACKGROUND OF THE INVENTION Coal fired boilers are employed world wide by thermal power plants, sugar industries and many other industries which require steam and / or power for its operation. The bulk solids feeding device vary the quantum of bulk solids (raw coal) fed to the pulverizer in proportion to demand and compute the amount of coal fed to the pulverizer over a period of time. It is essential to maintain the weighing accuracy of these feeding device on long-term basis. To achieve this, re-calibration of the feeding device is required to be done under the following conditions: - When any of the components in weighting system/speed measuring circuit is changed. - At regular intervals of around six months to take care of weighing system components wear and tear/change in characteristics. The bulk solids feeding device (raw coal feeders) deliver coal in proportion to the fuel demand generated from the combustion control device envisaged in a boiler. In the existing systems, the control functions such as weighing, sensing, computing, comparing, varying speed etc., to meet the demand are performed using handwired electronic (solid state) modules. The function of calibration is achieved by tuning the potentiometers located in the electronic modules. In the presently available hardwired electronic (solid state) control, more than eight varieties of electronic modules (Electronic cards) are used to perform weight sensing, speed measuring, rate multiplying computation and logic control functions. These modules are mounted in the card rack assemblies, one number rack fixed inside remote power cabinet and another mounted in the feeder integral cabinet. During calibration of feeders under the conditions described above, the potentiometers located in the electronic modules need to be adjusted to arrive at the calibration accuracy. Repeated potentiometers adjustment are required on trial basis, to achieve the accepted level of accuracy. Hence the calibration process takes more time (approximately one hour). Also the output of the potentiometers drift after few months of continuous operation due to feeder vibration etc. OBJECTS OF THE INVENTION An object of the invention is to provide a system for on-line computation and control of bulk-solids feeding rate to pulverizers envisaged in coal-fired boilers, which eliminates the disadvantages of the prior art. Another object of the invention is to provide a system for on-line computation and control of bulk-solids feed-rate to pulverizes envisaged in coal-fired boilers which is capable of automatic calibration of the feeding device without real-time adjustment of the electronic modules of the system. A further object of the invention is to provide a system for on-line computation and control of bulk-solids feed-rate to pulverizes envisaged in coal-fired boilers which provides compatible interfaces for integration with the combustion control device of the boiler. A still further object of the invention is to provide a system for on-line computation and control of bulk-solids feed-rate to pulverizes envisaged in coal- fired boilers which is easily adaptable, cost-effective and efficient. SUMMARY OF THE INVENTION Accordingly, there is provided a system for online computation and control of bulk solids feeding to pulverizers envisaged in coal-fired boilers, which comprises a feeding device having a motor, driving an eddy current clutch which drives a conveyor belt of the pulverizers. The feeding device accommodates a signal conditioning module, and additionally having an integral cabinet. A remote power cabinet having a man-machine interface. A card rack, the interconnections between the remote power cabinet and the integral cabinet is established via a screened cable. A plant-control desk stores and displays data relating to coal integration and feed rate for operator's control. And a calibration probe is provided which is operable to perform calibration by using test-weights attached to the feeding device. The card rack comprises atleast one microprocessor/microcontroller module, a power-supply and motor speed control, and a plurality of interface electronic modules. The microprocessor/ microcontroller module determines the actual feed rate based on a speed factor and a weight factor estimated during the calibration of the feeding device, the actual feed rate being compared with a fuel-demand feed rate signaled by the signal conditioning module to determine a motor-speed set-point by means of the power supply and motor speed control module which regulates the eddy current clutch thereby regulating the speed of the conveyor belt. The system of the invention is operable to integrate the microprocessor/microcontroller based modules to execute the functions, such as logical, sequencing, timing, counting, computation, closed loop control, Data archiving and communication related to control the coal feeding process. The application program developed based on the operational characteristics is stored in the read-write part of the memory of the microprocessor/microcontroller. The feeding device is operated as per the application program residing in the microprocessor/microcontroller. The man- machine interface provides apt guidance for easy operation/calibration in a user- friendly manner to the operating personnel. The microprocessor/microcontroller modules take care of the control functions such as weighing, computing, comparing, sequencing, counting etc. The system is user friendly such that calibration/recalibration can be done through data entry and without the use of potentiometers. The system is further configured to: -testing of the feeding device without microprocessor/microcontroller module. -allowing a continued operation of the feeding device in the event of failure of the microprocessor/microcontroller module. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1- Shows a block-diagram of a system for online computation and control of bulk solids feeding to pulverizers envisaged in coal-fired boilers according to the present invention. Figure 2- shows the block diagram of the existing system, (Solid state) arrangement. Figure 3- shows the block diagram of the Signal-conditioning module applicable to this invention. Figure 4- shows the block diagram of the Card rack assembled hardware details along with Man Machine interface applicable to this invention. DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE NUMBERED PARTS: As shown in Figure 1, the system comprises of a bulk solids feeding device, a Remote power cabinet, an Integral cabinet, and connecting means. The Remote power cabinet (4) consists of a card rack (1) which includes a microprocessor/microcontroller module, a power supply and motor speed control module, and a plurality of additional interface electronic modules. A Man-Machine interface (2) is mounted on the door of the Remote power cabinet (4). An Integral cabinet (5) is mounted on the Feeding device, which houses a signal- conditioning module (3). The feeding device consists of a motor (10) having an eddy current clutch (11) to drive a conveyor belt, and additionally having an integral cabinet (5). A remote power cabinet (4) having a man-machine interface (2), and a card rack (1), the interconnections between the remote power cabinet (4) and the Integral cabinet (5) are made by a special screened cable (6). A plant-control desk (7) storing and displaying data relating to coal integration and feed rate for operator's control; and a calibration probe (9) operable to perform calibration through test weights attached to the feeding device characterized in that the card rack (1) comprises atleast one microprocessor/micro controller module, a power supply and motor speed control, and a plurality of interface electronic modules, and wherein the microprocessor/micro controller modules determines the actual feed rate based on a speed factor and a weight factor estimated during the calibration of the feeding device, the actual feed rate being compared with a fuel-demand feed rate signaled by the signal conditioning module (3) to determine a motor-speed set point by means of the power supply and motor speed control module which regulates the eddy current clutch (11) thereby regulating the speed of the conveyor belt. The microprocessor/microcontroller maintains the feed rate accurately as per fuel demand signal from the combustion control, by regulating the current to the eddy current clutch (ECC). The regulation of the clutch current varies the speed of the belt conveyor. In order to regulate the clutch current, the microprocessor/ microcontroller estimates motor speed set point. To determine the actual feed rate, computation is carried out through programming. The computation includes the estimation of the feed rate by utilizing, speed factor and weight factor previously obtained during calibration. The actual feed rate is compared with the fuel demand feed rate to determine the motor speed set point. The system is designed with the additional following features: a) The front facia of power supply and motor speed control module has a lockable two position (ON-OFF) selector switch. With the lockable key selected to 'ON' position, the feeding device and the motor speed control circuit can be checked independently without the microprocessor / microcontroller module. b) In case of failure/non functioning of the microprocessor/microcontroller module while the bulk solids feeding device is working, the plurality of additional interface electronic modules will take up the complete operation without interruption. The interface electronic module also take care of the protection logics. The man- machine Interface (2) provided on the door of the remote power cabinet (4) communicates with the microprocessor/microcontroller module mounted in the card rack (1). Membrane type key board is provided for operation of the system. The Existing system incorporates solid-state circuitries and their functions are described below: The Figures 2 shows the methodology adopted for the computation and control of the feeding device using solid-state electronics. An Existing method means (Refer FIGURE 2) a measurement of feed rate signals from a load cell LCI (21) and LC2 (22) and measurement of belt travel by means of encoder (220). The signal-conditioning module (210) means processing of signal from load cells (200) and Encoder (220). Instrumentation Amplifier (23) amplifies the load cell output and is fed to the summer amplifier (24). The summer amplifier (24) sums the load cell signal and subtract the Tare signal (27) to arrive to the actual material weight. To calibrate the system a test weight is used . The Load cell amplifier (210) has facility to adjust its output by variable gain amplifier (25). The Encoder signal (220) means measurement of belt weight in terms of rotary motion of the drive pulley. Feed Rate means generation of frequency proportional to the load cell amplifier output multiplied by belt speed. Feed Rate= Kg/Cm X Cm/Sec= Load cell Output X Encoder Frequency. The LCA O/P is switched ON and OFF by switch (34) to produce a voltage. The Switching frequency depends on the factor of belt speed. The Voltage Controlled Oscillator output is maintained as per the feed rate by means of feed rate circuit employed by means of pulse generator (32) and switching circuit (35). The Feedback O/P is switched ON and OFF by switch (35) to produce opposite voltage to the error amplifier (30). The error amplifier output is given to an integrator and LPF. The Output of the integrator is easy to drive the Voltage controlled oscillator (33), which is the actual feed rate. FIGURE 3, shows the arrangement of signal conditioning module referred as 3 in FIGURE 1. The Weighing system (200) has two load cells LCI (21) and LC2 (22). These two signals are independently given to signal conditioning module. The milli volt signals from the load cell are given to an instrumentation amplifier (53 and 54), which amplifies the signal by a factor 'K' and provides a voltage to current converter circuit (55 and 56). The output of the voltage to current converter is between to 4-20 mA. A Calibration probe signal (210) is given to a pulse shaping circuit (57) to generate span timing. FIGURE 4 shows the arrangement inside the card rack referred as 1 in FIGURE 1. The card rack interfaces the signals. The Weight signal representing the Load cell LCA1 and LCA2 is given to the analog input module (60). The Customer demand signal representing feed rate in terms of Tonnes/hour is given to the analog input module (60). To determine the drive speed (11) of FIGURE 1 i.e., eddy current drive, the employed tacho generator output is given to a pulse input module (63). To determine the calibration probe timing the CALP signal is given to a pulse input module (63). A Man machine interface shown as 2 in FIGURE 1 provide capability to enter the constants to the CPU memory (61) like test weight, weigh span, volume of the weigh span, initial density and etc. The CPU (61) drives a analog output module to give feedback in terms of actual feed rate. The computed speed signal to maintain the feed rate is given to a transfer circuit (64). To make the control in operation in the event of CPU (61) failure a solid- state redundancy backup (65) is built in and its output is given to the transfer circuit (64). The Output of the transfer circuit is the set point for the speed regulation circuit (66). The Speed of the eddy current clutch refer llof FIGURE 1 is varied by varying the current through the clutch coil. A110V AC supply is given to the speed regulation circuit (64) for the speed regulation circuit to control the speed of the eddy current clutch drive. Normally the CPU computes LCA1 and LCA2 and tacho generator signal to determine the feed rate and the desired speed is derived as set point to the speed regulation circuit (66) and the feed rate is determined in terms of Tonnes/hour. In the event of the load cell failure the feeder will run and maintain the feed rate based on the density estimated from the historical data. In the calibration mode actual tare and test weight signals are measured and factorized and stored in the memory. The span time determined from the CALP signal is used with tacho signal to determine the speed signal. A. The System will switch over from normal to assumed density mode incase of the following factors: 1. If any of the load cell value is not within the acceptable limits, which is stored in permanent memory. 2. If the difference between the two loads cell outputs is more than the permissible limit ((LC1-LC2) > (LC1 + LC2)/8). 3. Manual mode changes over. B. Following are the steps adopted in the computation process: 1. Two load cell signals are summed and tare, which is estimated during calibration, is subtracted from it to get the weight of material on weighing span of belt. 2. The result obtained is multiplied with calibration factor to obtain the belt load per unit length. 3. The Weight of material on belt is divided by weigh span volume to arrive at the current density. 4. The Current density stored in memory is averaged for every 3 hours to get historic density, which is used in assumed density mode of operation. 5. The RPM of belt arrived from the tachometer output signal is multiplied by suitable scaling factor to get the belt travel per second. 6. The belt travel per second and belt load per unit length is multiplied to get the feed rate. 7. The feed rate is then compared with the demanded feed rate and the error obtained is processed to control the belt seed. 8. The feed rate is fed to the tantalizer as pulses to get the integrated fuel intake. C. Assumed Density mode of operation: In this mode of operation, 1. The historic density obtained in the actual density mode is multiplied with weigh span volume to get the approximate weight on belt. 2. The Weight on belt is divided by weigh span length to get the belt load per unit length. 3. The RPM of belt arrived from the tachometer output signal is multiplied by suitable scaling factor to get the belt travel per second. 4. The belt travel per second and belt load per unit length is multiplied to get the feed rate. 5. The feed rate is then compared with the demanded feed rate and the error obtained is processed to control the belt speed. 6. The feed rate is fed to the tantalizer as pulses to get the integrated fuel intake. We Claim: 1. A system for online computation and control of bulk solids feed rate to pulverizers adapted in coal-fired boilers, comprising: - a feeding device having a motor (10) driving an eddy current clutch (11) which drives a conveyor belt of the pulverizers, the feeding device comprising a signal conditioning module (3), and additionally having an integral cabinet (5); - a remote power cabinet (1) having a man-machine interface (2), and a card rack (1), the interconnections between the remote power cabinet (4) and the integral cabinet (5) being established via a screened cable (6); - a plant-control desk (7) storing and displaying data relating to coal integration and feed rate for operator's control; and - a calibration probe (9) operable to perform calibration by using test- weights attached to the feeding device, characterized in that the card rack (1) comprises atleast one microprocessor/microcontroller module, a power-supply and motor speed control, and a plurality of interface electronic modules, and in that the microprocessor/ microcontroller module determines the actual feed rate based on a speed factor and a weight factor estimated during the calibration of the feeding device, the actual feed rate being compared with a fuel-demand feed rate signaled by the signal conditioning module (3) to determine a motor-speed set-point by means of the power supply and motor speed control module which regulates the eddy current clutch (11) thereby regulating the speed of the conveyor belt of the pulverizers. 2. The system as claimed in claim 1, wherein the power supply and motor speed control module has a two-way on-off selector switch. 3. The system as claimed in claim 1, wherein the man-machine interface (2) provides diagnostic features enabling the operator to initiate remedial activities when necessitated. 4. A system for online computation and control of bulk solids feed rate to pulverizers envisaged in coal-fired boilers as herein substantially described and illustrated with reference to the accompanying drawings. The invention relates to a system for online computation and control of bulk solids feed rate to pulverizers adapted in coal-fired boilers, comprising a feeding device having a motor (10) driving an eddy current clutch (11) which drives a conveyor belt of the pulverizers, the feeding device comprising a signal conditioning module (3), and additionally having an integral cabinet (5), a remote power cabinet (1) having a man-machine interface (2), and a card rack (1), the interconnections between the remote power cabinet (4) and the integral cabinet (5) being established via a screened cable (6), a plant-control desk (7) storing and displaying data relating to coal integration and feed rate for operator's control; and a calibration probe (9) operable to perform calibration by using test- weights attached to the feeding device. The card rack (1) comprises atleast one microprocessor/microcontroller module, a power-supply and motor speed control, and a plurality of interface electronic modules, and in that the microprocessor/ microcontroller module determines the actual feed rate based on a speed factor and a weight factor estimated during the calibration of the feeding device, the actual feed rate being compared with a fuel-demand feed rate signaled by the signal conditioning module (3) to determine a motor-speed set-point by means of the power supply and motor speed control module which regulates the eddy current clutch (11) thereby regulating the speed of the conveyor belt of the pulverizers.

Documents:

358-KOL-2005-FORM-27-1.pdf

358-KOL-2005-FORM-27.pdf

358-kol-2005-granted-abstract.pdf

358-kol-2005-granted-claims.pdf

358-kol-2005-granted-correspondence.pdf

358-kol-2005-granted-description (complete).pdf

358-kol-2005-granted-drawings.pdf

358-kol-2005-granted-examination report.pdf

358-kol-2005-granted-form 1.pdf

358-kol-2005-granted-form 18.pdf

358-kol-2005-granted-form 2.pdf

358-kol-2005-granted-form 3.pdf

358-kol-2005-granted-gpa.pdf

358-kol-2005-granted-reply to examination report.pdf

358-kol-2005-granted-specification.pdf