|Title of Invention||
AN APPARATUS FOR FLOW SIMULATION FOR MEASURMENT OF PULVERIZED PARTICLE MASS FLOW
|Abstract||An apparatus for flow simulation for measurement of pulverized particle mass flow, said simulation apparatus comprising: a pulverized particle feeder; a simulator pipe for receiving said pulverized particles from the feeder; a cyclone for trapping the pulverized particles; and an induced draft fan arranged at the end of said simulator pipe for expelling the air from the system; thereby completing the mass flow of pulverized particles.|
FIELD OF APPLICATION
The present invention relates to an apparatus for flow simulation for measurement of pulverized particle mass flow. In particular it relates to flow simulation and measurement of particle mass flow of pulverized coal in a circular pipe through optical interception of laser through-beam.
BACKGROUND OF THE INVENTION
Pulverized coal is used as a base fuel in thermal power stations. The coal is pulverized in mills and discharged from the milling system through circular pipes into the furnace. The measurement of coal flow and the sampling of pulverized coal takes place in these pipes. For development of measurement systems, flow visualization systems and sampling systems for such pulverized flows as also other pulverized particles, it is required to have a scaled down simulator for pulverized particle flow where the calibrated quantities of flow can be made to be flown inside a pipe.
In Indian power stations, there is a difference to the tune of 20-30 % between the coal consumption computed from weigh bridge readings at the entrance to a plant and the actual consumption in the boilers. This calls for accurate measurement of pulverized coal flow into boilers. Measurement of coal flow is required for control of the input energy to coal fired thermal power plants. At present, indirect methods are used as parameters for control of the coal input in boilers.
Though the developments in information technology have been very rapid and swift, primary sensor technology is lagging behind and developments have not kept pace with the requirements of the thermal power stations. Instrumentation for reliable measurement of coal flow is not presently available.
The various methods used for pulverized coal flow measurement are:
Belt weighment at the entrance of the raw coal bunkers.
Bunker level calibration and flow measurement based on bunker level.
Volumetric measurement based on raw coal feeder speed.
Volumetric measurement based on pulverized coal feeder speed (wherever these exist).
Gravimetric measurement at outlet of raw coal feeder.
Pressure drop across pulverized coal pipe leading to the burner through fixed geometry
Variable orifice dampers.
Dirty pilot tube measurement in the coal pipe leading to the burner.
Passive electrostatic sensors.
Screw-in microwave sensors.
Passive acoustic sensors.
However, instrumentation for reliable measurement of coal flow is not available in the known systems. There was therefore, a need for development of a reliable technique for measurement of pulverized coal flow in the pipes leading to each of the burners in a coal fired thermal power station.
SUMMARY OF THE INVENTION
Thus the main object of the present invention is to provide an apparatus for flow simulation of pulverized particle mass flow, like for example, coal.
Another object of the invention is to provide a device for digital measurement of pulverized gross particle mass flow rate through optical interception of a laser through-beam perpendicular to the direction of flow.
These and other objects are achieved by providing a pulverized particle flow simulator in the apparatus of the present invention for simulating pulverized particle flow inside a pipe. The pipe can be of circular, square or rectangular section and horizontal, vertical or inclined in orientation. Such simulated gross mass flow of pulverized particles can then be digitally measured through optical interception of a laser through-beam perpendicular to the direction of flow.
The set-up used in the present invention for simulating uniform, reliable and accurate pulverized particle flow (typically coal) in a horizontal pipe of 200 mm diameter and 2000 mm length has been developed. The loss of pulverized particles to the environment is less than 0.05%. The capacity of pulverized particle flow simulator is 50-300 kg/h at an air to particle mass ratio of 1.5:2.5kg of air/kg of particles. The standard particle size (typically power station coal) that can be measured is sized at 70 % of the mass below 75 ^m size. However, particle sizes of 50-100 urn can be used. Pulverized particle mass with moisture contents of a maximum of 20 % can be used in the present system.
The pulverized particle simulator can be fabricated out of mild steel and stainless steel members. Active flow elements are used for inducing the flow. The simulator consists of three sections. A pulverized particle feeder, a simulator pipe and a particle trap and draft induction system.
The calibrated pulverized particle flow can be achieved through a vibratory feeder with a convergent-divergent nozzle which is vibrated through pneumatic activation which in turn is actuated from a compressed air source.
The simulator pipe consists of a circular pipe through which the particles flow in the predesigned manner. The particles arrive into the test pipe through the feeder and these are accelerated through primary air which is supplied through a blower which is capable of 0-100 % flow variation. This is typically horizontal but it can be vertical or inclined and the cross section can be rectangular, square, oval or of any geometry. It is typically of 200 mm diameter and 2000 mm length but the diameter and length can be altered depending on the test requirements. The flow measurement/visual imaging is possible through air-curtained ports which are located at the center of the pipe. The simulator pipe can be isolated from vibrations through rubber expansion bellows on either side and anti-vibration mounts for support.
The particle trap and draft induction system provided at the end of the test simulator pipe comprises a cyclone which traps the particles and this is followed by an induced draft fan (with facility for flow variation from 0 to 100 %) for expelling the air from the system and thereby completing the flow.
The overall size (L x B X H) of the unit can be about 7mx2mx4m and the electric
power requirement (composed of power to ID fan, air blower, air compressor, etc.) is typically 4.1 kW (230 V AC in single phase). The invention can be scaled up or down in size and power requirement.
For measurement of the pulverized particle mass flow a novel reliable, accurate, non-reactive, non-mixing type PC compatible portable device is provided. The device is capable of measuring pulverized particle flows (typically coal flows) of the order of 0-150 kg/h (for a pipe of 200 mm diameter) in the range of 0-5000 kg/m2/h. However the principle can be used for particles other than coal, for higher flows and for higher diameters of piping. The laser through-beam sensor is mounted across the flow without contact with the particle flow. The transmitter emits the radiation. The optical opacity offered by the pulverized particle mass flowing in the pipe across a given cross section tends to diffract the light proportionate to its mass flow at that section. Hence the receiver induces a voltage proportional to the intensity of light received. The voltage induced by the receiver is used to calibrate the mass flow rate. The digital output is acquired through RS 485 data protocol. The standard particle size that can be measured is fixed at 70% of the mass below 75 urn size. However, the principle can be used for other particles and other particles sizes as well. The normal primary air to particle mass ratio is around 1.5-2.2 kg of air/kg of partide mass. The instrument is insensitive to moisture contents up to 10 %. For very high moisture contents above 10 % and for fineness and air/particle mass ratio different from the above, calibration of the instrument is required.
The instrument is useful for field applications as a portable instrument (0.5 m x 0.5 mx 0.5 m) and it has an accuracy of 0.5 % and the response time is 0.5 ms. It operates on a power source of 230 V AC (100 W). However, the principle can be used for more compact, more accurate systems with a different power level.
For obtaining a digital output, PC-based data acquisition system is provided which consists of:
• Personal computer
• Signal conditioning
• DAQ hardware
Some of the salient aspects of signal conditioning and processing requirements for obtaining digital output from the sensor are:
Thus the present invention provides an apparatus for flow simulation for measurement of pulverized particle mass flow, said simulation apparatus comprising: a pulverized particle feeder; a simulator pipe for receiving said pulverized particles from the feeder; a cyclone for trapping the pulverized particles; and an induced draft fan arranged at the end of said simulator pipe for expelling the air from the system; thereby completing the mass flow of pulverized particles.
The invention further provides a device for measuring gross mass flow of pulverized particles through a simulator pipe of the present invention, said device comprising: a sensor for optically intercepting a laser through-beam perpendicular to the direction of pulverized particle flow; and a PC-based data acquisition system for obtaining digital output proportionate to said mass flow through said simulator pipe.
BRIEF DESCRIPTION OF THE INVENTION
The invention can now be described with the help of the figures of the drawing where
Figure 1 shows a view of the simulator used for simulating particle flow.
Figure 2 shows a view of the system for positioning of the coal flow sensor in
Figure 3 shows a view of the coal feeder used in the simulator of Figure 1.
Figure 4 shows a block diagram of pulverized particle flow sensing using
laser thrubeam sensor.
Figure 5 shows the block diagram of Figure 4 with all the blocks.
Figure 6 shows a connection diagram of the particle flow measurement system.
Figure 7 shows a working diagram of equipment used in particle (coal)
flow measurement of the present invention.
Figure 1 shows the three sections of a test set-up used for the present invention for simulating uniform reliable and accurate pulverized particle flow. A vibratory feeder 1 is provided for feeding pulverized particles to a simulator pipe 2. A given quantity of pulverized flow is achieved through the simulator pipe 2.
A blower 3 like a primary air fan is used for accelerating the particles through the simulator pipe 2. Uniform pulverized particle flow (typically coal) is achieved through the simulator pipe. The flow of pulverized particles-air mixture in the pipe (typically horizontal but it can also be vertical or inclined) is in the finely mixed turbulent mode. The velocity profile radially across the pipe is uniform in the X-X, Y-Y and any intermediate directions perpendicular to the flow axis.
The pulverized particle flow rate, air flow rate and thereby the pulverized particle- air ratio can be varied or set to any pre-fixed value depending on the requirement. The pulverized particle flow rate variation is achieved through a pneumatic feeder where vibrations of the hopper and the feeder are actuated through compressed air. The feed rate is adjusted by adjusting the vibration level and thereby the compressed air flow rate and pressure through the vibrating tool.
At the end of the simulator pipe 2 a cyclone 5 is provided for trapping the particles. The cyclone 5 is followed by an induced draft fan 6 for expelling the air from the system and thereby completing the flow. The ID fan 6 is configured for flow variation from 0 to 100%.
The recovery of the input pulverized particle mass at the end of the test section is almost complete. The loss of particles to the environment is less than 0.05%. This is achieved through the cyclone as well as the placement of the FD fan, which ensures that the pulverized particles after their flow through the test piping will get effectively trapped in the hopper of the cyclone.
The simulator pipe 2 is provided with air curtained ports 4 located at the center of pipe 2. The flow measurement and visual imaging is possible through these ports 4.
As shown in Figure 3, the flow simulation starts with a hopper 10 where weighed quantity of pulverized fuel is loaded. The flow is achieved by a feeder which is composed of a hopper which ends in a steel grate 11 of 5 mm thickness (typical) over which stainless steel balls 12 typically of 20 mm diameter are placed. Below the grate 11 and the stainless steel balls 12 is a convergent divergent nozzle 13 which restricts and controls the free fall of pulverized particle flow. The entire hopper and feeder are isolated from the main flow pipe through rubber bellows. The feeder is actuated by a pneumatic vibrator consisting of an eccentric plate rotating on a pneumatic air tool which is energized by a compressed air supply. The movement of particles through the vertical portion of the hopper and piping is thus achieved by the vibrator feeder. The particles are then accelerated by a primary air fan 3 which imparts momentum to the pulverized particles through the horizontal (it is typically horizontal and can be vertical or inclined if required) portion of the piping which is the test piping for flow simulation. A test window 4 is located at the center of the test pipe. After its passage in the test piping, the pulverized particle mass is extracted in a cyclone 5 while the air and dust is expelled through an induced draft fan 6. The ID fan 6 thus completes the flow by providing the suction force for the flow movement. During the passage of the pulverized particles through the test piping 2, various types of measurements can be conducted on the flowing particle mass for which the test window 4 is provided.
The test window 4 has special features of an air curtain where sealing air prevents the leakage of the particles outside the pipe while at the same time there is total accessibility for measurements, insertion of instruments, flow visualization, etc.
The simulator pipe 2 is fully isolated from vibrations arising from the pulverized particle feeder, blower and fans by rubber bellows in the flow piping. It is also isolated by anti-vibration mounts and hence free of any type of vibrations.
The measurement windows are designed with sealing air curtains and therefore can be used with and without glass cover. In the case of glass cover there is provision for maintaining cleanliness of the glass cover to prevent sticking of the flowing particles onto it.
Figures 4 and 5 show the sensing system or the measuring device for sensing the pulverized particle flow using a laser through-beam sensor.
The particle mass flow which is in turbulent flow (at a given setting of the feeder, primary air fan and induced draft fan) is proportional to the area of optical interruption of the laser through-beam.
The digital flow measurement is carried out through optical interruption of a laser through-beam perpendicular to the direction of the flow in the X-X, Y-Y or intermediate axes. Recording of instantaneous pulverized particles flow rate (kg/s of kg/h) and flow velocity (m/s) are done continuously. Computation of the average pulverized particles flow rate (kg/s or kg/h) over a period of time can be done through integration of instantaneous pulverized particles flow rate. Computation of total pulverized particles flow (kg) over a period of time can be done through integration of instantaneous pulverized particles flow rate and the time period. The sensor is non-reactive and nor-interactive. It does not come into direct contact with the pulverized particles. Sampling of pulverized particles is not required. The device is portable and light-weight. It can be used for field measurements.
According to the present invention the calibration for sensing pulverized particle (typically coal) flow is done using the pulverized particle (typically coal) flow simulator. A weighed quantity of pulverized particles (typically 15-25 kg) is loaded into the hopper. Uniform particle and air flow are maintained by adjustment of the particle feeder air flow (from the compressor), the primary air flow rate (blower) and the damper setting of the ID fan. The time taken for the depletion of the pulverized particles is noted. Simultaneously the readings of the laser sensor are recorded. The time intervals for the readings are 50-100 ms. The readings are taken over entire period of pulverized particle flow till the total mass of particles is depleted in the hopper. The quantity of particles is thus known as the the particle mass is already weighed. The output reading of the measuring device is processed to find the average reading in mV.
The tests are repeated for several particle flow rates ranging from low flows to high flow rates. Around 5 to 6 test runs are conducted and the readings of particle flow and voltage output of the device are fitted to a linear curve of the form.
Pulverized particle flow = Ao + Ai (Voltage)
Once calibrated, the constants are fed into data analysis software to provide digital partide flow measurements on-line on a computer screen.
Once calibrated, the calibration of the device can vary under the following circumstances for which fresh calibration is required.
Type of particles: Typically coal is used but for other particles the system is to be calibrated.
Fineness of pulverized particles: The standard particle size distribution is 70 % of the mass below 75 urn size. When the particle fineness is different from the standard particle size, calibration of the device is required.
Primary air to particle ratio is around 1.5-2.2 kg of air/kg of solid particle mass. This is the normal primary air fuel ratio in most pulverized coal systems used in power stations and the same is maintained.
Moisture content of the particle mass: The readings are insensitive to moisture contents up to 10%. For very high moisture contents above 10 %, calibration of the device is required.
The list of attachments describing the invention are given in the following attachments:
• Line regulation is measured from low line to high line at rated load.
• Load regulation is measured from 20 % to 100 % of rated load at 110 V AC input.
• Ripple & noise is measured by using a 0.1^F/630 V metalized capacitor & a
47|xF electrolytic capacitor parallel on the test point at rated load and 110 V
• Efficiency is measured at rated load and 110 V AC input.
• Hold up time is measured at full load and 110 V AC input.
1. An apparatus for flow simulation for measurement of pulverized particle mass flow, said simulation apparatus comprising:
a pulverized particle feeder;
a simulator pipe for receiving said pulverized particles from the feeder;
a cyclone for trapping the pulverized particles; and
an induced draft fan arranged at the end of said simulator pipe for expelling the air from the system;
thereby completing the mass flow of pulverized particles.
2. The apparatus as claimed in claim 1, wherein a blower, like for example, a primary air fan, is provided for imparting momentum to the pulverized particles through said simulator pipe.
3. The apparatus as claimed in claims 1 or 2, wherein said simulator pipe is substantially horizontal and is provided with a test window preferably located at the center of the simulator pipe, said test window comprising curtained ports for flow measurement and visual imaging.
4. The apparatus as claimed in claim 1, wherein said feeder is actuated by a pneumatic vibrator energized by compressed air for varying the air flow rate and thereby the pulverized particle-air ratio in said simulator pipe.
5. The apparatus as claimed in claim 1, wherein said induced draft fan for expelling the air from the system is configured for flow variation from 0 to 100%.
6. The apparatus as claimed in claim 1, wherein a steel grate is provided at the end of the hopper with stainless steel balls placed thereon and a convergent-divergent nozzle arranged below said steel grate for restricting and controlling free fall of pulverized particle flow.
7. The apparatus as claimed in the preceding claims, wherein said simulator pipe is isolated from the pulverized particle feeder and the blower fan using rubber bellows and anti-vibration mounts for making it free from any vibrations .
8. A device for measuring gross mass flow of pulverized particles through a simulator pipe, said device comprising:
a sensor for optically Intercepting a laser through-beam perpendicular to the direction of pulverized particle flow; and
a personal computer based data acquisition system for obtaining digital output proportionate to said mass flow through said simulator pipe.
9. The device as claimed in claim 8, wherein the area of optical interruption of said laser
through-beam is proportional to the mass flow for a given setting.
10. The device as claimed in claim 9, wherein said personal computer-based data
acquisition system comprises personal computers, transducers, signal conditioning and
11. The device as claimed in claim 8, wherein said PC based data acquisition system is
provided with an integrator for computation of average and total pulverized particle
flow over a period of time.
12. An apparatus for flow simulation for measurement of pulverized particle mass flow
substantially as herein described and illustrated in the accompanying drawings.
|Indian Patent Application Number||492/CHE/2005|
|PG Journal Number||23/2010|
|Date of Filing||27-Apr-2005|
|Name of Patentee||CENTRAL POWER RESEARCH INSTITUTE|
|Applicant Address||SIR C.V. RAMAN ROAD, SADASHIVANAGAR P.O. P.B. NO. 8066, BANGALORE 560 080, INDIA|
|PCT International Classification Number||G01F1/00|
|PCT International Application Number||N/A|
|PCT International Filing date|