A Study on Electro-Static Precipitator and its Voltage Controller (BAPCON)

A Study on Electro-Static Precipitator and its Voltage Controller (BAPCON) By

Chaitanya Krishna. Vallurupalli(091FA06055) Vignan University, Vadlamudi.

Under the Guidance of: Y. Suresh Kumar A.D.E/ EM-III/Stage-I/Dr. NTTPS

1. Rail Unloading House 2. Junction House 3. Coal Conveyor 4. Boiler Coal Bunker 5. Bucket Wheel Machine 6. Coal Feeder 7. Pulverizing Mill 8. Primary Air Fan 9. Boiler Burner 10. Boiler 11. Forced Draught Fan 12. Air Heater 13. Electrostatic Precipitator 14. Induced Draught Fan 15. Main Chimney 16. Superheater 17. High Pressure Turbine 18. Boiler Reheater 19. Intermediate Pressure Turbine 20. Low Pressure Turbine 21. Rotor 22. Stator 23. Generator Transformer 24. Condenser 25. Condensate Extraction Pump 26. Low Pressure Feed Heaters 27. Deaerator 28. Boiler Feed Pump 29. High Pressure Feed Heaters 30. Economizer 31. Steam Drum 32. Cooling Tower 33. Circulating Water Pumps 34. Circulating Water Make-Up Pumps 35. FGD Absorber Tower

An electrostatic precipitator is a large, industrial emission-control unit. It is designed to trap and remove dust particles from the exhaust gas stream of an industrial process. Precipitators are used in these industries:

o o o o o

Power/Electric Cement Chemicals Metals Paper

o Electrostatic precipitation is a method of dust collection that uses electrostatic forces, and consists of discharge wires and collecting plates. o A high voltage is applied to the discharge wires to form an electrical field between the wires and the collecting plates, and also ionizes the gas around the discharge wires to supply ions. o These dust-laden gases pass through an electrostatic precipitator that collects most of the dust. Cleaned gas then passes out of the precipitator and through a stack to the atmosphere.

o Precipitators function by electrostatically charging the dust particles in the gas stream o ELECTROSTATIC PRECIPITATOR is an aid in reducing atmospheric pollution by removing the fly ash before it goes out of the smoke stack o The air which enters ESP is almost up to 99.9% cleaner than when it is released.

o Ionization - Charging of particles o Migration - Transporting the charged particles to the collecting surfaces o Collection - Precipitation of the charged particles onto the collecting surfaces o Charge Dissipation - Neutralizing the charged particles on the collecting surfaces o Particle Dislodging - Removing the particles from the collecting surface to the hopper o Particle Removal - Conveying the particles from the hopper to a disposal point

o The filtration principle of electrostatic Precipitator attraction requires a constant source of charge (electric) to maintain filter efficiency and filter loading can insulate the particle from the charge. o the principle that positive-charged and opposing negative-charged objects attract to each other and similarly charged objects repel.

o The shell structure encloses the electrodes and supports the precipitator components in a rigid frame to maintain proper electrode alignment and configuration o Collection plates and discharge electrodes are normally attached to the frame at the top so that the elements hang vertically due to gravity. o ESP is installed on a coal-fired boiler, the flue gas temperature should be kept above 120°C (250°F) at all times to prevent any acid mists in the flue gas from . ESP shell condensing on ESP internal components

o Discharge electrodes emit charging current and provide voltage that generates an electrical field between the discharge electrodes and the collecting plates. o The electrical field forces dust particles in the gas stream to migrate toward the collecting plates. o The particles then precipitate onto the collecting plates. o The size and shape of the electrodes are governed by the for discharge wires mechanical requirements for the system, such as the industrial process on which ESPs are installed and the amount and properties of the flue gas being treated. Most designs have traditionally used thin, round wires for corona generation. o Some designers have also used twisted wire, square wire, barbed wire

Emitting Frame

Spiral Electrode

Collecting Electrode

Emitting System Support TEMPORARY HANGER BOLT

HANGER BOLT SUPPORT INSULATOR

CHANNEL WITH INNER ROOF

BEAM

VERTICAL BOX

HORIZONTAL EMITTING FRAME

BEAM

o Collection plates are constructed in various shapes, as shown o These plates are solid sheets that are sometimes reinforced with structural stiffeners to increase plate strength o Precipitator performance depends on its size and collecting efficiency. Important parameters include the collecting area and the gas volume to be treated. o This design minimizes the amount of excess rapping energy required to dislodge the dust from the collection plates, because the energy is distributed evenly throughout the plate.

o Rappers are time-controlled systems provided for removing dust from the collecting plates and the discharge electrodes as well as for gas distribution devices and for hopper walls . o Dust that has accumulated on collection and discharge electrodes is removed by rapping. o Rapping systems may be actuated by electrical or pneumatic power, or by mechanical means o Different Places of rapping.  Discharge Electrode Rapping  Collecting Plate Rapping  Gas Distribution Plate and Hopper Wall Rapping  Improving Rapping System Performance

COLLECTING FRAME

COLLECTING PLATE

SHOCK BAR

o Precipitator hoppers are designed to completely discharge dust load on demand. o Typically, precipitator hoppers are rectangular in crosssection with sides of at least 60-degree slope. o These hoppers are insulated from the neck above the discharge flange with the insulation covering the entire hopper area. o In addition, the lower 1/4- 1/3 of the hopper wall may be heated. Discharge diameters are generally 8" - 12". o When the electrodes are rapped, the dust falls into hoppers and is stored temporarily before it is disposed in a landfill or reused in the process .

o A discharge device is necessary for emptying the hopper and can be manual or automatic a periodic basis. o Pneumatic conveyers use blowers to blow or move the dust through the conveyor. o Pneumatic conveyors can be positive pressure (dust is moved by a blower) or vacuum type systems (dust is pulled by a vacuum). o In large ESPs, dust is usually discharged from hoppers by using a combination of devices. o Either rotary airlock or double dump valves empty dust into screw, drag, or pneumatic conveyers that move dust for final disposal into trucks or storage bins.

o An ESP is divided into a series of independently energized bus sections or fields in the direction of the gas flow. o Precipitator performance depends on the number of individual bus sections, or fields, installed.

o ESP consisting of four fields, each of which acts as an independent precipitator. This design feature, called field electrical Sectionalization, allows greater flexibility for energizing individual fields to accommodate different conditions within the precipitator.

o High-voltage equipment determines and controls the strength of the electric field generated between the discharge and collection electrodes. o This is accomplished by using power supply sets consisting of three components: a step-up transformer, a high-voltage rectifier, and control metering and protection circuitry (automatic circuitry). o The power system maintains voltage the highest level without causing excess sparkover between the discharge electrode and collection plate. o These power sets are also commonly called transformer-rectifier (T-R) sets.

o In a T-R set, the transformer steps up the voltage from 400 volts to approximately 50,000 volts. o This high voltage ionizes gas molecules that charge particles in the flue gas. The rectifier converts alternating current to direct current. o Direct (or unidirectional current) is required for electrical precipitation. Most modern precipitators use solid-state silicon rec-tifiers and oil-filled, highvoltage transformers. o The control circuitry in a modern precipitator is usually a Silicon-controlled Rectifier (SCR) automatic voltage controller with a linear reactor in the primary side of the transformer. o The transformer-rectifier set is connected to the discharge electrodes by a bus line.

o An automatic voltage control is an electronic device used to regulate the application of direct current (DC) power into a field of an electrostatic precipitator. o Voltage control varies the power to the transformer-rectifier in response to signals received from sensors in the precipitator and the transformer-rectifier itself. o It monitors the electrical conditions inside the precipitator, protects the internal components from arc-over damages, and protects the transformer-rectifier and other components in the primary circuit. o Its functions are:  Optimize power application  Spark reaction  Protect system components by adhering to component limitations  Tripping

They are two types of voltages controller:

 BAPCON  RAPCON

o BHEL's ADVANCED PRECIPITATOR CONTROLLER designed Specifically for Electrostatic Precipitators, is one of the most sophisticated power controllers available today. o The controller utilizes 8085 [INTEL] family of microprocessor components and support hardware. o Intermittent charging, requirement of wide charge ratio

(CR) range of 1:159. o Optimizer logic for C.R, avoids tedious manual tunning. o Peak & valley KV measurement : Diagnostic & tunning

facilitated.

FEATURES UP BAPCON o Effective spark rate control. o Detection of Spark / arc by di/dt or dv/dt. o Automatic current control based on step and ramp control settings. Intermittent charging technique. o Measurement of Peak, Mean & Valley ; secondary voltage. o Base charge setting & measurement. o Automatic Selection of charge ratio based on VI Characteristics of the ESP. o Annunciation of warning and trip alarms.

E H O 1 2 3 4 5 6 7 8 9 ■ P L

Precipitator current Precipitator voltage Sparks per minute Im limit Is limit S control Time control Stabilization time U.V. Limit C.R. Pulse current limit Repeat time Address Peak & valley voltage Base charge Base charge current

PARAMETER 

PRECIPITATOR CURRENT E PRE CIPITATOR VOLTAGE H SPARKS PER MIN 0 Im LIMIT 1 Is LIMIT 2 S CONTROL 3 T CONTROL

4

STABILE. TIME(SEC)

DESCRIPTION

RANGE

DEFAULT

METER --

--

SETTINGS --

--

--

--

--

--

--

0

0-104%

Operating Current Limit

Is

0-Im Limit

Step Control Time Control

LIMIT 2 3

SET 0-25% (Is) 0-109% 10.9 min.

Measured current in % of the Imax Measured Voltage in % of the kVmax No. of sparks per minute measured Max. current in normal mode

Stabilization Time in Sec.

POT.

4

0-127

100%

5% 20% 20 min. 20

PARAMETER 5 UV LIMIT 6 CHARGE RATIO 7 8

PULSE CURRENT LIMIT REPEAT TIME (x6 min)

9

ADDRESS

P

BASE CHARGE SET

L

BASE CHARGE CURRENT

DESCRIPTION

POT.

Under Voltage Limit

METER 5

Intermittent Charging Ratio

6-CR

Maximum Current when CR is set more than 1:1

7

0-209%

Optimisation Repeat Time

8

1-255

Address for control in remote mode. Base Charg Current Set

9

RANGE

DEFAULT

0-104%

SETTINGS 10% (kV max.)

1-159

1 200 20( 120min)

0-99

0

P

0-49%

0

—

—

—

Base Charg Current measured in % of Imax.

PEAK & VALLEY VOLTAGE Peak & Valley voltage measured.(% of kVmax)

o To release the ash from the collecting electrode into the hopper the rapping system is provided by BHEL is RAPCON. o The RAPCON is a dedicated microprocessor based device from controlling the rapping motors.

o Highly Reliable platform o Standalone operation o Local & Remote mode operation o Real Time Clock based motor operation o Advanced algorithms support o Standby mode

o o o o o o o o o o o o o o o

Error checking for the motors. Setting of rapper timings. Setting of real time. Auto on/off selection. Manual on/off selection. Password protection. Setting of program set no. Reading of rapper times. Reading of real time. Reading of program set no. Reading of rapcon address. Reset alarm. Stan by mode selection. Communication with IOS-PC Rapping factor selection - [IOS]

COMMAND TO RAPCON o Force stand alone / standby o Auto ON / OFF for all motors o Manual ON / OFF for all motors o Program set selection 1 64 o Time factor 0 - 25.5 o Alarm reset

REPLY FROM RAPCON o Remote local o Auto ON / OFF status o Manual ON / OFF status o Program set o Time factor o Alarm status o Motor status o Motor status 30 sec. In advance o Next on status

CONCLUSION

The increase of the demand, day-by-day, generation also increases, resulting the causes of air pollution adding in to environment. The fly-ash, the main waste is a hazards to human life , by using Electrostatic precipitator can purify the ash from flue gases. BAPCON and RAPCON are used to maximize the efficiency of collecting rate of fly-ash.