ASH HANDLING SYSTEM

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The Ash Handling of modern day boilers can be categorized into two major types i.e. Mechanical type and Pneumatic Type.

Pipe Rack for Ash handling System

 We can divide Mechanical type ash handling broadly into: 1.Use of Screw/Belt Conveyors and Bucket Elevators.
The use of screw/belt conveyors and bucket elevators is mostly done in small capacity plants with capacities not exceeding 2-3 TPH.The Limitation of screw conveyors and bucket elevators is that it cannot handle huge capacities and is maintenance prone.

Power Plant

Densveyor Arrangement

2. The use of Chain Conveyors.
Use of chain conveyors is highly successful in higher capacity plants up to 7-8 TPH. The chain conveyors use forged link chains and can operate extreme conditions with high degree of reliability and very less power consumption. Chain conveyors with high temperature of the bank ash as the bottom of chain conveyors can be lined with cast basalt.
 

·Pneumatic type ash handling is the most popular method used in medium level power plants. It uses dense phase conveying system for conveying ash is totally enclosed without any leakage.
Conveying material moves through the pipeline slowly as a coherent slug at a low velocity, which ensures minimum wear and tear. The system can convey materials up to a distance of around 200-250 mts. The general principle of operation for dense phase pneumatic conveying is as below.
General Principal Operation for Dense Phase Pneumatic Conveying
1. Conveying material from the ash collecting equipment is collected in hopper and is sensed by the permissive level probe provided in hopper and initiates conveying cycle. The system has dual operability either through level probe or through an auto timer. In timer mode of operation the system goes on continuous cycle after a preset time interval. Moreover the system has manual override facility.
2. The inlet valve on the top of vessel opens and allows material to gravitate into the vessel. The valve closes after the preset adjustable time delay.
3. Once the valve closing is ensured through a limit switch valve its circumferential inflatable seal inflates and ensures complete leak proof.
4. Now, convey air is injected into the vessel after ensuring seal pressure. Thus vessel is pressurised and material resistance leads to pressure build up which conveys material to destination point.
5. When conveying is complete, the pressure drops down to near atmospheric pressure and is sensed by control system. The conveying air supply to the system is then stopped.
6. Now the system is ready to accept next charge of material on command from level probe/auto timer.
7. Normally the destination side is also provided with high-level switch, which gives an alarm when filled up and prevents any further transfer of material into it.
8. The system is provided with various accessories like bag filters, ash conditioner to make the system environmental friendly. In a typical ash handling plant, the ash storage silo is designed for 1-day storage. The ash in silo is discharged on a lorry through an ash conditioner, which sprays water in mist form and prevents the ash from escaping to the atmosphere.

Low-velocity Dense-phase Pneumatic Conveying Systems
The ultimate system for handling difficult-to-convey materials; hot, abrasive, and wet materials; or for providing gentle handling of products to prevent degradation of friable materials or separation of blended materials.

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BASIC ELECTRICAL DESIGN

What is Ash Handling?

Ash handling refers to the method of collection, conveying, interim storage and load out of various types of ash residue left over from solid fuel combustion processes.
The most common types of ash include bottom ash, bed ash, fly ash and ash clinkers resulting from the combustion of coal, wood and other solid fuels.
Ash handling systems may employ pneumatic ash conveying or mechanical ash conveyors.
A typical pneumatic ash handling system will employ vacuum pneumatic ash collection and ash conveying from several ash pick up stations-with delivery to an ash storage silo for interim holding prior to load out and transport. Pressurized pneumatic ash conveying may also be employed.
Coarse ash material such as bottom ash is most often crushed in clinker grinders (crushers) prior to being transported in the ash conveyor system.
Very finely sized fly ash often accounts for the major portion of the material conveyed in an ash handling system. It is collected from baghouse type dust collectors, electrostatic precipitators and other apparatus in the flue gas processing stream.
Ash mixers (conditioners) and dry dustless telescopic devices are used to prepare ash for transfer from the ash storage silo to transport vehicles.
 

Ash System Components

•  Disc Type Ash Intake Valves
• Abrasion Resistant Pipe & Fittings
• Ash Receivers
• Pulse Jet Type Dust Collectors
• Rotary Airlock Feeders
• Double Dump Gate Airlock Feeder
• Exhauster Units (Vacuum Pneumatic Systems)
• Blower Units (Pressure Pneumatic Systems)
• Clinker Grinders
• Bottom Ash Hopper/Vertical Lifting Doors
• Ash Storage Silos
• Ash Conditioners
• Dry Unloaders
• Ash System Computerized HMI Controls

Combination Vacuum/Pressure Ash Handling Conveying Systems

Combination vacuum/pressure pneumatic ash conveying systems can be beneficially applied to take advantage of the simplicity of a vacuum system for the collection and delivery of ash to a transfer hopper from which it is reclaimed through an air lock feeding device for pressurized pnueumatic conveyance to a remote location silo for subsequent load out.

Silo 500Ton Silo erection on site for Ash Handling System 3x500Mw:

The Silo column after erection a ring beam with heavy fabrication placed on base plate. The bolts are tightened and the tie beam with other member are fixed in alignment. The Complete Silo erection to be done in many stages. The photos shows the final stages.

The 1500T Silo fabrication of Coulmn in intial stages are taken into utmost care for welding with good quality electrodes having high tensile strength. The bending machine is to be installed for the rolling of 10mm plate for making shell.The heavy bending machine is always required for bending of 40mmplate for ring beam.

This is really very precision heavy work to make shell in many parts and then it assembled with utmost care. The ash handling silo fabrication and erection is the first priority job which is to be taken in the early stages of project work.

The Civil Work for Cable Routing and Compressor House Building work:

In fact the civil work for excavation for cable route planned and casting of pedestal with raft are completed to all over from the substation to the transformer which is placed near the MCC room.The Trenches in the Compressor House Building are completed according to the its installation,routing of cables and its fixing arrangements etc. The cable tray support and cable Trays are fixed on the cable routing. The erection of Transformer and Bus duct are simultaneously taken. The Panels are placed on their base fixing arrangement.The Switch Gear Panel are installed according to their layout location. It is a proper planning are to be taken to all the above work during the rainy season. The digging the excavation work, casting the slabs, the civil work is more and consume major duration of Project. All MCC Panel were placed with plastic sheet wrapping so moisture could not enter into the inner control circuit.


THE GENERAL PROJECT SCHEDULE FOR COMPLETION:
OF COMPRESSRE HOUSE :

• Cable pool pit between compressor room & SWGR building cable trench Approx. 15Cum
• Vinaratex on external of compressor house building Approx.1000Sq.m
• Internal POP Approx.950Sq.m
• Oil bound distemper Approx.950 Sq.m
• Fixing of Doors & Windows 15Nos. --Approx.70Sq.m
• Roof Water Treatment -Approx.500Sq.m
• Plinth Protection And Drain- Approx. 70 Sq.m

ELECTRICAL TESTING TO BE CARRIED OUT.

HT & LT Transformers tests :

1) Insulation Resistance Test ( With 5KV Megger)

2) Magnetizing Current test ( at Normal Tap)

3) Magnetic Balance Test ( at Normal Tap)

4) Ratio test

5) Vector Group test ( at Normal Tap)

6) Winding resistance test at HV Side & LV Side

7) Short Circuit Current test

8) Open Circuit test

9) Functional Test of Transformer

10) NCT, CT testing

11) Transformer Oil Break down strength

12) Oil Filtration & others as per the requirement of commissioning of transformer.

HT Panels & LT panels:

1) Insulation resistance Value before HV test & after HV test

2) High Voltage test.

3) Circuit breaker testing.

4) Current transformer test, Potential transformer test

5) Relays Functioning test

6) Protection & interlock , functional test of panels.

Bus Ducts :

i) Resistance Check (Obtain milli-volt drop test results for bus bar joints

(welded joints&bolted joints)

2) Earth Resistance test before HV test & after HV test

3) Leakage Current .
HT Cable & LT Cables : 1) Insulation resistance ( HV test ) before HV test & after HV test
2) Continuity test.

HT MOTORS & LT MOTORS:

1) Insulation Winding resistance test

2) Polarization index test

3) Vibration & Noise level test
4)) Functional test

Installation of Ash Conditioner

BASIC ELECTRICAL  DESIGN

                                     

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Cable layout 

Bag Filters

Air Drier

Civil Work 

                     

Pipe connections

Cable Layout for 33KV