Case Study – Bed ash, Fly ash & Bed Material Handling System for CFBC Boiler

PROJECT SYNOPSIS

BED ASH HANDLING SYSTEM:

Macawber Beekay successfully installed dense phase ash handling system below the bed ash collection surge hopper, to a Bed Ash silo, equipped with truck Unloading system below the silo. Furnace ash is discharged on a continuous basis into chain conveyor to collect bottom ash from boiler and convey to a Surge Hopper.  Bed Ash Surge Hopper is provided with 2 (two) outlets having an Ash Vessels below each opening. Each Ash Conveying Vessel is be connected to an individual conveying pipeline. The pipeline isterminated on top of the BA Silo with the help of terminal box.
Brief write-up for System at APH:

The Ash Vessels below APH hoppers are clubbed together in series (Master + Slave) through a common conveying line. The ash shall be transferred to the BA Silo through a terminal box provided on its top.

Common 1 (one) Bed ash silo have been provided for collection of bed ash & APH fly ash from two boilers to collect coarse ash.

At top of silo, Vent Filter (reverse pulse jet type) is provided to vent out clean air to atmosphere. Level probe andcontinuous level monitoring is provided.

Unloading System for BA Silo: The BA Silo shall have Four outlet points. First and second outlet point shall be provided with bed ash unloading spouts for unloading of dry bed ash into trucks and third outlet is provided with an ash conditioner for moist ash disposal into open trucks. The fourth outlet is provided with blind flange for future opening. Conveying air requirement for both the units is met from a common bank of CA compressors, dedicated for bed ash handling.

FLY ASH HANDLING SYSTEM:

System consisting of Dense Phase Pneumatic Conveying System.

Fly Ash from ESP hoppers shall be conveyed through Dense Phase Pneumatic Conveying System to Fly Ash Silo.

There are five fields in ESP, each field have2 (two) ash collection Hoppers.

The Ash Vessels below ESPhoppers are clubbed together in series (Master + Slave) through a conveying line. Total 3 sets of fly ash conveying pipes have been provided for handling ESP ash for each boiler.

Each Ash Vessel is equipped with unique DOME VALVE at inlet along with necessary instrumentation.

System at Fly Ash Silo:

Common 1 (one) fly ash silo have been provided for collection of fly ash from two boilers.

At top of silo, Vent Filter (reverse pulse jet type) is provided to vent out clean air to atmosphere. High Level Probe andcontinuous level monitoring is provided in FA Silo.

Fly ash silo is provided with fluidizing arrangement to ensure free flow of fly ash while unloading.

Unloading System for FA Silo: The FA Silo shall have Four outlet points. First and second outlet point shall be provided with fly ash unloading spouts for unloading of fly ash into closed tankers and third outlet is provided with an ash conditioner for moist ash disposal into open trucks. The fourth outlet is provided with blind flange for future opening.

Conveying air requirement for both the units is met from a common bank of CA compressors dedicated for fly ash handling.

Separate Instrument Air compressors have also been provided for complete ash & limestone/bed material handling systems.

PRINCIPLE OF OPERATION (Dense Phase Pneumatic Conveying system):

The operation of the system is simple and completely automatic. System has dual operatability either through level probe material sensing or timerbased mode.

In timer based mode, the system shall convey material automatically in batches at preset programmable interval of time.

In level probe mode, level sensing probe provided in the hopper above conveying vessels or transfer vessel shall sense the presence of material in the hopper and initiate the conveying cycle.  Dome valve shall open and allow the material to gravitate into the transfer vessel for a preset time & then close automatically. On closure of dome valve, its seal gets inflated and signals the conveying air injection into the transfer vessel. The vessel gets pressurized and material resistance help pressure build up and conveys the material through steel piping to the destination silo.

When conveying is complete, the pressure drops down and is sensed by the control system, the air supply to the system is stopped and the cycle is complete now. The system is ready for the next cycle.

The total system is made automatic by use of level probe in destination silo to control the transfer of material. Complete system is flexible enough and programmable and automatically operated through a PLC based central control panel.

BED MATERIALHANDLING SYSTEM (Dense Phase Pneumatic Conveying system):

Total of 2 sets (One for each boiler) of bed material conveying system is provided for two boilers.

Bed Material is fed into MS surge hopper (by Purchaser). The Surge Hopper is provided with two sets of conveying systems, each connected to an individual conveying pipeline for conveying bed material to the boiler bunker.

At top of each boiler bunker, Vent Filter (reverse pulse jet type) andcontinuous level monitoring is provided.

LIMESTONE CONVEYING SYSTEM:

Continuous conveying system is provided for limestone handling. Macawber Beekay’s this technology has the capability to convey a wider range of materials with variable particle sizes using lower positive air pressures. This form of conveying is ideal for long distanceconveying and handling materials which are difficult to handle.

Total of 2 sets (One for each boiler) of limestone conveying system is provided for two boilers.

Crushed limestone from crusher house is collected in Product Hoppers below which conveying vessels are provided for conveying limestone to boiler bunkers.

System at Limestone Bunkers:

At top of each boiler bunker, Vent Filter (reverse pulse jet type) and continuous level monitoring is provided.
Dedicated conveying air compressors have been provided to for limestone conveying system, the other auxiliaries – common to ash handling system are retained.