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УДК 621.311.22:504

 M.Heeley, Y.Kolomiiets

Clyde Bergemann, Doncaster, England, United Kingdom

APPLICATION OF FLY ASH REMOVAL AND DISPOSAL TECHNOLOGY – 

OPPORTUNITY OF SIGNIFICANT INCREASE OF RELIABILITY, PROFITABILITYAND ENVIRONMENTAL REGULATORY COMPATIBILITY OF COAL FIRED

POWER PLANTS

ABSTRACT

Environmental regulations demand great efforts from

energy utilities to reduce the polluting load from power generation. Till now, many efforts have been dedicatedto reduce particularly gaseous emissions. However,

liquid effluents as well are under increasing scrutiny to be controlled and reduced. In the same time, the privatised energy markets are demanding ever higher 

cost-effectiveness.Application of effective fly ash removal and disposal

systems is able to conciliate these often conflictinginterests. In the paper Clyde Bergemann technology of 

fly ash removal and disposal is presented. Brief description of the various configurations of the ClydeBergemann fly ash removal and disposal systems is

given.

INTRODUCTION

Increasingly stringent environmental regulationshave become a concern for many power engineering

companies. In this regard power engineering companieswhich, include coal fired thermal power plants (TPPs)are examining how to reduce the emission levels fromTPPs in the form of fly ash escaping up the stacks alongwith the flue gases, and also reducing the cost of using

vast amounts of water to dispose of the ashes. Toaccomplish this they are looking to install modern ashremoval and handling equipment and to achieve as

close to a zero water usage as possible in all areas.An answer to both these issues can be found in

application of the Clyde Bergemann ash handling and

disposal technologies. These technologies providereliable removal of fly ash particles falling from the

hoppers of fly ash extraction technologies such asESP’s (electrostatic Precipitators) or bag filters of TPPs

 burning coal and other fossil fuels, strongly increasingreliability and profitability of the ash extraction anddisposal system, whilst also providing reduction of the

environmental impact of the plant. The pneumatic flyash handling system is designed to transport the fly ashin a totally enclosed manner utilising standard mildsteel conveying pipes, completely eliminating dustemissions, whilst the method of Dense slurry pumpingutilises a ash:water ratio of approx 1:1 greatly reducingthe use of water in the ash disposal system and,

accordingly, recirculation systems and waste water have

 been eliminated completely. Additional benefits includea higher reliability and dependability of the ash

handling system in comparison with traditional lean

slurry methods, resulting in decrease of forced

emptying of ESP hoppers and reduced maintenancerequired.

The Clyde Bergemann technology is developed and patented since 1974.

1. DESCRIPTION OF THE CLYDE BERGEMANN ASH HANDLING AND DISPOSAL SYSTEM

1.1. Typical fly ash handling system configuration

Basic equipment of the Clyde Bergemann ashhandling system consists of pneumatic conveying

vessels, mild steel conveying pipes, silo terminationequipment, conveying air systems and PLC controlsystems in varying forms and configurations. A typical

Configuration of the Clyde Bergemann ash handlingsystem is shown in the fig. 1.

Fig. 1. Typical Configuration of Ash Handlingequipment for a 2 x ESP system

`1.2. Dome Valve®

The Clyde Bergemann Dome Valve® is incorporated

into every Clyde Bergemann Fly Ash Handling systemand is used in the most crucial area for pneumaticconveying systems, the air- material interface. A DomeValve® typically used on the inlet of each conveying

vessel is shown in Fig. 2.The Dome Valve is unique in that it allows for 

unobstructed material flow through the valve when in

the open position, resulting in virtually zero wear on theinternal components of the valve. When in the closed

 position the valve is pneumatically sealed closed,completely isolating the ESP process from theconveying medium during the conveying cycle.

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Fig. 2. Typical inlet Dome Valve in both closed & openstates®

1.4. The Clyde Bergemann Dense Phase Conveying

Process

Clyde Bergemann pneumatic conveying technologyis based around the positive pressure type of conveyingas opposed to negative pressure systems. Positive

 pressure systems can be further divided into threecategories: Lean phase, medium phase and dense phase.

Clyde Bergemann technology operates in the Dense- phase mode, this is the most energy efficient of all three

modes, having the highest ash:air ratio and lowestconveying air consumption. The velocity of the materialin the pipeline typically ranges between 1.5 – 10.0m/secresulting in the least amount of system wear andmaintenance. This type of conveying can handle a widerange of both wet and dry materials and can typically

transfer fly ash over distances in excess of 1000 metreswithout the need for intermediate transfer stations.

Fig. 3. Conveying pipe cross-section during dense-phaseconveying.

1.5. Dense Slurry mixing and Pumping

Typically, Bottom Ash and Fly Ash created fromthe burning of coals is transported to ash settling pondsutilising a ‘lean slurry ‘ system, where the ashes arecollected in large sumps, where it is mixed with water 

in a water to solid ratio (W/S) of around 5 to 20,depending on the particle size of the ashes. This type of 

disposal system causes problems to power generatorsdue to the abundant amounts of water required, which is both costly in terms of usage and re-processing. The

area required for Ash settling ponds for these types of systems are vast and the disposed material remainsloose. Excess water is recovered and re-used in thesystem but the environment suffers with some of the

contaminated waters finding it’s way into nearby water systems etc.

1.6. The Mixing Process

In order to create the Dense slurry suitable for  pumping, fly ash and water demand intensive mixing.

In a few minutes homogenous suspension is producedwith density in the range of 1.25 to 1.70 g/cm

3. The

thick fluid has a grey colour and it’s temperature isusually less than 40 deg C. Bottom ash granulate,

gypsum and other solids can be added later.

1.7 Transportation of Dense Slurry

Dense slurry is thick suspension of fly ash and water that has higher density and viscosity than water has.This means that much higher pump heads are requiredfor transportation in pipelines than with clean water.

The bigger bottom ash or bed ash particles may besuspended in the fly ash slurry.

In order to prevent settling of solid particles and blockage of pipelines, flow velocity may not decrease

 below a limit value of about 1.2 to 1.5 m/s.Variable speed centrifugal pumps are used for 

transportation. For power plant to landfill distances

over 4km piston pumps or hydro-hoist can be used.

1.8 Dense Slurry Mixer System and Related

Equipment

The continuous Flow-through mixer has two mixingstages, the pre-mixer head, and below that the mixer tank for final mixing. The equipment is speciallydesigned for power plant high capacity ash handling

applications.A dosing device, like a rotary dosing vane feeds the

dry ash from a storage silo into the pre-mixer by

gravity.The make-up water enters tangentially into the

cylindrical shaped pre-mixer. The make-up water isdosed proportionally to the ash flow.

One slurry pump circulates the homogenous denseslurry from below the mixer tank to the pre-mixer slurrynozzles arranged around the fry ash drop tube.

The free slurry jet streams of the nozzles entertainthe ash, air and mak-up water, like a multi-jet injector.

The pre-mixed slurry enters the mixer tank on top of 

the mixer tank for final mixing.Other slurry pump(s) serve for transporting the

dense ash slurry from below the mixing tank, throughslurry circulation pipeline loop(s) through a slurry

discharge valve. The slurry level is generally controlled by the material feed.

The size of the mixer is designed to ensure proper 

residence time of the slurry mixture, taken intoconsideration the chemically reactive reactiveCaO(free) and CaSO4 components of the ash.

The long distance transport slurry pump for the by- product storage area can be either of centrifugal typeslurry pump if the transport distance is not too long or  positive displacement piston slurry pump type if the

transport distance is quite long requiring high distance pressure.

2. ADVANTAGES OF THE CLYDE BERGEMANN 

FLY ASH REMOVAL AND DISPOSALSYSTEM INTRODUCTION

Energy saving aspects- Low conveying air consumption

seal (inflated)seal (inflated)

seal inflationseal inflation

air inletair inlet

seal (inflated)seal (inflated)

seal inflationseal inflation

air inletair inlet

openopenopenopenclosedclosedclosedclosed

seal (deflated)seal (deflated)seal (deflated)seal (deflated)

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- Low water consumption- Waste water can be utilised to mix the slurry

Ecological aspects- High landfill density and less volume- Solid ash stone, no dusting- Very little water release at the landfill

- Pipelines can be laid underground- Low noise emmision

Financial aspects- Low investment cost- Low operating and maintenance costs- Standard ‘off the shelf’ mild steel pipework 

utilised for pneumatic conveying system

CONCLUSIONS

Introduction of  CLYDE BERGEMANN  fly ashremoval and disposal system instead of traditional wetdisposal ones allows the following:

· Increased dependability and reliability for both ashremoval and disposal system and TPP;

· Lowering the cost of energy production in real terms;

· Considerably improving ecological parameters of TPPs;

· Emissions reduction from both stack and landfill site

· Bringing the TPP’s in line with stricter environmentalregulations

REFERENCES

1. Pataki A. The Circumix® Process, Environmentallycompatible handling of firing residues .