Permission to use the attached copyrighted document provided to the U.S. EPA by email dated 

November 3, 2009 from J. Sloesen, Weir Minerals Netherlands b.v., to Steve Souders, U.S. EPA. 
GEHO® Info for sales representatives 

Volume 9, No. 1, January 1999

Slurry technology meets coal combustion 

residue deposition legislation 

Ledvice modernisation 

Elektrarna Ledvice (ELE) is a Czech power 

plant operated by CEZ a.s. During 1996 ELE 

commissioned a flue gas desulphurisation 

plant for boilers 2 and 3, 110 MW each. In 

1998 ABB Brno completed construction of 

the 110MW fluid bed boiler 4. Brown-coal 

residues produced by the boilers 2, 3, 4 are 

deposited on the "korridor" - a 100 to 200m 

wide and 1000m long dry disposal area in the 

pit of former brown coal mining. 

Physical/chemical deposit stability 

Czech environmental legislation is, in 

particular, concerned with seepage of ash 

ponds. Pumping and deposition of dilute 

slurries is no longer an option. The regulation 

prohibits release of more than a small 

percentage ‘bleed’ water from the carrier fluid. 

Handling bulk 

CEZ/ELE recognised the need to investigate 

alternative technologies to transport and 

dispose of residue more economically and 

environmentally friendly. Until that time, plant 

owners and FGD contractors had opted for 

either dump trucks or belt conveyors. Ash 

(wetted) is discharged on the deposit and 

spread mechanically. 

Spillage, dusting and contamination of 

equipment and surrounding area are the 

consequence. The operating expenditure of 

these methods of transportation is significant. 

Improved methodology

GEHO® has know-how and experience with 

dense slurries and pastes, including slurry 

preparation, transport and sloped disposal of 

for example red mud, mineral tailings, slimes 

and power plant fly ash. These slurries are 

extremely viscous and can’t be pumped 

efficiently using centrifugal pumps. At the 

power plant Velenje, a dense fly ash pumping 

and deposition test was run to evaluate 

pumping of dense ash slurries. It was 

demonstrated that water release was minimal. 

GEHO® studied the Ledvice application and 

concluded that the following claims were 

justified: 

• Sample testing would enable GEHO® to 

evaluate slurry flow behaviour and define 

the expected pump duty envelope for the 

likely range of residues to be pumped. 

• A GEHO® piston diaphragm positive 

displacement pump could reliably transport 

a wide range of high density coal tailings. 

• It would be feasible to use high concentrated slurry to build and maintain a 

stable deposit without needing mechanical 

spreading and water recovery. 

Composite slurries 

The ELE boilers produce diverse residues. 

These are stored in separate silos. Products 

are blended and water is added to produce 

pumpable slurries, which meet the permitted 

disposal requirements. 

• Slurry G3 - mixture of fly ash and FGD 

product, from boilers 2 and 3. 

• Slurry G2 - mixture of filter, cyclone and bed 

ash from boiler 4 plus bottom ash from 

boilers 2 and 3, as available. 

• Slurry G1 - ‘agitated’ mixture of G2 & G3. 

The production rate of each residue type 

varies with the power plant load and the level 

in the silos. So do the product mixing ratios. 

Test work at GEHO® determined the nature 

and rheological properties of (foreign) 

samples and showed that some slurries 

exhibited hardening (from CaO reaction) 

and settling behaviour. Defining a design 

operating envelope was a major challenge to 

GEHO® slurry experts. 
Undivided responsibility 

ELE recognised the complexity and sensitivity 

of the composite dense ash slurry 

preparation, transportation and disposal 

system. GEHO® was contracted to design 

and supply the slurry handling system. In 

addition it was charged to specify mixer 

performance requirements and prepare basic 

engineering for disposal. Detailed engineering 

and construction was performed by Chepos 

Engineering. The 

slurry feed from 

the mixers is 

homogenized in 

an agitated 

retention tank. It 

is diluted for the adjustment of viscosity and 

density as required. Slurry, which meets the 

stringent requirements for safe pipeline 

transportation and disposal is transferred to 

the mainline pumping station by charge 

pumps. Three GEHO® piston diaphragm 

pumps transport up to 135 t/h of bone dry 

ashes through two thermally insulated unlined 

surface pipelines to be disposed of about 

4500m away. Complex interactive control 

loops and operation procedures are designed 

for preventing pipeline plugging, to clear slurry 

from the pipeline by flushing and for pipeline 

drainage with compressed air by using a 

spherical pig. 

Commissioning 

The majority of problems experienced during 

commissioning were due to the inability of the 

existing mixers to produce slurry G3 to a 

proper consistency. Until the mixers were duly 

modified the FGD product was diverted and 

hauled with trucks. Wetted fly ash was then 

liquefied in the agitator tank with one charge 

pump re-circulating to the top of the tank. On 

occasion, oversize bed ash obstructed the 

GEHO® pump valves and foreign material 

blocked the trash screen. Downtime was 

caused by simultaneous commissioning of 

mixer 2 and the fluid bed boiler. On one 

occasion coarse material settled in the 

pipeline and created in one pipeline a hard 

bottom layer up to 40mm. The settlement 

eroded with each flushing operation. The 

inline viscosity probe was unable to monitor 

the slurry’s apparent viscosity consistently. 

The test loop was modified to monitor 

pressure gradients as a means of controlling 

viscosity. Operational practise was further 

refined. 

Conclusions 

• Variation in residue flow rate and quality 

results in slurries with different flow 

behaviour characteristics; is problematic 

and requires extensive test work. 

• The measured pump discharge pressure 

versus flow rate was within the predicted 

envelope for the installation, indicating 

that the correlations used to predict the 

pipeline system curve are acceptable for 

design purposes. 

• The pipeline spigots 

used to discharge 

the slurry along the 

edge of the disposal 

area allowing the ashes to be spread over 

a wide area, even in wintertime. 

• The GEHO® pump is reliable and 

extremely robust and pumps a wide range 

of densities and viscosities. 

• Pipeline and slurry handling equipment 

must be designed for preventing slurry 

packing in stagnant areas. 

• The control system allows operators to 

control and monitor the system from a 

local control room. Quality instrumentation is necessary for measuring 

density and pressure gradients. 

• Data and knowledge gathered and on-site 

experience help GEHO® to establish the 

most suitable future system 

configurations and design parameters. 

• System availability and reliability will 

depend on whether mixers can produce 

consistently good quality slurry and 

whether the system is operated in such a 

way that blockages are prevented. 

Weir Minerals Netherlands b.v. 

P.O. Box 249, NL-5900 AE Venlo 

Phone: +31(0)77-3895200 

Fax: +31(0)77-3824844 

Email: weir@weirminerals.com 

Website: www.weirminerals.com

Copyright © 1999, Weir Minerals Netherlands b.v. All 

rights reserved. 

Deposited slurries form a solid layer with no 

apparent run-off water. Subsequent layers 

form a cohesive interface with earlier layers.