### 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 cent rifugal 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 requirement s 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 alocal 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

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