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 14, No.4, July 2004

High concentrated slurry system flexibility 

Power plant renovation 

Electricity producer CESC is operating the 

Budge Budge power plant in Calcutta, 

(Kolkata) India. In 2004, CESC 

commissioned a high concentrated slurry 

disposal system for moving fly ash from 

existing silos to a landfill area more than 2 

kilometres away on the banks of the River 

Ganges. 

Ash from the two 250-MWe boilers that is 

not sold for industrial use, was previously 

wetted and trucked through urban areas to a 

remote dump. The Central Electricity 

Authority in Delhi approved the HCSD 

system as it addressed the environmental 

concerns with wet disposal and the 

shortcomings of truck traffic such as dusting 

and spillage. 

Demonstrated benefits 

High Concentration Slurry Disposal (HCSD) 

systems are all different and each one is 

unique. A well-designed and managed 

HCSD system exhibits the following distinct 

features and characteristics: 

• Optimized slurry rheology within a 

narrow range of solids concentrations. 

• Homogeneous flow regimes within the 

operating envelope. 

• Sustains transportation by pipeline over 

longer distances. 

• Gravity flow and wide spreading on the 

deposit. 

• Minimal release of water, if any. 

• Minimal or no dusting. 

• High storage capacity. 

• Low cost to re-vegetate. 

An arbitrarily high solids concentration does 

not necessarily enhance the overall HCSD 

system performance. 

Ash characteristics 

Examination of ash samples in the GEHO® 

laboratories revealed that a 58-64% solids 

by weight slurry was homogeneous, had a 

viscosity that assures proper spreading on 

the deposit and is best pumped with a 

GEHO® piston diaphragm pump. That slurry 

did not exhibit any solids segregation or 

hardening characteristics. 

During start up of the HCSD system the 

viscosity duplicated. However, the pumping 

pressure was higher than the estimate. It 

was found that the slurry was not 

homogeneous and the pressure loss 

increase was caused by coarse particles 

that settle out at the slurry velocity and 

viscosity prevailing in the pipeline. This is 

surprising because the boiler burns the 

same coal as before. 

Flexibility and risk of operation 

The pump did not allow an increase in the 

pipeline velocity that was sufficient for 

making the coarse ash particles “float” in the 

thick slurry. However, the pump was 

designed with enough flexibility to handle 

the higher operation pressure. 

The operation philosophy was based on the 

ability to restart within 24 hours without the 

need to empty the pipeline. The settling 

characteristics of the slurry have impaired 

the flexibility of operation. The operators 

have become very adapt at ramping up the 

capacity during a restart after a 15 minutes 

stop. They use the GEHO® to flush the 

pipeline for the removal of settlement when 

shutting the system down for a longer time. 
Further the capacity turn down range has 

been decreased. None of these operations 

are a critical issue because the mainline 

pump proved capable of de-blocking the 

pipeline. In addition, GEHO® installed a 

high-pressure flush water pump as back up. 

Modified filling procedures 

The non-homogenous character of the slurry 

affects the self-spreading capabilities at the 

disposal. The coarse material settles rather 

quickly after discharge of the slurry from the 

spigot. This phenomenon increases the 

angle of repose and decreases the distance 

the slurry spreads over the surface area. 

The storage area was designed as a socalled dry landfill with a liner. A series of 

tests were performed with a view to optimize 

the procedures for filling the deposit. They 

typically produced a 2.5 meters high conical 

stack that spread out only 80 meters 

diametrically. It demonstrates why the 

disposal cannot only be filled from spigots 

placed around the area. The procedures 

were adapted to gradually fill the disposal 

area in 60 m2 sectors by means of a 

movable discharge line. The flow from a 

spigot divides over two long hoses that are 

easy to position. 

Mechanical spreading of deposited slurry is 

not required other than for raising the edges 

of the pile. What really matters is that the 

storage volume will not be compromised in 

that a 30-meters high stack is built with a 

slope of 45 degrees on a 243.000 square 

meters land. 

Zero effluent 

The deposited stacks are left to dry and 

consolidate. All the water used to convey the 

ash is either absorbed by the material 

through a hydration reaction or is 

evaporated. Surface water and rain that falls 

on the disposal area is collected in decant 

dams. After settlement of possible solids, it 

is inspected and then pumped to the river. 

Fluidity ash 

McNally Bharat Engineering Company 

Limited built the disposal pipeline and slurry 

preparation plant. GEHO® PUMPS supplied 

a single-shaft high-shear horizontal 

continuous mixer that has a rubber shell for 

the prevention of scale. In addition, we 

supplied the ash dosing equipment, the 

agitator, a Warman charge pump and the 

controls. An agitated retention tank functions 

as buffer and homogenizes the slurry as 

required. It is fitted with a control loop that 

checks the slurry density. 

All equipment worked extremely well and 

met the performance criteria after fitting a 

valve to the silo outlet that prevents 

congestion of the screw feeder due to the 

static column and the fluidity of the dry ash. 

Co-active partnership 

This project is yet another proof that the 

characteristics of residue from coal 

combustion are all distinctly different and are 

sensitive to the performance of the disposal 

system. It was also illustrated how vital it is 

that the mixing and pumping systems are 

designed with "appropriate" flexibility. The 

GEHO® Pump Systems Department 

demonstrated its capabilities and 

commitment and assured that all objectives 

were achieved in spite of the difficulties 

faced, in particular, by working together in 

partnership with the contractor and the utility 

from the conceptual design until satisfactory 

deposition of the slurried ashes. 

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 (C) 2004, Weir Minerals Netherlands b.v. All 

rights reserved.