### 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 t he 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 oper ation. 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-spreadi ng 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 c ontractor 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.