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Notes from Meeting with GEA EGI Contracting/Engineering Co., Ltd.

March 31, 2014

On Monday, March 31, 2014, EPA and ERG participated in a meeting with GEA EGI

Contracting/Engineering Co., Ltd. (GEA EGI) at EPA Headquarters in Washington, D.C. to discuss GEA

EGI’s Circumix Dense Slurry System (DSS) technology. Participants in the meeting included

representatives from EPA, ERG, and GEA EGI, as listed in Table 1.

Table 1. List of Participants

Name Organization

István Kovacsics GEA EGI

Ron Jordan EPA

Phillip Flanders EPA

Jezebele Alicea EPA

Deb Bartram ERG (contractor to EPA)

Elizabeth Gentile ERG (contractor to EPA)

Mr. Kovacsics visited EPA to give a presentation on their DSS ash handling technology. The

presentation, company brochures, and other supporting documents provided by Mr. Kovacsics following

the meeting are included as attachments to these notes and listed in Table 2 below (see DCN

SE05926.A1). Mr. Kovacsics also provided copies of the public comments submitted on this rule and the

CCR rule (EPA‐HQ‐RCRA‐2013‐0209), which are available in the dockets.

Table 2. List of Attachments

Attachment Title

1 GEA Circumix Dense Slurry Technology Brochure

2 NAES Circumix Dense Slurry System (DSS) for Ash and Waste Water Management and

How it Addresses Proposed ELG and CCR Rule Change

3 NAES Corporation DSS Presentation

4 NAES Statement of Qualifications

5 NAES Corporation Brochure

6 Year Two Follow‐Up Investigation Report: Soil and Water Quality Evaluation St. Mary’s

Shoals Park Roadway Improvements

7 GEA EGI DSS Technology Photos

Mr. Kovacsics started with an introduction of the DSS technology, stating that if certain

conditions are met, mixing water with fly ash results in a product that solidifies naturally (due to the

compounds, chemical reactions and mineral structures that are formed). These reactions  involve

reactive compounds such as CaO, Al2O3

, MgO, SiO2 and are affected by slurry conditions including the

quantity of water, ash particle size, chemistry of the water and availability of reactive grain surfaces and

slurry homogeneity. For each installation, GEA EGI evaluates a diverse set of inputs to determine if the

DSS technology is an applicable ash handling technology for a specific plant. GEA EGI has been

experiencing a high level of interest in the system from the industry.
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The system is designed for coal‐fired generating units and one system is operating at a coke‐

fired plant; however, it is not an available technology for oil‐fired generating units (mainly due to the

negligible amount of ash generated). Extensive tests and working references have shown that the

technology can work with practically all coals from lignite and sub‐bituminous coals to bituminous coals

and anthracite. Mr. Kovacsics stated that pulverized coal boilers are preferred for the DSS technology

because of the high furnace temperature. Fly ash and bottom ash from circulating fluidized bed boilers

are also good candidates for the system because plants often add lime to the fluidized bed, resulting in

high calcium oxide content of the ash, and the bottom ash is very reactive (like the JEA Northside

(Jacksonville, FL) installation).

In order an ash slurry system to function efficiently, it is important to identify the optimal level

of water. If the slurry is too thick, energy consumption for pumping can be very high and capital costs

can increase significantly. If the slurry is too thin, the excess water can inhibit solidification reactions,

energy costs increase due to higher pumping volume and pipe abrasion can increase due to larger

particles rolling or sliding along the bottom of the pipe. The solids to water ratio in a traditional wet

sluicing system ranges from 1:10 to 1:15 which is far from the optimum. In a DSS, the solids to water

ratio typically ranges from 1:1 to 1.5:1 (between 50% and 60% solids).  

Typically, fly ash is only considered in the hydraulic calculations for the design of the DSS.

Bottom ash is too coarse to affect the viscosity of the slurry. When designing the system, GEA EGI

focuses on the extremes of different fuel types or coal blends that are used at the plant to calculate the

optimum solids‐to‐water ratio for the slurry, pipe diameters, mixer dimensions and other parameters of

the DSS system. The plant can make adjustments to this solids‐to‐water ratio when mixing the slurry if

necessary to adapt to changing coal quality. Typically, a plant does not need to adjust the solids to water

ratio day to day unless a very different type of coal is being burned. In terms of load control the Circumix

system is rather flexible since it uses variable frequency drives: the typical control range of a mixer’s

output is 40‐110%.

The mixer developed for the system makes the mixing of the dense slurry more efficient.  In a

pugmill‐based technology (which is commonly used) the mixing is typically done in two phases: the

pugmill (which is a screw with no paddles) first wets the dry fly ash and then drops it into to a larger,

agitated  mixing tank (second phase) where the mixing and adjustment of solids to water ratio takes

place. This is where paddles are typically used for agitation. Pugmill technology suffers from the

following drawbacks:

 Solidified deposits are easily formed in the pug mills. These deposits need to be frequently

removed by hard manual labor. This means cost and downtime.

 Wetting in the pugmill is commonly inadequate. Large lumps are usually formed which are

either dissolved in the mixing process later or are transferred as‐is to the disposal site.

 There are dead zones in the mixing tank which cannot be reached by the paddles. This is where

settling occurs and deposits usually form.
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 Paddle mixing results in an inhomogeneous mixture which adversely affects end‐product

quality.

 The wear/abrasion of the agitating paddles is high, leading to increased maintenance costs and

downtimes.  

In contrast, the Circumix DSS mixer implements a four‐stage mixing procedure. Mixing takes place in:

 The premixer head where the dry ash is wetted by high velocity jets of recirculated slurry,  

 In the two recirculation pumps where the impellers of the pumps intensively mix the slurry,  

 In the mixer tank where the entire contents of the tank is kept in constant swirling motion by

the tank recirculation, and  

 In the transport pipes where the flow is constantly kept in the turbulent range.

This very intensive mixing process results in a highly homogenous mixture and thus in very good end‐

product quality.   

Mr. Jordan asked if bottom ash that is currently wet sluiced could be transported by the DSS.

Mr. Kovacsics stated that bottom ash can be and in most of the reference plants is processed and

transported with DSS.  As the dense slurry requires a closely controlled s/w ratio, some of the water of

the sluiced bottom ash, however, must be removed by thickeners or other dewatering devices such as

hydrocyclones or settling tanks. The partially dewatered bottom ash slurry can then be introduced to

the Circumix mixer and processed together with fly ash.  

When processing bottom ash, it is important to keep its large and abrasive particles in

suspension to avoid settling and thus to minimize power consumption and transport pipe abrasion. The

viscosity of the dense slurry is adjusted exactly so that it would be sufficient to keep these particles

suspended but not too high to require too high pumping power. In order to process and transport

bottom ash, the largest particles (variable but about one inch diameter) must be crushed or removed

prior to mixing with the slurry.

Mr. Kovacsics stated that unlike bottom ash, gypsum helps with adjusting the viscosity of the

dense slurry because it is a fine powder.  

Mr. Kovacsics reiterated that all of these systems are custom built. Additionally, he stated that

the configuration of the ash handling system depends on the ash quantities and the philosophy of

availability for the plant. Usually there must be some redundancy to maintain high availability. If there is

one unit then 2 mixers and transport systems are usually employed. In case of multiple units, the most

common configuration is 3 mixers per two units (50% redundancy) but other configurations are also

possible. Normally each mixer is connected to a dedicated pump train and their own transport pipeline.

However there are backup mixers (100% or 50% redundancy typically) with their own pump trains.

There are crossover connections that make it possible to connect any pump train to any mixer and any

pump train to any pipeline in order to increase operational availability.
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In order to pump the slurry to the final destination, GEA EGI prefers to use centrifugal pumps

over the use of piston diaphragm pumps (PDP) because centrifugal pumps require less maintenance, are

less expensive and, more importantly, are highly tolerant of larger particles (as found in bottom ash).

Mr. Kovacsics stated that the technically feasible conveying distance for the DSS technology ranges from

15 to 20 kilometers, although that distance can be influenced by elevation differences. A further benefit

of DSS is that owing to the optimum viscosity, standard steel pipes can be used for slurry transport, no

expensive ceramic lining or other anti‐abrasion measure is necessary.

Mr. Kovacsics explained that in the conversion of a traditional wet sluicing system, DSS can be

integrated in any type of existing ash collection and storage system, regardless of whether the bottom

ash system is dry or wet. Some of the existing infrastructure can be retained and utilized, the most

important of which is the existing bottom ash system which typically does not require modification. This

is in contrast to a dry ash conversion which requires costly replacement/modification of the boiler

bottom and/or bottom ash collection and transport systems. In a DSS conversion project the existing

system remains the same up to and including the fly ash silos. Only a new mixer, transport pumps and

transport pipelines (and in the case of bottom ash processing) partial dewatering capabilities need to be

added.

Mr. Kovacsics stated that the total EPC cost of these systems can range from anywhere to $5

million to $60 million dollars, depending on plant size, number of units, redundancy requirements and

what CCRs need to be processed, excluding the costs related to the landfill. It is important that as

working reference plants confirm, DSS can process various CCRs including fly ash, economizer ash,

bottoms ash, FGD gypsum and FGD waste water or other plant waste waters in the same single system.

The main maintenance item associated with the system is with the pumps; however, the

standard centrifugal slurry pumps usually employed are easy to repair. If the pumps are running 24

hours per day, the impellers and volute liners need to be replaced every 6,000 to 15,000 operational

hours depending upon ash properties, such as SiO2 content. As parts those of the system that are

exposed to heavy abrasion , such as bottom ash slurry inlets and the mixer internals are lined with

ceramic chips. Overall maintenance period is long, major overhauls are needed every 5‐8 years.  As to

normal operation, an operator must inspect the systems and the entire length of pipe at least once a

day for any leaks or other faults.  

The buffer capacity of the silos which are part of the system enables uninterrupted plant

operation when the ash processing system is shut down for short repairs  or maintenance. The silos for

the system are usually designed for 8‐24 hours of capacity. Mr. Kovacsics stated that this is enough

capacity because any maintenance issue should be able to be resolved within 8 hours provided the plant

has the stocked spare parts required for the maintenance.  

Makeup water for the system is required; however, it can come from other wastewaters at the

plant (e.g., bottom ash transport water or wet cooling tower blowdown). Plants can also use FGD
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wastewater; GEA EGI has confirmed that chlorides in the FGD wastewater are not an issue in the system.

GEA EGI confirmed that there are four plants (three in Romania, one in Hungary) using FGD wastewater

as makeup water for the DSS. Flushing water is also required when the system is stopped to flush the

slurry pipelines to prevent solidification of the slurry and blocking of the system. In normal operation

such flushing is needed typically every 1‐2 weeks, thus the quantity of flushing water is low, about 0.2%

of the weekly slurry quantity.

The resulting ash by‐product is a solid that cures in the landfill. The compressional strength of

the cured deposit typically ranges from about 200 psi to over 2500 psi. The hydraulic conductivity is in

the range of 1x10‐5 to 1x10‐10. Hydraulic conductivity and compressional strength both improve as curing

progresses and the ash by‐product does not generate any dust. The resulting by‐product would not

typically be marketed.

At the disposal site, plants typically split the disposal area into cells and dikes are constructed to

separate and surround the cells. Using this approach, plants can discharge the dense slurry into one cell,

keep another cell in reserve, and work on the preparation of additional cells. Discharged slurry spreads

out and cures in place without the need to spread it. Because of the composition of the material, the

landfill can be built vertically in tiers. Mr. Kovacsics stated that water does not need to be added to the

landfill for dust suppression, nor it is necessary to scrape or spread the ash by‐product. Two operators

are required at the landfill only intermittently (every 1‐2 weeks) to switch the outflow point. Other on‐

site works include preparing cells and move the slurry pipelines when needed.  

The dense slurry is a roughly 1:1 ash‐water mixture. Approximately 5 to 10 percent of the water

is excess water that becomes a thin film on top of the ash by‐product at the landfill. This water either

evaporates or slowly seeps in and captured by the lower deposit layers. If any excess water remains it is

collected by a leachate collection system. This water and any precipitation that is captured are sent back

to the system for slurry make‐up water. GEA EGI confirmed that any leachate associated with the

system that can be collected and reused as makeup water to achieve zero discharge. The dikes built

around the landfill are typically 3 meters tall and are typically built using ash by‐product. Mr. Kovacsics

stated that there aren’t any run‐on issues and that any excess water from precipitation not absorbed by

the curing product can be recycled to the process together with leachate.  

Since the dense slurry cures to a hard product, it is suitable for capping existing impoundments.

The DSS may not be ideal in geographic locations that have cold climates (10‐15 ̊F) for extended

periods of time (e.g., Russia). If the slurry freezes it will not harden and set. However, this process is an

exothermic reaction; therefore, it may be OK in locations that have short periods of freezing weather.

Plants could also put slurry pipes underground to avoid the freezing of flush water or install trace

heating.