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### -1- September 21, 2015

Mr. Phillip Flanders Engineering & Analysis Division (4303T) 1200 Pennsylvania Ave., NW Washington, DC 20460

Subject: COMMENTS ON NOTES FROM MEETING BETWEEN ERG AND GEA EGI

Dear Mr. Flanders:
This letter and the attached document was prepared in response to a request received from Ms. Elizabeth Gentile, Environmental Engineer, East ern Research Group (ERG) dated September 9, 2015. Ms. Gentile sent meeting notes that were taken by ERG during a meeting that took place on Marh 31, 2014. At this meeting Mr. Istvan Kovacsics of GEA EGI Contracting Engineering Co., Ltd. (GEA EGI) pro vided a technical briefing to a group of ERG and EPA attendees. The topic of the briefin g was the Circumix Dense Slurry System (DSS) ash managment technology. As you know, you w ere one of the attendees.
This letter and response is being jointly submitted by NAES Corporation (NAES) and GEA EGI. NAES and GEA EGI formed an alliance in 2013 a ppointing NAES as the exclusive provider of the Circumix DSS technology in North Am erica. This submittal is on NAES letterhead and some of the comments were prepared b y me However, the comments, quotes and corrections made to the subjectmatter presented herein were prepared and/or approved by Mr. Kovacsics.
Quite a bit of time has elapsed since the meeting s o it is appropriate to review the discussions. GEA EGI and NAES Corporation have take n this opportunity to offer clairifications and details in the attached marked- up version of the document in an effort to make the final text as accurate as possible. There are quite a few clarifications.

In addition to the contents of the draft notes docu ment, there were some other topics that were discussed in the meeting, including the operat ion principle and controllability of the Circumix mixer, possibility of processing FGD gypsu m with ash, typical mixer sizes, references, history of the technology, special feat ures of pipelines; details of potential US DSS projects; major overhaul times, the global dist ribution of dense slurry and other technologies, physical parameters of the solidified end-product; and how to properly construct a disposal site (drainage, isolation); co vering existing impoundments with dense slurry. There were cursory discussions on these to pics during the meeting but the draftERG Meeting Notes on Dense Slurry Incorporating GEA EGI & NAES Comments September 21, 2015

Page 1 of 5 **Notes from Meeting with GEA EGI Contracting/Enginee ring Co., Ltd.**  **March 31, 2014**

On Monday, March 31, 2014, EPA and ERG participate d 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 list ed 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 o n their DSS ash handling technology. The presentation, company brochures, and other supporti ng documents provided by Mr. Kovacsics following the meeting are included as attachments to these no tes and listed in Table 2 below. 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

**DCN Title** 

SE059 36 A1 GEA Circumix® Dense Slurry Technology Brochure

SE059 36 A2 NAES Circumix® Dense Slurry System (DSS) for Ash and Waste Water Management

and How it Addresses Proposed ELG and CCR Rule Chan ge SE059 36 A3 NAES Corporation DSS Presentation

SE059 36 A4 NAES Statement of Qualifications

SE059 36 A5 NAES Corporation Brochure

SE059 36 A6 Year Two Follow

- Up Investigation Report: Soil and Water Quality Eva luation St.

Mary’s Shoals Park Roadway Improvements

SE059 36 A7 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 resul ts in a product that solidifies naturally (due to t he compounds, chemical reactions and mineral structure s that are formed). These reactions involve reactive compounds such as CaO, Al2O 3 , MgO, SiO 2 and are affected by slurry conditions including th e quantity of water, ash particle size, chemistry of the water, availability of reactive grain surfaces and slurry homogeneity. For each installation, GEA EGI evaluates a diverse set of inputs to determine if t he DSS technology is an applicable ash handling techno logy for a specific plant. GEA EGI has been experiencing a high level of interest in the system from the industry.ERG Meeting Notes on Dense Slurry Incorporating GEA EGI & NAES Comments September 21, 2015

Page 2 of 5 The system is designed for coal-fired generating u nits and one system is operating at a cokefired plant; however, it is not an available techno logy for oil-fired generating units (mainly due to the negligible amount of ash generated). Extensive test s and working references have shown that the technology can work with practically all coals from lignite and sub-bituminous coals to bituminous coa ls and anthracite. Mr. Kovacsics stated that pulverize d coal boilers are preferred for the DSS technology because of the high furnace temperature. Fly ash an d bottom ash from circulating fluidized bed boilers are also good candidates for the system because pla nts often add lime to the fluidized bed, resulting in high calcium oxide content of the ash, and the bott om ash is very reactive (like the JEA Northside pla nt in Jacksonville, FL)).

In order for an ash slurry system to function effi ciently, 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 capita l costs can increase significantly. If the slurry is too thin, the excess water can inhibit solidificati on reactions, energy costs increase due to higher pump ing volume and pipe abrasion can increase due to larger particles rolling or sliding along the botto m of the pipe. The solids to water ratio in a tradi tional wet sluicing system ranges from 1:10 to 1:15 which is far from the optimum. In a DSS, the solids to wa ter ratio typically ranges from 1:1 to 1.5:1 (between 5 0% and 60% solids).

Typically, fly ash is only considered in the hydra ulic 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 t his solids-to-water ratio when mixing the slurry if necessary to adapt to changing coal quality. Typica lly, a plant does not need to adjust the solids to water ratio day to day unless a very different type of co al is being burned. In terms of load control, the Circumix system is flexible since it uses variable frequency drives: the typical control range of a mi xer’s output is 40-110%.

The mixer developed for the system makes the mixin g of the dense slurry more efficient. In a pug mill-based technology (which is commonly used), the mixing is typically done in two phases: the pugmill (which is a screw with no paddles) first we ts the dry fly ash and then drops it into to a larg er, agitated mixing tank (second phase) where the mixi ng and adjustment of solids to water ratio takes place. This is where paddles are typically used for agitation. Pug mill technology suffers from the following drawbacks:

• Solidified deposits are easily formed in the pug mi lls. These deposits need to be frequently removed by hard manual labor. This means cost and d owntime.

• Wetting in the pug mill is commonly inadequate. Lar ge 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 canno t be reached by the paddles. This is where settling occurs and deposits usually form.

• Paddle mixing results in an inhomogeneous mixture w hich 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 fo ur-stage mixing procedure: Mixing takes place in:ERG Meeting Notes on Dense Slurry Incorporating GEA EGI & NAES Comments September 21, 2015

Page 3 of 5 • the premixer head where the dry ash is wetted by hi gh 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 hig hly homogenous mixture and thus in very good endproduct quality.

Mr. Jordan asked if bottom ash that is currently we t 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 dewa tered 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 consumpti on and transport pipe abrasion. The viscosity of th e dense slurry is adjusted exactly so that it would b e sufficient to keep these particles suspended but not too high to require too high pumping power. In orde r to process and transport bottom ash, the largest particles (variable but about one inch diameter) mu st 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 s ome redundancy to maintain high availability. If th ere is one unit then 2 mixers and transport systems are us ually 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 ded icated pump train and their own transport pipeline. However there are backup mixers (100% or 50% redund ancy typically) with their own pump trains. There are crossover connections that make it possib le to connect any pump train to any mixer and any pump train to any pipeline in order to increase ope rational availability.

In order to pump the slurry to the final destinatio n, GEA EGI prefers to use centrifugal pumps over th e use of piston diaphragm pumps (PDP) because centrif ugal pumps require less maintenance, are less expensive and, more importantly, are highly toleran t of larger particles (as found in bottom ash). Mr. Kovacsics stated that the technically feasible conv eying distance for the DSS technology ranges from 1 5 to 20 kilometers, although that distance can be inf luenced by elevation differences. A further benefit of DSS is that owing to the optimum viscosity, standar d steel pipes can be used for slurry transport, no expensive ceramic lining or other anti-abrasion mea sure 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 a nd storage system, regardless of whether the bottom ash system is dry or wet. Some of the existing infr astructure can be retained and utilized, the most important of which is the existing bottom ash syste m which typically does not require modification. Th is is in contrast to a dry ash conversion which requir es costly replacement/modification of the boiler bottom and/or bottom ash collection and transport s ystems. 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 andERG Meeting Notes on Dense Slurry Incorporating GEA EGI & NAES Comments September 21, 2015

Page 4 of 5 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 the se systems can range from anywhere to $5 million to $60 million dollars, depending on plant size, numbe r of units, redundancy requirements and what CCRs need to be processed, excluding the costs related t o the landfill. It is important that as working reference plants confirm, DSS can process various C CRs including fly ash, economizer ash, bottoms ash, FGD gypsum and FGD waste water or other plant waste waters in one system.

The main maintenance item associated with the syste m is with the pumps; however, the standard centrifugal slurry pumps usually employed are easy to repair. If the pumps are running 24 hours per da y, 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. The part s of the system that are exposed to heavy abrasion

, such as bottom ash slurry inlets and the mixer inte rnals are lined with ceramic chips. Overall maintenance period is long: major overhauls are nee ded every 5-8 years. As to normal operation, an operator must inspect the systems and the entire le ngth 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 sho rt repairs or maintenance. The silos for the syste m 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, i t can come from other wastewaters at the plant (e.g., bottom ash transport water or wet cooling to wer blowdown). Plants can also use FGD wastewater;
GEA EGI has confirmed that chlorides in the FGD was tewater are not an issue in the system. GEA EGI confirmed that there are four plants (three in Roma nia, one in Hungary) using FGD wastewater as makeup water for the DSS. Flushing water is also re quired when the system is stopped to flush the slur ry pipelines to prevent solidification of the slurry a nd 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% o f 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 ran ge 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 slurry disposal site, plants typically split the disposal area into cells and dikes are constructed to separate and surround the cells. Usi ng 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 wi thout the need to spread it. Because of the composition of the material, the landfill can be bu ilt 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 sprea d the ash by-product. Two operators are required at the l andfill only intermittently (every 1-2 weeks) to switch the outflow point. Other on-site works inclu de preparing cells and moving 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 l ower deposit layers. If any excess water remains it isERG Meeting Notes on Dense Slurry Incorporating GEA EGI & NAES Comments September 21, 2015

Page 5 of 5 collected along with leachate. This water and any p recipitation 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 achi eve zero discharge. The dikes built around the landfill are typically 3 meters tall and are typica lly built using ash by-product. Mr. Kovacsics state d 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 wit h 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 th at have cold climates (10-15 ̊F) for extended period s of time (e.g., Russia). If the slurry freezes it wi ll not harden and set. However, the curing process is an exothermic reaction. Therefore, it may be OK in lo cations that have short periods of freezing weather

. Plants could also put slurry pipes underground to a void the freezing of flush water or install trace heating.