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Project No.: 0172.09.029.042 DISTRIBUTION

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Project Name: Steam

TELEPHONE CALL RECORD

 Outgoing Call

Date:

6/14/2012

Time:

9:00 am ET

Company Name: Synthetic Materials

Contact Name: John Glasscock

Phone No.: 727-367-0400

Name: Danielle Lewis

GENERAL SUBJECT : Discuss Dewatering of Fly Ash and Gypsum Solids

TOPICS DISCUSSED AND ACTION TAKEN

ERG requested a call with Synthetic Materials (SYNMAT) after identifying a 2009 paper written by Alex Hohne (an employee) on the 

dewatering of FGD gypsum in combination with fly ash. The paper, titled A Novel Approach to the Handling and Disposal of Coal 

Combustion Products, discusses a process where FGD gypsum and fly ash can be dewatered simultaneously using the same vacuum 

belt filter. Based on the paper, the vacuum belt filter has two feedboxes, the first receives the FGD gypsum which is partially 

dewatered by the filter before the fly ash is applied at the second feedbox. The gypsum cake acts as the filter media for the fly ash. 

The process generates a layer fly ash cake that sits on top of a the gypsum cake. The cakes can be combined and landfilled together or 

mechanically separated and disposed of separately. The process requires the fly ash sluice to undergo a thickening step to bring the 

solids content up to 20 percent, either using a thickener or a clarifier, prior to applying the fly ash on top of the gypsum cake for 

dewatering.

ERG contacted John Glasscock, President of SYNMAT, on June 14, 2012 to gain a better understanding of the system further and ask 

specific questions regarding the system application. Mr. Glasscock explained that the theory behind the process is that FGD gypsum 

solids contains larger particles that function as a film to prevent the smaller fly ash particles from passing through the vacuum belt

filter media. As the gypsum is dewatered, it forms a cake on top of the vacuum belt because the larger particles do not pass through 

the mesh of the belt. While the fly ash particles would be small enough to permeate the belt filter, the gypsum cake acts as a primary 

filter media preventing the fly ash particles from reaching the belt filter. Through this process, the vacuum belt is able to dewater the 

fly ash and the gypsum simultaneously.

SYNMAT feels that this technology is feasible for the power industry and remains a viable option for plants needing to handle both 

wet sluiced fly ash and FGD gypsum solids. Mr. Glasscock is not aware of any power plants that are currently using this technology 

in the industry. SYNMAT does provide operational support to several steam electric power plants for the dewatering of those plants’ 

FGD gypsum; however, all those plants operate dry fly ash handling systems and therefore, do not have the need for this technology. 

To date, SYNMAT has only demonstrated this technology in their laboratories.

The process of dewatering fly ash in conjunction with FGD gypsum requires the fly ash sluice stream to undergo thickening, via a 

clarifier or thickener, to remove some water prior to depositing the solids onto the vacuum belt filter. Mr. Glasscock is not aware of

any plants in the industry that are currently operating a thickener or clarifier for the purpose of decanting or thickening fly ash sluice. 

Mr. Glasscock could not speak to the approximate costs for the thickener/clarifier and whether it would be cost prohibitive to install 

due to the potential size requirements to handle a plant’s entire fly ash sluice flow. Mr. Glasscock indicated that this would need to be 

evaluated on a case-by-case basis.

ERG inquired about several aspects specific to the process put forth by SYNMAT in the article. Regarding the operation of the 

clarifier to thicken the fly ash sluice, ERG asked if the overflow could be reused, treated, or discharged directly to a pond or POTW. 

Mr. Glasscock indicated that this would also need to be evaluated on a case-by-case basis depending on each plant’s individual permit 

limitations. 

ERG also inquired about the optimal proportion of fly ash solids to FGD solids. From the article it appears as through a significantly 

higher amount of FGD solids are required as compared to fly ash solids. Mr. Glasscock indicated that the system only needs sufficient 

gypsum solids to prevent the fly ash solids from bleeding through the vacuum filter. The thickness of this gypsum layer depends on 
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particle size, of both the gypsum and the fly ash. Mr. Glasscock indicated that plants can vary the rate at which both the gypsum and 

fly ash slurry are deposited on the filter, as well as the speed of the filter itself, to change the thickness of both the gypsum layer and 

the fly ash layer. Mr. Glasscock stated that dewatering of fly ash alone is not feasible because it would pass through the filter belt; 

therefore, either the fly ash slurry would need to be stored until sufficient gypsum slurry is available to operate the vacuum belt filter 

or the operation of the FGD process would need to be altered to accommodate the fly ash production rate.

The article by Mr. Alex Hohne states that the dewatered fly ash solid and gypsum solid can be mechanically separated and the 

resulting gypsum only product is of sufficient quality to market. Mr. Glasscock indicated that this is incorrect; the resulting gypsum 

would not be marketable. Instead, the combined dewatered product would most likely be disposed of in a landfill. According to Mr. 

Glasscock, if a plant desires to market its solid gypsum product, it would most likely operate separate dewatering processes. 

ERG inquired about the types of modifications that would be required for a plant that is wet sluicing its fly ash and dewatering its 

gypsum to convert to this type of system. Mr. Glasscock stated that the plant would need to make the following modifications:

• Install a thickener/clarifier to increase the solids content of the fly ash slurry;

• Install feedlines to transfer the fly ash slurry to the existing vacuum belt filter;

• Install a second feedbox on the vacuum belt filter for the fly ash;

• Install additional vacuum capacity to extract the additional water; and

• Install equipment to handle/treat the overflow from the ash thickener/clarifier.

Mr. Glasscock stated that he does not foresee any limitations to implementing this type of system at power plants. This system of 

dewatering fly ash and gypsum could work for plants producing all types of fly ash so long as a gypsum layer could be created to 

prevent the fly ash particles from passing through the belt filter.