United States Patent: 5362471

It's not exactly the end "Use" of Coal-fired power plant "Flue Gas Gypsum" that has been improved by Pennsylvania's Air Products and Chemicals company, but, rather, it's ease of handling and processing in the manufacturing facilities which utilize synthetic Gypsum in, especially, wallboard.

We've documented numerous times that synthetic Gypsum can be manufactured from Coal-fired power plant Flue Gas Desulfurization, FGD, "sludge" - the product generated by reacting limestone in  wet stack gas scrubbers with the exhaust gasses generated by the combustion of Sulfur-containing Coal.

One example of our reportage on that topic include:

Pittsburgh Makes Coal Flue Gas Gypsum for Fly Ash Cement | Research & Development; concerning:

"United States Patent 5,312,609 - Sulfur Dioxide Removal from Gaseous Streams with Gypsum Product Formation; 1994; Assignee: Dravo Lime Company, Pittsburgh; Abstract: A method is provided for removing sulfur dioxide from a hot gaseous stream while directly producing .alpha.-hemihydrate gypsum from a scrubber effluent. A portion of an aqueous scrubbing medium containing calcium and magnesium sulfite is removed from a scrubbing unit and passed to a pressurized oxidation vessel where the sulfites are contacted with an oxidizing gas at an elevated temperature to convert calcium sulfite directly to .alpha.-hemihydrate gypsum and magnesium sulfite to magnesium sulfate".

And, Dravo further explains one use to which such synthetic Gypsum can be put, in our report of:

West Virginia Coal Association | Pittsburgh Converts Coal Ash and Flue Gas into Cement | Research & Development; concerning: "United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste; 1998; Assignee: Dravo Lime Company, Pittsburgh; Abstract: Cement is produced by forming a moist mixture of a flue gas desulfurization process waste product containing 80-95 percent by weight calcium sulfite hemihydrate and 5-20 percent by weight calcium sulfate hemihydrate, aluminum, iron, silica and carbon (and) wherein said source of aluminum and iron comprises fly ash".

The above potentials for productively consuming other Coal utilization byproducts, i.e., "fly ash", aside, in the manufacture of a direct substitute for Portland-type cement, synthetic FGD Gypsum can also be utilized in the manufacture of wallboard, i.e., "dry wall", as explained in our report of:

West Virginia Coal Association | Synthetic Gypsum from Coal Power Plant Flue Gas | Research & Development; concerning: "United States Patent 7,776,150 - Process and Apparatus for Handling Synthetic Gypsum; 2010; Assignees: Koppern Equipment Company, NC, and Giant Cement Company, SC; Abstract: Method and apparatus for converting wet synthetic gypsum from a flue desulphurization process (FGD) to easily handled and metered briquettes"; which contains a separate reference to:

http://library.acaa-usa.org/2-FGD_Gypsum_in_Wallboard_and_Other_Products.pdf; "FGD Gypsum in Wallboard and Other Products; United States Gypsum Company; 2007. Gypsum Key Commercial Properties: Safe and non-toxic mineral; Common by-product from sulfur processing (i.e.,) FGD Gypsum. FGD Gypsum in Wallboard: 63% of all FGD Gypsum produced is recovered into wallboard (and over) 27% of wallboard (is) produced from FGD Gypsum".

There are other uses and applications for "FGD Gypsum", as well, which we will document in future reports; but, note that our above reference, "United States Patent 7,776,150 - Process and Apparatus for Handling Synthetic Gypsum", concerns itself primarily not with making FGD Gypsum, but, in making that synthetic Gypsum easier to handle, transport and further process.

And, that is actually to focus and intent of the technology we report in this dispatch.

First, we remind you of the demonstrated expertise of Pennsylvania's Air Products and Chemicals company in both the processing of Coal and the recycling of at least one specific Coal utilization byproduct, as seen, for just two examples, in:

Pennsylvania Converts Even More Coal to Liquid Fuels | Research & Development; concerning: "United States Patent 4,411,766 - Iron Catalyzed Coal Liquefaction Process; 1983; Assignee: Air Products & Chemicals, Incorporated, Allentown(PA)"; and:

Pennsylvania Hydrogenates CO2 | Research & Development; "United States Patent 4,766,154 - Process for the Production of Methanol; 1988; Assignee: Air Products and Chemicals, Inc., Allentown, PA; The present invention is a process for the production of methanol from a syngas feed containing carbon monoxide, carbon dioxide and hydrogen".

And, herein, we see that Air Products has also applied themselves to devising a technology, one similar to that disclosed in our above-cited report concerning "United States Patent 7,776,150 - Process and Apparatus for Handling Synthetic Gypsum", which enables the production of synthetic Gypsum from FGD waste in a form that makes it easier and more economical to handle, distribute and utilize.

As seen in excerpts from the initial link in this dispatch to:

"United States Patent 5,362,471 - Producing Gypsum Flake from Flue Gas Desulfurization

Date: November, 1994

Inventors: Timothy Roth, et. al., PA and NJ

Assignee: Air Products and Chemicals, Incorporated, Allentown

Abstract: This invention relates to an improved process for producing gypsum calcium sulfate dihydrate flakes from powdered gypsum calcium sulfate dihydrate obtained from the desulfurization of flue gas by the wet limestone process. The flakes have sufficient size and strength such that the gypsum calcium sulfate dihydrate can be handled and processed in conventional equipment commonly used by wallboard manufacturers and others in the construction industry, The intermediate calcium sulfate dihydrate from the desulfurization process is dewatered to about 5 to 12% by weight and then compressed into a thin sheet under a compaction or compression load of 4 tons force to 15 tons force per linear inch of sheet width. A linear speed of from 0.5 to 2.5 feet per second is maintained during compaction providing a compaction residence time of from about 0.2 to 1.2 seconds. An elevated temperature is maintained during the compaction process to enhance the reformation of the crystal size and shape of the gypsum calcium sulfate dihydrate. The combination of pressure and temperature on the moist gypsum calcium sulfate dihydrate alters the physical characteristics of the gypsum calcium sulfate dihydrate, thereby resulting a sheet which breaks into hard flakes on exit from the compaction zone.

Claims: In a process for producing gypsum calcium sulfate dihydrate flake, the improvement for producing gypsum calcium sulfate dihydrate from powdered synthetic gypsum calcium sulfate dihydrate obtained by the wet limestone process for the desulfurization of flue gas which comprises: 

a) adjusting the surface moisture content of the powdered gypsum calcium sulfate dihydrate to a level of from about 5 to 12% by weight thereby forming a moist powder; 

b) compacting the moist powder in a compaction zone comprising a roller press exerting a pressure of from 4 tons force to 15 tons force per linear inch of sheet width; 

c) forming the moist powder under compression into a sheet having a thickness of from 0.05 to 0.25 inches; 

d) maintaining the sheet under compaction for a period of from 0.2 to 1.2 seconds; and, 

e) fracturing the sheet into chips.

(We're compelled to interrupt here to provide a little more information on the the "wet limestone" Flue Gas Desulfurization "process" specified above by Air Products.

As seen in:

"Energy-Tech Magazine; October, 2008; 'Important Concepts of Wet-Limestone Flue Gas Desulfurization';  Many utilities in the United States are installing flue gas desulfurization (FGD) systems to reduce sulfur dioxide emissions from coal-fired boilers. The majority of these systems will be based on wet-limestone technology due to the reliability of the process and the abundance of the scrubbing reagent, limestone, in many areas of the country",

the "wet-limestone technology", as explained and described pretty well in the above Energy-Tech Magazine article, and as specified herein by Air Products as their preferred source for Flue Gas Gypsum, seems to be the more favored of the alternatives; of which, as taught by the US Environmental Protection Agency in:

http://www.epa.gov/ttncatc1/dir1/ffdg.pdf; concerning: "Air Pollution Control Fact Sheet EPA-452/F-03--034; Flue Gas Desulfurization; Wet, Spray Dry and Dry Scrubbers";

there seem to be several.)

Background and Field: This invention pertains to an improved process for producing flakes from gypsum calcium sulfate dihydrates obtained from the desulfurization of flue gas by the wet limestone process with forced oxidation. 

Gypsum, which is calcium sulfate, has wide application in the manufacture of construction products and particularly wallboard. Gypsum is obtained from two different sources, the predominant source being natural gypsum. Natural gypsum is mined and the particulate or rock form gypsum is ground to a powdery state wherein it is heated and mixed with other additives, etc. Natural gypsum is preferred by manufacturers of wallboard and other commercial products to synthetic gypsum because it lends itself to ease of handling and to the preparation of fine quality wallboard. 

Synthetic gypsum is generally obtained as a byproduct in the manufacture of phosphate containing fertilizers and as a byproduct in the desulfurization of flue gas. Neither byproduct has experienced widespread commercial (success) for the formation of quality products. Usually synthetic gypsum has represented a disposal problem rather than a commercial product to those associated with the byproduct manufacture of calcium sulfate. Synthetic gypsum has a different crystal size and shape than natural gypsum and that difference has been used as a basis for explaining the difference in physical properties obtained in commercial products. 

Desulfurization of flue gas is accomplished by one process known as the "wet process with forced oxidation" wherein the flue gas containing sulfur dioxide is contacted with calcium carbonate (limestone) or lime generating an intermediate calcium sulfite product. The interim calcium sulfite is oxidized to calcium sulfate dihydrate by contacting the mixture of calcium carbonate and calcium sulfite with an oxygen containing gas under oxidizing conditions.

(Other references confirm that plain old air works just fine as the needed "oxygen containing gas" in the conversion of FGD "calcium sulfite" into the desired "calcium sulfate dihydrate".)

Gypsum, calcium sulfate dihydrate, obtained from flue gas desulfurization by the wet limestone process is in the beta crystal form which is sometimes a crystal form of hemihydrate or anhydrite. The powder has extremely poor flow characteristics, it agglomerates or sticks together and does not exhibit free flow in storage hoppers and bins. As a result of these poor handling properties, synthetic calcium sulfate dihydrate obtained as a byproduct from the desulfurization of flue gas by the wet limestone process is not well suited for the manufacture of wallboard or well suited for other applications which require an easily processible material. 

There is substantial art regarding the generation of gypsum calcium sulfate dihydrate obtained as a byproduct from industrial processes.

This invention relates to an improved process for producing gypsum calcium sulfate dihydrate flakes having sufficient size and strength such that the gypsum calcium sulfate dihydrate, can be handled and processed in conventional equipment commonly used by wallboard manufacturers and others in the construction industry.

The flakes have sufficient hardness to minimize dusting and fracturing.

The (specified and described) combination of pressure and temperature on the moist gypsum calcium sulfate dihydrate alters the physical characteristics of the gypsum calcium sulfate dihydrate, thereby resulting (in) a sheet which breaks into flakes on exit from the compaction zone. The fractured sheet of gypsum calcium sulfate dihydrate is in the form of chips ranging in size from about 1/4" to 1" on a side. 

Several advantages are achieved by the process of this invention and these advantages include: the generation of chips which are resistant to breaking and resistant to abrasion. Other features of the chip include enhanced processibility due to improved flow characteristics, e.g., they may be mechanically conveyed, handled or stored, and they can be processed easily in conventional grinding and calcining equipment for conversion into wallboard. Other advantages include a product which has improved load bearing capability. Also, because the gypsum calcium sulfate is processed "wet" as compared to prior art processes, energy and capital costs associated in reducing such moisture are lower."

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We'll leave it at that, although Air Products commendably goes into considerable detail about how the FGD Gypsum flakes are to be handled, and processed into wallboard filler, in ways that maximize it's performance in that specific application.

And, they do emphasize that the product is compatible with the "conventional equipment commonly used"; thus reducing or eliminating any need for the customer, the wallboard maker, to incur additional expense for new or different processing equipment.

More specifically, this is a technology that processes "wet" scrubber sludge and converts it into a dry and more easily processed form, thus reducing, as in the concluding sentence in our excerpts, the "costs associated" with drying, or otherwise preparing, it that might be incurred by the end user.

That might seem a small thing, but, oddly, as we will document in a future report concerning this topic from another source, it is one of the issues standing in the way of greater use of Coal-fired power plant FGD wastes in certain industries, especially, as treated specifically in the full Disclosure of our subject, "United States Patent 5,362,471", wallboard manufacturing.


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