FINAL TECHNICAL REPORT

September 1, 1996, through February 28, 1998

Project Title: FURTHER DEVELOPMENT OF A COPPER OXIDE DESULFURIZATION AND NO_x REMOVAL SYSTEM

ICCI Project Number:     96-1/2.1A-5

Principal Investigator:       David G. Sloat, Sargent & Lundy

Other Investigators:          Jeri C. Penrose, Sargent & Lundy; Joseph N. Darguzas, Sargent & Lundy; Raj Gaikwad,                                                  Sargent & Lundy

Project Manager:             Ronald H. Carty, ICCI

ABSTRACT

This work supports continued development of the Copper Oxide process for controlling emissions of sulfur dioxide and nitrogen oxides from coal combustion. This advanced process utilizes a moving bed of regenerable sorbent to capture sulfur oxides from hot flue gas and recover the collected sulfur as a saleable by-product such as fertilizer, elemental sulfur, or sulfuric acid instead of producing large quantities of solid waste requiring disposal. At the same time, the sorbent catalytically reduces nitrogen oxides. Previous pilot studies have confirmed the process is capable of high removal efficiencies for both pollutants while firing high-sulfur Illinois coal; and previous economic studies have shown the process is an attractive alternative to conventional flue gas desulfurization technologies.

The current project builds on the successful pilot testing performed to date to advance the technical and economic basis for furthering commercialization of the process. This project includes:

• Review of potential for copper-catalyzed dioxin formation.

• Characterization of SO₃ removal efficiencies for and determination of resulting acid dew points in the desulfurized flue gas.

• Evaluation of byproduct recovery options for conversion of recovered SO₂ to sulfuric acid, elemental sulfur, or ammonium sulfate byproducts for sale.

In general, this work addresses technical issues peripheral to the main process which has been the focus of development efforts to date. These issues are important to eventual commercial acceptance of the process, and concurrent work in these areas in parallel with ongoing process development and scale-up through the U.S. Department of Energy LEBS program will hasten commercialization of the technology.

EXECUTIVE SUMMARY

The Copper Oxide process promises to be an economical and attractive flue gas desulfurization process for Illinois coals with medium to high sulfur content. The process uses a regenerable sorbent in a moving bed to simultaneously capture sulfur dioxide and catalytically reduce nitrogen oxides in flue gas. Regeneration of the sorbent then releases the sulfur dioxide in a concentrated stream for recovery. The sulfur dioxide is recovered as a byproduct such as fertilizer, elemental sulfur, or sulfuric acid for sale rather than generating large quantities of waste products as with some other FGD options.

The U.S. Department of Energy (DOE) Pittsburgh Energy Technology Center (PETC) has performed pilot scale parametric testing of the process which showed sulfur dioxide removals greater than 93% when firing a 2.6% sulfur Illinois coal. Over 90% NO_x removal was also realized. These results validated the process model and provided a basis for continued process development.

These results were confirmed by a pilot testing program at the Illinois Coal Development Park (ICDP) test facilities. In this program, a medium-scale Copper Oxide pilot plant was constructed and operated and which achieved SO₂ removals of 98% and NO_x removals approaching 100% with no ammonia slip. This pilot plant is an order of magnitude larger than the pilot plant at PETC and is one-tenth the size anticipated for commercial adsorber modules. Economic analysis indicated the process is competitive with other FGD technologies, particularly when NO_x removal is required.

The purpose of this study is to continue the development of the Copper Oxide process for controlling SO₂ and NO_x emissions from coal combustion. This work is focused on three areas important for commercial acceptance:

Potential catalytic formation of dioxin in the process

Removal efficiency of the trace amounts of SO₃ in the flue gas

Options for production of salable byproducts from recovered SO₂

Assessment of the Potential for Dioxin Formation

Low temperature formation of dioxins in municipal waste combustion facilities has been found to be promoted by copper-catalyzed reactions, so the use of copper in the Copper Oxide flue gas cleanup process has been brought into question. The Copper Oxide process relies on contacting flue gas with a copper and copper oxide based sorbent to capture SO₂ from the gas. This has raised suspicions that concurrent reactions similar to those in municipal waste combustors might promote dioxin formation as an unintended side reaction in the Copper Oxide process.

Published literature suggests that use of copper sorbents for desulfurization in the Copper Oxide process are not likely to cause increased polychlorinated dibenzodioxin (PCDD) and polychlorinated dibenzofuran (PCDF) formation in treated flue gas. High amounts of SO₂ in Copper Oxide process applications appear to provide protection against copper-catalyzed PCDD and PCDF reactions. In addition, the g-alumina supported copper oxide sorbent has been found to capture HCl instead of promoting Cl₂ formation, again protecting against PCDD and PCDF formation. Confirmation of these indications by direct measurement at the planned scale-up to a single commercial module test facility treating a slipstream of flue gas from coal-firing at a commercial site should be carried out.

Characterization of SO₃ Removal Performance

The Copper Oxide process was found to provide high removals of SO₃ and reduce levels in treated flue gas to below 2 ppm. For flue gas from typical boilers combusting high-sulfur coals, this would reduce acid dew points by about 50^o F. The additional heat recovery made available would improve boiler thermal efficiencies by 1.4 percentage points, with cost savings of about 15 to 20 cents per MWh. Alternatively, lower acid dew points would minimize corrosion from acid condensation in downstream ductwork. This collateral advantage provides additional commercial justification for use of the Copper Oxide process to treat flue gases from combustion of Illinois coals.

Evaluation of Byproduct Options

In order to be an economically viable flue gas cleanup process, the Copper Oxide technology must include byproduct production technology to convert SO₂ removed from the flue gas to a saleable byproduct. There are three primary byproduct options: sulfuric acid, elemental sulfur, and ammonium sulfate fertilizer.

Sulfuric acid and elemental sulfur can be produced by applying existing commercially available technology. Sulfuric acid will be an attractive option for large facilities only, because the chemical plant involved is capital intensive. Elemental sulfur can be economically produced at a wider range of plant sizes, but the market price has been depressed by high levels of byproduct production in natural gas fields for a decade and the economics of this byproduct are strongly influenced by proximity to customers.

Ammonium sulfate is an attractive third alternative, particularly with the high value of this material when manufactured in the most desirable grade. It will be especially appealing to smaller installations which cannot afford a sulfuric acid plant or which are not situated to compete in the elemental sulfur market. While ammonium sulfate has been produced both as a byproduct as well as from virgin raw materials for a century, a complete process utilizing the SO₂-rich offgas as a feedstock is not commercially available. Therefore, continued development of a process for producing ammonium sulfate fertilizer based on processing to produce concentrated ammonium sulfate solution in combination with commercially available crystallization technology is needed to enhance commercialization prospects.