No abstract

The 1990 amendments to the Clean Air Act have spurred the development of flue gas desulfurization (FGD) processes, several of which produce a dry, solid by-product material consisting of excess sorbent, reaction products containing sulfates and sulfites, and coal fly ash. Presently FGD by-product materials are treated as solid wastes and must be landfilled. However, landfill sites are becoming more scarce and tipping fees are constantly increasing, lt is, therefore, highly desirable to find beneficial reuses for these materials provided the environmental impacts are minimal and socially acceptable. Phase 1 results of a 4 and 1/2 year study to demonstrate large volume beneficial uses of FGD by-products are reported. The purpose of the Phase 1 portion of the project was to characterize the chemical, physical, mineralogical and engineering properties of the FGD by-product materials obtained from various FGD technologies being developed in the state of Ohio. Phase 1 also involved the collection of baseline economic data related to the beneficial reuse of these FGD materials. A total of 58 samples were collected and analyzed. Our results indicated the chemical composition of the FGD by-product materials were dominated by Ca, S, AI, and Si although the specific composition varies from one sample to another. Many of the elements regulated by the U.S. Environmental Protection Agency reside primarily in the fly ash. The presence of excess sorbent and reaction products causes a dilution of the concentrations of these elements in the FGD by-product materials as compared to the fly ash alone. Concentrations of the eight metals (Ag, As, Ba, Cd, Cr, Hg, Pb, and Se) regulated _)ythe Resource Conservation Recovery Act (RCRA)were below drinking water standards when measured by either the ASTM or TCLP leachate tests. Engineering tests revealed that samples made from the compacted FGD by-product materials were generally higher in strength and had greater stiffnessthan natural soils typically used in the construction of a highway embankment. Compacted densities were also lower than typical compacted soil densities. These data suggest that FGD by-product materials, used in construction of a highway embankment, would be lighter and require less right-of-way due to the possibility of constructing steeper slopes. Dry FGD by-products can react with with water to form ettringite, an expansive calcium sulfoaluminate hydrate mineral. This expansiion may affect how dry FGD byproduct is stockpiled and used by professional engineers and construction contractors. Based on analyses of the agricultural lime and supply demand relationships it was concluded that FGD by-product material, used as an agricultural lime substitute, would be entering a very competitive market. This substitution will be sensitive to transport distances and the FGD producer's willingness to subsidize its use in agricultural. In summary, Phase 1 results revealed that FGD by-product materials are essentially coal fly ash materials diluted with unreacted sorbent and reaction ...

BackgroundPerennial ryegrass is a cool-season grass species from the family Poaceae and is widely cultivated in temperate regions because it exhibits rapid growth and establishment, and possesses high forage quality. The extension of the growing season in Ireland in spring and autumn is a breeding target to make farming more profitable since a grass-fed diet based on grazing is the cheapest way of nutrition for ruminants.MethodsFifty-seven perennial ryegrass accessions were screened for their ability to grow under typical Irish spring conditions as taken from long term temperature records in controlled climate chambers. They were grown in low temperature (8 °C/2 °C day/night) and control conditions (15 °C/8 °C day/night) in three consecutive independent experiments. Fresh weight, height, chlorophyll content and electrolyte leakage were measured, and these parameters were used to rank plant performance under low temperature growth conditions.ResultsThe results showed that height, yield and electrolyte leakage are excellent measures for the impact of cold stress tolerance. Little variation in growth was seen under cold stress, but a wide variety of responses were observed under control conditions.DiscussionOur results suggest that cold stress is under tight physiological control. Interestingly, the various genotypes responded differentially to more amenable control conditions, indicating that a quick response to more amenable growth conditions is a better target for breeding programmes.

A new concept of power plant heat-sink system is presented which employs the combination of a conventional wet-tower and a conventional dry-tower. The purpose of this cooling system is to reduce wet cooling-tower makeup-water requirements in water-short areas. The dry tower operates all year around while the wet-peaking tower is used only above certain ambient dry-bulb temperatures. The two cooling circuits serve separate sections of a conventional, surface-type, steam condenser. Thermal performance analysis is presented for various combinations of cooling systems ranging from 100 percent wet to 100 percent dry. Annual makeup-water requirements are calculated for various sizes of towers located in 18 selected cities of the U.S.A. ranging from north to south and east to west.

The Clean Air Act, as amended in 1992, spurred the development of flue gas desulfurization (FGD) technologies. Several FGD processes produce a dry, solid byproduct material consisting of excess sorbent, reaction products containing sulfates and sulfites, and coal fly ash. Generally, dry FGD by-products are treated as solid wastes and disposed in landfills. However, landfill sites are becoming scarce and tipping fees are constantly increasing. Provided the environmental impacts are minimal, socially acceptable beneficial uses of dry FGD by-products can provide economic benefits to both the producer and the end user of the FGD by-products.A study was initiated in December, 1990 to demonstrate large volume beneficial uses of FGD by-products. A Phase 1 report provided results of an extensive characterization of chemical, physical, mineralogical and engineering properties of 58 dry FGD by-product samples. The Phase 1 report concluded that high volume beneficial reuses will depend on the economics related to their ability to substitute for existing materials for various types of applications (e.g. as an agricultural liming material, soil borrow for highway embankment construction, and reclamation of active and abandoned surface coal mine lands). Phase 2 objectives were (1) to conduct laboratory and greenhouse studies of FGD and soil (spoil) mixtures for agronomic and engineering applications, (2) to initiate field studies related to high volume agronomic and engineering uses, and (3) to develop the basic methodological framework for estimation of the financial and economic costs and benefits to society of several FGD reuse options and to make some preliminary runs of economic models.Laboratory studies were conducted to investigate time-dependent changes in solution chemistry and solid phase composition resulting from the forced leaching of mine spoil-FGD mixes (FGD applied at 0, I O , 20 and 40 wt %). Water quality of the leachate was primarily a function of FGD by-product type, application rate and reaction time. Spoil type had little effect on pore water quality except at the lowest FGD application rate. FGD by-products containing free lime (CaO or Ca(OH),) initially yielded leachate pH values above 12 but the pH rapidly decreased with time. Leachates were generally dominated by Ca, S and CI. If the sorbent used to scrub the flue gases contained Mg, then Mg concentrations were also found to be greatly increased in the leachate of the treated spoil. In contrast, AI and Fe concentrations, which often reach toxic levels in acid mine spoil, were decreased to near instrument detection limits when FGD was applied at rates of 10% or greater. Arsenic, Cd, Cr, Cu and Ni concentrations were below the maximum contaminate levels (MCL) defined for drinking water The MCL for Se was exceeded in 78% of the samples in the first leachate, but in only 25% of the samples after 26 days of reaction. Geochemical modeling of the leachate chemistry suggested that ettringite (Ca,AI,(S0,)3( OH),2.6H,0)forms as a reaction product in F...