Limestone reactivity

The limestone reactivity test procedure calls for the samples to be ground and screened to produce material in narrow particle size ranges for testing. Solution composition and pH are maintained constant throughout the measurement period (up to 20 hours) at preselected values. The selection of pH and solution compositions is based upon several design criteria including ... 

The experimental apparatus shown in Figure 1 was used to evaluate limestone reactivity. Conditions in the reactor approximate conditions in the reaction tank of a limestone scrubbing system. As the limestone dissolves, the pH in the reactor will begin to rise. Therefore, to insure a constant pH in the experimental reactor, a low pH test solution (see Table I) is metered to the reactor. As the low pH feed is added, an equal amount of reactor liquor is also withdrawn to maintain the reactor volume also remains constant (2.5L). In an actual scrubbing system, S02 absorbed from the flue gas will provide enough acidity such that the pH remains approximately constant. 

A.R. Ellis, An Investigation of UK Limestone Reactivity for the Limestone-gypsum FGD Process , from Desulfurisation in Coal Combustion Systems , Institution of Chemical Engineers Series 106, April 1989,19-21. 

Insufficient SO2 Removal Low liquid phase alkalinity Low mass transfer surface area and/or inadequate contact time between the flue gas and the stmibbing slurry LowL/G Low limestone reactivity... 

Except for dead-burned dolomite, all limes are much more reactive with acids than limestone. The high calcium types are the most reactive. 

Another thermally efficient kiln is the modem mixed-feed vertical kiln ia which coke is admixed with 8.5—20 cm lump limestone and charged into the top of the vertical kiln by a mobile, overhead charging system. However, use of this kiln is waning since the quaUty of mixed-feed kiln lime does not equal that of the other three kilns described above, owing to ash contamination from the coke and poorer reactivity and to the higher cost of coke in most areas. 

Miscellaneous Kilns. A U.S. kiln, the Fluo-Sohds, appears to be another vertical kiln type, but this is its only similarity. It operates on a different principle. It utilizes as kiln feed only a discrete granulation of 0.225—2.4 mm (65—8 mesh) sizes. DeHcately controlled by air and exhaust gas pressure, the kiln feed of granules is fluidized as a dense suspension. Because it is instmmented, this kiln can produce a very reactive lime at better than average thermal efficiency. The kiln, however, has limited utifity because the cost of obtaining the kiln feed with many hard, compact limestones is prohibitive. 

Ratios of U and U to Th and Ra daughters, combined with differences in chemical reactivity have been used to investigate the formation and weathering of limestone in karst soils of the Jura Mountains, and of the mountains in the central part of Switzerland. Uranium contained within calcite is released during weathering, and migrates as stable uranyl(VI) carbonato complexes through the soil. In contrast, the uranium decay products, Th and Ra,... 

Dry-Throwaway Processes. Dry-throwaway systems were the precursor of processes that removed SO2 iu the ductwork, eg, the BCZ and IDS processes. Here, however, the device is a spray chamber similar to the wet scmbbers such as the three modules of the Colstrip iastallation (Fig. 12). Into the upper portion of the chamber a slurry or clear solution containing sorbent is sprayed. Water evaporates from the droplets, the sorbent reacts with SO2 both before and after drying, and the dry product is removed ia a downstream baghouse or ESP (72). Unfortunately, dry scmbbiag is much less efficient than wet scmbbiag and lime, iastead of the much less expensive limestone, is required to remove SO2 effectively. Consequentiy, a search has been conducted for more reactive sorbents (72—75). 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Corrosive to most metals with the evolution of flammable and explosive hydrogen gas Stability During Transport Stable Neutralizing AgerUs for Acids and Caustics Flush with water and apply powdered limestone, slaked lime, soda ash, or sodium bicarbonate Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Leblanc wrestled with the problem for five years between 1784 and 1789. Then finally, somehow, someway, he stumbled on the solution. Ancient ironmakers had used carbon in the form of charcoal when hot, the carbon is highly reactive and wrests the oxygen from iron oxide ores. As Leblanc heated his sodium sulfate with charcoal, he added a key new ingredient—common limestone (chalk)—as his source of C03. Almost miraculously, the transformation took place ... 

Retarded acids are primarily applicable to sandstone acidizing. Fluoroboric acid slowly hydrolyzes to form the more reactive hydrofluoric acid (109,110). The time required for this hydrolysis process may enable deeper penetration of the HF into the formation although one report contradicts these findings (111). Na TiF and similar salts also slowly generate HF in acid media (112). Phosphorous acid addition to hydrochloric acid has been used to reduce the HC1 reaction rate with limestone (113). 

Sulfur Emissicms Sulfur present in a fuel is released as SO2, a known contributor to acid rain deposition. By adding limestone or dolomite to a fluidized bed, much of this can be captured as calcium sulfate, a dry nonhazardous solid. As limestone usually contains over 40 percent calcium, compared to only 20 percent in dolomite, it is the preferred sorbent, resulting in lower transportation costs for the raw mineral and the resulting ash product. Moreover, the high magnesium content of the dolomite makes the ash unsuitable for some building applications and so reduces its potential for utilization. Whatever sorbent is selected, for economic reasons it is usually from a source local to the FBC plant. If more than one sorbent is available, plant trials are needed to determine the one most suitable, as results from laboratory-scale reactivity assessments are unreliable. 

Reactive metal that easily forms many compounds found in limestone, lime, marble, and gypsum important component of bones and coral reefs. 

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