Salty coals

Other Nomenclatures Relevant to Gasification 3.3.5.1 Salty Coals 

Some low-rank coals can be classified as salty coals, if the Na20 content in the ash exceeds 4 or 0.5 wt% of the dry coal [15]. 

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The interaction of silica and sodium chloride, characteristic of such processes as salt-glazing, coking salty coals, and chloridizing roasts, has been investigated up to 1000° C. by Clews and Thompson.11 There are three distinct reactions corresponding with the equations... 

To produce comparable ash compositions, the conditions of ashing or combustion must be rigidly controlled. Hence, the coal sample mass, ashing temperature, time, atmosphere, and equipment specification are well defined. There are several standards with final ashing temperatures varying among 150 °C (plasma ashing), 575 C (for salty coals), 750 C (ISO 1171 [25]), and 815 C. 

In some rare cases (e.g., utilization of salty coals), anti-fluxing is also desired. This is the addition of mineral substances to increase the ash melting points if, for example, low ash fusion temperatures limit the carbon conversion or operation of dry-ash moving-bed or fluid-bed processes. 

Alkali metals occur in salty coals typically as chlorides, humates, sulfates, and carbonates. The reducing atmosphere in the gasifier favors the continuous liberation of volatile minerals, resulting in steadily changing eutectics causing transitions of the ash fusion behavior, which are nearly unpredictable. 

These partly competing and overlapping devolatilization mechanisms demonstrate that salty coals can cause severe corrosion problems, which are mostly accompanied by abnormal and unstable ash fusion behavior, if gasified in dry-... 

Halogen content represents an upper limit for combustion of a high-halogen coal in a salty (marine location) atmosphere. For typical low-halogen U. S. coals, the chloride concentration would be v 0.01 mol % and the NaCl pressures correspondingly less. 

At various times in the geological past, large areas of the sea were apparently cut off from the rest, and evaporation first made the water too salty to support life and then resnlted in deposits of salt and/or gypsum and anhydrite. Many other deposits are also recognized and inclnde wind-blown deposits and deposits in river valleys and lakes. However, somewhat nniqne in character among the sedimentary rocks are the vast accumnlations of plant material that formed at many different times to produce coal seams. 

For instance, in 2014, the local water conservancy district wanted to pump the water from Lake Quitchipa to a new percolation bed to allow the water to enter the local aquifer. Three students were assigned to this project. They collected water samples at different locations in the lake at different times. They measured total dissolved sohds of the samples they collected. They also measured the anions and other analytes in the lake. They determined the TDS concentrations at the Met (Coal Creek) to be approximately 400 mg/L and over, 6000 mg/L in the lake. They came to the conclusion the water was too salty due to the many years of evaporation. With this information, the conservancy district abandoned the project. 

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