Carbon dioxide coal mining

Although fire damp/ which is mainly methane, and choke damp (carbon dioxide) are frequent causes of mine accidents, Dr. William Brownrigg learned how to make good use of them. In 1741 he communicated to the Royal Society several papers on the gases of coal mines, but preferred to withhold them from publication until he could prepare a comprehensive treatise on the subject. His laboratory at Whitehaven was provided with several gas furnaces of his own design and a constant supply of fire damp from the nearby mines. Because of his skill in foretelling explosions by the rapid fall of the barometer, mine operators often consulted him. 

Cardox is a device for breaking coal in gaseous mines by the pressure produced on heating liquefied carbon dioxide. It is briefly described in Vol 2 of Encycl, p C67-R. Similar devices, Airdox and Armstrong Air Breaker, were developed in. 1930 in the US. More successful were Hydrox developed in 1955 and Chemecol developed by du Pont Co before 1958. They are also Hydraulic Coal Bursters (See Vol 3 of Encycl, p C434)... 

Part of the North Branch of the Potomac River runs crystal clear through the scenic Appalachian Mountains, but it is lifeless—a victim of acid drainage from abandoned coal mines. As the river passes a paper mill and a wastewater treatment plant near Westemport, Maryland, the pH rises from an acidic, lethal value of 4.5 to a neutral value of 7.2, at which fish and plants thrive. This happy "accident comes about because calcium carbonate exiting the paper mill equilibrates with massive quantities of carbon dioxide from bacterial respiration at the sewage treatment plant. The resulting soluble bicarbonate neutralizes the acidic river and restores life downstream of the plant.1... 

Mine atmospheres contg 5 to 15% of methane and no appreciable amt of carbon dioxide are explosive, and of these the most dangerous is the mixt contg 9.5% methane. Temp of expln of this mixt is ca 650°if duration of flame produced by a charge of expl used for blasting coal is ca 10 secs and if it is only 0.1 sec, the temp is ca 1000° (Ref 9, p222 Ref 31,... 

The actual proportion of carbon dioxide in the air varies very considerably according to circumstances. Whalley reported that in a Scottish mine the carbon dioxide in the air near the coal face reached T21 per cent., whilst on the pavement it was no less than 4-56 per cent. Levy,1 in discussing the abnormal air of New Granada, points out that owing to forest fires the percentage of carbon dioxide in the air would often rise to 0-49 per cent. These cases, however, are abnormal. 

The effect of gas solubility on the rate of foam destruction is of major practical importance. For example, in the production of firefighting foams for underground use in coal mines, it is advisable to use exhaust gases as a disperse phase. However, they contain a considerable amount of carbon dioxide and water vapour that sharply decrease the expansion ratio and stability of the foam produced. 

The porous structure of chars from a high volatile bituminous coal from mine Pumarabule in Spain, initial and preoxidized, then steam activated, was characterized by carbon dioxide and benzene adsorption measurements, as well as by immersion calorimetry molecular probes with increasing critical dimensions were used. The influence of preoxidation of the coal on the values of parameters describing the pore size distribution, with particular attention to micropores, evaluated according to each of the applied methods, is discussed. 

Derivation (1) From natural gas by absorption or adsorption. (2) From coal mines for use as fuel gas. (3) From a mixture of carbon monoxide and hydrogen (synthesis gas) obtained by reaction of hot coal with steam the mixed gas is passed over a nickel-based catalyst at high temperature. See methanation. Methane can also be obtained by a nickel-catalyzed reaction of carbon dioxide and hydrogen. (4) Anaerobic decomposition of manures and other agricultural wastes. (5) By horizontal drilling of coal seams. 

Another means to reduce man-made carbon dioxide emissions is sequestration in the land or the ocean. When carbon dioxide is produced locally it may be possible to efficiently separate it from other gases, concentrate it, and dispose of it. A number of complex scenarios may be envisioned to accomplish this disposal, from pumping it into the ocean, to displacing methane in coal mines, to storage in depleted hydrocarbon reservoirs. 

To meet the challenges discussed above, research opportunities for the chemical sciences may be envisioned in four areas. First, in carbon dioxide sequestration, an understanding is required regarding how molecular carbon dioxide interacts with various species present in coal mines or other geological formations where carbon dioxide might be stored. It is particularly important to understand... 

Novel techniques are being investigated by the Bureau of Mines in an effort to find new uses for coal, or products from coal and its derivatives. One technique under study involves chemical reactions in an ozonizer discharge. Initially the gas-phase reaction of carbon monoxide and steam to produce carbon dioxide and hydrogen has been investigated from an engineering viewpoint. 

Studies have shown that the storage of carbon dioxide is possible in various geological settings. The main candidates are sedimentary basins, e.g., oil and gas reservoirs (working or abandoned), deep unmineable coal-seams and saline formations (aquifers). Sub-surface storage can take place at both on-shore and off-shore locations access to the latter is via pipelines from the shore or from off-shore platforms. Other prospective sites for storage include salt caverns, basalts, oil/gas shales and disused mines. The various options are shown schematically in Figure 3.4. 

Figure 3.4 Options for the geological storage of carbon dioxide. 1. Deep unused saline formations (aquifers). 2. Use of carbon dioxide for enhanced oil recovery. 3. Depleted oil and gas reservoirs. 4. Deep unmineable coal seams. 5. Use of carbon dioxide in enhanced coal-bed methane recovery. 6. Other suggested options (e.g., salt caverns, basalts, oil/gas shales, disused mines)." (Courtesy of Intergovernmental Panel on Climate Change).

There are several operational and safety issues to be resolved before this option can be adopted in a major way. Thermodynamically, carbon dioxide should react with carbon (coal) to yield carbon monoxide, which is a highly toxic gas sometimes found in coal mines. In practice, this reaction will not take place at an appreciable rate at ambient temperatures, although it could become significant at depths where the temperature is much higher. If the inadvertent ingress of air to a coal seam that was saturated with carbon dioxide led to a fire, then the potential might exist for vast quantities of toxic carbon monoxide to be formed via the reaction CO2 + C -> 2CO, and subsequently liberated. It is known that the extraction of water from coal beds does allow air to enter and circulate more freely and that this sometimes results in underground fires. Such safety issues should be evaluated carefully. Other factors to be considered are ... 

On a smaller scale of operations, there are some industrial wastes and mine tailings that are alkaline and potentially more reactive than virgin minerals towards carbon dioxide. These include pulverized fuel ash from coal-fired power stations. In this situation, development of a practical means to react the ash with some of the attendant carbon dioxide would be most beneficial. Indeed, this may prove to be the most expedient route to introducing the technology required for sequestration via mineral carbonation. 

---