Water in coal

Cybulski [52] has also shown that very fine coal-dust may explode even when it contains less than 12% combustible volatile matter. The presence of a significant amount of water in coal-dust may lead to its explosion even if free from volatile matter. This indicates the particularly hazardous nature of fine coal-dust. Cybulski has also shown that under particularly unfavourable conditions the coal-dust must contain as much as 95% incombustible matter (e.g. by admixture with non-inflammable stone dust) if explosion is to be avoided. 

The gas reservoirs located in very deep waters, in coal beds, and in tight sands are now more accessible. Fifteen percent of the U.S. gas supply in 1992 was derived from tight sand formations and 1.4 x 1011 m3 of coal-bed methane was added to the proven reserves (22). In 1992, U.S. proven reserves were placed at 4.67 x 1012 m3 in the lower 48 states, and it was estimated that the identified gas resource in the United States and Canada exceeds 3.4 x 1013 m3. Based on the 1992 rate of natural gas consumption, the United States has between 8 and 10 years of proven reserves and a domestic resource base containing between 50 and 70 years supply. 

A reaction of considerable importance in water pollution is the production of high acidity waters in coal mines. The acidity of these waters seems to be the result of oxidation of pyritic compounds. Although the oxidation mechanism is not understood, several investigators feel that microorganisms accelerate this reaction rate (25). 

The role of water in coal and the quantitative measurement of water are complicated because water is present within the coal matrix in more than one form (Allardice and Evans, 1978). Thus, the total moisture includes both the surface moisture and the residual moisture remaining in the sample after determining the air-dry loss (ASTM D-3302). Thus,... 

The chemical methods of water determination invoke the concepts of direct titration of the water or a chemical reaction between the water and specific reagents that causes the evolution of gases the water is determined by measurement of the volume produced. Chemical methods used for determining moisture also include (1) application of the Karl Fischer method of determining water content, and (2) reaction of quicklime with water in coal and subsequent measurement of the heat generated by the reaction. 

The dielectric constant varies with coal rank (Chatterjee and Misra, 1989). The theorem that the dielectric constant is equal to the square of the refractive index (which is valid for nonconducting, nonpolar substances) holds only for coal at the minimum dielectric constant. The decreasing value of dielectric constant with rank may be due to the loss of polar functional groups (such as hydroxyl or carboxylic acid functions), but the role of the presence of polarizable electrons (associated with condensed aromatic systems) is not fully known. It also appears that the presence of intrinsic water in coal has a strong influence on the dielectric properties (Chatterjee and Misra, 1989). 

In the previous section, we discussed how steam could be used to distill immiscible organic compounds. The process can be reversed, and hot organic compounds can be used to remove water from materials. This method can be used to determine the amount of water in an apple, an orange, or a piece of watermelon without ruining the fruit for other analyses. This technique also is used to determine the water in natural rubber that affects the curing or the water in coal products that affects the burning rate. 

Physical model of high pressure water injection in coal seam is established by using FLUENT software, relevant boundary conditions and initial parameters are setted. Then seepage pressure field, velocity field distribution and coal wet conditions of water in coal seam under different water pressure are numerically simulated. 

As is known from the simulative Figure 4, the addition of water in coal reduces gradually from the center of hole to both sides under the action... 

Atkins, A.S. and Singh, R.N. 1982. A study of acid and ferruginous mine water in coal mining operations. International Journal of Mine Water, 2 37-57. 

The water in coal is bound in different forms to its constituents. It can be divided into three types (1) Free moisture, also referred to as external moisture, superficial moisture, or the primary moisture fraction, which is present in large cracks and capillaries. Water bound in this way retains its normal physical properties. (2) Inherent moisture, also referred to as internal moisture or the secondary moisture fraction, whose vapor pressure is lower, since it is absorbed within the pore structure of the coal. (3) Water of constitution, which is mainly combined with mineral matter normally present in coal. This water is generally driven off only at temperatures higher than those normally used for the determination of moisture content. Standard methods do not make use of these terms and define (1) the total moisture content of a coal and (2) the moisture content of the coal analysis sample. Total moisture determination must be made over the sample as received in the laboratory, in an air-proof recipient. The determination consists in drying in an oven at 105 °C till constant weight. Its value is of huge interest both in international and domestic coal trade (ISO 589, ASTM D3173). 

The advantages of hydraulic proof pressure testing are best demonstrated by reference to the failure of a large steam separator drum at Cockenzie Power Station in East Lothian, Scotland, on May 6, 1966. (Separator drums are large, horizontal, cylindrical, thick-walled steel pressure vessels used to separate steam and water in coal-fired or nuclear power stations.)... 

Marrey, D. T. 1985. Exporting Colorado Water in Coal Slurry Pipeline. Journal of Water Resources Planning and Management, 111, 207-221. 

The second source is process water blowdown, where the water has scrubbed coal-derived gases to remove coal ash and trace components. The raw process water in coal gasification processes contains various organic and inorganic compounds. Purification of this water removes most of the organic compounds, and the plant then recycles much of the water. The net amount of this wastewater effluent reflects the water-soluble inorganics in the feed coal (such as chlorides) and the amount of coal feed. Coal gasification (and direct coal combustion) with dry gas cleanup systems can reduce process water effluents. Coal plants also often use water effluents to control the dust and bulk density of the solid waste. 

Since 1960, about 95% of the synthetic ammonia made in the United States has been made from natural gas worldwide the proportion is about 85%. Most of the balance is made from naphtha and other petroleum Hquids. Relatively small amounts of ammonia are made from hydrogen recovered from coke oven and refinery gases, from electrolysis of salt solutions, eg, caustic chlorine production, and by electrolysis of water. In addition there are about 20 ammonia plants worldwide that use coal as a hydrogen source. 

Water-in-oil emulsions are used as fire-resistant hydrauhc fluids to replace petroleum hydrauhc fluids in general industry, coal mines, and rolling mills where a fire ha2ard exists (1). 

Naphthalenol. 1-Naphthol, a-naphthol, or l-hydroxynaphthalene/P(9-/j5 -iJ forms colorless needles, mp 96°C, bp 288°C, which tend to become colored on exposure to air or light. It is almost insoluble in water, but readily soluble in alcohol, ether, and benzene. 1-Naphthol and 2-naphthol are found in coal tar (56). 

Historical. Pyridines were first isolated by destructive distillation of animal bones in the mid-nineteenth century (2). A more plentifiil source was found in coal tar, the condensate from coking ovens, which served the steel industry. Coal tar contains roughly 0.01% pyridine bases by weight. Although present in minute quantities, any basic organics can be easily extracted as an acid-soluble fraction in water and separated from the acid-insoluble tar. The acidic, aqueous phase can then be neutrali2ed with base to Hberate the pyridines, and distilled into separate compounds. Only a small percentage of worldwide production of pyridine bases can be accounted for by isolation from coal tar. Almost all pyridine bases are made by synthesis. 

Mineral Matter in Goal. The mineral matter (7,38) in coal results from several separate processes. Some comes from the material inherent in all living matter some from the detrital minerals deposited during the time of peat formation and a third type from secondary minerals that crystallized from water which has percolated through the coal seams. 

Synthetic Natural Gas. Another potentially very large appHcation of coal gasification is the production of synthetic natural gas (SNG). The syngas produced from coal gasification is shifted to produce a H2-to-CO ratio of approximately 3 to 1. The carbon dioxide produced during shifting is removed, and CO and H2 react to produce methane (CH, or SNG, and water in a methanation reactor. 

The relationships between specific heat and water content and between specific heat and ash content are hnear. Given the specific heat on a dry, ash-free basis, it can be corrected to an as-received basis. The specific heat and enthalpy of coal to 1366 K (2000°F) are given in Coal Conversion Systems Technical Data Book (part lA, U.S. Dept, of Energy, 1984). 

The failure took place in a large water-tube boiler used for generating steam in a chemical plant. The layout of the boiler is shown in Fig. 13.1. At the bottom of the boiler is a cylindrical pressure vessel - the mud drum - which contains water and sediments. At the top of the boiler is the steam drum, which contains water and steam. The two drums are connected by 200 tubes through which the water circulates. The tubes are heated from the outside by the flue gases from a coal-fired furnace. The water in the "hot" tubes moves upwards from the mud drum to the steam drum, and the water in the "cool" tubes moves downwards from the steam drum to the mud drum. A convection circuit is therefore set up where water circulates around the boiler and picks up heat in the process. The water tubes are 10 m long, have an outside diameter of 100 mm and are 5 mm thick in the wall. They are made from a steel of composition Fe-0.18% C, 0.45% Mn, 0.20% Si. The boiler operates with a working pressure of 50 bar and a water temperature of 264°C. 

Reburning is a process involving staged addition of fuel into two combustion zones. Coal is fired under normal conditions in the primary combustion zone and additional fuel, often gas, is added in a reburn zone, resulting in a fuel rich, oxygen deficient condition that converts the NO, produced in the primai y combustion zone to molecular nitrogen and water. In a burnout zone above the reburn zone, OFA is added to complete combustion. 

---