Rocks bedded

Coal is Interspersed as individual beds within other types of sedimentary rock beds, including sandstones, limestones, clays, shales, and mixtures of these materials. The plant material that ultimately became coal deposits was accumulated in upland bogs, coastal or near-coastal swamps, or della plains. It is envisioned that the conditions were somewhat similar to the conditions existing today in the Okefenokce Swamp in Georgia or the Everglades of Florida. These areas may have varied from a few acres in several hundreds of square miles (hectares/square kilometers). Hence, the variation in ihe occurrence of coal as we find it today. 

The SP Curve recorded the differences in natural electrical potential between the fluids in the adjacent formations and those within the uncased borehole. This curve was soon accepted as an indicator of the porosity of the rock strata and as a means of focating the boundaries of rock beds. See Fig. 18. 

The slope of the water table is defined by three major factors the base of the drainage system (sea, lake, river), the topography of the land surface, and the occurrence of impermeable rock beds. 

Rock beds at the saturated zone that host flowing groundwater are called aquifers (from Latin aqua, water ferre, to bear or carry). Aquifer rocks contain the water in voids—pores and fissures. The size and number of voids and the degree of interconnection between those pores and fissures define the qualities of the aquifers. The same properties define infiltration efficiency and capacity of intake of recharge water. These properties are discussed below for different rocks. 

Fig. 2.5 Basic components of a phreatic groundwater system intake outcrops, an aerated zone, the water table, the saturated zone that constitutes a water-bearing aquifer, and impermeable rock beds of the aquiclude that seal the aquifer at its base.

Confined aquifers are water-bearing strata that are sealed at the top and the bottom by aquiclude rocks of low permeability (Fig. 2.6). Confined aquifers are commonly formed in folded terrains (section 3.4) and have a phreatic section, where the aquifer rock beds are exposed to recharge infiltration, and a confined section, where the aquifer rock beds are isolated from the landscape surface by an aquiclude (Fig. 2.6). 

Fig. 2.10 Rock beds in a subsidence basin. The part above the terminal base of drainage, for example, the sea, functions as a through-flow system (arrows). The deeper rock beds are fossil through-flow systems that host stagnant groundwater as they are (1) covered by impermeable rocks, (2) bisected by plastic impermeable rocks that have been squeezed into stretch joints in the competent rock beds and in between bedding plane thrusts, and (3) placed in a zone of zero hydraulic potential.

Many rock types have a layered structure, individual rock layers varying in thickness from a few centimeters to tens of meters. Layered rocks include marine sediments, most continental sediments, lava flows and volcanic ejecta, and intrusive sills. The hydraulic properties vary from one rock layer to another, often resulting in abrupt changes along the vertical axis. In terms of the permeability coefficient (k) the lateral coefficient (kx) may significantly differ from the vertical coefficient (kz). The alternation of aquifers and aquicludes results from the layered structure of different rocks, and the occurrence of springs is often controlled by the layering of rocks. Fissures may be restricted to individual rock layers or cross several rock beds, in which case water flow is improved, mainly in the vertical direction. 

Fig. 3.3 Factors controlling the flow direction of groundwater. (I) porous rock water direction is determined by topographic gradients alone (II) a tilted impervious rock bed deviates direction of water flow.

Confined aquifers (section 2.8) are rare in tectonically undisturbed regions with horizontal rock beds (Fig. 3.5). Tilting of the aquifer and aquiclude sandwich makes room for the formation of confined aquifers. It provides each case with a recharge outcrop section, forming a phreatic aquifer (section 2.8) and a confined section fed by the former (Fig. 3.6). 

Subsidence structures are common. They are formed by the gradual lowering of rock strata, forming basin shapes. Two major processes operate during subsidence burial of older rock beds and accumulation of new sediments at the surface forming new rock beds or lenses that eventually get buried as well, the water stored in them becoming trapped (Fig. 3.7). 

Fig. 3.5 Horizontal rock beds often allow for the formation of only one recharged (phreatic) aquifer, the first aquiclude preventing recharge water from reaching lower potential aquifers.

Fig. 3.6 Tectonic tilting of rock strata provides the necessary condition for the formation of a partially confined aquifer. A phreatic section, located at the outcrop of the rock bed, serves as recharge intake area feeding the confined section in cases where the inclined rock bed has a drainage outlet at its lower end enabling through-flow (which is a rare case).

Fig. 3.12 A sill intruded between carbonatic rock beds forming a local aquielude. Weathering into clay minerals may improve the sealing capacity of a sill.

Determination of the flow gradient between two wells (Fig. 4.11) is based on the assumption that the two wells are hydraulically interconnected, as shown in Fig. 4.13a. Flowever, wells may be separated by an impermeable rock bed with no hydraulic interconnection (Fig. 4.13b). Thus the gradient measurement between the two wells in the second case is meaningless. The... 

Fig. 4.13 Hydraulic interconnection between wells in fissured limestone terrain (a) wells I and II are interconnected and water flows down-gradient (b) similar-looking wells, separated by an impermeable rock bed wells III and IV are not interconnected, in spite of the apparent gradient.

A rock-bed thermal-energy storage unit is employed to remove energy from a hot airstream and store for later use. The schematic for the device is shown in the sketch. The surface is covered with a material having an overall R value of 2 h °F ft2/Btu. The inlet flow area is 5 x 5 = 25 ft2, and the rock-bed length is 10 ft. Properties of the rock are... 

The word substance does not designate what remains beneath, impervious to history, but what gathers together a multiplicity of agents into a stable and coherent whole. A substance is more like the thread that holds the pearls of a necklace together than the rock bed that remains the same no matter what is built on it... substance is a name that designates the stability of an assemblage. (1999, 151, cf. 167 and 170)17... 

Engineered reed-bed and constructed wetland systems for removal of heavy metals from wastewater using phytoremediation are in use in some developed Asian countries. The root system of the hyper-accumulator plant penetrates a permeable rock bed. The wastewater is introduced into one end of the bed and flows through the permeable rock layer. The rock layer should be inert to heavy metals binding so that it does not unwittingly serve as a sink for heavy metals. These metals are sequestered by the root system and translocated to the shoots. Periodically, the metal-containing shoots are harvested. The biomass can be burned off or composted to yield a low volume of metal-rich ash. 

Direction and Control of Solar Dryers with Rock-Bed Heat Storage.342... 

Natural or artificial materials may be employed for heat storage. Natural materials (water, pebble bed, and rock bed) are usually cheaper than synthetic materials (e.g., latent heat-storing salt solutions and adsorbents). Detailed discussion of heat stores is beyond the scope of this chapter. 

Figure 14.9 shows the arrangement of a solar dryer with rock-bed storage [20]. The dryer is a direct system the collectors 1 are located on the ground and have an area of 193 m. The air warmed in the collectors is forwarded into drying space 3 by a fan 2. The dryer has room for a maximum of 6.5 m timber 4. In the upper roof space two ventilators are placed that are used for continuous circulation of the air. Vents 6 are placed in the sidewalls of the roof... 

FIGURE 14,9 Solar timber dryer equipped with rock-bed heat storage. (From Read, W.R. et al.. Solar Energy, 15, 309, 1974.)... 

During drying and charging of heat storage, damper 9 is in the position shown in the figure by a solid line, air flows from the dryer space into the rock bed and back to the collector. 

During operation when there is no solar radiation, damper 9 is in the medium position, air flows from the dryer into the rock bed, is warmed, and flows again into the dryer. The operation of dampers 6 is controlled by the wet bulb temperature measured in the dryer. 

The economic design of the rock-bed storage device is of great importance [213]. 

The construction of a high-performance raisin dryer is shown in Figure 14.11 [19] with rock-bed heat storage. The collector system 1 consists of 42.7-m long units with a surface area of... 

In solar dryers with air-type collectors rock-bed storage (crushed stone or pebbles of 2-4 cm size) is used most commonly. When selecting the material for the rock or pebble bed, among other considerations, there is the question of the pressure drop across the bed. The flow resistance of a pebble is usually smaller than that of crushed rock. Uniform pebble or rock size must be chosen to obtain uniform air distribution in the bed. The necessary mass of rock-bed or pebble-bed heat storage is typically about threefold that of water-type heat storage. 

Because of the point contact between the particles in the rock bed, the heat conduction is negligible. Therefore, rock beds work practically as stratified heat stores no matter the arrangement for air inlet and exhaust. 

For dryers having separated rock-bed heat storage (see Figure 14.9) three main modes of operation should be applied ... 

In mode of operation 1, damper 8 in Figure 14.9 is open whereas damper 9 closes the air duct below the heat storage 7. In mode of operation 2, damper 9 closes the upper air duct and the air flows from the drying space into the rock bed. In mode of operation 3, damper 9 is in a medium position, fan 2 is out of operation, and the air flows from the dryer into the rock bed there it will be preheated and flown back into the drying space in the upper air duct. 

The regulation of the mode of operation can be realized manually or automatically. As a signal for regnlation, the temperatures of the drying space, the ontlet air of the collector, and the rock bed can be nsed. As a controlling signal for the operation of the dampers 6, the wet bnlb temperature or the relative humidity of the drying space can be applied. 

Air can also be used as the heat transfer fluid in collectors built for this purpose. The heat store in this case will most often be a rock bin or a rock bed, that is, an insulated container filled with crushed rocks or pebbles (called a bin if it is an upright container or a bed if it is a shallow layer under the floor). The solar heated air will warm the rocks, and at a later time the air flow in the distribution circuit will remove this heat and transport it to the spaces where it is needed. Figure 11 shows a basic air heating system diagram. Instead of small pipes, more bulky air ducts must be used, and instead of pnmps, fans, or blowers. A much larger quantity of air must be circulated than the volume of... 

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