REP33544 - Laserfiche WebLink

Home Browse Search

G The initial small shafts will be retained and used for ventilation, escape ways and mine dewatering. The large-diameter production and service shafts will be used for ventilation and to supply air for the retorting process. Detailed descriptions of mine development plans are in- cluded in Section III of the Modification to the DDP. 2. Description of In Situ Retorting Retorts are created by mining out only enough shale to provide a void fraction for rubbling the remaining shale by blasting and to provide permeability for gas flow during operation. These in situ retorts consist of groups or "clusters" of eight 200ft x 200-ft x 310-ft- high rubble columns or chimneys. Undisturbed pillars function as control partitions between operating retorts. The processing of a cluster of retorts consists of several steps. First, a retort within a cluster is kindled from the top by ex- ternally fueled burners. When the temperature at the top of the retort is sufficient to sustain reaction, the burners are shut off and a regulated mixture of air and steam is drawn into and through the retort by exhaust blowers on the surface. Residual organic material is combusted with the air in the feed gas. The hot combustion gases flow down through the retort and supply heat to the raw unretorted shale below. As the shale is heated, the organic material or kerogen decomposes into oil vapor and other gases that are carried along with the combustion gases while some residual organic material remains in the rubble. Steam in the feed gas acts as a diluent to the oxygen in the air to control the reaction temperature and reacts with the residual organic material, forming carbon monoxide and hydrogen to improve the heating value of the product gas. Some of the mineral carbonates in the shale are also decomposed to carbon dioxide gas and mineral oxides. At the same time, the oil and some of the water vapor are condensed. Product liquids and gas leave the bottom of the retort and move to the surface for further processing as a product oil, produced fuel gas, and water. As retorting progresses, the combustion and retorting zones move slowly down through the in situ retort. Between 7 and 8 months are required to process a cluster. When retorting is complete, the air and steam feed are stopped and the in situ retort is closed off. The spent shale remains underground with no need for surface disposal. Surface process facilities consist only of oil/water separa- tion equipment, exhaust blowers, a sulfur removal unit for treatment of product gas, and boilers to produce process steam from fuel values in the product gas. -14-