PEAT

organic fuel consisting of a light, spongy material formed in temperate humid environments by the accumulation and partial decomposition of vegetable remains under conditions of deficient drainage. Vast beds occur in Europe, North America, and northern Asia but are worked only where coal is deficient. Dried peat burns readily with a smoky flame and a characteristic odour. The ash is powdery and light, except in certain varieties that have a high content of sand and other inorganic matter. Peat is used for domestic heating purposes and forms a fuel suitable for boiler firing in either briquetted or pulverized form; it also has been used in gas producers. In Ireland millions of tons of peat are consumed annually; Russia, Sweden, Germany, and Denmark also produce and use considerable quantities, and peat is used locally in England and Scotland. Peat is usually hand cut, although progress has been made in the excavation and spreading of peat by mechanical methods. Peat is cut by spade in the form of blocks, which are spread out to dry (peat in its natural state contains 90 to 95 percent water); when dry, these blocks weigh from three-quarters of a pound to two pounds each. In one method of mechanized winning, a dredger or excavator digs the peat from the drained bog and delivers it to a macerator, which extrudes the peat pulp through a rectangular opening; the pulp is then cut into blocks, which are spread to dry. Maceration promotes drying and tends to yield more uniform shrinkage and a denser and tougher fuel. Hydraulic excavating can also be used, particularly in bogs that contain roots and tree trunks. The peat is washed down by a high-pressure water jet, and the pulp runs to a sump. There, after slight maceration, it is pumped to a draining ground in a layer about 230 mm (9 inches) thick, which after partial drying is cut up and then dried further. Peat deposition is the first step in the formation of coal. The humid climate of the Carboniferous Period (360 to 286 million years ago), which favoured the growth of huge tropical seed ferns and giant nonflowering trees, created the vast swamp areas that constitute the coal beds of today. As the plants died and fell into the boggy waters, which excluded oxygen and killed bacteria, they partially decomposed but did not rot away. The vegetation was changed into peat, some of which was brown and spongy, some black and compact, depending on the degree of decomposition. The sea advanced and withdrew over such deposits, and new sediments were laid down. Under pressure the peat dried and hardened to become low-grade coal, or lignite; further pressure and time created bituminous coal; and even more extreme pressures created anthracite.