|Infobox on Peat|
|Example of Peat|
|Stowage factor (in m3/t)||5,7 m3/t (bales of 48 kg.)|
|Humidity / moisture||-|
|Risk factors||See text|
Peat (turf) is an accumulation of partially decayed vegetation. One of the most common components is Sphagnum moss, although many other plants can contribute. Soils that contain mostly peat are known as a histosol. Peat forms in wetland conditions, where flooding obstructs flows of oxygen from the atmosphere, slowing rates of decomposition.
Mires, particularly bogs, are the most important source of peat, but other less common wetland types also deposit peat, including fens, pocosins, and peat swamp forests. Other words for lands dominated by peat include moors, or muskegs. Landscapes covered in peat also have specific kinds of plants, particularly Sphagnum moss, Ericaceous shrubs, and sedges (see bog for more information on this aspect of peat). Since organic matter accumulates over thousands of years, peat deposits also provide records of past vegetation and climates stored in plant remains, particularly pollen. Hence they allow humans to reconstruct past environments and changes in human land use.
Peat is harvested as an important source of fuel in certain parts of the world. By volume, there are about 4 trillion m3 of peat in the world covering a total of around 2% of global land area (about 3 million km²), containing about 8 billion terajoules of energy. Over time, the formation of peat is often the first step in the geological formation of other fossil fuels such as coal, particularly low grade coal such as lignite.
Depending on the agency, peat is not generally regarded as a renewable source of energy, due to its extraction rate in industrialized countries far exceeding its slow regrowth rate of 1mm per year, and as it is also reported that peat regrowth takes place only in 30-40% of peatlands. Because of this, the UNFCCC, and another organization affiliated with the United Nations classified peat as a fossil fuel. However, the Intergovernmental Panel on Climate Change (IPCC) has begun to classify peat as a "slow-renewable" fuel. This is also the classification used by many in the peat industry.
At 106 g CO2/MJ, the carbon dioxide emission intensity of peat is higher than that of coal (at 94.6 g CO2/MJ) and natural gas (at 56.1) (IPCC). Under the appropriate circumstances, peat could be considered an early component in the formation of coal.
Peat has a high carbon content and can burn under low moisture conditions. Once ignited by the presence of a heat source (e.g., a wildfire penetrating the subsurface), it smoulders. These smouldering fires can burn undetected for very long periods of time (months, years, and even centuries) propagating in a creeping fashion through the underground peat layer. Peat fires are emerging as a global threat with significant economic, social, and ecological impacts. Recent burning of peat bogs in Indonesia, with their large and deep growths containing more than 50 billion tons of carbon, has contributed to increases in world carbon dioxide levels.
Peat occurs in surface layers of 3-10 ft thick and has a water content of 85%. Before peat can be used for chemical or fuel purposes it must be field-dried to a water content of 30-40%. Since the dried product is susceptible to autoignition, storage conditions must be such as to minimize this risk.
Peat is soft and easily compressed. Under pressure, water in the peat is forced out. Upon drying, peat can be used as fuel. It has industrial importance as a fuel in some countries, such as Ireland and Finland, where it is harvested on an industrial scale. In many countries, including Ireland and Scotland, where trees are often scarce, peat is traditionally used for cooking and domestic heating. Stacks of drying peat dug from the bogs can still be seen in some rural areas. Peat's insulating properties make it of use to industry.
Peat is easily converted to hydrocarbons and is an excellent source of natural gas; when dry it can be used directly as a fuel.
Although peat has many uses for humans, it also presents severe problems at times. Wet or dry, it can be a major fire hazard, as peat fires can burn almost indefinitely (or at least until the fuel is exhausted). Peat fires can even burn underground, reigniting after the winter, provided there is a source of oxygen. Peat deposits also pose major difficulties to builders of structures, roads, and railways, as they are highly compressible under even small loads.
Shipment / Storage / Risk factors
The influence of self-heating on horticultural aspects of peat
The process of self-heating in peat and its influence on the characteristics important for horticulture, is not completely understood. In an experiment, a stockpile of young sphagnum peat was brought to self heating.
The experiment was ended when the temperature reached 70°C. Samples from positions with different temperatures were collected and analysed on chemical, physical and biological characteristics.
In the first temperature stage up to approximately 50°C the quality of the peat hardly changed. In the stage from 50° - 70°C, particularly towards the higher end, the peat was seriously affected. Due to increased decomposition at high temperatures, high concentrations of ammonium, phosphorus, calcium and trace elements were found in water extractions from the samples.
Water absorption decreased from wetness ratio 8.0 g.g1 to 6,5 g.g1 but at the same time air content increased. This indicates that in this treatment the peat became more water repellent. In this high temperature treatment the colour of the peat was darker, the peat had a special smell and occasionally became mouldy. A bio-assay with lettuce, garden cress, Impatients and kohlrabi showed growth reduction of the same treatment. The growth reduction was less after a two-year storage period of the self-heated peat.
In a glasshouse experiment Ficus was grown on peat substrates from the temperature stages 20, 40, 50 and 67°C. The growth of plants on peat of the 67°C stage was disturbed by nitrogen deficiency. This was caused by nitrogen absorption in a stage of decomposition under normal temperature conditions. By this decomposition the peat material also showed a high shrinkage.
Self heating has many influences on the quality of peat. In the first stage some heat is produced by micro-organisms. The temperature goes up to about 30°C, after which in the second stage the heating process rapidly rises to 70°C by heat producing thermophilic micro-organisms. In the third stage the temperature goes further up by exothermic chemical oxidations affecting the peat seriously. Micro-organisms do not survive these temperatures. The fourth stage is the spontaneous combustion stage.
The experiment showed that there was more microbial life found in peat substrates when the peat’s temperature rose to 67°C. Self heating originates in an aerobic decomposition, in which especially hemicelluloses are hydrolytically split into different kinds of monosaccharides. Therefore due to the self-heating process the material itself can be used as a medium for microbial life. In the Ficus experiment this was probably the reason why the plants in the peat substance made of self-heated peat of 67°C showed nitrogen deficiency symptoms and growth reduction, for micro-organisms consume nitrogen. Also the volume decrease of the peat substrate of 67°C in the Ficus experiment may be attributed to this phenomenon, because the peat itself has become a matrix for micro organisms.
Due to the decomposition of the peat by self-heating, chemical changes were found. The chemical changes of the extract of peat directly after the self-heating process were extreme. From 50°C upwards the EC and the concentrations of ammonium, phosphorus, calcium and micro-elements (especially iron and boron) became higher. By storing the material the concentrations decreased but were still recognizable for the micro-elements.
Results of the experiment suggest that requirements can be set for the maximum temperature that is allowed in the self-heating process of peat, when used as horticultural substrate. Peat which has been above 50°C is affected seriously by the self-heating process. Therefore the temperature should never reach 50°C when peat is used for horticultural purposes.
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