THE PELLETIZATION OF COMPOST FOR ENERGY UTILIZATION
If produced compost does not meet the legal requirements for application to agricultural land, it is not suitable for application in soil, and can therefore be tested as an alternative fuel when co-fired with fossil fuels.
Low-quality compost that cannot be applied to soils or for which there is no demand can be energy utilized for co-incineration with fuels of high calorific value. The pelletization of compost represents a type of processing that makes the handling of the material easier and enables more accurate dosing.
WHAT IS COMPOST?
Compost can be defined as decomposed organic matter. It can be produced from a wide variety of organic feedstocks. Many composts are produced from municipal (garden) wastes. The composting process can involve reducing the particle size of the biomass and then placing it in mounds where the composting is allowed to take place over an extended period of time. Fully composted material can, in some cases, be suitable for addition to soil. The heating value of compost will depend on the organic material that has been used to produce it and the time and extent of the composting process. Composts can have lesser heating values due to their high ash and moisture contents.
MATERIALS AND METHODS
Energy properties of the compost are studied. Raw materials for the production of composts consists mainly of wastes from city greenery maintenance, sludge from waste water treatment plants and wood chips. In order for the compost to be able to be utilized for energy, it needs to be dried to a value suitable for treatment and pelletization. After drying, the compost is crushed and the pellet mixture is moistened to a suitable value and then pelletized. A problematic parameter for compost pelletization is the moisture of the pelletized mixture. An oxygen bomb calorimeter is used to measure the calorific value of the compost to determine its energy value. Composts for energy utilization should be prepared in a sheltered area to prevent over-watering due to precipitation. Due to the lower average calorific value, composts should be used in a mixture with a higher calorific value. This can be achieved by pelletization of a mixture of compost and a higher calorific fuel or pelletization of only composts and then mixing then with a higher calorific fuel like coal, or wood chippings.
WHY USE COMPOST FOR ALTERNATIVE FUEL?
Composting represents an increasingly popular method of processing biodegradable wastes. Compost should preferably be applied to soil in order to increase its quality. During composting, composts that do not meet the legal parameters for their use in agriculture and re-cultivation (content of harmful substances, insufficient quality) are also produced or there is insufficient demand for the produced composts. If these composts meet the legal requirements, they may be used for energy utilization.
Energy utilization of composts is not intended for small incinerators (household boilers). One possible method of energy utilization of compost is the use in the form of pellets. Pelletization consists of adjustment of the material to a more compact form. The advantage of pelletization is easier to handle, lowers costs for transport and more precise dosing to combustion device.
Composts that do not meet the legal requirements for application to soil or for which there is insufficient demand can be used for energy utilization. Pelletization represents one possible form of utilization. In order to dry compost to the required value, waste heat can be used to reduce energy inputs necessary for compost pelletization. This problem can also be solved by composting biomass in a sheltered composting plant to prevent increase of moisture due to atmospheric precipitation. Due to the lower melting point of ash, it is suitable for co-combust pellets with coal. That is why the combustion of composts in small boilers is not recommended. Co-combustion is also suitable for increasing the calorific value of the fuel.
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