drying of grass, UPR, ecoinvent 3.6, Allocation, APOS
Reference product: drying of grass [l]
Location: CH - Switzerland
This dataset represents the drying process of grass. The functional unit is kg water evaporated. This module should be used when evaluating production of grass pellets.
[The full documentation of this dataset was originally provided in the corresponding ecoinvent report from the Swiss Centre for Life Cycle Inventories, which is accessible for free to guests and users of ecoinvent version 2 (https://www.ecoinvent.org/login-databases.html). The dataset may subsequently have been subjected to central changes to the database, as described in the respective change report for each new release.]
[This dataset has been generated using the system model “Allocation at the point of substitution" (APOS). A system model describes how activity datasets are linked to form product systems. The APOS model subdivides multi-output activities by physical properties, economic, mass or other properties allocation. By-products of treatment processes are considered to be part of the waste-producing system and are allocated together. Markets in this model include all activities in proportion to their current production volume.
Version 3 of the ecoinvent database offers three system models to choose from. For more information, please visit: https://www.ecoinvent.org/database/system-models-in-ecoinvent-3/system-models-in-ecoinvent-3.html)]
The inventoried process for grass- and maize drying consists in the drying process itself, dosage, chopping the wet stuff, ventilation, milling, pressing of pellets, cooling, and the weighing and packing of the finished dry product (Scheidegger 2002). Drying time depends on the initial water content (a function of grain ripeness, grain moisture, air humidity and temperature). The inventories are based on common grass and maize drying plants. Most of the 70 centralized grass- and maize-drying plants in Switzerland use rotary dryers (Christen 2002). The technology of rotary dryers is described in Stela (2002) as follows: The drying drum is supplied with the wet product by means of a suitable feed device. Transporting scoops on the feed side of the drum take up the product and carry it to the drum internals. The choice of drum internals is determined by the characteristics of the product. Drying is usually in concurrent flow with the wet product coming into contact with the hot drying gas, the temperature of which possesses a wide adjustment range, allowing the most suitable drying temperature to be set for each product. The residence time of the product in the dryer depends on drum speed, drum declination, the rate of flow of the drying gas and the damming device at the end of the drum.
As is commonly known, drying is a far quicker process when the drying air is heated. The drying plants are thus equipped with air heaters that raise the air temperature to different levels, depending on the product to be dried. It is important not to overheat any dried product, but bread- and seed grains in particular must not be heated to over 40 °C. This is because the individual grain must preserve its chemical and physical properties, especially its germination capacity and suitability for baking for subsequent use as seed and in food production. Cereals used as feedstuffs are more tolerant of high temperatures, so the grains may be dried in the drying plants at an air temperature 5 to 10 °C higher warmer than the air temperature permitted for bread grains (80-90 °C). This allows for a more efficient drying process and a lower fuel consumption per kg of water extracted.
Most grass- and maize-drying plants are equipped with direct air heating type of furnace (Christen 2002).The direct air heater consists of an outer casing, an inner sheath against radiation loss and a perforated combustion chamber of highly heat-resistant steel, placed centrally in the casing. The hot exhaust gases are mixed with the fresh air heated at the side of the combustion chamber, and warm air of a homogeneous temperature is generated. The combustion energy is consequently led directly into the dryer. This method is used primarily for drying feedstuffs and industrial raw materials (Stela 2002). Typical air heaters used in Swiss drying plants have a nominal power of 4 to 5 MW.
Scheidegger, F. Landi Landshut, Bätterkinden, Switzerland, November 2002 (personal communication).
Christen, J. (VSTB). Alberswil, Switzerland, July 2002 (personal communication).
Stela (2002) Tailor-made solutions. Website of Stela Laxhuber KG, Massing, Germany. Retrieved on April 2002 from http://www.stela.de/englisch/index.htm.