When during diffusion. Frequent maintenance of the slicer

When the sugar beets are delivered and stored, only 94 w/w% of the delivery is sugar beets, the other 6% is made up of impurities that are removed during pre-treatment. Pre-treatment is also in place to clean and cut the sugar beets. Sugar beets are stored openly, but this is unfavourable for a long period of time as temperature can drop to zero degrees on the west coast of Iceland so the beets are processed as quickly as possible to be stored as juice. Sugar beets are fed from storage into a drum stone separator to remove stones. We chose a drum stone-separator over a belt stone-separator due to it being more efficient, as it can remover up to 99% of stone and sand.The beets go through a rake trash separator to remove trash such as sugar beet leaves and weeds. The waste products from these separators go through further separation through a water flume treatment so they can be sold as soil products. The sugar beets are cleaned by a drum beet washer, and then fed through a drum beet slicer to cut the beets into cossets. We chose to select a drum slicer over a disk slicer, as the disk slicer can cut irregular shapes and the quality of beets can be varied depending on the pressure. The beets are cut into cossettes, V-shaped strips, to increase the sugar beets surface area which increases the sugar extraction during diffusion. Frequent maintenance of the slicer is necessary as the knives can be easily blunted. We chose slicing the beets into cossettes over mashing them because, even though this would give a larger surface area, the viscosity would be too high which would result in flow issues through the diffuser.Through the diffuser, the cossettes are preheated to denature the cells, allowing sucrose to be extracted. To denature the cells, the diffuser has to be at optimum temperature with maximum contact of the cossettes. This process can be carried out by tower diffusers and slope diffusers when dealing with sugar beet cossettes. The slope diffuser requires less steam for heating compared to the tower diffuser. However, we have chosen the tower diffuser for our process as we are able to recover and reuse the steam that is required to heat the water so overall we will use less steam. The tower diffuser works with continuous counter current diffusion, where the counter current flow of water is heated at 70 degrees. Any temperature above 80 degrees results in degradation of the cossettes. Diffusion juice and pulp are products of the diffusion. The diffusion juice is fed on to be purified while the pulp is prepared to be sold. The pulp is pressed first to remove water, then dried further to recover water, which can be recycled to the diffuser. The pulp being pressed first saves energy, as less is used to dry the pulp. The pulp is then pelleted to increase the density, making it easier to store and transport once sold as a by-product. Diffusion juice is purified to increase the sugar yield and remove any impurities before being fermented. Different methods sugar industries use to purify include liming and carbonation, membrane filtration and ion exchange purification. Liming and carbonation are two stages to complete the purification. During liming, impurities react with milk of lime. The impurities are then precipitated out during the carbonation stage, when carbonated gas is added. Membrane filtration involves separating the impurities using membranes of different molecular weight than the juice, this however would result in a loss of sugar so the purity of the juice would be decreased. Ion exchange purification works by exchanging non-sugars, the impurities, with less harmful ones resulting in a high cost. The most efficient way of removing the impurities is using lime and carbonation gas. Liming and carbonation is the desired purification process and milk of lime and carbonated gas are able to be produced on site. Firstly, quicklime and carbonation gas is produced by calcining. The carbonation gas is collected at the top of lime kiln and quicklime out of the bottom. The quicklime is then mixed with water to produce milk of lime. There are two types of preliming, hot and cold. We have selected cold preliming at 40 degrees as it is more efficient than hot preliming at 80 degrees, because when temperature decreases, the solubility of CaO of the juice increases allowing the lime to be dissolved in the mixture and the following reaction to occur; Ca(OH)2 + C12H22O11 ? Ca(C12H22O11) + 2H2OMore lime is added during main liming to further react with non-sugars. Limed juice from liming is heated to 90 degrees and is fed to the first carbonation tank where it reacts with carbon dioxide to release sucrose. The second carbonation tank heats the juice to 92 degrees, allowing for the hardness to be further decreased as well as prohibiting the formation of calcium bicarbonate. Thin juice is produced during juice purification which can be evaporated to decrease the water content, getting a thick syrup-like juice. This is done so we are able to store sucrose to use for fermentation during periods of no sugar beet harvest, allowing production to run continuously. Evaporation is done through a forward feed multiple effect evaporation system as a single effect evaporation is not efficient. The number of effects used are typically between 2 and 7 for sugar industries. The number effects chosen is 3 due to considering capital costs and operating costs.Fermentation breaks down glucose into carbon dioxide and ethanol using yeast selected, achieving the desired yield of ethanol. From continuous fermentation the product is passed through a centrifuge to remove the yeast, which is then recycled through the continuous fermenter. The ethanol is fed through a distillation column, which removes the non-volatile components, increasing the purity of ethanol. The ethanol-water mixture is an azeotrope mixture so the type of distillation we are going to use is *. We have chosen to have two distillation columns. Water will be fed out the bottom of the distillation column, and ethanol out of the top. There is a limit to the separation achievable during distillation because of the boiling points of ethanol and water so the remaining ethanol is further dehydrated through adsorption. This dehydration can be done through a molecular sieve system since there is a size difference of water and ethanol molecules. The ethanol is then denatured using methanol to achieve a mixture which is a fuel rather than a beverage to avoid certain taxes. It is denatured using a mixing vessel, which will then be fed to a storage tank where it will be held until it is sold and transported.