Design and Optimization of Molasses Treatment Plant to Reduce Scale Formation in Ethanol Production (The Case of Metahara Sugar Factory Ethanol Plant)
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Date
2012-10
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Addis Ababa University
Abstract
Fouling in industrial heat exchangers leads to economic penalties. To overcome this problem, either
cleaning of heat exchangers or reduction of the scaling is the two possible solutions. But, cleaning of heat
transferring unit is an expensive exercise. Therefore, this study has been conducted with the objective to
design and optimize molasses treatment plant to reduce scale formation in ethanol production.
The study has been conducted in such a way that, first scale samples collected from Metahara sugar
factory ethanol plant distillation column and characterized physically and it is hard scale with an
average thickness of 2.04cm and gray in color which shows that it is the result of crystallization. In
addition to this, it has been characterized chemically to determine its composition and the scale is
63.87% composed of CaO. Then, to assess cause of this scaling, process water and the raw molasses has
been characterized for their composition and pH which shows that process water is within a normal
hardness and pH range. But, the molasses of Metahara sugar factory is with an average of 2.41% CaO
which is abnormally high when compared to world average of 1.5% CaO % molasses. Therefore, the
main cause of heat transferring units scaling in the plant is the CaO content of the molasses. To overcome
this problem, treating the molasses with H2SO4 and heat is the best technology. Because, the reaction of
CaO with H2SO4 at higher temperature give CaSO4 which is insoluble in water and easily separated by
sedimentation. Experiments have been conducted with varying influential molasses clarification
conditions and 100OC temperature, 4 pH, 50o brix and 2hours retention time have been determined as the
optimum clarification process conditions. At these optimum conditions 54.43% of the CaO in the
molasses has been removed. At these process conditions, 1.08CaO% molasses has been obtained which is
too low when compared with world average of 1.5CaO% molasses.
Depending on the optimum conditions determined experimentally and the existing condition of the plant,
molasses treatment plant process flow sheet has been proposed and the equipments for clarification plant
have been designed in which case most of the equipments can be easily fabricated locally.
Finally, the plant is financially evaluated and its initial investment cost will be recovered fully within only
eight operation months which makes the plant viable.
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Process Engineering Stream