(639a) Optimal Integration of a Self Sustained Algae Based Facility with Solar and/or Wind Energy

Biodiesel is typically produced using methanol in the transesterification of the oil. While the use of methanol has been justified from the technical and economic points of view, quicker reaction times and cheaper than any other alcohol, it is mainly produced from coal or natural gas. Therefore, the second most important raw material in the production of biodiesel is currently a fossil based chemical. Ethanol can be produced from algae and can be competitively used instead for the production of biodiesel, namely fatty acid ethyl ester (FAEE), Martín & Grossmann (2013a). Alternatively, methanol can be produced from renewable sources including biodiesel main byproduct, glycerol, Martín & Grossmann (2013b). However, only two thirds of the demand of methanol could be covered in this way and the production cost was also higher.     

 In this work, we consider the design of an integrated facility that uses CO₂ as carbon source and solar and / or wind energy to produce methanol and algae based biodiesel. On the one hand, solar energy is used to grow algae and to produce power, solar photovoltaics (PV), for water splitting producing hydrogen and oxygen (Levene et al., 2005). Wind  turbines can also be used for power production. Lately, it has been proved that CO₂ can be hydrogenated to produce methanol (Van-Dal, Bouallou 2013; Trudewind et al 2014a&b), which represents a promising use for the captured CO₂. By producing methanol in this way, it is not only renewable, but it represents a way to store energy from intermittent sources. On the other hand, the oil is produced by growing microalgae from where lipids are extracted. The transesterification step is similar to current biodiesel production (Martín & Grossmann, 2012). The optimal flowsheet is synthesized with a multiperiod MINLP model whose solution provides the optimal source of energy and the operating conditions over a year for an average production of 60 Mgal/yr of FAME. Simultaneous optimization and heat integration is implemented within the formulation to address the tradeoff related to the operation of the reactors, governed by chemical equilibria, and the preparation and separation stages. Next, a heat exchanger network is designed and finally, a water network is synthesized.

 The proposed design uses only solar energy. The advantage is that the methanol and oil production rates are the same. The drawback can be related to the area available for the ponds and the solar panels allocation and the idle equipment along the year due to the variability of solar incidence. The investment costs adds up to 120 M€ for, a production cost of 0.85€/gal (0.28 €/kg). The energy consumption is 3.2 MJ/gal of FAME, capturing  4.05 kg CO₂ per kg of FAME and consuming 1L of water per littre of methanol produced, including the operation of the cooling tower and the boiler.

References

 Levene, J.I., Mann, M.K. , Margolis, R. , Milbrandt, A., 2005. An Analysis of Hydrogen  Production from Renewable Electricity Sources Conference Paper . NREL/CP-560-37612 September 2005

 Martín, M., Grossmann, I.E. (2012) Simultaneous optimization and heat integration for biodiesel production from cooking oil and algae. Ind. Eng. Chem Res. 51 (23) 7998–8014

 Martín, M., Grossmann, I.E., (2013) Optimal engineered algae composition for the integrated simultaneous production of bioethanol and biodiesel AIChE J. 59 (8) 2872–2883

 Martín, M.; Grossmann, I.E. (2013)  ASI: Towards the optimal integrated production of biodiesel with internal recycling of methanol produced from glycerol. Environmental Progress & Sustainable Energy 32(4) 791-801

Levene, J.I., Mann, M.K. , Margolis, R. , Milbrandt, A., 2005. An Analysis of Hydrogen  Production from Renewable Electricity Sources Conference Paper . NREL/CP-560-37612 September 2005

 Trudewind, C.A., Schreiber, A., Haumann, D., 2014. Photocatalytic methanol and methane production using captured CO2 from coal power plants. Part I a Life Cycle Assessment. J. Cleaner Prod. http://dx.doi.org/10.1016/j.jclepro.2014.02.014

Trudewind, C.A., Schreiber, A., Haumann, D., 2014. Photocatalytic methanol and methane production using captured CO2 from coal power plants. Part II – Well-to-Wheel analysis on fuels for passenger transportation services J. Cleaner Prod. http://dx.doi.org/10.1016/j.jclepro.2014.02.024 

Van-Dal., E.S., Bouallou, C., 2013. Design and simulation of a methanol production plant from Co3 hydrogenation. J. Cleaner Prod. 57, 38-45.