275293 Optimal Design of Integrated Electric-Power and Algal Biofuel Generation Systems
Optimal Design of Integrated Electric-Power and Algal Biofuel Generation Systems
César G. Gutiérrez-Arriaga,1 Medardo Serna-González,1 José M. Ponce-Ortega,1and Mahmoud M. El-Halwagi2,3
1Chemical Engineering Department, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacán, 58060, México.
2Chemical Engineering Department, Texas A&M University, College Station Texas, 77843, USA.
3 Adjunct Faculty at the Chemical and Materials Engineering Department, King Abdulaziz University, Jeddah, Saudi Arabia
With increasing concerns over global climate change resulting from increased concentration of greenhouse gases in the atmosphere, large reductions in CO2 emissions, while satisfying the worldwide increase of energy demands, will be needed to address this challenging issue. In this regard, fossil-fuel fired power plants play a significant role since they generate about 65% of the electricity used in the world and 35.8% of all of current anthropogenic emissions. To avoid the worst global warming scenarios, CO2 emissions from the electricity sector must be reduce by 50-80% below today's levels by 2050. Achieving this reduction involves many technical alternatives such as carbon capture, fuel switching, CO2 storage, and process integration. The CO2 biofixation by microalgal photosynthesis using flue gases from fossil-fuel fired power plants is also a suitable technology to reduce the CO2 emissions from the electricity sector, since it is a natural and environmentally friendly alternative. In addition, capture and utilization of CO2 from power plants by microalgae followed by algal biofuel production seems to be a good technology option to achieve sustainable integrated systems composed by a fossil-fuel fired power plant and an algae-based biorefinery.
Therefore, this work presents a multi-objective optimization methodology to determine simultaneously the optimal design of steam power plants, considering simultaneously economic and environmental criteria, together with microalgae CO2 sequestering from the combustion gases of different fossil fuels (coal, oil and natural gas) and biofuels (biogas, biomass, softwood and hardwood) selected in the boiler and the subsequent microalgae biomass conversion to biofuels (bioethanol and biodiesel). As can be seen in Figure 1, all or part of the algal biofuel produced can be used as fuel in the boiler. This system allows the sustainable reduction of the huge CO2 emissions from the fossil-fuel fired power plants.
Figure 1. Integrated scheme for the microalgal CO2 capture in power plants.
The proposed methodology is based on a search procedure through genetic algorithms due to the large number of non-convex terms present in the model and to avoid get trapped prematurely in local solutions. The methodology considers the optimal selection of the type of fuel to be used because this affects drastically and simultaneously the economic and environmental objective functions. The economic objective function considers the maximization of the total net profit accounting for the sales profit and the fuel costs, as well as the capital costs for the turbine, boiler, condenser, pumps, feed-water heaters and deaerator, as well as the costs to operate such equipment (fuel, electricity, cooling water, etc.), while the environmental objective function is based on the eco-indicator-99 constituted by harmful materials for the health and the ecosystem to measure the global environmental impact of these systems, following the life cycle analysis approach. An approach to determine a set of optimal solutions that simultaneously compensate both objectives is proposed. The problem can be easily solved using the proposed methodology in a relatively small computation time. The application of the proposed methodology for a case study in Mexico indicates that combination of fossil fuels (coal, oil and natural gas) and biofuels (biogas, biomass, softwood and hardwood) is required to compensate the economic and environmental objectives, in addition to the economic and environmental benefits obtained from the algal biofuel produced by the integrated system.
See more of this Group/Topical: Process Development Division