(737h) Superstructure Approach for the Design of Renewable-Based Utility Plants and Cost Estimation of Renewable-Based Steam

Utility plants are part of the chemical industry that provide steam and power for the operation of the processes. Work on the design and optimization of fossil-based utility plants is widely known (Papoulias and Grossmann 1983; Varbanov et al. 2004; Sun and Smith, 2015); the trend towards a sustainable production system has led to the need for the renewable production of both steam and power. Renewable power production has lately been addressed from different resources including wind and solar. However, steam production from renewable resources has only been addressed to generate low temperature utilities (Lauterbath et al, 2012, Di Lucia and Ericsson, 2012).

This work evaluates the use of renewable resources as feedstock to design renewable-based utility plants. The utility plant couples different technologies to process each renewable resource within a steam and power network. A superstructure was developed in order to select the best technology to process biomass, waste, solar radiation, and wind. Biomass can be sent to a biomass boiler or it can be sent to a gasifier reactor where syngas is obtained. Then, the produced syngas can be sent to a syngas boiler or to a waste heat recovery system consisting of a syngas turbine and a heat recovery steam generator (HRSG). Additionally, biogas can be used as fuel to produce steam, for which cattle manure (CM) and municipal solid waste (MSW) are considered as feedstocks. Once produced and purified, the biogas can be sent to a biogas boiler or to a heat waste recovery system. Solar radiation, another source considered in this work, is transformed into steam by using a concentrating solar power (CSP) plant. Once produced, the renewable-based steam is sent to a steam network that includes steam headers, a steam turbine, and a cooling system. The steam network comprises the alternative pathways to produce steam. Finally, the installation of wind turbines is considered. In this way, the production of electricity can become independent of steam generation. The problem yielded a superstructure that was formulated as an MINLP model, which was coded and solved using GAMS. The objective was to find the optimal structure of a renewable-based utility plant that minimizes the annualized cost while satisfying the steam and electricity requirements.

Two study cases were developed. In the first one, located in the south-west of Mexico, the utility plant is used to provide electricity to a city, while supplying steam to a bioethanol plant. In the second case, located in Scotland, the utility plant is used to meet the electricity and heating demands of the households. Moreover, the proposed approach also allowed the development of correlations that can be used to estimate the production cost of renewable-based steam for the different raw materials and facility scales. Finally, a sensitivity study of the impact of different factors on the cost of the renewable-based steam was carried out. Four factors are considered, namely, fluctuations in renewable resources prices, solar radiation, economies of scale, and the assignment of a power credit. Results show that availability plays an important role in technology selection. As solar radiation increases, it becomes a competitive resource against biomass to produce steam, while wind energy becomes competitive against biomass to produce electricity when wind velocity is high and the cost of the wind turbine is low. It is also shown the level at which the renewable-based utility plant provides a significant reduction in CO₂ emissions with respect to the use of fossil fuel.

Lauterbach, C., Schmitt, B., Jordan, U., & Vajen, K. (2012). The potential of solar heat for industrial processes in Germany. Renewable and Sustainable Energy Reviews, 16(7), 5121-5130.

Di Lucia, L., & Ericsson, K. (2014). Low-carbon district heating in Sweden–Examining a successful energy transition. Energy Research & Social Science, 4, 10-20.

Papoulias, S. A., & Grossmann, I. E. (1983). A structural optimization approach in process synthesis—I: Utility systems. Computers & Chemical Engineering, 7(6), 695-706.

Varbanov, P. S., Doyle, S., & Smith, R. (2004). Modelling and optimization of utility systems. Chemical Engineering Research and Design, 82(5), 561-578.

Sun, L., & Smith, R. (2015). Performance modeling of new and existing steam turbines. Industrial & Engineering Chemistry Research, 54(6), 1908-1915.