Technology review and thermodynamic performance study of a biogas-fed micro humid air turbine M. MosayebNezhad a, * , A.S. Mehr b , A. Lanzini a , D. Misul a , M. Santarelli a, c, d a Department of Energy, Politecnico di Torino, Turin, Italy b Department of Mechanical Engineering, University of Bonab, Bonab, Iran c Energiteknik, KTH, Stockholm, Sweden d Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, United States article info Article history: Received 14 September 2018 Received in revised form 24 January 2019 Accepted 13 March 2019 Available online 15 March 2019 Keywords: Micro humid air turbine CHP Wastewater treatment plant Biogas abstract Biogas is a proven and valuable energy source today for the combined production of heat and electricity (CHP). One of the most reliable and efficient technologies for the CHP application using biogas is rep- resented by microturbine (MT). This prime mover not only shows a very flexible behavior towards change in the fuel composition, but it also sticks out for its reliability, small size, and low weight. Moreover, micro humid air turbine (mHAT) cycle, which is still under development, provides a relatively simple and inexpensive solution to increasing the power output of the microturbines. In this paper, the thermodynamic model of a novel CHP system based on a 500 kW micro humid air turbine (mHAT) in a wastewater treatment plant (WWTP) is presented and discussed. Furthermore, some considerations regarding an appropriate biogas treatment system and heat recovery module are discussed. The results presented in this paper show how the proposed biogas-fed plant can achieve an electrical efficiency of 46.6% together with a CHP efficiency of 81.2%. The impact of integration with WWTPs is beneficial where both biogas and required water for inlet air humidification are available. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction The world’s hunger for energy is only set to grow as the global population rises. The challenge is expanding the ability of renew- able energy sources to cater for that growth in the number of people, especially in urban areas. Besides, climate change regula- tions have increased twenty fold in the past years, culminating in the Paris agreement of 2015. As a result, renewable energy has become the area of focus for mitigating climate change. Many governments have decided to develop aggressive long- term actions aimed at increasing the share of “decentralized clean energy”, with the goal of ensuring decentered renewable energy production as opposed to traditional fossil fuels based sources. In small applications of decentralized power and heat generation systems, which has a growing trend throughout the world, reciprocating engines with a power output of less than few megawatts have dominated the market. In recent years, however, microturbines have become severe competitors for the reciprocating engines given that the utilization of these latter has a significant impact from the economic and environmental perspectives. It is estimated that between 2008 and 2013, microturbines retained almost a 17% market share and that more recently, from 2013 to 2017, the microturbine market shareincreased to a record 25% of installations in between 100 kW and 5 MW in the United States (see Fig. 1). The main challenge for the use of biogas in thermal machines is associated with the low energy density of this fuel. At the early stage microturbines were designed to be fed by gaseous fossil fuels. However, as their technology became mature, modifications were done to operate them with biogas fuel. One method to compensate for the low energy content of biogas is that of increasing the mass flow rate through the MT to achieve the same thermal loads that could be otherwise attained using gaseous fossil fuels. Numerous researches are carried out on biogas fed micro- turbines so as to introduce environmental-friendly cogeneration system for the combined production of mechanical and thermal power. Backman et al. [2] discussed the potential of microturbines for small combined heat and power applications in the scale of less than 100 kWel. These microturbines are based on the principle of * Corresponding author. E-mail address: mohsen.mosayebnezhad@polito.it (M. MosayebNezhad). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene https://doi.org/10.1016/j.renene.2019.03.064 0960-1481/© 2019 Elsevier Ltd. All rights reserved. Renewable Energy 140 (2019) 407e418