SNG Generation via Power to Gas Technology: Plant Design and Annual Performance Assessment

Abstract

Power to gas (PtG) is an emerging technology that allows to overcome the issues due to the increasingly widespread use of intermittent renewable energy sources (IRES). Via water electrolysis, power surplus on the electric grid is converted into hydrogen or into synthetic natural gas (SNG) that can be directly injected in the natural gas network for long-term energy storage. The core units of the Power to synthetic natural gas (PtSNG) plant are the electrolyzer and the methanation reactors where the renewable electrolytic hydrogen is converted to synthetic natural gas by adding carbon dioxide. A technical issue of the PtSNG plant is the different dynamics of the electrolysis unit and the methanation unit. The use of a hydrogen storage system can help to decouple these two subsystems and to manage the methanation unit for assuring long operation time and reducing the number of shutdowns. The purpose of this paper is to evaluate the energy storage potential and the technical feasibility of the PtSNG concept to store intermittent renewable sources. Therefore, different plant sizes (1, 3, and 6 MW) have been defined and investigated by varying the ratio between the renewable electric energy sent to the plant and the total electric energy generated by the renewable energy source (RES) facility based on a 12 MW wind farm. The analysis has been carried out by developing a thermochemical and electrochemical model and a dynamic model. The first allows to predict the plant performance in steady state. The second allows to forecast the annual performance and the operation time of the plant by implementing the control strategy of the storage unit. The annual overall efficiencies are in the range of 42–44% low heating value (LHV basis). The plant load factor, i.e., the ratio between the annual chemical energy of the produced SNG and the plant capacity, results equal to 60.0%, 46.5%, and 35.4% for 1, 3, and 6 MW PtSNG sizes, respectively.

Impact of hydrogen injection on thermophysical properties and measurement reliability in natural gas networks

“…where: i) B is the second virial coefficient; ii) 𝜌𝜌 𝑚𝑚 is the molar density; iii) 𝜌𝜌 𝑟𝑟 is the reduced density; iv) 𝑏𝑏 𝑛𝑛 , 𝑐𝑐 𝑛𝑛 , 𝑘𝑘 𝑛𝑛 are constants; v) 𝐶𝐶 𝑛𝑛 * are the coefficient which depend on the temperature and NG mixture composition. The reduced density 𝜌𝜌 𝑟𝑟 is correlated to the molar density 𝜌𝜌 𝑚𝑚 through the below relation: 3 𝜌𝜌 𝑚𝑚 (15) where: i) K is a mixture size coefficient; ii) 𝜌𝜌 𝑚𝑚 is the molar density calculated using the following equation:…”

“…Currently, Power to Gas (PtG) represents the most suitable technology for storing excess electricity produced by non-programmable RES providing flexibility to the electrical system [2]. Exploiting the natural gas (NG) transmission and distribution networks, as well as the storage features of the existing NG infrastructure, the hydrogen produced from surplus renewable energy can be injected into the NG pipeline system allowing to store large amounts of energy on large-scale and for long-term period [3]. This will allow to decarbonize end-use sectors (e.g., buildings, transport, industry), since it is a zero-emission energy carrier, in addition to offer balancing and regulation services to the power grid.…”

Heat Recovery from a PtSNG Plant Coupled with Wind Energy

“…In a previous work [19], the authors evaluated the energy storage potential and the technical feasibility of the PtSNG concept to store intermittent renewable sources. For this aim, different plant sizes (i.e., 1 MW, 3 MW and 6 MW) were defined and investigated.…”

“…Owing to the fluctuating behaviour of the input energy source, the operation of the PtSNG plant sub-systems (i.e., electrolysis and methanation units) is characterised by frequent shutdowns, and consequently by frequent changeovers of state (i.e., cold-standby, hot-standby and production with different loads) [10,19,20]. On the basis of the plant management strategy, the energy consumption required to restart the SNG production from the cold-standby state, as well as the energy consumption necessary for keeping the sub-systems in a hot-standby state, could significantly increase the energy input required and therefore negatively affect the annual performance of PtSNG plants.…”

Power to Gas Plant Design, Modelling and Control for Precise and Flexible Methane Production

“…In [4], although a detailed modelling of some P2G processes (electrolysis, methanation) is done, source of CO2 is not considered. To obtain CO2, P2G is modelled together with Gas-fired Power Plant in [5].…”