## 3 Results and Discussion
### LAES-Powered Tri-Generation System  
This publication focusses on assessing the capability of a LAES plant to supply additionally cold air and steam for frozen French fries' production lines, as described in Sections 2.3 and 3.1, by employing tri-generation. For the purposes of comparison, the baseline LAES plant configuration described in Section 2.2 is taken as a reference (Figure 2). The analysis and design of the proposed hybrid tri-generation LAES system is performed by building on the strength of the already optimized baseline configuration (Section 2.2). The cold air demand of the French fry production line appears to be the critical parameter, which is most difficult to meet and thus characterizes the tri-generation plant capacity and size required. The discharge subsystem is redesigned and simulated in detail in a tailored manner by means of THERMOFLEX(r) [27]. The LAES plant's performance characteristics are thus identified and adjusted to match the targeted production process parameters (specified in Tables 1 and 2). The reference LAES plant--i.e., scenario A--operates in charging mode when electricity is abundant and inexpensive (e.g., in periods of oversupply from intermittent RES). It is assumed that the LAES plant charges during a low-demand period of 9 h. The stored energy is supplied back to the grid over a 9 h peak-demand period during the day. Under nominal conditions, the reference LAES plant provides a power output of 5823 kW and an overall power storage capacity of 52,407 kWh. The power input is 12,319 kW, or 110,871 kWh per charge cycle. The compression process involves two intercooled stages. Heat released is stored in sensible form using diathermic oil, acting as both a heat transfer fluid and a thermal storage medium. The oil in the hot storage tank is maintained at 374.2 \({}^{\circ}\)C, while in the lower-temperature thermal storage tank, it is maintained at an ambient temperature of about 20 \({}^{\circ}\)C. The heat input in hot storage is 11,800 kW or 106,200 kWh for every charge cycle. During the discharge stage, the expansion is accomplished through three stages of air turbines with parallel intermediate superheating, using thermal oil from the hot storage tank with a temperature of 373.8 \({}^{\circ}\)C. The residual heat is rejected to the environment through a heat exchanger, where the thermal oil temperature is reduced from 185.4 \({}^{\circ}\)C to 20 \({}^{\circ}\)C. As a result, 41,220 kWh of heat are wasted. The LAES plant with tri-generation capability--i.e., scenario B--is presented in Figure 4. As in scenario A, the plant charges during a low-demand period of 9 h. Power is returned back to the grid over a 9 h peak-demand period during the day, along with cold air and steam supplied to the food factory. The anticipated food factory has two production lines, each having cooling and heating demands as specified in Table 2. Such operation of the LAES plant provides all the energy needed by the food factory if it works in one shift. If the factory operates in two shifts, the energy needs of the second shift should be met by the conventionally installed facilities, such as a vapour-compression refrigeration plant and a fossil-fuel-fired boiler. While the charge section of the LAES plant in scenario B has the same configuration as in scenario A, the discharge section layout is rather different. As specified in Table 2, the processes of freezing and frozen storage of French fries require cold air at low temperatures, which is produced by means of a single-stage air turbine. As shown in Figures 5 and 6, prior to its expansion in the turbine, the airflow rate from the evaporator, amounting to 12.11 kg/s, is superheated with thermal oil at a temperature of 315.2 \({}^{\circ}\)C to ensure a turbine outlet temperature of \(-\)40 \({}^{\circ}\)C. The heat input in the superheater is approximately 4100 kW. As a result, the thermal oil temperature is reduced from 373.8 \({}^{\circ}\)C to 259.5 \({}^{\circ}\)C. The turbine drives an electric generator with a power output of 4255 kW.