Energy recovery systems based on high temperature phase change materials

Energy recovery from the waste heat released by industrial processes represents one of the greatest opportunity to reduce the consumption of primary energy and the related emission of greenhouse gases. Nevertheless, the fluctuating and/or intermittent nature of many energy-intensive processes (e.g. electric arc furnace in steel industry) hinders the deployment of current energy recovery systems. Thus, the development of technologies able to minimize the thermal power fluctuations released by such processes is required to enable the deployment of affordable energy recovery systems. With the aim of developing such type of technology, this thesis explores the potential of latent heat storage systems based on phase change materials (PCMs) to minimize the thermal power fluctuations of high-temperature waste heat sources. In particular, three significant areas of investigation characterised by different types of thermal power fluctuations are investigated: electric arc furnace, billet reheating furnace and waste-to-energy plant. An interdisciplinary approach is adopted to face the crucial issues of developing a PCM-based technology (e.g. thermo-mechanical stresses, transient heat transfer). Chapter 1 includes the background, the motivation, the aim, the methodology and the structure of thesis. In chapter 2, a general overview on the thermal energy storage systems with a particular focus on latent heat storage systems based on PCMs is provided. Chapter 3 addresses the issues related to the energy recovery from the electric arc furnace and proposes three different configurations of a PCM-based device to increase the efficiency and the capacity factor of the downstream energy recovery system. In Chapter 4 an existing waste heat recovery system of a steel billet preheating furnace is retrofitted by adding a PCM-based device. In Chapter 5 a refractory brick technology based on PCMs is proposed for the protection of the radiant superheaters against high temperature corrosion and temperature fluctuations. At the end of each chapter a series of conclusions are reported, concerning the performed investigations and the obtained results

Assessment of LNG cold energy utilization for road vehicles and data-centres cooling using liquid air

This paper assesses a novel use for LNG cold energy utilization which liquefies air to be used in cryo-cogeneration systems adopted in road vehicles and data centres. The study investigates four scenarios which contemplate different combinations and levels of integration between the LNG terminal, the cryo-cogeneration system, the road vehicles (namely Transport Refrigerated Units and Public buses). The comparison amongst the four scenarios was conducted by considering the impact of the proposed solutions on CO2 emissions reduction and running costs savings.Published versio

Association of kidney disease measures with risk of renal function worsening in patients with type 1 diabetes

Background: Albuminuria has been classically considered a marker of kidney damage progression in diabetic patients and it is routinely assessed to monitor kidney function. However, the role of a mild GFR reduction on the development of stage 653 CKD has been less explored in type 1 diabetes mellitus (T1DM) patients. Aim of the present study was to evaluate the prognostic role of kidney disease measures, namely albuminuria and reduced GFR, on the development of stage 653 CKD in a large cohort of patients affected by T1DM. Methods: A total of 4284 patients affected by T1DM followed-up at 76 diabetes centers participating to the Italian Association of Clinical Diabetologists (Associazione Medici Diabetologi, AMD) initiative constitutes the study population. Urinary albumin excretion (ACR) and estimated GFR (eGFR) were retrieved and analyzed. The incidence of stage 653 CKD (eGFR < 60 mL/min/1.73 m2) or eGFR reduction > 30% from baseline was evaluated. Results: The mean estimated GFR was 98 \ub1 17 mL/min/1.73m2 and the proportion of patients with albuminuria was 15.3% (n = 654) at baseline. About 8% (n = 337) of patients developed one of the two renal endpoints during the 4-year follow-up period. Age, albuminuria (micro or macro) and baseline eGFR < 90 ml/min/m2 were independent risk factors for stage 653 CKD and renal function worsening. When compared to patients with eGFR > 90 ml/min/1.73m2 and normoalbuminuria, those with albuminuria at baseline had a 1.69 greater risk of reaching stage 3 CKD, while patients with mild eGFR reduction (i.e. eGFR between 90 and 60 mL/min/1.73 m2) show a 3.81 greater risk that rose to 8.24 for those patients with albuminuria and mild eGFR reduction at baseline. Conclusions: Albuminuria and eGFR reduction represent independent risk factors for incident stage 653 CKD in T1DM patients. The simultaneous occurrence of reduced eGFR and albuminuria have a synergistic effect on renal function worsening

Renewable energy penetration in food delivery: Coupling photovoltaics with transport refrigerated units

Numbers of refrigerated transports are recording an impressive growth due to increased demand of chilled and frozen food. They require fuel consumption for traction, but also for feeding the diesel-driven refrigeration unit, which maintains the desired internal vehicle temperature. A photovoltaic integrated delivery process is investigated, in order to foster renewable energy penetration into the cold chain, thus improving its sustainability. It involves photovoltaic panels installed on the rooftop of semitrailers, a battery bank and a power conversion system to cover refrigeration requirements, removing the diesel engine from the refrigeration unit. A minimum cost multi-period Constraint Programming model is proposed to size the system, by matching refrigeration requirements with photovoltaic generation potential along the journey, both variable with daily and seasonal climate conditions. Application to a reference case of palletised frozen food distribution in North-Eastern Italy shows how drastic greenhouse gas emission reduction can be achieved per vehicle, with payback period expected to decrease below 2 years in the next decade. Sensitivity analysis on internal temperature for chilled food and different climate conditions, as well as the worst case analysis, are performed, confirming the capability of the model to act as a decision support tool for greening the cold chain

Fostering Renewables into the Cold Chain: How Photovoltaics Affect Design and Performance of Refrigerated Automated Warehouses

In the industrial food supply chain, cold storage is one of the most important processes where there is a huge but still unused potential for employing renewable energy technologies. This paper analyses how the integration of rooftop photovoltaics affects the design and performance of refrigerated automated warehouses, which are becoming the preferred choice for frozen food storage facilities. The problem is modelled and solved by means of Constraint Programming. Results for the reference case in north-eastern Italy show that photovoltaic installation can lead to both yearly total cost and energy savings. Simulations highlight how design and performance of the refrigerated automated warehouse strictly depend on supply chain decision variables. PV integration offers supply chain managers more opportunities to act on the storage temperature and the incoming product temperatures strictly related to upstream and downstream stages of the whole cold chain. Attention should be paid to system throughput, which presents an intermediate range for which the design optimization of volume and surfaces reduces the convenience of PV integration. Simulations on facility locations reveal how different climate conditions affect the economic and environmental performance of the refrigerated warehouse, as well as country specific carbon intensity and energy price

Coupling waste heat extraction based on phase change material with steam generation: evidence from steel industry

Waste heat recovery in steel industry represents one of the greatest opportunity to reduce the consumption of primary energy while increasing the sustainability of the steelmaking processes. One of the most important and challenging source of waste heat in steelmaking process is the off gas emitted by the Electric Arc Furnace (EAF), which represents about 30% of the total energy provided to the process. Due to the dynamic of the EAF process, the off gas parameters (temperature and mass flow rate) fluctuate intensively causing large variations in thermal power. Currently, the most modern heat recovery systems face these thermal power fluctuations generating saturated steam at around 220 \ub0C and storing it in Ruth\u2019s steam accumulator to feed an Organic Rankine Cycle (ORC). Since the average temperatures of the off gas are usually around 600 \ub0C, in order to reduce exergy losses a better solution would be to generate superheated steam at higher temperature to directly feed a steam turbine. For this aim, high temperature phase change materials (PCMs) can be employed to reduce the fluctuating thermal power entering the steam generator. Previous findings have shown technical and economic performances of a PCM-based device able to smooth off gas temperature profiles. The introduction of a heat transfer fluid (HTF) to overcome overheating issues in PCM containers has also been investigated. In this paper, the opportunity of actively managing the HTF flowing through the PCM device to enhance the steam parameters level is investigated. To this end, the PCM-based device is coupled with a steam generator: the effects of both off gas temperature smoothing and extraction of stored heat in the PCM by HTF on steam parameters and performance of the related energy conversion system are analysed. An analytical model is implemented in Fortran90 to predict the thermal behaviour of the PCM device. The Fortran code is interfaced with the TRNSYS software to analyse the performance of the whole heat recovery system (PCM device, steam generator and steam turbine) and to develop a proper control strategy. All thermo-physical properties are estimated using the REFPROP 8.0 package. Calculations are carried out in transient regime, adopting off-gas flow rates and temperature profiles representative of real EAF processes. Finally, an economic performance assessment of the whole system is carried out

Application of high temperature phase change materials for improved efficiency in waste-to-energy plants

This study reports the thermal analysis of a novel thermal energy storage based on high temperature phase change material used to improve efficiency in waste-to-energy plants. Current waste-to-energy plants efficiency is limited by the steam generation cycle which is carried out with boilers composed by water-walls (i.e. radiant evaporators), evaporators, economizers and superheaters. Although being well established this technology is subjected to limitations related with high temperature corrosion and fluctuation in steam production due to the non-homogenous composition of solid waste; this leads to increased maintenance costs and limited plants availability and electrical efficiency. The proposed solution in this paper consists of replacing the typical refractory brick installed in the combustion chamber with a PCM-based refractory brick capable to store a variable heat flux and to release it on demand as a steady heat flux. By means of this technology it is possible to avoid steam production fluctuation, to increase temperature of superheated steam over current corrosion limits (450°C) without using coated superheaters and to increase the electrical efficiency beyond 34%. In the current paper a detailed thermo-mechanical analysis has been carried out in order to compare the performance of the PCM-based refractory brick against the traditional ones. The PCM considered in this paper is aluminium and its alloys whereas its container consists of high density ceramics (such as Al2O3, AlN and Si3N4); the different coefficient of linear thermal expansion for the different materials requires a detailed thermo-mechanical analysis to be carried out to ascertain the feasibility of the proposed technology.NRF (Natl Research Foundation, S’pore)Accepted versio

Coupling waste heat extraction by phase change materials with superheated steam generation in the steel industry

To allow a better exergy exploitation than the current state-of-the-art waste heat to power solutions in the steel industry, a new type of energy recovery system based on Phase Change Materials is proposed. In particular, the use of high temperature PCMs evolves from simply smoothing off gas temperature, as in the most recent studies for energy recovery from electric arc furnaces, to generating constant superheated steam able to feed the downstream turbine nearly at nominal load. This result is achieved by introducing an auxiliary section between the PCM Section and the steam generation one, which provides the auxiliary heat needed to level the thermal content of off gas. The auxiliary heat is extracted from the PCM units by a heat transfer fluid flowing across the inner tube of each PCM container. Different models to properly size and simulate the operations of the proposed energy recovery system have been developed and integrated. Results show how the size of the steam generator and the turbine can be reduced of about 41% with respect to traditional solutions, while increasing electric power production by 22% thanks to the reduced fluctuation in steam parameters at the turbine inlet, which leads to a greater overall efficiency

Enhancing energy recovery in the steel industry: Matching continuous charge with off-gas variability smoothing

In order to allow an efficient energy recovery from off-gas in the steel industry, the high variability of heat flow should be managed. A temperature smoothing device based on phase change materials at high temperatures is inserted into the off-gas line of a continuous charge electric arc furnace process with scrap preheating. To address overheating issues, a heat transfer fluid flowing through containers is introduced and selected by developing an analytical model. The performance of the smoothing system is analyzed by thermo-fluid dynamic simulations. The reduced maximum temperature of off-gas allows to reduce the size and investment cost of the downstream energy recovery system, while the increased minimum temperature enhances the steam turbine load factor, thus increasing its utilization. Benefits on environmental issues due to dioxins generation are also gained

Enhancing energy recovery in the steel industry by off-gas variability smoothing

In order to allow an efficient energy recovery from off-gas in the steel industry, the high variability of heat flow should be managed. A temperature smoothing device based on phase change materials is inserted into the off-gas line. To address overheating issues of the phase change material containers, a heat transfer fluid is also introduced. Performances of the smoothing system are analysed by thermo-fluid dynamics simulations and economics of the resulting energy recovery are provided