Mauro Reini

Optimization of Distributed Trigeneration Systems Integrated with Heating and Cooling Micro-grids

ABSTRACT The article deals with the influence of the amortization period in the optimization of a distributed urban district heating and cooling trigeneration system. The model, presented in detail in [1], is based on a Mixed Integer Linear Program (MILP) and includes a set of micro-cogeneration gas turbines for producing electricity and thermal energy and a set of absorption chillers, driven by cogenerated heat, for producing cooling energy. Micro-gas turbines and absorption chillers can be used instead of purchasing electricity from the grid, producing thermal energy by boilers and cooling energy by compression chillers. Moreover, various building can be connected each other through a district heating and cooling network (DHC network). The optimization specifies the kind, the number and the location of cogeneration equipment and absorption machines, the size and the position of district heating and cooling pipelines as well as the optimal operation of each component. The objective function takes into ac...

Performance Analysis and Modeling of Different Volumetric Expanders for Small-Scale Organic Rankine Cycles

In the last years one of the main research topics in energy field is represented by Organic Rankine Cycles (ORCs), due to their applicability in energy recovery from waste heat and in distributed combined heat and power (CHP) generation, particularly in small and micro scale systems. One of the key devices of the cycle is the expander: it must have a limited cost (like all the other components, in order to ensure the economic feasibility), but also a high efficiency, since the temperature of the heat source is often low and then the cycle efficiency is inherently scarce. In the first part of this paper a literature review on various positive-displacement expanders is presented, in order to outline their performances and their application field. Then, the numerical model of a volumetric reciprocating expander is implemented. This model, and another one previously developed to simulate scroll expanders, is combined with a thermodynamic model of the whole ORC system, so that a comparison between the two technologies can be carried out. The results confirm the possibility of realizing small scale energy recovery and cogeneration (CHP) systems with acceptable electrical efficiency also adopting low-cost components, directly derived from large scale industrial components.

Optimal Lay-Out and Operation of District Heating and Cooling Distributed Trigeneration Systems

The paper deals with the optimization of a distributed urban district heating and cooling cogeneration system. The model is based on a Mixed Integer Linear Program (MILP) and includes a set of micro-cogeneration gas turbines and a district heating network potentially connecting each considered building to all the others. Absorption machines, supplied with cogenerated heat, can be used instead of conventional electrical chiller to face the cooling demand. In addition, a district cooling network can be introduced, independently from the district heating one. The objective of the paper is to obtain the optimal synthesis and operation strategy of the whole system, in terms of Total Annual Cost for owning, maintaining and operating the system. The solution has to specify the kind, the number and the location of cogeneration equipment and absorption machines, the size and the position of district heating and cooling pipelines as well as the optimal operation of each component. The effects of different plant options, comparing cogeneration and tri-generation machines adoption and district heating and cooling pipelines installation, are considered.Copyright

Effect of Different Economic Support Policies on the Optimal Definition and Operation of a CHP and RES Distributed Generation Systems

This paper deals about the application of MILP for economic optimization of complex cogenerative systems. In particular, it optimizes both the size and operating strategy of CHP systems and the lay-out of micro district heating networks applied to a urban contest. The proposed model considers the possible adoption of a set of micro-cogeneration gas turbines located in different buildings, and of a centralized cogeneration system thus allowing part of the required thermal energy to be produced in a single site. In addition, thermal and photovoltaic panels can be integrated into the system to improve thermal and electrical energy production, respectively. Each site can be connected to the others through district heating micro-grids. Hence thermal energy can be distributed inside the system. A further objective of the paper is to evaluate the effect of different economic support policies on the optimal solution, and to relate the economic effort implied in each support policy with the expected results in terms of CO2 emissions reduction and primary energy savings.Copyright

Performance Evaluation of a Small Scale High Efficiency Cogeneration System

In recent years, a big effort has been made to improve microturbines thermal efficiency, in order to approach 40%. Two main options may be considered: i) a wide usage of advanced materials for hot ends components, like impeller and recuperator; ii) implementing more complicated thermodynamic cycle, like combined cycle. In the frame of the second option, the paper deals with the hypothesis of bottoming a low pressure ratio, recuperated gas cycle, typically realized in actual microturbines, with an Organic Rankine Cycle (ORC). The object is to evaluate the expected nominal performance parameters of the integrated-combined cycle cogeneration system, taking account of different options for working fluid, vapor pressure and component’s performance parameters. Both options of recuperated and not recuperated bottom cycles are discussed, in relation with ORC working fluid nature and possible stack temperature for microturbine exhaust gases. Finally, some preliminary consideration about the arrangement of the combined cycle unit, and the effects of possible future progress of gas cycle microturbines are presented.Copyright

Optimization of an Industrial Area Energy Supply System With Distributed Cogeneration and Solar District Heating

The paper presents the optimization of an energy supply system for an industrial area. The system is mainly composed of a district heating network (DHN), of a solar thermal plant with long term heat storage, of a set of combined heat and power units (CHP) and of additional thermal/cooling energy supply machines. The thermal vector can be produced by solar thermal modules, by fossil-fuel cogenerator or by conventional boilers. The optimization algorithm is based on a Mixed Integer Linear Programming (MILP) model and it has to determine the optimal structure of the energy system and the size of the components (solar field area, heat storage volume, machines sizes, etc.). The model allows to calculate the economical and environmental benefits of the solar thermal plant compared to the cogenerative production, as well as the share of the thermal demand covered by renewable energies. The aim of the paper is to identity the optimal energy production mix able to meet the user energy demands and furthermore how the solar thermal energy integration affects the optimal energy system configuration. The average costs of the heat produced for the users have been evaluated for different optimal configurations, and it emerges that the solution including some cogenerators located in strategic production units, the district heating network, the long term heat storage and a solar plant of proper size, allows achieving the lowest cost of the heat. Thus, the integrated solution turns out to be the best from both the economical and environmental point of view.© 2012 ASME

Micro-Organic Rankine Cycle systems for domestic cogeneration

Abstract The Chapter presents the requirements and the main features of a domestic cogeneration unit, based on Organic Rankine Cycle (ORC) technology. The achievable electrical efficiency and proper sizing are discussed in detail, other matters of choice are also taken into account, such as reliability, safety, noise, and the cost of purchasing and operation. To better understand the possible benefits of a cogeneration system, even with low electrical efficiency, the Primary Energy Saving (PES) diagram and the Economic Recovery Index (ERI) diagram are introduced. Then, the claimed performance parameters of existing models and prototypes are discussed and a comparison is outlined with solutions based on Stirling engines. Afterwards, the main technical features of domestic ORC components are presented, with special attention given to the expander and the feed pump. Also the control strategy options for the unit are presented, taking into account the peculiarity of a domestic application. Finally, two possible options are discussed for the integration of a domestic cogeneration unit: a solar thermal system to drive the ORC and an ejector refrigeration cycle to obtain a Combined Cooling Heat and Power (CCHP) system.

Comparison of Rankine Cycles for Micro-CHP Generation Based on Inward Flow Radial Turbine or Scroll Expander

This contribution aims to analyze micro-CHP units based on Rankine cycles. Two types of expander are considered: a small scale inward flow radial turbine and a volumetric scroll type expander. This latter, should allow to overcome the limitation imposed by a standard steam-turbine that arise when the required shaft-power is very low. Moreover, the scroll expander will also allow to easily treat wet steams, which must be avoided when considering a turbo-expander. The final aim is to deduce which one of the two types of expander is more suitable, with a specified target performance and the availability of a certain hot source. In order to define the thermodynamic expansion process, the analysis uses a one-dimensional model of the radial turbine, previously developed by the authors, and of an estimation of the scroll expander efficiency. Also, the analysis is carried out for different working fluids, such as water, and two organic fluids, cyclohexane and toluene. Through the discussion of the results, for a specified set of constraints (e.g. expander inlet temperature, temperature of condensation, expander geometrical parameters) it is possible to deduce important indications on the most suitable expander for a given cycle layout.Copyright