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Modeling of a concentrating solar plant to produce steam

Introduction

In the recent years, has increased the need to reduce fossil fuel consumption, mainly responsible of air pollution and climate change.

The use of alternative energy sources have started to affect all sectors, from industrial to civil. Don’t forget that in this direction are moving all industrialized countries (Kyoto protocol 16 February 2005).

The alternative energy sources are multiple and can reduce the human dependence on fossil fuel. They are derived, directly or indirectly, from the sun.

It’s an inexhaustible source of energy, even if a random source, this problem is often solved by technical (tank of thermal energy).

In this thesis is considered the use of solar energy in the production of steam at a pressure of 6 bar and flow rate of 700 kg/h.

Design scheme

For the production of steam related to the conditions indicated below, an analysis in the technical/commercial scope prompted to choose the use of parabolic trough concentrators, which are a system for the capture of solar energy. These concentrators allow to lead heat transfer fluid to a high temperature, that is flowing within the central manifold. The solution provides the presence of two separate circuits: heat transfer fluid and water fluid. With the use of a tank of thermal energy, you can solve the problem of the uncertainty of the solar source, maintaining the steam at a constant temperature. The plant is completed with a natural gas boiler with integrative function, which comes into operation when the solar energy falls below the minimum threshold programmed.

Modeling System

The operation of the plant was analysed by a simulation software, in order to properly size the entire system.

For the dynamic simulation of the plant has been used the code TRNSYS, which stands for "TRaNsient SYstem Simulation Program”, version 16. The code was developed by "Solar Energy Laboratory” of the University of Wisconsin-Madison and currently is one of the most reliable tools for dynamic simulation of energy systems.

Analysis

Figure 2 shows the energy supplied to the boiler for different sizes of the absorbing surface throughout the year.

Conclusions

Energy saving increases with the extension of the solar field, but with non-linear law. This observation justifies the optimization of the plant, which makes maximum energy savings in relation to the cost of implementation.

Another important feature is the saving of natural gas, with consequent reduction of carbon dioxide emitted into the atmosphere.



 

LAYOUT
ENERGY NEEDED [GJ]
FUEL QUANTITY [m3]
REDUCTION OF CO2EMISSIONS [kg]
Boiler

 

27700 772018 0

Boiler+Solar field 4000m2

25400 707915 155998

Boiler+Solar field 9000m2


24400 680045 223823
Boiler+Solar field 15200m2
23900 666109 257735
Fuel necessary to provide the correct amount of energy to the heat transfer fluid and saving of CO2 emitted into the atmosphere.

 

Michele Rossi

Degree thesis, academic year 2013/2014

Department of Industrial Engineering

Supervisor: Prof. GIORGIO PAGLIARINI

Correlator: Ing. CARLO CORRADI

Correlator: Ing. RICCARDO GUERRA