Renewable Energy in Industrial Applications – an ... - Unido

RENEWABLE ENERGY IN INDUSTRIAL APPLICATIONS
solution for the melting or even the vaporisation
of small quantities of metals.
A similar device is installed in the Paul Scherrer
Institut (PSI) in Switzerland and known as High-
Flux Solar Furnace. The furnace consists of a 120m 2
sun-tracking flat heliostat on-axis with an 8.5 m-
diameter paraboloidal concentrator. It delivers up
to 40 kW at peak concentration ratios exceeding
5000 suns (1 sun = 1 kW/m 2 ²). The solar flux
intensity can be further augmented to up to
10 000 suns by using CPC secondary concentrators.
A venetian blind-type shutter located between the
heliostat and the concentrator controls the power
input to the reactor.
Examples of solar thermal systems applied
to the Greek dairy industry
Two applications of solar thermal systems in the
dairy industry in Greece are described in the box
below (Karagiorgas et al., 2001).
Mandrekas S.A.
Mandrekas S.A. is a small dairy situated on the outskirts of the city of Korinthos. Its main
industrial activity is the production of dairy products such as yoghurt, milk and cream. Steam is
required by a range of plant processes, including pasteurisation, sterilisation, evaporation and
drying, and hot water is required to maintain the yoghurt at 45°C during its maturing process.
Steam is provided by a steam boiler running on liquid propane gas (LPG), the cold water being
supplied by the water supply grid, and hot water is provided by the solar system. The factory
uses 15m 3 of hot water a day.
The solar system was installed in 1993. It consists of 170m 2 of tube-n, flat plate collectors
coated with black paint located on the roof of the factory, an open loop circuit and two parallel,
horizontal, 1000 l closed storage tanks located in the boiler room of the dairy. The water from
the water supply grid enters the solar storage tanks and from there is fed to the solar collectors
where it is heated and returned to the solar storage tanks. The hot water leaving the solar
storage tanks is either fed directly to the factory's washrooms or is fed to the yoghurt maturing
process and then returned to the tanks. Any auxiliary heating required by the yoghurt maturing
process is provided via a heat exchanger, which receives steam from the steam boiler.
The system is still operational and in very good working order. The hot water requirements of
the yoghurt maturing process are much smaller than the amount of hot water produced by the
solar system which is oversized for the need. In addition, given the low hot water requirement
of the yoghurt maturing process, the steam heat exchanger is heating the solar storage tanks
thereby reducing the efficiency of the solar system.
Mevgal S.A.
Mevgal S.A. is a dairy situated on the outskirts of the city of Thessaloniki. Its main industrial
activity is the production of dairy products such as butter, cheese and buttermilk. Steam is
required for pasteurisation, sterilisation, evaporation and drying and hot water is required for
the cleaning and disinfecting of utensils and machinery. Originally, steam was provided by steam
boilers running on heavy oil which fed cold water exchangers. Today the hot water produced by
a solar system is used to pre-heat the water; electric resistance heaters provide any auxiliary
heating required. The system is operational and in excellent working order.
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