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Research Papers

Design of a Phase Separation System for a Direct Steam Generation Parabolic Trough Collector Field

[+] Author and Article Information
Tobias Hirsch

German Aerospace Center (DLR), Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germanytobias.hirsch@dlr.de

Markus Eck

German Aerospace Center (DLR), Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany

J. Sol. Energy Eng 130(1), 011003 (Dec 28, 2007) (6 pages) doi:10.1115/1.2804621 History: Received September 21, 2006; Revised July 31, 2007; Published December 28, 2007

The dynamic behavior of a parabolic trough collector field with direct steam generation under varying solar conditions is analyzed using a transient simulation model. It is found that the peak water flow rates observed during transients may reach several times the steady-state design values. Taking into account these results, a method is developed for calculating the required separation efficiency of the water-steam separator between evaporating and superheating sections of the solar field. For a field with individual phase separators arranged in each collector row, the drainage system, used for transporting the separated water from the field to a central buffer tank, is dimensionally defined. It turns out that a buffer capacity of about 0.1m3 and a large-diameter drainage line have to be foreseen in order to cope with the high liquid loads under solar transients. The results are compared to a field layout with one central separation drum in terms of materials consumption and thermal inertia. It turns out that the originally intended effect of a reduced thermal inertia is not reached when transient conditions are taken care of in the design of the components.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Collector field with central (left) and distributed (right) separation system

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Figure 2

Triple irradiance disturbance (3×) moving across a collector loop under angle α

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Figure 3

Maximum values of liquid and gas mass flow at the end of the evaporator obtained for triple (3×)/single (1×) irradiance disturbances of duration Δt

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Figure 4

Mechanical and thermal stress due to steady-state temperature profile and due to shock cooling of magnitudes Δϑ (di=55mm, p=70bar)

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Figure 5

Allowable and equivalent stress in the absorber tubes for different shock cooling configurations and tube materials (di=55mm, p=70bar)

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Figure 6

Baffle separator

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Figure 7

Distributed phase separation system for a field with four parallel collector rows

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Figure 8

Pressure in the field separators and drainage line

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Figure 9

Steam fraction after an adiabatic expansion of saturated liquid (a). Methods to avoid the evaporation by means of external cooling (b) or mixing with cold feed water (c).

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Figure 10

Minimum field buffer capacity for different irradiance disturbances and directions of motion of the cloud field

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Figure 11

Impact of discharge valve reaction time on field buffer capacity

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