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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

Abstract

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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Figures

Figure 1

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

Figure 2

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

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

Figure 4

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

Figure 5

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

Figure 6

Baffle separator

Figure 7

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

Figure 8

Pressure in the field separators and drainage line

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).

Figure 10

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

Figure 11

Impact of discharge valve reaction time on field buffer capacity

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