In direct absorption receivers, the concentrated solar radiation is absorbed directly in a heat transfer medium.
This avoids technical restrictions by structural materials and the heat transfer medium can be heated up to very high temperatures. Two different particle receiver types are under development at DLR: centrifugal receiver (CentRec) and falling particle receiver.
Solar Tower Systems with Particle-Receiver
Solar tower systems with particle receiver can be applied for the production of electricity and for industrial process heat, especially high-temperature process heat. Ceramic particles are used as heat transfer medium because they are suitable for temperatures up to at least 1000°C. The particles are used in a closed circuit for receiving the power in the receiver and also as storage material.
Heat transfer material - ceramic particles
Actually, ceramic particles made from sintered bauxite (Figure 1) are favored as heat transfer material. The reasons for this choice are:
Centrifugal Receiver (CentRec) – Principle of Function
The Centrifugal Receiver consists of a rotating, isolated hollow cylinder (cavity). The particles are fed into the receiver at the top.
By centrifugal force, the particles are forced against the inside of the hollow cylinder and form a dense particle film which moves downwards.
Through the open bottom of the cavity, the so-called aperture, the concentrated solar radiation enters the cavity and is directly absorbed in the particle film.
A non-rotating collection ring captures the particles at the bottom and transfers them to the subsequent particle circulation.
Falling Particle Receivers - Principle of operation
In a falling particle receiver, the particles fall down freely in the receiver and form a "particle curtain". In this curtain occurs the direct absorption of the concentrated solar radiation.
A possible design of such a receiver is a concentric inner curtain in a downward open receiver cavity (Figure 2).
The particles are fed to the receiver at the top and fall down parallel and near to the receiver inner wall. At the bottom of the receiver, the particles are collected in a collecting ring and transported from there to the following application.
Recent work at DLR:
components for lab tests
receivers for demonstration plants
Development of simulation models for