Solar heat receiver

A receiver for converting solar energy to heat a gas to temperatures from 700.degree.-900.degree. C. The receiver is formed to minimize impingement of radiation on the walls and to provide maximum heating at and near the entry of the gas exit. Also, the receiver is formed to provide controlled movement of the gas to be heated to minimize wall temperatures. The receiver is designed for use with gas containing fine heat absorbing particles, such as carbon particles.

The invention relates to apparatus for collecting radiant energy and 
converting same into an alternate energy form, particularly to an 
apparatus for collecting solar radiant energy by having same absorbed by 
small particles disbursed in a fluid stream, and more particularly to an 
improved receiver for utilizing or transferring solar energy to heat a 
gas. 
Concentrated sunlight provides an intense source of radiant energy that 
offers an alternative to fossile fuels for operating heat engines, 
providing high temperature industrial heat, and for directly processing 
fuels and chemicals. Because sunlight originates from a radiating body at 
a considerably higher temperature than other familiar energy sources, 
solar radiation has quite different characteristics from those sources 
with which we gained our power conversion experience over the past 150 
years. 
Various prior approaches have been developed for utilization of solar 
radiation. These prior approaches have utilized different types of 
reflector and/or receiver apparatus for utilizing solar energy. These 
prior efforts are exemplified by U.S. Pat. No. 1,951,403 issued Mar. 20, 
1934 to R. H. Goddard; U.S. Pat. No. 3,908,632 issued Sept. 30, 1975 to H. 
W. Poulsen; U.S. Pat. No. 3,998,206 issued Dec. 21, 1976 to A. Jahn, and 
U.S. Pat. No. 4,116,222 issued Sept. 26, 1978 to W. Seifriend. In 
addition, various types of materials, such as ceramics, have been utilized 
in solar receivers to incerease the efficiency thereof, as illustrated by 
an American Chemical Society article entitled "Ceramic Solar Receivers", 
by P. O. Jarvinen, August 1979. 
More recently, a radiant energy collection and conversion apparatus has 
been developed in which the principal of operation differs from other 
solar energy conversion apparatus in that the solar-to-thermal conversion 
is accomplished by a dispersion of submicron particles suspended in a gas 
or working fluid to absorb radiant energy directly from concentrated 
sunlight. Such an apparatus is described and claimed in U.S. Pat. No. 
4,313,304 issued Feb. 2, 1982 to A. J. Hunt. 
While the apparatus and method of U.S. Pat. No. 4,313,304 has been shown to 
provide an effective conversion system, a need has existed for a more 
efficient receiver for directing the solar radiation onto the solar 
absorbing particle containing gas or other working fluid flowing through 
the receiver for heating same. 
SUMMARY OF THE INVENTION 
The present invention provides an improved solar heat receiver for more 
effectively converting solar energy to heat a gas or other working medium. 
The receiver of this invention is particularly adapted for heating a 
working medium such as a gas flowing through the receiver and in which is 
suspended submicron heat absorbing particles, such as carbon, which absorb 
the sunlight and act as very efficient heat exchangers to transfer the 
heat to the gas. The small heat absorbing particles continue to heat until 
they react chemically with the gas or vaporize. 
Therefore, it is an object of this invention to provide a solar heated 
receiver. 
A further object of the invention is to provide a receiver for converting 
solar energy to heat a gas or other working medium. 
Another object of the invention is to provide a solar energy receiver which 
minimizes impingement of radiation on the walls of the receiver and 
provides maximum heating at and near the entry of an exit into which a gas 
to be heated passes. 
Another object of the invention is to provide a solar thermal receiver 
which is designed for use with a gas containing fine energy absorbing 
particles which act as heat exchangers to heat the gas. 
Other objects of the invention will become readily apparent to those 
skilled in the art in view of the accompanying drawings and following 
description. 
The above objects of this invention are carried out by an improved solar 
thermal receiver placed at the focus of a central tower or parabolic dish 
concentrator system. The receiver, which confines the gas-particle 
mixture, includes a window through which the solar energy is directed, the 
window functioning to reduce the amount of infrared reradiation leaving 
the receiver, and because the window is at a lower temperature than the 
working medium, produce a high overall efficiency of the receiver. 
More specifically the solar heat receiver of this invention uses a gas 
containing fine carbon particles and which is capable of providing 
temperatures of 700.degree. to 900.degree. C. The receiver comprises a 
receiving chamber having cylindrical side walls, an inverted 
frusto-conical lower section having a window in its opening, a roof formed 
from an outer frusto-conical section and an inner inverted frusto-conical 
section, a manifold chamber formed around the cylindrical side walls, 
means to direct a gas containing fine particulate carbon into said 
manifold chamber in circular motion therein, walls forming openings 
between the manifold chamber and the interior of the receiver for 
directing the gas and particulate in cyclone fashion within the chamber, 
and a quartz tube extending through the top of the container in sealed 
relation with the inner conical section of the roof for directing heated 
gas from the receiver, said quartz tube having its lower end spaced from 
but close to the window. The receiver is used with a concentrating mirror 
system which directs solar radiation through a focal plane near the window 
and into the receiver. The system is designed to allow for the outer walls 
to be considerably cooler than the heated gas by the special shape of the 
container and the cyclonic gas flow.

DETAILED DESCRIPTION OF THE INVENTION 
The invention is a component of a system, such as in above-referenced U.S. 
Pat. No. 4,313,304, which operates by injecting a very small mass of 
ultrafine carbon particles into a gas stream and exposing the suspension 
to sunlight that is focused through a window of the component. The 
particles absorb the sunlight and act as very efficient heat exchangers to 
transfer the heat to the gas. The particles are very small and, therefore, 
not significantly affected by gravitational or inertial forces, and thus 
are effectively part of the gas. The particles continue to heat until they 
react chemically with the gas or vaporize. For gases containing oxygen, 
the maximum output temperature is determined by the oxidation rate of the 
carbon particles. The particles are used in a once-through mode because of 
the very low requirement for carbon and since they may be generated on 
site. For example, the generator for the carbon particles may be of the 
type described and claimed in copending U.S. patent application Ser. No. 
426,369, filed Sept. 29, 1982, now U.S. Pat. No. 4,452,771 issued Jun. 5, 
1984, entitled Carbon Particle Generator, and assigned to the assignee of 
this application. 
The receiver provides high temperature gas to operate a gas turbine or for 
use in industrial process heat applications, as well as being suitable for 
a wide range of powers and a variety of applications. The window in the 
receiver reduces the amount of infrared re-radiation leaving the receiver, 
and because the window is at a lower temperature than the working medium, 
it provides a high overall efficiency. 
Since the receiver uses small particles which act as heat exchanger 
elements, there is no need for heavy and complex heat exchanger elements, 
the receiver consists basically of a hollow chamber with a window, 
resulting in a light weight structure. Because of the heat exchanger 
effect of the carbon particles, the heat exchanger function is distributed 
throughout the chamber, it is not necessary to pump the gas through long 
tubes, which has the effect of considerably reducing the amount of energy 
required to overcome pressure losses. 
The receiver is designed to heat ambiant air to 700.degree.-900.degree. C. 
and is constructed such that more than 90% of the radiant energy entering 
the receiver is absorbed directly in the gas particle suspension. The 
receiver basically consists of a receiving chamber having cylindrical side 
walls and an inverted frusto-conical lower section having a window in its 
opening, the receiving chamber being an open volume in which the sunlight 
is absorbed, a gas injection system and a gas exhaust system. The receiver 
is designed to produce a significant cyclone motion to smooth out the 
effects of non-uniform solar flux density and to organize the internal 
flow. One unique aspect of the receiver is the use of a transparent tube 
that penetrates the high flux region, acts as an exhaust port, and insures 
that the gas particle suspension or mixture passes through the maximum 
flux density region before leaving the receiver. 
Referring now to the drawing, the solar heat receiver is positioned in a 
solar energy concentration system, as shown in FIG. 1, such that solar 
rays 11 are reflected by mirror elements 12, of a concentrating mirror 
assembly or field 13 containing numerous mirror elements 12 positioned 
thereabout, and are directed through a focal plane and into solar heat 
receiver 14. 
As shown in FIG. 2, the receiver 14 comprises a housing defining an inner 
chamber 16 having a quartz window 17 at its lower end, and a transparent 
quartz outlet or gas exhaust tube 18 having an opening near the window and 
extending upwards through the top of chamber 16. Chamber 16 is formed in a 
special geometric configuration in order to minimize wall temperatures. 
Thus, the housing defining the chamber 16 comprises a lower section or 
wall 19 in the shape of an inverted frusto-conical surface, a generally 
cylindrical section or side wall 21 adjacent to the lower wall, and a roof 
section composed of frusto-conical walls or members 22 and 23. Wall 19 is 
inclined to fit the travel of radiation reflected from the outer portion 
of the mirror system 13, and is typically about 45 degrees from the 
vertical, but may have an angle of 20 to 60 degrees. With this 
configuration, reflected solar radiation first passes through a focal 
plane, through the window 17, and then impinges on carbon particles 
suspended in the gas or other working medium in the chamber 16. 
In this way, minimal radiation strikes lower wall 19, and it is mostly 
absorbed before it reaches either the side wall 21 or roof walls 22 and 
23. By making quartz tube 18 transparent, solar radiation can also pass 
through the tube and heat the gas inside. From the drawing, it is seen 
that the position of maximum heating is just above the window 17 and that 
the gases are at maximum temperature as they pass through the first part 
of the exit or exhaust tube. At this location, the carbon particles will 
be vaporized or will chemically react with the gas when such particles are 
used, and further increase the temperature of the gas mixture. 
The walls of chamber 16 are not only formed to receive minimal energy, but 
also the chamber is constructed to be cooled by the entry gas or working 
medium. To that end, a manifold chamber 24 is formed around wall 21, and 
incoming gas is delivered into the chamber tangentially, by a delivery 
system not shown, to provide rotation of the gas in manifold chamber 24. 
The delivery system is described in report LBL-13755 entitled "The Design 
and Construction of a High Temperature Gas Receiver Utilizing Small 
Particles as the Heat Exchanger (SPHER)" by A. J. Hunt and D. B. Evans, 
September 1982, Lawrence Berkeley Laboratory, University of Calif. The gas 
circling in manifold chamber 24 is directed into chamber 16 through ports 
or nozzle openings 26. The gas is supplied to manifold chamber 24 by a 
plurality of nozzles (not shown). The nozzle construction is also 
described in the above-referenced report LBL-13755. 
Chamber 16 is also specially constructed to allow for expansion. The entire 
unit is supported from support ring 27, which in turn is carried on a 
plurality of legs 28 that may be supported further as required. Depending 
from the support ring 27 is a conical outer member sheet 29 which is 
secured to inner window ring or member 30 on its outer periphery and 
fitted but not secured to wall 19 of chamber 16 on its inner periphery. 
Ring 30 is formed to receive window assembly 17, which is formed by two 
window clamp rings or members 31 secured to ring 30 with suitable bolts 
(not shown). Chamber 16 is supported by a plurality of flat springs 32 
compressed between the lower surface of manifold chamber 24 and support 
ring 27. This allows for free and concentric expansion of the chamber. 
Quartz tube 18 is sealably secured in roof section 23 and it is free to 
move also when the chamber is expanded. 
As shown in the drawing, receiver 14 also comprises an outer casing or 
housing forming an outer chamber 35 spaced from the inner chamber 16 to 
provide an insulation space 36 for chamber 16. The space 36 is filled with 
high temperature insulating material. The outer chamber 35 is formed by 
lower wall 29, a cylindrical side wall 33, and an outer roof 34. Roof 34 
is formed with a stack assembly 37 through which quartz outlet tube 
passes. This stack contains a gas seal and bellows assembly which is more 
fully described in above-referenced report LBL-13755 and which allows for 
movement of said tube 18 upon expansion of chamber 16. 
In operation, gas containing fine carbon particles, for example having 0.01 
to 0.5 micrometer diameters, from a particle generator, not shown but 
described in detail in report LBL-13755, is directed into manifold 24. Air 
is also supplied to the receiver by induction with the gas particle 
stream. The flow is directed into manifold 24 in swirling motion and 
thence through nozzle openings 26 into the inner chamber 16. The upper 
nozzle openings 26 are tilted upwards to provide upward movement as the 
incoming gas flows (indicated by arrows 38) and to cool the roof sections 
22 and 23. The carbon particles in the gas pick up solar energy as the gas 
moves through the receiver and are greatly heated as the gas moves into 
exit tube 18 indicated by arrows 39. The heated gas will vaporize or 
chemically react with any carbon particles at the entry point or within 
the quartz tube, and the heated gas then flows toward the outlet as shown 
by arrow 40. 
The salient features of the invention are summarized below: 
(1) The transparent quartz tube is located to insure that the gas-particle 
mixture passes through the maximum flux density just before leaving the 
receiver. 
(2) The chambers are constructed of low-cost materials made possible by 
keeping the chamber walls at minimal temperatures. 
(3) Chamber walls are kept at minimal temperatures by using a geometric 
configuration that provides maximal impingement of solar radiation on the 
particle-gas mixture and minimal impingement on the walls of the chamber. 
(4) Further cooling of the chamber walls is provided by moving the 
gas-particle mixture in cyclone type flow first through a manifold 
exterior of the radiation-receiving chamber and thence through the chamber 
with an upward swirl provided to move inlet gas past the roof area. 
(5) The gas-particle mixture enters at ambient temperature and is heated to 
about 800.degree. C., providing a volumetric expansion of a factor greater 
than 3, thereby accelerating the gas flow significantly. These factors 
make it important to provide for the variations in expansion and the 
relatively large exit tube. 
(6) Special support and sealing structure is utilized to provide for 
thermal expansion. 
It has thus been shown that the invention provides an improved solar 
thermal receiver, particularly adapted for a working medium having small 
heat absorbing particles suspended therein, which has the capability of 
converting solar energy to heat the medium to temperatures of 
700.degree.-900.degree. C., while minimizing impingement of radiation on 
the walls of the receiver and providing maximum heating at and near the 
entry of the medium into an outlet conduit. Thus, the receiver of this 
invention has substantially improved the efficiency of solar heated 
receivers. 
While a particular embodiment of the invention has been illustrated and 
described, modifications will become apparent to those skilled in the art, 
and it is intended to cover in the appended claims all such modifications 
as come within the scope of this invention.