Power plants – Utilizing natural heat – Solar
Reexamination Certificate
2002-11-11
2004-03-09
Nguyen, Hoang (Department: 3748)
Power plants
Utilizing natural heat
Solar
C060S641150
Reexamination Certificate
active
06701711
ABSTRACT:
FIELD OF THE INVENTION
The present inventions relate to solar-thermal receiver systems, and, more particularly, to molten salt receiver systems having a cooling system to provide cooling upon a predetermined flow condition to permit redirecting heliostats from the receiver heat exchanger.
BACKGROUND OF THE INVENTION
Molten salt receiver systems are used in solar-thermal energy conversion systems. One of the most common applications of the molten salt system applies to solar tower systems such as is described in U.S. Pat. No. 5,417,052 to Bharathan et al. A similar system is generally depicted in
FIG. 1
illustrating an array or a field of heliostats
112
that follow the sun
110
and re-direct the solar radiation
114
to a central receiver system located atop a tower
118
.
The central receiver system typically has a receiver heat exchanger
116
that becomes heated by the reflected solar energy
114
. The heat is transferred to a molten salt, typically nitrate salts such as a combination of liquid sodium nitrate and potassium nitrate. The heated molten salt is directed to a hot storage tank
122
that provides energy to a power generation system
124
. The molten salt is returned to a cold storage tank
120
that supplies the central receiver system. In the power generation system
124
, the molten salt exchanges heat through a heat exchanger to a fluid such as water or air. For example, as described in the Bharathan patent, the molten salt is directed to an air heater that drives a hybrid gas power plant. A gas turbine converts the thermal energy into mechanical energy, which is then converted into electrical energy by a generator.
In molten salt receiver systems, the molten salt is not only a thermal storage fluid but also functions as a coolant that reduces the temperature of the receiver heat exchanger
116
. If the flow of molten salt is inadvertently reduced or terminated, the solar energy will quickly overheat the receiver heat exchanger
116
. In such a situation, it is desirable to defocus the heliostats
112
by moving them to a standby position so that solar energy is not directed toward the receiver heat exchanger
116
. However, an adequate supply of molten salt must be available to cool the receiver heat exchanger
116
for the amount of time required to redirect the heliostats
112
.
One molten salt receiver system
200
was devised to cause cooling while redirecting heliostats and is rather simply described by FIG.
2
. In this system, molten salt storage tanks
220
,
222
were located at ground level. A cold storage tank
220
stored the supply of cold molten salt to be sent to the receiver heat exchanger
216
, and a hot storage tank
222
stored hot molten salt for use in an energy generation system. A variable speed pump
224
provided molten salt from the cold storage tank
220
to a pressurized receiver inlet vessel
226
, which physically sat level to or slightly below the receiver heat exchanger
216
. The receiver inlet vessel
226
supplied flow of molten salt to the receiver heat exchanger
216
by way of a controlled throttle valve
228
. The throttle valve
228
controlled flow through the heat exchanger
216
based upon optimum heat exchange conditions. Typically, flow is throttled to maintain a receiver heat exchanger
216
outlet temperature of about 1050° F. After flowing through the receiver heat exchanger
216
, molten salt entered a receiver outlet vessel
230
, which sat physically slightly higher than the receiver heat exchanger
216
. The outlet vessel
230
was vented to atmosphere and permitted the release of entrained air in the molten salt. From the receiver outlet vessel
230
, a downcomer
231
provided the flow of molten salt to a hot storage tank
222
.
In this molten salt receiver system
200
, the downcomer
231
required a full head of molten salt in order to avoid the effects of potentially destructive rapid momentum changes to the flow. The receiver outlet vessel
230
included a level indicator (not shown) assuring that the downcomer
231
was full. Feedback controlled active drag valves
232
,
233
were located at the base of the downcomer
231
and maintained the head. At least two active drag valves
232
,
233
were provided for redundancy. As such, the drag valves
232
,
233
were controlled by feedback from the level indicator at the receiver outlet vessel
230
.
The pressurized receiver inlet vessel
226
served an emergency cooling purpose in the system
200
. The receiver inlet vessel
226
provided a flow of molten salt for cooling the receiver heat exchanger
216
in the event of loss of normal flow. When flow ceases, the heliostats are required to be redirected from the receiver heat exchanger
216
, a process that typically takes about one minute. In order to avoid overheating the receiver heat exchanger
216
, the flow from the receiver inlet vessel
226
must be provided during this one minute. Therefore, the level of the inlet vessel
226
was maintained at a predetermined value to keep at least a minute's worth of supplemental molten salt flow.
Because the drag valves
232
,
233
were actively opened by a control system, they could inadvertently close. In the absence of free space in the outlet vessel
230
, the inadvertent shutting of the drag valves
232
,
233
could prevent flow of the molten salt through the receiver heat exchanger
216
. As such, the level in the receiver outlet vessel
230
required available free space to accept the required amount of flow from the receiver inlet vessel
226
during the one minute period required to redirect the heliostats.
From the foregoing description, it becomes apparent that there are several control variables involved in the molten salt receiver system
200
. First, the flow through the heat exchanger
216
was controlled by the throttle valve
228
according to optimum heat exchange requirements, which vary greatly according to the intensity of sunlight throughout the day. In fact, cloud cover transients can have a sudden and dramatic effect on the temperature and necessary flow through the receiver heat exchanger
216
. Secondly, the level of the receiver inlet vessel
226
was controlled to maintain an appropriate level as required to cool the receiver heat exchanger
216
in the event of loss of flow. A variable speed pump
224
supplying the receiver inlet vessel
226
maintained appropriate pressure in the vessel
226
. Also, the variable speed pump
224
and an air feed and bleed cover gas system (not shown) maintained the appropriate level in the inlet vessel
226
. As can be seen, controlling the receiver inlet vessel level was also dependent upon the throttled flow through the receiver heat exchanger
216
, therefore affecting control of the speed of the pump
224
. Thirdly, the level of the receiver outlet vessel
230
was required to be maintained in a band, high enough to indicate a full head in the downcomer
231
, yet low enough to permit a minute's worth of volume to flow from the receiver inlet vessel
226
in the event of inadvertent drag valve
232
,
233
closure. The drag valve
232
,
233
controlled the level of the receiver outlet vessel
230
by feedback from the level indicator (not shown). As can be seen, the level of the receiver outlet vessel
230
is also dependent upon the flow through the heat exchanger
216
.
The cross dependence of the control variables in the foregoing system created a rather elaborate and complex control system for the molten salt receiver system
200
. As such, a need in the art exists for a less complex control system. However, the system must maintain the ability to provide adequate molten salt cooling to the receiver heat exchanger
216
in the event of a loss of flow. Additionally, the system must be capable of preventing momentum changes of the downcomer flow that can induce undesirable mechanical forces in the downcomer.
BRIEF SUMMARY OF THE INVENTION
Therefore according to the present inventions, a molten salt receiver system and method for cooling a receiver heat exchanger of a mol
Alston & BIrd LLP
Nguyen Hoang
The Boeing Company
LandOfFree
Molten salt receiver cooling system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Molten salt receiver cooling system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Molten salt receiver cooling system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3214054