Solar concentrator plant

Abstract

Which, using a heat transfer fluid in any thermodynamic cycle or system for using process heat, comprises: two-dimensional solar concentrator means for heating the heat transfer fluid from a temperature T1 to a temperature T2; three-dimensional solar concentrator means for overheating the heat transfer fluid from a temperature T2 to a temperature T3; such that the advantages of working at high-temperatures of the three-dimensional solar concentrator means are taken advantage of with overall costs similar to those of two-dimensional solar concentrator means.

Description

BRIEF DESCRIPTION OF THE FIGURES

To complete the description being made and in order to aid a better understanding of the characteristics of the invention, a detailed description will be made of a preferred embodiment based on a set of drawings accompanying this descriptive memory where, for purposes of illustration only and in a non-limiting sense, the following is shown:

FIG. 1 shows a Rankine thermodynamic cycle as used in a preferred embodiment of the invention.

FIG. 2 shows a schematic representation of the plant, as used in a preferred embodiment of the invention.

In the aforementioned figures, the numerical references correspond to the following parts and components:

1. Parabolic trough collector

2. Heliostat field and central tower

3. Low-temperature thermal storage

4. High-temperature thermal storage

5. Fossil fuel support

6. Turbine

7. Electric generator

8. Condenser

9. Compressor.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A detailed description will be given next of an application of the invention for generating electrical power, using a Rankine thermodynamic cycle. In this specific case the parabolic trough technology is selected as the two-dimensional sc technique and the central receiver technology is selected as the three-dimensional sc technique.

In Rankine thermodynamic cycles, most of the energy supplied to the cycle is supplied in the evaporation at constant temperature stage. Only the overheating stage requires the use of high temperatures. In the application of the combined plant of the invention to a Rankine cycle, it is proposed to use PTC technology for the heating and evaporation stages and possibly for a slight overheating to a maximum temperature of 400° C., then using central receiver technology only in stages requiring high process temperatures above 400° C. (the overheating stage reaches temperatures even higher than 550° C. in conventional overheated Rankine cycles).

As shown in FIG. 1, the cycle comprises four processes. Starting at the lowest temperature T0, the heat transfer fluid is pumped to the temperature T1 where it is heated at constant pressure by a two-dimensional concentrator system to the temperature T2. It is then heated by a three-dimensional concentrator system to temperature T3, where it is expanded in a turbine until it recovers its original temperature T0, closing the cycle with a condenser that converts the saturated vapor into a liquid.

As shown in FIG. 2, this plant will typically comprise the following:

• • a) Two-dimensional sc means (including the receiver) consisting of a parabolic trough collector (1) for generating saturated or slightly overheated vapor. This device will typically allow supplying heat to the water arriving from the condenser to raise its temperature from approximately 50° C. to 250° C. or 330° C. if saturated vapor is used (depending on the pressure selected for the cycle), or even to approximately 400° C. if slightly overheated vapor is used in the PTC stage;
  • b) Three-dimensional sc means (including the receiver) consisting of a heliostat field and a central tower (2) for overheating the vapor produced by the PTC stage;
  • c) A low-temperature thermal storage device (3);
  • d) A high-temperature thermal storage device (4);
  • e) A fossil fuel support device (5);
  • f) A turbine (6) coupled mechanically to an electric generator (7);
  • g) A condenser (8);
  • h) A pump (9).

The energy supply in a Rankine cycle for the overheating stage implies (with the temperatures specified above) only about 18% of the total energy supply to the cycle. This will allow designing a combined plant with a thermal power at the design point of the parabolic trough field of 82% of the thermal power required for the power block, the remaining 18% being provided by the heliostat field. The use of overheated vapor can allow implementing thermodynamic cycles of higher efficiency in the plants. For example, an 11 MWe plant with a saturated vapor cycle gives cycle yields of 28.5%. A plant of similar proportions using overheated vapor can incorporate cycles with yields of about 35% to 38% depending on the process temperature and pressure, which implies increasing the annual plant output by 20% or 30%.

To allow the plant to combine the two technologies in an efficient manner, it is important to consider their cosine effect; this is the variation of the solar power that can be used by TCP technology and the three-dimensional concentration technology (heliostat field and tower) throughout the year. In order to size the combined system properly there are several alternatives depending on the latitude and radiation of the plant location. The modes of operation described below are restricted to PTC plants with a N-S orientation (E-W tracking) combined with central receiver technology in latitudes similar to that of Spain.

To execute the overheating stage exclusively with solar power, we must oversize the heliostat field to ensure that in the summertime there is always 18% of solar power available for overheating. This will imply a size of the heliostat field at the design point slightly greater than 18%, leading in winter to excess power available for overheating; thus, this excess power must be used for the low and medium temperature preheating and evaporation processes. The overheating stage can also be executed with support of gas, so that it is not necessary to oversize the heliostat field to compensate the lack during the summer and the excess power for overheating in winter will be less. Another way to compensate the seasonal and daily differences is to use a heat storage system. This allows softening the phase differences of the systems. The combined use of fossil fuel support, storage system and proper sizing of the two-dimensional and three-dimensional concentration systems will lead to optimum operation conditions in each case.

Claims

1. Solar concentrator plant that uses a heat transfer fluid in any thermodynamic cycle or system for using process heat, characterized in that it comprises: two-dimensional solar concentrator means for heating the heat transfer fluid from a temperature T1 to a temperature T2;three-dimensional solar concentrator means for overheating the heat transfer fluid from a temperature T2 to a temperature T3;

2. Solar concentrator plant according to claim 1, characterized in that the two-dimensional solar concentrator means comprise a parabolic trough collector (1).

3. Solar concentrator plant according to claim 1, characterized in that the three-dimensional solar concentrator means comprise a heliostat field and central tower (2).

4. Solar concentrator plant according to claim 1, characterized in that it incorporates thermal storage devices (3), (4).

5. Solar concentrator plant according to claim 1, characterized in that it incorporates a fossil fuel device (5) to complement the concentrator devices (1), (2).

6. Solar concentrator plant according to claim 1, characterized in that the thermodynamic cycle is a Rankine cycle for generating overheated water vapor.