DSG plants in a once-through configuration convert water into superheated steam suitable for a steam turbine, with a single pass of the fluid through the receiver. The control problem is to manipulate the feed-water mass flow to maintain a desired steam condition (e.g. temperature) under variable solar radiation. This paper presents a full state linear feedback controller for the steam temperature for a once-through direct steam generation system, featuring a 500 m 2 paraboloidal dish concentrator and a mono-tube cavity receiver at the Australian National University. The controller manipulates the feed-water mass flow at the receiver inlet to maintain a predetermined specific enthalpy at the receiver outlet, compensating for variations in direct normal irradiation (DNI) and other ambient conditions. The linear controller features three separate regulation mechanisms: a feedforward law to anticipate changes in DNI; a full state feedback loop that uses a state observer for the receiver and an additional output feedback integrator loop for robustness. Experimental results show that the linear controller can successfully control the temperature of the SG4 receiver, provided that it is adequately tuned.

Performance analysis of a 500 MWe steam turbine cycle is performed combining the thermodynamic first and second-law constraints to identify the potential avenues for significant enhancement in efficiency. The efficiency of certain plant components, e.g. condenser, feed water heaters etc., is not readily defined in the gamut of the first law, since their output do not involve any thermodynamic work. Performance criteria for such components are defined in a way which can easily be translated to the overall influence of the cycle input and output, and can be used to assess performances under different operating conditions. A performance calculation software has been developed that computes the energy and exergy flows using thermodynamic property values with the real time operation parameters at the terminal points of each system/equipment and evaluates the relevant rational performance parameters for them. Exergy-based analysis of the turbine cycle under different strategic conditions with different degrees of superheat and reheat sprays exhibit the extent of performance deterioration of the major equipment and its impact to the overall cycle efficiency. For example, during a unit operation with attemperation flow, a traditional energy analysis alone would wrongly indicate an improved thermal performance of HP heater 5, since the feed water temperature rise across it increases. However, the actual performance degradation is reflected as an exergy analysis indicates an increased exergy destruction within the HP heater 5 under reheat spray. These results corroborate to the deterioration of overall cycle efficiency and rightly assist operational optimization. The exergy-based analysis is found to offer a more direct tool for evaluating the commercial implication of the off-design operation of an individual component of a turbine cycle. The exergy destruction is also translated in terms of its environmental impact, since the irretrievable loss of useful work eventually leads to thermal pollution. The technique can be effectively used by practicing engineers in order to improve efficiency by reducing the avoidable exergy destruction, directly assisting the saving of energy resources and decreasing environmental pollution.

This paper presents the implementation of an integrated solar combined cycle (ISCC) on the existing 44 MW Cameo Power Generating Station, located in Palisade, Colorado. The plant was originally built in 1957 as a coal fired power plant, to serve the Grand Junction community. This plant has been chosen to demonstrate the viability of the ISCC because of its time line to decommissioning and the availability of additional power from nearby stations to fulfill the community’s needs. The solar system at Cameo utilizes 8 aluminum parabolic trough collectors arranged in 4 loops. Each of these collectors is approximately 150 meters long and 5.77 meters wide. The hot heat transfer fluid used in the solar field is sent to a solar feed water heater, located in between two of the existing feed water heaters, to supplement the thermal energy required by the steam cycle. At design conditions, the solar field will provide 4 MW of thermal energy to the power plant. The development of this ISCC has faced several design and construction challenges not common in traditional power plant and solar power plant design. When first constructed, the Cameo station had no provisions made regarding solar field location, heat transfer fluid piping runs, heat transfer fluid pumping station, thermal expansion vessels, the addition of solar thermal energy to the feed water system, and the integration of a solar field control system into the existing plant distributed control system. Also unaccounted for are the affects the integration of a solar feed water heater has on the thermodynamic efficiency of the steam cycle. This paper discusses these challenges, as well as their resolution, as seen during the engineering, procurement, construction, and commissioning phases of this project. The Cameo Power Generating Station is located in the DeBeque Canyon, 4 miles east of Palisade, Colorado along the Colorado River and Interstate 70. The solar feed water heating demonstration will be in operation for 1 to 2 years, at the discretion of Xcel Energy, to test and develop operating and maintenance methods for large scale application. After such time, both the plant and the solar field will be decommissioned. After decommissioning all applicable solar field equipment shall be refurbished and utilized at additional testing facilities.