Shams uses parabolic trough technology to convert solar irradiation into solar heat, which is fed into a steam turbine to provide power generation.

The steam exiting the steam turbine is condensed with an air-cooled condenser.

The solar field is a modular distributed system of solar collector assemblies (SCAs) connected in parallel via a system of insulated pipes. Cold heat transfer fluid (HTF) flows at approximately 280°C-300°C from the steam generator into a cold HTF header that distributes it to 192 loops of SCAs in the solar field. Each loop consists of four SCAs. HTF is heated in the loop and enters the hot header, which returns hot HTF from all loops to the solar steam generator. The HTF enters the solar field at 280°C-300°C and leaves the field at 400°C.

The SCAs collect heat via a trough of parabolic mirrors, which focus sunlight onto a line of heat collection elements (HCE), welded in line at the focus of the parabola. The mirror-HCE trough is mounted on a mechanical support system that includes steel pylons and bearings. Single-axis tracking of the sun ensures best use of sunlight.

The absorber tubes are contained within the HCE and serve to convert solar irradiation to heat. A dual-fuel fired HTF heater (gas or diesel) is used in the HTF loop to provide the required thermal energy during cloud cover or low-solar insolation to avoid shut down of the steam turbine and ensure Shams is capable of producing its 100MW capacity power output.

In the solar steam generator, the HTF generates steam with a temperature of approximately 380°C. To enhance the efficiency of the steam turbine, the steam is further heated in a dual-fuel fired booster heater to a temperature of 540°C. The superheated steam is supplied to the condensing steam turbine, which generates power. An air-cooled condenser is used to condense the exhaust steam flow coming from the steam turbine. The condensate is then returned to the solar steam generator.

CSP Configurations

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Components of Parabolic Trough Solar Field

  • Mirrors: One of the most important components of the parabolic solar field are the mirrors due to their high reflective properties, which allow to reflect a considerable fraction of the incident radiation. Most of the common parabolic trough mirrors are silver coated glass mirrors.
  • Absorber Tubes: The absorber tubes or Heat Collection Elements (HCEs) allows to absorb part of the reflected energy by the mirrors due to their high radiation absorption and low radiative heat losses. The diameter of the absorber tubes needs to be sufficient to reach a high intercept factor without being too big in order to maintain low thermal losses. The intercept factor is the ratio of the total reflected radiation to the reflected radiation that hits the absorber surface.
  • Hydraulic Drives Units: The hydraulic drives units allows the movement of the solar collector assemblies to track the sun along the day. The drive unit consists of two cylinders, which are controlled by two valves, determining the direction of rotation.
  • Ball Joints: The ball joints are used to connect the HTF piping from the loops to the main headers, and in the crossover piping between adjacent rows of the collectors. These connections absorb the thermal expansion of the collector tube that extends the length of the collectors, and allow the collectors to rotate from the stowed position and rotate to track the sun during operation.
  • Bearing Structure: The bearing structure of a parabolic trough has the function to carry the mirrors in the right position, to give stability to the troughs and to allow an exact Sun tracking. This structure consists of a main body, which in most cases is a space frame or tube structure made out of steel. Further elements of the bearing structure are the mirror support points on the space frame structure or on special cantilever arms, the receiver supports or heat collection element (HCE) supports, the structure for the mounting to the pylons, the pylons, among them drive pylons, and foundations.

Main Characteristics of the HTF Main Pumps

  • The HTF main pumps are horizontal centrifugal pumps designed to circulate thermal oil at high temperatures.
  • The pumps are designed to withstand outdoor conditions.
  • The pumps are equipped with variable speed drives to adapt the flow requirement for the parabolic trough solar field.
  • The pumps are physically and functionally identical and are connected in parallel. One of them is installed as standby.
  • The materials used for the pumps is corrosion and erosion resistant, in line with operation conditions.

Main Characteristics of the Expansion System

  • The Expansion System is composed by an Expansion Tank and several Overflow Tanks. The Expansion Tank is always located above the Overflow Tanks and in a high position.
  • The Expansion System is inverted and pressurized by the use of nitrogen allowing to maintain the pressure of the thermal oil above the boiling pressure in the complete HTF system.
  • The operation of the Expansion System consists:
    • When the HTF level in the Expansion Tank decreases below a safety value, the overflow recirculation pumps are activated allowing to increase the level of this tank from the thermal oil stored in the Overflow Tanks. Compensation of the HTF Contraction due to a decrease of the HTF Temperature.
    • When the HTF level in the Expansion Tank increases above a safety value, a dedicated valve is opened to allow storing part of the thermal oil in the Overflow Tanks. Compensation of the HTF Expansion due to an increase of the HTF Temperature.
    • The venting of thermal oil vapours and nitrogen out of the Expansion and Overflow Tanks are conducted to the Ullage System.
  • This system also allows the HTF make-ups by a dedicated line.

Main Characteristics of the HTF Heaters

  • There are seven (7) HTF heaters installed in Shams Power Plant, which use natural gas as fuel.
  • Each HTF heater has an internal recirculation in order to increase the temperature before sending the thermal oil to the parabolic trough solar field.
  • The HTF heaters are foreseen to be used during operation periods or outage periods in which the weather conditions do not allow to maintain the HTF temperature in the solar field only by recirculation mode above the freezing value.

Main Characteristics of the Steam Generator System

  • There are two steam generation trains installed and working in parallel at 50% load each of them.
  • Each steam generation train is composed by:
    • 1 Economizer
    • 1 Drum
    • 2 Evaporators
    • 1 Superheater
  • The main characteristics of this system is to produce high pressure superheated steam and to send it to the High Pressure body of the Steam Turbine, where its first expansion is produced. HTF is used as the hot fluid.
  • The Economizer heats the feed water from the Feed water Preheaters outlet temperature up to the Evaporator saturation temperature (nearly). The HTF circulates through the shell and the Water through the tubes side.
  • The water to steam phase change is produced in the Evaporator and Drum being the water / steam circulating through the shell side and the HTF circulates through the tubes side in this equipment.
  • The Superheater overheats the steam from the saturation temperature to the design superheated temperature and is sent to the Booster Heaters before entering into the Steam Turbine. In this case, the HTF circulates through the shell side and the steam circulates through the tubes side.

Main Characteristics of the Booster Heaters

  • There are two Booster Heaters which use natural gas as fuel.
  • Each Booster Heater allow to increase the steam temperature from 376 degC to 540 degC. The mass flow manages by each equipment is 50% of the total mass flow provided by the Steam Generator System.
  • The main parts of each Booster Heater are:
    • For the Steam, the Radiant and Convective zones.
    • For the air, the combustion air preheater, which allows improving the combustion.
  • The main control loop is a outlet temperature control. Additionally, the ratio air/fuel is controlled to get the maximum efficiency and lower emissions.

Main Characteristics of the Steam Turbine

  • The Steam Turbine Generator Unit consists of:
    • A Turbine High Pressure module
    • A Turbine Low Pressure module
    • Main Steam Connections
    • Six steam bleedings
    • Emergency Stop Valve
    • Control Valve
    • Gland Steam System
    • Gland Steam System
    • Lubrication oil system
    • Control oil system
    • Electrical Generator
    • Casing
  • Basic Steam Rankine Cycle.
  • The Live Steam Temperature and Pressure of Shams Power Plant Steam Turbine is 540 degC and 100 bara.
  • The Steam Turbine Generator and auxiliary systems has been designed and fabricated considering the operational conditions of this plant, among others, cyclic operation and quick up start-ups minimizing the time for start-up and changing operation mode.
  • Maintaining the water/steam parameters within the allowable range recommended by the manufacturer is vital for the lifetime of the turbine.
  • The regulation systems can be “Throttle control” or “ Sliding Pressure”.

Main Characteristics of the Air Cooled Condenser

  • The Air Cooled Condenser is mainly composed by:
    • One steam duct including risers elements, drain pot, upper steam manifolds for distribution of the steam in the fin tube bundles, rupture discs among other components.
    • Every module of the Air Cooled Condenser includes finned tube bundles, fans, motors among other components.
    • ACC Drainage pumps
    • Condensate Tank
    • A vacuum system
  • This system is designed to safely receive and condense any steam flow from the turbine, bypass system or drainage from other pipelines at high pressures.
  • This dry-cooling system allows to save a considerable amount of water in comparison with a cooling tower system.
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