A DIRECT STEAM GENERATION SOLAR POWER PLANT WITH INTEGRATED

THERMAL STORAGE

Guided by : Presented by :Mr.Daniel C.Ribu Akshay ss kumar Asso. Prof. S7 ME-AME Dept. Roll no:33LMCST Lourdes Matha College of Science and Technology kuttichal thiruvananthapuram

Rankine cycle

The Rankine cycle is a model that is used to predict the performance of steam turbine systems.The Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into mechanical work.

The four processes in the Rankine cycle

Process 1-2: The working fluid is pumped from low to high pressureProcess 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapour

Process 3-4: The dry saturated vapour expands through a turbine generating power. This decreases the temperature and pressure of the vapour, and some condensation may occur

Process 4-1: The wet vapour then enters a condenser where it is condensed at a constant pressure to become a saturated liquid.

INTRODUCTION

THERMAL STORAGE SYSTEM

solar-thermal power plants are one of the key technologies for production of electricity from renewable energy resource. It is a system which helps to store thermal energy in excess for later use.Solar energy in summer can be stored for use in winter.In parabolic trough collector row oil as a heat transfer fluid is heated by concentrated solar irradiation.

Parabolic Trough collector.

It is a type of solar thermal collector that is straight in one dimension and curved as a parabola in other two, lined with a polished metal mirror.The solar energy which enters the mirror parallel to its plane of symmetry is focused along the focal line where object is positioned to heat.Usually a parabolic trough collector generates thermal energy which is consumed by a heat absorbing medium(oil).

working.

Figure shows the working principle of the TROUGH collector at the Platform Solar. By tracking the sun from sunrise to sunset, the parabolic Trough collectors concentrate the sun’s radiation with their parabolic mirror facets on the absorber tubes along their focal line. Through these absorber tube circulates a heat transfer fluid (HTF), usually synthetic oil, which is heated to a temperature of nearly 395°C.

This heat absorbing oil transfer heat to water for producing steam in a heat exchanger to accomplish power generation from a steam cycle.

But these heat absorbing oil is only capable of absorbing heat up to a temp of 395°C due to chemical stability, therefore main steam temp is limited.

Since the performance of thermal cycle depends on the steam parameters some alternatives should be tested and a direct steam generation solar power plant with a thermal storage is an example.

Phase change material (pcm)Basically salts are used as pcmMolten salts can are used for storing heat at high temp.Potassium nitrate, calcium nitrate, etc are example for such salts..Sodium nirate is an interesting salt with a melting point of 306°C .A 10°C temp difference is assuming as a driving force btw storage and steam.

Therefore the steam has to condense at 316°C during charging and evaporate at 296°C discharging.

From steam tables, the pressure corresponding to the saturation temp is 316°C is 107 bar and 296°C is 81 bar.

It reveals that higher operating pressure is required during charging and then discharging.

Another pcm pottasium nitrate which result in a steam pressure of 156bar for charging and 116bar for discharging

ANALYSIS OF PLANT CONFIGURATION.

Three section of heating takes places

1. Preheating

2.Evaporation

3.Superheating

For preheating and super heating, sensible heat storage system is used and for evaporation, latent heat storage system is used.

Both system uses a salt

During charging ,the salt has to melt to a constant ,material dependent temp and during discharging it will back to freezed position.

For a solar thermal power plant a thermal storage system allow a higher utilization of the power block and to produce electricity on demand

The solar field is operated in recirculation mode with a phase separator between pre-heating, evaporation and superheating sections.

An injection cooler is placed before the last collection of each row to stabilize the steam temperature.

The steam feed the high- pressure turbine(HP),is re-heated and directed through the low-pressure turbine(LP).

The thermal storage system is arranged similar to the solar field with a sensible heat storage system for pre-heating and superheating and a latent heat storage system based on a pcm for evaporation and a sensible heat storage system for superheating.

For charging ,steam from the solar field is directed through the storage system in reverse direction.

The steam is cooled down in the superheating section, condensed in the evaporation section and cooled down to pre-heating section.

The condensate water is mixed with the feed water from the power block and it feed in to the solar field.

The plant configuration cycle sub dived in to three cycles

The plant configuration cycle sub dived in to three cycles

Evaporator

Pre-heating

Superheater

Superheater

Evaporator

Pre-heating

Solar fieldThermal storage system

CHARGING

.

Evaporator

Pre-heating

Superheater

Turbine

Condenser

Pump

Thermal storage system Power block

DISCHARGING

.

Evaporator

Pre-heating

Superheater

Turbine

Condenser

Pump

Solar field Power block

Advantages of the DSG technology:

Smaller environmental risks because oil is replaced by water.Higher steam temperature (maximum steam temperature with oil = 395C)The overall plant configuration is more simpleLower investment and higher plant efficiency

Disadvantages of the DSG technology:

Solar field control under solar radiation transients.

Instability of the two-phase flow inside the receiver tubes

CONCLUSIONS The integration of a thermal storage system increases the complexity of a direct steam generation solar power plant.The usage of a pcm storage system for the evaporation of water implies that the pressure for discharge is significantly lower than the pressure level required for charging.A reheat system is necessary to avoid high moisture content in the low pressure turbine.The work presented demonstrated that there are significant differences in the plant layout of a parabolic trough power plant with direct steam generation compared to a plant with indirect steam generation.

REFERENCES1 Eck, M.; Hennecke, K.: Heat transfer fluids for future parabolic trough solar

thermal power plants. In:Goswami, D. Yogi; Zhao, Yuwen [Ed.]: ISES Solar World Congress 2007, ISES Solar

World Congress, Beijing(China), S. 1806 - 1812.

2 Benz N.: Next generation receivers, NREL Trough Work Shop, March 7-8, Golden,http://www.nrel.gov/csp/troughnet/wkshp_2007.html (2007).

3 Zarza, E.; Valenzuela, L.; León, J.; Hennecke, K.; Eck, M.; Weyers, H.-D.; Eickhoff, M.: Direct Steam

Generation in Parabolic Troughs - Final Results and Conclusions of the DISS Project, Energy, Vol. 29 (2004),

pp. 635-644.4 Nava, P.; Hermann, U.: Trough Thermal Storage - Status Spring 2007, NREL

Trough Work Shop, March 7-8,Golden, http://www.nrel.gov/csp/troughnet/wkshp_2007.html (2007).

5 Steinmann, W.-D.; Tamme, R.: Latent heat storage for solar steam systems, 13th International Symposium on

Concentrated Solar Power and Chemical Energy Technologies, June 20-23 (2006) Seville, Spain.

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