GB/T 41087-2021Technical specification for heat exchange system of solar thermal power plant (English PDF)

3.1 Heat exchange system

It consists of a series of equipment and its accessories for heat exchange between heat transfer medium and working medium or heat storage medium.

NOTE: It mainly includes steam generation system and oil-salt heat exchanger system.

3.2 Oil-salt heat exchanger

A device for heat exchange between molten salt medium and thermal oil medium.

3.3 Preheater

4.2 Basic parameters

4.2.1 The basic parameters of design input mainly include the following:

a) Operating parameters: including flow, temperature, pressure, heat load;

b) Physical parameters: including medium composition, density, specific heat capacity or enthalpy, vapor partial pressure, viscosity, thermal conductivity;

c) Allowable pressure drop;

d) System operation mode: including the number of starts and stops, the frequency of load changes under various working conditions of the power plant;

e) Others.

4.2.2 The system and equipment life shall not be less than 25 years.

4.2.3 The system design pressure shall not be lower than the maximum working pressure that may be reached during operation.

4.2.4 The system design temperature is not lower than the maximum operating temperature that can be reached during operation.

4.2.5 The number of starts and stops of the heat exchange system of solar thermal power generation can be performed as follows. The specific times shall be comprehensively determined according to the operating characteristics of the power plant:

a) Cold start (stop over 72h) 10 times/year (24 times/year during commissioning);

b) Warm start (stop between 10h~72h) 250 times/year (320 times/year during commissioning);

c) Hot start (stop time is between 1h~10h) 300 times/year (400 times/year during commissioning);

d) Extremely hot start (within 1h of unit shutdown) 50 times/year (100 times/year during commissioning);

e) Load step (load change value per minute > 10% of nameplate power) 15750 times / 25 years.

4.2.6 The temperature rise rate of the heat exchange system of solar thermal power generation shall meet the operation requirements of the power station. On the premise of ensuring the safe operation of the system and equipment, the temperature rise rate of the heat exchange system of the tower solar thermal power plant shall not be lower than 6°C/min. The temperature rise rate of the heat exchange system of the trough solar thermal power plant shall not be lower than 8°C/min.

6.1 General requirements

6.1.1 The rated evaporation of the steam generation system shall match the rated working conditions of the steam turbine. The maximum continuous evaporation shall match the full open condition of the steam turbine valve. At the same time, the variable working characteristics of the system shall be considered.

6.1.2 The rated working condition of the oil-salt heat exchanger system shall match the rated working condition of the steam turbine.

6.1.3 The thermal efficiency of the system under the design conditions of the heat exchange system shall not be less than 98%.

6.1.4 The main steam temperature of the steam generation system shall meet the requirements of the rated working conditions of the steam turbine.

6.1.5 The total pressure drop of the heat exchange system under the rated working conditions of the steam turbine shall meet the requirements of Table 1.

6.2.2 Molten salt side

6.2.2.1 Molten salt shall comply with the provisions of GB/T 36376.

6.2.2.2 The design of molten salt equipment and pipelines shall adopt a certain inclination angle for self-flow evacuation.

6.2.2.3 When designing the system, a certain height difference shall be set between each molten salt heat exchanger.

6.2.2.4 Under all operating conditions, the final return salt temperature in the system shall not be lower than the crystallization temperature of molten salt plus 15°C.

6.2.2.5 The gasket on the molten salt side shall not be made of graphite.

6.2.2.6 The sewage and exhaust of pipes and equipment shall be considered when designing the system.

6.2.2.7 A complete evacuation salt system shall be equipped when designing the system.

6.2.3 Thermal oil side

6.2.3.1 The thermal oil shall meet the requirements of GB 23971.

6.2.3.2 The final return oil temperature in the system shall not be lower than the crystallization point temperature of thermal oil plus 50°C.

6.2.3.3 The sewage and exhaust of pipes and equipment shall be considered when designing the system.

6.2.3.4 When the use temperature of the thermal oil exceeds its ignition point, the fire safety of the system, equipment and site shall be considered. The system design shall comply with the provisions of GB 50016 and GB 50974.

6.2.3.5 A complete oil evacuation system shall be equipped when designing the system.

6.2.3.6 When the thermal oil leaks, the leaked thermal oil shall be collected and disposed of in time.

6.3 Oil-salt heat exchanger system

6.3.1 The oil-salt heat exchange system shall meet the heat exchange requirements of both heat storage and heat release conditions.

6.3.2 The oil-salt heat exchange system shall take the heat storage condition as the design condition, the exothermic condition as the check condition.

6.3.3 The temperature of the thermal oil entering the oil-salt heat exchanger shall not be lower than the crystallization temperature of the molten salt plus 20°C.

6.3.4 The molten salt side in the oil-salt heat exchange system shall meet the requirements in 6.2.2.

6.3.5 The thermal oil side in the oil-salt heat exchange system shall meet the requirements in 6.2.3.

6.4 Heat exchanger

6.4.1 The heat exchanger of the heat exchange system mainly includes: oil-salt heat exchanger, thermal oil/steam-water heat exchanger and molten salt/steam-water heat exchanger.

6.4.2 The technical requirements of the heat exchanger shall comply with the provisions of TSG 21 and GB/T 151.

6.4.3 The type and capacity of the heat exchanger shall be comprehensively and optimally determined according to factors such as system load, operating characteristics, manufacturing capacity, transportation conditions, site layout and installation requirements.

6.4.4 The heat exchanger shall be able to operate stably under normal working conditions and meet the performance requirements under various working conditions.

6.4.5 The structural design of the heat exchanger shall consider the convenience of maintenance and pipe blocking.

6.4.6 The molten salt heat exchanger shall be horizontal. At the same time, the complete emptying of the molten salt medium under the action of gravity shall be ensured. Eliminate the dead zone of salt discharge.

6.4.7 The shell-and-tube medium of the heat exchange equipment of the steam

6.6 Valve and instrument control

6.6.1 The valve shall comply with the regulations of NB/T 47044.

6.6.2 Instrument control requirements shall comply with the provisions of GB/T 51307 and HG/T 20507.

6.6.3 The valve actuator on the thermal oil side shall meet the explosion-proof design requirements.

6.6.4 The design of thermal oil and molten salt valve body shall avoid the occurrence of residual medium.

6.6.5 The influence of thermal oil and molten salt medium on valve sealing shall be considered.

6.6.6 For molten salt side shut-off valve above DN100, butterfly valve shall be used.

6.6.7 The regulating performance of the regulating valve shall meet the system operation requirements.

6.7 Electric heater

6.7.1 The molten salt steam generation system shall be equipped with a start-up electric heater.

6.7.2 The power of the electric heater shall meet the requirements of the heating rate of the water supply in the system piping and equipment.

6.7.3 Electric heaters shall be designed in groups.

6.8 Pump

6.8.1 The steam generation system shall be equipped with a start-up circulation pump or a recirculation pump.

6.8.2 The circulating pump shall comply with the provisions of GB/T 5657.

6.8.3 The forced circulation pump motor shall adopt a water-immersed seal. Set up the cooling system.

6.9 Pipeline

6.9.1 The design of the steam-water pipeline shall comply with the provisions of GB 50764 and DL/T 5054.

6.9.2 The design of the thermal oil pipeline shall comply with the provisions of GB/T 20801 (all parts) and GB/T 24259.

6.9.3 The design of the molten salt pipeline shall comply with the provisions of GB/T 20801 (all parts) and HG/T 20549.

6.9.4 The design of the pipe support and hanger shall comply with the provisions of GB/T 17116 (all parts) and SH/T 3073.

6.9.5 The design of the pipeline shall meet the needs of thermal stability and safe displacement of the pipeline.

6.9.6 The molten salt pipeline shall adopt the heat-insulating support hanger pipe clamp.

6.9.7 Pipes shall be connected by butt welding.

6.10 Anti-condensation requirements

6.10.1 The heat exchange system shall adopt anti-condensation measures of electric heat tracing or steam tracing.

6.10.2 Electric heat tracing shall comply with the provisions of GB/T 32348 (all parts) and GB/T 19518 (all parts). Steam tracing shall comply with the provisions of SH/T 3040.

6.10.3 All equipment, valves and pipelines through which molten salt flows on the molten salt side shall take anti-condensation measures.

6.10.4 Anti-condensation measures shall be provided for thermal oil pipelines with a risk of solidification.

6.10.5 The equipment, valves and pipelines in the system shall adopt a segmented heat tracing system.

6.10.6 Each electric heat tracing branch circuit shall be provided with electrostatic grounding and shall comply with the provisions of GB 12158 and SH/T 3097. […]