VGB POWERTECH 10 (2019)

A
VGB
journey
PowerTech
through
1/2
100
l 2013
years VGB | VGB POWERTECH 1/2 (2013)
Heat storage systems
solar energy
generation
of power
e.g. CCPP
steam charging
steam
steam discharging
electrolysis
wind energy
methanation
gas
network
generation
of heat
isolated
pressure
vessel
water
gas tank
charging / discharging water
Fig. 4. Power to gas concept.
stated earlier, this paper will focus on the
large-scale systems for heat storage in connection
with heat and power generation
plants.
Thermal energy storage systems/
heat and power generation
Generally speaking, heat can be stored in
the form of thermal or chemical energy
(F i g u r e 5).
In the context of large-scale applications
in the heat and power generation industry,
however, the focus is on thermal energy
storage. The following examples are intended
to explain the basic principle.
Andasol solar power plant/
thermal storage [17]
The Andasol 1 and 2 solar thermal power
plants are located in the vicinity of Granada
in Spain. They went on line in 2008,
and 2009 respectively. Ta b l e 1 shows a
selection of technical data of these plants.
Both power plants use thermal energy
storage systems which operate on the basis
of salts. The energy storage concept is
designed to store solar energy during the
day in order to use it for power generation
at night. This way, it is possible to almost
double the annual operating hours of the
plant. F i g u r e 6 shows a simplified process
flow diagram of the Andasol power
plants.
The “dual-salt-tank system” in the centre
uses salt which is a mixture of KNO 3 and
NaNO 3 . There are intensive R&D activities
in many countries that focus on the
development and testing of the associated
plants and systems. Their main objective is
to optimise the storage material in order to
achieve:
– high storage capacity
– thermal stability
Table 1. Data Andasol 1 and 2.
Steam turbine
Power output
Inlet pressure
2 x SST-700
2 x 50 MW(e)
100 bar
Inlet temperature 377 °C
Fig. 7. Ruths‘ storage system.
– long lifetime
– low impact on environment and health
– non-corrosive
– cost-effective.
liquid
water
aquifer
solid object
stone
thermal energy
heat storage
solid-liquid
melting
In addition, experts are working on the advancement
and optimisation of the entire
energy storage system and its integration
into the power plant or energy supply system.
Of particular relevance in this context
are the aspects of process engineering, system
integration, energy efficiency (plant
efficiency, energy losses, etc.), the operational
long-term behaviour, as well as the
cost-benefit ratio. In summary, it must be
stated that, at the moment, thermal storage
tank systems for high temperatures
(> 300 °C) are rarely used in power plants
sensible heat latent heat heat of reaction
Fig. 5. Heat storage systems.
Solar field
510,000 m²
Heat
Transfer
NG
2-Tank salt
storage
Hot
salt
tank
Cold
salt
tank
Max
390
Fig. 6. Process flow diagram Andasol power plants.
Solar
superheater
liquid-gaseous
steam
Water Steam
Cycle ~380
Steam
generator
Solar
preheater
Solar reheater
Expansion
vessel
Deaerator
chemical energy
Steam turbine
50 MWe
Condenser
Low pressure
preheater
71
81