Kairu Li, Shen Guo, Jacek Wojcik, Jihong Wang

26/11/2014

Feasibility Study of Integration of a Power Plant Steam Cycle with Thermal Energy Storage

Outline

1. Background

2. Investigation of implementation strategy

3. Simulation study

4. Summary

1. Background

Geothermal power plants

Hydroelectric power plants

Wind power plants

Biomass power plants Fossil-fuelled power plants

Nuclear power plants

Power generation from fossil to multiple energy sources.

The role of traditional thermal power plants is changing!

Fossil-fuelled power plants

%

Solar power plants

1. Background

Flexible

• The charging and discharging process of thermal energy is quicker than tuning the fuel (e.g. coal) supply

Efficient

• The higher load level is, the more efficient the power plant is.

• Energy saving

Economical

• To retrofit based on existed power plants

• Less investment in peaking power plants

Thermal Energy Storage (TES) may help to make a power plant more:

2. Investigation of implementation strategy

Two principles:

Maintain the stability of the generation process Minimize the impact on the power plant

Keeping power plants running at full load state (higher efficiency) as long as possible

Following the demand by extracting steam from power generation system

Storing the thermal energy of extracted steam in Thermal Energy Storage for later use (charging process)

Releasing the stored thermal energy for peak time generation or other uses (eg. heating) (discharging process)

2. Investigation of implementation strategy

Boiler Section： React slowly,

complicated

Turbine Section: React quickly

• Is it possible to extract steam from the plant operation process?

• Which stage of the turbines (HP, IP or LP) should be connected for thermal energy extraction?

• In which way and where, can the thermal energy stored be fed back to the power plant process?

• How will the plant operation and dynamic performance be influenced?

……

2. Investigation of implementation strategy

3. Simulation study

Simulator

Tested by thousands of data from real power plant operation process

A commercial software for training staff working at power station

“A power plant in a laptop”

(1) Feasibility study:

Is it possible to extract steam out? First, try to extract steam from Intermediate Pressure Turbine (IP turbine) and see its impact on the power generation system.

(1) Feasibility study:

(a)Auto mode (b) Manual mode (c) Adding steam back

Feasibility? Yes! Adding steam/ water back is necessary to maintain the

balance of power generation process.

Extracting steam from Intermediate Pressure Turbine (IP turbine)

(2) Where to add steam/ water back

In which way and where to feed steam/ water back to the process? • Turbine part (Low Pressure turbine, LP turbine) • Out of turbine part (Deaerator)

(a)At LPTB (Low Pressure Turbine) (steam) (b)At Deaerator (water)

• Extracting at most 20% of steam (due to the mechanical limit of turbine)

• The lowest output power is about 580MW

• Extracting at most 10% of steam (if extracting more steam, the transient time of response is too long, up to 180min)

• Control method will be applied to extract more steam, and then the output power can be tuned in a larger range.

(2) Where to add steam/ water back

(3) Where is the most suitable location to extract steam? Which stage of the turbines (HP, IP or LP) should be connected to

thermal energy extraction? • Intermediate Pressure Turbine (IP turbine) • Low Pressure turbine (LP turbine)

(3) Where is the most suitable location to extract steam?

(a)At IPTB (Intermediate Pressure Turbine)

• IEV0: the valve used to extract steam from IPTB

• IEV0 opening = 0.1, 10% steam

Adding water back into deaerator

(b)At LPTB (Low Pressure Turbine)

• IEV6: the valve used to extract steam from LPTB

• IEV6 opening = 0.5, 15% steam

Considering the adjusting range of output power and the future discharging process of thermal energy, IPTB is a better choice to extract steam.

(4) Efficiency

The efficiency η can be calculated by:

𝜂 =𝐸𝐸+𝑇𝐸

𝐻𝐸𝐶𝑜𝑎𝑙*100%

where E is the power of output electricity, T represents the energy stored in Thermal Energy Storage (TES) and H is the energy contained in coal before combustion.

The energy stored in TES can be calculated by:

𝑇𝐸 = 𝐻𝑖 − 𝐻𝑜 ∙ 𝑤 ∙ 𝑡 where 𝐻𝑖 and 𝐻𝑜 are the specific enthalpies of inlet and outlet stream of TES, 𝑤 is the mass flow rate of extracted steam, and t is the time.

The energy loss in TES is ignored in calculation. The energy used to maintain the operation of TES system is unknown, so this part of energy

consumption is not considered when calculating the efficiency.

(4) Efficiency

• Adding steam back into Low Pressure Turbine (LPTB) Strategy A

• Adding water back into Deaerator (calculated by the steam condition of LPTB) Strategy B

• Adding water back into Deaerator (calculated by the water condition of D) Strategy C

• Extracting steam from Intermediate Pressure Turbine (IPTB)

• The coal consumption keeps constant as the level of running at 600MW

Taking extracting 10% steam (45kg/s) to Thermal Energy Storage for example:

(a) Strategy A

(b) Strategy B

Output power: 590.27MW Stored thermal energy: 18.43MW

Output power=608.70MW>600MW η= 45.31%>44.66%

Output power=597.83MW<600MW η= 44.50%<44.66%

Output power=687.08MW>600MW η= 51.16%>44.66%

Output power: 551.69MW Stored thermal energy: 46.14MW

Is it feasible for the TES?

(4) Efficiency

(C) Strategy C

Output power: 551.69MW Stored thermal energy: 135.39MW

Summary

• It is feasible to extracting steam from the power generation process for Thermal energy Storage (TES).

• Adding steam back into the system is necessary to keep the balance of

power generation process.

• Extracting steam from Intermediate Pressure Turbine (IPTB) and adding them back into Deaerator can adjust the output power in a larger range than extracting or adding steam at Low Pressure Turbine (LPTB).

• In order to enlarge the range of output power’s variation, proper control method is expected to be applied to the integrating system.

The integrating system is expected to help power plant run more flexibly and more efficiently. Storing thermal energy at off-peak time and reusing it at peak time will avoid excessive infrastructure investment for peaking power plants.

Thank you!