Energy and Exergy Analysis of Sensible Thermal Energy Storage—Hot Water Tank for a Large CHP Plant in Poland †
Abstract
:1. Introduction
2. System Description
- Collector Part—the boilers supply a common steam collector from which the steam is directed to the turbines (number of boilers—4, number of turbines—5, electrical capacity—170 MWel).
- Blocks Part—each block consists of its own boiler and its own turbine (number of blocks—3, electrical capacity—110 MWel each, heating capacity—175 MWth each).
- Condensing turbine with steam extraction (electrical capacity—125 MWe).
- Water boilers (number of boilers—6, total heating capacity—884 MWth).
3. Materials and Methods
- operation without TES,
- operation with TES—charging process,
- operation with TES—discharging process.
- Return Pumps—ηRP = 80%,
- Supply Pumps—ηSP = 82%,
- Discharging Pumps (TES pumps)—ηDP = 90%.
3.1. Energy Analysis
3.1.1. CHP Plant Operation without TES
3.1.2. CHP Plant Operation with TES—Charging Process of TES
3.1.3. CHP Plant Operation with TES—Discharging Process of TES
3.2. Exergy Analysis
- the tank insulation is 500 mm thick (glass wool), therefore heat losses to ambient air are very low,
- the storing periods are short, not usually more than a few hours,
- stratification and thermocline are observed as good and very stable.
3.2.1. CHP Plant Operation without TES
3.2.2. CHP Plant Operation with TES—Charging Process of TES
3.2.3. CHP Plant Operation with TES—Discharging Process of TES
4. Results and Discussion
5. Conclusions
- Power of the TES pumps is relatively low in relation to the power of the block and is approx. 500–800 kW, which equates to approx. 0.5–0.8% of the block electric power.
- For the lowest considered outside temperature Tex = −20 °C TES pumps power represents only 2% of pumps total power in the Blocks Part of the CHP plant.
- Differences in powers and losses of the RP and SP pumps are negligible during operation of the CHP plant without and with the TES.
- The biggest exergy destruction appears in the heat exchangers, but the differences between them for the analyzed cases, i.e., during operation of the Blocks Part of CHP plant without the TES and the charging and discharging processes of the TES, are negligible.
- Throttling losses during the charging process of the TES and exergy destruction in Discharging Pumps (TES Pumps) are also low and fluctuate in the range 120–450 kW depending on the considered case.
Author Contributions
Funding
Conflicts of Interest
Nomenclature
cp | specific heat capacity (kJ/kg·K) |
h | specific enthalpy (kJ/kg) |
m | mass (kg) |
mass flow rate (kg/s) | |
p | pressure (bar) |
heat rate (kW) | |
s | specific entropy (kJ/kg·K) |
entropy rate (kW/K) | |
T | temperature (°C or K) |
W | power (kW or MW) |
Greek letters | |
η | energy efficiency (—or %) |
exergy destruction rate (kW or MW) | |
Subscripts and superscripts | |
0 | dead state (environment) condition |
ex | external air temperature |
el | electrical |
s/c | steam/condensate |
th | thermal |
thr | throttling losses |
w | water; ′—liquid, ″—vapor states |
Abbreviations | |
CHP | Combined Heat and Power |
DHS | District Heating System |
DHP | District Heating Plant |
DP | Discharging Pump |
RP | Return Pump |
SP | Supply Pump |
TES | Thermal Energy Storage |
XA, XB | Heat Exchanger (Network Water Heater) |
DCS | Distributed Control System |
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Parameter | Value | Unit |
---|---|---|
Total volume of the tank | 30,400 | m3 |
Diameter of the tank | 30 | m |
Height of shell of the tank | 43 | m |
Radius of room dome | 45 | m |
Insulation thickness | 0.5 | m |
Charging/discharging flow rate | 1250 | kg/s |
Temperature of stored water | 98/40 | °C |
Total mass of the tank | 53,000 | kg |
Power (MW) | Block No | ||||||||
---|---|---|---|---|---|---|---|---|---|
7 | 9 | 10 | |||||||
Tex (°C) | |||||||||
−20 | 1 | 15 | −20 | 1 | 15 | −20 | 1 | 15 | |
Operation without TES | |||||||||
RP pumps | 7.9 | 1.4 | 1.2 | 8.3 | 1.4 | - | 2.5 | 1.5 | - |
XA heat exchanger | 113.6 | 103.7 | 97.6 | 117.0 | 131.0 | - | 117.3 | 94.4 | - |
XB heat exchanger | 91.4 | 89.8 | 84.9 | 58.6 | 74.0 | - | 75.3 | 96.9 | - |
SP pumps | 2.6 | 2.4 | 1.5 | 2.7 | 2.0 | - | 3.9 | 2.7 | - |
Charging process of TES | |||||||||
RP pumps | 8.1 | 1.4 | 1.2 | 8.8 | 1.2 | - | 2.6 | 1.5 | - |
XA heat exchanger | 111.2 | 108.9 | 112.5 | 125.0 | 140.5 | - | 113.6 | 101.0 | - |
XB heat exchanger | 108.9 | 94.7 | 95.1 | 68.5 | 71.0 | - | 78.4 | 91.8 | - |
SP pumps | 3.0 | 2.5 | 1.6 | 2.8 | 1.8 | - | 2.5 | 2.8 | - |
Discharging process of TES | |||||||||
RP pumps | 7.9 | 1.4 | 1.0 | 7.8 | 1.4 | - | 2.6 | 1.5 | - |
XA heat exchanger | 112.0 | 105.8 | 75.4 | 126.3 | 133.8 | - | 119.9 | 99.6 | - |
XB heat exchanger | 89.1 | 91.4 | 65.2 | 68.9 | 72.3 | - | 77.3 | 96.0 | - |
SP pumps | 3.4 | 3.4 | 1.6 | 2.6 | 2.0 | - | 2.9 | 2.9 | - |
DP pumps | 0.7 | 0.8 | 0.5 | 0.7 | 0.8 | - | 0.7 | 0.8 | - |
Exergy Destruction (MW) | Block No | ||||||||
---|---|---|---|---|---|---|---|---|---|
7 | 9 | 10 | |||||||
Tex (°C) | |||||||||
−20 | 1 | 15 | −20 | 1 | 15 | −20 | 1 | 15 | |
Operation without TES | |||||||||
RP pumps | 4.63 | 0.39 | 0.36 | 5.06 | 0.48 | - | 1.10 | 0.52 | - |
XA heat exchanger | 4.93 | 5.1 | 4.4 | 1.04 | 8.9 | - | 6.97 | 7.09 | - |
XB heat exchanger | 1.96 | 2.48 | 2.13 | 1.56 | 2.85 | - | 1.77 | 3.95 | - |
SP pumps | 0.65 | 0.60 | 0.73 | 0.67 | 0.20 | - | 1.22 | 0.48 | - |
Charging process of TES | |||||||||
RP pumps | 4.80 | 0.38 | 0.44 | 5.56 | 0.46 | - | 1.10 | 0.48 | - |
XA heat exchanger | 4.93 | 5.33 | 5.04 | 1.27 | 9.08 | - | 6.97 | 7.78 | - |
XB heat exchanger | 2.28 | 2.82 | 2.33 | 1.87 | 2.33 | - | 1.77 | 3.57 | - |
SP pumps | 0.87 | 0.49 | 0.68 | 0.83 | 0.37 | - | 1.22 | 0.84 | - |
Discharging process of TES | |||||||||
RP pumps | 4.66 | 0.39 | 0.35 | 4.65 | 0.48 | - | 1.22 | 0.49 | - |
XA heat exchanger | 5.10 | 5.30 | 3.69 | 1.27 | 8.76 | - | 7.50 | 8.56 | - |
XB heat exchanger | 2.36 | 2.74 | 1.87 | 0.95 | 2.59 | - | 1.77 | 3.72 | - |
SP pumps | 0.65 | 0.87 | 0.69 | 0.58 | 0.20 | - | 1.22 | 0.80 | - |
Exergy Destruction (MW) | Tex (°C) | ||
---|---|---|---|
−20 | +1 | +15 | |
Charging process of TES | |||
Throttling losses | 0.32 | 0.16 | 0.45 |
TES charging process | 0.12 | 0.12 | 0.12 |
Discharging process of TES | |||
DP pumps | 0.15 | 0.15 | 0.13 |
TES discharging process | 0.15 | 0.24 | 0.16 |
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Zwierzchowski, R.; Wołowicz, M. Energy and Exergy Analysis of Sensible Thermal Energy Storage—Hot Water Tank for a Large CHP Plant in Poland. Energies 2020, 13, 4842. https://doi.org/10.3390/en13184842
Zwierzchowski R, Wołowicz M. Energy and Exergy Analysis of Sensible Thermal Energy Storage—Hot Water Tank for a Large CHP Plant in Poland. Energies. 2020; 13(18):4842. https://doi.org/10.3390/en13184842
Chicago/Turabian StyleZwierzchowski, Ryszard, and Marcin Wołowicz. 2020. "Energy and Exergy Analysis of Sensible Thermal Energy Storage—Hot Water Tank for a Large CHP Plant in Poland" Energies 13, no. 18: 4842. https://doi.org/10.3390/en13184842