Numerical study on dynamic performance of low temperature recuperator in a S-CO₂ Brayton cycle

Figures & data

Figure 1. The reheat and recompression arrangement of S-CO₂ Brayton cycle.

Figure 2. Temperature-entropy diagram of a reheat and recompression S-CO₂ Brayton cycle.

Table 1. Design parameters of the base cycle [26].

Parameter	Unit	Value
Output power	MWe	600
Mass flow rate of S-CO2	kg·s^−1	4160.79
HPT inlet pressure	MPa	32.70
HPT inlet temperature	°C	600
HPT out pressure	MPa	15.85
LPT inlet temperature	°C	620.00
MC inlet pressure	MPa	7.60
MC inlet temperature	°C	32.00
HTR pinch temperature	°C	5.00
LTR pinch temperature	°C	5.00
Recompression split ratio	–	0.318
CO2 physical properties	–	NIST REFPROP

Figure 3. S-CO₂ recompression Brayton dynamic simulation system.

Table 2. Geometrical parameters of the HTR and LTR [26].

Parameters	Unit	Values of HTR	Values of LTR
Length of PCHE	m	4.9	5.76
Width of PCHE	m	6	6
Height of PCHE	m	12	6
Diameter of semicircular channel	mm	2	2
Thickness of cold side	mm	3	2.5
Thickness of hot side	mm	2.5	2.5
Heat transfer area	m^2	129238.6	86950.0

Figure 4. Segmented model for PCHE with semicircular channels.

Figure 5. Compressor characteristics curves: (a) relative compression ratio; (b) relative efficiency.

Figure 6. Turbine characteristics curves: (a) relative expansion ratio; (b) relative efficiency.

Figure 7. Pressure and split ratio control schemes.

Figure 8. Temperature profiles on the cold- and hot-side, and temperature difference in the PCHE.

Table 3. Comparison of the calculation results and literature data of S-CO₂ cycle [26].

Parameters	Calculated values	Literature Values	Deviation/%
Boiler output heat/MW	1163.56	1147.22	1.42
HTR duty/MW	1432.38	1403.03	2.1
LTR duty/MW	741.47	734.33	0.97
PC duty/MW	564.25	547.23	3.11
Power generation efficiency/%	48.73	49.48	−1.516

Figure 9. Comparison in the relative turbine efficiency variation with relative rotating speed.

Figure 10. Fluctuations of mass flow (a) and pressure (b) following with set values.

Figure 11. Variations of the S-CO₂ Brayton cycle load under different inventory withdraw-mass.

Figure 12. The effects of withdraw-mass from cycle to inventory vessel.

Table 4. Parameters in the cycle in different off-design conditions.

Withdraw-mass	$\dot{m}$h,in of HTR	$\dot{m}$h,in of LTR	Th,in of HTR	Th,in of LTR	Th,in of PC	pin of MT	pin of RT
/kg	/kg·s^−1	/kg·s^−1	/°C	/°C	/°C	/MPa	/MPa
0	4356.64	2971.23	529.58	234.26	92.03	32.581	15.727
2000	3987.89	2719.74	537.49	205.75	83.65	28.724	14.756
4000	3630.12	2475.74	545.63	179.44	76.44	25.266	13.827
6000	3277.71	2235.4	554.13	154.48	69.89	22.146	12.937
8000	2878.52	1963.15	564.38	128.67	63.21	18.940	11.953
10000	2513.95	1714.51	574.40	106.98	58.28	16.348	11.102
12000	2237.57	1526.02	582.44	92.23	54.35	14.597	10.491

Figure 13. Outlet temperature transient variations of cold-side (a) and hot-side (b) fluids under mass flowrate stepwise varying conditions.

Figure 14. Pinch point location transient variations under mass flowrate stepwise-varying conditions.

Figure 15. Pinch point temperature difference (a) and heat exchanger effectiveness (b) transient variations under mass flowrate stepwise-varying conditions.

Figure 16. Outlet temperature variations of cold-side (a) and hot-side (b) fluids with time under pressure stepwise-varying conditions.

Figure 17. Pinch point location variations with time under pressure stepwise-varying conditions.

Figure 18. Pinch point temperature difference (a) and heat exchanger effectiveness (b) variations with time under pressure stepwise-varying conditions.

Figure 19. Outlet temperature variation of cold-side (a) and hot-side (b) fluids with time under temperature stepwise-varying conditions.

Figure 20. Pinch point location variations with time under temperature stepwise-decreasing (a) and stepwise-increasing (b) conditions.

Figure 21. Pinch point temperature difference (a) and heat exchanger effectiveness (b) variations with time under temperature stepwise-varying conditions.

Figure 22. Comparison between the segmented model and the prediction model.

Figure 23. The variations of upper and lower CSRs with the temperature at the outlet of the precooler.

Figure 24. The upper and lower critical split ratio variation with isentropic efficiency of compressor.

Y. Zhang, H. Li, M. Yao, and Y. Wang, “Conceptual design of the recuperator and precooler for a 600MW fossil-based supercritical CO2 power generation system,” Proc. CSEE, vol. 37, no. 24, pp. 7223–7229, 2017. DOI: 10.13334/j.0258-8013.pcsee.162449.(in Chinese)

 Google Scholar