Enhancements and optimization of LNG cold energy recovery via advanced binary working fluid power cycle systems

Shing-hon Wong; Gongkui Xiao; Dongke Zhang; Shing-hon Wong; Gongkui Xiao; Dongke Zhang

doi:10.48130/een-0026-0007

Figures (11) Tables (16)

Figure 1.
A schematic of the two-stage Rankine cycle.
Figure 2.
A schematic of a basic Kalina cycle.
Figure 3.
A schematic of the basic regeneration configuration.
Figure 4.
Schematic of a basic reheating configuration.
Figure 5.
Schematic of (a) Rankine-regeneration process configuration, and (b) Rankine-reheating process configuration.
Figure 6.
Schematic of (a) Kalina-regeneration process configuration, and (b) Kalina-reheating process configuration.
Figure 7.
The genetic algorithm flowsheet.
Figure 8.
Net power output for single working fluid combinations.
Figure 9.
Txy diagram of a binary mixture.
Figure 10.
Net power output for mixed working fluids combinations.
Figure 11.
Net power output for advanced cycle configurations.

Ref.	Power cycle (s)	Working fluid (s)	Heat source	LNG flow (t·h⁻¹)	Power output (kW)	Thermal efficiency (%)
[9]	RC + DEC	Propane	Seawater	1.62	59.79	N/A
[10]	RC	Propane	Seawater	108	2,200	10
[11]	Three-stage RC	Propane	Seawater	3.6	106	12.5
[12]	Two-stage RC	Ethane, propane	Seawater	3.6	96.1	11.1
[13]	Two-stage RC	Ethane, ethylene	Seawater	N/A	N/A	N/A
[14]	RC	Ammonia-water	Waste heat	8.87	389.4	25.9
[15]	BC + RC + DEC	Nitrogen (BC), ammonia-water (RC)	Waste heat	N/A	N/A	53.1
[16]	BC + DEC	Helium	Combustion	3.6	1,650	53.7^a
[17]	BC + DEC	Flue gas	Combustion	N/A	N/A	55.5
[18]	BC + RC + two-stage DEC	Flue gas (BC), propane (RC)	Combustion	N/A	N/A	33.9^b
^a Exergy efficiency; ^b Thermal efficiency of the gas turbine in the Brayton cycle.

Table 1.

Summary of single fluid power generation designs

Ref.	Power cycle (s)	Working fluid (s)	Cold reservoir (°C)	Hot reservoir (°C)	LNG flow (t·h⁻¹)	Power output (kW)	Thermal efficiency (%)
[20]	RC	CO₂-based mixtures	−55 to −30	25	3.6	13.5	N/A
[21]	Three-stage RC	Mixtures of R14, methane to pentane	−160	25 to 85	Varying	151.8 to 248.8^a	18.6 to 27.1
^a Per kg of LNG flow.

Table 2.

Summary of mixed working fluid power generation designs

Ref.	Power cycle (s)	Working fluid (s)	Power output (kW)	Thermal efficiency (%)	Other applications
[22]	ORC	CO₂	31.2	5.0	Energy storage, chilled water, cold dry air
[23]	Three-stage ORC	Ethane	11240	13.3^a	Desalination
[24]	ORC	R1270	58870	63.8^b	Carbon capture
ORC: Organic Rankine cycle; ^aExergy efficiency; ^b System exergy efficiency.

Table 3.

Summary of multi-objective power generation systems

Working fluid	Chemical name	Chemical formula	T_C (°C)	P_C (kPa)	T_TP (°C)	P_TP (kPa)	T_S @ 100 kPa (°C)	P_S @ −70 °C (kPa)	P_S @ −30 °C (kPa)	P_S @ 0 °C (kPa)	Category
R1150	Ethylene	C₂H₄	9.2	5,032	−169.2	0.12	–104.3	517.6	1,062	4,109	Wet
R116	Hexafluoroethane	C₂F₆	19.9	3,060	−100	26.1	–79	157.9	377.3	1,872	Dry
R23	Fluoroform	CHF₃	25.9	4,836	−155.1	0.058	–82.2	193.3	479.5	2,525	Dry
R170	Ethane	C₂H₆	32.3	4,884	−182.9	0.0011	–89	250.9	553	2,401	Wet
R125	Pentafluoroethane	C₂HF₅	66	3,620	−100.6	2.9	–48.4	30.6	92.4	668	Dry
R143a	1,1,1-Trifluoroethane	C₂H₃F₃	72.7	3,764	−111.8	1.1	–47.4	29.8	88.3	620	Dry
R32	Difluoromethane	CH₂F₂	78.5	5,820	−136.8	0.048	–51.9	36	110.5	821	Wet
R290	Propane	C₃H₈	96.7	4,242	−187.6	1.7e–7	–42.7	25.3	71.9	476	Wet
R1270	Propylene	C₃H₆	92.4	4,664	−185.2	7.5e–7	–48.3	33.4	92.6	586	Wet
R134a	1,1,1,2-Tetrafluoroethane	C₂H₂F₄	101	4,056	−103.3	0.39	–26.4	8.2	29.8	292	Dry
R14	Tetrafluoromethane	CF₄	−45.7	3,745	−153.2	11.3	–128.3	1,739	3,302	N/A	Dry
R152a	1,1-Difluoroethane	C₂H₄F₂	113.9	4,444	−118.6	0.064	–24.8	8.2	28.7	266	Dry
RC318	Perfluorocyclobutane	C₄F₈	118.8	2,330	−39.8	19.5	–3.3	N/A	10.8	113	Dry
R600a	Isobutane	C₄H₁₀-2	134.8	3,655	−159.4	2.3e–5	–12.4	5.1	17.5	158	Dry
R600	n-Butane	C₄H₁₀-1	152	3,796	−138.3	6.7e–4	–0.86	2.6	9.7	103	Dry
R601a	Isopentane	C₅H₁₂-2	187.2	3,334	−160.5	9e–7	27.5	0.53	2.4	35	Dry
R601	n-Pentane	C₅H₁₂-1	196.4	3,375	−129.7	7.8e–5	35.9	0.29	1.4	24	Dry
R744	Carbon Dioxide	CO₂	31	7,384	−56.6	517.9	N/A	N/A	677	3,474	Isentropic
R717	Ammonia	NH₃	132.3	11,310	−77.7	6.1	–33.4	10.7	40.2	427	Wet
TC: Critical temperature; PC: Critical pressure; TTP: Triple point temperature; PTP: Triple point pressure; TS: Saturation temperature; PS: Saturation pressure.

Table 4.

Working fluid candidates for low-temperature power cycle

Parameter	Value
LNG compositions (mol%):
Methane	85
Ethane	10
Propane	2.5
n-butane	2.5
LNG inlet temperature (°C)	−130
LNG outlet temperature (°C)	−95
LNG pressure (kPa)	1,000
LNG mass flow rate (kg·s⁻¹)	60
Pump/turbine adiabatic efficiency (%)	75
Pressure drop in the heat exchanger (kPa)	10
Minimum pinch point in heat exchangers (°C)	5

Table 5.

LNG conditions and simulation parameters

Parameters	Range
Top cycle evaporation pressure	200 kPa to P_S @ 0 °C
Top cycle condensation pressure	100 kPa to P_S @ 0 °C
Bottom cycle evaporation pressure	200 kPa to P_S @ 30 °C
Bottom cycle condensation pressure	100 kPa to P_S @ 30 °C
Bottom cycle evaporation temperature	–70 to –30 °C
Additional parameters for mixed fluid
Top mixture composition (component 1)	0.1 to 0.9
Bottom mixture composition (component 2)	0.1 to 0.9
Additional parameters for reheating configuration
Top cycle evaporation pressure 2	200 kPa to P_S @ 0 °C
Additional parameters for Kalina configuration
Separator ratio*	0.1 to 0.9
* Vapor fraction of the separator feed on a molar basis.

Table 6.

Parameter value ranges

Algorithm settings	Value
Total generations	50/100*
Populations per generation	100/200*
Mutation probability	0.2
* For integrated configurations with Kalina, reheating, and regeneration.

Table 7.

Genetic algorithm settings

Bottom cycle working fluid	Top cycle working fluid
Bottom cycle working fluid	R1150	R116	R23	R170	R32	R744
R1150	1	2	3	4	5	6
R116	7	8	9	10	11	12
R23	13	14	15	16	17	18
R170	19	20	21	22	23	24
R14	25	26	27	28	29	30

Table 8.

Combinations of single working fluid

Top cycle	Bottom cycle	Power (MW)	Top cycle power (MW)	Bottom cycle power (MW)	Thermal efficiency (%)	2^nd law efficiency (%)
R116	R170	7.5	4.4	3.2	24.1	52.8
R116	R1150	7.4	4.4	3.0	23.8	52.1
R116	R14	7.1	4.0	3.2	23.1	50.7
R1150	R14	5.7	1.9	3.8	19.4	42.5
R1150	R116	4.8	2.6	2.2	16.7	36.6
R23	R116	4.7	2.5	2.2	16.5	36.2

Table 9.

Performance comparison of selected single working fluid combinations

Bottom cycle working fluid	Top cycle working fluid
Bottom cycle working fluid	R116– R125	R116– R143a	R116– R1270	R23– R125	R23– R143a	R23– R1270	R116
R14–R170	1	2	3	4	5	6	7
R14–R23	8	9	10	11	12	13	14
R14–R116	15	16	17	18	19	20	21
R1150–R170	22	23	24	25	26	27	28
R1150–R23	29	30	31	32	33	34	35
R1150–R116	36	37	38	39	40	41	42
R170	43	44	45	46	47	48	49

Table 10.

Combinations of mixtures of working fluids

Top cycle	Bottom cycle	Power (MW)	Top cycle power (MW)	Bottom cycle power (MW)	Thermal efficiency (%)	2^nd law efficiency (%)
R116	R1150–R23	7.7	4.3	3.4	24.6	53.8
R116	R14–R116	7.4	4.7	2.8	24.0	52.5
R116–R143a	R14–R23	6.8	2.5	4.3	22.3	48.9
R23–R143a	R1150–R23	6.0	1.9	4.1	20.3	44.5
R23–R143a	R14–R23	6.0	3.9	2.1	20.2	44.3

Table 11.

Performance comparison of selected mixed working fluid combinations

Bottom cycle configuration	Top cycle configuration
Bottom cycle configuration	Regeneration Rankine cycle	Reheating Rankine cycle
Rankine cycle	Configuration 1	Configuration 2
Kalina cycle	Configuration 3	Configuration 4

Table 12.

Advanced configurations

Bottom cycle working fluid Top cycle working fluid

R116

R14–R170 1

R14–R23 2

R14–R116 3

R1150–R170 4

R1150–R23 5

R1150–R116 6

Table 13.
Working fluid candidates for advanced cycle configurations

Cycle configuration	Power (MW)	Top power (MW)	Bottom power (MW)	Top P_evap (kPa)	Top P_evap 2 (kPa)	Top P_cond (kPa)	Bottom P_evap (kPa)	Bottom P_cond (kPa)	Bottom T_cond (°C)
Single fluid	7.5	4.4	3.2	1,030	–	100	550	100	–50
Mixed working fluid	7.7	4.1	3.5	870	–	100	770	120	–46
Rankine–reheating	9.2	5.0	4.2	1,830	510	100	1,000	110	–34
Rankine–regeneration	7.5	4.2	3.4	940	–	100	840	150	–48
Evaporation pressure (turbine inlet); Pcond: Condensation pressure (turbine outlet); Tcond: Condensation temperature (turbine outlet).

Table 14.

Performance comparison of cycle configurations with identical working fluids

Top cycle	Bottom cycle	Power (MW)	Top cycle power (MW)	Bottom cycle power (MW)	Thermal efficiency (%)	2^nd law efficiency (%)
Baseline Rankine cycle configuration
R116	R1150–R23	7.7	4.3	3.4	24.6	53.8
R116	R1150–R170	7.7	4.1	3.5	24.4	53.5
R116	R14–R23	7.6	4.1	3.5	24.2	53.1
Rankine-regeneration configuration
R116	R1150–R23	7.6	4.1	3.5	24.3	53.3
R116	R1150–R170	7.5	4.2	3.4	24.1	52.9
R116	R14–R23	7.5	4.4	3.1	24	52.7

Table 15.

Performance comparison of regeneration and baseline configurations

Top cycle	Bottom cycle	Power (MW)	Top cycle power (MW)	Bottom cycle power (MW)	Thermal efficiency (%)	2^nd law efficiency (%)
Rankine-reheating configuration
R116	R1150–R23	8.7	5.2	3.5	26.8	58.8
R116	R1150–R170	9.2	5.0	4.2	27.9	61.2
R116	R14–R116	8.7	5.1	3.6	26.9	58.9
Kalina-reheating configuration
R116	R1150–R23	8.8	5.0	3.8	27.1	59.4
R116	R1150–R170	8.6	5.1	3.5	26.5	58.1
R116	R14–R116	8.7	5.0	3.7	26.8	58.6

Table 16.

Performance comparison of Rankine and Kalina style configurations

Bottom cycle working fluid	Top cycle working fluid
	R116
R14–R170	1
R14–R23	2
R14–R116	3
R1150–R170	4
R1150–R23	5
R1150–R116	6