Power recovery system using a rankine power cycle incorporating a two-phase liquid-vapor expander with electric generator

1. A power recovery system for recovery of part of the required energy input during regasification of LNG using consecutive first and second Rankine power cycle sub-systems, the first and the second Rankine power cycle subsystems of the power recovery system each comprising:

a working fluid contained in a closed loop system, the closed-loop system comprising a pump two-phase liquid-vapor expander generator having (i) a feed pump, (ii) an induction generator and (iii) a two-phase liquid-vapor expander all mounted on a common, rotating axial shaft, the feed pump pumping liquid-phase working fluid to a high pressure for producing a pressurized liquid-phase working fluid, the pressurized liquid-phase working fluid then passing through the induction generator to become partly heated and vaporized therein, and then flowing out of the pump two-phase liquid-vapor expander generator;

a first heat exchanger with a heat source, the first heat exchanger connected to the pump two-phase liquid-vapor expander generator via the closed-loop system, the heat source heating the pressurized liquid-phase working fluid flowing out of the induction generator into higher vapor content while it is passing through to produce a heated and pressurized two-phase working fluid, the heated and pressurized two-phase working fluid then re-entering the pump two-phase liquid-vapor expander generator at the two-phase liquid-vapor expander wherein the heated and pressurized two-phase working fluid expanded and driving the rotating center shaft, and subsequently the induction generator, the expanded two-phase working fluid flowing out of the pump two-phase liquid-vapor expander for cooling and condensation;

a second heat exchanger with pressurized LNG as a heat sink, the second heat exchanger connected to the pump two-phase liquid-vapor expander generator via the pipe system, the heat sink absorbing the heat and cooling the expanded two-phase working fluid while it is passing through, the expanded two-phase working fluid condensed back to the liquid-phase working fluid state, the liquid-phase working fluid then re-entering the pump two-phase liquid-vapor expander generator at the feed pump, and repeating the cycle;

a heat sink pipeline feeding pressurized liquefied natural gas to the second heat exchanger of the first Rankine power cycle sub-system, the heat sink pipeline subsequently carrying the heated, pressurized LNG with a higher vapor content discharged from a sink of the first Rankine power cycle sub-system and feeding to the heat sink of the second Rankine power cycle sub-system, eventually carrying the further heated, fully vaporized and pressurized LNG discharged out of the power recovery system; and

a casing containing the entire expander generator assembly; a stationery flat circular nozzle ring portion at the bottom of the two-phase liquid-vapor expander generator assembly, the nozzle ring portion further having a center aperture and a plurality of converging nozzles on its rim for generation of high velocity vortex flow of the pressurized and heated two-phase working fluid as it flows through; a rotating turbine runner portion sitting on to of the aperture of the nozzle ring portion.

2. The LNG regasification power recovery system of claim 1 in which the working fluid, operational conditions of the first and the second Rankine power cycle sub-systems are identical.

3. The LNG regasification power recovery system of claim 1 in which the working fluid, operational conditions of the first and the second Rankine power cycle sub-systems are different.

4. The LNG regasification power recovery system of claim 1 in which the heat source is sea water.

5. The LNG regasification power recovery system of claim 1 in which the heat source is steam.

6. The LNG regasification power recovery system of claim 1 in which the heat sink is pressurized liquefied natural gas.

7. The LNG regasification power recovery system claim 1 in which the working fluid is liquefied natural gas.

8. A method for power recovery using consecutive, dual Rankine power cycles A and B operated in series in an LNG regasification plant, the method comprising the following steps:

in each cycle, passing the working fluid through heat exchangers and a pump two-phase expander generator, the pump two-phase expander generator consisting of a compact assembly of a pump, a two-phase expander and an induction generator integrally mounted on one rotating, axial shaft, such that the following steps are performed in the following sequence:

in a first step in each cycle, with work input, the pump pressurizes a non-saturated liquid single phase working fluid from low pressure to high pressure for producing a pressurized non-saturated liquid single-phase working fluid;

in a second step in each cycle, the pressurized non-saturated liquid single phase working fluid is heated and partially vaporized by passing through the induction generator, and a first heat exchanger with the heat provided by sea water or other heat sources;

in a third step in each cycle, the pressurized and heated two-phase saturated working fluid flowing out of the first heat exchanger expands from high-pressure to low pressure across the two-phase expander for generating a work output;

in a fourth step in each cycle, the low pressure two-phase saturated working fluid flowing out of the two-phase expander passes through a second heat exchanger with a heat sink, such that the low pressure two-phase saturated working fluid condenses from saturated liquid-vapor two-phase to non-saturated liquid single phase; this condensation process serves as the heat source for the LNG regasification process and the LNG at the second heat sink is heated and partly or completely vaporized;

passing the heated and partly or completely vaporized LNG from the second heat exchanger of the Rankine power cycle A through a heat sink of a second heat exchanger of the Rankine power cycle B to be further heated and vaporized; and

discharging the heated and vaporized LNG at the heat sink of the second heat exchanger of the Rankine power cycle B to a gas pipe line;

wherein the expander generator of each cycle further comprises: a casing containing the entire expander generator; a stationery flat circular nozzle ring portion at the bottom of the two-phase expander, the nozzle ring portion further having a center aperture and a plurality of converging nozzles on its rim for generation of high velocity vortex flow of the pressurized and heated two-phase saturated working fluid as it flows through; a rotating turbine runner portion sitting on to of the aperture of the nozzle ring portion.

9. A method for power recovery using a plurality of consecutive, Rankine power cycles operated in series in an LNG regasification plant, the method comprising the following steps:

in each cycle, passing a non-saturated liquid single phase working fluid through heat exchangers and a pump two-phase expander generator, the pump two-phase expander generator consisting of a compact assembly of a pump, a two phase expander and an induction generator integrally mounted on one rotating, axial shaft, such that the following steps are performed in the following sequence:

in a first step in each cycle, with work input, the pump pressurizes the non-saturated liquid single phase working fluid from low pressure to high pressure for producing a pressurized non-saturated liquid single phase working fluid;

in a second step in each cycle, the pressurized the non-saturated liquid single phase working fluid is heated and partially vaporized by passing through the induction generator, and a first heat exchanger with the heat provided by sea water or other heat sources;

in a third step in each cycle, the pressurized and heated two-phase saturated working fluid flowing out of the first heat exchanger expands from high-pressure to low-pressure across the two-phase expander for generating a work output;

in a fourth step in each cycle, the low pressure two-phase saturated working fluid flowing out of the two-phase expander passes through a second heat exchanger with a heat sink, such that the low pressure two-phase saturated working fluid condenses from saturated liquid-vapor two-phase to non-saturated liquid single phase; this condensation process serves as the heat source for the LNG regasification process and the LNG at the second heat sink is heated and partly or completely vaporized;

passing the heated and partly or completely vaporized LNG from the second heat exchanger of one Rankine power cycle through a heat sink of a heat exchanger of an adjacent Rankine power cycle to be further heated and vaporized; and

discharging the heated and vaporized LNG at the heat sink of the second heat exchanger of the adjacent Rankine power cycle to a gas pipe line;

wherein the expander generator of each cycle further comprises: a casing containing the entire expander generator; a stationery flat circular nozzle ring portion at the bottom of the two-phase expander, the nozzle ring portion further having a center aperture and a plurality of converging nozzles on its rim for generation of high velocity vortex flow of the pressurized and heated two-phase saturated working fluid as it flows through; a rotating turbine runner portion sitting on top of the aperture of the nozzle ring portion.