WO2021171312A1

WO2021171312A1 - Two stage regenerative organic rankine cycle (orc) heat recovery based power generation system

Info

Publication number: WO2021171312A1
Application number: PCT/IN2021/050178
Authority: WO
Inventors: Satyanarayanan Seshadri; Anandu SURENDRAN BINDU
Original assignee: INDIAN INSTITUTE OF TECHNOLOGY MADRAS (IIT Madras)
Priority date: 2020-02-26
Filing date: 2021-02-24
Publication date: 2021-09-02

Abstract

Embodiments disclosed herein provide a two stage regenerative ORC heat recovery based power generation system (200). The power generation system (200) includes an organic fluid pumped at one of HP and LP. A LP pump circulates the organic fluid through the power generation system (200). Further, the power generation system (200) includes first loop performing supercritical evaporation (206) of the organic fluid to obtain supercritical vapor of the organic fluid and a second loop for obtaining sub-critical vapor of the organic fluid. Further, the power generation system (200) includes two stage expander generating power from trans-critical expansion of organic fluid by converting mechanical energy of two stage expander into electrical energy, energy is recovered from superheated vapor resulting from trans-critical expansion of the organic fluid and a condenser (205) is used for condensing the superheated vapor of the organic fluid into saturated fluid after generation of power.

Description

Two stage regenerative Organic Rankine Cycle (ORC) heat recovery based power generation system

FIELD OF INVENTION

[0001] The embodiments disclosed herein generally relate to the field of power generation, and more particularly, to a two stage regenerative Organic Rankine Cycle (ORC) heat recovery based power generation system with trans- critical evaporation and regeneration. The present application is based on, and claims priority from an Indian Application Number 202041008106 filed on 26^th February, 2020 the disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] Generally, huge amount of waste heat is generated from various industrial and commercial processes. Many cases of heat recovery involve two or more heat sources present concurrently at different heat loads and temperatures. Common examples of the heat sources include refineries, internal combustion (IC) engines, solar-geothermal combined power sources, and other process industries such as cement, steel and textiles. Heat recovery using Organic Rankine Cycle (ORC) is employed across many applications such as the IC engines, geothermal heat sources, the solar thermal power systems etc.

[0003] In general, ORCs are utilized for multiple heat sources either using single cycle systems or multiple cycle systems. In the single cycle system configuration, low temperature heat sources are used to pre-heat a pressurized a low boiling organic fluid such as hydrocarbons, refrigerants etc. High temperature heat sources are utilized to evaporate the organic fluid and generate vapor to be expanded in an expander (such as turbines, screw expanders, scroll expanders) producing work. Vapor exiting the expander is then condensed in a condenser and is pumped back into the power generating system. Undesirable results of the configuration include very low heat utilization from the low temperature heat sources, lower thermal efficiency and lower net power output. Two cycle configurations use two separate loops, and each loops comprises expanders, condenser, pump and evaporator. The organic fluids comprises, a high boiling fluid for the high temperature (HT) heat source cycle and the low boiling fluid for the low temperature (LT) cycle. The heat from the expander exit of the high temperature cycle is transferred to the low temperature cycle by means of a heat exchanger. The heat exchanger serves as the condenser for a High Temperature (HT) cycle and as an evaporator for a Low Temperature (LT) cycle. The separate two loop system is able to recover more heat than a previous single stage system. However, the separate two loop system does not perform well over a wide range of heat source conditions. Also, the requirements of additional heat exchangers for cascaded heat transfer, along with the separate expanders for the different organic fluids make the separate two loop system less competitive for multi-source heat recovery.

[0004] In some conventional systems, different pressure levels and different expanders in high and low pressure modes are disclosed. The conventional system discloses a Rankine system integrated with engine block and the organic fluid circulates and cools the engine block. Some conventional system and method discloses recovery of waste heat from dual heat sources. In an architecture, two heat sources, one being a discharged exhaust and another being inter cooler air stream, is exploited. The exhaust heat from High Temperature (HT) expander pre-heats the organic fluid for Low temperature (LT) expander resulting in a complex layout that needs separate expanders and high heat exchange requirements.

[0005] Some conventional systems disclose a modification of dual loop ORC termed as “Advanced Tandem ORC (AT-ORC)” that uses two separate expanders in two separate layouts, and also required two condensers. The conventional system comprises a parallel two stage ORC (PTORC) having two HT and LT loops connected to the two separate HT and LT expander stages. The exhaust heat from the LP expander is utilized by means of a recuperator prior to the condenser. In some convention systems, heated vapor first passed through the HP expander and the exhaust heat from the HP expander gives heat to the LP fluid that is vaporized and expanded in the LP expander. The exhaust heat then pre-heats the HP fluid before being supplied to the HP evaporator. In some embodiments of conventional systems, organic fluid is pre -heated using the recuperator on the LP part and is boiled using mid-grade heat source and finally superheated using a high temperature recuperator and further superheated using high grade heat source. The conventional system operates on a single pressure level with three heat exchangers for high pressure part and the one in condenser side.

[0006] Some conventional systems having two stage cascaded systems combine the advantage of simplicity offered by the use of the single organic fluid and the improved heat extraction from the available heat sources due to the use of two pressure levels. However, the conventional systems often have poor thermal efficiencies and like the two cycle system, the existing two stage systems can deliver improved performance only for certain heat sources conditions. Some conventional systems of the two stage ORCs allow super critical evaporation in the HP stage, and shows increase in cycle thermal efficiency for single heat source applications. The use of supercritical evaporation leads to very high superheat in the inlet of the condenser and also at the exit of HP expander. The high superheat is because most of the organic fluids used in ORC are dry fluids that tend to get superheated as the fluid is expanded. Therefore, if supercritical evaporation in HP stage is deployed, it leads to high condenser losses. This can negatively affect the system when more than one heat source of different heat contents are is utilized.

[0007] More often in the case of waste heat recovery, multiple heat sources exist concurrently. Existing ORC architectures are either too complex architectures with higher heat exchanger requirements and less economical or would have very low thermal efficiency and performance. Furthermore, there is a very high superheat of the expanded vapor in the condenser that is a major source of irreversibility. Therefore, there exists a pressing need to develop advanced ORC architectures that are not too complex so that they can be used as a single stop solutions for multi-source heat recovery.

[0008] Thus, it is desired to address the above mentioned disadvantages or other shortcomings or at least provide a useful alternative.

OBJECT OF INVENTION

[0009] The principal objective of this invention is to provide a two stage regenerative ORC heat recovery based power generation system. The two stage ORC heat recovery based power generation system provides higher thermal efficiencies and are capable of delivering improved power outputs using trans- critical evaporation and regeneration stages.

SUMMARY

[0010] Embodiments disclosed herein provide a two stage regenerative Organic Rankine Cycle (ORC) heat recovery based power generation system. The two stage regenerative ORC heat recovery based power generation system comprises a fluid tank having an organic fluid to be pumped at a high pressure (HP) and a low pressure (LP), a LP pump for circulating the organic fluid through the power generation system, a LP pre -heater for pre -heating the organic fluid, a first loop of the power generation system for performing supercritical evaporation of the organic fluid to obtain super-critical vapor of the organic fluid, a second loop of the power generation system for performing sub-critical evaporation of the organic fluid to obtain sub-critical vapor of the organic fluid and a two stage expander for generation of power from the trans- critical expansion of the organic fluid by converting mechanical energy of the two stage expander into electrical energy. Further, the two stage regenerative ORC heat recovery based power generation system comprises a regenerator for energy recovery from the superheated vapor resulting from the trans -critical expansion of organic fluid and a condenser for condensing the superheated vapor of the organic fluid into a saturated fluid after the generation of the power.

[0011] In an embodiment, the first loop of the power generation system comprises a HP pump, a HP evaporator for generating a supercritical HP vapor using a primary heat source.

[0012] In an embodiment, the second loop of the power generation system comprises a LP evaporator for generating a saturated LP vapor sing a secondary heat source.

[0013] In an embodiment, the two stage expander comprises of a HP stage expander and LP stage expander.

[0014] In an embodiment, the regenerator is one of a direct mixing vapor generator, an ejector connected between the HP expander and the LP expander, an ejector connected after the LP expander, a recuperator at an exit of the HP expander, and the recuperator at an exit of the LP expander.

[0015] In an embodiment, the ejector connected between the HP expander and the LP expander uses one of the superheated HP vapor as the primary fluid.

[0016] In an embodiment, the ejector connected between the HP expander and the LP expander uses the preheated fluid from the HP pump as primary fluid.

[0017] In an embodiment, the ejector connected after the LP expander uses the preheated fluid from the HP pump as primary fluid.

[0018] In an embodiment, the ejector connected after the LP expander receives preheated fluid from the HP pump as primary fluid generating a backpressure in the LP expander for reducing the pressure at exit of the LP expander. [0019] In an embodiment, the vapor generator for mixing the superheated vapor from the HP expander and the two phase organic fluid from the LP evaporator.

[0020] In an embodiment, the recuperator provided at the exit of the HP expander produces LP saturated vapor.

[0021] In an embodiment, the recuperator provided at the exit of the LP expander produces LP saturated vapor.

[0022] In an embodiment, a HP pump and throttle valve is used for generating subcritical vapor.

[0023] Accordingly, the embodiments herein provide a method for recovering heat using a two stage regenerative ORC heat recovery based power generation system. The method comprises pumping, by the two stage regenerative ORC heat recovery based power generation system, an organic fluid at one of High Pressure (HP) and Low Pressure (LP) and circulating, by the two stage regenerative ORC heat recovery based power generation system, organic fluid through the power generation system. Further, the method discloses pre-heating, by the two stage regenerative ORC heat recovery based power generation system, the organic fluid to perform super-critical evaporation of the organic fluid to obtain super-critical vapor of the organic fluid and generating power from the super -critical expansion of the organic fluid by converting mechanical energy of the two stage regenerative ORC heat recovery based power generation system into electrical energy. Further, the method discloses recovering heat from a superheated vapor resulting from the trans-critical expansion of organic fluid.

[0024] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the scope thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES

[0025] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0026] FIG. 1 is a schematic diagram illustrating a two stage regenerative Organic Rankine Cycle (TR-STORC) heat recovery based power generation system, according to the embodiments as disclosed herein;

[0027] FIG. 2A illustrates a schematic diagram of the TR-STORC heat recovery based power generation system using a vapor regenerator for the heat recovery, according to the embodiments as disclosed herein;

[0028] FIG. 2B illustrates a temperature-entropy (T-s) diagram of the TR-STORC heat recovery based power generation system using the vapor regenerator for the heat recovery, according to the embodiments as disclosed herein;

[0029] FIG. 3 illustrates a schematic diagram of the TR-STORC heat power generation system using an ejector for the heat recovery, according to the embodiments as disclosed herein;

[0030] FIG. 4 illustrates a schematic diagram of the TR-STORC heat recovery based power generation system using the ejector between an High Pressure (HP) expander and Low Pressure (LP) expander, according to the embodiments as disclosed herein;

[0031] FIG. 5 illustrates another schematic diagram of the TR-STORC heat recovery based power generation system using the ejector between the HP expander and LP expander stage, according to the embodiments as disclosed herein; [0032] FIG. 6A illustrates a schematic diagram of the TR-STORC heat recovery based power generation system using a recuperator at an exit portion of the HP expander, according to the embodiments as disclosed herein;

[0033] FIG. 6B is a temperature-entropy (T-s) diagram of the TR- STORC heat recovery based power generation system using the recuperator at the exit portion of HP expander on (HP mode), according to the embodiments as disclosed herein;

[0034] FIG.7A illustrates a schematic diagram of the TR-STORC heat recovery based power generation system using the recuperator at the exit portion of the LP expander, according to the embodiments as disclosed herein;

[0035] FIG. 7B is a temperature-entropy (T-s) diagram of the TR- STORC heat recovery based power generation system using the recuperator of the LP expander exhaust vapor, according to the embodiments as disclosed herein; [0036] FIG. 8 is the schematic diagram of TR-STORC heat recovery based power generation system using the recuperator at the LP expander exit and throttle valve, according to the embodiments as disclosed herein; and

[0037] FIG. 9 is a flow chart illustrating a method for regeneration of the power using the two stage regenerative ORC heat recovery based power generation system, according to the embodiments as disclosed herein.

DETAILED DESCRIPTION OF INVENTION [0038] Various embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. In the following description, specific details such as detailed configuration and components are merely provided to assist the overall understanding of these embodiments of the present disclosure. Therefore, it should be apparent to those skilled in the art that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0039] Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0040] Herein, the term “or” as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0041] Accordingly, the embodiments herein provide a two stage regenerative Organic Rankine Cycle (ORC) heat recovery based power generation system, the two stage regenerative ORC heat recovery based power generation system comprises a fluid tank having an organic fluid to be pumped at a high pressure (HP) and a low pressure (LP), a LP pump for circulating the organic fluid through the power generation system, a LP pre-heater for pre heating the organic fluid, a first loop of the power generation system for performing super-critical evaporation of the organic fluid to obtain super critical vapor of the organic fluid, a second loop of the power generation system for performing sub-critical evaporation of the organic fluid to obtain sub- critical vapor of the organic fluid and a two stage expander for generation of power from the trans-critical expansion of the organic fluid by converting mechanical energy of the two stage expander into electrical energy. Further, the two stage regenerative ORC heat recovery based power generation system comprises a regenerator for energy recovery from the superheated vapor resulting from the trans-critical expansion of organic fluid and a condenser for condensing the superheated vapor of the organic fluid into a saturated fluid after the generation of the power.

[0042] The proposed invention provides the improved thermal efficiency and the improved regeneration. Also, the proposed invention provides higher power outputs and reduced superheat in the condenser inlet.

[0043] The conventional systems comprising multistage evaporation Organic Rankine Cycle (ORC) waste heat recovery generation system and a process provided with an organic medium waste heat boiler, a multistage organic expander with an intermediate vapor supplementation port, condenser, a water cooling tower, a draught fan according to required generation capacity. The conventional two stage ORC heat recovery generation system converts medium-low temperature waste heat into high-grade electric energy to improve the efficiency just by 2-5 percent in comparison with the single-stage evaporation organic ORC. The proposed cycle architectures are called the Trans critical Regenerative Series Two Stage ORCs (TR-STORC). The proposed ORC is an improvement on the existing series two stage ORC (STORC) architecture focusing on dual/multi source heat recovery. The TR- STORC adopts a super-critical evaporation process in the HP stage. In the LP stage, the organic fluid is can either be partially evaporated or fully evaporated. Regenerative use of the superheat from expander exhaust is used to improve thermal efficiency of proposed system. The improvement of the thermal efficiency can be done either by direct constant pressure mixing or by means of an ejector or via a recuperator. Though, the conventional systems discloses partially evaporating organic medium, high/low pressure stage super heater and evaporator of the ORC system, unlike the proposed invention the existing ORC architecture do not refer to vapor regeneration.

[0044] The conventional ORC system comprises an expander and a generator unit, a condenser for condensing the organic work fluid, a feeder pump for circulating and pressurizing the organic work fluid and the evaporator for evaporating the organic work fluid. The expander unit can be a turbine, a screw expander and a piston expander. The expander is mechanically connectable to the generator which generates electricity.

[0045] Another conventional two stage ORC system comprises of the organic cycle for guiding an organic medium, a HP and a LP pump, a 2 stage expander and a generator, and a condenser. The organic cycle has the heat exchanger for transferring heat to the organic medium. The organic medium is evaporated at two different pressure levels. Unlike the conventional two stage ORC system, the proposed system comprises two stage regenerative ORC heat recovery based power generation involving evaporation process in the HP stage, partial evaporation process in the LP stage, utilizing superheat and regenerating low pressure vapor to recover heat.

[0046] The proposed invention allows extracting heat at two different temperatures using the same organic fluid that is pumped at different pressures. The organic fluid is pre-heated using a pre -heater utilizing heat from LP heat source. The pre-heated organic fluid is then split into two streams. One of the streams is pumped to a higher pressure and is evaporated in the HP evaporator utilizing heat from the HP heat source. The other stream is evaporated in LP evaporator. The proposed invention allows the use of two expanders that can be connected in series, since the system operates with the single organic fluid. The vapor from the HP evaporator is expanded in the HP expander and mixes with vapor from the LP evaporator and is finally expanded through the LP expander. Such forms of two stage cascaded systems combine the advantage of simplicity offered by the use of a single organic fluid and improved heat extraction from available heat sources due to the use of two pressure levels.

[0047] Referring now to the drawings, and more particularly to FIGS. 1 through 9, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

[0048] FIG. 1 is a schematic diagram illustrating a two stage regenerative Organic Rankine Cycle (TR-STORC) heat recovery based power generation system, according to the embodiments as disclosed herein.

[0049] Referring to FIG. 1, a new stage ORC Trans critical Regenerative STORC (TR-STORC) is proposed, focusing on dual source heat recovery. The TR-STORC adopts a super-critical evaporation process in HP stage (101). The supercritical cycle is a cycle with a maximum pressure higher than the critical pressure. In LP stage, organic fluid is only partially evaporated (102). At stage (104), full evaporation of the LP stage fluid is achieved by utilizing high superheat of vapor existing from an HP expander. The combination of supercritical heating in the HP stage, partial evaporation and regeneration in the LP stage improve the thermal match and can also achieve increased heat source utilization. Two cycle configurations use two separate loops (at stage 105), and each loop comprises expanders pump, evaporator and a common condenser. The organic fluids are for example can be fluids like pentane, cyclopentane, butane or refrigerants like R245fa, R365mfc.

[0050] FIG. 2A illustrates the schematic diagram of the TR-STORC heat recovery based power generation system using regenerator (203) for the heat recovery, according to the embodiments as disclosed herein.

[0051] Referring to FIG. 2A, the system (200) consists of a High pressure (HP) evaporator (207), a Low Pressure (LP) evaporator (209), a regenerator (203), a HP pump (Pump 2), a LP pump (Pump 1), a two stage expander (HP expander (201) and LP expander (202) connected in series) and a condenser (205). An organic fluids such as refrigerants, alkanes or cyclic alkanes can be used as organic fluids in this cycle. A trans-critical evaporation is at the part of the HP evaporator (2-6) (207), usually the evaporation operation is performed at a low pressure, and in the proposed system (200) the evaporation is performed at high pressure, that is higher than the critical pressure of the fluid and such evaporation is called as trans-critical evaporation. The superheat generated from the trans-critical expansion in the HP expander is utilized in the regenerator (203) to generate additional vapor via evaporation. The HP evaporator (207) and the LP evaporators (209) recover heat from the primary (high temperature) and secondary (low temperature) heat sources respectively. The saturated organic fluid from the condenser (205) is pressurized to an intermediate pressure by the LP pump (9-1). A part of the organic fluid is pressurized to a higher pressure by the HP pump (2-4). In the LP evaporator (209), the organic fluid absorbs heat from the secondary heat source and is partially evaporated (1-2-3). In the HP evaporator (207), the organic fluid absorbs heat from the primary heat source and generates HP supercritical vapor (206) (4-5). The HP vapor is expanded in the HP stage of the induction expander(5-6).The entire vapor exiting the HP stage then mixes with organic fluid from the LP evaporator (209) and achieves full evaporation in the regenerator (203), that is essentially a mixing vessel, to produce low pressure saturated vapor (at 3-3” and 6-3”). The vapor is then expanded to the condenser pressure via the LP expander (202) (3”-7). The mass flow rate of the organic fluid through the LP evaporator (209) can be adjusted either by controlling the speed of pump 1 or by means of a flow control valve in order to ensure full evaporation in the regenerator (203). In other words, the quality of state point 3 can be adjusted so as to ensure full evaporation in the regenerator (203). The mechanical work from the expander is converted to electrical power by the regenerator (203). The superheated vapor (204) exiting the LP expander (202) is then de-superheated (7-8) and condensed to saturated liquid in the condenser (205) (8-9) completing one cycle. [0052] FIG. 2B illustrates the temperature-entropy (T-s) diagram of RT-STORC heat recovery based power generation system using the regenerator for the heat recovery, according to the embodiments as disclosed herein.

[0053] Referring to FIG. 2B, the T-s diagram shows the exchange of heat sources. The heat sources can be the primary heat sources and the secondary heat sources. The bell shaped curve (1-2, 3”, 8) shows the liquid and vapor states of the fluid. The left part of the curve (1-4) represents liquid state and the right part of the curve represents vapor state. The liquid state fluid is pumped with certain pressure at pump land the fluid is pre-heated to the high temperature at point (1-2) and the pressure is increased at the pump 1. At point (1-2) the heat is exchanged and the temperature is increased. Further, point 2 is split into two streams. The streams at point 2, takes heat from the secondary source that is at low temperature. At point (2-3) evaporation process is performed by extracting heat from the secondary heat source. At point 7, the heat exchange is performed and the fluid is cooled and at point (2-3) the fluid is again evaporated. The state points 4-5 shows super-critical evaporation. At the state points 5-6, the pressure is decreased by means of the turbine or expander (201,202). The point 6 is at higher temperature and point 3” is at lower temperature. The points (3-3”) shows the mixing process of the vapor at intermediate temperature. At the point (7, 8 and 9) represents the cooling process of the vapor completing one cycle. The heat sources indicate high temperature and the heat sink indicates the low temperatures.

[0054] FIG. 3 illustrates the schematic diagram of the TR-STORC heat power generation system using the ejector for the heat recovery, according to the embodiments as disclosed herein.

[0055] Referring to the FIG. 3, in conjunction to the FIG. 2, the regenerator (203) is replaced with the ejector (401). In the FIG. 3, the superheated vapor (204) from the HP expander (201) mixes with the two phase (partially evaporated)/saturated vapor/ superheated vapor(204) of organic fluid from the LP evaporator (209). The superheat in the vapor is utilized to provide a pressure rise to the saturated/slightly superheated vapor (204) before entering the LP expander (202). If the HP expander (201) exhaust pressure is more than the LP evaporator pressure (pressure at 6 is higher that pressure at 3), the HP expander (201) exhaust acts as the primary fluid and drives the flow. The LP fluid is entrained inside the ejector (401) and mixed with the superheated HP expander (201) exhaust and pumped into the LP evaporator (209) at a pressure higher than the original LP evaporator pressure. Another mode of operation in the FIG. 3 would be to pump the LP fluid at the higher pressure (pressure at 3 is higher that pressure at 6). In FIG. 3, the same ejector (401) can be operated with the secondary fluid being the superheated vapor (204) from HP expander

(201) and the organic fluid from the LP evaporator (209) acting as the primary fluid. In this case, the backpressure on the HP expander (201) is reduced due to the entrainment of the vapor inside the ejector (401) by the LP evaporator (209) organic fluid. This decrease in backpressure leads to improvement in expander work output.

[0056] FIG. 4 illustrates the schematic diagram of the TR-STORC heat recovery based power generation system using the ejector between the HP expander (201) and LP expander (202), according to the embodiments as disclosed herein.

[0057] Referring to the FIG. 4, in conjunction to the FIG. 3A, the superheated vapor (204) from the exit of the HP expander (201) mixes with the vapor from the LP evaporator (209). The vapor is then fed to the ejector (401). The hot fluid from the high pressure pump (Pumpl) acts as the secondary fluid that gets entrained inside the ejector (401). The ejector (401) boosts the pressure of the mixed fluid, resulting in increased inlet pressures at the LP expander

(202).

[0058] FIG. 5 illustrates another schematic diagram of the TR-STORC heat recovery based power generation system using the ejector (401) between the HP expander (201) and LP expander (202), according to the embodiments as disclosed herein.

[0059] Referring to the FIG.5, the superheat available at the exit of the LP expander (202) is used for regenerating the power. The ejector (401) is connected to the LP expander (202) exit. The high pressure preheated fluid from the HP pump (2) is supplied to the ejector (401) and acts as the primary fluid. The vapor from the LP expander (202) is entrained inside the ejector (401) creating a backpressure in the LP expander (202), thereby reducing the exit temperature and pressure of the LP expander (202) exhaust, leading to the improvement in the LP expander (202) work output. At the exit of the ejector (401), the organic fluid would in the two phase state and the pressure would be higher than the expander back pressure allowing for heat rejection in the condenser (205).

[0060] FIG. 6A illustrates the schematic diagram of the TR-STORC heat recovery based power generation system using the recuperator(701) at the exit portion of the HP expander (202), according to the embodiments as disclosed herein.

[0061] Referring to FIG. 6A, the sub-cooled organic fluid is pumped from the condenser (205) to an intermediate pressure (9-1) by the LP pump (pump 2). The organic fluid is preheated to saturated liquid (1-2) by utilizing a part of the heat from the secondary heat source. The saturated liquid is then split into three streams. One of these is pressurized to supercritical pressures in the HP pump (2-4) and is vaporized in the HP evaporator (4-5), utilizing the primary heat source. This vapor is then expanded in the HP expander (201) to the intermediate pressure (5-6), resulting in superheated vapor (204) at the expander exit.

[0062] The second fluid stream undergoes the same evaporation process (2-3) in the LP evaporator (209) by utilizing the secondary heat source, thereby generating saturated vapor at low pressure (2-3). The superheated vapor (204) exiting the HP expander (201) transfers heat (6-3") to a third organic fluid stream in the recuperator (701). Similar to the LP evaporator (209), the recuperator (701) also generates vapor at low pressure (2-3). The superheated vapor (204) exiting the recuperator(701) (state point 3') and the saturated vapor from the recuperator (701) and LP evaporator (209) (both at state point 3) is mixed together, resulting in slightly superheated vapor ( state point 3""). This mixed stream is then expanded through the LP expander (202), thereby producing additional power output. In the condenser (205), the LP expander (202) exhaust is cooled to saturated/sub-cooled liquid (7-8-9) and is pumped back (9-1).

[0063] FIG.6B is the temperature-entropy (T-s) diagram of the TR- STORC heat recovery based power generation system using the recuperator(701) at the exit of the HP expander (201) on (HP mode), according to the embodiments as disclosed herein.

[0064] Referring to FIG. 6B, the T-s diagram shows the exchange of heat sources. The bell shaped curve (1-2, 3”, 8) represents the liquid and vapor states of the fluid. The left part of the curve (1-4) represents liquid state and the right part of the curve represents vapor state. From the condenser (205), the sub-cooled organic fluid is pumped to an intermediate pressure (9-1) by the LP pump (pump 2). The organic fluid is preheated to saturated liquid (1-2) by utilizing a part of the heat from the secondary heat source. The saturated liquid is then split into three streams. One of these is pressurized to supercritical pressures in the HP pump (2-4) and is vaporized in the HP evaporator (4-5), utilizing the primary heat source. The streams at point 2, takes heat from the secondary source that is at low temperature. The second fluid stream undergoes the same evaporation process (2-3) in the LP evaporator (209) by utilizing the secondary heat source, thereby generating saturated vapor at low pressure (2- 3). The superheated vapor (204) exiting the HP expander (201) transfers heat (6-3") to a third organic fluid stream in the recuperator (701). The points (3-3 ’ ’) shows the mixing process of the vapor at intermediate temperature. At the point (7, 8 and 9) represents the cooling process of the vapor completing one cycle. The heat sources indicate high temperature and the heat sink indicates the low temperatures.

[0065] FIG. 7A illustrates the schematic diagram of the TR-STORC heat recovery based power generation system using the recuperator(701) at the exit portion of the LP expander (202), according to the embodiments as disclosed herein.

[0066] Referring to FIG. 7A, a location of the recuperator (701) is at the exit of the LP expander (202). The superheated vapor (204) exiting the HP expander (201) is not utilized for recuperation. Instead, the superheated vapor (204) is mixed with the saturated vapor from the LP evaporator (209) and recuperator (701) (3' and 3 mixed to 3")· The resulting superheated stream is expanded through the LP expander (202) (3"-7). Between the expander stages, vapor feeding alone occurs, and the design is devoid of any vapor extraction. The vapor exhausted from the LP expander still possesses significant superheat and is at a temperature range similar to that of the secondary heat source. This superheated vapor (204) is utilized to evaporate additional organic fluid in the recuperator (701) (7-7' for the hot side and 2-3 for the cold side). The resulting saturated vapor is mixed with saturated vapor from the LP evaporator (209) and is fed to the LP expander (202), generating additional power. Other processes for this mode are same as those for the previous cases.

[0067] FIG. 7B is the temperature-entropy (T-s) diagram of the TR- STORC heat recovery based power generation system using the recuperator of the LP expander (202) exhaust vapor, according to the embodiments as disclosed herein.

[0068] The superheated vapor (204) exiting the HP expander (202) is not utilized for recuperation, as in the previous HP mode. Instead, it is mixed with the saturated vapor from the LP evaporator (209) and recuperator (701) (3' and 3 mixed to 3") .The resulting superheated stream is expanded through the LP expander (3"-7). Between the expander stages, vapor feeding alone occurs, and the design is devoid of any vapor extraction. The vapor exhausted from the LP expander (202) still possesses significant superheat and is at a temperature range similar to that of the secondary heat source. The streams at point (7-T) for the hot part and the streams at point (2-3) for the cold part.

[0069] FIG. 8 is the schematic diagram of the TR-STORC heat recovery based power generation system using the recuperator (701) at the LP expander (202) exit and the throttle valve (801), according to the embodiments as disclosed herein.

[0070] Referring to the FIG. 8, in conjunction to the FIG. 7A the recuperator (701) is integrated into the LP preheater (210) and the LP evaporators (209) that are multi- stream heat exchangers. Instead of two separate pumps, the entire organic fluid is pumped by the HP pump and LP vapor is generated using a throttle valve (801). Other processes for the LP mode are the same as those for the LP mode.

[0071] The heat source in the proposed invention is a 20 cylinder 4 stroke turbocharged natural gas fired engine. At engine design point, high temperature exhaust gases (705K, 4.591 kg/s) from the engine are the primary heat source and the hot jacket water (363K, 14 kg/s) is the secondary heat source. The composition of primary heat source used for determining its properties is 02 17.3%, N2 59.3%, C02 12.9% and H20 10.5 % by mass. In order to explore a wide range of IC engine conditions, the primary and secondary heat source temperatures and mass flow rates are varied in this study. At the engine design point, using cyclopentane as the organic fluid, TR-STORC delivers 16% and 23% higher power output than STORC and pre-heated ORC respectively. The fraction of heat available from the primary and secondary heat source is varied in this study. Typically, in dual source applications, one of the heat sources would have heat content higher than the other. Heat ratio which is the ratio of heat available from the primary heat source to the secondary heat source can be defined as: Qp mpxCppX(Tp,i_n— Tp,_out min) _{/ i \} r Qs m_sxCp_sx(T_S i_n-T_{S out min})

[0072] For heat ratios ranging from 2.28 to 0.279, using cyclopentane as organic working fluid, TR-STORC delivers 23-37% increased power output than single pressure pre-heated ORC and 19-25% increased power output than STORC. This indicates that TR-STORC is a superior cycle architecture for all range of dual source heat recovery.

[0073] FIG. 9 is the flow chart illustrating the method for regeneration of power using the two stage regenerative ORC heat recovery based power generation system (200), according to the embodiments as disclosed herein.

[0074] Referring to FIG. 9, at step 902, the fluid tank holding the organic fluid is pumped at the HP and the LP.

[0075] At step 904, the LP pump (1) circulates the organic fluid through the power generation system (200).

[0076] At step 906, the LP pre-heater (210) pre-heats the organic fluid.

[0077] At step 908, the first loop of the power generation system (200) performs the super critical evaporation of the organic fluid to obtain supercritical vapor (206) of the organic fluid.

[0078] At step 910, a two stage expander generates power from the trans-critical expansion of the organic fluid by converting mechanical energy of the two stage expander into electrical energy.

[0079] At step 912, the regenerator (203) recovers the energy from the superheated vapor (204) resulting from the trans-critical expansion of the organic fluid.

[0080] At step 914, the condenser (205) condenses the superheated vapor (204) of the organic fluid into a saturated fluid after the generation of the power. [0081] The various actions, acts, blocks, steps, or the like in the method may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the invention.

[0082] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

CLAIMS We claim:

1. A two stage regenerative Organic Rankine Cycle (ORC) heat recovery based power generation system (200), the two stage regenerative ORC heat recovery based power generation system (200) comprising: a fluid tank holding an organic fluid to be pumped at a high pressure (HP) and a low pressure (LP); a LP pump (1) for circulating the organic fluid through the power generation system (200); a LP pre-heater (210) for pre-heating the organic fluid; a first loop of the power generation system (200) for performing supercritical evaporation of the organic fluid to obtain supercritical vapour (206) of the organic fluid; a second loop of the power generation system (200) for performing sub-critical evaporation of the organic fluid to obtain sub- critical vapor of the organic fluid; a two stage expander for generation of power from the trans- critical expansion of the organic fluid by converting mechanical energy of the two stage expander into electrical energy; a regenerator (203) for energy recovery from the superheated vapor resulting from the trans-critical expansion of organic fluid; and a condenser (205) for condensing the superheated vapour of the organic fluid into a saturated fluid after the generation of the power.

2. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 1, wherein the first loop of the power generation system (200) comprises HP pump (2), a HP evaporator (207) for generating a supercritical HP vapour (206) using a primary heat source.

3. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 1, wherein the second loop of the power generation system (200) comprises a LP evaporator (209) for generating a saturated LP vapor using a secondary heat source.

4. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 1, wherein the two stage expander comprises of a HP expander (201) and LP expander (202).

5. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 1, wherein the regenerator (203) is one of a direct mixing vapour generator, an ejector (401) connected between the HP expander (201) and the LP expander (202), an ejector (401) connected after the LP expander (202), a recuperator (701) at an exit of the HP expander (201), and the recuperator(701) at an exit of the LP expander (202).

6. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 5, wherein the ejector (401) connected between the HP expander (201) and the LP expander (202) uses one of the superheated HP vapour (204) as the primary fluid.

7. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 5, wherein the ejector (401) connected between the HP expander (201) and the LP expander (202) uses the preheated fluid from the HP pump (2) as primary fluid.

8. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 5, wherein the ejector (401) connected after the LP expander (202) uses the preheated fluid from the HP pump as primary fluid.

9. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 5, wherein the ejector (401) connected after the LP expander (202) receives preheated fluid from the HP pump (2) as primary fluid generating a backpressure in the LP expander (202) for reducing the pressure at exit of the LP expander (202).

10. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 5, wherein the regenerator (203) for mixing the superheated vapour (204) from the HP expander (201) and the two phase organic fluid fromthe LP evaporator (209).

11. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 5, wherein the recuperator (701) provided at the exit of the HP expander (201) produces LP saturated vapour.

12. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 4, wherein the recuperator (701) provided at the exit of the LP expander (202) produces LP saturated vapour.

13. The two stage regenerative ORC heat recovery based power generation system (200) as claimed in claim 11, wherein a HP pump (2) and throttle valve (801) is used for generating subcritical vapor.

14. A method for recovering heat using a two stage regenerative ORC heat recovery based power generation system (200), the method comprising: pumping, by the two stage regenerative ORC heat recovery based power generation system (200), an organic fluid at one of High Pressure (HP) and Low Pressure (LP); circulating, by the two stage regenerative ORC heat recovery based power generation system (200), organic fluid through the power generation system; pre-heating, by the two stage regenerative ORC heat recovery based power generation system (200), the organic fluid; performing, by the two stage regenerative ORC heat recovery based power generation system (200), super-critical evaporation of the organic fluid to obtain super-critical vapor of the organic fluid; generating, by the two stage regenerative ORC heat recovery based power generation system (200), power from the trans-critical expansion of the organic fluid by converting mechanical energy of the two stage regenerative ORC heat recovery based power generation system (200) into electrical energy; and recovering, by the two stage regenerative ORC heat recovery based power generation system (200), heat from a superheated vapor resulting from the trans-critical expansion of organic fluid.

15. The method as claimed in claim 14, further comprising: condensing, by the two stage regenerative ORC heat recovery based power generation system (200), the superheated vapor of the organic fluid into a saturated fluid after the generation of the power.

16. The method as claimed in claim 14, wherein the two stage regenerative Organic Rankine Cycle (ORC)heat recovery based power generation system (200) comprises: a fluid tank comprising an organic fluid to be pumped at a high pressure (HP) and a low pressure (LP); a LP pump (1) for circulating the organic fluid through the power generation system (200); a LP pre-heater (210) for pre-heating the organic fluid; a first loop of the power generation system (200) for performing supercritical evaporation of the organic fluid to obtain supercritical vapour (206) of the organic fluid; a second loop of the power generation system (200) for performing sub-critical evaporation of the organic fluid to obtain sub- critical vapor of the organic fluid; a two stage expander for generation of power from the trans- critical expansion of the organic fluid by converting mechanical energy of the two stage expander into electrical energy; a regenerator (203) for energy recovery from the superheated vapor resulting from the trans-critical expansion of organic fluid; and a condenser (205) for condensing the superheated vapour of the organic fluid into a saturated fluid after the generation of the power.

17. The method as claimed in claim 16, wherein the first loop of the power generation system (200) comprises a HP pump (2), a HP evaporator (207) for generating a supercritical HP vapour (206) using a primary heat source.

18. The method as claimed in claim 16, wherein the second loop of the power generation system (200) comprises a LP evaporator (209) for generating a saturated LP vapor using a secondary heat source.

19. The method as claimed in claim 16, wherein the two stage expander comprises of a HP expander (201) and LP expander (202).

20. The method as claimed in claim 16, wherein the regenerator (203) is one of a direct mixing vapour generator, an ejector (401) connected between the HP expander (201) and the LP expander (202), an ejector (401) connected after the LP expander (202), a recuperator (701) at an exit of the HP expander (201), and the recuperator (701) at an exit of the LP expander (202).

21. The method as claimed in claim 20, wherein the ejector (401) connected between the HP expander (201) and the LP expander (202) uses one of the superheated HP vapour (204) as the primary fluid.

22. The method as claimed in claim 20, wherein the ejector (401) connected between the HP expander (201) and the LP expander (202) uses the preheated fluid from the HP pump (2) as primary fluid.

23. The method as claimed in claim 20, wherein the ejector (401) connected after the LP expander (202) uses the preheated fluid from the HP pump as primary fluid.

24. The method as claimed in claim 20, wherein the ejector (401) connected after the LP expander (202) receives preheated fluid from the HP pump

(2) as primary fluid generating a backpressure in the LP expander (202) for reducing the pressure at exit of the LP expander (202).

25. The method as claimed in claim 20, wherein the regenerator (203) for mixing the superheated vapour (204) from the HP expander (201) and the two phase organic fluid from the LP evaporator (209).

26. The method as claimed in claim 20, wherein the recuperator (701) provided at the exit of the HP expander (201) produces LP saturated vapour.

27. The method as claimed in claim 20, wherein the recuperator (701) provided at the exit of the LP expander (202) produces LP saturated vapour.

28. The method as claimed in claim 16, wherein a HP pump (2) and throttle valve (801) is used for generating subcritical vapor.