Power generation system utilizing LNG cold energy and industrial waste heat recovery and its working method

Abstract

The present invention discloses a power generation system utilizing LNG cold energy and industrial waste heat recovery, including an LNG loop, a two-stage ORC / KC integrated power generation system, and a two-stage ORC waste heat recovery system. After the LNG is pressurized by a circulating pump, heat is exchanged with the two-stage ORC / KC integrated power generation system through the LNG loop, and at the same time, the two-stage ORC waste heat recovery system is used to recycle and utilize low-grade industrial waste heat resources. A working method thereof is also provided. The present invention utilizes the Kalina cycle and the organic Rankine cycle to absorb high-temperature and low-temperature industrial waste heat respectively, utilizes LNG cold energy to recover industrial waste heat and converts the two into electrical energy, and performs heat exchange with LNG through multiple working fluids and combined heat exchange with working fluids of each system, thereby improving the comprehensive utilization efficiency of LNG cold energy and realizing reasonable cascade utilization of LNG cold energy and low-grade waste heat resources of steel plants.

Description

Technical Field

[0001] The invention relates to the technical field of LNG cold energy utilization and industrial waste heat recovery, and in particular to a power generation system utilizing LNG cold energy and industrial waste heat recovery and a working method thereof. Background Art

[0002] Liquefied natural gas (LNG) is an efficient, high-quality, clean energy source that is widely used in industrial production and daily life. Natural gas will liquefy into LNG at an atmospheric pressure and a low temperature of about -163°C. LNG is colorless, odorless, non-toxic, non-corrosive, and its volume is about 1 / 625 of that in gaseous state, so it is easy to store and transport over long distances. However, natural gas consumes a lot of energy in the liquefaction process. For different liquefaction methods, the liquefaction energy consumption per ton of LNG is between 700 and 850 kWh. At the same time, when LNG rises from -162°C to 25°C, it releases about 830 kJ / kg of cold energy. However, most LNG regasification terminals currently release cold energy into seawater or air, which not only wastes a lot of cold energy, but also damages the ecological environment.

[0003] In addition, a large amount of waste heat is generated during my country's industrial production process. The waste heat resource structure is complex and the recovery rate is low. In particular, medium and low temperature waste heat is difficult to recycle. It is necessary to develop more advanced and reasonable waste heat recovery technologies to enhance the waste heat recovery rate.

[0004] How to organically combine the cold energy released by LNG heating and the recovery of industrial waste heat to improve energy utilization is an urgent problem to be solved. Summary of the invention

[0005] Purpose of the invention: In view of the above problems, the purpose of the present invention is to provide a power generation system that utilizes LNG cold energy and industrial waste heat recovery, realizes the cascade utilization of LNG cold energy and medium and low temperature industrial waste heat, ensures the safety and stability of the power generation system, achieves more efficient energy saving and is more environmentally friendly. And provides its working method.

[0006] Technical solution: A power generation system utilizing LNG cold energy and industrial waste heat recovery, comprising a first working fluid pump, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a second mixer, a second working fluid pump, a seventh heat exchanger, an eighth heat exchanger, a first expander, a first separator, a third working fluid pump, a ninth heat exchanger, a flash tank, a second expander, a first mixer, and a two-stage ORC waste heat recovery system;

[0007] The first working fluid pump, the first heat exchanger, the second heat exchanger, the third heat exchanger, and the fourth heat exchanger connected in sequence through pipelines constitute an LNG loop; the first heat exchanger, the second heat exchanger, the second mixer, the second working fluid pump, the seventh heat exchanger, the fourth heat exchanger, the eighth heat exchanger, the first expander, and the first separator constitute an ORC integrated power generation system; the second heat exchanger, the second mixer, the second working fluid pump, the seventh heat exchanger, the fourth heat exchanger, the eighth heat exchanger, the first expander, and the first separator are connected in sequence through pipelines to form a closed loop; the first separator, the first heat exchanger, and the second mixer are connected in sequence through pipelines; the seventh heat exchanger, the third working fluid pump, the third heat exchanger, the fourth heat exchanger, the ninth heat exchanger, the flash tank, the second expander, and the first mixer, which are connected in sequence through pipelines to form a closed loop, constitute a KC integrated power generation system; the third heat exchanger and the fourth heat exchanger are respectively connected to the two-stage ORC waste heat recovery system;

[0008] The first power generation working fluid circulates in the ORC integrated power generation system, and the second power generation working fluid circulates in the KC integrated power generation system; after being pressurized by the circulation pump, the LNG exchanges heat with the ORC integrated power generation system and the KC integrated power generation system respectively through the LNG loop. At the same time, the two-stage ORC waste heat recovery system recovers low-grade industrial waste heat resources.

[0009] The Organic Rankine Cycle (ORC) is a power cycle that uses low-boiling-point organic matter as a working fluid. By utilizing the low phase change temperature of organic fluids, ORC can absorb heat from low-temperature heat sources and generate high-pressure gas under relatively low temperature conditions, thereby driving the expander to work and the generator to generate electricity, thus converting low-grade waste heat energy into electrical energy.

[0010] The Kalina cycle (KC) is a power cycle that uses ammonia-water mixture as the working fluid. It is an improvement on the traditional steam Rankine cycle. Since the ammonia-water mixture has the characteristic of boiling under temperature changes, the Kalina cycle has a higher thermal efficiency than the Rankine cycle. Since the ammonia-water mixture is easy to decompose above 250°C, the Kalina cycle can only be used for medium and low temperature heat sources.

[0011] In the LNG loop, after being pressurized by the first working fluid pump, the LNG passes through the first heat exchanger, the second heat exchanger, the third heat exchanger, and the fourth heat exchanger in sequence, absorbs heat, vaporizes, and is discharged from the outlet.

[0012] In the ORC integrated power generation system, the first power generation working fluid is pressurized by the second working fluid pump, and then passes through the seventh heat exchanger, the fourth heat exchanger, and the eighth heat exchanger in sequence to be heated to superheated steam, and expands and performs work in the first expander. The expanded working fluid is separated into two parts by the first separator, and enters the first heat exchanger and the second heat exchanger respectively for heat exchange and condensation into saturated liquid, and then enters the second mixer for mixing and enters the next cycle.

[0013] In the KC integrated power generation system, the third working fluid pump pressurizes the second power generation working fluid after heat exchange in the seventh heat exchanger, and it passes through the third heat exchanger, the fourth heat exchanger, and the ninth heat exchanger in turn to be heated to a superheated liquid, and then enters the flash evaporator for flash evaporation. The gas phase enters the second expander to expand and do work, and the liquid phase is mixed with the expanded second power generation working fluid, enters the seventh heat exchanger to be condensed into a saturated liquid, and then enters the next cycle.

[0014] Further, the two-stage ORC waste heat recovery system includes an ORC1 waste heat recovery system and an ORC2 waste heat recovery system;

[0015] The ORC1 waste heat recovery system includes a fourth working fluid pump, a fifth heat exchanger, a tenth heat exchanger, and a fourth expander connected in sequence, and the fourth working fluid pump inlet and the fourth expander outlet are respectively connected to the third heat exchanger to form a closed loop of the ORC1 waste heat recovery system; the ORC2 waste heat recovery system includes a fifth working fluid pump, a sixth heat exchanger, a tenth heat exchanger, and a third expander connected in sequence, and the fifth working fluid pump inlet and the third expander outlet are respectively connected to the fourth heat exchanger to form a closed loop of the ORC2 waste heat recovery system;

[0016] The first heat recovery working fluid circulates in the ORC1 waste heat recovery system, and the second heat recovery working fluid circulates in the ORC2 waste heat recovery system.

[0017] In the ORC1 waste heat recovery system, the fourth working fluid pump pressurizes the first heat recovery working fluid, passes through the fifth heat exchanger and the tenth heat exchanger in turn for heat exchange, and expands and performs work in the fourth expander. The expanded working fluid enters the third heat exchanger for heat exchange with the second power generation working fluid circulating in the KC integrated power generation system and the LNG in the LNG loop. The first heat recovery working fluid is condensed into a saturated liquid and enters the next cycle.

[0018] In the ORC2 waste heat recovery system, the fifth working fluid pump pressurizes the second heat recovery working fluid, passes through the sixth heat exchanger and the tenth heat exchanger in sequence for heat exchange, and expands and performs work in the third expander. The expanded working fluid enters the fourth heat exchanger for heat exchange with the first power generation working fluid circulating in the ORC integrated power generation system, the LNG in the LNG loop, and the second power generation working fluid circulating in the KC integrated power generation system. The second heat recovery working fluid is condensed into a saturated liquid and enters the next cycle.

[0019] Optimally, the first heat recovery working fluid in the ORC1 waste heat recovery system adopts a mixed working fluid, and the second heat recovery working fluid in the ORC2 waste heat recovery system adopts R600.

[0020] Optimally, the fifth heat exchanger uses the circulating water of steelmaking and ironmaking as the heat source; the tenth heat exchanger uses the high-temperature flue gas generated by coking and steel rolling processes as the heat source; the sixth heat exchanger uses the circulating water of steelmaking and ironmaking as the heat source, and the fourth heat exchanger uses the two logistics heated by the third heat exchanger and the logistics heated by the tenth heat exchanger as heat sources at the same time.

[0021] Furthermore, the ninth heat exchanger uses the high-temperature flue gas generated by the coking and steel rolling processes as a heat source, and the eighth heat exchanger uses the flue gas generated by the coking and steel rolling processes as a heat source.

[0022] Furthermore, the first power generation working fluid in the ORC integrated power generation system is R1150, and the second power generation working fluid in the KC integrated power generation system is an ammonia solution with a mass fraction of 0.85.

[0023] The second working fluid pump pressurizes the R1150 after heat exchange with the LNG in the LNG loop, passes through the seventh heat exchanger and the fourth heat exchanger in sequence, and respectively exchanges heat with the second power generation working fluid ammonia solution and R600 circulating in the KC integrated power generation system.

[0024] The first power-generating working fluid expands and performs work in the first expander. The expanded working fluid is separated into two parts by the first separator and enters the first heat exchanger and the second heat exchanger respectively to exchange heat with the LNG in the LNG loop to reduce heat transfer losses. Finally, the first power-generating working fluid is condensed into a saturated liquid.

[0025] The third working fluid pump pressurizes the ammonia solution after heat exchange with the first power generation working fluid in the ORC integrated power generation system to 7MPa, passes through the seventh heat exchanger, the third heat exchanger, and the fourth heat exchanger in sequence, and respectively exchanges heat with the first power generation working fluid R1150, the mixed working fluid, and R600 circulating in the ORC integrated power generation system.

[0026] Furthermore, a gas output end and a liquid output end are provided on the flash tank. The gas output end is connected to the second expander. The liquid output end and the second expander are respectively connected to the two inlets of the first mixer. The outlet of the first mixer is connected to the seventh heat exchanger to form a closed-loop structure.

[0027] A working method of the above-mentioned power generation system utilizing LNG cold energy and industrial waste heat recovery comprises the following steps:

[0028] Step 1: After being pressurized by the first working fluid pump, the LNG is subjected to heat exchange with the first power generation working fluid through the first heat exchanger and the second heat exchanger, and then to heat exchange with the second power generation working fluid and the first heat recovery working fluid through the third heat exchanger, and then to heat exchange with the first power generation working fluid, the second power generation working fluid and the second heat recovery working fluid through the fourth heat exchanger, and then absorbs heat to vaporize and expand and is discharged from the outlet, thus completing the cold energy release process of the LNG;

[0029] Step 2: After the first power generation working fluid is pressurized by the second working fluid pump, it exchanges heat with the second power generation working fluid through the seventh heat exchanger, exchanges heat with LNG, the second power generation working fluid, and the second heat recovery working fluid through the fourth heat exchanger, and exchanges heat with the flue gas generated by the coking and steel rolling processes through the eighth heat exchanger. It is gradually vaporized and heated to superheated steam, and enters the first expander to expand and do work, converting mechanical work into electrical energy; the expanded working fluid is separated into two parts through the first separator, and enters the first heat exchanger and the second heat exchanger respectively to exchange heat with LNG and condense into saturated liquid, and enters the second mixer to complete an ORC power generation cycle;

[0030] Step 3: The second power generation working fluid is pressurized by the third working fluid pump, and then passes through the third heat exchanger to exchange heat with LNG and the first heat recovery working fluid, passes through the fourth heat exchanger to exchange heat with LNG, the first power generation working fluid, and the second heat recovery working fluid, passes through the ninth heat exchanger to exchange heat with the high-temperature flue gas generated by the coking and steel rolling processes, and is gradually heated to become a superheated liquid, and enters the flash evaporator for flash evaporation. The gas phase enters the second expander to expand and do work, converting mechanical energy into electrical energy, and the liquid phase is mixed with the expanded second power generation working fluid, and enters the seventh heat exchanger to be condensed into a saturated liquid, completing a KC power generation cycle;

[0031] Step 4: After the first heat recovery working fluid is pressurized by the fourth working fluid pump, it is heat exchanged with the circulating water of steelmaking and ironmaking through the fifth heat exchanger, and is heat exchanged with the high-temperature flue gas generated by the coking and steel rolling process and the second heat recovery working fluid through the tenth heat exchanger, and is gradually vaporized and heated to superheated steam, and enters the fourth expander to expand and do work, and converts mechanical work into electrical energy. The expanded working fluid enters the third heat exchanger to heat exchange and condense with the second power generation working fluid and LNG to enter the next cycle; at the same time, the second heat recovery working fluid is pressurized by the fifth working fluid pump, and is heat exchanged with the circulating water of steelmaking and ironmaking through the sixth heat exchanger, and is heat exchanged with the high-temperature flue gas generated by the coking and steel rolling process and the first heat recovery working fluid through the tenth heat exchanger, and is gradually vaporized and heated to superheated steam, and enters the third expander to expand and do work, and converts mechanical work into electrical energy. The expanded working fluid enters the fourth heat exchanger to heat exchange and condense with LNG, the first power generation working fluid, and the second power generation working fluid to enter the next cycle, completing a power generation cycle of the waste heat recovery system.

[0032] Beneficial effect: Compared with the prior art, the advantages of the present invention are: the present invention couples the organic Rankine cycle and the Kalina cycle according to their operating temperatures, utilizes the Kalina cycle and the organic Rankine cycle to absorb high-temperature and low-temperature industrial waste heat respectively, utilizes LNG cold energy to recover industrial waste heat and converts both into electrical energy, and performs heat exchange with LNG through multiple working fluids and through combined heat exchange with working fluids of each system, thereby improving the comprehensive utilization efficiency of LNG cold energy and realizing reasonable tiered utilization of LNG cold energy and low-grade waste heat resources of steel mills. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a system connection diagram of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0035] A power generation system that utilizes LNG cold energy and industrial waste heat recovery, such as Figure 1 As shown, it includes LNG loop, ORC integrated power generation system, KC integrated power generation system and two-stage ORC waste heat recovery system. After being pressurized by the circulating pump, LNG exchanges heat with the ORC integrated power generation system and the KC integrated power generation system through the LNG loop, and at the same time, the two-stage ORC waste heat recovery system is used to recycle low-grade industrial waste heat resources.

[0036] The LNG circuit includes a first working fluid pump P-1, a first heat exchanger HX-1, a second heat exchanger HX-2, a third heat exchanger HX-3, a fourth heat exchanger HX-4 and the system's cold source LNG, and the first working fluid pump P-1, the first heat exchanger HX-1, the second heat exchanger HX-2, the third heat exchanger HX-3 and the fourth heat exchanger HX-4 are connected in sequence through pipelines; the LNG is pressurized to 0.65MPa by the first working fluid pump P-1, passes through the first heat exchanger HX-1, the second heat exchanger HX-2, the third heat exchanger HX-3 and the fourth heat exchanger HX-4 in sequence, absorbs heat and vaporizes and is discharged from the outlet.

[0037] The ORC integrated power generation system includes a first heat exchanger HX-1, a second heat exchanger HX-2, a second mixer MIX-2, a second working fluid pump P-2, a seventh heat exchanger HX-7, a fourth heat exchanger HX-4, an eighth heat exchanger HX-8, a first expander T-1, a first separator SEP-1 and a first power generation working fluid (R1150) circulating in the ORC integrated power generation system, and the second heat exchanger HX-2, the second mixer MIX-2, the second working fluid pump P-2, the seventh heat exchanger HX-7, the fourth heat exchanger HX-4, the eighth heat exchanger HX-8, the first expander T-1, and the first separator SEP-1 are connected in sequence through pipelines to form a closed loop The structure is as follows: the first separator SEP-1, the first heat exchanger HX-1, and the second mixer MIX-2 are connected in sequence through pipelines to form a loop; the first power generation medium (R1150) is pressurized by the second medium pump P-2, and then passes through the seventh heat exchanger HX-7, the fourth heat exchanger HX-4, and the eighth heat exchanger HX-8 to be heated to superheated steam, and expands and works in the first expander T-1. The expanded medium passes through the first separator SEP-1 and is separated into two parts, respectively entering the first heat exchanger HX-1 and the second heat exchanger HX-2 to exchange heat with the LNG in the LNG loop and condense into saturated liquid, and then enters the second mixer MIX-2 for mixing and then enters the next cycle. The eighth heat exchanger HX-8 uses the flue gas generated by the coking and steel rolling processes as a heat source.

[0038] The KC integrated power generation system includes a seventh heat exchanger HX-7, a third working fluid pump P-3, a third heat exchanger HX-3, a fourth heat exchanger HX-4, a ninth heat exchanger HX-9, a flash tank V-100, a second expander T-2, a first mixer MIX-1 and a second power generation working fluid (an ammonia solution with a mass fraction of 0.85) circulating in the second-stage LNG cold energy utilization power generation system, and the seventh heat exchanger HX-7, the third working fluid pump P-3, the third heat exchanger HX-3, the fourth heat exchanger HX-4, the ninth heat exchanger HX-9, the flash tank V-100, the second expander T-2, and the first mixer MIX-1 are connected in sequence through pipelines; the flash tank is respectively provided with a gas output end and a liquid output end, and the gas output The outlet is connected to the second expander T-2 through a pipeline; the liquid output end and the second expander T-2 are respectively connected to the two inlets of the first mixer MIX-1 through pipelines, and connected to the seventh heat exchanger HX-7 to form a closed loop structure; the third working fluid pump P-3 pressurizes the second power generation working fluid (ammonia solution with a mass fraction of 0.85) after heat exchange in the seventh heat exchanger HX-7 to 7MPa, and passes through the third heat exchanger HX-3, the fourth heat exchanger HX-4, and the ninth heat exchanger HX-9 in turn to be heated to superheated liquid, enter the flash evaporator for flash evaporation, the gas phase enters the second expander to expand and do work, and the liquid phase is mixed with the expanded second power generation working fluid, enters the seventh heat exchanger HX-7 to be condensed into a saturated liquid and enters the next cycle. The ninth heat exchanger HX-9 uses the high-temperature flue gas generated by coking and steel rolling processes as a heat source.

[0039] The two-stage ORC waste heat recovery system includes an ORC1 waste heat recovery system and an ORC2 waste heat recovery system; the ORC1 waste heat recovery system includes a fourth working fluid pump P-4, a fifth heat exchanger HX-5, a tenth heat exchanger HX-10, a third heat exchanger HX-3, a fourth expander T-4 and a first heat recovery working fluid (mixed working fluid) circulating in the waste heat recovery system, and the fourth working fluid pump P-4, the fifth heat exchanger HX-5, the tenth heat exchanger HX-10, the fourth expander T-4, the third heat exchanger HX-3, the fourth expander T-4 and the first heat recovery working fluid (mixed working fluid) circulating in the waste heat recovery system. X-3 are connected in sequence through pipelines to form a closed-loop structure; the fourth working fluid pump P-4 pressurizes the first heat recovery working fluid (mixed working fluid), passes through the fifth heat exchanger HX-5 and the tenth heat exchanger HX-10 in sequence for heat exchange, and expands and works in the fourth expander P-4. The expanded working fluid enters the third heat exchanger HX-3 and exchanges heat with the second power generation working fluid circulating in the KC integrated power generation system and the LNG in the LNG loop. The first heat recovery working fluid (mixed working fluid) is condensed into a saturated liquid and enters the next cycle. The fifth heat exchanger HX-5 uses the circulating water of steelmaking and ironmaking as the heat source; the tenth heat exchanger uses the high-temperature flue gas generated by the coking and steel rolling processes as the heat source.

[0040] The ORC2 waste heat recovery system includes a fifth working fluid pump P-5, a sixth heat exchanger HX-6, a tenth heat exchanger HX-10, a third expander T-3, a fourth heat exchanger HX-4 and a second heat recovery working fluid (R600) circulating in the waste heat recovery system, and the fifth working fluid pump P-5, the sixth heat exchanger HX-6, the tenth heat exchanger HX-10, the third expander T-3, and the fourth heat exchanger HX-4 are sequentially connected through pipelines to form a closed-loop structure; the fifth working fluid pump P-5 pressurizes the second heat recovery working fluid (R600), sequentially passes through the sixth heat exchanger HX-6 and the tenth heat exchanger HX-10 for heat exchange, and expands and performs work in the third expander P-3. The expanded working fluid enters the fourth heat exchanger HX-4 for heat exchange with the first power generation working fluid circulating in the ORC integrated power generation system, the LNG in the LNG loop, and the second power generation working fluid circulating in the KC integrated power generation system. The second heat recovery working fluid (R600) is condensed into a saturated liquid and enters the next cycle. The sixth heat exchanger HX-6 uses the circulating water of steelmaking and ironmaking as the heat source; the fourth heat exchanger HX-4 uses the two streams heated by the third heat exchanger HX-3 and the stream heated by the tenth heat exchanger HX-10 as the heat source.

[0041] The working method of the power generation system utilizing LNG cold energy and industrial waste heat recovery comprises the following steps:

[0042] Step 1: After being pressurized by the first working fluid pump, the LNG is subjected to heat exchange with the first power generation working fluid through the first heat exchanger and the second heat exchanger, and then to heat exchange with the second power generation working fluid and the first heat recovery working fluid through the third heat exchanger, and then to heat exchange with the first power generation working fluid, the second power generation working fluid and the second heat recovery working fluid through the fourth heat exchanger, and then absorbs heat to vaporize and expand and is discharged from the outlet, thus completing the cold energy release process of the LNG;

[0043] Step 2: After the first power generation working fluid is pressurized by the second working fluid pump, it exchanges heat with the second power generation working fluid through the seventh heat exchanger, exchanges heat with LNG, the second power generation working fluid, and the second heat recovery working fluid through the fourth heat exchanger, and exchanges heat with the flue gas generated by the coking and steel rolling processes through the eighth heat exchanger. It is gradually vaporized and heated to superheated steam, and enters the first expander to expand and do work, converting mechanical work into electrical energy; the expanded working fluid is separated into two parts through the first separator, and enters the first heat exchanger and the second heat exchanger respectively to exchange heat with LNG and condense into saturated liquid, and enters the second mixer to complete an ORC power generation cycle;

[0044] Step 3: The second power generation working fluid is pressurized by the third working fluid pump, and then passes through the third heat exchanger to exchange heat with LNG and the first heat recovery working fluid, passes through the fourth heat exchanger to exchange heat with LNG, the first power generation working fluid, and the second heat recovery working fluid, passes through the ninth heat exchanger to exchange heat with the high-temperature flue gas generated by the coking and steel rolling processes, and is gradually heated to become a superheated liquid, and enters the flash evaporator for flash evaporation. The gas phase enters the second expander to expand and do work, converting mechanical energy into electrical energy, and the liquid phase is mixed with the expanded second power generation working fluid, and enters the seventh heat exchanger to be condensed into a saturated liquid, completing a KC power generation cycle;

[0045] Step 4: After the first heat recovery working fluid is pressurized by the fourth working fluid pump, it is heat exchanged with the circulating water of steelmaking and ironmaking through the fifth heat exchanger, and is heat exchanged with the high-temperature flue gas generated by the coking and steel rolling process and the second heat recovery working fluid through the tenth heat exchanger, and is gradually vaporized and heated to superheated steam, and enters the fourth expander to expand and do work, and converts mechanical work into electrical energy. The expanded working fluid enters the third heat exchanger to heat exchange and condense with the second power generation working fluid and LNG to enter the next cycle; at the same time, the second heat recovery working fluid is pressurized by the fifth working fluid pump, and is heat exchanged with the circulating water of steelmaking and ironmaking through the sixth heat exchanger, and is heat exchanged with the high-temperature flue gas generated by the coking and steel rolling process and the first heat recovery working fluid through the tenth heat exchanger, and is gradually vaporized and heated to superheated steam, and enters the third expander to expand and do work, and converts mechanical work into electrical energy. The expanded working fluid enters the fourth heat exchanger to heat exchange and condense with LNG, the first power generation working fluid, and the second power generation working fluid to enter the next cycle, completing a power generation cycle of the waste heat recovery system.

Claims

1. A power generation system utilizing LNG cold energy and industrial waste heat recovery, characterized in that: It includes a first working fluid pump, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a second mixer, a second working fluid pump, a seventh heat exchanger, an eighth heat exchanger, a first expander, a first separator, a third working fluid pump, a ninth heat exchanger, a flash tank, a second expander, a first mixer, and a two-stage ORC waste heat recovery system; The first working fluid pump, the first heat exchanger, the second heat exchanger, the third heat exchanger, and the fourth heat exchanger connected in sequence through pipelines constitute an LNG loop; the first heat exchanger, the second heat exchanger, the second mixer, the second working fluid pump, the seventh heat exchanger, the fourth heat exchanger, the eighth heat exchanger, the first expander, and the first separator constitute an ORC integrated power generation system; the second heat exchanger, the second mixer, the second working fluid pump, the seventh heat exchanger, the fourth heat exchanger, the eighth heat exchanger, the first expander, and the first separator are connected in sequence through pipelines to form a closed loop; the first separator, the first heat exchanger, and the second mixer are connected in sequence through pipelines; the seventh heat exchanger, the third working fluid pump, the third heat exchanger, the fourth heat exchanger, the ninth heat exchanger, the flash tank, the second expander, and the first mixer, which are connected in sequence through pipelines to form a closed loop, constitute a KC integrated power generation system; the third heat exchanger and the fourth heat exchanger are respectively connected to the two-stage ORC waste heat recovery system; The first power generation medium circulates in the ORC integrated power generation system, and the second power generation medium circulates in the KC integrated power generation system; after being pressurized by the circulation pump, LNG exchanges heat with the ORC integrated power generation system and the KC integrated power generation system through the LNG loop, and at the same time, the two-stage ORC waste heat recovery system recovers low-grade industrial waste heat resources; The two-stage ORC waste heat recovery system includes the ORC1 waste heat recovery system and the ORC2 waste heat recovery system; The ORC1 waste heat recovery system includes a fourth working fluid pump, a fifth heat exchanger, a tenth heat exchanger, and a fourth expander connected in sequence, and the fourth working fluid pump inlet and the fourth expander outlet are respectively connected to the third heat exchanger to form a closed loop of the ORC1 waste heat recovery system; the ORC2 waste heat recovery system includes a fifth working fluid pump, a sixth heat exchanger, a tenth heat exchanger, and a third expander connected in sequence, and the fifth working fluid pump inlet and the third expander outlet are respectively connected to the fourth heat exchanger to form a closed loop of the ORC2 waste heat recovery system; The first heat recovery working fluid circulates in the ORC1 waste heat recovery system, and the second heat recovery working fluid circulates in the ORC2 waste heat recovery system; The first heat recovery working fluid in the ORC1 waste heat recovery system adopts a mixed working fluid, and the second heat recovery working fluid in the ORC2 waste heat recovery system adopts R600; The fifth heat exchanger uses the circulating water of steelmaking and ironmaking as the heat source; the tenth heat exchanger uses the high-temperature flue gas generated by the coking and steel rolling process as the heat source; the sixth heat exchanger uses the circulating water of steelmaking and ironmaking as the heat source, and the fourth heat exchanger uses the two streams heated by the third heat exchanger and the stream heated by the tenth heat exchanger as the heat source; The ninth heat exchanger uses the high-temperature flue gas generated by the coking and steel rolling process as a heat source, and the eighth heat exchanger uses the flue gas generated by the coking and steel rolling process as a heat source; The first power generation working fluid in the ORC integrated power generation system is R1150, and the second power generation working fluid in the KC integrated power generation system is an ammonia solution with a mass fraction of 0.85; The flash tank is provided with a gas output end and a liquid output end. The gas output end is connected to the second expander. The liquid output end and the second expander are respectively connected to the two inlets of the first mixer. The outlet of the first mixer is connected to the seventh heat exchanger to form a closed loop structure.

2. A method for operating a power generation system utilizing LNG cold energy and industrial waste heat recovery as claimed in claim 1, characterized in that The following steps are involved: Step 1: After being pressurized by the first working fluid pump, the LNG is subjected to heat exchange with the first power generation working fluid through the first heat exchanger and the second heat exchanger, and then to heat exchange with the second power generation working fluid and the first heat recovery working fluid through the third heat exchanger, and then to heat exchange with the first power generation working fluid, the second power generation working fluid and the second heat recovery working fluid through the fourth heat exchanger, and then absorbs heat to vaporize and expand and is discharged from the outlet, thus completing the cold energy release process of the LNG; Step 2: After the first power generation working fluid is pressurized by the second working fluid pump, it exchanges heat with the second power generation working fluid through the seventh heat exchanger, exchanges heat with LNG, the second power generation working fluid, and the second heat recovery working fluid through the fourth heat exchanger, and exchanges heat with the flue gas generated by the coking and steel rolling processes through the eighth heat exchanger. It is gradually vaporized and heated to superheated steam, and enters the first expander to expand and do work, converting mechanical work into electrical energy; the expanded working fluid is separated into two parts through the first separator, and enters the first heat exchanger and the second heat exchanger respectively to exchange heat with LNG and condense into saturated liquid, and enters the second mixer to complete an ORC power generation cycle; Step 3: The second power generation working fluid is pressurized by the third working fluid pump, and then passes through the third heat exchanger to exchange heat with LNG and the first heat recovery working fluid, passes through the fourth heat exchanger to exchange heat with LNG, the first power generation working fluid, and the second heat recovery working fluid, passes through the ninth heat exchanger to exchange heat with the high-temperature flue gas generated by the coking and steel rolling processes, and is gradually heated to become a superheated liquid, and enters the flash evaporator for flash evaporation. The gas phase enters the second expander to expand and do work, converting mechanical energy into electrical energy, and the liquid phase is mixed with the expanded second power generation working fluid, and enters the seventh heat exchanger to be condensed into a saturated liquid, completing a KC power generation cycle; Step 4: After the first heat recovery working fluid is pressurized by the fourth working fluid pump, it is heat exchanged with the circulating water of steelmaking and ironmaking through the fifth heat exchanger, and is heat exchanged with the high-temperature flue gas generated by the coking and steel rolling process and the second heat recovery working fluid through the tenth heat exchanger, and is gradually vaporized and heated to superheated steam, and enters the fourth expander to expand and do work, and converts mechanical work into electrical energy. The expanded working fluid enters the third heat exchanger to heat exchange and condense with the second power generation working fluid and LNG to enter the next cycle; at the same time, the second heat recovery working fluid is pressurized by the fifth working fluid pump, and is heat exchanged with the circulating water of steelmaking and ironmaking through the sixth heat exchanger, and is heat exchanged with the high-temperature flue gas generated by the coking and steel rolling process and the first heat recovery working fluid through the tenth heat exchanger, and is gradually vaporized and heated to superheated steam, and enters the third expander to expand and do work, and converts mechanical work into electrical energy. The expanded working fluid enters the fourth heat exchanger to heat exchange and condense with LNG, the first power generation working fluid, and the second power generation working fluid to enter the next cycle, completing a power generation cycle of the waste heat recovery system.

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