CN-122015423-A - Energy-saving natural gas liquefaction process system based on waste heat recovery

CN122015423ACN 122015423 ACN122015423 ACN 122015423ACN-122015423-A

Abstract

The invention provides an energy-saving natural gas liquefaction process system based on waste heat recovery, which belongs to the technical field of natural gas liquefaction and comprises a cooling circulation system and a waste heat recovery system. The system not only fully utilizes high-temperature waste gas discharged by the gas turbine to drive the steam turbine to generate power, but also further recovers medium-low grade waste heat in the exhaust of the steam turbine and heat generated in the compression process of the mixed refrigerant, and is used for precooling raw material natural gas. The multi-stage and multi-source waste heat recovery mode remarkably reduces the energy consumption of the traditional pre-cooling link, improves the overall thermodynamic perfection of the system, and realizes the efficient and low-carbon utilization of energy.

Inventors

PENG YIFEI
LI SHIQI
PENG ZIYAN
ZHANG SHUKAI
WANG JIAYU
LI RONGXIANG
ZHAO HONGZHEN
Tie Shengbin

Assignees

河南聚能深冷技术装备有限公司

Dates

Publication Date: 20260512
Application Date: 20260127

Claims (10)

1. An energy-saving natural gas liquefaction process system based on waste heat recovery is characterized by comprising a cooling circulation system and a waste heat recovery system; the cooling circulation system comprises a first heat exchange device (1), a compressor (2), an expansion device (3), a gas turbine (4), a refrigerant supply module (5) and a second heat exchange device (6), wherein a heat flow channel of the first heat exchange device (1) is used for passing natural gas to be liquefied, a cold flow channel of the first heat exchange device (1), the compressor (2), a heat flow channel of the second heat exchange device (6) and the expansion device (3) are connected through pipelines to form a cooling circulation pipeline, the refrigerant supply module (5) is communicated with the cooling circulation pipeline and used for supplementing mixed refrigerant, and an output shaft of the gas turbine (4) is connected with the compressor (2) and used for driving the compressor to operate; The waste heat recovery system comprises a waste heat boiler (7), a steam turbine (8), a generator (9), third heat exchange equipment (11), a liquid storage bin (12) and a driving pump (13), wherein a hot flow channel of the waste heat boiler (7), the steam turbine (8), the third heat exchange equipment (11), the liquid storage bin (12), the driving pump (13) and a cold flow channel of the second heat exchange equipment (6) are communicated through pipelines to form a recovery circulation pipeline for recovering waste heat generated by the operation of the steam turbine (8) and the compressor (2).
2. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 1, wherein the gas turbine (4) comprises an air inlet, a feed inlet and a discharge outlet, the feed inlet of the gas turbine (4) is connected with a fuel supply device (20) for providing natural gas fuel for the gas turbine (4), the waste heat boiler (7) comprises an air inlet, an air outlet, a liquid inlet and a liquid outlet, the discharge outlet of the gas turbine (4) is communicated with the air inlet of the waste heat boiler (7) and is used for providing high-temperature waste gas for the waste heat boiler (7), the high-temperature waste gas enters the waste heat boiler (7) and can heat liquid in a furnace body to generate steam, and the high-temperature waste gas after use is discharged through the air outlet of the waste heat boiler (7).
3. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 2, wherein the steam turbine (8) comprises a steam inlet and a steam outlet, a liquid outlet of the waste heat boiler (7) is communicated with the steam inlet of the steam turbine (8) and is used for providing steam for the steam turbine (8), the steam turbine (8) is driven to work, an output shaft of the steam turbine (8) is connected with a generator (9), the generator (9) is driven to work through the steam turbine (8), electricity generation and energy saving are achieved, and a heat flow channel inlet of the third heat exchange device (11) is communicated with the steam outlet of the steam turbine (8).
4. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 3, wherein the waste heat recovery system further comprises a raw material supply module (14) and a transfer valve (15), the transfer valve (15) comprises a feeding port, a first feeding port and a second feeding port, a discharging port of the raw material supply module (14) is communicated with the feeding port of the transfer valve (15), the first feeding port of the transfer valve (15) is communicated with a cold flow channel inlet of the third heat exchange device (11), and the second feeding port of the transfer valve (15) and a cold flow channel outlet of the third heat exchange device (11) are both communicated with a hot flow channel inlet of the first heat exchange device (1).
5. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 4, wherein a first temperature detection device (16) is arranged at a steam outlet of the steam turbine (8) and used for detecting the temperature W1 of a gas-liquid mixture, and a second temperature detection device (17) is arranged at a feed inlet of the switching valve (15) and used for detecting the temperature W2 of natural gas entering the switching valve (15).
6. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 5, wherein the temperature W1 of the gas-liquid mixture and the temperature W2 of the natural gas are obtained, if the temperature W2 of the natural gas is higher than the temperature W1 of the gas-liquid mixture, the first feeding port is controlled to be opened, the second feeding port is controlled to be closed, the gas-liquid mixture discharged from the steam outlet of the steam turbine (8) can exchange heat with the natural gas to be liquefied in the cold flow channel of the third heat exchange device (11) when flowing through the hot flow channel of the third heat exchange device (11), so that the temperature of the gas-liquid mixture can be increased, the temperature of the natural gas to be liquefied can be reduced, and the preliminary precooling of the natural gas can be realized; if the temperature W2 of the natural gas is lower than or equal to the temperature W1 of the gas-liquid mixture, the first feeding port is controlled to be closed, and the second feeding port is controlled to be opened, so that the natural gas in the transfer valve (15) can enter a heat flow channel of the first heat exchange equipment (1).
7. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 6, wherein the driving pump (13) is used for controlling the liquid inside the liquid storage bin (12) to circularly flow in the recovery circulation pipeline.
8. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 7, wherein a third temperature detection device (18) is arranged at the inlet of a heat flow channel of the second heat exchange device (6) and is used for detecting the temperature W3 of the mixed refrigerant when the mixed refrigerant enters, and a fourth temperature detection device (19) is arranged at the outlet of the heat flow channel of the second heat exchange device (6) and is used for detecting the temperature W4 of the mixed refrigerant when the mixed refrigerant is discharged.
9. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 8, wherein a target temperature T is set, a temperature W3, a temperature W4 and a pump speed S of a driving pump (13) are obtained, an obtained heat recovery coefficient K is calculated, and the rotating speed of the driving pump (13) is adjusted according to the obtained heat recovery coefficient K to ensure that the temperature W4 is equal to the target temperature T.
10. The energy-saving natural gas liquefaction process system based on waste heat recovery according to claim 9, wherein the first heat exchange device (1), the second heat exchange device (6) and the third heat exchange device (11) are all coiled tube type heat exchangers.

Description

Energy-saving natural gas liquefaction process system based on waste heat recovery Technical Field The invention belongs to the technical field of natural gas liquefaction, and particularly relates to an energy-saving natural gas liquefaction process system based on waste heat recovery. Background Natural gas is a clean, efficient fossil energy source with a continuously growing global consumption. To facilitate long distance transportation and storage, natural gas is often cooled to about-162 ℃ at atmospheric pressure to be converted to liquefied natural gas. However, the natural gas liquefaction process is a high energy industrial process in which the mixed refrigerant compression cooling link is the primary source of energy consumption. Therefore, the method reduces the energy consumption in the liquefaction process, and has important significance for improving the economy of projects and promoting the development of green low carbon. In the prior art, in order to improve energy efficiency, partial liquefaction plants have attempted to recover high temperature exhaust gases (typically at 400-600 ℃) discharged from gas turbines, for example, by using a waste heat boiler to generate steam power. However, this recycling mode has significant limitations and incompleteness, as follows; Firstly, the high-temperature waste gas is not thoroughly recovered, the medium-low grade gas-liquid mixture discharged after the power generation of the steam turbine still carries considerable heat, and the heat is often directly discharged into the environment through a condenser in the existing system, so that the secondary waste of energy is caused; Secondly, medium and low grade waste heat in the core refrigeration cycle is ignored, the temperature and pressure of the mixed refrigerant are obviously increased after the mixed refrigerant is discharged through a compressor in a cooling circulation system, and before the mixed refrigerant enters an expansion device (such as a throttle valve or an expander) for cooling and liquefying, a high-temperature and high-pressure refrigerant working medium must be cooled in a heat exchanger, and the existing technology generally adopts external cold sources such as ambient air or cooling water to directly cool the mixed refrigerant working medium, which is basically heat which is obtained by converting compression work and has a grade obviously higher than that of the environment, and simply and unidirectionally dissipates a large amount of medium and low temperature heat energy, so that the energy contained in the compression work is not fully utilized, and the method is an important reason for low thermodynamic perfection of the whole liquefaction system; Finally, the precooling link is disjointed from the internal waste heat, and at the front end of the liquefaction process, raw natural gas usually needs to be precooled before entering the main liquefaction heat exchanger, and at present, the precooling link depends on an independent precooling unit for combusting more fuel or consuming additional power, so that the energy consumption and carbon emission of the system are further increased. Therefore, in order to solve the above problems, an energy-saving natural gas liquefaction process system based on waste heat recovery is needed. Disclosure of Invention The invention aims to provide an energy-saving natural gas liquefaction process system based on waste heat recovery, and aims to solve the problem that low-grade waste heat is wasted in the natural gas liquefaction process in the prior art. In order to achieve the above purpose, the present invention provides the following technical solutions: an energy-saving natural gas liquefaction process system based on waste heat recovery comprises a cooling circulation system and a waste heat recovery system; The cooling circulation system comprises a first heat exchange device, a compressor, an expansion device, a gas turbine, a refrigerant supply module and a second heat exchange device, wherein a heat flow channel of the first heat exchange device is used for passing natural gas to be liquefied, a cold flow channel of the first heat exchange device, the compressor, a heat flow channel of the second heat exchange device and the expansion device are connected through pipelines to form a cooling circulation pipeline, the refrigerant supply module is communicated with the cooling circulation pipeline and used for supplementing mixed refrigerant, and an output shaft of the gas turbine is connected with the compressor and used for driving the compressor to operate; The waste heat recovery system comprises a waste heat boiler, a steam turbine, a generator, a third heat exchange device, a liquid storage bin and a driving pump, wherein a heat flow channel of the waste heat boiler, the steam turbine and the third heat exchange device, the liquid storage bin, the driving pump and a cold flow channel of the second heat exchange device are communic