阅读说明：本技术 一种井口高压天然气节流制备lng的系统及工艺 (System and process for preparing LNG (liquefied natural gas) by throttling wellhead high-pressure natural gas ) 是由 唐建勋 王建国 白俊生 王琪 于 2020-06-01 设计创作，主要内容包括：本发明提供了一种井口高压天然气节流制备LNG的系统及工艺,该工艺包括对来自井口的高压天然气进行除砂,再对除砂后的天然气进行过滤分离,以除去天然气中所携带的游离水、部分重烃及杂质；对过滤分离后的天然气进行第一次干燥；对第一次干燥后的天然气进行节流降压降温；利用节流后的低温天然气对高压饱和混合冷剂进行预冷并得到复热后的天然气；对复热后的天然气经脱酸处理后进行第二次干燥；第二次干燥后的天然气于液化冷箱中被混合冷剂预冷后进行重烃分离,分离重烃后的天然气再于液化冷箱中降温后出液化冷箱,得到LNG。本发明可实现对边远天然气井进行天然气回收利用并充分释放边远天然气井的产能,提高经济及社会效益。(The invention provides a system and a process for preparing LNG (liquefied natural gas) by throttling wellhead high-pressure natural gas, wherein the process comprises the steps of desanding the high-pressure natural gas from a wellhead, and filtering and separating the desanded natural gas to remove free water, partial heavy hydrocarbon and impurities carried in the natural gas; drying the filtered and separated natural gas for the first time; throttling, depressurizing and cooling the natural gas after the first drying; precooling the high-pressure saturated mixed refrigerant by using the throttled low-temperature natural gas to obtain reheated natural gas; carrying out secondary drying on the reheated natural gas after deacidification treatment; and (3) precooling the natural gas subjected to secondary drying in the liquefied cold box by the mixed refrigerant, then separating heavy hydrocarbons, cooling the natural gas subjected to heavy hydrocarbon separation in the liquefied cold box, and then discharging the natural gas out of the liquefied cold box to obtain the LNG. The invention can realize the natural gas recycling of the remote natural gas well, fully release the productivity of the remote natural gas well and improve the economic and social benefits.)

1. The utility model provides a system for preparation LNG of well head high-pressure natural gas throttle which characterized in that, system for preparation LNG of well head high-pressure natural gas throttle includes:

the system comprises a sand remover, a filtering separator, a primary molecular sieve dehydration sledge, a deacidification sledge, a secondary molecular sieve dehydration sledge, a precooling heat exchanger, a liquefaction cold box and a heavy hydrocarbon separator;

a high-pressure natural gas outlet of a wellhead gas production tree is connected with a gas inlet of the desander through a pipeline, the gas outlet of the desander is connected with a gas inlet of the primary molecular sieve dehydration sledge through a pipeline via a filter separator, the gas outlet of the primary molecular sieve dehydration sledge is connected with a gas inlet of the precooling heat exchanger through a pipeline via a manual throttling angle valve, so that a high-pressure saturated mixed refrigerant is precooled in the precooling heat exchanger to obtain reheated natural gas, and the precooled high-pressure saturated mixed refrigerant outlet of the precooling heat exchanger is connected with a refrigerant channel inlet of the liquefied cold box through a pipeline;

the natural gas export after the reheat of precooling heat exchanger passes through the pipeline in proper order via deacidification sledge, secondary molecular sieve dehydration sledge with the natural gas precooling passageway entry of liquefaction cold box links to each other, the natural gas precooling passageway export of liquefaction cold box pass through the pipeline with the gas inlet of heavy hydrocarbon separator links to each other, the gas outlet of heavy hydrocarbon separator pass through the pipeline with the natural gas cryrogenic passageway entry of liquefaction cold box links to each other, and the export of natural gas cryrogenic passageway passes through the pipeline and links to each other with LNG storage tank or tank wagon.

2. The system of claim 1, further comprising a demercuration debenzolization skid, wherein a gas outlet of the secondary molecular sieve dehydration skid is connected with a gas inlet of the liquefaction cold box through a pipeline via the demercuration debenzolization skid;

preferably, the system further comprises a throttling pressure regulating valve, and a gas outlet of the primary molecular sieve dehydration sledge is connected with a gas inlet of the precooling heat exchanger through a manual throttling angle valve and the throttling pressure regulating valve in sequence through a pipeline;

more preferably, the system further comprises a pressure transmitter, and a gas outlet of the primary molecular sieve dehydration sledge is connected with a gas inlet of the precooling heat exchanger through a manual throttling angle valve, a throttling pressure regulating valve and the pressure transmitter in sequence through a pipeline.

3. The system of claim 1, wherein the heavy hydrocarbon outlet of the heavy hydrocarbon separator is connected via a heavy hydrocarbon JT valve via a line to a heavy hydrocarbon passage inlet of the liquefaction cold tank to provide refrigeration for the liquefaction cold tank, and the heavy hydrocarbon passage outlet is connected via a line to a fuel gas system to use heavy hydrocarbons reheated to ambient temperature as fuel for the fuel gas system.

4. The system of claim 1, wherein the natural gas cryogenic path outlet of the liquefaction cold tank is connected by piping to an LNG storage tank or tanker via a liquefied natural gas JT valve.

5. The system of claim 1, further comprising a plurality of stages of mixed refrigerant compressors and a plurality of stages of mixed refrigerant coolers; the mixed refrigerant is alternately compressed and cooled by a plurality of stages of mixed refrigerant compressors and a plurality of stages of mixed refrigerant coolers, then enters the precooling heat exchanger, and exchanges heat with the throttled natural gas in the precooling heat exchanger.

6. The system as claimed in any one of claims 1 to 5, further comprising a cryogenic mixed refrigerant separator, wherein the refrigerant channel outlet of the liquefaction cold box is connected with the inlet of the cryogenic mixed refrigerant separator through a mixed refrigerant JT valve by a pipeline so as to divide the throttled two-phase mixed refrigerant into two phases, and the two phases are fully mixed with the return channel inlet of the liquefaction cold box and then enter the liquefaction cold box to provide cold for the liquefaction cold box; the two-phase mixture is reheated to a gas phase and then flows out of a return channel of the gasification cold box to enter a plurality of stages of mixed refrigerant compressors and a plurality of stages of mixed refrigerant coolers to be alternately compressed and cooled again for recycling.

7. The process for preparing LNG by throttling the wellhead high-pressure natural gas is characterized by comprising the following steps of:

(1) desanding the high-pressure natural gas from a wellhead, and filtering and separating the desanded natural gas to remove free water, partial heavy hydrocarbon and impurities carried in the natural gas;

(2) drying the filtered and separated natural gas for the first time;

(3) throttling, depressurizing and cooling the natural gas after the first drying;

(4) precooling the high-pressure saturated mixed refrigerant by using the throttled low-temperature natural gas to obtain reheated natural gas; preferably, the temperature of the natural gas after reheating is 30-35 ℃;

(5) carrying out secondary drying on the reheated natural gas after deacidification treatment; also preferably, the natural gas after deacidification treatment contains CO₂Content less than 50ppm, H₂The S content is lower than 4 ppm; also preferably, the water dew point of the natural gas after the second drying is below-70 ℃;

(6) the natural gas after the secondary drying is precooled by the mixed refrigerant in the liquefaction cold box and then subjected to heavy hydrocarbon separation, and the natural gas after the heavy hydrocarbon separation is cooled in the liquefaction cold box and then is discharged from the liquefaction cold box to obtain LNG;

also preferably, the temperature of the precooled natural gas is-65 ℃ to-68 ℃; also preferably, the temperature of the cooled natural gas is below-158 ℃; still preferably, the LNG enters an LNG storage tank or a tanker after being throttled to 0.05-0.2MPa by a liquefied natural gas JT valve.

8. The process of claim 7, wherein in step (2), the filtered and separated natural gas is subjected to a first drying so that the dew point of the first dried natural gas at 5MPa is less than-50 ℃.

9. The process of claim 7, wherein in the step (3), the throttling, depressurizing and cooling of the natural gas after the first drying comprises:

primarily throttling the natural gas after the primary drying to 5-7MPa, further throttling and regulating the pressure to 4.5-5.5MPa, and reducing the temperature of the natural gas to below-36.3 ℃.

10. The process according to any one of claims 7 to 9, further comprising cooling and throttling the pre-cooled high-pressure saturated mixed refrigerant, separating the two phases, and allowing the separated two phases to enter the liquefaction cold box after being sufficiently mixed at the inlet of the return channel of the liquefaction cold box so as to provide cold for the liquefaction cold box; the two-phase mixture is reheated to a gas phase and then flows out of a return channel of the gasification cold box to enter a plurality of stages of mixed refrigerant compressors and a plurality of stages of mixed refrigerant coolers to be alternately compressed and cooled again for recycling;

preferably, the temperature of the cooled high-pressure saturated mixed refrigerant is below-161 ℃;

also preferably, the process further comprises the step of carrying out mercury removal and benzene removal treatment on the natural gas after the second drying before the step (6);

preferably, the process further comprises the step of recycling heavy hydrocarbon obtained by heavy hydrocarbon separation in the step (6) to the liquefaction cold box to provide cold for the liquefaction cold box; and then the heavy hydrocarbon reheated to normal temperature is used as fuel of a fuel gas system.

Technical Field

The invention relates to a system and a process for preparing LNG (liquefied natural gas) by throttling wellhead high-pressure natural gas, and belongs to the technical field of oil and gas field exploitation.

Background

Along with the continuous development of domestic gas fields, scattered wells and remote wells are increased continuously, some yields do not meet the requirement of laying pipelines, some locations are far away and cannot be merged into a gathering and transportation pipe network, so that the gas wells are closed all the year round, the productivity of the gas wells cannot be released, resources cannot be reasonably utilized, the early drilling investment cannot be timely recovered, and the great energy waste is caused.

The small-size LNG device is a more mature remote gas well gas recovery unit in China, and the device utilizes the characteristics of small LNG volume and high storage and transportation efficiency, and can better recover the remote gas well. And meanwhile, skid-mounted design is carried out, so that the device can be conveniently transported, quickly installed and flexibly moved, and the utilization performance of the device is improved.

Because the pressure of the natural gas at the well mouth from the stratum is generally higher, particularly for various atmospheric fields in the northwest, the pressure of the natural gas at the well mouth is more than 15MPa, and the conventional method at present is to throttle and reduce the pressure of the high-pressure natural gas to about 5MPa and then enter an LNG production device, so that huge pressure energy is wasted.

Therefore, it has become an urgent technical problem in the art to provide a novel system and process for preparing LNG by throttling natural gas at high pressure at a wellhead.

Disclosure of Invention

To address the above-described shortcomings and drawbacks, it is an object of the present invention to provide a system for throttling the production of LNG from a wellhead high pressure natural gas.

It is yet another object of the present invention to provide a process for producing LNG at a wellhead high pressure natural gas throttling.

In order to achieve the above object, in one aspect, the present invention provides a system for preparing LNG by throttling a wellhead high-pressure natural gas, wherein the system for preparing LNG by throttling the wellhead high-pressure natural gas comprises:

the system comprises a sand remover, a filtering separator, a primary molecular sieve dehydration sledge, a deacidification sledge, a secondary molecular sieve dehydration sledge, a precooling heat exchanger, a liquefaction cold box and a heavy hydrocarbon separator;

a high-pressure natural gas outlet of a wellhead gas production tree is connected with a gas inlet of the desander through a pipeline, the gas outlet of the desander is connected with a gas inlet of the primary molecular sieve dehydration sledge through a pipeline via a filter separator, the gas outlet of the primary molecular sieve dehydration sledge is connected with a gas inlet of the precooling heat exchanger through a pipeline via a manual throttling angle valve, so that a high-pressure saturated mixed refrigerant is precooled in the precooling heat exchanger to obtain reheated natural gas, and the precooled high-pressure saturated mixed refrigerant outlet of the precooling heat exchanger is connected with a refrigerant channel inlet of the liquefied cold box through a pipeline;

the natural gas export after the reheat of precooling heat exchanger passes through the pipeline in proper order via deacidification sledge, secondary molecular sieve dehydration sledge with the natural gas precooling passageway entry of liquefaction cold box links to each other, the natural gas precooling passageway export of liquefaction cold box pass through the pipeline with the gas inlet of heavy hydrocarbon separator links to each other, the gas outlet of heavy hydrocarbon separator pass through the pipeline with the natural gas cryrogenic passageway entry of liquefaction cold box links to each other, and the export of natural gas cryrogenic passageway passes through the pipeline and links to each other with LNG storage tank or tank wagon.

Preferably, the system further comprises a throttling pressure regulating valve, and a gas outlet of the primary molecular sieve dehydration sledge is connected with a gas inlet of the precooling heat exchanger through a manual throttling angle valve and the throttling pressure regulating valve in sequence through a pipeline;

more preferably, the system further comprises a pressure transmitter, and a gas outlet of the primary molecular sieve dehydration sledge is connected with a gas inlet of the precooling heat exchanger through a manual throttling angle valve, a throttling pressure regulating valve and the pressure transmitter in sequence through a pipeline.

The pressure transmitter is used for detecting the pressure behind the throttling pressure regulating valve to determine the opening degree of the throttling pressure regulating valve, and therefore the pressure behind the throttling pressure regulating valve is guaranteed to be in a relatively stable range.

Preferably, the system also comprises a demercuration debenzolization skid, and a gas outlet of the secondary molecular sieve debenzolization skid is connected with a gas inlet of the liquefaction cold box through a pipeline by the demercuration debenzolization skid.

In the system described above, preferably, the heavy hydrocarbon outlet of the heavy hydrocarbon separator is connected to the heavy hydrocarbon passageway inlet of the liquefaction cold tank via a heavy hydrocarbon JT valve by a pipeline to provide cooling capacity for the liquefaction cold tank, and the heavy hydrocarbon passageway outlet is connected to the fuel gas system by a pipeline to use the heavy hydrocarbon reheated to normal temperature as fuel for the fuel gas system.

In the system described above, preferably, the natural gas cryogenic channel outlet of the liquefaction cold box is connected with the LNG storage tank or the tanker through a pipeline via a liquefied natural gas JT valve.

Preferably, the system further comprises a plurality of stages of mixed refrigerant compressors and a plurality of stages of mixed refrigerant coolers; the mixed refrigerant is alternately compressed and cooled by a plurality of stages of mixed refrigerant compressors and a plurality of stages of mixed refrigerant coolers, then enters the precooling heat exchanger, and exchanges heat with the throttled natural gas in the precooling heat exchanger.

Preferably, the system further comprises a low-temperature mixed refrigerant separator, wherein a refrigerant channel outlet of the liquefaction cold box is connected with an inlet of the low-temperature mixed refrigerant separator through a mixed refrigerant JT valve by a pipeline so as to divide the throttled two-phase mixed refrigerant into two phases, and the two phases are fully mixed at a return channel inlet of the liquefaction cold box and then enter the liquefaction cold box so as to provide cold energy for the liquefaction cold box; the two-phase mixture is reheated to a gas phase and then flows out of a return channel of the gasification cold box to enter a plurality of stages of mixed refrigerant compressors and a plurality of stages of mixed refrigerant coolers to be alternately compressed and cooled again for recycling.

In the system described above, the filter element used in the filter separator has a pore size greater than 40 μm to filter solid particles and macromolecules having a size greater than 40 μm.

In the above system, the pre-cooling heat exchanger and the liquefaction cold box are both aluminum plate-fin heat exchangers.

In the system described above, the mixed refrigerant compressor is a screw compressor.

Because the pressure of natural gas at a well mouth fluctuates, the throttling pressure regulating valve used in the system has good adaptability to the fluctuation of the pressure at the valve inlet within 3 MPa.

The equipment used by the system, such as a sand remover, a filtering separator, a primary molecular sieve dehydration sledge, a deacidification sledge, a secondary molecular sieve dehydration sledge, a precooling heat exchanger, a liquefaction cold box, a low-temperature mixed refrigerant separator, a heavy hydrocarbon separator and the like, is conventional equipment and can be obtained commercially.

The system for preparing LNG by throttling the wellhead high-pressure natural gas is designed and built in a skid-mounted mode, so that investment can be saved, the specification and size of main equipment are obviously reduced, the occupied area is further reduced, the building period is shortened, the system is convenient to move and reutilize at any time, and modularization, skid-mounted liquefaction and integration of natural gas liquefaction equipment of an edge well are facilitated.

On the other hand, the invention also provides a process for preparing LNG by throttling the wellhead high-pressure natural gas, wherein the process for preparing LNG by throttling the wellhead high-pressure natural gas comprises the following steps:

(1) desanding the high-pressure natural gas from a wellhead, and filtering and separating the desanded natural gas to remove free water, partial heavy hydrocarbon and impurities carried in the natural gas;

(2) drying the filtered and separated natural gas for the first time;

(3) throttling, depressurizing and cooling the natural gas after the first drying;

(4) precooling the high-pressure saturated mixed refrigerant by using the throttled low-temperature natural gas to obtain reheated natural gas;

(5) carrying out secondary drying on the reheated natural gas after deacidification treatment;

(6) and (3) precooling the natural gas subjected to secondary drying in the liquefied cold box by the mixed refrigerant, then separating heavy hydrocarbons, cooling the natural gas subjected to heavy hydrocarbon separation in the liquefied cold box, and then discharging the natural gas out of the liquefied cold box to obtain the LNG.

In the above process, since the pressure at the wellhead of the natural gas from the formation generally exceeds 15MPa and contains sand with water to various degrees, the natural gas exiting the wellhead needs to be pretreated before liquefaction, and the process includes: desanding and filteringSeparating free water and impurities, primary drying, throttling, pressure regulating, deacidifying and secondary drying, thus purifying H in natural gas₂S、CO₂And the contents of water, impurities and the like are all less than indexes required by natural gas liquefaction, and the liquefied natural gas enters a natural gas mixed refrigeration liquefaction device to be liquefied into a product LNG.

In the above process, preferably, in the step (2), the filtered and separated natural gas is subjected to primary drying, so that the dew point of the primary dried natural gas at 5MPa is lower than-50 ℃.

In the above process, preferably, in the step (3), throttling, depressurizing and cooling the natural gas after the first drying includes:

primarily throttling the natural gas after the primary drying to 5-7MPa, further throttling and regulating the pressure to 4.5-5.5MPa, and reducing the temperature of the natural gas to below-36.3 ℃.

In the above process, preferably, in the step (4), the temperature of the reheated natural gas is 30-35 ℃.

In the above process, preferably, in the step (5), CO is contained in the natural gas after the deacidification treatment₂Content less than 50ppm, H₂The S content is less than 4 ppm.

In the above process, preferably, in step (5), the water dew point of the natural gas after the second drying is lower than-70 ℃.

In the above process, preferably, in the step (6), the temperature of the precooled natural gas is-65 ℃ to-68 ℃.

In the above process, preferably, in the step (6), the temperature of the cooled natural gas is-158 ℃ or lower.

In the above process, preferably, in step (6), the LNG is throttled to 0.05-0.2MPa by a JT valve of the LNG and then enters an LNG storage tank or tanker.

In the above-mentioned processes, the deacidification treatment and the drying treatment can be realized by the conventional deacidification treatment and drying process in the field, for example, in the embodiment of the invention, the acid gas is removed in the deacidification skid by adopting an amine liquid method, and the saturated water is adsorbed in the primary molecular sieve dehydration skid and the secondary molecular sieve dehydration skid by adopting a molecular sieve adsorption method, so as to realize the drying treatment.

Preferably, the process further comprises the steps of cooling and throttling the precooled high-pressure saturated mixed refrigerant, then separating the two phases, and fully mixing the two phases obtained after separation at the inlet of the return channel of the liquefaction cold box and then feeding the two phases into the liquefaction cold box to provide cold energy for the liquefaction cold box; the two-phase mixture is reheated to a gas phase and then flows out of a return channel of the gasification cold box to enter a plurality of stages of mixed refrigerant compressors and a plurality of stages of mixed refrigerant coolers to be alternately compressed and cooled again for recycling.

In the above process, the temperature of the high-pressure saturated mixed refrigerant after temperature reduction is preferably-161 ℃ or lower.

Preferably, the process further comprises the step of carrying out mercury removal and benzene removal treatment on the natural gas after the second drying before the step (6).

Preferably, the process further comprises the step of recycling heavy hydrocarbon obtained by heavy hydrocarbon separation in the step (6) to the liquefaction cold box to provide cold for the liquefaction cold box; and then the heavy hydrocarbon reheated to normal temperature is used as fuel of a fuel gas system.

The system and the process for preparing the LNG by throttling the wellhead high-pressure natural gas can throttle the wellhead high-pressure natural gas which is far away and can not be connected into a gathering and transportation system on site, and can perform acid removal and secondary drying by reheating after utilizing the cold energy of the wellhead high-pressure natural gas, so that the wellhead high-pressure natural gas can be liquefied into the LNG which can be transported by roads. According to the system and the process provided by the invention, the cold energy generated after the wellhead high-pressure natural gas is throttled is utilized, so that the pressure energy of the stratum is fully utilized, compared with the conventional process, the energy consumption of a mixed refrigerant compressor of a liquefying device can be reduced by more than 19%, the equipment investment is reduced, the natural gas can be recycled for remote natural gas wells, the capacity of the remote natural gas wells is fully released, the economic benefit and the social benefit are improved, and the safety performance of the system is also improved.

The system and the process provided by the invention can realize the on-site direct liquefaction of the natural gas wellhead gas, avoid the upstream investment of gas field gathering and transportation and purification treatment, and further can obviously reduce the investment.

The system and the process provided by the invention are not limited by the number of wellheads in a well site, are suitable for single well sites and multi-well sites, and the total treatment scale of the system and the process can reach 5000Nm³/d-30×10⁴Nm³/d。

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a system for throttling and preparing LNG from wellhead high-pressure natural gas according to embodiment 1 of the present invention.

The main reference numbers illustrate:

1. a gas production tree at a wellhead;

s-01, a desander;

v-01, a filtering separator;

j-01, a manual throttle angle valve;

PV-01, a throttling pressure regulating valve;

PI-01, a pressure transmitter;

b-01, primary molecular sieve dehydration sledge;

b-02, deacidifying the sledge;

b-03, a secondary molecular sieve dehydration sledge;

b-04, demercuration and debenzolization sledge;

c-01, a first-stage mixed refrigerant compressor;

c-02, a second-stage mixed refrigerant compressor;

e-01, a primary cooler;

e-02, a secondary cooler;

e-03, precooling a heat exchanger;

e-04, a liquefaction cold box;

JT-01, heavy hydrocarbon JT valve;

JT-02, mixed refrigerant JT valve;

JT-03, a liquefied natural gas JT valve;

v-02, a heavy hydrocarbon separator;

v-03, low-temperature mixed refrigerant separator.

Detailed Description

In order to clearly understand the technical features, objects and advantages of the present invention, the following detailed description of the technical solutions of the present invention will be made with reference to the following specific examples, which should not be construed as limiting the implementable scope of the present invention.

Example 1

The embodiment provides a system for preparing LNG by throttling wellhead high-pressure natural gas, which is shown in fig. 1, and as can be seen from fig. 1, the system comprises:

a sand remover S-01, a filtering separator V-01, a primary molecular sieve dehydration sledge B-01, a deacidification sledge B-02, a secondary molecular sieve dehydration sledge B-03, a demercuration debenzolization sledge B-04, a precooling heat exchanger E-03, a liquefaction cold box E-04 and a heavy hydrocarbon separator V-02;

the high-pressure natural gas outlet of the wellhead gas production tree 1 is connected with the gas inlet of the desander S-01 through a pipeline, the gas outlet of the desander S-01 is connected with the gas inlet of the primary molecular sieve dehydration sledge B-01 through a filtering separator V-01 by a pipeline, the gas outlet of the primary molecular sieve dehydration sledge B-01 is connected with the gas inlet of the precooling heat exchanger E-03 through a manual throttle angle valve J-01, a throttle pressure regulating valve PV-01 and a pressure transmitter PI-01 in sequence by a pipeline, precooling the high-pressure saturated mixed refrigerant in the precooling heat exchanger E-03 to obtain reheated natural gas, the precooled high-pressure saturated mixed refrigerant outlet of the precooling heat exchanger E-03 is connected with the refrigerant channel inlet of the liquefaction cold box E-04 through a pipeline;

the pressure transmitter PI-01 is used for detecting the pressure behind the throttling pressure regulating valve PV-01 to determine the opening degree of the throttling pressure regulating valve PV-01, and further ensure that the pressure behind the throttling pressure regulating valve PV-01 is in a relatively stable range;

the reheated natural gas outlet of the precooling heat exchanger E-03 is sequentially connected with the natural gas precooling channel inlet of the liquefied cold box E-04 through a deacidification sledge B-02, a secondary molecular sieve dehydration sledge B-03 and a demercuration debenzolization sledge B-04 by pipelines, the natural gas precooling channel outlet of the liquefied cold box E-04 is connected with the gas inlet of the heavy hydrocarbon separator V-02 by a pipeline, the gas outlet of the heavy hydrocarbon separator V-02 is connected with the natural gas cryogenic channel inlet of the liquefied cold box E-04 by a pipeline, and the natural gas cryogenic channel outlet is connected with an LNG storage tank or a tank car by a liquefied natural gas JT valve JT-03 by a pipeline; a heavy hydrocarbon outlet of the heavy hydrocarbon separator V-02 is connected with a heavy hydrocarbon channel inlet of the liquefaction cold box E-04 through a heavy hydrocarbon JT-01 valve by a pipeline so as to provide cold energy for the liquefaction cold box, and the heavy hydrocarbon channel outlet is connected with a fuel gas system by a pipeline so as to use the heavy hydrocarbon reheated to normal temperature as fuel of the fuel gas system;

in the embodiment, the system further comprises a first-stage mixed refrigerant compressor C-01, a first-stage cooler E-01, a second-stage mixed refrigerant compressor C-02 and a second-stage cooler E-02, wherein the mixed refrigerant is alternately compressed and cooled by the first-stage mixed refrigerant compressor C-01, the first-stage cooler E-01, the second-stage mixed refrigerant compressor C-02 and the second-stage cooler E-02 in sequence to obtain high-pressure saturated mixed refrigerant, and the high-pressure saturated mixed refrigerant enters a precooling heat exchanger E-03 and exchanges heat with the throttled natural gas in the precooling heat exchanger E-03;

in this embodiment, the system further includes a low-temperature mixed refrigerant separator V-03, an outlet of a refrigerant passage of the liquefaction cold box E-04 is connected to an inlet of the low-temperature mixed refrigerant separator V-03 through a mixed refrigerant JT-02 via a pipeline to divide the throttled two-phase mixed refrigerant into two phases, and the two phases are fully mixed at an inlet of a return passage of the liquefaction cold box E-04 and then enter the liquefaction cold box E-04 to provide cold energy to the liquefaction cold box E-04; the two-phase mixture is reheated to be in a gas phase and then is taken out of a backflow channel of the liquefaction cold box E-04 to be alternately compressed and cooled by a first-stage mixed refrigerant compressor C-01, a first-stage cooler E-01, a second-stage mixed refrigerant compressor C-02 and a second-stage cooler E-02 in sequence and then recycled to the precooling heat exchanger E-03.

Example 2

The embodiment provides a process for preparing LNG by throttling wellhead high-pressure natural gas, which is implemented by using the system for preparing LNG by throttling wellhead high-pressure natural gas provided by the embodiment 1, and the process comprises the following specific steps:

high-pressure natural gas from a wellhead passes through a sand remover S-01 to remove impurities such as fine sand and the like in a stratum which goes out of the wellhead along with the natural gas;

the natural gas after sand removal enters a filtering separator V-01 to filter and separate free water, partial heavy hydrocarbon and impurities carried in the natural gas in a large amount;

the filtered and separated natural gas enters a primary molecular sieve dehydration sledge B-01 for primary drying, so that the dew point of the primarily dried natural gas at 5MPa is lower than minus 50 ℃;

then the natural gas after the first drying is primarily throttled to about 5-7MPa through a manual throttle valve J-01, and is further throttled and regulated to 4.5MPa through a throttling pressure regulating valve PV-01, and the temperature of the natural gas is reduced to below minus 36.3 ℃;

the throttled and pressure-regulated low-temperature natural gas enters a precooling heat exchanger E-03, and a high-pressure saturated mixed refrigerant which is subjected to two-stage compression by a first-stage mixed refrigerant compressor C-01 and a second-stage mixed refrigerant compressor C-02 and two-stage cooling by a first-stage cooler E-01 and a second-stage cooler E-02 is precooled; the low-temperature natural gas after throttling and pressure regulating in a precooling heat exchanger E-03 is reheated to 30 ℃, the reheated natural gas enters a deacidification sledge B-02 to remove CO in the raw material natural gas₂And H₂S, make it CO₂Content less than 50ppm, H₂The S content is lower than 4 ppm; the deacidified natural gas enters a secondary molecular sieve dehydration sledge B-03 to carry out secondary drying on the natural gas, so that the water dew point of the dried natural gas is lower than-70 ℃;

after meeting the index of entering a natural gas liquefaction system, the dried qualified natural gas enters a natural gas precooling channel of a liquefied cold box E-04, so that the natural gas is precooled to about-65 ℃, then enters a heavy hydrocarbon separator V-02 to separate heavy hydrocarbon, a gas phase which is discharged from the heavy hydrocarbon separator enters a natural gas cryogenic channel, is cooled to below-158 ℃, then is discharged from the cold box, and LNG which is throttled to 0.05MPa (G) by a liquefied natural gas JT-03 valve enters an LNG storage tank or a tanker;

heavy hydrocarbon at the bottom outlet of the heavy hydrocarbon separator V-02 is throttled by a heavy hydrocarbon JT valve JT-01 and then cooled again, then enters a heavy hydrocarbon channel of a liquefaction cold box E-04 to provide cold for the liquefaction cold box, and enters a fuel gas system to be used as fuel after being reheated to normal temperature;

the return refrigerant after the high-pressure mixed refrigerant precooled in the precooling heat exchanger E-03 enters a refrigerant channel of the liquefied cold box E-04 to be throttled is further cooled to a supercooled state, for example, the temperature is lower than-161 ℃, then the throttle pressure reduction is carried out through a mixed refrigerant JT-02, the throttled two-phase mixed refrigerant is separated into two phases by a low-temperature mixed refrigerant separator V-03, the two phases are fully mixed at the inlet of the return channel of the liquefied cold box E-04 and then enter the return channel of the liquefied cold box E-04, further cold energy is provided for the cold box to cool the natural gas to the temperature lower than-158 ℃, meanwhile, the two-phase mixture is reheated to a gas phase and then goes out of the return channel of the liquefied cold box E-04 to sequentially pass through a primary mixed refrigerant compressor C-01, a primary cooler E-01, a secondary mixed refrigerant C-02, And the secondary cooler E-02 is alternately compressed and cooled and then recycled to the precooling heat exchanger E-03.

The above description is only exemplary of the invention and should not be taken as limiting the scope of the invention, so that the invention is intended to cover all modifications and equivalents of the embodiments described herein. In addition, the technical features and the technical inventions of the present invention, the technical features and the technical inventions, and the technical inventions can be freely combined and used.