CN103555382A - Coproduction technology employing mixed-refrigerant cycle (MRC) natural gas liquefaction and direct heat exchange (DHX) tower light hydrocarbon recovery - Google Patents

Abstract

At present, natural gas liquefaction mainly adopts hybrid refrigeration process, and light hydrocarbon recovery mostly adopts DHX tower or expander refrigeration process. Both utilize refrigeration processes. The invention proposes a novel MRC natural gas liquefaction and DHX tower light hydrocarbon recovery co-production process, which combines the MRC natural gas liquefaction and DHX tower light hydrocarbon recovery process, and uses the mixed refrigeration cycle of the liquefaction process to provide refrigeration for light hydrocarbon recovery. At the same time, the heavy components in the raw gas are separated and processed through the light hydrocarbon recovery process. By analyzing the co-production process, the separation efficiency of heavy components in the liquefaction process can be improved, so that the C ₃ content is ≤0.3%, and the C ₄ and C ₄ ⁺ content is reduced to about 0%. At the same time, the cogeneration process is suitable for feed gas with a C ₂ ⁺ content ≥ 0.1. The average increase in LNG production is 71.89%, and the average reduction in unit energy consumption is 17.64%.

Description

MRC natural gas liquefaction and DHX tower light hydrocarbon recovery co-production process

technical field

The invention relates to the technical field of natural gas processing, in particular to a co-production process of MRC natural gas liquefaction and DHX tower light hydrocarbon recovery.

Background technique

Natural gas is the energy with the fastest growing consumption in the 21st century, accounting for an increasing proportion of primary energy consumption. However, the distribution of global natural gas resources is uneven, mainly concentrated in the Middle East and the former Soviet Union. my country's natural gas is mainly distributed in the western and eastern regions. Therefore, in some rich natural gas producing areas or remote areas, it must be transported through pipelines or in the form of liquefaction to areas with small natural gas production and high consumption. During pipeline transportation, in order to prevent heavy hydrocarbons from condensing, freezing, and blocking pipelines due to cooling, heavy hydrocarbons need to be separated through the light hydrocarbon recovery process to reduce the dew point of hydrocarbons and meet the requirements of pipeline gas transportation. At present, most of the natural gas processing is to separate the two processes, the natural gas is first recovered from light hydrocarbons, and then liquefied.

The key to the recovery of light hydrocarbons is how to refrigerate, so that C ₂ ⁺ can be liquefied and separated more. At present, the main means are expansion machine refrigeration and DHX tower reabsorption process. The former is only for high-pressure lean gas, and the latter also requires that the C ₃ content is not more than 11%. The use of the two processes has certain requirements on the raw gas. If the mixed refrigerant refrigeration process commonly used in natural gas liquefaction is used, the complexity of the process and the investment cost will be increased. During the liquefaction process, if relying on refrigerant refrigeration alone, it cannot reach -160°C. Therefore, a throttling valve is often used after refrigeration to achieve the effect of throttling and cooling. The throttling and cooling is mainly to vaporize the part of CH ₄ with the lowest boiling point by reducing the pressure, and the purpose of cooling is achieved by utilizing the heat that needs to be absorbed during gasification. If there are too many heavy hydrocarbon components in the natural gas, the effect of throttling and cooling will be affected.

In recent years, there have been relevant elaborations on which process is used to refrigerate the light hydrocarbon recovery process and the technology related to the cogeneration process of natural gas liquefaction. CN202968508U, CN102994184A, CN102517108 etc. have had comparatively detailed explanation for the technology and device thereof that utilize natural gas liquefaction process to carry out liquid nitrogen co-production, it is mainly to add rectifying tower and then methane and nitrogen are separated in liquefaction process, utilize refrigeration cycle simultaneously Nitrogen is liquefied to achieve the purpose of co-production. CN202246578U, CN102408910A, etc. propose the process of applying the mixed refrigeration cycle to the light hydrocarbon recovery process. Through this process, the _C3 yield can be effectively improved, the benefit of the device can be increased, energy consumption can be reduced, and the adaptability of the device can be enhanced.

Therefore, the co-production process of recycling the mixed refrigerant in natural gas liquefaction in the recovery process of light hydrocarbons can be used for raw gas that needs to recover light hydrocarbons and liquefy, and has greater economic benefits.

Contents of the invention

The invention proposes a co-production process of MRC natural gas liquefaction and DHX tower light hydrocarbon recovery. The object of light hydrocarbon recovery and processing is C ₂ ⁺ , and the processing object of natural gas liquefaction is C ₁ and C ₂ . The mixed refrigeration cycle in the liquefaction process is used to provide cooling capacity for the recovery of light hydrocarbons. At the same time, the heavy components in the raw gas are separated and processed through light hydrocarbon recovery. . On the one hand, it avoids the phenomenon that the load of the subcooling section increases and the liquefaction rate decreases due to incomplete separation of heavy components. On the other hand, it avoids the problems of complex equipment and large investment when the mixed refrigeration cycle is used solely for the recovery of light hydrocarbons. In short, the process is simple, the energy consumption is low, and the comprehensive utilization rate of natural gas can be effectively improved.

The technical scheme that the present invention takes for solving its technical problem is:

The co-production process that combines the MRC natural gas liquefaction with the light hydrocarbon recovery process of the DHX tower uses the mixed refrigeration cycle in the liquefaction process to provide cooling capacity for the recovery of light hydrocarbons, and at the same time uses the deethanizer and debutanizer in the light hydrocarbon recovery process to Removal of heavy hydrocarbons in natural gas. The mixed refrigerant enters the main cold box, and after cooling down to -70°C, the gas and liquid phases are separated through the separation tank. The gas phase passes into the subcooling box to cool down, and then throttles down to about -155°C through the throttle valve, which serves as a cold source to provide cooling capacity for the subcooling box. The liquid phase is cooled by throttling and then mixed with the refrigerant returned from the subcooler and reheated in the main cold box. After reheating, it returns to the main cold box through pressurization and cooling cycle. The raw material gas is cooled to -80°C through the main cold box and then passed into the low-temperature separator. The gas phase enters the heavy contact tower, and the liquid phase enters the deethanizer tower through the cold box. The gas phase at the top outlet of the heavy contact tower passes into the subcooler to cool down, and then cools down to -161.5°C through the throttle valve before entering the storage tank. The gas phase at the top of the deethanizer is cooled by a cold box and used as the absorbent of the heavy contact tower, and the liquid phase at the bottom of the tower is passed into the debutanizer for rectification to obtain liquefied petroleum gas and stable light oil.

Beneficial effect:

1. It avoids the phenomenon that the load of subcooling section increases and the liquefaction rate decreases due to incomplete separation of heavy components.

2. It avoids the problems of complex equipment and large investment when the mixed refrigeration cycle is used alone for light hydrocarbon recovery.

3. It is suitable for feed gas with C ₂ ⁺ content ≥ 0.1. Under this condition, the LNG output can be increased by an average of 71.89%, and the unit energy consumption can be reduced by an average of 17.64%.

4. It can improve the separation efficiency of heavy components in the liquefaction process, so that the content of C ₃ is ≤0.3%, and the content of C ₄ and C ₄ ⁺ is reduced to about 0%.

Description of drawings

Accompanying drawing 1 is technological process of the present invention.

Marks in the figure: A1 is a cold box, B1 and B2 are separation tanks, B3 is an absorption tower, B4 is a deethanizer, B5 is a debutanizer, B6 is a condenser, B7 is a compressor; a is the raw material gas, b is liquefied natural gas (LNG), c is liquefied petroleum gas (LPG), d is stable light oil, and 1-17 is the stream number.

Detailed ways

Below by example the present invention is further described.

Example 1:

The molar composition (mol%) of the raw material gas in this example is: C ₁ 80.2, C ₂ 3.95, C ₃ 6.63, iC ₄ 1.67, nC ₄ 2.7, iC ₅ 1.22, nC ₅ 1.14, C ₆ ⁺ 1.49, N ₂ 0.96, _CO2 0.04. The feed temperature is 25° C., the pressure is 2.8 MPa, and the flow rate is 740 kmol/h.

The mixed refrigerant enters the main cold box, and after cooling down to -70°C, the gas and liquid phases are separated through the separation tank. The gas phase passes into the subcooling box to cool down, and then throttles down to about -155°C through the throttle valve, which serves as a cold source to provide cooling capacity for the subcooling box. The liquid phase is cooled by throttling and then mixed with the refrigerant returned from the subcooler and reheated in the main cold box. After reheating, it returns to the main cold box through pressurization and cooling cycle. The raw material gas is cooled to -80°C through the main cold box and then passed into the low-temperature separator. The gas phase enters the heavy contact tower, and the liquid phase enters the deethanizer tower through the cold box. The gas phase at the top outlet of the heavy contact tower passes into the subcooler to cool down, and then cools down to -161.5°C through the throttle valve before entering the storage tank. The gas phase at the top of the deethanizer is cooled by a cold box and used as the absorbent of the heavy contact tower, and the liquid phase at the bottom of the tower is passed into the debutanizer for rectification to obtain liquefied petroleum gas and stable light oil. The number of trays in the deethanizer is 10, the pressure at the top of the tower is 1800kPa, the pressure at the bottom of the tower is 1850kPa, and the feed position is the fourth tray. The number of trays in the debutanizer is 12, the pressure at the top of the tower is 1300kPa, the pressure at the bottom of the tower is 1350kPa, and the feeding position is the sixth tray.

The production and composition of stable light oil and liquefied petroleum gas produced by the final co-production process and the traditional process have little change. The content of _C3 in LNG is 0.08%, and the content of C4 is 0.00%. The output of LNG is 190.65t/d, and the unit energy consumption is 423.88MJ/t, under the same conditions, the content of _C3 in LNG of traditional technology is 1.48%, C4 is 0.21%, the output of LNG is 116.52t/d, and the unit energy consumption is 524.05MJ/t. Comparing the two processes, the LNG output of the co-production process is increased by 63.62%, and the unit energy consumption is reduced by 19.11%.

Claims (5)

1.MRC natural gas liquefaction and DHX tower lighter hydrocarbons recovery joint process, in by natural gas liquefaction, also can coproduction lighter hydrocarbons, the hybrid refrigeration cycle of utilizing liquefaction process provides cold for lighter hydrocarbons recovery, by lighter hydrocarbons recovery process, the heavy constituent in unstripped gas is carried out to separation, processing simultaneously, technique is mainly divided into mix refrigerant refrigeration cycle part and natural gas liquefaction, lighter hydrocarbons recovery part, it is characterized in that comprising following steps:

(1) compression section: by mix refrigerant supercharging 1～5MPa;

(2) hybrid refrigeration cycle: the mix refrigerant after supercharging enters main ice chest, through cooling after by separating tank separation give vent to anger, liquid two-phase;

Gas phase passed into ice chest cooling lowers the temperature by throttling valve throttling again, as low-temperature receiver, for crossing ice chest, provides cold;

After liquid phase is lowered the temperature by throttling and by refrigerant mixed re-heat in main ice chest of crossing ice chest backflow;

After re-heat, by supercharging, cooling, loop back compression section section;

(3) unstripped gas complete processing section: unstripped gas passes into low-temperature separator by main ice chest cooling, and gas phase enters heavy contact tower, and liquid phase is heated up and entered deethanizing column by ice chest,

The tactile column overhead of reclosing is worked off one's feeling vent one's spleen and was passed into mutually ice chest cooling, then flows to storage tank after lowering the temperature by throttling valve,

Deethanizer overhead gas phase by ice chest, lower the temperature after as the absorption agent of heavy contact tower, at the bottom of tower, liquid phase passes into debutanizing tower rectifying and obtains liquefied petroleum gas (LPG) and stable light oil.

2. according to processing method claimed in claim 1, it is characterized in that: mix refrigerant is mainly comprised of methane, ethane, propane, nitrogen, and wherein ratio of components is about: 5:3:1:1; Its intake pressure is about 0.1MPa, and temperature is about 25 ℃.

3. according to processing method claimed in claim 1, it is characterized in that: the temperature that mix refrigerant goes out main ice chest is about-70 ℃; Mix refrigerant pressure after throttling valve step-down is about 200kPa.

4. according to processing method claimed in claim 1, it is characterized in that: the temperature that unstripped gas goes out main ice chest is about-70 ℃.

5. according to processing method claimed in claim 1, it is characterized in that: the stage number of deethanizing column is 10, feed entrance point is the 4th block of column plate; The stage number of debutanizing tower is 12, and feed entrance point is the 6th block of column plate.

Images