Temperature control method of deethanizer and light hydrocarbon fractionation system thereof

Abstract

The invention relates to the technical field of light hydrocarbon fractionation, and particularly discloses a temperature control method of a deethanization column and a light hydrocarbon fractionation system.The temperature control method comprises the steps that an initial fluid is separated through a first low-temperature separator, and a first gaseous fluid and a first liquid fluid are obtained; after expanding and cooling the first gaseous fluid, separating to obtain a second liquid fluid; the second liquid-state fluid enters a second low-temperature separator, and third liquid-state fluid is obtained after separation; dividing the first liquid-state fluid to obtain a first liquid-state divided flow and a second liquid-state divided flow; the first liquid split flow and the third liquid fluid are converged and then reheated, and fourth liquid fluid is obtained through separation; inputting the fourth liquid-state fluid into the middle position of a deethanization column for fractionation; and inputting the second liquid split flow into the top end of the deethanizer for cooling the top end of the deethanizer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of light hydrocarbon fractionation, and particularly relates to a temperature control method of a deethanizer and a light hydrocarbon fractionation system. BACKGROUND

[0002] At present, permanent light hydrocarbon recovery mainly adopts a condensation separation method, an expander + refrigerant refrigeration and a rectifying column fractionation process. Natural gas is cooled to below the dew point temperature, so that C3 and above components are condensed and separated from gas and liquid, thereby obtaining natural gas condensate rich in heavier hydrocarbons. Figure 2 For example, the inlet gas pressure is 1.0 Map, is boosted to 2.5 Mpa by a compressor, enters a molecular sieve dehydration device, the water dew point is reduced to about -70 DEG C, after four-stage heat exchange and temperature reduction through a dry gas reheater, an ammonia evaporator, a liquid hydrocarbon cooler and a main heat exchanger, is reduced to about -50 DEG C, enters a low separation column, the gas phase enters an expander to be reduced to 1.2 Mpa and -70 DEG C, enters a second low separation column for gas-liquid separation again, is heated through a main heat exchanger and a dry gas reheater, is boosted to 1.4 Mpa by an expander and is externally supplied.

[0003] The condensate from the second low separation column is boosted by a light hydrocarbon pump and mixed with the condensate from the first low separation column, enters a deethanizer for fractionation, the gas phase outlet from the deethanizer enters an ammonia condenser for condensation, C3 and above components are condensed into liquid and enter a deethanizer reflux tank, are pumped into the top of the deethanizer and are used as cold reflux of the rectifying section of the deethanizer. The amount of reflux is controlled to make the column top temperature be 0-5 DEG C, the column bottom temperature is controlled by adjusting the steam flow to be 65 DEG C and the column pressure is controlled to be 1.7 Mpa. The mixed light hydrocarbon from which C1 and C2 are removed enters a stable light hydrocarbon column for further warming and fractionation. This results in the following technical defects of the existing light hydrocarbon fractionation system:

[0004] Technical defect one: the process is complicated and the refrigerant refrigeration has large energy consumption. The refrigerant refrigeration includes four processes of compression, condensation, expansion and evaporation. The saturated steam of ammonia is compressed by a compressor to high pressure and high temperature superheated steam, is condensed into high pressure saturated liquid by a water heat exchanger, is changed into low pressure liquid by a throttle valve V1, is evaporated, absorbs heat and thus makes the column top gas be cooled, and the low pressure ammonia saturated steam after heat absorption returns to the inlet of the compressor and enters the next cycle.

[0005] Technical defect two: the reflux pump cavitation does not reach the required amount, the column top temperature is high, the condensate components in the reflux tank are about 400-500 kg / m3, the boiling point is about -20 DEG C under the working condition, the components are light and the boiling point is low, are easy to evaporate, the deethanizer reflux pump often does not reach the required amount after shutdown and restart, often causes the column top temperature to be high and the C3 and above components in the column top reflux tank to be vented in large amount. SUMMARY

[0006] Based on this, the application provides a temperature control method of a deethanizer and a light hydrocarbon fractionation system thereof, which is applied to a light hydrocarbon fractionation process of natural gas, can accurately control the top temperature of the deethanizer, improve the light hydrocarbon yield, and reduce energy consumption.

[0007] According to a first aspect of the application, a temperature control method of a deethanizer is provided, which comprises:

[0008] Separating an initial liquid stream through a first low-temperature separator to obtain a first gaseous stream and a first liquid stream;

[0009] After the first gaseous stream is expanded and cooled, a second liquid stream is separated;

[0010] The second liquid stream enters a second low-temperature separator, and a third liquid stream is obtained after separation;

[0011] The first liquid stream is split into a first liquid split stream and a second liquid split stream;

[0012] The first liquid split stream is reheated after being combined with the third liquid stream, and a fourth liquid stream is separated;

[0013] The fourth liquid stream is input into a middle position of the deethanizer for fractionation;

[0014] The second liquid split stream is input into a top end of the deethanizer for cooling the top end of the deethanizer;

[0015] The temperature of the top end of the deethanizer is adjusted by adjusting the ratio of the flow rate of the first liquid split stream to the flow rate of the first liquid stream;

[0016] The ratio of the flow rate of the first liquid split stream to the flow rate of the first liquid stream ranges from 0.26 to 0.36.

[0017] According to a second aspect of the application, a light hydrocarbon fractionation system used in the above-mentioned temperature control method of a deethanizer is provided, which comprises:

[0018] A cold box is used to collect and temporarily store an initial liquid stream after molecular sieve dehydration treatment, and to pre-cool the initial liquid stream through heat exchange;

[0019] A first low-temperature separator is used to separate the pre-cooled initial liquid stream into a first gaseous stream and a first liquid stream;

[0020] An expander is used to depressurize and cool the first gaseous stream entering the expansion end of the expander to form a second gaseous stream and a second liquid stream, and to discharge the second gaseous stream;

[0021] a second low temperature separator for collecting a second liquid stream from the expander and separating the second liquid stream into a third gaseous stream and a third liquid stream;

[0022] a deethanizer for collecting the first liquid stream and the third liquid stream and separating the first liquid stream and the third liquid stream into a fifth gaseous stream and a fifth liquid stream;

[0023] a bottom processing unit for collecting the fifth liquid stream and separating the fifth liquid stream into stable light hydrocarbon and liquefied petroleum gas by gasification fractionation.

[0024] According to an embodiment of the present application, the system further comprises a first loop;

[0025] The first loop is configured to flow the third gaseous stream in the second low temperature separator back to the cold box and perform reheat by heat exchange with the initial stream.

[0026] The re-heated third gaseous stream enters the pressurized end of the expander, is pressurized and heated, and then flows out.

[0027] According to an embodiment of the present application, the system further comprises a second loop;

[0028] The second loop is configured to flow the third liquid stream in the second low temperature separator back to the cold box and perform reheat by heat exchange with the initial stream.

[0029] According to an embodiment of the present application, the first liquid stream flowing out of the first low temperature separator is split into a first liquid split stream and a second liquid split stream.

[0030] According to an embodiment of the present application, the first liquid split stream and the third liquid stream are combined and flow into the cold box, perform reheat by heat exchange with the initial stream, and form a fourth gaseous stream and a fourth liquid stream.

[0031] According to an embodiment of the present application, the fourth liquid stream enters the middle section of the deethanizer.

[0032] The fourth gaseous stream enters a light hydrocarbon storage tank for storage.

[0033] According to an embodiment of the present application, the second liquid split stream enters the top end of the deethanizer and is used to cool the top end of the deethanizer.

[0034] According to an embodiment of the present application, the bottom processing unit comprises a bottom reboiler and a stabilizer column.

[0035] The bottom reboiler is configured to gasify the fifth liquid stream flowing out of the bottom of the deethanizer, obtain a sixth liquid stream and a sixth gaseous stream, flow the sixth gaseous stream back to the deethanizer, and output the sixth liquid stream to the stabilizer column.

[0036] According to an embodiment of the present application, the stabilizing column is used to separate the sixth liquid stream into stable light hydrocarbon and liquefied petroleum gas.

[0037] From the above technical solution, the deethanizer temperature control method and light hydrocarbon fractionation system provided by the present application have the following beneficial effects:

[0038] The deethanizer temperature control method and light hydrocarbon fractionation system provided by the present application utilize the low-temperature condensate of the first low-temperature separator in the light hydrocarbon condensation separation process of the light hydrocarbon recovery system and the pressure difference between the first low-temperature separator and the deethanizer, adjust the flow of the low-temperature condensate of the first low-temperature separator into the deethanizer through the opening degree of the automatic valve, and control the temperature of the deethanizer.

[0039] The deethanizer temperature control method and light hydrocarbon fractionation system provided by the present application cancel the ammonia compression system by reconstructing the temperature control process, realize the stability of the column top temperature, utilize the low-temperature condensate of the first low-temperature separator and the pressure difference between the first low-temperature separator and the deethanizer, make the condensate of the first low-temperature separator enter the top of the deethanizer through the pressure difference, and control the temperature of the deethanizer through the flow control of the proportional valve. The method can stably control the column top temperature, reduce the column top vent gas, reduce the loss of light hydrocarbon, and improve the yield of light hydrocarbon. The ammonia compressor, ammonia evaporator, ammonia heat exchanger, ammonia storage tank, reflux pump and other devices are canceled, and the system operation out of control caused by the cavitation of the moving device light hydrocarbon pump and the failure of the ammonia compressor is eliminated. The method has the characteristics of temperature stability, simple process and low energy consumption.

[0040] Compared with the conventional refrigerant compression refrigeration column top reflux process, the method cancels the ammonia compressor, ammonia evaporator, ammonia heat exchanger, ammonia storage tank, reflux pump and other devices in the conventional column top reflux process. The problems of high column top temperature, large vent gas volume and low light hydrocarbon yield caused by the failure of the moving device and the selection deviation are eliminated. The method has the characteristics of simple process, stable control and low energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a light hydrocarbon fractionation deethanization temperature control system diagram in the embodiment of the present application;

[0042] Figure 2 is a light hydrocarbon fractionation system diagram in the comparative example 1 of the present application;

[0043] Figure 3 is a deethanizer column top temperature curve diagram of the embodiment 1 of the present application;

[0044] Figure 4 is a deethanizer vent gas component curve diagram of the embodiment 1 of the present application.

[0045] Reference signs:

[0046] 1. Cold box; 2. First cryogenic separator; 3. Second cryogenic separator; 4. De-ethanizer; 5. Reboiler at the bottom of the tower; 6. Light hydrocarbon pump; 7. Expander; 8. Storage tank; 9. Stabilizer; V1. De-ethanizer temperature proportional control valve; V2. First cryogenic separator level proportional control valve; V3. De-ethanizer pressure proportional control valve; V4. De-ethanizer feed switch control valve; V5. Second cryogenic separator high level switch valve. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0048] like Figure 2 The ethane stripper shown is based on a traditional reflux process, primarily consisting of an ammonia compressor, heat exchanger, liquid ammonia storage tank, ammonia evaporator, reflux tank, and reflux pump. Through refrigerant phase change and evaporation, the temperature of the overhead gas is lowered, condensing C3 and higher concentrations into a liquid. This liquid is then pressurized and pumped back to the top of the column as cold reflux. The temperature at the top is controlled by pump V2; as the temperature increases, V2 increases, and as the temperature decreases, V2 decreases.

[0049] Technical Defect 1: The process is complicated and the refrigerant refrigeration consumes a lot of energy. Refrigerant refrigeration includes four processes: compression, condensation, expansion and evaporation. The saturated vapor of ammonia is compressed into 1.2MPa high-pressure, high-temperature superheated vapor by the compressor. It then passes through a water heat exchanger and condenses into high-pressure saturated liquid. After passing through the throttling valve V1, it becomes 0.05MPa low-pressure liquid, which reduces its evaporation temperature. Then it enters the evaporator to absorb heat, thereby cooling the gas at the top of the tower. The low-pressure saturated vapor of ammonia after absorbing heat returns to the compressor inlet and enters the next cycle.

[0050] Compressor power:

[0051] W S =m(h2-h1)Wact=Ws / ηs / ηP

[0052] W act - Actual power of the compressor (kJ / h); Ws - Theoretical power of the compressor (kJ / h); m - Ammonia refrigerant circulation rate (kg / h);

[0053] ηsηP - The isentropic efficiency and mechanical efficiency of the compressor;

[0054] h2-h1- The specific gravity of refrigerant at the compressor outlet and inlet during theoretical compression (kJ / kg);

[0055] W S =31.78kW.

[0056] Technical defect two: the reflux pump cavitation does not increase the amount of tower top temperature, reflux tank in the condensate composition light about 400-500kg / m3, under the working condition of boiling point-20℃ or so, due to the composition of light, low boiling point, volatile, deethanization reflux pump after shutdown restart often cavitation does not increase the amount, often cause the tower top temperature is high, tower top reflux tank C3 above the composition of air quantity.

[0057] Therefore, it is necessary to provide a new deethanization tower temperature control method, and a new light hydrocarbon fractionation process applied to natural gas to improve the light hydrocarbon yield.

[0058] According to the first aspect of the present application, a temperature control method of a deethanization tower 4 is provided, which comprises:

[0059] The initial flow is separated by the first low-temperature separator 2 to obtain a first gaseous flow and a first liquid flow;

[0060] The first gaseous flow is expanded and cooled to obtain a second liquid flow;

[0061] The second liquid flow enters the second low-temperature separator 3 to obtain a third liquid flow after separation;

[0062] The first liquid flow is split to obtain a first liquid split and a second liquid split;

[0063] The first liquid split is combined with the third liquid flow to obtain a fourth liquid flow after reheat;

[0064] The fourth liquid flow is input into the middle part of the deethanization tower 4 for fractionation;

[0065] The second liquid split is input into the top end of the deethanization tower 4 to cool the top end of the deethanization tower 4;

[0066] The temperature of the top end of the deethanization tower 4 is adjusted by adjusting the ratio of the flow rate of the first liquid split to the flow rate of the first liquid flow;

[0067] The ratio of the flow rate of the first liquid split to the flow rate of the first liquid flow is in the range of 0.26-0.36.

[0068] As Figure 1As shown, the molecular sieve gas 2.5Mpa enters the cold box 1 and is pre-cooled by heat exchange with the second low-temperature separator 3-70℃ gas, which is reduced to about-45℃, enters the first low-temperature separator 2 for gas-liquid separation, the gas phase enters the expander 7 to be reduced to 1.2Mpa-70℃, and after further refrigeration, cooling and condensation separation, enters the second low-temperature separation. The condensate separated by the first low-temperature separator 2 is divided into two streams, one of which is mixed with the condensate separated by the second low-temperature separator 3 and then enters the de-ethane column for partial distillation, and the other of which is the condensate with a flow rate Q2 which enters the de-ethane column 4 to control the column top temperature. According to the HYSYS modeling calculation, as shown in Table 1, when the processing gas volume is 10-100 million cubic meters, the Q1 / (Q1+Q2) ratio is between 0.26 and 0.36, and the de-ethane column 4 top temperature can be reduced to-10℃. The present application has a wide application range and can be applied to the temperature control of the de-ethane column 4 of the light hydrocarbon recovery system under different operating loads.

[0069] The present application provides a temperature control method for a de-ethane column 4 and a light hydrocarbon fractionation system thereof. The method utilizes the low-temperature condensate of the first low-temperature separator in the light hydrocarbon condensation separation process of the light hydrocarbon recovery system and the pressure difference between the first low-temperature separator 2 and the de-ethane column 4, adjusts the flow rate of the low-temperature condensate of the first low-temperature separator 2 entering the de-ethane column through the opening degree of the automatic control valve, and controls the temperature of the de-ethane column 4.

[0070] According to the second aspect of the present application, as Figure 1 As shown, a light hydrocarbon fractionation system for use in the above-mentioned temperature control method for a de-ethane column 4 is provided, comprising:

[0071] A cold box 1 is used to collect and temporarily store the initial flow from the molecular sieve dehydration treatment, and to pre-cool the initial flow by heat exchange;

[0072] A first low-temperature separator 2 is used to separate the pre-cooled initial flow into a first gaseous flow and a first liquid flow (-45℃);

[0073] An expander 7 is used for the first gaseous flow to enter the expansion end of the expander 7 to reduce the pressure and temperature, forming a second gaseous flow and a second liquid flow (-70℃), and discharging the second gaseous flow;

[0074] A second low-temperature separator 3 is used to collect the second liquid flow from the expander 7 and separate it to obtain a third gaseous flow and a third liquid flow;

[0075] A de-ethane column 4 is used to collect the first liquid flow and the third liquid flow, and separate them to obtain a fifth gaseous flow and a fifth liquid flow;

[0076] A bottom treatment unit is used to collect the fifth liquid flow, and separate it by gasification fractionation to obtain stable light hydrocarbon and liquefied petroleum gas.

[0077] According to an embodiment of the present application, the system further comprises a PLC station control system, a proportional control valve V1, a proportional control valve V2, a proportional control valve V3, a switch control valve V4 and a switch control valve V5.

[0078] The present application provides a temperature control method of a deethanizer 4 and a light hydrocarbon fractionation system thereof, which realizes stable tower top temperature by reconstructing the temperature control process and canceling the ammonia compression system. The condensate of the first low-temperature separator 2 enters the top of the deethanizer 4 through the pressure difference, and the temperature of the deethanizer 4 is controlled by the flow control of the proportional valve. This method can stably control the tower top temperature, reduce the tower top vent gas, reduce the loss of light hydrocarbon, and improve the yield of light hydrocarbon. The ammonia compressor, ammonia evaporator, ammonia heat exchanger, ammonia storage tank, reflux pump and other devices are canceled, and the system operation out of control caused by the cavitation of the moving device light hydrocarbon pump and the ammonia compressor failure is eliminated. The present application has the characteristics of temperature stability, simple process and low energy consumption.

[0079] Compared with the conventional refrigerant compression refrigeration tower reflux process, the present application cancels the ammonia compressor, ammonia evaporator, ammonia heat exchanger, ammonia storage tank, reflux pump and other devices in the conventional tower reflux process. The problems of high tower top temperature, large vent gas volume and low light hydrocarbon yield caused by the failure of the moving device and the selection deviation are eliminated. The present application has the characteristics of simple process, stable control and low energy consumption.

[0080] The main logical relationship of temperature control is as follows:

[0081] Step 1, V1 controls the temperature T1 of the deethanizer 4. When T1 increases, V1 is opened, the flow of-40℃ low-temperature condensate entering the top of the deethanizer 4 increases, and T1 decreases. Conversely, when T1 decreases, V1 is closed, the flow of-40℃ low-temperature condensate entering the top of the deethanizer 4 decreases, and T1 increases. The tower top is always kept at-10℃.

[0082] Step 2, V3 controls the pressure of the deethanizer 4. When the pressure increases, V3 is opened, the tower top gas enters the low-pressure system, and the tower pressure decreases. Conversely, when the pressure decreases, V3 is closed, the tower pressure gradually increases, and the tower pressure is kept at 1.7Mpa, so that the deethanizer 4 and the first low-temperature separator 2 maintain a pressure difference of 0.8Mpa, and the condensate of the first low-temperature separator 2 can enter the top of the deethanizer 4 through the pressure difference.

[0083] Step 3, V2 controls the liquid level L1 of the first low-temperature separator 2. When L1 increases, V2 is opened, and conversely, when L1 decreases, V2 is closed. The liquid level increases, and L1 is kept stable at 50%.

[0084] Step 4, the liquid level L1 is lower than 30%, the temperature T1 of the deethanizer 4 is still raised, V1 and V2 are closed at the same time, V4 is closed, and the deethanizer 4 stops feeding. When the liquid level L2 of the second low-temperature separator 3 is raised to 80%, V5 is opened, the liquid level of the second low-temperature separator 3 enters the storage tank 8, and when L2 is lowered to 40%, V5 is closed. After L1 is raised to 50%, V1, V2 and V4 are opened, V5 is closed, and the normal logic program is restored.

[0085] According to an embodiment of the present application, the system further comprises a first loop;

[0086] The first loop is used to return the third gaseous flow in the second low-temperature separator 3 to the cold box 1, and perform reheat by heat exchange with the initial flow;

[0087] The third gaseous flow after reheat enters the boost end of the expander 7, and flows out after boost and temperature rise.

[0088] According to an embodiment of the present application, the system further comprises a second loop;

[0089] The second loop is used to return the third liquid flow in the second low-temperature separator 3 to the cold box 1, and perform reheat by heat exchange with the initial flow.

[0090] According to an embodiment of the present application, the first liquid flow out of the first low-temperature separator 2 is divided into a first liquid sub-flow and a second liquid sub-flow.

[0091] According to an embodiment of the present application, the first liquid sub-flow is combined with the third liquid flow to flow into the cold box 1, and performs reheat by heat exchange with the initial flow, to form a fourth gaseous flow and a fourth liquid flow.

[0092] According to an embodiment of the present application, the fourth liquid flow enters the middle part of the deethanizer 4 for fractionation;

[0093] The fourth gaseous flow enters the light hydrocarbon storage tank 8 for storage.

[0094] According to an embodiment of the present application, the second liquid sub-flow enters the top end of the deethanizer 4 for cooling the top end of the deethanizer 4.

[0095] According to an embodiment of the present application, the bottom processing part comprises a bottom reboiler 5 and a stabilizer 9;

[0096] The bottom reboiler 5 is used to gasify the fifth liquid flow out of the bottom of the deethanizer 4, to obtain a sixth liquid flow and a sixth gaseous flow, to return the sixth gaseous flow to the deethanizer 4, and to output the sixth liquid flow to the stabilizer 9.

[0097] According to an embodiment of the present application, the stabilizer 9 is used to separate the sixth liquid flow into stable light hydrocarbons and liquefied petroleum gas.

[0098] The technical solution of the present invention will be described in detail below through preferred embodiments. It should be noted that the specific embodiments in the following text are for illustrative purposes only and are not intended to limit the present invention.

[0099] Example 1

[0100] like Figure 1 As shown, the incoming gas pressure of 2.5 MPa after dehydration by molecular sieve enters cold box 1 and is pre-cooled by heat exchange between the incoming gas temperature of -70℃ and the light hydrocarbon cryogenic stream temperature of -50℃ in the second cryogenic separator. The stream temperature drops to approximately -45℃ and then enters the first cryogenic separator 2 for gas-liquid separation. The gaseous stream enters the expansion end of expander 7, where the pressure drops to 1.2 MPa and the temperature drops to -70℃ for further cooling. After condensation and separation, the stream enters the second cryogenic separator 3 for gas-liquid separation. The gaseous stream from the outlet of the second cryogenic separator 3 enters cold box 1 for reheating. The reheated stream then enters the pressurization end of expander 7, and the pressurized stream is supplied as dry gas.

[0101] The condensate separated by the first cryogenic separator 2 is divided into two streams. A portion of the stream, Q1, is mixed with the condensate separated by the second cryogenic separator 3 and then enters a cold box for reheating. The reheated stream is then divided into two streams, which enter a light hydrocarbon storage tank for storage and then enter a de-ethylation tower for partial distillation.

[0102] The remaining portion of the condensate separated by the first cryogenic separator 2 enters the top of the deethanizer. The flow rate Q2 is controlled by V1, which in turn controls the top temperature of the deethanizer. V3 controls the pressure of the deethanizer; when the pressure increases, V3 opens wider, and the top gas enters the low-pressure system.

[0103] The light hydrocarbon liquid, from which C1 and C2 have been removed, is partially vaporized in a reboiler. The gas phase rises along the column, and the remaining liquid, as the bottom product, enters the middle section of stabilizer column 9. Inside the stabilizer column, it is further heated and fractionated. Liquefied petroleum gas is produced at the top of the column, and stabilized light hydrocarbons are produced at the bottom.

[0104] Comparative Example 1

[0105] like Figure 2 The ethane stripper shown is based on a traditional reflux process, primarily consisting of an ammonia compressor, heat exchanger, liquid ammonia storage tank, ammonia evaporator, reflux tank, and reflux pump. Through refrigerant phase change and evaporation, the temperature of the overhead gas is lowered, condensing C3 and higher concentrations into a liquid. This liquid is then pressurized and pumped back to the top of the column as cold reflux. The temperature at the top is controlled by pump V2; as the temperature increases, V2 increases, and as the temperature decreases, V2 decreases.

[0106] The process is complicated and the refrigerant refrigeration energy consumption is large. The refrigerant refrigeration includes four processes of compression-condensation-expansion-evaporation. The saturated steam of ammonia is compressed to high pressure and high temperature superheated steam by the compressor, and then is condensed to high pressure saturated liquid by the water heat exchanger. The liquid is changed to low pressure liquid by the throttle valve V1, and then is evaporated. The evaporated low pressure ammonia saturated steam is returned to the compressor inlet and enters the next cycle.

[0107] Compressor power:

[0108] W S = m (h2 - h1) Wact = Ws / ηs / ηP

[0109] W act - actual power of the compressor kJ / h; Ws - theoretical power of the compressor kJ / h; m - circulation amount of the ammonia refrigerant kg / h;

[0110] ηsηP - isentropic efficiency and mechanical efficiency of the compressor;

[0111] h2-h1 - specific enthalpy of the refrigerant at the outlet and the inlet of the compressor during the theoretical compression of the compressor kJ / kg;

[0112] W S = 31.78 kW.

[0113] The cavitation of the reflux pump does not reach the amount, the temperature of the top of the tower is high, the condensate composition in the reflux tank is about 400-500 kg / m3, the boiling point is about -20°C under the working condition, and the composition is light, the boiling point is low, and the volatile is easy. After the deethanization reflux pump stops and restarts, the cavitation often does not reach the amount, and the temperature of the top of the tower is often high. The C3 composition in the reflux tank of the top of the tower is discharged in a large amount.

[0114] The gas pressure of the stream after the molecular sieve dehydration is 2.5 MPa, enters the cold box 1, exchanges heat with the second low temperature separator gas temperature -70°C and light hydrocarbon low temperature stream -50°C for precooling, the stream is reduced to about -45°C, enters the first low temperature separator 2 for gas-liquid separation, the gas phase stream enters the expander 7 and is reduced to 1.2 MPa and -70°C for further refrigeration and cooling, and the stream after condensation separation enters the second low temperature separator 3 for gas-liquid separation. The gas phase outlet stream of the second low temperature separator 3 is included in the reheating of the cold box 1, the reheated stream enters the pressurizing end of the expander 7, and the pressurized stream is dry gas supply.

[0115] The separated light hydrocarbon stream is reheated by the cold box 1 and then enters the middle part of the deethanizer 4. The gas phase outlet stream of the deethanizer top enters the ammonia evaporator for cooling and condensation, and the C3 and above are condensed into liquid and enter the reflux tank 12. The C3 and above liquid hydrocarbon in the deethanizer top reflux tank is pumped into the top part of the deethanizer as the cold reflux of the deethanizer rectification section. The top temperature is controlled by the reflux amount control. The saturated steam of ammonia is high-pressure and high-temperature superheated steam. The steam is cooled to saturated liquid by the water heat exchanger, and then is changed into 0.05 MPa low-pressure liquid by the throttle valve V1, so that the evaporation temperature is reduced. Then the low-pressure ammonia saturated steam enters the evaporator to absorb heat, so that the top gas is cooled and the heat is absorbed. The low-pressure ammonia saturated steam after heat absorption returns to the compressor inlet and enters the next cycle.

[0116] The liquid drawn from the bottom of the column is partially gasified by the reboiler, the vapor rises along the column, and the remaining liquid is used as the bottom product and enters the stabilizer 6. The stabilizer is further warmed and fractionated, the top produces liquefied gas, and the bottom produces stable light hydrocarbon.

[0117] Experimental Example 1

[0118] In Example 1, the molecular sieve gas at 2.5 MPa enters the cold box 1 and is pre-cooled by heat exchange with the -70℃ gas of the second low-temperature separator to about -45℃, and then enters the first low-temperature separator 2 for gas-liquid separation. The gas phase enters the expander 7 to be reduced to 1.2 MPa at -70℃, and is further cooled and condensed to separate and enter the second low-temperature separation. The condensate separated by the first low-temperature separator 2 is divided into two streams, one of which is mixed with the condensate separated by the second low-temperature separator 3 and enters the middle part of the deethanizer 4 for fractionation, and the other of which is the condensate with a flow rate Q2 and enters the top of the deethanizer 4 to control the top temperature. According to the HYSYS modeling calculation, as shown in Table 1, when the processing gas volume is 10-100 million cubic meters, the Q1 / (Q1+Q2) ratio is between 0.26 and 0.36, and the deethanizer top temperature can be reduced to -10℃. The application can be applied to the temperature control of the deethanizer 4 of the light hydrocarbon recovery system with different operating loads.

[0119] Table 1: Top flow rate\temperature calculation table

[0120]

[0121] Experimental Example 2

[0122] The application is applied to the light hydrocarbon stabilizer of the Yongqing gas treatment station, as shown in Figures 3-4 The deethanizer top temperature is from -4 to 29℃, and is stabilized to -5 to -10℃. The C3 + The C3 component is reduced from 5%-30% to 2.5-5%

[0123] As shown in Table 2, daily light hydrocarbon production is increased by 1.5 tons, light hydrocarbon yield is 87.9%, which is increased by 12.9 percentage points, ammonia refrigeration system is shut down, ammonia compressor, ammonia evaporator, ammonia heat exchanger, ammonia storage tank, reflux pump and other equipment are cancelled, energy consumption is reduced by 31.78*10 4 Kwh, and the risk is eliminated.

[0124] Table 2 Light hydrocarbon yield statistics of Yongqing gas treatment station

[0125]

[0126] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method of temperature control of a deethanizer, characterized by, The system comprises: separating an initial liquid by a first low-temperature separator to obtain a first gaseous liquid and a first liquid; after the first gaseous liquid is expanded and cooled, a second liquid is obtained by separation; the second liquid enters a second low-temperature separator to obtain a third liquid after separation; the first liquid is split into a first liquid split and a second liquid split; after the first liquid split is combined with the third liquid, it is reheated to obtain a fourth liquid by separation; the fourth liquid is input to a middle position of the deethanizer for fractionation; the second liquid split is input to a top end of the deethanizer to cool the top end of the deethanizer; wherein the temperature of the top end of the deethanizer is adjusted by adjusting the ratio of the flow rate of the first liquid split to the flow rate of the first liquid; the ratio of the flow rate of the first liquid split to the flow rate of the first liquid ranges from 0.26 to 0.

36.

2. A light hydrocarbon fractionation system for use in the temperature control method of the deethanizer of claim 1, characterized by, The system comprises: a cold box for collecting and temporarily storing an initial liquid after molecular sieve dehydration treatment, and pre-cooling the initial liquid by heat exchange; a first low-temperature separator for separating the pre-cooled initial liquid into a first gaseous liquid and a first liquid; an expander, the first gaseous liquid enters the expansion end of the expander to reduce pressure and cool down, forming a second gaseous liquid and a second liquid, and discharging the second gaseous liquid; a second low-temperature separator for collecting the second liquid from the expander and separating it to obtain a third gaseous liquid and a third liquid; a deethanizer for collecting the first liquid and the third liquid, and separating to obtain a fifth gaseous liquid and a fifth liquid; a bottom processing unit for collecting the fifth liquid, and separating the fifth liquid by gasification fractionation to obtain stable light hydrocarbon and liquefied petroleum gas.

3. The system of claim 2, wherein, The system further comprises a first loop; the first loop is used to flow the third gaseous liquid in the second low-temperature separator back to the cold box, and reheat by heat exchange with the initial liquid; the reheated third gaseous liquid enters the pressurized end of the expander, and flows out after being pressurized and heated.

4. The system of claim 2, wherein, The system further comprises a second loop; the second loop is used to flow the third liquid in the second low-temperature separator back to the cold box, and reheat by heat exchange with the initial liquid.

5. The preparation method according to claim 4, characterized in that, The first liquid flowing out of the first low-temperature separator is split into a first liquid split and a second liquid split.

6. The production method according to claim 5, wherein The first liquid split and the third liquid flow into the cold box and reheat by heat exchange with the initial liquid to form a fourth gaseous liquid and a fourth liquid.

7. The production method according to claim 6, characterized by, The fourth liquid enters the middle fractionation of the deethanizer; The fourth gaseous liquid enters a light hydrocarbon storage tank for storage.

8. The preparation method according to claim 5, characterized in that, The second liquid split enters the top end of the deethanizer to cool the top end of the deethanizer.

9. The preparation method according to claim 2, characterized in that, The bottom processing unit comprises a bottom reboiler and a stabilizer column; the bottom reboiler is used to gasify the fifth liquid flowing out of the deethanizer to obtain a sixth liquid and a sixth gaseous liquid, make the sixth gaseous liquid flow back to the deethanizer, and output the sixth liquid to the stabilizer column.

10. The preparation method according to claim 8, characterized in that, The stabilization column is used to separate the sixth liquid fluid into stable light hydrocarbon and liquefied petroleum gas. The stabilization column is used to separate the sixth liquid fluid into stable light hydrocarbon and liquefied petroleum gas.

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