RU77949U1 - INSTALLATION OF LOW-TEMPERATURE SEPARATION OF A HYDROCARBON GAS - Google Patents

Abstract

The utility model relates to low-temperature hydrocarbon gas separation plants for the production of methane, ethane, a wide fraction of light hydrocarbons (BFLH) and helium concentrate, and can be used at gas processing plants. The objective of the utility model is to increase the efficiency of the installation by providing insignificant fluctuations in the efficiency of the turboexpander unit from the maximum possible values with a wide range of changes in the load on the unit. A low-temperature hydrocarbon gas separation unit consists of a gas pre-cooling unit including a heat exchanger, a propane cooler and a first stage separator, a gas condensation and cooling unit including heat exchangers, second and third stage separators, strippers and a turbine expansion unit in the form of a turbine module containing turboexpander and turbocompressor, ethane separation unit and a wide fraction of light hydrocarbons, including demethanizer, deethane isator, heat exchangers, helium concentrate production unit and connecting pipelines. The turbo-expander unit contains two or more parallel installed turbine modules, the number of which is determined depending on the volume of gas entering the turbo-expander. Using the proposed utility model allows to expand the range of permissible loads on the turboexpander unit within ± 25% of design values while maintaining the maximum value of isentropic efficiency in the range of 75-85% and, accordingly, the maximum amount of low-temperature cold generated during this [1n.p.f. , 1 Fig.].

Description

The utility model relates to low-temperature hydrocarbon gas separation plants for the production of methane, ethane, a wide fraction of light hydrocarbons (BFLH) and helium concentrate, in which gas is cooled, in particular, by expanding the return flows in a turboexpander, and can be used in gas processing enterprises.

A known installation for low-temperature separation of hydrocarbon gas, described in the method for the simultaneous production of helium, ethane and heavier hydrocarbons, including a feed pipe for the processed gas, heat exchangers, separators, a helium distillation column with a liquid phase removal line, an expander, a demethanizer column with column feed lines, a line removal of bottoms liquid, pump, fluid supply line to the deethanizer column [USSR Author's Certificate No. 1645796, IPC F25J 3/02, publ. 04/30/91]. The purified, dried gas, divided into streams, enters the heat exchangers, in which it is cooled and partially condensed due to the cold throttled and expanded in the expander of the inverse fractions of the separation gas, demethanization and power supply of the demethanizer column. Then the flows are mixed and separated in the first separator. The liquid evolved in this case is throttled and sent for further separation into a second separator, from where the evaporated helium and light hydrocarbons are fed to the lower part of the helium distillation column. The steam from the first separator is condensed and supercooled in heat exchangers, throttled and fed to the top of the helium distillation column for stripping the helium dissolved in the liquid. The liquid phase of the column is divided into two streams, one of which is throttled, partially

evaporated in a heat exchanger and separated in a third separator. The released liquid is throttled, mixed with the liquid released in the second separator, and fed as a feed to the demethanizer column. The steam released in the third separator is expanded and cooled in the expander, combined with the rest of the liquid phase of the helium column, separated in the separator and the liquid is sent as a cold irrigation to the demethanizer column. The bottom liquid of the demethanizer column is divided into ethane and broad fractions of light hydrocarbons in the deethanizer column.

The closest to the claimed combination of essential features and the achieved result is the installation of low-temperature separation of natural gas to produce ethane fraction, BFLH, helium concentrate and methane fraction, which is currently used at the Gazprom Dobycha Orenburg Helium Plant [V.V.Nikolaev and other. The main processes of physical and physico-chemical gas processing., Moscow, "Nedra", 1998, p.164-167]. The installation comprises a gas pre-cooling unit, including a heat exchanger, a propane cooler and a first stage separator, a gas condensation and supercooling unit, including heat exchangers, second and third stage separators, stripping columns and a turbo-expander unit in the form of a turbine module containing a turboexpander and a turbocharger, a unit separation of ethane and a wide fraction of hydrocarbons, including heat exchangers, demethanizer, deethanizer, a block for the production of helium concentrate.

The feed gas stream passes sequentially through a heat exchanger, a propane cooler, where it is pre-cooled and partially condensed due to the cold return flow of the methane fraction and propane, then it enters the separator to separate the liquid phase. The liquid hydrocarbons separated in the separator are fed to the strengthening section of the demethanizer. The gas stream from the separator is separated

to flows, which, after cooling and partial condensation in heat exchangers, by the return flows of methane fractions are combined and enter the first separator of the second stage, in which the gas stream is enriched with helium, and the liquid with ethane. The vapor phase from this separator is sent to complete condensation in the heat exchangers, after which the flow of supercooled liquid enters the first stripping column. The ethane-enriched liquid from the first separator of the second stage enters the second separator of the second stage. The vapor phase from it is fed into the first stripping column as a stripping gas, and the liquid is fed to the demethanizer.

Gas sequentially passed through two stripping columns and enriched with helium is fed to the distillation column of the helium concentrate production unit, where helium concentrate is released as a result of cooling and condensation of hydrocarbon and nitrogen residues when passing sequentially through heat exchangers.

From the cube of the first stripping column, a high-pressure methane fraction (MPHE) is discharged, one part of which is sent to heat exchangers to cool the natural gas received at the plant, and the other is fed through a heat exchanger for separation into a third-stage separator. The gas phase from the separator is combined with the upper product of the reinforcing section of the demethanizer and enters the expansion into the turbo-expander of the turbo-expander unit. Further, this stream (methane fraction of medium pressure), passing through heat exchangers and combined with the reverse flow of methane fraction of the cube of the first stripper after recovering cold in the heat exchangers, is compressed by the turbocompressor of the turboexpander unit and removed from the unit. The liquid from the separator of the third stage is fed to the irrigation demethanizer.

In the demethanizer, by distillation, the methane fraction is isolated as a distillate and the C _{2 +} hydrocarbon fraction is _higher as the bottom residue of the demethanizer. VAT residue demethanizer goes to

separation into a deethanizer by distillation to obtain the ethane fraction as a distillate, and BFLH as the bottom residue.

A disadvantage of the known installation, as well as its analogue, is that the existing installation design under varying process conditions does not allow to obtain a sufficiently high cooling capacity during the expansion of the high-pressure methane fraction in a turboexpander, sufficient to lower the temperature of natural gas to a given degree of cooling and condensation. This is due to the fact that significant deviations of the load of feed gas supplied to the installation from the nominal design lead to a decrease or increase in the number of MPPHs involved in the expansion process, which accordingly leads to a sharp decrease of up to 30% from the most efficient isentropic efficiency of the turboexpander unit and , therefore, to a decrease in its cooling capacity. As a result, the efficiency of the installation for the production of target products (methane, ethane, BFLH, helium concentrate) drops significantly. At the same time, the working interval of the permissible loads of the technological and tubing equipment of the installation significantly exceeds the working interval of the loads of the turbo-expander unit.

The objective of the claimed utility model is to increase the efficiency of the installation by providing insignificant fluctuations in the efficiency of the turboexpander unit from the maximum possible values with a wide range of changes in the load on the unit.

The task in the proposed installation of low-temperature separation of hydrocarbon gas, consisting of a gas pre-cooling unit, including a heat exchanger, a propane cooler and a first stage separator, a gas condensation and cooling unit, including heat exchangers, second and third stage separators, stripping columns and a turbine expansion unit in the form of a turbine module containing a turboexpander and a turbocompressor, allocation unit

ethane and a wide fraction of light hydrocarbons, including a demethanizer, deethanizer, heat exchangers, a helium concentrate production unit and connecting pipelines, is decided by the fact that the turboexpander unit contains two or more parallel installed turbine modules, the number of which is determined depending on the volume of gas entering the turbine expander.

The choice of the number of turbine modules is carried out depending on the interval of possible unit loads and, accordingly, the number of MPPD supplied for expansion, as well as on the interval of acceptable module loads of the turboexpander unit, at which their maximum isentropic efficiency is achieved.

The technical result obtained due to the fact that the turboexpander unit contains two or more parallel installed turbine modules consists in providing the ability to regulate the operation of the turboexpander unit under variable load conditions by redistributing the MPPD extending to the expansion between the modules so that the turboexpander of each module operates in the maximum possible effective performance mode (i.e., the isentropic efficiency varied in the range of 75 ÷ 85% depending on the change in load of raw gas within ± 25% of the optimal design) in order to achieve the lowest temperature of the MFSD at the outlet of the turbo-expander modules at a given overall degree of expansion as a whole. This makes it possible to increase the efficiency of using a turboexpander unit by 1.25-1.3 times due to its more efficient (operation at a high value of isentropic efficiency) operation under conditions of not only nominal, but also variable loadings of the installation, and to reduce unit specific energy costs per unit products and increase the productivity of the installation for the development of target products.

Figure 1 presents the block diagram of the proposed installation of low-temperature separation of hydrocarbon gas.

The installation contains:

- a gas pre-cooling unit, including a hydrocarbon gas supply pipe 1, a heat exchanger 2, a propane evaporator 3, a first stage separator 4;

- gas condensation and supercooling unit, including heat exchangers 5-7, sequentially installed second stage separators 8-9, third stage separator 10, stripping columns 11, 12 and turbo-expander 13, containing turbo-expanders 14 and turbocompressors 15 (the diagram shows the unit, consisting of of three turbine modules);

- a unit for the separation of ethane and a wide fraction of light hydrocarbons, including a demethanizer, consisting of a reinforcing 16 and stripping 17 sections, and a deethanizer 18;

- a block for producing helium concentrate 19;

- connecting pipelines.

Installation low-temperature separation of hydrocarbon gas works as follows.

Natural gas, previously dried and purified from sulfur compounds and carbon dioxide in previous installations, enters the installation through pipeline 1 to the gas pre-cooling unit. The gas flow passes sequentially through a heat exchanger 2, a propane evaporator 3, where it is pre-cooled and partially condensed due to the cold of the reverse flow of medium pressure methane fraction (MPSD) and boiling propane, then it enters the first stage separator 4 to separate the liquid phase. The liberated liquid phase is removed from the separator 4 and sent to a demethanizer 16 for supply, and the gas phase is first supplied to the heat exchanger 5 of the condensation and gas cooling unit for further cooling and condensation and then to the separator of the second stage 8. The liquid from the separator 8 is throttled to the separator 9 s so that the vapors containing helium formed in this case are sent to the first stripping column 11 as stripping gas, and the remaining liquid is sent to

demethanizer 16 as power. The vapor phase from the separator 8 is sent to complete condensation in heat exchangers 6, 7, after which the stream of supercooled liquid is throttled to the first stripping column 11, from where the stripped gas enriched with helium enters the second stripping column 12 and then to the helium concentrate production unit 19 .

From the cube of the stripping column 11, a high-pressure methane fraction (MPHE) is discharged, part of which, partially evaporating in the heat exchanger 6, is fed to the separation in the separator of the third stage 10, from where the liquid enters the first plate of the demethanizer 16 as the main reflux. The vapor phase from the separator 10 is mixed with MFVD from the top of the demethanizer 16, then the combined stream is fed to the expansion of the turboexpander 14 of each or part of the modules of the turboexpander unit 13. The gas flow between the modules is redistributed by sequentially opening or closing the control valves (not shown in the drawing), feeding gas to turbo expanders of specific modules. The number of modules involved in the process depends on the MFVD flow rate, which is expanded into turbo expanders. So, if the MFVD flow rate exceeds the nominal calculated value of the turbo-expander 14 by more than 25%, then it is necessary to use the turbo-expander 14 of the next module of the turbo-expander unit 13. If the MFVD's flow rate decreases, the turbo-expanders will be excluded from the process by opening and closing the control valves accordingly. The expanded methane fraction in a combined stream passes through heat exchangers 5 and 2, cooling the flows of natural gas received at the plant.

The remaining part of the bottoms liquid of the stripping column 11 is throttled and, after the recovery of the cold in the heat exchangers 7, 6, 5, 2, is combined with the methane fraction stream after expansion, is compressed in the turbocompressor 15 of the turboexpander unit 13 and removed from the installation. In the demethanizer 16, 17, a hydrocarbon mixture is rectified to obtain a methane fraction as a distillate and a hydrocarbon fraction

With _{2 + higher} as the bottom residue, taken away for rectification into the deethanizer 18 to obtain the ethane fraction as a distillate, and as the bottom residue - a wide fraction of light hydrocarbons (BFLH).

Thus, the use of the proposed utility model allows us to expand the range of permissible loads on the turboexpander unit within ± 25% of the design values while maintaining the maximum value of isentropic efficiency in the range of 75-85% and, accordingly, the maximum amount of low-temperature cold generated during this.

Claims (1)

A low-temperature hydrocarbon gas separation unit consisting of a gas pre-cooling unit including a heat exchanger, a propane cooler and a first stage separator, a gas condensation and cooling unit including heat exchangers, second and third stage separators, stripping columns and a turbine expansion unit in the form of a turbine module, containing a turboexpander and a turbocompressor, an ethane separation unit and a wide fraction of light hydrocarbons, including a demethanizer, de anizator, heat exchangers, receiving unit helium concentrate and connecting pipelines, characterized in that the turbo-expander unit comprises two or more parallel modules mounted turbine, the number of which is determined depending on the amount of gas entering the expansion turbine.