Method For Producing Methane-Rich Stream And C2+ Hydrocarbon-Rich Stream, And Related Facility

PATENT
Method For Producing Methane-Rich Stream And C2+ Hydrocarbon-Rich Stream, And Related Facility
Pub. No.:  WO/2011/004123
International Application No.:  PCT/FR2010/051437
Publication Date:  13.01.2011
IPC:  F25J 3/02 (2006.01), C07C 7/09 (2006.01)
Applicants:
TECHNIP FRANCE [FR/FR]; 6-8 Allée de l'Arche Faubourg de l'Arche ZAC Danton F-92400 Courbevoie (FR)
Inventors:
GAHIER, Vanessa; (FR).
GOURIOU, Julie; (FR).
BARTHE, Loïc; (FR).
THIEBAULT, Sandra; (FR) 
Abstract:  
Said method includes cooling the supply stream in a first heat exchanger (20), separating in a first disengager (22) so as to produce a light “head” stream (44) and a heavy “foot” stream (45), and dividing the light “head” stream (44) into a dynamic expansion turbine supply fraction (48) and into a supply fraction (46) for a first distillation column (30). The method includes forming a cooled ebb stream (56) from an effluent (54) of a dynamic expansion turbine (26), the portion of the effluent being cooled and at least partially liquefied in a heat exchanger (28). The method includes placing the cooled ebb stream (56) of the heat exchanger (28) into the first distillation column (30).
A method for producing a methane-rich stream and a stream rich in hydrocarbons in C ₂ ⁺ , and associated installation
The present invention relates to a method for producing a methane-rich stream and a stream rich in C 2 hydrocarbons ⁺ from a feed stream containing hydrocarbons, comprising the following steps:
- Cooling at least a first fraction of feed stream in a first heat exchanger;
- Introduction of the first feed fraction cooled in a first separator drum to produce a light stream of head and foot of a heavy stream;
- Current lightweight division head in a split power turbine and power in a fraction of the column;
- Relaxation of the feed fraction in a first turbine expansion turbine dynamic and introducing at least a portion of the expanded fraction in the first turbine in a middle part of a first distillation column;
- Cooling and at least partial condensation of the fraction column feed in a second heat exchanger, relaxation and introduction of the feed fraction in a column cooled upper part of the first distillation column;
- Relaxation and partial vaporization of the heavy stream of foot in the first heat exchanger and introduction of current heavy foot relaxed in a second separator tank to produce an overhead gas fraction and a liquid fraction of a foot;
- Relaxation of the liquid fraction and the foot of introduction into the middle part of the first distillation column;
- Cooling and at least partial condensation of the gaseous fraction head in the second heat exchanger and introduction into the upper part of the first distillation column;
- Recovering a stream of column bottom at the foot of the first distillation column, the stream rich in hydrocarbons in C ₂ ⁺ being formed from the column bottom stream;
- Recovery and heating of a column overhead stream rich in methane,
- Compressing at least a fraction of the column overhead stream in at least a first compressor coupled to the first expansion turbine dynamic and in at least a second compressor;
- Formation of methane-rich stream from the overhead stream of heated and compressed column;
- Taking a slip stream in the current column header;
- Cooling and introduction of the slip stream cooled in an upper part of the first distillation column.
Such a process is intended to produce hydrocarbons in C2 ⁺ , especially as ethylene, ethane, propylene, propane and heavier hydrocarbons, particularly from natural gas, refinery gas or synthetic gas obtained from other hydrocarbon sources such as coal, crude oil, naphtha.
Natural gas usually contains a majority of methane and ethane constituting at least 50 mol% of the gas. It also contains more negligible quantity of heavier hydrocarbons such as propane, butane, pentane. In some cases, it also contains helium, hydrogen, nitrogen and carbon dioxide.
It is necessary to separate heavy hydrocarbons from natural gas to meet at least two requirements.
First, economically, hydrocarbons C ₂ ⁺ , including ethane, propane and butane can be recovered. In addition, demand for natural gas liquids as a feedstock for the petrochemical industry increases continuously and should continue to increase in coming years.
In addition, for reasons of method, it is desirable to separate heavy hydrocarbons to prevent them condense during transport and / or handling of gas. This helps prevent incidents such as the arrival of liquid plugs in the transmission facilities or processing for gaseous effluents.
To separate the hydrocarbons C ₂ ⁺ gas, it is known to use a method of absorbing oil which can recover up to 90% propane and up to about 40% ethane.
To achieve higher recovery rates, expansion of cryogenic processes are used.
In a method known cryogenic expansion, part of the feed stream containing the hydrocarbons is used for reboilers side of a separation column methane.
Then, the various effluents, after partial condensation, are combined to power a gas-liquid separator.
As described in US 5,555,748, the light current obtained at the head of the separator is divided into a first feed fraction of the column, which is condensed before being sent to the feed head of the distillation column and a second fraction that is sent to an expansion turbine dynamic before being reintroduced into the distillation column.
This method has the advantage of being easy to start and provide significant operating flexibility, combined with good efficacy and good safety.
However, economic constraints require further increase process efficiency while maintaining an ethane extraction yield very high. It is also necessary to minimize the footprint of facilities and reduce or eliminate the intake of external refrigerants such as propane, including the implementation of the process of floating on or in sensitive areas in terms of safety.
An object of the invention is therefore to obtain a production process for separating a feed stream containing a hydrocarbon stream rich in hydrocarbons C ₂ ⁺ and a stream rich in methane, a very economical manner, compact and very efficient.
To this end, the invention relates to a method of the aforementioned type, characterized in that the method comprises the following steps:
- Formation of a cooled reflux stream from at least a portion of an effluent from a dynamic expansion turbine, the part of the effluent from the dynamic expansion turbine is cooled and at least partially liquefied in a heat exchanger to form the cooled reflux stream.
The method of the invention may comprise one or more of the following, taken (s) alone or following any (s) combination (s) technically feasible (s):
- It includes the following steps:
- Taking a reboil stream in the first distillation column at a sampling;
- Placing in heat exchange relation with current reboiling part of the effluent from an expansion turbine in the dynamic heat exchanger to cool and at least partially liquefy the part of the effluent from the turbine relaxation dynamics, and
- Reintroduction current reboiling in the first distillation column at a level below the removal level;
- The effluent from the dynamic expansion turbine is formed by the expanded fraction after the first expansion turbine dynamic, the method comprising introducing the expanded fraction after the first expansion turbine dynamic in the second heat exchanger in order to be cooled and partially liquefied;
- It includes the following steps:
- Separating the feed stream into a first fraction of the supply current and at least a second fraction of the supply current,
- Introduction of the first fraction of the supply current in the first heat exchanger;
- Introducing at least a portion of the second fraction of the supply current in a second expansion turbine dynamic, distinct from the first expansion turbine dynamic, the expanded fraction after the second turbine dynamic forming the effluent from the dynamic expansion turbine;
- It includes the following steps:
- Introduction of the expanded fraction after the second expansion turbine dynamic downstream in a separator drum to form a third gaseous overhead stream and a third bottoms stream liquid,
- Cooling of the third gaseous overhead stream in the heat exchanger to form the cooled reflux stream;
- The third gaseous overhead stream is introduced, after cooling, in an auxiliary distillation column, the reflux stream cooled being formed from the bottom stream of the auxiliary distillation column;
- It includes the following steps:
- Cooling and partial condensation of the second fraction of feed stream;
- Introduction of the second fraction of feed stream in a separator drum cooled to form a second upstream gaseous fraction and a second liquid fraction;
- Introduction of the second gas fraction in the second expansion turbine dynamics;
- Introduction of the second liquid fraction, after expansion, in a lower portion of the first distillation column;
- The entire second fraction of the feed stream is introduced into the second expansion turbine without cooling between the dynamic step of separating the feed stream and the step of introducing the second feed stream fraction of the in the second expansion turbine dynamic;
- It includes the following steps:
- Taking a minor fraction of compression in the column overhead stream rich in methane, before the passage of overhead stream rich in methane column in the first compressor,
- Passage of the minor fraction of compression in a third compressor coupled to the second expansion turbine dynamic;
- Introduction of the minor fraction of compressed compression end of the third compressor in the overhead stream of compressed column, downstream of the first compressor;
- It includes the following steps:
- Removal of an extra cooling flow in the column overhead stream rich in methane or in a stream formed from the column overhead stream rich in methane;
- Relaxation and introduction of extra cooling flow expanded in a current flowing upstream of the first expansion turbine, preferably in the first fraction of the cooled feed stream fraction or in the power turbine;
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