Gas separation: processes – Solid sorption – With plural indirect heat transfer steps on solid sorbent or...
Reexamination Certificate
1999-06-02
2001-06-26
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
With plural indirect heat transfer steps on solid sorbent or...
C095S143000, C095S231000
Reexamination Certificate
active
06251165
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solvent recovery process integrated in a gas treating process, the gas, processed or not, can be at least at two temperatures, the difference between these two temperatures being sufficient to ensure the adsorption and desorption operations required for recovery of the solvent.
The process according to the invention is applied for recovering the solvent used in a process for treating a gas containing methane, at least one higher hydrocarbon and water, the aim of the treatment being notably to eliminate the water and/or to extract the higher hydrocarbons.
The process according to the invention applies to any gas treating process using a solvent, during which the gas loads with solvent, and it can have at least two temperature values, the difference between these two temperatures being sufficient to ensure adsorption and desorption operations in order to recover the solvent from the processed gas. The two temperatures are referred to as low temperature and high temperature in the description hereafter.
The process according to the invention advantageously allows to reach additional gains in the operating costs linked with the processing of the gas and to improve the recovery of condensates.
Solvent losses in the gas can lead operators, in the case of offshore processing for example, to consider low-temperature scrubbing processes to be uneconomical. In fact, the costs induced by solvent supply can be very high.
Furthermore, in order to comply with specifications linked with the standards of use, the solvent content in the processed gas, a dehydrated gas for example, can be limited.
The process according to the invention advantageously allows to carry out operations of dehydration and separation of at least part of the condensable hydrocarbons included in the natural gas, within an integrated and optimized process, on account of the recycling of the solvent.
It is also applied in natural gas treating processes in which the solvent used allows to eliminate unwanted constituents such as hydrogen sulfide and/or carbon dioxide.
BACKGROUND OF THE INVENTION
The prior art describes various gas treating processes.
For example, in the claimant's patent FR-2,605,241, the process describes the treatment of a gas using a refrigerated solvent, during which all of the processing operations are carried out: dehydration alone, or associated with extraction of the higher hydrocarbons and/or elimination of the acid gases possibly present.
Another patent registered by the claimant, FR-2,636,857, discloses a process comprising a step of separation of the higher hydrocarbons (NGL in a shortened form), where the solvent can be recovered by washing the liquid hydrocarbons with the water resulting from the dehydration of the gas.
SUMMARY OF THE INVENTION
The present invention proposes a new process allowing to recover the solvent carried along by the processed gas in order to use it again in the gas treating process. The process according to the invention advantageously uses the temperature difference of the gas taken at two points of the treating process in order to carry out the adsorption and the desorption steps performed with suitable devices for recovering the solvent.
The invention relates to a process for recovering a solvent from a fluid such as a gas coming from a treating process using said solvent, the treating process allowing to obtain the gas at two different temperatures, a low temperature, Ta and a high temperature Td, so that the temperature difference Td-Ta is sufficient to perform an adsorption step and a desorption step.
It is characterized in that a) a first solvent-containing gas stream is sent to an adsorption step, said gas being at a temperature Ta, after this adsorption step the gas is practically solvent-free and the solvent is collected in a first adsorption means, b) a second gas stream at a temperature Td, said second gas stream being solvent-free, is sent to carry out desorption of a second adsorption means loaded with solvent during a previous step a), and c) said solvent is recovered and sent at least partly to a step of the treating process using the solvent.
The adsorption means comprise for example adsorbent beds.
According to an embodiment, the second gas stream consists for example of at least part of the gas from step a), said gas having been heated by heat exchange with at least part of the gas to be treated so as to bring its initial temperature close to Ta to a temperature substantially equal to Td.
According to another embodiment, the second gas stream can consist of part of the gas to be treated diverted prior to being subjected to the solvent treating process.
Temperature Td will be obtained by using additional heating means.
The invention also relates to a solvent recovery process integrated in a natural gas treating process using a solvent wherein the natural gas loads with solvent and can be at two temperatures Ta and Td.
It is characterized in that it comprises at least the following steps:
a) the gas to be processed is contacted with a mixture comprising at least one solvent and a gas enriched in solvent is obtained at the end of this step,
b) said solvent-enriched gas is sent to a refrigeration step in order to bring its temperature to a temperature Ta,
c) said solvent-containing gas at a temperature Ta is sent to an adsorption step in a first adsorption means at the outlet of which a practically solvent-free gas is obtained,
d) a step of desorption of a second adsorption means already loaded during a previous adsorption step is carried out by sending a practically solvent-free gas stream at a temperature Td, the temperature difference between Ta and Td being sufficient to carry out the desorption step so as to recover the solvent,
e) the solvent recovered is sent to a step of the gas treating process.
The gas stream used in step d) is for example withdrawn before contacting step a) and the as from step a) is discharged after being used to cool the solvent-rich gas to a temperature substantially close to Ta.
This gas stream used for step d) corresponds for example to a fraction of the gas from adsorption step c), said gas having been heated to a temperature Td by heat exchange with the solvent-rich gas.
Temperature Ta is selected, for example, in the [−60, 25°C] range and preferably in the [−30, 0°C] range.
The value of temperature Td can be selected in the [0, 100°C] range and preferably in the [25, 50°C] range.
The value of temperature Td can be obtained by using additional heating means.
Steps c) and d) can be operated at a pressure value ranging between 0 and 20 MPa and preferably between 3 and 10 MPa.
All of the solvent recovered can for example be sent with the gas to one of the treating steps of the process.
A solvent allowing dehydration of a natural gas can be used, dehydration of the natural gas can be achieved and a mixture of solvent recovered and of natural gas can be reinjected before heat exchange.
Adsorbents such as silicalite, Y type zeolites, a hydrophobic sieve or activated charcoal can be used for example.
The process according to the invention is applied to recover a solvent contained in a gas, the concentration of said solvent ranging between 0 and 500 ppm, preferably between 0 and 200 ppm.
The process according to the invention advantageously allows to recover the natural liquefied gas (NLG), such as the C
3
+.
Integrated in a dehydration process, it allows to independently fix the dew point values for the hydrocarbons and the water. The temperature of the cold drum will be fixed to reach the desired hydrocarbon specification whereas the dew point for the water will be done with the adsorbent. The advantage of this procedure is that the temperature of the cold drum does not have to be lowered too much.
REFERENCES:
patent: 2632726 (1953-03-01), Ringham et al.
patent: 3007543 (1961-11-01), Maher
patent: 3055157 (1962-09-01), Lavery et al.
patent: 3989478 (1976-11-01), Jones
patent: 4043770 (1977-08-01), Jakob
p
Jullian Sophie
Lebas Etienne
Thomas Michel
Antonelli Terry Stout & Kraus LLP
Institut Francais du Pe'trole
Spitzer Robert H.
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