STRIPPING GAS SEPARATION AND RECYCLING PROCESS

Abstract

The invention relates to a stripping separation process primarily applicable to the concentration or separation of liquid mixtures or the drying of solids. The process relies on the recycling of the stripping gas. The compounds carried by the stripping gas are separated by condensation before or after recompression. The heat of condensation is reused to heat the mixture to be separated, while the stripping gas is returned to the chamber. This process combines energy recovery with stripping gas recycling to reduce energy and stripping gas consumption.

Description

Title of the invention: SEPARATION PROCESS WITH RECYCLING OF STRIPPING GAS

[0001] The invention relates to a process for separation by stripping (evaporation of a liquid mixture or drying of a solid) which can be developed for domestic purposes and for industry. It proposes to carry out the separation operation in an economical manner from an energy point of view and with reduced consumption of stripping gas. This process can be applied in the petroleum, chemical or pharmaceutical fields to the separation (or concentration) of liquid mixtures or in the agri-food field to the drying of food, wood, textiles, etc.

[0002] Stripping is a separation operation that uses a gas to lower the partial pressure of the compound that is to be separated from the mixture (liquid or solid). The gas is introduced into a chamber containing the mixture to be separated or dried, it is brought into contact with the mixture, its presence reduces the partial pressure of the compound to be separated which then partially passes into the gas phase so that its partial pressure rises to its vapor pressure (thermodynamic equilibrium). The compound has thus been separated from the mixture, the gas phase consisting of the gas and the evaporated compound(s) is then extracted from the chamber. The repeated operation makes it possible to achieve the desired level of separation. This process is generally used when it is not possible to separate by caloric input (heat-sensitive product) or because the quantity of compound to be extracted is too small to justify heating the mixture.

[0003] In certain applications involving large quantities of compounds to be separated, this process has the disadvantage of being expensive because it consumes said Gas and / or energy. A compromise is sought between energy consumption and that of the stripping Gas. Energy recovery is frequently carried out on the Gas (loaded with compound) at the outlet of the chamber, in particular when the Gas is water vapor.

[0004] Given the rising cost of energy and raw materials, stripping processes present savings challenges.

[0005] The object of the invention is therefore to suggest a method which allows very reduced gas consumption compared to the current art while being energy-efficient.

[0006] [Fig. 1] represents the principle of implementation of the method of the invention from which a person skilled in the art is capable of designing embodiments.

[0007] The process consists of recycling the Gas so as to be able to use it without economic limitation and to create an atmosphere in the separation enclosure which is both favorable to the evaporation of the compounds which it is desired to separate and to the recovery of the energy contained in the Gas + the vapors of the compounds.

[0008] Thus, the method according to the invention comprises a chamber in which the separation (by evaporation, stripping) of a liquid mixture or the separation of a liquid / solid mixture is carried out. A gas (air, nitrogen for example) enters the chamber and takes charge of the compound(s) to be separated. This vapor mixture (gas + compounds) is compressed then condensed. A liquid / vapor separator (4) recovers the (condensed) liquid phase while the vapor phase is returned to the chamber (sometimes called a column in refining) and constitutes said gas.

[0009] The heat recovered during condensation is reused by the chamber to cause the evaporation of the compound(s). This heat can be received directly by the mixture to be separated (by the liquid phase of the chamber, for example), or conveyed by an external fluid depending on convenience (in a closed loop, the fluid recovers the heat of condensation and transfers it to the chamber). In another version, this energy is used to preheat the load (liquid mixture entering the chamber (1), sometimes called feed) or for any other use (for example to create steam which could be used by the compressor turbine), in this case to compensate, an external source of energy (heat exchanger, reference 7, in dotted line in the figure) is to be provided.

[0010] Condensation by a condenser (3) of the gas + compounds leaving the chamber (1) can be carried out before compression. In this case the compressor (2) will only compress the non-condensed part. Beforehand, a liquid / vapor separation allows the compressor (2) to only suck in the vapor. Then the compressed vapor (which contains the heat of compression) can either be returned directly to the chamber or be condensed again by cooling and then returned to the chamber (1) as described previously. When the vapor (gas + compound) is compressed and returned to the chamber (1) without cooling, taking into account the heat of compression, the process may be excess in energy, heat removal by an external means may be necessary.

[0011] An external supply and / or removal of heat can be added (air cooler, heat exchanger, etc.) positioned freely in the process in such a way that the heat is respectively found in the chamber (1) to heat it or removed from the process to ensure the energy balance of the system.

[0012] The pressures in the chamber (1) and at the compressor discharge are maintained at a chosen level by causing pressure losses using pressure-reducing devices (markings 6, orifices, pressure reducers, regulating valves, etc.) which maintain the circuits (reference 9) and the equipment at a chosen pressure by causing pressure losses. The regulation of pressures and level (in the liquid / vapor separator (4) is conventionally ensured by valves (depressurizing devices) and an external circuit of said pressurized gas, nitrogen, air or combustible gas (in an oil refinery) and a torch network not shown in the figure.

[0013] A supply of fresh gas from outside and / or a purge of said gas can be carried out somewhere in the process circuit.

[0014] The temperature / pressure adjustment parameters are set so as to carry out the separation operation under favorable economic conditions depending on the nature of the compounds to be separated and the said chosen gas but also with regard to their impact on the dimensions of the equipment.

[0015] It may also be of interest to provide a vacuum pump on the process circuit to operate at low pressures and facilitate the evaporation of the compounds to be separated.

[0016] Note that during the condensation of the compressed vapor, the compounds do not condense completely, said Gas returned (recycled) to the chamber therefore contains the non-condensed compounds, generally in small quantities. However, to avoid confusion, we continue to call it Gas.

[0017] It is also possible with this system to operate at a lower pressure than that of the atmosphere in the chamber, for this it is necessary to make a purge towards the outside of the process at the discharge of the compressor (preferably after condensation) to compensate for the air inlets from the outside. It is also possible to use a vacuum pump or any other vacuum system (ejectors, etc.) to maintain the chamber under vacuum.

[0018] A portion of the liquid condensates from the condensation(s) can be returned to the chamber, thus acting as reflux to modify the quality of the separation.

[0019] The nature of the mixture to be separated, the duration of the operation or even the domestic or industrial application condition the practical realization by the use of appropriate accessories and equipment. In general, the conceptual realization of the separation system (or apparatus) (stripping, drying, mixture concentrator, etc.) to which this new process can be applied takes up the known elements of such a system.

Claims

[Claim 1] Claims Process for separating a liquid mixture or a liquid / solid mixture, characterized in that it comprises at least the following steps: - Separation in a chamber (1) by evaporation of one or more compounds of said mixture, - The crossing of said chamber by a gas which takes charge of the compound(s), - Compression by a compressor (2) of the vapor phase coming from the chamber and consisting of the mixture Gas + compound(s), - Condensation by a condenser (3) by cooling this compressed vapor, - Liquid / vapor separation by a separator (4) of the products of said condensation, - The recovery and return to the chamber of said gas.

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