Claims:WE CLAIM:
1. A process for recovery of propylene and LPG from a gaseous product mixture produced by contacting a heavy hydrocarbon feed with a fluid catalytic cracking (FCC) catalyst in a fluid catalytic cracker; the process comprising:
a. partially condensing and distilling the gaseous product mixture to obtain a liquid fraction comprising heavier hydrocarbons and a gaseous fraction comprising light hydrocarbons having a boiling point below 216° C;
b. condensing said gaseous fraction to obtain a first gas-liquid mixture;
c. separating said first gas-liquid mixture to obtain a first liquid fraction and a first gaseous fraction, wherein said first liquid fraction is unstabilized naphtha;
d. sequentially compressing, and cooling said first gaseous fraction to obtain a second gas-liquid mixture;
e. separating said second gas-liquid mixture to obtain a second gaseous fraction and a second liquid fraction; wherein said second gaseous fraction comprises fuel gases;
f. de-ethanizing said second liquid fraction obtained in the step (e) to obtain a first top fraction comprising C2 and lower hydrocarbons and a first bottom fraction comprising C3+ hydrocarbons;
g. de-butanizing said first top fraction obtained in the step (f) to obtain a second top fraction comprising C3 and C4 hydrocarbons and a second bottom fraction comprising C5+ hydrocarbons;
h. depentanizing a portion of said second bottom fraction obtained in the step (g) to obtain a third top fraction comprising C5 and lower hydrocarbons and a third bottom fraction comprising C6+ hydrocarbons;
i. absorbing C3 and C4 hydrocarbons from said second gaseous fraction comprising fuel gases obtained in the step (e), through liquid-vapor phase absorption using said unstabilized naphtha obtained in step (c), a portion of said second bottom fraction obtained in step (g) and a portion of said third bottom fraction obtained in step (h) to obtain a fourth top fraction comprising C2 and lower hydrocarbons and a fourth bottom fraction comprising recovered C3 and C4 hydrocarbons.
2. The process as claimed in claim 1, wherein said fourth bottom fraction comprising recovered C3 and C4 hydrocarbons is combined with said second gas-liquid mixture in the process step (e).
3. The process as claimed in claim 1, wherein said first top fraction obtained in step (f) is combined with said second gas-liquid mixture in the process step (e).
4. The process as claimed in claim 1, wherein the process step (a) is carried out under in the range of 1.4 kg/cm2 to 3 kg/cm2.
, Description:FIELD
The present disclosure relates to the field of propylene and LPG recovery in Fluid catalytic cracking, refineries and petrochemical units.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Heavier hydrocarbon feed: The heavy hydrocarbon feed comprises hydrocarbons with carbon number greater than 10.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Fluid catalytic cracking process comprises cracking of heavy hydrocarbons to produce valuable products of different boiling points, wherein the products are separated in a fractionator.
Particularly, the product obtained by distillation comprises a mixture of light hydrocarbons such as propylene, LPG and the like. The light hydrocarbons are generally used in various applications. Hence, there is a need to recover the light hydrocarbons from the products.
The amount of propylene and LPG recovered using a conventional process is limited up to 97 wt%.
However, there is a scope to further increase the recovery of propylene and LPG from the product mixture obtained from cracking of heavy hydrocarbons over a mixture of zeolitic catalyst.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to enhance recovery of propylene and LPG from the product mixture obtained from cracking of heavy hydrocarbons over a mixture of zeolitic catalyst.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to improving the process for recovery of propylene and LPG from a gaseous mixture produced by contacting a heavier hydrocarbon feed with a fluid catalytic cracking (FCC) catalyst in an Fluid Catalytic Cracker; the recovery process comprises following steps.
• The gaseous product mixture is partially condensed and distilled to obtain a liquid fraction comprising heavier liquid hydrocarbons and a gaseous fraction comprising light hydrocarbons having a boiling point below 216° C.
• The gaseous fraction comprising light hydrocarbons is condensed to obtain a first gas-liquid mixture. The first gas-liquid mixture is separated to obtain a first liquid fraction and a first gaseous fraction, wherein said first liquid fraction is unstabilized naphtha.
• The so obtained first gaseous fraction is sequentially compressed, cooled and then separated to obtain a second gas-liquid mixture. The second gas-liquid mixture is further separated to obtain a second gaseous fraction and a second liquid fraction. Typically, the second gaseous fraction comprises fuel gases.
• The second liquid fraction is subjected to de-ethanization to obtain a first top fraction comprising C2 and lower hydrocarbons and a first bottom fraction comprising C3+ hydrocarbons.
• The first bottom fraction comprising C3+ hydrocarbons is then subjected to de-butanization to obtain a second top fraction comprising C3 and C4 hydrocarbons and a second bottom fraction comprising C5+ hydrocarbons.
• The portion of the second bottom fraction comprising C5+ hydrocarbons is then subjected to de-pentanization to obtain a third top fraction comprising C5 and lower hydrocarbons and a third bottom fraction comprising C6+ hydrocarbons.
• The unstabilized naphtha, a portion of the second bottom fraction comprising C5+ hydrocarbons and a portion of the third bottom fraction comprising C6+ hydrocarbons are further used to absorb C3 and C4 hydrocarbons present in the second gaseous fraction through vapor- liquid absorption to obtain a fourth top fraction comprising C2 and lower hydrocarbons and a fourth bottom fraction comprising the recovered C3 and C4 hydrocarbons.
The process of the present disclosure comprises the step of combining a fourth bottom fraction comprising recovered C3 and C4 hydrocarbons with the second gas-liquid mixture. The process of the present disclosure comprises the step of combining first top fraction from de-ethanizer comprising C2 and lower hydrocarbons with the second gas-liquid mixture.

BRIEF DESCRIPTION OF THE DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 is a schematic illustration of a system for the enhanced recovery of propylene and LPG in accordance with the present disclosure.
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Heavy hydrocarbons are cracked to produce valuable products having different boiling points. These products comprise a mixture of light hydrocarbons such as propylene, LPG and heavier hydrocarbons, which are separated by a sequence of steps comprising of cooling, condensation, compression distillation and absorption. The light hydrocarbons like C3 (propylene) and C4 hydrocarbons (LPG) are highly valuable products. Hence, there is a need to recover the light hydrocarbons from the products. In the conventional processes, the amount of C3 (propylene) and C4 hydrocarbons (LPG) recovered are limited up to 97 wt%. However, the amount of recovery can be increased further. Therefore, the present disclosure envisages a process for enhanced recovery of propylene and LPG.
The present disclosure, therefore, provides a process for enhanced recovery of propylene and LPG from a product mixture obtained by contacting a heavy hydrocarbon feed, such as vacuum gas oil, with a catalyst, such as zeolitic catalyst, in a fluid catalytic cracking process. The process of the present disclosure comprises the following steps:
Initially, the gaseous product mixture is partially condensed and distilled in a fractionator to obtain a liquid fraction comprising heavier hydrocarbons and a gaseous fraction comprising light hydrocarbons having a boiling point below 216° C. The gaseous fraction comprising the light hydrocarbons is condensed in an overhead condenser to obtain a first gas-liquid mixture. The first gas-liquid mixture is separated to obtain a first liquid fraction and a first gaseous fraction, wherein said first liquid fraction is unstabilized naphtha.
In accordance with the embodiments of the present disclosure, the unstabilized naphtha is used as a lean oil in a primary absorber to absorb propylene and LPG.
The so obtained first gaseous fraction is sequentially compressed, cooled and then separated in a two stage wet-gas compressor train to obtain a second gas-liquid mixture. The second gas-liquid mixture is further separated in a high pressure separator to obtain a second gaseous fraction and a second liquid fraction.
In accordance with the embodiments of the present disclosure, the second gaseous fraction comprises fuel gases.
The second liquid fraction is subjected to de-ethanization in a de-ethanizer column to obtain a first top fraction comprising C2 and lower hydrocarbons and a first bottom fraction comprising C3+ hydrocarbons.
In accordance with the embodiments of the present disclosure, the first top fraction comprising C2 and lower hydrocarbons is combined with the second gas-liquid mixture.
The first bottom fraction comprising C3+ hydrocarbons is then subjected to de-butanization in a de-butanizer column to obtain a second top fraction comprising C3 and C4 hydrocarbons and a second bottom fraction comprising C5+ hydrocarbons.
In accordance with the embodiments of the present disclosure, a portion of the second top fraction comprising C5+ hydrocarbons is used as a lean oil in a primary absorber to absorb propylene and LPG present in the second gaseous fraction comprising fuel gases. The remaining portion of the second top fraction is de-pentanized.
The remaining portion of the second top fraction comprising C5+ hydrocarbons is further subjected to depentanization in a depentanizer column to obtain a third top fraction comprising C5 and lower hydrocarbons and a third bottom fraction comprising C6+ hydrocarbons.
In accordance with the embodiments of the present disclosure, the portion of the third bottom fraction comprising C6+ hydrocarbons is used as a lean oil in a primary absorber to absorb propylene and LPG present in the second gaseous fraction comprising fuel gases.
In accordance with the embodiments of the present disclosure, C3 and C4 hydrocarbons present in the second gaseous fraction are recovered through liquid-vapor phase absorption using unstabilized naphtha, a portion of the second bottom fraction comprising C5+ hydrocarbons and a portion of the third bottom fraction comprising C6+ hydrocarbons to obtain a fourth top fraction comprising C2 and lower hydrocarbons and a fourth bottom fraction comprising recovered C3 and C4 hydrocarbons.
The process of the present disclosure further comprises the step of combining the fourth bottom fraction comprising recovered C3 and C4 hydrocarbons with the second gas-liquid mixture.
In accordance with one embodiment of the present disclosure, the pressure in the overhead condenser is in the range of 1.4 kg/cm2 to 3 kg/cm2.
The present disclosure provides an improved process, wherein the portion of the de-butanized liquid free of C4 and lower components and a portion of the de-pentanized liquid free of C5 and lower components, are recycled to the absorber, thus minimizing the recycle flow of C5 components to the de-butanizer column. The hydraulic margin thus created in the de-butanizer is utilized for recycling more absorber naphtha to the primary absorber for achieving propylene recovery beyond 97%. Thus, the amount of propylene remaining in the untreated fuel gas is in the range of 0 to 3 mol%. Further, the total amount of propylene and LPG present in the untreated fuel gas is less than 4 mol%.
In accordance with an exemplary embodiment of the present disclosure, the process for recovering the propylene and LPG from the product mixture obtained by contacting a hydrocarbon feed with a catalyst in a fluid catalytic cracking is explained with reference to Figure1.
The product mixture in vapor state produced by contacting a heavy hydrocarbon feed with a fluid catalytic cracking (FCC) catalyst in a FCC process is quenched and the liquid fraction thus obtained is separated in a fractionator 1. The uncondensed vapors exiting a top of fractionator 1 are supplied to an overhead cooler-condenser 3 via a gas conduit 2. The uncondensed vapors are converted into a first gas-liquid mixture in the overhead cooler-condenser 3. The first gas–liquid mixture is then fed to an overhead receiver cum separator 5, via a conduit 4, wherein the first gas-liquid mixture is separated into a first gaseous fraction and a first liquid fraction. The separated first liquid fraction is referred to as unstabilized naphtha, and further supplied as a lean oil in an absorber section 28 via a conduit 7 after cooling the unstabilized naphtha to a temperature between 30 °C to 40 °C, in a heat exchanger 39. Whereas, the first gaseous fraction obtained from the overhead receiver cum separator 5 is led through a conduit 6 to the first stage compressor 8, which is then fed to an inter stage cooler 10 via a conduit 9 to obtain a second gas-liquid mixture. The second gas-liquid mixture is fed to an inter-stage receiver 11, wherein the gas and liquid fractions are separated. The gaseous fraction is then fed to a second stage compressor 14 via a conduit 12. The liquid fraction is fed to a conduit 15 via a conduit 13. The liquid fraction is combined with the gaseous fraction in the conduit 15 to obtain a combined stream. The combined stream in the conduit 15 is further mixed with a rich oil stream (fourth bottom fraction) from an absorber bottom section 29 via a conduit 30 and the overhead gaseous fraction (first top fraction) from a de-ethanizer 21 via a conduit 20. The resultant stream is cooled in a high pressure cooler 16 to obtain a cooled mixture, followed by separating the cooled mixture into gas and liquid fractions in a high pressure receiver cum separator 17.
The liquid fraction (second liquid fraction) from the separator 17 is fed to the de-ethanizer 21 via a conduit 19, wherein the components lighter than ethane are stripped off from the second liquid fraction as a first top fraction and are recycled back to the high pressure separator 17 via a sequence consisting of the conduit 20, the conduit 15 and the heat exchanger 16. The first bottom fraction obtained from the de-ethanizer 21 obtained after stripping the components lighter than ethane, is fed to a debutanizer column 23 via a conduit 22, wherein the components lighter than butane are separated as a second top fraction and are fed further to a propylene separation unit (not shown in diagram) via a conduit 24. Further, the portion of the second bottom fractions from the Debutanizer 23 are fed to a depentanizer 42 via a conduit 26. The depentanizer 42 distills off C5 hydrocarbons from the second bottom fractions (debutanizer naphtha) to obtain a third bottom fraction, which is free of C5 components. Part of this third bottom fraction, referred to as depentanized naphtha, after being cooled in a heat exchanger 46 to a temperature preferably in the range of 20 °C to 30 °C, is supplied to an absorber section 27 via a conduit 44. The third top fraction comprising C5 hydrocarbons obtained from the depentanizer 42 is sent to a gasoline pool (not shown in diagram) via a conduit 43.
The present disclosure provides an improved process comprising an absorber having upper section (27), middle section (28) and lower section (29). In accordance with the present disclosure, the portion of the third bottom fraction (de-pentanized naphtha) and part of the second bottom fraction (de-butanized naphtha) are supplied to an absorber section 27 via the conduit 44 and the conduit 25 respectively, which act as a lean oil for absorbing C3 and C4 hydrocarbons. Further, the unstabilized naphtha is supplied as a lean oil in an absorber section 28 via the conduit 7 for absorbing C3 and C4 hydrocarbons. A fourth bottom fraction comprising C3 and C4 hydrocarbons from an absorber bottom section 29 is recycled via a conduit 30 to the combined stream in the conduit 15. The hydraulic margin thus created in the de-butanizer is utilized for recycling more absorber naphtha to the primary absorber for achieving propylene recovery beyond 97%. Thus, the amount of propylene remaining in the untreated fuel gas is in the range of 0 to 3 mol%. Further, the total amount of propylene and LPG present in the untreated fuel gas is less than 4 mol%.
Thus, the additional capacity is made available for increased recycle of debutanized and depentanized naphtha to the primary absorber resulting in higher absorption and recovery of propylene. Therefore, by replacing at least a part of recycled debutanized naphtha with the depentanized naphtha, a significant improvement in propylene recovery can be achieved with no additional loading of the debutanizer column.
The main advantage of the invention of the present disclosure is that an improvement in recovery of propylene and LPG from FCC fuel gases is achieved with no increase in hydraulic loads in debutanizer.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process:
- for improving the recovery of propylene and LPG.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.