Description:FIELD OF THE INVENTION

The present invention provides a process for the removal of rust (iron) from isomerization unit to prevent catalyst poisoning without use of any form of acid including anhydrous hydrochloric acid. The invention provides process of overhauling / maintenance of the equipments by blowing hot nitrogen under positive pressure without exposing the equipment surface to external moisture.

BACKGROUND OF THE INVENTION

Generally, ISOM units prior to start-up have an inner surface of their equipment exposed to air and/or water. The catalysts used for the Catalytic Isomerization processes is designed to isomerize the light naphtha (c5/c6) to the corresponding iso-paraffins to produce high-octane number gasoline stocks, and are very sensitive to moisture and rust. Moisture/rust particles act as poison to costly Isomerization catalyst which has platinum content. To avoid the poisoning of the catalyst during the commissioning/ start up stage, a process called “Acidization” is used for the removal of poisons from the reactor loop. “Acidization” removes last traces of rust (Fe) remaining in micro-pores, which cannot be removed during pre-commissioning. As per the known literature, acidization process involves injecting the anhydrous hydrochloric acid (HCl) in the circulating naphtha, which then reacts with iron (Fe) to form FeCl3 and H2O. The HCl introduced in the circuit is in a very controlled way and all excess acid is neutralized by a soda ash bath. The peaks of moisture content are monitored using a moisture analyser during the process which gradually decreases as Fe content in the system gets reduced.

However, such treatments often require the purchase and shipment of significant amounts of an anhydrous hydrogen chloride to chemically treat the inner surface of the equipment to convert metal oxides, such as rust, to metal chlorides. Due to the hazards associated with shipping and storing of hydrogen chloride, along with increasing government regulations, such materials are difficult and expensive to obtain and handle.

Further, handling of hazardous fluid (Anhydrous HCl) increases the infrastructural requirement for managing such fluid. For neutralization of acid vapour, Soda ash bath (having very high base value, PH > 12) is required to be put to use.

Moreover, during the plant operations, if any exchanger /equipment lying in the acidized loop needs maintenance or overhauling, the requirement is to go for acidization of the entire loop. This process of “Acidization” is time consuming and costlier and also has hazards of handling anhydrous acid. Moreover, reliability of the entire circuit also can be an issue, judging from the fact that any minor imperfections, particularly, during acid removal process, may lead to failure of static parts (pipes/ valves, dead ends etc.) of the circuit. Trapped residual acid in any crevices/ dead end of the reactor loop can lead to unforeseen untoward incident. Under these circumstances alternative processes of Acidization is the need of the hour to the refiner. As a consequence, there is a desire to find another suitable mechanism for providing a surface treating substance to for the isomerization unit. Hence, present invention has developed a method of treating the inner surface of the equipments in the acidization loop for removal of rust by involving a method that requires no acid. Instead inert fluid like Nitrogen is used rendering the system more stable and reliable. Additionally, the process is less time consuming leading to the advantage of getting back the unit on-stream considerably faster compared to the conventional “Acidization”. The new procedure provide the user a much safer, easier and effective solution when it comes to taking an equipment or part of pipeline, located in an already acidized loop, after an overhauling /maintenance activity is carried out. The procedure is efficient in terms of quality, cost effectiveness, ease of execution and time.

OBJECT OF THE INVENTION

The main object of the present invention is to provide a process for the treatment and maintenance of interior of the equipment of ISOM unit for the removal of rust (Fe) without use of any form of acid including anhydrous hydrochloric acid.

Another object of the present invention is to provide a process for treating/preservation/prevention of ISOM unit from rust (iron) and which requires lesser time for Start-up of the unit making the process cheaper without compromising on quality/requirement.

Another object of the present invention is to provide a process and system for the removal of rust from the ISOM unit wherein the process involves use of nitrogen rather than conventional method using anhydrous HCL.

Another object of the present invention is to provide an alternate process to Acidization in ISOM unit which is much safer, easier and effective solution when it comes to taking an equipment or part of pipeline, located in an already acidized loop , after an overhauling /maintenance activity is carried out.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides N2 BLOW – NAPHTHA WASH Program that is an easier and efficient alternative to the conventional Acidization process. Present invention further provides a process for treating/preservation/prevention of isomerization unit from rust (iron) and which requires lesser time for Start-up of the unit making the process cheaper without compromising on quality/requirement

In one more aspect, the present invention provides a process for treating and maintenance of an interior of equipment of an ISOM unit, for removal of rust (iron), wherein said process comprising:
a) taking out exchanger from isomerization unit and blowing hot nitrogen while maintaining dew point of nitrogen at a temperature of -60oC or less under positive nitrogen pressure before de-blinding;
b) maintaining pressure of shell side connected to the reactor of the unit lesser than the pressure of tube side of the unit during isolation activity of blinding;
c) providing shell side body blind after the exchanger bundle removal to ensure positive isolation from atmosphere;
d) performing re-tubing wherein said re-tubed exchanger is kept wrapped under polythene sheet with silica gel to avoid free moisture on tube surface;
d) performing pneumatic test for the shell to avoid any ingress in the tube external side; and
e) de-blinding of the ISOM unit equipment, wherein said treated ISOM unit equipment is used for isomerization of naphtha.

In another aspect, the present invention provides a treated ISOM unit equipment [100]. The Isomerisation unit comprises of:
a) atleast one exchanger zone containing reactor feed exchanger [102] for receiving the feed [101] and first stage reactor exchanger [103]; wherein said exchanger zone is treated for removal of rust (Iron) by blowing hot nitrogen while maintaining dew point of nitrogen at a temperature of -60oC or less under positive nitrogen pressure before de-blinding;
b) at least one drying zone containing two feed driers [111] and [112], and hydrogen driers [113] for drying of the naphtha feed and compressing and drying of hydrogen;
c) at least one isomerization reactor zone containing 1st stage isomerization reactor [106] and 2nd stage isomerization reactor [107], wherein 1st stage isomerization reactor [106] is attached to a chlorinating agent injection package [105];
d) a desuperheater [109] which generate desuperheated MP steam passing into a reactor feed heater [104]; and
e) a stabilizer zone containing a stabilizer [108] for collecting the isomerized stream.

BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described in detail with reference to the accompanying drawings.
These and other features, aspects and advantages of the present drawings will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represents like parts throughout the drawings, wherein:
Fig. 1 represents a flowchart showcasing method of treating of the ISOM unit equipment using inert gas, nitrogen during re-tubing;
Fig. 2 represents a flowchart showcasing method of isomerization of naphtha feed;
Fig. 3 represents a schematic diagram of a typical Acidization loop in an ISOM unit;
Fig. 4 represents a typical Acidization loop in an ISOM unit.

DETAILED DESCRIPTION OF THE INVENTION
For the purpose of better understanding of the invention, reference will now be made to the embodiments illustrated in the drawings. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further application of the scope of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

Reference throughout this specification to “one aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in atleast one embodiment of the present disclosure. Thus, appearances of the phrase “one embodiment”, “another embodiment” and similar language throughout this specification, may but not necessarily, all refer to the same embodiment.

Definitions:
As used herein, the term “naphtha feed” can include various hydrocarbon molecules, such as straight-chain, branched, or cyclic alkanes, alkenes, alkadienes, and alkynes. The feed can also include aromatic and non-aromatic hydrocarbons. Moreover, the hydrocarbon molecules may be abbreviated C1, C2, C3 . . .Cn where “n” represents the number of carbon atoms in the one or more hydrocarbon molecules.

As used herein, the term “zone” can refer to an area including one or more equipment items and/or one or more sub-zones. Equipment items can include one or more reactors or reactor vessels, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment item, such as a reactor, dryer, can be included in one or more zones.

As used herein, the term “blinding” can refer to positive isolation and the term “de-blinding” can refer to normalization of blinding.

Herein, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, to provide a thorough understanding of embodiments of the disclosed subject matter.

Referring to the Fig. 1, that illustrates a flowchart showcasing method of treating of the inner walls of the ISOM unit using inert gas, nitrogen, during re-tubing according to the present invention. Herein, method 200 provides a process for treating and maintenance of an inner surface of equipment of an ISOM unit for removal of rust (iron). At step 201, the method includes taking out exchanger from ISOM unit and blowing hot nitrogen while maintaining dew point of nitrogen at a temperature of -60oC or less under positive nitrogen pressure before de-blinding, and
At step 202, the method includes maintaining the pressure of shell side connected to the reactor [106] and [107] of the unit lesser than the pressure of the tube side of the unit during isolation activity of blinding, and
At step 203, the method includes providing shell side body blind after the exchanger bundle removal to ensure positive isolation from atmosphere, and
At step 204, the method includes performing re-tubing wherein said re-tubed exchanger is wrapped under polythene sheet with silica gel, and
At step 205, the method includes performing pneumatic test for the shell to avoid any ingress in the tube external side, and
At step 206, the method includes de-blinding of the ISOM unit.

At the outset the N2 BLOW – NAPHTHA WASH Program stands as an easier and efficient alternative to the conventional Acidization process.

Accordingly, in one embodiment, the present invention provides a process for treating and maintenance of an interior of equipment of an ISOM unit for removal of rust (iron), wherein said process comprising:
a) taking out exchanger from isomerization unit and blowing hot nitrogen while maintaining dew point of nitrogen at a temperature of -60oC or less under positive nitrogen pressure before de-blinding;
b) maintaining pressure of shell side connected to the reactor of the unit lesser than the pressure of tube side of the unit during isolation activity of blinding;
c) providing shell side body blind after the exchanger bundle removal to ensure positive isolation from atmosphere;
d) performing re-tubing wherein said re-tubed exchanger is wrapped under polythene sheet with silica gel to avoid free moisture on tube surface;
d) performing pneumatic test for the shell to avoid any ingress in the tube external side; and
e) de-blinding of the isomerization unit.

In another embodiment, the exchanger in step c) above is boxed under positive nitrogen pressure after completion of pneumatic test. As Shell side of the unit is sensitive to moisture, hence Pneumatic test (Nitrogen) to be done for Shell to avoid any moisture ingress in tube external side. It is ensured that the Pneumatic/ hydrotest had cleared before de-blinding activities.

In another embodiment, the hot N2 blowing from each low point discharge (LPD)/high point vent (HPV) in reactor feed heater circuit is performed before de-blinding.

In another embodiment, the shell side of step b) is maintained at dew point of -60oC or less which is ensured by blowing nitrogen.

In another embodiment, the shell side of step b) is maintained at dew point of -60oC or less which is ensured by blowing nitrogen prior to naphtha introduction.

In another embodiment, the pressure of the shell side of step b) is monitored regularly to ensure positive N2 atmosphere.

In another embodiment, the pressure of the shell side of step b) is monitored regularly to ensure positive N2 atmosphere, wherein said pressure is maintained through pressure gradient (PG). Herein, the positive pressure at shell side helps in avoiding moisture in the tube.

In another embodiment, the pressure of shell side connected to the reactor of the unit is maintained to be lesser than the pressure of tube side of the unit during isolation activity of blinding in step b) above. Herein the steam lining of the tube side and drying of the shell side of the unit is done at micro level. Further, the steam lining of the tube side is tested by performing hydrotest.

In another embodiment, the shell side body blind provided after exchanger bundle removal in step c), keeps shell preserved till re-tubing job is completed.

In another embodiment, during re-tubing in step d), cleanliness of external part of each and every tube is ensured and scale is removed by emery paper.

As per Axens acidizing is alternative to high grade cleaning such as buffing/sand blasting etc. As per the present invention tube external surface and shell is cleaned and scale is removed by use of emery paper.

In another embodiment, the shell side pressure of the unit is lower than tube side pressure to avoid the leakage of steam. Herein, in case tube leakage is detected, draining of all condensate is performed followed by depressurizing steam condensate circuit of the isomerization unit.

In another embodiment, the pressure of the reactor in step b) is kept at 6- 7 kg/cm2 pressure while the shell side of the exchanger is maintained at 1-1.5 kg/cm2 pressure.

Referring to the Fig. 2, that illustrates a flowchart showcasing method of isomerization of naphtha feed in the acidized isomerization unit of the present invention. Herein, Method 300 describes the process of isomerization of naphtha feed under steps 301-310.
At step 301, light de-sulphurized naphtha feed from NHT and De-isohexanizer recycle product is washed by blowing hot nitrogen and then is mixed in reactor feed exchanger [102].
At step 302, the mixed feed of step 301 is fed to dryers [111] & [112] for drying of the feed in order to remove the moisture that act as poison for catalyst.
At step 303, hydrogen is compressed in hydrogen dryer [113] to remove water and potential CO/CO2.
At step 304, all above feeds of steps 302-303 are mixed to form combined feedstock containing dried naphtha feed and hydrogen.
At step 305, pre-heating of the feed is performed in exchanger which is boxed under positive nitrogen.
The pre-heated mixture is then combined with de-superheated MP steam in a unit [104] under step 306.
At step 307, the pre-heated mixture passing from [104] is then mixed with catalyst promoter of step 308, continuously at regular intervals and passed to 1st stage Isomerization reactor [106] for first isomerization wherein, in presence of hydrogen and catalyst (present in the unit [106]), benzene is hydrogenated to cyclohexane.
At step 309, the feed from [106] is cooled in exchanger [103].
At step 310, the feed is then passed to final 2nd stage Isomerization reactor [107] for final isomerization, and the final product is then passed to stabilizer unit [108].

Herein, the system or equipment of the ISOM unit treated by a process involving blowing of hot nitrogen for removal of rust from the inner surface of the equipment of the ISOM unit as represented in schematic diagram under Fig. 3 and Fig. 4 that represents a typical Acidization loop in an ISOM unit (also referred as unit 100).

Herein, the equipment of ISOM unit [100] can include atleast one exchanger zone, at least one drying zone, at least one isomerization reactor zone, and at least one stabilizer zone.

In addition, an ISOM unit [100] includes exchanger zone containing reactor feed exchanger [102] for receiving the feed [101] and first stage reactor exchanger [103]. The drying zone includes two feed driers [111] and [112] and hydrogen driers [113] for drying of the naphtha feed and compressing/drying of hydrogen.

The shell side of the ISOM unit that is connected to the reactor [106] and [107] is sensitive towards moisture and hence is treated by blowing hot nitrogen while maintaining dew point at a temperature of -60oC or less under positive nitrogen pressure before de-blinding (starting up the unit).

The ISOM unit [100] further contains a desuperheater [109] which generate desuperheated MP steam passing into a reactor feed heater [104] to heat the combined feedstock to required inlet temperature.

In an illustrative embodiment, as shown in the Fig. 3 & 4, the stabilizer zone contains a stabilizer [108] for collecting the isomerized stream.

In another embodiment, the present invention provides a process of isomerization of naphtha in a ISOM unit equipment (exchanger) 100, comprising the steps of:
i) washing with light de-sulphurized naphtha feed from NHT and De-isohexanizer recycle product [101] after blowing hot nitrogen;
ii) compressing hydrogen gas and drying in hydrogen driers [113] to remove water and potential CO/CO2;
iii) mixing the dried hydrogen gas with naphtha feed of step i);
iv) pre-heating the combined feedstock of step iii) in a feed exchanger [103] followed by passing through de-superheated MP steam in a unit [104] to heat the combined feedstock to required inlet temperature, wherein RIT is maintained at 110 to 116oC
v) passing the pre-heated feedstock of step iv) to reaction zone containing a 1st stage Isomerization reactor [106] having catalyst comprising platinum on an alumina support, wherein a small amount of chlorinating agent is continuously injected [105] into reactor feed to maintain the chloride balance on the catalyst;
vi) passing the effluent of step v) to upstream of 2nd stage isomerization reactor [107] operating in lead-lag position after cooling the effluent in the exchanger [103], and
vii) passing the effluent of step vi) to stabilizer column [108] under pressure control.

In another embodiment, the rate of injection in step v) is kept around 15kg/m3 during normal operation to maintain a dragger level of more than 1000 ppm HCL in the off gases.

In another embodiment, the pressure of stabilizer column in step vii) is maintained at 14.2kg/hr.

In another embodiment, the feed for isomerization process include hydro-treated light straight-run naphtha, light natural gasoline, or condensate.

In another embodiment, the feed dryers maintain the water content in the feedstock to minimum and hence protects the isomerization catalyst from irreversible damage with water, which is extremely poisonous to the reactor catalyst.

In another embodiment, hydrogen gas is compressed and dried in hydrogen driers to remove water and potential CO/CO2 which are extremely poisonous to the reactor catalyst. The feedstock is combined with make-up and recycled hydrogen which is then directed to a heat exchanger [103] for heating the reactants to reaction temperature.

In another embodiment, the pre-heating of the combined feedstock in heat exchanger [103] can be carried out by using high-pressure steam.

In another embodiment, the pre-heated combined feedstock passing to 1st stage Isomerization reactor [106] in step f) is reacted with hydrogen contained the feedstock itself, in presence of catalyst present in the reactor [106]. This causes 1st isomerization that results into hydrogenation of benzene to form a stream of cyclohexane. The typical isomerate product (C5+) yields are 97 wt% of the fresh feed, and the product octane number ranges from 81 to 87, depending on the flow configuration and feedstock properties.

In another embodiment, inlet temperature of the isomerization reactors [106] and [107] are maintained at 110-116oC depending on the reaction kinetics.

In another embodiment, the isomerization reaction in the ISOM unit 100 takes place in high pressure environment of 32-35 kg /cm2.

In another embodiment, the removal of rust (iron) from inner surface of ISOM unit by treating with hot nitrogen is regularly tested. Samples of naphtha are checked for Fe (rust) for which the desired result is Fe < 10 ppb.
Isomerization processes are widely used by many refiners to rearrange the molecular structure of straight chain paraffinic hydrocarbons to more highly branched hydrocarbons that generally have higher octane ratings. The purpose of this process unit is to increase the RON of the light Naphtha cut from upstream unit NHT in order to meet the required target of gasoline pool production.

There are principally two fundamental reactions occurring in isomerization section:
1. Benzene hydrogenation
Benzene and hydrogen react to form cyclohexane. This reaction takes place in the first stage isomerization reactor. The Benzene hydrogenation is an exothermic reaction.

2. Isomerization:
Many isomerization processes employ a chlorinated catalyst, such as chlorinated alumina catalyst, chlorinated platinum aluminium catalyst, and the like, in a reaction zone i.e. first stage reactor exchanger. The conversion takes place over a chlorinated platinum based catalyst in the presence of hydrogen.

The chlorinated catalyst requires a continuous addition of chloride to replace chloride removed from the surface of the catalyst and carried away in the reaction-zone effluent. Typically, a fresh feed of chloride promoter, such as perchloroethylene, is continuously injected into a feed stream upstream from a reactor in the reaction zone. Inside the reactor, the chloride promoter decomposes to form hydrogen chloride that activates, e.g., promotes or regenerates, the catalyst by replenishing the chloride removed from the catalyst's surface. The reactors contain chloride platinum-alumina catalyst, which is contacted with a light naphtha feed, hydrogen gas, and a trace organic chloride promoter injection, all of which have been dried under positive nitrogen pressure to ensure that water that acts as a catalyst poison and corrosion enabler, is not introduced into the process. In conventional method, generally above mentioned drying of naphtha feed and isomerization unit is performed by using “Acidizing” process involving the use of Anhydrous HCL. If “Acidizing” is not carried out, rust will react with HCL formed from already injected PerChloro Ethylene, PCE, ( injected in reactor loop for maintaining catalyst chloride content) to form iron chloride & water, which would consequently damage the expensive catalyst permanently. As known and mentioned above, conventionally, the process of acidizing is done using anhydrous hydrochloric acid. The Fig. 4 shows a typical “Acidization” loop in an ISOM unit along with the point for injection of Anhydrous HCL. The acid flow path is marked with the dotted blue arrows. A look at the schematic will make it evident that acidization loop is a complex circuit wherein numberof static parts/equipment is involved. Conventionally anhydrous HCL is injected upstream of exchangers. Naphtha and anhydrous HCL is heated through feed pre-heater exchanger. After passing through reactors loops naphtha and HCL vapours are sent to the stabilizer column. The HCL vapours at Stabilizer overhead are neutralized downstream. Acidizing is completed if the two consecutive peaks reading of moisture analyzer is less than 1 ppmw at stabilizer inlet. However, If the circuit where “Acidizing” is required to be done has multiple loops and dead ends, the conventional method becomes more susceptible ( higher probability) to failure of its static parts (pipes/ valves, dead ends etc.) due to localized corrosion (due to presence of acid), chokage (due to Ferric chloride formation). This is because of higher probability of presence of residual acid in dead ends borne out of improper or incomplete rinsing/ presence of residual Ferric Chloride. In fact the method does not address localized abnormalities, if any. Also, the time taken for a conventional “Acidization” to get completed is considerably higher than the proposed methodology. This gets manifested in the form of quicker Start up time when the process of the present invention is used. Thus from cost point of view, the conventional method requires not only acids and bases in addition to other infrastructural requirement to handle them but extra loss also gets incurred due to higher time for startup compared to the proposed method.

In one preferred embodiment, the Acidization process of the present invention is performed in absence of any form of acid, wherein said process provides removal of iron (rust) from the unit equipment’s. The removal of rust is tested by checking sample of naphtha from LPD for Fe (iron).
Advantages of the Acidization process of the present invention for treating isomerization unit :
The present invention, which uses Nitrogen rather than anhydrous HCL, circumvents the deficiencies of prior art. The disadvantages of the conventional method are almost offset by the proposed method due to the following:
1) No acid or hazardous liquid is in use.
2) The process of preservation/ prevention is with inert gas in a closed system.
3) Effectiveness (as has been experienced in a big facility) is equivalent (or better) compared to the conventional method in terms of end result (quality) and time to obtain the same.
This method saves time duration of 5 days for startup. The conventional method of Acidization takes around 6 days’ time to complete while this method is achieved in a day.
The output of the method is comparable to the Acidization, as the study of thickness measurement of the exchanger before and after the overhaul at a gap of 6 months shows minimum depletion of the surface thickness.
4) Lesser time required for Start-up of the unit makes this methodology far cheaper without compromising on quality/requirement.
5) Easy to implement compared to the conventional process.
6) The conventional method requires acids and bases in addition to other infrastructural requirement to handle them which is replaced by easily handled nitrogen.
7) The use of hazardous anhydrous hydrochloric acid is omitted in toto.
8) Importantly, in present process the plant personnel do not get exposed to anhydrous HCL considered to be extremely hazardous. Thus the new process eliminates the requirement of handling hazardous chemicals, an important step towards safe execution of job.
9) The system of the present invention can also be used after the unit has already been commissioned and “Acidization” with conventional method has already been done once during commissioning.

EXAMPLES

Example 1: Acidizing process of isomerization unit without use of anhydrous hydrochloric acid during re-tubing:

Took out (isolate) the exchanger from service (ISOM unit [100]), before de-blinding and maintained the pressure of the shell side (connected to the Reactors [106] and [107]) lower than pressure of the tube side (containing saturated medium pressure steam) during isolation activity. Monitored the pressure to ensure positive N2 atmosphere on the shell side as part of abundant precaution. Shell side body blind is provided after exchanger bundle removal to ensure positive isolation from atmosphere. During re-tubing, cleanliness of external part of each and every tube is ensured and scale is removed by emery paper. Performed Pneumatic test (Nitrogen) for Shell side to avoid any moisture ingress in tube external side. The re-tubed exchanger is kept wrapped under polythene sheet with silica gel to avoid free moisture on tube surface.

Isomerization unit
Shell Side Tube Side
Fluid name Reactor Feed (HC + H2) Saturated Medium Pressure Steam
Fluid quantity, total kg/h 68 715 (4) 5 901 (7)
Vapor (in/out) kg/h 467 2 060
Liquid (in/out) kg/h 68 248 66 655
Steam (in/out) kg/h 5 901
Free water (in/out) kg/h 5 901

Comparative Example 2:
Acidizing Flow description
The Fig. 1 shows a typical “Acidization” loop in an ISOM unit along with the point for injection of Anhydrous HCL. The acid flow path is marked with the dotted blue arrows. A look at the schematic will make it evident that acidization loop is a complex circuit wherein number of static parts/equipment is involved.
Anhydrous HCL is injected upstream of exchangers. Naphtha and anhydrous HCL is heated through feed pre-heater exchanger. After passing through the reactors loops, naphtha and HCL vapours are sent to the stabilizer column. The HCL vapours at Stabilizer overhead are neutralized downstream. Acidizing is completed if the two consecutive peaks reading of moisture analyzer is less than 1 ppmw at stabilizer inlet.

Example 3: Process of isomerization of naphtha feedstock.

Light desulphurized naphtha from NHT and De-isohexanizer recycle product [101] are mixed in feed surge drum [102] and then pumped to enter the two feed dryers [111] and [112]. The feed dryers protect the isomerization catalyst from irreversible damage with water, which is extremely poisonous to the reactor catalyst. The make-up hydrogen gas is compressed and dried in hydrogen driers to remove water and potential CO/CO2 which are extremely poisonous to the reactor catalyst. Dried hydrogen is then mixed with dried Naphtha. The combined feed is preheated in feed exchanger [103] and finally with desuperheated MP steam generated from desuperheater [109] to required inlet temperature. A small amount of chlorinating agent [105] is continuously injected into reactor feed to maintain the chloride balance on the catalyst. This is a make-up for catalyst chloride, which is lost in reactor effluent. The mixture is routed to first stage Isomerization reactor [106], where Benzene hydrogenation and isomerization reactions occur. The reactor effluent is cooled in the exchanger [103] before entering the second stage isomerization reactor [107]. In the second isomerisation reactor, remaining isomerization reactions occur. The isomerization reactors are designed to operate in the lead-lag position. The effluent is then routed to stabilizer column under pressure control. The reactions take place in high pressure environment of 32-35 kg /cm2. The Reactor inlet temperatures are maintained at 110-116oC depending on the reaction kinetics.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. , Claims:1. A process for treating and maintenance of an interior of equipment of an ISOM unit for removal of rust (iron), wherein said process comprising:
a) taking out exchanger from isomerization unit and blowing hot nitrogen while maintaining dew point of nitrogen at a temperature of -60oC or less under positive nitrogen pressure before de-blinding;
b) maintaining pressure of shell side connected to the reactor of the unit lesser than the pressure of tube side of the unit during isolation activity of blinding;
c) providing shell side body blind after the exchanger bundle removal to ensure positive isolation from atmosphere;
d) performing re-tubing wherein said re-tubed exchanger is kept wrapped under polythene sheet with silica gel to avoid free moisture on tube surface;
d) performing pneumatic test for the shell to avoid any ingress in the tube external side; and
e) de-blinding of the ISOM unit equipment, wherein said treated ISOM unit equipment is used for isomerization of naphtha.

2. The process as claimed in claim 1, wherein said exchanger in step c) is boxed under positive nitrogen pressure after completion of pneumatic test.

3. The process as claimed in claim 1, wherein said shell side of step b) is maintained at dew point of -60oC or less which is ensured by blowing nitrogen.

4. The process as claimed in claim 3, wherein said blowing of nitrogen is performed before naphtha introduction.

5. The process as claimed in claim 1, wherein the pressure of the shell side of step b) is monitored regularly to ensure positive N2 atmosphere.

6. The process as claimed in claim 1, wherein during re-tubing in step d), cleanliness of external part of each and every tube is performed by using emery paper.

7. The process as claimed in claim 1, wherein said isomerization of naphtha in step e) is carried out in steps comprising of:
i) washing light de-sulphurized naphtha feed from NHT and De-isohexanizer recycle product [101] by blowing hot nitrogen and mixing in reactor feed exchanger or feed drum [102] to form a feedstock, wherein said feed exchanger is treated by blowing hot nitrogen while maintaining dew point at a temperature of -60oC or less under positive nitrogen pressure before de-blinding;
ii) pumping the feedstock into two feed dryers [111] and [112] to get dry feedstock under positive nitrogen;
iii) compressing hydrogen gas and drying in hydrogen driers [113] to remove water and potential CO/CO2;
iv) mixing the dried hydrogen gas with dried feedstock of step ii);
v) pre-heating the combined feedstock of step iv) in a feed exchanger [103] followed by passing through de-superheated MP steam in a unit [104] to heat the combined feedstock to required inlet temperature, wherein said exchanger is boxed under positive nitrogen pressure;
vi) passing the pre-heated feedstock of step v) to reaction zone containing a 1st stage Isomerization reactor [106] having catalyst comprising platinum on an alumina support, wherein a small amount of chlorinating agent is continuously injected [105] into reactor feed to maintain the chloride balance on the catalyst;
vii) passing the effluent of step vi) to upstream of 2nd stage isomerization reactor [107] operating in lead-lag position after cooling the effluent in the exchanger [103], wherein said exchanger is boxed up under positive nitrogen pressure; and
viii) passing the effluent of step vii) to stabilizer column [108] under pressure control.

8. A treating equipment of ISOM unit [100] comprising of:
a) atleast one exchanger zone containing reactor feed exchanger [102] for receiving the feed [101] and first stage reactor exchanger [103]; wherein said exchanger zone is treated for removal of rust (Iron) by blowing hot nitrogen while maintaining dew point of nitrogen at a temperature of -60oC or less under positive nitrogen pressure before de-blinding;
b) at least one drying zone containing two feed driers [111] and [112], and hydrogen driers [113] for drying of the naphtha feed and compressing and drying of hydrogen;
c) at least one isomerization reactor zone containing 1st stage isomerization reactor [106] and 2nd stage isomerization reactor [107], wherein 1st stage isomerization reactor [106] is attached to a chlorinating agent injection package [105];
d) a desuperheater [109] which generate desuperheated MP steam passing into a reactor feed heater [104]; and
e) a stabilizer zone containing a stabilizer [108] for collecting the isomerized stream.

9. The treating equipment of ISOM unit as claimed in claim 8, wherein said unit contains shell side and tube side and wherein the pressure of shell side connected to the reactor of the unit is maintained to be lesser than the pressure of tube side of the unit.

10. The treating equipment of ISOM unit as claimed in claim 8, wherein the pressure of the reactor is kept at 6- 7 kg/cm2 pressure while the shell side of the exchanger is maintained at 1-1.5 kg/cm2 pressure, and wherein said shell side is treated by blowing hot nitrogen while maintaining dew point at a temperature of -60oC or less under positive nitrogen pressure before de-blinding.