Feature

Innovative Approach for Increasing Petroleum Refinery Margins

Posted on 25 January, 2010 | Tags: Fluid Catalytic Cracking, Refinery Margins, Value Addition

Integration of solvent extraction unit of lube refinery and FCC unit of fuel refinery provides a unique concept of converting fuel oil components into premium refinery products, leading to significant increase in GRM

Indian Institute of Petroleum (IIP) is a centre of excellence for development of cutting edge 'solvent extraction' based technologies successfully operating in a number of Indian petroleum refineries. Recently, IIP conceptualized an innovative approach to integrate solvent extraction unit of lube refinery and FCC unit of fuel refinery, a unique concept that demonstrates zero fuel oil production from FCC unit and enhanced refinery margins. To develop this technology, IIP carried out a systematic and in-depth science based study which   included detailed physico-chemical characterization of clarified oil, design of liquid-liquid extraction runs in terms of temperature, solvent-to-feed ratios, water dosage in solvent, temperature gradient in continuous extraction column, interface position, interpretation of lab data, optimization of process conditions to achieve products (raffinate and extract) of desired quality etc. The lab study concluded that there is tremendous potential to produce premium value products such as good quality feed stocks for Fluid Catalytic Cracking (FCC) and premium grade Carbon Black Feed Stock (CBFS) from fuel oil components (clarified oil) through solvent extraction. The study also established the optimum process conditions. This technology has since then been successfully commercialized at HPCL Mahul Refinery in Mumbai which is reaping the benefits of producing additional amount of good quality clean feed stock for FCC and also premium quality feed stock for carbon black production from clarified oil.

Issues
Fluid Catalytic Cracking (FCC) is one of the versatile processes in modern petroleum refining industry. It is used to convert high boiling petroleum fraction ie Vacuum Gas Oil (VGO) into low boiling more valuable transportation fuels like gasoline and middle distillates. The product slate of FCC includes gas, gasoline, kerosene, jet fuel, diesel and clarified oil. Clarified Oil (CLO) is the bottom product of the FCC unit (residue) and is considered as the lowest value product coming out of FCC unit because it contains polynuclear aromatic hydrocarbons. Up-gradation of clarified oil into transportation fuels through catalytic process is practically not possible because polynuclear aromatics present in it are thermally much more stable, difficult to crack and also act as 'coke precursors'.
The disposal of clarified oil in refinery is considered to be a problem. Hitherto, this was being overcome to some extent by partially recycling it to FCC unit along with fresh feed and sending the major part to 'fuel oil pool'. FCC unit is the main workhorse of any fuel refinery but it is also very sensitive towards feed stock quality. The presence of coke precursors in feed adversely affects the catalyst life, conversion, product quality etc. Clarified oil mainly consists of unconverted hydrocarbons boiling in the range of 340 to 5900C. It contains substantial amount of polyaromatics, depending upon process severity of the FCC unit. Aromatic content in the fresh FCC feed ie VGO is in the range of 20-25 wt percent. On recycling clarified oil, concentration of aromatics in fresh feed may go upto 35-40 wt percent, which is undesirable. The blending of greater amount of clarified oil with VGO has an additional adverse effect like rapid deactivation of active sites of the cracking catalyst. The recycling of clarified oil also affects, besides the quality of feed, the quality and yields of distillate products. Moreover, presence of greater amount of polyaromatics (carbon precursors) in FCC feed results in heavy coke lay down on FCC catalyst, which makes the FCC regenerator limiting in some cases. Thus, the quantity of recycling of clarified oil to FCC unit is limited to a certain extent, usually upto a maximum of 15percent by volume on FCC feed basis. The blending of clarified oil to fuel oil pool does not contribute towards any value-addition to refiners as the price of fuel oil is sometimes lower than even the crude oil prices. Moreover, the market for fuel oil has been continuously declining in recent years.
To address the above problem of petroleum refiners, an 'innovative process' has been developed and commercially exploited at HPCL's Mahul Refinery with joint efforts by IIP and HPCL.  This process leads to better FCC product yields and higher overall profitability.
The aim of process technology development was to extract out good quality feed stock components suitable for catalytic cracking from clarified oil and recycle them with FCC feed to improve yield of FCC products. This process at the same time also produces aromatic rich material which is suitable for production of carbon black and other high value industrial/ advanced carbon materials.

Process Description
This process is based on an innovative concept of combining apparently two distinct and unrelated disciplines ie 'solvent extraction' and 'catalytic cracking'. This novel approach provides a unique solution for producing additional quantity of de-aromatized feed for secondary conversion unit ie FCC, which otherwise is going to be wasted by getting blended into fuel oil pool.
The simplified schematic for this process which is in operation at HPCL, is given in Figure1.
In the process, clarified oil is fed into the extraction column from bottom and contacted counter-currently with a solvent, introduced from the top of column. Solvent selectively extracts undesirable polynuclear aromatics from feed. The de-aromatized clarified oil is collected from top of the column as 'raffinate phase'. The raffinate phase containing minor amount of solvent is then vacuum flashed and steam stripped to recover solvent.  The 'extract phase' containing major part of solvent is withdrawn from bottom of the extraction column. It is heated and flashed in high pressure and low pressure flash columns to recover most of the solvent and thereafter steam stripped to recover last traces of solvent from hydrocarbons. The solvent from flash drums and stripper is sent to a solvent drying column and re-circulated back to the extraction column top after cooling. While the raffinate is circulated back to FCC unit along with fresh feed, the extract is taken out as standalone marketable refinery product suitable for carbon black manufacture.
The process concept was established by carrying out experimental studies with clarified oil obtained from HPCL. The studies included single and multi stage liquid-liquid extraction and catalytic cracking studies to ascertain the impact of solvent extraction of FCC CLO and recycle of the raffinate on FCC product yields and quality. It was observed that solvent selectively extracts out aromatics from clarified oil and simultaneously produces high BMCI extract at various solvent circulation rates.

General Features
This technology was first developed at lab scale followed by fine tuning of process parameters according to current operation of HPCL refinery, tested by giving trial runs and finally proven by conducting successful commercial run at HPCL. The technology is currently operating successfully.

Process Advantages
The recycle of raffinate provides significant economic advantages with enhanced gas and gasoline yields and reduced coke production
Some of the key advantages/ distinguishing features of this technology are

1. Improvement in FCC Recycle Stream Quality
It provides an improved quality feedstock, which is as clean as fresh FCC feed (ie VGO) itself. The improved quality feedstock (raffinate) has a low percentage of aromatics which results in reduction in coke lay down on cracking catalyst. The improved quality feedstock (raffinate) also helps to increase the life of cracking catalyst.

2. Increase in FCC Products Yields
This process technology also helps to increase the yields of FCC products (gas/ distillate) as well as improvement of FCC recycle stream quality in terms of sulfur reduction.

3. Premium Quality CBFS as By-product
Along with production of improved quality feed for catalytic cracking from clarified oil, this process also co-produces high BMCI aromatic extract which can be used as premium quality feed stocks for carbon black production. It leads to reduction in fuel oil components. Aromatic extract can also be value added by converting it into Mesophase pitches, a starting material for various industrial/advanced carbon materials.

4. Low  Cost  Adaptability and Enhanced Refinery Profitability
This process is easily adoptable by a refinery which also has conventional lube refining facility. The process utilizes the existing solvent extraction and FCC units within the refinery, needing no major additional investment for setting up of any new units.
It may be profitable even for fuel refineries with no lube block/spare capacity in existing solvent extraction unit by having a new dedicated solvent extraction unit as the capital investment required for such a unit won't be very large.
Commercial operation shows significant increase in Gross Refinery Margins (GRM) by adopting this process.

5. Increased Catalyst Life and Reduced  CO2  Emissions
Since, this technology lowers down carbon deposition on catalyst, it helps in reducing catalyst consumption as well as load on FCC catalyst regenerator. This will also reduce CO2 emissions and will help in meeting future carbon emission legislations of the refinery.

Other Applications of Technology 

• An important possible application of CLO raffinate is that it may be used as feed for production of high performance Group-II and Group-III lubricating base oils for automotive meeting current stringent high viscosity index (VI) and sulfur. A plant, based on isodewaxing/ isocracking technology for production of group - II and group - III base oils. This requirement can be partly met by CLO raffinate which is predominantly paraffinic rich feed stocks. This is perhaps a futuristic vision of the operating petroleum refinery.
• Aromatic extract produced from this process is an excellent feed stock for production of premium quality needle coke required by graphite electrode industry and presently the entire demand of needle coke is met through import. There is tremendous value addition if the aromatic extract is used for needle coke production.

World Wide Positioning of Technology
Innovative technology, integration of solvent extraction of clarified oil and catalytic cracking of raffinate, is unique of its kind in its application and is the first reference worldwide, which has been exploited in actual petroleum refinery operation at commercial scale. No reference of such type of process or its commercial usage is available nor there is any equivalent or alternate process available.

Impact of Technology
Economic Impact
Enhanced Refinery Margins  Analysis showed that installation of the extraction facility on recycle loop had a fairly attractive economics due to production of very rich aromatics extract along with significant increase in FCC distillate products by 5-10percent. The estimates show that the integration of FCC unit with solvent extraction unit leads to enhanced Gross Refinery Margins (GRM) of Mahul Refinery of HPCL by USD 0.30 per barrel (~Rs10 cores per MT of crude processed).

Societal Impact: Employment Generated
Integration of fuel refinery and lube refinery, to process CLO in solvent extraction unit of lube plant, generates aromatic rich extract. This extract is a good feed for production of impregnating, binder and mesophase pitches. Currently, there is no indigenous production of these pitches. Setting-up of a ancillary medium and small sized plant for pitch production will provide enough employment opportunities.

Value Addition to Extract Stream
In this process, aromatic rich extract is also produced which can as such be sold as good quality feed stock for carbon black. We have successfully further upgraded this extract by converting it into 'impregnating pitch' which is 2/3 times costlier and 'mesophase pitch' which is roughly 4 times costlier than the extract (See Photograph of mesophase pitch). These pitches are, in one way or other, the vital materials/ precursors for producing industrial or advanced nano-carbon materials such as needle coke, binder for carbon-carbon composites, activated carbon fibers, battery anodes, high temperature lubricants etc. The entire demand of these high value materials currently is met through imports. These materials are required by DRDO/ ISRO also for many strategically important applications.

Refinery Product Slate

• This technology helps the refinery to add a new product (premium quality carbon black feed stocks) in the refineries products slate.

Strategic Impact

• The aromatic extract produced in this process is also an excellent feed stock for makingmany industrial/ advanced carbon materials of strategic importance. These carbon materials namely mesophase or liquid crystalline pitch and carbon fibers are required for various defence and space research programmes. Since, there is no indigenous production of such materials currently, this process may be regarded as the first step towards providing feed stock for development of strategically important materials.

Adaptability of Technology
The significant aspect of this technology is it can be adopted without any hardware change/ major investment in the refineries and can prove good synergistic integration between 'fluid catalytic cracking unit' and 'conventional lube refining unit'.
 

• HPCL implemented this innovative process technology at its Mahul Refinery in Mumbai and is reaping the benefits of producing additional amount of good quality clean feed stock for FCC and also premium quality feed stock for carbon black production from clarified oil.
• This technology has a great potential to be implemented in many more refineries.

Patents Filed in India
A patent has been filled in India on the Process for Production of Improved Quality Feedstock from FCC Bottoms for Catalytic Cracking and Conversion into Industrial Carbon Materials

Acknowledgments
Authors wish to acknowledge the contribution of team members of FCC Group at IIP and also wish to thank Mr Rajesh Sharma and Gokul Prasad for assistance in lab work and Mr Ashish Raturi for typing manuscript in the present form.

Dr M O Garg 
The  author  is Director IIPand  is one  of the   leading Chemical Engineers of India. He has more than thirty year of experience in petroleum refining. His expertise is in the area of solvent extraction/ advance process control, energy integration and upgradation of residues. He is one of the top experts in pinch analysis worldwide. He earned his PhD in Chemical Eng  from Melbourne, Australia.

Dr Manoj Srivastava 
The author is Scientist at IIP, Dehradun.  He has more than fifteen years of professional experience for the development of industrial carbon materials such as tailor made petroleum derived pitches including binder, impregnating for graphite electrodes and mesophase pitches for Carbon Fibers/ Carbon Nanotubes (CNT).He earned his PhD Degree in Chemistry from Agra University.

Mr Manoj Kumar
The author is    Chemical
Technologist involved with Process Development work at IIP, Dehradun. He has more than ten years experience. Presently, Technical Officer working in Lube and Wax Area. His expertise is in lube processing.

Mr U C Agrawal 
The author is Chemical Engineer having more than thirty years of professional experience. Presently holds the position of Head of Division Heavy Oil Processing Division including, Lube, Wax and Bitumen Processing and Thermal Conversion processes at IIP, Dehradun.