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Development and incorporation of novel technologies to cope up with future challenges are essential for oil companies all over the world to remain competitive in business. In Indian petroleum industry there has been a significant increase in refining capacity during the last decade. However the highest demanded product LPG is still in deficit. The residue up gradation capacity as a percentage of the total refining capacity is poor. Also certain products like naphtha are produced in surplus. Keeping in mind the requirement of Indian petroleum industry, Indian Oil has developed new processes for increasing the refinery profitability through Indmax, Indalin and Dual solid process.
Indmax is a novel cracking process, which can produce very high yield of LPG and light olefins from heavy petroleum. Indalin is a single step catalytic conversion process of olefin rich naphtha range hydrocarbon streams into lighter hydrocarbons such as LPG with adequate process flexibility. Dual solid process is a new scheme of sequential processing for heavy petroleum residues using a mixture of two solid catalysts to obtain higher catalytic activity and coke selectivity. Indian Oil is also considering the commercialization of these new technologies, which are economically viable, highly efficient and involve novel concepts.
21-st century refining will be shaped by the factors like consolidation of oil companies, dramatic changes in market demand, customization of products and an increase in specific gravity and sulphur content of the oil. The future of refining industries will base on the following factors like
1) Increased operating costs or investments due to stringent environmental, health and safety requirements of products and facilities.
2) Accelerating globalization resulting in stronger international competition.
The effect of these factors is likely to reduce refinery profit margins further.
Oil companies all over the world need to make significant changes in their operation and structure to be competitive on global basis. Development and incorporation of novel technologies to cope-up the future challenges are essential to remain competitive in the business.
There has been significant increase in refining capacity during capacity during the last decade, which rendered some of the products like naphtha, gasoline and fuel oil in surplus. However LPG, which is still deficit and highest demanded is likely to remain so due to certain reasons like the use of LPG as a cooking gas and as an automobile fuel is increasing. On the other hand the naphtha consumption is likely to decrease because the power and fertilizer industries are changing to natural gas as their fuel. If there is no additional value for this naphtha generated the refinery margins will decrease further.
The residue up gradation capacity as a % of total refining capacity is poor in India. Also the refineries are not equipped with modern residue up gradation technologies. The yield of heavy petroleum products from Indian refineries is as high as 25% compared to 10% of US refineries. This will further increase as crude is getting heavier. The present technologies of residue up gradation â€œ thermal, hydro, catalytic and solvent-based carbon rejection processes are not of acceptable product quality and are expensive.
In view of the above, it is evident that significant opportunity exists for increasing the refinery profitability through the development of novel technologies for:
1) Conversion of residue for the maximum production of LPG and light olefins.
2) Conversion of poor quality olefinic naphtha into LPG, light olefins etc.
3) Low cost catalytic residue up gradation.
Keeping in mind the requirement of Indian petroleum industry Indian Oil Corporation have developed new processes for each of the above.
Crude petroleum reaches the surface of earth from an oil well as foam consisting of a mixture of solid, liquid and gaseous hydrocarbons along with sand and water. The crude petroleum is treated before it is send to the refineries. They are passed through baffles to condense the volatile portion and through mist extractors to get rid of moisture from the gases. The resultant gas issued as natural gas. In an oil refinery the crude oil is fractionally distilled and separated into groups of compounds with specific boiling point ranges (fractions) and the residue of high boiling constituents (bottoms). These bottoms are subjected to cracking processes to convert them into useful fractions.
The distillation is a continuous process, in which crude oil is preheated in a furnace to about 380C and fed into the fractionating tower. The fractionating tower consists of a large number of trays. The tower is heated with pre heated steam send from the bottom .A temperature of around 300C is maintained at the bottom and 150C at the top of the tower. There are reflux passages and volatile overheads provided to improve the yield.
The operation of a fractionating tower is based on the principle that when the sum of partial pressures is equal to the atmospheric pressure condensation will occur to form a mixture of liquid hydrocarbons. The number of fractions obtained will vary according to the demand of products and nature of crude oil. The heavy products obtained by fractional distillation is subjected to vacuum distillation at pressure less than 5 cm of Hg to obtain high vacuum gas oil (HVGO).
Because of the wide differences between two types of crude oil it can be said that no two refineries work on the basis of the same principle of processing scheme. The refining of oil is an economic problem. The processing plan is based on the following factors like the value and accessibility of the crude stock, value of products, yield of products expected, cost to process stock etc.
The most important method of separating petroleum products is distillation, and hence the products should be compared with one another in the order of their boiling ranges. The products obtained by distillation are called raw products and most of them cannot be sold until they are further refined.
Raw naphtha and gasoline are often treated with chemicals agents such as caustic soda, copper chloride, or doctor solution. Much naphtha is now catalytically reformed into high-octane gasoline. Kerosene usually requires a sweetening treatment; but for fine colors, acid treatment or filtration is used. Diesel fuels, distillate fuels, gas oils, and residual fuel oil are usually sold without treatment. Pressure distillate or cracked gasoline is obtained by cracking or thermal decomposition. Natural gasoline, obtained from natural gas usually requires only a sweetening agent for removal of hydrogen sulphide and mercaptan compounds.
Wax distillate, the raw stock for the manufacture of the light lubricating oils or neutral oils contains crystalline wax. The wax removed by chilling the distillate and filtering the wax from the oil in filter process. Two unfinished stocks, slack wax and pressed distillate, are obtained in the processing operation. Neutral oils are produced from the pressed distillate by distillation and subsequent filtration through the fullers earth. Crude scale is produced from wax by sweating; by slowly warming the chilled wax so that the oil and low melting materials are drained from wax. Crude scale is slightly yellow in color, and this coloration can be removed by treatment with acid or caustic soda. Cylinder stock is another wax bearing product, but the wax is such that it cannot be filtered from the oil by wax presses. Dissolving the oil naphtha, filtering the oil to proper color and centrifuging the solution in high-speed centrifuges may remove this amorphous wax or petroleum stock. The products from this separation process are solutions of bright stock and petrolactum. The naphtha is removed from the solution by distillation, leaving finished bright stock and petrolactum.
The dewaxing process explained above have been largely replaced by use of solvents for dewaxing the distillate and the cylinder stock. Likewise lubricating oils are being treated with furaral, phenol etc, for removal of low viscosity olefinic portions.
Materials such as cracking still gases, pressure distillate, cracked gas oil and pressure still tar are products of cracking. By cracking we refer to the decomposition of heavy or high boiling fractions by exposure to extreme temperatures. At temperature exceeding 680 f materials such as gas oil, fuel oil, and tars are decomposed into gas volatile materials having the same boiling range as gasoline and residue of heavy material or coke. Pressure distillate receives it name by reason the high pressures that are maintained in the cracking equipment. Cracked gasoline from pressure distillate is valuable as a high anti knock superior motor fuel. Likewise the cracked residue, if the cracked residue, if the cracking is not conducted for the ultimate formation of coke is called pressure still tar.
Recycle stock or cracked gas oil, an intermediate between the two foregoing products is also produced. Recycle stock has about the same boiling range and somewhat the same physical characteristics of gas oil. This material is normally recycled through the cracking system until it is completely converted into gasoline, but a part is usually sold as distillate or gas oil.
Catalytic cracking have now been widely used. It differs from thermal cracking mainly in the introduction of an adsorbent-based catalyst, which holds the asphaltic, or tar like products of cracking on the surface of the catalyst in the form of coke. Only distilled charging stocks are employed.
4.CATALYTIC CRACKING PROCESS
Among the secondary processes, fluid catalytic cracking (FCC) unit is a major producer of LPG, gasoline and diesel. Cracking is a phenomenon by which large molecules are thermally decomposed into smaller lower boiling molecules at the same time certain of these molecules which are reactive combine to give even large molecules than in original stock.
Catalytic processes are now replacing old thermal processes and they constitute about 60% of all cracking capacity. Porous adsorbent catalysts of silica alumina type are widely used. The fact that one or more hydrous metal oxide are present in all successful catalysts suggests that water in some way is important in this type of catalysis.
Studies reveal that:
1) Paraffins crack preferentially at such linkages that fragments containing 3 or 4 C atoms are produced. Normal paraffins tend to crack at the gamma C-C bonds to yield less methane. Long chains tend to crack simultaneously at several points.
2) Naphthenes also tend to yield 3 or 4 C atoms.
3) In substituted aromatics the link to the chain is selectively attacked, leaving a bare aromatic chain back.
4) Olefins react, as the paraffins more readily with many auxiliary are secondary reactions.
The overall mechanism involves at least four types of reactions:
1) Thermal decomposition 2) primary catalytic reactions at the catalyst surface 3) secondary catalytic reaction between primary products 4) removal of polymerizable products from further reaction by adsorption of them on the surface of the catalyst as coke.
Adsorption is of great practical significance because it permits large conversions without technical difficulties. Adsorption of polymerizable products allows the decomposition reactions to be completed to an extent, which is never possible, by thermal cracking.
Four main ways of handling catalyst are given below:
1) Fixed bed:
In the fixed bed process a series of chambers are employed some being on-stream and others in the process of cleaning regeneration etc. Regeneration is attained by steaming remnants of oil from the catalyst, burning C from the catalyst by hot flue gases and removing the last tracesbysteaming.
2) Moving bed:
In such a system the catalyst moves through the oil zone causing the reaction and then through regeneration zone where air continuously burns the coke deposit from the catalyst. Catalyst in the form of billets is lifted by air to a higher position so that it flows downward by gravity through reaction and regeneration zones.
3) Fluidized bed:
In such a system finely powdered catalyst is lifted into the reaction zone by the incoming oil, which immediately vaporizes upon contact with the hot catalyst, and after reaction is complete it is lifted into the regeneration zone by air.
In the reaction and regeneration zones the catalyst is held in a suspended stage by passage of gases through the catalyst dust, and a small amount of catalyst is currently moved from the reactor to the regenerator and vice versa.
Oil tends to saturate the enormous volume of pulverized catalyst in the reactor and hence the catalyst must be carefully stripped by means of steam before it enters the regenerator.
4) Once-through process: the catalyst (spend lubricating oil clay) passes through the cracking furnace along with the oil and is removed from the fuel oil by a filter.
5.CONVERSION OF RESIDUE FOR PRODUCTION OF LPG AND LIGHTER OLEFINS
Among the secondary processes FCC is the largest producer of LPG. In a FCC the HVGO is catalytically cracked in a fluidized bed reactor to produce LPG, gasoline, diesel etc.
However the yield of LPG is only about 10%. By increasing the reaction severity the yield can be increased up to 25% but it also increases the yield of coke and dry gas. So the yield of LPG is limited. With increasing residue content in FCC feed LPG yield comes down further.
An alternative for FCC is DCC (deep catalytic cracking) by which LPG yield can be increased to 40% wt. DCC uses bed cracking reactor having longer catalyst to vapor contact time at high severity produce LPG. However due to longer contact time coke and gas make also increases significantly.
Indian Oil has developed a novel cracking process, which can produce very high yield of LPG and lighter olefins from heavy petroleum feed stocks. The yield of LPG is around 45-65 % of feed depending on the feedstock quality and operation severity. Since the objective of this process is to maximize the production of Indane, IOCâ„¢s brand name for LPG, the process is named INDMAX.
Essentially indmax is an extension of FCC process with continuous catalytic regeneration using circulating fluidized bed reactor regenerator system. It works preferably in riser cracking condition with catalyst to oil ratio 15-25 and reactor temperature of 530 -600 C.
The process and the catalyst are highly selective towards the production of very high yield of light olefins while keeping the coke and gas make low. The heart of the indmax unit is a short contact time riser â€œregenerator, where the liquid feed stock is injected in the riser bottom with significant amount of steam. Coming in contact with the hot regretted catalyst the feed vaporizes and the resultant vapor and catalyst move up in the riser.
The coke deposited on the catalyst is runt in the regenerator and the heat produced is utilized for feed vaporization and endothermic cracking reactions. The lower coke make of the catalyst allows resid processing without catalytic cooling or two stage regeneration.
The catalyst used in indmax process consist of multiple components-
1) Bottom cracking component to upgrade bottom.
2) Shape selecting component to maximize the production of light olefins.
3) Y-Zeolite with synergistic effect.
The features of indmax catalyst are
High catalytic activity with excellent coke and dry gas selectivity.
Excellent bottom up gradation ability.
Very high selectivity for light olefins.
Very high metal tolerance particularly against vanadium.
Higher resistance against deactivation.
WT% OF PRODUCTS
A comparison of yield pattern with DCC is shown in the figure, which clearly indicates the superiority of the indmax process as far as the yield of desired products is concerned. The LPG yield is highly olefinic with more then 40%wt of propylene and 18%wt of iso butylene. The total olefinic content in LPG could be as high as more than 90%wt. dry gas contains about 50% ethylene. In addition gasoline obtained has octane number as high as 95.
The catalyst is designed to have very high metal tolerances. In the figure the relative activity of indmax catalyst is compared to FCC catalyst at different levels of vanadium in the feed. At 18000 PPM of vanadium on indmax catalyst, the activity is reduced to only by 30%. Therefore with resid feedstock the catalyst consumption is much lower than RFCC process. Feed hydro treating is not necessary unless sulphur is to be removed from the feed.
Indmax is a short contact time riser cracking process for heavy petroleum fractions to produce high yield of LPG and light olefins. The cracking is severe but highly selective, producing more propylene and iso butylene but less dry gas and coke.
The process employs single stage regerator without any catalytic cooler and the catalyst consumption is lower than RFCC with same feed. Based on this newly developed technology a semi commercial unit of 0.1 M MTPA capacity is currently being put up at one of IOC refinery.
6.CONVERSION OF OLEFINIC NAPHTHA TO LPG, LIGHT OLEFINS AND AROMATIC RICH GASOLINE.
Traditionally naphtha is thermally cracked in pyrolysis furnace to produce lighter olefins mainly ethylene and partly propylene. Naphtha cracker is the mother unit in a petrol chemical complex, which supplies light olefinic feed stocks. One of the major problems in conventional naphtha cracker is that the propylene selectivity is not good vies a Vis ethylene. The yield of hydrogen and methane are also higher.
With the advent of reformulated gasoline, the demand for alkylate and oxygenates are increasing as well as the demand for propylene is going up as a petrochemical feedstock. Therefore it is desirable to maximize the production of light olefins from naphtha.
Indian Oil has developed a new single step catalytic conversion of naphtha into LPG and C3-C4 olefins and aromatic compounds. INDALIN provides adequate flexibility to vary the ratio of production of olefinic and aromatic hydrocarbons.
Indalin process employs a solid catalyst (ZSM 5 Zeolite with increased acid strength by steam treatment) comprising of several ingredients in different proportions based on the feed and operating objectives. The process uses a fluidized bed reactor similar to that of FCC. However the reactor configuration is different as a dense bed is provided at the riser end to increase the contact time.
The average temperature in the riser reactor lies in the range 500-560 C which is much lower than that of steam cracking. At the exit of the dense bed the catalyst the catalyst falls down by gravity and product hydrocarbons are removed from the untrained catalyst using a cyclone separator.
The typical yields of the important products of indalin and steam cracking can be compared. The LPG yield in indalin is very high ranging between 40-60%wt of the feed depending on the olefinic content of the feed. The yield of propylene, isobutylene and ethylene could be as high as 23%, 15% and 11% respectively. The propylene and isobutylene yields are significantly higher than that of thermal cracking of naphtha. If ethylene is the desired product, the proper catalyst and operating condition can maximize it. The coke yield is also relatively low resulting in lower investment and operating costs.
Heavier residues contain higher quantity of CCR, metals like nickel, vanadium and basic nitrogen products. All of these have significant effect on the performance of the catalyst and FCC unit itself. High CCR of the feed forms more coke on the catalyst affecting the activity and selectivity of the catalyst. Also the regenerator temperature increases, which in turn increase the catalyst/oil ratio, affecting the conversion and product yields further. Moreover there is limitation of the maximum temperature in the regenerator beyond which it is not possible to operate.
At present resid FCC with two stage regenerator and catalyst cooler can handle unto 8-10% wt of CCR. Among the deleterious metals, the effects of nickel (Ni) and vanadium (V) are significant. Ni promotes the dehydrogenation, producing more dry gas and coke and V destroys the Zeolite, reducing the activity of the catalyst. At present using metal passivation technologies it is possible to handle 30 ppm of Ni and 15 ppm of V on the feed.
DUAL SOLID PROCESS
Indian Oil has come out with a new scheme of sequential processing of heavy petroleum residues using a mixture of two solids. One is the host catalyst and other is an adsorbent. The catalyst and adsorbent particles significantly differ in chemical and physical properties as well as cost. The heavy residue is first contacted with the hot adsorbent particles at the riser bottom for preferential deposition of CRR, metals and other impurities. The adsorbent particles are low cost catalyst and can be withdrawn from the system as and when required.
As the metal and CRR laden adsorbent and hydrocarbon vapors ascend towards the top of the riser, hot generated catalyst particles are introduced at an intermediate location. In the remaining portion of the riser the cracking reaction of the feed hydrocarbons is achieved.
At the exit of the riser, solid particles comprising of both catalyst and the adsorbent are steam stripped and then sent to a separator where catalyst and adsorbent are separated. The FCC catalysts are pneumatically transported to a regenerator for burning of coke and then recirculated to the intermediate location of the riser. The adsorbent particles, which form a dense or bubbling bed in the separator, may be taken through a standpipe to a separate vessel for regeneration
Here the coke deposited on the adsorbent is burnt completely or partially. There is a provision of withdrawal of contaminated adsorbent particles and addition of fresh particles to maintain the metal level on the adsorbent particles. The regenerated adsorbent is then introduced with the heavy feed at the bottom of the riser in the next cycle.
This new process offers tremendous potential in the economic processing of heavy petroleum resids. The efficiency of the scheme is illustrated by the comparison of the activity and coke selectivity while processing feeds with and without vanadium.
The activity is defined as the weight percentage of the products boiling below 216C at the reaction temperature of 519C and WHSC of 110 hour.
The coke selectivity is defined as the coke yield (wt% of the feed) at 38% conversion level.
The coke selectivity and activity is compared for different schemes in the table shown below:
It is seen that at 10000 ppm of V, activity drops from 38.6 to 10.1 while the coke selectivity increases from 1.87 to 5.93.
If mixture of adsorbent and catalyst is used both the conversion and the coke selectivity improves marginally. When the sequential deposition of V is done first on the adsorbent and then the base catalyst is contacted with the clean feed both the activity and coke selectivity return to almost original values as if there is no V on the feed. This clearly demonstrates the efficiency of the novel concept employed in the newly developed process.
With the changing face of refining, use of tailor made technologies will provide the edge to move ahead. This is more so when the refining margins are shrinking day to day due to several emerging factors such as stringent product qualities, strict environmental regulations, increasing feed heaviness, high crude prices etc. Worldwide efforts are on for developing economically viable technologies to meet the future challenges.
In the same endeavor Indian Oil is engaged in developing new refining processes. The US patents for the three processes detailed above have been obtained. Indian Oil is also putting up pilot plants incorporating the developed technologies for their commercialization. Further research is also being conducted at different R&D centers for refinement of these processes.
1) Development of new refining technologies to meet future challenges.
(PROCESS & PLANT ENGINEERING JOURNAL-2000)
By Sobhan Gosh, Debasis Bhattacharyya, IOCL, R&D Centre, and Faridabad.
2) Engineering Chemistry- Rajaram & Kuriakose (TMH Publishers)
3) Petroleum Refinery Engineering-W.L.Nelson (McGraw Hill publishers)