In this assignment, we have chosen the petrochemical industry as our subject title. Under petrochemical industry, oil refinery has been decided as our case of study. Basically, many processes have involved in oil refinery, such as distillation, hydrotreating, isomerization, cracking, coking and alkylation. Through oil refinery process, we are able to get few products. For example, gasoline, diesel, petroleum coke and so on. Out of these processes, we have chosen to elaborate on certain processes, namely distillation, fluid catalytic cracking, hydrocracking, coking and hydrotreating process.
This is the diagram for oil refinery processes.
Importance of petrochemical industry
Petrochemical industry has played a significant role in our daily life. In general, petrol is act as a fuel in order to operate vehicle such as cars and motorcycles. However, petrochemical make petrol can be synthesized to many different kind of products that is essential in our daily life. For example, plastic and polymers is made from the petrol; plastics are important in packaging and preserving food, polymers have variety usages in our daily life like sporting equipment, fabrics, kitchen stuffs and so on. To make the products more reliable and valuable, petrochemical industry is needed.
In addition, petrochemical also advance the products in all sectors of society, like technology and house construction. In other words, petrochemical has made our life more comfort, healthier and systematic by the advanced products .For example, our house. Petrochemical make our house become warmer and durable during the windy season through the insulation of the wall, roof and pipes, because insulation can prevent heat to be escaped to the surrounding faster. Insulation also has improved the energy conservation between heating and cooling in our house. This is because insulation has lowered the cost of cooling and heating.
Most of the items that we used in our daily are produced from petrochemical; this statement indicates that petrochemical is also essential in manufacture and production of different products. For manufacture industry like electrical industry, it cannot produce a product without the material that is derived from the petrochemical. For example, the chips and transistor used in television, radio and computer, the plastic that is used to package the milk bottle and so on.
Supply
Every one knows the oil supply can't last forever, but no one has a very good estimate when it will end. Saudi Arabia has the largest amount of oil, but they aren't willing to tell the world exactly how much they think they have or when it may be depleted. Other countries have almost completely depleted their oil reserves such as the US and some other developed countries. Mexico announced in 2004 that their largest oil field and the second fastest producing field in the world, Cantarell Field, have begun a steep decline in production. In 2002 Cantarell produced 2.1 million barrels a day. By 2008 it is predicting to only produce 1 million a day. The largest oil field is Ghawar field in Saudi Arabia. According to the Saudi Government the field has 75-83 billion barrels of oil and should be able to increase production in the future. The field considered to be second largest is Kuwait's Burgan Field at 66-72 billion barrels. In 2005 it was announced to Burgan field will begin decreasing production and is estimated to have a lifespan of 30-40 years.
One different oil source is not an oil field as much as a tar pit. Canada's Athabasca Oil Sands have been estimated to hold 1.6 trillion barrels of crude oil. While this sounds like a wonderful supply of oil the extraction process is very expensive and difficult. Someday this process will certainly be refined and if oil prices continue to increase the Athabasca Oil Sands will become a huge supplier of gasoline to North America.
Oil Demand
Oil demand is predicted to continue to increase despite the high price of oil. There are many sources of demand for oil. As countries develop and industrialize their oil consumption grows with their economy. Today China and India are the big players when it comes to growing economies. The world has never seen economic growth like it has with these two countries and the impact on oil demand has already began. Developed countries are also yet to seriously change their oil habits, but will likely adapt at a faster pace if oil prices continue to rise.
Prospect of the Industry
Petrochemical sector is a high technology industry. Nowadays, petrochemical industry is an important growth industry for Malaysia among the other chemical sub-sectors. For instance, inorganic chemicals and oleochemicals. Moreover, the growth of the petrochemical industry is supported by the Malaysian Government and Petroliam National Berhad (PETRONAS). Petronas, provides 32% of the federal budget in taxes, dividends and royalties. Futhermore, the company has the ranking record by being 95th in 2008 in terms of revenue and 8th most profitable company in the world. Furthermore, it is estimated that Petronas will be the most profitable company in Asia by 2020.
Petrochemical indusry contributes major income in the economic growth of our country. Currently, 40% of oil fields in Malaysia are developed. The rapid growth of the industry is mainly due to the availability of oil and gas as feedstock. Our advanced technology can provide good infrastructure which can scale up our production. For example, a well-developed infrastructure in the petrochemical zones in Kerteh, Gebeng and Tanjung Langsat are able to increase the future profit of the country. Morever, there are many plants that have never been discovered yet in Malaysia. Our future petrochemical engineers play an important role to discover more plants in Malaysia to increse our supply and demand in this industry. Estimated, about 60% of oil fields in Malaysia will be devoloped by the year 2020.
There are many countries that depends on the petrochemical industry to increse the revenue of the economics of the country, such as Singapore. In Singapore, the petrochemical industry is one of the fastest growing industries. Singapore has a market share in Malaysia and also in China. Singapore's export shares to most of the key markets boost the growth of the Singapore's domestic chemical exports. Singapore are currently in a stronger financial position and given modern technologies to enhance their positon in the global petrochemical industry. Therefore, in the next few years, Singapore's petrochemical firms appear well positioned to benefit from the expected pick-up in regional demand.
The growth of the industry has transformed Malaysia from a net importer to exporter of major petrochemical products. For example, Shell and ExxonMobil, Dow Chemicals and ConocoPhilips; these company had shown that Malaysian government is providing a good environment to attract investments. Therefore, we believe that our country is able to establish a new milestone for the economic development of the country.
Impact of petrochemical to environment
Oil refinery is one of the processes in the petrochemical industry which contribute to environmental pollution. This is because the effluents from oil refining contain varieties of chemicals at different concentrations including hydrocarbons, phenol, ammonia and sulphides. The accurate composition, however cannot be generalized as it depends on the type of refining process and which units are in operation at any specific time. Thus, it is difficult to predict how the effluent may effects the environment thoroughly but still, the refinery effluents are rather toxic to the environment as shown by the toxicity test. Extensive chemical testing has found out that these effluents can be deadly and have sublethal effects on the reproduction and growth of an organism. This will greatly affect the flora and fauna residing in that area.
Secondly, in an oil refinery there are a lot of smoke stacks and a lot of processing going on, and which can all be regulated. But when there are miles and miles of pipes which is typical in an oil refinery, that move the partially processed products from one location to another, there could be vents or cracks in the pipe that allow fugitive emissions to take place. These fugitive emissions, emitted from oil refinery that is not under any control, pollute the air and the ground. This post health risks towards people living within 30 miles radius of the oil refinery as many of the gases emitted from the refineries are harmful and can cause permanent damage and even death. They can cause respiratory problems, skin irritations, nausea, eye problems, headaches, birth defects, leukemia, and cancers especially in young children and the elderly. On the other hand, pipeline accidents, unregulated industrial waste, and leaking underground storage tanks in oil refining can all permanently contaminate large areas of soil, making them economically useless as well as dangerous to the health of organisms living in and around them
Lastly, processing of crude oil also releases sulphur dioxide (SO2) into the atmosphere. sulfur dioxide is the gaseous part, or the vaporous part, of sulfur. It is the main cause of acid rain in this modern era. Acid rain causes the water to have a lower pH value and as a result, the seas, lakes and river have fewer biodiversity. Acid rain also causes the leaching of minerals and precipitation of heavy metals from the soil. The heavy metals are harmful when consumed. Furthermore, acid rain also destroys the photolytic cell in plants, which are responsible for the photosynthesis process.
Crude Oil Distillation Unit (CDU)
(Prepared by Pan Chen Wah, 09UEB0709)
Crude oil distillation unit is the first processing unit in oil refining process. The purpose of the crude oil distillation unit (CDU) is to distill the crude oil into the fraction of different boiling range for further process in other refinery processing unit. Besides, this process also often referred to the atmospheric distillation unit, because the operation is worked slightly above the atmospheric pressure.
Basically, the product produced in this process can be categoried into 4 group, they are: light distillates, middle distillates, heavy distillates and others. The example of light distillates are liquid petroleum gas (LPG), gasoline, and kerosene. Apart from that, the products that can be classified as middle distillates are residential heating fuel and aautomoblie diesel fuels. Additionally, bunker fuel oils is an example of heavy distillataes, while petroleum cokes, lubricating oils and carban black are the other products in this distillation process.
The brief description of crude oil distillation unit (CDU) process is as follow. First of all, the incoming crude oils is heating up before it is entering the fractionation column by heat exchanger. After that, the crude oil will pass through an equipment, called desalter, to remove water droplets and inorganic salts that contained in crude oil. Then, it will be further heating by heat exchanger.
Next, crude oil will enter a furnace. At here, it will be heating up to 330-350 °C. The crude oil then is flashed in the atmospheric distillation column. At here, it is separated into a number of fraction with a particular boiling range. When each fraction in the distillation column reaches a tray where the temperature is just below its own boiling point, crude oil will be condensed and changes back into liquid phase.
Moreover, heaviest fractions will condense on the lower trays and lighter fractions will condense on the higher trays in the column. At different elevations in the column, the fractions actually can be drawn out on gravity through pipes, for further processing in the refinery process by using a special trays called draw-off trays. The fraction is drawn out from the top, side and bottom of the distillation column. These fraction is the products that produced in this distallation process.
Vacuum Distillation Unit (VDU)
(Prepared by Pan Chen Wah, 09UEB0709)
For vacuum distillation unit (VDU), its main purpose is to separate the heavier end products such as vacuum gas oil and slop wax that is from the atmospheric distillation unit. The brief description of the process is as follow. First of all, heavy crude oil is heated by a series of heat exchanger and crude furnace to the desired temperature, which is 350-390 °C.
After that, the crude oils flashed into the vacuum distillation column to separate the heavy crude oil. The separation is same as the separation in CDU process; light vapors is rised to the top and heavier hydrocarbon liquids, then it will fall to the bottom. Next, crude steam is injected into the base of the distillation column to enhance the division of lighter boiling components from the bottom liquid.
Then, light vapour gases are abtracted at the top of the distillation column, it condenses and recycles back to the column as reflux. For light naphtha, it draws off and excess gases are sent to flare. However, for further treatment in hydrotreating units, vacuum gas oil (VGO) and lubricating oils are drawn off and routed. Apart from that, vacuum residue from the bottom of the distillation column is sent to intermediate storage for further processed in fluidic catalytic cracking (FCC) process or delayed coking unit.
Fluid Catalytic Cracking
(Prepared by Krubanandhan a/l Kasinathan, 08UEB05129)
Fluid catalytic cracking is the primary conversion process in petroleum refinery. It is the unit which utilizes a micro-spherodial catalyst (zeolitic catalyst) which fluidizes when properly aerated. The purpose of this process is to convert high-boiling petroleum fractions (gas oil) to high-value, high-octane gasoline and heating oil. This process uses the instrument called Circulating Fluidized Bed. This Circulating Fluidized Bed has fast fluidization regime and also good for catalyst is the size of less than 0.2 mm. They are also excellent in Gas-solid effective contact, Catalyst effectiveness, Catalyst internal temperature control, and Catalyst regeneration.
The operating characteristics of this instrument are;
Particle Diameter = 150 mm
Geldart Classification = A
Temperature = 650 0C
Pressure = 100 kPa
Superficial gas velocity = 10 m/s
Bed depth = 0.85 m
Fresh feed flow rate = 300,000 kg/hr
Catalyst to oil ratio = 4.8
There are 6 steps of processes that occur in FCC. Reactor, Riser, Cyclones, Stripper, Regenerator, Standpipe and Slide Valve.
Firstly, the reactor performance, the feed oil enters the riser near the base and contacts the incoming regenerated catalyst. Then the cracking reactions occur in the vapor phase. The expanded volume of vapors lifts the catalyst and vaporized oil rises. This reaction occurs at a very high speed, usually about few seconds of contact time.
Secondly, the riser, which has diameter of 1.2 meters and height of 36.6 meters, has a plug flow with minimum back-mixing. Steam is used to atomize the feed, this increases the availability of the feed. The outlet vapor velocity would reach up to 18 ms -1. The hydrocarbon residence time is 2 seconds.
Followed by, Cyclones. It is located at the end of riser to separate the bulk of the catalyst from the vapor. It uses a deflector device to turn catalyst direction downward. It will later undergo two stage cyclones in order to separate the remaining of the catalyst. It then returns the catalyst to the stripper through the diplegs. The product vapors exit the cyclones and flow to the main fractionator column.
Then, the spent catalysts fall into the stripper. The valuable hydrocarbons are absorbed within the catalyst bed. Stripping steam, at a rate of 4 kg per 1000 kg of circulating catalyst, is used to strip the hydrocarbons from the catalyst. The catalyst level provides the pressure head which allows the catalyst to flow into the regenerator.
The regenerator basically has two functions, one, restores catalyst activity. Two, it supplies heat to crack the feed. Air is the source of oxygen for the combustion of coke. The air blower with 1 m/s (3 ft/s) air velocity to maintain the catalyst bed in a fluidized state. About 14 kPa (2 psi) pressure drops in air distributors to ensure positive air flow through all nozzles.
In standpipe and slide valve, it provides the necessary pressure head needed to circulate the catalyst around the unit. The catalyst density in standpipe is 642 kg/m3 (40 lbs/ft3). Slide valve is used to regulate the flow rate of the regenerated catalyst to the riser. Slide valve function is to supply enough catalyst to heat the feed and achieve the desired reactor temperature.
Hydrocracking process
(Prepared by Thurgga Moorthy, 10UEB01404)
Crude oil undergoes hydrocracking process after undergoing vacuum distillation and coking processes. Hydrocracking process is a catalytic chemical process used in petroleum refineries convert the high-boiling constituent hydrocarbons in petroleum crude oils to more valuable lower-boiling products. For instance, gasoline, kerosene, jet fuel and diesel oil. The process takes place in a hydrogen-rich atmosphere at elevated temperatures (260 - 425 °C) and pressures (35 - 200 bar). This process removes feed contaminants such as nitrogen, sulfur, metals.
Hydrogenation occurs in fixed hydrotreating catalyst beds to improve hydrogen/carbon ratios. The size of the molecules must decrease and the atomic H/C ratio must increase if the products are to become useable as conventional fuel products. This is followed by one or more reactors with fixed hydrocracking catalyst beds to dealkylate aromatic rings, open naphthene rings, and hydrocrack paraffin chains. Major products from hydrocracking are jet fuel and diesel, while also high octane rating gasoline fractions is produced. All these products have a very low content of sulfur and other contaminants.
Hydrocracking is normally facilitated by a bifunctional catalyst that is capable of rearranging and breaking hydrocarbon chains as well as adding hydrogen to aromatics and olefins to produce naphthenes and alkanes. This process cracks the high-boiling, high molecular weight hydrocarbons into lower-boiling, lower molecular weight olefinic and aromatic hydrocarbons and then hydrogenates them. Any sulfur and nitrogen that is presented in the hydrocracking feedstock are hydrogenated and form gaseous hydrogen sulfide (H2S) and ammonia (NH3) which are subsequently removed. On the other hand, it is important for the hydrocracking products are free of sulfur and nitrogen impurities and consist mostly of paraffinic hydrocarbons. Basically, hydrocracking process consist of the splitting or breaking of straight or cyclic hydrocarbons and hydrogenation of the broken bonds.
Example:
For futher details about the yield and disposition, refer to the table below:
Product
Yield, volume% feed
Disposition
Light ends
Varies depending upon objectives
LPG
Naphtha
Gasoline, catalytic reformer
Diesel
Diesel
Total volume yield
130 - 140
Gas oil conversion
60 - 99%
They are two stages of hydrocracking unit; Single Stage Process and Multi Stage Hydrocracker. Single Stage Process is where treating step is combined with cracking reaction to occur in one reactor. When high or full conversion is required, it needs to switch to a multi-stage process, in which the cracking reaction mainly takes place in an added reactor. Two versions of the multi stage hydrocracker have been developed; two stage hydrocracker and series flow hydrocracker.
Schematic of a two-stages hydrocraking unit
Hydrotreating Process
(Prepared by DING TIONG SOON, 10UEB01031)
Hydrotreating technology is used in refinery processes to remove contaminants such as sulfur, nitrogen, condensed ring aromatics, or metals to produce a clean product for further processing. Hydrotreating process includes Naphtha Hydrotreating, Gasoline Hydrotreating, Mid-Distillate Hydrotreating and FCC Feed Pretreating.
The feeds used in this process range from vacuum resid to naphtha , and the products are used as environmentally acceptable clean fuels. In the hydrotreating process, oil fractions are reacted with hydrogen to produce the high-value clean products in the presence of catalyst. The operating conditions will depend on the final application.
Hydrotreating process began when the a stream of hydrogen-rich recycle gas joins with liquid feed stream. The mixture is then preheated by flowing through a heat exchanger. After that, it is heated to the desired hydrotreating temperature using a fired heater where the feed mixture is totally vaporized. Hydrotreating takes place when the feed mixture flows through a fixed-bed reactor, in the presence of a catalyst which consist an alumina base impregnated with cobalt and molybdenum.
The hot reaction products are cooled by letting it flows through a water-cooled heat exchanger before it is flowed to the pressure controller. Next, its pressure will be reduced to about 3 to 5 atm. The resulting mixture of liquid and gas are entering the high pressure separator which separates the liquid hydrocarbon from the hydrogen , hydrogen sulfide or ammonia gas.
Howevrer, most of the hydrogen-rich gas (from gas separator vessel) are recycling by routing through an amine contractor for the removal of acid gas and reuse in reactor section. Any excess gas from the gas separator vessel will react with sour gas; which is came from the stripping of the reaction product liquid.
Apart from that, the liquid from the gas separator vessel is routed through a reboiled or steamed stripper distillation tower. The stripper only have two products ,a top and a bottom. With a steam stripper, downstream processing, typically a salt dryer which is preceded by a vacuum dryer, is required to remove water from treated products. If multiple products are produced, then a fractionator with a fired reboiler is also used. Further separation of LPG gases occurs in the low pressure separator prior to sending the hydrocarbon liquids to fractionation. Meanwhile, the sour gas is sent to refinery's central gas processing plant to remove hydrogen sulfide in the refinery's main amine gas treating unit and through a series of distillation towers.
The Importance of hydrotreating is that it helps to improve air quality by desulfurization of fuel oils. Hydrotreating prepares valueable hydrocarbon products from heavy carbon streams and the production of low-sulfer-level fuel oil from residual stocks after distillation of crude oil.
Coking
(prepared by Soo Voo Yee, 10UEB01889)
Coking is a thermal process for the conversion of low value residue to valuable products and coker gas oil. There have two types of coking process, which are delayed coking and fluid coking.
For the delayed coking process, at first, the residual oil from the vacuum distillation unit is pumped into the bottom of the main fractionators. Along the way it is pumped to the furnace, some steams are injected to heat it to its thermal cracking temperature of about 4800C. The injected steam helps to minimize the deposition of coke within the furnace tubes. Besides that velocity inside the tube of the furnace is very fast. This is to reduce the loss of heat as a waste of source.
Because of the short period in the furnace, so the coking of the feed is delayed until it reaches the large coking drum. Compared to the furnace, drum provides a longer period for the cracking process to proceed to completion. For the gas oil and the lighter components will leave from the top of the drum, left behind the components of liquids and solids. The gasses will be directed to the main fractionators to separate it into gases, naphtha and light and heavy gas oils based on each boiling point. In the coke drum, the solid coke is deposited and remained in a porous structure that allows flow through the pores. 16 to 24 hours are needed to fill the drum full as a complete coke drum cycle.
The hot mixture is switched to another empty drum, when the first drum is full of the solidified coke. While second drum is filling, the first drum is steamed out in order to reduce the hydrocarbon content of the petroleum coke. Then, it is cooled down with water. The top and bottom heads of the full coke drum and the solid petroleum coke is removed from the coke drum via hydro jetting. The pressure of the water is about 1250psig to 4000 psig and the flow rate is about 750GPM to 1250 GPM.
Fluid coking is a continuous process which consists of 2 units, reactor and furnace. In the reactor, the coke particles are fluidized by steam. The preheated feed will be injected directly into the reactor when it reached temperature of 2500C to 3500C. The temperature inside of the reactor is around 4800C to 5700C. On the surface of the coke particles, cracking process is occurred, causing the lighter components are being vaporized. To separate the entrained coke particles with the vapors, cyclones are used.
The vapor is then sent to the bottom of the scrubber and condensed into heavy tar; meanwhile the remaining coke is removed and recycled back to the coke reactor. The overhead of the vapor is directed to the fractionators where it is separated into the desired boiling point fractions. Then the coke particles flow to the stripping zone to remove any product vapor between the coke particles. After that, the coke particles are sent to the burner. A part of the coke is burned to remain the average bed temperature. Hot coke is then sent back to the reactor. To maintain the coke inventory in the burner, coke which is one of the products, required to withdraw from the burner. The large coke particulate will be replaced by the smaller seed particles to prevent the circulating coke is too coarse.
Compare to delayed coking process, fluid coking will be carried out at a more uniform and higher temperature and shorter contact time. The products produced by using fluid coking process are more valuable and less coke.
Role of chemical engineering in industry
One of the roles of chemical engineer is to design process plants that convert crude oil into more valuable products such as gasoline, LPG, diesel and jet. The plants are designed based on the view of economic and safety. They have to optimize the processes that can make the money most from the refinery.
Chemical engineers also need to do tests and research that can operate the oil refinery processes smoothly. They will discuss with the operators when find any opportunity to optimize the processes. If they feel that it is good thing to do, they will try to change the temperature and pressure, to see whether there is more lube oil produced. When it is successes, chemical engineers are required to prepare reports as a record of why it is worked. This can ensure that idea forward and the processes are going in optimize way. Thus, preparation of reports is one of the roles of chemical engineers.
In addition, chemical engineers are also required to find and solve the potential problems that found in the oil refinery processes. Chemical engineers examine the parameters such as temperature, pressure and flow rates to check whether there is any problem in the refinery process. They also will analyse the sample of the products. If they find out any potential problems, they are required to solve them.
Skills/Knowledge Required by Chemical Engineers
As chemical engineers, they required knowledge of chemistry, physics, mathematics and engineering to design machines that able to turn a raw material, like crude oil, to useful and valuable products, such as diesel, gasoline, LPG and jet. Thus, at the same time, chemical engineers required to have a keen scientific mind, so that they can design effective machines for the oil refinery processes by using their knowledge.
Besides, chemical engineers also need strong analysis skills. This is because they are required to analyse a lots of document, processes, diagrams, tables and equations when they are preparing for their reports. In addition, chemical engineers also must have good research skills. Chemical engineers also do researches to find out certain information based on their projects of the oil refinery processes. In order to get the results that they expected, the research must perform in good deal. Thus, good research skill is required.
Chemical engineers also should be able to pay attention to detail. They need to pick up any potential problems in the oil refinery processes based on the data from system. Chemical engineers also need the ability to solve the problems so that the oil refinery processes can move on smoothly. Furthermore, chemical engineers must be precise. If a small careless mistake in the calculations is done by a chemical engineer, not only it will cause waste of rare material, but also may cause serious accidents, such as explosion.
Conclusion
Based on our research, we have learned that petrochemcical industry has a very good prospect future in our world. This is due to the current high demand of the petrol, which is produced through the oil refinery process, in this new era. However much the industry has given good contribution to our society, it does has its own dark side, which is pollution problems to environment. Therefore, for us as chemical engineering, we should come out a plant for oil refinery process which give less pollution, or if possible no pollution to our environment.
