The process engineering of refineries undertook rapid changes in the past century, especially during the WWII. While pre-WWI refineries expanded their crude oil feed capacities based on economies of scale and scope, the demand for fuels rose exponentially with the popularization of the automobile. Shortly afterwards, WWI excited an even greater market shift towards increased fuel production. The stability of this fuel, measured by octane number, was rapidly increasing with newly developed catalytic processes (reforming, FCC, and alkylation) that would ultimately overtake thermal cracking. After being developed during the heat of WWII, these new processes would not take place in industry until the 1940s.

Perhaps the title is misleading: WWII was not the first war to require innovations to power a victorious campaign. Previous wars would experience horse-powered cavalries, wind-powered navies, and whale oil. All of these adaptations of warfare required visionaries to take their current environment and use it to their benefit. The trend remains consistent to this day: innovation drives energy density and stability of fuels (one horsepower is a bit outdated). Nevertheless, the military-industrial fossil fuels complex remains an ever-changing geopolitical case study. As new processes are developed, novel products and byproducts flood the market with tremendous potential to further the flexibility of the refinery.

Perhaps the most element in this stage of the oil and gas industry was the environmental tradeoffs that were made for the end goal of fuel efficiency. Tetra ethyl lead, a gasoline additive that has since been prohibited from use due to health and environmental hazards, was the perfect example of the military-fuel complex forcing geopolitical agendas without the immediate environmental concern. In this case, as in many times of war, citizens and elected officials will pay more attention to military mobilization than ecological conservation. In order to prevent such mistakes from taking place again, government agencies must work with media networks to promote federal registers and public comment periods for specific geopolitical developments, especially as they pertain to the way we power the world.

In a golden age of corporate personhood, U.S. refineries may actually have more in common with humans than ever before. Water sustains both human and refinery life. As a community’s water consumption increases, so must its municipal wastewater treatment capacity increase. Likewise, as regulations necessitate more hydrotreatment processing, refineries must increase sour water treatment capacity. While this notion might harmoniously unify a refinery and its perpetually protesting community, in reality it causes downstream issues with contamination risks galore.

As a general rule in wastewater treatment, “do not mix different wastewater streams before treatment.” Although cooling water and sanitary sewage may require the least amount of treatment, an operator must be mindful of the refinery’s process and instrument drawing (P&ID) in the event of an oil spill, in which these flows could be contaminated. Storm water may be contaminated by air pollutants and should be dealt with accordingly. The most heavily polluted wastewater feeds stream from process water and steam units; these must be sweetened, and oils and solids must be separated from the wastewater.

In order to minimize the load on the treatment units, the operator must separate different wastewater streams based on their characteristics. A complete wastewater characterization includes biochemical oxygen demand (Standard Methods 5210), chemical oxygen demand (Standard Methods 5220), suspended solids, hydrocarbon content, nitrogen content, phenols [all in mg/L], and acidity [pH]. The EPA provides guidelines for industrial wastewater limitations and Standard Methods for the Examination of Water and Wastewater provides EPA-approved wastewater analytical procedures.

In July 2012, The Carlyle Group and Sunoco, Inc. formed a joint venture, Philadelphia Energy Solutions, to continue refinery operations at the oldest continuously operating refinery on the east coast. The Carlyle Group and the Commonwealth of Pennsylvania agreed to provide funding for the catalytic cracker unit, a train terminal for transporting Bakken crude oil, and a mild hydrocracker unit. All of these modifications will increase the water consumption as well as the required wastewater treatment capacity of the refinery. The EPA required Sunoco to continue to remove groundwater contaminants such as hydrocarbons and heavy metals. On the other hand, the new owners must increase their wastewater treatment capacity. While there are plenty of people who might disagree, I believe this has been the healthiest business agreement in past decade between industry and government in the PA energy sector.

Similar to cracking processes, reforming processes add utility to a refinery’s end product, gasoline. Catalytic reforming converts heavy naphtha to high octane isoparaffins and aromatics for gasoline blending. Using a noble metal catalyst, the reformer dehydrogenates, cyclizes, and isomerizes the feed compounds at a high temperature, low pressure, low space velocity, and low H₂ byproduct to hydrocarbon ratio. As these conditions promotes C-C breaks and formations, they also lead to slight carbon rejection, which results in coke deposits on the catalyst. Therefore, the end goal of catalytic reforming is to enhance the octane rating of the stream while limiting the amount of coke buildup.

In order to limit the production of petroleum coke, compressed hydrogen is injected into the stream at a relatively low pressure. At high H₂ pressures, hydrocracking overtakes reforming processes. While high operating temperatures could inhibit hydrocracking, this parameter is limited by the material defects of the reactor. A high space velocity can also suppress the cracking reaction, however this is detrimental to reforming effectiveness. Ultimately, these parameters must be included in a cost analysis to better define the appropriate operating conditions for a specific feed.

The various process configurations also dictates the optimal working conditions of the reformer. An example from our favorite Honeywell Company, UOP, provides a simplified version of their patented continuous catalyst regeneration (CCR) Platforming^TM Process. Despite the highly favored continuity concept, the seemingly endless list of processes are all very expensive, which explains why in Fig. 1 (below) U.S. refineries will not function at full capacity in the near future. Furthermore, economics are not the only driving forces in catalytic reforming operations: regulations play an important role.

Fig. 1: The amount of reformer feed remains annual cyclical for the past four years. (Source: EIA)

On May 15^th, the EPA’s director signed a rule proposal that could affect conversion processes in refineries throughout the country. The amended regulations would require air concentration monitors along the fenceline of refineries with an expected reduction of 5600 tons per year of toxins and 52,000 tons per year of volatile organic compounds. In order to prolong the life of the catalyst, catalytic reformers include regeneration cycles which burn off coke with air, producing air pollutants. Preceding the catalytic reformer, a hydrotreatment process removes heteroatoms from the feed but subsequently pollutes the atmosphere if not mitigated appropriately. The new rule will eliminate the previous exemption to refinery emissions limits during startup and shutdown, so the aforementioned processes may need additional scrubbing systems. This regulatory scenario illustrates the delicate balance between engineering efficiency (catalyst maintenance) and pollution mitigation.

Let me know if you would like to collaborate while commenting on the new EPA proposals!

Reference:

1. blog 8 catalytic reforming capacity

The downstream sector of the oil and gas industry relies heavily on effective conversion processes throughout the year. In order to protect the bottom-line, the refinery operator must understand the high temperature, rapid discharge catalytic conversion processes that determine the end products. Fluid catalytic cracking (FCC) and hydrocracking encompass the two most significant types of conversion processes in today’s refinery. Each possesses advantages in converting specific feedstocks to more desirable products.

FCC involves a carbon rejection. This endothermic process uses an acid catalyst to convert low-value feed to useable gas, gasoline, light and heavy cycle oil, and decant oil as well as petroleum coke. According to the EIA, FCC has greatly impacted the fuels industry in the U.S.’s gasoline-driven society. An important process feature involves the need for catalyst regeneration by means of burning off the catalyst coke. There are seemingly endless design configurations throughout the industry to limit the cost of this energy intensive process. This process produces higher octane products than thermal cracking products for gasoline production due to the isomerization mechanisms that produce iso-paraffins. This process may require some pre-hydrotreatment stage to protect the catalyst from poisoning.

Similarly, hydrocracking usually involves a two-stage conversion process. First, the feed is hydrotreated to remove heteroatoms that might poison the hydrocracking catalyst. Then, the feed completes an H/C ratio enhancement that hydrogentates the feed and removes impurities (cracking). This EIA article illustrates the general flow of the feed through the reactor, separator, and fractionator to produce jet fuel, diesel, and kerosene among other products. Compared to FCC, hydrocracking is much more suitable for processing heavy crudes with aromatic characteristics. The heteroatoms may be removed with this process and even utilized as a byproduct.

Both processes have strengths and weaknesses, and given the increase in demand for gasoline and distillates such as jet fuel and diesel, these processes will continue to be developed in tandem.

Fig. 1: “Petroleum conversion process” by Fred Koch (Source)

Now that we have exhausted the virtually endless range of separation processes, we concentrate on the set of thermal processes that engrained the oil and gas industry in transportation. Unlike the separation byproduct, asphalt, which is one of many pavement options, the products of thermal conversion processes are inimitable in today’s American market (unless, of course, you are an electric motor fanatic like me!). Before delving into the invaluable products, we review a brief history lesson on thermal processes in refineries.

Chemical engineer, Fred Koch, might not be the father of thermal processes, but he certainly is credited with “spreading the wealth”. Fig. 1 (above) references his patent that enabled smaller entities to profit in the spoils of big oil and gasoline production. Ironically, despite building his chemicals empire in the Soviet Union, the esteemed MIT graduate took a strong political stance against communism. But, I digress!

Fig. 2: Fred Koch (Source)

The use of automobiles increased the demand for gasoline beyond the rate of straight-run gasoline distillation. Despite a sharp increase in drilling activity, the refining industry required more light gas oil through the thermal processing of the heavy gas oil and vacuum distillate residue (VDR). Conveniently, the first applications fueled WWI and subsequent wars. Thermal cracking chiefly produces in light gas oil, gasoline, residual fuel oil, and petroleum coke. While the demand for these products has only increased since its inception, catalytic cracking has usurped the attention of industry and academia alike.

Recent concerns of aging refineries call for enhanced control systems. Perhaps, the most hazardous process takes place in the coking drums, where three phase system could lead to unexpected pressure changes. Flowserve provides an example of this complex system. An intriguing mechatronic advancement involves the use of automated decoking systems. As long as thermal cracking provides ethylene production for the petrochemical industry, engineers will continue to develop best practices for safe operation of these units.

Just when you thought separation processes could not be more drawn out, dewaxing appears! Undoubtedly another slightly misleading process title, dewaxing is chiefly concerning the lubricating oil base stock product more so than the wax byproduct. The lube oil base stock market price depends on its volatility, viscosity, viscosity index, and thermal stability. Depending on the process employed, the resultant lube oil base stock may not require as many additives to enhance engine performance.

Solvent dewaxing requires a tremendous amount of energy and solvent to remove wax from the lube oil base stock. We discussed the use of solvents such as methyl ethyl ketone and propane along with the need for refrigeration units and steam-stripping to remove wax. Bechtel Corp. displays a general layout of its own solvent dewaxing process. Notably, Bechtel uses inert gas instead of energy-intensive steam for stripping. Regardless, the operating costs illustrate how significant the dewaxing footprint is within the refinery. No wonder those oil leaks cost me a fortune!

You may question the utility of wax on the open market, like I do. Never fear, catalytic dewaxing is here!

Shell Global Solutions’ website illustrates the company’s catalytic dewaxing technology for the work to study (and purchase). This separation process actually involves catalytic cracking of n-paraffins using a selective catalyst. To mitigate fouling of the catalyst, hydrogen is also applied. This process enables the operator to produce even more distillates and lube oil base stock. This is tremendously lucrative since it requires a lower capital investment; the selection of this process relies on the robustness and effectiveness of the catalyst. Perhaps, I should invest in the catalyst industry…

Fig. 1: Shell Global Solutions’ proprietary catalyst (Source)

In the oil and gas industry, the bottom line is the most essential metric of success. We have discussed the complexity of crude oil and the general refinery path which it takes. Certainly, the most energy intensive portion of refining, separation processes, dictates the success or failure of an oil refinery. Along with the increase in light distillates, we observe an increasing need for heavy crude deasphalting capacity. As distillation columns use pressure and temperature gradients to fractionate distillates and bottoms, solvent fractionation is a “carbon rejection” process that uses a “chemical gradient” to separate asphaltenes and resins from deasphalted oil (DAO) in vacuum distillation residue. Additionally, solvent dewaxing involves solvents and temperature gradient to produce wax and lube oil. Ultimately, solvents may enhance the overall refinery profitability while adding product flexibility and utilizing the entire barrel of crude oil!

In order to understand solvent fractionation, we must understand the gradient solubility model. For engineers to able to characterize the seemingly fruitless vacuum distillation residue. Resins in the crude oil dissolve asphaltene molecules in a solution, preventing precipitation. Miscibility, or the “mixabilty” property, must be altered through the use of a solvent. Paul J. Flory, a Standard Oil Development Co. scientist, correlated the difference in molecule sizes (solvent versus VDR) with system entropy; as the difference in molecule size increased, the entropy (or disorder) increased, causing large deviations from ideal miscible behavior. With this understanding, we can attempt to quantify the strength of various solvents to compare.

Fig. 1: Paul J. Flory, 1974 Recipient of Nobel Prize in Chemistry (Source – Nobelprize.org)

At this point in the separation stages, large hydrocarbons such as asphaltenes and waxes can precipitate out of the crude oil solution given a specified paraffinic solvent. The strength of these non-polar solvents are defined by Hildebrand Solubility parameters. While Wikipedia only displays the Hildebrand parameter as a function of vaporization enthalpy, temperature, and molar volume, a similar value may be approximated using surface tension and molar volume. As surface tension increases (or the enthalpy of vaporization increase), the solvent’s strength increases.

The variety of compounds in crude oil range from light paraffins to heavy, aromatic compounds, each with its own set of operable temperatures and pressures ranges. In the first stage of distillation, the atmospheric distillation column is used to separate the heavy and residual oil from the light compounds that limit the further separation of the crude oil. Vacuum distillation involves a depressurized system, which increases volatility of the heavy oil and is ideal for separating the residual heavy compounds for further processing.

It is important to understand the limitations of input crude oil to avoid unwarranted cracking within the atmospheric distillation column, and the Watson Characterization Factor provides a rough estimation on that range. The relationship between K_W and the decomposition zone at which temperatures alter the chemical bonds of the lighter compounds are well documented throughout academia and industry. To avoid coking within the distillation column with tremendous certainty, one must stay outside of the decomposition zone. However, as the video in the previous blog showed, decreasing the temperature gradient (from top to bottom of the distillation column) decreases the yield of other distillates or at least the rate of production.

Contrary to the trends we have studied, this Reuters article illustrates an ongoing issue with U.S. refineries processing lighter crudes. The demand for lighter, straight-run fuels is much more desirable in the non-American market. While heavier crudes continue to be discovered and exploited, the domestic supply of light crudes and condensates will certainly require more simulations and infrastructure to handle such wide varying capacities.

https://www.youtube.com/watch?v=gYnGgre83CI

The three distillation methods of interest include true boiling point distillation, ASTM distillation, and equilibrium flash vaporization. Each process can be called upon depending on the level separation precision necessary for a specific use. Perhaps, the most important method is simulated distillation, which has increasingly beneficial implications as opposed to physical distillation (i.e. true boiling point distillation). Nonetheless, compared to the other three refinery processes (conversion, finishing, and support), separation requires the most energy, so the method choice must maximize the use of energy for precision.

Figure 1: Repsol (Source)

True boiling point distillation (TBPD) is used to characterize the incoming crude oil. It is important to have an approximated crude assay to properly prepare the refinery controls. An unexpected high pressure in the distillation column could be catastrophic economically and environmentally. Precision is of the utmost importance in this distillation, and since this process is used for the crude oil and not preprocessed petroleum products.

ASTM distillation are more useful than true boiling point distillation for petroleum products although the mechanisms for separation are similar (batch process). Unlike TBPD, ASTM distillation does not utilize a condenser-receiver system for refluxing as described in the YouTube video, nor does it require the materials for the TBPD plates. While this may lead to more overlap in crude oil separation, this level of separation precision is acceptable for petroleum products with less probability of overlap.

Equilibrium flash vaporization is utilized in at the extreme ends of the distillation column. The re-heater at the bottom of the atmospheric distillation column is used in an EFV process. This provides the least effective separation of the three.

Unfortunately, I am a bit surprised that no Google patent searches could display findings of renewable energy integration in this energy intensive process. I would imagine that concentrated solar energy may not be relied on as a baseline power source for the pre-heating and re-heating processes. However, I could imagine that on a normal Louisiana summer day, this could be reasonably beneficial. If anyone has any information that I have failed to come across, please let me know!

Reference:

http://chemeng-processing.blogspot.com/2009/01/refinery-distillation.html

Fig. 1 Finished Motor Gasoline does not include blending components

The EIA provides a plethora of data on U.S. petroleum fuels production. The “Weekly U.S. Refiner Net Production” graph (Fig. 1) illustrates the comprehensive “Weekly Petroleum Status Report”. The “WPSR Highlights” provide a condensed sketch of the report. During the week ending May 16, 2014, U.S. refineries operated at 88.7% capacity, consuming 15.9 million barrels of crude oil per day and producing 9.6 million barrels of gasoline and 5.0 milion barrels of distillate fuel oil. The U.S. imported 6.5 million barrels per day as well as over 1.1 million barrels of finished gasoline, gasoline blending components, and distillate fuel. Given that roughly 60% of a barrel of crude oil is used to produce gasoline, diesel fuel, and heating oil, and thus that imports account for 3.5 times that of finished imports, it is safe to say that U.S. refineries are essential components in the U.S. As my classmate readily points out, the U.S. is bridging the gap between imports and exports. However, it is unclear whether the domestic production is sustainable. As tight oil extraction continues, the world is only one subsea engineering feat away from revitalizing easy oil.

Along with weekly reviews, the EIA provides quarterly forecasts of the petroleum fuels market. As Memorial Day approaches and summer vacations commence, the EIA predicts the price of gasoline to increase slightly above the prices from this time last year before dipping below last year’s numbers for the remainder of the year. This trend correlates to crude oil prices, and ultimately results from an expected overproduction from the non-OPEC supply, especially in North America.

The most notable trend in Fig. 1 is noted in the Annual Energy Outlook 2014: gasoline production is declining while distillate fuel production increases. The EIA anticipates more gasoline-producing refineries to either convert to distillates or increase capacity to meet the market demand.

U.S. crude oil stocks are very high compared to the 5-year average. The distillate fuel stock is below average which might also imply a regression to the mean with increased imports and domestic refinery capacity.

Fig. 2 Distillate fuel oil includes No. 1, No. 2, and No. 4 distillate

Notably, the conflict in Crimea may not have noticeably impacted the recent refinery outputs, but it may account for the decline in U.S. exports of distillate fuel oil. While distillate fuel oil consists of many uses, from space heating to diesel engines, “Distillate Fuel Oil Imports and Exports” (Fig. 2) displays a sharp decrease in exports and imports after the week of Russia’s occupation of Crimea. Despite this period of March, April, and May being termed the refinery maintenance season, this span of time includes a critical period of market uncertainty. Crimea already faces fuel shortages. Germany could face price surges, as pressure increases to diversify crude oil and natural gas imports.

The refinery exemplifies the peak of fuel chemistry application, with each refinery having unique capacity, inputs, and products. The environmental concerns posed by greenhouse gas emissions from internal combustion engines is mitigated within the refining process. A baghouse is used to capture particulate matter. Sulfur content may be removed through hydrodesulfurization or hydrotreating. Volatile metallic compounds are extracted by precipitation using a solvent such as propane. All of these processes are either energy-intensive and/or materials intensive, and would greatly benefit from regenerative solvents and materials.

References:

1. Pricing Highlights: http://www.eia.gov/petroleum/marketing/monthly/pdf/hilites.pdf
2. Supply Overview: http://www.eia.gov/petroleum/supply/weekly/pdf/highlights.pdf
3. http://www.nytimes.com/2014/05/18/world/europe/in-taking-crimea-putin-gains-a-sea-of-fuel-reserves.html?_r=0
4. http://www.reuters.com/article/2014/04/25/ukraine-crisis-crimea-energy-idUSL6N0NH4NR20140425
5. http://www.eia.gov/forecasts/steo/special/summer/2014_summer_fuels.pdf
6. Supply Data: “blog 1 data.xls”
7. Petroleum Refining