Opinion: The fuel quality and tank design disconnect
Whether buried underground, positioned above ground, or exposed in a basement, fuel-storage tanks have kept millions of cars and trucks, as well as businesses, industry, aircraft, homes, and the like adequately supplied with gasoline, diesel fuel, aviation fuel, and home heating oil for as long as distillate fuels have needed some form of bulk storage. Generally, the consumer rarely notices these tanks, nor does the consumer think about how fuel quality could be impacted by factors such as tank design.
Over the past few years, a great deal of attention has been given to what appears to be an increase in premature filter plugging and corrosion activity in the underground storage tank (UST) systems across the country, which can affect every type of distillate fuel. Given my 30 years of experience storing, blending, and shipping fuel, not much surprises me when the phone rings and a concerned fleet manager begins to share his story of an early morning filter-plugging problem that’s causing him to experience his worst nightmare—costly downtime.
The petroleum supply chain
To appreciate what could be happening to these fuel storage systems, we need to understand how the petroleum supply chain functions and how quality standards are used to maintain fuel quality while the fuel type is “in commerce” from the point of manufacture to the point of sale. It is interesting to contrast fuel-quality management practices between the aviation industry and the pleasure-craft industry. In the case of the former, the airline industry worldwide has invested millions of dollars and hundreds of thousands of hours to develop a fuel management program that ensures that jet fuel maintains stringent fuel quality standards by filtering and dewatering it every step along the distribution network. From production, transport and storage to fueling the aircraft, industry practices ensure and maintain optimum fuel quality, resulting in reliable aircraft operation and, in turn, passenger safety during flight.
In stark contrast to the aviation industry is the marine retail market, selling diesel fuel, gasoline and E10. These fuel storage tanks are typically near a body of water, subjected to diurnal temperature fluctuation, and in humid conditions. Over time, these elements lead to the formation of sediment and bottom water that remains with the stored fuel until the tank is physically cleaned and dewatered.
The situation with middle-distillate fuel used in home heating oil lies between these two extremes. Even though the industry is committed to maintaining fuel within specification while in commerce, fuel-handling, storage and maintenance practices may be much less rigorous before the fuel reaches the consumer.
What contributes to fuel quality degradation?
The road to fuel quality degradation begins with the process in which crude oil is transformed into the finished petroleum products. Refiners are driven to maximize each barrel of crude oil. Their objective is to optimize technology in order to produce as much high-value product per barrel of crude that enters the refinery as they can. Through several distinct processes—distillation, cracking, reforming, blending and treating—refiners convert barrels of crude oil into higher-value products such as gasoline, diesel fuel, jet fuel and home heating oil. Once the products exit the refinery, they are transported through a network of pipelines, barges, ships and rail cars to their final destination. During the various transfers, the fuels are subjected to the ravages of time, temperatures and organic and inorganic contaminants, all of which can potentially compromise their future performance and the storage systems in which they will be held until they are sold to the general public. From the time the fuels are produced to the time they reach the downstream marketplace, they are in the process of degrading (the initial point of recognized fuel instability).
When a fuel product arrives at a regional petroleum deep-water pipeline or a break-out terminal strategically located in the U.S., it is then redistributed to a local distribution zone and placed in a large storage tank with other products, all of which must coexist by way of “like” fuels (i.e., fuels that meet their respective ASTM specifications).
For example, ASTM D975 benchmarks standards for diesel fuels, ASTM D396 benchmarks standards for home heating oil, and ASTM D6751 benchmarks standards for B100 biodiesel. Subsequent designations for biodiesel blends (i.e., B6–B20), must conform to their respective benchmark specifications. Biodiesel blends of up to 5 percent biodiesel (B5) in either diesel or heating oil fall under core diesel and heating oil specifications—D975 and D396, respectively. Biodiesel blends that range between B6 and B20 percent are governed under ASTM D7467.
During the period of time before a product is sold to the consumer for use as a transportation fuel or heating fuel, the custodian of these fuels may blend other products into the fuel stream to optimize both supply and economics. These blend stocks may be light cycle oil (LCO), Russian Gas Oil (RGO), or even various types of biodiesel; all of these blends must continue to meet their respective specifications.
In the end, millions of gallons of fuel products produced at home or abroad are transported daily through thousands of miles of a “fungible” product network in order to arrive to the end user. Imagine, in the absence of a minimum fuel quality standard throughout the storage and distribution network, these fuels could initiate and contribute to fuel product degradation during transport, ultimately affecting the integrity and performance of the fuel product and fuel storage systems.
Can it get worse?
In addition to the physical aspects associated with fuel quality and fuel storage, fuel dealers must also address growing negative perceptions on the part of consumers regarding fuels, price fluctuations of their respective fuel products, and attacks from market competition anxious to take their rightful place in the 21st Century energy market by offering an alternative energy solution to the long-term traditional fuel market. The very issues that bulk-storage system professionals are trying to grapple with and understand—unexplained increases in dispenser filter plugging, premature tank failure, corrosion and microbial events—can also be reflected in the local home heating oil dealers who are fighting for their economic survival in the face of the natural gas industry’s effort to devour every last oil heat customer.
The reason home heating oil dealers remain challenged in ensuring a customer’s total satisfaction with heating oil is in part due to their inability to control what is happening inside the homeowner’s tank. For example, large aboveground storage tanks typically have man ways that allow access to the tank interior for inspection and cleaning.
Contrast this to the typical home heating oil tank, which is sealed and virtually inaccessible to the removal of any degraded fuel product, water or microbial contamination that has accumulated inside. After decades of accumulation, fuel-degradation product, water and microbes at the bottom of these home heating oil tanks are roiled each time fuel is delivered, which ultimately leads to plugged fuel lines, filters, strainers, and worse, degraded burner nozzle performance.
Taking on the challenges
So what can we do to make a better product? Many industry observers understand that to compete with cleaner burning technologies, government intervention is needed to help reduce the environmental impacts of available fuels by way of establishing legislation/mandates/incentives to use low sulfur fuel and/or renewable fuel. The liquid fuel industry will have to transition to selling lower-sulfur fuels, consider blending biodiesel into middle distillates, and, if they wish to truly compete, begin paying attention to what they are buying and find ways to protect the fuel prior to sale.
The question on the minds of many marketers at the moment is: How will ultra-low sulfur heating oil (ULSHO) impact the industry’s challenges associated with heating oil systems? For example, the high levels of hydro treatment required to make ULSHO will have a significant impact on many chemical and physical properties of the fuel. These changes can subsequently affect field performance and result in end user problems. As ULSD becomes more common in the home heating oil market, we will gain better insight on how this lower sulfur product will interact with existing home heating oil systems, however, one should be able to anticipate the impact of potential changes based on experiences with ultra low sulfur diesel (ULSD) fuel.
There have been a great number of industry discussions regarding ULSD’s potential role in causing corrosive activity and hardware failure in fuel dispensers. Industry leaders were quick to address these isolated incidents and formed a task force to explore the problem. To date, there have been no findings that clearly indicate cause and effect of those reported incidences. But one question remains: Should the oilheat and Bioheat fuel industry be concerned about ULSHO as more and more states adopt the ultra low sulfur fuel?
One of the major contributors to a customer’s fuel-related, “no-heat call” has been degradation material derived from unstable fuels. This situation occurs because the fuel itself contains material that readily degrades under the right circumstances. These degradation materials form particles and sludge that can plug filters, lines and burner nozzles. Preventing fuel degradation is of paramount importance to eliminating fuel related no-heat calls and goes a long way in extending the life expectancy of a fuel storage tank.
For example, as a result of the desulphurization process for making ULSHO fuels, many of the potential degradation precursors are transformed to materials that are insensitive to traditional storage (oxidative) degradation. Thus sludge production is expected to be negligible (and great for the consumer, fuel merchant and tank environment).
It is rare, however, that changes in the processing of fuel result in one simple phenomenon. It is well documented that heavily hydro-processed fuels readily generate aggressive free radicals that can form peroxides in the fuel. Upon achieving certain minimum levels, these peroxides easily attack and degrade fuel system elastomeric seals and gaskets.
The same peroxides can initiate the premature degradation of biodiesel/heating oil blends, resulting in fuel instability, high acid content and sludge formation. ULSHO, again by nature of desulphurization, does not have the natural peroxide inhibitors that would protect the consumer and tank from this phenomenon. Fortunately, properly formulated additives focus on this new problem and can protect against peroxide formation.
Existing sludge/ULSHO solvency
The absence of newly formed degradation material should not imply that existing sludge will not be problematic. Both heating oil systems and diesel fuel storage systems that have not been proactively protected may have years of built up sludge. This buildup occurs over a long period of time and reaches a state of equilibrium.
Part of this phenomenon is due to the solvency effect of high sulfur fuels. The solvency of ULSHO can be markedly different from high sulfur diesel or low sulfur diesel, and may have a negative impact in mobilizing sludge. Agitation during the fill process and change in solvency may cause sludge to be “sloughed off” and can result in filter and strainer plugging and negatively impact nozzle and injector performance.
A mild dispersant may effectively control the rate and size of sludge particle removal. Dispersants function to gradually mobilize sludge and to keep sludge particles at a microscopic and filterable size so as not to have a detrimental impact on the fuel delivery system. Many premium diesel and heating oil packages currently marketed by oil companies contain these components to aid the fuel dealer by way of offering a higher quality product.
As mentioned earlier, the petroleum industry is currently trying to determine the reasons why corrosion problems have increased so rapidly over the past few years. Multiple technical associations have formed groups to study the root cause and determine the appropriate path forward. It is only logical to assume that ULSHO, being made and handled in the same manner as ULSD, may have similar problems.
Some have postulated that it is the overuse of corrosion inhibitor additives in the fuel that is potentially causing the corrosion problem. However, others postulate that it may not be the presence of the corrosion inhibitor additive that is causing the corrosion but rather the lack of the corrosion inhibitor additive in the bulk fuel. Specifically, corrosion inhibitors work by binding to bare metal surfaces to protect them from attack by corrosive contaminants. However, freely available metal contaminants in the bulk fuel can preferentially bind to molecules of the corrosion inhibitor while it is in the bulk fuel, forming what is termed as “soap.”
By definition, the process of forming soaps results in removing the corrosion inhibitor from the fuel and, as a result, removes ability of the corrosion inhibitor to provide protection to the metal surface. Keep in mind that the soaps would not have formed if it were not for the trace contaminants that some feel should not be in fuel in the first place. Regardless, the fuel will most likely need to be treated (with a properly formulated additive) to provide corrosion protection for the entire fuel handling system, including the storage tanks.
The growth of microorganisms in middle distillate fuels is nothing new. What is new is their potential new home. ULSHO will, like ULSD, have numerous changes in chemical composition due to desulfurization. The changes in fuel composition may directly impact chemistries that were responsible for inhibiting growth of certain microorganisms. This is not unlike a weakened immune system that is vulnerable to infection.
Microbes will consume fuel for energy and growth while generating sludge and short chain acids as by-products of their metabolic processes. These short chain acids can cause not only corrosion problems in the tank (wetted surface) but, due to their volatility, they can also cause corrosion on metallic surfaces above the level of the fuel. ULSHO has no defense against these corrosion issues and may offer a more favorable environment for this to occur.
In a nutshell, microbial contamination can be minimized if tank owners establish and implement a proactive review of their storage system every quarter. Keeping tanks water free, incorporating a desiccant dryer on the vent alarm and managing the water content by immediately removing it to avoid that “perfect storm” when water and temperature combine to manifest microbial contamination. This is in fact the one place where tank owners can lend a helping hand to their fuel supplier and make a big difference in both fuel performance and storage tank longevity.
Fuel buyers and sellers need to look beyond the tank system to the entire fuel supply chain and understand that no matter what happens in that fuel tank, whether good or bad, it is still a direct result of its entire product life cycle. It is clear that all parties involved in the fuel distribution business need to work together to establish an easy-to-follow road map for quality fuel preservation from upstream to downstream. Open communication will be required if we are to minimize fuel quality issues that have compromised performance both under the hood and inside the tank system.
Author: Paul Nazzaro
President, The Nazzaro Group LLC