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New and sophisticated technology fuel systems are being introduced by diesel engine and turbine manufacturers due to strict emissions regulations. New technology includes higher injection pressures burning low sulfur and bio-diesel fuels with high recirculating systems return flows. This process increases equipment breakdown without clean fuel consumption. This calls for improved fuel storage design and handling with greater performance filtration for stiff fuel quality control and monitoring.
Although delivered fuel meet ASTM/EN standards, the fuel quality in terms of cleanliness with regards to ISO 22/21/18 specifications still fall on the “dirty” category. Fuel may appear clean but laboratory tests will reveal otherwise. Contaminated fuel may be caused by improper handling, humidity and temperature. Use of poor fuel quality will result in higher equipment maintenance rate and operation stoppage.
The aim of Supply Chain is to guarantee that clean and dry diesel fuel meeting quality standards and specifications is readily available for purchase and use by consumers. The principal assumptions of this objective are as follows:
- The Supply Chain equipment will be designed to address specific issues like high levels of free water from marine transportation and environmental conditions.
- The level of protection from water and particulate contamination will rise as the product nears its destination.
- Internationally recognized standards will be practiced to meet handling, testing and settling regimes.
Fuel storage facilities must have the necessary equipment to accept, keep and redistribute fuel. Standard specifications for diesel storage facilities depend on the requirements of each supply chain and the final method of transfer into the engine system. Pipeline or ship fed terminals have high fuel turnover, while road or rail fed terminals are limited. These situations have their advantages and disadvantages.
Today’s strict emissions regulations cause diesel engine and turbine manufacturers to introduce sophisticated technology into the fuel system in order to increase efficiency. These new technology fuel systems usually include higher injection pressures through smaller orifices, the ability to burn low sulfur and bio-diesel fuels, and recirculating systems with high return flows. The mean time between equipment failures dramatically increases without the use of substantially cleaner fuels. This requires tighter control of fuel quality and continuous fuel monitoring. As a result, improved fuel storage design and handling as well as higher efficiency filtration is required.
Generally, new fuel is delivered meeting current ASTM/EN specifications, and this may have an average cleanliness in terms of particulate of ISO 22/21/18. In a word: dirty. Attempting to use fuel of this poor quality will inevitability lead to increase equipment maintenance and unplanned downtime.
Fuel may be delivered clean, but dirty handling systems and poor environmental storage conditions (i.e. humidity, temperature, etc.) will contaminate it. Even when fuels appear visually clean, filtration and laboratory analysis can reveal heavy contamination.
The overall objective of the Supply Chain is to ensure that Clean, Dry and On-Specification Diesel Fuel is consistently and reliably available in the appropriate quality for purchase and use by customers. The principal implications of this objective are as follows:
- The supply chain will have spare capacity to accommodate seasonal fluctuations, variations in customer demand, or other operational disruptions, strategic stock directives and the receipt of variable fuel quality.
- The method of supply chain delivery will be towards the method(s) that are most efficient for the particular volume, distance and terrain requirements.
- The supply chain equipment will be tailored to address the particular issues presented by the supply chain (e.g. higher levels of free water, especially following marine transportation and environmental conditions).
- The degree to which handling equipment design protects against water and particulate contamination will generally increase as the product moves closer to delivery to final destination.
- The handling, settling and testing regimes will comply with internationally recognized standards.
Fuel Storage facilities, whether intermediate or for final use, will consist of the necessary equipment to receive, store and redistribute the fuel. Requirements for diesel storage facilities are highly dependent on the specifics of each supply chain and the final method of delivery into the engine system.
Larger terminals may be pipeline or ship fed and have high turnover of fuels. Smaller terminals may be road or rail fed and turnover may be limited. There are advantages and disadvantages to both of these situations.
There are known regional variations in the levels of contamination seen in diesel fuels and this should also be a considered factor when proposing a storage, handling and delivery system for diesel powered systems. High particulate in diesel is endemic in many parts of the world.
However, what is less well known is that water levels in diesel fuel also have a regional aspect (although less data is available here) The impact of both water and dirt levels has a major impact on the recommended design and handling operations of a diesel fuel supply facility. Some tanks are better at handling and separating water than others. Some filters only separate dirt and even here their performance is impaired by the presence of bulk water in the fuel supply. Regional solutions may be appropriate. Temperature variation will result in accumulation of water in storage tanks.
In addition to these geographic factors, the air quality can also significantly impact fuel quality as tanks breath during the filling and discharge operation. High levels of airborne dust, particulate and water can contaminate clean fuel storage unless precautions are taken.
It is important to note that water can accumulate in diesel within a tank even if the fuel was dry to begin with. As a tank is emptied, the space in the tank is taken by air coming in through the vents. This incoming air can contain considerable moisture depending on the environment. The air above the fuel will cool overnight much more quickly
than the fuel. This cooling may produce condensation inside the tank. High humidity environments and environments subject to large temperature changes from day to night are especially vulnerable.
In terms of fuel cleanliness and filtration, the specification is set by the needs of the injection nozzle tolerances and the pump. The nozzle dimensions are getting tighter and the injection pressure has been increased to match latest requirements in terms of legislation and fuel efficiency.
As nozzle tolerances get tighter, they require cleaner fuel to avoid plugging, abrasion and deposit forming. Although particulate may be removed to clear tight tolerances,small particulate in volumes (as small as 6µm) will act as a slurry causing significant wear to both pressure pumps and nozzle/injector, and premature failure and unexpected downtime.
The most common method for reporting diesel fuel cleanliness is through the use of ISO4406 which consists of three numbers relating to the total number of particles per milliliter greater than 4µm, 6µm and 14µm sizes. Using the following look up table, once the number of particles are known greater than each size, the user than can find the code associated with the particle count. According to ISO4406, a count is accurate at +/-1 code due to equipment, testing, sampling and human variables. For this reason we believe that continual testing looking for trends in fuel quality is as or more important than the actual number recorded in time, and the recommendation for real-time on-line reporting is strongly encouraged when possible, or frequent on-site testing at a minimum in order to assure fuel quality is continually met.
It is common for diesel equipment users to inquire as to what fuel qual-ity needs to be attained for their application or equipment. Firstly, this question should be posed to the equipment or engine OEM. Some OEM’s have published required fuel cleanliness levels and OEM’s may deny warranty claims if these stan-dards are not met. Although, most equipment will have on-board filters to achieve the required cleanliness level, in order for the on-board filters to be effective, the fuel delivered to the vehicle must be of a realistic quality.
Poor to fair fuel quality may have a sufficient level of contamination to overwhelm the on-board filters, increasing equipment wear, caus-ing either short or long term issues. Further, some OEM’s require a given level of fuel quality to be delivered to the vehicle to maintain the engine warranty. A single fuel related un-planned equipment upset can easily surpass the same cost of several years of a well-run fuel maintenance program which includes the bulk fuel filtration costs.
Storage Tank Design Issues
Inadequate storage facilities can lead to issues such as:
- Lack of homogeneity at initial Batch Certification
- Contamination with particulates
- Contamination by incompatible lining materials
- Contamination with water
- Microbiological growth
As fuel reduces in temperature while in a storage tank, water that is
entrained within the fuel becomes free water and falls to the bottom of the tank. The failure to frequently (daily) remove this free water will lead to significant fuel system contamination. The interface between the water and fuel is an ideal medium for rapid bacterial growth. Once a system becomes contaminated with biological growth, the bacteria can form biofilm which can prove to be very difficult to remove from the fuel system. For light bacterial growth, many commercial biocides may be found effective, but for heavy contamination, a completetank draining and mechanical cleaning regiment many need to be employed. The importance of keeping water from collecting in the system may is easily stated: an ounce of prevention is worth a pound of cure.
This section refers primarily to storage tanks and aims to primarily address features which are specific to storage tanks in diesel fuel Service. Tank features which require specific focus for high quality fuel storage tanks include:
- Roof Design – Prevention of water ingress
- Floor Design – Migration of water (and dirt) to sumps
- Tank Dewatering – Removal of water (and dirt)
- Tank Lining – Minimization of particulate shedding
- Vents – Minimization of airborne particulate and water ingress
- Floating Suctions – Minimization of particulate and water shipped downstream
Tank dewatering in particular must be fit for purpose, and as stated previously, must be conducted often. Marine Terminal tanks (ship fed) and tanks in very high rainfall areas must have highly effective dewatering capabilities. With the advent of higher percentage (>B5) biodiesel blends mandated by many governments the water separation characteristics of diesel fuel have deteriorated and absence of effective dewatering in tank design is leading to a marked increase in microbiological spoilage of fuels in storage. In many cases where the fuel is supplied “wet”, it is necessary to install effective water coalescing filtration system upon receipt as well as in a “kidney loop” in the primary storage tank, which will be discussed further in the next section.
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