1. FIELD OF THE INVENTION

The present invention is directed to maintenance of low-volume hydrocarbon tank systems. The present invention is more directly related to the systems and methods for use of inert gas to maintain hydrocarbon tanks.

2. BACKGROUND OF THE INVENTION

Nitrogen Blanketing has been proposed to stabilize the vapor/gas in the ullage above the liquid fuel level within hydrocarbon fuel tanks. However, small above ground tanks, or low volume tanks, that may or not have been treated with an inert gas (such as a nitrogen gas, a noble gas, or compound gas, or other gas known in the art to provide passive preservative and/or prevention of oxidation) will often leach the inert ullage gas to the environment by venting during high pressure events, during discharge, leaking, etc. For small above ground tanks such as home heating oil tanks the daily, seasonal, or exposure to sun/elements, will cause the tank to heat up or otherwise experience higher pressure events as the gas and hydrocarbon fuel expands (sometimes via vaporization, etc.). Often tanks exposed to the elements may “breathe-out” during the day/sun exposure, and “breathe-in” at night when temperature drop. These high pressures are often alleviated by venting gas to the environment. Similarly, during low-pressure events, the vent may allow uptake of ambient air (which may include water vapor) into the tank. Water vapor entering the tanks ullage can interact and absorb into the liquid hydrocarbon, or otherwise provide for a breeding ground for oxidative events and/or bacteria growth. This also applies to tanks that have low throughput volumes of fuel, (back-up) generators and storage tanks that may have small and large tanks (such as for cellular towers), or tanks that have low throughput fuel volumes and mobile tanks (such as railcar and train engines or other vehicle tanks). Biodiesel is particularly hygroscopic (absorbs water) leading to phase separation and may cause Fatty Acid Methyl Ester (commonly referred to as FAME), allowing organics (such as bacteria, etc.) to consume/digest the diesel or fuel.

A common solution to water entering the system, (typically through the vent (in/out) is use of desiccant (tablets) in or in absence with a filter. Desiccants used in the air intake may be a pellet of granulated desiccant. This desiccant system is used in long-term storage tanks that “breath.” However, over long periods of time, the desiccants lose potency, and/or may not be able to keep up with high demand for intake air.

While there are more complex systems for protecting underground storage tanks and above-ground storage tanks (USTs and ASTs), the benefit of using a dry inert gas, such as Nitrogen, to prevent moist air from being pulled into a tank from the normal diurnal heating and cooling or due to the removal or use of the fuel in a tank. Nitrogen fills a large portion 25-80%, but more preferably 100% of the gas in the ullage. N2is not immiscible with hydrocarbon vapors, and typically lighter (with the exception of very light hydrocarbons (perhaps e.g., methane) that may be lighter than N2and pass through N2blanket) thus will sit at top of tank. N2will be vented at high pressure events and prevent hydrocarbon off-gassing. During dispensation of fuel from the tank, gas must be interred in the tank (ullage). Preferably, such gas is provided by a source of inert gas.

Moist air condensing on the inside of said tank, or condensation, provides water necessary for microbes to multiply in the ullage of a tank, the water that runs down the sides of the tank or precipitates into the fuel, all provide water for the microbes in the tank and the fuel to multiply. The water may run to the bottom of the tank (below liquid hydrocarbon fuel) and accumulate in the bottom of the tank leading to further damage to the tank bottom surface, and/or may contaminate and degrade the fuel further. If enough water accumulates, the water may be pulled into the delivery portion of the fuel system. This combination of microbes (one example of common bacteria that is damaging to fuel, acetobacter, commonly found in fuel and air) excrete acetic acid. This acid, along with other organic and inorganic compounds, have been documented to produce phosphoric and other very aggressive acids acidifying the fuel, damaging tanks and tank equipment. Additionally, this acidification will corrode and destroy fuel delivery components and the fuel line to equipment downstream of the tank including engines or boiler furnaces. The corrosion of the tank material can drop particles large and small in the tank. The particles drop to the bottom of the tank and cause microbial colonies. Also, smaller particles that fall into the fuel may become suspended in the fuel during movement, vibration, or fuel delivery into the tank. The particles that fall into the tank will clog filters and causing abrasive wear in fueling components.

Nitrogen that flows into the headspace of a tank, can prevent the normal/ambient air from being pulled into the tank. The inert gas displaces the moist air that would have flowed into the tank to alleviate partial vacuum. The inert gas reduces/eliminates water availability onto tank ullage surfaces, water running/dripping into the fuel, and displaces the oxygen that would have been pulled in with the (moist) air normally aspirated into the tank. The inert gas reduces/eliminates the potential of explosion in what is normally a hydrocarbon vapor filled space of fuel and air, the ullage of the tank. Replacing the oxygen with N2deprives the aerobic microbes of the O2 needed to reproduce in the ullage of the tank. By replacing most of the oxygen available to the surface of the fuel with nitrogen, oxidation, a normal event with fuel exposed to oxygen is reduced.

Therefore, a dry inert gas, such as nitrogen, source is desirable to inert the headspace of a low-volume tank to prevent fuel contamination and equipment damage.

Therefore, it is an object of the present invention to provide an apparatus capable of providing an inert gas on demand to a hydrocarbon fuel tank.

It is a further object of the present invention to provide a method for maintaining a hydrocarbon fuel tank.

These and other objects of the present invention will become apparent to those skilled in the art as the description thereof proceeds.

SUMMARY OF THE INVENTION

The present invention includes an automated hydrocarbon tank maintenance system whereby a hydrocarbon tank is used. The tank would include a standard liquid fuel line level and an ullage. The tank will be vented via a tank system. Preferably, the vent emanates via a pipe at the top (or side) of the tank through a pressure vacuum relief valve and out of a vent exit. A source of inert gas (such as nitrogen) is in fluid communication with the tank, preferably at the vent system, and more preferably connected directly or indirectly near or at the PV valve. The source may include a reservoir tank and/or a nitrogen generator. The inert gas supply source is in fluid communication with the ullage, wherein it can provide an inert gas into the tank system to fill the ullage (and prevent in-gassing from atmosphere). A pressure regulator joins the inert gas source with the vent, and the pressure regulator selectively allows inert gas to enter the hydrocarbon tank when a low-pressure is registered below a first predetermined low-pressure threshold.

The pressure regulator may be coupled to the pressure relief valve. The pressure regulator may open the vent system to accept gas from an external source (i.e., ambient atmosphere) when the pressure regulator registers a low-pressure below a second predetermined low-pressure threshold which is further below the first low-pressure threshold. The first predetermined low-pressure level may be set at approximately (give or take 100% pressure relative to 0 inches of pressure) two inches of water column pressure. The second predetermined low-pressure level may be set approximately (give or take 100% pressure relative to 0 inches of pressure) at or below negative four inches of water column pressure, but will be set at or below the first threshold.

A differential pressure switch may be used to activate an alarm when the lower second predetermined low-pressure threshold is met. The alarm may be in communication with said differential pressure switch and the switch may set off the alarm when the lower pressure condition is met. The alarm may be powered by an electrical power source, and may provide an audible, and/or wireless communication alert.

The invention may include a dual tank system for maintenance of hydrocarbon storage systems. A hydrocarbon tank can include a vent system with a pressure relief valve and a gauge to monitor and display a tank pressure. A source of inert gas (e.g., nitrogen gas) is in fluid communication with the interior of the tank and capable of supplying an inert gas thereto via a conduit. A pressure regulator may be coupled to the conduit between the source and hydrocarbon tank interior, whereby the pressure regulator controls inert gas entry into the hydrocarbon tank from the source when the pressure regulator registers a low-pressure below a first predetermined low-pressure threshold. An alarm may be used. The Source of inert gas may also include a nitrogen or inert gas generator with a compressor and filter.

The present invention also includes a method to maintain and monitor a hydrocarbon tank system via an inert gas source coupled to the tank. Hydrocarbon fuel is provided into the tank. The tank is then pressure sealed. A source of inert gas is coupled to the tank along a conduit having a pressure regulator. The tank ullage may be initialized by replacing the ambient gas in the ullage with inert gas. During operation, inert gas is released from the source of inert gas into the tank when the pressure regulator senses an internal tank pressure below a first predetermined threshold. The conduit may be coupled to the tank via a pressure relief valve.

High pressure may be relieved from the tank via the pressure relief valve when the tank pressure exceeds a second predetermined high threshold. When a third, lowest threshold is met, such as no or negative pressure in the tank relative to the atmosphere, an alarm alerting than internal tank pressure is too low may go off. The alarm may be audible at the site, and/or may be made via a wireless signal to a remote receiver.

