What is Tank Blanketing? Tank Blanketing, sometimes referred to as “padding”, is the process of filling the empty space of a liquid storage tank with an inert gas, most likely Nitrogen. Nitrogen is generally the blanketing gas of choice due to its inert properties, availability, and relatively low cost.
Why is tank blanketing Important? Blanketing protects people, the environment, product and equipment. If the media is combustible, blanketing removes the Oxygen required for combustion. Blanketing protects food and other substances from oxidation, contamination or evaporation. Vapor recovery prevents harmful vapors from escaping into the atmosphere. Reducing corrosion through oxidation helps maintain the integrity of the tank.
Who uses tank blanketing? The bulk of tank blanketing applications are in the Chemical, Petrochemical and Oil & Gas Industries with a smaller percentage in the Food & Beverage, Pharma / Biopharm, Personal Care / Cosmetics and Semiconductor industries.
A variety of products are protected in the market segments listed above. Blanketed products include but are not limited to adhesives, catalysts, chemicals, deionized water, fats and oils, flavors, foods, fragrances, fuels, industrial coatings, inks, juices, pharmaceuticals, photographic chemicals, sealants, soaps, solvents, volatile combustibles, and water for injection.
How do Blanketing Regulators Work? Blanketing regulators, also referred to as padding or “make-up” regulators, are controlling the pressure inside the tank. The blanketing valve is typically mounted on top of a storage tank. The piping from the blanketing gas supply is connected to the valve inlet and the valve outlet is piped to the tank. In most cases, a sensing line runs from the tank to the valve’s sensing port.
When the regulator senses a decrease in the pressure, the valve opens to introduce more gas into the tank until the vapor pressure in the tank reaches the desired set point. When the pressure reaches or begins to exceed the set point, the valve moves to the closed position and pressure returns to the set point.
Controlling the blanket – In a “two sided” system, there is a Tank Blanketing (Padding) regulator and a Vapor Recovery (De-Padding) regulator. When the vapor pressure in the tank drops below preset limits, the padding regulator’s diaphragm moves the plug away from the seat, allowing the blanketing medium to flow in. On the de-pad side, the regulator moves the plug away from the seat in response to higher pressure vapors, allowing excess vapors to flow out of the tank.
The padding and de-padding valves work together. The padding valve is a pressure reducing valve (PRV) and controls the pressure in the tank. The de-padding valve (BPRV) is also controlling the pressure in the tank. The padding valve ensures there is sufficient pressure in the tank and the de-padding valve ensures there is not too much pressure in the tank. The set point of the De-padding valve is slightly higher than the padding valve.
The volume of media in the tank will vary due to a variety of factors including pumping media in and out, temperature changes, air and / or moisture entering the tank and vapors escaping the tank. As the volume changes, the vapor space in the tank changes as well.