Refilling Tanks: Impacting Air Pollution And Our Future

Air pollution is a pressing issue that affects human health and the planet. It refers to the release of pollutants into the atmosphere, with nearly seven million deaths globally attributed to indoor and outdoor air pollution each year. One source of air pollution is the release of emissions from tanks during the refilling process. When tanks are filled or refilled, turbulence is created, causing vapors to escape into the atmosphere. These vapors can contain harmful substances such as volatile organic compounds (VOCs) and other hazardous organic compounds. The impact of refilling tanks on air pollution depends on various factors, including the type of tank, the loading method, and the frequency of refilling. Understanding and managing these emissions are crucial to minimize their contribution to air pollution and its detrimental effects.

How does refilling your tank affect air pollution?

The type of tank and liquid being stored affects the emission of air pollutants

The type of tank and the liquid being stored significantly affect the emission of air pollutants. Firstly, the liquid's temperature and volatility influence vapour emissions. For instance, liquids with high vapour pressures, such as asphalt and No. 6 fuel oil, can result in higher emissions due to their volatility. The viscosity of the liquid also matters, as thicker liquids may require heating, increasing emissions.

Secondly, the tank's design and parameters play a crucial role. Fixed-roof tanks, for example, can benefit from installing internal floating roofs and seals to reduce evaporation. The tank's diameter, shape, colour, finishing, and roof type all influence emissions. Floating roof tanks, in particular, may emit more pollutants when the roof lowers with the liquid level, exposing the tank walls.

Additionally, the frequency of loading and unloading operations impacts emissions. Tanks that undergo frequent filling and draining release more vapours, especially if the liquid is pumped. Cleaning and degassing tanks can also release pollutants, which must be accounted for in emissions estimates.

Finally, the type of liquid stored is a key factor. Tanks containing heavy fuels, such as asphalt, No. 6 fuel oil, and other petroleum products, often emit harmful chemicals, including VOCs, which can pose health risks and contribute to climate change. Accurate estimation and measurement of emissions from these tanks are essential for compliance with air quality regulations.

Vapours are released into the atmosphere during the refilling process

The vapours released during the refilling process can contain volatile organic compounds (VOCs), which are a primary pollutant of concern. VOCs react with nitrogen oxides (NOx) in the presence of sunlight and heat to form ground-level ozone, a harmful pollutant. Gasoline vapours, in particular, have been found to contain VOCs and other toxic substances, such as benzene, which is a known carcinogen.

To mitigate the release of vapours during the refilling process, various control methods and technologies can be employed. For example, pressure/vacuum (PV) vent valves are installed on storage tank vent pipes to prevent vapours from escaping into the atmosphere. Additionally, a Stage 1 vapour recovery system can be implemented to capture and recycle or destroy vapours released during the refilling of gasoline storage tanks, significantly reducing VOC emissions.

It is important to note that regulations and standards, such as the Clean Air Act in the United States, aim to address and minimise the impact of air pollution on public health and the environment. These regulations often outline specific emission control programs and permit requirements to manage and reduce emissions from various sources, including storage tanks. By implementing these control measures and adhering to regulations, the release of vapours during the refilling process can be minimised, contributing to improved air quality and reduced pollution levels.

Cleaning and degassing tanks can release dangerous air pollutants

The cleaning and degassing of tanks can release dangerous air pollutants. Degassing is the forced removal of vapours from a tank, typically done to tanks storing gasoline or crude oil, to prepare for or during cleaning. The vapours are often hazardous, and if released without proper controls, they can cause environmental and regulatory problems.

The degassing process can vary depending on the type of tank and its contents. For example, fixed-roof tanks will have different vapour displacement characteristics compared to floating-roof tanks. Tanks that store chemicals, solvents, or petrochemicals will contain volatile organic compounds (VOCs), which can be harmful if released directly into the atmosphere.

During the degassing process, the tank must go through the "explosive range", where the concentration of gas or vapour could explode if an ignition source is introduced. This makes degassing very dangerous when performed incorrectly. To ensure safety, companies like Air Clear implement multiphase safety features and provide training for operators to understand how to use degassing equipment properly.

After the degassing process, the remaining gas vapours in the tank need to be removed or treated. This can be done through abatement technology, such as thermal oxidizers, which destroy the hazardous vapours and eliminate concurrent odours. Chemical scrubbers can also be used to abate VOCs and HAPs from chemical tanks.

The release of built-up vapours during the cleaning and degassing process contributes to annual reportable emissions. These emissions are essential to manage and control to minimise air pollution and comply with regulations such as the Clean Air Act Amendments of 1990.

Vapour recovery units can be attached to tanks to reduce emissions

Air pollution is the release of pollutants into the air, which is detrimental to human health and the planet. The World Health Organization (WHO) reports that each year, indoor and outdoor air pollution is responsible for nearly seven million deaths worldwide.

Storage tanks emit pollutants during various processes and when they are standing within a facility. These emissions are released when liquid is pumped in and out of the tank, and the frequency of refilling affects the amount of emissions. When filling a tank, the liquid rises and reduces the vapour space, releasing it into the atmosphere.

Vapour Recovery Units (VRUs) are systems designed to capture and control these vapours, reducing emissions. They are commonly used to capture methane emissions from crude oil and condensate storage tanks, as well as other low-pressure vented gas sources in oil and gas operations. The captured vapours can be redirected for recovery and reuse, providing economic benefits through the collection of natural gas, natural gas liquids (NGLs), and other hydrocarbons.

VRUs can be attached to a single storage tank or multiple tanks and are effective in reducing emissions from low-pressure tanks about 95% of the time. The keys to a cost-effective VRU project include a steady source and adequate quantity of crude oil, condensate, or other low-pressure sources of organic vapours, along with an economic outlet for the collected products.

Additionally, VRUs can be customized to meet specific requirements and emission compliance standards. The use of VRUs helps to control emissions, minimize environmental pollution, and maintain compliance with clean air regulations.

The colour of a tank affects heat absorption and vapour pressure

The colour of a tank has an impact on heat absorption and vapour pressure. Lighter colours reflect light and heat, absorbing less heat than darker colours. Dark colours absorb more sunlight and, therefore, heat up faster. This is why propane tanks, for example, are painted a heat-reflective colour, usually a lighter shade, to avoid the absorption of heat.

The colour of a tank is particularly important if the tank is exposed to sunlight. A black plastic tank, for instance, will absorb more sunlight than a silver stainless steel tank. This is because the black tank will absorb more of the incoming sunlight, while the silver tank will reflect it.

The impact of colour on heat absorption can also be observed when wearing clothes. On a hot summer day, light-coloured clothing is more comfortable as it reflects sunlight and absorbs less heat. Conversely, on a cold day, a dark-coloured jacket is preferable as it will absorb more heat from the sun.

The relationship between colour and heat absorption is due to the conversion of light energy into heat energy. When light is absorbed by an object, it is typically converted into heat. This is why darker tanks, which absorb more light, also experience greater heat absorption and increased vapour pressure.

The effect of colour on heat absorption and vapour pressure is an important consideration for tank design and operation. By choosing the appropriate colour, the amount of heat absorbed by the tank can be controlled, thereby influencing the vapour pressure within the tank. This knowledge can help to reduce emissions and improve the efficiency of the tank system.

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