Petrochemicals focus: Storage tank farms
Many criteria should be followed when building a storage tank farm
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Storing product is important factor in any industry, and in the petrochemical industry products are generally stored into specialised tanks which very in strength and cost depending on the properties of the product.
A storage tank is a container usually for holding liquids and sometimes for compressed gases (gas tank).
The term can be used for reservoirs (artificial lakes and ponds), and for manufactured containers.
Storage tanks are available in many different shapes. Depending on the status of the product, It could be vertical and horizontal cylindrical, open top and closed top, flat bottom, cone bottom, slope bottom and dish bottom. Large tanks tend to be vertical cylindrical, or to have rounded corners corners (transition from vertical side wall to bottom profile, to easier withstand hydraulic hydrostatically induced pressure of liquid). Most container tanks for handling liquids during transportation are designed to handle varying degrees of pressure.
To install a storage tank, there are many regulations and standards which should be respected. “Tanks are to be installed according to American Petroleum Institute (API) regulations,” says Andre Petersen, global product manager responsible for PLM of software systems at tank farms for Terminal Inventory Management at Honeywell ENRAF. “The API G13650 regulation describes a number of innovative and socially responsible actions taken by exploration and production companies to minimise impacts to air, water, land and wildlife,” he adds.
“The main criteria is to select right the material of construction or the inner lining of the tanks – the material or the coating should be compatible with the products intended for storing,” says Satyabrata Mukherjee, terminal director at Dubai Based Petrochemical Middle East. For the tank storage destined to petrochemical industry, the API specifications are also applied,” says John Joosten, product manager for Radar and Safety at Honeywell ENRAF.
Tank storage must be differed according to the materialistic state of the product, whether it is in gas, solid or liquid state. “Oil products can be stored in open or closed tanks with or without heating depends on the density. LPG and light petroleum fractions are stored in pressurised tanks and LNG is refrigerated under -162GRC tanks,” says Petersen.
Building a storage tank facility includes a lot of challenges including the location. “Finding a suitable site near a jetty is a big challenge, and of course very high standard of safety is a must,” says Mukherjee.
“Getting the concrete floor stable enough to hold the huge tank is another challenge,” says Peterson.
“Stability of the tank and its measurement points are very important to prevent future movement of a tank causing uncertain measurement results and worse a leakage. Of course tanks must be completely tight preventing leakage,” he adds.
“Furthermore the entire site, from two up to 200 tanks, must be safe and continuously monitored regarding the available product and safety. To meet the required safety customers can rely on safety systems taking immediate action preventing damages. For regular terminal operation Honeywell have portfolio covers the whole range from gauging equipment, networks to monitoring and control systems,” says Joosten.
The cost of building a storage tank differs from facility to another depending on the nature of the product and other factors. “It depends on the volume and type of product,” says Peterson. “ A simple unheated tank may cost some hundreds of thousands dollars. Infrastructures also cost a lot,” he adds.
“Heated tanks to keep heavy oil fractions flowing are more expensive, whereas a site with pressurised tanks for LPG or refrigerated tanks for LNG can cost several millions of dollars,” says Peterson. Though the expensive cost of investment, the life span of tank storage facility may reach to several decades depending on the maintenance, “Tank storage facilities will last for a number of decades. The tanks and installed systems however will have regular maintenance and sometimes also replacement, tank inspection and regular maintenance are obligated by the authorities and specified in API regulations,” he adds.
“The same counts for machinery where electrical installations will be replaced after some years. PC-based systems will last 5 to 10 years, electronic systems may last up to 20 years, whereas wiring can last even longer,” he adds.
Gauging the level of product inside the tank storage is critical as it helps the company to know the level of the product inside the tank. “For gauging and calculations API D1250 is applicable. For overfill detection and protection the API 2850, IEC61508 and IEC61511 standards are applied that define the whole life cycle of all kind of installation, including bulk terminals. Those regulations are applied to prevent environmental damage,and maintain safely,” says Joosten.
Gauging methods depend on the nature of the product whether it is in solid, liquid or gas state.
“Differences can be found in the product density and vapour above the liquid. Honeywell Enraf provides two types of gauges, Servo and Radar based gauges. Both can measure a wide variety of liquids. Due to the type of measurement the Servo gauges is less affected by the present amount of vaporised product, resulting in a higher accuracy of “light” products, such as LNG and Ammonia. By using different types of antennas for the radar we are succeeding in obtaining an equal accuracy with the radar gauge,” says Peterson.
The environmental safety measurements are crucial and should be respected before building tank storage.
“All tanks are kept under nitrogen blanket. Thus vapours of the chemicals are not released to the atmosphere,” says Mukherjee. “All the tanks are fitted with vapour return lines. Thus during the filling of the tanks from the vessels, vapours are returned to the vessel,” Mukherjee explains.
“All the tanks are surrounded by a dyke wall. In case of a major disaster, the chemicals can be contained within the dyke wall and there is no free run,” he adds.
“There is an HDPE layer below the concrete flooring of the tank farm. This prevents any sub soil water contamination should there be a crack in the flooring,” says the terminal director.
At a time when the Gulf downstream industry is booming, the nature of the tanks and the technology that is deployed, sits firmly in the hands of the developers and end-users. The technology is out there, but it remains to be seen whether cleaner, clearer thinking will change the tank farm buyer’s mentality.
American Petroleum Institute regulations and standards are considered as the references and benchmarks that describe a number of innovative and socially responaible actions taken by energy companies to minimise impacts to air, water, land and wildlife.