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Infrastructure & Design

Designing State of the Art Terminals
Shriram Hemant, Oil, Gas & Petrochemicals Division, Mott MacDonald
Marketing Storage Terminals are crucial for any oil and gas company or refinery as they store products, which are to be marketed to direct or indirect customers. If not managed with proper plan or strategies, these terminals can affect the overall business of an organisation. The article not only highlights the significance of design and construction of storage terminals for oil, gas and petrochemical companies, but also brings issues like minimising risk of accidents, quality of product mix, need of transportation, safety etc to light.

Associated with every refinery are the marketing storage terminals, capable of storing a large inventory of finished products for sale and dispatch by road, sea and rail. These marketing terminals comprise a large tank farm with a number of different types of tanks for storing various finished products plus product pumps of varying sizes and capacities for pumping different products. They also include loading bays for trucks and railway wagons, fire fighting system with ring main network, vapour recovery unit, control room, switchgear room, and valve cluster for shutdown, security systems and isolation stations.

These storage terminals are designed, constructed and operated in accordance with international standards, with specific emphasis on prevention and control of fire and explosion hazards, as well as meeting stringent environmental norms. Modern terminals are designed with a very high degree of automation in order to minimise risk of accidents, improve the quality of product mix, reduce the number of vehicle movements, assist with accurate loading and billing, while at the same time increase the productivity of operations.

Safety and security is paramount in such terminals throughout their operational life. These aspects are considered at the design stage and normally include a fire alarm system, fire fighting system, emergency shutdown system, gas monitoring system, fire and gas system, valve control system, pipeline leak detection system, public announcement system, video surveillance (CCTV) and automated vehicle entry system. Regular monitoring and control of various process parameters also take place in real time. All these systems are normally integrated to form a common platform called a Terminal Automation System (TAS).

This in turn is seamlessly integrated with the management information system, improving operations and profitability. The design must consider the plot plan, provision of inter-distances between the tanks and with other facilities in line with the latest oil industry safety directives, routes for entry and exit of tank trucks and escape and emergency exits for operational teams.

Because of the hazardous nature of these tank farms, continuous monitoring of critical process parameters is required. To prevent overfill situations, which can cause significant soil and ground water contamination, an accurate and reliable tank level monitoring system (tank farm management system - TFMS) is required. Normally the tanks are connected with the refinery through long pipelines and suitable isolation and shutdown valves are required. Valves for transfer of products for dispatch and homogenisation also feature. Following a recent incident at one terminal, stringent rules have been put in place which require secondary level measurement, detailed locations of automatic isolation valves and dyke height. These all need to be taken into account during the design.

The design must also consider individual secondary containment for tanks to further minimise the risk. This includes using double bottom and double wall containments, impervious linings under the tanks and concrete surfaces with polyethylene sheeting in areas of possible leaks and spills. Various safety studies like risk, environmental, security, escape route, hazard and operability study, hazard identification study, are undertaken during the design phase. These are in addition to specific technical recommendations from qualified and experienced professionals relating to soil stability and surge analysis.

Prevention of emissions from volatile organic products and compounds is paramount. Fixed roof tanks are fitted with internal floating roofs to minimise emissions of such volatile organic compounds. In case of floating roof tanks, the roof portion rises and falls with the liquid level in the tank to minimise emissions. Sleeves are provided on slotted guide poles to eliminate emissions from slotted guide poles.

A vapour recovery system is provided for tank truck and railcars which are ideally loaded using bottom loading arms. Vapour detection systems - an invaluable contribution to safety - include a hydrocarbon leak detection system comprising infrared point and open path detectors installed across the terminal. They are used to trigger alarms if a specified concentration of the gas or vapour exceeds a certain limit.

Design must include implementing safety procedures for loading and unloading of products to transport systems like rail and tanker trucks and ships. These include the use of fail safe digital control valves and emergency shutdown systems to prevent potential ignition sources. Proper grounding permissive interlocks can be used to avoid static electricity build-up and lightning hazards. Use of certified and intrinsically safe instruments, such as non-sparking tools, along with a fire fighting and suppression system, which includes sprinklers and rim seal fire protection are also possible features. Mobile and portable equipment such as fire extinguishers and specialised vehicles can be utilised as can specialised harness thermal imaging cameras, which are remotely operated alongside other fire fighting monitors. Foam pourers are also strongly recommended. Fire fighting systems must be designed for the worst case scenario and to the latest national and international standards along with water demand calculations.

Terminal operations benefit from a holistic approach to industrial safety, which calls for a complete integrated terminal automation system (TAS) with advanced technology and plant protection layers to help end-users. In such cases all the safety systems are integrated to TAS for monitoring and reporting.

TAS also performs accurate monitoring and control for the dispensation of products through loading bays, minimising the losses and human errors. Integrating the tank farm management system with TAS simplifies the material balance at the terminal at all times, by optimising the required products to be taken from the refinery depending on market conditions.

TAS is an efficient and cost effective solution based on a technology platform that not only handles the complex valve sequencing and process demands, but also provides consistency and standardisation, ease of software configuration, quick and ease of installation as well as integration with management information systems.

Security systems must also include perimeter camera sur veillance and operational area monitoring systems with built-in analytics, access control and turnstile gates to restrict unauthorised entry. A public announcement system for emergency communication integrated with safety systems and with the telephone network is required in the latest terminal designs.