How to Prevent Frost Heaving in Cryogenic Tanks
Cryogenic tanks are essential in receiving and storing Liquefied Natural Gas (LNG) up to -162°C which can be described as cryogenic conditions. LNG is produced when natural gas has been cooled and condensed into its liquid state at -162°C. This allows for easier transportation as LNG occupies 600 times less space than in its gaseous state. Furthermore, LNG remains at normal atmosphere, even though it has been compressed in volume in its liquid state, as it remains at normal atmospheric pressure. Thus, cryogenic tanks are also known as LNG storage tanks.
Implications of Frost Heaving in Cryogenic Tanks
Cryogenic tanks are used to store LNG on land while awaiting transportation, which can be held over extended periods of time. This leaves the storage tanks highly susceptible to frost heaving due to the cryogenic temperatures they are being exposed to. The cryogenic temperatures inside the tank can seep through onto the surface and can cause ice to amass on the ground. As a result, it is highly possible for cryogenic tanks to collapse under these conditions.
Frost heaving can also create cracks in the structure and foundation of the cryogenic tanks which might lead to LNG leaking. In the case of a leak, the LNG vaporises quickly which reverts it back to its gaseous state. When mixed with the air in the atmosphere, there is a high risk of ignition if it is within the flammable range. Therefore, an LNG leak can trigger an explosion and is considered a thermal radiation and fire hazard to the environment. This is especially dangerous if the LNG tank is located near facilities that are densely populated.
Furthermore, seeing as LNG gas is costly to produce and cryogenic storage tanks are expensive to construct, it only makes financial sense for businesses to install a frost heave prevention system as a safety net.
Therefore, it is important that a frost heave prevention system is properly installed in cryogenic tanks to prevent such accidents from occurring.
How does a Frost Heave Prevention System Work in a Cryogenic Tank?
Once the power of the system is turned on, the heater cable in the frost heave prevention system will be energised and maintained at the minimum designated temperature, which is required at the top of the LNG tank base. In this case, the minimum temperature required at the top of the LNG tank base is 15°C.
However, once the resistance thermometer (RTD) detects that the set temperature has been reached at the desired areas, the RTD will send a signal to the programmable logic controller (PLC) to cease any further heating from the system.
Vice versa, once the RTD detects that the temperature is below the designated threshold temperature, it will re-energise the heater cable to start the maintenance of the temperature in the cryogenic tank again.
Components of a Frost Heave Prevention System
A typical frost heave prevention system consists of Raychem’s self-regulating heat cables, components, temperature sensors and a power/control panel. The heating cables are installed inside the conduit embedded in the concrete walls or dry sand that form part of the tank’s foundation. Approved Raychem components must be used for power connections and end terminations.
These systems are designed to meet project-specific requirements, and therefore must be installed in compliance with requirements established in the installation instructions and the project-specific engineering documentation that Raychem provides. All heat-tracing-systems must be installed in compliance with all national or local electrical regulations and codes of practice.
Supermec is providing the design engineering and supply of frost heave prevention system cables and accessories to Hai Linh LNG Tank Terminal in Vietnam. The specific design and installation techniques of frost heave prevention systems are very specialised and require the use of specially certified components and materials by Raychem.
Future for Frost Heave Prevention Systems in Cryogenic Tanks
The demand for LNG is predicted to grow exponentially over the next few decades due to rising demand from emerging markets like China and India. As a result, LNG tanks will have to be constructed at a rapid pace in order to match this rising demand. This symbiotic trend explains the prevalence of frost heave prevention systems used in cryogenic tanks today.
Supermec’s experience and position as an industrial expert in heat tracing have led to the streamlining of activities associated with the supply and installation of frost heave prevention systems for cryogenic tanks. Seeing as the demand for LNG storage tanks will only continue to expand in the future, these specialised innovations, procedures and equipment developed to date for frost heave prevention systems will surely value add Supermec’s future customers.
To find out more about how you can install frost heave prevention system for your business today, contact us now.
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