Nov 04, 2021
Carriage of liquified petroleum gas (LPG) dates back to 1931, when the world’s first custom built gas carrier, the ‘LPG Agnita’, traded parcels of LPG in pressurized tanks. Typically, a by-product of more sought-after products in the oil and gas industry, being able to utilize this asset instead of simply flaring it off, is a benefit not only to the producer but to numerous allied industries, including petro-chem, which use LPGs as part of their dedicated processes.
The composition of the various LPG grades, primarily Butane and Propane, allow not only for simple storage but for efficient transportation and a higher efficiency, cleaner-burning hydrocarbon. As most LPGs are not identified as greenhouse gases (GHG), they can be used as propellants and refrigerants, replacing the previous generation of GHG based solutions which are no longer permitted under international law.
Under the International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC) code, specifically written for the safe transportation of liquefied gases, all gas-carrying ships should be equipped with an emergency shutdown link enabling a vessel to connect its own safety shutdown equipment to the terminal with which it is trading. Although LNG developed to include fully connected emergency shut-down (ESD) systems during transfers, LPG transfers were limited to the exchange of a manual shutdown pendant between supplier and receiver. In the event of an emergency being detected, this meant that an individual had to be present to witness the event and push the stop button.
Integrating ESD links during a transfer has recently been highlighted as not only a way to allow safety to be enhanced, but as a mechanism to allow increased flow rates during transfer. The issues of pressure surge, which typically define the maximum flow rate, can be alleviated by having closer monitoring of the entire transfer pipe through active monitoring of the ESD in the system. Instead of working to a potential of a filling manifold or tank valve closing onto a full flow transfer, linking the ESD means the transfer pump can be stopped as soon as the same signal that instructs the valve to close, is triggered. This reduces the effect of calculated surge by shortening the time between event detection and process stopping.
Such measures can also reduce the likelihood of premature equipment failure by keeping the process equipment within normal operating conditions. Valves and pipework will benefit from reduced surge pressures and there are fiscal benefits to being able to transfer cargo at potentially faster rates, as the surge conditions present in unlinked shutdown events are now mitigated. Correct utilization of such measures can allow for more vessels to be loaded and even improve tidal quayside operations, if said vessels can complete loading and leave on an earlier tide.
As we see an increasing focus on sustainability, more gases are being used as marine fuels for the first time on non-gas-carrying vessels, aided by the fact that LNG carriers have burnt methane as fuel for many years. LNG has made a strong push for its place as a marine fuel. However, with new rules allowing other gases to be used as marine fuels, engine manufacturers are able to provide solutions for the LPG gases. The very first LPG-powered gas carriers have recently been delivered, which substantially reduce the emissions profile when compared to the traditional fuel mixes. There is scope for smaller vessels, perhaps coastal trade vessels to utilize LPG as a fuel, especially if large volumes are readily available. Even if not used directly, LPG compressors are used in the liquefaction process of LNG, enabling this greener approach to continue.
Sustainability efforts can be further enhanced by incorporating Ship Performance Monitoring Systems (SPM) within operations that allow for improved operational efficiencies onboard vessels, which in turn, can reduce environmental impact. By actively monitoring and taking action to correct inefficiencies, the vessel can be sailed under more optimum conditions, which reduces fuel consumption and excessive exhaust emissions.
As attitudes shift within world shipping towards the importance of incorporating cleaner fuels into its operations, with an increase in popularity in the use of LNG, the COVID-19 pandemic could not have arrived at a more critical point in time. Industry impacts as a result have meant that demand for LNG has slowed, with buyers cancelling more than 100 US cargoes globally and fuel prices collapsing to record lows in Europe and Asia. Although this has impeded efforts in the short term, as came out of 2020 with a decline in the rate of cancellations, there is a positive outlook on the sector emerging more prosperous than before, solidifying the hope that the industry is still serious about change for a better and more sustainable future.
 Than coal, wood or oil burning alternatives