Once natural gas is liquefied, it must be kept at cryogenic temperatures of - 163°C to prevent it from reaching its boiling point (- 161°C) and evaporating. Therefore, insulation is vital to the LNG supply chain from liquefaction, to insulation of vessels, to the regasification terminal where it is offloaded into storage tanks. For example, the loss of LNG during ocean transportation is a significant problem, accounting for millions of dollars of lost value during a ship’s lifetime. Although LNG vessels are designed and insulated to minimize boil-off, shippers experience varying degrees of boil-off rate (BOR) due to ship turbulence and temperature differences between the ocean water, ambient air and LNG.
Depending on the type of propulsion system, some of the boil-off gas can be used to power the ship. However, since the ship doesn’t always run at peak speed and engines are becoming more efficient, excess boil-off gas is created that has to be incinerated or re-liquefied. Therefore, some ship builders and owners are investing in on-board re-liquefaction plants. Others incinerate excess gas, leading to lost cargo, decreased revenue and greenhouse gas emissions.
The choice of foam blowing agent used to insulate the ship’s containment system plays a significant role in minimizing LNG losses. Historically, LNG vessels have used foam insulation formulated with HCFC-141b blowing agent, which is being phased out in many regions around the world due to its ozone-depleting potential (ODP). The transition from HCFC-141b is already underway in the LNG carrier industry with more than 50% of the LNG ships being built in 2014 using HFC-245fa.1 In addition to being non-ozone depleting and nonflammable, HFC-245fa improves insulating efficiency compared to 141b.
The membrane-type carrier pictured is insulated with foam made with HFC-245fa. It demonstrated a BOR of 0.09%/day, which is 5-6% better than foam made with HCFC-141b, and almost 10% better than foam made with carbon dioxide (water-blown). Similarly, an HFC-245fa and glass wool combination in a different membrane-type carrier design was more than 30% better than the perlite baseline and delivered a BOR of 0.108%/day. 2
In addition to ship insulation, rigid polyurethane foam is often used to make cryogenic insulated pipes used in the process to liquefy natural gas. Many LNG pipe insulation producers use HCFC-141b or pentanes as their blowing agent. By converting from pentanes to an HFC-245fa/pentanes blend, some producers have seen significant improvements in processability and insulating performance.
Looking ahead, heightened awareness about climate change is spurring a movement away from HFCs to alternative blowing agents, such as hydro-fluoro-olefins (HFOs). HFOs are also non-ozone depleting but offer an ultra-low global warming potential (GWP) of one, 99.9% lower than HFC alternatives. HFOs also improve insulating performance and can be a near drop-in replacement for many blowing agents being phased out under global environmental treaties or regulatory action. Not only is it important to select the right LNG insulation, the choice of foam blowing agent can significantly improve insulation performance, environmental impact and ultimately, profitability.
To know more about technological developments and applications in the gas industry, attend the CoTEs programme. The Centres of Technical Excellence (CoTEs) is a free-to-attend technical seminar programme at the Gastech Exhibition.
Pre- Gastech webinar on Asia Gas and LNG demand: Speakers include Arnaud Dubois Denis from BG Group, Gavin Thompson from Wood Mackenzie, Guy Broggi from Total and David Morris, Head of Asian LNG Business at E.ON Global Commodities.
1. Honeywell Enovate® 245fa (HFC-245fa) in LNG Carrier technical sheet
2. BOR data confirmed by ship builder.
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