The Challenges of Insulating Liquid Natural Gas Plants
Natural gas is a natural source of energy now exploited extensively around the world. It is clean, efficient, and environmentally friendly. It can be transported via pipelines or in tankers in liquefied form. Liquefaction is achieved by refrigerating it to -160°C, reducing its volume by over 700 times, which yields liquefied natural gas (LNG). Natural gas producers with surpluses over their domestic requirements, as well as consuming nations without their own domestic supplies or access through pipelines, have provided the catalyst for the growth of the LNG market.
At the end of 2004, total proven world gas reserves were around 180 trillion cubic meters, the vast majority of which was in the Middle East and Russia. Demand for natural gas is growing at rates in excess of 10 percent in Europe, the United States, and China. Investment in the next 5 years is expected to be two and a half times that of the last 5 years. China and India have now entered the market for imports. Large producers of natural gas such as Russia, Iran, and the U.S. Gulf states are committing to LNG production. The leading producers of LNG are Indonesia, Malaysia, Qatar, Nigeria, and Venezuela. The major consuming nations are Japan, Europe, and the United States.
As natural gas travels from underground to the final user, industrial or domestic, it moves through pipelines, a processing plant, storage facilities, and various methods of transportation. From the gas field, it is piped to the export terminals, where the gas is purified, compressed, and liquefied in LNG trains. It is stored in large holding tanks to await transportation by sea in purpose-built LNG tankers to the import-receiving terminals where it is again stored. It is then restored to its gaseous state before being fed into the gas transmission system, which brings it into our homes. LNG has no smell, so a further process at the import terminal involves giving it an odor so that leaks can be detected.
Typically, an LNG process train will produce around 6 billion cubic meters of gas annually. The world’s largest LNG export terminals currently comprise six to eight trains. The storage tanks typically hold up to 200,000 cubic meters per tank. Owners are beginning to build “super trains” capable of doubling production capacities. Some 18 LNG export terminal projects are expected to be built around the world within the next 5 to 10 years, with at least another 17 planned. For each export terminal, there is a corresponding requirement for LNG tanker and import terminal capacity.
The development of LNG, from the late 1970s on, presented a challenge to thermal insulation manufacturers and contractors. An industry primarily concerned with heat conservation had to engage with owners to find solutions—not only to the conservation of very low temperatures, but also to the particular stresses involved at those temperatures. As one of the pioneers, Shell developed many of the specifications, enshrined in its Design and Engineering Practices (DEP), now CINI.
For these plants to function, efficient insulation systems are needed for cryogenic service. When a plant is operating at -160°C, the environment is unforgiving. Inefficient insulation will result in much higher refrigeration requirements as the boiloff is increased. Ineffective vapor barriers will allow moisture to enter the insulation system, causing icing and major disruption. The relative movements between the plant, the equipment, and the insulation systems due to thermal contraction and expansion as they cool down or warm up become major considerations. Complex insulation systems are required to withstand the rigors of differential expansion and contraction, thermal shock, and vapor drive.
Most of the insulation systems adopted have involved the application of multiple layers of preformed insulation sections with appropriate slip joints, vapor barriers, and expansion and contraction joints and claddings.
Multilayer, rigid, preformed insulants such as polyisocyanurate (PIR) foam or cellular glass with staggered joints—often with wet-applied primary and secondary vapor barriers—are the proven means of insulating LNG plants. The systems are tested and—like most systems—require close, rigorous quality control (QC) and protection from adverse weather conditions. They are also labor intensive. A combination of the two insulants can be used, depending on the importance of overall insulation thickness as a requirement for additional mechanical strength and/or fire protection.
A variant has been the combination of rigid, preformed, and injected PIR (foamed in situ). With the preformed material providing the inner layer and the injected material the outer, this provides a cost-effective, labor-saving specification. Further, it requires no separate vapor barrier, as the injected foam adheres to the inside of the outer cladding. The performance of the primary vapor barrier relies on the integrity of the foam to the cladding-adhered bond and the effective sealing of cladding overlaps. The controlled mixing of chemicals in a site environment requires particularly tight QC, and the technique is not easily applied during inclement weather.
Outer-cladding protection has taken the form of sheet metal, as with heat-conservation systems. Given the saline and chemically sensitive environments in which LNG plants tend to be built, however, corrosion has been a problem. Specifiers often opt for 316L stainless steel and aluminized steel.
The application of such complex insulation systems on site is likely to involve production rates of between 5 and 10 man-hours per square meter, and is therefore very labor intensive. The insulators and sheet-metal workers require a hierarchy of supervision, quality assurance (QA) inspectors, and material controllers. At the outset of the project, the manpower loadings are smoothed to provide efficient utilization. As the project proceeds, delays inevitably occur and, as one of the back-end activities, the insulation application is also delayed. As project management tries to keep the completion date from slipping, more manpower is required, resulting in increased labor and all of the associated resource and cost consequences. Increased manpower results in other, less tangible, costs—particularly the potential delay of project completion. Many of the LNG sites around the world do not have sufficient local accommodations and so require the labor to live in camps, and additional people require appropriate facilities. Manpower requirements typically rise from 300 to a peak of 700 or 800 personnel. Finding skilled personnel to carry out such complex work makes great demands on recruitment, training, housing, and management. Clearly, anything that can be done to successfully complete the insulation work earlier in the project—from decoupling from the main construction to reducing the labor content—will help both the client and the contractor achieve their goals.
As the demand for gas accelerates, the number of new plants increases. Owners are looking for reduced construction programs and shorter completion times. Also, there is a continual squeeze on costs. The challenge for the successful contractor is to find innovative ways to perform the insulation work on this type of plant.
Preinsulation of straight pipework is a way to get a percentage of the work completed earlier in the project and avoid the delays caused by other trades. Pipes can be sent directly from manufacturers to a factory location where the insulation can be applied in controlled conditions. An effective system that can be applied in this environment involves sprayed PIR foam covered with a glass-reinforced epoxy coating. The system, proven on a number of Shell installations, incorporates crack arrestors and slip joints, and a resilient inner layer that allows for thermal and mechanical contraction and expansion. It provides a low-maintenance, high-performance cryogenic insulation with a robust, chemical-resistant, noncorrosive finish. While resistant to mechanical damage, it also accommodates the stresses and strains associated with thermal cycling—particularly those that are associated with the jetty lines. The result is a high-quality insulation and finish applied in factory-controlled conditions.
Another area for attention is the primary vapor barrier, which involves many man-hours in application and critical QC inspection. Traditionally, vapor barriers have been applied as wet systems, but costs can be high due to the composition and low manufacturing volumes. These materials also have shelf-life issues, which can have a major impact if projects are delayed. The vapor barriers are normally applied in three layers, with glass cloth reinforcement applied between the layers. Alternatives to the wet-applied systems are required to speed application and reduce the necessary QC. A number of laminates in sheet form, such as butyl laminate, are becoming available. Insulation suppliers are also developing their products with factory-applied coatings.
The advent of ultraviolet-cured glass-fiber reinforced plastic (GRP) offers another external cladding system. With mylar foil double, it can be used as a vapor barrier, avoiding the need for wet-applied vapor barriers. Supplied in flexible sheet form and cured by natural or artificial light, ultraviolet-cured GRP provides a seamless, successful alternative to the traditional metallic cladding finish for complete plants. The recent reinsulation of the cryogenic heat exchangers at Brunei LNG was successfully undertaken with such a finish. These advancements lead the way as the industry strives to innovate and improve.
The significant investment taking place in this area is making demands on available skills; and in the mature markets in Europe and the United States, there is limited skill available in “cold” insulation, for lack of demand. It is important that the industry continues to develop ways to help clients meet demanding cost and program budgets.
The insulation industry has an interesting time ahead as it continues to rise to the challenge of insulating the world’s latest generation of LNG plants in an efficient, cost-effective, and timely manner.