Table of Contents
1 Introduction & Background
LNG is becoming more and more competitive against piped natural gas. Conventionally, transporting petroleum products and natural gas through pipelines is considered the most efficient. This does not hold with the introduction of SSLNG (Small Scale LNG) technologies that enable natural gas distribution in geographically scattered areas with small energy needs. A 2019 study  carried out to assess the economic efficiency of four energy generation options using SSLNG – various combinations of Heat and Electricity generation in the range of 0.3 – 3 MW. The study results indicated that the average cost increase for electricity (end-use application) is 1.23% per km and 2.51% per km for heat with SSLNG transportation via rail or road compared to piped gas.
Gas pipelines are long-term assets with inherent inflexibility for direction (away from existing asset location) of gas delivery destination or gas supply source. Gas pipelines often stretch in lengths of hundreds of kilometres, and their maintenance and protection are not easy – not to mention land-related issues that hinder pipeline projects in the development stage and sometimes continue during the asset’s operational life. When gas pipelines are laid across international borders, there are additional international coordination, geopolitics and operational issues linked with multiple jurisdictions and regulatory regimes.
According to GIIGNL Annual Report 2021, LNG traded quantity in 2020 increased by 0.4% over 2019 quantity. Around 356 million tons of LNG were traded in 2020 despite reducing overall global energy consumption due to the Covid-19 pandemic and resultant lockdowns. The report describes the reasons behind 2020 LNG consumption growth, in an otherwise depressed energy market, as increased investments in LNG regasification capacities and deployment of new RLNG (Regasified LNG or Natural Gas) usage technologies.
SSLNG technological chain provides solutions to problems related to gas pipeline flexibility with improved payback periods and shorter construction times than large-scale LNG (LSLNG) technological chains. Additionally, SSLNG can conveniently adapt to and become an effective part of a large LNG technological chain. This can be achieved through contractual LNG supply arrangements with liquefaction plants, LNG storage operators or provisioning of SSLNG transport and regasification services to remote areas for gas utility operators. In another study,  conducted in 2018, intended to factor in directional flexibility of SSLNG in cost of gas transportation, provided a fair comparison of costs involved in transporting small LNG quantities by road in various directions as against pipeline transportation. The referred study concluded that SSLNG production and transportation costs could be significantly lower than gas transportation through pipelines where delivery distance is more than 930 km (or more), and delivery directions are five or more.
2 Understanding Energy Requirements for Remote Areas
First and foremost, consideration of energy requirements relates to isolated small population concentrations in areas like the island of Tristan Da Cunha in the South Atlantic (around 2,000 km from the closest neighbour) or Siwa Oasis in the middle of Saharan Desert Egypt. These remote areas are not the only isolated places in the world – developed nations like the US, Australia, Canada, and Sweden also provide many examples of remote settlements. According to a World Bank report , around 44% of the world population lives in remote and rural areas away from utility grid supplies. Due to the intermittent nature of renewable energy supplies, such isolated populations mostly rely on wood, briquettes, coal, LPG and the like for heating/cooking. Diesel is the most viable option to run diesel-powered generators for continued electricity supply and as fuel for transport. Storage arrangements and replenishing fuel supplies are demanding tasks to be accomplished to ensure continued energy availability. The provision of clean drinking water is another challenge faced by residents of remote areas.
Other requirements include commercial and industrial applications that exist at remote locations due to unique geographical, social or economic reasons. Examples are film making industry working in remote locations or tourism industry.
We may safely describe energy requirements of remote areas to be a combination of the following:
- Energy needs related to electricity generation
- Energy needs related to Cooking / Heating
- Energy needs related to the availability of tap water for household functions and clean drinking water (RO plants for clean drinking water)
- Energy needs related to commercial, industrial, recreational activities and waste disposal/recycling.
- Energy needs related to transportation (CNG / LNG as transport fuel)
This article focuses on providing energy (gas and electricity) related utilities (including the provision of tap water and drinking water) for sustaining life and business at remote locations – away from the energy grid. This includes SSLNG stand-alone systems meeting the community requirements and combinations of renewable energy supplies, depending on location and type of available renewable energy sources, supplemented by energy supplies from SSLNG operations. It is to be stressed here that, to date, renewable energy sources have not demonstrated to provide an independently sustainable and dependable supply of energy round the clock or in all weather conditions.
3 Remote Areas Energy Supply Through Skid Mounted LNG Regasification Units
Now that the energy requirements for remote areas have been identified, it is time to look for solutions offered by SSLNG supplies regasified at consumption sites through skid-mounted LNG regasification units. Before doing that, let’s identify the components and requirements for an SSLNG value chain.
SSLNG chain may start from an LNG production site, an FSU (Floating Storage Unit), an FSRU (Floating Storage and Regasification Unit) or a land LNG storage. In case the destination approach requires marine transportation, small LNGC (LNG Carriers) are used. Otherwise, LNG is loaded in ISO containers for road or rail transportation to the consumption site. Once the ISO container filled with LNG reaches the consumption site, regasified LNG (natural gas) is available for use similarly to gas delivered from the wellhead.
4 Design Philosophy for Skid-mounted LNG Regasification Systems
Designing of Skid-mounted LNG Regasification Systems is done for specific site requirements. Considerations are not limited to specifications related to natural gas supply flow rates, pressure and temperature requirements. Other important design parameters that affect the size and performance of skid-mounted LNG regasification units are:
- Maximum and minimum water temperatures during the year (for barge-mounted units)
- Maximum and minimum ambient air temperatures during the year (for land units)
- Maximum and minimum relative humidity during the year (for land units)
- Maximum and minimum wind speeds during the year (for land units)
- Prospective change in climate (global warming effect) at site
- Heat exchange technology used for regasification
Following technology options are available for heat exchange in skid-mounted LNG regasification units:
- Open Rack Vaporisers (ORVs) for use (barge-mounted) near sea-shore, lake or river
- Submerged combustion vaporisers (SCVs) for use (barge-mounted) near sea-shore, lake or river
- Shell and tube vaporisers (STVs) for use on land as well as close to sea-shore, lake or river (barge-mounted)
- Intermediate Fluid Vaporisers for use on land as well as close to sea-shore, lake or river (barge-mounted)
- Ambient Air Vaporizers (AAVs) for use on land
- Forced Air Vaporizers (FAVs) for use on land
Ambient air vaporisers (AAVs) are considered most cost-competitive, especially in areas with warmer ambient temperatures. Despite these being larger compared to those using other heat exchange technologies, their operation is simple and inexpensive (maybe at the cost of derated performance under severe weather conditions). Arrangements can be made for burning part of regasified LNG (or using boil off-gas) for supplemental heating during winter months – colder weather conditions may significantly affect the working of the regasification unit and the heating source is recommended for smooth functioning. Due to direct LNG heating by ambient air, frost formation is a likely occurrence. Frost build-up reduces the heat transfer coefficient and coefficient of performance of AAV heat exchangers, necessitating large space requirements to prevent ambient air from recirculating.
A common occurrence at the site of AAVs is the generation of fog. Fog gets generated under certain conditions related to temperature and ambient air dewpoint value. The fog bank that is generated can be large, which may cause sighting issues. Fogbank is otherwise benign.
In a recent study carried out at Queensland University of Technology in 2017, it was shown that LNG regasification technologies are now available to utilise cold energy stored in LNG. Cold energy is the physical (potential) energy stored in LNG during the liquefaction process and is estimated at around 830 kJ per kg of LNG. This cold energy is available for air chilling applications or other low-temperature fractionation (liquid nitrogen, liquid oxygen, etc. production), cold storage, cryogenic crushing and seawater desalination as per site requirements and utilisation options.
5 Economics Related to Skid Mounted Regasification
As discussed in the study referred earlier in this article, much like the competitive advantage of SSLNG delivery for multi-directional small consumption centres over pipeline gas delivery, skid-mounted regasification provides economical service for small gas supply requirements in the range of 100 – 1000 MSCFD gas (1 MSCFD = One Thousand Standard Cubic Foot Per Day). SSLNG is increasingly being identified as the best possible alternative solution (where the supply of piped natural gas is either not possible or uneconomical) and can provide much-needed energy at remote locations in a sustainable manner.
Focus on SSLNG has been very recent but growing rapidly. It is expected that developments of technologies to transport LNG at point of consumption conveniently, regasify onsite, use as a primary fuel or supplement renewable energy sources already existing at the site, all taken together point to a promising future for this energy supply chain.
SSLNG is more feasible and attractive when connected with skid-mounted regasification systems that also incorporate the use of “cold energy” stored in LNG as physical property. SSLNG, as part of an SSLNG connected supply system, requires less capital than large-scale LNG facilities. Thus, an efficient and commercially successful gas supply model for remote areas can be developed having the following essential components in the supply chain:
- Independent and multiple LNG supply commitments from various large LNG supply chains or components of supply chains like LNG land storages or sea bunkers
- Road tankers fleet for LNG transportation to a site that is fueled by natural gas (boil-off LNG)
- LNG storage tankers for onsite installation of LNG road tankers parked onsite as storage
- Skid-mounted LNG regasification units installed safely onsite (barge-mounted when site conditions require)
- Skid-mounted LNG regasification units that cater for efficient utilisation of LNG “cold energy.”
- Hybrid energy supply systems – a combination of renewable energy systems supplemented by SSLNG chain
- Natural gas distribution network onsite downstream of LNG regasification unit for various site requirements
Important safety note:
In the end, it is essential to highlight the challenges related to the creation and maintenance of high safety standards associated with the SSLNG supply chain requiring low-temperature-rated (cryogenic) materials for storage and transportation. Liquid LNG is itself at a temperature of minus 162-degree Celsius, and its exposure could be fatal. Due to the implementation of such safety standards, the average shipping cost per ton of LNG is high for SSLNG, compared to large-scale LNG transportation. Operators of the SSLNG supply chain should never compromise the implementation of OSHA standards and recommendations of the latest GIIGNL Handbook to ensure the safety of personnel and equipment.