Small scale LNG to the rescue

Natural gas poses a challenge due to its lower energy density compared to conventional fuels. Consequently, it necessitates cryogenic cooling to approximately -162°C, resulting in a volume reduction of around 600 times. This process facilitates easier storage and transportation in its liquid form. As the world transitions towards cleaner energy sources, LNG serves as a vital bridging fuel, providing a low-carbon alternative while renewable energy technologies continue to develop and deploy. The expanding use of LNG in new markets such as bunker fuel and transportation fuel reflects the growing environmental concerns regarding carbon, nitric oxide, and sulfur emissions.

Currently, the majority of LNG production occurs in large scale facilities with significant economies of scale serving well connected gas sources. However, with the growing demand for cleaner energy sources, small scale LNG plants are enabling commercialisation of stranded gas resources like biogas, flared gases, stranded gas, and coal-bed methane (CBM) fields. Small scale LNG plants focus on minimising lifecycle costs through the adoption of energy-efficient technologies and standardised modular designs. This approach enables smaller plants to target specific markets or regions where large scale LNG production may not be feasible or economically viable.

The rapid growth of the LNG market underscores its importance as a transition fuel in the global market. Its versatility, cleanliness, and cost-effectiveness position LNG as a key player in the journey towards a more sustainable energy future. This article will explore small scale LNG liquefaction technologies and their advancements, particularly those that offer solutions such as open methane zero refrigerant systems and utilising lean standardised modular methods.

Small scale LNG technologies

Small scale LNG technologies encompass a variety of processes and equipment designed to liquefy natural gas on a smaller scale, typically for niche markets or applications where traditional large scale LNG plants are impractical or economically unviable. Two basic refrigeration cycles have been used in LNG liquefaction scheme namely expander cycles and vapour compression cycles.

Vapour-compression cycles

These technologies depend on hydrocarbon liquids (refrigerant) absorbing heat as they transition from a liquid to a gas state. Within LNG plants, liquid refrigerants circulate in a closed loop, undergoing compression, liquefaction, and subsequent evaporation in a heat exchanger against the feed natural gas. This process cools and liquefies the natural gas. Historically, refrigerant cycles consisting of hydrocarbon mixtures or multiple cascaded single-component hydrocarbon refrigerant loops have been employed efficiently for large scale LNG plants; however, due to the process complexity, safety concerns, low efficiency, and high number of equipment required, these are not preferred for small scale applications.

In the case of standalone small scale LNG plants, nitrogen expander cycles are dominant, being offered by several companies. Propane vapour compression cycle 5000 tpy modular plants are also available at a relatively low capital cost but at a much lower methane-to-LNG conversion, resulting in a high lifecycle cost unless the feed gas is inexpensive.

While methane expansion technologies have been used widely for peak shaving on gas pipelines, small scale standalone methane expander plants are only coming onto the market now. The methane expander cycle technology clearly offers the best option for future small and micro scale LNG based on the thermodynamic advantage of methane and innovative compact and simple process design increasing the overall efficiency, as well as very efficient small expanders becoming available.

Zero refrigerant utilising an open methane loop is a newer methane expander cycle technology that can obtain higher product yield and utilises energy efficient liquefaction processes. It is tailored for small scale applications with best in class liquefaction yield, lower energy consumption and a flexible feed gas range.

Enjoyed what you've read so far? Read the full article and the rest of the April issue of LNG Industry by registering today for free!

Read the article online at: https://www.lngindustry.com/special-reports/25042024/small-scale-lng-to-the-rescue/