Evolution, not revolution

Development of any new technology for an existing market sector implicitly requires that the new solution must provide something more than already in play.

The ‘Streamlining the System’ article that appeared in the February 2021 issue of LNG Industry detailed the safety and operational aspects of ecoSMRT^® – a single mixed refrigerant (SMR) LNG reliquefaction system developed by Babcock’s LGE business. This update covers the ongoing development of the system and the incorporation of operational feedback from close to 500 000 hours of operation.

To achieve this, the company defined a set of criteria at the beginning of the journey as integral components of the value proposition of ecoSMRT, i.e. to be more efficient, physically smaller, and easier to operate.

In the end, the system succeeded in meeting all three criteria, resulting in a 1.9 tph reliquefaction unit that is installed on more than 110 LNG carriers ranging in size from 174 000 – 200 000 m³.

Initial and ongoing development of ecoSMRT could not be done in isolation. By closely working with the owners and operators through Owner Support and Service Packages (OSSP), the development items could be tailored to give the customer maximum benefit. As a key enabler of improvements to the existing ecoSMRT solution, and in addition to the conventional correspondence and meetings (both office-based and onboard the LNG carriers), Babcock’s LGE business utilised live operating data from the plant, allowing for a greater degree of reliability and accuracy of actual plant performance and enabling more efficient analysis and informed development decisions.

Increase in reliquefaction capacity

One of the most immediate changes to come from the operational feedback was the increase in guaranteed reliquefaction capacity. Guaranteed reliquefaction capacity refers to the quantity of boil-off gas (BOG) generated onboard the ship which can be continuously captured, reliquefied and returned to the cargo tanks. The initial capacity guarantee on ecoSMRT – developed in line with competing systems in the market at the time – was for a reliquefaction unit that would give 1.5 tph, based on pure methane, and this became the guaranteed performance figure. With growing feedback from plants in operation and analysis of the data, it was shown that ecoSMRT could offer 0.2 tph more than suggested and thus it was possible to raise this guaranteed figure to 1.7 tph. This guarantee was disseminated across all ships with ecoSMRT, installed as a zero-cost added benefit for owners. As more operating data becomes available, it may be possible to further increase this guaranteed value but for the present time it remains at 1.7 tph.

Incremental improvements

As with all technologies, there are numerous incremental improvements which occur as the system matures. Many of these are simple within themselves, but the value added far outweighs the apparent change and often the maxim of ‘1 + 1 = 3’ applies. Since the first ecoSMRT system was ordered in 2018, it is now on variant number sev-en. It is important to note that the fundamentals remain unchanged throughout, but operational feedback plus innovative engineering practices internally has meant several improvements have been identified and implemented as the system has evolved.

The two main changes which have been introduced based on feedback from gas trials, first loadings, and voyages are:

• Incorporation of the standalone refrigerant top-up skid into the main module.
• Option to remove the condensate flash drum.

The earlier variants of ecoSMRT had a primary module which contained the reliquefaction plant components and a secondary module which contained the refrigerant bottles for the automatic system that ‘topped up’ the mixed refrigerant to maintain the composition as close as possible to the design optimum. This, of course, required inter-connections between the modules which impacted on where access ways could be defined etc., and a higher CAPEX considering the full design and build cost. The decision was made to incorporate the filling skid into the main module but at the same time to not increase the footprint of same, the end result being as depicted in Figures 1 and 2. One of the more obvious changes that was made was to alter the orientation of the expansion vessel from horizontal to vertical to free up more floor space, which does not compromise the operation in any way. During the work around the filling skid and the top-up system, the need for a continuous automatic top-up was reviewed and the decision made to change this to a more operator driven system as feedback showed that the system was tolerant to greater changes in the refrigerant mix composition than initially thought. Another change that was introduced was to change the gas analysis from a chromatograph to an infra-red based system, thereby removing the continuous consumption of carrier gas, one less thing for the crew to worry about.

Design concept evolution

The condensate flash drum (CFD) was included in the original design concept to provide a buffer between the condensate produced in the BOG condenser and the condensate return to the cargo tanks in case of any impact from two-phase flow in the condensate return header feeding back into the reliquefaction system. After feedback from the operation of the first units in service, a bypass around the CFD was installed on two ecoSMRT plants to allow the system to be tested with and without the CFD in service. The results of the investigations were correlated against the desktop calculation work and found to be consistent. There was no negative impact on the capacity of the system with the CFD not in service and, in fact, in several cases the reliquefaction capacity was increased with the bypass open. However, as several shipowners looked to retain the CFD on the basis of consistency with vessels already in service, the module design was not modified to remove the CFD, and it has become an option dependent on client preference.

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Read the article online at: https://www.lngindustry.com/special-reports/20122023/evolution-not-revolution/