Level and flow instrumentation suppliers Allison Engineering has enjoyed success with a specialist flow meter application for their ST110 gas flow meters being used on board LNG ships to measure boil-off gas (BOG), the natural wastage gas generated in the storage tanks. As demand for liquefied natural gas (LNG) has risen significantly in recent years, the need for transportation capacity has concurrently increased. The expansion of trade has resulted in a large expansion of tanker fleets where today LNG ships are typically carrying up to 266 000 m3 across the globe.
To facilitate transportation, the process involves the cooling of natural gas to - 163ºC at atmospheric pressure, at which point the gas condenses to a liquid ready for transportation via tankers. The tanks on board an LNG carrier ensure the liquid gas remains cold during storage. However, as no insulation is perfect, liquid is often boiling during the voyage and the solution is for reliquefaction and boil-off.
Typically LNG tankers are powered by steam turbines with dual fuel (DF) boilers so they can run on either methane or oil, or a combination of both, and conveniently the BOG produced is diverted to the boilers and used as fuel for the vessel. However, where ‘low emission’ zones exist, especially within European Union waters, it is mandatory for tanker operators to accurately measure how much BOG they are using in their engines, as part of MARPOL Annex Vl, the current marine propulsion regulations.
Accurate and reliable measurement and specifically, in-line calibration and verification of BOG, is crucial to tanker operators helping them to comply with current regulations.
The ST110 is unique in its ability to be functionally tested and calibrated without the need to remove the sensor from the pipeline. It features an internal purge tube that runs the length of the sensor and allows the operator to generate a known flow across the sensor element. The resultant signal output can then be compared to the factory baseline test certificate.
The ST110 flow meter is ATEX certified and complies with the ETS phase ll requirements for carbon trading. Materials of construction is 316 stainless steel for the housing and Hastelloy C for wetted parts, with control options via 4-20 m A signal, HART, Profibus PA and Fieldbus H1 as required. It can operate at process temperatures up to 450ºC and offers a turndown ratio of 1000:1.
This week, Allison Transmission Holdings Inc. opened a new multi-purpose facility in the Netherlands to serve customers across Europe, the Middle East and Africa. Located in Sliedrecht, the building centralises the company’s parts distribution, product customisation and customer training functions for the region.
Edited from various sources by Ted Monroe
Read the article online at: https://www.lngindustry.com/liquid-natural-gas/16012014/allison_engineering_supply_flow_meters_to_measure_bog/