A new high-pressure boil-off gas compressor was unveiled at Gastech this year which promises significantly increased reliability over conventional designs
A new six-stage boil-off gas (BOG) compressor has been launched by Atlas Copco, designed to tackle the specific challenges of cryogenic high-pressure BOG.
BOG occurs where LNG leaves its cryogenic liquid state and turns into gas when ambient conditions and temperatures increase. It requires continuous mitigation to keep tank pressures and temperatures stable.
Atlas Copco’s new design combines two cryogenic and four warm stages on a single gearbox and skid, providing a compact footprint. The use of a single bull gear improves reliability and availability, as well as contributing to the smaller footprint, says the company.
As an integrally geared compressor, each stage is independent from other stages meaning that intercooling and different materials for casings can be more easily accommodated. This helps improve efficiency and cost, both in terms of initial capital expenditure and ongoing operational expenditure.
The system uses dry gas seals that are designed to provide higher efficiency during operation, and which result in lower methane leakage rates in comparison to traditional carbon-ring seals, says the company.
The new design is suitable for use across the LNG value chain, including liquefaction plants, shipping and receiving plants, where LNG is stored below cryogenic temperatures and needs to be kept stable in both storage and onloading/offloading.
Atlas Copco Gas and Process has also secured a breakthrough compressor order for the LNG carrier market from Samsung Heavy Industries in Korea for a total of eight centrifugal gas compressors, eight oil-free gas screw compressors, and accompanying heaters and vapourisers. The equipment will be used on four gas carrier vessels commissioned by Celsius Tankers.
The new vessels will use oil-free gas screw compressors to feed the Winterthur Gas & Diesel dual-fuel X-DF engines. The new compressor technology was designed to meet modern carrier needs, including pressure requirements for X-DF engines and reduced flow of BOG, due to improved insulation.
The compressors’ oil-free design allows for longer maintenance intervals compared to oil-flooded compressors, according to the company, and can be used with a reliquefaction system without any risk of oil contamination in heat exchangers or LNG cargo. “This order is a milestone in our marine LNG product development,” said Robert Radimeczky, president of the gas and process division. “To be able to provide the first ever oil-free gas screw compression technology for carrier vessels is a significant step in the evolution of our products.”
The first units will be delivered from Atlas Copco beginning October 2019, with the remainder of the machinery to be delivered in the second quarter of 2020.