Hydraulic LNG Fuel Systems as a marine fuel has shown great potential as a clean, safe, reliable, and cost effective alternative to diesel fuel in an ever changing global environment. Perhaps the most significant of these changes has been the International Maritime Organization implementation of MARPOL Annex VI. MARPOL Annex VI was initially implemented in 2005 to lower global SOX and NOX emissions, and then revised later that year, with the revision being implemented in 2010. This revision called for further increases in global emission regulations, as well as for the development of emission control areas (ECA) in which emissions would be further regulated. To comply with these regulations, a large focus was placed on the quality and compositions of fuels used in maritime service, resulting in a plan that would reduce the current diesel fuel sulfur limits from 3.50% to just 0.50%, to be effective as of January 1, 2020. As often occurs when necessity stokes the flames of ingenuity and invention, the notion of this potentially more costly and less available lower sulfur diesel fuel inspired many to look for prospective alternatives. Eventually this resulted in a push to research and implement the use of liquefied light hydrocarbons – LNG being the most common – as marine fuels. ACD has experience with both low pressure (approximately 8 bar) port injected engines, and high pressure (approximately 300 bar) direct injected engines, the more intricate of which is the high pressure variety.
High pressure fuel gas systems vary somewhat in design from one application to another, however they typically consist of several primary components, namely the reciprocating high pressure pump, drive motor, power transmission system (such as a gearbox or belt drive), centrifugal feed pump (often referred to as a boost pump), a high pressure heat exchanger (often referred to as a vaporizer), a lubrication system of one of various forms, piping and valves, control and diagnostic electronics, and a base frame. ACD has built these systems in both single pump and dual pump configurations, depending on the level of redundancy requested by the ship owner.
Pump Selection and Operation
At the heart of the fuel gas system is the high pressure pump. To achieve output pressures in excess of 300 bar, reciprocating piston type positive displacement pumps are utilized. Selecting the appropriate pump for this application is crucial, as there are many challenging demands placed upon it. As LNG is a cryogenic fluid, the pump must be specially designed for this service, employing unique technologies, geometries, and material selections. The pump must be capable of running continuously for days or even weeks at a time. It must be of sufficient size to satisfy the relatively large (as far as reciprocating cryogenic pumps are concerned) flow rates required by an engine operating at maximum power, yet be able to turn down to comparatively small flow rates required by an engine operating at idle conditions. Finally, and perhaps most importantly, it is imperative that the pump be able to operate reliably, as the only opportunity to perform major maintenance is typically every five years in dry dock. ACD has made high pressure pumps of various sizes (ranging from just 1 liter/min to as high as 750 liter/min) and configurations for many decades, and based on the aforementioned criteria, a pump was chosen from ACD’s SLS enhanced oil recovery line. While this was not a pump initially designed specifically for maritime service, it has decades of reliable operating experience in service conditions much more severe than those now being demanded of it, making it the ideal candidate to be configured into what is now known as the MSPSL, the world’s first high pressure pump to ever supply high pressure LNG fuel to an ME-GI engine in a marine environment.
Read more: High Pressure LNG Fuel Systems in Marine Service