Published in Turbomachinery International, September/October 2020. Written by Klaus Brun, the Director of R&D at Elliott Group, and Rainer Kurz, the Manager for Systems Analysis at Solar Turbines Inc.
Supported by Paul Bullara, Camfil Power Systems and Jim Bertsch, Solar Turbines.
The commercial shipping industry has generally avoided gas turbines for primary propulsion and onboard electric power needs, turning instead to reciprocating engines, which have a history of operating on low-cost liquid fuels. Ships’ crews have experience working on these engines, and operations and maintenance staffing and infrastructure tend to be centered around them.
Sweeping emissions rules implemented in 2020, however, are changing the marine landscape. The International Maritime Organization is working toward the carbon-reduction standards laid out in the 2050 Paris Accord. The industry is under pressure to identify clean fuels to meet these goals. The low-grade fuels reciprocating engines burn generate NOx emissions as well as sulfur oxides, particulates and heavy metals. Meeting stricter emissions standards while continuing to run reciprocating engines will significantly increase operating costs for commercial shipping operators. To support low emissions, liquified natural gas (LNG) is becoming a key marine fuel due to increasing availability and clean combustion. In addition, LNG carriers (i.e., tankers that carry liquefied natural gas) are becoming more popular.
Gas turbines provide a clean, cost-effective alternative to reciprocating engines under these conditions. The arguments against gas turbines — often focused on efficiency, fuel suitability, costs and noise — are based on outdated perceptions. Today’s turbines already serve marine applications like offshore platforms and floating production storage and offloading (FPSO) vessels.
Concerns about using gas turbines are often centered around efficiency requirements for clean combustion air, fuel suitability and noise. Since we find gas turbines abundantly in other types of marine applications, like offshore platforms and FPSOs, the question is certainly admissible as to why gas turbines are not used in commercial shipping. Today, gas turbines are significantly more efficient than the available types used 15 or 20 years ago, and provide superior durability and reliability. They can be installed as combined cycle, or combined heat and power systems. Combined cycle systems for gas turbines are more efficient and smaller than similar systems for reciprocating engines due to the higher turbine exhaust temperatures. To optimize efficiency, the systems should be sized to match the operation profile of the ship.
Additionally, today’s air inlet systems use considerably improved technologies that have brought about lowered operational costs. Despite the higher air throughput of gas turbines, compared to reciprocating engines, modern air filtration media and construction technology effectively removes particulate, water and salt from the air, thus reducing engine fouling and performance deterioration.
Meeting stricter marine emissions standards while continuing to run reciprocating engines will significantly increase operating costs for commercial shipping operators. To support low emissions, LNG is becoming a key marine fuel due to increasing availability and clean combustion.
The use of heavy liquid fuels, like heavy fuel oil (HFO) still favors reciprocating engines, but these are the very fuels that become less desirable due the environmental impact. If an owner runs High Sulfur HFO, they will need to install scrubbers in the exhaust system. These scrubbers are expensive both to install and to operate. This reduces any advantage of running on so-called cheaper fuel.
LNG has become a viable alternative marine fuel. LNG is more economical than HFO. It creates significantly less harmful emissions, such as NOx, particulates, sulfur, unburned hydrocarbons or heavy metals. This is particularly true for LNG tankers, where some of the transported LNG is available as boil-off gas.
Gas turbine lifecycle costs are comparable to those of reciprocating engines, especially considering that the higher power density, lower weight and reduced space requirement of gas turbine installations allow for higher payload. Additionally, air inlet systems on today’s gas turbines help lower operational costs. Despite a higher air throughput than reciprocating engines, modern gas turbine air filtration media and construction technology effectively collect particulate, water and salt, therefore reducing engine fouling. In addition, the lower maintenance needs of gas turbines require fewer crew.
Therefore, it is surprising that we don’t see a greater interest in gas turbines for electric power and propulsion for LNG carriers, cruise ships and other commercial shipping. Being turbomachinery people, we’re looking forward to seeing more gas turbines in commercial shipping services. Maybe we will see a similar situation as when, in 1894, the first (steam) turbine powered ship, the Turbinia, ran circles around the more conventional ships of the Royal Navy.
We would like to acknowledge the help from Paul Bullara, Camfil Power Systems, and Jim Bertsch, Solar Turbines.