Piston Less Power For LNG Fuelled Mega Container Ship
A technical and feasibility study was released by GTT, CMA CGM (and its subsidiary CMA Ships) and DNV GL for a new mega container ship today – the Piston Engine Room Free Efficient Containership PERFECT.
The concept vessel will be
- Powered by a combined gas and steam turbine
- Electrically driven.
The new propulsion concept combining the above criteria has the potential to offer a more efficient, more flexible and greener box ship design than current 20,000 TEU two-stroke diesel engine driven ultra large container vessels.
The advantages are:
- LNG enables the implementation of new propulsion concepts as demonstrated by the PERFECt design.
- It can increase a vessel’s efficiency
- Reduce fuel consumption
- Offer a cost-effective solution
- It will also increase the utilization of LNG as ship fuel over the next few years
The COGAS, which is a system for combined gas and steam turbine power generation, has the fuel-to-power efficiency ratios higher than conventional diesel engines, which can achieve up to 52 per cent. A modern, land-based combined cycle LNG-fuelled power plant will reach of up to 60 per cent as the power density by volume and weight is much higher for a COGAS system.
“CMA CGM and its subsidiary CMA Ships position themselves as pioneers by contributing to this worldwide leading innovation by rethinking the ship’s design. The lower footprint of the machinery system and increased flexibility of the electric propulsion system increase the capacity of the vessel, despite LNG tanks requiring more space than traditional fuel oil tanks, thereby generating greater revenues and reducing the payback time for the additional CAPEX required.”
“Gas turbines associated with steam turbines are ideal for the efficient utilization of LNG as a fuel. This new design saves even more cargo space compared to a conventional design,” says Arthur Barret, LNG Bunkering Program Director at GTT.
The two 10,960 m³ LNG fuel tanks are located below the deck house, giving the vessel enough fuel capacity for an Asia/Europe round trip. With the gas and steam turbines integrated at deck level within the same deck house, the tanks increases the cargo capacity significantly.
The dissociation of electric power generation from electric propulsion allows a great deal of flexibility dispensing with the engine room. The three electric main motors, which are arranged on one common shaft, can be run fully independently of each other providing increased redundancy and reliability and a high level of safety.
The gas turbine-driven power production and the electric propulsion simplify the ship’s machinery systems leading to new maintenance strategies seen in the aviation industry. It reduces the ship’s engine crew dramatically and save costs. The next phase of the study aims to optimize the propulsion system and ship design to attain even greater efficiency and increased cargo capacity.
The partners in the study — LNG containment system specialist GTT, containership operator CMA CGM (and its subsidiary CMA Ships) and classification society DNV GL — say the concept that has the potential to offer a more efficient, more flexible and greener box ship design than current 20,000 TEU two-stroke diesel engine driven ultra large container vessels.
They have dubbed the vessel the "Piston Engine Room Free Efficient Containership" (PERFECt).
Essentially, the concept ship takes advantage of the flexibility of electric drive to use space previously occupied by the main to carry cargo, more than offsetting the extra volume required by the LNG fuel tanks in comparison with conventional HFO tanks.
A comprehensive analysis with the DNV GL COSSMOS tool simulated components of the power production and propulsion system to analyze the COGAS system, making it possible to get detailed data for the calculation of the overall fuel efficiency for a complete round voyage.
Using a global FEM analysis, the project partners also evaluated the impact of the changes that were made to the general arrangement.
The two 10,960 cu.m LNG fuel tanks are located below the deck house, giving the vessel enough fuel capacity for an Asia/Europe round trip.
With the gas and steam turbines integrated at deck level within the same deck house as the tanks, space normally occupied by the conventional engine room can be used to increase cargo capacity significantly.
The dissociation of electric power generation from electric propulsion allows the electric power plant to be moved away from the main propulsion system, giving a great deal of flexibility. In fact, say the partners "an engine room is not needed any more."
The three electric main motors, which are arranged on one common shaft, can be run fully independently of each other providing increased redundancy and reliability and a high level of safety.
With gas turbine-driven power production utilizing a very clean fuel as well as electric propulsion, the ship's machinery systems will be simplified and more robust. This approach is also expected to lead to new maintenance strategies, already common practice in aviation, that would enable shipping companies to reduce the ship's engine crew and save costs.
The study also suggests that optimizing the power plant through minimizing the steam turbine size, reducing power capacities, condenser cooling, and using a two-stage pressure steam turbine and steam generator will increase the system's efficiency further. The next phase of the study aims to optimize the propulsion system and ship design to attain even greater efficiency and increased cargo capacity.
THE PRICE TAG
As part of the analysis, costs for additional and reduced systems to the base case ship (CMA CGM's 20,000 TEU Marco Polo) were considered.Additional costs included:
- membrane tanks,
- gas and steam turbines,
- fuel gas handling, and
- structural reinforcements (needed as there is no aft engine casing).
Costs that could be eliminated or reduced in compared to the two-stroke engine system included:
- scrubber, which is eliminated,
- cooling system capacity, which is reduced and the system simplified, and
- HFO treatment or tank heating, which is not needed.
At the end, the CAPEX (capital expenditure) for the COGAS ship are seen as being to be 20% to 24% above those for a conventionally-fueled vessel.
The OPEX (operating expenditure) costs largely depend on the difference in fuel price, the additional income related to the additional containers which can be transported and the savings related to a possibly higher system efficiency.
On the basis of the current gas price in Europe, which is nearly the same as the HFO price a business case in comparison with a two stroke ship using HFO plus scrubber as a reference therefore "needs compensation either by a larger difference between gas and LNG price or by additional benefits from efficiency improvement and additional revenue from additional container slots."
Still, the partners say that the results of the feasibility study, including the CAPEX and OPEX calculations, encourage them to plan a more detailed evaluation of the overall system in a follow-up project.