The path to cleaner inland waterway shipping master

The path to cleaner inland waterway shipping

Up until quite recently LNG was utilized as fuel only in select vessel types or in selected geographical areas. This situation is changing very rapidly. Today the use of LNG as a marine fuel is available to virtually all ship types, including smaller vessels like inland waterway vessels.

Text: KOEN VONK Photo: -
The path to cleaner inland waterway shipping master
Fig. 1 – A sister vessel to the Kooiman design project.

Three years ago, the adoption of liquefied natural gas (LNG) as a marine fuel was limited to large LNG carriers, a handful of vessels in Norway, and a couple of pilot projects in varying stages of maturity. Many companies had heard of LNG as a means to reduce emissions and of these, a select few were already actively informing themselves and preparing their strategy towards implementation. The process highlighted in this article started then; when owners were learning of LNG and new applications were being pioneered.

A cluster of companies in the south of the Netherlands involved with short sea and/or inland waterway vessels was among this group of potential early adopters. They recognized the joint challenge, choosing to communicate openly amongst each other about their projects. The local government and class societies shared this enthusiasm and their realistic view regarding feasibility and safety. The Interreg MariTIM and European TEN-T subsidy programmes helped enable a handful of projects to be started in earnest.

The relatively new application of technology using LNG as a fuel would require a strong technical focus from the beginning. For optimal integration, a system design approach was adopted that considered the complete vessel well beyond the LNG hardware scope. Frequent customer contact was a natural consequence.

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Fig. 2 – Alternatives typically analyzed to determine the optimal configuration.
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Fig. 3 – Specific fuel cost as a function of power at the propeller.

Technical-commercial decision-making

Understanding the vessel’s operations is fundamental to selecting the optimal configuration from a technical, as well as from a business, perspective. This naturally should include the propulsion systems, but the hotel load, bow thrusters, and cargo specific equipment like boilers and pumps on tankers, also need to be considered. A large amount of power is often installed on existing inland waterway vessels. The most common reasons for this are the resale value of the vessel, and the emotional security of having enough power available for extremely high flow rates on the river. On many such vessels, the average power consumed is well below 60% maximum continuous rating (MCR). Consultation with an owner/operatoron how much power is actually required often yields important initial savings in both fuel and investment costs.

At this stage, a comparison between a reference case and several alternatives is typically made. Over 30 different projects havebeen analyzed. Rather than highlighting a specific case, the resulting trends will be discussed below based on the representative configurations “Reference”, B and C in Figure 2.Each of these configurations represents the next generation of greener vessels with the latest generation of engines, after treatment, fuel or combinations thereof.

Presenting performance data in an unconventional, but intuitive way is often an eye-opener. For example, the specific cost of fuel can be presented based on the engine power, but by including the transmission losses to the propeller more insight into the drive train performance can be attained. Figure 3 presents the specific fuel cost based on power delivered to the propeller using several assumptions, such as a representative fuel price.

Figure 3, however, only tells half the story. The specific fuel cost must be multiplied by the instantaneous power to arrive at the total hourly fuel cost. This has the effect of reducing the relative impact of the low power range relative to the high power range on the total fuel bill (Figure 4). As would intuitively be expected, the greatest fuel cost saving with LNG fuel is achieved when the engines are well utilized. This further illustrates the importance of installing power in line with what is actually required.

Before any investment decisions can be made, the capital expenditure (CAPEX) side requires consideration. When combined with the operating profile and the Figures 3 and 4, the payback time can be assessed. Skipping forward to the compilation of calculations performed, the following trends are typically encountered for conventional inland waterway vessels. Note that the below is intended as a first indication. A dedicated analysis of specific cases is warranted before making investment decisions.

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Fig. 4 – Total fuel cost as a function of power at the propeller.
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Fig. 5 – 3D illustration of the Danser Group conversion design.

Conventional diesel engines with exhaust after treatment (Reference)

Exhaust after treatment is the favorable choice for vessels with few operating hours (less than 3000 hours per year) or relatively low average power consumption relative to the installed power (less than 50% MCR).

Gas generating sets with electric power distribution (B)

Calculations concerning the payback potential of gas electric installations often disappoint the business-minded customer. Closer examination of many cases indicates several effects that limit the payback potential of a “gas electric” configuration:

  • In this power range, electric configurations are based on high-speed engines. To illustrate this, the reference configuration with a single, medium-speed engine operates at variable speed. The small high-speed engine in the gas electric configuration (B) is more efficient when the reference medium-speed engine operates below ~25% power if we neglect transmission losses. For higher loads, the larger medium-speed engine is more efficient. Furthermore, the absolute amount of fuel saved at these low powers is relatively small compared to the additional fuel consumed at high powers.
  • Electric transmission introduces additional losses in the order of 6% at full load when compared to the traditional mechanical transmission via a gearbox and shaft line. This relative difference in the transmission losses further reduces the power range at which the gas electric system is best with respect to fuel consumption.
  • Auxiliary power demand is typically low on these vessels. The gain from combining all consumers onto a small number of generating sets is thus limited.

Despite the challenging economics of gas-electric systems, there are other good reasons for some projects to select an electric distribution system. This is demonstrated by the two gas-electric and the handful of diesel-electric vessels operating successfully on inland waterways.

To begin with, the electric system enables the use of high-speed, pure gas engines with their relatively poor torque acceptance at low load. Redundancy, arrangement flexibility, and noise/vibration reduction are the other traditional arguments. These benefits can enable cost reductions in other parts of the vessel, for example, by allowing a rigidly mounted deck house in lieu of the flexible mounting, which is commonplace today. Electric power distribution is also an enabler for innovative hull and propulsion concepts.

Dual-fuel mechanical (C)

The dual-fuel mechanical installation is quite similar to the conventional installation. As can be expected, vessels that operate many hours at high power settings have the best returns with such an installation. Typically, a payback time of 5 to 8 years is achievable for inland waterway vessels that are operating more than 5000 hours per year, and with a fuel price difference of 20% relative to the conventional low sulfur marine gas oil (MGO) fuel. Shorter payback times can be achieved when including other consumers, like boilers for cargo heating, large auxiliary consumers, or by simply having more running hours at high loads. Based on such analyses, the Danser Group, Kooiman and Chemgas projects mentioned in this article selected the dual-fuel mechanical configuration.

The system integration approach

Following the selection of the most favourable concept, the desired functionality of the system performance is developed in close cooperation with the customer, designer, and the main suppliers. An important outcome of this process is a list of requirements regarding each of the components, for example, the drive train.

Inland waterway vessels have traditionally used fixed pitch propellers to reduce the potential for damage resulting from rocks, sand, logs, tires and other debris encountered on a regular basis. For many vessels in inland waterways and short sea shipping, a nozzle is applied around the propeller. The nozzle improves the thrust in both free sailing and maneuvering conditions, thus reducing fuel consumption. Enabling the use of a fixed pitch propeller in a nozzle was thus essential to the projects.

To be able to use a fixed pitch propeller, the installation must be capable of clutching-in, i.e. connecting the propeller to the engine. Clutch-in is a careful balance between the torque the engine can produce at a certain low rate of revolutions, and the heat generated in the clutch during the slipping time. Furthermore, after clutching-in the rpm must be as low as possible to be able to operate the vessel at low speed.

The combined knowledge of the vessel’s operations, the propeller characteristics, the engine performance, and the control logic thus allow for a realistic assessment of how this functionality can be realised.

Establishing that all the components will deliver the required performance still neglects the fact that the equipment needs to fit into the vessel. Conversions are often more challenging than new builds in this respect. In the Danser Group conversion project, the challenge was how to replace end-of-life equipment by larger engines and additional auxiliary equipment. Based on the original drawings and a couple of visits to the vessel, the conversion feasibility was further developed into concrete plans.

The geometric solution was found in careful 3D optimization within the multitude of limitations regarding safety distances, personnel access, acceptable pipe diameters, etc. (Figure 5). The aft part of the hold will be sectioned off to create an additional space, accessible only from outside. The water ballast tanks in this newly created tank compartment will be modified significantly to allow the LNG tank and gas valve units (GVUs) to fit. An open top LNG compartment with protection against falling containers was considered the best achievable solution from ventilation and rule compliance perspectives. Special care was given to promote natural ventilation of this compartment, in addition to the forced ventilation installed to reach every corner. This solution had not been approved before, so all aspects were considered multiple times.

The resulting system design proves that a conversion of an inland waterway vessel to LNG fuel is feasible. To the best of our knowledge, this is the first conversion of an inland waterway vessel anywhere in the world. Furthermore, a good retrofit solution has been established for placing an LNG tank on a vessel with an open top hold.

For new build projects, modifying the design to suit LNG fuel operation is often the opportunity to incorporate other improvements. In the Kooiman pushboat design project, the ideal outcome would be to put the LNG tank at the buoyancy centre point, such that the vessel trim does not change as the fuel is consumed. This central location was, however, occupied by the main machinery and partially by the flexibly mounted deck house. The required general arrangement modifications opened the door to reducing the draft and adding a fourth shaft line. These measures allow the vessel not only to operate more days of the year, but to do so more efficiently. For a vessel with more than 4000 kW installed power operating 24/7, this adds up to significant annual savings.

A sound systems approach also means that some options are analyzed, but are discarded for various good reasons. For example, operating four shaft lines potentially allows for all the electric power to be redundantly sourced from power take-offs (PTOs) on the gearboxes. Analysis of the power generation and distribution was a very useful optimization step. However, the selection of a simpler approach proved nearly as efficient and more cost effective for this vessel, so the PTO configuration was not adopted.

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Fig. 6 – The Kooiman pushboat design seen from the stern quarter with green LNG tank and safety distance spheres from the vent stack.
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Fig. 7 – A sister vessel to the Chemgas LNG fuelled coasters.

Dispensation from authorities

Using LNG as fuel or carrying LNG as cargo on inland waterways is technically not allowed. The Central Commission for Navigation on the Rhine (CCR) authorities, who regulate shipping on the Rhine, have issued special permits to allow pilot projects to use LNG as fuel. This dispensation can be obtained subject to the vessel being built and maintained under class, and the successful outcome of a safety assessment. The latter is popularly called a HAZID study. The lessons learned from these pilot vessels is then used to determine workable rules for inland waterways. In this setup, the designers and class take responsibility for the sensible implementation of the IGF draft rules and other valid references, such as the Agreement on the Transport of Dangerous Goods on the Rhine (ADNR) rules for shipping dangerous goods on the Rhine.

Class approval

For inland waterways, the rules for LNG as fuel have developed in parallel with the first projects. In the meantime, the class bodies have issued their inland waterways rules for gas fuelled vessels. These rules are based on the first projects, the preliminary IGF rules, and the ADNR rules for transport of dangerous goods on the Rhine. The projects now in design and under consideration are different from those already sailing. For example, the Kooiman project is the first push boat. This requires critical thinking by the designers on how best to apply the rules. The classification bodies involved in the mentioned projects recognize their role in getting LNG as fuel accepted in a prudent, but realistic, way. The active dialogue is proving very constructive.

Risk assessment / HAZID

LNG as fuel is a relatively new area of expertise for many designers. The prescribed HAZID makes all parties more aware of the risks involved and how to mitigate them, by design or procedure. Such a risk based approach is not common for inland waterways and is generally considered a healthy addition to the vessel design process.

The engine room is normally designed as a non-hazardous area. This is possible due to the double-walled piping on the Wärtsilä 20DF dual-fuel engine and the gas supply system. The other main component, the LNG tank, is executed as a vacuum-insulated, double-wall tank with a double safety barrier, or a true type C tank with an excellent track record on existing gas carriers.

A number of focussed, component level topics are typically considered, but most of the risk assessment focuses on the vessel and the multi-system level. A successful integrated system engineering approach covers these topics. The operating area also warrants closer investigation of some specific or unconventional risks. For example, colliding with a bridge or surviving a car dropping from a bridge onto the LNG tank, while not expected to occur frequently, should nevertheless be considered.

The failure mode and effect analysis (FMEA) approach has proven to be challenging in some areas, for instance the LNG bunkering. The current practice is to use trucks to bunker LNG at a designated quay. This is now possible in four strategic locations. The target is to have LNG supplied in the same way as fuel oils are supplied, i.e. at a shore side bunker station or ideally by a bunker vessel. Such facilities are in the design (approval) phase, but not yet realised. Bunkering whilst underway is common in inland transport, but may take a bit longer to become accepted. A selection of bunkering scenarios can thus be assessed, but a safety assessment of the actual situation will still be required at a later stage. Despite such inevitable points, the Kooiman, Chemgas and Danser Group projects have been granted dispensation to sail on LNG as fuel.

Realisation

Chemgas is now in the process of realising an LNG fuelled inland waterways vessel and two LNG fuelled sister ships to the coaster in Figure 7.

The Danser Group project is also close to the actual realisation. The engine factory acceptance test (FAT) has been passed successfully and the conversion yard is fully engaged in the final preparations. The subsequent trials will be an important moment in validating all the effort that has gone into these projects.

 

The learning loop

The developed solutions are founded in a thorough analysis of the gas fuelled system as an integral part of the complete ship and the vessel operations. Much of the developed logic and some of the developed solutions are thus re-useable. Smart standardization enables future projects to be handled much quicker. These building blocks can be re-used for inland waterway vessels, but equally well on short sea vessels 
(e.g. Chemgas) and local ferries that are quite similar in many respects.

CONCLUSION

Systems integration and an open attitude towards cooperating within the local maritime cluster have been essential in successfully developing these projects. The resulting best solutions demonstrate the suitability of LNG as a marine fuel for the large fleet of smaller vessels, including 
inland waterway vessels, short sea vessels, and local ferries.

 

This article was written on behalf of the project teams who have worked relentlessly on these LNG fuelled projects.

 

The European Union TEN-T program

Wärtsilä Merchant solutions

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