Essay: Design of the engine room based on dual-fuel

Introduction
Stolt-Nielsen is a shipping company with around 100 chemical tankers. The Stolt-Nielsen Short Sea fleet has 20 ships out of which 6 ships at 23 years of age , in 2 years they will be too old for the most oil companies acceptance. So between now and 2 years they have to start building 6 new ships in order to maintain its fleet side. The ships are now running on heavy fuel oil, also called HFO. Another subject in the shipping sector is the new rules for SOx reduction worldwide, the fuel may contain a maximum 0f 0,5 % sulphur. The HFO will not be able to comply with the SOx rule, so they have to add a scrubber(exhaust gasses cleaner) to their installation. The other option is to run on the cleaner marine gas oil(MGO). The third option is to install a dual-fuel system, this systems runs on a combination of diesel and LNG. This system is more complicated than the normal diesel system, which will be outlined in detail in this report .
This report answers the question, what is the best combination of components in a system that is required to be reliable, safe and approved by the class society DNV GL? This will be answered based an investigation to all the component options according to the safety rules and regulations. This investigation is just about the dual-fuel system, not about scrubbers or other options.
The structure of this report starts with an explanation of assumptions and assumptions. Followed by a global view of the system is shown in the LNG system introduction chapter and after that all the components and options will be explained in the chapter component choice. Hereafter the concept design will start. Next to the concept design will be an extensive sketch of the system. The concept is reviewed thereafter and required adjustments are shown. Finally, the approval of the system will be discussed.
Assumptions and assumptions
Assumptions
NOx= Generic term for the nitrogen oxides NO and NO2
SOx= Generic term for the sulphur oxide SO
LNG= Liquefied Natural Gas
Dual-fuel= Combination of diesel and LNG
Auxiliary engine= Generator engine
MGV= Master Gas Valve. MGV is a valve that is able to shut off the LNG supply. Every valve in our design is manually, remotely and automatically controlled.
Block and Bleed valves= The block and bleed valves are taking care for the safety of the system. The block valves will isolate the supply and the consumers from each other and the bleed valve vents the LNG from the fuel line to the burner.
GVU= Gas Valve Unit
Assumptions
Design will be based on an existing design of a potential 6000 tdw Chemical Tanker.
Design assumptions:
Based on dual-fuel
Propulsion engine power: 3000 kW
Total required auxiliary engine power: 1140kW
Manoeuvring 740kW
Idle/anchorage 140 kW
Loading 256 kW
Discharging 746 kW
Cleaning 182 kW
Summary
LNG and the system
This chapter will be an introduction to the system. First started with the composition of LNG and the subject dual-fuel, followed by an global overview of the system with the required components.
Composition of LNG
Liquefied Natural Gas (LNG) is natural gas which has been compressed 50-80 times in atmospheric pressure and then cooled to -162C° (-260°F) to condense into liquid for ease of storage and transportation. LNG takes up 600 times less space than natural gas. To maintain this form LNG needs to be kept in cryogenic tanks. LNG is odourless, colourless, non-corrosive and non-toxic. It is only flammable in concentrations of 5-15% of LNG vapour in air. Below 5% it will not ignite, and above 15% there is too much gas and not enough oxygen to burn.
LNG can self-ignite at temperatures between -188 to -135C°, and therefore it is classified as a Low Flashpoint Liquid (LFL). LFL have flash point below 60C° and also include di-methyl ether (DME), liquid petroleum gas (LPG) and methanol.
LNG is a fossil fuel composed of a mixture of methane, ethane, propane and butane with small amounts of heavier hydrocarbons and some impurities nitrogen, water, carbon dioxide and hydrogen sulphide. The impurities are removed during liquefaction process. Compared to diesel, LNG contains no sulphur or particulate matter, about 85-90% less nitrogen oxides and 25% less carbon dioxide
Differences between the systems of HFO and LNG
In this chapter the differences will be mentioned shortly.
Fuel tanks
The fuel tanks are completely different, the HFO is required to be heated between 40 and 60 C° and the tanks are quite simple. The fuel tanks are hull integrated and are part of the ship construction . The system has also two types of tanks, heavy oil tanks and settling tanks. The HFO is already separated from impurities in the settling tanks.
The LNG tanks are required to stay under -162 C° and the tanks are required to be vacuum isolated to remain the temperature below -162 C°. The tanks are not able to be a part of the ship construction with this temperature range. The tanks could be placed on deck, but also in the cargo area(not right, ask loek).
Fuel preparation
The HFO is required to be heated up between 50 and 100 C° to be injected to the engine. The HFO is required to be separated and purified twice, between the heavy oil tank to the settling tank and between the settling tank to the engine inlet.
The LNG is required to be heated from -162 to a temperature between 0 and 60 C°. With this temperature the LNG will be ready to be burned in the engine. The LNG is required to be filtered by fuel drain filters in order to get rid of the impurities in the gas.
Engines
The conventional diesel engine could run on HFO, HDO, MDO and MGO. The diesel is injected and together with the air it becomes a flammable mixture under pressure.
The dual fuel engine has the same possibilities to run as a diesel engine but the engine could also run on a mixture of LNG and MGO. First the LNG is injected into the cylinder and MGO is injected hereafter, the LNG will be ignited by the MGO. The MGO works as a pilot fuel when it ignites another fuel. The dual-fuel engine starts on MGO and it will switch over to LNG when the engine is on his operation load. The system works in the same way but reverse when the engine shuts down, the reason behind this is that the LNG is not efficient enough to work on low loads. Another reason for the engine shut down on diesel is that all the gasses will not be present anymore in the engine, and therefore safe for any (unexpected) maintenance while engine is shut off.
Quick overview of the required dual-fuel system
The system will run on a combination of MGO and LNG whereby LNG will be the main fuel and MGO act as the pilot fuel and back up fuel. So there won’t be a HFO system on board.
The main reason of this chapter is to have a clear view which components are required in the system. The first assumption that is made that the ship is required to sail 6000 miles with 3 days reserve. In order to achieve that is the ship required to have storage tanks. The system also needs fuel lines to transport the liquid from the tanks to the engine. The LNG has to be in gas phase at the engine inlet so the system requires a vaporizer. The LNG has to be regulated to serve the engine with the exact amount of natural gas and to keep the system safe, therefore is a valve room. The system is required to have double walled fuel lines to the engine, when the pipe ruptures the second wall will hold the natural gas. And the system needs the engine for propulsion. For the diesel system is less required, we could use normal tanks like the HFO tanks who are mentioned in the explanation of the differences. For the fuel lines are single walled fuel lines used and the only parts that the system needs are fuel pumps, filters, a cooler and valves to regulate the system.
Component choice
In this chapter the possibilities will be described of all the components that are used in the system. The possibilities will be compared after the explanation of all the possibilities per component. Electrical energy in use and maintenance aspects( such as costs) will not be calculated in this chapter because there is no information for every component.
Fuel storage tanks and placing of the tanks
There are three types of tanks, tank type A, type B and type C. Type A is a membrane tank, type B is the conventional tank with some extra hull protection and C is a cylindrical tank.
The three tank types are displayed below.
Tank type A
This tank has a self-supporting construction with an inner structure, this type is without a second barrier of insulation. Membrane tanks have a maximum pressure of 0.7 bar. Safety wise, this tank will not be very safe. The tank doesn’t have a second barrier, so there will be a large gas leak when the first barrier fails.
Tank type B
Tank type B is the conventional tank. For LNG there are some extra safety layers, for example when there is a leakage, then the fluid needs to be caught before it is damaging the hull of the ship or some other parts. The maximum pressure is also 0.7 bar. There is a possibility that this tank will have small leakages at the tank structure. The next disadvantage of this tank is that the gas release is limited and it has to be handled.
Tank type C
This tank is a cylindrical tank with a minimum pressure of 2 bar and a maximum pressure of 10 bar. This tank is a leakage free tank and the only possibility for leakage is by the valves connections at the tank. Tank type c is cryogenic insulated, this means that there is a vacuum between the first and second layer, the space between the layers is also filled with perlite powder. For tank type c there are two options of placement. You can place them vertical and horizontal. The cylindrical tank can be placed on deck, so no cargo tank space of the vessel is used for this.
Comparison between tank types
Tank type A and type B are the tanks with a low maximum pressure. With a low pressure it is more difficult to contain the required temperature of the LNG. With these tanks you need re-liquefaction units. The other disadvantage of these tanks is that the tank takes cargo space while Tank type C is placed on deck. And the last disadvantage of these tanks are that they are less safe than tank type C, tank C has a second barrier and very good insulation. Type c is also safer because the tank is resistant to higher pressures, so they can purge inert gas to the tank without any safety issues when there is a dangerous situation.
Advantages of vertical type C in relation to horizontal type C tank
Cost savings for material and construction
When the diameter of the tank increases , the tank price will increase too. The vertical tanks is able to increase the length of the tank and to decrease the diameter easier than the horizontal tanks. The horizontal tanks have to be fitted on deck and are dependent of the ship lay out.
Stability and stress distribution
It is more easy to place a vertical tank on a solid flat surface, this will be more difficult with a horizontal tank because the horizontal tank will take more space and the chance that you have to make a type of support will be bigger. The stress distribution of the tank will be less when the tank is bolted on a flat surface. The cylindrical vertical storage tank design provides a better pressure distribution due to elimination of stress points that are in horizontal and square tanks.
Vertical tanks have also less issues with free surface aspects like fuel sloshing.
Efficiency
The vertical tank has a better efficiency because all the weight of the LNG is pushing down to a smaller area, so it will be easier for the pump.
Reduction of footprint
The space used by a vertical tank is much lower than a horizontal tank.
When you’re looking at the design of the ship, then there will be 2 options of placement of the fuel tanks. In the front of the ship just before the accommodation or behind the funnel at the back of the ship. In the middle of the ship are a lot of pipes, manifolds and cargo handling equipment so this will not be an option. To make the idea visible there is a drawing here below that indicates the possible options.
Bunker options for LNG
For every bunkering operation the hoses and pipeline to the tank are required to be cooled down to -162 C°. The lng will have a temperature of -169 C° to keep their liquid phase while bunkering.
The tank is also required to be cooled down when the temperature is above -162 C°. For all the bunker options there is still no approval to carry out cargo ops and bunker LNG at the same time.
Bunkering by terminal
This bunkering is in almost the same way as diesel bunkering. The bunkering of diesel is nowadays still possible at the terminal after the cargo is carried out. The amount of terminals who allows the fuel bunkering will become less because of the bunker spill risk. It takes a lot of time when there is a fuel spill, everything needs to be cleaned and checked before the next vessel can load or discharge cargo. There will be a separated fuel bunker terminal, the vessel needs to sail to the terminal. The LNG terminal is nowadays in the same way as the separated diesel terminal in the future.
Bunkering by truck
Bunkering by truck is most of the times possible. The ship requires to have their own manifold for reloading the fuel tanks. Every discharge of one truck takes 2 hours, with the manifold you can discharge more trucks at the same time, it depends on your manifold. From the information of Shell the maximum amount of trucks that can do simultaneous bunkering is 12 trucks.
Tank swap
Put a fuel tank unit at the mounting plate on the ship. Connect the fuel pipes and sail, when the tank is empty disconnect the fuel pipes and lift the fuel tank of the ship. And just load a new fuel tank unit, reconnect the fuel pipes and sail again.
There is still no approval for this option, because this is only a concept.
Ship to ship bunkering
It’s in the same way as HFO and MGO are bunkered by ship, but then with LNG.
Fuel lines and insulation
In this chapter are the fuel lines and insulation discussed. The subjects are separately discussed, both started with the specifications. Followed by a analysis based on thermal properties, price and feasibility.
Fuel line specifications
The material of the fuel line is required to approve all the specifications of the list below.
Corrosion resistant
There are impurities in LNG, water is the one that makes the LNG corrosive. The risk of corrosion is that corrosion can damage the fuel pipe in a way that the fuel line will leak LNG.
Able to resist temperatures between -180 and 100 ˚C.
The LNG will be colder than -162 C° while bunkering the fluid. This is because of remaining the temperature of -162 in the tank, there are a lot of vapours inside of the tank when it is 15% full. The gasses are warmer than the -162 C. So the temperature in the tank drops back to -169 while bunkering.
10 bar working pressure, able to resist 40 bar pressure
For safety reasons from the class the fuel line is required to resist 4 times the working pressure. The second wall of the double walled fuel lines is also required to resistant this pressure.
Non flammable
Pipes are required to be fire proof and never react to fire or static/electrical energy.
Made of stainless steel
The fuel lines are required to be made of stainless steel. This is a conclusion based at the first 2 specifications.
The fuel lines are required to be double walled
The fuel lines from the tanks to the valve room are required to have a second enclosure for leakages or small spills. From the valve room to the engine are double walled fuel lines with between the first and second layer an overpressure of inert gas.
Strength specifications
The fuel line material is required to have a minimal yield strength of 4 mPa.
Fuel line material
There is an material analysis made based on:
Point 1 to 8 of the material specifications above
Thermal properties
Price
Feasibility
Weldments
Application shipyards
Material availibility
Selection criteria Minimum Maximum
Yield strength 4 mPa –
Tensile strength 410 mPa –
Fracture toughness 4 mPa –
Maximum service temperature 100 C° –
Minimum service temperature – -180 C°
Water (fresh) Excellent –
Water(Salt) Excellent –
Galling resistance Acceptable/excellent –
Flammability Non-flammable –
Maximum price 15 euro/kg
In this first diagram is the price set against the minimum service temperature. All the possible materials are shown in the diagram.
Name Price
(EUR/kg) Yield
strength
(MPa) Tensile
strength
(MPa) Fracture
toughness
(MPa.m^0.5) Maximum
service
temperature (C°) Minimum
service
temperature (°C) Specific heat
capacity
(J/kg.°C) Thermal
conductivity
(W/m.°C)
Stainless steel, austenitic, AISI 201L 2,34 – 2,51 275 – 350 899 – 1,19e3 60 – 75 795 – 845 -175 490 – 530 15 – 17
Stainless steel, austenitic, AISI 316 4,19 – 4,83 205 – 310 749 – 866 55 – 75 750 – 925 -200 490 – 530 13 – 17
Stainless steel, austenitic, AISI 316L 4,19 – 4,83 170 – 310 580 – 780 53 – 72 750 – 925 -200 490 – 530 13 – 17
Stainless steel, austenitic, AISI 317 4,67 – 5,45 210 – 277 490 – 690 64 – 78 750 – 925 -200 490 – 530 13 – 17
Stainless steel, austenitic, AISI 317L 4,67 – 5,45 195 – 262 560 – 680 55 – 72 750 – 925 -200 490 – 530 13 – 15,5
When we look to this diagram, the best option will be with the highest value of specific heat capacity and the lowest value of thermal conductivity. In the diagram below the best option will be AISI 317L stainless steel. The second option will be AISI 316L stainless steel.
The price of AISI 317L is 5,06 euro/kg and AISI 316L is 4,40 euro/kg according the ces edupack database. The AISI 317L has better thermal properties, but this material is not used very often at a shipyard. The AISI 316L is commonly used in shipbuilding and especially for chemical tankers, so the shipyards have experience with the welding. So the AISI 316L will be a better option for the fuel pipe material, price and fabrication wise.
Fuel pipe insulation
The fuel insulation needs to be able to remain the temperature of the LNG lower than -162 C° when the outside temperature is around 30 C°. The temperature in the tank is -169 C°, from the tank to the valve unit is 70 meter, so the temperature range is 0,1 C°/m.
The required specifications are shown in the table below.
Property Minimum Maximum
Density 500 kg/ m3
Thermal conductivity 1 W/m K
Specific heat capacity 1000 J/kg K
Maximum service temperature 100 C° –
Minimum service temperature -180 C°
Magnetic Non magnetic –
Water(fresh) Acceptable/excellent –
Flammability Non flammable –
Material Minimum service temperature (°C) Maximum service temperature (°C) Flammability Water (fresh)
Glass foam (0.13) -273 410 – 560 Non-flammable Excellent
Graphite foam (0.12) -273 2,58e3 – 2,69e3 Non-flammable Excellent
Mullite foam (NCL)(0.46) -273 1,52e3 – 1,54e3 Non-flammable Excellent
Silicon carbide foam (0.5) -273 1,19e3 – 1,21e3 Non-flammable Excellent
Cordierite foam (0.5) -273 1,19e3 – 1,21e3 Non-flammable Excellent
Aluminum-SiC foam (0.07) -273 140 – 200 Non-flammable Excellent
Alumina foam (99.8%)(0.4) -273 1,8e3 – 1,9e3 Non-flammable Excellent
Phenolic foam(0.035) -200 120-130 Non-flammable Excellent
Polyurethane foam( 0.062) -185 135-177 Highly-flammable Excellent
The possible insulation materials according CES Edupack are:
The best material cost wise will be polyurethane foam, polyurethane foam is highly flammable when there is less than 20% oxygen in the area. There will always be a small percentage of oxygen in the enclosure when it’s purged with nitrogen, so the foam will be flammable. The best insulation material is Phenolic foam. Phenolic foam is non-flammable and has really good thermal properties. Phenolic foam is also the second best option cost wise, after the flammable polyurethane.
Polyurethane will have a thickness of 1 mm, the required surface will be 0,04 m³ and costs around €57,25.
Combination of LNG with phenolic foam
The combination of LNG with phenolic foam is reviewed in this chapter. In normal situation they are not exposed to each other, only when the fuel pipe leaks the LNG will be slowly drained to the insulation
material. This review is to be sure there will not be a reaction or a dangerous situation when there is a leakage. Here below is the stability, reactivity and the composition of LNG and phenolic foam listed. The information was available from Linde and Dyplast products.
Material Safety Data Sheet(MSDS) LNG (LINDE gas)
Stability and reactivity
Stability: Stable.
Incompatible Products: Oxidizing agents.
Conditions to Avoid: Heat, flames and sparks.
Hazardous Decomposition Products: Carbon monoxide (CO). Carbon dioxide (CO2).
Composition LNG
Chemical Name CAS-No Volume % Chemical Formula
Methane 74-82-8 62-93 CH4
Nitrogen 7727-37-9 1-9 N2
Propane 74-98-6 1-7 C3H8
Ethane 74-84-0 3-11 C2H6
N-Butane 106-97-8 1-3 C4H10
Isobutane 75-28-5 1-3 C4H10
Helium 7440-59-7 <2 He
Isopentane 78-78-4 <1 C5H12
Pentane 109-66-0 <1 C5H12
Carbon dioxide 124-38-9 <1 CO2
Here below is the stability, reactivity and the composition of glass foam listed. This information was available from Industrial Insulation.
Material Safety Data Sheet(MSDS) Phenolic ( Dyplast products)
Stability and reactivity
Stability: stable
Conditions to avoid: Temperatures above 260 C°
Materials to avoid: None
Hazardous reactions: None
Hazardous decomposition products: None.
Composition Phenolic foam
Chemical name CAS-no Volume % Chemical Formula
Modified polyisocyanurate Polymer None >90 –
Hydrocarbon blowing agent 78-78-4 <10 CH
Conclusion
The flammable range of LNG is between the 5 and 15 percent air in the mixture.
Between the fuel pipe and the second enclosure is a space of 0,040538 m3 over full length. The second enclosure will be purged with nitrogen and when there is fire possibility in normal condition, the phenolic foam will isolate the fire. The water absorption in 24 hours is between 5 and 6%. So the sensors have a couple hours to measure a difference between values of the pump sensor and the pressure gauge sensor who’s fitted before the valve unit. In those hours the fuel will slowly drain and become gas, because the insulation layer still keep the fluid from the outside pipe.
Inert gas lines
On every chemical tanker there is an inert gas system installed for the cargo tanks, it can be arranged as such that the two duties can be combined. The inert purge gas is to keep the area safe, the nitrogen that is purged to the area brings the percentage of air to such a low level that the cargo or LNG fuel can’t be ignited. The system for the fuel lines will have 3 inert gas lines to be sure that the system is always kept safe when a dangerous situation appears. The gas that is used to purge the fuel lines is nitrogen. The cargo tanks are purged with nitrogen, the LNG fuel system will only be purged when a dangerous situation appears. An example of a dangerous situation is that there will be a 40% LEL gas detection measured by a gas sensor. LEL means lower explosive limit, this value is the lowest concentration of a gas or a vapour in air capable of producing a fire with or without an ignition source.
Vaporizer
The required temperature of the LNG for combustion is between 0 and 60 ˚C. The LNG will be transported from the tank with a temperature of -162 ˚C. The vaporizer needs to be able of rising the temperature with a minimum of 162 ˚C and with a maximum of 222 ˚C.
There are 4 ways to vaporize the LNG:
Open Rack Vaporizers (ORV)
Submerged Combustion Vaporizers (SCV)
Ambient Air Vaporizers (AAV)
Intermediate Fluid Vaporizers (IFV)
Open Rack Vaporizers(ORV)
The open rack vaporizer is a heat exchanger that uses seawater as the source of heat. This kind of heat exchanger is worldwide used at LNG terminals. The temperature of the seawater needs to be at least 5 C°. The piping is made of aluminium alloy for mechanical strength and the tubes are arranged in panels. The process of this vaporizer is shown in the picture on the right. This system is totally explosion proof. There is an calculation made for the surface required to vaporize the LNG, the calculations are shown in appendix 5.
It´s a quick calculation, calculated with an unlimited heating volume flow.
Submerged Combustion Vaporizers (SCV)
The submerged combustion vaporizer is a heat exchanger that uses a burner to heat up a water bath. LNG flows through a tube coil that is submerged in a water bath, the water bath is heated by a gas burner which blows flue gases into the bath. This system has a high transfer rate and high thermal efficiency. SCV units are proven equipment, are safe and very reliable . This vaporizer is used in colder countries which are not able to use seawater of ambient air. When there is a leakage of gas the plant will be shut down and the main engine will run on MGO.
The Submerged combustion vaporizer uses 1,5% of the vaporized LNG out of the fuel system. Total Yearly kW requirement of ship: 9,148,652 kW
(at sea) 6,401,808 kW
(in port) 2,447,544 kW
Heating 299,300 kW
This will result total 3,329 m3 need of LNG every year, equivalent to about 1228,40 euro every year. If you look over a ship life time of 25 years the operating cost will be in the range of 30710 euro depending on fuel prices.
Ambient Air Vaporizers (AAV)
This vaporizer is using ambient air to vaporize the LNG, this is another source of free heat.
The design of the AAV is shown in figure … AAV consists of vertical long heat exchange pipes that provide downward air draft. The warmer air has a lower density and will be working on the higher part of the system, the lower part has the cold denser air. The only disadvantage on this system is that the ice needs to be removed from the LNG pipelines in an 4-8 hour time schedule otherwise the ambient air will not be able to vaporize the LNG. This type of vaporizer are used in the warmer countries , where the ambient air is high all year round.
There is an calculation made for the surface required to vaporize the LNG, the calculations are shown in appendix 5.
It´s a quick calculation, calculated with an unlimited heating volume flow.
The Shell and Tube vaporizer
The Shell and Tube vaporizer is a conventional heat exchanger, the LNG tubes are inside the shell surrounded by the heated fluid that will vaporize the LNG.
This LNG vaporizing plant works via an intermediate fluid that utilizes heat transfer fluids in a closed loop to transfer heat to vaporize LNG. Three types of heat transfer fluids who are used in the systems are:
Glycol-water
Hydrocarbon based HTF
Hot water
The commonly used fluid is glycol-water, glycol-water has a low freezing point and will not freeze by vaporizing the LNG. These glycol-water IFVs are very compact exchangers (vertical shell and tube design) due to the high heat transfer coefficients and the large temperature approach.
To warm up the glycol-water there are several options, they can use an air heater, seawater heat exchanger, reverse cooling tower and a waste heat recovery unit or fired heater.
Using air for heating will generate water condensate, especially in the equatorial regions. The water condensate is of rain water quality which can be collected and purified for in-plant water usage and/or export as fresh raw water. Conventional air fin type exchanger consists of fin tubes are not designed for ice buildup. With the use of an intermediate fluid such as glycol-water, the glycol temperature can be controlled at above water freezing temperature hence avoiding the icing problems.
Similarly, the reverse cooling tower design, which extracts ambient heat by direct contact with cooling water via sensible heat and water condensation, would require an intermediate fluid. The heat of the cooling water can be transferred to the intermediate fluid by a heat exchange coil.
Seawater may be also be used. However, the use of seawater is more prone to exchanger fouling, and the exchanger (plate and frame type) need to be cleaned periodically. The plate and frame exchangers are very compact and low cost. Typically, spare seawater exchangers are provided for this option.
Fired heater may be used at the costs of fuel expense. For environmental compliance related to CO and NOx emissions, a selective Catalytic Reduction System can be fitted into the flue gas duct of the fired heater.
There are calculations made for the shell and tube vaporizer heated by engine coolant, the complete calculations are displayed in appendix 3. The calculations are based on the Wartsila 6L34DF engine. The vaporizer needs an surface of 2m² and it will be a one-time expense.
Combination of ORV and STV
This heat exchanger works in two steps, first heated by the sea water and hereafter heated by the shell and tube exchanger. This exchanger type will vaporize the LNG with a low energy per second value.
Comparison between the vaporizers
The ambient air vaporizer is not an option for the company’s short sea fleet who are operating in the North Sea area, there ships are sailing in Europe and in winter conditions the air temperature may not be high enough to vaporize the LNG. The sea water vaporizer is an option because the temperature of the seawater will not drop lower than 5 C°, the only problem with this system is that in extreme conditions the seawater system is taking too long time. When it takes a long time, there is more fuel pipe required and this is expensive. The shell and tube design is an interesting option because there is a possibility to re-use the free heat of the cooling water of the turbo. This cooling water has a temperature of 30/35 C°, another option is the cooling system of the main engine and the auxiliary engines. This cooling water is around 80-90 C°. The submerged combustion vaporizer is an option, but the disadvantage about this vaporizer is that you always have costs for heating the water. When you are using the shell and tube vaporizer, this is a one-time expense and the energy for 25 years is for free. The advantage of this system is that the system lowers the temperature of the cooling water. In the normal system will be cooled with sea water, this system stays on board, only the pump will be able to run at lower routes per minute.
Gas lines
The gas lines operates from the vaporizer till the engines and there will only flow gas through this pipe lines. The lines will supply the engine with natural gas therefore are two options to design. The options are single walled pipelines and double walled pipelines. The system is more complicated when single walled pipelines are used. Every room where a single walled pipeline is suited is required to be gas tight, carried out with gas sensors and is also required to have their own ventilation system. By the double walled pipelines is only required that the space is vented with nitrogen between the first and second enclosure. The double walled pipeline will be cheaper and easier to install. The gas lines from the bulkhead of the engine room to the main engine will be double walled. For the auxiliary engine is the fuel line single walled, this is because the double walled line will be too big to be installed to an engine of this size. This decision is based on information from Caterpillar.
Main engine
The main engine for the newbuilding design requires an output power of 3000 kW. There are 3 possibilities available at this moment in dual-fuel. The possibilities are the MAK M34DF, the MAN L35/44DF and the Wartsila 6L34DF. The main engine is not further elaborated because the design will be used in the future with a minimum period of 2 years and then the engine specifications could be totally different.
Engines Wartsila 34DF Man L35/44DF MAK 34DF
Dimensions
L(mm) 5325 6485 5934
L1(mm) 5265 4462
W 2380 2539 2418
H 3705 4163 3836
Dry mass (t) 35 40.5 39.5
Engine facts
kW 3000 3180 3000
Number cilinders 6 6 6
Bore(mm) 340 350 340
Stroke(mm) 400 440 460
Speed(rpm) 750 750 750
Map(bar) 22 20,0 19,9
Fuel consumptions gas(kJ/kWh)
85% 8250,48 8048 7995,75
50% 8560,65 8700 –
Fuel consumptions MGO as pilot fuel(g/kWh)
85% 1,9 1,8
50% 4,5 4,5
Fuel consumptions full MGO
85%
50%
Auxiliary generator sets
There are some assumptions made to design the generator set lay out. The assumptions for the newbuilding design :
Required generator power is 1042 kW.
The design is based on the dual-fuel concept, so the possibility of 3 diesel generators isn’t discussed in this report.
The power is divided over 3 generator sets.
The required engine power is around 350 kW or another distribution of the generator power, for example with 2 big and one small generator. At this moment there is no engine supplier with a dual-fuel engine at this power range, the smallest dual-fuel generator set is the MAN %L 16/24DF and has a power of 590 kW. The system could use pure gas engines alternatively to run on LNG. The redundancy will reduce when we run 3 pure gas engines because these engines are not able to switch over to diesel. So every engine will shut down when a component in the fuel system fails. The other point why they are not reliable is that a gas engine has a very low efficiency on low loads, this is also the reason that dual-fuel engines switches over to diesel at low loads.
Conclusion
My selection will be two gas auxiliary generators and one diesel auxiliary generator to remain the overall reliability of the power generating plant. Just in case something went wrong in the LNG supply chain. In the future it may be possible to run on 3 gas auxiliary engines when the efficiency is higher at low loads.
The auxiliary engines are not further elaborated here because the vessel design will be used in the future and during that period from now until then and the engine specifications could be totally different. Systems are fully in research and development phase, no major roll-out taken place yet.
Boilers
The boilers installation is intended with a gas and diesel burner to be sure that they could run whenever it’s needed. The research is kept to the already known boiler suppliers. The suppliers are Alfa Laval/Aalborg, Miura and Saacke. There are three types of boilers, the hot water boiler, the steam boiler and the thermal oil boiler. The thermal oil boiler is most commonly used at the Inter-European fleet. The boilers could be heated by HFO,HDO, MDO, MGO, sludge oil and LNG.( almost every oil could be burned). The research is kept to boilers that could also run on LNG. The suppliers offer only LNG fired steam heated boilers at this moment.
Boiler systems Saacke Saacke
Alfa laval/Aalborg
Boiler type FMB-VS FMB-VF-LONOX OS-KBOG-E
Heating medium Steam Steam Steam
Capacity range(kg/h) 5000 6000 5400
Design pressure( MPa) 1 1 1
Water content(m3) 6,5 9,7 5,9
Measurements(Diameter x hight in mm) 2260×5520 2250×7475 2470x 5910
Consumptions Gas
Consumptions nr.2 oil