Joris van Kreij, Global Sales Manager – LNG Ship Fueling Solutions, Chart Industries presentation during the 2015 GREEN4SEA Forum
A typical LNG ship fuel installation consists of a tank with integrated ‘coldbox’ which is an air-tight enclosure of all the plumbing, valves, evaporation equipment and instrumentation attached to the tank. The advantage of such configuration is that the gas-hazardous space is limited to this coldbox only, instead of the whole tank compartment. Insulation of the tank is of high importance to minimize heat leak into the tank, warming up the LNG. The more heat leak occurs, the faster the pressure will rise and the shorter the tank holding time (time before the safety valve opens) becomes.
You are aware of the current and future emissions regulation, no need to talk further on that. It is cleaner operation of engines. Fuel cost savings, on specific cases. It is not always the case, but obviously US shipowners mainly are very much aware of that. Low noise operation and it eliminates the risk of oil spills. What we could add to this is your image improvement that is also sometimes a driver for a shipowner to switch to LNG. We have seen that in particular in this case, when we have built LNG fuel system for an Argentinian shipowner.
Apparently, a typical LNG ship fuel solution is whole set of things, is not only a tank, what you need. But, it is also a lot of instrumentation around it.
- Integrating with the tank is the coldbox, which is air-tight space with all the gas hazardous equipment inside. It is the evaporation equipment, it is the plumbing, it is the instrumentation, etc.
- Then, we have the water-glycol circuit, which is connected to that and it basically takes the heat, for example from cooling water or exhaust gases to the coldbox to evaporate LNG.
- Bunker stations, obviously, are able to take in the LNG, which is connecting the tanks with vacuum insulated lines. Or, it can also be a foam insulated and there is a vapour return line.
- Then, the engine lines, the gas supply lines, coming from the evaporator going to the gas self-units of all the engines.
- Lastly, the control system and the safety system can be part of the whole solution.
In general, this is how a ship fuel tank would look like and how we are building it today. You have the conical support of the inner vessel, which basically allows for that thermal expansion and contraction, when you have different temperatures. You have on the inside the straps, which also allows for that type of movement. It is supported by the fix support and the sliding support. So, this support is able to move the outer shell in a way, so the outer shell can have the temperatures changes. Then, we have the coldbox with all the equipment inside. This is basically what glass looks like ESD protected machinery space. Outside the coldbox, it is an inherently safe and get safer machinery space, because all the piping outside is going throughway double wall piping for example.
One of the system that we build with the coldbox. You can see the main evaporator. In the back of this, you can see a pump. Typically, there is no pump needed, if you have a low pressure and gas supply requirements.
The types of the heat leak to the inner vessel that you have to deal with are two:
- It is, obviously, the piping going through vacuum insulation to the tank.
- It is also the supports. So, we are trying to engineer them in a way that there is at least an amount of heat ingress.
- Obviously, the wall and the insulation are the main factors
The importance of the high grade insulation stems for the tank holding time, which is the time before the pressure relieve valve opens and start to vent natural gas. All the time depends on the level of LNG in the tank. The pressure, which also means the temperature of the received LNG, if you already receive a very warm LNG, which comes in 8 bar and your tank allowed working pressure is only 10 bar, then of course you have a very short tank holding time. Maximum allowable working pressure (MAWP) is obviously a factor. And then, of course, the heat ingress, which is dependent on the tank design, but mainly, the insulation is a big factor. High grade insulation translates into operational flexibility, because the longer your holding time is the better. You are able to plan your voyages and if you do have some time, where there are no consumption on LNG gas, you are still able to continue without having to empty the tank for example.
Therefore, there are all kind of insulations. I will focus on three of them. Mechanical insulation, typically polyurethane insulation. It can be used for every single shell tank, usually for very large tanks. Vacuum insulation is most used. We have two options perlite or multilayer insulation. Those are the two types, that we also build within chart and we have different experience. Both they have their pros and cons.
Mechanical insulation, in general, is 10-15 times worse than perlite. That means that you have more of that in order to have the same heat resistance. Superinsulation is 2-3 times better than perlite, but actually is a bit less due to the support heat leak, because superinsulation is likely differently engineered and constructed.
Another very important topic is vacuum integrity. Thus, the prerequisite is the reinstalling of the gettering system in annular space. That means, we are installing Molecular sieve in that vacuum space, that is actually absorbing the remaining gas and also the released gas, which is coming from the wall inside the annular space. Also, we have a hydrogen converter, because hydrogen atoms are too small for the molecular sieve to be absorbed. So, that converter forms water and that water can then be taken by the sieve. It is very important because it results in a higher vacuum level in the tank, which basically means less heat ingress. And, it also makes the vacuum lasts longer because overtime any insulated tank will lose their vacuum very slowly. Even though the vacuum level will deteriorate, but this gettering system will make sure that actually will last as long as possible, which means it can be used for decades without needing to have downtime or repeal the vacuum or any other problems.
Mechanical insulation is obviously cheaper on your initial investment, which is of course an important factor. Another advantage is that you are able to build a larger tank. This kind of tanks are short shop-built, so if you want to build a tank of 12 meters diameter, you also need a ship with that amount of height and a lot of space around it to be able to construct it. So, in this kind of cases, mechanical insulation can be a solution.
The cons are
- You have a higher leak compared to vacuum
- Obviously you may need replacement because of the different thermal contraction and the cracking that you can get due to that.
- Mechanically insulated tanks are difficult to insulate from the supports, that is another heat leak source
- There is no secondary containment, so you don’t have the outer shell, which means you need to have some sort of containment around your tank system integrated in the ship’s design and makes it more complicated So, not only look at the tank cost, but also look at the costs that you have to add to that in order to make your ship suitable for that.
- There is more space required
- In a 200m3 tank, you have much more space that you need especially on the diameter of the tank and on the length. Surely, it can make a difference. If your tank is suited on deck and you have sufficient space because for example you are having chemical tanker or product tanker, usually there is sufficient deck space, but it’s not always the case especially when you are looking at ferries.
In conclusion:
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Above article is an edited version of Joris van Kreij presentation during the 2015 GREEN4SEA Forum
You may view his presentation video by clicking here
Click here to view all the presentations on this GREEN4SEA Forum |
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About Joris van Kreij
Global Sales Manager – LNG Ship Fueling Solutions, Chart Industries
Joris van Kreij has been active in the maritime industry for over 15 years. He started his professional career at sea, working as engineer and navigation officer on board of both cargo- and cruiseships. He holds a Bachelor degree in Maritime Operations and a Master degree in Business Administration. Before joining Chart , Joris has been active in the propulsion and engine manufacturing industry. At Chart he is since 2012 responsible for the development of the marine business with Chart’s maritime LNG solutions.
See also Linkedin public profile: http://www.linkedin.com/in/jorisvankreij
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