In the last article we studied about the scrubbing tower and the demister which help to clean, clear and cool the flue gases coming out of the exhaust and make them free from sulphur oxides, soot and high temperatures. Now these gases are ready to be delivered to their intended destination and IG blowers are meant for this very purpose.
Inert Gas Blowers
The next step after generation or rather cleansing of the inert gas is the delivery to the distribution system. SOLAS Regulations 62.3.1 require that inert gas shall be provided to the cargo tanks at a rate which is at least 125% times higher than the volumetric rate of discharge of cargo from the ship. The reasons for this are anybody’s guess since this is only meant to ensure safety of the ship and the crew during cargo operations. It is also required to have two blowers for this purpose which should be capable of doing so jointly. However in actual situations a variety of combinations are used by manufacturers depending on the exact requirements. This is acceptable as long as the regulations of 125% are complied with.
Some ships have one large blower and one small blower, wherein the former is used for main cargo operations whilst the latter caters to topping up operations. The disadvantage of such a combination is that if the bigger blower goes bust, the smaller would have to be used till the other one is repaired and the ships cargo rate would have to be reduced accordingly to match with blower capacity for safe operations. Therefore it is also not uncommon to have two large blowers of equal capacity which are used alternatively and also helps in case one of them develops and fault.
There are other factors which should also be kept in mind while installing the blowers such as adequate space for cleaning and inspection, use of corrosion resistant materials, drainage arrangements and so forth. The blower capacity should be such that it could withstand various losses in pressure which occur at various points on the systems such as the scrubbing tower, deck water seal and the distribution pipelines.
The blowers are normally run by electric motors attached to their impellers and the capacity and ratings of these motors should be kept sufficiently large to take care of the maximum possible load on the blowers during system operation.
The inert gas mixture from the blowers is then delivered to a non-return arrangement known as the deck water seal which passes it on to the distribution system on deck and we will learn about this in the next article.