Multi Inlet scrubber units, STI-TN-20170919-1

After some project experiences, Sox scrubber system from STI has been found to be effective in terms of installation space, weight, and power consumption. Our experience is to have one scrubber unit per each exhaust gas pipe; so called as “In-Line system with Single inlet”. This has been found to be useful when the installation takes place on existing ships as scrubber units can replace silencer units so that the amount of installation work and funnel casing modification work can be minimum.


The situation becomes a little different when comes to new building projects. Having a ‘large’ scrubber unit to accommodate exhaust gas flows from various diesel combustion units have some advantage over installing as many scrubber units as the number of diesel combustion units. Of course, there are some different considerations are to be made, like by-pass lines, isolation dampers, etc. This type of scrubbers are called as “In-Line system with Multi inlet”.


STI has modified its own scrubber design from “In-Line system with Single inlet” to “In-Line system with Multi inlet”. As a result, this is made as a new line of scrubber design together with the existing designs. As the scrubber units from STI are of “In-Line type” design, we call the new design as “Multi inlet system”.


Multi Inlet scrubber units are found to have some advantages of reducing the ‘overall volume’ of scrubber units installed onboard as the design is made by taking the operation modes into account. It, as a result, reduces overall installation weight as well as cost.


System sizing for multi inlet scrubber units are not very straight forward as there are many issues to be checked in advance. For example,

  1. Number of diesel combustion units to be connected to the scrubber unit.
  2. Operation modes (ex. Sea going, Port, Maneuvering, Cargo cooling, etc.) for the scrubber sizing and utility sizing
  3. Considerations for the bypass lines by regulatory requirements? and/or maintenance point of view. (For the case of the scrubber system design from STI, bypass pipes are not necessary as it can be switches between “dry operation” and “(wet) operation” without making any changes.)


STI is pleased to include some design cases to help customers to have some ideas about scrubber unit size, weight, and utilities as below.


In-line, Multi Inlet Scrubber Project Cases (19 September 2017), STI reserves the copyright.



This is a 3D rendering image of an In-line Multi Inlet Scrubber unit for Case 1.


Multi Inlet Scrubber – Case1

Please feel free to contact STI for additional information to deal with the condensates from scrubber system.?


19 September, STI

Technical Note; Corrosion resistance of Stainless steel 316L as a scrubber material, STI-TN-20170818-2

This is a STI Technical note on the Corrosion resistance of 316L Stainless steel as a scrubber material,?STI TN Corrosion resistance of SUS316L 18Aug2017

In this technical note, we have shown the corrosion rate of SUS316L material in the presence of sulfuric acid as per the weight concentration in %. Expected annual corrosion of the scrubber body, when SUS316L is used, is ~0.03mpy, corresponding to?0.000762mm/year of corrosion speed.


The corrosion speed depends on the weight concentration of sulfuric acid during scrubber operation. STI has shown that it is in the range of ~10-4% of weight concentration of sulfuric acid, which is well below the concentration ranges where other types of stainless steel material like duplex, super duplex, etc.


As a summary, SUS316L is good enough to make marine SOx scrubber units considering the weight concentration of sulfuric acid (being very low) and the operation temperature of <100degC.?

Technical Note; Calculating pH from Sulfuric Acid concentration, STI-TN-20170818-1

This is a STI Technical Note for ?Sulfuric Acid concentration and ph, STI-TN-20170818-1, ?from STI about “Calculating pH from Sulfuric Acid concentration”.


In this note, STI shows

  • How to calculate pH value from a given weight concentration of Sulfuric Acid, and vice versa.
  • A graph showing the relationship between the pH value to a given weight concentration in %.


As a summary, the scrubber effluent with pH=~3.0 is a sulfuric acid solution with ~10-4% of weight concentration.


? ? pH vs. weight concentration of sulfuric acid (%)




This will be used as a guideline in selecting the scrubber material.