German technology group Andritz which produces both wet and dry scrubbers has received orders for two systems including one for its SeaSOx dry system.
An unamed shipping company in Belgium has ordered a SeaSOxwet scrubber for a bulk carrier operating between South America and China. The system will be designed as a spray scrubber in open-loop mode and will use seawater to clean the exhaust gas from the main engine. Andritz is responsible for the engineering work and supply of all the main equipment, including pumps, scrubber tower, continuous emission measurement system (CEMS), and the instrumentation and control (I&C) equipment.
For the second project, a cooperation agreement was signed between Andritz, the French ferry operator La Méridionale, and the Belgian chemical group Solvay to install the first Bicar dry exhaust gas cleaning system (SeaSOXdry) worldwide on the ro-ro vessel Piana . One main engine and one auxiliary engine will be routed to the filter system. In addition to SO2 removal, this new technology will reduce the particulate emissions to lowest values. Furthermore, no wash water will be discharged into the sea. Andritz is responsible for the design, engineering, and supply of the main equipment
The process in both types of wet scrubbers – open loop and closed loop – are will know and although the former has been chosen in most of the recent scrubber purchase announcements, its use is considered controversial and has attracted criticism.
Dry scrubbing systems are far less common with only one or two having been announced over the years. Andritz is the only maker offering both systems. It has long experience with dry scrubbers in shore side applications.
In the dry desulphurisation process, sodium bicarbonate (NaHCO3) is injected as a dry powder into the existing exhaust pipe. Due to the prevailing high temperature and adequate residence time, the NaHCO3 particle is activated, which increases the reactive surface by a high factor. This activation is necessary for the NaHCO3 to react with the sulphur components. Such a process requires a temperature of at least 150°C. If the temperature of the exhaust gas stream from the engines is higher than 250°C, a quench is connected upstream, which brings the exhaust gas to the desired temperature by means of evaporative cooling.
At the downstream dust filter, on which other particles such as dust and soot are deposited in addition to the sodium bicarbonate, a filter cake builds up on the filter cloth. Here a chemical reaction takes place in which SO2 reacts with NaHCO3 to form sodium sulphate (Na2SO4), which is also present as a powder. After a defined period of time or due to the maximum allowed pressure loss, the dust filter is cleaned by means of a pulse-jet process. During operation, a short stream of air is introduced at high pressure into the bag filter, whereby the filter cake peels off and drops into a collecting funnel. From there, the product is carried off by compressed air and stored in a silo.
Sodium sulphate is a ph neutral salt used in various applications ashore. It is produced in numerous chemical processes and also found as a naturally occurring substance.