TEXTE Environmental Impacts of Exhaust Gas Cleaning Systems for Reduction of SOx on Ships — Analysis of status quo 
Report compiled within the framework of the project ImpEx 
2 Technical description of the EGCS technology 
There are several information sources from classification societies, governmental authorities, 
research institutes and manufacturers describing the fundamentals and operation of the EGCS 
technology on board ships. Especially EGCSA (2012), ABS (2019), Lloyd’s Register (2012), 
Kjglholt et al. (2012) and US EPA (2011) offer an extensive technical description of EGCS. This 
report does not aim to describe into detail the EGCS technology. Thus, only a general description 
is presented in this chapter. Aspects related to the water management are discussed more 
extensively. 
EGCS, also called scrubber, is an established technology in the land-based industry sector for air 
pollution abatement (e.g. flue gas from combustion plants) and for recovery of valuable products 
from a gas stream. Depending on the medium used for removal of the target compounds, EGCS 
can be classified as dry and wet; the first type uses packed bed granulated chemicals and the 
latter a liquid stream (typically water) as absorption medium. 
In the maritime industry, wet EGCS dominate the market, while for dry EGCS just one 
manufacturer (EGCSA, 2012) and four installations (DNV GL, 2020) are reported. The reasons 
for the low acceptability are among others, the requirement for extensive space for dry EGCS 
installations which cannot be met by many ships and the huge amount of solid waste produced 
(gypsum). Wet EGCS are divided in open (OL) and closed loop (CL) EGCS, depending on the 
mode of operation; if the installation can be operated in both modes it is called hybrid EGCS. 
Figure 1 depicts the differences in the water management between open loop and closed loop 
EGCS. Independently of the type of system, water is pumped into an absorption tower and 
sprayed into the exhaust gas stream. In the absorption tower, SO, is transferred from the gas to 
the liquid phase and subsequently oxidized to sulphate species. The SO2 removal efficiency for 
every system depends on several factors (e.g. amount and quality of water, system design, 
temperature, initial SO» concentration, and chemical addition) that affect diffusivity and 
equilibrium solubility (US EPA, 2002). Removal efficiency can be above 98% (Fridell and Salo, 
2014; Lloyd’s Register, 2012). This process is called flue gas desulphurisation or SOx scrubbing. 
Figure 1: Process flow for the two modes of operation of wet EGCS: open loop (left) and 
closed loop (right) 
Open loo* > 
xhaust 
3 aut 
Scrubber 
YJilntion 
Water 
reatmen 
{unusua" 
im Ib“ 
+ 
Sloased loo05 ZGCS 
Exhaust 
gas out 
icrubber 
Process. 
+ap! 
a: 
Fresh- 
water 
Water 
Dr 
Jilution Water 
(optional) 
Holding tank 
{optional for zerc 
discharge) 
— 
il Discharge 
"water 
Source: BSH (2020). 
17