Marine organisms frequently experience pH fluctuations but prolonged periods of depressed pH can cause considerable harm (Knutzen, 1981), therefore, the scrubber discharge pH recovery must occur very rapidly. This paper is structured as follows: in Section 2, we describe 17-AAG datasheet mathematical fluid flow and chemistry models that describe the behaviour of acidic jets and plumes in an alkaline environment. In Section 3, design solutions are proposed to satisfy the necessary IMO MEPC guidelines for acidic discharges which take into account the discharge acidity, required flow rate, seawater alkalinity, ship power, the size of the discharge
port and dilution prior to discharge. Conclusions are presented in Section 4 and the titration procedure that is critical to determining the seawater buffering capacity is described in Appendix A. Consider a scrubber
generating an acidic effluent from seawater with a volume flux QsQs and acidity Cas. Onboard the ship, the wash water may be diluted with an additional QwQw resulting in a total volume flux Q0=Qs+QwQ0=Qs+Qw at the point of discharge. The onboard see more dilution factor DonboardDonboard and the resulting acidity Ca0 at the point of discharge are equation(1a,b) Donboard=QwQs,Ca0=(Cas-Cb0)QsQs+Qw,where Cb0 is the alkalinity of the ambient seawater. The inclusion of DonboardDonboard may be useful to ensure pH recovery in especially low seawater alkalinity regions. At the outlet why Q0Q0 can be increased with a larger number of nozzles N equation(2) Q0=Qs(1+Donboard)=πb02u0N,where b0b0 is the radius of the nozzle and u0u0 is the discharge velocity. Between the wash water leaving the ship and reaching a distance of 4 m, the fluid has been diluted by a factor of DjetDjet. The total dilution (DTDT) that has occurred from the scrubber to the distance of 4 m from the discharge nozzle is equation(3) DT=(1+Djet)(1+Donboard)-1.DT=(1+Djet)(1+Donboard)-1.In
a time averaged jet DjetDjet indicates the amount of dilution on the jet centre line, a region where dilution will be at it’s lowest. Two characteristic velocities are of importance in this problem, the flow velocity in the discharge pipes upup and the discharge jet velocity u0u0 at the nozzle. The constraint on the flow within the pipe is that cavitation does not occur, requiring that the pressure P satisfies equation(4) P=Pa+ρgh-ρup22>Pv,where PvPv is the cavitation pressure of the water, PaPa is the atmospheric pressure, ρρ is the the density of the water, g is acceleration due to gravity and h is the depth of discharge. Observations on the phenomena of cavitation were first published by Reynolds (1873). The potential to cavitate depends on water depth, water quality and the smoothness of the pipe internal surface. The flow speed can be increased by reducing the friction coefficient of the pipe through e.g. acrylic coating.