reduction of the emissions for trailing suction hopper dredges during operation

Abstract

The International Maritime Organisation (IMO) is a specialized agency responsible for the safety and security of shipping and the prevention of marine and atmospheric pollution by ships. Air pollution is one of the contributors, CO2 emission is recognised as the biggest contributor to the increasing temperature of the Earth. Global warming is a controversial topic and actions are taken to reduce further rising of the temperature on Earth. The IMO has set limits for vessels on the emission of NOx and SOx. Currently, the IMO is negotiating on how to limit the emissions of CO2 to reach a reduction of 50% in comparison to 2008. The purpose of this research is to provide an emission model for TSHDs showing an emission profile (CO2, SOx and NOx) per cycle of operations, and present emission reduction methods. Within the emission model there are eight main parts that are connected and create the results. The results are shown per cycle of operation and are calculated per phase. The six main phases of a cycle of operation are: Loading, transit loaded, connecting, discharge, disconnecting and transit empty. The first part of the emission model determines the hull resistance. The second part consist of the trailing resistance. This part is split up into three more detailed segments: the calculations for the cutting force, cutting depth and trailing force. The trailing and hull resistance together form the total resistance within the loading phase. For the transit phases, only the hull resistance is used for the total resistance. With the total resistance known, the propeller is matched to the main engine in the third part. The fuel consumption and emitted emissions are calculated in the fourth and fifth part. The power requirement for the other engines, pumps and auxiliary equipment are calculated in part 6th through 8th. For each job, specific input is required for the calculations. Combining this input and the calculation parts, the emissions, fuel consumption and fuel cost are given per dredged m3.
Five methods to reduce the emissions for TSHDs are researched. First, the type of power arrangement is researched. A mechanical power arrangement with a combined drive and a direct drive, an electrical power arrangement and a hybrid power arrangement are investigated. The variations of power arrangements are implemented on the Dodge Island. Second, the difference between a fixed (FPP) and controllable pitch propeller (CPP) is researched. Most modern day TSHDs use a CPP, as the efficiency during the wide variation of operating conditions is greater than a FPP. The third method to reduce the emissions is to find the optimal loading speed. The optimal speed is researched for a floating visor and a fixed visor. The most common solutions to comply to the limit of the SOx emission is using ultra low sulfur diesel or installing a scrubber. The fourth reduction method is focussed on the use of scrubbers. The most used types of scrubber are the dry, open loop, closed loop and hybrid scrubber. The last method to reduce the emissions is shutting off the engines when not in use. The trade-off is the wear of the engine. To verify the results of the emission model, the fuel consumption of multiple completed jobs is compared with the predictions of the emission model.