Emission Profile and Emission Reduction for Trailing Suction Hopper Dredges During Operation
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
C.M.D. de Roode, S.A. Miedema, M.D. Beton
"The largest dredging company in the United States is Great Lakes Dredge and Dock (GLDD). GLDD operates multiple large dredges, including six trailing suction hopper dredges (TSHD). 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. 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 the Dredge 1. 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. The results show that for Dredge 1 a mechanical power arrangement with a combined drive emits the least CO2. With a CPP, the fuel consumption and thus the emissions are reduced. It is found that the optimal loading speed depends on the manually set limit for the penetration depth of the jets. Within the model the optimal speed is 0.70 m/s. The most promising scrubber for TSHDs is a closed loop scrubber which reduces the SOx emission with 96% and reduces the particular matter with 60%. Reviewing one operation of Dredge 1 shows a reduction of 0,5% in fuel with shutting off the main engines when not in use."
Keywords: TSHD, dredge, carbon footprint, emission reduction, emission profile