Presenting an Ecco-Sustainable Approach to Decommission Offshore Wind Parks by Designing a New Ship, New Tools and Efficient and Reliable Procedure

Abstract

Comprehensive research has been performed about involved fleets and offshore supply chain in installation and decommissioning of offshore wind parks. The finding revealed that lack of suitable cargo vessel in this industry compel the contractor to transport the wind farms’ components with installation vessel. This logistic configuration which is coveted in this industry is not so efficient in terms of cost and environmental footprint, in particular, for the wind farm with large number of wind turbines, with long distance from shore and with deep water. This fact was proofed in the third chapter where the time-cost-emission analysis of various case studies explained. High charter rate of the installation vessel contributes to increase in the overall cost of decommissioning or installation, if the transportation of components performs with installation vessel. Thus, the authors strived to design a multi-function and multi-purpose green vessel in order to bring down the cost of decommissioning of offshore wind parks. Plausible explanations regarding the specification of the Decom Tools vessel are provided including the dimension, engines, onboard equipment, propulsion system, solar system and so forth. Moreover, the stability and motion analysis have been performed in the chapter 7 and 8 which shows the seaworthiness of the vessel in different situations and operations under different conditions and sea states. Significantly, after establishing the proper procedures and describing the method statements regarding all phases of decommissioning including, disassembly of wind turbine, removal of transition pieces, extraction of foundation and recovery of submarine power cables, time-cost-consumption-emission analysis for all above-mentioned phases of decommissioning undertake. Time-cost-consumption-emission analysis for disassembly of wind turbine has been explained in chapter 3. The mentioned analysis for the transition piece removal, pile extraction and cable recovery have been described in chapter 6. Offshore wind farm by the name of Hornsea 1 was the main case study in this document. The mentioned analysis for this wind farm for the phase of disassembly of wind turbines which includes dismantling of rotor, nacelle and tower, removal of transition pieces and extraction of monopile have be conducted. However, for recovery of out-of-service submarine cables, Anholt wind farm is selected as case study since more information and sources about this wind farm is available. The time-cost-consumption-emission analysis has been conducted with two different scenarios. The first analysis has been carried out based on base scenario which is execution of decommissioning reverse to the installation. In this case, the same vessels and logistic configuration has been selected for the analysis. Thus, in the first run of the analysis, the resulting cost, fuel consumption and emission are calculated with developed program for the base scenario. In the second run of the analysis, the analysis has been performed according to the proposed procedure and utilization of the Decom Tools vessel. This time, the logistic configuration and involved fleet of the decommissioning have been changed in order to reduce the offshore operation duration, project cost and mitigate the consumption and consequently the emission. The Decom Tools vessel is a multi-function and multi-purpose green vessel which can carry considerable number of wind turbine components. This capability led to reduction of the sailing time which lessen the fuel consumption and mitigate the CO2 emission. Furthermore, the designed blade seafastening (blade rack) and designed cutting tools, enable to cut the blades into the small pieces without spread of small piece of blades material into the sea and environment which pave the way for easier and cheaper onshore materials handling, transportation and recycling. Equally important, the designed hydraulic gripper at the stern of the vessel allows removal of transition pieces without deployment of construction vessel. Implementation of this tool onboard Decom Tools vessel eliminate utilization of construction vessel which has high charter rate, considerable fuel consumption and emission. The analysis of transition piece removal operation indicates that this innovative tool diminishes the cost and emission enormously. Not only the hydraulic gripper tool can be used during transition piece removal but also it can be utilized for pile extraction. Pile extraction can be executed with hydraulic grippers and the potent buoyancy of the vessel. In general, one of the cost drivers of the installation or decommissioning operations is construction vessel which can be either jack up vessel or floating heavy lift vessel. The proposed method of pile extraction with the hydraulic gripper and vessel’s buoyancy eliminates the use of heavy lift vessel, the diving system and subsea operations such as subsea cutting tools. The results of time-cost-consumption-emission analysis proofed that substantial saving in terms of time, cost and fuel consumption can be achieved if such tool and procedure can be executed. The other innovation which was presented in this document is the design of cable hydraulic gripper as well as establishment of the procedure for the recovery of out-of-service submarine cables. It is demonstrated that recovery of out-of-service cables can be conducted with some widely available tools and without using cable laying vessel. The proposed procedure is discussed with specialist of this industry and they confirmed the feasibility of the procedure