Developing a sustainable dredging strategy

The environmental impact of dredging  activities has been a point of discussion  for a long period. Over recent years more emphasis is put on sustainability  by different stakeholders in answer to the  effects of pollution, shortage of resources  and stress on ecosystems. It is our task to combine sustainability requirements with  the ever increasing demands on dredging  applications.  To date, dredging equipment has been designed from an economical point of  view. The social balance is more or less easily attained depending on the situation.  The challenge is to balance this design  philosophy with ecological requirements,  without compromising economy. To influence  this development, instruments such as  EIA (Environmental Impact Assessment)  and legislation have been used and/or are  further developed. Legislation has been  a key driver for the balance with ecology,  however, execution of dredging projects  in a more sustainable way can also present  important social and economical benefits. 

EcoShape project 

The Dutch dredging community, guided  by Boskalis and Van Oord took up this  challenge by announcing the start of  their “EcoShape: Building with Nature”  programme (www.ecoshape.nl). As a major  dredge designer and builder, IHC Merwede  also participates in this initiative in order  to be able to use the results in their own  development programmes for more sustainable  dredging technology. Only incremental  adaptations will not be sufficient to develop  really sustainable products which requires  more challenging innovative steps. Product  innovation will allow more accurate and  better controlled dredging, minimise and  if possibly eliminate the negative effects of  dredging on the environment and optimise  its profitability  Besides supporting the EcoShape  programme, IHC has defined its own long  term development programme which should  result in “green” dredging technology and  equipment that will meet the future requirements  on sustainable dredging equipment.  This must assist the dredging world to cater  for the required sustainable ways of operation.  IHC’s long term programme called  “Sustainability and dredging” commenced  in October 2007 to look at all sustainability  issues within the dredging industry and  identify the consequences for the requirements  of our future products.  Over the last two decades, IHC Merwede  has made adaptive and innovative progress  on development of sustainable dredging  to reinforce its market leading position,  including techniques, equipment and  management aspects of dredging. Critical  research was carried out in close cooperation  with governments, leading research  institutes, environment consultancy, and  dredging contractors. Advanced knowledge  has been successfully implemented leading  to the state of the art of ‘green’ dredging  equipment and techniques.  Driven by a number of global trends  of growing economy, migration towards  coastal zones, high demand for energy and  other natural resources, dredging projects  become more demanding and sensitive.  These changes require extensive innovative  dredging projects, which challenged IHC to  take incremental steps towards innovative  equipment, systems and components. Most  important improvements involve deeper  dredging, larger capacities, higher accuracy  and efficiency improvement. 

Awareness grows of environmental and  water ethics, and the welfare of future generations  both human and nature. As a result,  IHC recognises that incremental steps of  continuous adaptation and innovation of  dredging equipment and technologies are  not sufficient. More proactive steps towards  sustainable dredging, shifting paradigms,  are on the agenda to explore new technical  solutions. These solutions are required to  achieve the vision of dredging harmonised  with nature.

Minimising turbidity

 The major incremental steps of the last  decades focusing on dredging process,  equipment and construction: incremental  steps to reduce turbidity included careful  choice/adaptation of dredging equipment  and procedures. For instance, to minimise  development of turbidity clouds, screen  undersize discharge is placed underneath  the keel of the vessel of a gravel dredger.  Other, currently available solutions for  turbidity reduction include: strong, cone shaped  overflow control valves; automatic  starting and stopping of the dredge pump  only when the drag head suction pipe is near  the bottom; hopper dredgers with variable  volume to cater for silt dredging; and the  reduction of direct impact of dredging activities  has also been achieved by improving  accuracy of the dredging activities.  Optimised hull design of at the stem  (bulbous bow) and stern (twin gondola  design) has also led to a significant reduction  of the resistance and improved inflow,  increasing the efficiency of the propulsion  system. An increase of the hull width at  equal length and draught boosted carrying  capacity, further improving transport  capacity of the dredger. This relatively small  draught makes these vessels extremely  suitable for beach nourishments as they  can access beaches much easier, saving on  pumping distance. Energy saving is also  achieved by development of high efficiency  pumps, that require less power than comparable  standard pumps. All these improvement  are heavily supported by required  CFD calculations.  As society becomes more and more aware  of the importance of the development of  sustainable products and sustainable production  the industry must take the responsibility  to take the lead in development of  sustainable dredging equipment, balancing  economy, ecology and society, and these  have been defined in the following three  spearheads of the sustainability programme:  turbidity control; energy issues and emission  control, and sustainable design & construction  methods involving the whole chain  During dredging activities, concern for  turbidity and suspended sediment impacts  increases if ambient water conditions are  normally clear. Submerged aquatic vegetation,  corals and other species requiring clear  water habitats are especially vulnerable.  These species may be adversely affected  by changes in light penetration or by thin  layers of fine suspended sediment  During dredging, increases in the level of  suspended sediment will particularly occur  as result of the excavation process, vertical  transportation, overflow losses, pumping  poor mixture overboard and underwater  disposal. During the dislodging process the  cohesion of the in-situ material is broken  and part of the material can be brought into  suspension by the cutting movement.  During vertical transportation, dredged  material sediment in direct contact with  the surrounding water (in an open bucket  for instance) dilutes, resulting in an increase  in suspended sediment content in the  surrounding water. The overflow of excess  water from the hopper without precaution  measures to the overflow system inevitably  brings sediment into the water. Dumping  material through the bottom doors at relocation  sites causes results in dispersion  during the fall from surface to sea floor.  Turbidity control is foremost defined by the  dredging process and equipment adaptation  and innovation of technology plays an  important role.  The EcoShape programme, Building  with Nature includes interesting topics to  improve understanding of the dynamic,  adaptive behaviour of complex ecosystems  and their resilience in the face of disruptions.  The ability of an environment to  tolerate external stress factors and maintain  its life-supporting capacity is called  ecosystem resilience. Ecosystem resilience is  a complex concept, and there is no internationally  recognised procedure to determine  it. Therefore, it is necessary to identify  site specific indicators and parameters to  measure and analyse ecosystem resilience.  Turbidity is not very harmful until its  level is significantly higher than the natural  level in a water body, as local flora and  fauna have adapted to these levels. Case  studies are required to determine the how  ecosystem resilience is affected by increased  turbidity levels.  Recently, IHC have initiated a variety of  R&D topics on sustainable dredging. Studies  are being carried out to gain understanding  of the ecosystems IHC customers operate  in, and to bridge the gap between society,  economy and ecology, so that dredging can  be evaluated against a broader picture of  natural resources, interest of society and  economy. 

Alternative Energy 

IHC is also evaluating alternative energy  needs. Ships use lower grade fuels as  energy source. On world scale these fuels  are merely considered a bi-product of the  refinery process. These low grade fuels  could be upgraded, albeit at high costs.  Primary worldwide energy streams would be  disrupted if all ships turned to other, hydrocarbon  based, energy sources such as light  distillates. As a result, stakeholders accepted,  until recently, the disadvantageous harmful  emissions in the exhaust gases of the ships’  prime movers that resulted from use of these  lower grade fuels  In April 2008, a new text of Marpol Annex  VI was agreed upon by the IMO’s Marine  Environmental Protection Committee in  London [MEPC, 2008]. Implementation of  this legislation will have a dominating impact  on the development of propulsion systems in  the near future. Annex VI demands a significant reduction of the emissions of Nitrogen  Oxides and Sulphur Oxides. 

In Sulphur Emission Control Areas  (SECA’) only fuel of class DMA or light  distillates will be accepted from 2010  onwards. After 2014 sulphur content  of most fuels as we know now will be too  high for use in SECA’s. Only diesel fuel  used in cars is sufficient. In other areas  the requirements are less severe and gasoil  of grade DMX or better is still sufficient.  IHC believes that we either continue the  use of fuel oil as energy source, or change  to alternative energy sources. To reduce  NOX emissions with the required 80% in  2016, only two potentially feasible solutions  are available at this moment. TNO  in the Netherlands is developing a plasma  assisted gas cleaning process. This process is  claimed to remove about 50% of the NOX  emissions, while the target is a reduction of  70%. Selective Catalytic Reduction (SCR)  potentially reduces NOX emissions by 90%.  Wärtsilä has already successfully tested out  SCR on a paper carrier.  Although this system has a lot of potential,  IHC still sees problems blocking implementation  on a large scale. The reduction  of SOX to acceptable levels requires reduction  of sulphur in the fuel before burning it  in the diesel engine, or removal of sulphur  from the exhaust gasses. On board sea water  scrubbers could be used and this process  potentially removes up to 75% of SOX from  the exhaust gases  The scrubbing process produces CO2  (about 2.64 kg of CO2 per kg of removed  sulphur), but taking into account the entire  production process including refinery emissions,  use of Heavy Fuel Oil (HFO) with  a sea water scrubber produces slightly less  CO2 than use of MDO with a scrubber. As  a positive effect of the scrubbing process,  particular matter (PM) in the exhaust gasses  is reduced (claims are up to 80%). The sea  water disposed after the scrubbing process  has a reduced pH of approximately 6.5. An  alternative is to remove sulphur from HFO  in the refinery but it is expensive to adapt  the refineries for sulphur removal from  HFO, both in price and in man-hours and  it is not expected that oil companies will  be willing to provide shipping with HFO  without sulphur.  Shipping could also turn away from  use of HFO, and only use light distillates.  This will have a significant impact on oil  prices. HFO consumption by ships amounts  approximately 9.4% of the worldwide oil  production. Shifting to light distillates will  further stress the market of these fuels.  HFO demand will drop. The impact on  prices and availability are significant. This is  not a desirable option. All these considerations  discard the real sustainability problem.  At the end of the line use of oil as energy  source is not sustainable. World oil reserves  are finite and sooner or later we will have to  consider other energy sources.  Synthetic fuels might be an option for  shipping, but a solution of this kind should  come from the oil industry and chemical  industry. If this possibility emerges, IHC  will certainly consider this possibility. LNG  is certainly a potential solution, particularly  on short sea shipping. Gas production is  much higher than gas consumption, and the  excess production is more than sufficient  to supply all ships with energy. For energy  conversion we could use either a dual-fuel  diesel-engine, or a gas turbine. Especially  the latter solution has a very high power  density, saving space and weight. Disadvantages  are the space requirements of the gas  tanks and the strict requirements imposed  on such ship by the authorities.  Batteries are a potential solution, but  at this moment far too expensive and too  heavy to be a feasible alternative. Fuel cells  may form an alternative in the future. At  this moment, the largest available units  provide about 20 kW. In the future, we could  consider fuel cells as alternative for auxiliary  or port generators. Wind energy could be  an option for auxiliary too. As main energy  source, wind energy is not a feasible option.  A large wind mill produces about 1000 kW  of power. About 20 large wind mills are  required to supply energy to a large dredger,  such as HAM 318. As auxiliary energy  source for remotely located consumers,  small windmills could be an option. Solar  cells currently produce too little energy per  square meter (approximately 120 W/m2).  Current generation solar cells could only be  used for small, remotely located consumers.  Contrary to wind mills, solar cells may be  strongly improved in the future. This would  make solar cells a potential auxiliary energy  source. Finally, bio fuels are subject to a lot  of discussion at this moment.

 Functionality requirements

 IHC is also addressing the re-design of its  products starting at the level of functionality  requirements, instead of only improving  existing products, which allows for a careful  choice of materials and production processes,  which in turn, should result in more  sustainable products. An integral life cycle  perspective that addresses the more important  issues in each phase of the product’s life  cycle can also lead to significant improvements  in the equipment’s sustainability and  optimises the effective and profitable use of  dredging equipment.  Design for dismantling has been identified as a potentially important issue.  Guiding principles are improvement of  maintainability and maximisation of re-use  of parts and materials. Further development  of LCCA (Life Cycle Costing Analysis)  tools will lead to progress in this direction  together with the introduction of controlled  dismantling facilities for dredging equipment.  Such facilities stimulate re-use and  recycling, create local jobs at the dismantling  sites and decreases risk of accidents  and spills. IHC believes this is a desirable  development in its CSR (Corporate  Social Responsibility), with very positive  impacts in terms of social acceptance and  market leadership. Additional advantages  are control of the destination of key technology  components (avoiding unauthorised  use/copy) and reduction of old, low efficiency, more polluting dredging equipment  in a controlled way. This also eliminates  unwanted competition for direct customers  by third parties with the use of second-hand  or even third-hand equipment.  Lastly the issue of maintenance: with  dredging vessels being often used intensively  and under extreme conditions, the design  for maintenance has an important impact  on the minimisation of equipment downtime.  This includes design for assembly (e.g.  shortest possible replacement time of wear  parts such as cutting tools, dredge lines and  centrifugal pumps), and optimising maintenance  activities. Improvement of the  wear-resistance of materials and monitoring  critical wear components will further reduce  maintenance costs and down-time.  The future dredging equipment should  both keep its quality and profitability, and  have a positive contribution to the environment  and society during its entire life cycle  (production- use and maintenance-end-of life).  This is the great challenge, IHC believes,  and the company looks forward to future  dialogue with stakeholders who are willing  to discuss these areas and provide them with  their suggestions and co-operation.  The Central Dredging Association  (CEDA) is an international professional  membership association for all those involved  in dredging related activities and who live or  work in Europe, Africa, or the Middle East  . CEDA provides an independent forum for  the exchange of knowledge in fields related  to dredging, maritime construction and  dredged material management. Members  are drawn from many fields and include  consultants, research and educational institutes,  port authorities, government agencies,  dredging contractors, builders of dredging  vessels, and suppliers of ancillary equipment.  CEDA encompasses a wide range of disciplines  and activities and does not represent  the interests of any particular industry sector.  (www.dredging.org) 

This article is based on a presentation  given by MTI Holland B.V. at the CEDA  Dredging Days Conference held in October  2008 in Antwerp. Research by MTI staff  R.G. van de Ketterij, M.B.G. Castro, R.  Li, H. van Muijen, C.H.M.Kramers, P. M.  Vercruijsse, H.H. Bugdayci.  For further information www.mtiholland.  com.  Copyright – CEDA. Reproduced with the  kind permission of CEDA secretariat. www.  dredging.org