A Practical Implementation of the Slurry Transport Theory to Determine Dredging Performance
Type:
Presented during:
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
Authors:
R.P.C. Bekkers, E.A. van Duursen
Abstract
"For dredging operators it is crucial to know the performance of their dredging equipment before executing a project. Frequently asked questions are: what will be the production? Is the dredger applicable for this type of project? Do I need a booster station on shore? Most of the questions can be answered by the practical experience of the operator in the field. However, it might be the case that an operator is too conservative or is dredging at a sub-optimal working point while facing projects with changed circumstances. Within the literature, different theoretical slurry transport models are available to determine the working limits of a pump-pipeline combination. While they generate useful information, small and inexperienced contractors are still struggling to use these theoretical models in their project. Within Damen, an intuitive tool ProDredge is created to make the theoretical model practically available for its customers. ProDredge can be used for all different types of dredging operations and is based on the DHLLDV model of S.A. Miedema. To use this tool only a limited amount of input parameters of the dredge system must be known. Starting with the soil characteristics. Pre-programmed soils can be selected that cover most of the soils in the dredging industry. When the required type of soil is not available or a detailed soil investigation is done by the operator, for instance the particle size distribution can easily be adjusted by changing the input values. Next is the project lay-out. Here, the dredge system can easily be configured by adding pipes with different properties such as length, diameter, size and roughness (figure 1). Bends can be added in a different radius and multiple pumps can be incorporated in the dredge system with different characteristics. In addition to the DHLLDV model, a drive characteristic model (power vs revs) is integrated, incorporating the smoke and power limit as well as the minimum and maximum revolutions. All Damen dredgers are standard configured in the ProDredge. For non-Damen dredgers, the pump/drive characteristics can be added to the program. When the dredge system is determined, a working point can be found by changing the dredge pumps rpm and material concentration. As a result, four different graphs are generated by the program: The first graph shows the QH- curves (the total head vs the capacity). Two lines are presented, one line represents the resistance of the discharge pipe when pumping water or a mixture and makes a distinction between stratified, heterogeneous and homogeneous flow. The second line represents the total head of the pump. The intersection between the two curves, represents the working point. When the anticipated concentration is known, ProDredge can iteratively find its optimal working point. When there is no working point found, the dredge system exceeds one of the limits, such as the limit deposit velocity or the amount of power available. The second graph shows the required power at the pump shaft at the given working point. Here, you want to keep some margin in available power to be able to cope with sudden changes in the dredging process. The third graph shows the efficiency of the pump, where the operator can look for the best efficiency point to dredge as sustainable as possible and reduce the amount of wear to the dredge pump. The last graph shows the required NPSHr (net positive suction head required) of the pump in combination with the NPSHa (net positive suction head available). The NPSHa should be above the NPSHr at the working point for avoiding cavitation. All the graphs are automatically built into a report which is easily readable for the"
Keywords: ProDredge, DHLLDV, Slurry, Transport, Sediment, Pipeline, CSD, TSHD, DOP, Production, Pump, Drive Systems.