PIPELINE DREDGE ANALYTICAL AND SCHEDULINGPROGRAM

Derek Wilson1

ABSTRACT

A pipeline Dredge Scheduling and Analysis Program will assist the U.S. Army Corps of Engineers (USACE)Dredge Operations personnel streamline and improve the pipeline dredge planning process by providing ananalytical program to perform dredge pipeline transport analysis and a scheduling program to provide multi-ple hypothetical project comparison. These programs serve to reduce much of the labor intensive calculationsand analyses in pipeline dredge planning and scheduling. This paper provides the theoretical backgroundinvolved with the Pipeline Analysis Program and Dredge Scheduling Program. This paper further providesa hypothetical Corps pipeline dredge project with the scheduling results and calculations. This paper finallydescribes the benefits and limitations of the program based on the program output.

Keywords: Pipeline dredging, Dredge pump performance, Slurry transport, Pipeline dredge scheduling,Beneficial use of dredge material

INTRODUCTION

The Pipeline Dredge Analytical Program and DMPS Scheduling Program reduce much of the labor inten-sive tasks of analyzing and scheduling Corps pipeline dredge projects by consolidating the efforts into twoseparate and equal programs that rely on the attributes of the dredge, navigation channel, dredge materialplacement site (DMPS) and pipeline route involved in the dredge process. The programs rely on the factthat productivity depends on the dredge pump (or series of pumps) and the pipeline system. Productivitythen determines the possible schedule that the dredge project will follow while dredging the channel. Theprograms then output this resulting schedule as well as the dredge attributes associated with this schedulesuch as DMPS remaining capacity, environmental benefit and resulting pumping cost due to fuel consump-tion. This program output uses a concise graphical user interface display to provide Corps dredge operationspersonnel the essential information they need to conduct the dredge operation efficiently and effectivelywithout the need to perform intensive and repetitive calculations.

SOFTWARE METHODOLOGY

The program software consists of two basic parts: the DMPS Scheduling Program and the Pipeline AnalysisProgram. Each of these programs rely upon data objects to provide the variables and characteristics necessaryto perform the dredge calculations. The Pipeline Analysis Program calculates pumping cost and pumpproduction rates given the data objects in a dredge project. The DMPS Scheduling Program determines thedredge schedule, DMPS capacity and beneficial use of dredge material possibilities from the data objects ina dredge project.

Dredge Pipeline Transport Analysis

The pipeline analytical program solves for two important parameters on a given pipeline dredge and dredgepump configuration, production and power consumption. Production rate directly governs the time requiredto dredge material in the channel while power consumption correlates to fuel consumption, an increasinglyimportant cost factor. The pipeline analysis program incorporates slurry transport dynamics in the pipelinesystem and digitized pump manufacturer’s pump performance curves to determine the operating pointbetween the pipeline system and the dredge pump or pumps in series.

1Research Hydraulic Engineer, U.S. Army Corps of Engineers, Coastal and Hydraulics Laboratory, 3909 Halls Ferry Road,Vicksburg, Mississippi 39180, T: 601-634-4174, Fax: 601-634-3080, Email: derek.a.wilson@usace.army.mil

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Pipeline-Slurry Transport Dynamics

The pipeline analytical program develops a pipeline system relationship between volumetric flow rate in thedredge pipeline and the total dynamic head required to transport the material based on slurry transportprinciples developed and published by Wilson, Addie, Sellgren and Clift(1997). These transport principlesrelate system total dynamic head (TDH) to volumetric flowrate (Q) in the pipe. The system head curvesvary predominately with pipeline length, pipeline diameter, and bulk specific gravity of material delivered.Operations managers must consider a wide range of these pipeline lengths over the span of the entire dredgeproject. The pump manufacturer provides the pump-curve data for a given dredge pump. This pump curveillustrates the dynamic relationship between flowrate and TDH the pump imparts on the fluid and theresulting brake horse-power (b.h.p.) required to maintain this given TDH and Q.

Pump-Curve Intersection

The pump and pipeline system will always act at the intersection between the pump and pipeline systemcurve. The pipeline analytical program determines the intersection of the pump and system curves based onknown parameters of the pipeline system and dredge material such as the pipeline diameter, pipeline length,median sediment grain size, and in-situ bulk specific gravity (Smi). The analytical program incorporatesa bulking factor based on the in-situ material median grain size diameter to calculate a nominal deliveredspecific gravity, Smd. Given these system parameters, the pipeline analytical program develops a familyof pipeline system curves and plots them against the digitized pump curves. The program determines themaximum pump operating curve based on a maximum allowable RPM for the impeller and the maximumb.h.p. the dredge pump motor can deliver. The program then calculates the intersection of these curves todetermine the operating point for any given pipeline length. Figure 1 illustrates the system curves of varyingpipeline length, the pump curves and the maximum operating curve.

The pipeline analytical program plots this family of curves and reads off the intersection of the system curveand maximum pump operating curve through interpolation routines to determine a resulting flow rate, TDH,b.h.p., RPM and efficiency. The program determines the in-situ material production rate from flow rate as:

M = Q

(Smd − Sf

Smi − Sf

)(3600) (1)

where

M = production rate [m3/hr]Q = flow rate [m3/s]Smd = delivered material specific gravitySmi = in-situ specific gravitySf = carrier fluid specific gravity

The analytical program then returns the data table containing these parameters illustrated in Table 1.

Table 1: Pump and pipeline operating parametersPipeline Length [ft(m)] System Power [b.h.p.(kW )] Production Rate [yd3/hr(m3/hr)]

1,000 (304) 2,065 (1,538) 606 (466)2,000 (609) 1,810 (1,348) 491 (378)

4,000 (1,219) 1,526 (1,137) 373 (287)6,000 (1,829) 1,346 (1,003) 306 (235)10,000 (3,048) 1,094 (815) 211 (162)14,000 (4,268) N/A N/A

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Figure 1: Pump series and pipeline performance curves showing intersection between systemcurve and pump series composite curve and resulting performance point on one of the pumpsin the series.

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Pump Series Composite Curve

The pipeline analytical program computes production and b.h.p. for pumps in series to effectively calculatepump and pipeline production over long distances. The analytical program computes the resulting pumpperformance curve for pumps in series by vertically adding the TDH at every flow rate for each maximumpump performance curve in the series. Figure 1 illustrates the composite pump curve for a pump series. Theanalytical program then determines the resulting flow rate by the intersection of the system and compositepump curve illustrated by point B4 in Figure 1. The program then determines the performance of eachpump in the series by reading off the maximum pump performance curve at that flow rate denoted by pointB′

4. The program then adds up the b.h.p. for each pump to determine a total power consumption for theentire pump series. The pipeline program then outputs the pump and pipeline performance table similar tothat of Table 1. The analysis program then feeds these table data to the scheduling program for pump costanalysis.

Placement Site Scheduling Optimization Program

The Dredge Sequence Optimization Program provides Corps operations managers with the ability to base adredge project’s schedule by forecasting the factors and trade-offs involved with cost, production, placementsite capacity and beneficial use of dredge material. The optimization program uses rules–based programmingto evaluate different scenarios of which section of channel a pipeline dredge operates in and when and thelength and diameter of pipeline involved in the material transport. The optimization program determinesfour primary factors involved in the dredge project: pipeline pumping cost, pipeline production rate, DMPScapacity and beneficial use of dredged material. The optimization program evaluates these parametersbased on the relevant characteristics associated with sections of navigation channel, available DMPS’s andpipeline transport process all stored as objects within the program. The optimization program returns thelist of possible dredge combinations of dredge,navigation channel, and DMPS along with the resulting cost,production rate, DMPS capacity and beneficial-use parameters. The optimization program then feeds thesedata to a graphical user interface for users to view the dredge sequencing schedule results in a logical andconcise view.

Dredge Station Projects

The dredge sequencing optimization program starts with the user input of which channel sections to dredgefor any given dredge operation, the DMPS’s available, the pipeline routes available between channel andDMPS and the pipeline size and pumping capacity of the available pipeline dredge involved. The op-timization program bases the factors associated with the dredging operation on objects representing thegeographical, physical and functional characteristics of the dredge project. These objects provide the neces-sary and relevant attributes to calculate the efficiency, effectiveness and viability of the dredging outcome.

The Scheduling and analysis program analyzes the overall dredge project by dividing the project into indi-vidual channel station projects scheduled for dredging. The program forms these individual projects intodredge-station-project objects. The purpose of these objects is to break the problem solution down intofeasible channel increments where the program can analyze the dredge pumping cost and production param-eters on a step–by–step basis through the dredge process.

The Dredge station project objects contain the relevant parameters of the dredge process for a particularlocation. Each dredge station project will contain a value for DMPS used and the pipeline length spanningbetween the DMPS and the channel station. The program calculates the total pipeline length as the lengthof the pipeline route given in the pipeline-route object plus whatever distance remains between the entrancestation of the pipeline-route and the distance from there to the dredge station. Figure 2 illustrates this point.

The dredge station project object obtains values for the material type and volume of dredge material fromthe navigation channel object which contains the dredge material volumes for each station. The programdetermines the pipeline production rate and power requirement by sending the pipeline length and materialtype to the pipeline analysis program for output results. Given a dredge and booster pump series for thedredge object, the pipeline analysis program will determine the resulting production rate and power require-ment from pipeline length and material type.

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Figure 2: Relationship between scheduling program objects such as navigation channel sta-tions, pipeline route and DMPS.

After calculating the power requirement and production rate, the scheduling program will determine anominal pumping cost and time requirement. The program determines time from production rate, materialvolume and a bulking factor based on the type of dredge material. The Pipeline Analysis Program providesthe production rate and power consumption rate based on pipeline length. The scheduling program calculatesa pumping cost for the dredge project based on typical marine diesel engine consumption rates and the unitcost of marine diesel.

Dredge Station Sequences

The scheduling program develops a complete sequence of dredging projects for all of the channel stationsscheduled for dredging based on possible dredge station projects for each of the channel solutions. For eachchannel station, the program selects one of the possible dredge projects for that station and inserts it intothe sequence. For each and every channel station scheduled for dredging, the scheduling program developsevery possible sequence of dredge station projects in the order of the channel-station-dredge sequence. Thesedredge station sequence objects then form the cumulative dredging schedule and production results for theentire channel. The dredge station sequence objects contain the scheduling information the operations man-agers would rely upon to apply his or her engineering judgement.

The dredge station sequence objects contain the information of the resulting dredge project. The schedul-ing program determines the resulting capacity of each DMPS in the sequence, the aggregate pumping costof the sequence and the total volume of beneficial use of dredge material placed in the DMPS’s approvedfor beneficial-use. The scheduling program develops a timeline of the DMPS usage based on the DMPS’sobjects listed for the dredge-station-sequence. The program calculates the DMPS capacity timeline basedon the volume of material delivered through the pipeline, the DMPS area and the DMPS berm-height. Theprogram then outputs this DMPS timeline to a timeline graph as shown in Figure 3.

The scheduling program determines the dredge schedule for each of the channel stations in the sequencebased on the volume of material in the channel and the production rate of the pump and pipeline systemcalculated for the dredge station project. The program uses the early start date for the navigation channel

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Figure 3: Scheduling output with timelines of channels, DMPS and economic data.

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object as the initial start date. Then the program determines the finish date for the dredge project basedon the duration. The program then schedules each subsequent project’s start date and end date based oneach project duration. The program then outputs the Gantt chart of these projects to the graph as shownin Figure 3.

The program determines the timeline of cost and beneficial use volume from the dredge sequence objects.The program sums up the individual pipeline pumping costs of all the dredge station projects to producea total aggregate pumping cost and volume of material placed into the DMPSs approved for beneficial use.The program outputs these economic and environmental data to graphical form as shown in Figure 3.

Each of these parameters (timeline, DMPS capacity, pumping cost, and beneficial use dredge materialvolume) provide the operations managers with the basic and essential dredge project factors. These factorswill ultimately control whether or not any given dredge project proves feasible and economically viable.

SOFTWARE EXAMPLE APPLICATION

An example dredge project scenario provides the input required for the dredge scheduling program to calcu-late production and pump power requirements as well as to formulate viable dredge sequences and identifythe most economically viable dredge schedule. The example scenario starts with the Barataria Waterwayin Southeast Louisiana. The dredge scenario consists of a 3,500ft (1,067m) long channel section in need ofpipeline dredging. The two DMPS’s stand ready to receive material from this dredge project. the first DMPSserves as a regular DMPS for this channel material within close proximity. The dredge can place pipelinealong two routes in this channel for ease in pumping. The second DMPS serves as a beneficial use dredgematerial site approved as a restored wetland, but requires a 4.0 mile (6.5km) pipeline length to transport thematerial. Figures 4 and 5 illustrates this relationship and Tables 2, 3 and 4 provide the detailed parametersfor the Navigation Channel, DMPS’s and their pipeline routes, respectively. The example scenario considerstwo pipeline dredges for this operation, one 20 inch (0.508m) dredge and one 26 inch (0.661m) dredge. Bothof these dredges have identical hull and booster pumps. A 2,200b.h.p.(1,640kW) diesel powers the hull pumpcapable of 600RPM while a 1,850b.h.p. (1,378kW) diesel powers the booster pump also capable of 600RPM.

Table 2: Navigation channel dredge material volume by station.Station Number Station Volume [105m3]

105+00 2.60110+00 2.81115+00 1.18120+00 0.96125+00 0.70130+00 0.83135+00 0.61

Table 3: Dredge material placement site attributes.DMPS Area [km2] initial berm clearance [m]

DMPS-1 2.0 2.4DMPS-2 10.0 1.2

This example scenario evaluates the pump and pipeline production and pumping cost associated with dredgesolutions that identify the most economical dredge solution and the dredge solution with the maximumbeneficial use of dredge material volume.

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Figure 4: Example dredge scenario location illustrating navigation channel, DMPS andpipeline routes.

Figure 5: Close–up of dredge scenario location illustrating pipeline stations.

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Table 4: Pipeline route attributes.Pipeline Route Pipeline Length [km] Start Station DMPS Exit

Pipeline-1 0.4 105+00 DMPS-1Pipeline-2 0.5 130+00 DMPS-1Pipeline-3 6.5 135+00 DMPS-2

APPLICATION RESULTS AND DISCUSSION

The DMPS Scheduling Program and Pipeline Analytical Program solved for many possible solutions giventhe dredge material requirement in the navigation channel and the dredging resources in terms of pipelinedredge and placement sites. The scheduling program analyzed the performance metrics at the two extremeends of the dredging projects considering both a 20inch (0.508m) and 26inch (0.601m) pipeline dredge. Theprogram analyzed the dredging result of placing all of the dredge material in DMPS-1 and an alternativedredging result for placing all of the material in DMPS-2. These two different dredge scenario results offervaluable insight about the dynamics involved in varying the parameters in pipeline dredging.

The scheduling and pipeline analytical program calculated a fuel consumption cost of $164,946.32 for the20inch (0.508m) dredge to place all of the material in the closest DMPS (DMPS-1) spanning a total of21 days. The program calculated the 26inch (0.601m) pipeline dredge to take 19 days at a pumping costof $137,004.61 for the same DMPS. The program also calculated the results for pumping all of the dredgematerial along the 6.5km pipeline to DMPS-2. The 20inch (0.508m) pipeline requires a pumping cost of$326,401.87 spanning 50 days while the 26inch (0.601m) dredge completed the task for $270,747.73 in only31 days. Table 5 summarizes these results while Figures 6–9 illustrate the timeline, DMPS resulting capacityand economic factors for each dredge project.

Table 5: Pipeline dredge example scenario results.PipelineDredge Diam-eter

Beneficial UseMaterial Vol-ume [m3]

DredgePumpingCost [$]

Total Dura-tion [days]

26inch(0.601m) 0 $137,004.61 192,011,692 $270,747.73 31

20inch(0.508m) 0 $164,946.32 212,011,692 $326,401.87 50

By comparison, the 26inch (0.601m) dredge outperforms the 20inch (0.508m) dredge in terms of time andcost due to its lower friction resistance. These numbers indicate that the larger pipeline conserves cost byconsuming less fuel. While this principle holds true to some extent, the DMPS scheduling and pipeline ana-lytical program leave out consideration for other important factors such as the capitol and maintenance costsfor larger diameter pipelines and dredges. These factors could prove prohibitive under actual circumstances.Furthermore, the scheduling and pipeline analysis program consider only a constant maximum productionrate and subsequent project time based on production rates and dredge material volume. This principleneglects changes in production rate with fluctuations in the channel profile, dredge efficiency of the dredgecutterhead and maximum ”walking” speed of the dredge. Therefore, while the scheduling and pipeline ana-lytical program offer a reasonable start basing cost and time on the pump and pipeline system capacity, theprogram requires further refinement and incorporation of important factors in order to lend more accurateand valid results.

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Figure 6: Resulting timeline, DMPS capacity and economic factors for 20inch (0.508m)pipeline on DMPS-1

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Figure 7: Resulting timeline, DMPS capacity and economic factors for 20inch (0.508m)pipeline on DMPS-2

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Figure 8: Resulting timeline, DMPS capacity and economic factors for 26inch (0.601m)pipeline on DMPS-1

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Figure 9: Resulting timeline, DMPS capacity and economic factors for 26inch (0.601m)pipeline on DMPS-2

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CONCLUSIONS AND RECOMMENDATIONS

The Pipeline Dredge Scheduling and Analytical tool solves for the fuel consumption cost and pipeline pro-duction time for a given dredge operation with minimal required user input. While this program requiressome refinement concerning the incorporation of other factors governing cost and production, it does cur-rently offer Corps dredging personnel the ability to determine what a dredge can produce in terms of dredgematerial, how much fuel it will consume and the resulting DMPS capacity given the volume of material in thechannel, the size and initial capacity of the DMPS, the dredge and dredge pumps involved in the operationand what size and length pipeline spans between the dredge and DMPS. This will offer a reasonable pointfrom which to develop the program to assist the Corps operations managers plan and estimate costs for adredge project from start to finish incorporating and considering all necessary and appropriate factors. Thiswill result in reduced time and demand from Corps managers and their staff on the meticulous and laborintensive details of the dredge project freeing up their time and efforts to apply engineering judgement tomore pressing matters of the Corps dredge operation.

ACKNOWLEDGEMENTS

This paper summarizes the results of research conducted by the U.S. Army Engineer Research and Develop-ment Center, Waterways Experiment Station. Funding was provided by the USACE Dredging Operationsand Environmental Research Program. Permission to publish this information was granted by the Chief ofEngineers.

REFERENCES

Wilson, K.C., Addie, G.R., Sellgren, A., Clift, R., “Slurry Transport Using Centrifugal Pumps”,Blackie Academic and Professional, 1997. London.

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