Civil Design for Fire Fighting - Term Paper Example

NEC 3202 Civil Engineering Design 1 Part 2 Semester 2 2016. 1.0 Pump system and pipeline design 1 The Arthurs Seat area above Dromana on the Morniton Peninsula (Melway Ref map 159) is in need of an emergency water supply. At present the area is supplied from the East along Arthurs Seat Road but is of limited capacity, and the intention is to look for another major pipe system to supplement the existing supply. The emergency to be met is a fire fighting capacity of 30l/s for a 6 hr period, but also to augment the limited daily supply. The permanent population is 350 at present, but daytrippers in summer take this to population equivalent 850 all with a demand of 150 l/h/d. The pump where ever it is located has to be able to lift the water to the top of existing steel tank at RL 312 m The water from this high level tank is to supply the local residents around the summit and be available for fire fighting emergencies. Your team is required to determine the pipe alignment, design the pipes - the rising main, the suction main for the pump, and detailed pipe work within the pumping station, and specify a suitable pump(s) to provide the duty. Sketches of the detailed layout in the pump station are required. Total water requirement for fire fighting Water requirement 30l/s for 6hrs Total water requirement =30x6x3600=648000l/day=648m3 Equivalent population = 850 Demand=150l/h/d Total water demand for the equivalent population=150x850=127500l/day=127.5m3 From the calculation it can be seen that he water requirement for fire is much higher than that for normal use of the population. Bearing in mind the high cost associated with water infrastructure the design will be such that during a fire incident all the water will be directed towards fighting the fire. We are to consider the design that will be able to supply enough water for fire fighting Therefore for this design we are taking the pumping requirement to be total water requirement for fire fighting Taking the pumping time per day to be 8hrs Velocity through pipe= ie  Discharge= Total volume/Time =648/(8x3600)=81m3/h =0.0225m3/s Taking the speed through pipe to be 1.5m/s And using  But A= Or  2.0 Total static head The static head for any pumping system can be identified as being the difference in water level at the suction point and delivery reservoir. These means that that the total static headis dependant on the prevailing site conditions between suction point and delivery reservoir and the point where the suction and discharge points are found on the reservoir. The determination of this is to be through site conditions. 2.1Pressure loss due to friction head in pipeline The head due to friction (hf) gives all the pressure losses incurred attributable to fluid flows within the pipes. The friction head loss is compost of the losses in the pipe due internal wall roughness and the losses that come as a results that are on the pipeline right from the inlet up to the discharge point. Assuming a constant flow ate in a pipe , the losses in head attributable to friction comes as a result of the material from which the pipe is made of, the length of the pipe, the size in terms of diameter and the type and number of fitting that are on the pipe. Thus it is possible for one to compute the loss upon the pipeline specifications are established. 2.2 Total head The total head that is to be overcome by a pumping system is given by expression Giving the Total or dynamic head that the pumping system is to overcome - Represents the height to which the water is to be raised by the pump - fluid friction losses experienced in pipeline 3.0 Preliminary design procedure for pumping system In coming up with a design of a pumping system we look at the following Site conditions surveys Pipeline selection Pump selection 3.1 Site conditions surveys This is the step that is important in determining the available opportunities and constraints that are presented by the environment where there is installation of the pumping system. Here the important data that is being sought is the static head that the pumping system is to overcome and the length of the pipeline. Pipeline route and length The specification of pipeline length is determined through a survey of the intended pipeline route Determination of static head This is the level difference between suction reservoir and delivery reservoir. 3.2 Pipeline selection The pressure loss due to fluid friction in a pipeline depends on several factors: pipe size, material, length, fittings and flow velocity. The total (dynamic) pressure head that the pump much overcome partly depends on the pressure loss due to fluid friction in pipeline and hence on pipeline data. The selection of the pipeline should therefore be done before that of the pump, because pipeline data will influence the selection of the pump. A preliminary selection of the pipeline is therefore made using a recommended flow velocity for water pipelines. This flow velocity recommended for preliminary design of water pipelines is chosen such that pressure losses due to fluid friction in pipeline are kept within acceptable limits. This ensures that pumping equipment size and costs are also kept within limits. The recommended range of flow velocities for water pipelines, to be applied during preliminary design, is between 1 and 3m/s. After this preliminary stage , the design specifications should guide further decisions Pipe size selection In a system design selecting the size of pipe to be used comes first. In selecting the size, the flow in the pipe should be such that the velocity in the pipe when the right discharge is passing through should in the right range (between 1m/s and 3m/s). The flow speed guide is important as it aims at ensuring that the speed is not too high to reul to turbulent flow that would mean high friction loss at the same time very slow speed are to be discouraged as this would required higher diameter pipes which are expensive in order to deliver the desired discharge. Also too low speed in some pipe will result to some solid settling in the pipeline which would eventually lead to pipe blockage. There is to be address on the size of the pump to be used and size of pipe to use. The pump should be of a size that will be able to overcome the total head. In long distance pipelines the friction depends highly on the size (diameter) of pipe and this determine the size of the pipe. This means that a small diameter pipeline would require to have a bigger size pump. Pipe material selection The loss in pressure within a pipeline is a product of the diameter of pipe, the material type and finishing, the length of the piping system and fittings included on the pipeline. This means that selecting of the material to be used in the pipeline is a very important aspect. While some materials may be durables, other may be good because of being cheap, others may be lighter and easy to install but in making a choice one need to be aware the consequence on head loss. Head loss due to friction in pipeline With the size of pipe selected, it will be the right time for head loss attributed to friction to be selected. Total pressure head on pump The total head which the pumping system is to overcome is is the dynamic pressure head that is to be overcome by pumping -Total static head to be overcome by pumping -Pressure head loss due to fluid friction in pipeline In the present case the total pipe work length is 2km The energy loss can is given by the Darcy-Weisbach equation Where head loss in metres in the fluid =is dimensionless friction factors taking 0.002 for PVC L=Pipe length in m=500m D=Pipe diameter in round pipes g=gravitational acceleration (9.8m/s2) The head loss due to friction is seen to be relatively low and can be increased to 5m to carter for minor losses due to connections and bends in the pipeline The static head =HL = 312m 3.2 Choosing of pump able to satisfy specifications The person designing the system is then expected to make a choice of for the pump type and size that will serve purpose putting into consideration the total head that is to be overcome and also the discharge required. 3.2.1 Net positive suction head (NPSH) It is important to note that a pump is not supposed to such liquid so as to pump. This means that there is need to have a positive pressure head at the pump inlet so that the liquid can be pushed in the pump. NPSH gives a measure of this pressure head that is needed at the inlet of the pump. 3.2.2 Net Positive Suction Head Required (NPSHR) Net positive suction head required (NPSHR) is an important characteristics associated with pump. The NPSHR necessary for a pump is the least pressure needed at the inlet of the pump in order for the pump to give satisfactory performance. The NPSHR for any pump is determined from the design and this is one of the information that is given by the manufacturer. 3.2.3 Net Positive Suction Head Available (NPSHA) Net positive suction head available (NPSHA) is the actual fluid pressure at the pump inlet, which comes as a result a certain suction design and for a particular site conditions. The difference between (NPSHA) and NPSHR is a variable that is of interest by the design in controlling suction. It is the endeavour of the designer that the NPSHA should be above NPSHR for any selected pump in order for pumping to take place The (NPSHA) for a particular suction design is given by the expression: NPSHA (for design with positive suction head  NPSHA (for design with negative suction head  -atmospheric pressure operating at site moW -Pressure head loss due to fluid friction in pipeline -vapour pressure With NPSHA partly being determined by the prevailing site conditions while NPSHR being the characteristic of the pump, it is important for the two factors to be considered with utmost care more so in a situation where there is anticipation of negative static suction. 3.2.3 Increasing NPSHA With an existing suction piping network, there is little that can be done to have NPSHA increased. However, these are the few possibilities Having the free liquid level increased with respect of pump as these will cause an increase in the static head or it will result to a reduction in static suction lift. Reduction in the distance between the suction point and the pump location, as these will result to reduction of the suction pipe length and thus reduction in fluid friction in intake pipe Elimination of fittings that are in the suction pipe inlet as these will ensure reduction in minor losses 3.2.4 Reducing NPSHR Reduction may be through Placement of a throttling valve in the discharge line so as to ensure increased total head that the pump is supposed to overcome, thereby reducing the discharge flow rate of pump. By so doing the operating point of the pump is shifted to a point with lower discharge that has a lower corresponding NPSHR. Having a double suction pump being substituted for a single suction where there is lower NPSHA requirement 4.0 Cavitation It is a malfunction in the pumping system, that has a link to the suction design and this means cavitation avoidance should be an important consideration when it comes to planning a water pumping system . a reduction in pressure fluif below vapour pressure will see the formation of vapour pockets ie there will be boiling. Upon the vapour pockets reaching the impeller surface , they will collapse as a result the higher pressure . these is accompanied by noise, vibration and may also result the pump being damaged 4.1 Procedure for checking for cavitation The check for cavitation is an important step in suction design. The object of this step is to ensure that the NPSHA at pump inlet exceeds the NPSHR of the selected pump, by the required margin of safety. The procedure below provides such a check: i. Determination of the NPSHR for selected pump. ii. Calculate the NPSHA. The steps involved are Establishing the atmospheric pressure and altitude with the variation being as shown in table 1 while the variation of vapour pressure of water with temperature is as in table 2 Determination of temperature at the pumping station and hence vapour pressure of the water using table Conversion of atmospheric pressure to meters of water Conversion of the vapour pressure into meters of fluid to be pumped Having a solution of NPSHA using expression NPSHA (for design with positive suction head  NPSHA (for design with negative suction head  iii. If the NPSHA obtained from step 2 is greater than the NPSHR obtained from (1), no cavitation will occur. A good safety margin is 1 meter head of liquid iv. If NPSHA is insufficient, certain steps may be taken to remedy the problem. The two options for this are : increase NPSHA or reducing NPSHR Table 3.1 Variation of atmospheric pressure with altitude Altitude in m Average atmospheric pressure 0 10.33 250 10.0 500 9.75 1000 9.20 1500 8.60 2000 8.00 3000 7.00 Table 3.2 : Variation of vapour pressure with temperature for water Temperature in Vapour pressure of water in (MWH) 10 0.12 15 0.17 20 0.23 30 0.43 40 0.77 50 1.26 90 7.30 100 10.33 5.0 Calculating NPSHA for the system NPSHA  The atmospheric pressure is taken at 0 altitude since the location is near the sea The system for this design will have negative suction head =3m since the pump will be located above water source The friction head loss  will be approximated to zero as the pipe work from abstraction point to pump will be small approximately 10m The vapour pressure loss is taken at 30 =0.43 Therefore NPSHA  Taking a maximum NPSHR of 15m it can be seen the NPSHA of 102.9m is sufficient for use with any pump with the design that has been proposed 6.0 Other factors to be put into consideration Other factors to be put into consideration in the design of a pumping system for water Nature of liquid to be pumped in terms of solid matter content and the possible effect of this on the clogging and wear off the pump; Economic viability of the installation 7.0 Pumping power requirements Water horsepower Power needed for pumping water is established by the flow rate, and the total head generated as shown Water Horsepower  where  is the density of water in kg/m3  is gravity in m/s2 Q is the flow rate in m3/s H is the total pumping head in moW The water horse power that the pump must inject into the water is therefore fixed once the design specifications of the pumping system are determined. Taking  8.0 Calculating power requirement The power requirement Arthurs Seat area emergency water supply In which Q=0.0225m3/s H=total heat=317m 9.0 Choosing appropriate pump The pump to be selected should be able to raise water pressure to 317m. This head relatively high and most centrifugal pumps may not be able to meet this requirement. The recommended pump is the Horizontal end-suction multistage pumps which is shown in below The pump is capable of delivering a maximum of 1320hpm (5002.8l/min or 83.38l/s) and a maximum head of 1595ft (478.5m) The desire is to have the pump delivering at H=317m =1056.6ft At this point the discharge will be 150gpm (568.5l/min or 9.48l/s 0.0095m3/s) 10.0 Revised pipe dimensions Our desire is to maintain the pipe velocity at 1.5m/s With a new discharge of 0.0095m3/s And using  But A= Or  Retaining the pumping hours per day at 8hrs the total volume is given as Volume V= 0.0095x8x3600=273.6m3 This is relatively low and thus the pumping time should be doubled to double the volume Therefore the new total volume V=2x273.6=547.2. This is enough to serve the purpose bearing in mind that at time of emergency there will be continuous pumping of water to replenish what is in tank. 11.0 Calculating new power requirement The power requirement Arthurs Seat area emergency water supply In which Q=0.0095m3/s H=total heat=317m 12.0Pump shaft-power The power that must be injected into the pump shaft by the prime-mover includes the water horse power as well as losses, namely Hydraulic losses in the pump; Mechanical losses in the transmission shaft and the coupling between the pump and the prime –mover. The input power require at the pump shaft is thus given by Where we have  being the overall pump efficiency In centrifugal pumps at 1450rpm the efficiencies are Rating 0.55 5kW 0.65 5-10kW 0.70 10-20kW 0.75 20-30kW 0.78 30-40kW 0.82 Above 40kW Efficiency of transmission coupling, with indicative values being Rating 1.0 Direct coupling 0.95 V-belt or gears 0.80 Flat belt drive In this case the we are not dealing with a centrifugal pump but we will still use the efficiency of 78% since in all pumps generally efficiency increase with the size of pump For coupling we use direct coupling efficiency of 100% Therefore Pump system and pipeline design for the Olympic Whitewater Canoeing events at the 2020 Tokyo Olympic Games. The Stadium for this event location is the Kasai Rinkai Park. Part of the design work involve choosing appropriate location of the facility. The design of the pumping system is design to conform to the International Canoeing Federation flow requirement for the Olympic competition, however as this resource will be available for public use most of the time after the Olympic Games, the design should provides a number of different flow conditions according to the user capability /requirement for their event/use. In the design of this sporting facility we look at the pump and pipeline system to meet the above flow requirements, and also examine the power requirement and how this might be met in the present age. In the design concept to be created here, a lot is to be drawn from previous constructed facilities worldwide. Here the most resourceful will be the cases where there is absence of natural whitewater river flow. Here we look at the Olympic facility of Augsburg (1972); in Atlanta in 1996 at La Seu d’Urgell where it required building a water recycling artificial slalom course similar to Penrith (2000), Athens in 2004, 2008 in Beijing and 2012 in London. Here we are looking at a pumping system that that has ability to circulate 10m3 to 14m3 depending on the need. The stadium course is expected to have about 280m course rapids and with side slopes that can host close to 9000 spectators with caution taken to minimise ecological disturbance of the venue The water drop The sports facility will have a self contained lake so as to be able control the qual;igy of water much easily. There will be incorporationof a water treatment system so as to allow high standards of water quality that conforms to the criteria of the World Health Organization standards (WHO,2003). There is need to use a risk based approach in setting up standards on the basis of the likely exposure to the water. There are steps that should be taken so as to minimize the treatment level required , like steps being taken to minimize pollution in the lake, including having the sides sloping away from the lake edge as a precaution of preventing contaminants and nutrients washing in , then there should be avoidance of shallow margins and provision edges hat are near vertical so as wildflow is discouraged. The pumps of choice are the axial-flow pumps, because of this pumps having high-flow and low-head situations. This pumps have been used on other Olympic water course facilities and thus this was a low risk strategy in play. These pumps are very sensitive to flow conditions at the water inlet point, meaning that the pump will ensure that the there is uniform flow, steady without any swirl being experienced, no vortices or air being entrained. Thus the design is such that there will be good flow conditions from end of the courses to the pumping station So as to inform the selection of appropriate head, the overall performance characteristics of the white –water venues already in existence were looked into. The channel is 250m long, with flow varying up to 14m3/s and a head of 5.0 slightly above that of Brazil of 4.5m and slightly lower than that of England which was 5.5m. The course will be trapezoidal in section with the width averaging at 10m. Just as in some several of other Olympic courses , the will be a separate wing for training or intermediate level completion. The wind will be 150m long with slightly lower flow rate of 9.5m3/s and head of 17m and the average width will be 6.5m for this course at the base. References ICF (International Canoe Federation) (2002) Olympic Manual – Requirements for Olympic Candidate Cities, Games of the Olympiad. International Canoe Federation, Lausanne, Switzerland. RIBA (Royal Institute of British Architects) (2007) Outline Plan of Work. RIBA, London, UK. WHO (World Health Organization) (2003) Guidelines for Safe Recreational Water Environments, Volume 1, Coastal and Fresh Waters. WHO, Geneva, Switzerland. Read More

Thus it is possible for one to compute the loss upon the pipeline specifications are established. 2.2 Total head The total head that is to be overcome by a pumping system is given by expression Giving the Total or dynamic head that the pumping system is to overcome - Represents the height to which the water is to be raised by the pump - fluid friction losses experienced in pipeline 3.0 Preliminary design procedure for pumping system In coming up with a design of a pumping system we look at the following Site conditions surveys Pipeline selection Pump selection 3.

1 Site conditions surveys This is the step that is important in determining the available opportunities and constraints that are presented by the environment where there is installation of the pumping system. Here the important data that is being sought is the static head that the pumping system is to overcome and the length of the pipeline. Pipeline route and length The specification of pipeline length is determined through a survey of the intended pipeline route Determination of static head This is the level difference between suction reservoir and delivery reservoir. 3.2 Pipeline selection The pressure loss due to fluid friction in a pipeline depends on several factors: pipe size, material, length, fittings and flow velocity.

The total (dynamic) pressure head that the pump much overcome partly depends on the pressure loss due to fluid friction in pipeline and hence on pipeline data. The selection of the pipeline should therefore be done before that of the pump, because pipeline data will influence the selection of the pump. A preliminary selection of the pipeline is therefore made using a recommended flow velocity for water pipelines. This flow velocity recommended for preliminary design of water pipelines is chosen such that pressure losses due to fluid friction in pipeline are kept within acceptable limits.

This ensures that pumping equipment size and costs are also kept within limits. The recommended range of flow velocities for water pipelines, to be applied during preliminary design, is between 1 and 3m/s. After this preliminary stage , the design specifications should guide further decisions Pipe size selection In a system design selecting the size of pipe to be used comes first. In selecting the size, the flow in the pipe should be such that the velocity in the pipe when the right discharge is passing through should in the right range (between 1m/s and 3m/s).

The flow speed guide is important as it aims at ensuring that the speed is not too high to reul to turbulent flow that would mean high friction loss at the same time very slow speed are to be discouraged as this would required higher diameter pipes which are expensive in order to deliver the desired discharge. Also too low speed in some pipe will result to some solid settling in the pipeline which would eventually lead to pipe blockage. There is to be address on the size of the pump to be used and size of pipe to use.

The pump should be of a size that will be able to overcome the total head. In long distance pipelines the friction depends highly on the size (diameter) of pipe and this determine the size of the pipe. This means that a small diameter pipeline would require to have a bigger size pump. Pipe material selection The loss in pressure within a pipeline is a product of the diameter of pipe, the material type and finishing, the length of the piping system and fittings included on the pipeline. This means that selecting of the material to be used in the pipeline is a very important aspect.

While some materials may be durables, other may be good because of being cheap, others may be lighter and easy to install but in making a choice one need to be aware the consequence on head loss. Head loss due to friction in pipeline With the size of pipe selected, it will be the right time for head loss attributed to friction to be selected. Total pressure head on pump The total head which the pumping system is to overcome is is the dynamic pressure head that is to be overcome by pumping -Total static head to be overcome by pumping -Pressure head loss due to fluid friction in pipeline In the present case the total pipe work length is 2km The energy loss can is given by the Darcy-Weisbach equation Where head loss in metres in the fluid =is dimensionless friction factors taking 0.

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