In the Australian mining industry, greenfield projects and the associate design processes are no longer the priority. The key objectives now are shutdown, maintenance and improved efficiency of existing plants.
When considering potential efficiency savings, it is worth noting that there are few mines where pumping is not a key part of the process, so this area must be a target for energy-saving projects.
Industry figures suggest that around 80% of pump electric motors could be the incorrect size with the majority over specified by as much as 10% or 15 %.
According to Accutech 2000 , this fact suggests a serious loss of energy and a worthwhile focus for an efficiency audit. It might also indicate that the pumps themselves are also incorrectly sized so an analysis of an existing pipe flow system could lead to some significant cost savings. This could be analysed by the following procedure.
The first step is to develop a hydraulic model of the pumped system. The software package FluidFlow3, available form Accutech 2000, is ideal for this operation. A schematic layout of the system is developed using data from drawings and site inspection. Pump and equipment data needs to be sourced and verified.
The model needs to be calibrated against actual measurements of flow and pressure. A simple pipe flow system can be modelled in FluidFlow3. In a real scenario, an existing system would be much more complicated. FluidFlow3 can effectively simulate systems containing hundreds of pipes and line equipment items.
The performance of the model can then be interrogated under varying operating conditions and the potential for energy savings determined. Energy savings can be determined by assessing the hydraulic performance of the line equipment in the model.
For instance, are velocities excessive in any of the pipes leading to higher than acceptable friction loss? If so, can these pipes be replaced, reducing the required pump head and motor power? Or, does a comparison of model-calculated friction loss with actual measurements on site indicate scaling of the pipes. FluidFlow3 allows pipe scaling to be simulated providing an immediate indication of the associated excess energy cost.
Closed control valves can be an indication of oversized pumps and motors. Again a model developed in FluidFlow3 and calibrated to simulate site conditions, can indicate the potential energy savings of modifying pump/motor configurations.
Pipe network analysis programmes generally provide a steady-state simulation of flows and pressures, a ‘snapshot’ of how the system is performing at an instant of time. But, often, systems have a varying performance over time as reservoir levels change or demands vary.
Pump and motor performance need to be considered over the full range of operating conditions. FluidFlow3 allows this type of extended-time simulation through its unique ‘scripting’ language. A script can generate an automatic sequence of time-increment based calculations, for instance changing the speed of a pump until associated control valves move out of range.
With the reducing cost of variable speed drives (VSDs) it is becoming beneficial to replace control valves, which essentially just burn energy when in use and burn money when they require maintenance and control flow by pump speed alone. So the scripting example described above could be modified to provide a cost-benefit analysis of replacing control valves in a system with VSDs.
FluidFlow3 allows the export of data to Excel. This then is the final part of the economic analysis of the performance an existing pipe flow system. With calculated data on power, pipe size, equipment performance now in Excel, its calculation capabilities can be used to estimate cost savings based on other inputs such as replacement cost of pipes, pumps and motors.