Periodic symbols
3. Water reticulation projects
3.2. Pumping system project Savings strategy
As discussed, water is pumped from underground in phases. The water reticulation system usually comprises two to four pumping stations, each with a hot dam to store water before it is pumped to the next level. This means the pumps are stopped and started in order to empty the dams. This process can be automated to ensure that the least amount of electricity is used during the evening peak period (18:00 to 20:00). One way of reducing electricity usage at this time is by automating these pumps to stop and start remotely, avoiding the necessity of manpower from travelling up and down the shaft.
Automating pump projects have been shown to shift up to 12 MW from the peak periods (Kleingeld et al., 2011). The electricity usage in deep-level mines is high and as a result, mines are forced to adopt a Time-of-Use (TOU) electricity tariff. Being able to schedule the pumping times allows the mine to extract the water at times when electricity is the cheapest.
HG Brand 2013 60 The automated pumping system measures the dam level and maintains a specified level depending on the time of day. To achieve this goal, the hot dams are emptied during the period preceding the evening peak period, from 15:00 to 18:00. This allows the dams to fill during the peak period without overflowing. This strategy relies on two factors: the availability of large storage dams to ensure that dams do not overflow, and being able to predict the water consumption profile (Kleingeld et al., 2011). It is also necessary to have redundancy in the pumping system.
Automating pumping can be achieved using Real-Time Energy Management System for Pumps (REMS-Pumps™) to ensure that the cost saving is sustainable. This type of project is an example of a load shift project (Vosloo, 2008), as discussed in Chapter 2.
When implementing this type of project, it is necessary to install measuring equipment to ensure that the pumps are operating safely. Some of the important variables that must be measured include pump temperature and vibration, suction and discharge pressure, pump flow, cooling water flow and discharge valve status (Schoeman et al., 2011). The typical installation set up can be seen in Figure 21.
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PLC
PLC
PLC
P Pressure
F Flow
T Temperature
P Pressure
F Flow
T Temperature
P Pressure
F Flow
T Temperature
Pump
Pump Pump
Fibre network switch
Fibre network switch
Fibre network switch Fibre optic cable Discharge valve
Discharge valve
Discharge valve
L Vibration
L Vibration
L Vibration
Figure 21: Pumping project installation (adapted from Schoeman et al., 2011)
From Figure 21 it can be seen that the pump and discharge valve are controlled by the programmable logic controller (PLC). The PLC also measures the pressure, flow, temperature and vibration of the pump to ensure the pump is operating correctly and at peak efficiency.
These signals are transmitted using an Ethernet, which is not capable of transmission ranges over 100 m when not enhanced. For this reason a fibre optic network switch is installed to convert the electrical signals to light signals that are transmitted through the fibre optic cables. The fibre optic cables are installed down the shaft to allow communication to the underground PLCs from the surface.
HG Brand 2013 62 The SCADA system thus monitors the system from the surface. The values are subsequently read by REMS-Pumping™ which is capable of controlling the system by making decisions based on the inputs from the SCADA system. The control signal is then sent down the shaft to stop and start some of the pumps in order to shift the load from peak periods.
It was found that these projects shifted too much of the load to the standard tariff periods leading to an electricity-supply shortage in these periods. This is known as the comeback load. For this reason Eskom is currently only funding load shift projects that shift the load to off-peak periods: from 21:00 to 06:00 (Kleingeld et al., 2011).
The pumps on a pumping station usually pump the water into a common manifold. This is because the cost of installing a pipe column from one station to the next is high. As a result, the more pumps are started, the higher the water flow in the pipe column becomes. The problem with this setup is that with an increase in flow, there is a corresponding increase in friction- and pipe-losses (Vosloo, 2008). This emphasises the need to minimise the pumps running simultaneously and the speed of the water flow.
Simulated saving
Firstly it is necessary to look at the system layout before the project implementation. This can be seen in Figure 22.
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Figure 22: Mine A pumping layout
For determining the savings associated with each project it will first be necessary to develop a simulation to gather baseline data. The simulated pump power usage after the installation of this project is compared to the simulated baseline usage in Figure 23.
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Figure 23: Pump power after pumping project installation
From Figure 23 it is evident that the pumping power is predicted to be significantly reduced during the morning peak period from 07:00 to 10:00 and the evening peak period from 18:00 to 20:00. This pumping load was shifted to other periods of the day when electricity is cheaper.
According to the simulation, the load that can be shifted from the morning peak is 10.67 MW or 65.3% of the total baseline consumption during this period. Similarly the load shift during the evening peak period is predicted to be 13.6 MW or 99.5% of the baseline power consumption. It is predicted that not all the load can be shifted from the morning peak period because the dams do not have sufficient capacity to store all the water settling in the hot dams during the morning peak period of three hours.
3.3. Pumping project results and interpretation