This waste water pumping system is a combination of electrical and instrumentation works which i installed in a power station in the North of Holland.

Water from a man-made canal is pumped into an auxiliary boiler where it is converted into high pressure steam which powers a turbine resulting in electricity being generated.

At the beginning of this process, the water pumped in from the canal passes through a filtering system which removes waste silt, sand and other foreign bodies. When the auxiliary boiler cannot facilitate any more water, due to maintenance or a cooling down period, a valve is mechanically opened which allows the stagnant water in the pipe between the canal and the boiler to flow into a 20,000 litre holding tank situated below ground level.

Picture 1: Cover of the holding tank. Situated flush with ground level.

My colleague and I started to construct this system by fabricating a steel frame made from unistrut and we installed it at ground level beside the cover of the holding tank. This frame is used for mounting our 2no. power junction boxes. We cut our unistrut to our required lengths using a chopsaw and tied the various lengths together using cross brackets, tee brackets, spring nuts, bolts and washers. We then fixed this frame to 3no. unistrut shoes which we had already bolted to the concrete base beside the tank.


                                                                                                                 

Picture 2: Power junction boxes mounted to unistrut frame.

We then installed 2no. sump pumps at the base of the holding tank. One of these power junction boxes supplies one of the sump pumps and the other power junction box supplies the other sump pump. One of these pumps is fed from a generator, via the power J.B, to ensure the pump can still operate in the result of a power failure. This pump is known as a back-up.

The level indicator, temperature transmitter and the pressure transmitter used are part of a DCS, (distributed control system).  The level indicator is situated in the tank and it dictates the volume of water therein at all times. When desired water level in the tank is reached, the level indicator will instruct a control valve to open, via the instrument junction box, which in turn will instruct the pump to energise so the contents of the tank can be pumped back out to the canal where it originally came from.

Picture 3: Level indicator.

The temperature transmitter is used to measure the temperature of the water in the pipe that is flowing into the tank. If the water in this pipe is above desired temperature level, the temperature transmitter will instruct a by-pass valve to open meaning this water will not enter tank. This is to avoid a reaction between very hot and very cold water. This reaction is known as a blow-back.

The pressure transmitter is used to measure the pressure of the water in the pipe that is flowing out of the tank. This will indicate if the pump is operating to its full potential. It will also indicate if there is a blockage in the pipe as a blockage would change the pressure reading.

Note: When I received the drawings for this system, having studied them, I questioned the engineering department as I did not believe it was a good idea to situate the power J.Bs where they instructed. I felt the J.Bs should be located in such a way that if you are working on them you should not be standing on the cover of the tank. My opinion was over-ruled and I was told to install as per drawing.