Hydropower, next to thermal generation, plays a vital part in the energy mix. Hydropower can serve both the purposes i.e., it can be utilized for the industrial sector as well as for domestic household purpose too. If there is a case, where one has to face with a repowering of generators which give an increase to changes in water pressure which affects the valves utilized in cooling of generators – an important function.
Primarily the issue begins with the old pressure regulating valves that feed the turbines, which are making too much noise due to cavitation and the valves have become deteriorated to such an extent that it has to be decided to uninstall them and search for another option. A few years back they were replaced by “multi-stage valves” , which were actually a pipe along with four plates of two holes installed in series, in a particular manner that they generate the required pressure drop (through trial and error) from 15kg/cm2 (213 Psi) to about 3kg/cm2 (43 Psi) (Cavitation Element o = 0.33 – extremely acute cavitation). This valve caters to each of the cooling systems (generator radiators, four-bearing exchangers, carbon gasket, or packing gland which operates with the least pressure required).
A few years back, a particular industrial house began repowering of generators. This necessitated more cooling in the radiators. There was a valve at the downstream of the radiator cooling circuit, which monitored the flow through the radiators. The pressure of the total circuit dropped due to the rise in this flow. Due to this, it was inevitable to move the two-hole plates in a particular way so as to see that the pressure drop is lower. To provide with an understanding, the stroke of the valve has 20 turns for its total opening and if we turn only a quarter of a turn of the stroke, the group of the cooling system will shut off because of mechanical failure brought about by low pressure in the carbon board.
UNDER PRESSURE
In order to be in good working condition, the water-bearing, crucial parts of a hydropower plant has to be safeguarded from hydrodynamic impact, commonly known as cavitation. This phenomenal happening better known as cavitation is the result of a fast and noticeable pressure decrease and increment in fluid velocity. If there is any reluctance in controlling this, it will give rise to shock bubbles, which may harm or wipe out components through gradual destruction e.g., internal valves producing noise and vibration as well as hindering the flow significantly.
Further, at this juncture the main criteria is to make sure that renewable energy should keep flowing. The question here is to decide that which valve will prove to be more feasible as far as durability and dependability taking in to consideration the particular flow and the state of pressure which is there at the power plant.
As for paving the way for the solution a 4Matic pressure reducing control valve was installed. The SRD, i.e., Single Rolling Diaphragm technology gives smooth, stable and exact pressure control from highest to practically zero flow. The bonnet is very small and light in weight as compared to a flat diaphragm, therefore the actual area of a single rolling diaphragm remains constant. An evaluated quantity into the bonnet control chamber continually provides the same smooth movement of the inner valve through the whole stroke. The smaller size of the bonnet makes the valve lighter in weight, which becomes safer as far as maintenance is concerned. Whereas the small size of the control chamber makes it possible to react quickly to alterations in pressure. By getting rid of the seat chatter at low flows, the SRD keeps away from injecting small pressure pulses into the piping. This ultimately results into the avoidance of leakage, losses or bursting of pipes over a period of time.
The practical installation of the needed four valves, one was additionally being kept in reserve, was done before some time, which did not have any complexity. With the proposal of using the valves to monitor pressure and have the anti-cavitation system, the move was to have optimum result for getting the required flow without dropping the pressure. After the finishing off with the installation, the radiator outlet valve was opened and the pressure dropped only 100 g/cm2 which completely surpassed the expectations and it did not produce any noise. These new valves were flowing at 12000 Its/min, the radiators outlet open only six laps, and it was thought that through opening two more laps would be to surpass 12000 Its/min and the pressure was going to go down but it did not occur and the system was able to completely open the valve.
After the realization of the job, the plant operators may now again pay attention to their key business – the provision of electricity – putting aside the botheration of possible damage to the crucial parts of the plants and also get rid of the worry of blackouts. This has become a vital element as it is being planned to substitute the present 118 MW generators with 140 MW variations.
To conclude it can be said that the above project had a noticeable success by way of having an uninterrupted supply of electrical power to the industry along with the excessive balance of the same can be diverted for the household utilization.
