Valves by Schroeder protect pumps at thyssenkrupp Steel Europe
thyssenkrupp Steel Europe AG has opted for Schroeder pump protection valves for the general overhaul of unit 4 of its power station “Hermann Wenzel", Duisburg. In the previous system, valves from another manufacturer were installed, but these had repeatedly caused problems because the minimum flow control was carried out via two valves: on the one hand from a pulse generator (non-return valve on the pump discharge nozzle) and on the other hand from a minimum flow valve with adjusting piston and throttle. “This design often led to an increase in the drive power requirement and a drop in overall efficiency", explains Ralf Poot, who supervised the general overhaul of the block.
So thyssenkrupp Steel Europe looked out for a better solution. The required valves had to have a nominal size of 125 mm (for the electric pumps) or 200 mm (for the turbopump) and a nominal pressure of PN 630 bar. The decision fell on the minimum flow system “SMA“ by Schroeder Valves. These are high-pressure valves, which automatically protect centrifugal pumps against damage that may occur as a result of the partial evaporation of the pump content when the pumps are operated under low load. As soon as the main pump flow falls below a predetermined value, the valve opens the bypass and safely drains the minimum volume, even if the pumping volume in the main flow direction drops to zero.
The bypass is always completely opened or closed through its pilot-controlled valve piston. This "ON/OFF" control makes it possible to increase the load limit of the valves up to 630 bar (pumping pressure). The preferred utilization range is thus between PN 250 and PN 400 or ANSI CLASS 2500. The bypass amount may be up to 35% of the main pumping volume. The minimum quantity can be up to 10–12 percent of the full-load delivery rate.
“The SMA valve is a compact system that combines the performance formerly achieved by the two built-in valves," says Poot. “A second valve is no longer necessary.” The Schroeder valves also convinced thyssenkrupp Steel Europe, because in other plants they have proven to be very reliable, durable and extremely low-maintenance due to their construction and the high-quality materials used. In the event that maintenance should ever be necessary, Schroeder Valves has attached particular importance to ease of maintenance: For the replacement of wearing parts such as pistons and seat rings, it is not necessary to remove the minimum flow line or even the complete valve.