Having Difficulty Locating the Right Pump
A large power generation plant in Louisiana was having difficulty locating the right pump for sampling a hot well in a condenser. The company was looking for a hot well sampling pump that could pump a small amount of water from the feed water return system of the condenser to the laboratory. The condenser maintained a partial vacuum of approximately 26" Hg in the top portion of the vessel and the water level in the condenser varied in depth from 6 feet to less than 1 foot at peak loads.
The company’s engineers tried several different types of pumps. These pumps operated satisfactorily as long as the suction head was 2-1/2 feet or more. However, as soon as the water level in the condenser dropped below a level of 2-1/2 feet, the pumps could no longer supply sample water to the laboratory.
Parameters for this difficult application were:
| Product: | Hot water @ 185º F |
| Flow: | 2 GPM |
| Pressure: | 20.25 feet |
| NPSHA: | 45 feet |
NETZSCH’s Solution to the Problem
NETZSCH’s solution to the problem was a NEMO® Model NE30A Progressing Cavity Pump operating in reverse at 75 RPM. (The pump was operated in reverse in order to remove the stuffing box from the suction, thereby providing better suction lift capability). The pump was mounted at the same level at the bottom of the condenser and as close as possible to the condenser. One ball valve was used in the suction line; the total suction line was only 18 inches long.
With this pump and piping arrangement, NPSHA had been reduced to a point where NPSHA was always greater than the NPSHR required for the NEMO® NE30A Progressing Cavity Pump. This allowed the pump to operate over the complete range of water level fluctuation in the condenser.
The Final Result
The plant engineer reports that he cannot put a dollar amount on the cost savings of this pump solution. However, he says they now have the ability to continually sample the hot well, and therefore can ensure proper water chemistry is maintained on the water being supplied to the boilers. This in turn ensures that the steam produced meets the quality standards required for the main turbines and auxiliary equipment.
