Clarifying the usage of frequency converters in acid pumps

For acid production and absorption pumps, once the amount of acid fed in is stable, there is no need for frequent adjustments; otherwise, it will be detrimental to the manufacturing process. In my opinion, the frequency converter serves to ensure stable starting and stopping, as well as to reduce current surges in this regard. For frequency conversion control, adjustment based on changes in pump current can be considered.

We have always used valves to regulate the three-tower circulation pumps; once the amount of acid added is stable, we rarely adjust them.

The acid pump we use now is started directly, with the outlet valve then opened fully. The problem is the diameter of the three towers; the packing volume is the same, and the amount of acid added is also the same. Adding acid during drying is done to ensure that the moisture content is within acceptable limits. It’s also possible to do this during the first absorption stage due to high levels of sulfur trioxide; however, by the time of the second absorption stage, the amount of gas absorbed is less and the level of sulfur trioxide is lower as well. Is it still necessary to add the same amount of acid? In process design, a margin is usually left when selecting equipment; using the same model of pump for all three towers is intended to facilitate uniformity in maintenance and spare parts management, so that if one pump fails, another pump of the same type can be used as a replacement. I don’t know what this margin is. My understanding of frequency converters is that the required volume of cycles for production is adjusted using the frequency converter to that level, thereby achieving energy savings. It is this amount that is adjusted based on those data, and that’s what confuses me. If an inverter is installed merely for starting and stopping pumps, it loses its intended purpose.

According to the principles of the three-tower process, generally, a higher spray density is used in the drying tower while a lower spray density is used in the second absorption tower. After making these adjustments, the current values should be recorded, and no further adjustments are needed. When using variable frequency for the first time, it is necessary to determine the settings based on specific circumstances; there is no one-size-fits-all approach. The settings can be adjusted by taking into account factors such as the moisture level after drying, the acid mist generated during absorption, the temperature difference related to acid absorption (with the temperature of the cooling water as a reference), and the temperature of the flue gas. It’s all empirical; the spray density is the same as well.

First, determine the minimum frequency based on the spray rate of the tower, and then adjust the frequency according to the acid temperature at the inlet and outlet of the tower. Finally, check the metrics and make adjustments. As long as it meets the requirements, that’s fine.

To make adjustments, it’s necessary for the flow meter to measure a flow rate that meets the spraying density, right?

Variable frequency control is not recommended for circulating acid pumps. The reasons have already been stated above

How can this be explained? Pump model: JHB450-30. Motor power: 110KW. Pump speed: 1470 revolutions per minute. Butterfly valve at the pump outlet. Current: 20° – 188A, 30° – 185A, 40° – 183A, 50° – 182A, 60° – 181A, 70° – 181A, 80° – 181A

All of our acid pumps for drying, the first suction pump, the second suction pump, and the third suction pump are equipped with variable frequency drives; currently, the frequency of the drying pump is 39.5 Hz, that of the first suction pump is 36 Hz, and that of the second suction pump is 30 Hz. Not only is it energy-efficient, but adjusting the frequency on the DCS is also more convenient and accurate than adjusting the valves on-site; it is also more intuitive, allowing for quicker detection of problems.

Is there a flow meter on the pump outlet pipe? If not, how can it be determined whether the flow rate at that frequency meets the spraying requirements?