An important part of confirming a Mueller Multiple Effect Still (MES) is operating correctly is ensuring it is properly balanced. A balanced MES has many benefits. With proper balancing, the feedwater supply to the unit is kept constant. Since the feedwater supplies roughly half of the cooling to the condenser, consistent feedwater contributes to consistent cooling. Proper balancing also helps to eliminate nuisance alarms and warnings, such as high levels in the effects, distillate high temperature, or a distillate analyzer fault.
A Mueller Multiple Effect Still is balanced correctly when the unit is producing at or above the design capacity of Water for Injection, the levels in each of the effects are at, or slightly above the overflows of each effect, and the feedwater to the unit is constantly running. If these conditions are met, the unit temperatures should be steady, and operation should be consistent.
The following steps can be taken to ensure that an MES is balanced and operating efficiently.
Determine the appropriate first effect temperature setpoint.
Most Mueller Multiple Effect Stills are controlled by the first effect temperature. Some units are controlled by first effect pressure, but since the relationship between pressure and temperature of saturated steam is known, these two control approaches are the same and can be treated as such.
The first effect temperature is one of the primary driving forces determining the operational capacity of the unit. The unit orifice disk sizing is secondary. First, you will need to verify that the orifice disks installed on the unit are appropriate for the capacity of the MES. This can be verified on the unit’s P&ID. If there are questions about orifice disk sizing, consult Mueller engineering.
In the system turnover package is a Production Data Report document. This is the factory capacity check for the unit. It will give you a good starting point for the first effect temperature setpoint. Using that setpoint, start the unit. Once the first effect is up to temperature and there is water level visible on the flags of the effects, check the capacity of the unit. If the capacity is too low, raise the first effect temperature setpoint in one or two degree increments until the correct capacity is reached. If the capacity is too high, lower the first effect temperature setpoint in one or two degree increments until the correct capacity is reached. During this process, you will likely need to adjust the incoming feedwater to ensure that there is water in all the effects. At this point you are looking for gross adjustments, the feedwater flow will be fine-tuned next.
It may be necessary to change the first effect temperature setpoint later in the process, but note that if the setpoint is changed, it will require you to go back through the rest of the balancing procedures.
Adjust the feedwater flow to the unit.
Most Mueller Multiple Effect Stills include a pressure regulator on the feedwater feeding the unit. This regulator, along with an orifice disk just downstream of it, work together to regulate the flow of feedwater to the unit.
A Mueller Multiple Effect Still is running correctly when all of the effects are at roughly the same level (at the overflow), and the feedwater to the unit is constantly on. If the unit has a feedwater pump, that pump should be on continuously when the unit is running. When the unit starts up, it is normal to see some high levels and some cycling of the feedwater to the unit, however, the level should not stay high long enough to cause an alarm, and the cycling of the feedwater should stop after a few cycles.
If after startup, the feedwater to the unit is cycling on and off due to high level in one or more effects, then the feedwater to the unit should be reduced. The feedwater pressure regulator should be closed off slightly, reducing the pressure after the regulator. Note that the unit is sensitive to changes in the feedwater pressure, so only small changes should be made. In most cases, quarter or half turns on the pressure regulator should be sufficient to see a change in unit operation. Smaller changes such as 1/8 or 1/16 turns may be necessary to fine tune the balancing of the unit.
If after startup, the level in one or more effects is low or not showing on the flag indicators, then the feedwater to the unit should be increased. The feedwater pressure regulator should be opened up slightly, increasing the pressure after the regulator. Again, small changes should be made to make certain that the operation point is not overshot.
Monitor the unit level and feedwater.
After the unit is balanced, it should be monitored to verify that the levels are good, and that the feedwater is staying on. If either of these conditions are not met, return to step 2 to further balance the unit. It is quite possible that the unit may take one or more hours to raise or lower the level in an effect, especially if the unit is very close to being balanced.
After the initial monitoring period is finished, periodically check on the operation of the Multiple Effect Still to confirm that conditions have not changed.
Keeping a Mueller Multiple Effect Still correctly balanced will ensure that the unit is producing the design capacity and will keep the unit from having nuisance alarms due to level or distillate temperature.
If you have additional questions or are in need of service support, please reach out to 1-888-281-5800.