Separate make-up, feedwater and boiler water
Make-up is the new water replacing losses. Feedwater may combine make-up with returned condensate and chemical conditioning. Water inside the boiler concentrates substances as steam is generated. Confusing these locations can lead to specifying an RO outlet against a limit intended for a different stream.
Ask the boiler-house team for the approved quality at each point, operating pressure and steam application. Turbines and sensitive process uses may impose additional steam-purity requirements. A generic low-pressure table should not be transferred to a system with a different boiler configuration and operating regime.
Understand hardness, silica and conductivity
Hardness describes calcium and magnesium associated with deposits. An ion-exchange softener reduces hardness but is not equivalent to demineralisation. Conductivity supports monitoring of ionic content and concentration; it does not replace silica analysis or establish the absence of organic contamination in the water.
Silica needs specific attention. It can occur in different analytically defined forms and becomes particularly important in high-pressure systems and steam supplied to turbines. Request silica with its method, alongside alkalinity, sodium, iron and the other parameters required by the specification. Low-conductivity permeate does not automatically demonstrate compliance with every requirement.
Select the train around the condensate balance
Assess returned-condensate quality and proportion, blowdown and steam demand. RO salt rejection depends on the element and actual conditions; project permeate quality using the complete feed analysis and design temperature. Additional polishing stages may be needed where the required quality justifies them, rather than being assumed necessary for every boiler.
Include the concentrate destination and membrane protection against oxidants, fouling and scaling. The objective is a practical treatment train with a defined role for each stage. External treatment does not remove the need to manage dissolved gases, corrosion and boiler-water chemistry through the approved conditioning programme.
Define acceptance and monitoring by stream
State where conductivity, hardness, silica and other relevant properties are measured, how often and what action follows a deviation. Provide a means of preventing off-specification water from entering the feed tank. Alarm criteria should reflect the final duty and equipment, rather than simply the sensor’s usual reading.
Compare quotations against the same guaranteed quality and inlet conditions. Ask how temperature, water-source changes and condensate proportion affect the selection. Actual limits must come from the specification applicable to the equipment; pressure alone, without boiler type and service, is insufficient to define them.
Common questions
Can a softener replace reverse osmosis?
It depends on the objective. Ion exchange removes hardness but leaves other salts. Where total salts or silica must be reduced, assess suitable additional treatment.
Does RO eliminate the need for deaeration?
Not automatically. Salt separation is different from controlling dissolved oxygen and carbon dioxide. Deaeration and conditioning must be defined for the complete steam-water circuit.