Install RO System to reduce Boiler Blowdown

Case Study

The Case for Using Reverse Osmosis in Packaged Boiler Applications

Location:  Throughout World
Capacity: 1-2400 m³/day

  • The Need

    There is a popular misconception that the only way to get the quality of water that is appropriate for boiler applications is to pass towns mains (or private supplies of sufficiently good quality) through either a dealkalisation, twin bed or mixed bed demineralisation plant or indeed be supplied in bulk with demineralisation water of the appropriate quality.

    Many organisations do not realise what money is spent in manufacturing high quality water, purchasing and handling acid and caustic, discharging effluent (sometimes involving specialist lined drainage systems), hydraulic loadings on effluent plants etc.etc.

    Although modern dealkalisation and demineralisation plants can be configured to have short cycle regeneration times, they do need copious amounts of high quality water in order to carry out their regeneration sequence within 30-40 minutes.

    Traditional demineralisation systems require up to 3 hours carrying out their regeneration, and as such, large strategic storage arrangements need to be made.

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  • The Solution

    Depending on the quality of the local water supply depends the running costs of a dealk or demineralisation water plant.

    The cost of acid and caustic regenerant plus disposal is often ignored in the initial evaluation of plant requirements and specifications.

    As a result, decisions are often made based on initial capital costs and not on running costs, which as well as regenerants must also include both environmental and hydraulic impact.

    By using the well proven alternative to ion exchange/demineralisation plants i.e. reverse osmosis (R.O.) considerable savings in running costs can be made on moderate to high TDS waters in all areas of running costs.

    R.O. systems have three main consumables, power, water and maintenance chemicals, whether they be salt for water softening or antiscalant type products.

    Even if we take into account the water required to manufacture pure R.O. water being 25% of the forward flow rate, this compares well with demineralisation systems which consume approximately 20% of treated water produced during the regeneration process. Dealkalisation plants use about 10% of their forward flow as regeneration water

  • The Benefits

    Well configured R.O. plants can give water qualities of between 5and 30 ppm (as TDS) (25-50 microsiemans) very easily, have the advantage of producing zero BOD and COD and have very low running costs especially if run on softened water.

    The concentrate water if softened can very easily be used in less critical applications for initial chemical dilutions, washdown, general-purpose cleaning etc.

    It can also be further reprocessed through a nanofiltration membrane and the permeate from the unit recycled to the front end of the RO reducing total water losses to the same level as dealkalisation i.e. 10%. 

    R.O. water quality and stability tends to be more reproducible than that produced by demineralisation systems.

    Water production and quality is less affected by changes in towns mains water ionic loading (TDS).

    The import ant thing to remember is that boiler blowdown on an RO water will reduce to less 1.5% of evaporation whatever the rate of condensate return.

    If the hotwell on the boiler is properly designed then carbon dioxide is stripped out of the water at the same time as the water is deoxygenated.

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