Boiler feedwater demineralization

The dissolved solids, such as calcium carbonates, are removed by hot-lime softening or demineralization.1 Demineralized water (also called deionized water) typically has essentially all anions and cations removed by ion-exchange resin. Demineralized water is preferable to hot-lime-softened water as boiler feedwater for several reasons. 

It is really the quality of the treated boiler feedwater that sets the blowdown rate. Deionized or demineralized water might require a 1 to 2 percent blowdown rate. Hot-lime-softened water might require a 10 to 20 percent blowdown rate. 

The reformed gas leaves the furnace at a high temperature where high grade heat is recovered successively to a reformed gas boiler, steam superheater process feedstock heater and boiler, feedwater heater. The reformed gas then passes to the distillation area where low grade heat is efficiently recovered via column reboilers and a demineralized water heater. 

I ppm total solids specified for boiler feedwater at 900 psig operation for package boilers. Such a limit will probably require complete feedwater demineralization as well as return condensate polishing (demineralization). Certainly, this information must be factored into any decision on package versus field erected boilers and included in cost estimates. 

Two substances that are frequently of concern in ion exchange demineralization are silica and organics. The organics are frequently present in natural waters as aromatic polycarboxylic acid derivatives known as humic and fulvic acids. Silica may be the limiting factor in the efficiency of the anionic resins, and (particularly in boiler feedwater applications) the lower the concentration before ion exchange demineralization, the better. Reverse osmosis will frequently produce 90% or greater reductions in total silica concentrations. However, performance should be tested on the specific water to be treated since trie results can be variable and the reason for differences between waters is not yet understood. 

Demineralized water, however, W ithout boiler feedwater for internal and external steam production. 

The water demineralization plant in Geleen (NL) for the production of boiler feedwater from surface water with a capacity of 1560 mVh uses RO and UF for the pretreatment [73]. In this study, a series of pilot scale study was made using different UF membranes and a suitable UF membrane was selected. As for the RO membrane, Filmtec BW 30 LE 440 was chosen primarily due to its high-flux and high-salt-rejection capacity. 

Often the problem with CO accumulation inside the channel head results not so much in corrosion, but in the loss of heat transfer. This is due to the tubes below the bottom pass partition baffle filling with non-condensable CO gas. I have observed this problem even in plants using demineralized boiler feedwater. Venting from beneath the bottom pass partition baffle will restore heat transfer rates. Venting above the pass partition baffle or from the top of the channel head is futile. Unfortunately, most such channel head vents are installed on the top of the channel head, and thus are completely ineffective. 

Demin plant—Boiler feedwater is treated using ion exchange resin in a demineralization plant. 

Boiler feedwater Water that has been softened or demineralized and deaerated. 

Process condensate collected from the front end of the plant is condensed steam and therefore quite clean except for traces of soKds and a small amount of dissolved gases. The process condensate is stripped with steam and then sent to a demineralizer unit, where the solids are removed from the water so it can be recycled as boiler feedwater. The volatile by-products are carried with the steam into the reformer, where they are reprocessed. 

For a high-pressure boiler plant with a high evaporation rate, demineralized feedwater is classified as having an electrical conductivity of less than... 

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