Type a line (feed 20 ppm boiler limit 2000 ppm steam 3 t/h) or fill in the fields: the line and the fields stay in step.
Enter the feed water figure, as TDS, chloride or conductivity, and the boiler water limit for the same quantity, and the calculator gives the blowdown: as a share of the feed and of the steam, with the steam rate as the blowdown and feed rates in kg/h, and the cycles of concentration. In reverse it gives the concentration the boiler water reaches with a given blowdown. It shows the working with your numbers, draws the balance of the boiler, and gives a line you can copy or add to a request.
Boiler water limits for TDS, chloride and alkalinity are set by the boiler maker and the water treatment supplier. The calculator prints no limit figure and does not assume one: without a limit it asks for it. Conductivity is turned into TDS only with a factor you enter. The heat lost with the blowdown and the dosing of treatment chemicals are not worked out here.
The dissolved solids come in with the feed water and leave only with the blowdown: the steam carries next to none of them. In steady running F x Cf = B x Cb, so the blowdown as a share of the feed is B/F = Cf / Cb. Feed water at 20 ppm with a limit of 2000 ppm entered: B/F = 20 / 2000 = 1.00 %.
The feed is the steam plus the blowdown, F = S + B, so B/S = Cf / (Cb - Cf) = 20 / 1980 = 1.01 %. At 3 t/h of steam the blowdown is B = 3000 x 20 / 1980 = 30.3 kg/h, and the feed is F = 3030 kg/h.
The cycles of concentration Cb / Cf = F / B say how many times the boiler water is more concentrated than the feed: 100 in the example. In reverse, a blowdown of 2 % of the feed at 25 ppm brings the boiler water to 25 / 0.02 = 1250 ppm, 50 cycles; compare that with the limit for your boiler.
| Quantity | Relation | Note |
|---|---|---|
| Blowdown, share of the feed | B/F = Cf / Cb | Cf the feed water, Cb the boiler water, the same quantity |
| Blowdown, share of the steam | B/S = Cf / (Cb - Cf) | from F = S + B |
| Blowdown rate | B = S x Cf / (Cb - Cf) | kg/h with the steam rate S in kg/h |
| Feed rate | F = S + B | kg/h |
| Cycles of concentration | Cb / Cf = F / B | the inverse of B/F |
| Reverse | Cb = Cf / (B/F) | B/F = (B/S) / (1 + B/S) when the blowdown is given of the steam |
| Conductivity to TDS | TDS = k x conductivity | k entered; without it the units are not mixed |
| Units | 1 t/h = 1000 kg/h; 1 kg/s = 3600 kg/h | 1 mS/cm = 1000 uS/cm; 1 mg/l taken as 1 ppm |
The balance holds for one and the same quantity in the feed water and the boiler water. Solids carried over with the steam and water lost other than by the blowdown are not counted; mg/l is taken as equal to ppm, as for boiler and feed water.
The blowdown relations are the steady mass balance of a dissolved quantity that leaves the boiler only with the blowdown. The blowdown as a share of the feed water, Cf / Cb, is given in water efficiency and energy management guides and in an industrial water treatment handbook, and the cycles of concentration as its inverse in a water efficiency guide and a boiler maintenance reference. That the feed water is the steam plus the blowdown, F = S + B, is stated in the same water treatment handbook and in a steam engineering tutorial. The blowdown as a share of the steam, Cf / (Cb - Cf), and the blowdown rate B = S x Cf / (Cb - Cf) follow from these two relations by arithmetic; engineering data tables give the rate in the same form. Water treatment references measure the cycles by the ratio of the chloride or of the conductivity of the boiler water and the feed water. A factor of 0.7 ppm per uS/cm for a neutralised boiler water sample at 25 °C is given by two steam engineering references; a general reference on natural waters gives 0.55 to 0.8, which is why the calculator asks for the factor. That the boiler water limits come from the boiler maker and the water treatment supplier is stated in a boiler maintenance reference, a steam engineering tutorial and a chemical engineering journal. 1 ppm = 1 mg/l for water follows two unit references.
From a mass balance. The dissolved solids come in with the feed water and leave only with the blowdown, because the steam carries next to none of them, so F x Cf = B x Cb, and the feed F is the steam S plus the blowdown B. The blowdown is B/F = Cf / Cb of the feed and B/S = Cf / (Cb - Cf) of the steam. Feed water at 20 ppm with a limit of 2000 ppm entered: B/F = 20 / 2000 = 1.00 % of the feed and B/S = 20 / 1980 = 1.01 % of the steam. At 3 t/h of steam the blowdown is 3000 x 20 / 1980 = 30.3 kg/h, and the feed is 3030 kg/h.
How many times the boiler water is more concentrated than the feed water: Cb / Cf, which equals F / B, the inverse of the blowdown as a share of the feed. At 20 ppm in the feed and 2000 ppm in the boiler water the cycles are 100, and the blowdown is 1/100 of the feed. The cycles can be measured by the ratio of the TDS, of the chloride or of the conductivity of the boiler water and the feed water.
The one given for this boiler. Boiler water limits for TDS, chloride and alkalinity are set by the boiler maker and the water treatment supplier. The calculator prints no limit figure and does not assume one: without a limit it asks for it. Enter the limit for the same quantity as the feed water figure: TDS with TDS, chloride with chloride, conductivity with conductivity.
Yes. With the feed water and the limit both in uS/cm the blowdown comes straight from the ratio of the conductivities. With one figure in uS/cm and the other in ppm or mg/l, a factor from conductivity to TDS is needed (TDS = factor x conductivity), and the calculator asks for it instead of assuming one. Two steam engineering references give 0.7 ppm per uS/cm for a neutralised boiler water sample at 25 °C; the factor depends on the water, so take it from the meter or the water treatment supplier.
Enter the blowdown and the feed water: the boiler water reaches Cb = Cf / (B/F). A blowdown of 2 % of the feed with feed water at 25 ppm gives 25 / 0.02 = 1250 ppm, 50 cycles of concentration, and 2 / 98 = 2.04 % of the steam. A blowdown as a per cent of the steam (2 % of steam), as cycles (cycles 50) or as a rate with the steam rate (blowdown 30 kg/h, steam 3 t/h) is read too. With a limit entered as well, the calculator says whether the boiler water stays within it.
The feed water and the boiler water limit in ppm, mg/l (taken as equal to ppm for boiler and feed water) or uS/cm (mS/cm too), as TDS, chloride or conductivity; the steam rate in kg/h, t/h or kg/s if wanted; a blowdown in per cent, as cycles or as a rate for the reverse; a factor from conductivity to TDS when the units are mixed. A boiler pressure or a water temperature in the line is read and named as not used: the mass balance does not depend on them, and the heat lost in the blowdown is not worked out here.
The calculator gives the blowdown from the solids balance. When blowdown valves, TDS sensors or other boiler parts are needed, send the line from the calculator with the boiler details and a photograph of the nameplate, and Vessel Core checks the details before an offer goes back.
