Chemical Dosing


Thread Starter


Dear Sir,
We are using 22 bar, 155 TPH Steam boiler for power Generation and process steam.

We are maintaining 200 to 300 PPM caustic OH alkalinity in the boiler water & maintaining 30 to 70 PPM phosphate in the boiler water. The PH vary from 10.5 to 11.5 and TDS vary from 1500 to 1700 PPM.

The blow down is measured and it is 8 TPH and process steam losses 9 TPH and all together 15 TPH water we are adding as make-up & rest 140 TPH condensate returning from the evaporators.

The return condensate having 20 PPM OH alkalinity & and makeup water 15 TPH no alkalinity. Please advise how to calculate the dosing rate of the caustic to maintain the OH alkalinity 200 to 300 PPM?

How to do the programming in the DCS?

Steam flow signal available in the DCS & Feed water flow into the Boiler signal is avaiable in the DCS.

Is the blow down flow rate available in the DCS?

Please help and advise


What sort of pretreatment are you using for the make up water? and is contamination of the process condensate causing the need for such heavy treatment?
Hi Sir,


We are using pure condensate about 87 %. 13 % of water we are sending to the Boiler from the Multiple effect evaporators.

We are adding Caustic & phosphate for maintaining the pH< alkalinity & TDS.

Use of process condensate (in most plants) requires separate pre-treatment and storage capacity. If not, the treatment controls will be driven by the boiler demand and much more complex.

Direct reuse of process evaporant, especially where so much pre-treatment is required is going to be difficult at best.

good luck,