When steam is supplied to a cold steam line, a large amount of steam condenses in the first minutes to heat the steel. This commissioning condensate load is often 5–20 times the load during operation, and traps and drainage points must be selected accordingly. Otherwise, water accumulates in the line and water hammer occurs.
Formulas
m₂ = q · L · T/HFG (heat loss during warm-up)
c = 0.51 kJ/(kg· K) specific heat of steel, W: pipe meter weight (from the table), Ts: steam saturation temperature, hfg: latent heat of evaporation, q: pipe heat loss (TS EN ISO 12241), t: heating time.
Example
If a 200 m long, DN150 steam line insulated with 50 mm rock wool is heated with 10 bar(g) steam in 15 minutes, a total of 161 kg of condensate is generated (152 kg of which is for heating steel). The average condensate flow rate is 644 kg/h; in operation, the line produces only 35 kg/h of condensate.
The heat loss component is taken at its steady-state value; this errs on the safe side. It is common practice to choose the steam trap with a capacity of 2–3 times the average commissioning flow rate. To evaluate your steam system as a whole, you can check out our steam boiler guide and get a free quote for your project.