Steam boiler capacity determines the amount of steam that can be produced per unit time and its correct calculation is critical for the energy efficiency, safety and continuity of the system.
What is Steam Boiler Capacity?
Steam boiler capacity is usually expressed in the following units:
- kg/h (kilogram/hour)
- t/h (tons/hour) → 1 t/h = 1000 kg/h
- kcal/h → 1 kcal = 4.1868 kJ
- MW → Thermal power (1 kcal/h = 1.163 × 10-⁶ MW)
This capacity is calculated depending on parameters such as steam flow rate, pressure, temperature, feed water temperature and type of steam.
Capacity Ranges According to Boiler Types
| Boiler Type | Capacity Range (Ton/Hour) |
|---|---|
| Scotch Type | 1 – 40 |
| Stokerli | 1 – 10 |
| Type D | 4 – 40 |
| Fluidized Bed | 6 – 100 |
| Rotary Grill | 4 – 40 |
This table is prepared according to Hisarmak steam boiler engineering data.
Basic Capacity Calculation Formula
The main thermodynamic equation used to determine boiler capacity:
Q = m × (hv - hf)
- Q: Thermal power requirement (kcal/h)
- m: Steam flow rate (kg/h)
- hv: Specific enthalpy of steam (kcal/kg)
- hf: Specific enthalpy of feedwater (kcal/kg)
Note: Enthalpy values should be taken from IAPWS IF97 or TS EN 12952 steam tables.
Enthalpy Values (Pressure-Temperature Basis)
Vapor and water enthalpy values according to saturation pressure are given below:
| Pressure (bar) | Temperature (°C) | hv (kcal/kg) | hf @ 80 °C (kcal/kg) |
|---|---|---|---|
| 6 | 158 | 659 | ~335 |
| 10 | 184 | 660 | ~335 |
| 16 | 201 | 662 | ~335 |
In caseof superheated steam use, the hvhv value increases to the range of 700-850 kcal/kg.
Practical Example Calculation
Process Data:
- Steam requirement 12.000 kg/h
- Pressure 10 bar (saturated vapor)
- Feed water temperature: 80 °C
- hv: 660 kcal/kg
- hf: 335 kcal/kg
Q = 12,000 × (660 - 335) = 3,900,000 kcal/h
Conversion to Thermal Power (MW)
1 kcal/h = 1.163 × 10-⁶ MW
3,900,000 × 1,163 × 10-⁶ ≈ 4.54 MW
In this case, the steam boiler should have a minimum thermal power of 4.54 MW.
Fuel Consumption Calculation (According to LHV)
Fuel Energy = Q / η
Default boiler efficiencies:
| Boiler Type | Yield (η) (%) |
|---|---|
| Scotch | 85-88 |
| Fluidized Bed | 80-90 |
| Type D | 88-92 |
Example: If the efficiency is 88%: 3,900,000 / 0.88 = 4,431,818 kcal/h
📌 F uel lower heating values (LHV):
| Fuel Type | LHV (kcal/kg) |
|---|---|
| Natural Gas | 8.500 |
| Stone Coal | 6.500 |
| Biomass | 3.500 – 4.500 |
In case of natural gas use :Fuel consumption = 4.431.818 / 8.500 ≈ 521.4 kg/h
Simultaneous Load and Peak Consumption
In the capacity calculation, not only the total equipment but also the load of the systems operating simultaneously should be taken into account. If all equipment is not operating simultaneously, a weighted average is taken with multiplier factors.
📌 Also, in peak consumption scenarios, a short-term extra load of 10-15% may occur. This should be included in the calculation.
Condensate Recovery
Condensate return increases the feed water temperature and hf, so the boiler consumes less fuel.
If there is 80% condensate return, the feed water temperature can be 95-100 °C instead of 80 °C.
In this case hf ≈ 400 kcal/kg → energy difference decreases significantly.
Steam Type: Saturated vs Angry
| Steam Type | Area of Use | Enthalpy (kcal/kg) |
|---|---|---|
| Saturated Steam | Heat transfer, process steam | 640-670 |
| Superheated Steam | Turbine, power generation | 700-850 |
In the use of superheated steam, the enthalpy value should be increased in the capacity calculation.
Safety and Expansion Factor
Industry recommended design reserve:
Total Capacity = Q × 1.15
This multiplier ensures stable operation of the system against future production growth and possible sudden load increases.
Steam boiler capacity calculation is an energy engineering analysis, not just a steam flow rate multiplier. In this analysis
- Enthalpy differences
- Boiler efficiency
- Fuel lower heating values
- Condensate system
- Steam type
- Pressure-temperature relations
- Peak loads and simultaneous operation such as
many parameters must be taken into consideration.
Based on all these engineering criteria,Hisarmak offers customized, accurate capacity and high efficiency steam boiler solutions for industrial plants.
