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. You can review the steam boiler models page to compare different solution types, and the boiler selection guide for other criteria in the selection process.
What is the Steam Boiler Capacity?
Steam boiler capacity is usually expressed in the following units:
- kg/h (kilogram/hour)
- t/h (ton/hour) → 1 t/h = 1000 kg/h
- kcal/h → 1 kcal = 4.1868 kJ
- MW → As thermal power (1 kcal/h = 1.163 × 10⁻⁶ MW)
This capacity; It 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 – 25 |
| Stoker | 1 – 10 |
| D Type | 4 – 40 |
| Fluidized Bed | 6 – 100 |
| Rotary Grate | 4 – 40 |
This table has been 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 feed water (kcal/kg)
Note: Enthalpy values should be taken from IAPWS IF97 or TS EN 12952 steam tables.
Enthalpy Values (Based on Pressure-Temperature)
Below are the steam and water enthalpy values according to saturation pressure:
| Pressure (bar) | Temperature (°C) | hv (kcal/kg) | hf @ 80°C (kcal/kg) |
|---|---|---|---|
| 6 | 158 | 659 | ~335 |
| 10 | 184 td> | 660 | ~335 |
| 16 | 201 | 662 | ~335 |
In case of superheated steam usage, the hvhv value increases to 700–850 kcal/kg.
Practical Example Calculation
Process Data:
- Steam requirement: 12,000 kg/h
- Pressure: 10 bar (saturated steam)
- 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 must have a minimum thermal power of 4.54 MW.
Fuel Consumption Calculation (Based on LHV)
Fuel Energy = Q / η
Default boiler efficiencies:
| Boiler Type | Efficiency (η) (%) |
|---|---|
| Scotch | 85–88 |
| Fluid Sleeper | 80–90 |
| D Type | 88–92 |
Example: If the efficiency is 88%: 3,900,000 / 0.88 = 4,431,818 kcal/h
📌 Fuel 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 capacity calculation, not only the total equipment but also the load of simultaneously operating systems should be taken into consideration. If all equipment is not working simultaneously, a weighted average with multiplier factors is taken.
📌 Additionally, in peak consumption scenarios, a short-term 10–15% extra load may occur. This should be included in the calculation.
Condensate Recovery
Condensate return increases the hf by increasing the feed water temperature, and thus the boiler consumes less fuel.
If there is 80% condensate return, the feed water temperature may be 95–100 °C, not 80 °C.
In this case, hf ≈ 400 kcal/kg → the energy difference drops significantly.
Vapor Type: Saturated vs Superheated
| Type of Steam | Area of Use | Enthalpy (kcal/kg) |
|---|---|---|
| Saturated Steam | Heat transfer, process steam | 640–670 |
| Superheated Steam | Turbine, energy production | 700–850 |
In the use of superheated steam, the enthalpy value should be increased in the capacity calculation.
Security and Expansion Factor
Industry recommended design reserve:
Total Capacity = Q × 1.15
This multiplier ensures stable operation of the system against future production increases and possible sudden load increases.
Steam boiler capacity calculation is an energy engineering analysis, not just a steam flow multiplier. In this analysis:
- Enthalpy differences
- Boiler efficiency
- Fuel lower calorific values
- Condensate system
- Steam type
- Pressure-temperature relations
- Many parameters such as peak loads and simultaneous operation should be taken into account.
Hisarmak offers special, accurate capacity and high efficiency steam boiler solutions for industrial facilities based on all these engineering criteria.
