If you are using the right formula to Calculate Steam Consumption, only then can you get an accurate result. Steam is one of the most widely used utilities in the industrial sector. Mostly, it is used for chemical plants and for food processing work. That is why you need to understand how to precisely calculate steam consumption. It helps to use the energy properly. Plus, you can control the overall costs.
We have prepared this guide for you for steam calculations. If you are inexperienced and working on a bigger project. It is recommended to get professional mechanical estimating services and get pinpoint results. If you are doing it yourself without understanding different factors, it will not provide you with accurate numbers.
Understanding Steam Consumption Basics
Steam consumption is the amount of steam required by a process for a specific time. This measurement is in:
- Pounds per hour (lb/h)
- Kilograms per hour (kg/h)
- Tons per hour
Accurate Steam Consumption Calculation helps engineers to design a reliable steam system. It helps to select the right boiler capacities. However, the methods are different because it depends on the requirement. It can be for:
- Heating a liquid
- Maintaining the temperature in a vessel
- Driving a turbine
- Supplying steam for chemical reactions
Fundamental Steam Consumption Formula
The simple formula for calculating specific steam consumption is:
= Heat Required / Available Heat in Steam
More specifically:
m = Q / (hg – hf)
- m = mass flow rate of steam (kg/h or lb/h)
- Q = heat required (kJ/h or BTU/h)
- hg = enthalpy of steam at supply conditions (kJ/kg or BTU/lb)
- hf = enthalpy of condensate leaving the system (kJ/kg or BTU/lb)
The difference of hg – hf shows the latent heat available from the steam.
Step-by-Step Calculation Process
Step 1: Determine the Heat Required
You need to calculate the total heat required for your process. This process includes multiple factors.
- Sensible Heat is needed to raise the temperature of a material
Q sensible = m × Cp × ΔT
- m = mass of material (kg or lb)
- Cp = specific heat capacity (kJ/kg·°C or BTU/lb·°F)
ΔT = temperature change (°C or °F)
- Latent Heat requirements are included when the process needs a phase change.
- Heat losses occur through insulation, piping, and other surfaces. Keep in mind that 10-25% of the calculated heat requirement depending on insulation quality.
Step 2: Identify Steam Properties
Make sure that you are aware of the steam properties. For that, you need:
- Steam pressure at the point of use
- Corresponding saturation temperature
- Enthalpy of saturated steam (hg)
- Enthalpy of condensate (hf)
Step 3: Apply Safety Factors
Expert engineers also apply a safety factor of 1.1 to 1.3 to the calculated steam consumption. This is to consider fluctuating demands and system inefficiencies.
It may look easy, but every calculation matters. For this reason, you must get an expert steam piping estimation for accurate numbers. A little mistake can lead to consequences.
Example of Heating Water in a Tank
- Mass of water: 10,000 kg
- Initial temperature: 20°C
- Final temperature: 80°C
- Specific heat of water: 4.18 kJ/kg·°C
- Steam pressure: 6 bar gauge (7 bar absolute)
- From steam tables at 7 bar: hg = 2,763 kJ/kg
- Condensate leaves at approximately 165°C: hf = 697 kJ/kg
- Heat losses: 15%
Calculation:
Heat required for water
= 10,000 kg × 4.18 kJ/kg·°C × (80 – 20)°C = 10,000 × 4.18 × 60
= 2,508,000 kJ
Accounting for heat losses:
Total heat required = 2,508,000 × 1.15 = 2,884,200 kJ
Available heat from steam = hg – hf = 2,763 – 697 = 2,066 kJ/kg
Steam consumption = 2,884,200 / 2,066 = 1,396 kg for the entire process
Since this occurs over one hour:
Steam consumption rate = 1,396 kg/h
With a safety factor of 1.2: Design steam consumption = 1,396 × 1.2 = 1,675 kg/h
Special Considerations for Different Applications
Jacketed Vessels
For this type of vessel, you need to calculate the initial heating load and heat loss through the vessel walls.
Reboilers and Evaporators
You have to consider the latent heat. The formula is:
Steam consumption
= (Feed rate × Latent heat of process fluid) / (Available heat in steam)
Steam Tracing
For this one, the consumption depends on:
- Pipe length
- Diameter
- Ambient temperature
- Insulation quality
Steam Turbines
The steam consumption is calculated based on two things:
- Power output required
- Isentropic efficiency of the turbine
Best Tips!
To reduce steam consumption you must:
- Maximize condensate return to recover sensible heat
- Use flash steam from high-pressure condensate where possible
- Install proper insulation on all steam lines
- Maintain steam traps to prevent steam losses
- Control steam pressure for each application
- Get professional material takeoff services to prevent mistakes
- Monitor actual consumption against calculated values
Conclusion
To calculate steam consumption accurately, you need to understand how it works. Plus, you have to carefully consider the process. Also, make sure to properly use steam tables. By following the methods we have given in this guide, the engineers can accurately size equipment and maintain the process. Make sure to regularly monitor this steam consumption. This will help you identify the opportunities for improvement.
