How to Calculate Steam Requirements for Heating Water in a Heat Exchanger: A Step-by-Step Guide

 Steam Requirements for Heating Water in a Heat Exchanger

When designing and operating heat exchangers, one common question is: how much steam is required to raise the temperature of water to a desired level? This blog provides a detailed step-by-step guide to perform these calculations using two different examples.

Example 1:

Case Study:

 We have a hot water absorption heater with the following parameters:

 Mass flow rate of hot water: 131.9 cubic meters per hour (36.63 liters per second).

Initial temperature of water: 85°C.

Desired temperature increase: From 85°C to 92°C (ΔT = 7°C).

The specific enthalpy of steam at 8 bar is 2767 kJ/kg, and the specific heat capacity of water is 4.19 kJ/kg°C.

 

Solution:

 Calculate the Heat Load (Q):

𝑄=𝑚˙×𝐶𝑝×Δ𝑇

𝑚˙=36.63 kg/s

C p =4.19 kJ/kg°C

Δ𝑇=7°𝐶

Q=36.63×4.19×7=1074 kJ/s

 

Calculate the Required Steam Flow Rate:

Δℎ=2767−419=2348 kJ/kg

𝑚˙steam=𝑄/Δℎ=1074/2348=0.457 kg/s

𝑚˙steam=0.457×3600=1646 kg/hr

 

Account for Inefficiencies:

Adjusted steam flow rate=1646×1.10=1811 kg/hr

Adjusted steam flow rate=1811/1000=1.811 tons/hr

 

 Conclusion:

Approximately 1.81 tons of steam per hour are required to increase the water temperature from 85°C to 92°C, considering a 10% inefficiency factor.

 

Example 2:

Case Study:

 We have a hot water absorption heater with the following parameters:

 

Mass flow rate of hot water: 100 cubic meters per hour (27.78 liters per second).

Initial temperature of water: 70°C.

Desired temperature increase: From 70°C to 85°C (ΔT = 15°C).

The specific enthalpy of steam at 8 bar is 2767 kJ/kg, and the specific heat capacity of water is 4.19 kJ/kg°C.

 

Solution:

 Calculate the Heat Load (Q):

𝑄=𝑚˙×𝐶𝑝×Δ𝑇

𝑚˙=27.78 kg/s

𝐶𝑝=4.19 kJ/kg°C

Δ𝑇=15°𝐶

Q=27.78×4.19×15=1745.43 kJ/s

 

Calculate the Required Steam Flow Rate:

Δh=2767−419=2348 kJ/kg

𝑚˙steam=𝑄/Δℎ=1745.43/2348=0.743 kg/s

m˙steam =0.743×3600=2676 kg/hr

 

Account for Inefficiencies:

Adjusted steam flow rate=2676×1.10=2943.6 kg/hr

Adjusted steam flow rate=2943.6/1000=2.944 tons/hr

 

Conclusion:

Approximately 2.94 tons of steam per hour are required to increase the water temperature from 70°C to 85°C, considering a 10% inefficiency factor.

 

By following the steps outlined in these examples, you can accurately determine the amount of steam needed for heating water in a heat exchanger for different scenarios.

 Thanks for Reading !