Steam consumption calculation
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Our company is now adding the condensate water from the heaters to the circulation tank as make-up water in order to raise the water temperature. Please check whether the calculations are correct. It is known that the temperature of the superheated steam is 150°C, with a pressure of around 0.5–0.6. The circulating water temperature is 30°C, the flow rate of circulating water is 36 m³/h, the flow rate of condensate water is 5 m³/h, and the condensate water temperature is 80°C. 1. To calculate the increase in temperature of the condensate water due to the addition of circulating water, use the formula Q = W * C * (t1 – t2). Applying this formula: 5 * 4.2 * (80 – t1) = 36 * 4.2 * (t1 – 30). The calculation yields t1 = 36°C, meaning the temperature increases by 6°C. 2. Calculate the amount of superheated steam that can be saved (the superheated steam is directly introduced into the tank). The heat absorbed by the water is equal to the heat released by the steam. Heat absorbed by water = 36*1000*4.2*6 = 907200 kW. Heat released by steam: 2.1. When steam at 150°C condenses into water at 150°C, latent heat is released; the latent heat of vaporization is 2118.5 kJ/kg. Q1 = W*R = 2118.5 W. 2.2. When water at 150°C cools down to 36°C, latent heat is released. Average temperature = (150 + 36)/2 = 93°C. The specific heat capacity of water at 93°C is 4.2 kj/(kg*°C). Q2 = W*C*(T1 – T2); Q2 = 4.2*114 W = 478.8 W. 2.3 Heat released by steam: Q1 + Q2 equals the heat absorbed by water. 907200 = 478.8 W + 2118.5 W; therefore, w = 349.3 kg, which means that 349.3 kg/h less steam is required
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1. Do you recycle your steam condensate? If it is to be recycled, has the cost of producing pure water been considered? 2. Isn’t 30 degrees for the circulating water perfect? Why raise the temperature?
The calculation seems fine. What is the purpose of your circulating water? Why do you need to raise its temperature? Condensate is used to supplement industrial water; compared to 350 kilograms of superheated steam, doesn’t using 5 tons of condensate increase costs?
I would like to ask: if saturated steam at 0.4 MPa is already at 151.5°C, why is the superheated steam at 0.5–0.6 MPa only at 150°C? I don’t understand, please advise!
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Condensate water should be recycled; the cost of water softening treatment has not been taken into account
The original poster’s calculation overlooked one thing: since the condensate water is at 80 degrees, it has nothing to do with the latent and sensible heat at 150 degrees. Calculating using enthalpy values is more accurate. Let me do the calculation now. The enthalpy of water at 30 degrees is 125.6 kj/kg, at 36 degrees it is 150.73 kj/kg, at 80 degrees it is 334.94 kj/kg, and the enthalpy of steam at 150 degrees is 2750.7 kj/kg. 5*971.8*334.94 + 30*995.7*125.6 = 36*993.6*150.38; therefore, 36 degrees is an appropriate choice. 5*971.8*（334.94-150.73）=x*2.543*2750.7; X=127.96 kg. In fact, this type of calculation is quite simple – by using the enthalpy values at each state for mass and energy balance calculations, it’s very difficult to make mistakes.
The calculation upstairs is very simple and clear! Learned* it
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