Steam consumption calculation
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I’m a newcomer; please forgive any lack of professionalism. I recently encountered a problem related to estimating the amount of steam required for heat exchange. The given conditions are: design pressure Ps = 1 Mpa, Pt = 0.4 Mpa; the fluid on the shell side is steam, while the fluid on the tube side is water, with a volume of water of 2500 L. The water needs to be heated from 25°C to 130°C at a rate of 2°C per minute. The steam used for heat exchange is at 180°C and needs to be cooled to 100°C. I need to determine the amount of steam required. My understanding is that Q_absorbed = Q_emitted. Q_absorbed = C*M*ΔT = 4.2 KJ/Kg·°C * 2500 Kg * (130 – 5) = 1,102,500 KJ. Therefore, the mass of steam produced is 1,102,500 KJ / (2.562 KJ/Kg·°C * 80) = 5,383 Kg. What is wrong with my calculation? What if the water is heated to 130°C multiple times? How should that be considered?
1. Basically, using steam for heating takes advantage of the latent heat of steam; therefore, it is only a \"phase\" change… the temperature does not change from 180 to 100 degrees. 2. Heating multiple times…?? Unless a heat exchanger is installed later to use the hot water at 180 degrees for heating
For steam heaters, only the heat of condensation of the steam should be taken into account; changes in the temperature of the condensed water are not considered, otherwise the heat exchange area required for the heat exchanger would have to be significantly increased.
What the heck is the number 2.562? ? ?
Let me add that this calculation takes into account heating by a heat exchanger, with a heat exchange area of around 12 m^2. If I were to use enthalpy values for the calculations, how should the enthalpy of the condensate be determined? Is the degree of dryness taken into account? There are many factors that influence this, and since many conditions are not clear, it’s impossible to carry out precise calculations. In actual production processes, we need to understand the temperature of the medium to be heated as provided by the client, as well as the target temperature, along with the steam temperature, in order to estimate the amount of steam required.
I’ll provide my own calculation method for your reference: 1. First, it’s necessary to know the basic information about the material to be heated, including flow rate, its current temperature and the temperature difference to which it needs to be heated, as well as its physical properties (such as viscosity, density, specific heat) – this helps in calculating how much heat is required. 2. If the customer has already decided on the pressure level of steam to be used for heating, then it’s necessary to understand the relevant physical properties at that pressure level (including temperature and latent heat) – this helps in calculating the amount of steam needed. 3. Next, calculate the size of the heat exchanger surface area required. 4. Based on the available space on site, determine the length of the tube bundle and the overall volume of the heat exchanger. 5. Use simulations to conduct further verification (there is excellent information provided by wiseboy** regarding heat exchanger plates; unfortunately, I’m unable to use it on my computer). That’s how it can be done. PS. Since all the data used in these calculations are based on empirical values, don’t forget to include a safety margin (we usually use 20–25%). As for the dryness of the steam… I haven’t considered that yet