Calculation of steam consumption for heating saltwater
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Question: When using a shell-and-tube heat exchanger to raise the temperature of sodium chloride brine with a flow rate of 1 t/h, a concentration of 15%, and a temperature of 40°C to 55°C, how is the steam consumption calculated? (Saturated steam pressure: 0.5 kg; steam condensate temperature to be controlled at 65°C) – Please provide the calculation formula. Thank you!
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Let me explain my calculation method: I looked up relevant information or directly found the specific heat capacity of 15% saline. The saturated vapor pressure of 0.5 kg corresponds to the specific latent heat of vaporization and the temperature of saturated vapor. Calculated the specific heat capacity of water from the saturated steam temperature down to 60 degrees Celsius. Settled according to the law of conservation of energy. The heat released by the hot fluid is equal to the temperature absorbed by the cold fluid. The cold fluid absorbs heat amounting to Q = m (flow rate) × CP (specific heat capacity of brine) × (55 – 40). The hot fluid releases heat equal to Q = m (steam flow rate) × r (vaporization latent heat) + m (steam flow rate) × Cp (specific heat capacity of water) × (temperature of saturated steam – 65). These two amounts of heat are theoretically equal, and this allows for an approximate calculation of the amount of steam required. This is probably the most basic calculation in chemical engineering principles, utilizing the law of conservation of heat.
Thank you for the explanation. But is it usual not to take into account the sensible heat in calculations, and only consider the latent heat of the steam that is utilized? That is, Q = m (steam flow rate) × r (vaporization latent heat), that part