Project ForgeAn aqueous suspension at 60°C is fed to a forward-feed double-effect evaporator at 1.25 kg/s. Total water evaporated (both effects) is 1.0 kg/s. Exit stream temperatures are 100°C (effect 1) and 60°C (effect 2). Specific heat=4 kJ/kg·K, latent heat=2200 kJ/kg (both effects). The steam economy (kg/kg) is (round off to 2 decimal places)
Explanation
Effect 1: S×2200=1.25×4×(100−60)+W1×2200=200+2200W1. Effect 2 (fed by effect-1 vapor plus the flashing liquid from effect1): W1×2200+(1.25−W1)×4×40=W2×2200. With W1+W2=1.0, solving gives W1≈0.472, W2≈0.528, S≈0.563 kg/s. Steam economy=(W1+W2)/S=1.0/0.563≈1.78.
Source: GATE CH 2020 (2020)
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