吸收与冷凝——成酸过程中的传热

Absorption and condensation—heat transfer in becoming sulphuric acid

传热不影响吸收,而吸收减缓传热,所需填料量与吸收率相关。吸收率99.99%的一吸塔,填料高度1.63 m,2/3高度的填料完成了99.9%的吸收,吸收率从99.9%到99.99%则用了1/3高度的填料,气液温差随填料高度指数减小,于50%高度下归零。初始吸收的均匀性不影响传质,但对空间冷凝至关重要,分酸不均就会发生空间冷凝。避免空间冷凝的关键是提高下塔酸温。二吸塔所需填料比一吸塔多,相应吸收率下的填料高度都有增加,在1/4填料高度前完成传热。表面冷凝的反应热发生在气相,成为气液间传热,表面冷凝比吸收容易。空间冷凝时传热制衡传质,传热与传质相互协同,相变与颗粒同时产生,大部分相变热留在气相。表面能与粒径成反比,冷凝器出口的空间冷凝更难、初始粒径更小。

Heat transfer does not affect absorption,while absorption slows heat transfer,and the amount of packing required is related to the rate of absorption.For the interpass absorption tower with an absorption rate of 99.99%,the packing height is 1.63 m,and the packing at 2/3 height completes the absorption of 99.9%.When the absorption rate is from 99.9%to 99.99%,the packing at 1/3height is used.The gas-liquid temperature difference varies with the packing.The height index decreases,returning to zero at 50%height.The uniformity of initial absorption does not affect mass transfer,but is critical for space condensation,which occurs due to uneven acid distribution.The key to avoid space condensation is to increase the acid temperature of the lower column.The final absorption tower requires more packing than the interpass absorption tower,and the packing height under the corresponding absorption rate increases,and the heat transfer is completed before 1/4 of the packing height.The reaction heat of surface condensation occurs in the gas phase and becomes heat transfer between gas and liquid,and surface condensation is easier than absorption.During space condensation,heat transfer balances mass transfer,heat transfer and mass transfer cooperate with each other,phase transition and particles are generated at the same time,and most phase transition heat remains in the gas phase.The surface energy is inversely proportional to the particle size,the space at the condenser outlet is more difficult to condense and the initial particle size is smaller.