| 摘要 |
The exchanger contains a number of elements (6) exchanging heat between the first and second fluids, parallel to the plates. The elements are placed next to each other both parallel and perpendicular to the plates over their whole length and at their ends are distributors and guides so the fluids circulate in contra-flow in each element and follow the whole length of each element in succession Plate heat exchanger with first and second fluids circulating through it, with a considerable length, in particular for an installation for crystallizing a substance contained in a liquid (aqueous) solution comprising first and second fluids. The heat exchange elements are parallelepipeds with square or rectangular bases. The distributor and guides includes collectors fixed to the ends of the heat exchange elements so the two fluids flow from the end of one element to the adjacent one. At least some collectors have walls dividing them into two compartments to distribute the first and second fluid respectively. The distributor and guides also have pipes connecting distribution and reception collectors, one for each fluid. Crystallization process for a chemical contained in solution, for example aqueous, in the form of purified and calibrated crystals, using such a plate heat exchanger where a first fluid containing non-calibrated and impure crystals is circulated to be heated by exchange with a second fluid at a dissolution temperature to produce a homogenous solution containing the impurities. This solution is introduced into a reactor to separate the impurities out and produce a second purified solution, which is circulated through the heat exchanger as the second fluid. At the outlet for the second fluid, water and purified and calibrated crystals are recovered. The fluids flow through the exchanger at a rate of between 0.5 and 1 m/s and a pressure of the order of 200 bars. The channels in the exchanger have a length of between 20 and 300m. The first solution is heated to a temperature of the order of 300 degrees C before passing to the reactor. The chemical being crystallized is paraxylene, dimethyl naphthalene, an aromatic carboxylic acid or an anhydride such as terephthalic acid or isophthalic acid, trimellitic acid, trimellitic anhydride, dicarboxylic naphthalene acid, diphenylcarboxylic acid, pyromellitic acid or pyromellitic anhydride and oxybisbenzoic acid.
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