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The heart of any urea plant is the high pressure synthesis section where the two feeds, ammonia and carbon dioxide, are converted to urea with water as a byproduct. As this conversion reaction is an equilibrium reaction, a purification/recirculation section is needed to separate urea (and water) from the more volatile non converted feeds. Downstream of the recirculation section, urea and water are separated in a concentration/evaporation section. Under vacuum conditions water is evaporated and the urea melt is concentrated to about 96 or 99.6 wt-% depending on the type of finishing section present.

The first subject to be discussed is the problem of foaming in the purification and concentration sections of a urea plant. Problem No. 1 Foaming in purification and concentration section. Mr Muhammad Ahsan Sarfraz of Fatima Fertilizer Limited in Pakistan posts a serious operational problem, which he experienced in the Pak-American Fertilizer Limited urea plant in Mianwali, Pakistan, where he previously worked: We have been experiencing a strange problem in our urea plant. It is now the third time that all the sight glasses of the high and low pressure decomposer, concentrators and flash tank start have indicated a sort of soap foam. When this phenomenon happens we experience higher free NH3 in the product but all the operating parameters of the synthesis and concentration section remain the same. No abnormality in lab results are observed indicating slippage of NH3 to the concentration section. Moreover the operating vacuum pressure in the concentrators remained the same i.e. 190 mm Hg and 45 mm Hg respectively. The high free NH3 in the product doesn’t affect the vacuum and the operating conditions of the section also remain the same. Is there anybody who can help me out?

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任何尿素装置的核心都是高压合成部分,原料氨和CO2在此处转化为尿素和副产物水。由于该转化反应为平衡反应,因此需要提纯/循环系统把尿素(和水)从更易挥发的未转化的原料中分离出来。尿素和水在下游浓缩/蒸发系统中分离。在真空条件下,水分蒸发,尿素水溶液将根据所采用造粒技术浓缩成96wt-%或99.6wt%的熔融尿素。

第一个讨论的主题是尿素装置循环和浓缩系统的起泡问题。第一个问题是提纯和浓缩系统起泡。巴基斯坦Fatima Fertilizer公司的Muhammad Ahsan Sarfraz先生提出了一个严重的操作问题,这是他以前在巴基斯坦Mianwali市Fatima Fertilizer公司尿素装置工作的经验:在尿素装置上我们一直经历着一个很奇怪的问题。现在这已经是第三次在高压和低压分解塔、蒸发器和闪蒸槽的试镜上观察到一种肥皂泡沫。当这种现象发生时,产品中的游离氨含量就会增加,但是合成和浓缩系统的所有操作参数都未变化。除指示NH3进入浓缩系统外,实验结果中未观察到任何异常现象。同时蒸发器的操作真空度也未变化,例如分别是190 mmHg 和45mmHg。产品中游离氨含量高并未影响到真空度和系统的操作条件。有人能帮助我吗?

 

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