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    石化领域中聚乙烯生产

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    聚乙烯(PE)生产/POLYETHYLENE (PE) PRODUCTION

    1. 详细信息

    问题
    在聚乙烯生产过程中,一部分乙烯和其他碳氢化合物原料将有损 失。损失的原料价值巨大,一个典型的聚乙烯装置每年损失约一百 万到三百万美元。主要的损失发生在生产工艺过程中的三个点:在乙烯回收和提纯单元中精馏塔顶排气,反应器排气和树脂脱挥排气。
    VaporSep® 解决方案

    在树脂脱挥应用中,排气物料经过压缩和冷凝分理出碳氢化合物。但气体离开冷却器后仍有大量的碳氢化合物。这部分气体进入到膜回收单元,将物料分离为富碳氢化合物渗透物料和提纯的氮气残余物料。渗透过去的物料循环到压缩机入口,之后经冷凝器回收碳氢化合物。提纯的氮气经循环返回到脱气仓。对于精馏塔塔顶和反应器排气应用,VaporSep®单元非常简单,只包含膜模块,没有运动部件。离开塔或反应器的物料通常含有轻组分如氮气和氢气。VaporSep®单元将这股物料分离成富碳氢化合物物料和富轻组分物料。富碳氢化合物物料返回到精馏塔中或反应器中回收碳氢化合物,富轻气体物料排放或去火炬。VaporSep®单元被当今主要聚乙烯生产商使用,包括:埃克森美孚,Formosa塑料,沙比克,和中石化。

    优点

    ■ 回收有价值的单体和其他碳氢化合物,回收周期小于一年;
    ■ 提纯氮气在工艺中再利用

    ■ 撬装结构,最少的安装时间和费用
    ■ 减少焚烧或火炬需求
    ■ 与单一冷凝的方法相比,有更高的回收率
    ■ 与单一冷凝的方法相比,回收的温度和压力更缓和
    ■ 最小化的尺寸和重量

    ■ 不产生二次污染源

    Problem
    During the production of polyethylene (PE), a portion of the ethylene and  other hydrocarbon feedstock is lost. The value of the lost feedstock is substantial, ranging from $1 million to $3 million per year for a typical PE plant. Losses occur primarily at 3 points in the production process: distillation column overhead  vents in the ethylene recovery and purification step, reactor purge vents,  and resin degassing vents.

    VaporSep® Solution

    For resin degassing applications, the vent stream is compressed and cooled to condense hydrocarbons. The gas leaving the condenser still contains a significant amount of hydrocarbon. This gas is fed to the membrane section, which separates the stream into a hydrocarbon-enriched permeate stream and a purified nitrogen residue stream. The permeate is recycled to the inlet of the compressor and then to the condenser where the hydrocarbon is recovered. The purified nitrogen stream is recycled to the degassing bin.
    For distillation column overhead and reactor purge applications, the VaporSep® unit is very simple, consisting of membrane modules only, with no moving parts. The stream leaving the column or reactor is typically contaminated with light gases such as N2 and H2. The VaporSep® unit splits this stream into a hydrocarbonenriched stream and a light-gas-enriched stream. The hydrocarbon-enriched stream is returned to the distillation column or reactor where the hydrocarbon is recovered, and the light-gas-enriched stream is vented or flared. VaporSep® units are currently used by major PE producers including ExxonMobil, Formosa Plastics, SABIC, and Sinopec.
    Benefits

    ■  Recovers valuable monomers and other hydrocarbons with typical payback time of less than 1 year

    ■  Purifies nitrogen for reuse  in the process

    ■   Minimizes installation time  and expense with  skid-mounted construction

    ■  Reduces incineration and  flare requirements

    ■  Achieves significantly higher hydrocarbon recovery than possible  by condensation alone

    ■  Allows recovery at more moderate temperatures and pressures than condensation alone

    ■  Minimizes footprint and weight

    ■  Creates no secondary waste streams