It is time to examine process stream analysis

The number of laboratory methods for the analysis of samples from process streams has increased tremendously so that the analytical chemist need only review the literature to find one suitable for his application..The literature cites many methods by gas and liquid chromatography, atomic absorption , infra-red, ion chromatography, etc. The direct application of analytical methods to continuous analysis of process streams has recently grown as rapidly or as profusely as laboratory methods. There are many advantages to continuous analysis for example, increased yield of a pure chemical such as in the fractional distillation of benzene, toluene, and xylene. Here, when the operator finds toluene distilling with benzene, he diverts the distillate to a separate tank so that the pure distilled benzene is not contaminated. But it is difficult to assess when all the pure benzene has been distilled and the results of laboratory analysis on stream samples would be too late to be of any value to the operator. On-stream analyzers reduce quality variations of manufactured products in the petroleum and chemical industries. There is better yield of the valuable chemical and both operating costs and energy consumption are reduced. Plant capacity is increased and a reduction in standard deviation leads to a more uniform product. Reprocessing of off-specification material is reduced which increases customer satisfaction and ultimately sales. In the petroleum industry on stream analysis contributes to longer catalyst life, less coking, and less distillation flooding. combustible occupational environments, consumer product quality and safety have also contributed to expanding interest in on-stream analyzers. Microprocessors are replacing mechanical cams, punched or magnetic tape and logic circuit programmers in many designs and following improved reliability and flexibility, more complex sequences are possible. Also, they are well-suited to handling signal manipulations associated with identifying and measuring peak heights and peak areas of detector outputs, compensating for drift, providing automatic calibration to accommodate changing background substances, alarming measurements outside established limits, and rejecting signals caused by spurious transmission noise. Flexibility exists in the form of output that can be specified, and these instruments are easily interfaced with the plant computer for monitoring or control. In representative distillation column applications, the chromatograph-based control has been found to reduce energy requirements by 10-20%. Other benefits include a 5-10% throughput increase, a 5-30% rise in recovery of the more valuable product, upgrade of the less valuable product and smoother operation of the fractionator or downstream equipment. …