A petrochemical plant in Haifa uses on line NIR (Near Infra Red) analysis to monitor its processes and provide data for process control. A sketch of the plant is shown in Figure 1. The NIR instrument is a PetroMetrix Beacon Analyzer. The Analyzer, which is located in the control room, connects to the field units throughout the plant using a multiplexer and telecommunication fiber optics. It interfaces to a Honeywell TDC3000 through a Modbus interface.
The NIR analyzer replaces gas chromatographs that have been previously used in these applications. The NIR analysis has much faster response time and lower maintenance requirements than the GCs typically used in these applications. The faster response time and reliable continuous data provided by the analyzer (see Table 1) resulted in improved control of the process units:
Analysis of naphtha feed to the catalytic reformer allows advanced control of the reformer.
Analysis of the reformate, used as feed for the petrochemical plant, can be applied for advanced control of the petrochemical processes. The reformate is also analyzed for octane number, as it is used in the refinery for gasoline blending.
In the ortho-Xylene process, the instrument monitors the ortho-Xylene to total Xylenes ratio. This allows higher recovery, better purity and increased production of ortho-Xylene. Less contaminants enter the para-Xylene process, due to the improved ortho-Xylene recovery.
In the para-Xylene process, the NIR analyzer monitors the contents of para-Xylene and other aromatics in the process, allowing greater throughput and recovery while maintaining product purity.
Although one might not expect NIR to be able to distinguish between Xylene isomers, the high resolution of the instrument allows this on-line analysis. Multiplexing several probes results in cost efficient analysis at several points in the plant. Installation was very straightforward: telecommunications fiber optic was laid in existing trays to the probe locations. The only other utility required was standard electric power.
The field units (sample cells) are maintenance free. No sample conditioning was required, beyond cooling some of the streams to be within the pre-defined range.
Table 1: Properties measured with the NIR instrument
|Field Unit 1:
|Field Unit 2:
|Field Unit 3:
|Field Unit 4:
|Initial Boiling Point||Toluene||ortho-Xylene||Total Xylenes|
|50% Distillation||Ethyl Benzene||Ethyl Benzene|
|Final Boiling Point||Total Aromatics|