Measurement of O2 Concentrations in Vacuum Distillation Column in Petroleum Refining

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Introduction

O2 measurement in hydrocarbon vapor is used for safety monitoring in vacuum distillation columns in petroleum refining. With conventional paramagnetic oxygen analyzers, O2 concentrations are obtained through an extractive sampling system, which conditions the sample prior to being analyzed. Sample systems cause measurement response time delays, which are very critical in safety systems. Moreover there are many problems related to maintenance and operational costs of sample systems. The process gas to be measured contains high concentration of H2S that leads to quick corrosion of the sample system and analyzer. Another issue when using sampling systems is the sample is not representative of the process after the sample has been conditions and dew point of the sample has been modified, which affects the volume concentration of the sample.

The TDLS8000 Laser Analyzer is the solution to all these problems.

 

Expected Benefits

  • High-speed response to meet all requirements of safety control
  • Continuous monitoring of O2 concentration in-situ
  • Eliminates the need for sampling and reduces the maintenance and running costs of the sampling system

 

Process Overview

The vacuum distillation column is used to distill the residual oil from the atmospheric distillation column. The distillation must be performed at absolute pressures as low as 2 to 15 kPa so as to limit the operating temperature to less than 370 to 380°C and to avoid hydrocarbons cracking processes. The presence of oxygen in the process can be caused by suction and can lead to explosion. Thereby there are rules to control the O2 level in vacuum columns. At level 2 to 5 % O2 the alarm and purging of vapor line by inert gas has to be switched on. That is why high-speed response and high reliability are required for O2 measurements.

 

Advantage

  1. vs Conventional Paramagnetic O2 Analyzer
    Conventional Paramagnetic O2 analyzer cannot be used in-line measurement.
    The TDLS8000 is capable of directly measuring the O2 concentrations in the vapor line, instead of conventional paramagnetic oxygen analyzers that perform measurements through a sampling system. When using traditional analyzer systems, since the application is for a process working under depression (vacuum), a pump is required. The deeper vacuum the more difficult it is to provide the proper pump. Sometimes it results in seal failure and air leakage and failure measurement results.
  2. vs Other TDL Analyzers
    The shape of O2 absorption spectrum become very sharp under this vacuum condition, which is difficult for other TDL analyzers to measure O2 concentration accurately.
    But only TDLS8000 can measure O2 concentration accurately under such vacuum condition by True Peak integration (area) method. For the pressure variation test data, see next page.
Vacuum Distillation Column
Vacuum Distillation Column

Solution Details

Measurement System

TDLS (O2 Analyzer):
  • TDLS8000-☐☐-X1-☐☐-A1-☐-N/Z
    /Z: Very low pressure
Isolation Flange:
  • IF8000-☐☐-☐☐-☐☐-12-N
    Note: It is needed the suitable pressure class of the used flanges.

Measuring points of vacuum distillation column
Measuring points of vacuum distillation column
Measuring points of vacuum distillation column

Pressure Variation Test Data

This graph shows O2 measurement on 21%, 4%, 0.8% level under condition which gas pressure change from 1 BarA to 0.2 BarA by TDLS, and shows the measurement done stably and correctly without influence of pressure change.

O2 absorption spectra shape is big changed by pressure change, but the spectrum peak area change to pressure proportionally, so TDLS can compensate pressure influence correctly.

Measurement Value of O2 Concentration under Pressure Change 1 BarA to 0.2 BarA
Measurement Value of O2 Concentration under Pressure Change

產業別

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    石化公司的需求極為多樣繁雜。為了在當今競爭激烈的市場中脫穎而出,生產企業必須努力提高質量和生產力。橫河電機在石化領域長期耕耘具有廣泛的經驗,我們可以為客戶的需求提供量身定制的解決方案。

     

     

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  • 精煉

    在不斷變化的市場中,煉油廠不僅是原油加工單位,而且是利潤中心。同時,人們強烈意識到煉油廠設施安全性的重要。為了實現盈利,效率及環境保護的長期目標,需要包括計劃,調度,管理和控制的總體生產解決方案。憑藉在自動化領域多年積累的專業知識,橫河可以為您提供經濟實惠的完善的整體解決方案,改善操作並使世界更清潔。

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