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5.1 Introduction

This section is intended to provide an overview of existing codes of practice and design consideration when designing and operating carbon dioxide producing facilities. It is envisaged that during the early stage of the industry’s development carbon dioxide may be stored in large tanks and vessels and transported in relatively large quantities by road, rail or ship. With this in mind, considerable guidance is given on storage and handling of carbon dioxide in containers of varying size, which may be relevant to plant operation.

Current carbon dioxide sources

Most operational carbon dioxide plants capture carbon dioxide from industrial or natural sources, where it is then purified, compressed and often liquefied for transport by sea, rail or road. In the current carbon dioxide industry the most common sources of carbon dioxide are:

  • Chemical processes (e.g. ammonia, hydrogen, ethylene oxide plants).
  • Fermentation processes (e.g. ethanol plants).
  • Carbon dioxide natural wells.

Carbon dioxide purification

Each feed gas source is unique and since the carbon dioxide plant is designed specifically to remove the impurities in the feed gas, each plant is also unique.

After the typical impurities in the feed gas have been determined, equipment to remove each impurity to meet the required specification is incorporated into the plant design. A quick synopsis of common removal equipment is listed below:

  • Dryers - used to remove moisture from the carbon dioxide but could be used to remove some types of hydrocarbons depending on the bed media selected.
  • Guard beds - used to remove a variety of trace impurities. Type of bed material selected will be dependent on the type of impurity that needs to be removed.
  • Catalytic combustors - used to remove very large quantities of hydrocarbons by combusting the hydrocarbons with oxygen across a catalyst bed.
  • Water wash columns - designed to remove water soluble impurities such as alcohols and amines by scrubbing the carbon dioxide with water.
  • Permanganate towers - used to remove Nox or Sox by scrubbing the carbon dioxide feed gas with potassium permanganate.
  • Sulphur removal/recovery systems - use different technologies including amines, depending on the sulphur compounds to be removed and their concentration in the carbon dioxide.

Non-condensable gases, such as nitrogen, are generally removed in the carbon dioxide liquefaction plant by distillation.