Treatment of off-gases
The utilization of off-gases has become increasingly important. In the past, process waste gases were mainly conducted by an activated carbon adsorber before being directly discharged into the atmosphere. Today elaborate measures must be applied to comply with the emissions standards.
Depending on the type and the amount of these off-gases, different technical solutions are provided: In particular is the recompression with an off-gas compressor or thermal utilization. The cleanest of these solutions is undoubtedly reinsertion into the main gas stream. Usually piston or membrane compressors which compress the excess waste gases to process pressure are applied for this purpose. However, to avoid damage to the compressor these gases should not contain any free liquids before the compression. Furthermore this variant requires a continuous stream of flash gases and the excess amount should be large enough to justify the high investments.
As an alternative to the off-gas compressor, a burning chamber can be used. In this case, not only the offgases but also the vapours of the regeneration may be thermally disposed of. This flexible system enables low-emissions operation of dehydration plants, even at strongly varying amounts of waste gases.
Mercury removal and deep desulfurization
In the natural or associated gas compositions containing mercury or small amounts of H2S, the main gas stream and the off-gases must be freed of these compounds. Adsorb units with various adsorbents are specially designed to do this. The design of these units is not only defined by throughput and loading but also the impurities and liquid loads are to be taken into consideration.