Decarbonisation Technology - February 2022 Issue

Recovering CO 2 and H 2 S from waste streams Thanks to the development of innovative technologies, a European refinery is now able to recover CO 2 and H 2 S from its waste gas streams

Mahin Rameshni and Stephen Santo Rameshni & Associates Technology & Engineering (RATE) USA

U S and European refineries must comply with some of the most stringent environmental regulations in the world. In the US, these include the Clean Air and Clean Water Acts and the Toxic Substances Control Act (TSCA) (EPA, 1970) (EPA, 1972) (EPA, 2016). Some of these regulations are progressive in that they incorporate mechanisms designed to reduce the level of allowable emissions over time, such as the European Emissions Trading Scheme for carbon dioxide (CO 2 ) emissions and 'Best Available Techniques', or BAT, for reducing emissions of specified pollutants (European Commission, 2021), (Concawe, 2013). In addition, the new marine emissions regulation, IMO 2020, mandates a maximum sulphur content of 0.5% in marine fuels globally. The driver of this change is the need to reduce air pollution created in the shipping industry by lowering the sulphur content of fuels for ships not fitted with scrubbers. The additional processing to produce these low sulphur marine fuels results in increased amounts of waste streams containing SO 2 , NOx, and CO 2 in refineries. Under these environmental regulations, refinery residuals, gases, or materials that would otherwise be emitted to air or water or disposed of as waste are required to be recovered and, where possible, converted to useful products. Conventional processes to restore molecules and energy from waste streams are designed by creating a chemical reaction that combines the carbon-based materials in the waste streams with air or oxygen, breaking them down into molecules, removing pollutants and impurities, and recovering the sulphur.

Waste recovery plants are designed differently to other types of units and, due to environmental regulations, investors are trying to convert such waste streams into useful products and accepting the challenges. Sulphur recovery and CO 2 capture Recently, we have been working on a project developed for CO 2 recovery and SO 2 emissions control in Europe. The technologies developed are unique and the proprietary design is patented by RATE. They include:  The RATE CO 2 liquefaction unit  The RATE two-stage sour water stripper (with H 2 S absorber)  The RATE carbonyl sulphide (COS) hydrolysis reactor – an additional reactor after the hydrogenation reactor in the tail gas unit (TGU)  RATE SETR technology, as alternate to caustic scrubbing, to capture SO 2 before the stack  The acid gas partial enrichment unit by using a tail gas treating absorber. Recovered H 2 S is converted to sulphur through processing in the sulphur recovery unit (SRU) using oxygen enrichment technology. Recovered CO 2 is compressed and sent to the RATE CO 2 liquefaction unit to purify CO 2 further. CO 2 can then be reinjected or used in different applications (such as the transport medium for solid waste conveying, pressure medium for the lock hopper system, seal gas for feeding and withdrawing screw feeders, or as a stripping gas). In this project, CO 2 was used as a stripping gas. There were many challenges in this project