Sulphur-scrubbing products

A thorough understanding of the chemical and mineralogical composition of CCPs is necessary for proper management of these materials. This chapter will cover (1) the composition of coal (2) the formation of CCPs (3) the physical, chemical, and mineralogical characteristics of CCPs (4) characterization of North American fly ashes (5) hydrated minerals in fly ash/ water pastes (6) sulphur scrubbing products and (7) environmental impact of CCPs. 

For many years a major route to the production of vinyl chloride was the addition of hydrochloric acid to acetylene (Figure 12.5). The acetylene is usually prepared by addition of water to calcium carbide, which itself is prepared by heating together coke and lime. To remove impurities such as water, arsine and phosphine the acetylene may be compressed to 15 Ibf/in (approx. 100 kPa), passed through a scrubbing tower and chilled to -10°C to remove some of the water present and then scrubbed with concentrated sulphuric acid. 

After scrubbing to remove loosely attached corrosion products, cathodically polarise in hot dilute sulphuric acid under the following conditions ... 

In the coal gasification, as well as in the FT process massive amounts of CO are inevitably produced. CO is the main component of the off-gas in the Sulphur recovery plarft (see above) and in the Benfield plant (which scrubs CO2 from the Synthol tailgas). The latter source is the purer of the two. CO is used in fire extinguishers and the production of "dry ice". 

In liquid fuels, the sulphur is present in many different chemical forms primarily combined in organic molecules such as sulphides, disulphides and mercaptans. To remove it from the liquid fuel, the sulphur values are converted to hydrogen sulphide by reaction with hydrogen. At present solid fuels (coal) are usually combusted prior to removal of sulphur and the resulting sulphur dioxide is scrubbed from the flue gas producing waste sludge or by-product acid. However, most coal liquifaction and gasification processes favor removal of sulphur... 

There are three basic stages to the process, shown in Figure 11.9, external to the electrolysis section. SO2 is absorbed and reacts with the bromine. The reactor product solution is then concentrated by evaporation using the sensible heat contained in the entering flue gas. All the HBr and the majority of the water are vaporised and an 80% to 85% sulphuric acid solution is produced. The desulphurised gas leaving the reactor is scrubbed with water to remove the HBr and the acid droplets. In the ISPRA plant the total electrode surface area is 64 m. The current density of operation is 2000 A m and at a temperature of 50°C the cell voltage is between 1.3-1.4 V and the current efficiency for bromine production is 90%. 

Collection of products. H2 is obtained 99.9% pure by countercurrent scrubbing with cooling water. CI2 is obtained 97% pure (1.5% O2) by direct or indirect cooling with water followed by countercurrent drying with 98% sulphuric acid. It is then compressed and liquefied in steel pressure tanks. NaOH is obtained in 50-70% concentration by evaporating in nickel or ferritic steel evaporators. 

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