Carbon cuts chemical release

Hickson & Welch specialise in difficult chemistry, producing multipurpose fine organic chemical intermediates in a variety of multistage chemical reactions. These include nitrations, chlorinations, hydrogenation, phosgenation and similar types of complex reactions in 16 chemical production facilities at its Castleford site.

Fire risk exists due to the nature of many organic solvents, and to prevent this the company uses nitrogen gas to excluide oxygen from the reacting mass. As a consequence there are inert gases carrying significant concentrations of solvents in the discharges that require eliminating.

Carbon recycle

Hickson & Welch, however, has successfully reduced releases to atmosphere from 400 tons/annum to 12 tons/annum in a period of three years. Waterlink Sutcliffe Carbons of Ashton-in-Makerfield, which supplies a complete carbon recycle service, can take some credit. At the eight final release points in which the carbon is used, the mean release has been reduced to an undetectable amount of less than 1mg/m3.

The gas flow follows a condensation process, using low temperature calcium brine which removes 90 per cent of solvents. The gas throughput, almost 900m3/hr and at 20,000mg/m3 concentrations, first enters one of two identical in-series cylindrically shaped static beds, each holding 750kg of carbon. During its progress through the first bed, the gas has its solvent concentration reduced to a maximum of 300mg/m3 and subsequently to less than one on passage through the second cylinder.

Solvent concentration levels are monitored daily and when the maximum 300mg/m3 level is reached at the first carbon bed discharge point, this indicates the bed is becoming exhausted. The exhausted bed is replaced, flow is reversed, and the secondary bed becomes the first. It is then returned to Waterlink Sutcliffe Carbon where the spent carbon is regenerated.

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