The Greenbank Cylindrical Riffle
The distribution of pulverised fuel (PF) to the burners in a large generating station or industrial boiler is a major factor affecting combustion performance. Bad PF distribution may result in reduced combustion efficiency, high excess air, fireside corrosion, increased fouling, excessive temperatures
and emissions. It is well established that good PF distribution to the burners will cause a marked improvement or elimination of these problems. A reliable way to achieve good PF distribution
is to use a riffle, preferable of the type developed by the Central Electricity Generating Board Laboratories in the UK (C.E.R.L.) at each split or bifurcation in the pipeline.

For ease of construction for the internal parts, riffles have historically been housed in flat-sided asings of rectangular cross section.

The advent of higher design pressures for all the constituents of a pulverised fuel system, except the mill, has resulted in an extremely heavy, complicated and expensive external bracing of all flat sided components. A better solution is substitution by cylindrical components of modest wall thickness, which do not require additional strengthening. Furthermore, the cylindrical riffle offers a lower pressure drop over the traditional type as the change in cross section is significantly more subtle.

A skilful redesign of the standard C.E.R.L. riffle has enabled the riffle internals to be housed in a plain cylindrical, lined or unlined, casing to produce the Greenbank patented Cylindrical Riffle. Such simplifications of the casing mean that it is no longer necessary to provide access doors to remove the internal riffles. This higher-wearing section can be supplied as an expendable, replaceable unit.

The basic riffle unit is available in six sizes. The body, inlet and outlet sections can be specially designed to suit the inlet and outlet parameters of any application.

The Cylindrical Riffle is also well suited to satisfy a one into four splitter arrangements which is normally achieved using three separate C.E.R.L. riffle boxes and complicated transition pieces. Since, by connecting two units together so the two outlets of the first each connect with half the inlet of the second, a simple one-in-four unit can be produced. To complete the high pressure PF system, the Greenbank cylindrical Riffle is complemented by the Greenbank KleNEflo valve, a simple and effective non return or isolation valve fitted again into a cylindrical housing.