Byworth take the Steam Tug ‘Challenge’
The Steam Tug ‘Challenge’ was originally equipped with a 2 pass triple furnace marine ‘Scotch’ type boiler, originally coal fired.
Later converted to simple pressure jet heavy oil burners. The boiler is very short overall length but large in diameter.
Having succumbed to the ingress of sea water severe corrosion resulted in the boiler being condemned finally as a pressure vessel.
A boiler was required to fit into the quite confined and restricted space available in the boiler room and arranged in such a manner that tubes could be replaced by withdrawing through the passageway from Engine to Boiler-room: very narrow.
A boiler 15000 lb/h and 180 psig was required.
Byworth designed a special replacement and the final design comprised a boiler this time a triple pass, with twin furnaces and modern electronic digitally controlled pressure jet dual oil fuel burners. (Ultra Low Sulphur Gas Oil and Low Sulphur Intermediate Fuel)
The boiler will produce a maximum continuous rating of 6,800 kg/h and can operate up to 13.8 bar.g.
The flame length determined the length of the furnace and the overall length possible for the boiler.
Byworth were uniquely able to incorporate special xiD tubes in the design.
The tubes have an internal spiral ribs which increase the turbulence within the tubes thus increasing the rate of heat transfer.
The enhancement the heat transfer from the products of combustion enables considerable reduction in the length of the boiler compared to a conventional boiler.
The turbulence also assists the prevention of deposits with the tube increasing the periods between boiler cleaning.
The precise air/fuel ratio control of the burners and the design of the boiler produce a full load efficiency in excess of 84% gross basis.
The boiler is very liberally designed with a heat release rate within the parallel section of the furnace a low 1.29MW/M^3. This compares with rates in excess of 1.6MW/M^3 on many standard ‘packaged’ boilers. The boiler resistance is also low and the combined effects of these design parameters are low electrical energy to drive the burners and high overall thermal efficiency giving considerable fuel savings. Lower NOx levels are also a function of low furnace heat release rates and lower flame temperature.
The burners can be selected to fire independently and under normal conditions the burners modulate in unison.
An interesting and diverse project involving the expertise of experienced engineers from both boiler and combustion design disciplines.