Abstract: A dc power supply (1) for a dc arc torch (6) comprising: an input port (4, 8) for connection to a source of direct current and an output port for connection to the electrodes (5, 7) of an arc torch; a controlled switch (2) and an inductance (3) connected in series between the input port and the output port; a free-wheeling diode (9) connected such that, in use, it is reverse biased when the switch (2) is ON, and forward biased when the switch (2) is OFF to maintain direct current flow through the arc and the inductance (3); and a feedback circuit (10) having a current sensor (11) to sense the instantaneous value of current flowing through the arc, and a control terminal (26) connected to the switch (2), the feedback circuit, in use, operating to provide a control signal at the control terminal (26) to turn the switch (2) ON when the instantaneous value reaches a first level and OFF when the instantaneous value reaches a second level.

Abstract: A gas cooled cathode for a direct current plasma torch. The cathode has a tip connected to a body. A gas passage for working gas passes through the body of the cathode, passes proximate the tip and exits the body adjacent the tip. The cathode is spaced apart from and insulated from the anode by means of a collar of insulation material.

Abstract: A burner which is suitable for use in combusting pulverized coal and which can be used as an igniter for igniting the main burners in steam raising plant. The burner has an electrically powered torch which generates a continuous plasma which extends into a devolatilization zone of the burner, and primary conduits are provided for directing a primary supply of dense phase pulverized coal into the devolatilization zone. The burner is constructed also to include a combustion zone which surrounds the devolatilization zone. The burner is constructed also to include a comubstion zone which surrounds the devolatilization zone, and secondary conduits are provided for directing a secondary supply of pulverized coal into the combustion zone along with a supply of combustion supporting air.