MPD Powder Dispenser and Recarburizer


MPD POWDER DISPENSER AND RECARBURIZER

  1. The Monocarb Powder Dispenser is a portable self-contained unit which injects solid metallurgical particles into the bath of molten metal. This system allows re-carburisation of iron to high carbon equivalents. De-sulphurisation and re-carburisation can be carried out simultaneously. Iron oxides may be injected into steel making furnaces, and the dispenser is suitable for many non-ferrous applications.

    MONOCARB POWDER DISPENSER

    The Monocarb Power Dispenser is a highly effective tool for the injection of powders into metallurgical processes, having been developed by Monometer and British Oxygen Company (BOC) specifically for use with Rotary Furnaces and Induction Furnaces. Since the Dispenser was first introduced, many units have been supplied to the foundry industry, proving the injection system to be effective over a diverse range of metal melting processes.


    The unit is shown in the accompanying illustration, consisting of a pressure vessel mounted on a portable trolley, all strongly fabricated. The unit is fitted with a filling hopper and screen and a pressure regulator. Each unit is supplied with a gas inlet and gas a powder discharge hoses.


    General Description

    The purpose of the dispenser is to entrain powder in a stream of gas at a pressure above atmospheric so that the gas/powder stream may then be injected into a process via a lance and against a back-pressure (for example, into a bath of molten metal).


    The graphite, sulphur or other powder is placed in the container via the filling hopper and quick-acting valve, which, when shut, seals the internal gas pressure.


    To charge the dispenser, the top cover is first removed and material poured into the receiving hopper is received into the steel pressure vessel. The lid is then closed and the operator opens the gas valve. The carrier gas then passes the bottom of the vessel picking up material for injection with the gas into the process via a lance. A gas pressure regulator mounted on the carriage of the dispenser controls the operating gas pressure, and the gas flow rate is controlled by valve A.


    When the valve B is open, gas leaving via the tub T will carry powder to the point of exit. Gas may also leave the container through the filter F and the valve C (if open). This serves a double purpose – a) to dilute the powder gas stream and b) give extra gas alone when the valve B is closed.

    The dispenser is easily moved on its 3 wheels and may be secured by means of a foot-operated wheel lock.


    Performance

    The dispenser will handle any dry, free-flowing powder of particle size less than 3mm. To eliminate larger particles, a top sieve of No.2 mesh and a bottom sieve of No.6 mesh is incorporated in the filling hopper.

    The useful volume of the container is 70 litres. For example, this volume equates to approximately 50 kg of graphite powder, and more or less of any other material depending on the material density.


    The rate of powder delivery depends on a number of circumstances – 1) the type of powder, 2) the applied pressure, 3) the degree of opening of the valves and, 4) the system through which powder is fed after leaving the dispenser.

    The normal operating range is 4.5 kg to 22.5 kg of graphite powder per minute. The maximum working pressure of the container is 50 psi, with the relief valve being set at this level. As a guide, the flow rate of powder and gas is approximately proportionate to pressure under normal operating conditions, with 18 kg per minute attained at 30 psi. However, flow rate will decrease when the dispenser is used with long hoses and with the lance submerged deeply into a liquid metal bath.


    Typical carrier gas consumption is approximately 0.04 m3 per 1kg of material.


    Adjustment of the gas/powder ratio by means of the valve C allows control of the degree of turbulence imported to the liquid metal bath by the gas flow. 


    If maximum stirring is required, this valve is opened fully, otherwise it is opened just sufficiently to give a stable flow.

    When choosing the carrier gas for use with the dispenser, nitrogen is suitable for most applications, but other gases may be used as required for specific processes.


    The injection lance consists of a graphite tube for immersion into the molten metal, which is screwed by means of an adaptor to a thick-walled mild steel tube. The steel tube is bent through an angle of approximately 45 degrees, close to the graphite tube to enable it to be inserted through the burner port of a Rotary Furnace, or into the crucible of an Induction Furnace.






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