Transfers of pharmaceutical powders can be toxic, cause dust and prone to explode. Dec describes its safe system for charging reactors with powder.
A safe solution to the problematic and often hazardous operations of powder transfer and charging in process industries is the Powder Transfer System (PTS), developed and patented by Dec.
The system is capable of automatically transferring toxic, explosive or other types of powder into closed vessels containing dangerous vapors and liquids, at any temperature.
The PTS is designed for pressure and is installed directly onto existing process equipment, predominantly reactor vessels. By using a source of absolute vacuum and pressure, the PTS can transfer powders in the same way that liquids can be conveyed, over large distances (horizontal and vertical), in a variety of volumes, and directly into vessels in a safe and contained way. This means that a powder room on the ground floor can be used to charge reactors installed several floors up.
The PTS works for all powders regardless of their characteristics, even those that are extremely fine, lumpy or even solvent wet, as during the transfer of such materials the PTS will not modify the homogeneity of the powder.
Full vacuum draws powder from the storage container (drums, bags, FIBCs or hoppers), usually via a simple stainless steel lance held by the operator, and conveys it into the PTS cylindrical chamber. A flat filter membrane separates the chamber from the vacuum line preventing powder reaching the vacuum pump. When the chamber is filled with powder the vacuum valve closes and pressurized nitrogen or other inert gas is supplied to the chamber.
Once an overpressure is created within the chamber the powder is pneumatically discharged into the designated receptacle as soon as the outlet valve is opened. The overpressure also prevents gas and vapor that may already be present within the reactor from rising back up into the PTS chamber. Furthermore, the source of pressure also serves to clean the filter membrane at the top of the chamber (reverse jet) after every cycle of the PTS, thus ensuring each cycle performs under optimum conditions.
The PTS uses pneumatic logic to power the entire process, and forms a physical barrier between the designated receptacle and the PTS chamber, reducing the risk of explosive atmospheres developing without the need for isolation valves.
The system excludes most sources of ignition owing to the earthed, conductive components, and the lack of moving parts that could produce incendive mechanical sparks. Its pneumatic operation does not require a source of electricity or motors, obviating electrical sparks and hot surfaces that could also be ignition sources.
Electrostatic discharge remains the only potential ignition source; however, this is avoided due to the plug flow of powder in the dense conveying phase through the hose into the PTS chamber. The usual ratio of powder to air is more than 100:1, which is well above the upper explosion limit of most powders.
Due to the low conveying velocity it has been calculated and measured by the Swiss Institute of Safety & Security that insufficient energy is created to form an electrostatic discharge and powders with an MIE (minimum energy required for ignition) below 1 milijoule can be safely conveyed.
Oxygen enrichment of recipient vessels, which increases the potential for explosion, is an inherent problem of most powder transfer systems; the only exception is the PTS. A combination of the plug flow conveying, vacuum within the PTS chamber and inertion by nitrogen ensures that the oxygen concentration in the reactor remains below the limiting oxygen concentration at which explosions are possible.
Protection for operator, product and environment
In addition to the safe transfer of explosive powders and the reduction in operator manual handling, the transfer of highly toxic materials can also be achieved with the PTS. As it is a completely closed system it offers protection to the operators, product and the environment.