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Explosion protection and process safety

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.
Vacuum transfer
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.
PTS Inox version
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.
Intrinsically safe
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
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.
Oxygen concentration PTS
 
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.