A pharma manufacturing company needed air at a temperature of around 55OC and RH of minimum 65%. Air has absolute moisture content of 70.4g/kg of dry air at that condition. The process involved air intake at 25OC and 50% RH (10 g/kg of dry air) and raising its temperature and RH to the desired level of 55OC and 65% RH.
Psychrometric chart – old process Figure 3: Psychrometric chart – new process
The process equipment manufacturer had supplied equipment which first added steam for humidification and subsequently heated the air (see Figure 2). However, even as air at 25OC and 50% RH was humidified directly, it reached saturation at moisture content of 20.2 g/kg with a resultant relative humidity level of 20% at the desired temperature of 55O C as the air was heated. Any further addition of moisture was impossible.
The solution was to heat the air to 55OC first and then add steam (see Figure 3). Fortunately the client had a supply of pure steam available. A steam dispersion pipe fitted with a modulating valve to control the steam supply, complete with condensate drain arrangement, was proposed.