Are the non-condensable bleeds on thermocompressor sections necessary?

Process Optimization

Most thermocompressor sections are equipped with a non-condensable bleed (NCB) which are are applied to thermocompressor sections to prevent accumulation of non-condensable gases in the dryers.

If allowed to accumulate, the non-condensable gases will diminish heat transfer rates for paper dryers in the steam section and cause non-uniform cross direction dryer surface temperature profile. This will lead to non-uniform cross direction sheet moisture profile.

Today, most boilers generate steam with extremely low levels of non-condensable gases and some producers seem to "get by" with no NCB's on their thermocompressor sections. Still, most steam system suppliers advocate having a NCB to safeguard against costly operational problems.

The discharge from NCB's is usually directed to atmosphere or a condenser. In this case, the presence of the bleed has negative effect on energy efficiency. In some cases the need for a NCB is avoided by arranging an individually controlled dryer (that drains to a condenser) to draw its steam from a thermocompressor section. Where allowable, this is an advantageous concept.

The most prevalent improvement opportunity for NCB's is to gain an appropriate flow rate. For a typical thermocompressor section, an NCB flow of 100 to 200 lbs/hr is generally considered adequate to protect against accumulation of non-condensable gases. To ensure the desired flow rate is achieved, the bleed should be equipped with a properly sized stainless steel orifice plate.

When it comes to NCB's, avoiding excessive flow rate will save steam. Your mill might benefit from a review of your NCB's.

Source: Kadant

We use cookies to improve your experience on our website. You consent to the use of cookies by continuing the use of the site. Read more about our cookie policy and privacy statement.