Redeployment of the BKM Condensate Heater

Rudra Bandyopadhyay
Process Engineer, Australian Paper Maryvale Mill, Australia

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Keywords: Condensate, heat exchanger, waste heat recovery

There is a close interdependence between the Fibrelines and chemical recovery unit operations at Maryvale apart from the obvious one of white and black liquor. In the Batch Kraft Mill a Chemiwasher (horizontal belt washer) is employed which uses hot water (evaporator condensate) for pulp washing applications. This hot water is sent from the chemical recovery plant at around 75 degrees Celsius. A couple of years back a project was designed to use the hot condensate from the pulp cooking process and use it to heat the incoming evaporator condensate by about 8 C. This would help with steam savings in recovery as they were using steam to heat up the evaporator condensate just for the Batch Kraft Mill. Thus, a condensate heat exchanger was designed to achieve the aforementioned effect; however, the heat exchanger was designed with no control/interlocks, which nearly resulted in a safety incident, and it was taken offline around 12 months back in August 2020.

This was costing about 3t/hr of additional steam used in the chemical recovery section of the plant. Further there was an additional 3 t/hr of flash steam being wasted in the Batch Mill which was being generated from the cooking process. We decided to redesign the heat exchanger by adding more instrumentation/controls and logic to ensure that it can safely be used. The heat exchanger has recently been commissioned, all the necessary documentation has been updated and is saving the business about 6 t/hr of steam and also providing hot water to the chemiwasher for better pulp washing. During my presentation, I will be talking about all the improvements made to ensure that the heat exchanger can be run in a safe fashion and be optimized to produce the maximum heat transfer that it was designed for. I will also be talking about the steps taken to ensure all the operators were aware of the changes made to the process and how the condensate heater was designed to be operated.