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Replacement Digester Liquor Heater

Increasing the heat transfer area to eliminate the need for direct steam injection.

Dates: 2016-2019
Solution Type: Chemical processing / by-product recovery

Project Overview


A mill in the southern US contacted Lundberg to replace an old external digester liquor indirect heater. The customer provided drawings for the existing unit along with current process information to see if design improvements could be made. The customer also expressed that significant scaling was occuring on the tubeside, and as such, frequent acid washing was required.

Lundberg analyzed the existing unit design and process information.  In doing so, Lundberg determined that the current operating tubeside liquor velocity was lower than design.  Lundberg’s proposed design resulted in maintaining the design flow rate through the heater and tubeside liquor velocity, while increasing the heat transfer area. This was achieved while maintaining the existing vessel dimensions to allow for minimal modifications to the existing piping and supports.  In addition, Lundberg recommended a change to the acid washing procedure to allow for the tubeside metallurgy to be a less costly material than the existing unit.

The digester liquor heater was successfully installed and exceeded operations expectations.  Prior to installing the replacement liquor heater, the mill was using direct steam injection to heat liquor in addition to the indirect liquor heater.  With the increase in heat transfer area, direct steam injection is not needed now.  Furthermore, acid washing frequency has been decreased.  Due to the operational improvements, the client has ordered additional replacement liquor heaters for their other digesters.

Q: Why Lundberg?

A:  Our long history in solving problems with heat transfer applications and our ability to analyze customer process information and equipment and to improve on existing designs. 


  • Replace existing old digester liquor heater
  • Improve liquor heating design


  • Heat transfer
  • Heat exchangers 
  • Lundberg know-how and engineering expertise


  • Increased throughput
  • Fewer acid washes
  • Reduced steam usage
  • Eliminate need for direct steam injection