Technical Papers 2017-05-02T18:57:10+00:00

Collecting and Burning Noncondensable Gases

Ben Lin, P.Eng.

Kraft pulp mills are normally characterized by a distinct foul odor. This odor is caused by sulfur compounds, referred to as Total Reduced Sulfur, (TRS) that are generated in Kraft pulping process when wood is cooked with Kraft liquor. TRS can also be generated in direct contact evaporators, in recovery boilers, and in lime kilns. The TRS gases involved are hydrogen sulfide (H2S), methyl mercaptan (CH3SH), dimethyl sulfide (CH3SCH3), and dimethyl disulfide (CH3SSCH3).

TRS gases that are emitted from digesters, evaporators, turpentine systems, strippers, brown stock washers and liquor storage tanks are contained in gases referred to as noncondensable Gases (NCG).

Attempts to collect and burn NCG were first tried in the late 1950’s. The initial systems collected the gases in pipelines, using fans as motivators to move the gases.  These systems usually diluted the gases with air to bring the TRS concentrations below their  lower explosive limits. This was not always successful, especially with concentrated gases coming from digesters and evaporators, and many early systems experienced fires or explosions.

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The Basics of Foul Condensate Stripping

Ben Lin, P.Eng.

Foul condensates from the digesters and evaporators contain reduced sulfur gas and organic compounds, such as methanol (MeOH) and turpentine, which contribute greatly to pulp mill water pollution in the form of Biochemical Oxygen Demand (BOD) and toxicity, and air pollution in the form of Volatile Organic Compounds (VOC), and odor.

For this reason, foul condensates are collected and treated by stripping, using either air or steam, to remove the pollutants.  In many cases, the pollutants can be economically used as a fossil fuel substitute.

This paper will cover the condensates that are collected, various stripping methods, types of stripping columns, basic theory, operating problems, the latest operating procedures, and disposal of the stripper off gas (SOG) which contains the pollutants removed.

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Methanol Purification System

Allan Jensen, P.Eng. – A.H. Lundberg

Trevor Ip, P.Eng. – Alberta Pacific Forest Products

Jamie Percy – Alberta Pacific Forest Products

Presented to PEERS Conference, 2012 

Methanol is formed as a by-product of the kraft pulping process. Due to its high relative volatility to water, a large fraction of this methanol will be present in the vapour phase and therefore can be captured in a relatively small foul condensate stream. Many kraft facilities, including the Alberta Pacific Forest Industries (Al-Pac) mill, operate a foul condensate steam stripping system, producing methanol rich stripper off gas (SOG).

At Al-Pac, SOG is currently disposed of through incineration in the lime kiln or power boiler: this flow is to be diverted to the new methanol purification system designed and supplied by A.H. Lundberg Systems Limited. The methanol is recovered by separating it from water and other contaminants through distillation, producing a methanol product at a minimum of 99.85 wt% purity. Some of the purified methanol is to be used internally for the production of chlorine dioxide with the balance for external sale.

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Heat Exchanger Evaluation, Case Studies & A Bit of Theory

Bruce Der, P.Eng.

Presented to PAPTAC Steam, Steam Power & Energy Committee Joint Meeting, Dec 6, 2006

Review of Heat Exchanger Design fundamental theories, Fourier equations, calculation of LMTD and etc.

Case studies include analysis on:

  • surface condenser addition
  • green liquor cooler replacement
  • stripper pre-heater reconfiguration
  • liquor cooler augmentation
  • digester liquor heater replacement
  • bleach caustic effluent heat exchanger

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