Patented Methanol Purification System
The AHL methanol recovery and purification system is a patented process that produces the following streams from kraft pulp mill foul process condensates or refinery sour water streams:
As separate products, both the recovered methanol and the stripped condensate contribute operational and economic value to the plant.
The benefits of methanol recovery include:
Our commercial system is capable of processing a SOG stream of up to 6000 kg/hr containing up to 2100 kg/hr methanol. Turn-down capability is in excess of 4:1 from design maximum flow. Larger system designs are available on demand.
Methanol Recovery Process Overview
Methanol is produced as a by-product of the kraft pulping process. A large fraction of this methanol is recovered in the foul condensate steam stripping system. The stripper off gas (SOG) is condensed to produce a crude methanol solution, which is upgraded to minimum 99.85wt% in the methanol purification system. Methanol purification is based on the unit operation of distillation, including two separate stages.
In the first “topping” stage, the compounds more volatile than methanol, such as H2S and ammonia, are removed in the vapour phase while the methanol, water and other less volatile compounds remain in the bottoms. In the second “rectification” stage, the purified methanol is recovered from near the top of the column while the water and other less volatile compounds are removed in the bottoms
Historically, the recovery of methanol from kraft pulping condensates has several unique characteristics that inhibit separation by distillation:
- Azeotropes of methanol and organic contaminants
- Immiscibility of terpenes
- Dissociation of hydrogen sulphide and methyl mercaptan
- Ammonia reacting to produce ammonium sulphate (fouling)
AHL has developed and patented features to deal with each of these design issues.
Economics Analysis Of Methanol Recovery
Methanol at a purity level of 99.85wt% can be worth over five times as much as a traded commodity than in crude form as a combustion fuel, displacing light fuel oil or natural gas.
With a SOG stream of 2000 kg/hr containing up to 700 kg/hr methanol, this can provide savings of $3 to 4 million CAD per year for the mill.