10 VALMET


Unleashing the green value of methanol


Methanol, a by-product of pulp mill operations, has great potential. Its better use may help mills lower fuel costs, lower carbon footprint and increase productivity, writes Andreas Liedberg


C


ommercially-available methanol is primarily made from natural gas which is a fossil-based


fuel therefore not carbon neutral. In contrast, pulp mill methanol is a renewable, green fuel. A mill produces some 10 to 15 kg of methanol per tonne of air-dry pulp (ADT), and this is enough to make many modern pulp mills operate without the need for any fossil fuel at all. Instead, they use liquid methanol that is produced and stored in the mill.


New purification technology But using pulp mill methanol can be a challenge. It is concentrated in gaseous form in the evaporation plant, and after some heat recovery steps and the reduction of the moisture content, the gas is sent to either incineration, typically to the lime kiln or to the recovery boiler, or to a liquid


Stripper off gas H2


H2


SO4 O2


Stripper off gas H2


H2


SO4 O2


Low NOx purification


Traditional methanol plant


• Red oil (turpentine) • CNCG (Sulfur) • Condensate with (NH4


Purified methanol


Pulp Paper & Logistics


)2


SO4


Existing methanol plants in pulp mills can be upgraded with a purification step located upstream from the methanol plant. The resulting purified methanol is a high-quality fuel that can be used at the mill or sold


methanol system. The methanol is heavily


contaminated and has a very strong odour. Handling is therefore difficult, and combustion results in emissions of NOx and SO2


. The


methanol can also vary in water content and quality, and this


has resulted in lime kiln capacity issues. To take the pulp mills forward,


Valmet and several industry partners have developed a new purification technology. Today, it’s possible to upgrade existing methanol systems so pulp mills


can produce purified methanol – bio-methanol.


Higher profits and a lower carbon footprint “The benefits of purifying methanol can come from using it as a fuel at the mill, selling


Low NOx purification


Traditional methanol plant


• Red oil (turpentine) • CNCG (Sulfur) • Condensate with (NH4


2 stage distillation


Distilled methanol Purified methanol


)2


SO4


Purified and distilled methanol is clean enough to be used in other chemical processes like chlorine dioxide production. This will displace fossil methanol used for this purpose at the mill


July/August 2020


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