Metso water management solutions are based on the installation of independent kidneys in pulp and paper mills. Compact and controlled water management is dependent on a good basic process solution. The reduction of fresh water consumption always starts by optimizing the main process itself.
Therefore, in order to be sure that additional water treatment is worthwhile and can positively affect paper machine runnability and product quality, the basic process connections have to be taken care of.
Pulp and paper mills can be categorized in terms of the fresh water consumed at the mill. Mills with high fresh water consumption levels can normally achieve good runnability and board quality without any additional kidneys. However, it is necessary to take care of the main process connections. Internal kidneys are needed to increase the runnability when the fresh water consumption level decreases.
In order to reduce fresh water consumption to a low level in tissue mills, OptiCycle W is the key technology. OptiCycle W (= membrane filtration) is installed in the tissue mill’s filtrate waters, in order to purify the water to a level where it can be used as an alternative to fresh water.
Ultrafiltrated water can be used instead of fresh water for certain low and high pressure showers in the wire section and for chemical dilutions.
Microflotation is used case by case to treat press section waters.
When total fresh water consumption is extremely low ,special attention has to be paid to the efficiency of salt removal. Part of the ultrafiltrated water is treated with OptiFilter nanofiltration, which includes tighter membranes than OptiCycle W.
The figure below describes the typical fresh water consumption levels [ m3/t net final paper] for tissue grades and the actions to be taken in paper mills when closing the water system.
Metso Water Concept
NOTE: In water consumption is incl. Both Paper Mill and Stock Preparation
- OptiCycle W and OptiFilter NF to purify PM’s clear filtrate to the level when it can be used instead of
fresh water at certain applications
- Microflotation for press section waters