It’s always a big challenge for every fibre cement specialist to minimize the wet waste in fibre cement manufacturing.
Even little quantity originated in some part of the fibre cement production plant – like the bottom of sedimentation cones, weekend tank or during cleaning or plant stop operation – is always too much to be stocked, handled, adjusted in concentration and reintroduced – at least partially – in the production cycle if not directly dumped.
Obviously, it’s not only a matter of cost saving in raw material and maintenance but also a quality issue.
1 . Why is it useful to minimize wet waste in fiber cement production ?
Minimizing the wet waste allows you to reduce the reintroduction of the same in the fiber cement production cycle, often affecting qualities of the final product, like physical or visual properties.
It’s known that wet waste is not constant in composition: quantity , mix of raw material, their hydratation stage and and their concentration may vary depending on many parameters.
Here is a delicate issue of the fiber cement operation process :
- handling those variations, together with fresh raw material usual parameters fluctuations, during the reintroduction in the main cycle,
- keeping an eye on avoiding building up stock of wet waste to be dumped with consequent cost.
Another good reason to minimize wet waste in your fiber cement production, is to reduce the activities related to handling this wet waste, i.e.:
- cleaning of manufacturing equipment of all the water cycle system,
- maintenance for equipment meant for wet waste slurry density adjustment and dosing.
Using a military terminology, the pincer movement – double envelopment to reach the goal – relies on two subjects: mechanical and chemical.
Doesn’t matter how you take it, but any point you start from will influence the other, and fortunately, in a positive way.
2 . Mechanical strategy to reduce wet waste in fiber cement production
A good design of the fiber cement equipment with a proper calculation of flow speed in the pipes, in the mixers, vats, pits and sedimentation cones avoids undesired sedimentation.
Water circle design is also crucial to reach a good result in your fiber cement production: flows from the bottom of the recuperation cones, backwater pit and green cuts recuperation system could result in a big problem if not properly managed and addressed.
Backwater volume from fiber cement sheet production machine, containing too much solid content, could be too much for undersized recuperation cones; this especially in technologies that require low concentrations in the homogenizer (feeding tank) resulting in high backwater flow and consequent poor sedimentation rates.
New concept water system design and accurate calculation of decantation time into the cones are crucial: closed water cycle together with proper chemicals utilization minimizes wet waste building up and results also in a clean process water as a very relevant side effect.
3 . Chemical strategy to reduce wet waste in fiber cement production
Given the desired raw material mix, it is very important to choose the proper flocculant, coagulant, antifoam and dispersant that could optimize retention at the sheet machine.
It is obvious that the first aim of a good retention is not to minimize wet waste but optimize film formation at the sheet machine and its efficiency. This is a huge subject in the fiber cement production process, which will be developed in another article.
Optimizing this parameter allows you to be in control of the hydratation time of your raw material, exploiting the best performance in your fiber cement production and avoiding hydratation in undesired position like mixers, recuperation cones and dosing tanks instead of the green sheet and then in hydrothermal treatment, in the case.
As a consequence, it minimizes the flow of raw material in the opposite direction you desire and allows the decreasing amount of wet waste as a result.
Benefits from all those activities are cost savings in your fiber cement operations and, even more interesting, better control on quality of the final product.
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