A soap plant is a chemical building dressed as a food plant
Soap and detergent manufacture involves saponification with caustic, neutralisation with acid, blending with perfumes and dyes, and drying or spray towers. It reads like a food process because the product is a consumer good, but the materials behave like a chemical plant.
The chemicals are the design driver
Caustic soda at strength attacks steel, aluminium and skin. Sulphuric acid attacks most metals when dilute. Perfumes and dyes are solvents that soften coatings. All of them reach the floor through drips, sampling and washdown.
Where a plant handles several of these in the same building, the exposure is not one environment but several, in patches: a caustic area, an acid area, a solvent area. A single coating specification across all three will fail in at least one of them.
The spray tower is a tall structure
Spray drying of detergent powder involves a tall tower with hot air, and that tower sets the building height in the same way an evaporator does in a paste plant.
It also produces a fine powder that is extremely hygroscopic. Detergent powder that settles on a steel surface absorbs moisture from the air and becomes a wet, alkaline deposit that stays there.
Powder handling is a dust problem with a corrosion twist
Conveying, sieving and packing powder produce dust that settles everywhere. Unlike most organic dust, it does not simply sit — it draws water out of the air, so it stays damp and it stays aggressive.
That is why a detergent plant's roof fails from the inside before it fails from the outside, and why cleanable surfaces matter more here than heavy coatings.
Bar soap lines are wet and warm
Soap finishing — milling, plodding, extruding, cutting, stamping — runs warm and slightly wet, and the equipment is washed. The floor is slippery and continuously damp.
Falls, gullies and a plinth at every column base are the same three items that appear in every wet production building. They are also the three that get value-engineered out.
Solvent and perfume stores need separation
Perfumes, dyes and any solvent-based additives are flammable. Storing them in the production hall because it is convenient is how a small fire becomes a plant fire.
A separate compartment with its own ventilation and its own bund is the standard answer, and it should be on the drawing before the hall is laid out.
What I want before drawings
- The chemicals used, their concentrations and where each is handled.
- Whether spray drying is in scope, and the tower height.
- The powder handling and packing arrangement.
- The washdown regime and the floor drainage concept.
- The flammable and solvent store volumes, and whether they are separated.
- The wind speed for the site in km/h from the applicable local code, not a round number.
Soap and detergent plants are usually built as an extension of a consumer goods business, which means the building brief arrives late. The chemistry should reach it first, not last.
Written by Johnny Joe, who advises owners and project managers in Africa and South America on steel buildings. If this decision is live on a project, send the layout and the constraint that worries you and I will tell you what it changes.
Related: a chemical process with a food finish · a small building handling chemicals · a salt environment · separating a chemical store
