A rendering plant is the hardest neighbour on the site
Rendering cooks and separates animal by-products into fat, protein meal and water. It is a heat process that handles wet material, and it produces an odour that is unmistakable and persistent.
The building is hot and humid continuously
Cookers, dryers and evaporators all release heat and moisture. Unlike a batch process that heats and cools, rendering tends to run continuously for long periods, so the building never dries out.
That produces a saturated atmosphere at high level and a wet floor at low level — the same profile as a sugar mill, and the same corrosion consequence. The roof underside is a condensing surface and the wall base is an immersion zone.
Corrosion is accelerated by the chemistry
Rendering releases fatty acids, ammonia and sulphur compounds. In the presence of moisture and heat, that mixture is considerably more aggressive to steel than water alone.
The consequence is that a rendering plant needs an exposure classification closer to a chemical plant than to a food plant, and the details that matter are the ones that let air circulate and water drain.
Odour leaves with the air, so the air is the design
Containing odour means controlling where the air goes. In practice that means the building is kept under slight negative pressure, exhaust is collected rather than allowed to leak, and the discharge point is high enough and far enough not to fall back onto the site or the neighbours.
A building with large open doors and louvres on all sides cannot be held under negative pressure. That is a design conflict that has to be resolved on the plan: the openings that serve the process and the openings that keep the building usable are not the same openings.
The raw material receiving area is the worst zone
Raw material arrives in vehicles and is tipped or unloaded. That moment releases the strongest odour and the most liquid, and it happens at a door.
A enclosed receiving bay with a fast-acting door, a drained floor and its own extraction is the arrangement that keeps the rest of the plant and the site boundary usable. An open tipping apron under a canopy will not.
Effluent and condensate need a route
Rendering produces a large volume of water with a high organic load. It has to leave the building in a designed channel rather than across the yard, and the channel has to be accessible for cleaning.
That is a civil decision that reaches into the building as a floor level and a slope.
What I want before drawings
- The process and the heat and moisture release at each stage.
- The raw material receiving method and the vehicle types.
- The odour control concept, and who is designing the extraction.
- The effluent volume, load and route.
- The washdown regime and the chemicals used.
- The wind speed for the site in km/h from the applicable local code, not a round number.
Rendering plants are usually sited away from towns, which reduces the odour problem and increases the transport problem. Both should reach the layout before the building is drawn.
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: the hardest envelope in food processing · odour as a site boundary problem · wet and hot in the same room · corrosion class as a selection input
