This is a paid asset, but now you can download 3D Industrial Background Free.
Detail this asset from Unity Store: Original Link
3D Industrial Background v1.0
“If possible, please buy the package to support the developer”
Realistic and vibrant 3d industrial background for your scene/game.
With this asset you can enhance your game in a few clicks.
All background objects are moved into one prefab.
Also you can arrange the models yourself.
Moving objects: sky, cranes, wind turbine, trash particle, smoke particle.
Asset includes: sounds, 17 models, particles, scripts for object animation, background textures.
Models are low poly: ~50-300 per model
One mesh and one material for all models (For mobile optimization)