Most of these pieces of equipment are very large and it takes much education to learn how to size these pieces of equipment. It is a very difficult problem that chemical engineers must solve. You should also know that there are many other types of engineers. Civil engineers design roadway systems much like the road you took to school today. They also design drainage systems for sewers and many other things.
Mechanical engineers design mostly machines.
Cars are usually designed by mechanical engineers. Mechanical engineers also design other complex machines that are necessary in industry. Mechanical engineers design these complex machines. Another type of engineer is an Industrial engineer. Industrial engineers design specifications for building.