Packed towers are commonly used in chemical engineering as equipment for gas-liquid contact operations, such as absorption and stripping processes. They are versatile and efficient devices that can be used for various applications.

Absorption Tower:
An absorption tower is a type of packed tower that is used for the absorption process. Absorption is a chemical process in which a gas or vapor component is transferred into a liquid phase. The liquid phase, called the absorbent or solvent, captures the desired component from the gas stream. Packed towers provide a large surface area for the gas and liquid to come into contact, promoting efficient mass transfer between the phases. The packed bed in the tower consists of structured or random packing materials, which increase the surface area available for contact and enhance the absorption efficiency.

Stripper:
A stripper, also known as a desorption tower, is another type of packed tower commonly used in chemical processes. It is the opposite of an absorption tower. In a stripper, a liquid phase is heated or subjected to reduced pressure to remove a volatile component. The volatile component is transferred from the liquid phase to the gas phase. Packed towers are used in strippers to provide a large surface area for the gas and liquid to interact, facilitating efficient mass transfer of the volatile component. The packing materials used in the tower help to enhance the stripping efficiency by increasing the surface area available for contact.

Absorber or Stripper:
Since packed towers can be used for both absorption and stripping processes, they are often referred to as absorbers or strippers. The same tower can be used to absorb a component from a gas stream or strip a component from a liquid stream, depending on the operating conditions and the desired outcome. The versatility of packed towers makes them a preferred choice for many gas-liquid contact operations in the chemical industry.

All the mentioned:
Therefore, the correct answer is option 'D' - packed towers can be used as absorption towers, strippers, or absorbers depending on the specific process requirements. They are versatile equipment that can handle various gas-liquid contact operations efficiently.