ANS:D - truck/tunnel.

A truck/tunnel dryer, also known as a tunnel kiln or a tunnel dryer, is a type of continuous drying system commonly used in industrial settings for drying various materials including refractories. Here's how it generally works:

1. Tunnel Structure: It consists of a long tunnel-like structure with a conveyor belt system running through it. The tunnel is divided into different zones, each with its own temperature and airflow controls.
2. Conveyor Belt: The refractory materials to be dried are loaded onto trays or placed directly on a conveyor belt. The conveyor belt moves continuously through the tunnel, carrying the materials along its length.
3. Heating System: Heat is applied to the tunnel through various means such as gas burners, electric heaters, or steam coils. The temperature settings can be adjusted to meet the specific drying requirements of the refractories.
4. Air Circulation: Proper airflow is maintained within the tunnel to ensure even drying of the materials. This is often achieved through the use of fans or blowers that circulate heated air throughout the tunnel.
5. Controlled Environment: The drying process is typically conducted in a controlled environment to optimize drying efficiency and ensure the quality of the dried refractories.
6. Continuous Operation: One of the key advantages of a truck/tunnel dryer is its ability to handle large volumes of material continuously. As the conveyor belt moves through the tunnel, new batches of material can be loaded at one end while dried material is unloaded at the other end, allowing for a continuous production process.