The cross-flow vertical furnace is also called a KHD furnace. It is characterized by an ejector for circulating gas inside. The limestone is decarbonated by the sensible heat of a large amount of circulating gas. The calcining gas passes horizontally through the lime filling layer to provide decomposition heat to the limestone. The gas that has descended after calcination is circulated to the combustion chamber by the ejector, and after being heated, it enters the furnace again as calcination gas.

The advantages of this furnace are as follows:
(1) Because calcination is carried out with high-temperature gas generated by combustion, the limestone does not come into contact with the flame, so
overburning does not occur;
(2) The furnace has a small cross-section and there is no quality fluctuation caused by gas deviation;
(3) The furnace is easy to operate and convenient for quality management;
(4) It can calcine smaller limestone (20-40mm);
(5) The furnace has a small volume, the product is less pulverized in the furnace, and the yield is high.

Structure and composition
‌Main structure‌
The kiln body is usually cylindrical and consists of refractory bricks, insulation layer and steel shell. The interior is divided into preheating zone, calcining zone and cooling zone from top to bottom.

‌Preheating zone‌: The raw materials are preheated and dehydrated by the rising hot air flow.
‌Calcination zone‌: The core area, the temperature reaches 1000-1200℃, and the limestone is decomposed into calcium oxide and carbon dioxide.
‌Cooling zone‌: The calcined lime is discharged after heat exchange and cooling with cold air.
‌Supporting equipment‌
Includes feeding device (mechanical feeding at the top), discharging device (ash discharger at the bottom), combustion system (coal or gas fuel) and ventilation equipment.

Technical features
‌Energy saving and environmental protection‌: Modern technology reduces pollution by optimizing airflow distribution and introducing dust removal and desulfurization devices (such as cyclone water film dust removal tower). Some kiln types can recycle industrial waste gas as fuel.
‌High-efficiency production‌: The utilization coefficient can reach more than 0.85 t/d·m³, and the heat consumption is less than 130kg standard coal/ton of lime.
‌Strong adaptability‌: It can handle raw materials with high pulverization rate. For example, the block powder separation tower structure developed by Sinosteel Thermal Energy Institute solves the problem of fine particle blockage and improves airflow uniformity.

Application value
The equipment is widely used in metallurgy, construction and other industries. Its technological innovation has promoted the green transformation of lime production and helped the industry reduce consumption and increase efficiency.