Scope of Application for Combined Drying Equipment

A combination dryer is a system that integrates two or more drying methods. For the material being dried, the process is primarily arranged in series; that is, during operation, the material passes sequentially through two or more dryers. Combination drying is primarily designed to meet the requirements of a specific drying process. As is well known, every type of dryer has certain limitations. By connecting one or more units of the same or different types in series and leveraging their respective advantages, it is often possible to achieve results that a single unit cannot. Recently, there has been widespread adoption of drying systems that combine different drying methods and principles, allowing each to leverage its strengths while compensating for its weaknesses. For example, direct and indirect drying methods are often used in combination, with the indirect method providing the vast majority of the heat required for drying. This approach increases the drying rate and results in a compact, highly thermally efficient drying system that integrates both direct and indirect drying methods. Combined dryers are also becoming increasingly widespread. Examples include combinations of spray dryers and vibrating fluidized-bed dryers; rake dryers and vibrating fluidized-bed dryers; and rotary agitated dryers, conductive agitated dryers, air-flow dryers, and fluidized-bed dryers. The goal is to achieve a low moisture content. Using a spray dryer alone can produce products with a moisture content of 1% to 3%. However, if a moisture content below 0.3% is required, the exhaust gas temperature often needs to exceed 120°C, resulting in significant heat loss. Similarly, if the moisture content must be further reduced to below 0.1%, the exhaust gas temperature must exceed 130°C. To conserve thermal energy, the design typically employs a spray dryer with an exhaust temperature of 90°C to achieve a moisture content of 2%. The 60°C hot air recovered from this process can then be fed into a series-connected horizontal fluidized-bed dryer, ultimately reducing the moisture content to below 0.1% while saving 20% in thermal energy.