What are the Types of PFR Kiln
The PFR kiln, also known as a twin shaft lime kiln or Maerz kiln, has two major characteristics: a parallel flow characteristic and heat storage recovery. The lime calcined by the PFR kiln is of high quality and can easily meet the standard of special-grade metallurgical lime. At the same time, it has a notable energy-saving effect and exhibits the lowest energy consumption among all currently available lime kiln types. However, its internal design has evolved into a variety of structures based on different production requirements and material properties. Among them, the bracket-type PFR Kiln and the suspended PFR Kiln are the two most important and widely used types. This article will introduce the structural characteristics, working principles, and applicable scenarios of these two PFR kilns in detail to help you choose the appropriate type according to your production needs.
PFR Kiln Process Principle
1. Parallel Calcination
Fuel (such as natural gas, pulverized coal, etc.) and combustion air are introduced from the top or middle of the kiln chamber A. In the combustion zone, hot gases produced by the burning fuel flow in parallel with the downward-moving limestone. This parallel flow of high-temperature flames directly contacts the relatively cool material, ensuring uniform calcination and avoiding overburning, which helps to produce highly active lime.
2. Heat Storage Stage
The high-temperature exhaust gas discharged from kiln chamber A enters kiln chamber B. The interior of kiln chamber B is filled with limestone to be calcined. As the high-temperature exhaust gas passes upward through the limestone in kiln chamber B, it transfers the heat it carries to the limestone. The limestone in kiln chamber B is gradually preheated by absorbing heat from the exhaust gas, while the temperature of the exhaust gas itself decreases.
3. Cycle Switch
After a certain period of time, usually a few minutes to more than ten minutes, the operation of the kiln will be switched. At this time, kiln chamber B is transformed into a “combustion kiln” and kiln chamber A is transformed into a “heat storage kiln”.
Corbel Type PFR Kiln VS Hanging Type PFR Kiln
- Structural Form
The passage of the corbel-type pfr kiln is formed by refractory masonry, and the structure is relatively complex. The weight of the refractory increases by more than 100 tons compared with the suspended cylinder kiln, and the types of refractory increase by more than 20 types. The complex structure of the bull leg channel is more prone to dust accumulation and nodules, and the channel needs to be frequently inspected and cleaned; otherwise, it will affect normal production. Subsequent maintenance costs may increase.
The structure of the suspended pfr kiln uses a hollow high-temperature resistant alloy as a skeleton suspended in the kiln. The inside and outside of the suspension cylinder are built with refractory materials. Compared with the traditional corbel structure, the structure is simpler and more reliable. It can save about 20% of refractory materials. At the same time, there is no place for dust to adhere, the annular channel is not easy to form nodules, the kiln condition is more stable, and the workload of channel cleaning is greatly reduced.
- Device Configuration
To avoid blockage of the passage of the corbel-type PFR kiln, air cannons are installed between the corbels to continuously force air into the furnace to avoid dust accumulation in the passage. Frequent injection of cold air into the furnace can easily cause the refractory materials in the furnace to cool or heat rapidly, further affecting the life of the refractory materials.
The hanging cylinder of the suspended pfr kiln is hung upside down in the kiln chamber and requires cooling air. Therefore, the air supply system of the double-chamber kiln with a hanging cylinder structure needs to be equipped with not only conventional combustion-supporting fans, cooling fans, and spray gun cooling fans, but also 3 additional hanging cylinder cooling fans and 1 emergency standby fan.
How to Choose the Right PFR Kiln Type
1. Material Characteristics: The particle size of the limestone is one of the determining factors. Large, uniformly sized materials may be more suitable for a PFR Kiln with a corbel structure, as its internal support structure helps the material fall steadily. For materials with smaller or more widely distributed particle sizes, a suspended PFR Kiln will generally provide a more uniform material-airflow contact.
2. Product Requirements: If the goal is to produce high activity, high whiteness lime, then a suspended Parallel Flow Regenerative Kiln is usually the better choice. If the product has relatively loose requirements on activity or is mainly pursuing output and cost-effectiveness, then the Parallel Flow Regenerative Kiln may also be an affordable option.
3. Capacity Requirements: For large-scale, high-output production lines, the suspended Parallel Flow Regenerative Kiln is often the first choice due to its higher unit volume output efficiency and better heat transfer performance. It can support large-scale industrial production. For small and medium-sized production capacities, both Parallel Flow Regenerative Kiln types may be suitable, and other factors need to be considered comprehensively.
4. Investment and Operating Costs: A comprehensive economic benefit analysis must be conducted to select the type of Parallel Flow Regenerative Kiln. Initial construction investment includes equipment procurement, civil engineering, and installation costs. In addition, maintenance costs (such as refractory life and kiln cleaning frequency) and labor costs need to be evaluated.
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