Heat recovery heat exchangers utilize kiln tail heat to dry cement.
When calcining clinker in a cement rotary kiln, the kiln tail preheater will continuously discharge a large amount of medium to high temperature exhaust gas. Most of these exhaust gases were originally directly discharged, which not only wastes valuable heat energy but may also have a certain impact on the environment. In fact, the temperature of the exhaust gas discharged from the kiln tail can reach 350 to 450 ℃. Even after recovering some heat from the SP waste heat boiler for power generation, the temperature can still be maintained at 150 to 250 ℃. This waste heat is sufficient to meet the needs of limestone drying. Enterprises only need to design reasonable pipelines to extract these medium temperature waste gases from the outlet of the kiln tail preheater. After being transported by a high-temperature fan, regulated by a regulating valve, and treated with dust removal, they can be directly sent to the dryer, replacing traditional hot blast stoves to provide heat sources for limestone drying and achieving efficient utilization of waste heat in a cascade manner.
In actual production, the process of drying limestone with waste heat at the kiln tail is closely integrated with the cement production system, without the need for additional complex equipment, and has strong adaptability. After crushing treatment, the wet limestone with a particle size controlled within 80 millimeters will be sent to the drying system, where it will fully contact with the waste heat and exhaust gas introduced from the kiln tail, and heat exchange will be completed through reverse or parallel flow. The moisture in wet limestone gradually evaporates after absorbing the heat from the exhaust gas, while the cooled exhaust gas undergoes dual treatment of cyclone dust removal and bag dust removal to recover the dust for subsequent production. After the clean gas meets the emission standards, it is discharged, which not only avoids waste of heat energy but also reduces dust pollution. After drying, the moisture content of limestone can be stably controlled within 1%, fully meeting the process requirements of raw material grinding and subsequent calcination, effectively avoiding problems such as mill blockage and efficiency decline caused by high moisture content in raw materials.
For cement enterprises, the most intuitive benefit of using kiln tail heat to dry limestone is the dual improvement of energy conservation and environmental protection. The traditional coal-fired hot blast stove drying mode requires a large amount of standard coal consumption. However, by utilizing the waste heat at the kiln tail, the heat consumption per ton of clinker can be reduced by 80 to 150 kcal. A clinker production line with a capacity of 5000 tons/day can save more than 8000 tons of standard coal per year, corresponding to a reduction of CO ₂ emissions of over 20000 tons. At the same time, it can also reduce the emission of harmful gases such as SO ₂ and NO ₓ, helping enterprises achieve their green production goals. At the same time, this model can significantly reduce the production costs of enterprises, saving investment in hot blast stoves, fuel consumption, and equipment maintenance costs. Usually, the renovation investment can be recovered within 1 to 3 years, and the overall economic benefits are considerable in the long run.
Of course, the smooth progress of drying limestone with waste heat at the kiln tail also needs to take into account some key details. Due to the high concentration of dust in the kiln exhaust gas, an efficient dust removal process is essential. Otherwise, it may not only affect the drying effect but also cause equipment wear and tear; At the same time, the SO ₂ and alkali dust contained in the exhaust gas can corrode the equipment, so it is necessary to carry out anti-corrosion and anti condensation treatment of the equipment, control the dew point of the exhaust gas to not be lower than 65 ℃, and avoid equipment damage that affects production stability. In addition, the drying system also needs to be interlocked with the kiln system for control. When the kiln conditions fluctuate and cause changes in exhaust gas temperature and air volume, the hot air parameters can be automatically adjusted to ensure stable limestone drying effect and not affect subsequent production processes.
Nowadays, drying limestone with waste heat from kiln tail has become the mainstream choice for energy-saving transformation in the cement industry. Whether it is building new cement production lines or upgrading old ones, the application of this process can be seen. It not only solves the pain points of high energy consumption and high pollution in traditional drying modes, but also realizes the recycling of heat energy in the cement production process, allowing "waste heat" to truly play its value. Compared with the waste heat drying of the kiln grate cooler, the waste heat temperature at the kiln tail is higher, more stable, and the processed raw material dust is easier to handle. It is more suitable as the preferred heat source for limestone drying, especially for the drying needs of high moisture limestone. It can effectively ensure the continuous and stable operation of the raw material mill during rainy season or wet ore production.
With the deepening of the green and low-carbon concept in the cement industry, energy conservation, consumption reduction, and resource recycling have become key factors for enterprises to enhance their core competitiveness. The process of drying limestone with kiln tail waste heat may seem like a simple waste heat reuse, but it is actually an important measure for cement enterprises to achieve cost reduction, efficiency improvement, and green transformation. It not only meets the requirements of the national "dual carbon" strategy, but also helps enterprises reduce operating costs and improve production efficiency in fierce market competition. In the future, it will be widely applied in more cement enterprises, injecting new impetus into the green and high-quality development of the cement industry.
