MER Group
Source: Proceedings of the 2025 China Lime Industry Technology Exchange and Cooperation Conference
Abstract: This paper analyzes the types of waste heat and waste heat utilization technologies in lime rotary kiln production lines, and introduces the technological innovations and application cases of Dingzheng Heavy Machinery in waste heat utilization.
1 Introduction
Energy conservation and emission reduction is a basic national policy and the primary task of the energy development strategy. Driven by this policy, the lime rotary kiln industry has achieved positive transformations such as technological upgrading and industrial structure optimization, shifting from extensive production to standardized green intelligent manufacturing. Under the impetus of policies, reducing energy consumption and improving the level of waste heat utilization technology of lime rotary kilns have become the core competitiveness of various production enterprises.
This paper briefly introduces the types of waste heat of lime rotary kilns, waste heat utilization technologies, and the technological innovations in this field by Handan Dingzheng Heavy Machinery Co., Ltd.
2 Types of Waste Heat in Lime Rotary Kiln Production Lines
Among all energy conservation and emission reduction targets, high-energy-consuming industries have achieved the most significant results. Due to its unique process and roasting method, the rotary kiln lime production line produces activated lime of the best quality under the same raw material and fuel conditions, which well solves the problems of under-burning, over-burning and uneven calcination of lime, and has high activity. Therefore, the rotary kiln lime production technology has been rapidly promoted in the lime industry.
The energy consumption of the rotary kiln lime production line is relatively slightly higher, mainly because part of the heat is taken away by waste heat and equipment heat dissipation. The main heat losses are as follows:
(1) Part of the heat is taken away by the exhaust gas emission at the kiln tail;
(2) Part of the heat is taken away by the discharged finished lime;
(3) Part of the heat is taken away by the radiant heat of the preheater, rotary kiln and cooler. Especially, the rotary kiln has a large surface area, so the heat taken away by radiant heat is more obvious.
Problems arising: The above working conditions contain abundant waste heat. If directly discharged, it will not only cause energy waste but also aggravate environmental thermal pollution. Therefore, waste heat recovery and utilization technology has become a research topic for various production enterprises and lime kiln design and construction enterprises, and is a major factor to improve enterprise competitiveness. The waste heat utilization of rotary kilns is of great significance. Through waste heat recovery and utilization technology, it not only effectively reduces energy consumption but also greatly reduces harmful emissions, reduces the degree of environmental pollution and damage, and promotes enterprises to complete various mandatory indicators of energy conservation and emission reduction.
3 Waste Heat Utilization Technologies for Lime Rotary Kiln Production Lines
In view of the causes of waste heat: waste heat of exhaust gas at the kiln tail, waste heat of finished lime and radiant heat of three major main equipments, waste heat utilization and reduction of heat energy loss are mainly promoted around equipment upgrading, process optimization and intelligent control.
3.1 Equipment and Material Upgrading
Optimize preheating equipment, develop high pre-decomposition rate calcination technology and high-efficiency preheater, increase preheating area, make flue gas distribution uniform, improve the heat conversion efficiency of the preheater, and reduce calcination fuel consumption.
Optimize cooling equipment, develop high-efficiency vertical kiln cooler, increase the preheating temperature of secondary air, minimize the direct participation of cold air in combustion, which can effectively increase the firing temperature in the kiln and reduce fuel consumption.
Upgrade refractory materials, especially kiln lining materials, adopt refractory castables with good thermal shock resistance and wear resistance, strictly control the temperature of the kiln body in the calcination zone, and reduce the heat dissipation loss of the kiln body.
3.2 Cascaded and In-depth Utilization of Waste Heat
Construct a cascaded utilization system of "raw material and fuel preheating - waste heat power generation - heating/production steam supply" to improve the overall waste heat utilization rate.
In the lime rotary kiln production line system, preheater and cooler technologies are the core technologies of this type of kiln. The preheater reduces the exhaust gas emission at the kiln tail by preheating limestone to realize waste heat utilization, and the cooler reduces the ash discharge temperature by preheating combustion air to realize the function of preheating heat utilization.
Waste heat heating/steam supply technology: Transfer the waste heat of tail gas to cold water or cold air through heat exchangers to generate hot water (80～120°C) or steam (0.3～0.6MPa), which is used for factory heating, employees' domestic water or auxiliary production steam. It has low investment cost and is suitable for small and medium-sized enterprises or parks with heating demand in the surrounding area.
The exhaust gas at the kiln tail requires a denitrification process. The waste heat of the rotary kiln tail gas meets the requirements of the low-temperature denitrification process, so there is no need to add additional hot blast stove heat supplement equipment, which reduces the construction investment of the denitrification process.
Low-temperature waste heat refrigeration technology: Adopt absorption refrigeration units, which use tail gas waste heat as the driving energy to cool water to 7～12°C for workshop air conditioning or process cooling. It is suitable for lime deep processing enterprises in high-temperature areas or with refrigeration demand, and forms a "warm winter and cool summer" comprehensive waste heat utilization system with heating technology.
For rotary kiln lime production lines using pulverized coal as fuel, the hot exhaust gas at the kiln tail is used to dry raw coal, so that the waste heat of the kiln tail exhaust gas is fully utilized.
3.3 Intelligent Control and Parameter Optimization
Deploy an expert intelligent control system to accurately regulate parameters such as calcination temperature and fuel ratio through algorithms, predict kiln conditions in advance, reduce coal consumption of the firing system, and optimize the rotation speed and inclination angle of the kiln body to improve the heat exchange efficiency between materials and hot gas. Install sensors for temperature, pressure, flow rate, etc., real-time adjust the load of heat exchange equipment through the PLC system to match the fluctuation of rotary kiln working conditions, and realize precise control combined with AI algorithms.
4 Innovations in Waste Heat Utilization by Handan Dingzheng Heavy Machinery Co., Ltd.
As a pacesetter in the lime industry, Handan Dingzheng Heavy Machinery Co., Ltd. takes the initiative to optimize the design, relies on the accumulated technical and experience advantages over the years, keeps pace with the times, actively introduces new technologies and concepts, and has made a series of innovations in energy conservation, consumption reduction and waste heat utilization.
(1) The preheater adopts the international advanced large-compartment design concept. On the basis of ensuring the heat exchange area, it minimizes the number of equipment (pushing devices) and reduces the failure rate; adopts independent compartment type and adjustable compartment material level technology, which makes the preheating temperature of materials in each preheating compartment easier to adjust and control, and the preheating temperature more stable.
(2) The cooler adopts a large-area cooling method. The cooler is divided into four cooling and discharging areas, and the discharging speed of each area can be independently controlled according to the material temperature; the cooling air is in direct contact with the hot lime in the cooler, with good cooling effect and low ash discharge temperature (about 70°C higher than the ambient temperature); after the cooling air cools the lime, the temperature can be preheated to above 750°C and used as the secondary combustion-supporting air of the rotary kiln. It has high heat exchange efficiency and high waste heat utilization rate.
(3) Through theoretical simulation and actual production line operation, Dingzheng has optimized the structure of the cooling air duct and cold air distribution device of the vertical cooler, specifically improved the heat-resistant material performance of heat-resistant parts, and adopted Dingzheng's unique distributor. Compared with ordinary coolers, it has better cooling effect and longer service life.
(4) For large-scale production lines and fragile lime, a multi-cooling fan design is adopted. According to the different pressure and height of each part of the vertical cooler, fans with different air volume and pressure are used, which is convenient for adjustment, can effectively prevent abnormal phenomena such as material sticking and red material, and improve heat exchange efficiency.
(5) For rotary kiln lime production enterprises using pulverized coal as fuel, using the flue gas at the kiln tail to dry raw coal is a very economical and safe process. It not only saves the heat energy required for drying but also ensures the safety of coal grinding. This process is very mature and has been promoted and applied.
(6) The heat dissipation of the lime rotary kiln cylinder is one of the main reasons for the high heat consumption of the rotary kiln. An effective way to reduce the cylinder temperature is to use refractory materials with good thermal insulation performance. Our company adopts proprietary composite brick technology with good temperature resistance, wear resistance and thermal insulation performance, which effectively reduces the kiln skin temperature, reduces the heat dissipation of the kiln body, and takes the lead in introducing 5S super thermal insulation materials into the calcined white rotary kiln production line.
(7) The surface heat of the rotary kiln cylinder is also a research direction. Adding a heat collection cover in the calcination zone of the rotary kiln to collect and utilize this part of heat can solve the heating problem of offices and employees' dormitories and the employees' bathing problem with less investment and quick results. Our company has adopted this scheme in many projects, mainly applied in cold northern areas.
5 Application Cases of Waste Heat Utilization by Handan Dingzheng Heavy Machinery Co., Ltd.
As a leading enterprise in the rotary kiln lime industry, Handan Dingzheng Heavy Machinery Co., Ltd. responds to market demand in the design and engineering construction process and always puts energy conservation and emission reduction in the first place. Several application cases of projects are listed below.
(1) In an 800T/D rotary kiln lime production line of a steel plant, more than 90% of the drying heat source required for the pulverized coal of the coal mill comes from the exhaust gas at the kiln tail. In addition, a shell-and-tube heat exchanger is added at the air outlet of the preheater. The 90°C hot water generated after heat exchange is used for the centralized refrigeration process in the plant. At the same time, the temperature of the hot exhaust gas at the outlet of the preheater is reduced to about 170°C, which plays a good role in protecting the cloth bag of the high-temperature resistant dust collector at the kiln tail and prolongs its service life. Figure 1 shows the heat exchanger and the kiln tail temperature before and after heat exchange displayed in the central control system.
(2) In a rotary kiln lime production line of a steel plant in Hebei Province, a cylinder heat collection device is installed in the calcination section of the rotary kiln to meet the winter office heating demand in the production area and the employees' bathing demand in summer. A waste heat boiler is added at the air outlet of the preheater, and the generated steam is used for the needs of other industrial chains of the company.
(3) In a rotary kiln lime production line of a steel plant, low-temperature SCR denitrification technology is adopted for tail gas denitrification, and the waste heat of the tail gas fully meets the requirements of the denitrification process.
6 Conclusion
Waste heat utilization is a key path for the lime industry to reduce costs and increase efficiency and achieve the "dual carbon" goals. The principle of process waste energy and waste heat recovery and utilization is "cascaded utilization, high-quality and high-efficiency utilization". For the recovery and utilization of flue gas waste heat from industrial furnaces, in principle, it should first be fully utilized for preheating air, fuel and materials. If it cannot be recovered by itself, it should be used for external heat recovery facilities. The flue gas at the tail of the lime rotary kiln is generally not more than 250°C, which belongs to low-temperature flue gas. Its waste heat utilization technology is subject to certain constraints, and there is still great room for development in the technology of recovering flue gas waste heat.
Lime rotary kiln production is a high-energy-consuming and high-emission industry. Waste heat recovery and utilization to achieve energy conservation and emission reduction have attracted increasing attention from lime production enterprises. How to further improve the thermal efficiency of rotary kilns, make full use of the low-temperature flue gas waste heat resources in rotary kiln production, and recover and apply them to the heat consumption or cooling demand of enterprises to achieve energy conservation and emission reduction, reduce production costs and protect the environment is an important topic worthy of in-depth research.
Handan Dingzheng Heavy Machinery Co., Ltd.
