Project overview

The production line of 2500t/d kiln #1 of a company was started in March 2007 and put into production in May 2008. The company’s geographical location is about 2300m above sea level, which is a high altitude condition. The selection of the firing system is particularly increased in terms of system specifications. The rotary kiln with 4.3m×62m is adopted, the five-stage cyclone preheater with CDC decomposer and the third-generation grate cooler with air beam. After running in recent years, the clinker output has been stable at about 2600t/d for a long time, but there are still some problems, such as high standard coal consumption, high power consumption of clinker process, poor clinker cooling effect and so on.

02 Basic situation and technical reform objectives before technical reform

2.1 Host configuration of firing system before technical modification

See Table 1 for the configuration of the main engine of the firing system before technical modification.

Table 1 Host configuration of firing system before technical modification

Name	Parameters
Rotary kiln	Specifications:Φ4.3MX62M; Main transmission power: 420KW
Decomposition furnace	Type :CDC pipe type;Φ6.1 mx36m
Preheater system	C1:2-ΦD5.6m;C2:1-Φ7.0m;C3:1- Φ7.0m;C4:1-Φ7.4 m;C5:1-Φ7.4m
Kiln head burner	Type: four channels
The cooling machine	Type: 3rd generation grate cooler with air beam (LBTF2750) Effective area of grate bed :70.09 m2

2.2 Problems existed before technical improvement

Before technical transformation, the production line mainly has the following problems:

(1) The standard coal consumption of clinker is high. The average standard coal consumption of the production line was 123.03kg/t before technical upgrading.

(2) High power consumption in clinker process. The average clinker process power consumption is 37.15 kWh /t before technical modification.

(3) Poor cooling effect of clinker. The clinker temperature of the outlet cooler is as high as 203℃, the first stage cooling effect is poor, the heat recovery efficiency is only 64.58%, the second and third air temperature is low (the secondary air temperature is about 1000℃, the third air temperature is about 850℃).

(4) The preheating system has poor stability and large pressure loss. The temperature of the calciner is difficult to control, the tailings coal addition and reduction range is large, the raw material decomposition rate fluctuates greatly, and the preheater pressure loss is large. Under the existing output, the negative pressure at C1 outlet reaches 5500Pa, and the outlet temperature is as high as 338℃.

2.3 Technical Transformation Objectives

(1) System output: ≥2800t/d.

(2) Clinker burning heat consumption: ≤112kg/t.

(3) The clinker temperature of the cooling machine: <65℃+ ambient temperature.

(4) The clinker 28d compressive strength: ≥ 59Mpa.

(5) Clinker power consumption: decreased by 3kWh/t.

03 Technical Improvement Plan

3.1 Raw fuel

The composition of raw fuel used in the production line after technical modification is shown in Table 2 and Table 3.

Table 2 industrial analysis of pulverized coal in kiln

Table 3 Chemical analysis of raw clinker

3.2 Preheater modification

The wind speed at the outlet of each type of cyclone is normally higher (15.96-18.90m /s), the wind speed at the inlet is higher (21.47-25.80m /s), and the apparent section wind speed of C1 cyclone is higher (4.47m/s).

In order to reduce the resistance loss of the preheater system, improve the separation efficiency of C1 cyclone cylinder and reduce the amount of fly ash at C1 outlet, the technical improvement plan was determined: the cone of C1 was not moved, the high-efficiency and low-resistance structure was adopted, the diameter of C1 body was increased to 5.6m, and the air inlet of C2 ~ C4 was appropriately increased to reduce the resistance. Replace the spilling box of C1 ~ C4 pipe, optimize the location of the spilling box, strengthen the disperse heat transfer of materials in the pipe connected with the cyclone cylinder, and improve the heat transfer rate; Replace the flap lock valve on C1 ~ C5 feeding pipe to reduce internal air leakage.

3.3 Calciner modification

The capacity of the calciner is 1120m³, and the residence time in the gas furnace is short (4.70s). Therefore, the calciner needs to be expanded to ensure the full combustion of pulverized coal in the furnace, improve the decomposition rate of materials into the kiln, and determine the technical reform plan. As shown in Figure 1, the space inside the kiln tail frame was fully utilized, square tubes were used instead of round tubes, and the increased part of furnace body was placed in the frame. The effective volume of the calciner was increased to 1465m³, and the residence time was increased by 1.45s.

Fig. 1 Reconstruction diagram of calciner

3.4 Transformation of smoke chamber

At present, when the net size of the cone of the calciner is 1440×1440mm and the output is 2600t/d, the wind speed of the calciner can be calculated to be about 45m/s, which is obviously too large, which not only leads to great resistance, but also is not conducive to the ventilation and system operation in the kiln. As shown in Figure 2, expand the effective area to about 3.06m² and control the wind speed here about 30 ~ 32m/s.

Fig. 2 Schematic diagram of reformation of smoke chamber

3.5 Retrofit of grate cooler

The clinker cooling system of #11 production line of the company adopts the third-generation air beam grate cooler, and the effective area of grate bed is 70.09m². The operation data show that the second and third air temperature is low, the clinker temperature of the outlet cooler is high, and the grate bed material layer resistance is large. In order to improve the heat exchange efficiency, reduce the clinker temperature of the outlet cooler and increase the air temperature for the second and third times to save energy and reduce consumption, the fourth generation grate cooler is replaced as a whole, as shown in Figure 3.

Fig.3 Modification of grate cooler

04 Technical improvement effects

After a period of production debugging, the sintering system runs stablly and all indexes are greatly improved. The clinker output rises to 2800t/d, the standard coal consumption decreases by 10.62kg/t, the clinker process power consumption decreases by 3.97kWh/t, and the clinker temperature of grate cooler drops to 112℃, which meets the requirements set by the technical reform goal.

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