Introduction
Since the production of clinker in a company began in July, the burning loss increased suddenly, which had a serious impact on the clinker strength and water requirement. In order to solve this problem as soon as possible, improve the quality of clinker quickly, and ensure the clinker leaves the factory smoothly, the company specially set up a special team to solve the problem, by taking the concept and measures of “temperature control alkali”, the clinker burning loss was reduced to below 0.5% in early October, strength and standard thickness to achieve the desired effect. This article will share the experience gained from solving this problem.

Analysis of the reason for the increase of the burning loss of clinker

The basic reason for the high burning loss of clinker is that the raw material is calcined in the burning zone and the chemical reaction of mature material is not complete or the fuel combustion is not sufficient. Insufficient calcination temperature or poor burning easiness of raw materials are the main reasons for the increase of burning loss. The main influencing factors include harmful ingredients and burning easiness of raw materials, quality of pulverized coal, burner of kiln head, usage amount of pulverized coal of kiln head, decomposition rate of raw materials in preheating of kiln tail, etc. The clinker chemical test data and process parameters of the company are shown in Table 1. As can be seen from Table 1:

Table 1 Clinker chemical test data and process parameters table

indicators	Ignition loss	W(SO3)	Water requirement for standard consistency	Alkali content	w(f-CaO)	w(C3S)	w(C2S)	Secondary arthritis
	%				°C
first half of a year	0.48	0.59	24.2	0.73	0.94	56.48	20.25	1113
Jul.	0.86	0.86	25.5	0.75	0.91	56.73	19.92	1088
Aug.	1.27	0.58	28.0	0.89	0.98	55.64	20.48	1087
Sep.	1.28	0.52	29.3	0.95	0.99	55.64	20.27	1094
Oct.	0.47	0.58	24.9	0.82	0.89	57.58	19.12	1130

(1) Since July, the burning loss of the clinker increased month by month, and in August and September, the burning loss of the whole month averaged over 1.0%. In October, the burning loss of the clinker began to decrease to 0.47% on average, and gradually returned to normal. Under its influence, the water requirement for standard consistency of clinker increased synchronically, from 24.2% to 29.3%, and gradually decreased to the normal level in October, and all other indexes returned to the normal control range.

(2) The reason for the increase of clinker burning loss has little correlation with the harmful components SO₃ and F-CaO in raw materials, but has obvious correlation with the alkali content of harmful components in raw materials.

(3) in the clinker burning loss of higher in July ~ September, the clinker mineral phase relative normal level is low, and there is a relatively lower C₂S, C₂S relative increase trend; At the same time, the secondary air temperature is lower than the normal level above 1113℃, indicating that the calcination temperature is lower than the normal level during this period.

(4) In July, August and September, when the burning loss of clinker was high, the free calcium oxide was 0.90%, with no obvious change, which was the same as normal, while the secondary air temperature was lower than normal, indicating that the burnability of raw materials became better during this period. This change in burnability should theoretically be caused by the increase of alkali content. In conclusion, it is preliminarily concluded that the increase of burning loss is caused by the increase of alkali content in raw materials. After the preliminary judgment, a large number of data such as limestone alkali content, quality of pulverized coal, burner of kiln head, usage amount of pulverized coal of kiln head, and decomposition rate of kiln tail were collected for verification. The specific situation is as follows:

(1) Limestone alkali content. Limestone accounts for more than 85% of the raw material ingredients of the company. From the perspective of alkali content of raw materials used in daily use, the main source of alkali in raw materials is limestone, and its chemical detection is shown in Table 2.

Table 2 Chemical test data of limestone (%)

Month	Ignition loss	w(SO2)	w(Al2O3)	w(Fe2O3)	w(CaO)	w(MgO)	Alkali content
first half of a year	39.83	5.32	1.39	0.63	49.45	1.88	0.33
Jul.	39.69	5.16	1.79	1.31	48.62	1.78	0.39
Aug.	39.1	5.88	2.34	1.14	48.19	1.60	0.51
Sep.	39.05	6.37	2.01	0.93	47.44	2.16	0.50
Oct.	39.76	5.36	1.54	0.65	49.12	1.67	0.40

Since July 15, the limestone production was affected by the mining level, which could not be effectively matched, and the limestone alkali content in the mine increased month by month. In August and September, the highest, lowest and average alkali content of daily limestone in the factory was 0.62%, 0.36% and 0.51%. It can be seen that the increasing trend of alkali content in the clinker was consistent with the change of alkali content in the total analysis results of limestone.

(2) Quality of pulverized coal. The quality parameters of pulverized coal are shown in Table 3. In order to reduce the burning loss of clinker, the laboratory strengthened the quality control of pulverized coal: in early August, the fineness index of pulverized coal was controlled from the original 10% ± 2% to ≤ 8.0%, and the ash content and moisture content of pulverized coal were appropriately reduced. As can be seen from Table 3, although the quality of pulverized coal in August and September improved significantly, the improvement of pulverized coal quality did not have a favorable impact on combustion loss in combination with Table 1. It is concluded that the quality of pulverized coal is not the main reason for the increase of burning loss of clinker.

Table 3 Quality parameters of pulverized coal (%)

	In 2015	In the first half of 2016	In July 2016	In August 2016	In September 2016	In October 2016
ash content	16.78	16.96	16.31	14.58	14.35	14.15
fineness	11.3	10.1	9.2	7.2	7.3	8.1
moisture	2.92	2.69	2.69	2.72	2.65	2.67
w(SO3)	0.89	0.92	0.96	0.89	0.85	0.87

(3) Kiln head burner. The position of the kiln head burner of the company has been fixed and used since it was put into production with good results. During the suspected burner head sinking or close to the flame cover wear caused by pulverized coal involved in the material, resulting in insufficient pulverized coal combustion, resulting in increased burning loss, several attempts to adjust the position and gap, to avoid pulverized coal involved in the material, have brought adverse effects. Therefore, it is judged that the burner of kiln head is not the main reason for the increase of burning loss.

(4) Usage amount of pulverized coal at kiln head. During the search for the reasons for the increase in burning loss, for a considerable period of time, especially in the early stage, it was believed that the increase in burning loss was caused by the large amount of head coal and the insufficient burning of pulverized coal, and attempts were made to reduce the amount of head coal, which further worsened the phenomenon of the increase in burning loss. After searching for a large amount of data of pulverized coal used in kiln head, it was found that the influence of pulverized coal on the increase of burning loss was still uncertain.

(5) Decomposition rate. Through multiple sampling and analysis of the five-stage feeding tube, the decomposition rate is in the range of 92% ~ 95%, all reaching the theoretical data, which will not affect the clinker calcination in theory. Therefore, the decomposition rate is not the main reason for the increase of burning loss.

Through the above analysis the clinker ignition loss increase is mainly caused by the limestone high alkali content and the increase of alkali content of limestone slurry is easy to burn sex good, in the clinker calcined to equally qualified under the condition of free lime, calcined process of chemical reactions or fuel combustion is inadequate compared with the normal state, thus leading to higher clinker ignition loss.

02 Solutions

Through analysis, it is concluded that: 1) controlling and reducing the content of limestone alkali is the most direct and effective measure. 2) Increasing the amount of pulverized coal used in kiln head and appropriately raising the calcination temperature in kiln can reduce the burning loss of clinker. However, due to the impact of the mining level of the limestone mine of the company, measures to reduce the limestone alkali content cannot be adopted directly. Therefore, appropriate increase in the amount of pulverized coal used at the kiln head is formulated to improve the calcination temperature in the kiln. The idea and idea of minimizing the alkali content of limestone (raw material). Specific requirements: stable control kiln head temperature above 1100℃, the best to reach 1150℃; Limestone alkali content should be controlled below 0.40% as far as possible, and clinker alkali content should not exceed 0.85%. Specific measures are as follows:

(1) strengthening the mines and other auxiliary materials production and processing prehomogenization collocation, reduce or eliminate the usage of interlining, adopt high quality low JianKuang collocation is used, appropriate adjustment of alkali content of raw ingredients of raw material will be controlled under 0.50%, at the same time increase the rate of the soil of value and alkali content inspection frequency, guarantee the clinker alkali content control to no more than 0.85% as much as possible.

(2) Inform the central control operator of kiln to strictly control the air used in grate cooler, appropriately increase the amount of head coal, increase the temperature and temperature of secondary air, and keep it stable above 1100 ° C and strive to control it above 1150 ° C.

(3) Process technicians strengthen process inspection and adjustment, and improve the calcination temperature by adjusting the gap and position of the burner, adjusting the opening of the tertiary air valve and other technical means with the central control operation; When the calcination temperature is not easy to increase, the burner of kiln head shall use diesel oil appropriately to assist in increasing the calcination temperature in the kiln.

Through the above measures, the burning loss of clinker in October has been effectively controlled, and the strength and standard density have reached the expected effect.

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