A New Distinguish Method of Blending Coals Slagging Characteristic

The slagging characteristic of coal effects the safe operation of boiler unit directly, the study on coal slagging is paid more and more attention by scholars of the world. Because of the complexity of coal characteristic, the blending coals slagging characteristic is more complex than single coal. The study method of blending coals characteristic is the same as the single coal method, but the simple method can’t distinguish the blending coals slagging characteristic well and truly. This paper gives the new distinguish method of blending coals slagging characteristic based on experimentation condition, it is the rate of slag and furnace refuse. The rate of slagging on furnace wall and the refuse on furnace bottom has utilized to distinguish the slagging characteristic of coal. The result shows that the rate of slag and furnace refuse method has better veracity.


Introduction
The slagging characteristic of coal effects the safe operation of boiler unit directly.So, scholars of the world attach importance to the study of coal slagging.At present, the study of slagging characteristics of blending coals is depended on the study of single coal.
The fuel character, boiler structure and operation mode are the factors of deciding boiler slagging.The fuel character is the basic of boiler design and operation.So, the study on fuel slagging characteristic is important.The study on distinguish slagging character is paid more and more attention by scholars.There are many distinguish methods and index of single coal slagging characteristics.The most of the methods are ash melting temperature slagging index method, ash element slagging index method, ash viscosity slagging index method, special type method and integrative distinguish method [1][2][3].
In USA, every slagging distinguish method are studied in 130,300 MW and upwards units.The results show that no method can forecast slagging trend complete accurately.The resolution of the softening temperature and silicon aluminum ratio is the highest.Harbin complete institute distinguishes the slagging trend of 250 kinds of Chinese coal; the resolution is 65%.Harbin boiler factory and Harbin Institute of Technology study on lignite slagging trend, the results show that the resolution of the softening temperature and silicon aluminum ratio is 74% [4].
Many scholars study on blending coals slagging characteristics [9,10].They consider that the slagging character of blending coals is more complex than single coal because of the complex of single coal slagging character.The blending coals research method is the same as single coal research method, but it can't distinguish blending coals slagging trend by single coal slagging trend.It means that the difference of slagging character between blending coals and singles coal is great.
This paper gives the new distinguish method of blending coals slagging characteristic based on experimentation condition, it is the rate of slag and furnace refuse.The rate of slagging on furnace wall and the refuse on furnace bottom has utilized to distinguish the slagging characteristic of coal.

Coal Analysis
The single coal analysis and the rate and numbers of blending coals are shown in Table 1 and Table 2.

Test Rig
This study is conducted at Combustion Research Facility (CRF) test rig, which is introduced from Canada.It's designed for a maximum coal feed rate of 20 kg/h medium sulfur coal at a firing rate of 640 MJ/h (see Figure 1).Its advantages are complete equipment, advanced control system, on-line measurement and recurring of experimental result.The test rig is composed of five systems, which are the combustion system, data acquisition and control system, compressing air and cooling system, the system of sampling and analysis of flue gas and milling system.The furnace is a refractory-lined cylindrical chamber, composed of four identical modules, the bottom three with cylindrical cooling jackets.It is 3.6 m high, and 0.3 m in diameter.The furnace temperature is measured by plati-num-rhodium thermocouple.The flue gas that leaving the furnace is continuously monitored by O 2 , NO x , CO 2 , CO and SO 2 analyzers.The slag is got in the cooling drawer at the bottom of the furnace and the fly ash is sampled at the bottom of ESP.The coal feed rate of 20 kg/h.

Experimental Process
In this paper, the slag is got in the water-cooling drawer at the bottom of the furnace, the fly ash is sampled at the bottom of ESP.The coke adhered to furnace wall.The coke is scratched from wall after test.

Test Results and Discussion
Slagging is a complex physical and chemical process.It is not only related to the composition of coal ash, but also influenced by the type of burners, the structure of furnace, the temperature level in furnace, the aerodynamic field of furnace and atmosphere in furnace.Now, there are a few methods to predict and estimate the slagging of pulverized-coal combustion, such as ash fusion, ash composition and ash viscosity, but none of them is accurate enough to predict correctly in practice.
According to the conditions of the test rig, this paper got the ratio of the amount of coke attached to the wall to the amount of slag on the bottom of the furnace.It is presented as a discriminant parameter of slagging and used to evaluate the extent of slagging in furnace in this paper.The bigger the ratio is, the easier the slagging happens.Table 3 shows the result of the ratio of coke and slagging.On the basic of Table 3, the tendency of  slagging of Meihe coal and 5#(2Y8H) coal is obvious, while that of Huolinhe coal is weak.It fundamentally agrees with the practice slagging tendency in boilers of Shuangliao Power Plants on the whole.The ratio of coke and slagging is a reasonable discriminant parameter of slagging.From slagging characteristic of Meihe coal, 2# coal, Yangcaogou coal, 1# coal, 6# coal, Huolinhe coal, the results show that the slagging characteristic of blending coals is between componential coals basically.The slagging serious coal changed the slagging characteristic by blended not easy slagging coal, thereby achieved the aim that lighten slagging.
According to the Table 3, the slagging property of 9# (4M3F3Y) coal and Meihe coal is more serious than that of Huolinhe coal and Yangcaogou coal.This shows when the blending of a coal of high slagging potential with another coal with low slagging potential is used, the trouble of slagging perhaps gets worse instead of getting better.This is because the eutectic phenomenon of ash composition makes the ash fusion of the mixed coal lower than that of any of the coals used in the blending.Therefore, improper blending of coals will cause serious slagging.

Slag Type Analysis
From the slag scratched from wall, the slag color of Meihe coal, No. 9 and No.

Fusion Behavior Analysis
The fusion behavior of coal ash is shown in Table 4.This paper adopts the Harbin boiler factory and Harbin Institute of Technology method distinguishes the slagging character.The result is that Meihe coal, No. 1, No.

Compare of Three Methods
Up to now, there is no method has 100% resolution.So, the test result is most important.The compare of three methods is shown in Table 5.The result shows that the rate of slag and furnace refuse method has better veracity.

Conclusions
This paper gives the new distinguish method of blending coals slagging characteristic based on experimentation condition, it is the rate of slag and furnace refuse.The result shows that the rate of slag and furnace refuse method has better veracity.

Table 4 . Fusion behavior of coal ash.
2 blending coals is hoar and dust color.It has alveolate hole.The intensity is high and rigidity is great.The surface of slag is smooth.It belongs to glaze type slag.It shows that the slagging is serious.The slag color of Yangcaogou coal, No. 1, No. 7 and No. 5 blending coals is black, the character is relaxation.It shows that the slagging is middling.No. 3, No. 4, No. 8, No. 6 blending coals and Huolinhe coal slagging is ightly.l