Yuan Wei-jun LI Jian-sheng Zhang Fuliang
(Tangshan Keyuan Environmental Protection Technology Equipment Co., Ltd. Hebei Tangshan 063020)
Abstract: The combination of atmospheric fixed bed gasifier gasification reaction principle expounded define atmospheric fixed bed gasification ash fusion temperature indicators necessity, and accordingly put forward a gasification reactivity-based indicators ash melting point defined methods. Meanwhile on the ash melting point indicators defining the problem, analyze the gasification of coal ash fusion temperature indicators in the national standards in defining the scope and definition of hierarchical aspects of irrationality.
Keywords: atmospheric fixed bed; gas furnace; coal gasification; ash melting point; ash melting point indicator; gasification reactivity
The definition of ash fusion point index for atmospheric fixed-bed gasification
Yuan weijun Li jiansheng Zhang fuliang
(Tangshan Keyuan Environmental Protection Technology & Equipment Co., Ltd 063020)
Abstract: Combined with the gasification principle of atmospheric fixed bed coal gasifier, the necessity to define the ash fusion point index for atmospheric fixed-bed gasification is expounded, and accordingly the ash fusion point index definition methods based on gasification reactivity is indicated. At the same time, analysis the irrationality of definition scope and grading for ash fusion point index in coal gasification national standard.
Keywords: atmospheric fixed-bed; coal gasifier; coal for gasification; ash fusion point; ash fusion point index; gasification reactivity
Introduction
        Coal gasification and rational utilization of coal conversion is one effective way, in line with China's development of clean coal technology, energy diversification strategy, China is still a long-term matter of great significance. In recent years, atmospheric fixed bed gasification technology as the main small-scale fuel gas supply unit, its scale of production, the cost of investment, construction period, which qualify for the majority of metallurgical, chemical, building materials and machinery industries such as gas demand application of the more extensive.
        Atmospheric fixed bed gasifier, gasification of coal for more stringent requirements, since the late 1980s, the state has promulgated a series of coal gasification and updates the relevant standards, in 1988 promulgated the "atmospheric fixed bed gas furnace coal quality standards "(GB9143-88), 1994 promulgated the" two-stage gas furnace coal gasification technology indicators "(GB50195-94), (GB9143-88) in 2001 and 2008 carried out two revision to upgrade, but the standard was renamed as "atmospheric fixed bed coal gasification technology requirements and test methods." These standards on the gasification of coal ash melting point indicators are put forward specific demands to ST> 1100 or ST ≥ 1250 ℃, the choice of the actual trial burn coal gasification process of discovery, although not reach some coals ash melting point specified in the standard indicators, but still can get a better effect of gasification. For more accurate identification and selection of coal gasification, coal is necessary to combine some of the relevant characteristics of the standard indicators specified in the systematic analysis of ash melting point and refocusing sentenced identification standards.
1 gasification ash melting point of the necessity of defining indicators
        Atmospheric fixed bed gasifier gasification of coal as raw material, air and steam as gasification agent, the production of CO and H2 and other combustible ingredients-based producer gas, the furnace is divided into various functional layers dry layer, retorting layer, the reduced layer, the oxide layer and the ash layer. The main reaction furnace occurs as follows: the air layer through the fuel oxidation reaction and the steam and air mixture through the fuel bed to a reduction reaction, the oxidation reaction in the oxide layer for the coal gasification agent of the carbon is oxidized by oxygen in the into carbon dioxide and give off a lot of heat, to provide heat for the next reduction reaction and the reactants CO2 as the reaction equation (1); reduction layer, the restore completion, the oxidation reaction of CO2 and the heat released by the oxidation reaction heat Coal burning after reduction reaction, generating combustible gases CO; Meanwhile, steam and hot coal to a reduction reaction, generating combustible CO and H2, the reduction reaction is an endothermic reaction, exothermic heat of the oxidation reaction depend on maintenance of the reaction equation as (2), (3).
        C + O2 = CO2; △ H = -409 KJ / mol (1)
        CO2 + C = 2CO; △ H = 162KJ/mol (2)
        C + H2O = CO + H2; △ H = 119 KJ / mol (3)
        In summary, to maintain normal occurrence gasification furnace, the furnace must be guaranteed to occur reduction reaction of reducing layer completely as possible, to generate as many other flammable gases CO and H2; while the furnace must ensure that all levels of resistance, air to flow freely, so as to effectively ensure the oxide layer and restore normal gas-solid reaction layer and gas output smooth conduction of the furnace. Complete reduction reaction is carried out or not, depending on the reduction provided by the oxidation reaction of the reactants required for the reaction of CO2 and heat is sufficient to ensure complete reduction furnace, the furnace to ensure that the oxidation reaction as fully as possible, the requirements into the oxidation Burning coal layer more fully as possible, but over a certain temperature combustion of coal, the melting of the ash will appear, after melting gasifying agent hinder smooth ash ash layer into the oxide layer by means of participating in the reactions of the oxide layer the oxidation reaction is not complete, thus affecting the reduction zone of the reduction reaction sufficiently.
        Ash melting phenomenon occurs when the temperature corresponding to the melting point called coal ash, coal ash melting point is itself have the characteristics of coal, coal ash and ash melting point component related to coal ash is composed of a mixture of various minerals , without a fixed melting point, and only one melting range, ash at high temperature, its deformation, softening temperature, and flow of the corresponding, respectively, DT, ST, FT said pressure fixed bed gasification furnace gas coal indicators, generally ash softening temperature (ST) for the ash melting point indicators judgment parameters.
        Thus, for purposes of atmospheric fixed-bed gasification, coal gasification is essential to choose, the furnace must be guaranteed in the event of normal coal gasification, coal ash slagging melting phenomenon does not appear that the coal determine an ash melting point indicator, that is, the occurrence of coal gasification furnace as defined by a normal temperature data indicator, if the coal ash melting point higher than this indicator, the normal melting gasification ash slagging phenomenon does not appear, then the coal can be used for gasification, can not be used otherwise the coal gasification.
2. National standards for coal gasification ash melting point indicators defined problems
2.1 gasification of coal ash melting point of the national standard indicators defined
        Table 1 for the gasification of coal ash melting point defined by the national standard indicators, it can be seen, the standard for the gasification of coal ash melting point indicator considerable attention, (GB9143-2001) for (GB9143-88) in the ash melting point indicators were amended accordingly, but (GB9143-2008) and restored (GB9143-88) of the ash melting point indicator. Because two-stage gas furnace in the 1990s began to be widely used, so in 1994 it issued specifically for this purpose (GB50195-94), this standard has been revised and upgraded.
Table 1 national standard coal gasification ash melting point indicators defined

2.2 Scoping unreasonable
        (GB9143-2008) pointed out that the gasification of coal types include: lignite, long flame coal, non-caking coal, weakly caking coal, gas coal, lean coal, lean coal, lean coal and anthracite, and unify the ash melting point indicator is defined as Ad ≤ 18% when 1150 ℃ and Ad> 18% when 1250 ℃, so they put a lot of easy-gasification and ash melting point lower than 1150 ℃ excluded from the gasification of coal outside the ranks of coal, while, according to the standard We can understand that, if only one indicator of coal ash melting point evaluation, as long as the ash melting point greater than or equal to 1250 ℃ can be used on coal gasification, which is obviously unreasonable. In the actual gasification process, found that most low metamorphic grade coal (such as lignite, bituminous young) atmosphere at a lower temperature gasification can be good, for this coal ash melting point does not need to index requirements too high.
2.3 define improper classification
        Literature [1] The heat of the exothermic oxidation is divided into two parts, one for the water gas shift reaction and CO reduction reaction heat (about 57%) and the heat of the reaction heat (about 43%). Part of the reaction heat of reaction is used to overcome the resistance of the structure of coal, another part of the heat is ash, furnace cooling, gas and water vapor sensible heat, etc. away. It can be seen, the exothermic heat of oxidation smaller part as a reaction part of the heat for heating the ash content of the coal ash, the reaction heat coal with low ash content than high, (GB9143) based on the gray ash content melting point of the corresponding classification indicators for smaller ash content of coal ash melting point of its indicators appropriate to reduce, may be out of this point to consider. But (GB9143) ash melting point indicators defined: Ad ≤ 18% when, ST ≥ 1150 ℃; Ad> 18% when, ST ≥ 1250 ℃, only slightly different ash content, ash melting point indicator will appear such a big difference, which is clearly lacking theoretical basis, but there are obvious irrationality. Moreover, in the actual gasification process found high ash coal is often more easily vaporized low temperature atmosphere, do not need high ash melting point targets.
3 Use the gasification reactivity index defined ash melting point
        Coal gasification reactivity is an important feature, means and in a heated state coal gasifying agent (air + water vapor) effect the chemical reaction of the strength, coal gasification reactivity represents the coal for gasification the degree of difficulty, the gasification reactivity is stronger, the gasification reaction, the faster the same duration carbon conversion rate is higher, the time required for complete gasification of the shorter, in the event of the furnace, the gasification of the coal, the stronger reactivity , when it reaches the corresponding complete gasification of the lower reaction temperature.
        Scholars study found that over the years, coal gasification reactivity is affected by many factors, East China University of Xu Shen Kai et al [2] found in experiments the presence of alkali metal Na Coke can significantly reduce the degree of graphitization, improve coal gasification reactivity, while the presence of ash with an alkali metal has the same trends, but the impact is weak compared to the alkali metal. For coal gasification reactivity properties on the impact of the literature [3,4,5] were also reached the following conclusion: the greater the catalytic effect of minerals, coal gasification reactivity of the larger size of its catalytic coal metamorphism related to the higher degree of metamorphism of coal mineral catalysis smaller; enables the pore structure of coal pyrolysis rich, factors that increase the specific surface area, help to improve coal gasification reactivity; Coke coal gasification reactivity with the degree of metamorphism increases. East China University of Wu Jiaqi, etc. [6] experimental study was carried out through the following conclusion: coal and coal gasification reactivity of the fixed carbon content varying inversely with the volatile content in coal and basic factor was positive change. Thus, the subject matter of the coal from the objective existence of a number of factors, different coal gasification reactivity of its different, so the ash melting point must also be an indicator of coal must be defined.
        Gas furnace including coal gasification and CO2 responses and reactions of coal with steam, Kora, etc. [7] found through experiments, lignite and bituminous steam reaction rate is 2-5 times the CO2 reaction rate; Zhang Xianlin etc. [8] 1193-1323K at atmospheric pressure and under the conditions studied by thermal gravimetric analysis of water vapor and CO2 Chinese anthracite chars gasification reactivity, experimental results show that the anthracite char gasification with CO2 reactivity was significantly less than with steam gasification reactivity of the latter is about 10 times larger. Literature [9,10] that the water vapor atmosphere, the gasification reactions occur in more than 0.6nm microporous surface, while in a CO2 atmosphere, the gasification reactions occur in the larger pores of the outer surface, is greater than 15nm in microporous surface fishes gasification play a role, so, coal and water vapor and CO2 reaction rate until there is such a big difference.
        Gasification ash fusion temperature indicators defined, should be primarily focused on the coal at what temperatures can occur sufficiently gasification furnace, the temperature is defined mainly by coal gasification reactivity effect, with the coal gasification activity varies. Coal gasification reactivity expressed in many ways, often with a CO2 reduction rate (α) to indicate the size, the reduction rate (α) and the size of the coal gasification temperature. Determining whether a coal gasification ash melting point meets the requirements, you first need to be determined gasification reactivity, and then according to the determination result of defining the coal for gasification ash melting point indicator, and finally the index compared with the ash melting point, If the ash melting point higher than the melting point of the ash of coal index, then only the ash melting point, the gasification of the coal can be used, defining the specific methods are as follows: First, the reduction rate of CO2 coal samples (α) is determined, and its CO2 reduction rate (α) as a percentage of the temperature corresponding to point A to define the basis, considering furnace temperature oxide layer may occur volatility, based on the increase at this temperature is defined as the ash melting point B ℃ indicators. Wherein the value of A is equivalent to the furnace gas CO2 reduction ratio, can be achieved by existing gasification gas derived data determined to a coal, for example, in the gasification furnace gas main components of the gas: CO2-5.0%; CO-27.4%; H2-14.0%, specific calculation process is as follows:
        Assuming all by 100Nm3 H2 gas reaction between steam and coal, by the aforementioned reaction formula (3), the water, the amount of CO gas produced by the reaction should be the same amount of H2, namely: CO = H2 = 14.0 Nm3; 100Nm3 coal gas in the reaction of CO2 and the amount of generated CO: CO = 27.4-14.0 = 13.4Nm3; reaction by the foregoing equation (2) shows that the amount of CO2 reaction with coal: (13.4 ÷ 2) = 6.7 Nm3; oxide layer total CO2 generation: CO2 = 6.7 +5. 0 = 11.7 Nm3, the gas furnace CO2 reduction rate: 6.7 ÷ 11.7 = 52.5%.
        Table 2 shows the same method to calculate several sets of data corresponding to the reduction of CO2 gas rate, it can be seen the furnace gas CO2 reduction rate is generally about 60%, so the above defined method, the ash melting point of the A indicator as 60% Comparative Good . When the coal gasification reactivity than 60%, the gasification reaction rate there was a substantial increase in the oxide layer at this time if the temperature rises, the resulting dramatic reduction reaction, heat will also increase, so as to maintain the oxide layer temperature is relatively stable, so the oxide layer is generally not drastic temperature fluctuations, so B does not have to value is too large, I believe that the B value in order to get 100 ℃ appropriate. Table 3 is based on the method described above for several typical coal ash melting point indicators defined data.
Table 2 atmospheric fixed bed reduction rate of CO2 gas furnace

Table 3 atmospheric fixed bed gasification ash fusion temperature indicators defined (α = 60% Time)

Conclusion
        Ash melting point indicator is the atmospheric fixed bed coal gasification choose one of the important sub-identification standards, national standards for the gasification of coal ash melting point indicators defined, define the scope and define its classification there are serious irrationality, there necessary, amending them. The use of gasification reactivity to define its specific method of ash melting point indicators: the CO2 reduction rate (α) of 60% corresponding to a defined temperature point basis, considering the furnace temperature oxide layer volatility may occur at this temperature for foundation to increase the ash melting point 100 ℃ defined as indicators index so defined ash melting point is more scientific and reasonable.
References:
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Author Profile
First Author
Name: Yuan Wei-jun (born October 1968), Gender: Male, Birthplace: Bazhou, title: Senior Engineer, Degree: Master of Engineering, engaged in work content: coal gasification industry, research direction: Gasification Technology and equipment. Tel :0315-3855283, E-mail: ywj680820@sohu.com.