Abstract
Alekseev S. V. – Research of thermopreparation of coal pitch in experimental setup
In the theses, the process of thermal preparation of pitch to obtain an electrode binder is considered. A pilot facility to study the process without air supply is proposed, which is expected to lead to decrease in the volatiles of the product.
Keywords
coal pitch, volatile substances output, viscosity, density
Research of thermopreparation of coal pitch in experimental setup
Coal pitch holds a specific place among products of processing of coal both on the output, and on value. It finds a set of applications, in particular, is primary binding for all types of carbon and graphite materials, electrode products, the electrode and anode masses, structural carbon and graphite materials, electro coal products[1].
Now in our region there are factors which complicate receiving qualitative electrode pitch from which it is necessary to distinguish the following:
– change of the technological modes of coking;
– inconstancy of initial raw materials composition;
– outdated technologies of coal tar distillation;
– the changing market condition.
The most important technological properties of pitch are density, superficial tension, viscosity, wettability, heat stability, caking and ability to give the coke rest. These properties depend on quality of initial raw materials and features of production.
The quality of pitches is estimated on such indicators as an exit of volatiles, ash-content, temperature of softening and group structure.
The last one is the characteristic giving the greatest number of information on properties of pitch. The group structure is determined by solubility of pitch in various substances having the selective dissolving ability. The following fractions of group structure are the most important:
1. The substances insoluble in quinoline (α1–fraction), – is the most high-molecular carbonaceous solid dispersed component, when processing pitch promotes formation of the coke rest, which, however, worsens ability of material to connect filler grains as has no plastic and adhesive properties.
2. The substances insoluble in toluene (α–fraction), which contain the substances insoluble in quinoline (α1–fraction), and the substances soluble in quinoline, but insoluble in toluene are (α2–fraction). These substances are the most valuable component of group structure as they have the binding properties and provide a high exit of the coke rest [2].
The features of coke-chemical production in region listed above demand the development of the optimum modes of pitch processing without which it is impossible to receive the product that conforms to standards.
Now, the production technology of electrode medium temperature pitch, binding by thermooxidation, which results by single coal tar evaporation in distillation columns is used at the domestic plants. The essence of this method consists of inheat treatment of medium temperature pitch at 340–370 °С in cubes reactors of continuous action at continuous air bubbling through reactionary weight. Oxygen of the air is the factor which intensifies consolidation reactions (polycondensation and polymerization) and leads to necessary changes of physical and chemical properties of pitch.
Density of the coal pitches received in similar conditions linearly grows with softening temperature increase. With the increase of heating temperature the linear dependence density from temperature of softening of pitch remains.
Raise of temperature or duration of pitch heating increase leads to accumulation of high-molecular products in pitch. However, the prevalence in the raw materials coming for processing to the tar-distilling shop, pitches of low degree of a pyrolization is characteristic now (with low values α and α1), that leads to decrease in degree of a pyrolization of the raw materials coming for processing to the tar-distilling shop.
When receiving electrode pitches from low pyrolization pitch, insignificant mass fractions of primary fractions insoluble in quinoline or in toluene, lead to an imbalance of such indicators of quality as the softening temperature, an exit of volatiles, a mass fractions ratio of group structure.
In such conditions use of thermooxidizing technology often does incompatible bringing group structure of electrode pitch to the required values with preservation up to standard of other quality indicators (first of all – softening temperatures). Especially it affects by production of the most liquid of high-temperature brands of pitch for electrode products now.
The existing technology in the changed conditions does not allow to receive pitch with preset values of an exit flying (for brand A – 59–63 %, for brand B – 58–62 %), at a heating temperature raising amount of volatiles increase (depending on the brand of pitch) that negatively affects the final product. The weight of evidence suggests that in the possible ways of maintenance of an exit of volatiles at the required level it is necessary:
– to increase the time of pitch stay in reactors;
– to except an air supply in reactionary weight.
However, these assumptions need experimental check.
It should be noted that besides the function of the thermooxidation reactions participant the air bubbling through pitch provides hashing of the heated weight. Interruption in supply of air will inevitably lead to violation of temperature condition in the reactor.
The easiest way to provide uniformity of warming up of reactionary weight and by that to avoid local overheating of substance is to use mechanical mixers.
Thermopreparation of pitch without use of oxidizer demands at first a research of whether receiving the indicators established by standards is possible in principle (not only volatiles), and in case of success – working off the necessary parameters of the technological mode. Under production conditions it is difficult to make therefore laboratory installation is created.
The skilled laboratory reactor (fig. 1) is a cylindrical capacity made of stainless steel on legs. Also it has special places for measuring devices connection (temperature sensors) and sampling. The reactor is supplied with the mixer set in motion by the electric motor.
Figure 1 – Experimental laboratory reactor
For carrying out researches the interval of temperatures of 340–370 °С is chosen as such interval is supported in production reactors. Reach and maintenance of this temperature is carried out by means of the external heat heater.
The pitch heated to the specified temperature continuously mixes up by means of the mixer, sampling for definition of a volatiles exit and contents α – fractions is made at regular intervals.
Also the consumed electric power which depends on viscosity of pitch is measured. It allows indirectly to estimate the change of a group structure.
References
1. Кауфман, А.А. Технология коксохимического производства / А.А. Кауфман, Г.Д. Харлампович. – Е: ВУХИН, 2005. – 288 с.
2. Губанов, С.А. Технологические особенности производства каменноугольного пека из низкопиролизированных каменноугольных смол и варианты совершенствования процесса / С.А. Губанов, А.А. Букка, Е.Ю. Иващенко. // науч. тех. журн. Кокс и химия – 2017. – № 11 – 64 с.