RU2458107C2 - Method for microwave gradient activation of coal - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: method consists in microwave gradient activation of coal in high-gradient microwave field in velocity control mode of microwave field rise. Boundaries of coal lump are arranged in zones of zero or close-to-zero intensities of microwave field. Activation is performed till deep cracks appear in coal lump, which do not lead to its complete destruction. End of activation process stage is appearance of persistent flame of activation volatile hydrocarbons.

EFFECT: quick and effective heating of coals; improving energy use efficiency for coal heating; processing of compound hydrocarbons to easier and more volatile hydrocarbons deep in coal lump prior to the combustion beginning; possibility of controlling the modes of power pumping to various forms of activated volumes of coal, which allows implementing various modes of action on coal.

2 cl, 2 ex, 2 tbl, 8 dwg

Description

The invention relates to a technology for the preparation of coal fuels of various grades for combustion in power boilers of various types.

A known method of burning coal fuel with additional ignition of a jet of coal dust in boilers by passing this jet through plasma arcs. As a result, the coal particles of the jet, which are almost always less than 1-2 mm, heat up and burn further faster inside the large boiler (Zhukov MF Plasma oil-free kindling of boilers and stabilization of the combustion of the coal-dust torch / Zhukov MF, Karpenko E .I., Peregudov V.S. et al. - Novosibirsk: Nauka, 1995. - 304 p. [1], (Imankulov E.R. Plasma ignition and stabilization of torch burning in Donetsk AS / Imankulov E.R., Messerle V .E., Zakipov Z.E., Seitimov T.M., Ustimenko A.B. // Thermal Engineering. - 1990. - No. 1. - S.51-53) [2].

The disadvantages of this method: 1 - high power consumption by the plasma torch, sometimes up to 10% of the electricity generated by the boiler of the TPP, 2 - introduction of the sprayed material of the plasma electrodes into the combustion stream and 3 - rapid wear, 4 - this conditionally called fuel activation does not allow it to be applied to small (less than 0.1 MW) and ordinary household boilers. Since plasma torches are complex and expensive technical devices, they can be paid off only in certain situations and only on large boilers with the injection of finely ground coal into the torch.

A known method of activation in high-frequency microwave plasma of coal powder grinding (Burov V.F., Strizhko Yu.V. "Microwave plasmatron with a freely floating plasmoid /" // Combustion and plasma chemistry, - v.4, No. 2, 2007, C. 103-109) [3],

(Burov V.F., Strizhko Yu.V. "Microwave plasmatron with a freely floating plasmoid" // Collection of reports of the VI All-Russian conference "Combustion of solid fuel" November 8-10, 2006, Novosibirsk: IT SB RAS, 2006 [4 ]; (Burov V..F., Strizhko Yu.V. "Microwave plasmatron: we use a free-floating plasmoid for igniting coal dust" Equipment. Developments. Technologies, No. 2 (02), 2007, p. 45-48) [ 5]. Patent of the Russian Federation No. 2328095 dated June 23, 2006. “Microwave plasmatron”, applicant of COTES-Siberia CJSC (RU) [6].

In this embodiment, a microwave electrodeless plasma is also ignited at the base of a jet of coal powder, however, a plasmon-type discharge is created due to ionization of the carrier gas of the powder.

The disadvantages of this method are: extremely low efficiency - almost all microwave energy is spent on heating the gas and maintaining the gas discharge, and fuel particles less than 1-2 mm absorb only a small fraction of the energy expended; The microwave plasmon at the base of the jet is very unstable and requires special complex structures with gas streams for its implementation, the power and available operating frequency of microwave industrial magnetrons of wide industrial production are limited to narrow ranges, which does not allow varying the capabilities of this method, coal particles of small sizes (less than 1-2 mm) in microwave fields of such frequencies (of the order of 2.45 GHz, a wavelength of about 13 cm) is actually in a gradientless spatial microwave field, which does not allow us to use, as we found out, temperature gradient and stress fields inside the carbon matrix.

The objective of the invention is to create a method with high energy and environmental characteristics, providing highly efficient combustion of a wide class of coal fuels

Technical result: the efficiency of energy use for heating coal is 20-30 percent higher than the usual method, the constructive ease of execution of various technical options for implementing this method, the ability to use easily adjustable modes of pumping different capacities in different forms of activated coal volumes allow for different modes of exposure to coal or coal briquettes - from their collapse into smaller pieces and to the smooth regulation of the laminar flame from slots with a given int nsivnostyu combustion.

The problem is solved by the claimed method of microwave gradient activation of coal fuel, in which, according to the invention, microwave gradient activation is performed in a high-gradient microwave field in the mode of controlling the rate of increase of the microwave field until deep cracks occur in a piece of coal, not leading to its complete destruction, but by the end of activation is the occurrence of a continuous flame of activated volatile hydrocarbons, while the boundaries of a piece of coal are located at zero or close to them tension H field

With continued activation above the threshold for the occurrence of light hydrocarbon combustion torches, the mineral inclusions present in each natural coal begin to rapidly coagulate (merge) in sizes up to microns and higher. In this state, the activation efficiency of coal decreases, since large particles change the microwave absorption coefficient in the volume and do not have the necessary catalytic properties for the decomposition of heavy hydrocarbons to simpler and combustible ones.

When combining the microwave activator with the volume of the combustion boiler in one design, the maximum microwave gradient field is combined with the front of the filling of fresh coal pieces.

The implementation of the invention

The process of activation of coal in a high-gradient microwave field is multi-parameter, with the initial determining factors for effective activation being the coordination of the dimensions of the gradient microwave volume and the sizes of a piece of coal and a carbon matrix.

The most important condition, as our experiments and numerical calculations show, is the condition for placing the boundaries of a piece of coal in zones of zero or close microwave field strengths. If these conditions are not met, when a piece of coal is significantly larger than the size of the inhomogeneities of the microwave field obtained in the resonant method of its excitation, the process sharply loses the intensity of energy transfer to the sample even in the same locally inhomogeneous microwave volumes. The rate of injection of energy into the coal matrix decreases 5-15 times, depending on the type of coal and their specific geometry.

Example 1. A sample of cylindrical coal several centimeters in size was installed so that the maximum microwave field was in its center or close to the center.

The figure 1 presents a series of IR thermograms of a piece of coal of a cylindrical shape under the action of microwave radiation with a local focus outside the resonator. White contours outline in black and white version of this figure the areas of maximum internal heating of coal samples at the maximum intensities of the microwave fields.

The results of the study for the maximum gradient of 3.2 cm activation time by the threshold for the decomposition of hydrocarbons in a coal sample are shown in table 1 (Kemerovo section) and table 2 (Ust-Iskitim section).

Table 1 Sample Diameter (cm) one 2.2 3 5 8 fourteen Activation Time (sec) 33 16 3 19 38 120

table 2 Sample Diameter (cm) 1,5 2.1 3.3 6 9 12 Activation Time (sec) 17 9 1,5 9 21 82

Under optimal conditions for matching the fields and loading the activation volume with coal, especially in the regime of angular expansion of the microwave field from the magnetron head, we have shown by calorimetric measurements in thermostats that it is possible to pump more than 85% of the power from a magnetron into a piece of coal several centimeters in size. For comparison, in this mode the flash of the first volatiles begins in less than 10 seconds of activation on magnetrons of relatively low power of 800 watts and with a duty cycle of 25-50 Hz.

Example 2

The figure 2 presents the results of the activation of large coal (25-30 cm) in a resonator volume excited by a 1 kW power magnetron, a zone of microwave inhomogeneity of 3.2 cm. Due to the appearance of several heating zones in the matrix of a large piece of coal, the magnetron power was distributed between them, and this distribution changes all the time during the activation process due to changes in the dielectric absorption constants of the microwave wave depending on the temperature and properties of the heated coal, which as a result leads to a sharp increase in time Change the activation of the whole piece for more than 30 minutes for Kemerovo samples. The process efficiency is below 20-25%.

For the purposes of the practical application of the method, provided that the coal load is sized according to the size and the inhomogeneity gradient of the microwave field, as shown by us in experimental studies, it is necessary and sufficient to have one parameter for controlling the process - the change in temperature of the sample over time.

Temperature measuring points can be different and determined by the geometry of the installation. For example, an averaged IR control from 5-10 points on the surface of the coal, thermocouple both from the surface and from the depth of coal, using the manufacture of a micro-hole in the coal matrix (the thermocouple is performed in the microwave interference compensation model). And finally, the most important, IR thermal imaging control method with an attached video camera and access to a computer.

The main task of optimal activation is to create at the initial stage of the process (often the first seconds) at least two cracks in different planes relative to the main direction of “cleavage” of this particular piece of coal.

Creation of cracks is associated with the need to remove dislocation stresses in a piece of coal, the growth of which usually leads to uncontrolled collapse of the entire coal piece into much smaller fragments, inside which gradient activation is no longer possible. The second most important task of creating cracks is the organization of the controlled release of internal water vapor, both hygroscopic and bound, at further stages of activation.

The study of the role of cracks that occur during microwave exposure and under mechanical loads on pieces of coal of different sizes, to optimize the process of microwave activation of coal in environmentally friendly combustion is shown in Figure 3.

After the internal pressure of the water vapor has been relieved, the release of volatile hydrocarbons begins, which was recorded by the real-time experiment on a portable field chromatograph ECHO.

It is this criterion — the rate of release of volatile hydrocarbons — that should be the main criterion for the stage of activation processes in the preparation of activation coals of various grades in the proposed method.

Possible implementations of the claimed method are tested in many model experiments with pieces of coal of different grades and different sizes. It was shown that with an optimal process, it is always possible to achieve the opening of a stressed dislocation matrix to a small number of discharge cracks.

The degree of release of both volatile hydrocarbons and water was controlled by us in the setting mode of a specific activator using various methods (ECHO field chromatograph, mass spectrometer, aerosol meters like AZ-6, nephelometers of various types, spectroscopic portable prisms, vacuum aerosol samples of different type, etc.).

The use of various modern highly sensitive chromatographic instruments, laboratory and expeditionary, for experiments, which allow the initial kinetics of heating of coal, including microwave methods, to analyze the kinetics of the appearance of light and medium hydrocarbons, made it possible to understand the basics of processes occurring during microwave internal high-gradient heating and the role in them emerging deep cracks.

In this laboratory chromatographic mass spectroscopic methods allow you to determine the mass of hydrocarbons, but require for the analysis of special conditions and time of at least half an hour per sample (Figure 4A); whereas calibrated by these laboratory methods, the field expeditionary device ECHO allows you to study the processes of activation of coal with a resolution in time of less than a minute (Figure 4b).

The graphs show that under optimal conditions for the activation of the coal pieces specified in the proposed application, from the cracks of activated carbon, to a temperature on their surface of not more than 100-120 ° C, mainly only light hydrocarbons are released, up to a mass of not more than 150 atomic units (Figure 4a).

Moreover, the process of separation of such hydrocarbons is stable, that is, with an increase in their concentration by 6 orders of magnitude, the ratio to the limiting mass of hydrocarbons remains almost unchanged, which was established using a fast ECHO mass spectrometer (Figure 4b).

We have developed numerical programs that allow, according to the IR temperature data on the surface of the sample, to dynamically restore the foci of heat release inside activated carbon and the propagation of the heat wave front to the surface of the coal in the mode before cracks appear. Calculations show that when the internal pressure of water vapor is 40 -50 atmospheres, the specimen splits in an uncontrolled mode of cracking and expansion of fragments.

Figure 5 shows the calculation of the output of a heat wave from the depth of coal pieces of different sizes (based on the obtained experimental data on the constants of the complex dielectric constant at relatively low temperatures and thermal conductivity for Kemerovo coal). The curves differ in time and in terms of primary microwave heating, both in size and power.

The microwave activator can be made on the basis of standard magnetrons that are widely used in everyday life for microwave household stoves with relatively low power (less than 3 kW, even without the use of water cooling), and by changing their number and the focusing geometry of the microwave fields, it is possible to achieve the required gradient inhomogeneity activation microwave field, and its various capacities.

The geometry of the activation installation can be very different, as well as the system for introducing pieces of coal (stationary, quasi-stationary, continuously flowing). For example, to activate coal in small volumes - up to 10 kg per hour, for domestic coal-fired boilers, we used both the basic structures and the control electronics of ordinary household stoves, with small modifications. These modifications are already determined by the specific requirements for the parameters of activated carbon.

Processing microwave microwave activation of coal in a large volume is a very poor regime for the efficiency of pumping microwave power into structural changes inside the coal, even in local zones of maximum power, since the conditions for matching the volume of the gradient field and the size of the piece are not met.

Any natural coal contains a mineral component from a few percent to 50. This mineral component contains many components, but usually the main - tens of percent - are aluminum and silicon components. An analysis of the literature and our analysis, performed on reflective optical and scanning microscopes, showed that in non-activated carbon the mineral components are incorporated into the coal structure very uniformly. Upon microwave activation, in this homogeneous structure, homogeneous inclusions of silicon and aluminized formations begin to form. With continued activation above the threshold for the occurrence of light hydrocarbon combustion torches, these formations reach a size of up to 5 nm (Figure 6a), after which they quickly coagulate (merge) into sizes up to microns and higher. Figure 6b shows the surface of the coal with the release of large particles along all microcracks. In this state, the activation efficiency of coal decreases, since large particles change the microwave absorption coefficient in the volume and do not have the necessary catalytic properties for the decomposition of heavy hydrocarbons to simpler and combustible ones.

A significant advantage of the proposed new method in comparison with analogs is the extremely high efficiency of energy transfer to the sample with an optimal design, taking into account the above-described features of the whole process.

Also a big advantage of the proposed method is the use of coarse coal (up to 5-6 centimeters in diameter), rather than fine coal grinding, less than 1-2 millimeters in size, which is traditionally used in large thermal power plants and powerful boilers. This allows you to apply the method to increase the efficiency of use in small and domestic boilers in such boiler rooms that serve less than several tens of thousands of residents. This greatly expands the applicability of the new method for coal power.

Calculations of economic feasibility were carried out on the basis of model experiments on boilers from 0.1 to 1 MW power. With the cost of a ton of coal from 1000 to 2000 rubles per ton and with the efficiency of the coal burning process with activation of 15%, it was found that in Siberia (the heating season is more than 200 days), the cost of the boiler pays off in 1-3 years depending on the type low and medium power boilers. The warranty period of boilers is usually not less than 10 years, so there will be a multiple payback period for boilers of such capacity (calculations were carried out for equipment of the Cherepanovsky boiler plant in Novosibirsk Region).

ENVIRONMENTALITY. Activated carbon differs in one clearly distinguished feature - its ignition takes place in several seconds at the upper activation threshold and proceeds practically without smoke and emission of harmful hydrocarbons in the gas and aerosol phases. This is because the decomposition of hydrocarbons of the carbon matrix in this method does not occur on the surface of the coal when interacting with an oxidizing agent - air, as in conventional thermal ignition. During microwave activation, the processes of destructuring occur inside a closed volume of coal. We made measurements of the smoke component and the gas component using different activation methods and showed a decrease in the integral emission of volatile components of hydrocarbons into the external atmosphere by tens and hundreds of times.

Thus, the proposed method has the following advantages:

1. Heating of primary coals occurs quickly and efficiently, unlike traditional methods of their ignition in any type of boiler.

2. The efficiency of energy use for heating coal is 20-30 percent higher than the usual method.

3. Constructive ease of execution of various technical embodiments of this method.

4. The processing of complex hydrocarbons into simpler (and therefore more combustible) for the first time occurs in the depth of a lump of coal before burning, and not on the surface or in a gas flame, as in traditional devices.

5. The possibility of using easily adjustable modes of pumping different capacities into different forms of activated volumes of coal allows for various modes of exposure to coal or coal briquettes - from their collapse into smaller pieces and to the smooth regulation of the laminar flame from cracks with a given burning intensity.

We carried out testing on the application of this activation method on boilers of a medium-capacity boiler plant in the city of Cherepanov, Novosibirsk Region, which confirmed its effectiveness in a number of physicochemical parameters of the flames of combustion and combustion of individual coal particles in the boiler room.

Claims (2)

1. The method of activation of coal fuel, including microwave exposure to coal fuel, characterized in that they produce microwave gradient activation in a high-gradient microwave field in the control mode of the rate of increase of the microwave field until a crack of deep fault occurs in a piece of coal that does not lead to it complete destruction, and an indicator of the end of activation is the occurrence of a continuous flame of activation volatile hydrocarbons, while the boundaries of a piece of coal are located at zero or close to them values of the microwave field strengths. 2. The method according to claim 1, characterized in that when combining the microwave activator with the volume of the combustion boiler in one design, the maximum of the microwave gradient field is combined with the front of the fill of fresh coal pieces.

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