K. Yu. Vershinina

Differences in the ignition characteristics of coal–water slurries and composite liquid fuel

The processes of the inert heating, ignition, and combustion of the drops of typical coal–water slurries and promising composite liquid fuel were experimentally studied with the use of high-speed (to 105 frame/s) video recording facilities. The particles of brown and black coals with of sizes 80–100 μm were used as the basic components of the coal–water slurries and composite liquid fuel. Spent automobile oil (from an internal combustion engine) was also added to the composite liquid fuel (relative mass concentration, 0–15%). The characteristic stages of the processes of the inert heating and evaporating of liquid components and the ignition and combustion of coal–water slurries and composite liquid fuel (the initial radii of drops varied from 0.5 to 2 mm) were established. The ignition delay and complete combustion times of the drops of fuel compositions were determined under changes of the temperature of an oxidizing agent (air) in a range from 600 to 900 K at fluid velocities from 0.5 to 5 m/s. Representative temperatures at the centers of coal–water slurry and composite liquid fuel drops were measured at all of the established stages of the combustion initiation process. The necessary and sufficient conditions for the steady ignition of the drops of the test fuel compositions were recognized.

Environmental benefits and drawbacks of composite fuels based on industrial wastes and different ranks of coal

A promising solution to many problems that thermal power industry is facing today would be switching from conventional coal dust combustion to coal-water slurries containing petrochemicals (CWSP). Here, we perform an experimental study of the most hazardous anthropogenic emissions (sulfur and nitrogen oxides) from the combustion of high-potential CWSP. We identify the main benefits and potential drawbacks of using CWSP in thermal power industry. A set of components and additives to CWSP are explored that significantly affect the environmental and energy performance of fuels. The anthropogenic emissions from the combustion of CWSP made of widespread coal and oil processing wastes are no higher than those from coal dust combustion. Using specialized additives to CWSP, we can change the concentrations of NOx and SOx several times. The most appealing additives to CWSP are sawdust, straw, charcoal, limestone, and glycerol. They provide better environmental, economic, and energy performance and improve the rheological properties of CWSP. Waste oils and oil sludge added to CWSP may impair the environmental performance but boost the cost and energy efficiency. Using coal-water slurries containing petrochemicals as a fuel at thermal power plants is an environmentally friendly as well as cost- and energy-efficient way to recover industrial wastes.

Ignition of coal suspensions based on water of different quality

The ignition of individual droplets (radius 0.5–1.5 mm) of water–coal fuel based on water of different quality (industrial-grade, tap, and distilled water) in a flux of heated oxidant (at 700–1000 K) is studied experimentally. The influence of water quality on the ignition time and the time for complete combustion of the fuel droplet and also on the maximum combustion temperature is investigated. Experimental data are presented regarding the influence of the concentration of the different water samples in the fuel on its ignition. The delay of fuel ignition does not depend greatly on the water quality. (For industrial-grade, tap, and distilled water, the difference is no more than 10–15%.)

Influence of the preparation of organic coal–water fuel on its ignition

The integral ignition characteristics of a single droplet (initial radius 0.3–1.0 mm) of various organic coal–water fuels (prepared by means of a homogenizer or a ball mill) in an oxidant flux at 800–1100 K are compared. The fuel samples are based on spent motor, turbine, and transformer oils, filter cake from K coal, water, and plasticizer. The influence of the drop radius, the fuel composition, and the method and duration of sample preparation on the properties of the fuel (in particular, its structural stability and viscosity in the initial state) and on its ignition characteristics (the ignition delay, the time for total combustion, and the duration of the initiation stage) is determined. The limiting duration of structural stability is compared for samples of organic coal–water fuel prepared by means of a homogenizer and by means of a ball mill.

Characteristics of the ignition of organic coal–water fuels for boiler installations

The ignition processes of organic coal–water fuels (OCWFs) in the flow of a heated oxidant (temperature, 700–1000 K; velocity, 0.5–5 m/s) were studied. The experiments were carried out with the small single drops of OCWFs (radii, 0.2–0.5 mm), which correspond to the injection devices of typical boiler installations. The component base of the test composition fuels included B2 brown coal, typical waste coals (the filter cakes of G and D coals), spent motor and transformer oils, and petroleum residue. The influence of the component composition (the properties and concentrations of solid and liquid combustible components) on the characteristics of the initiation of the combustion of single OCWF drops was found. The dependences of the delay times of ignition and complete combustion on the temperature of an oxidant and on the drop sizes of OCWFs were determined. It was established that, at maximum oxidant temperatures (above 900 K) and minimum drop sizes (smaller than 300 μm), difference between the integral characteristics of ignition was sufficiently small (smaller than 10%) for the fuels prepared from components with substantially different properties.

Droplet ignition of coal–water slurries prepared from typical coal- and oil-processing wastes

The requirements for stable ignition (and subsequent combustion) of fuel suspensions prepared from typical coal- and oil-processing wastes are studied experimentally. Attention focuses on the differences between the ignition characteristics of coal–water slurries (containing petrochemicals) obtained on the basis of filter cakes containing T, K, SS, Zh, D, and G coal. To eliminate the influence of the droplet holder (traditionally, thermocouple junctions, ceramic rods, or metal wire) on the ignition characteristics of the fuel droplet, the experiments employ a special model combustion chamber and a device for introducing a single drop of suspension. The ignition time and the minimum temperature of stable ignition of a droplet of coal–water slurries suspended in an oxidant flux are established. The influence of the following factors on the initiation of fuel combustion is determined: the oxidant temperature, the droplet size, the size of the coal dust, and the properties and concentrations of the components. The compositions of the coal–water slurries corresponding to optimal ignition (minimum inertia) are identified.

Regimes of the Combustion of Organic Coal–Water Fuels

The results of an analysis of the combustion behavior of the drops of organic coal–water fuels (OCWFs) prepared based on the flotation products (cakes) of the enrichment the coal of five grades (longflame, gas, coking, low-caking, and lean coals) and two petroleum products (petroleum residue and spent turbine oil) are presented. The experiments were performed under the conditions of the stationary fastening of an OCWF drop on the junction of a quick-response thermocouple in a flow of heated (from 500 to 1000°C) air. The following three combustion regimes were revealed for all of the test OCWF compositions: stepwise regime with slow heating (smoldering), intense gas generation regime with the boiling of liquid fuel components (boiling), and regime with a distinct tear-off zone of gas flow (torch). It was shown that the occurrence of the above combustion behaviors substantially depends on the characteristics of the OCWF components: the ash content and the yield of volatile substances of coal cakes and the boiling points and the ignition and combustion temperatures of the petroleum products used. Based on the results of the experiments, the ranges of air temperature changes characteristic of each of the three combustion regimes of fuel suspensions were established.

Ignition of Fuel Slurries Based on Waste Products of Coal Processing and Oil Refining

Results of an experimental study of conditions and characteristics of ignition of fuel slurries prepared on the basis of typical waste products of coal washing and oil refining are reported. The main attention is paid to analyzing the differences in the characteristics and conditions of ignition of organic coal–water slurries prepared on the basis of coal washing waste products (nonbaking, coking, low-caking, fat, gas, and flame coals are considered). The ignition delay time and the minimum (threshold) temperature of ignition of the examined slurries are estimated. Conclusions on the influence of the properties and concentrations of the slurry components on the combustion initiation characteristics are formulated.

Characteristics of the ignition of the drops of organic coal–water fuels based on waste oils and industrial oils

For expanding raw-material and energy supply sources in large- and small-scale power engineering, organic coal–water fuels (OCWFs) based on typical waste coal (the filter cake of K coal) and automobile and turbine oils with a weight concentration of 10% were prepared. The delay times of ignition and complete combustion, the minimum temperatures of ignition, and the maximum temperatures of combustion were determined for the OCWF drops of different compositions. It was shown that the ignition characteristics of the OCWF compositions based on oils before and after of base service differed insignificantly. The experimental results demonstrated that it is reasonable to use a wide group of industrial and automobile oils with different service life periods as the components of OCWFs.

Ignition of droplets of coal–water–oil mixtures based on coke and semicoke

To permit expansion of the resource base and utilize industrial waste, coal–water–oil fuels may be prepared on the basis of coke and semicoke, as well as common petroleum derivatives (fuel oil and spent compressor, turbine, and transformer oils). The minimal oxidant temperature corresponding to stable ignition of coal–water–oil slurries is established. Typical variation in fuel temperature in the course of reaction is determined, as well as the delay time of ignition and the total combustion time for individual droplets of such fuel suspensions. For droplets of initial size 0.5–1.5 mm, the influence of the various factors (droplet size, oxidant temperature, and concentration of the components) on the threshold (minimum) temperature and inertia of ignition is studied. It is shown that stable ignition of coke and semicoke in such fuel is possible at moderate oxidant temperatures: 700–1000 K.