Thermal Engineering

The results of full-scale studies of the corrosion and abrasive resistance of the surfaces of experimental samples of tubular steel 20 with a protective ion-plasma coating based on Cr–CrN and without it during their exposure for 1000 h in the furnace of a boiler with a nominal capacity of 200 kW operating on granulated biofuels are presented. Samples were held at operating mode for 220 h, and at idle mode for 780 h. The temperature inside the rear smoke box, where the experimental samples were placed, was approximately 700°C. Chemical analysis of the composition of ash obtained during the burning of sunflower husks showed the presence of potassium, phosphorus, sulfur and chlorine, i.e., those elements whose presence can lead to the formation of highly aggressive corrosion-hazardous compounds when moisture is condensed during periods of boiler downtime. It was revealed that the studied coating was not subjected to corrosion destruction, its adhesive strength did not change during the holding time, the initial thickness of the coating decreased by an average of 10–15%, and the surface roughness remained the same. There was a slight deviation in the morphology due to oxidation of the surface layer of the coating at the maximum holding time, no oxidation of the material under the coating on the transverse splines of the coated samples was detected. Tests conducted at the incidence angles of the air-abrasive flow of 30°, 60° and 90° tests of steel samples 20 with a protective ion-plasma coating based on Cr–CrN after holding in the furnace of a biofuel boiler for 1000 h showed that the abrasive resistance at a steady speed increased by at least 2.5 times compared to samples without coating. According to the results of metallographic, corrosion, and abrasive studies, Cr–CrN-based ion-plasma coating is promising for the protection of pipe surfaces of biofuel boilers exposed to corrosion and abrasive effects of alkali metal salts and ash particles at high temperatures and variable load.

Results from an analysis of permissible initial steam temperatures and heating rates of the outlet headers of high-pressure steam superheaters and the steam lines of combined-cycle plants at which their cyclic strength is ensured are presented. A procedure is proposed using which startup assignment schedules for different thermal states can be constructed proceeding from the heating rates and initial steam temperatures selected depending on the initial temperature state of the high-pressure steam superheaters’ outlet headers.

In the paper, the results of experimentally studying of spontaneous vapor explosion triggering are presented. They were obtained under model conditions when heated solid hemispherical samples were used and under laboratory conditions during the interaction of molten NaCl droplets with a distilled water pool at 15–70°C. It is shown that the development of violent, disordered 3-D perturbations (oscillations) of the vapor film surface precedes spontaneous vapor explosion triggering. Such oscillations are accompanied by vapor film destruction and the creation of local short-term contacts of hot and cold fractions and intense, explosion-like formation of a vapor phase of the volatile fraction. The experiments also showed that, under laboratory conditions, spontaneous vapor explosion at the molten droplets of usual metals and alloys (lead, tin, POS-61 solder, Wood’s and Rose’s alloys, etc.) occurred very seldom and researchers are forced to apply an external triggering to provide a vapor explosion. At the same time, during the interaction of NaCl melt with water spontaneous vapor explosion triggering was practically attained with a probability of 100%. It was also shown that, during the simultaneous interaction of several NaCl melt droplets with water, the spontaneous vapor explosion triggering that has been originated at one of the droplets after a time lag of some tens of microseconds provokes explosion-like water evaporation at the other droplets also. Spontaneous triggering is accompanied by a typical sharp pressure pulse in the working medium and luminescent flashes at the molten droplet surfaces. The thesis was postulated that there is no common mechanism of fine hot fraction fragmentation, which is true for any situations and regime conditions.

We present the results obtained from chemical and carbide analyses and a study on determining short-term mechanical properties and critical brittleness temperature, as well as data on the heat strength and heat resistance properties of new Grade 10Kh9V2MFBR-Sh steel, which is an analog of Grade Kh10CrWMoVNb9-2 (P92) steel.

The article is devoted to studying the parameters of wells that are used as part of vertical gas extraction systems for degassing landfills. To this end, approaches to modeling the main processes occurring in the landfill’s porous medium are considered. The considered approaches served as a basis for elaborating a thermophysical gas and heat transport model that takes into account variation in the hydrodynamic properties of wastes resulting from their secondary settlement. The adequacy of the results obtained using the developed model is confirmed by the data of classic works. The effect the secondary settlement of wastes has on the distribution of pressure and temperature in the landfill body is determined. It is shown that compaction of wastes due to their secondary settlement results in a growth of pressure by 40% on the average.

We give a comparative assessment of risks related to impacts on the heath of population due to atmospheric emissions from coal-fired units of thermal power stations. The scope of analysis includes both power units that are already in operation and those being designed, which are more advanced in terms of technology employed and environment protection features used in them. Gas-fired units of thermal power stations are also included in the analysis of risks. Geographically, the analysis encompasses thermal power stations located in central regions of Russia (the Central Region, the Volga Region, and part of the Northwest Region adjacent to the Central Region).

This paper reports the results of an experimental investigation into initiation of the electric discharge in service water by means of explosion of aluminum foil having various mass and dimensions. The electric discharge was formed in a chamber with a movable wall (the piston). As an electric energy storage, the capacitor bank having the capacity C = 200–600 μF with charging voltage U 0 = 2–5 kV (stored energy Q 0 = 0.4–7.5 kJ) and the rate of rise of the discharging current dI/dt = (3–4) × 109 A/s. The results of experiments showed that destruction (loss of conductivity) of foil occurs at the value of the integral of the current density h j = (0.3–0.65) × 109 (A2/cm4)/s. The stage of the repeated breakdown in the electric discharge occurs when the value of the intensity of the electric field along the discharge channel is of E rb ≥ 50 V/mm. Geometric dimensions and mass of the initiating conductor that provide the maximum efficiency of conversion of the value of Q 0 into kinetic energy of the piston have been determined.

Methods of thermal reprocessing of wood and peat to obtain high-calorific gas mixtures are considered. The comparison of the existing technologies and those under development as to heating values of the gas mixtures obtained, quantitative yield of these mixtures, and effectiveness of transformation of the initial raw material into gas is given. Certain attention is paid for the analysis of a possibility to put into effect waste-less technologies.