Experimental and computational evaluation of a gas-solid suspension density distribution under circulating fluidized bed conditions

The paper presents the results of operational measurements of the suspension density distribution in the 966 MWth supercritical Circulating Fluidized Bed boiler. The tests were carried out for four different unit thermal loads, i.e. 40, 60, 80, and 100% MCR. The conducted operational measurements showed that the suspension density distribution of the particulate material in the combustion chamber of the CFB boiler has the form of an exponential curve with maximum values occurring in the bottom part of the furnace. On the basis of the operational data, an attempt was made to reflect the suspension density distribution in the combustion chamber of the boiler using the ANSYS CFD software. The calculations were carried out using the Eulerian multiphase model in an unsteady state condition. As revealed by the simulations, the Eulerian multiphase model allows for a quantitative representation of the suspension density distribution of the granular material only for the maximum boiler load. For other thermal loads, quantitative representation of experimental distributions of suspension density using the Eulerian method is possible except for the dense region.

Calculation analysis of heat transfer in a four-vortex furnace of a pulverized coal boiler when operating at various loads

The work is devoted to the mathematical modeling of heat and mass transfer processes during flare combustion of coal dust in a four-vortex combustion chamber. For modeling, a set of interrelated models is used that describes the gas movement, thermal and radiant energy transfer, the processes of destruction and burnout of coal particles, and the formation of NOx. The simulation results showed that in a wide range of changes in the boiler load in the furnace, a stable four-vortex flow structure is formed with a fairly uniform temperature distribution in the furnace volume and a low level of NOx formation.

Energetic and Exergetic Performances of a Retrofitted, Large-Scale, Biomass-Fired CHP Coupled to a Steam- Explosion Biomass Upgrading Plant, a Biorefinery Process and a High-Temperature Heat Network

This paper aims at assessing the impact of retrofitting an existing, 730 MWe, coal-fired power plant into a biomass-fired combined heat and power (CHP) plant on its energetic and exergetic performances. A comprehensive thermodynamic model of the power plant was developed and validated against field data, resulting in less than 1% deviation between the model and the measurements for the main process parameters. The validated model was then used to predict the behaviour of the biomass CHP after retrofitting. The modelled CHP unit is coupled to a steam-explosion biomass upgrading plant, a biorefinery process, and a high-temperature heat network. 13 scenarios were studied. At constant boiler load, delivering heat to the considered heat clients can increase the total energy efficiency of the plant from 44% (electricity only) to 64%, while the total exergy efficiency decreases from 39% to 35%. A total energy efficiency of 67% could be reached by lowering the network temperature from 120∘C to 70∘C. Identifying the needed heat clients could, however, represent a limiting factor to reach such high efficiencies. For a constant power demand, increasing the boiler load from 80 to 100% in order to provide additional heat makes the total energy efficiency increase from 43% to 55%, while the total exergy efficiency decreases from 39% to 36%.

Application of extraction steam graded heat storage in peak shaving of condensing units

In order to alleviate the peak shaving pressure of power grid and further improve the deep peak shaving capacity of coal-fired units, this paper applies staged heat storage to condensing units. Under the condition of constant boiler load, the heat of regenerative steam extraction is stored to reduce the electrical load output of the unit. Taking a 660MW ultra-supercritical unit as an example,30%THA,40%THA and 50%THA were taken as the initial conditions of heat storage respectively to discuss the peak shaving range and power regeneration efficiency of different extraction steam positions for heat storage. The results show that the “storage 1# HP heater extraction steam” scheme with “two-stage three tank” heat storage and release structure has the largest peak shaving range of 37.3%~56.9% under 50% initial conditions. When the “two-stage three tank” heat storage and release structure selects the “storage 1# HP heater extraction steam ”scheme under 40% initial working condition, the “power regeneration efficiency” reaches the highest——78.3%. And the “power regeneration efficiency” of “two stage three tank” storage structure are always higher than the “single-stage” storage structure.

Analysis of Two-Stage Fuel Combustion in Multi-Fuel Boilers

The significant growth of industry in the second half of the 20th century led to a number of problems, one of the most important problems is the protection of the environment from pollution. The main source of air pollution is heat and power generating plants, which are based on combustion processes. The largest pollutant is thermal power plants, which burn a large volume of fossil fuel and form a corresponding amount of toxic substances, in particular nitrogen and sulfur oxides. In this paper, combustion processes with various burner devices will be considered and two fuels – natural gas, fuel oil. One of the most important tasks operation of power equipment is the development and widespread use of effective methods to reduce the formation of harmful substances and determining the optimal modes of fuel combustion, ensuring a minimum level of emissions of toxic combustion products. Two-stage fuel combustion is an effective method of reducing nitrogen oxide emissions. In two-stage combustion, one fuel burnout zone is replaced by several zones, as isolated as possible. The paper will compare several options for the implementation of two-stage combustion in the boiler. The influence of boiler load on the concentration of nitrogen oxides in the exhaust gases is analyzed. Also at two-stage combustion of fuel oil in gas-oil boilers reliability of screen surfaces of heating as a result of decrease in the maximum falling heat streams on a screen surface of heating of a copper increased.

Numerical Study of the Influence of Secondary Air Uniformity on Jet Penetration and Gas-Solid Diffusion Characteristics in a Large-Scale CFB Boiler

The uniformity of secondary air (SA) in large-scale CFB boilers has an important influence on gas-solid flow and combustion, but was seldom considered in previous studies. Numerical simulation based on the Eulerian–Eulerian and RNG k-ε turbulence models was conducted to explore the influence of SA uniformity and load variation on jet penetration, diffusion characteristics and gas-solid mixing in the first 600 MW supercritical CFB boiler. The results showed that better SA uniformity was conductive to the uniformity of SA penetration and gas-solid mixing along the furnace height, although the penetration depth and diffusion distance showed an opposite trend. In addition, the penetration depth and diffusion distance got enhanced with higher boiler load. The inner and outer SA jets could not cover the furnace width, and the uneven SA uniformity led to a huge deviation of the solid concentration within 10 m of the air distributor. Eventually, a calculation model was successfully established for predicting the penetration depth of inclined thermal SA jets during boiler operation.

The review of the possibility to increase the integrated power system of Ukraine' balance reliability by implementing electric heat generators

The paper considers one of the possible options to solve the actual task for the Integrated Power System (IPS) of Ukraine regarding creating deficit-free primary, secondary and tertiary reserves, which is an important condition for successful integration of IPS of Ukraine into ENTSO-E. The increase of the level of reserves of IPS of Ukraine could be provided by the implementation of the dedicated technological system (NPP+powerful electric boilers) which should be connected at the "points" where a nuclear power plant (NPP) is connected to the grid. It is assumed that the use of the proposed technological system with electric boilers' capacity of 2000 MW in the IPS of Ukraine will allow the substitution of about 10 thermal power plant's (TPP) units, which provide secondary reserves. Implementation of proposed option also aimed at fulfillment "National Plan on Reduction of Emissions from big burning units", and also allow reduce consumption of organic fuel, namely the coal, that is prescribed by Energy Strategy of Ukraine till 2035. According to preliminary estimates, the proposed technological system complies with the main categories of "Methodology for the analysis of costs and benefits of projects for the development of electrical networks". Keywords: integrated power system, electric boiler, load profile, wholesale electricity market

DEVELOPMENT OF CONCEPTUAL TECHNICAL SOLUTIONS AND METHODS OF THEIR IMPLEMENTATION DURING THE DESIGN OF A DUST COAL STEAM GENERATOR OF SUPER-SUPER CRITICAL PARAMETERS OF STEAM 28 MPa / 600 °С / 600 °C FOR 300 MW ENERGY UNIT. PART 2

In the second part of the work, using the mathematical model described in first unit, a direct-flow pulverized coal boiler with supercritical steam parameters of 28 MPa /600 °C /600 °C was calculated for a 300 MW power unit at loads of 50–70 %. It is shown that: a) the temperature of contaminated screens 1234 °С in the active combustion zone, where 92 % of the initial fuel burns out, is lower than the temperature of slagging beginning (1268 °С) of ДГ-100 coal, which indicates the slag-free operation of the screens of the lower radiation part (LRP) b) over the entire range of the boiler load change of 50–100 %, the temperature at the exit from the active combustion zone will be higher than the minimum permissible temperature of 1250 °C, below which the flame is attenuated; c) upon transition to 50 % load, the temperature of gases at the outlet from the active combustion zone decreases from 1506 °C to 1342 °C, as a result of which the specific thermal stress of the LRP screens decreases by 1.469 times, while the feed water consumption at the inlet of the boiler falls by 2 times, which leads to an increase in the temperature of the LRP steam, the middle and upper radiation parts, screens of the ceiling and rotating chamber; d) to reduce the thermal stratification of the inlet stage of the secondary steam superheater (ППП1), and as a consequence, the pipe wall temperature, it is necessary to divide the ППП1 surface into two packets, installing an intermediate mixing manifold between them with full steam mixing. Bibl. 5, Fig. 13, Tab. 3.

USE OF THE REBURNING TECHNOLOGY WITH BIOMASS PYROLYSIS PRODUCTS AS A REBURNING FUEL TO REDUCE EMISSIONS OF NITROGEN OXIDES FROM TPP 312 BOILER

In Ukraine, a three-stage coal combustion system fueled by a natural gas as a reburning fuel for nitrogen oxides emission reduction was mounted on Unit № 4 of the Ladyzhyn TPP. This system was developed in cooperation with Combustion Engineering (USA), VTI (Russia) and the Gas Institute of the National Academy of Sciences of Ukraine and was assembled by the Ladyzhyn TPP staff in 1992. The test runs of this system had confirmed the effectiveness of this method of reducing emissions of nitrogen oxides into the atmosphere (up to 50%).Unfortunately, due to the high price of natural gas and the introduction of limits on its use, currently the use of natural gas as a fuel for reburning is impossible. One of the possible ways to reduce emissions of nitrogen oxides from the coal-fired boiler TPP 312 is the operation of Reburning technology with the biomass pyrolysis product as reburning fuel. The aim of the work was to evaluate the possibility of the application the biomass pyrolysis products as a reburning fuel in Reburning technology to reduce nitrogen oxides from the coal-fired boiler TPP 312. For this purpose, a detailed computer model of a standard TPP 312 boiler and a TPP 312 boiler with a coal reburning combustion system was developed and built. The study of the operation the Reburning coal combustion system, which is mounted on the unit №4 DTEK Ladyzhynska TPP, on the design parameters of the operation for the boiler load of 280 MWe was carried out. It was determinate that the supply of reburning fuel at 12% of the total heat capacity of the boiler gives a good level of the reduction of nitrogen oxides (up to 25%), provides no slag conditions for superheater pipes and does not lead to increase of the fuel losses with unburnt carbon.