Plasma-fuel Systems Research Articles

Плазменно-топливные системы и принципы их функционирования

В настоящей статье представлены основные типы плазменно-топливных систем и принципы их функционирования, обеспечивающие эколого-экономические преимущества, по сравнению с традиционными технологиями топливо использования. В плазменно-топливных системах осуществляется облагораживание угля любого качества до его сжигания. В общем случае плазменно-топливная система представляет собой топливное устройство (в которое подается топливо) с плазменным источником. В плазменно-топливных системах осуществляются процессы плазменной подготовки и/или переработки твердых топлив. Основной принцип функционирования плазменно-топливных систем заключается в организации электротермохимической подготовки и/или переработки угольной пыли в электродуговой плазме. Использование плазменно-топливных систем позволяет расширить гамму сжигаемых в одном и том же котле углей и, в конечном счете, снизить чувствительность пылеугольных котлов к качеству топлива. Показано, что важным преимуществом плазменной технологии являются быстрая окупаемость и малозатратность ее внедрения при одновременном снижении выбросов оксидов азота, серы и пятиокиси ванадия и мехнедожога топлива при плазменной подсветке пылеугольного факела, что делает их практически единственным на сегодня реальным средством повышения эколого-экономической эффективности использования твердых топлив и замещения в необходимых объемах дефицитного и дорогого мазута в топливном балансе ТЭС.

Modeling of Coal Ignition in Plasma-Fuel Systems With an Electric Arc Torch

Results of numerical experiments on ignition of pulverized coal in a plasma-fuel system (PFS) are presented. PFS is designed for fuel oil-free startup of the boilers and stabilization of pulverized coal flame and represents a pulverized coal burner equipped with plasma torch. The calculations were carried out using the PlasmaKinTherm program. It combines kinetic and thermodynamic methods for calculating the processes of motion, heating, thermochemical transformations, and ignition of the fuel mixture in the volume of the PFS. The ignition conditions of the fuel mixture had previously been determined for two operating parameters of the PFS: the electric power of the plasma torch and the ash content of coal. Also, one of the main regime parameters of the PFS providing ignition of the fuel is the concentration of coal dust in the fuel mixture. It can vary within a wide range. Therefore, conditions for fuel mixture ignition in the PFS have been investigated, depending on the concentration of coal in the fuel mixture in the range from 0.4 to 1.8 kg of coal per 1 kg of air. Calculations were performed for cylindrical PFS of 0.2 m diameter and 3 m of length at fixed consumption of coal (1000 kg/h), the plasma torch power (60 kW), and three values of coal ash content (20%, 40%, and 70%). Nontrivial regularities of the process of plasma thermochemical preparation of fuel for burning were revealed.

Plasma methods for efficiency of solid fuel utilization improvement

After oil, coal makes the largest contribution to the global balance of primary energy production. Thus, since the first oil crisis, global coal consumption has increased by 45%, and reached a share of 22% in the total production of primary energy resources (PPER). Coal is most used in power generation: about 40% of the world's electricity is generated by burning coal. Necessity of fuel utilization new technologies development is justified. One of the promising technologies is plasma ignition and incineration of power coals, application of which allows substitution of expensive oil by cheap coal in thermal power plants. Plasma technology of oil-free boilers start up and pulverized coal flame stabilization has been tested in thermal power plant of Russia, Republic of Kazakhstan, Ukraine, China, Mongolia, Korea, Slovakia and Serbia. Theoretical and experimental methods of investigation of coal plasma ignition, thermochemical preparation, incineration and gasification are described. Methods of plasma-fuel systems computation are discussed. Ensuring eco-economical advantages in compare with conventional technologies of fuel utilization basic principles of plasma-fuel systems functioning are presented.

Plasma–fuel systems for clean coal technologies

This paper presents plasma technology for pulverised-coal ignition and improving energy efficiency of power stations. Plasma–fuel systems (PFS) were developed to accomplish this technology. PFS are a combination of pulverised-coal burners with arc plasmatrons. The main idea of the technology using PFS is to replace the traditionally used fuel oil for flame stabilisation and starting coal-fired boilers with the products of plasma chemically treated pulverised-coal. The coal–air mixture is fed into the PFS where the plasmatron induces heating, devolatilisation and gasification of the coal particles and partial oxidation of the char carbon. As a result, a highly reactive two-component fuel (mixture of combustible gases and partially oxidised char particles) is formed at the exit of the PFS. At the entry to the furnace, this highly reactive two-component fuel is easily ignited. PFS increase the efficiency of coal ignition and combustion, eliminate fuel oil expenditure for boiler start-up and flame stabilisation and decrease unburned carbon, nitrogen oxides (NOx), sulfur oxides (SOx) and vanadium (V) oxide emissions. PFS have been tested at 30 coal-fired power stations and steam coals of all ranks were used. The volatile content of steam coals varied from 4 to 50%; ash from 15 to 56%; and heat of combustion from 6700 to 25 000 kJ/kg.

Plasma ignition of dust-coal flame

One of the promising power engineering technologies is the plasma thermochemical preparation of pulverized coal to burning using plasma-fuel systems (PFS). This technology allows increasing the efficiency of fuel use and environmental indicators of thermal power plants, as well as eliminating the use of fuel oil, traditionally used to start-up the boilers and stabilize the combustion of a pulverized coal flame. This paper presents the results of numerical experiments on ignition of pulverized coal in PFS. PFS is designed for fuel oil-free start-up of the boilers and stabilization of pulverized coal flame, and represents a pulverized coal burner equipped with plasma torch. Via PlasmaKinTherm software which combines kinetic and thermodynamic methods of calculating the processes of motion, heating, thermochemical transformations and fuel mixture ignition in the volume of PFS, impact of the power of the plasma torch and ash content of coal onto efficiency of fuel mixture ignition have been determined. Also one of the main regime parameters of PFS providing ignition of the fuel is concentration of coal dust in the fuel mixture which can vary within a wide range. Therefore, conditions for fuel mixture ignition in PFS have been investigated, depending on the concentration of coal in the fuel mixture in the range from 0.4 to 1.8 kg of coal per 1 kg of air. Calculations were performed for cylindrical PFS of 0.2 m diameter and 2 m of length at fixed consumption of coal (1000 kg/h) and the plasma torch power (60 kW) for three values of coal ash content (20, 40 and 70%). The basic regularities of the process of plasma thermochemical preparation of fuel for burning were revealed.

Plasma thermochemical preparation for combustion of pulverized coal

A plasma model of thermochemical preparation for the combustion of pulverized coal implemented through the PlasmaKinTherm program for the calculation of plasma-fuel systems has been described. Such systems are used at nonfuel-oil start-up of boilers and the stabilization of the combustion of a pulverized coal torch. The model combines kinetic and thermodynamic methods describing the process of the thermochemical preparation of fuel in the volume of the system. The numerical study of the regime parameters of the plasma-fuel system as a function of plasmatron power providing the ignition of the high-ash coal air-petrol mixture is carried out. Distributions of temperatures and velocities of gas and coal particles and concentrations of products of the thermochemical preparation over the length of the system are obtained. The main regularities of the process of the plasma ignition of fuel are revealed consisting in the displacement of the maxima of temperatures and velocities of products of thermochemical preparation upstream (in the direction of the plasmatron), and the independence of plasmatron power maximal values of temperatures and velocities. The results of calculations are compared with experimental data confirming the validity of assumptions accepted at the development of the model.

Modeling and full-scale tests of vortex plasma-fuel systems for igniting high-ash power plant coal

The processes of supplying pulverized-coal fuel into a boiler equipped with plasma-fuel systems and its combustion in the furnace of this boiler are investigated. The results obtained from 3D modeling of conventional coal combustion processes and its firing with plasma-assisted activation of combustion in the furnace space are presented. The plasma-fuel system with air mixture supplied through a scroll is numerically investigated. The dependence of the swirled air mixture flow trajectory in the vortex plasma-fuel system on the scroll rotation angle is revealed, and the optimal rotation angle at which stable plasma-assisted ignition of pulverized coal flame is achieved is determined.

Plasma-Aided Coal Ignition and Combustion: Modeling and Full-Scale Trials

Applications of the modern plasma technology for solid fuel ignition and combustion are presented. This technology provides a more efficient and environmentally friendly low-rank coal incineration. To implement this technology at coal-fired thermal power plants, plasma-fuel systems (PFSs) were developed. The PFS is a pulverized coal burner equipped with an arc plasma generator producing a high temperature air stream of 4000 °C-6000 °C. The PFS technology is plasma thermo-chemical preparation of coal for burning. It includes plasma heating of air-coal mixture up to the temperatures, when coal volatiles are released and partial gasification of char carbon occurs. To show the advantages of plasma-aided coal combustion as compared with the conventional one, the numerical simulation of the process was carried out. The numerical modeling was performed for the low-rank bituminous coal of 40% ash content incinerated at a boiler of 420-t/h steam productivity. Full-scale trials of the plasma-aided combustion confirmed the possibility of high-ash coal ignition in the cold furnace without heating of primary air.

Plasma assisted power coal combustion in the furnace of utility boiler: Numerical modeling and full-scale test

This work presents modern plasma technology for solid fuel ignition and combustion. It promotes more effective and environmentally friendly low-rank coal incineration. To implement this technology at coal fired thermal power plants plasma-fuel systems (PFSs) were developed. PFS is a pulverized coal burner equipped with arc plasmatron producing high temperature air stream of 4000–6000°C. Basis of technology PFS is plasma thermo-chemical preparation of coal for burning. It consists in plasma heating of air–coal mixture up to temperature of coal volatiles release and char carbon partial gasification. In PFS air–coal mixture is deficient in oxygen therefore carbon is oxidized mainly to carbon monoxide. As a result, at the PFS exit a highly reactive mixture is formed of combustible gases and partially burned char particles, together with products of combustion, while the temperature of the mixture is around 1050°C. Further mixing with air promotes intensive ignition and combustion of the prepared in the PFS fuel.PFS have been tested for boilers start up and pulverized coal flame stabilization at 30 power boilers of 75–950t/h steam productivity. The boilers were equipped with different types of pulverized coal burners: direct flow, muffle and swirl burners. At tests of the PFS power coals of all ranks (lignite, bituminous, anthracite and their mixtures) were incinerated. Volatile content of them was in range of 4–50%, ash varied from 15% to 48% and heat of combustion was from 6690 to 25100kJ/kg.To show advantages of the plasma technology of coal combustion before conventional one numerical investigation of plasma ignition, gasification and thermo-chemical preparation of air–coal mixture for incineration in a power boiler was fulfilled. The numerical modeling was performed for low-rank bituminous coal of 40% ash content incinerated at a boiler of 420t/h steam productivity. Both analysis of the numerical modeling and experience of PFS industrial use showed ecological efficiency of the plasma technology. When plasmatrons operate in the regime of plasma stabilization of pulverized coal flame, NOX emission is reduced twice and amount of unburned carbon is reduced four times. The PFSs reduce the temperature at the exit of the furnace. Tests of the PFS for the boiler BKZ-420 of Almaty TPP-2 cold startup confirmed the possibility of high-ash Ekibastuz coal ignition in the cold furnace without heating of primary air.

Plasma preparation of coal to combustion in power boilers

This paper presents plasma technology for solid fuel ignition and combustion promoting more effective and environmentally friendly low-rank coal incineration. To realize this technology at coal-fired power plants plasma-fuel systems (PFS) were developed. PFS are pulverized coal burner equipped with plasmatron. The technology is based on plasma thermo-chemical preparation of coal for burning. It consists of heating of the pulverized coal and air mixture by arc plasma up to temperature of coal volatile release and char carbon partial gasification. In the PFS carbon is oxidized mainly to carbon monoxide. As a result, at the PFS exit a high reactivity mixture is formed with combustible gases and partially burned char particles, together with the products of combustion, while the temperature of the products is around 1000°C. Further mixing with air promotes intensive ignition and complete combustion of the prepared fuel.Combustion of pulverized coal flame was numerically simulated. The results of calculations of the processes of conventional and plasma activated coal combustion in experimental and full-scale furnaces are discussed. Influence of plasma activation of combustion onto thermo-technical characteristics of the flame, decrease of unburned carbon and nitrogen oxide concentrations at the furnace exit was discovered.

Using plasma-fuel systems at Eurasian coal-fired thermal power stations

The development of plasma technology for igniting solid fuels at coal-fired thermal power stations in Russia, Kazakhstan, China, and other Eurasian countries is briefly reviewed. Basic layouts and technical and economic characteristics of plasma-fuel systems installed in different coal-fired boiles are considered together with some results from using these systems at coal-fired thermal power stations.

Plasma-Supported Coal Combustion in Boiler Furnace

Plasma activation promotes more effective and environmentally friendly low-rank coal combustion. This paper presents Plasma Fuel Systems that increase the burning efficiency of coal. The systems were tested for fuel oil-free start-up of coal-fired boilers and stabilization of a pulverized-coal flame in power-generating boilers equipped with different types of burners, and burning all types of power-generating coal. Also, numerical modeling results of a plasma thermochemical preparation of pulverized coal for ignition and combustion in the furnace of a utility boiler are discussed in this paper. Two kinetic mathematical models were used in the investigation of the processes of air/fuel mixture plasma activation: ignition and combustion. A 1-D kinetic code PLASMA-COAL calculates the concentrations of species, temperatures, and velocities of the treated coal/air mixture in a burner incorporating a plasma source. The 1-D simulation results are initial data for the 3-D-modeling of power boiler furnaces by the code FLOREAN. A comprehensive image of plasma-activated coal combustion processes in a furnace of a pulverized-coal-fired boiler was obtained. The advantages of the plasma technology are clearly demonstrated.

Plasma-aided solid fuel combustion

Plasma supported solid fuel combustion is promising technology for use in thermal power plants (TPP). The realisation of this technology comprises two main steps. The first is the execution of a numerical simulation and the second involves full-scale trials of plasma supported coal combustion through plasma-fuel systems (PFS) mounted on a TPP boiler. For both the numerical simulation and the full-scale trials, the boiler of 200 MW power of Gusinoozersk TPP (Russia) was selected. The optimization of the combustion of low-rank coals using plasma technology is described, together with the potential of this technology for the general optimization of the coal burning process. Numerical simulation and full-scale trials have enabled technological recommendations for improvement of existing conventional TPP to be made. PFS have been tested for boilers plasma start-up and flame stabilization in different countries at 27 power boilers steam productivity of 75–670 tons per hour (TPH) equipped with different type of pulverised coal burners. At PFS testing power coals of all ranks (brown, bituminous, anthracite and their mixtures) were used. Volatile content of them varied from 4 to 50%, ash—from 15 to 48% and calorific values—from 6700 to 25,100 kJ/kg. In summary, it is concluded that the developed and industrially tested PFS improve coal combustion efficiency and decrease harmful emission from pulverised coal-fired TPP.