Research Institute of Experimental and Theoretical Physics of Kazakhstan National University, Almaty, Kazakhstan

Transcription

1 IMPROVING EFFICIENCY OF COAL IGNITION BY MEANS OF PLASMA: NUMERICAL MODELING AND EXPERIMENTAL VERIFICATION V.E. Messerle Combustion Problems Institute, Almaty, Kazakhstan Institute of Thermophysics of SB RAS, Novosibirsk, Russia AB A.B. Ustimenko, OA O.A. Lavrichshev h Research Institute of Experimental and Theoretical Physics of Kazakhstan National University, Almaty, Kazakhstan ust@physics.kz 11 th ECCRIA -European Conference on Coal Research and its Applications 5th-7th September 2016, University of Sheffield, Sheffield, UK

2 PROBLEM WORLD ENERGY RESOURCES Conventional (fuel oil) start up of a pulverized coal 6 1.9% boiler and pf flame stabilization % % % % 2 6.9% 1 coal, 2 oil fuel, 3 gas, 4 nuclear power, 5 waterpower, 6 renewable. (Key World Energy Statistics)

3 Fuel oil rate for different steam productivity it pulverized coal boilers Boiler steam productivity, Fuel oil rate for 1 start up, t/h t

4 SOLUTION Direct flow plasma-fuel system (PFS) for coal ignition 1 furnace of a boiler, 2 plasma torch, 3 air fuel mixture, 4 high reactive two component fuel The technology is based on plasma thermo- chemical preparation of coal for burning and allows substituting of gas or fuel oil by coal.

5 EXPERIMENTAL PFS IN OPERATION: IGNITION OF ECIBASTUZ COAL Plasmatron power 100 kw; Coal consumption through PFS 1000 kg/h; Temperature of the flame 1180 О С. 5

6 PFS layout at a boiler of 160 ton steam productivity (Almaty TPP-3)

7 PFS FOR FUEL-FREE BOILERS START-UP AND PULVERISED COAL FLAME STABILIZATION Scheme of the 640 t/h steam boiler furnace equipped with PFS: Gusinoozersk TPP, Russia

8 PFS layout at a boiler of 420 ton steam productivity (Almaty TPP-2) 420 t/h steam boiler furnace equipping with PFS (Almaty TPP-2, Kazakhstan) : I main pulverized coal burners, II PFS.

9 Conventional technology Concurrence Plasma technology NOx reduction 1. Fuel Oil Rate for Russian TPP 250 ppm PFS ppm 5.1 mln. t/year (cost is more than $ 2.5 billion) 2. Fuel Oil Rate for Kazakhstan TPP ~1 mln. t/year (cost is 0 about $ 500 mln.) Unburned carbon reduction 3. Investments for TPP 100% 3-5% 4. Operating costs 100% 28-30% 4 % 5. Electric power consumption for TPP auxiliary 3-5% % 1 ton of fuel oil equivalent (by caloricity) to 2 tons of coal 1 ton of fuel oil equivalent (by price) to 20 tons of coal 1 % PFS

10 Model PLASMAKINTHERM The following assumptions were made in formulation of the mathematical description of a coal-dust gasification process. 1) The process is one dimensional and steady state. 2) The equation of state of an ideal gas applies. 3) The mixture of gas and particles at the reactor inlet is homogeneous. 4) A local heat transfer between gas and solids includes convective and conductive components. 5) The temperature gradients within the particle are negligible. 6) The heat of the solid gas-phase reaction only affects the temperature of the solids, while that of the gas-phase reaction only affects the gas-phase temperature. 7) A particle particle interaction and solid-wall friction are neglected due to the dilute system. 8) The viscosity effects are appreciable only in the gas solid-phase interaction. 9) Ash is an inert component.

11 Model PLASMAKINTHERM The concept of mixing i fuel mixture : 1 - mixing length, 2 - the flow of fuel mixture, 3 - the first cylinder of the partition, 4 - the law of mixing, 5 - the final mixing zone, 6 - the final diameter of the cylinder, 7 - the diameter of the first cylinder of the partition

12 Equations of PLASMAKINTERM The equation of conservation of momentum of the gas phase L d( u) u dx, where l1 F l ( u u ) F C R N 2 2 l 2 l Dl l l The equation of conservation of momentum of fractions l coal particle k di dn i dul mu l dx F The equation of conservation of energy of the gas phase u u I Q Q Q dx dx L l 2 i l r p, where 4 i1 l1 The equation of conservation of energy of coal particles di dx l u Ql Qc The equation of fuel mixture flow and plasma-forming gas Q T T R N l l l l l dm dt mixture dm plasma dt * u * d 4 2

13 Reactions of devolatilization and carbon oxidation k j A j exp Ea j RT Reaction LgA Eа, kcal/mole 1 Н 2 s= Н Н 2 Оs= Н 2 О СОs = СО СО 2 s= СО СН 4 s= СН С 6 Н 6 s= С 6 Н C + O 2 = CO Chemical composition of the gaseous components was found using code TERRA for thermodynamic calculations l

14 Computation by PlasmaKinTherm Initial data for the calculation of the ignition of coal in PFS Feature Value Plasma torch power, kw 20, 40, 60, 80, 100 Initial temperature of the fuel mixture, o С 30 Coal consumption through the PFS, kg/h 1000 Air flow through h the PFS, kg/h 1700 Length of the PFS, m 3.0 Diameter of the PFS, m Compound of coal for the program PlasmaKinTherm, Wt.% Ash C H 2 H 2 O CO CO 2 CH 4 C 6 H Fractional composition of coal dust Fraction No Diameter of particle, µm Mass portion of fraction, %

15 Variation of gas and coal particles temperature along PFS a b (а) - Plasma torch power 60 kw, (b) kw 1, 2, 3, 4, 5 fractions of coal particles 10, 30, 60, 100, 120 µm, 6 gas

16 Variation of gas temperature along PFS by varying the power 1, 2, 3, 4, 5 plasma torch power of 20, 40, 60, 80 and 100 kw, respectively

17 Variation of gas and coal particles velocity along PFS a b (а) - Plasma torch power 60 kw, (b) kw 1, 2, 3, 4, 5 fractions of coal particles 10, 30, 60, 100, 120 µm, 6 gas

18 Variation of gas velocity along PFS by varying the power 1, 2, 3, 4, 5 plasma torch power of 20, 40, 60, 80 and 100 kw, respectively

19 a b c Variation of gas phase composition along PFS at a power of the plasma torch 20 (a), 60 (b) and 100 (c) kw

20 Initial data for the calculation of the ignition of coal in PFS Feature Value Plasma torch power, kw 60 Initial temperature of the fuel mixture, o С 300 Coal consumption through the PFS, kg/h 1000 Air flow through the PFS, kg/h 1700 Length of the PFS, m 3.0 Diameter of the PFS, m 0.2 Compound of coal for the program PlasmaKinTherm, Wt.% Ash C H 2 H 2 O CO CO 2 CH 4 C 6 H 6 20, 40, 60,

21 a Variation of gas phase temperature (а) and velocity (b) along PFS by varying ash from 20 to 70%: 1, 2, 3, 4 ash content of coal 20, 40, 60, 70%, respectively. b

22 Parameters of the products of plasma thermochemical preparation of coal to burning at the exit of PFS Ash, % C i, vol.% H 2 CO O 2 CO 2 H 2 O N 2 T f, o C X C, % X C =(C in -C fin )/C in 100%

23 Comparison between calculated results and experimental parameters of plasma thermochemical preparation of Ekibastus bituminous coal ( = 06кг/кг) 0.6 Experiment Calculation No G, P, Сi, vol. % С i, vol. % kg/h kw Т, о С Т, о С СО Н 2 СО 2 N 2 СО Н 2 СО 2 N

24 Conclusion PlasmaKinTherm code is intended for computing of plasma-fuel systems. In the code kinetic and thermodynamic methods for description of the process of plasma thermochemical preparation of coal to burning are combined. The numerical study of regime parameters of PFS depending on the power of the plasma torch and the ash content of coal in a wide range of their values was fulfilled. Calculations showed that in power range of plasma torch kw and air-coal mixture consumption of 1667 kg/h stable ignition of high-ash coal is achieved. Shift of the maxima of temperature and velocity of the products of plasma processing of fuel upstream (in the direction of the plasma source) is observed with increasing power of the plasma torch. The maximum temperature and velocity vary in a narrow range of values and practically do not depend on the power of the plasma torch. With increasing ash content of coal from 20 to 60% H 2 and CO concentrations decrease at the exit of the PFS, the temperature of the gaseous products and the degree of carbon conversion are increased to the maximum values when the ash content of 60%, decreasing sharply with further increase in the ash content. The model predictions demonstrate satisfactory agreement with the experimental data. It allows applying PlasmaKinTherm code to design PFS.