CO2 dissociation energy efficiency

Threshold Value of Specific Energy Input in T] Ey) - Comparison of One- and Two-Temperature Approximations. Using Fig. 5-2, compare the threshold of specific energy input, maximum, and other qualitative features of the CO2 dissociation energy efficiency rj(Ey), calculated in one- and two-temperature approximations. 

The one-temperature approximation (see Section 5.2.4) permits one to find out all major qualitative features of the plasma-chemical CO2 dissociation energy balance, including threshold, maximum, and decrease of energy efficiency dependence on specific energy input energy efficiency dependence on ionization degree, initial gas temperature,... 

Figure 5-20. CO2 thermal dissociation energy efficiency as a function of heating temperature in plasma gas pressure p = 0.16 atm (1) ideal quenehing, (2) super-ideal quenehing, (3) upper limit of super-ideal quenehing related to energy balanee.

Major Experimental Results on CO2 Dissociation in Different Plasma Systems and Energy Efficiency of the Process... 

CO2 dissociation was investigated in numerous thermal and non-thermal plasma systems. The most critical point in the experiments was the maximization of the energy efficiency of the process (5-1), r], determined by the ratio of the dissociation enthalpy AH = 2.9eV/mol to the actual energy cost Eco of one CO molecule produced in a plasma system ... 

Figure 5-2. Energy efficiency of CO2 dissociation as a function of specific energy input. (1, 2), nonequilibrium calculations in one- and two-approximations non-equilibrium calculations for supersonic flows (3)M = 5 (4)M = 3.5 calculations of thermal dissociation with (5) ideal and (6) super-ideal quenching (7) thermal dissociation with quenching rates 10 K/s, (8) 10 K/s, (9) 10 K/s. Different experiments in microwave discharges o, , A, x. Experiments in supersonic microwave discharges . Experiments in different RF-CCP discharges o,V. Experiments in RE-ICP discharges 0. Experiments in different arc discharges ,. ...

Figure 5-4. Energy efficiency rj and energy cost AW of CO2 thermal dissociation as functions of temperature at atmospheric pressure and different quenching rates (1) K/s, (2) 10 K/s, (3) 10> K/s, (4) 10 K/s,...

The difference between vibrational and translational CO2 temperatures (Tv > 7 o)results in a maximum energy efficiency increase to 60% even in the case of the quasi-equilibrium balance of direct and reverse reactions (Evseev, Eletsky, Palkina, 1979), because direct endothermic reactions are mostly stimulated by molecular vibration, whereas reverse exothermic reactions are mostly stimulated by translational temperature (see the Fridman-Macheret a-model in Chapter 2). This efficiency corresponds to the case of super-ideal non-equilibrium (TV > To) quenching of the CO2 thermal plasma dissociation products (Potapkinetal., 1983). 

The mechanism of CO2 dissociation stimulated by vibrational excitation in plasma (5-6), (5-7) has the following three essential qualitative advantages in energy efficiency with respect to alternative non-equilibrium plasma-chemical mechanisms of CO2 dissociation ... 

Three major effects limit the energy efficiency of the CO2 dissociation in plasma by means of electronic excitation of the molecnles ... 

The energy efficiency of the CO2 dissociation through dissociative attachment is limited by the loss of an electron in the process (the energy price of an electron is quite high, usually 30-100 eV). Getting the electron back in the process of associative detachment. 

Figure 5-17. Energy efficiency of CO2 dissociation in plasma at the specific energy input ftv = 0-5 eV/mol as a fimction of plasma ionization degree e/ o-...

This energy efficiency decreases lyperbolically with the specific energy input ( a 1 / v), in good agreement with experiments (see Fig. 5-2). This decrease takes place when Ey exceeds the optimal value E > where the energy efficiency of CO2 dissociation reaches a maximum ... 

Energy Losses Related to Excitation of CO2 Dissociation Products Hyperbolic Behavior of Energy Efficiency Dependence on Specific Energy Input... 

Figure 5-19. One-temperature approximation of energy efficiency of CO2 dissociation as a function of specific energy input, specifically taking into account energy losses related to excitation of the dissociation products ffco = OeV (curves 1 and 4), eco = 1 eV (curves 2 and...

ENERGY EFFICIENCY OF CO2 DISSOCIATION IN QUASI-EQUILIBRIUM PLASMA, AND NON-EQUILIBRIUM EFFECTS OF QUENCHING PRODUCTS OF THERMAL DISSOCIATION... 

Energy Efficiency of CO2 Dissociation in Quasi-Equilibrium Plasma... 

In this relation, x, (p, T) = / o is the relative concentration of component / of the mixture of dissociation products li is the total enthalpy of component / and o is the total density of the quasi-equilibrium gas mixture. Let us assume that each CO2 molecule gives CO molecules after quenching therefore, the parameter characterizes the conversion degree of the dissociation process. Then the energy efficiency of the quasi-equilibrium dissociation process can be presented as... 

Combination of equations (5-75)-(5-77) permits one to derive the formula for calculations of the energy efficiency of thermal CO2 dissociation in plasma in the case of ideal quenching ... 

The cooling rate limitations required to reach the conditions of ideal quenching can be estimated from Fig. 5-4 one can say that a cooling rate of about 10 K/s is practically sufficient at atmospheric pressure to use relation (5-78) for practical calculations. The energy efficiency of thermal CO2 dissociation with ideal quenching rj T), calculated as a function of temperature in the thermal zone using equation (5-78) for pressure p =... 

Maximum Value of Energy Efficiency of CO2 Dissociation in Thermal Plasma with Super-Ideal Quenching of the Dissociation Products... 

---