Preventing Thermal Runaways of LENR Reactors. Jacques Ruer sfsnmc

Transcription

1 Preventing Thermal Runaways of LENR Reactors Jacques Ruer sfsnmc 1

2 Temperature activated reactions Several authors report that the LENR power increases with the temperature. 2

3 Temperature activated reactions The temperature dependence is described by an Arrhenius law The rate of a process, for instance heat-producing reactions, is a function of an activation energy E and the temperature T : w = A.exp(-E/kT) With : w : heat production power (W.m -3 ) A : pre-exponential factor E : activation energy k : Boltzmann s constant T : absolute temperature of the reactive medium. 3

4 How to control such a reactor? TB : thermal barrier Storms How Basic Behavior of LENR can Guide. A Search for an Explanation, JCMNS, 20 (2016), The stability of T activated reactors is frequently discussed with a diagram similar to this one Such diagrams refer to the operation of batch reactors in the chemical industry 4

5 Batch reactor Reactant 1 Reactant 2 Reactor vessel Double wall Coolant inlet Product outlet to vent system Temperature sensor S rrer Coolant outlet Largely used for synthesis of many different chemical products The reactor is loaded with the reactants, the reaction is completed, the products are unloaded 5

6 Batch reactor Reactant 1 Reactant 2 Reactor vessel Double wall Coolant inlet Product outlet to vent system Temperature sensor S rrer Coolant outlet Endothermic reaction: Reaction controlled by heating, no problem Exothermic reaction: If temperature goes out of control, things may go wrong 6

7 Batch reactor control Reactant 1 Reactant 2 Reactor vessel Double wall Coolant inlet Product outlet to vent system Temperature sensor S rrer Coolant outlet Temperature is controlled by the combination of wall cooling and stirring to enhance heat exchange between charge and wall 7

8 Heat flow Batch reactor control Point of non return Basics: Reaction heat power Cooling power Temperature must be maintained below the point of non return at any time Temperature 8

9 Heat flow How to start the reaction? Initial temperature After loading, the temperature is low Temperature 9

10 How to start the reaction? As long as the temperature is low, the reaction has no reason to start 10

11 How to start the reaction? To start the reaction you have to tease the dragon s tail 11

12 Heat flow How to start the reaction? Start-up by heating Initial charge temperature Heating fluid temperature Heating with hot water or steam Temperature 12

13 How to control the reaction? Taming the dragon with water cooling 13

14 Heat flow How to control the reaction? Reaction rate is controlled by adjusting the cooling Heat is removed at this temperature Operating point Temperature 14

15 Heat flow Loss of control If cooling is not sufficient the temperature goes out of control Temperature 15

16 Loss of control RUNAWAY! 16

17 Temperature Role of thermal inertia Example: Polystyrene polymerization Reactor loaded with reactants at the beginning of the operation «All on board» T max (styrene vapor pressure) Ini al hea ng Point of non return Reac on start Decay due to reactant exhaus on Time T rises slowly because of thermal inertia T decays when reactants become exhausted 17

18 Control by thermal inertia Exhausting the dragon 18

19 Temperature Control of reactants input Example: Synthesis of nitroglycerin Acid is added slowly to the charge T max (explosion safety margin) Point of non return Ini al addi on of reactant Addi ons of reactant End of batch reac on Time Reaction start: 22 C If T> 30 C, the charge is dumped out in water 19

20 Control of reactants input Feeding the dragon slowly 20

21 Heat flow Control with a large heat exchange Heating power P Cooling power h.dt Heat is recovered at this temperature DT Reaction is controlled by adjusting the coolant temperature Operating point Temperature 21

22 Heat flow Stability dp/dt > h cooling EXTINCTION Temperature 22

23 Heat flow Stability dp/dt > h cooling RUNAWAY UNSTABLE Temperature 23

24 Heat flow Heat flow Stability dp/dt > h cooling UNSTABLE dp/dt < h cooling SELF HEATING Temperature Temperature 24

25 Heat flow Heat flow Stability The reactor is stable if h cooling > dp/dt heating dp/dt > h cooling UNSTABLE dp/dt < h cooling SELF STABLE COOLING Temperature Temperature 25

26 Differences between LENR Reactor and Batch Reactor LENR : Reaction is continuous Thermal inertia can only help during transients Activation energy may be high, so that temperature sensitivity may be high Heat is preferably recovered at high temperature (for conversion efficiency) Reference to the thermal behavior of batch reactors is inappropriate 26

27 Continuous reactors In the chemical industry some reactors are designed for continuous operation Example : Production of synthetic fuels by the Fischer-Tropsch process 27

28 Fischer-Tropsch Process Production of synthetic fuels from CO+H 2 gas Reaction (synthesis of alkanes - simplified) : nco + (2n+1)H > C n H 2n+2 + nh 2 O DH =-n.165kj Yields a blend of hydrocarbons : methane, gasoline, distillates, waxes, etc. The proportions depend on the type of catalyst (Fe-Co-Ni) and the process conditions (pressure and temperature) 28

29 Fischer-Tropsch Reactors FT reactors must be designed to allow an efficient control of the heat flow: 1. The reaction is highly exothermic 2. The temperature must be maintained in a narrow range to produce the valuable hydrocarbons 29

30 Fischer-Tropsch Reactors Example: Multitube reactor ARGE design 2000 tubes dia 50mm Main features: High heat transfer capability Initial heating and heat removal by a hot fluid (steam) 30

31 Fischer-Tropsch Reactors Some concepts utilize microchannels technology to ensure a very high heat exchange and a uniform temperature in the reactor 31

32 Multitube design Multitube design is already used in the nuclear industry to guarantee the high heat flux required This design provides an efficient heat transfer, limits the surface temperature of the tubes and avoids water splitting Nuclear fuel assembly for a PWR 32

33 Potential design LENR systems LENR reactors can be controlled via the cooling fluid temperature Additional control possible for some types of reactors via gas pressure, electrical excitation input, etc. If the reactor is sensitive to the temperature, a high heat exchange design is compulsory 33

34 LENR cell Plate and tubular types LENR reactors Cells immerged in a forced flow of cooling fluid thickness 2t dia 2r Condition for stability? 34

35 LENR cell Plate and tubular types LENR reactors thickness 2t dia 2r Hypotheses: LENR specific power : w (W.m -3 ) Arrhenius law activation energy : E (J) Operating temperature : T (K) Heat exchange coefficient : h (W.m -2.K -1 ) 35

36 LENR cell Plate and tubular types LENR reactors Conditions for stability thickness 2t dia 2r h > Ewt/kT 2 h > ½ Ewr/kT 2 Hypotheses: LENR specific power : w (W.m -3 ) Arrhenius law activation energy : E (J) Operating temperature : T (K) Heat exchange coefficient : h (W.m -2.K -1 ) 36

37 LENR Reactor Heat Control LENR cell liquid flow Heat exchange by forced liquid flow and/or boiling liquid hot gas channel Heat exchange by forced organized gas flow LENR cell cold gas channel 37

38 How to improve the COP? Temperature controlled reactor : COP = ( Ein + Exs) / Ein Small reactor : Low volume / surface ratio High heat losses Ein >> Exs HIGH HEAT LOSSES 38

39 How to improve the COP? Temperature controlled reactor : COP = ( Ein + Exs) / Ein Cluster of many reactors : High volume / surface ratio Low heat losses Exs >> Ein HIGH HEAT LOSSES LOW HEAT LOSSES 39

40 HEAT LOSSES HEAT LOSSES How to improve the COP? Temperature controlled reactor : COP = ( Ein + Exs) / Ein HEAT RECOVERY LENR cell Hea ng Insula on CLUSTER OF LENR CELLS COP = 1.X COP >> 1 40

41 Please do no longer refer to such diagrams for continous LENR reactors 41

42 Thank you for your attention 42