NEW INSIGHTS IN THE BURNING AND COMBUSTION OF HEAVY –NON VOLATILE ORGANIC LIQUIDS.

 

 

 

Ladies and gentlemen,

 

To start with an introduction, I am a colloidchemist, trained at the Van 't Hoff Laboratory of the Dutch State University of Utrecht. Soon after, I got involved in electrochemical research at the Philips Physical Laboratory at Eindhoven and later in high temperature physics and chemistry at the Central Laboratory of Philips Lighting.

 

I appreciate this opportunity to present results of my private research about the existence of a thermal phenomenon, that controls the atomization of heavy fuels by carbonized substrates. To my knowledge this phenomenon has so far not been studied scientifically.

 

Having concluded the exploratory studies I approached Shell - Amsterdam to discuss my results. After some reverting, Rob Tausk, a former colleague of my Van 't Hoff period, prompted me to contact Lionel Clarke of Shell GSUK. I am indebted to these gentlemen!

 

It is to be understood that I will present today this thermal phenomenon, only, in terms of outlines, features and potential opprtunities that might be of interest to Shell. Details of my model for atomization are excluded from this non-confidential presentation.

 

A few years ago I came across the phenomenon that bitumen does not readily burn, generally considered to be a down to earth fact.  When I tried to explain the aspects of bitumen combustion I failed miserably.

 

Being trained a colloid chemist; I got annoyed by this unexpected failure. Familiar with colloid chemical, electrochemical and high temperature methods I have explored some of the phenomena that accompany the combustion of non-volatile organic liquids, bitumen included - experimentally nd have formulated their main features.

 

My focus is on the atomization phenomena involved in the combustion of non-volatile organic liquids. This category also includes fire retardant polymeric materials that melt when burning. The results prompted me to conclude that such atomization is governed by pyrolysis and by electrochemical processes.

 

  • Slides 4 up to 7 are items judged of potential interest to Shell applications.
  • In slide 8 leads are formulated as to the relation between the molecular structure of non-volatile liquids and the kinetics of atomization.
  • In slide 9 arguments are presented to support that the principles of this kind of atomization also apply to cracking processes of organics.
  • Slide 10 reviews methodologies applied in electrochemical testing.
  • Slide 11 presents - in general terms - a summary of guidelines and prospects.

 

My experiments with wicks carrying candle flames unravelled the processes involved in atomization of fuels of different molecular structures. By varying the oxygen content of the gaseous atmosphere and by changing the composition of inert gas the electrochemical behaviour of the wick in the dark zone could be studied in detail.

 

Surprising effects emerged! The fuel consumption could be manipulated by doping fuel with small amounts of specific aromatics. The limiting oxygen index (LOI) of paraffinic combustion could be lowered by increasing the heat conductivity of the atmosphere. It showed that the carbonization of the cotton substrate of the wick seemed to obtain a specific activity imprinted by the molecular structure of the fuel used during its carbonization.

 

These findings fitted in a comprehensive model. The main features of which are:

  • Pyrolysis generates gas, radicals and electrochemical active species.
  • Solid/liquid and liquid/gas interfaces become electric charged.
  • At the surface of the wick electrical forces govern the emission of droplets and their size distribution.

 

My experiments with wicks carrying candle flames unravelled the processes involved in atomization of fuels of different molecular structures. By varying the oxygen content of the gaseous atmosphere and by changing the composition of inert gas the electrochemical behaviour of the wick in the dark zone could be studied in detail.

 

Surprising effects emerged! The fuel consumption could be manipulated by doping fuel with small amounts of specific aromatics. The limiting oxygen index (LOI) of paraffinic combustion could be lowered by increasing the heat conductivity of the atmosphere. It showed that the carbonization of the cotton substrate of the wick seemed to obtain a specific activity imprinted by the molecular structure of the fuel used during its carbonization.

 

These findings fitted in a comprehensive model. The main features of which are:

  • Pyrolysis generates gas, radicals and electrochemical active species.
  • Solid/liquid and liquid/gas interfaces become electric charged.
  • At the surface of the wick electrical forces govern the emission of droplets and their size distribution.

 

Combustion retardants are added to polymer materials to reduce their rate of combustion. Such additives accomplish this reduction by acting upon several mechanisms, viz. by quenching free radical chain reactions and shifting the heat balance. To position the effects of pyrolytic atomization in the scene of models of fire retardancy one may scrutinize the aspects of atomization by charred polymers.

 

Patches of char are charged by redox processes at solid/liquid/gas interfaces. The electrochemically active species involved have two sources, viz. the pyrolysis at the interior of the polymer and the gaseous exterior of the combustion process.

 

Combustion retardants imprint the charring process in such a manner that the rate of atomization decreases. It is my understanding that common retardants are inorganic components that have been selected by trial and error.

 

I have developed a methodology to classify molecular structure of additives that suppress atomization and techniques to identify electrochemical processes inside chars. This approach could open inroads to the further development of combustion retardants.

When compared to Combustion Retardants most Flame Retardants operate in a quite different chemical scene, viz. applied being diluted with water and sprayed, to suppress a fire consuming "green materials" that are made up from water, carbohydrates, cellulose and the like. An often quoted view on the effect of Flame Retardants is their facility to form a combustion barrier between the fire and the fuel. Some sort of barrier that effectively reduces the rate of advance of the fire.

 

Approached from the considerations relevant to pyrolytic atomization the existence of such a barrier indicates a transient reduction of the local rate of atomization of liquids - evolved by pyrolytic processes situated "behind and inside" this barrier.

 

The major part of this atomized liquid should be a hydrous solution of carbohydrates, alcohols, polar reaction products and also some electrolytes. The minor part of the atomized liquid would be constituted of apolar solutions - insoluble in water. I am not aware of references to the very composition of such atomized liquids.

 

An interesting finding is that ammonium salts chemically combine with cellulose as the "fuel" is heated. This observation may be interpreted as "ammonium salts control to some degree the imprinting during charring of the atomizing substrate".

 

I expect that exploration of the colloid and electrochemical aspects of charring and atomization could open new leads to manipulate "fire and combustion" processes.

During the development of my model of "Pyrolytic Atomizing" it gradually became evident that pyrolytic processes convert an apolar organic liquid into an uncommon sort of "mixed-conductivity" solvent. The conversion is irreversible. The conductivity properties are partly transient. It was first realised that the electric resistivity controls to some degree the rate of atomization by carbonized substrates. The second step was the perception that in the case of a candle flame atomization links two quite different combustion processes. The third step was the apprehension that pyrolytic atomization is just a common mechanism generated by a combination of thermophysical conditions and that there should be more and similar mechanisms. This consideration initiated the fourth step, viz. tracking mechanisms involved in cracking of non-volatile organics, e.g. of the type liquid to solid/liquid/emulsion/gas.

 

With all due respect, this staircase opened up like a great turkey shoot. There is a common bottom line to these studies. Compared to the huge amount of thermal energy released by combustion processes, just tiny amounts of  energy are stored to stabilize the colloid-chemical conditions at  two-phase interfaces, viz. liquid/liquid, liquid/solid, liquid/gas and solid/gas.

 

This energy is partly of an electrical nature and belongs as such to the domain of electrochemistry. The most common sources of electric energy involve reactions between three phases - solid/liquid/gas. Reactions between phases of the type solid/liquid generate electrical energy by pathways of the type solid/liquid/solid.

While reviewing the ins and outs of hydrocarbon processing no references turned up to electrochemical phenomena involved in cracking of heavy organics. This lack heartened and disheartened me at the same time. Cracking, visualized as a pyrolytic decomposition process inherently generates specific charge carriers, radicals, electrochemical active gas. Species that are reputed to take part in electrochemical phenomena!

 

Could scarcity & deficiency of carbon substrate explain the virtual absence of electrochemical phenomena? This consideration was highlighted by the observation that in the U.S. market glass fibre wicks compete with cotton wicks. My testing of such glass fibre wicks showed readily that white virginal glass fibre substrates atomized paraffin at rates comparable to their carbonized cotton counterparts.

 

How so? Does carbon atoms, once unfastened inside pyrolyzing liquid, cluster and start to deposit on glass substrates? Is a certain amount of surface conductivity already sufficient to cause charge transport along interfaces? This last question  refers to the gigaohm resistivity of wetted carbonized wicks. Such extreme resistivity implies that the structure of carbonized cotton wick is made up of nanoparticles carbon that are mutually electrically isolated to some degree. This kind of argument could also highlight the development of zeolite catalysts that reform light and heavy organics - developed without considering electrochemical involvements.

 

Cracking of heavy organics most certainly will show to involve electrochemical phenomena and - hopefully - inroads to manipulate the refining parameters.

The irreversible nature of pyrolysis renders electrochemical observables transient. This complication could be overcome by making use of multi-technique analyses to obtain data sets as a function of time.

 

The analysis of such time frames could reveal parameters of the progress of pyrolysis, viz. electrical conductivity, redox potential and complex impedance at liquid/solid interfaces; inclusive their temperature dependencies. The rate of carbon deposition at glass/liquid interfaces can be observed by making use of optical fibre sensors that record internal reflectivity.

 

By situating sets of sensors at fixed distances one can also record transients generated by flow and (de-)mixing.

 

The state of the art of multi-technique analysis allows the design of multiprobes.

 

While reflecting on the effects of pyrolytic atomization I conclude that I just stumbled across this thermal phenomenon. Its very nature seems to have remained hidden by the mix of disciplines involved in its unravelling. 

 

I have learned to appreciate and respect the complexity of the domain of organic fuel technology. At that time, being acquainted with the fundamentals of solid state physics, I sought refuge in the niche of conductive organic molecules and polymers. There I got just baffled by the intricacy of pathways available to electric charge transport. Another sphere of the organic physics and chemistry realm mushrooms!

 

And what about cracking of heavy organics? I suspect that there is no comprehensive physical or chemical description of the electrical conductivity properties of pyrolyzing organic liquids! Yet the importance of organic fuel technology is evident and becomes more so by the efforts to reduce generation of soot and toxity of reaction products.

 

A comprehensive effort to expand "organic pyrolytic state physics" is essential to the development of applications involving colloid and electrochemical effects!

 

I am thankful for this opportunity to outline results of my private research.

 

Appeltern, 26-09-2005

Joris J.C. Oomen