The Cool Fire Story

The Technology

Coolfire® Catalytic Heating versus Open Flame Combustion


FLAME BASED HEATING:

In order for heat to be generated by a flame-based process, the fuel molecules and oxygen molecules in the air must collide with sufficient kinetic energy (molecular speed) to overcome an energy barrier that normally keeps the molecules from reacting (i.e. exothermic reaction product) and releasing heat. The high energy barrier requires a high flame temperature (> 1000°C) to sustain the reaction, as well as, to start it (match, spark, etc). 

CATALYTICALLY BASED HEATING:

Coolfire® technology employs a catalyst within the reaction zone to produce a flame free, low temperature ( < 260°C) heat reaction. The basic principle of operation is that the catalyst lowers the energy barrier between the fuel molecules and the oxygen molecules so that they may combine at a much lower temperature. The catalyst is not consumed in the reaction. Instead, it acts as a kind of “broker” to ensure that the molecules combine at a much lower temperature than would normally be required. It then proceeds to perform this function in a continuous manner as new, unreacted fuel and oxygen enter the reaction zone. Although catalytic heating is not a new concept, the Coolfire® approach is a unique and patented method of optimizing catalytic heating for small, portable, beverage and food heating applications.


FLAME BASED HEATING:

The kinetic energy required to start the reaction is generally supplied in the form of a high energy mechanism (match, spark, etc) or process of some sort to produce a temperature above the autoignition point. The automated starting of flame-based products depend on spark based mechanisms. Portable products, that utilize a spark starting approach, universally depend on a manually switched piezoelectric component. Piezoelectric starters are prone to damage and tend to have high failure rates, are cumbersome to operate (high starting force manually applied ), and relatively noisy.  

When the high-temperature flame contacts the much cooler cooking utensil surface, an unsteady boundary layer is formed at the surface. The gases within the boundary layer transfer their heat energy to the cooking utensil and as a result, some of the fuel/air mixtures within this layer drops below a critical temperature. This can prevent the flame from completing the combustion of the fuel/air mixture. Consequently, incomplete combustion products often form which include the toxic emission of carbon monoxide. 

CATALYTICALLY BASED HEATING:

Coolfire® technology does not require a flame or spark to start the reaction. Instead, a micro-miniature, electrically driven (joule heating) resistance coil is embedded within the catalytic media and raises the local temperature to a point (well below the autoignition point) where the reaction begins. The reaction then spreads rapidly throughout the reaction chamber, allowing completion of the heat-generating fuel/air reaction without noxious by-products (i.e. no CO or NOx ). The starting process is completely automated, noise-free and requires a very low energy draw ( 0.5 W-sec)  per start. This allows Coolfire® products to adapt automatically to the environment and user requirements using sensors and software.


FLAME BASED HEATING:

 Because of their high temperature, (typically above 1000 °C) and the lack of a flame isolating envelope, flame-based portable heaters present a serious fire hazard if knocked over or placed too close to flammable material.  The lack of a flame isolating envelope also contributes to safety issues during the starting process. For instance, inexperienced or inattentive users, who inadvertently let the unignited fuel/air mixture build up too much before manually igniting the flame, may see a sudden and unexpected back flash that propagates out of the air vents, exposing the user to potential harm.  

The high flame temperatures also tend to produce a high degree of local turbulence which can adversely affect heat transfer. 

CATALYTICALLY BASED HEATING:

Coolfire® catalytic technology produces a reaction that runs at an average temperature of about 260°C, which is well below flame-based heat sources.  The Coolfire® catalytic heat-generating technology is completely enclosed within a porous, open-cell, metal foam structure. Heat transfer occurs uniformly and efficiently without local hot spots.

In addition, the metal foam, in which the catalytic reaction is maintained, has geometric properties that cause it to behave as a flame arrestor, further limiting the potential for any kind of flame formation or propagation.


FLAME BASED HEATING:

Naked flames can only be sustained by a careful balance between flame propagation speed (which is determined by fuel type and fuel/air ratios) and the rate at which the raw fuel/air feed enters the reaction zone. Because of the need to balance these and other parameters within a narrow range of settings, flames may be thought of as essentially borderline stable. This tendency toward instability (i.e. flame out condition) also makes them susceptible to being extinguished by wind currents that interrupt this balancing act. 

In addition, flame-based products have other restraints, such as being sensitive to the physical orientation of the product (i.e. the flame is always vertical), so it is necessary to provide (a reasonable degree) of product leveling to ensure proper heat transfer and optimum performance. Another limiting factor for flame-based products is that fuel/air mixtures must be within a relatively narrow operating range. If the mixture is too lean or too rich, flame ignition becomes unreliable.  

CATALYTICALLY BASED HEATING:

Coolfire® catalytic technology avoids most of the limitations of flame-based heat sources. The reaction cannot be extinguished by wind effects and is not susceptible to flame lift-off or flashback effects. Moreover, catalytically driven combustion operates over a very wide range of fuel/air ratios not achievable with flame combustion.  It is also not dependent on product orientation. Because of this and other properties, Coolfire® accommodates a much wider design space resulting in more desirable product attributes.


 DME has the highest well-to-wheel energy efficiency, 25% better than synthetic diesel fuel, and the lowest greenhouse gas emissions of any biomass-based fuel.

Production of DME from pulpwood is under development in the US by Oberon Co.

Well-to-wheel analysis for energy efficiency and greenhouse gases (Courtesy – A. Röj, Volvo Technology Corporation). These estimates include production, transport, and end use GHG emissions. KEY: DME dimethyl ether; MeOH methanol; CNG compressed natural gas; RME rapeseed methyl ester; GHG greenhouse gas.