Challenge


Sulphur Combustion for Energy Generation: An alien notion that can forestall climate change. A Challenge to the Science and Engineering

As a technological entrepreneur, after years of poring through scientific and technical literature for a versatile, adaptable, state-of-art waste remediation platform, I unexpectedly discovered a fascinating body of work which asserts that global warming, human-induced climate change and other environmental impacts can to some extent be averted through a comprehensive, global effort to use sulphur as an ancillary fuel. Is this notion feasible? 

It is valid to say that aside from carbon and hydrocarbons, sulphur is the only other naturally-occurring material from which energy can be harnessed by combustion. However, the utilization of sulphur for direct heat energy generation is an idea very alien to the power engineering community, which traditionally identified it in power production as an undesirable source of pollution and corrosion.  Sulphur dioxide (SO2), a product of sulphur combustion, when dissolved in water droplets forms acid and when discharged to environment interacts with other gases and particles in the air to form sulphates and other products that can be harmful to people and the environment. Therefore, the combustion of sulphur has been limited to sulphuric acid production. 

Furthermore, in contrast to other liquid fuels, sulfur does not have a light fraction and has a rather high boiling point (450° C). It has a greater heat of evaporation, surface tension, ignition temperature, and specific gravity, but a lower heat of combustion than, for example fuel oil. Sulfur also loses out to fuel oil with regards to conditions for spraying because of the low-pressure drop across the spray jet due to its higher viscosity and surface tension. 

In addition, sulphur vapor constitutes a dissociating system consisting of all molecules from S2 to S8 in temperature- and pressure-dependent equilibria and the sulphur enters the oxidation reaction only as molecule S2, the "diatomic sulphur" a predominant species in sulphur vapor at temperatures above 600° C. Therefore, in the conventional sulphur burner more than 60% of the heat reaction (about 9,400 kJ/kg S) liberated in the combustion of sulphur to sulphur dioxide is theoretically required for preheating the air and sulphur and for evaporation and decomposition of the sulphur. Even so, a sulphuric acid plant produces a prodigious amount of high-level waste heat and nearly all of the high-level waste heat is utilized to produce electricity through a steam turbo/generator.

Be that as it may, there are advantages in sulphur properties that hardly can be ignored. To begin with, is has the capability to attain a very high temperature when burning sulphur in oxygen. The theoretical temperature of adiabatic burning of sulphur vapour in oxygen taking in to consideration dissociation process is about 3000-3500° C.  However, burning diatomic sulphur (S2) in pure oxygen in stoichiometric quantities would produce an even higher temperature - more than 5,000° C! To makes possible to burn sulphur directly in a stream of oxygen sulphur can be evaporate by bubbling oxygen through molten sulphur at a temperature at which the sulphur boils, which ensures maximum evaporation of sulphur. This industrial proven method is called submerged combustion. 

In addition, sulphur dioxide (SO2), if dry, is not corrosive and, in contrast to carbon dioxide, can be relatively easily reduced by carbonyl sulphide (COS) to yield carbon dioxide (CO2) in a form that can readily be captured, in addition to forming sulphur in a potentially 100% conversion process.  Lastly, if the sulphur compound COS is generated by conversion of CO2 from power plants, industrial facilities or the atmosphere and utilised as an intermediate a hybrid correlation energy system can be designed whereby energy is obtained from two different prime sources, such as coal and sulphur, without detrimental atmospheric impact of sulphur oxides. It is important to note that CO2 conversion is a proven commercial process. Also, every element in this proposed system has passed beyond the laboratory bench; most are already implemented somewhere at demonstration and/or full industrial scale.  

The Supposition: We Can Ameliorate the Earth’s Climate Problem with Current Technologies without Disruptive Changes in the Global Energy System. Can this be Demonstrated? This is the Challenge!

Bogdan Wojak