Flame Interactions of K, S Cl and CO in Oxygen Enriched Atmospheres.

[NNadir]

Last edited Tue Jan 28, 2020, 08:00 PM - Edit history (1)

The paper I'll discuss in this post is this one: Chemical Interactions between Potassium, Sulfur, Chlorine, and Carbon Monoxide in Air and Oxy-fuel Atmospheres (Thomas Allgurén and Klas Andersson, Energy & Fuels 2020, 34, 900?906).

Energy & Fuels, a publication of the American Chemical Society, an organization of which I am a long time member, is a journal I access every month, even though most issues are chock full of papers about a topic I absolutely deplore, dangerous fossil fuels. Of course, there are papers about dangerous fossil fuels that are well worth reading because the science therein may well prove to apply to things that actually are safe and sustainable. It is often the case that useful information can be obtained about energy and the environment by reading about systems that are either insidious or won't work, or are a little bit of both. For example I read papers all the time about making fuels using solar thermal plants, even though the small number of solar thermal plants that have actually been built end up being expensive, unreliable junk that damages or destroys pristine desert habitats. The reason is that the technologies that appear in solar thermal papers are adaptable to any source of high temperatures, even those that work. Many thermochemical cycles for splitting carbon dioxide, water or both, for example, make the requisite popularly driven genuflection to so called "renewable energy" but despite this appeal to unsustainable technologies, would work quite well with cleaner and far more sustainable nuclear energy.

This paper, cited at the outset, is not about technology that is directly applicable to nuclear energy, but it is very much about a product that is very useful for the removal of carbon dioxide from the air, pure oxygen, this being a side product of water or carbon dioxide splitting. The paper briefly mentions how this might work, specifically in the safe combustion of biomass (and or municipal garbage) in such a way as to make smoke stacks unnecessary. This type of combustion is called "oxy-fuel" combustion.

The combustion of biomass and/or municipal wastes is responsible for slightly less than half of the air pollution deaths which kill people continuously, at a rate of about 19,000 people per day while airheads run around complaining about so called "nuclear waste," which has a spectacular record of not killing anyone.

This is the world we live in. No wonder we now have a party - one dominated by a corrupt uneducated immoral moron - of people who used to wrap themselves in a flag threatening to nuke the planet to fight communism now bending all over itself to kiss the sphincter of a former KGB agent who now runs Russia.

And, it's not just them. We now have "environmentalists" who applaud the ripping up of wilderness for roads for trucks to drag wind turbine parts made from strip mined materials on diesel trucks.

Anyway, there is a difficulty with the combustion of biomass that anyone who has run a fireplace for a few decades will recognize. Biomass combustion effluents are not only toxic; they are corrosive.

I have been thinking and reading about this problem for quite some time: I'm jealous of my son studying materials science engineering and I'm always openly or surreptitiously working to pick his brain.

That's why this paper appealed to me.

From the introduction:

Today, it is generally accepted that the global temperature increase is largely a result of anthropogenic use of fossil fuels.(1) As a consequence, interest in alternative energy sources, such as biomass and waste-based fuels, has increased drastically in recent years. The global total primary energy supply has increased by an average annual rate of 1.9% since 1990, while at the same time, the primary energy supply from renewable sources has grown at a rate of 2.2%. In 2014, 13.8% of the global total primary energy supply was generated from renewable energy sources.(2) Despite this increase in renewable energy supply, there has been an increase in fossil CO2 emissions of almost 40% between 1990 and 2014. The largest share of global CO2emissions, 42%, is attributed to heat and power generation.(3) According to the International Energy Agency (IEA), in year 2014, more than 65% of the global electricity generation was based on the combustion of fossil fuels and more than 40% was from coal alone. Hydro represents the largest source of renewable electricity production (16%), whereas only 2% of the worldwide electricity generation is from the combustion of biofuels and waste. In addition, solar and wind, which are believed to play an important role in the future electricity production mix, are together with geothermal generation responsible for 4% of the total electricity production.(4) Thus, there is still a long way to go toward replacing the present use of fossil fuels.

A point: Reference 4, featuring the "4%" figure in "percent talk" - the talk that proponents of the wind and solar industry utilize to obscure its obvious failure of these hyped industries to address climate change - is not about total energy but rather about electricity. Specifically the reference is this: (4) International Energy Agency (IEA). Electricity Information 2016;
IEA: Paris, France, 2016; ISBN: 978-92-64-25865-5. After half a century of wild cheering, according to the 2019 edition of the World Energy Outlook, also published by the IEA but about primary energy, not electrical energy, as of 2018 all the world's solar, wind, tidal and geothermal sources on the planet produced 12.26 exajoules of energy out of 599.34 exajoules of energy consumed by humanity, in "percent talk," 2.04%.

The introduction continues:

An alternative path toward the replacement of fossil fuels is to lower the emissions of CO2 from the use of fossil fuels in stationary combustion facilities by adopting the concept of carbon capture and storage (CCS). CCS allows for the continued use of fossil fuels without emissions to the atmosphere of carbon dioxide; CCS is often referred to as a bridging technology that will allow for fast and drastic cuts in emissions, while more sustainable energy sources are being developed that can be adopted in a cost-effective and secure manner in the future.

An interesting possibility to reduce global warming is to combine the combustion of biofuels and CCS; this is commonly referred to as “bioenergy with carbon capture and storage” (BECCS). BECCS can help not only to reach a zero-emission target for power or industrial plants but also to achieve negative emissions locally. BECCS could be used to compensate for fossil CO2 emissions from sources for which a reduction might be more difficult to achieve. BECCS has also been proposed for the actual removal of CO2 from the atmosphere. Azar et al.(5) have shown that it is possible to reach the 2 °C target even if we, for a while, reach an atmospheric concentration of greenhouse gases otherwise considered too high, provided that BECCS is deployed.
With this background, this paper provides experimental and modeling work on the combustion chemistry relevant to fuel or fuel mixes with high concentrations of alkali, chlorine, and sulfur. The conditions are relevant for suspension-fired systems in both air–fuel and oxy-fuel combustion systems. In comparison to coal, biomass contains high levels of alkali metals and chlorine and low levels of sulfur. Given the fuel composition, significant amounts of alkali chlorides may be formed during the combustion of biomass, which increases the risk of high-temperature corrosion (HTC). However, during co-combustion of coal and biomass, fuel-bound sulfur in the coal may promote the sulfation rather than the chlorination of the alkali metals. The formation of HTC-related alkali species is investigated in the present work under both in-flame and post-flame conditions. The focus of this investigation is on the homogeneous gas-phase chemistry and includes both experimental work and detailed kinetic modeling

By the way, carbon capture and storage will not work and is not safe. However, carbon capture and use is very much worth considering. It is feasible, I think, to make materials now made through the agency of dangerous fossil fuel derived products from "Boudouard Carbon" - carbon made from the disproportionation of carbon monoxide, coal combustion in reverse, which obviously requires an energy input but is feasible with nuclear energy.

The interesting point raised in the paper is that the closed (smokestack free) combustion of biomass allows for concentrated and easy to separate carbon dioxide.

In biomass combustion in an oxygen environment - which involves high temperature - salts like potassium chloride and sodium chloride, which are always present in biomass are molten and hot enough to develop a significant vapor pressure and become gaseous and at high temperatures these salt gases are corrosive. Oxidized sulfur, from the combustion of the amino acids methionine and cysteine, as well as other thiolated molecules, generates sulfur dioxide and sulfur trioxide, the latter being the anhydride of sulfuric acid, and in the presence of steam, sulfuric acid itself.

The authors developed an apparatus to explore these gases present in flames. A schematic of the apparatus:



The caption:

Figure 1. Schematic of the 100 kW test unit at Chalmers University of Technology. The red arrows indicate the positions for the injection of KCl and SO2. The locations of the 15 measuring ports are indicated as M1–M15.

The behavior of KCl was monitored by spectroscopy using a system the authors dubbed IACM (in situ alkali chloride monitor) which is shown in the following schematic:




The caption:

Figure 2. Schematic of the IACM setup used in this work to measure the concentration of KCl over the cross section at M7: 1, UV light source; 2, aperture; 3, parabolic mirror; 4, ball valve with window inside; and 5, collimator connected to a spectrometer via an optical fiber.

Other gases in the system were analyzed by a piece of apparatus called an NGA 2000 which, as I understand it is a type of compact GC with an FID (Flame Ionization Detection) system. Since I am generally not familiar with this instrument, it probably behooves me to let the authors describe their analytical system. To wit:

. A NGA 2000 analyzer was used for measuring the levels of CO, CO2, O2, and SO2. This instrument uses the paramagnetic principle (O2), non-dispersive ultraviolet sensors (SO2), and non-dispersive infrared sensors (CO and CO2). A BINOS 100 analyzer was used to measure the levels of CO2 and O2 using infrared (IR) and electrochemical sensors. Two different Fourier transform infrared spectroscopy (FTIR) systems were used: MB9100 (Bomem, Inc., Québec City, Québec, Canada) and MultiGas 2030 (MKS Instrument, Inc., Andover, MA, U.S.A.). These systems generally measure warm (190 °C) and wet gases and can be used to detect a wide range of different compounds. In this work, they were, however, used to measure HCl. The temperature of the gas inside the furnace was measured using a suction pyrometer. The suction pyrometer is a water-cooled suction probe equipped with a thermocouple (type B).

The combustion here did not take place in a pure oxygen atmosphere. In fact the gas supporting combustion was carbon dioxide slightly enriched, with respect to air, in oxygen, to 25% and is thus designated OF25 in the paper.

Th oxygen/carbon dioxide system is a system about which I've been thinking "thought experiments" for quite some time, and I am pleased to see it discussed here. Note that if all of the oxygen in this system is consumed, the residual gas will be a mixture of CO and CO2, depending on the amount of unoxidized fuel in the system. If water is present, it will consist of small amounts of hydrogen gas and carbon dioxide, a very interesting system.

To return though, to the present case:

The reaction conditions are described in this table, Table 1, showing the amounts of KCl and SO2 injected into the system:



The overall conditions are shown in Table 2:



Here are the flames, pictured in the air and OF25 cases with and without KCl injections:



The caption:

Figure 3. Photos of the flame taken during operation. The air case both without and with KCl injection is shown in panels a and b, respectively, and both photos are taken in measurement port M2. The OF25 case is shown in panels c and d without and with KCl injection, respectively. The OF25 photos are from port M3.

What is being measured here is the interaction between sulfur, oxygen and potassium, in which case a significant portion of the gas is present as HCl gas, hydrochloric acid, which is obviously corrosive.

The effect of the potassium to sulfur ratio in the next graphic shows its effect on the resulting concentrations of HCl gas:



The caption:

Figure 4. (a) Measured and modeled HCl concentrations. (b) Measured and modeled available concentration of KCl. The KCl measurements were carried out using the IACM instrument.

The "degree of sulfation" refers to the amount of potassium being in the form of K2SO4. It is defined in this equation, equation 1 in the paper:



Graphically it is shown here under various reaction conditions:



The caption:

Figure 5. Degree of sulfation at the outlet of the isothermal PFR as a function of the temperature for four out of six investigated cases.

The following figures are probably best explained with some text from the paper:

Figure 6 shows the degree of sulfation as a function of time at a temperature of 1200 °C (Figure 6a) and 850 °C (Figure 6b) for the same four cases, as shown in Figure 5. The degree of sulfation is initially higher for those cases where CO is oxidized (N2–CO and CO2–CO). However, the influence of CO is even more evident in Figure 6b (850 °C), where the sulfation in the CO case is not only higher at the outlet compared to both the reference case at 850 °C and all cases at 1200 °C but also proceeds much faster. Note that, in the 850 °C case, there were no differences between nitrogen- and carbon-dioxide-based atmospheres; these data were therefore omitted.

The first 2 s of residence time in the 850 and 1200 °C cases in Figure 6 were used for a reaction path analysis, as presented in Figures 7 and 8. The thicknesses of the lines in these figures are proportional to the activity levels for that specific reaction or set of reactions. There are clearly higher sulfation activities in the N2–CO and CO2–CO cases (panels a and b of Figures 7 and 8, respectively) compared to the atmospheres that do not contain any carbon monoxide (panels c and d of Figures 7 and 8). The main activity is, however, not the formation of K2SO4 but the sulfation of KCl to KSO4 and KHSO4, of which the latter is thereafter desulfated back to KCl without reacting via the final step to form potassium sulfate. These reactions create a loop that acts as a net producer of sulfur trioxide. Therefore, in the N2–CO and CO2–CO cases, the SO3 concentrations are substantially higher for temperatures of <1000 °C compared to the cases in which no CO oxidation occurs, i.e., N2reference and CO2 reference.

Figure 6. Degree of sulfation in the PFR as a function of the residence time for the two different operating temperatures: (a) 1200 °C and (b) 850 °C.

The next two figures show all of the species identified in the flame as recorded over a period of a few seconds and the pathways between them, as described in the excerpted text above:

Figure 7:





The caption:

Figure 7. Reaction path analysis of the first 2 s in the PFR, representing the results presented in Figure 6b.

"PFR" designates the reactor, a "Plugged Flow Reactor."


Figure 8:



The caption:

Figure 8. Reaction path analysis of the first 2 s in the PFR, representing the results presented in Figure 6a.

The disproportionation of KO- species into potassium metal is interesting; I have considered this reaction for the two higher alkali metals, rubidium and cesium for certain applications. When I was a kid this reaction would have surprised me, but now older, I am aware of it. In this setting potassium metal is only meta stable, and won't survive very long, as the pathways clearly indicate. Nevertheless at 1200°C, its formation is a major reaction.

The thermal decomposition of oxygen containing species is always of interest, although clearly in this system, the recombination is very fast, the free metal is a transitory intermediate.



The next graphic is also relevant to thermochemical water splitting, because the equilibrium it shows between SO3/H2SO4 and SO2 gas is a component of the famous and widely explored sulfur-iodine cycle, which I'm sure I've discussed somewhere on the internet, if not here. This is not my favorite thermochemical cycle, but it's growing on me, owing to certain insights as to how it may become a continuous process. Continuous processes, while they can be challenging, when fully developed are always or at least always more economically viable than batch processes. (Which is yet another reason why solar thermal schemes are doomed to economic failure.)




The caption:

Figure 9. Ratio of SO3/SO2 at the oulet of the PFR for different temperatures in the reactor. The included experimental data are taken from Fleig et al.(17)

A graphic relating to the presence of free radicals, which are nice things when one is getting potential pollutants to decompose.



The caption:

Figure 10. Concentrations of (a) H and (b) OH radicals when the PFR temperature was set at 1200 °C. Note that the CO and reference cases are presented on separate y axes in panel a.

Finally, the effect of distance from the burner on CO concentrations with injections of SO2 and KCl:



The caption:

Figure 11. CO concentrations for (a) five air cases and (b) six OF25 cases with and without injection of KCl, SO2, and water. The cases are defined as follows: ref, reference case (no injection); W, injection of pure water; K, injection of KCl; S, injection of SO2; KS, injection of both KCl and SO2; and 2K, double amount of KCl injected.

Although I'm generally dismissive of so called "renewable energy," biomass represents a special case, since there are areas where there is biomass as a pollutant, i.e. lakes and seas suffering from eutrophic oxygen depletion, and because biomass may represent the lowest cost path to removing the dangerous fossil fuel waste from the atmosphere.

From the paper's conclusion:

The use of biomass and waste as fuels for combustion processes is expected to increase during the coming years because this represents a possibility to reduce fossil CO2 emissions. The relatively high content of alkali metals and chlorine found in biomass compared to coal increases the risk for problems related to deposition and high-temperature corrosion. The related chemistry is therefore important to use the biomass in the best way possible, i.e., to maximize the thermal efficiency in power plants. This work focuses on the K–Cl–S chemistry relevant for combustion in flames. The work includes experiments performed in a 100 kW combustion test unit together with kinetic modeling performed using Chemkin.

In this work, detailed kinetic modeling was performed to examine the influence on potassium chloride sulfation of CO oxidation in combination with the replacement of nitrogen with carbon dioxide. The oxidation of CO enhances the kinetics of alkali sulfation, in particular, at temperatures of <1000 °C. At higher temperatures, sulfation is promoted even further if the concentration of CO2 is also high. The experimental data presented in this work show that favorable conditions for alkali sulfation are naturally mediated by flue gas recirculation in oxy-combustion, leading to elevated SO2, CO2, and CO concentrations...

This is an esoteric but important paper, to my thinking, on engineering the removal of the dangerous fossil fuel waste carbon dioxide from the atmosphere, something future generations - all who come after us - will need to do, simply because we were rotten forebears and didn't care a whit for them.

History will not forgive us, nor should it.

Have a nice evening.

[Atticus]

1. I will not even pretend to understand this or even most of your posts, but that should be

understood as a comment based on my ignorance, not the quality of your content. I "skim" most of them in search of a few pearls that I can mention the next time I talk with my niece who is nearly finished with her PhD dissertation in physics. Maybe she will not think I am a total numbskull.

Thanks for your interesting and challenging posts.

[NNadir]

2. Thank you for your kind words.

I write these posts to fix things in my head, to clear my thinking and to make sure I understand what's being said.

They also function as a kind of "sticky note."

Some of the issues in this particular paper have been rolling around in my head for many years, since I spend a lot of time daydreaming about oxyfuels, high temperatures, and the nature of chemical reactions therein. It is very difficult to edit myself toward more comprehensibility.

It is a matter of some importance to me that I understand that there will be a way out for future generations, particularly as I approach the end of my life. When I think about these things, and when I meet these very smart, if ripped off, young people, I am filled with something a cynic like myself has problems finding, that Pandoraian jewel of hope.

Also, I think we often see science through the prism of journalist descriptions. I regret to say that the scientific understanding of journalists, particularly in the age of Twitter and blogs, is declining. This is true, unfortunately for the press that leans left as it is for the press that leans to the right. A lot of what one reads about science would make you want to laugh, were it not for the fact that it also makes one want to weep.

I think the frequent poster here Judi Lynn does an outstanding job surveying the scientific "news" sites and press releases, but even with all of her outstanding effort, hard work, and passion for the truth, she sometimes ends up posting "out there" stuff that does not stand scrutiny. This is not to say that she is anything but an outstanding filter on this news. I miss sometimes. Everyone misses.

I know that this stuff may be hard for others to comprehend, as difficult as it is for me to contemplate the performance of a ballet, or the profound symbolism and evocations in a great painting. But as I try to understand art by wading in it, and listening to artists, curators and critics, I very much appreciate anyone who makes an effort to wade into science.

Science, of course, is an inherently human activity, and it brings all of humanity's flaws as well as its strengths with it. What I am trying to do, besides my selfish reasons stated at the outset in this post, is to let people who really care understand the raw front lines of science, which is what regular reading in scientific journals can bring, unfiltered by journalist "spin." I often pepper my remarks with acerbic commentary in order to say that science is not oracular or perfect, but is like all parts of culture, an evolving struggle to reach the pinnacles of human experience, and as such, is prone to failure and missteps.

And trust me, science is more influenced by culture than culture is influenced by science, particularly in the age of (gasp!) "alternate facts," a concept that is a paean to stupidity. We are living in an increasingly dark age; but I feel this young generation can relight the good in humanity. These kids are great!

Thanks again.

.