From 2efd370717203dd37b8d91892e4d7c7c0369646d Mon Sep 17 00:00:00 2001 From: "Robin P. Clark" Date: Wed, 27 May 2026 12:17:51 +0100 Subject: [PATCH] more amonia concerns --- .../chemiluminescence_strengths_ammonia.tex | 148 +++++++++++++++--- 1 file changed, 127 insertions(+), 21 deletions(-) diff --git a/papers/chemiluminescence_strengths_ammonia.tex b/papers/chemiluminescence_strengths_ammonia.tex index 747be42..3b3739b 100644 --- a/papers/chemiluminescence_strengths_ammonia.tex +++ b/papers/chemiluminescence_strengths_ammonia.tex @@ -7,6 +7,7 @@ \usepackage{hyperref} \usepackage{siunitx} \usepackage{enumitem} +\usepackage{tabularx} \hypersetup{ colorlinks=true, @@ -92,7 +93,7 @@ These quantities can reveal thermoacoustic oscillation, unstable premixing, puls The detector can view the flame through a window, sight tube, quartz optic or sapphire optic. This avoids placing a fragile probe directly into hot, corrosive or dirty flue gas. In industrial settings this is a real advantage, provided the optical path can be kept clean or monitored for fouling. -\subsection{Possible Fuel Fingerprinting} +\subsection{Possible Fuel Fingerprinting; syngas analysis potential} Changing the fuel changes the radical population and reaction pathways. For example, hydrogen addition, ammonia addition or syngas variation can alter the balance of OH*, CH*, NH*, NH$_2$*, C$_2$* and related emissions. @@ -146,46 +147,150 @@ The stronger and more defensible claim is: ``Chemiluminescence gives a fast, non-contact, reaction-zone diagnostic of flame state, stability, dynamics, burner balance and fuel-dependent combustion behaviour.'' \end{quote} -This allows the technology to complement conventional instruments rather than pretending to replace them. +This allows the technology to complement conventional instruments (i.e. flue situated zirconia based O2/NOx sensors and CO sensors) rather than replacing them. \section{A Practical Sensor-Fusion View} -A sensible industrial architecture would be: +An optimal industrial burner senor architecture could be: \begin{center} -\begin{tabular}{lll} +\begin{tabular}{| p{3cm} | p{6cm} | p{6cm} | } \toprule Measurement & Best at & Weak at \\ \midrule -OH*/CH* optics & flame-front state, dynamics, instability & exact stack O$_2$/CO \\ -Zirconia O$_2$ probe & residual oxygen after burnout & fast local flame dynamics \\ -CO analyser & incomplete combustion product measurement & fast flame-front diagnosis \\ -NOx analyser & integrated NOx production outcome & local flame stability \\ -IR/UV flame scanner & flame presence / safeguard function & rich chemical diagnostics \\ +OH*/CH* optics & flame-front state, dynamics, instability & exact stack O$_2$/CO \\ \hline +Zirconia O$_2$ probe & residual oxygen after burnout & fast local flame dynamics \\ \hline +CO analyser & incomplete combustion product measurement & fast flame-front diagnosis \\ \hline +NOx analyser & integrated NOx production outcome & local flame stability \\ \hline +IR/UV flame scanner & flame presence / safeguard function & rich chemical diagnostics \\ \hline \bottomrule \end{tabular} \end{center} The strongest product concept is therefore an augmented flame-quality instrument: optical flame diagnostics plus conventional gas sensing where absolute exhaust-gas concentrations are required. -\section{Ammonia Combustion: UV and Visible Radical Signatures} +\section{Ammonia in Fuel Streams and its Relationship to NOx Formation} + +The presence of ammonia ($NH_3$) within a fuel stream is highly significant for combustion chemistry because ammonia contains chemically bound nitrogen. Unlike conventional hydrocarbon fuels, where most nitrogen originates from atmospheric $N_2$ (i.e. thermally generated), ammonia combustion can directly generate nitrogen-bearing radicals within the flame front. + +\subsection{Fuel NOx versus Thermal NOx} + +Conventional methane combustion primarily produces NOx through the thermal NOx mechanism: + +\[ +N_2 + O \rightarrow NO + N +\] + +This mechanism becomes significant at elevated flame temperatures, typically above approximately $1300^\circ C$. + +However, ammonia-containing fuels additionally generate \emph{fuel NOx}. During combustion, ammonia decomposes through a sequence of intermediate radicals: + +\[ +NH_3 \rightarrow NH_2 \rightarrow NH \rightarrow N \rightarrow NO +\] + +As a result, NO formation may occur even when flame temperatures are lower than those normally required for strong thermal NOx production. + +\subsection{Why Ammonia is Industrially Important} + +Although ammonia can increase NOx formation, it is also increasingly important as: + +\begin{itemize} +\item a potential hydrogen carrier, +\item a carbon-free energy vector, +\item a component of low-carbon combustion systems, +\item and a constituent of some syngas streams. +\end{itemize} + +Ammonia combustion therefore represents both: +\begin{enumerate} +\item an opportunity for decarbonisation, +\item and a major combustion-control challenge. +\end{enumerate} + +The key engineering difficulty is that conditions promoting complete ammonia burnout may simultaneously increase NO formation. + +For example: +\begin{itemize} +\item higher oxygen availability tends to improve ammonia destruction, +\item higher flame temperatures improve combustion efficiency, +\item but both effects may increase NOx generation. +\end{itemize} + +Consequently, ammonia combustion systems often require: +\begin{itemize} +\item staged combustion, +\item flue gas recirculation, +\item selective catalytic reduction (SCR), +\item selective non-catalytic reduction (SNCR), +\item or advanced combustion diagnostics. +\end{itemize} + +\subsection{Chemiluminescence Signatures in Ammonia Flames} + +Ammonia flames can exhibit additional radical chemiluminescence signatures compared with conventional hydrocarbon flames. Potentially relevant species include: + +\begin{itemize} +\item OH* near 309 nm, +\item NH* near 336 nm, +\item NO* ultraviolet emission, +\item NH$_2$* visible-band emission. +\end{itemize} + +These emissions may provide useful information regarding: +\begin{itemize} +\item flame stability, +\item ammonia burnout quality, +\item combustion staging, +\item equivalence ratio, +\item and NO-forming reaction conditions. +\end{itemize} + +Importantly, such optical sensing techniques observe the active reaction zone itself, rather than the final equilibrium flue-gas composition. + +\subsection{Possible Sources of Ammonia in Syngas} + +Ammonia may appear within syngas streams from several industrial processes, particularly where nitrogen-containing feedstocks are used. Possible sources include: + +\begin{itemize} +\item biomass gasification, +\item sewage sludge gasification, +\item municipal waste gasification, +\item coal gasification, +\item pyrolysis of nitrogen-containing organic material, +\item incomplete cracking of amines or nitrogen compounds, +\item and deliberate ammonia addition for combustion or emissions control. +\end{itemize} + +Biomass-derived syngas may contain measurable ammonia concentrations due to the decomposition of proteins and other nitrogen-containing biological material during gasification. + +Consequently, ammonia may become both: +\begin{itemize} +\item a combustion variable, +\item and a potential diagnostic indicator +\end{itemize} + +within future flexible-fuel combustion systems. + + +\subsection{Ammonia Combustion: UV and Visible Radical Signatures} Ammonia combustion introduces nitrogen-containing radical chemistry. Published ammonia-flame chemiluminescence work commonly reports UV and visible signatures from species such as NO*, OH*, NH* and NH$_2$*. Important reported bands include approximately: \begin{center} -\begin{tabular}{lll} +\begin{tabular}{|p{3cm}|p{6cm}|p{6cm}|} \toprule Species & Approximate region & Comment \\ \midrule -OH* & about \SI{309}{\nano\metre} & still an important high-temperature oxidation marker \\ -NH* & about \SI{336}{\nano\metre} & nitrogen-hydrogen radical signature in UV \\ -NH$_2$* & visible, often red/orange bands around \SI{600}{\nano\metre}--\SI{650}{\nano\metre} & contributes to visible ammonia-flame colour \\ -NO* & UV region & related to nitrogen oxide formation chemistry \\ -NO$_2$* & visible broadband contribution, especially in lean post-flame regions & can affect blue/visible colour balance \\ -CH* & about \SI{430}{\nano\metre} & present when hydrocarbon co-fuels such as methane are present \\ -CN* & UV/visible bands in some ammonia/hydrocarbon cases & possible carbon--nitrogen chemistry marker \\ +OH* & about \SI{309}{\nano\metre} & still an important high-temperature oxidation marker \\ \hline +NH* & about \SI{336}{\nano\metre} & nitrogen-hydrogen radical signature in UV \\ \hline +NH$_2$* & visible, often red/orange bands around \SI{600}{\nano\metre}--\SI{650}{\nano\metre} & contributes to visible ammonia-flame colour \\ \hline +NO* & UV region & related to nitrogen oxide formation chemistry \\ \hline +NO$_2$* & visible broadband contribution, especially in lean post-flame regions & can affect blue/visible colour balance \\ \hline +CH* & about \SI{430}{\nano\metre} & present when hydrocarbon co-fuels such as methane are present \\ \hline +CN* & UV/visible bands in some ammonia/hydrocarbon cases & possible carbon--nitrogen chemistry marker \\ \hline \bottomrule \end{tabular} \end{center} @@ -203,11 +308,12 @@ For hydrocarbon flames, OH*/CH* may be useful for rich/lean trend and stability. \item NH* near \SI{336}{\nano\metre}; \item CH* near \SI{430}{\nano\metre}, where hydrocarbon fuel is present; \item NH$_2$* visible bands around the orange/red region; - \item C$_2$* Swan bands for carbon-rich or hydrocarbon/syngas flames; - \item time-domain statistics and FFT analysis for instability. + \item C$_2$* Swan bands (green) for carbon-rich or hydrocarbon/syngas flames; + \item time-domain statistics (standard deviation and/or FFT) analysis for instability. \end{itemize} -This supports the idea of a multi-channel combustion-state sensor. The most credible use would be fast flame-quality and instability monitoring, with possible fuel-composition fingerprinting. Absolute gas concentration measurement should remain the role of validated gas sensors. +This supports the idea of a multi-channel combustion-state sensor. The most credible use would be fast flame-quality and instability monitoring, with possible fuel-composition fingerprinting. +Absolute gas concentration measurement should remain the role of validated gas sensors. \section{References and Starting Points}