Experimental study on the effect of pressure on single and two stage combustion of decomposed ammonia (NH3-H2-N2) blends over a swirl stabilized burner

Ammonia (NH3) is a practical hydrogen vector for gas turbine power generation, but struggles to be deployed commercially due to many unresolved technical and fundamental challenges. This experimental investigation focuses on combustion of fuel blends representatives of various NH3 decomposition (or cracking) ratios in a combustor fitted with a swirl-stabilized burner, exploring pressures ranging from atmospheric to 10 bar. The study presents measurements of flame stability and emissions of NOx and N2O in combustor strategies relevant to both conventional single lean operation and staged with a rich primary zone, as a function of decomposition ratios (DR) and primary zone equivalence ratio. The findings reveal a notable pressure-dependency of nitrogen oxides (NOx) during combustion of ammonia containing fuels. For a fully decomposed mixture (H2 single bondN2 at 75/25 %vol.), NOx emissions increase with increasing pressure. Conversely, when ammonia is present in the fuel, the trend reverses. However, the majority of NOx reduction occurs within a limited range of pressure increase and reaches a plateau thereafter. The transition at which the pressure effect declines depends on other factors, and was seen to occur between 5 and 9bar in the conditions of this study. Notably, NOx levels in flames containing NH3 are significantly higher, rendering the pressure sensitivity on NOx primarily governed by NH3 presence, irrespective of its concentration in the fuel (i.e. DR). Furthermore, the study reveals a non-monotonic relationship between NOx emissions and NH3 concentration in the fuel, peaking at mid-decomposition ratios. All factors tending to weaken flame stability (e.g. increasing fuel NH3 content, approaching lean/rich blow off limits, or increasing burner exit velocity) favour emissions of N2O emissions. As a general trend, it appears that longer residence times, increased pressure, and rich primary zone operation are all parameters limiting NOx formation from all partially decomposed blends of ammonia, but that they only positively add to a certain limit of a few hundred ppm. This NOx plateau level being higher at higher NH3 content in the fuel. Finally, the fuel obtained by perfectly decomposing ammonia appears to be the optimal fuel associating strong flame stability and low NOx propensity, even for the non fully premixed burner type of this study.publishedVersio

Chemical Looping Combustion of wood pellets in a 150 kWth CLC reactor

Carbon-negative solutions have got increased attention in the recent years as being a necessary measure to mitigate climate change and limit the global temperature rise to 2°C. Bio-Energy Carbon Capture and Storage (BECCS) is at present the most mature and the only large-scale technology that can achieve CO2 negative emissions. One attractive option for realising BECCS is by using chemical looping combustion (CLC) technology in combination with sustainable biomass as fuel (bio-CLC). Bio-CLC is a very promising CO2 capture technology because of the potentially low energy penalty and low CO2 capture cost. Bio-CLC pilot scale tests in a 150 kWth CLC reactor system has been carried out using ilmenite as oxygen carrier and whole wood pellets as fuel. The work is part of the project "Negative CO2 Emissions with Chemical Looping Combustion of Biomass", one of three ongoing flagship projects funded by the Nordic Energy Research. Fuel feeding rate was kept stable at a fuel power equivalent to 140 kWth. The operation of the reactor was then nearly auto-thermal, as the only additional heating of the reactor was preheating of the primary air for the air reactor. The minimum oxygen demand was calculated to about 23% and the CO2 capture efficiency varied between 94 – 97%. The specific fuel reactor inventory during the test was 140 – 180 kg/MW. This is low compared to what is used in most other studies and is mainly a consequence of the fuel reactor being a CFB type of reactor, operating close to a fast fluidization mode. Even though significant amount of additional oxygen is needed for full fuel conversion, the results may be considered good bearing in mind the relatively small size, and thus short residence time, of the reactor compared to an industrial scale reactor, and the low-cost oxygen carrier material usedacceptedVersio

Experimental study on high pressure combustion of decomposed ammonia: How can ammonia be best used in a gas turbine?

Hydrogen, a carbon-free fuel, is a challenging gas to transport and store, but that can be solved by producing ammonia, a worldwide commonly distributed chemical. Ideally, ammonia should be used directly on site as a fuel, but it has many combustion shortcomings, with a very low reactivity and a high propensity to generate NOx. Alternatively, ammonia could be decomposed back to a mixture of hydrogen and nitrogen which has better combustion properties, but at the expense of an endothermal reaction. Between these two options, a trade off could be a partial decomposition where the end use fuel is a mixture of ammonia, hydrogen, and nitrogen. We present an experimental study aiming at finding optimal NH3-H2-N2 fuel blends to be used in gas turbines and provide manufacturers with guidelines for their use in retrofit and new combustion applications. The industrial burner considered in this study is a small-scale Siemens burner used in the SGT-750 gas turbine, tested in the SINTEF high pressure combustion facility. The overall behaviour of the burner in terms of stability and emissions is characterized as a function of fuel mixtures corresponding to partial and full decomposition of ammonia. It is found that when ammonia is present in the fuel, the NOx emissions although high can be limited if the primary flame zone is operated fuel rich. Increasing pressure has shown to have a strong and favourable effect on NOx formation. When ammonia is fully decomposed to 75% H2 and 25% N2, the opposite behaviour is observed. In conclusion, either low rate or full decomposition are found to be the better options. Copyright © 2021 by ASME.publishedVersio

Experimental and Numerical Results of a Non-DLE Aeroderivative GT Combustion System Burning Methane-Ammonia Blends at Intermediate Pressures

Ammonia is considered as a practical hydrogen carrier, as it can be stored in liquid form at moderate pressures and temperatures and is commonly produced and transported today. Ammonia could be used directly as a Gas Turbine fuel to replace current hydrocarbon-based fuels, but its low reactivity and propensity to produce high NOx will require major combustor design changes. Alternatively, ammonia can be fully or partially converted back into hydrogen and nitrogen before using it as a fuel with additional equipment and penalty on cycle performance. Another option is to replace only part of the natural gas with ammonia to minimize the changes of combustion properties and hence combustor design. Although this only partially decarbonizes the fuel, it may be a viable intermediate step to reduce the gas turbine footprint in the short term and with minimum hardware changes to the GT. This experimental and numerical study investigates combustion of methane-ammonia blends with a simplified version of the non-DLE Siemens Energy SGT-A35 turbine combustion system (Rich-Quench-Lean system, RQL) at pressures up to 8 [bar] and powers up to 100 [kW]. The effect of ammonia/methane ratios and Primary Zone Equivalence Ratio (PZER) on emissions of NOx, CO and N2O has been investigated for different pressures and power. A pressure exponent has been extracted based on this experimental data to provide an order of magnitude of NOx emissions at engine conditions. To complement these experimental results, a simple Chemical Reactor Network (CRN) has been used to support the experimental results further. The experimental results showed that even small amounts of ammonia in methane result in unacceptably high NOx emissions for all Primary Zone temperatures and pressures investigated. Although increasing pressure reduces NOx emissions (as previously reported), extrapolation to engine conditions showed that the order of magnitude of NOx emissions will remain unacceptably high. It is also shown that flame stability becomes insufficient for fuels containing more than 40–50 [% by vol.] of NH3 as blow out occurred for these fuels. Furthermore, the results showed that N2O emissions are very low for rich Primary Zone Equivalence Ratios and increase approximately exponentially with decreasing equivalence ratios, but remained below 10 [ppm] for cases at higher pressures. Finally, the CRN results reproduced the experimental trends qualitatively well for %NH3 variations but PZ ER variations and absolute values could not be matched for all cases simultaneously without re-tuning of the CRN.Experimental and Numerical Results of a Non-DLE Aeroderivative GT Combustion System Burning Methane-Ammonia Blends at Intermediate PressuresacceptedVersio

Lean burn versus stoichiometric operation with EGR and 3-way catalyst of an engine fueled with natural gas and hydrogen enriched natural gas

Engine tests have been performed on a 9.6 liter spark-ignited engine fueled by natural gas and a mixture of 25/75 hydrogen/natural gas by volume. The scope of the work was to test two strategies for low emissions of harmful gases; lean burn operation and stoichiometric operation with EGR and a three-way catalyst. Most gas engines today, used in city buses, utilize the lean burn approach to achieve low NOx formation and high thermal efficiency. However, the lean burn approach may not be sufficient for future emissions legislation. One way to improve the lean burn strategy is to add hydrogen to the fuel to increase the lean limit and thus reduce the NOx formation without increasing the emissions of HC. Even so, the best commercially available technology for lowemissions of NOx, HC and CO today is stoichiometric operation with a three-way catalyst as used in passenger cars. The drawbacks of stoichiometric operation are low thermal efficiency because of the high pumping work, low possible compression ratio and large heat losses. The recirculation of exhaust gas is one way to reduce these drawbacks and achieve efficiencies that are not much lower than the lean burn technology. The experiments revealed that even with the 25 vol% hydrogen mixture, NOx levels are much higher for the lean burn approach than that of the EGR and catalyst approach for this engine. However, a penalty in brake thermal efficiency has to be accepted for the EGR approach as the thermodynamic conditions are less ideal

Evaluation of CLC as a BECCS technology from tests on woody biomass in an auto-thermal 150-kW pilot unit

In this work, woody biomass is converted by chemical looping combustion (CLC) in the auto-thermally operated 150-kW pilot unit at SINTEF Energy Research in Norway, using ilmenite as an oxygen carrier. The pilot unit consists of two inter-connected circulating fluidized bed reactors, being the air and fuel reactor, respectively. The unit is simplified compared to many other lab and pilot units by not having a carbon stripper. The aim of the present study is to evaluate the main performance parameters when operating a relatively large CLC unit in auto-thermal mode, using a cheap natural mineral, ilmenite, as oxygen carrier. Another aspect with the tests is to verify if the omission of a carbon stripper can provide high enough capture efficiencies for solid fuels as biomass, with a large share of volatiles and a char remnant with high reactivity. As a comparison, tests with petcoke were performed, to assess the effect when using a fuel with a low share of volatiles and slow char conversion. The results imply that CO2 capture efficiencies can be well above 95 % in a larger industrial unit operating on biomass, even without a carbon stripper, but that a carbon stripper is definitely needed for fuels with less volatiles and low char reactivity.Evaluation of CLC as a BECCS technology from tests on woody biomass in an auto-thermal 150-kW pilot unitpublishedVersio

CLC of waste-derived fuel and biomass in a 150-kW pilot unit

In this work, solid recovered waste-derived material (SRF) and biomass are converted in the 150-kWth CLC pilot unit at SINTEF Energy Research in Norway, using ilmenite as an oxygen carrier. The very first tests show that SRF and the biomass reference fuel seem to behave rather similar with respect to fuel reactor gas conversion efficiency and CO2 capture rate. Two tests with biomass and one with SRF have been performed, and they all show high capture rates, about 98 %. FR gas conversion efficiency is also rather similar, though, not higher than about 70%. In earlier biomass tests in the same unit, a FR gas conversion efficiency of about 80 % was achieved, with ilmenite particles of smaller size. What seems to be the largest difference between the two fuels is the FR carbon conversion (i.e., the percentage of carbon fed with the fuel that is leaving the FR in gaseous form), which is significantly lower for the SRF. This means more carbon particulates are leaving the FR in the SRF case, and since the capture rate is high, they are not passed to the AR but seems to leave with the FR exhaust gas in larger amount than for the biomass case. Both fuels used were in the form of pellets with 8 mm diameter. The fuel feed rate was 19.5 kg/h for all cases, equivalent to 103 kW for the biomass case, and 111 kW for the SRF case. Operation with biomass and SRF is attractive since they can both contribute to negative CO2 emissions due to the biogenic carbon content. Combustion of such fuels in standard fluidized bed furnaces is a commercially available technology. This work is a first test to investigate how waste-derived materials will behave in the 150-kWth fluidized bed CLC system at SINTEF Energy Research. The pilot unit does not include a carbon stripper. Another aspect with the tests is therefore to verify if such a system simplification still can provide a high capture rate. For reactive fuels, such as SRF and biomass, the presented tests show that this might be achieved.acceptedVersio

Corrosion performance of different alloys exposed to HTL conditions – a screening study

The corrosion and material evaluation study in (a) water-based simulated black liquor and (b) water-based simulated black liquor at super-critical conditions was successful. The conclusion from the testing program was that the most resistant alloy for the defined conditions is the chromium-rich carbon steel candidate P91 (UNS K91560). This is a type of creep strength-enhanced ferritic alloy, which is steel designed to retain strength at high temperatures. The P91 abbreviation represents the material's chemical composition, that is, 9 wt% chromium (Cr) and 1 wt% molybdenum (Mo). Further work is required to conclude the corrosion resistance for the P91 quality at supercritical conditions in the welded condition and to better understand caustic corrosion mechanisms.publishedVersio

Three-dimensional unsteady numerical simulation of a 150 kWth full-loop chemical looping combustion pilot with biomass as fuel: A hydrodynamic investigation

A hydrodynamic model for a full Chemical Looping Combustion (CLC) unit was established, and simulations performed using the code NEPTUNE_CFD, which is based on an Euler-Euler approach. The unit is a 150 kWth pilot constructed at SINTEF Energy Research. Three-dimensional unsteady numerical simulations were carried out for studying the local and instantaneous behavior inside the system, and its effect on the mean quantities relevant to the process. Solid volume fraction, mass flow rate and phase velocities were computed and analyzed. Comparison with experimental results showed that the pressure was globally well predicted. Two collision models were also investigated. The agitation between neighboring particles was found to be rather uncorrelated; for this reason, the two collision models led to almost the same results. This work represents a hydrodynamic assessment of CLC using biomass as fuel. It allows to provide insight in the flow within the system, with fairly moderate computational costs. © 2022 Elsevier LtdThree-dimensional unsteady numerical simulation of a 150 kWth full-loop chemical looping combustion pilot with biomass as fuel: A hydrodynamic investigationacceptedVersio

Sub-Supercritical Hydrothermal Liquefaction of Lignocellulose and Protein-Containing Biomass

first_pagesettingsOrder Article Reprints Open AccessArticle Sub-Supercritical Hydrothermal Liquefaction of Lignocellulose and Protein-Containing Biomass by Ayaz Ali Shah 1,2,*,Kamaldeep Sharma 1ORCID,Tahir Hussain Seehar 1,2,Saqib Sohail Toor 1,Judit Sandquist 3ORCID,Inge Saanum 3 andThomas Helmer Pedersen 1 1 Department of Energy Technology, Aalborg University, Pontoppidanstræde 111, 9220 Aalborg Øst, Denmark 2 Department of Energy and Environment Engineering, Dawood University of Engineering & Technology, Karachi City 74800, Pakistan 3 SINTEF Energy Research, Sem Sælands vei 11, 7034 Trondheim, Norway * Author to whom correspondence should be addressed. Fuels 2024, 5(1), 75-89; https://doi.org/10.3390/fuels5010005 Submission received: 7 December 2023 / Revised: 15 January 2024 / Accepted: 3 February 2024 / Published: 26 February 2024 Downloadkeyboard_arrow_down Browse Figures Versions Notes Abstract Hydrothermal liquefaction (HTL) is an emerging technology for bio-crude production but faces challenges in determining the optimal temperature for feedstocks depending on the process mode. In this study, three feedstocks—wood, microalgae spirulina (Algae Sp.), and hydrolysis lignin were tested for sub-supercritical HTL at 350 and 400 °C through six batch-scale experiments. An alkali catalyst (K2CO3) was used with wood and hydrolysis lignin, while e (Algae Sp.) was liquefied without catalyst. Further, two experiments were conducted on wood in a Continuous Stirred Tank Reactor (CSTR) at 350 and 400 °C which provided a batch versus continuous comparison. Results showed Algae Sp. had higher bio-crude yields, followed by wood and lignin. The subcritical temperature of 350 °C yielded more biocrude from all feedstocks than the supercritical range. At 400 °C, a significant change occurred in lignin, with the maximum percentage of solids. Additionally, the supercritical state gave higher values for Higher Heating Values (HHVs) and a greater amount of volatile matter in bio-crude. Gas Chromatography and Mass Spectrometry (GCMS) analysis revealed that phenols dominated the composition of bio-crude derived from wood and hydrolysis lignin, whereas Algae Sp. bio-crude exhibited higher percentages of N-heterocycles and amides. The aqueous phase analysis showed a Total Organic Carbon (TOC) range from 7 to 22 g/L, with Algae Sp. displaying a higher Total Nitrogen (TN) content, ranging from 11 to 13 g/L. The pH levels of all samples were consistently within the alkaline range, except for Wood Cont. 350. In a broader perspective, the subcritical temperature range proved to be advantageous for enhancing bio-crude yield, while the supercritical state improved the quality of the bio-crude. Keywords: sub-supercritical HTL; lignocellulosic biomass; microalgae; bio-crudeSub-Supercritical Hydrothermal Liquefaction of Lignocellulose and Protein-Containing BiomasspublishedVersio