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Review

Efficient Combustion of Low Calorific Industrial Gases: Opportunities and Challenges

by
Long Zhang
1,
Shanshan Zhang
1,
Hua Zhou
2,
Zhuyin Ren
2,*,
Hongchuan Wang
3 and
Xiuxun Wang
4
1
School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
2
Institute for Aero Engine, Tsinghua University, Beijing 100084, China
3
Beijing Shenkebosi Thermal Engineering Technology Co., Ltd., Beijing 100084, China
4
Zhonglu International Technology Co., Ltd., Beijing 100084, China
*
Author to whom correspondence should be addressed.
Energies 2022, 15(23), 9224; https://doi.org/10.3390/en15239224
Submission received: 13 November 2022 / Revised: 30 November 2022 / Accepted: 1 December 2022 / Published: 5 December 2022
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Abstract

:
It is becoming increasingly important to develop effective combustion technologies for low calorific industrial gases (LCIG) because of the rising energy demand and environmental issues caused by the extensive use of fossil fuels. In this review, the prospect of these opportunity fuels in China is discussed. Then, the recent fundamental and engineering studies of LCIG combustion are summarized. Specifically, the differences between LCIG and traditional fuels in the composition and fundamental combustion characteristics are described. The state-of-the-art combustion strategies for burning LCIG are reviewed, including porous media combustion, flameless combustion, oxy-fuel combustion, and dual-fuel combustion. The technical challenges and further development needs for efficient LCIG combustion are also discussed.

1. Introduction

The amount of energy consumed globally has risen 17-fold in the past century, and the primary contributors to air pollution are emissions of CO2, CO, SO2, and NOx from the burning of fossil fuels. Currently, fossil fuels with a carbon footprint, e.g., coal, oil, and natural gas, provide 85% of the world’s energy needs [1]. To address the high energy demand in the industrialized world and achieve the goal of carbon neutralization, it is also important to make efficient use of low calorific industrial gases (LCIG), in addition to developing the advanced combustion technology of non-carbon fuels such as hydrogen and ammonia [2,3].
Low calorific industrial gases can be mainly divided into three categories: biogas, syngas, and byproduct gas. Biogas is a clean and sustainable energy source that is often produced from waste treatment, primarily agricultural waste, sewage sludge, and industrial organic waste streams [4]. Methane, hydrogen, carbon dioxide, nitrogen, and hydrogen sulfide are the main components of biogas. Biogas is essentially a low-grade natural gas with a heat value varying from 5.0 to 7.5 kWh/m3, with increased methane concentration, which is the result of organic breakdown in the absence of molecular oxygen. Syngas is often generated by gasifying coal or by reforming biogas, which is mostly made up of hydrogen, carbon monoxide, and carbon dioxide [5]. Since syngas composition varies greatly with different production processes, the low calorific value of syngas varies between 1.0 and 2.6 kWh/m3. Byproduct gas comes from a number of industrial processes in the metallurgy, steel, and chemical industries [6]. Blast furnace gas (BFG), coke oven gas (COG), converter gas, tail gas, cracked gas, pyrolysis gas, and other typical byproduct gases are mostly composed of H2, CO, CH4, N2, and H2O. In comparison to methane, Table 1 shows the typical compositions and key characteristics of low calorific industrial gases. Despite being produced from a variety of processes, low calorific industrial gases share similar characteristics in having the major energy sources of H2, CO, and CH4.
The rapid economic expansion in China has led to drastically rising energy consumption, which has led to a significant increase in the production of low calorific industrial gas sources. There are already more than 30.5 million residential biogas digesters in China, and they produce 12.4 billion m3 of biogas annually, which is equal to 19.0 million tons of standard coal [7]. In China, about 600 downdraft biomass gasification facilities are operational, and can provide syngas to over 209,600 households [8]. There are already more than 260 blast furnaces in China with effective volumes of more than 1000 m3, which generate a significant amount of byproduct gases [9]. In this circumstance, China foresees the great opportunity and challenge in the efficient use of low calorific industrial gases.
Considering that low calorific industrial gases contain many combustible components, it is most common and effective to use these gases by direct combustion in gas turbines, internal combustion engines, and specific burners. For example, Blakey [10], Wright [11] et al. reviewed the application of low calorific industrial gases in gas turbines. Singh [12], Pradhan [13] et al. conducted systematic studies on the utilization of low calorific industrial gases in internal combustion engines. Huang [14], Song [15] et al. adopted specific burners to achieve stable and efficient combustion of low calorific industrial gases. Among a number of issues raised by the dilution of combustible gases with inert components, the most serious challenges involve lower flame temperatures and, consequently, lower burning rates, tighter stability bounds, and lower combustion efficiencies. To facilitate the efficient combustion of low calorific industrial gases, numerous tailored combustion techniques have been developed and used in practice. In accordance with the aforementioned literature, the current study offers up-to-date information on the efficient combustion of low calorific industrial gases.
The following sections will cover the composition and combustion characteristics of LCIG, state-of-the-art combustion strategies of LCIG, and the technical challenges for fuel-flexible stable LCIG combustion.

2. Composition and Combustion Characteristics of LCIG

2.1. Composition Characteristics

The fundamental combustion characteristics of LCIG are quite different from those of traditional gaseous fuels, considering their complexity in the mixture composition. Typical composition ranges of biogas, syngas, coke oven gas, and blast furnace gas are listed in Table 2. As shown, the variable components in biogas are mainly CH4 and CO, with a variation range of about 10%. Combustible components (CH4, H2, CO) in syngas and byproduct gases from different sources vary significantly, and the variation range of H2 can reach 20% at most.
Flame structures, such as flame height and standoff distance, have a positive correlation with the H2 content in LCIG, which contributes to the augmentation of blowoff velocity [16]. CH4 content in LCIG has more effects on the combustion temperature than CO content. Thermal diffusivity is affected by increasing inert content in LCIG, which also lowers the combustion temperature and laminar flame speed [17]. Differences in CH4 content and H2 content in LCIG will cause changes in chemical reaction paths during combustion, and thus affect the ignition delay time and laminar flame speed. For H2-rich LCIG, it has been discovered that the reactions OH + HO2 = H2O + O2 and HO2 + H = OH + OH are crucial. For CH4-rich LCIG, the reactions CH2O + OH = HCO + H2O and CH4 + HO2 = CH3 + H2O2 are crucial [18]. Increasing the H2/CO ratio in LCIG causes an increase in flame length and flame temperature.
Since certain LCIG are highly loaded with components containing sulfur and nitrogen, the direct burning of these LCIG generally results in unacceptable emissions. During the combustion process of LCIG, the pollutant emissions are mainly NOx and CO. Fuel NOx and thermal NOx are the two main causes of NOx emissions. Fuel NOx is produced by the oxidation of nitrogen-containing compounds, such as HCN and NH3, which may be formed during gasification. Thermal NOx is produced in appreciable amounts at high combustion temperatures, when molecular nitrogen in the combustion air is oxidized. The main source of CO emission is from incomplete combustion of LCIG, especially for LCIG with high CO contents.

2.2. Fundamental Combustion Characteristics

Compared with traditional gaseous fuels (CH4 and H2), when burning LCIG, the chemical reaction rate is slower and the chemical reaction intensity is lower, resulting in low combustion efficiency, narrow flammable range, and high combustion instability. As for the fundamental combustion characteristics, the impact of LCIG composition on ignition delay time, flame instability, and laminar and turbulent flame speeds are summarized here. The ignition delay time of low calorific industrial gas is mainly affected by the H2 content in LCIG. Higher H2 content leads to shorter ignition delay time. The ignition delay time of LCIG is also sensitive to the initial temperature and pressure of the LCIG combustion system [19].
Laminar flame speed increases nonlinearly with an increase in H2 concentration in LCIG. Laminar flame speed noticeably increases with equivalence ratio. Flame instability increases with the CO2 concentration in LCIG, but decreases with a decrease in the equivalency ratio. High pressure, high H2 concentration, and low equivalence ratio are the conditions under which the cellular flame self-accelerates. Markstein length and hydrodynamic instability both decrease with a rise in LCIG initial pressure, while the thermal mass diffusion instability has no effect [20]. For autoignition-assisted laminar flame propagation, the scaling laws for H2/CO/CH4 have been developed to characterize the negative temperature coefficient (NTC) behavior, with one branch indicating flame propagation, and the other indicating autoignition-assisted flame propagation [21].
For turbulent flame speed, the ratio of turbulent flame speed to laminar flame speed exhibits a nonlinear declining trend with H2 concentration in LCIG, and the growth rate progressively declines. The influence of turbulence on the flame speed steadily declines as the H2 concentration of LCIG approach 50% [22]. CO concentrations in LCIG have a significant impact on the turbulent flame structure. Reduced turbulent flame speed and enhanced combustion instability result from an increase in CO concentration. These effects increase when the equivalence ratio decreases [23].

3. Combustion Strategies of LCIG

For stable combustion of low calorific industrial gases, the commonly used combustion strategies include porous media combustion, flameless combustion, oxy-fuel combustion, and dual-fuel combustion. Among them, porous medium combustion and flameless combustion increase the flame temperature of LCIG through preheating, and enhance flame stability and combustion efficiency. Oxy-fuel combustion and dual-fuel combustion improve chemical reaction intensity during the LCIG combustion process by changing oxidants and adding high-calorific-value fuels, in order to achieve stable combustion of LCIG. Some representative LCIG combustion strategies are summarized in Table 3.

3.1. Porous Media Combustion

One of the most practical solutions for efficient combustion of LCIG is porous media combustion (PMC) [31]. A porous substance is one that has interconnected spaces that allow combustible gases to readily pass through the medium. As an internally self-organized mechanism of heat recovery, PMC varies significantly from homogeneous flames for the following reasons:
(1)
The complex and diverse inner surface of the porous medium results in efficient heat transfer between the reactant flow and the inert solid;
(2)
Dispersion of the reactant flowing through a porous media promotes effective heat transfer and diffusion between the two phases.
As a result, an internal mechanism for energy recovery is engaged. This procedure makes it possible to have stable combustion under a variety of reactant velocities, oxygen-to-fuel ratios, and power loads. The possibility of NOx and CO generation diminishes as the combustion efficiency increases.
Porous medium burners typically have two major zones. In the first zone, the inflowing combustible mixture is preheated by the hot porous solid matrix, which also serves as a flame arrester. In the second zone, flame is stabilized throughout a wide range of equivalence ratios and inflowing velocities. Varied porous media, such as metal foils, combs, ceramic pebbles, and ceramic foams can produce different porous matrix characteristics [32].
The internal heat recovery of porous medium burners and the high heat capacity of porous matrices are effective methods to overcome the challenges of burning LCIG stably. Extensive research has been conducted on the impacts of operational conditions on stable operating limits, locations of the reaction zone, temperature distribution, and radiation efficiency for PMC. Research shows that combustion stability in PMC is sensitive to LCIG gas components (e.g., H2 content), which relates to changes in certain critical combustion characteristics, primarily laminar flame speed and adiabatic flame temperature [33]. Porous medium burners yield both high power density and low pollutant emissions. However, the influence of porous media materials and shapes, and their distribution on PMC performance is significant, which still necessitates further study. Recently, Al-Hamamre et al. [34] compared SiC and Al2O3 porous structures and discovered that compared to Al2O3, the use of SiC increases the propensity of flashbacks due to its superior radiation characteristics. Some new porous media structures [15] and air preheating methods [35] have also received considerable attention.

3.2. Flameless Combustion

Flameless combustion is defined as a combustion regime for which the flame is invisible, stable, with high combustion efficiency, low temperature gradients, and emits very few pollutants (CO and NOx) [25]. Figure 1 shows the flameless combustion regime as a function of the recirculation rate and temperature of the reactants [26]. As shown, the flameless combustion regime can be distinguished as a regime that operates at high temperatures of diluent, and at relatively low oxygen contents (direct consequences of recirculation/dilution). When the O2 concentration is quite low (12% or below), flameless combustion is possible only if the reactants are above the auto-ignition temperature of the mixture.
In order to achieve a flameless combustion regime, the following three steps are often necessary [27]:
(1)
Produce a stable flame and operate the combustor in the classic flame mode. Continuously increase the combustor temperature until it exceeds the fuel’s auto-ignition temperature;
(2)
Increase the velocity of inflowing reactants, in order to raise the recirculation ratio, which causes the flame front to vanish and the mean temperature of the combustor to drop;
(3)
Diminish the visible and audible flame, and the reaction region spreads towards the downstream of the combustor. The whole combustion chamber enters flameless combustion mode.
With the benefits of flameless combustion, low calorific industrial gases can be efficiently combusted in the flameless mode. Recently, many studies have been reported in this area. Results show that an increase in hydrogen in LCIG increases the high-temperature region of the flameless combustion field. A reduced oxygen level in LCIG facilitates the formation of flameless combustion [28]. Investigations on NOx emission in the flameless combustion of LCIG demonstrate that the NNH path for the low oxygen concentration (3%) and the thermal NOx mechanism for the high oxygen concentration (21%) are the most prevalent NO generation pathways for burning LCIG. When the oxygen concentration is between 3% and 21%, the most prevalent NO generation pathways are the NNH route for hydrogen concentrations up to 5%, the CO2 path for hydrogen concentrations from 5% to 10%, and the thermal NOx mechanism for hydrogen concentrations greater than 10% [36].

3.3. Oxy-Fuel Combustion

The oxy-fuel combustion strategy [37] is a common technology used for the efficient combustion of low calorific industrial gases, and is widely applied in various combustion systems to capture CO2 and control NOx emissions. In this approach, oxygen is used as the oxidant for burning LCIG rather than air. Thus, the laminar flame speed increases, the heat release rate increases, the flammability limit is widened, and NOx emissions are greatly reduced, as shown in Figure 2.
Numerous research has been reported on various aspects of oxy-fuel combustion technology, such as flame temperature, flame instability, the radiation impacts of CO2, and pollutant emissions, and attempts are being made to commercialize this technology through full-scale application [38]. The examination of flame instability diagrams as a function of the inflowing reactant velocities, thermal power, oxygen concentration, and preheated temperatures can reveal the flame instability limits and the stable combustion regimes attained under various oxy-fuel combustion circumstances. To improve thermal efficiency and LCIG flame stability, oxy-fuel combustion with fuel and/or oxygen preheating can be used to recover heat from the flue gas [37]. In this case, the oxy-fuel flame properties are significantly enhanced without using a high-calorific-value fuel. Considering the high flame temperature of oxy-fuel combustion, it is prone to produce a large variety of NOx when burning LCIG, since LCIG usually contains significant N2 content. Using O2/CO2 mixtures as the oxidant for oxy-fuel combustion is an effective solution [38]. It can reduce the flame peak temperature, leading to a dramatic reduction in NOx emissions. In the practical application of oxy-fuel combustion, pure CO2 is difficult to obtain. Considering that the flue gas contains a large amount of CO2 and H2O, the flue gas recirculation (FGR) strategy is widely used in the oxy-fuel combustion of LCIG. Due to the large specific heat of H2O, the flame temperature can be decreased more significantly using wet flue gas. Research results showed that even at a low H2O content in the flue gas, NOx emissions could be decreased by approximately 50%. When oxy-fuel combustion is combined with staged combustion strategy, NOx emissions can be further reduced.

3.4. Dual-Fuel Combustion

Another popular and common way for LCIG combustion is dual-fuel combustion [39]. This method increases the calorific value of the LCIG by adding high-grade fuel, or by burning the inflowing reactant in two stages; a high-calorific-value fuel is used to stabilize the flame during the combustion of LCIG–air mixtures. The high-calorific-value fuels commonly used in dual-fuel combustion include gasoline, diesel, hydrogen, methane, propane, etc.
The heat released In dual-fuel combustion comes from both high-calorific-value fuel and LCIG. On the basis of efficient combustion of LCIG, dual-fuel combustion aims to reduce the use of high-calorific-value fuel. To that end, the appropriate amount of high-calorific-value fuel to be used throughout the whole power range of operating circumstances must be limited in order to decrease specific high-calorific-value fuel consumption, and to provide efficient combustion performance at varying LCIG loads.
In traditional LCIG burners, dual-fuel combustion, on the one hand, supplies high-calorific-value fuel in the pilot stage, forming a stable high temperature zone and ignition source. On the other hand, LCIG is supplied in the main stage, which releases a lot of heat after ignition by the pilot flame. Internal combustion engines are the main subject of recent dual-fuel combustion research. Compression ignition (CI) engines [29,40], spark ignition (SI) engines [41,42], and direct injection spark ignition (DISI) engines [30,43] have been studied experimentally and numerically under LCIG operating circumstances. Such engines’ emissions and performance have been thoroughly examined and evaluated. In CI engines that burn biogas and diethyl ether, for example, biogas with a high methane concentration may successfully substitute diethyl ether and contribute up to 60% of total energy input. In SI engines, hydrogen blending with syngas increases flame speed and decreases distortion, resulting in flames that evolve closer to the spark plug. Blending methane with syngas increases CO and CO2 emissions, while potentially lowering NOx and unburnt hydrocarbon emissions. However, due to the complexity of dual-fuel combustion, more research in this area is still needed. The review papers of Mustafi et al. [44] and Qian et al. [45] provided comprehensive descriptions of the applications of biomass gas in internal engines, including effects of cylinder pressure, air-fuel ratio, engine life, engine knock, and engine emissions.

4. Technical Challenges

Fluctuating compositions and high concentrations of inert components in LCIG provide significant challenges in achieving stable combustion. The main technical challenges faced in the practical applications of burning LCIG include oscillating combustion, pollutant emissions, and system optimization.

4.1. Oscillating Combustion

Influenced by the production process of LCIG, the gas components and gas flow rates in the combustion chamber fluctuate obviously, which is prone to cause oscillating combustion [46,47]. Meanwhile, when there is a fuel switch during the combustion process, this causes dramatic changes in the gas composition, which lead to complex chemical kinetics and combustion instability [48,49].
For example, in the Shiheng steel plant of China, oscillating combustion of a hot air heater burning LCIG may result from the intrinsic interaction between mixing, kinetics and heat loss, inflowing flow rate and calorific value fluctuations, superposition of inflowing reactant fluctuations, and fuel switching, as shown in Figure 3 [48]. For the first type of LCIG oscillating combustion with high H2 concentration, periodic fuel burnout, fuel replenishment, and ignition processes result in an oscillating temperature of 28 K at 20 Hz in an industrial hot air heater, due to the intrinsic interaction between mixing, kinetics, and heat loss. The second type of oscillating combustion phenomena occur from the passive response to inflowing flow rate fluctuations and calorific value fluctuations. The superposed inflowing reactant fluctuations cause the phenomena of fuel burnout, fuel replenishment, and ignition in the third type of LCIG oscillating combustion. The most complicated oscillating combustion phenomenon is caused by the combination of chemical dynamics and abrupt composition variations in the fourth type of LCIG oscillating combustion during the fuel switching process.
Oscillating combustion has adverse effects on the combustion system, causing severe vibration of the combustion system, or increasing the generation of pollutant emissions. Thus, optimizing combustion organization and suppressing oscillating combustion are the core issues in designing LCIG combustion systems. In recent years, many scholars have made great efforts to develop oscillating combustion prediction models of LCIG [49,50,51], and to construct effective active control methods to eliminate or suppress the oscillating combustion in LCIG combustion systems [52,53].
For the oscillating combustion prediction of LCIG, prediction models for specific LCIG combustion scenarios have been proposed. For example, a prediction model using the nonlinear autoregressive moving average method (NARMAX) and neural network method was established to predict the long-term oscillations of LCIG combustion, which had been verified to be effective for the above four types of LCIG oscillating combustion [49,50]. Furthermore, this prediction model was optimized and accelerated using the active subspace method to meet the requirements of the oscillating combustion controller. Another 0D prediction model [51] was constructed to determine the autoignition and combustion mechanisms as well as the components of LCIG during the oscillating combustion of internal engines. For the active control strategy of LCIG, the core purpose of the control system is to ensure the stability of LCIG combustion. Since the H2 content in LCIG resulted in a high flame speed and combustion instability, an automatic controller [52] and an interactive controller [53] were developed to monitor whether the flame spreads to the fuel and air supply pipeline, and blocks flame propagation to restore a stable operating range by blowing the flame out of the supply pipeline without extinguishing the flame, thereby avoiding structural destruction of the fuel burner, and decreasing the time required to shut down the LCIG combustor.
Although there are prediction models and control strategies applicable to LCIG oscillating combustion, their adaptability and robustness are limited under the influence of complex LCIG components and diverse combustion scenarios. Prediction and control models with strong universality still need to be developed in the future, and the effectiveness of these models should be verified and improved in the specific LCIG combustion systems.

4.2. Pollutant Emissions

Previous findings [54] indicated that NOx emission levels in LCIG combustion varied dramatically, and depended a lot on both the specific combustion apparatus and its operating circumstances; in addition, emission levels depended on the quantity of fixed-nitrogen pollutants in the LCIG. The principal sources of CO during the combustion of LCIG were unburned CO in the LCIG and CO products from the incomplete combustion of carbon-containing components in the LCIG.
There appeared to be a trade-off relationship between NOx emissions and CO emissions for burning LCIG [55]. For example, under the dual-fuel combustion of internal engines, the emissions of NOx, CO2, and particulate matter significantly decreased. However, the hydrocarbon and CO emissions may become several times larger. Therefore, in order to ensure efficient combustion of LCIG, limiting the two main pollutant emissions of NOx and CO is a major challenge in the application of LCIG combustion.
A variety of methods can be used to limit the pollutant emissions of LCIG. For CO emissions, dual-fuel combustion can significantly improve the flame temperature to reduce CO emissions [56,57]. For NOx emissions, both in-furnace and post-combustion control methods can be applied [58,59]. Low NOx burners, fuel and/or air staging, flue gas recirculation (FGR), and water dilution are examples of in-furnace control technologies. Selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) are two post-combustion control procedures that require the injection of a reagent such as ammonia or urea. For fuel NOx management, fuel and/or air staging is the most effective approach, which may be achieved by physical staging (supplying oxidant in sections to regulate the local equivalence ratio) or aerodynamic staging (adjusting the space location of fuel and air mixing through jet, swirl, bluff body, etc.). Flue gas recirculation and water dilution are two typical strategies used for limiting peak flame temperatures inside the combustion chamber for thermal NOx reduction. Water dilution takes heat from the flue gas by vaporizing the water, whereas flue gas recirculation decreases peak flame temperatures by blending the reactant mixture with the flue gases.
Despite the above methods to suppress CO and NOx emissions during LCIG combustion, it is still difficult to achieve low pollution emissions under low load conditions, load switching conditions, and parameter fluctuation conditions. Therefore, on the one hand, it is necessary to further develop combustion strategies that consider both high efficiency and low pollutant emissions. On the other hand, reducing the component fluctuation and parameter fluctuation (pressure, flow rate, etc.) of LCIG in the supply process is equally important.

4.3. System Optimization

Considering the complex composition of LCIG and fluctuations in the gas supply pressure and flow rate, the parameters of different LCIG in the previous combustion strategies are significantly different. The combustion parameters of LCIG for specific application scenarios need to be optimized, which often requires a lot of experimental tests or numerical simulations. For example, in porous media combustion of LCIG, the material, size, and distribution of porous media are the core parameters to be optimized, because the flame temperature usually increases first and then decreases with increasing of porosity and pore density. The smaller pore density and the larger porosity of the porous media have great benefits for the quick startup of burning LCIG [60,61].
In view of the differences in thermodynamic characteristics of LCIG, several optimization methods for combustion parameters of LCIG have been proposed, which have important guiding significance for the efficient combustion of LCIG [62,63]. For example, LCIG were burnt in specific burners with a strong swirl nozzle in the incinerator combustion system of Dagang Petrochemical of China, as shown in Figure 4. A combustion state regulation strategy combined with an active subspace method was proposed to identify the optimal regulation path of combustion parameters, in order to increase the combustion state index [62]. In this regulation strategy, the combustion state index of LCIG was calculated with the non-adiabatic perfectly stirred reactor (PSR) model, which could further obtain the complete steady-state solution with the arc-length continuation method in the temperature–residence time parameter space. This combustion state index could quantitatively indicate the stable operation region of burning specific LCIG. The operating parameters of LCIG burners were optimized by another efficient algorithm [63] that adopted the heat recirculation rate and the thermal efficiency as the evaluation indicators, including the equivalent ratio (chemical parameter), Reynolds number (aerodynamic parameter), and gas channel number (geometrical parameter). Recently, other models based on LCIG combustion characteristics [64,65,66] have also been proposed, and demonstrated successful optimization of combustion parameters in burners and engines.
Although there are many strategies for optimizing the geometric structure and operating parameters of LCIG burners, these strategies can only be used to optimize specific combustion systems. When the combustion system considers heat loss and parameter fluctuations, the difficulty of system optimization further increases. At present, a large number of numerical and experimental studies are still needed to promote the development of universal optimization methods for LCIG combustion systems.

5. Conclusions

The large amount of low calorific industrial gas in China offers great opportunities for mitigating the demand on hydrocarbon fuel and reducing extra CO2 emissions. The combustion characteristics of LCIG are sensitive to H2 content, are and significantly different from those of traditional fuels in the following aspects:
(1)
Low combustion efficiency;
(2)
Narrow flammable range;
(3)
High combustion instability.
The efficient combustion strategies of low calorific industrial gas for practical applications are mainly the following:
(1)
Porous media combustion;
(2)
Flameless combustion;
(3)
Oxy-fuel combustion;
(4)
Dual-fuel combustion.
At present, the key technical challenges for the efficient combustion of low calorific industrial gas include the following:
(1)
Mitigation of oscillating combustion;
(2)
Reduction in pollutant emissions;
(3)
Optimization of operating conditions for fuel flexibility.
In order to address the variability in LCIG composition and industrial operating requirements, further studies are needed in the following aspects:
(1)
Fundamental combustion characteristics under the industrial operating conditions;
(2)
In situ adaptive control for burning LCIG;
(3)
Optimization of LCIG combustion during operation.

Author Contributions

Conceptualization, Z.R.; investigation, H.W. and X.W.; writing—original draft preparation, L.Z.; writing—review and editing, S.Z. and H.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China grant number 52025062 and 52106166.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Hajiyev, N.; Abdimomynova, A.; Trukhan, D. Global and local aspects of world energy consumption: Forecast and risks. Proc. Inst. Civ. Eng. Energy 2022, 7, 1–32. [Google Scholar] [CrossRef]
  2. Li, S.; Zhou, H.; Hou, L.; Ren, Z. An analytic model for the effects of nitrogen dilution and premixing characteristics on NOx formation in turbulent premixed hydrogen flames. Int. J. Hydrogen Energy 2017, 42, 7060–7070. [Google Scholar] [CrossRef]
  3. Shu, T.; Xue, Y.; Zhou, Z.; Ren, Z. An experimental study of laminar ammonia/methane/air premixed flames using expanding spherical flames. Fuel 2021, 290, 120003. [Google Scholar] [CrossRef]
  4. Lu, J.; Gao, X. Biogas: Potential, challenges, and perspectives in a changing China. Biomass-Bioenergy 2021, 150, 106127. [Google Scholar] [CrossRef]
  5. Jung, S.; Lee, J.; Moon, D.H.; Kim, K.H.; Kwon, E.E. Upgrading biogas into syngas through dry reforming. Renew. Sustain. Energy Rev. 2021, 143, 110949. [Google Scholar] [CrossRef]
  6. Pena, J.G.C.; de Oliveira, V.B.; Salles, J.L.F. Optimal scheduling of a by-product gas supply system in the iron- and steel-making process under uncertainties. Comput. Chem. Eng. 2019, 125, 351–364. [Google Scholar] [CrossRef]
  7. Jiang, X.; Sommer, S.G.; Christensen, K.V. A review of the biogas industry in China. Energy Policy 2011, 39, 6073–6081. [Google Scholar] [CrossRef]
  8. Yao, X.; Zhao, Z.; Chen, S.; Zhou, H.; Xu, K. Migration and transformation behaviours of ash residues from a typical fixed-bed gasification station for biomass syngas production in China. Energy 2020, 201, 117646. [Google Scholar] [CrossRef]
  9. Zhou, D.; Cheng, S.; Wang, Y.; Jiang, X. The production of large blast furnaces during 2016 and future development of ironmaking in China. Ironmak. Steelmak. 2017, 44, 714–720. [Google Scholar] [CrossRef]
  10. Blakey, S.; Rye, L.; Wilson, C.W. Aviation gas turbine alternative fuels: A review. Proc. Combust. Inst. 2011, 33, 2863–2885. [Google Scholar] [CrossRef]
  11. Wright, I.G.; Gibbons, T.B. Recent developments in gas turbine materials and technology and their implications for syngas firing. Int. J. Hydrogen Energy 2007, 32, 3610–3621. [Google Scholar] [CrossRef]
  12. Singh, P.; Kumar, R.; Sharma, S.; Kumar, S. Effect of engine parameters on the performance of dual-fuel CI engines with producer gas—A review. Energy Fuels 2021, 35, 16377–16402. [Google Scholar] [CrossRef]
  13. Pradhan, A.; Baredar, P.; Kumar, A. Syngas as an alternative fuel used in internal combustion engines: A review. J. Pure Appl. Sci. Technol. 2015, 5, 51–66. [Google Scholar]
  14. Huang, R.; Cheng, L.; Qiu, K.; Zheng, C.; Luo, Z. Low-calorific gas combustion in a two-layer porous burner. Energy Fuels 2016, 30, 1364–1374. [Google Scholar] [CrossRef]
  15. Song, F.; Wen, Z.; Dong, Z.; Wang, E.; Liu, X. Ultra-low calorific gas combustion in a gradually-varied porous burner with annular heat recirculation. Energy 2017, 119, 497–503. [Google Scholar] [CrossRef]
  16. Nurmukan, D.; Chen, T.J.M.; Hung, Y.M.; Ismadi, M.; Chong, C.T.; Tran, M. Enhancement of biogas/air combustion by hydrogen addition at elevated temperatures. Int. J. Energy Res. 2020, 44, 1519–1534. [Google Scholar] [CrossRef]
  17. Chen, J.; Chen, G.; Zhang, A.; Deng, H.; Wen, X.; Wang, F.; Sheng, W.; Zheng, H. Numerical simulation of the effect of CH4/CO concentration on combustion characteristics of low calorific value syngas. ACS Omega 2021, 6, 5754–5763. [Google Scholar] [CrossRef]
  18. de Castro, R.R.; Brequigny, P.; Dufitumukiza, J.P.; Mounaim-Rousselle, C. Laminar flame speed of different syngas compositions for varying thermodynamic conditions. Fuel 2021, 301, 121025. [Google Scholar] [CrossRef]
  19. Benaissa, S.; Adouane, B.; Ali, S.M.; Mohammad, A. Effect of hydrogen addition on the combustion characteristics of premixed biogas/hydrogen-air mixtures. Int. J. Hydrogen Energy 2021, 46, 18661–18677. [Google Scholar] [CrossRef]
  20. Hu, Z.; Wang, Y.; Zhang, J.; Hou, X. Experimental study on self-acceleration characteristics of unstable flame of low calorific value gas blended with hydrogen. Int. J. Hydrogen Energy 2019, 44, 25248–25256. [Google Scholar] [CrossRef]
  21. Gong, X.; Ren, Z. Flame speed scaling in autoignition-assisted freely propagating n-heptane/air flames. Proc. Combust. Inst. 2021, 38, 2153–2161. [Google Scholar] [CrossRef]
  22. Jiang, Y.; Li, G.; Li, H.; Zhang, G.; Lv, J. Study on the effect of hydrogen fraction on the premixed combustion characteristics of syngas/air mixtures. Energy 2020, 200, 117592. [Google Scholar] [CrossRef]
  23. Liu, H.; Wang, Y.; Yu, T.; Liu, H.; Cai, W.; Weng, S. Effect of carbon dioxide content in biogas on turbulent combustion in the combustor of micro gas turbine. Renew. Energy 2020, 147, 1299–1311. [Google Scholar] [CrossRef]
  24. Devi, S.; Sahoo, N.; Muthukumar, P. Effect of combustion zone material on the thermal performance of a biogas-fuelled porous media burner: Experimental studies. Biomass Convers. Biorefin. 2022, 12, 1555–1563. [Google Scholar] [CrossRef]
  25. Ding, C.; Li, P.; Shi, G.; Liu, Y.; Wang, F.; Hu, F.; Huang, S.; Liu, Z. Comparative study between flameless combustion and swirl flame combustion using low preheating temperature air for homogeneous fuel no reduction. Energy Fuels 2021, 35, 8181–8193. [Google Scholar] [CrossRef]
  26. Rao, A.G.; Levy, Y. A new combustion methodology for low emission gas turbine engines. In Proceedings of the 8th HiTACG Conference, Poznan, Poland, 5–7 July 2010; p. 13. [Google Scholar]
  27. Romero-Anton, N.; Huang, X.; Bao, H.; Maitin-Eskudero, K.; Salazar-Herran, E.; Roekaerts, D. New extended eddy dissipation concept model for flameless combustion in furnaces. Combust. Flame 2020, 220, 49–62. [Google Scholar] [CrossRef]
  28. Mardani, A.; Mahalegi, H.K.M. Hydrogen enrichment of methane and syngas for MILD combustion. Int. J. Hydrogen Energy 2019, 44, 9423–9437. [Google Scholar] [CrossRef]
  29. Singh, H.; Mohapatra, S.K. Production of producer gas from sugarcane bagasse and carpentry waste and its sustainable use in a dual fuel CI engine: A performance, emission, and noise investigation. J. Energy Inst. 2018, 91, 43–54. [Google Scholar] [CrossRef]
  30. Hagos, F.Y.; Aziz, A.R.A.; Sulaiman, S.A. Effect of injection timing on combustion, performance and emissions of lean-burn syngas (H2/CO) in spark-ignition direct injection engine. Int. J. Engine Res. 2016, 17, 921–933. [Google Scholar] [CrossRef] [Green Version]
  31. Gentillon, P.; Singh, S.; Lakshman, S.; Zhang, Z.; Paduthol, A.; Ekins-Daukes, N.J.; Chan, Q.N.; Taylor, R.A. A comprehensive experimental characterisation of a novel porous media combustion-based thermophotovoltaic system with controlled emission. Appl. Energy 2019, 254, 113721. [Google Scholar] [CrossRef]
  32. Peng, Q.; Yang, W.; Jiaqiang, E.; Xu, H.; Li, Z.; Tay, K.; Zeng, G.; Yu, W. Investigation on premixed H2/C3H8/air combustion in porous medium combustor for the micro thermophotovoltaic application. Appl. Energy 2020, 260, 114352. [Google Scholar] [CrossRef]
  33. Arrieta, C.E.; García, A.; Yepes, H.A.; Bedoya, I.; Amell, A. An experimental study of combustion stability and emissions characteristics of a surface-stabilized combustion burner fueled with natural gas-syngas blends. J. Phys. Conf. Ser. 2019, 1257, 012018. [Google Scholar] [CrossRef]
  34. Al-Hamamre, Z.; Diezinger, S.; Talukdar, P.; Issendorff, F.V.; Trimis, D. Combustion of low calorific gases from landfills and waste pyrolysis using porous medium burner technology. Process Saf. Environ. Protect. 2006, 84, 297–308. [Google Scholar] [CrossRef]
  35. Wang, G.; Tang, P.; Li, Y.; Xu, J.; Durst, F. Flame front stability of low calorific fuel gas combustion with preheated air in a porous burner. Energy 2018, 170, 1279–1288. [Google Scholar] [CrossRef]
  36. Kim, N.; Kim, Y.; Jaafar, M.N.M.; Rahim, M.R.; Said, M. Effects of hydrogen addition on structure and NO formation of highly co-rich syngas counterflow nonpremixed flames under MILD combustion regime. Int. J. Hydrogen Energy 2021, 46, 10518–10534. [Google Scholar] [CrossRef]
  37. Bâ, A.; Cessou, A.; Marcano, N.; Panier, F.; Tsiava, R.; Cassarino, G.; Ferrand, L.; Honore, D. Oxyfuel combustion and reactants preheating to enhance turbulent flame stabilization of low calorific blast furnace gas. Fuel 2019, 242, 211–221. [Google Scholar] [CrossRef]
  38. Kim, D.; Ahn, H.; Yang, W.; Huh, K.Y.; Lee, Y. Experimental analysis of CO/H2 syngas with NOx and SOx reactions in pressurized oxy-fuel combustion. Energy 2021, 219, 119550. [Google Scholar] [CrossRef]
  39. Berenjestanaki, A.V.; Kawahara, N.; Tsuboi, K.; Tomita, E. Performance, emissions and end-gas autoignition characteristics of premier combustion in a pilot fuel-ignited dual-fuel biogas engine with various CO2 ratios. Fuel 2021, 286, 119330. [Google Scholar] [CrossRef]
  40. Feroskhan, M.; Thangavel, V.; Subramanian, B.; Sankaralingam, R.K.; Ismail, S.; Chaudhary, A. Effects of operating parameters on the performance, emission and combustion indices of a biogas fuelled HCCI engine. Fuel 2021, 298, 120799. [Google Scholar] [CrossRef]
  41. Bui, V.G.; Tran, V.N.; Hoang, A.T.; Bui, T.M.T.; Vo, A.V. A simulation study on a port-injection SI engine fueled with hydroxy-enriched biogas. Energy Sources Part A Recovery Util. Environ. Eff. 2020, 8, 1–17. [Google Scholar] [CrossRef]
  42. Meng, F.; Wang, H.; Ma, Q.; Wang, D.; Lin, J. Emission characteristics of vehicles fueled by hydrogen-enriched syngas under no-load condition. Int. J. Hydrogen Energy 2020, 45, 3840–3845. [Google Scholar] [CrossRef]
  43. Hagos, F.Y.; Aziz, A.R.A.; Sulaiman, S.A. Methane enrichment of syngas (H2/CO) in a spark-ignition direct-injection engine: Combustion, performance and emissions comparison with syngas and compressed natural gas. Energy 2015, 90, 2006–2015. [Google Scholar] [CrossRef] [Green Version]
  44. Mustafi, N.N.; Raine, R.R.; Bansal, P.K. The use of biogas in internal combustion engines: A review. Int. Combust. Engine Div. Spring Tech. Conf. 2006, 42061, 225–234. [Google Scholar] [CrossRef]
  45. Qian, Y.; Sun, S.; Ju, D.; Shan, X.; Lu, X. Review of the state-of-the-art of biogas combustion mechanisms and applications in internal combustion engines. Renew. Sustain. Energy Rev. 2017, 69, 50–58. [Google Scholar] [CrossRef]
  46. Zhang, K.; Lupo, G.; Duwig, C. Investigation of wet combustion instability due to bio-syngas fuel variability. Fuel 2021, 285, 119120. [Google Scholar] [CrossRef]
  47. Lee, M.C.; Yoon, J.; Joo, S.; Kim, J.; Hwang, J.; Yoon, Y. Investigation into the cause of high multi-mode combustion instability of H2/CO/CH4 syngas in a partially premixed gas turbine model combustor. Proc. Combust. Inst. 2015, 35, 3263–3271. [Google Scholar] [CrossRef]
  48. Zhang, L.; Xie, W.; Ren, Z. Combustion stability analysis for non-standard low-calorific gases: Blast furnace gas and coke oven gas. Fuel 2020, 278, 118216. [Google Scholar] [CrossRef]
  49. Zhang, L.; Xue, Y.; Xie, Q.; Ren, Z. Analysis and neural network prediction of combustion stability for industrial gases. Fuel 2021, 287, 119507. [Google Scholar] [CrossRef]
  50. Zhang, L.; Wang, N.; Wei, J.; Ren, Z. Exploring active subspace for neural network prediction of oscillating combustion. Combust. Theory Model. 2021, 25, 570–587. [Google Scholar] [CrossRef]
  51. Yamasaki, Y.; Kaneko, S. Prediction of Ignition and Combustion Development in an HCCI Engine Fueled by Syngas; SAE Technical Paper; No. 2014-32-0002; SAE Technical Paper Series; SAE: Tokyo, Japan, 2014. [Google Scholar] [CrossRef]
  52. Daniele, S.; Jansohn, P.; Boulouchos, K. Flashback propensity of syngas flames at high pressure: Diagnostic and control. Turbo Expo Power Land Sea Air 2010, 43970, 1169–1175. [Google Scholar] [CrossRef]
  53. Jaramillo, J.; Zapata, J.; Bedoya, I.D. Interactive control of combustion stability and operating limits in a biogas-fueled spark ignition engine with high compression ratio. Int. J. Interact. Des. Manuf. 2018, 12, 929–942. [Google Scholar] [CrossRef]
  54. Whitty, K.J.; Zhang, H.R.; Eddings, E.G. Emissions from syngas combustion. Combust. Sci. Technol. 2008, 180, 1117–1136. [Google Scholar] [CrossRef]
  55. Wei, L.; Geng, P. A review on natural gas/diesel dual fuel combustion, emissions and performance. Fuel Proc. Technol. 2016, 142, 264–278. [Google Scholar] [CrossRef]
  56. de Castro, R.R.; Brequigny, P.; Mounaïm-Rousselle, C. A multiparameter investigation of syngas/diesel dual-fuel engine performance and emissions with various syngas compositions. Fuel 2022, 318, 123736. [Google Scholar] [CrossRef]
  57. Prabhu, A.V.; Avinash, A.; Brindhadevi, K.; Pugazhendhi, A. Performance and emission evaluation of dual fuel CI engine using preheated biogas-air mixture. Sci. Total Environ. 2021, 754, 142389. [Google Scholar] [CrossRef] [PubMed]
  58. Mariani, A.; Minale, M.; Unich, A. Use of biogas containing CH4, H2 and CO2 in controlled auto-ignition engines to reduce NOx emissions. Fuel 2021, 301, 120925. [Google Scholar] [CrossRef]
  59. Mehregan, M.; Moghiman, M. A numerical investigation of preheated diluted oxidizer influence on NOx emission of biogas flameless combustion using Taguchi approach. Fuel 2018, 227, 1–5. [Google Scholar] [CrossRef]
  60. Dai, H.; Dai, H.; Zhu, H.; Zhang, B.; He, S.; Wang, Z. Combustion characteristics of a low calorific gas burner with ceramic foam enclosed by alumina pellets. Heat Mass Transf. 2022, 58, 221–231. [Google Scholar] [CrossRef]
  61. Habib, R.; Yadollahi, B.; Saeed, A.; Doranehgard, M.H.; Li, L.K.B.; Karimi, N. Unsteady ultra-lean combustion of methane and biogas in a porous burner—An experimental study. Appl. Therm. Eng. 2021, 182, 116099. [Google Scholar] [CrossRef]
  62. Zhang, L.; Li, S.; Yao, M.; Zhou, H.; Ren, Z. Analysis of operating limits and combustion state regulation for low-calorific value gases in industrial burners. Int. J. Hydrog. Energy 2022, 47, 1306–1318. [Google Scholar] [CrossRef]
  63. Shinoda, M.; Tanaka, R.; Arai, N. Optimization of heat transfer performances of a heat-recirculating ceramic burner during methane/air and low-calorific-fuel/air combustion. Energy Convers. Manag. 2002, 43, 1479–1491. [Google Scholar] [CrossRef]
  64. Al-Attab, K.A.; Zainal, Z.A. Design and performance of a pressurized cyclone combustor (PCC) for high and low heating value gas combustion. Appl. Energy 2011, 88, 1084–1095. [Google Scholar] [CrossRef]
  65. Smith, J.D.; Sreedharan, V.; Landon, M.; Smith, Z.P. Advanced design optimization of combustion equipment for biomass combustion. Renew. Energy 2020, 145, 1597–1607. [Google Scholar] [CrossRef]
  66. Duan, X.; Lai, M.C.; Jansons, M.; Guo, G.; Liu, J. A review of controlling strategies of the ignition timing and combustion phase in homogeneous charge compression ignition (HCCI) engine. Fuel 2021, 285, 119142. [Google Scholar] [CrossRef]
Energies 15 09224 g001 550
Figure 1. Schematic of different combustion regimes.
Figure 1. Schematic of different combustion regimes.
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Figure 2. Effects of oxy-fuel combustion on combustion characteristics. (a) laminar flame speed; (b) adiabatic temperature.
Figure 2. Effects of oxy-fuel combustion on combustion characteristics. (a) laminar flame speed; (b) adiabatic temperature.
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Figure 3. LCIG oscillating combustion in the Shiheng steel plant of China. (a) hot air heater body; (b) LCIG burner; (c) first type oscillation; (d) second type oscillation; (e) third type oscillation; (f) fourth type oscillation. Reprinted from Ref. [48].
Figure 3. LCIG oscillating combustion in the Shiheng steel plant of China. (a) hot air heater body; (b) LCIG burner; (c) first type oscillation; (d) second type oscillation; (e) third type oscillation; (f) fourth type oscillation. Reprinted from Ref. [48].
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Energies 15 09224 g004a 550Energies 15 09224 g004b 550
Figure 4. LCIG oscillating combustion in the Dagang incinerator system of China. (a) LCIG burner; (b) temperature contour from CFD; (c) temperature evolution calculated from PSR; (d) optimal regulation path of combustion parameters. Reprinted from Ref. [62].
Figure 4. LCIG oscillating combustion in the Dagang incinerator system of China. (a) LCIG burner; (b) temperature contour from CFD; (c) temperature evolution calculated from PSR; (d) optimal regulation path of combustion parameters. Reprinted from Ref. [62].
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Table
Table 1. Typical compositions and key characteristics of LCIG compared with methane.
Table 1. Typical compositions and key characteristics of LCIG compared with methane.
FuelMethaneBiogasSyngasCOGBFG
Volume fraction (%)H2//9625
CH410052728/
CO//14623
CO2/4020423
N2/850/49
Calorific Value (kWh/m3)9.945.171.444.750.95
Density (kg/m3)0.671.201.180.381.27
Stoichiometric mixture fraction Zs (/)0.340.480.200.240.88
Ignition delay time at 1200 K (ms)45.5051.900.930.320.15
Laminar flame speed (cm/s)38.2821.8214.8580.078.95
Table
Table 2. Typical composition ranges of LCIG.
Table 2. Typical composition ranges of LCIG.
FuelBiogasSyngasCOGBFG
Volume fraction (%)CH455–658–1220–300–3
H20–135–4550–701–5
CO/20–309–2020–30
CO235–4515–250–515–25
N20–33–51–1160–75
Table
Table 3. Overview of LCIG combustion strategies.
Table 3. Overview of LCIG combustion strategies.
Ref.StrategyFuelOperating ConditionsFindings
[24]Porous media combustionBiogasMaterial: SiC, ZrO2;
Porosity: 10 ppi.		SiC foam offered:
Wider working conditions;
Higher radiation efficiency;
Lower emissions.
[15]Porous media combustionSyngasPorosity: 10–50 ppi;
Heat recirculation.		Gradually varied porous media enlarged the flame stability limits and decreased CO emissions.
[25]Flameless combustionSyngasInlet Reynolds number: 10,000–15,000;
H2 content: 10–80%.		Syngas enriched with H2 in the flameless regime was insensitive to the oxidizer dilution and inlet Reynolds number.
[26]Flameless combustionSyngasH2 content: 0–20%;
O2 content: 3–21%.		H2 enrichment and O2 augmentation influenced the NO emission characteristics and the dominant NO production route.
[27]Oxy-fuel combustionBFGLoad: 25–180 kW;
Preheat temperature: 300–850 K;
O2 content: 10–100%.		Flame instability decreased by reactant preheating, and flame structure was affected by O2 content.
[28]Oxy-fuel combustionSyngasLoad: 15–21 kW;
Pressure: 0–10 barg;
Flue gas recirculation.		Heat flow rate increased by a higher H2O fraction, and radical H had a significant impact on the NOx and SOx emissions.
[29]Dual-fuel combustionBiogasCompression ignition engine;
Compression ratio: 12–18;
Dual fuel: diesel.		Brake power, brake thermal efficiency, and NOx emissions were reduced, and noise increased slightly.
[30]Dual-fuel combustionSyngasDirect injection spark ignition engine;
Engine speed: 1500–2400 r/min;
Dual fuel: CNG.		Late injection of syngas improved combustion performance and emissions. Low calorific value resulted in operational limitations for direct injection system
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Zhang, L.; Zhang, S.; Zhou, H.; Ren, Z.; Wang, H.; Wang, X. Efficient Combustion of Low Calorific Industrial Gases: Opportunities and Challenges. Energies 2022, 15, 9224. https://doi.org/10.3390/en15239224

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Zhang L, Zhang S, Zhou H, Ren Z, Wang H, Wang X. Efficient Combustion of Low Calorific Industrial Gases: Opportunities and Challenges. Energies. 2022; 15(23):9224. https://doi.org/10.3390/en15239224

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Zhang, Long, Shanshan Zhang, Hua Zhou, Zhuyin Ren, Hongchuan Wang, and Xiuxun Wang. 2022. "Efficient Combustion of Low Calorific Industrial Gases: Opportunities and Challenges" Energies 15, no. 23: 9224. https://doi.org/10.3390/en15239224

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