Chemical Recuperation Research Articles

Near-zero carbon emission power generation system enabled by staged coal gasification and chemical recuperation

Generating clean, efficient, and low-carbon electricity from coal is imperative for limiting the global temperature rise to 1.5 °C. This study presents a near-zero-carbon-emission power generation system that utilizes staged coal gasification. The innovation of this system is the division of coal gasification into two stages: intermediate-temperature pyrolysis, followed by high-temperature gasification. This process begins with utilizing waste heat from the exhaust of a gas turbine to drive the partial gasification of coal during pyrolysis. The nongaseous products from this stage are then completely gasified in the gasifier, and chemical recuperation is performed, in which heat from the syngas at the gasifier's outlet preheats the reactants at the inlet and aids in reforming pyrolysis gas. For CO2 capture, an oxyfuel combustion strategy is used. Our system produced net electricity and exergy efficiencies of 43.01 and 47.57 %, respectively, surpassing both pre-combustion CO2 capture systems based on staged coal gasification (improvements of 3.04 and 5.37 %, respectively) and coal-water slurry gasification (improvements of 3.55 and 5.8 %, respectively). Moreover, the carbon emissions from our system are approximately 90 g/kWh lower than those from these systems. Thus, this study offers an environmentally sustainable approach to utilizing coal that may facilitate achieving global environmental goals.

A novel biogas-driven CCHP system based on chemical reinjection

In the process of vaporizing water within the biogas-driven CCHP system based on chemical recuperation, a significant temperature disparity in heat transfer exists, leading to increased irreversible loss, and the methane conversion rate is low because the gas turbine exhaust gas is difficult to drive efficient methane conversion. This paper proposed a novel biogas-driven CCHP system based on chemical reinjection. Through the reinjection of a portion of the exhaust gas into the reactor, a self-thermal reforming reaction process is engineered, leading to a substantial enhancement in methane conversion rate. The heat matching of the heat exchange unit is optimized by the reheat air, and the power generation and cooling capacity of the system are improved. Notably, the electricity and cooling generation of the new system increased by 55.52 kW (6.20 %) and 542.49 kW (101.49 %), respectively, while the exergy efficiency increased by 8.31 %. The study delves into the influence of key parameters on the system thermal performance. During the reforming process, the exhaust gas split ratio has a significant impact on carbon deposition and methane conversion. When the methane is nearly completely converted, there is no significant change in electricity generation of the system. Excessive turbine inlet temperature is found to be unfavorable for improving the exergy efficiency of the new system from a holistic system perspective. Finally, a comprehensive comparison of the thermal performance between the new system and the reference system is conducted under various ambient temperatures. This study offer a new design scheme for the efficient utilization of biogas.

Hydrogen production system with near-zero carbon dioxide emissions enabled by complementary utilization of natural gas and electricity

The complementary utilization of different energy sources is a promising strategy for consuming excess electricity and improving system efficiency. In this study, complementary utilization of electricity and natural gas is proposed for a hydrogen production system based on chemical recuperation. The system uses electrolysis technology to convert excess electricity generated from intermittent and fluctuating renewable energy into green hydrogen. It also utilizes the by-product oxygen for oxy-fuel combustion to achieve near-zero carbon dioxide emissions after subsequent compression, transportation, and storage. The system uses natural gas for steam methane reforming to generate hydrogen. A portion of flue gas generated by the combustor is introduced into the reformer, replacing high-temperature steam for reforming with methane. In addition, the waste heat from the flue gas is introduced into the electrolysis cell to save electricity. Energy and exergy analyses of the proposed and reference systems were performed. The results revealed that the energy and exergy efficiencies of the proposed system are 81.20% and 73.29% at near-zero carbon dioxide emission, representing an improvement of 7.09 and 6.41 percentage points, respectively, compared to the reference system. It also appeared that 98.68% in situ oxygen consumption was achieved. The hydrogen mass flow generated by the proposed system is 33.83 kg/h, which is 8.78% higher than the 30.88 kg/h of the reference system. This study introduces a promising method for developing a hydrogen production system with high efficiency and near-zero carbon dioxide emissions.

Efficient coal-based power generation via optimized supercritical water gasification with chemical recuperation

Supercritical water gasification (SCWG) is promising as a clean coal technology and is an emerging topic of interest in sustainable energy. Here, we introduce a clean and efficient power generation system that optimizes SCWG of coal through chemical recuperation. Central to our approach is the innovative utilization of both exhaust and a portion of the syngas as dual heat sources for gasification, simultaneously producing the requisite supercritical water. This chemical recuperation strategy effectively enhances the transformation of coal chemical energy into syngas. The introduced system achieves power generation and exergy efficiencies of 56.64 and 55.30%, respectively, outperforming those of a baseline system by 8.43 and 8.23%, respectively. This gain is primarily attributed to the irreversible losses in the gasification, air separation, and heat-exchange processes of the introduced system, which were reduced by 8.75, 2.47, and 4.17%, respectively, compared with the corresponding values of the baseline system. In order to elucidate and validate the reduced irreversible losses in the introduced system compared with those in the baseline system, we incorporated the energy utilization diagram methodology into our analysis. In summary, the introduced system represents a pivotal advancement in clean and efficient coal-based power generation and underscores the need for continuous innovation in this sector.

High-efficiency power generation system with CO2 capture based on cascading coal gasification employing chemical recuperation

Coal-based power generation systems combined with CO2 capture can generate clean, efficient, decarbonized electricity and have recently received significant attention. This study proposes a high-efficiency power generation system with CO2 capture using cascading coal gasification coupled with chemical recuperation. The proposed system involves using waste heat from the gas turbine exhaust to start coal pyrolysis, achieving the first stage of chemical recuperative pyrolysis. Pyrolysis products, excluding coal gas (CG), are fed into the gasifier for the second stage of coal gasification. Furthermore, the sensible heat of syngas at the gasifier outlet is sequentially used to preheat the gasification agent and tar, supply heat for CG reforming, and generate steam. The cascading coal gasification and stepwise utilization of thermal energy decrease oxygen consumption during gasification and reduce the proportion of partially oxidized coal. The results indicate that, at a 90% carbon capture rate, the net power generation efficiencies of the proposed and reference systems are 40.26 and 37.58%, with exergy efficiencies of 39.22 and 36.55%, respectively. The improvements in the proposed system primarily stem from its highly efficient coal utilization, which decreased exergy destruction for the gasification process by 43%. These results imply the system may enhance efficient, low-carbon coal use.

Waste heat recovery optimization in ammonia-based gas turbine applications

E-fuels are promising alternatives to fossil fuels in the transition towards zero-emission energy system. In this study, a novel chemical-recuperated and humidified gas turbine concept aiming at the application of e-fuel ammonia is proposed to overcome the technical hitches and exploit the waste heat to enhance the cycle performance. The thermodynamic analysis shows that the highest net electrical efficiency (56.7%) under the design conditions exceeds that of the ammonia-fueled Brayton cycle by 20.6%-points. The chemical recuperation of fuel contributes to the efficiency improvement by 7%-points under dry condition, while steam injection provides 8%-points to 12%-points efficiency increase corresponding to the ammonia decomposition ratio of 5%–96%. A non-monotonic relation between the net electrical efficiency and steam-to-air ratio is found to be the result of the competition between the enthalpy change from to the varied steam and air mass flow rates. Analyzing the flame characteristics in the combustor under the design conditions, we found that conditions with high decomposition ratio (>88%) and high steam-to-air ratio (>0.3) exhibit similar flame speed with that of methane fueled combustor and thus existing designs can be reused. The prediction shows the NOx emission can be restricted when the steam-to-air ratio exceeds 0.4.

Effect of enhanced heat transfer structures on the chemical recuperation process of advanced aero-engine

Regenerative cooling process of advanced aero-engine with endothermic hydrocarbon fuel is a typical chemical recuperation process that always happens in heated cooling channels with severe thermal stratification. In order to study the effect of enhanced heat transfer structures on the heat sink utilization and non-uniform chemical recuperation process, numerical models of cracking hydrocarbon fuel flow in the cooling channel with the micro-rib and dimple embedded in one-step reaction model were built and validated. The results indicate that the dimple and micro-rib could enhance heat transfer but bring drawbacks to the chemical recuperation process especially under higher heat flux due to the nonlinearity of thermal cracking reaction, which mainly happens in the thermal boundary layer and velocity boundary layer. And the micro-rib will cause larger disturbance than dimple because it gives global enhancement on flow mixing between the mainstream and flow near the wall. Besides, increasing micro-rib height and decreasing its width could not change the situation but make it worse although the nonuniformity of heat absorption is remarkably alleviated. Compared with the single micro-rib unit, the periodic micro-rib array has a significantly continuous influence on heat transfer and heat absorption in the chemical recuperation process of cracking hydrocarbon fuel.

Performance investigation of a new cooling, heating and power system with methanol decomposition based chemical recuperation process

A novel combined cooling, heating and power system, which mainly consists of an internal combustion engine power block with the capacity of 500 kWe, a chemical recuperation block, an absorption refrigeration block and a hot water supply block, is proposed to improve the energy conversion efficiency in this work. The high temperature exhaust gas from the internal combustion engine is first used to drive methanol decomposition to produce syngas of CO and H2 via the chemical recuperation, and the produced syngas is fed into the ICE for power generation. The exit exhaust gas flows into a double-effect lithium bromide-water absorption refrigerator, and finally the rest of the gas sensible heat is used to generate hot water for district heating. The temperature of the exhaust gas reduces to approximately 280 °C by the chemical recuperation process, and the temperature difference between the heat resource and the absorption cooling requirement thereby decreases and leads to lower exergy loss. Numerical simulation results indicate that the developed combined cooling, heating and power system achieves favorable thermodynamic performances, and the matching characteristics between energy production and energy demand can be enhanced. The system annual averaged energy efficiency is increased to 58.05%, and the methanol consumption is reduced to 842.54 tons/year with an annual primary energy saving ratio of 9.75%. Additionally, the system achieves lower annual total cost, i.e., 538.95 k$. The research findings provide a promising method to improve the performances of the combined cooling, heating and power system.

Solar-clean fuel distributed energy system with solar thermochemistry and chemical recuperation

A new solar-hybrid fuel-fired distributed energy system incorporating thermochemical reaction driven by mid- and low-temperature solar heat and exhaust heat is proposed, for increased solar energy utilization and exhaust heat recovery efficiency. Solar energy is upgraded to syngas (H2 and CO) chemical energy via the solar thermochemical process of the methanol decomposition reaction, and the syngas drives the internal combustion engine to output power. Some of the exhaust heat is stored and drives the methanol decomposition reaction to supplement the syngas via the chemical recuperation process, enhancing the exergy efficiency of the exhaust heat recovery. The overall energy efficiency and net efficiency of solar energy to electricity conversion are improved by integrating solar thermochemistry and chemical recuperation, and excellent off-design thermodynamic performance under varying user loads and solar irradiation levels is achieved. The overall energy efficiency, exergy efficiency, and net solar-energy-to-electricity efficiency reach 80.55%, 42.18% and 24.66%, respectively. These research findings indicate that the proposed system embodies an efficient and stable approach towards utilization of solar energy and clean fuel in distributed energy systems.

Thermodynamic analysis of a CCHP system integrated a chemical recuperation process of methanol decomposition

A novel combined cooling, heating and power (CCHP) system is proposed in this work, which mainly consists of an internal combustion engine (ICE) power block, a chemical recuperation block, an absorption refrigeration block and a hot water supply block. The high temperature exhaust gas from the ICE (500 kWe) is firstly used for driving the methanol decomposition to produce syngas of CO and H2 via the chemical recuperation, the produced syngas is input into the ICE for power generation. The exit exhaust gas flows into the water/lithium bromide absorption refrigerator, finally the rest sensible heat of the gas is used for generating the hot water for domestic use or district heating. The system thermodynamic performance evaluation is implemented. The results indicate that the power, cooling and heat of the system under the design condition are 500 kW, 203.4 kW and 255.36 kW, respectively. Correspondingly, the system energy and the exergy efficiencies reach to 78.54% and 45.59%, respectively. Compared with the scheme of directly combusting the methanol for the CCHP, the generated cooling energy is decreased to 203.4 kW from 477.76 kW, while the electric efficiency is improved to 40.98% from 34.21%. Moreover, the required methanol consumption rate is reduced by 16.54%, the exergy losses within the fuel combustion and refrigeration process are decreased evidently. The research findings provide a promising method for improving the performances of the CCHP system.

Performance investigation of a new solar-hybrid fuel-fired distributed energy system integrated with a thermochemical process

A new solar-hybrid fuel-fired distributed energy system integrated with a thermochemical reaction driven by mid-and-low solar thermal energy and exhaust heat is proposed. The methanol is decomposed into the syngas (H2 and CO) through the solar thermochemical receivers/reactors, and the syngas drives an internal combustion engine to output power. Then a part of the exhaust heat is recovered and drives the methanol decomposition reaction to supply the syngas via the chemical recuperation process. With the combination of the solar thermochemical and chemical recuperation process, the solar energy and exhaust heat is utilized effectively. The thermodynamic performances of the proposed system are investigated, and the overall energy efficiency and net solar to electricity efficiency on the design condition reaches to 80.55% and 24.66%, respectively. The promising results provide an efficient and stable utilization approach of the solar energy and clean fuel in distributed energy systems.

Performance investigation of a new distributed energy system integrated a solar thermochemical process with chemical recuperation

A new distributed energy system that integrates a solar thermochemical process with chemical recuperation cycle is proposed. The methanol is converted into synthesis fuel through the endothermic decomposition reaction using the mid-and-low temperature solar energy in solar receivers/reactors, and the solar thermal energy is upgraded into the chemical energy of the synthesis fuel. The synthesis fuel releases its chemical energy in a micro gas turbine to drive a distributed energy system to output cooling, heating and power. A part of the flue heat from the synthesis fuel is stored and drives the methanol decomposition in a fixed bed reactor to replenish the synthesis fuel. Energy analysis and exergy analysis are implemented to evaluate the thermodynamics performances of the proposed system. Results indicate that the proposed system achieves a primary energy ratio of 75.42%, and the net efficiency of solar to electricity is 23.26% on the design condition. Due to the interaction of the thermochemical process and the energy storage, the power generation is insensitive to the variations of solar radiations, and has a good performance under varying user's load demands. The promising results can provide an efficient and stable utilization approach of the solar energy in distributed energy systems.

Feasibility Study of Biogas Reforming To Improve Energy Efficiency and To Reduce Nitrogen Oxide Emissions

The goal of this research was to determine the feasibility of employing the catalytic steam reforming of biogas to increase its energy content by converting the methane it contains into a hydrogen-rich syngas mixture and using this reformate product intermixed with raw biogas in a lean-burn gas engine in order to enhance combustion stability and to reduce NOX emissions. The field-testing component of the project involved catalytically reforming a side stream of biomethane from a landfill gas collection system at a California landfill via a waste energy chemical recuperation process, in which waste heat from a gas engine was used to promote the reforming reaction of biogas. In the study, the total flow of raw biogas diverted to the engine remained constant. A fraction of that biogas was, however, separated and directed to the aforementioned catalytic reactor. The reformer exit stream was then dried, blended with the remaining biogas, and burned in an internal combustion engine to produce electricity. When ...

Effect of channel aspect ratio on chemical recuperation process in advanced aeroengines

The working process of an advanced aeroengine such as scramjet with endothermic hydrocarbon fuel cooling is a chemical recuperative cycle. The design of cooling channel in terms of engine real working conditions is very important for the chemical recuperation process. To study the effects of channel aspect ratio (AR) on chemical recuperation process of advanced aeroengines, three dimensional model of pyrolysis coolant flow inside asymmetrical rectangular cooling channels with fins is introduced and validated through experiments. Cases when AR varies from 1 to 8 are carried out. In the pyrolysis zone of the cooling channel, decreasing the channel aspect ratio can reduce the temperature difference and non-uniformity of fuel conversion in the channel cross section, and it can also increase the final conversion and corresponding chemical heat absorption. A small channel aspect ratio is beneficial for the chemical recuperation process and can guarantee the engine cooling performance in the pyrolysis zone of the cooling channel.

Analysis of energy cascade utilization in a chemically recuperated scramjet with indirect combustion

The working process of scramjet with regenerative cooling, which was actually the chemical recuperation process, was analyzed in view of energy cascade utilization. The indirect combustion was realized through pyrolysis reaction of fuel. The relative yields of thermal exergy obtained by indirect combustion have been predicted both assuming an ideal pyrolysis reaction and using the experimental results of thermal pyrolysis of n-decane. The results showed that the influence mechanism of regenerative cooling improved the scramjet engine performance by the energy cascade utilization, and the combustion process was supposed to be designed with the cooling process together to utilize the chemical energy of fuel in a more effective way. A maximum value of 11% of the relative yield was obtained with the ideal pyrolysis reaction while a value less than 3% existed in the thermal pyrolysis experiments because of the domination of chemical kinetics rather than chemical thermodynamics in the real experiments. In spite of the difference between the ideal and the present experimental results, the indirect combustion was prospective to achieve a better energy cascade utilization in a chemically recuperated scramjet if the pyrolysis reaction was further optimized. The results in this paper were beneficial for the performance optimization of a regenerative cooling scramjet.

Thermal behavior in the cracking reaction zone of scramjet cooling channels at different channel aspect ratios

To study the thermal behavior in the cracking reaction zone of regeneratively cooled scramjet cooling channels at different aspect ratios, 3-D model of fuel flow in terms of the fuel's real properties and cracking reaction is built and validated through experiments. The whole cooling channel is divided into non-cracking and cracking reaction zones. Only the cracking reaction zone is studied in this article. The simulation results indicate that the fuel conversion presents a similar distribution with temperature because the fuel conversion in scramjet cooling channels is co-decided by the temperature and velocity but the temperature plays the dominate role. For the cases given in this paper, increasing the channel aspect ratio will increase the pressure drop and it is not beneficial for reducing the wall temperature because of the much severer thermal stratification, larger conversion non-uniformity, the corresponding M-shape velocity profile which will cause local heat transfer deterioration and the decreased chemical heat absorption. And the decreased chemical heat absorption caused by stronger temperature and conversion non-uniformities is bad for the utilization of chemical heat sink, chemical recuperation process and the ignition performance.

Low Ni-Containing Anodes Using Titanate-Based Perovskites for Methane Direct Internal Reforming Power Generation

Direct internal reforming SOFCs (DIR-SOFCs), which directly utilize hydrocarbons as fuels in the anode, can achieve high power generation efficiency due to chemical recuperation of the anodic reaction heat by endothermic reforming reactions. DIR-SOFCs often suffer from carbon deposition on the anode and the resultant severe degradation of power generation performance and stability [1]. Nickel contained in SOFC anodes as an electronic conductor acts as catalytic sites for carbon decomposition in the first step of hydrocarbon fuel conversion. Accordingly, these Ni-related issues can be lessened by reducing the Ni content in the anode. In this study titanate-based Ni-cermet anodes such as Ni-LaxSr1-xTiO3+ d (LST) have been investigated as an alternative anode to conventional Ni-YSZ cermets. LST is a mixed ionic and electronic conducting material with a relatively high electronic conductivity of the order of 10 S/cm2[2]. Ni-LST anodes were fabricated by a conventional method using a ball mill and by an impregnation method, and the stability as well as tolerance to carbon deposition of the anodes were evaluated. Titanate-based perovskites ware prepared via Pechini method. A desired amount of the respective nitrates and acetates were mixed with titanium isopropoxide and citric acid, and then dissolved in ethylene glycol. The mixture was heated to 150ºC on a hot stirrer to complete the polymerization of the mixture. The resultant powder was calcined in air at 800ºC for 3 h to form a perovskite oxide. The obtained powders were mixed with NiO particles at a desired ratio, and ball-milled for 24 h, followed by calcination at 1200°C for 5 h in air. The thus prepared cermets were pulverized into powder, and then mixed with polyethylene glycol to form slurry, with which an YSZ disk of 20 mm in diameter and 0.5 mm in thickness was painted in a circular shape of 6 mmφ as an anode using a screen. Then the disk was calcined at a desired temperature for 5 h in air. In addition, Ni cermets were prepared by an impregnation method. LST powders prepared by the Pechini method were impregnated with an aqueous solution of nickel nitrate on a steam bath at 80°C, dried, and then calcined at 1000 ºC in air for 2 h. Thus obtained Ni-LST powder was used to prepare the anode in the same manner as conventional cermets. Current-voltage characteristics of the anode was evaluated at 1000 ºC by feeding humidified H2 and dry O2 to anode and cathode, respectively, at 100 ml/min. Direct internal reforming power generation performance was measured by feeding steam-to-carbon ratio of 0.1 under constant current load of 200 mA/cm2. The durability of the cells was evaluated by AC impedance spectra measured under open circuit condition at 1000 ºC with a Princeton VersaSTAT3 in humidified H2 feed before and after the power generation at S/C = 0.1. Figure 1 shows current-voltage characteristics of SOFCs with Ni-LST and Ni-YSZ anodes prepared by the ball-mill and impregnation methods. The power generation characteristics of 60wt%Ni-LST prepared by the ball-mill method was slightly lower than that of 60wt%Ni-YSZ by the ball-mill method, but still high performance was observed over the 60wt%Ni-LST. On the other hand, when the nickel content was decreased to 40wt% in Ni-YSZ by the ball-mill, a significant deterioration of power generation characteristics was observed over the Ni-YSZ anode, while Ni-LST prepared by the impregnation method maintained power generation performance despite the low Ni content of 10wt%. The durability of 60wt%Ni-LST by the ball-mill method and 10wt%Ni-LST by the impregnation method was evaluated by feeding a steam-methane mixture at S/C = 0.1 at 1000 ºC under a constant current load of 200 mA/cm2. A gradual decrease in the terminal voltage appeared for 60wt%Ni-LST anode, and a large increase in the impedance was found on the impedance spectra after CH4/H2O direct reforming power generation. In contrast, 10wt%Ni-LST by the impregnation method exhibited a stable power generation characteristics under the low S/C of 0.1 and constant current load of 200 mA/cm2. The impedance became slightly smaller after the power generation.

Thermal management of fuel in advanced aeroengine in view of chemical recuperation

Advanced aeroengine with endothermic hydrocarbon fuel cooling works as chemical recuperative cycle. In order to study the thermal management of fuel in view of chemical recuperation, models of flowing cracked hydrocarbon fuel inside engine cooling channels are developed and validated. Based on 1-D model, different methods are put forwarded to control the chemical recuperation effectiveness and effective residence time is defined to distinguish global methods and local methods. The control of fuel mass flow rate or height of cooling channel can be regarded as global methods, while the control of operating pressure can be considered as a local method. The efficiency of the global method is limited by the allowable wall temperature. In contrast, the local method can both control the chemical recuperation effectiveness and improve the heat transfer performance. Based on the multiple dimensional models, conclusions got from the 1-D model can be modified and extended. The results of multiple dimensional models show that 3-D phenomena have significant effects on the chemical recuperation effectiveness. Nonuniformities of temperature and conversion caused by the 3-D phenomena are bad for improving the chemical recuperation effectiveness. Reduction of the cooling channel width is good for improving the conversion and the chemical recuperation effectiveness.

High-efficiency Power Generation System improved by Exhaust Heat Recovery using Chemical Reaction—Innovative Approach to Natural Gas Utilization by Chemical Recuperation

High-efficiency Power Generation System improved by Exhaust Heat Recovery using Chemical Reaction—Innovative Approach to Natural Gas Utilization by Chemical Recuperation

A technical and financial analysis of two recuperated, reciprocating engine driven power plants. Part 1: Thermodynamic analysis

This paper is the first of a two part study that analyses the technical and financial performance of particular, recuperated engine systems. This first paper presents a thermodynamic study of two systems. The first system involves the chemical recuperation of a reciprocating, spark ignited, internal combustion engine using only the waste heat of the engine to power a steam–methane reformer. The performance of this system is evaluated for different coolant loads and steam–methane ratios. The second system is a so-called ’hybrid’ in which not only the waste heat of the engine is used, but also a secondary heat source – the combustion of biomass. The effects of the reformer’s temperature and the steam–methane ratio on the system performance are analysed.These analyses show that the potential efficiency improvement obtained when using only the engine waste heat to power the recuperation is marginal. However, results for the hybrid show that although the overall efficiency of the plant, defined in terms of the energy from both the methane and biomass, is similar to that of the conventional, methane fuelled engine, the efficiency of the conversion of the biomass fuel energy to work output appears to be higher than for other biomass fuelled technologies currently in use. Further, in the ideal limit of a fully renewable biomass fuel, the burning of biomass does not contribute to the net CO2 emissions, and the CO2 emission reduction for this second plant can be considerable. Indeed, its implementation on larger internal combustion engine power plants, which have efficiencies of around 45–50%, could result in CO2 emissions that are as much as 10–20% lower than typical natural gas combined cycle (NGCC) power stations. This appears to be a significant result, since NGCCs are commonly considered to have the lowest CO2 emissions of all forms of fossil fuelled, power generation currently in use.