Lower Heating Value Basis Research Articles

Process Analysis of Chemical Looping Gasification of Biomass for Fischer–Tropsch Crude Production with Net-Negative CO2 Emissions: Part 1

Large-scale biofuel production plants require an efficient gasification process that generates syngas of high quality (with minimal gas contaminants and inert gases) to minimize the extent of the syngas cleaning processes required for liquid biofuel production. This work presents process modeling of the chemical looping gasification (CLG) process for syngas production. The CLG process is integrated with a Fischer–Tropsch synthesis (FTS) process to produce Fischer–Tropsch (FT) crude with net-negative CO2 emissions, enabling process and system-level analyses of this novel biomass-to-liquid process. CLG resembles indirect gasification in an interconnected circulating fluidized bed reactor, where instead of inert bed material, a solid-oxygen carrier, such as mineral ores rich in iron or manganese oxides, is used. The oxygen carrier particles undergo oxidation and reduction in the air reactor and fuel reactor, respectively, thereby providing heat and oxygen for gasification. This work uses data from CLG experiments performed with steel converter slag as the oxygen carrier and investigates its potential when integrated with different downstream gas cleaning trains and the subsequent fuel synthesis process with the primary objective of quantifying and evaluating the performance of the integrated CLG–FT process plant. Syngas with a high energy content of 12 MJ/Nm3 (lower heating value basis) is predicted with a cold gas efficiency of 73%. CO2/CO ratios, higher than indirect biomass gasification, are also predicted in the raw syngas produced; thus, there exists an opportunity to capture biogenic CO2 with a relatively lower energy penalty in the subsequent gas cleaning stages. This work quantifies other key performance indicators, such as heat recovery potential, negative CO2 emission capacity, and FT crude production efficiency of the CLG–FT plant. A 100 MWth CLG plant produces roughly 677–696 barrels per day of FT crude, with net-negative emissions of roughly 180 kilotonnes of CO2 annually.

Thermochemical Recuperation to Enable Efficient Ammonia-Diesel Dual-Fuel Combustion in a Compression Ignition Engine

A thermochemical recuperation (TCR) reactor was developed and experimentally evaluated with the objective to improve dual-fuel diesel–ammonia compression ignition engines. The novel system simultaneously decomposed ammonia into a hydrogen-containing mixture to allow high diesel fuel replacement ratios and oxidized unburned ammonia emissions in the exhaust, overcoming two key shortcomings of ammonia combustion in engines from the previous literature. In the experimental work, a multi-cylinder compression ignition engine was operated in dual-fuel mode using intake-fumigated ammonia and hydrogen mixtures as the secondary fuel. A full-scale catalytic TCR reactor was constructed and generated the fuel used in the engine experiments. The results show that up to 55% of the total fuel energy was provided by ammonia on a lower heating value basis. Overall engine brake thermal efficiency increased for modes with a high exhaust temperature where ammonia decomposition conversion in the TCR reactor was high but decreased for all other modes due to poor combustion efficiency. Hydrocarbon and soot emissions were shown to increase with the replacement ratio for all modes due to lower combustion temperatures and in-cylinder oxidation processes in the late part of heat release. Engine-out oxides of nitrogen (NOx) emissions decreased with increasing diesel replacement levels for all engine modes. A higher concentration of unburned ammonia was measured in the exhaust with increasing replacement ratios. This unburned ammonia predominantly oxidized to NOx species over the oxidation catalyst used within the TCR reactor. Ammonia substitution thus increased post-TCR reactor ammonia and NOx emissions in this work. The results show, however, that engine-out NH3-to-NOx ratios were suitable for passive selective catalytic reduction, thus demonstrating that both ammonia and NOx from the engine could be readily converted to N2 if the appropriate catalyst were used in the TCR reactor.

Numerical Study on Nitric Oxide Production of Moderate or Intense Low-Oxygen Dilution Combustion Using Ammonia and City Gas

Ammonia (NH3) is attracting attention as a carbon-free fuel that does not emit carbon dioxide, but there is concern that a large amount of nitrogen oxides is emitted during its combustion. The mixtures of NH3 and city gas are used as fuels, and the effectiveness of Moderate or Intense Low-oxygen Dilution (MILD) combustion to reduce nitric oxide (NO) emissions is investigated through zero-dimensional and three-dimensional numerical simulations for various NH3 concentrations of the fuels at the lower heating value basis, ENH3. The zero-dimensional numerical simulations show that NO emissions reach their maximum value for ENH3 = 20–40%, and that dilution of the fuel and oxidizer by exhaust gas recirculation reduces NO emissions. On the other hand, the three-dimensional numerical simulations of an actual furnace show that MILD combustion is valid for reducing NO emissions for ENH3 = 0%, 20% and 100%. For burner design, the nozzle diameters used for the oxidizer, D, and the distance between the fuel and the oxidizer nozzles, L, are important parameters. For ENH3 = 20%, a 0.39-fold reduction in D and a 2.5-fold increase in L make the NO emissions 56% and 74%, respectively.

Bark as feedstock for dual fluidized bed gasifiers-Operability, efficiency, and economics

The demand for biofuels and biochemicals is expected to increase in the future, which will in turn increase the demand for biomass feedstock. Large gasification plants fueled with biomass feedstock are likely to be a key enabling technology in a resource-efficient, bio-based economy. Furthermore, the costs for producing biofuels and biochemicals in such plants could potentially be decreased by utilizing inexpensive low-grade residual biomass as feedstock. This study investigates the usage of shredded tree bark as a feedstock for the production of biomethane in the GoBiGas demonstration plant in Gothenburg, Sweden, based on a 32 MWth industrial dual fluidized bed gasification unit. The plant was operated with bark feedstock for 12 000 hours during the period 2014 to 2018. Data from the measurement campaign were processed using a stochastic approach to establish the plant's mass and energy balances, which were then compared with operation of the plant with wood pellets. For this comparison, an extrapolation algorithm was developed to predict plant performance using bark dried to the same moisture content as wood pellets, ie, 8%w.b. Plant operation with bark feedstock was evaluated for operability, efficiency, and feedstock-related cost. The gas quality achieved during the test period was similar to that obtained for operation with wood pellets. Furthermore, no significant ash sintering or agglomeration problems were observed more than 750 hours of operation. The calculated biomass-to-biomethane efficiency is 43% to 47% (lower heating value basis) for operation with wet bark. However, the predicted biomass-to-biomethane efficiency can be increased to 55%–65% for operation with bark feedstock dried to 8% moisture content, with corresponding feedstock costs in the range of 24.2 to 32.7 EUR/MWh; ie, a cost reduction of about 40% compared with wood pellets.

Fuel Cell Electric Vehicle‐to‐Grid: Experimental Feasibility and Operational Performance as Balancing Power Plant

AbstractThe world's future energy supply will include intermittent renewable sources, such as solar and wind power. To guarantee reliability of supply, fast‐reacting, dispatchable and renewable back‐up power plants are required. One promising alternative is parked and grid‐connected hydrogen‐powered fuel cell electric vehicles (FCEVs) in “Vehicle‐to‐Grid“ systems. We modified a commercial FCEV and installed an external 9.5 kW three‐phase alternating current (AC) grid connection. Our experimental verification of this set‐up shows that FCEVs can be used for mobility as well as generating power when parked. Our experimental results demonstrate that present‐day grid‐connected FCEVs can respond to high load gradients in the range of –760 % s−1 to + 730 % s−1, due to the parallel connection of the high voltage battery and the fuel cell stack. Virtual power plants composed of multiple grid‐connected FCEVs could perform higher power gradients than existing fast‐reacting thermal power plants with typical power gradients of 1.67 % s−1. Hydrogen consumption in 9.5 kW AC grid‐connected mode was 0.55 kg h−1, resulting in a Tank‐To‐Grid‐AC efficiency of 43% on a higher heating value basis (51 % on a lower heating value basis). Direct current to alternating current efficiency was 95 %.

Techno-Economic Analysis of a Carbon Capture Chemical Looping Combustion Power Plant

High energy penalty and cost are major obstacles in the widespread use of CO2 capture techniques for reducing CO2 emissions. Chemical looping combustion (CLC) is an innovative means of achieving CO2 capture with less cost and low energy penalty. This paper conducts a detailed techno-economic analysis of a natural gas-fired CLC-based power plant. The power plant capacity is 1000 MWth gross power on a lower heating value basis. The analysis was done using Aspen Plus. The cost analysis was done by considering the plant location to be in the United Arab Emirates. The plant performance was analyzed by using the cost of equipment, cost of electricity, payback period, and the cost of capture. The performance of the CLC system was also compared with a conventional natural gas combined cycle plant of the same capacity integrated with post combustion CO2 capture technology. The analysis shows that the CLC system had a plant efficiency of 55.6%, electricity cost of 5.5 cents/kWh, payback time of 3.77 years, and the CO2 capture cost of $27.5/ton. In comparison, a similar natural gas combined cycle (NGCC) power plant with CO2 capture had an efficiency of 50.6%, cost of electricity of 6.1 cents/kWh, payback period of 4.57 years, and the capture cost of $42.9/ton. This analysis shows the economic advantage of the CLC integrated power plants.

China’s national demonstration project achieves around 50% net efficiency with 600 °C class materials

The bottlenecks in developing high-efficiency ultra-super critical (USC) coal power technology are analyzed within the context of the growing pressure on the coal power industry to reduce carbon dioxide (CO2) emissions. To meet these demands, further improving the annual average operating efficiency of coal power is essential. A cross-compound double reheat unit design characterized by an elevated and conventional turbine layout is proposed in this paper. This new design can greatly shorten the length of expensive high-temperature piping required, significantly cut piping costs as well as reducing pressure drops and heat losses, resulting in a much higher efficiency and performance-price ratio than conventional double reheat design. The engineering study demonstrates the feasibility and advantages of this design. Now this new design is being implemented on Pingshan Phase II Project as a demonstration coal power unit in China. Despite the new turbine arrangement, Pingshan Phase II Project also adopts a series of energy saving, environmental protection, efficiency preservation and safety technologies, of which some have already gained success in Shanghai Waigaoqiao No. 3 Power Plant. Based on the new design and further optimization, the unit net efficiency of Pingshan Phase II is expected to achieve 49.8% under rated conditions on a lower heating value (LHV) basis. Combined with a series of innovative technologies that can keep the efficiency from decreasing under operational conditions, the annual average net efficiency can achieve 48.8% on LHV basis. This efficiency level is high enough to meet the strict CO2 emission standard proposed by United States Environment Protection Agency (U.S. EPA) based on the Pittsburgh #8 bituminous coal, showing significant potential for reducing CO2 emissions. A series of low-energy-consumption and even energy-saving pollutants removal technologies are also be applied on this project to harmonize high efficiency and low emissions.

Parametric study of a direct-fired supercritical carbon dioxide power cycle coupled to coal gasification process

The direct-fired supercritical carbon dioxide power cycle not only has the potential of reaching high efficiency, but also achieves near 100% carbon capture in a more inherent and natural manner. A conceptual flow sheet of the direct-fired supercritical carbon dioxide power cycle that is coupled to the coal gasification process is built in this study. A detailed turbine cooling model is added to better assess the performance of the power plant. To investigate the effect of key cycle variables on the cycle performance and determine potential chances for efficiency improvement, a parametric study is conducted in this paper. The result shows that the turbine inlet temperature and turbine outlet pressure have significant effect on the cycle efficiency while the effect of the turbine inlet pressure is minor. The cycle efficiency is susceptible to the inlet condition of the carbon dioxide pump, which is the weakness of the supercritical carbon dioxide power cycle. The flow sheet and some of the cycle parameters are modified based on the conclusions drawn from the parametric study. The net efficiency of the power plant is calculated to be 38.87% (on lower heating value basis) at a turbine inlet temperature of 1200 °C, while capturing most of the carbon dioxide derived from combustion.

Techno-economic assessment of the by-products contribution from non-catalytic hydrothermal liquefaction of lignocellulose residues

Hydrothermal liquefaction of biomass continues to show promise in experimental and pilot scale tests for carbon partitioning toward desirable multi-phase organic products. Results from a techno-economic investigation are presented for a commercial scale stand-alone plant with primary production of renewable liquid fuels compatible with current transportation infrastructure. The plant feedstock was forest residues and the non-catalytic hydrothermal conditions were set to 330 °C and 210 bar. A sequential flowsheet was developed and simulated on Aspen Plus® that includes pre-treatment, hydrothermal liquefaction, fuel upgrading and residue recovery functional blocks. Different scenarios for the valorization of the liquefaction residue streams are examined to maximize organic recovery and eliminate process waste streams. The highest plant thermal efficiency on lower heating value basis was recorded for the polygeneration of renewable liquid fuels, Bio-char and hydrogen gas at 85.2%. The plant recorded a minimum selling price of 66 € per MWh of co-products. The break-even prices of the co-products under existing market conditions was found to be 1.03 € per kg of gasoline or 2.46 € per kg of hydrogen gas or 51.4 € per MWh of Bio-char.

NGCC post-combustion CO2 capture with Ca/carbonate looping: Efficiency dependency on sorbent properties, capture unit performance and process configuration

This paper evaluates the potential of post-combustion CO2 capture from a natural gas combined cycle (NGCC) through the use of solid sorbents at high temperatures. Experimental deactivation and residual sorption capacity parameters for various sorbents reported in the literature, as well as from own lab, are reviewed and the performance of three different Ca-based sorbents is studied in more detail: natural CaCO3, natural dolomite and synthetic CaO. Results from steady-state simulations of the Ca/carbonate looping unit show how the energy requirement for sorbent regeneration varies with sorbent properties, sorbent make-up ratio, internal heat recuperation and CO2 recirculation temperature. Net electric efficiency for a reference NGCC power plant without CO2 capture is 58.1% on a lower heating value basis and 49.5% for 90% CO2 capture rate with MEA. In comparison, an NGCC combined with looping of synthetic CaO sorbent and an advanced secondary steam cycle reaches a net electric efficiency of 53.1% for a capture rate above 90%. It is concluded that in addition to improved sorbent capacity and stability, heat recuperation in the solid streams between the carbonator and calciner as well as high CO2 recycle temperature are important for obtaining the high overall power plant efficiency.

Exergy-based comparison of indirect and direct biomass gasification technologies within the framework of bio-SNG production

Atmospheric indirect steam-blown and pressurised direct oxygen-blown gasification are the two major technologies discussed for large-scale production of synthetic natural gas from biomass (bio-SNG) by thermochemical conversion. Published system studies of bio-SNG production concepts draw different conclusions about which gasification technology performs best. In this paper, an exergy-based comparison of the two gasification technologies is performed using a simplified gasification reactor model. This approach aims at comparing the two technologies on a common basis without possible bias due to model regression on specific reactor data. The system boundaries include the gasification and gas cleaning step to generate a product gas ready for subsequent synthesis. The major parameter investigated is the delivery pressure of the product gas. Other model parameters include the air-to-fuel ratio for gasification as well as the H2/CO ratio in the product gas. In order to illustrate the thermodynamic limits and sources of efficiency loss, an ideal modelling approach is contrasted with a model accounting for losses in, e.g. the heat recovery and compression operations. The resulting cold-gas efficiencies of the processes are in the range of 0.66–0.84 on a lower heating value basis. Exergy efficiencies for the ideal systems are from 0.79 to 0.84 and in the range of 0.7 to 0.79 for the systems including losses. Pressurised direct gasification benefits from higher delivery pressure of the finished gas product and results in the highest exergy efficiency values. Regarding bio-SNG synthesis however, a higher energetic and exergetic penalty for CO2 removal results in direct gasification exergy efficiency values that are below values for indirect gasification. No significant difference in performance between the technologies can be observed based on the model results, but a challenge identified for process design is efficient heat recovery and cogeneration of electricity for both technologies. Furthermore, direct gasification performance is penalised by incomplete carbon conversion in contrast to performance of indirect gasification concepts.

Small-scale production of synthetic natural gas by allothermal biomass gasification

The gasification of biomass can be coupled to a downstream methanation process that produces synthetic natural gas (SNG). This enables the distribution of bioenergy in the existing natural gas grid. A process model is developed for the small-scale production of SNG with the use of the software package Aspen Plus (Aspen Technology, Inc., Burlington, MA, USA). The gasification is based on an indirect gasifier with a thermal input of 500 kW. The gasification system consists of a fluidized bed reformer and a fluidized bed combustor that are interconnected via heat pipes. The subsequent methanation is modeled by a fluidized bed reactor. Different stages of process integration between the endothermic gasification and exothermic combustion and methanation are considered. With increasing process integration, the conversion efficiency from biomass to SNG increases. A conversion efficiency from biomass to SNG of 73.9% on a lower heating value basis is feasible with the best integrated system. The SNG produced in the simulation meets the quality requirements for injection into the natural gas grid. Copyright © 2012 John Wiley & Sons, Ltd.

Experimental Determination of the Efficiency and Emissions of a Residential Microcogeneration System Based on a Stirling Engine and Fueled by Diesel and Ethanol

Renewable forms of energy, such as biofuels, have the potential to displace fossil fuels in a wide variety of applications. Further benefit can be achieved through the use of combined heat and power devices, as this is accompanied with a considerable increase in energy efficiency and lower costs associated with fuel consumption. In this study, we examined the performance of a residential microcogeneration system based on a Stirling engine and fueled by diesel and ethanol. Run on diesel, and on a lower heating value basis, the system achieved a power efficiency of 12.1%, a thermal efficiency of 73.3%, and a total efficiency of 85.4%. Powered by ethanol, the corresponding efficiencies were 11.8%, 73.9%, and 85.7%, respectively. During steady state operation, the total unburned hydrocarbon emissions for both fuels were negligible, while the particulate emissions for ethanol and diesel were found to be 0.40 mg/kWh and 0.42 mg/kWh, respectively. Emissions were extremely low, as the combustor features a continuous premixed flame that facilitates the complete burnout of already evaporated fuel. Though emissions of nitrogen dioxide, methane, formaldehyde, and acetaldehyde were also negligible for both fuels, carbon monoxide and nitric oxide emissions for diesel (71 and 67 mg/m3, respectively) were much higher than those observed for ethanol (50 and 19 mg/m3, respectively). Lower nitric oxide emission levels for ethanol were attributed to its lower flame temperature, whereas reductions in carbon monoxide emissions were likely a result of a higher degree of fuel/air mixing with ethanol, due to higher gas jet velocities of the fuel exiting the orifices of the evaporator. Lastly, parametric studies on primary engine set points, including coolant temperature and exhaust temperature, were conducted to understand their effect on engine performance.

Strong and flexible thermal and environmental pairing between pulp drying and sugar process

A new combination of two technologies, i.e.: low temperature belt drier and indirect triple-pass turbo-drier is introduced for drying of beet pulp, to reduce energy consumption thereby increasing pellet quality, lowering environmental impacts and meeting more stringent regulations. A coupling with the beet sugar factory is studied in order to minimize fossil fuel consumption using a low temperature belt drier. Calculated results for a 10,000 t/d beet sugar factory are given. In case of installations independent from a beet sugar plant, fuel consumption is reduced by 50% or more based on Lower Heating Value basis (LHV) ) to evaporate the desired water quantities without any coupling. In case of integration into a beet sugar factory fuel consumption for pulp drying can be reduced by 70% to 90% (LHV basis) to evaporate the desired water quantities with simple coupling.

蓄熱槽を持った太陽熱ハイブリッド型CO<sub>2</sub>回収火力発電システムの特性と経済性評価

For wide-use of a power plant utilizing solar energy, the improvement of its economics is important. Both economics and characteristics of a CO2-capturing solar thermal hybrid power generation system have been evaluated in this paper. Since relatively low temperature steam of 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine, the solar collector can attain high heat collecting efficiency. The net fuel-to-electricity conversion efficiency of the hybrid system was estimated to be higher than 60% on lower heating value basis. It has been estimated that the gross income and the period of depreciation of the proposed system are 34.8×105 yen/year and 8.89 years, respectively, and that the system is economically feasible, when the system is assumed to have the solar collector area of 10 ha, the maximum net power output of 4 MW and the heat storage capacity of 2000m3. The amount of the fuel saving and the reduction of CO2 emission of this system, compared to a conventional natural gas firing plant, have also been estimated in the paper.