Preheater Research Articles

Comprehensive effect of increased calcium content in coal on the selenium emission from coal-fired power plants: Combined laboratory and field experiments

Coal combustion is the major contributor to global toxic selenium (Se) emissions. Inorganic elements in coals significantly affect Se partitioning during combustion. This work confirmed that the calcium (Ca) in ash had a stronger relationship with Se retention at 1300 °C than other major elements. Ca oxide chemically reacted with gaseous Se, and its sintering densification slightly affected Se adsorption capacities (44.45 −1840.71→35.17 −1540.15 mg/kg) at 300 − 1300 °C. Therefore, Ca in coals was identified as having potential for hindering gaseous Se emissions, and coals with increased Ca contents (2.74→5.19 wt%) were used in a 350 MW unit. The decreased Se mass distribution (3.54%→2.63%) in flue gas at air preheater inlet (320 −362 °C) confirmed the effectiveness of increased Ca content on gaseous Se emission reduction. More gaseous Se further condensed and was chemically adsorbed by fly ash when passed through an electrostatic precipitator, resulting in a significant increase in the Se content of fly ash. Additionally, the corresponding Se leaching ratio decreased from 4.88 − 35.74% to 1.87 − 26.31%, indicating enhanced stability of Se enriched in fly ash. This research confirmed the feasibility and environmental safety of sequestration of gaseous Se from flue gas to fly ash by increasing the Ca content in coals.

Thermoeconomic analysis of a novel cogeneration system for cascade recovery of waste heat from exhaust flue gases

In low-grade waste heat recovery scenarios, an absorption refrigeration cycle (ARC) or organic Rankine cycle (ORC) can be used because of its widespread acceptance in combined cooling and power applications. This paper introduces a cogeneration configuration employing a cascade waste-heat recovery architecture (including an ARC, ORC, and intermediate heating loop) to harness waste heat from the flue gas of a gas turbine (GT). The results demonstrated that the first-law efficiency and total power generation were largely influenced by the ARC, whereas the second-law efficiency and total available energy were primarily affected by the ORC. When the ARC generation temperature difference and ORC evaporation temperature were adjusted, the first- and second-law efficiencies exhibited divergent trends, suggesting the absence of a unified strategy to enhance both efficiencies simultaneously in the current system. The system achieved its highest first-law efficiency of 54.84 % and maximum total power generation of 1866.10 kW at an ORC evaporation temperature of 145 °C and a heat-source inlet temperature of 160 °C. Furthermore, at an ORC evaporation temperature of 150 °C and a heat-source inlet temperature of 200 °C, the system reached its highest second-law efficiency of 34.57 % and maximum total available energy of 1233.3 kW. The case study revealed that the GT system (including air compressor, air preheater, combustion chamber, and gas turbine) accounted for the highest level of irreversibility, comprising 74 % of the overall system. Specifically, the combustion chamber in the GT system produced a significant irreversibility due to chemical reactions. Compared with traditional combined cooling and power systems, the proposed system can increase the first-law efficiency and lower the unit energy cost of the output.

Design and Analysis of the Waste Heat Recovery System for Stenter Exhaust

In this study, combined with the exhaust adsorption, desorption and catalytic combustion technology, a waste heat recovery scheme using stenter exhaust to heat desorbed air and preheat stenter suction air was proposed. Using Aspen Plus to design the waste heat recovery system, and using Aspen EDR to design the structure of heat exchangers. The energy utilization efficiency of waste heat recovery system was evaluated through the exergy analysis, and the influence of exhaust flow rate variation on exergy efficiency of heat exchanger under different exhaust temperatures were discussed. Moreover, the influence of fluid parameter variations on the heat transfer process was also analyzed. Finally, the economic calculation was carried out and the overall energy-saving effect of waste heat recovery system was demonstrated. The results showed that the utilization of this waste heat recovery system can recover 537 kW, the exergy efficiency of desorbed air heat exchanger and preheating air heat exchanger were 51% and 58.9% respectively. In terms of the economic evaluation, the annual energy-saving economic benefits was about $ 89,312, and the static investment payback period was 1.17 years.

A Novel Numerical Simulation Study of Air Leakage in Rotary Air Preheaters Based on Rotor Thermal Deformation

Thermal deformation of the rotor is a critical factor leading to radial air leakage in rotary air preheaters. However, previous studies have not comprehensively established the correlation between rotor thermal deformation during thermal operation and radial air leakage. This study addresses this gap by introducing a novel model for calculating radial air leakage, incorporating the thermal deformation of the rotor. To achieve this, we selected a three-section rotary air preheater from a 330 MW coal-fired unit boiler for investigation. This research begins by constructing a heat transfer–structure coupled numerical simulation model using Fluent and ANSYS Workbench. This model is employed to analyze the thermal deformation of the rotor under varying unit power generation loads. This paper meticulously examines the thermal deformation patterns of the rotor in diverse circumstances, explores their impact on air leakages, and provides a comprehensive analysis of air leakage fluctuations in different ducts. The influence of rotor thermal deformation on the local radial leak characteristics is ultimately established. The results indicate that incorporating the impact of preheater thermal deformation into the examination of preheater air leakage enhances the model’s capacity to accurately simulate values of leakage distribution at various cell clearances. This research concludes by offering recommendations for effectively managing hot end radial air leakage in preheater systems, providing valuable insights for the design and adjustment of sealing systems.

Sustainability of flameless combustion mode with hydrogen addition to liquid kerosene fuel at high-intensity conditions

The application of hydrogen for fuel enrichment and blending has recently gained importance. The sustainability and performance enhancement through hydrogen addition in flameless combustion mode for liquid fuels needs further investigation to enhance our understanding. Therefore, the present study reports the effect of hydrogen addition on the flameless combustion of a kerosene-fired 30 kW swirl combustor with hydrogen addition. A divergence-shaped conical combustor with tangential air injection and asymmetric fuel injection scheme is adopted. The liquid fuel was injected using a solid-cone swirl nozzle with 34 μm Sauter Mean Diameter. The hydrogen addition was varied from 0 to 20% on a thermal input basis, and the thermal input of liquid fuel was maintained at a 30 kW level. Computational studies helped understand the flow physics behavior within the combustor volume. The hydrogen addition was observed to improve the reactant dilution ratio (Rdil). The maximum values of the Rdil increased from 4.47 to 5.44 with hydrogen addition. Hydrogen addition further helped extend the flameless combustion regime to φ = 0.3 without any air preheating. A uniformly distributed reaction with a reduced-temperature gradient is observed with extended combustion stability limits. A marginal increase in NOx emissions was observed with hydrogen addition, albeit within permissible limits, accompanied by ∼8–20 dB reduction in acoustic emissions.

Design on a novel waste heat recovery system integrated with the bypass flue and outside primary air preheater for bitumite-fired power plants

Bitumite is widely used in coal-fired power plants. However, due to its high volatile content, the temperature of primary air to coal mills is limited to a lower value because of its high risk of spontaneous combustion. The method to reduce primary air temperature by mixing with cold air leads to irreversible loss and reduces the power generation efficiency of the power plant. To address the issue, a novel flue gas waste heat recovery system integrated with the bypass flue and outside primary air preheater for bitumite-fired power plants was suggested. The thermo- and techno-economic analysis models of the waste heat recovery system were developed, and the design parameters were optimized to maximize profit. The thermo-economic analysis shows that the exergy efficiency of the waste heat recovery system can reach 49.8 %, and the coal consumption rate can be reduced by 4.75 g (kW h)−1 by integrating the optimal waste heat recovery system. The techno-economic analysis shows that the net present value of the power plant during ten years can reach 10.6 M$, and the discounted payback period is 0.6 years. The novel waste heat recovery system can effectively improve the thermo- and techno-economic performance of bitumite-fired power plants.

Effect of Fuel Injection Strategies on Performance, Regulated and Unregulated Emissions of a Gasoline Compression Ignition Engine

Abstract Gasoline compression ignition (GCI) mode engines are characterized by partially premixed charge combustion, leading to significant and simultaneous reductions of nitrogen oxides and particulate matter emissions. However, gasoline compression ignition engine operation suffers from a limited operating window. Air preheating and low-research octane number fuels are required to improve the engine performance. This experimental study used a blend of 70% (v/v) gasoline and 30% diesel as test fuel in a direct injection medium-duty compression ignition engine. Experiments were carried out at 5- and 10-bar brake mean effective pressure (BMEP) engine loads at 1500–2500 rpm engine speeds using a triple injection strategy (two pilots and one main injection) for all test conditions. The combustion phasing was kept constant with respect to crank angle to produce a high power output. The investigations examined engine performance and regulated and unregulated emissions. The test engine was initially operated in conventional diesel combustion mode with diesel for baseline data generation. Gasoline compression ignition mode operation demonstrated a remarkable 16% increase in the brake thermal efficiency and a substantial reduction of 65% in nitrogen oxide emissions compared to the baseline conventional diesel combustion mode. The GCI engine exhaust showed higher concentrations of regulated emissions, namely hydrocarbons and carbon monoxide, and unregulated trace emissions, such as methane, acetylene, toluene, inorganic gaseous species, and unsaturated hydrocarbons.

Ash conveying system upgrade from hydraulic to pneumatic system in a 550MW coal-fired power plant in Taiwan

The paper presents a comprehensive study on the ash handling system upgrade from a hydraulic conveying system to a pneumatic system in a 550 MW coal-fired power plant located in Taiwan. The ash pond used to dispose of ash from the economizer and air preheater is almost full due to having been in service for more than forty years. An alternative location to dispose of the ash is sought. The design process of finding the new location and the equipment to be used is explored. Some options for the new economizer and air preheater ash disposal site, including building a new silo or using an existing silo, are taken into consideration in terms of design, cost, and timing of execution. The project’s execution procedure is reviewed, taking into account aspects of system integration, equipment installation, and commissioning. The primary objective of this paper is to detail the design, implementation, and outcomes of the ash handling system upgrade. This upgrade is accomplished in an effort to enhance operational efficiency, reduce maintenance requirements, and improve environmental compliance. The study explores the motivations behind adopting pneumatic conveying technology, focusing on its advantages over hydraulic systems, such as reduced maintenance needs and improved dust control. The case study provides insight into the lesson learned and recommendations for similar ash conveying system upgrades in other coal-fired power plants.

IMPROVEMENT OF PERFORMANCE OF HEAT RECOVERY UNITS BY USING MAGNETIC NANOFLUID

Waste heat recovery units are systems that are widely used in the preheating of clean air, which is needed in industrial and waste heat facilities, without contact with polluted air, especially during the pandemic period. In this study, it is aimed to increase the operating temperature range by improving the performance of a heat exchanger consisting of a heat pipe bundle and an integrated heat recovery unit. The originality of the work is in the use of NiFe<sub>2</sub>O<sub>4</sub>/water, ZnFe<sub>2</sub>O<sub>4</sub>/water, and CoFe<sub>2</sub>O<sub>4</sub>/water nanofluids as the working fluid in the heat pipes and the improvement rates in the heat recovery unit's thermal performance were determined compared to pure water, which is the basic fluid. The turbulence of the flows in the channel prevented the establishment of a linear relationship between the Reynolds number and the thermal improvement in performance. However, by using nanofluids instead of pure water, thermal performance improvement was achieved for all Reynolds numbers. According to the results obtained it is seen that higher performances are obtained in the case of using nanofluids compared to pure water. The average performance values are 14%, 18%, 19%, and 20% for water, NiFe<sub>2</sub>O<sub>4</sub>, ZnFe<sub>2</sub>O<sub>4</sub>, and CoFe<sub>2</sub>O<sub>4</sub> nanofluids, respectively, according to the Re number on the cold fluid side, while the average performance improvement rates of NiFe<sub>2</sub>O<sub>4</sub>, ZnFe<sub>2</sub>O<sub>4</sub>, and CoFe<sub>2</sub>O<sub>4</sub> nanofluids compared to the base fluid (pure water) are 29%, 38%, and 44%, respectively. When the Re number in the hot air flow channel is taken into account, it is seen that the average performance values are 13%, 19%, 20%, and 22% in the same order, while the improvement rates are 48%, 57%, and 72%. Therefore, according to the average performance and improvement values, the CoFe<sub>2</sub>O<sub>4</sub> nanofluid was found to be a more suitable fluid than the others.

Distributed energy generation based on jet-vortex bioheat generators

The article explores transforming Ukraine’s energy system using the “Smart Grid” concept and distributed generation. It emphasizes the need for decentralizing thermal and electric energy sources with small-scale, renewable local biofuels. The significance of thermochemical distribution systems for bio-waste using jet-vortex generator-incinerators in energy-intensive technologies is highlighted. New methods for generating thermal energy in agro-industrial processes, such as grain drying, are proposed. Heat-technical means for bio-waste decomposition, heat exchange, and combustion product utilization have been developed. Production tests of automated jet-vortex generator-incinerators were conducted, considering variable technological parameters. The cost of thermal energy for grain drying is significantly lower than traditional methods. The process, with a functional heat exchanger, uses preheated clean air, improving grain quality. A cogeneration plant project, based on a generator-incinerator and air turbine, is proposed to address Ukraine’s electricity sector challenges. This plant converts thermal energy into mechanical energy using a heat exchanger and compressor. Electrical energy is produced with an electromechanical converter to meet the thermal-technical module’s needs. The cogeneration plant achieves a total efficiency of approximately 80%.

Numerical and experimental study to examine methods to increase the convectional heat transfer of recuperator tubes

The use of structured tubes in tube bundle recuperators is intended to improve the energy efficiency of gas-fired industrial furnace systems with central air preheating. Currently, smooth tubes as well as smooth tubes with internal twisted tape are commonly utilised. The increased surface area of structured tubes leads to an increased heat transfer between the off-gas and the combustion air. However, structuring leads to an increased pressure loss. The aim is to find an optimal operating range in which the pressure losses are still acceptable and the greatest increase of heat transfer compared to the reference will be achieved. Smooth tubes and also smooth tubes with twisted tapes are considered as reference systems in comparison to two concave structured tubes. CFD simulations were used to investigate the influence of the operating parameters of combustion air velocity and off-gas velocity on heat transfer according to industrial scale. The simulations have shown that the heat flow increases with the honeycomb depth and strongly depends on the operating conditions. Experimental measurements in a test bench were carried out to validate the model and confirm the positive influence of structuring on heat transfer.

CFD modelling of the air preheater fired with gas mixture to find the cause of the preheater damage

Since various fuels, such as natural gas, blast furnace gas, coke oven gas, and a mixture of the three, are burned in the boiler, there is a danger of corrosion caused by sulphuric acid. Sulphur dioxide produced after combustion and condensed water vapour from flue gases on cold tube surfaces form sulphuric acid. Sulphuric acid solution flowing down the vertical tubes of the air heater causes corrosion not only of the air heater tubes but also of the horizontal water heater tubes located below. A simulation of the flow and heat exchange on the flue gas and air sides was performed to determine the areas of the air heater where the temperature of the air heater tubes is low and condensation may occur. Based on the measured air and flue gas mass flows, the measured flue gas temperatures behind the heater, and the air temperature at its inlet, the flue gas temperature before the air heater was determined using the ε-NTU (Effectiveness-Number of Transfer Units) method. Based on CFD modelling and experimental research, the areas in the heater where sulphuric acid can form at given outside air temperatures were determined.

Topology characteristics of liquid ammonia swirl spray flame

The utilization of liquid ammonia in gas turbines can reduce energy loss and start-up time. However, the flash boiling phenomenon and the high latent heat of liquid ammonia make the spray flame difficult to stabilize. Increasing the preheated air temperature or adding a small amount of hydrogen as a piloted fuel are considered as effective methods to enhance the stability. To understand the flame topological structure, simultaneous Mie scattering and planar laser-induced fluorescence of OH (OH-PLIF) techniques were used to visualize the liquid ammonia spray structure and flame region information. Results show that the liquid ammonia swirl spray flame exhibits the flame topological structure of distinct zoning characteristics, including the droplet zone, the mixing zone, and the flame zone. Increasing the preheated air temperature accelerates the evaporation of liquid ammonia, leading to an increase in the local equivalence ratio and radial flame splitting. At lower air temperature conditions, increasing the hydrogen blending ratio has minimal impact on the flame topological structure. However, at higher temperature conditions, hydrogen blending significantly promotes reaction intensity upstream and reduces the flame lift-off height, which makes the mixing zone smaller. In general, to achieve a better flame stability effect, the two factors need to be reasonably matched, which has important reference value for the development of liquid ammonia fueled gas turbine combustors.

Experimental and computational (Chemical Kinetic + CFD) analyses of Self-Recuperative annular tubular porous burner for NH3/CH4 -air Non-Premixed combustion

Ammonia is now being explored as a potential gas turbine fuel because of its renewable and carbon-free nature. Ammonia combustion possesses various limitations, such as high NO emissions, low burning velocity, and high auto-ignition temperature. Moreover, dual-fuel combustion approaches can be used to mitigate these drawbacks. However, the limitations of available information about the resulting emissions are insufficient to encourage widespread adoption. In this work, an NH3/CH4-air fueled self-recuperative high aspect ratio annular tubular porous burner is developed for gas turbine power applications. In this burner, an annular zone surrounds the combustion chamber to preheat the incoming air, while two perforated discs are mounted between the combustor and annular zone for uniform distribution of air. Eight Zirconia foams (4 of 10 PPI and 4 of 20 PPI) are stacked at the upstream side of the combustor. Experimentally, air preheat temperature, combustor exit temperature, NO, and CO emissions are analyzed and measured for various ammonia addition (0–41 % by weight) percentages, equivalence ratio of 1.0, and heat inputs of 17 & 21 kW for 10 PPI and a combination of 10 and 20 PPI porous foams. A preheated air stream coming from the annular zone speeds up fuel dissociation and helps in stabilizing the flame on the upstream side of the combustor. Combustor exit temperatures are lower in sandwich cases of 10 + 20 PPI than the porous foams of 10 PPI. However, with porous foams of 10 PPI, the air preheat temperature is higher. The insertion of porous foams shows better recirculation of heat and stable combustion is observed for higher percentages of ammonia and higher thermal inputs. The OH radicals are distributed for larger areas inside the dumb combustor, while for porous combustion, it is distributed near the porous foams. The porous sandwich cases of 10 + 20 PPI shows higher combustion efficiency compared to 10 PPI and without porous cases. The chemical kinetic analysis shows that the HNO and HCO radicals act as the main intermediate channel for NO and CO production.

Gas-liquid contact evaporation of concentrate leachate from disk-tube reverse osmosis treatment in waste incineration plant

In order to utilize waste heat such as exhaust steam and hot air passing through air preheater in the waste incineration plant to heat air used for evaporating leachate concentrate (LC) by gas-liquid contact evaporation technology, hot air of 600 °C, 450 °C and 250 °C was used to evaporate LC in a laboratory-scale evaporator to obtain purified condensate used for supplying water for circulating cooling water system. The influence of pH, hot air temperature and evaporation rate on COD and NH3–N in condensate were investigated to identify the optimum operation of this technology. The results showed that COD concentration in condensate obviously decreased with increase in hot air temperature. Higher hot air temperature led to higher initial evaporation temperature, and evaporation rate of water was significantly greater than that of small molecular organic matter with lower boiling point than water with increasing hot air temperature. Reduction in contents of phenol, ketone and benzene was responsible for COD decreasing in condensate. COD in condensate decreased with increase in pH, as the amount of volatile organic matter such as fatty acids escaped from LC to condensate decreased. The pH had little influence on the DOM in condensate according to EEM spectra analysis. Evaporation rate had little influence on COD in the condensate water. NH3–N concentrations in condensate in all experimental groups were far away from the limit value (10 mg/L) in the water quality standard. Under the premise of meeting water quality standard, the lowest temperature (450 °C) of hot air was selected to save energy and use lower grade waste heat. Therefore, the optimum condition was 450 °C of hot air, pH = 7 of LC and CF = 10. At this condition, molecular weight of DOM in the condensate was smaller and humification degree and aromaticity of DOM were lower according to UV–visible absorption spectrum analysis.

Exergoeconomic Evaluation of a Cogeneration System Driven by a Natural Gas and Biomass Co-Firing Gas Turbine Combined with a Steam Rankine Cycle, Organic Rankine Cycle, and Absorption Chiller

Considering energy conversion efficiency, pollution emissions, and economic benefits, combining biomass with fossil fuels in power generation facilities is a viable approach to address prevailing energy deficits and environmental challenges. This research aimed to investigate the thermodynamic and exergoeconomic performance of a novel power and cooling cogeneration system based on a natural gas–biomass dual fuel gas turbine (DFGT). In this system, a steam Rankine cycle (SRC), a single-effect absorption chiller (SEAC), and an organic Rankine cycle (ORC) are employed as bottoming cycles for the waste heat cascade utilization of the DFGT. The effects of main operating parameters on the performance criteria are examined, and multi-objective optimization is accomplished with a genetic algorithm using exergy efficiency and the sum unit cost of the product (SUCP) as the objective functions. The results demonstrate the higher energy utilization efficiency of the proposed system with the thermal and exergy efficiencies of 75.69% and 41.76%, respectively, while the SUCP is 13.37 $/GJ. The exergy analysis reveals that the combustion chamber takes the largest proportion of the exergy destruction rate. The parametric analysis shows that the thermal and exergy efficiencies, as well as the SUCP, rise with the increase in the gas turbine inlet temperature or with the decrease in the preheated air temperature. Higher exergy efficiency and lower SUCP could be obtained by increasing the SRC turbine inlet pressure or decreasing the SRC condensation temperature. Finally, optimization results indicate that the system with an optimum solution yields 0.3% higher exergy efficiency and 2.8% lower SUCP compared with the base case.

Recovery of Flared Natural Gas with High CO<sub>2</sub> Content Using SOFC CHP System: Feasibility Study for Neem-Field, Sudan

Flared natural gas emissions are one of the main sources of environmental pollution and global warming. To recover this gas, the presence of impurities like CO2 in high concentrations forces oil producers to escape from investing in such intensive processing. Several implementations of no flaring methods have been reported in the literature, however, there have been limited concerning the bulk-CO2 natural gases. This research developed an innovative idea for the use of the SOFC CHP system to recover flared bulk-CO2 associated gas of Neem-Field in Western Sudan. The exergy of the system and the performance of the SOFCs are investigated in this paper, in addition to environmental and economic analysis. The simulation (Cycle-Tempo©) results demonstrate that the proposed system can generate 1 MW electrical power and 0.068 MW thermal energy with efficiency approached 43.3% (based on LHV). The exergy analysis showed that 38% of system losses occurred in the air preheaters. Instead of conventional gas-burning, recovering the flared gas reduced the equivalent CO2 GHGs emissions by 80%. Overall, the novel solution found to be environmentally friendly, and economically appealing with a total capital investment estimated to be US$1.175 million and a cost of electricity (COE) of 4.07 cents per kWh.

Advanced energy recovery systems design of stenter processes: Energy, exergy and Techno-economic analyses

Stenters used for drying during the dyeing process, waste considerable thermal energy through exhaust gas. This energy waste is one of the major bottlenecks to improving the sustainability of the textile dyeing field. To find the most efficient recovery of the waste heat from the stenters for supplying various energy sources and reducing energy consumption within overall textile system, this study compares three heat recovery systems: (Case- 1) air preheating, (Case-2) hot-water generation, and (Case-3) power generation. Energy, exergy, and economic analyses indicated that all cases demonstrated superior results those obtained using the base case. In terms of energy consumption, Case-1 demonstrated a 60.8 % reduction achieved through decreased fuel consumption. In particular, the economic analysis indicated that Case-1 was the most favorable option because it possesses the lowest operating costs by significantly reducing fuel consumption for air preheating. Additionally, the simple configuration of the process and the use of a small heat exchanger contribute to a lower capital cost. Thus, Case-1 could the most efficiently recover and utilize the heat wasted from the stenter at a relatively low investment cost among proposed systems. This demonstrated the potential for energy and cost savings within the textile industry.

PROSPECTS OF USING ALTERNATIVE FUELS FOR HEATING OF REGENERATIVE AIR HEATERS FOR BLASТ FURNACES

Landfill gas as one of the promising artificial gaseous fuels is analyzed for use in heating system of regenerative air heaters for blast furnaces. Increasing the temperature of blast is one of the most effective ways for metallurgical coke saving and increase the productivity of blast furnaces. To increase this temperature, a mixture of blast-furnace and coke oven gases is used as fuel for regenerative heat exchangers. Considering the current shortage of coke oven gas, landfill gas, the main combustible element of which is methane, is proposed as a high-calorie additive to the main fuel. Calculations were made for the combustion of a mixture of gaseous fuels in three combinations: blast-furnace gas, blast-furnace and coke gases mixture, blast-furnace and landfill gases mixture. The possibility of increasing the temperature of the hot blast to 1250 °C for the air supply system of a blast furnace with a volume of 1033 m³ was considered. Calculations showed that in order to achieve such a temperature, the adiabatic combustion temperature should be 1423 °C, and the flue gas temperature in the crown should be 1300 °C. Such temperatures cannot be reached using only blast-furnace gas, so two possible options were considered. The first option is the use of a coke and blast furnace gases mixture with a coke gas content of 6.3 % and combustion air heating to 180 °C by exhaust gases from blast furnace air heaters. The second option is combustion of a mixture of blast-furnace and landfill gas with combustion air heating to 180 °C (the content of landfill gas is 7.6 %). The flow rate of the fuel mixture for the second option is 68,523 m³ /h, and the required amount of landfill gas is 5208 m³ /h. The volumes of gas output from landfills in large cities are reported to be 5–10 MCM a year, which is less than the amount of biogas required to heat an air heater. Therefore, to achieve the required temperature it makes sense to consider a tree gas mixture that is blast-furnace, coke and landfill gases an appropriate proportions. The use of landfill gas contributes to the solution of an important environmental problem of land and atmosphere pollution during the accumulation of municipal solid waste.

Fundamental characteristics of an integrated reactor with catalytic combustor and air pre-heater for compact solid oxide fuel cell systems

Bulky volume limits the application of solid oxide fuel cell (SOFC) systems in some scenarios. In this paper, a compact integrated reactor with combustor and air pre-heater is proposed. It is adapted by coating combustion catalyst to the hot-side of a plate-fin heat exchanger. The fundamental steady/transient characteristics of the reactor are investigated at different inlet settings in the warmup condition of a metal-supported SOFC.Results show that the reactor has a balanced combustion performance with a minimum methane conversion rate of 85.1%, while it can be effectively improved by reducing the excess air ratio. The reactor has better heat exchange capability than the traditional series arrangement of independent combustor and air pre-heater. There is about 68.7% of the reaction heat extracted by direct metal-substrate conduction and this dominates the heat exchange process. The reactor also has a good transient response. Methane conversion can be stable within 12.5 min; meanwhile, the output air temperature shows a good capability to track the development of stack temperature. Both the air temperature rise rate around 35 ˚C min−1 and the rise trend of first fast and then slow can meet the requirements of stack quick warmup. Overall, the methane conversion development within the reactor and the temperature rise of the stack reinforce mutually, and both can stabilize more quickly in this case.