Heating Value Of Gas Research Articles

Sliding Mode Control of Underground Coal Gasification Energy Conversion Process

The control of highly complex and nonlinear underground coal gasification (UCG) energy conversion process is a challenging job. As the process occurs under the surface of the earth, so it is either impossible or very expensive to measure all the important parameters, which further complicates the control design. The input of the UCG process is the flow rate of the injected air and the heating value of the product gas is the output. In this paper, a sliding mode control (SMC) algorithm is designed for a simplified model of an actual UCG process in order to maintain a desired constant heating value. The relative degree of the sliding variable is zero, because the input is readily available in it. As the heating value is the only measurement available, the trivial control design is not possible. Therefore, the time derivative of the control is selected as the system input, and then the relative degree becomes one and the conventional SMC may be implemented. This approach let us maintain the output at the desired level and provides insensitivity with respect to different types of uncertainties. The stability of the zero dynamics is proved, which ensures that the overall system is stable. The simulation results demonstrate the robustness of the SMC design against the input disturbance and the modeling inaccuracies.

Effect of Feed Gas Flow Rate on CO2 Absorption through Super Hydrophobic Hollow Fiber membrane Contactor

Carbon dioxide is pollutant in natural gas that could reduce the heating value of the natural gas and cause problem in transportation due to corrosive to the pipeline. This study aims to evaluate the effects of feed gas flow rate on CO2 absorption through super hydrophobic hollow fiber contactor. Polyethyleneglycol-300 (PEG-300) solution was used as absorbent in this study, whilst the feed gas used in the experiment was a mixture of 30% CO2 and 70% CH4. There are three super hydrophobic hollow fiber contactors sized 6 cm and 25 cm in diameter and length used in this study, which consists of 1000, 3000 and 5000 fibers, respectively. The super hydrophobic fiber membrane used is polypropylene-based with outer and inner diameter of about 525 and 235 μm, respectively. In the experiments, the feed gas was sent through the shell side of the membrane contactor, whilst the absorbent solution was pumped through the lumen fibers. The experimental results showed that the mass transfer coefficient, flux, absorption efficiency for CO2-N2 system and CO2 loading increased with the feed gas flow rate, but the absorption efficiency for CO2-N2 system decreased. The mass transfer coefficient and the flux, at the same feed gas flow rate, decreased with the number of fibers in the membrane contactor, but the CO2 absorption efficiency and the CO2 loading increased.

CFD modeling of sawdust gasification in a lab-scale entrained flow reactor based on char intrinsic kinetics. Part 1: Model development

The heterogeneous reactions between char and gases are crucial for the whole biomass gasification process due to their slow reaction rates. In this study, the intrinsic kinetics of birch wood chars react with CO2 and O2were investigated through thermogravimetric analysis (TGA) experiments. For char-CO2 reaction, the pre-exponential factor, activation energy and reaction order were 2.130 × 102 1/s Pam, 160.01 kJ/mol, and 0.525, respectively. For char-O2 reaction, the intrinsic kinetic parameters were 0.570 1/s Pam (pre-exponential factor), 134.15 kJ/mol (activation energy), and 1.796 (reaction order). Biomass gasification model was then built based on the Euler-Lagrange approach, and the intrinsic kinetic parameters were adopted in the char-gas reaction submodel to calculate the heterogeneous reaction rates with consideration of mass diffusion limitation and chemical reaction. Sawdust-air gasification in an entrained flow reactor under different equivalence ratios (ERs) and temperatures were simulated. The relative errors for produced gas compositions were mainly less than 20%, and the relative errors for gasification performances were 9.65–23.33% (gas heating value), 1.17–5.95% (gas production), and 9.76–16.57% (carbon conversion efficiency), respectively. The model based on intrinsic kinetics can therefore be employed to predict the biomass gasification performances.

A study of the in-situ CO2 removal pyrolysis of Chinese herb residue for syngas production

The in-situ CO2 removal pyrolysis of Chinese herb residue was studied by thermodynamic equilibrium simulation and experimental methods. The effects of temperature, pressure, and CaO loading on the gas composition, heating value and yield were determined. The simulation results indicate that the heating value of product gas increases with the increase of Ca/H and pressure, and slightly decreases with the increase of temperature. The simulation results were verified by the experiments conducted with a micro fixed-bed reactor. Under the simulated reaction conditions including atmospheric pressure, reaction temperature of 700 °C and the Ca/H of 0.65, the CO2 in the product gas was effectively removed, resulting the syngas with a high heating value. The product gas was mainly composed of H2, CO, CO2 and CH4 with the contents of 47.52, 22.04, 9.01 and 14.02 respectively by experiment. And the lower heating value of the product gas reached 18.1 MJ/Nm3.

Experimental study of biomass gasification with oxygen-enriched air in fluidized bed gasifier

Considering the universality, renewability and cleanness of biomass, an experimental research is carried out using rice straw in a two-stage fluidized bed. The experimental analysis identified the relevant parameters in the operation of the two-stage fluidized bed to investigate the properties of biomass enriched air gasification. Results show that higher gasification temperature is conducive to enhance the gasification performance. An increasing ER is shown to go against adding gas heat value. When oxygen concentration increases from 21% to 45%, the gas heating value increases from 4.00MJ/kg to 5.24MJ/kg and the gasification efficiency increases from 29.60% to 33.59%, which shows higher oxygen concentration is conducive to higher quality gas and higher gasification efficiency. A secondary oxygen injection leads to reduction of tar concentration from 15.78g/Nm3 to 10.24g/Nm3. The optimal secondary oxygen ratio is about 33.00%. When the secondary oxygen ratio increased to 46.86%, monocyclic aromatics reduced from 28.17% to 19.65% and PAHs increased from 34.97% to 44.05%, leading to the increase aromatization of tar.

Urban gas production from low H2/CO biogas using Re-promoted Ni catalysts supported on modified manganese sand

Re-promoted Ni catalysts supported on the raw manganese sand (RMS) and HNO3/ NH3·H2O/H2O2 modified manganese sand (MMS) were prepared by co-impregnation method. The catalysts were tested for urban gas production from low H2/CO biogas by partial methanation coupling with water gas shift (WGS). A series of characterization analysis including XRF, ICP, nitrogen isothermal adsorption, XRD, H2-TPR, H2-TPD, TG, XPS, TEM, SEM and DRIFTS were employed to comprehensively investigate the physico-chemical properties of the supports and catalysts. The results showed that the Ni-Re/RMS catalyst was more active than the Ni/RMS catalyst due to the improved dispersion of Ni particles. Through further modification on the RMS, it was found that Ni-Re/MMS-H2O2 catalyst showed a superior synergy effect on catalyzing methanation coupling with WGS over the other four catalysts. The addition of Re promoter facilitated to increase the proportion of β-type NiO for forming more Ni active sites after reduction as well as to inflict electronic effect, which could enhance the electron cloud density of Ni atoms to promote CO disassociation during the reaction. H2O2 was more suitable to be the modification reagent than HNO3 and NH3·H2O, owing to its positive contribution to the enhancement of anti-sintering and anti-coking ability of the catalysts. The lower heating value of outlet gas catalyzed by Ni-Re/MMS-H2O2 catalyst at the condition of H2/CO = 0.8, H2O/CO = 1.0 and 400 °C was 10.63 MJ/Nm3, implying the feasibility of using Re-promoted Ni catalysts for urban gas production from low H2/CO biogas and the promising potential of utilizing low-cost manganese sand as catalyst support.

An integrated kinetic model for downdraft gasifier based on a novel approach that optimises the reduction zone of gasifier

A kinetic model was built to estimate the optimum working parameters of a downdraft gasifier, in which a set of chemical kinetics at each zone of the gasifier was described. The model deals with a wide range of biomass types with elemental composition ranges of (38 ≤ C ≤ 52) %, (5.5 ≤ H ≤ 7) %, and (36 ≤ O ≤ 45) %. This model is able to predict gas composition, tar content, temperature and height of each zone, as well as temperature, velocity and pressure distribution at reduction zone with heating value of product gas. The model also gives full design dimensions of a downdraft gasifier. The final results, which proved to be in a good agreement with experimental works under different working conditions of biomass type, moisture content, and air-to-fuel ratio, are based on a new approach that includes calculation of the optimum height of the reduction zone. Calculation based on the optimum height ensures that all the char produced is consumed in the reduction zone, thus leading to the production of the maximum amount of gases. Results conclude that biomass with a moisture content less than 10% and equivalence ratio of 0.3–0.35 leads to the production of higher yield of syngas with low tar content. In particular, woody biomass materials are found to give the higher heating value for producer gas with a reasonable amount of tar.

Process Simulation of a 620 Mw-Natural Gas Combined Cycle Power Plant with Optimum Flue Gas Recirculation

The main objective of this investigation is to obtain an optimum value for the flue gas recirculation ratio in a 620 MW-Natural Gas Combined Cycle (NGCC) power plant with a 100% excess air in order to have a composition of the exhaust gas suitable for an effective absorption by amine solutions. To reach this goal, the recirculated flue gas is added to the secondary air (dilution air) used for cooling the turbine. The originality of this work is that the optimum value of a Flue Gas Recirculation (FGR) ratio of 0.42 is obtained from the change of the slope related to the effects of flue gas recirculation ratio on the molar percentage of oxygen in the exhaust gas. Compared to the NGCC power plant without flue gas recirculation, the molar percentage of carbon dioxide in the flue gas increases from 5% to 9.2% and the molar percentage of oxygen decreases from 10.9% to 3.5%. Since energy efficiency is the key parameter of energy conversion systems, the impact of the flue gas recirculation on the different energy inputs and outputs and the overall efficiency of the power plant are also investigated. It is found the positive effects of the flue gas recirculation on the electricity produced by the steam turbine generator (STG) are more important than its cooling effects on the power output of the combustion turbine generator (CTG). The flue gas recirculation has no effects on the water pump of the steam cycle and the increase of energy consumed by the compressor of flue gas is compensated by the decrease of energy consumed by the compressor of fresh air. Based on the Low heating value (LHV) of the natural gas, the flue gas recirculation increases the overall efficiency of the power plant by 1.1% from 57.5% from to 58.2%.

Performance testing of a downdraft biomass gasifier stove for cooking applications

A down draft biomass gasifier stove with four steps of cleaning gas system was developed to produce the producer gas for replacing LPG for cooking applications in lunch project for the student in rural school area. This project has been implemented at Bangrakam primary school that located at Pitsanuloke Province, Thailand. The biomass fuels used are Mimosa wood twigs. The gasifier stove was developed based on down draft fixed bed gasifier with the maximum fuel capacity of fourteen kilograms. The performance testing of the biomass gasifier stove showed that the heating value of the producer gas is 4.12 MJ/Nm3 with the thermal efficiency in the percentage of 85.49. The results from this study imply that it has high potential to replace LPG with producer gas.

Evaluation of Carbonisation Gas from Coal and Woody Biomass and Reduction Rate of Carbon Composite Pellets

Carbon composite iron oxide pellets using semichar or semicharcoal were proposed from the measured results of the carbonisation gas release behaviour. The carbonisation was done under a rising temperature condition until arriving at a maximum carbonisation temperature Tc,max to release some volatile matter (VM). The starting point of reduction of carbon composite pellets using semicharcoal produced at Tc,max = 823 K under the rising temperature condition was observed at the reduction temperature TR = 833 K, only a little higher than Tc,max, which was the aimed phenomenon for semicharcoal composite pellets. As Tc,max increases, the emitted carbonisation gas volume increases, the residual VM decreases, and, as a whole, the total heat value of the carbonisation gas tends to increase monotonically. The effect of the particle size of the semicharcoal on the reduction rate was studied. When TR is higher than Tc,max, the reduction rate increases, as the particle size decreases. When TR is equal to Tc,max, there is no effect. With decreasing Tc,max, the activation energy Ea of semicharcoal decreases. The maximum carbonisation temperature Tc,max may be optimised for reactivity (1/Ea) of semicharcoal and the total carbonisation gas volume or the heat value.

Characteristics of rice husk gasification in cyclone pyrolysis-suspended combustion system

The cyclonic gasification technology could realize self-separation of syngas and residual carbon, simplifying the purification system. In cyclone pyrolysis-suspension combustion system, bottom air was fed into carbon-rich area of gasifier. Due to the high height/diameter ratio and uneven temperature distribution in cyclone gasifier, the primary/secondary/bottom air rates were 30%, 20%, and 50%, respectively. Effects of gasification intensity and air equivalent ratio on rice husk gasification performance were explored. The results show that for cyclone pyrolysis-suspension combustion, the optimum gasification intensity is 885.24 kg/m2h. Strengthening the subregion of air supplement could cause a gradual increasing of temperature along the axis of gasifier. The syngas yield was independent of gasification intensity, but increased from 0.98 Nm3/kg at ER = 0.23 to 1.38 Nm3/kg at ER = 0.32. At ER = 0.26~0.29, the gasification performance is best, with gas heat value of 4.99~5.37 MJ/Nm3, cold gasification efficiency of 48.25~49.67% and tar content of 5.38~5.75 g/Nm3.

Design and construction of Ni3−xCoxO4nanorods grown on Ni foam for tuning synthetic natural gas heating values

Ni3−xCoxO4nanorods with different Ni/Co ratios were fabricated on Ni foam, which show excellent catalytic activity and can tune synthetic natural gas heating values.

Gasification of Charcoal in Air, Oxygen, and Steam Mixtures over a γ-Al2O3 Fluidized Bed

Charcoal was gasified using air and oxygen as well as with mixtures of oxygen and steam, aiming to produce a gas stream with high hydrogen content. The effects of the equivalence ratio (ER) and steam-to-carbon ratio (S/C) on carbon conversion, producer gas yield, gas heating value, and composition as well as on the apparent energy efficiency (AEE) of the process were studied. The gasification experiments were performed in a laboratory-scale fluidized bed rig working at 1173 K and atmospheric pressure and using γ-Al2O3 as bed material. Results showed that, on a N2-free basis, the composition of the producer gas obtained by gasification with air and pure oxygen were comparable when using the same ER. Furthermore, carbon fraction converted into gas improved when ER was increased from 0.25 up to 0.35, as well as when the S/C was increased to 0.625. The highest producer gas yield was obtained using ER = 0.35 and S/C = 0.625, while the highest hydrogen concentration in the produced gas was achieved using ER = 0...

Kinetics and Performance of Raw and Torrefied Biomass in a Continuous Bubbling Fluidized Bed Gasifier

This paper is an experimental study of the kinetics of gasification of olive kernel by using a thermogravimetric fluidized bed reactor technique. Gasification of ‘as received’ and torrefied olive kernels were investigated in a lab-scale bubbling fluidized bed gasifier, operating at up to 3.2 kg/h. The effect of bed temperature between 550 and 750 °C in 50 °C increments on the gasification product gas at mass-based equivalence ratios of 0.15 and 0.2 was studied. To explore the potential of torrefied biomass, the gasification results were compared to that of the ‘as received’ biomass. The product gas from torrefied biomass produced higher H2, CO and CH4 concentrations at identical oxidant flow rates in addition to higher cold gas efficiency and higher product gas heating value. The influence of equivalence ratio in gasification was also investigated at reactor temperatures of 750 °C and five equivalence ratios (0.15, 0.2, 0.25, 0.3, and 0.35). The results revealed that the torrefied biomass has the highest HHV at an equivalence ratio of 0.2 with a value of 6.09 MJ/Nm3, while ‘as received’ biomass 4.72 MJ/Nm3. Kinetic experiments under isothermal conditions were performed for the gasification of the materials in continuous mode. A mass balance model was successfully used to provide the capability of separately determining the rate constant of the reactions taking place. The kinetic parameters were calculated by a first order reaction model giving activation energies for ‘as received’ olive kernels of 84 kJ/mol and for torrefied olive kernels of 106 kJ/mol.

Investigation of a novel & integrated simulation model for hydrogen production from lignocellulosic biomass

Process simulation and modeling works are very important to determine novel design and operation conditions. In this study; hydrogen production from synthesis gas obtained by gasification of lignocellulosic biomass is investigated. The main motivation of this work is to understand how biomass is converted to hydrogen rich synthesis gas and its environmentally friendly impact. Hydrogen market development in several energy production units such as fuel cells is another motivation to realize these kinds of activities. The initial results can help to contribute to the literature and widen our experience on utilization of the CO2 neutral biomass sources and gasification technology which can develop the design of hydrogen production processes. The raw syngas is obtained via staged gasification of biomass, using bubbling fluidized bed technology with secondary agents; then it is cleaned, its hydrocarbon content is reformed, CO content is shifted (WGS) and finally H2 content is separated by the PSA (Pressure Swing Adsorption) unit. According to the preliminary results of the ASPEN HYSYS conceptual process simulation model; the composition of hydrogen rich gas (0.62% H2O, 38.83% H2, 1.65% CO, 26.13% CO2, 0.08% CH4, and 32.69% N2) has been determined. The first simulation results show that the hydrogen purity of the product gas after PSA unit is 99.999% approximately. The mass lower heating value (LHVmass) of the product gas before PSA unit is expected to be about 4500 kJ/kg and the overall fuel processor efficiency has been calculated as ∼93%.

Experimental results of gasification of walnut shell and pistachio shell in a bubbling fluidized bed gasifier under air and steam atmospheres

The present study investigates gasification of biomass in a laboratory scale set-up to obtain product gas. The gasifier is a bubbling fluidized bed (BFB) type. The bed material in the reactor is silica sand. Walnut shell and pistachio shell are gasified in the reactor under air and steam atmospheres. A gas analyzer is used to measure the CO, CO2, CH4, H2 and O2 concentrations of the product gas. The effects of equivalence ratio (ER) and steam to fuel ratio on the components of the product gas are studied for air and steam gasification cases, respectively. The lower heating value (LHV) of the product gas is calculated by using the measurement of concentrations. In the case of air gasification, the components and LHV of the product gas linearly change with varying ER. The LHV of pistachio shell is higher than that of walnut shell by 8–12% for the ER range of 0.2–0.4. The LHV increases from 3.2 to 5.4MJ/Nm3 with the decrease in ER from 0.4 to 0.2 for pistachio shell. In the case of steam gasification, the LHV is nearly constant with changing steam to fuel ratio. A product gas with a calorific value of 9.9MJ/Nm3 is generated. A recent review on biomass gasification in both pilot and laboratory scale bubbling fluidized bed gasifiers is presented. The operating conditions of the gasifiers and the components of the product gas are provided for air and steam gasification cases.

Influence of Addition of a High Amount of Calcium Oxide on the Yields of Pyrolysis Products and Noncondensable Gas Evolving during Corn Stalk Pyrolysis

The effects of addition of a high amount of CaO on the yields of pyrolysis products and the evolving of noncondensable gas from corn stalk pyrolysis at different temperatures were investigated using a fixed-bed pyrolysis system. The results showed that almost all the CO2 generated during the pyrolysis process could be absorbed by CaO (CaO/C = 1) at a lower temperature of 550–650 °C, and a low CO2 concentration of only 0–0.7 vol % was obtained in the noncondensable gas. The CO2 fixation into the solid phase (CaCO3) caused a big decrease in noncondensable gas yield and a significant increase in H2 concentration. Furthermore, CaO addition could catalyze the pyrolysis process and intensify the secondary pyrolysis of volatiles to produce more H2 and CH4. The higher heating value of noncondensable gas could achieve 19.3 MJ/m3 at 550 °C. However, beyond 700 °C (700–850 °C), the CO2 absorption capability of CaO declined greatly and the CO2 in the noncondensable gas increased obviously, but CaO addition could stil...

Investigation on biomass nitrogen-enriched pyrolysis: Influence of temperature

Biomass (bamboo waste) nitrogen-enriched pyrolysis was carried out in a fixed bed with NH3 atmosphere at 400–800 °C, and formation mechanism of N-containing species was explored in depth. Results showed that N-enriched pyrolysis greatly increased bio-oil and gas yields. H2 yield increased sharply to 130 mL/g (32.93 vol%) and became the main composition at higher temperature, while CH4 and CO yields deceased, and the lower heating value of gas reached ∼14 MJ/Nm3. For bio-oil, the content of phenols (main compositions) and N-containing species increased significantly, and the maximums reached 61.33% and 11.47%, respectively. While that of acetic acid (disappeared), O-containing species (aldehydes/ketones/furans/esters) and aromatics decreased largely accordingly. For biochar, Nitrogen content increased, and it contained abundant pyridininc-N, pyrrolic-N, quaternary-N, and pyridone-N-oxide. Possible reaction pathways of biomass N-enriched pyrolysis was proposed based on products evolution. In conclusion, biomass N-enriched pyrolysis could obtain high-valued N-containing chemical species and functional biochar.

Design and experimental study of pilot scale throat-less downdraft gasifier fed by rice husk and wood sawdust

ABSTRACTIn this work, pilot scale throat-less downdraft gasifier is fabricated and tested on rice husk and blend of rice husk-sawdust. The test aims to investigate effect of equivalence ratio on temperature profile, propagation front (flame propagation rate, bed movement rate, and effective propagation rate), and performance of the gasifier (composition of producer gas, heating value of producer gas, and thermal efficiency of the gasifier). Equivalence ratio investigated are 0.15, 0.20, and 0.25, while the blend ratio is 1:1 by mass. The results show that axial temperatures in the reactor surge faster with increasing equivalence ratio during the rice husk gasification and the blend gasification. Typically, flame propagation rate, bed movement rate, and effective propagation rate improve with rising equivalence ratio from 0.15 to 0.25. The best higher heating values and thermal efficiencies are obtained at equivalence ratio of 0.2 and 0.15 for the rice husk gasification and the blend gasification, respectively.

Energy benchmarking of thermal power plants using Pinch Analysis

Benchmarking of process industries with respect to energy consumption has always been a challenging issue for effective management of energy resources. Having developed a precise model for estimating the energy consumption, we have a powerful tool to measure and identify the opportunities for improvements through a plant. In this study, a mathematical-conceptual model is presented for one-way benchmarking of thermal power plants applying Pinch concepts. Using the environmental variables of the ambient air and relative load of gas turbine, the model presented for the combined cycle power plants provides a standard for the functional parameters of the unit. Another model is presented for the conventional steam cycle power plants enabling the prediction of the results of energy retrofit projects on these power plants based on combined Pinch and Exergy Analysis. By this model, the relationships between minimum temperature difference in heat exchanger networks and the enhanced efficiency, heat transfer area increment, and energy consumption decline are specified. A mathematical model is also proposed for estimating the natural gas heating value and CO2 emission based on natural gas composition. The proposed models have been validated using data of other existing power plants and showed enough accuracy of given targets.