Preheated Gas Research Articles

Theoretical Derivation of Thermal Value Equations for Heating Furnaces

Based on thermal value theory, the aim of this paper is to deduce the theoretical formulas for evaluating the energy effective utilization degree in technological pyrological processes exemplified by metallurgical heating furnaces. Heat transfer models for continuous heating furnaces, batch-type heating furnaces, and regenerative heating furnaces are established, respectively. By analyzing the movement path of injected infinitesimal heat attached on steel or gas, thermal value equations of continuous, batch-type, and regenerative heating furnaces are derived. Then the influences of such factors as hot charging, gas preheating and intake time of heat on energy effective utilization degree are discussed by thermal value equations. The results show that thermal value rises with hot charging and air preheating for continuous heating furnaces, with shorter intake time when heat is attached on steel or longer intake time when heat is attached on gas for batch-type heating furnaces and that with more heat supply at early heating stage or less at late stage for regenerative heating furnaces.

Polarization characteristics and fuel utilization in anode-supported solid oxide fuel cell using three-dimensional simulation

A three-dimensional numerical simulation for anode-supported tubular solid oxide fuel cell (SOFC), which is characterized by good electrical conductivity, has been carried out. Performance results by simulation are in good agreement with those by experiments, reported in [7]. Effect of various process conditions such as operating temperature, inlet velocity of fuel, and flow direction of inlet gases on the cell performance and fuel utilization has been further scrutinized. Polarization curve rises with increasing temperature of preheated gases and chamber, resulting from the incremented activity of catalysts within electrode. An effective way to reduce the temperature variation in the single cell with increasing current density has been sought, considering the temperature-dependent thermal expansion of materials. It has also been found that the fuel utilization is enhanced by increasing the cell length and operating temperature and lowering the inlet velocity of fuel.

Large eddy simulation of a pulverized coal jet flame ignited by a preheated gas flow

Large eddy simulation (LES) is applied to a pulverized coal jet flame ignited by a preheated gas flow. The simulation results are compared to experimental data obtained for the inlet stoichiometric ratios of 0.14, 0.22, and 0.36. An accurate and computationally inexpensive devolatilization model suitable for combustion simulation in LES is proposed and incorporated into the LES. The numerical results of gas temperature and coal burnout on the centerline show good agreement with the experimental data. Two kinds of lift-off heights are introduced to verify the combustion simulation. One is the height from the primary nozzle exit to the starting point of the growing flame region. The other is the height from the primary nozzle exit to the starting point of the continuous flame region. The calculated results of the two lift-off heights show good agreement with the experimental data. In contrast to LES, the standard k– ε model overestimates the lift-off heights because it calculates time-averaged temperature which does not contain information about local flame structure. The stoichiometric ratio in the gas phase at the starting point of the growing flame region is found to be independent of the inlet stoichiometric ratio in the range from 0.14 to 0.36.

Uhde EnviNOx® technology for NOX and N2O abatement: a contribution to reducing emissions from nitric acid plants

Nitrous oxide (N2O) emissions from nitric acid production worldwide have been estimated at about 400,000 t/a, equivalent to 120 million t/a CO2e, making nitric acid manufacture the largest single industrial process source of N2O. Uhde's NOX and N2O abatement technology has been developed to permit high rates of N2O abatement for tail gas temperatures between 330°C and 600°C. For plants with a cooler tail gas it is possible to raise the temperature to a suitable level by tail gas preheating. A large proportion of the world's nitric acid plants can thus be equipped with Uhde's N2O abatement technology. Existing abatement units routinely achieve N2O removal rates of 98–99% and above. This N2O abatement technology can thus play a significant role in lowering greenhouse gas emissions.

Experimental Study on Preheated Air and Flue Gas Recirculation in Solid Waste Incineration

The application of high temperature air combustion in incineration of solid waste was investigated. The combustion with preheated diluted secondary combustion air had effectively more energy saving and NOX emission reduction, but required a sufficient amount of preheated secondary combustion air to save more energy than non-dilution condition. The minimum preheated secondary combustion air temperature of 15 and 17% oxygen concentration conditions are 621 and 532°C, respectively. The optimum condition is preheated-diluted secondary combustion air at 900°C and 17% oxygen concentration and the operating ranges are preheated secondary combustion air above 621 to 900°C and diluted between 15 and 21% oxygen concentrations.

Using Preheated Inactive Gas for Vacuum Hardening and Isothermal Heat Treatment after Carburizing

Using Preheated Inactive Gas for Vacuum Hardening and Isothermal Heat Treatment after Carburizing

Antibacterial Property of Cold Sprayed Chitosan-Cu/Al Coating

The antibacterial behavior of CS-Cu (chitosan-copper complex) powder and their composite coatings were investigated against Escherichia coli (DH5α). CS-Cu powder and Al (aluminum) based CS-Cu composite powders were synthesized using in-house powder processing techniques. The results indicated that the antibacterial effect of all the powders increased with the proportion of CS-Cu powder. These composite powders were subsequently used as feedstock to generate antibacterial coatings via cold spray technology. The ratios of CS-Cu to Al in their composite powders were 25:75, 50:50, and 75:25 (wt.%). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and FTIR. Antibacterial composite CS-Cu/Al coatings were successfully deposited using cold spraying parameters of 6-8 bars at preheated helium gas, temperature between 140 and 150 °C. The coatings retained the antibacterial properties of the original feedstock powders.

Failure analysis of air pre-heater tubes of a petrochemicals plant

Heat resistant alloy tubes used in the higher temperature range of 1150–1273 K depends on the protective scale integrity for prevention of corrosion induced premature failures in a mixed gas environment with potential corrodents for oxidation, carburization and sulphidation attack. Cast HK40+Nb alloy tubes of an air pre-heater unit of a petrochemical industry failed prematurely after 13,000 h in service. The unit used smoke gas containing gaseous corrodents that could cause oxidation/sulphidation/carburization type of attack. Failed parts showed crack/punctures below the corrosion product filled pits. The crack occurred in the fully carburized zone present at the thinned out centre of the pit. Factors like excessive temperature cycling, overheating, presence of impurities either in the pre-heating gas mixture or that got introduced while in operation were found to be the reasons for breach of protective scale integrity leading to unwarranted corrosion attack resulting in thinning of tube material and internal corrosion penetration which finally led to premature failure.

Direct synthesis of highly crystalline transparent conducting oxide nanoparticles by low pressure spray pyrolysis

In this article, we firstly reported a general preparation method for the production of highly crystallized and single crystalline transparent conducting oxide (TCO) nanoparticles: tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), aluminum-doped zinc oxide (AZO), and gallium-doped zinc oxide (GZO). Low-pressure spray pyrolysis was applied by means of a modified-atomizer and preheated carrier gas. The effects of pyrolysis pressure, temperature and carrier gas temperature on the size and morphology of the synthesized TCO nanoparticles were systematically investigated. The synthesized TCO nanoparticles were 17 nm large with crystallite size of 8–11 nm. The resistivities of the formed pellets were measured and compared. These results showed that this method successfully produces various TCO nanoparticles using neither dispersing agents nor post-heating treatments, which allows rapid, continuous, single-step preparation.

Turbulent combustion of preheated natural gas–air mixture

The flame structure at small Damköhler number and large Karlovitz number is still unknown. In the present study, the reaction zone structure in a distributed reaction zone regime was investigated extensively. The OH–PLIF images suggested that there are no thin laminar flamelets and that the reacting eddies were distributed throughout the reactor. With the cross-correlation of ion signals, the scale of the reacting eddies was determined to be of the order of 4 mm, and the convection velocity of these eddies or zones was found to coincide with the mean flow velocity of the order of 100 m/s. In this combustion regime, high intensity combustion can be realized with extremely low NO x emission. These features are very attractive for the practical use (for example, vehicles and aircrafts) to meet the environmental requirements.

Evaluation of different alternatives for increasing the reaction furnace temperature of Claus SRU by chemical equilibrium calculations

Application of different alternatives for increasing the reaction furnace temperature of Claus sulfur recovery units (SRUs) are investigated by chemical equilibrium calculations. The Gibbs free minimization method based on Lagrangian multipliers is used for formulating the problem. The usefulness of different techniques such as fuel gas spiking, indirect air and/or acid gas preheating, oxygen enrichment, acid gas enrichment and direct air preheating for increasing the furnace temperature are determined by the proposed algorithm. In the case of lean feed acid gases, it may be necessary to use a combination of methods in order to attain the minimum furnace temperature required for flame stability and complete destruction of acid gas hydrocarbon contaminants. It is found that the acid gas enrichment is a reliable technique for providing the required reaction furnace temperature when a high flow of too lean acid gas is to be processed in a Claus unit. The predicted reaction furnace temperatures are in good agreement with the measured experimental values.

The accretion and cooling of pre-heated gas in dark matter haloes

We use a one-dimensional (1D) hydrodynamical code to investigate the effects of pre-heating on gas accretion and cooling in cold dark matter (CDM) haloes. In the absence of radiative cooling, pre-heating reduces the amount of gas that can be accreted into a halo, and the accreted gas fraction is determined by the ratio of the initial specific entropy of the gas to the virial entropy of the halo, S ph /S v . In the presence of radiative cooling, pre-heating affects the gas fraction that can cool in two different ways. For small haloes with masses M 1013 h -1 M ⊙ , but has little effect on smaller haloes. We suggest that this may be the reason why the stellar mass function of galaxies breaks sharply at the massive end. Such pre-heating also helps create the hot diffused haloes within which the 'radio mode' feedback of AGNs can act effectively. In the second case, the intergalactic medium is assumed to be warm. Here, the total amount of gas that can cool in a halo scales with halo mass as ∝ M 2 , as would be required to match the observed stellar- and H I-mass functions in the current CDM model at the small mass end. Since the accretion in a CDM universe is expected to be lumpy, we discuss the limitation of our model due to the assumption of smooth mass accretion.

Preliminary studies of using preheated carrier gas for on-line membrane extraction of semivolatile organic compounds

In this paper, we present results for the on-line determination of semivolatile organic compounds (SVOCs) in air using membrane extraction with a sorbent interface-ion mobility spectrometry (MESI-IMS) system with a preheated carrier (stripping) gas. The mechanism of the mass transfer of SVOCs across a membrane was initially studied. In comparison with the extraction of volatile analytes, the mass transfer resistance that originated from the slow desorption from the internal membrane surface during the SVOC extraction processes should be taken into account. A preheated carrier gas system was therefore built to facilitate desorption of analytes from the internal membrane surface. With the benefit of a temperature gradient existing between the internal and external membrane surfaces, an increase in the desorption rate of a specific analyte at the internal surface and the diffusion coefficient within the membrane could be achieved while avoiding a decrease of the distribution constant on the external membrane interface. This technique improved both the extraction rate and response times of the MESI-IMS system for the analysis of SVOCs. Finally, the MESI-IMS system was shown to be capable of on-site measurement by monitoring selected polynuclear aromatic hydrocarbons emitted from cigarette smoke.

PAH emissions from high-temperature oxidation of vaporized anthracene

The presence of polycyclic aromatic hydrocarbons/compounds (PAH/PAC) in the exhaust of combustion equipment as well as their growth to soot particles depends on the balance of formation and depletion reaction pathways. Detailed understanding of PAH oxidation is necessary for a correct quantitative description of combustion processes. This study focuses on the high-temperature oxidation of anthracene, a 3-ring PAH, by molecular oxygen. By reacting this already formed PAH, under non-sooting conditions, its oxidative depletion processes were isolated from its formation processes, as well as from soot formation pathways. Anthracene powder, fluidized in nitrogen, was introduced into a two-stage electrically heated laminar-flow drop-tube furnace. In the first stage, kept at 900 °C, anthracene was vaporized. Thereafter, upon mixing with preheated oxygen-containing gases in a venturi, gaseous anthracene was oxidized in the second furnace at oxygen mole fractions of 1–5% and gas temperatures of 950–1050 °C. Gas temperature and velocity profiles in the furnaces, as well as anthracene particle vaporization trajectories were obtained with a computational fluid dynamics code. Sampling, followed by chemical analysis, was conducted at three locations within the oxidizing furnace. Trends with residence time show increasing CO and CO 2 yields in the furnace and gradually decreasing O 2. CO increased with higher oxidizing temperatures and oxygen concentrations. Acetylene was the most abundant light hydrocarbon, followed by methane, ethylene, benzene, propylene and ethyl acetylene. Prevalent PAC included fluorene-9-one, 9,10-anthracenodione, biphenylene, dibenzofuran, fluorene, indene, naphthalene, anthrone, xanthone and 2-naphthalenecarboxaldehyde. Most species’ yields increased with rising oxidation temperatures. A global anthracene reaction rate with oxygen was deduced, and an activation energy of 71 kJ/mol was calculated. An anthracene oxidation reaction scheme was proposed.

Numerical simulation of temperature field during gas preheating and start-up of drained aluminum reduction cell

The method of numerical simulation was applied to investigate gas preheating and start-up process in a drained aluminum reduction cell. The transient temperature and velocity fields of a 156 kA drained aluminum reduction cell were numerically calculated. The results show that the method of gas preheating and bake-out can basically meet the technical requirements of the start-up process for the drained cell. If the same distributing scheme of gas nozzle as that in the general cells is used, there are problems of great temperature gradients and low temperature zone at the top of cathode near the side of nozzles. In order to promote the effect of gas preheating and baking the drained cell, the jetting angle of end nozzle is adjusted and the temperature distribution in the drained cell is obviously improved. By means of simulating the temperature field in the case that jetting angle varies from 0° to 30°, it is concluded that better temperature distribution can be obtained if the jetting angle of end nozzle is approximately 15°.

Low-Temperature Growth of Vertically Aligned Carbon Nanotubes Using Binary Catalysts

We have investigated a low-temperature growth process for vertically aligned carbon nanotubes on a normal glass plate, which is applicable to the preparation of large field emission devices. This process involves the preheating of a carbon source gas and the use of binary catalysts. Three binary catalysts, Fe/Al, Fe/Ti and Co/Ti, have been examined. It has been found that the Al base layer enhances the reactivity of Fe with acetylene gas but the Ti base layer does not. The combination of the Ti base layer and Co is effective for the growth of the aligned nanotubes at low temperatures.

Failure analysis of ruptured pipe connected to natural gas pre-heater

Failure Analysis was made on a ruptured low carbon steel pipe that was connected to a natural gas pre-heater in a chemical plant. The pipe has been in service for about 30 years. The analysis indicated that failure of the pipe was due to thin-lip rupture, resulting from high temperature sulphidation. The rate of sulphidation was much faster at the bend areas where turbulent flow was occurring. The pipe also suffered from graphitization due to decomposition of the pearlite phase as a result of long service time at moderately high temperature. It was recommended to replace the pipe with a new one and to regularly monitor the pipe thickness with special emphasis on bend areas. The plant was also advised to minimize the ingress of humidity and oxygen into the piping system during shutdowns.

Cold gas in dark matter halos and the formation of late-type galaxies

We use recent observations of the HI mass function to constrain the amount of cold gas in dark matter halos. It is found that the cold gas mass in a halo decreases rapidly with decreasing halo mass for low-mass halos with M< 10 12 h −1 M� . This result is in conflict with the standard model, in which most of the gas in a low-mass halo is assumed to settle into a gaseous disk, and the cold gas is depleted by star formation and supernova-driven outflow until the disk becomes gravitationally stable. Heating by the UV background can reduce the amount of cold gas in halos with masses < 10 10 h −1 M� , but is insufficient to explain the observational result. A consistent model can be found if low-mass halos are embedded in a preheated medium, with a specific gas entropy ∼ 10 keV cm 2 . Such a model can also explain why the faint-end slope of the galaxy luminosity function is flat. We propose a preheating model in which the medium around low-mass halos is preheated by gravitational pancaking. Since large-scale tidal fields tend to suppress the formation of low-mass virialised halos while promoting the formation of pancakes, the formation of massive pancakes may precede that of low-mass dark halos at the present time. 'Previrialisation' of such pancakes can heat the intergalactic medium. The preheated gas has a cooling time longer than the age of the Universe at z ∼ 2, and has a specific entropy comparable to that required to reduce the amount of cold gas and star formation activity in galaxy halos.

Intracluster and Intragroup Entropy from Quasar Activity

We investigate how the hierarchical merging of dark matter halos, the radiative cooling of baryons, and the energy feedback from supernovae and active galactic nuclei or quasars combine to govern the amount and the thermal state of the hot plasma pervading groups and clusters of galaxies. We show that, by itself, supernova preheating of the external gas flowing into clusters falls short of explaining the observed X-ray scaling relations of the plasma luminosity L_X or the plasma entropy K versus the X-ray temperature T. To account for the scaling laws from rich to poor clusters takes preheating enhanced by the energy input from active galactic nuclei. In groups, on the other hand, the internal impacts of powerful quasars going off in member galaxies can blow some plasma out of the structure. So they depress L_X and raise K to the observed average levels; meanwhile, the sporadic nature of such impulsive events generates the intrinsic component of the wide scatter apparent in the data. The same quasar feedback gives rise in groups to entropy profiles as steep as observed, a feature hard to explain with simple preheating schemes. Finally, we argue a close connection of the L_X-T or the K-T relation with the M_{\bullet}-\sigma correlation between the host velocity dispersion and the masses of the black holes, relics of the quasar activity.

Parameter optimization through performance analysis of model based control of a batch heat treatment furnace with low NOx radiant tube burner

Abstract A model based control structure for heat treating a 0.5% C steel slab in a batch furnace with low NO x radiant tube burner is designed and tested for performance to yield optimal parameter values using the model developed in the companion paper. Combustion is considered in a highly preheated and product gas diluted mode. Controlled combustion with a proposed arrangement for preheating and diluting the air by recirculating the exhaust gas that can be retrofitted with an existing burner yields satisfactory performance and emission characteristics. Finally, the effect of variable property considerations are presented and critically analyzed.