Effect Of Bed Temperature Research Articles

Direct Combustion of Olive Cake Using Fluidized Bed Combustor

A fluidized bed combustor of 0.146 m diameter and 1 m length was fabricated from stainless steel to burn olive cake. Initially, and in order to obtain fluidization, the system was operated under cold conditions using a sand with particle size in the range of 500 to 710 microns. The continuous combustion experiments were carried out under controlled conditions, such that the effects of bed temperature, olive cake feed rate, fluidization velocity, and particle size on combustion efficiency and flue gas composition were investigated. It was found that the combustion efficiency decreases with the bed temperature, fluidization velocity, and the feed rate, while it increases with the particle size used. Further, the gas products analysis carried out using a gas chromatography analyzer have shown a nonmeasured amountof SO2, and small amounts of CO. Finally, the temperature distribution along the bed indicated that the temperature throughout the bed is fairly uniform, demonstrating a good mixing of reactants, which is important for efficient combustion.

Splash-Zone Heat Transfer in Bubbling Fluidized Beds: an Experimental Study of Temperature Effects

Abstract Experimental results are reported for the heat transfer between a high-temperature fluidized bed and a horizontal tube located within the splash zone. Of specific interest in this study is the effect of bed temperature. Four bed operating temperatures (700, 810, 908, and 1003 K) were investigated. At each temperature, five circumferential local time-averaged values of the total and blackbody radiative heat transfer coefficients were measured for three tube locations. The tube was located at 406, 64, and −127 mm relative to the packed bed-freeboard interface. These locations are representative of a tube in the freeboard, in the splash zone, and totally immersed in the bed, respectively. The tube outside diameter was 51 mm, the mean bed particle size was 2.9 mm, and the superficial fluidizing velocity varied from near minimum fluidization conditions ( U mf ) to over 1.5U mf . The work was performed in the Oregon State University high-temperature fluidized-bed test facility.

The amounts of NO x and N 2O formed in a fluidized bed combustor during the burning of coal volatiles and also of char

Three quite different coals were burned batchwise in electrically heated beds of sand fluidized with O 2 and N 2 at either 800 or 900°C. The coal was injected into the bed either as a single piece (1 or 2 cm in size) or as 1.0 g batches of smaller particles (either 1.4–1.7 or 2.0–2.4 mm in diameter). The concentrations of NO x (i.e., [NO] + [NO 2]), N 2O, CO, and CO 2 in the off-gases were measured as functions of time whilst the coal was burning. It proved relatively easy to separate the emission of any one of these gases into that from the initial, devolatilization stage of combustion and that from the subsequent burning of the char. The first stage of coal combustion, when the volatile matter burns, turns out to be very important. For a low rank coal, 70%–90% of all the N 2O produced appears while the coal is undergoing devolatilization. The fraction drops to 40% for a coal with a low volatile content. The figures for NO x emissions range from 55% of the NO x arising from the volatiles in a low rank coal to 25% for a coal of high rank. In general, the effects of bed temperature and coal size were much less important than a coal's volatile content. Interestingly, changing the bed temperature altered the ratio [N 2O] [NO x] in the off-gases and not the total quantity of oxides of nitrogen emitted. Lower concentrations of O 2 resulted in slightly less N 2O and NO x being produced. The rates of production of NO x and N 2O during combustion of the volatiles were found to be proportional to one another. This seems to derive from a lack of mixing of the volatiles. The fact that large (> 1 cm) coal particles float on top of a fluidized bed during devolatilization is important and, e.g., can result in large particles producing less NO x and N 2O during devolatilization than tiny particles. The observations made during devolatilization conform to effectively all the fuel-nitrogen in the volatile matter being converted to HCN. Nitric oxide is then produced most probably heterogeneously on the sand from CN radicals, which alternatively can yield NCO radicals. N 2O is generated during devolatilization by the reaction NCO + NO → N 2O + CO occurring, probably in the gas phase. As for the burning of char in a fluidized bed, the particle size (> 1 mm) here is large enough for there to be control by mass transfer of oxygen to a particle. Oxidation is thus confined to the exterior of the char. It appears that CO, from burning char, is important, together with reaction between NO and solid carbon, in converting NO to N 2. This is why the yield of NO from char-N is less than that from volatile-N.

Coating efficiency of seed particles in a fluidized bed by atomization of a powder suspension

Seed particles were coated with a powder in a fluidized bed by atomizing a suspension of the powder and then measuring the coating efficiency. This depends on the operating conditions, for example, the concentration of the powder and binder in the suspension, the bed temperature, the humidity of fluidizing gas and the feed rate of the suspension. An index, R, which evaluates quantitatively the drying conditions in a fluidized bed, is defined as the ratio of the humidity of outlet gas to its maximum humidity achieved at the saturation. It was confirmed that the effects of bed temperature, humidity of fluidizing gas and feed rate of suspension on the coating efficiency were all correlated by the index. The index proposed here is useful for estimating the coating ability of the materials used and of the fluidized bed coater.

Heterogeneous Oxidation of Toluene in the Bed Region of a Spouted Bed Combustor; Effect of Bed Temperature and Bed Material

Abstract Toluene was used as the fuel in a heterogeneous spouted bed combustor to investigate the effect of bed material on pollutant emissions. Experimental measurements were conducted in the annulus region (preflame) and include Destruction and Removal Efficiency (DRE) of the fuel, and concentrations of three products of Incomplete combustion (PICs) of toluene; CO, benzene and benzaldehyde. Two types of bed material were used: Sand and quartz. Higher conversion of the fuel (higher DRE) and higher concentration of CO, benzene and benzaldehyde (up to one order of magnitude) were observed with sand particles. Predictions of a detailed homogeneous gas phase mechanism for the oxidation of toluene (Emdee et al., 1992), were compared to the experimental data to reveal possible influences of surface reactions on the conversion of toluene and formation of CO, benzene and benzaldehyde.

Splash-zone heat transfer in bubbling fluidized beds: An experimental study of temperature effects

Experimental results are reported for the heat transfer between a high-temperature fluidized bed and a horizontal tube located within the splash zone. Of specific interest in this study is the effect of bed temperature. Four bed operating temperatures (700, 810, 908, and 1003 K) were investigated. At each temperature, five circumferential local time-averaged values of the total and blackbody radiative heat transfer coefficients were measured for three tube locations. The tube was located at 406, 64, and −127 mm relative to the packed bed-freeboard interface. These locations are representative of a tube in the freeboard, in the splash zone, and totally immersed in the bed, respectively. The tube outside diameter was 51 mm, the mean bed particle size was 2.9 mm, and the superficial fluidizing velocity varied from near minimum fluidization conditions ( U mf ) to over 1.5U mf . The work was performed in the Oregon State University high-temperature fluidized-bed test facility.

Combustion characteristics of shredded waste tires in a fluidized bed combustor

The effects of bed temperature (700–900 °C), freeboard temperature (600–800 °C) and excess-air ratio (0–100%) on CO, NO x and SO 2 emissions, axial temperature profiles, and combustion efficiency of shredded waste tires have been determined in a 76.2 mm i.d. × 1.2m high fluidized-bed combustor. CO-emission levels are maintained below 400 ppm at freeboard temperatures above 750 °C with a 25% excess-air ratio. The freeboard temperature increases sharply at lower excess-air ratios or at bed temperatures below 750 °C. The overall combustion efficiency for waste tires is higher than for bituminous coal and increases with increasing excess-air ratio and bed temperature. The NO x concentration in the flue gas based on 6% O 2 has been correlated with the bed temperature, nitrogen fraction in the fuel and excess-air ratio.

Effects of fuel type and operating conditions on SO2 emission in fluidized bed combustion

AbstractThe SO2 emission from six fluidized bed combustors was examined. Approximately 71.5% of the fuel sulphur was found to be emitted as SO2 in sorbent‐free tests. General observations on the effects of Ca/S molar ratio, limestone size and recycle systems are presented. The effects of limestone type and superficial velocity were found to be insignificant, as was the effect of bed temperature in the range 800‐950°C. In tests with fine solid and liquid fuels, circulating FBC's were found to provide significantly better sulphur capture than bubbling FBC's.

Heat transfer characteristics for tubular arrays in a high-temperature fluidized bed: An experimental study of bed temperature effects

Experimental results are reported for the heat transfer between a high-temperature fluidized bed and an immersed horizontal tube array. Of specific interest in this study was the effect of bed temperature. Three bed operating temperatures were used: 705, 761, 812. At each temperature, measurements were taken to evaluate both local and average values of the total heat transfer coefficient and the radiation contribution. Mean bed particle sizes examined were 0.97, 1.53, and 2.37 mm. Superficial velocities were varied such that the heat transfer results apply over the range from packed bed conditions through minimum fluidization to well over twice the minimum fluidization velocity. A comparison is made between the heat transfer behavior of a tube with near neighbors, that is, in a bundle, and that for a single tube at the same operating conditions. This comparison illustrates the competing nature of both gas convection and radiation with neighboring tubes present.

Effect of bed temperature on bubble size and bubble rising velocity in a semi-cylindrical slugging fluidized bed.

On observe, a une temperature de lit elevee (600 K), les bulles et/ou les bouchons en utilisant un lit semicylindrique afin de determiner leurs dimensions et leurs vitesses d'ascension. Les donnees obtenues sont comparees aux resultats obtenus a la temperature ambiante (300 K)

タール含有ガス用流動層熱交換器の開発 タール捕集と流動性の検討

Tar coking might lead a serious trouble in the coal gasification plant, especially when the gasification temperatures are relatively low. Fluidized-ed heat exchanger has a good potential not only to prevent such a coking trouble but to recover heat from a hot gas leaving the gasifier. In this parer, effects of bed temperature and bed height on tar capture were investigated using an apparatus with 0.208m in diameter and 1.4m in height. The amount of accumulated coke on solid in fluidized-bed heat exchanger did not very significantly at temperatures ranging 392 to 554 t . However, at a temperature as low as 427 t, condensed tar did not decompose rapidly and a small amount of liquid tar was expected to appear on the fluidized solids, resulting agglomeration and unstable operation of the fluidized-bed heat exchanger.At temperatures of 447°C or higher, fluidzed-bed heat exchanger could be operated steadily without agglomeration of the solids. The bed height of the fluidized-bed heat exchanger affected strongly the amount of tar removed through the bed.

Heat transfer to horizontal tubes immersed in a fluidized-bed combustor

Experiments are carried out to measure the heat transfer rates to water-cooled horizontal tubes (D T = 25.4 mm) immersed in an atmospheric fluidized-bed combustor burning North Dakota lignite. Silica sand, with average diameter ranging from 0.544 mm to 2.335 mm, is used as bed material. The tests are conducted at average bed temperatures ranging from 587 to 1205 K. For bed temperatures less than 950 K, the bed is heated by a propane gas heater. The superficial velocity is varied from 0.73 to 2.58 m/s. Thus, the effect of bed temperature (T B = 587 – 1205 K), particle size (d̄ p = 0.544 – 2.335 mm), and fluidizing velocity (U = 0.73 – 2.58 m/s) on the heat transfer rate to horizontal tube immersed in a fluidized-bed combustor (0.45 m × 0.45 m) is investigated. Among the existing correlations, those correlations proposed by Glicksman and Decker, Zabrodsky et al., Catipovic et al., Grewal, and Bansal et al. are found to predict the present data quite well, when the contribution due to radiation is included. The radiative heat transfer is estimated as the difference between the heat transfer to oxidized boiler tube and gold-plated tube. The relative contribution of radiation is found to be 13% for a bed of sand particles (d̄ p = 0.9 mm) operating at 1087 K.

The effect of bed temperature and fluidization velocity on the chemistry of bench scale fluid bed retorting of Kentucky oil shale

A 3.8 cm diameter bench scale fluid bed retort was used to study the effects of varied bed temperature and fluidization velocity at atmospheric pressure on the distribution of pyrolysis products from Kentucky oil shales. Fluidization velocity was varied from 28 to 44 m/min at steady state bed temperatures from 500 to 625°C. Results indicated that secondary reactions (primarily cracking) were minimal at all fluidization velocities studied at lower bed temperatures (<550°C). This was supported by offgas composition and fixed carbon deposition data. At the lowest fluidization velocity (28 m/min) and bed temperatures under 550°C, greater residual volatile organic carbon was left in the spent shale and lower oil and gas yields were obtained. Decreased evaporation of oil from shale particles due to higher hydrocarbon partial pressures at low sweep velocities, could explain these results. Maximum oil yield was obtained at bed temperatures of 500–525°C and sweep velocities of 34 m/min to 44 m/min.

Heat transfer investigations for in-bed and freeboard vertical U-tubes in a fluidized bed at moderate temperatures

The heat transfer coefficients for a single U-tube immersed vertically in fluidized beds of silica sands ( d ̄ p = 222, 488, and 778 μ m ) and for a bundle of six hair-pin shaped nested vertical tubes mounted in the freeboard have been measured as a function of fluidizing velocity at bed temperatures ranging from 365 to 535 K. Simultaneous measurements of bed voidage were also made in each case. The effects of bed temperature, fluidizing velocity and particle size on in-bed and freeboard heat transfer coefficients and voidage are examined and explained.

Elimination d'anhydride sulfureux par réaction sur l'oxyde de cuivre en couche fluidisée

AbstractReaction between cupric oxide, oxygen, and sulphur dioxide has been studied in a fluidized bed reactor continuously fed with solid reactant. The effect of bed temperature, solid flow rate, gas flow rate and the hight at minimum fluidization conditions has been investigated.Experimental conversions are between 20 to 60%.Olcutt and Davidson's fluidized bed reactor model slightly modified for our particular reactor has been compared with experimental data. The assumption of plug flow of gas in the dense phase is good for the height of 5 cm, on the contrary, the assumption of perfect mixing of gas in the dense phase is better for the deepest bed.