A. Paul Watkinson

Preparation of activated carbon from lignin by chemical activation

Activated carbons were prepared from lignin by chemical activation with ZnCl2, H3PO4 and some alkali metal compounds. The influence of carbonization and activating reagent on the pore structure of the activated carbon was investigated. It was found that the maximum surface areas were obtained at the carbonization temperature of 600°C in both ZnCl2 and H3PO4 activation, and that the surface areas were as large as those of the commercial activated carbons. On the other hand, in alkali metal activation it was found that the maximum surface areas were obtained at the carbonization temperature of 800°C. Except for Na2CO3 maximum surface areas were much larger than those of the commercial activated carbons. The activated carbon prepared by K2CO3 activation showed a surface area of nearly 2000 m2/g. It was shown that ZnCl2 works effectively as dehydration reagent below 600°C. On the other hand, K2CO3 works effectively in two temperature ranges, below 500°C and above 600°C. Below 500°C, the carbonization behavior was modified by impregnation with K2CO3, but the pore structure changes little. Above 600°C, carbon was consumed by K2CO3 reduction and then the surface area was increased.

Spouted, fluidized and spout-fluid bed combustion of bituminous coals

Abstract Spouted, fluidized and spout-fluid bed combustion of three bituminous coals or coal rejects of differing ash contents was carried out in a 0.3 m internal diameter combustor. Coal feed rates were between 6 and 22 kg h −1 , excess air was usually 15–20%, the internal coil coolant was either air or water, and the average bed temperature ranged from 740 to 980 °C. Each of the three contacting modes was able to burn the coal to which it was subjected. Although differences in combustion performance between the three modes were generally small, the experimental results indicated that the spout-fluid bed tended to give somewhat higher combustion efficiencies at the lower temperatures, greater temperature uniformity and improved bed-to-immersed-surface heat transfer compared with the other two modes of operation. For all three modes, combustion efficiencies were over 90%, provided that bed temperatures were higher than 870 °C and that fines captured in the primary cyclone were recycled to the bed. The size and density of inert bed materials played a significant role. Denser and coarser inert particles tended to segregate, leaving burning char particles at or near the bed surface. Bed-to-cooling-coil heat transfer coefficients were of similar magnitude to those measured in earlier studies.

Fractal dimensions of activated carbons prepared from lignin by chemical activation

the form of adsorbents, catalysts and catalyst supports. In was mixed with one of the activating reagent and water,principle, there are two methods for preparing activated and was kneaded. An impregnation ratio [(the weight ofcarbons: physical activation and chemical activation. The activating reagent)/(the weight of lignin)] of 1.0 was usedphysical activation method comprises two steps: a carboni- in this work. The mixture was then dried at 383 K tozation step and an activation step. In chemical activation, a prepare the impregnated sample. The impregnated sampleraw material is impregnated with an activating reagent and was heated up to the carbonization temperature under N

Coal gasification in a pressurized spouted bed

Abstract Gasification characteristics are described for five coals of different rank which were gasified with air-steam or oxygen-steam mixtures in a 5 kg coal h −1 continuous spouted bed reactor at pressures to 1440 kPa. Results show the suitability of the different coals for dry ash spouted-fluid bed gasification, the processing requirements for low and medium calorific value gas, and the approach to equilibrium expected for various coals. For one of the coals, a comparison is made between results from the bench scale reactor and those for a forty times larger demonstration plant.

Gasification of oil sand coke

Abstract Cokes derived from two Alberta oil sands operations were gasified at feed rates of about 20 kg h −1 in steam and oxygen using a 0.30 m diameter atmospheric pressure gasifier operated as either a fluidized or a spouted bed. Effects of oxygen/coke ratio and temperature on gas composition, heating value and carbon conversion are presented. In situ sulphur capture using dolomite was demonstrated and the effect of gasification catalyst shown. Gas composition is compared with predictions of an equilibrium model.

DEPOSITION FROM CRUDE OILS IN HEAT EXCHANGERS

Deposition in flow lines and processing and heat transfer equipment arises from fouling species, which may either be present in the fluid or generated in the vicinity of the equipment surface. Recent research on deposition during heat transfer from petroleum feedstocks is reviewed. For low-sulfur light crude oils, deposition is largely due to particulates and gums. For medium-sulfur crude oils, the formation of iron sulfides plays a major role in deposition. In unstable heavy oil systems, suspended asphaltenes are the fouling species. Trace quantities of impurities such as dissolved oxygen or suspended corrosion products add markedly to deposit formation. The influences of flow velocity, bulk and surface temperatures, and particulate concentrations are demonstrated through experimental results and compared to expectations from simple models. Through an understanding of the key steps in the deposition processes, a rational mitigation strategy can be formulated.

Fluidized-bed gasification of some Western Canadian coals

Abstract Three Western Canadian coals were gasified with air and steam in a fluidized bed of 0.73 mm sand and coal, at atmospheric pressure and temperatures of 1023–1175K to produce a low-calorific-value gas. One non-caking and two caking coals were tested. The effects of temperature, coal feed rate, air coal ratio, steam coal ratio, coal quality, coal particle size and bed depth on gas composition, gas calorific value and operating stability of the gasifier were established. Results are compared with those previously obtained for the same three coals when gasified in essentially the same equipment, but operated as a spouted bed.

PRECIPITATION AND FOULING IN HEAVY OIL–DILUENT BLENDS

Heavy oil fractions rich in asphaltenes were mixed with diluents containing from 0.6 to 25% aromatics, and the resulting blends subjected to batch precipitation experiments at 85°C, and thermal fouling tests at surface temperatures in the range 230–310°C. Deposit compositions were determined, and are compared with suspended asphaltene composition. When the heavy oils were blended with the most aromatic diluents, precipitation and fouling were negligible. As the aromaticity of the diluents was decreased, the extent of asphaltene precipitation and the fouling rates increased. The solubility parameter of the blends, δ mix , and the flocculation solubility parameter for asphaltenes, δ f , were determined from measurements of the asphaltene flocculation onset by titration with heptane at temperatures from 25 to 50°C. Literature models predict no asphaltene precipitation (and presumably little fouling) will occur when [δ mix – δ f ] > 0. Both the amount of asphaltene precipitated in the batch experiments and the rate of thermal fouling decreased as the solubility parameter difference [δ mix – δ f ] increased from negative to positive values. However, some precipitation and fouling were observed at the expected condition for mixture stability δ mix ≥ δ f . As the temperature of the flocculation titration was raised toward the bulk temperatures of the experiments, values of [δ mix – δ f ] decreased, and the agreement of the data with prediction of the point for zero precipitation and fouling improved. For unstable oil blends, the solubility parameter provides a good predictive measure of the tendency for asphaltene precipitation and for heat exchanger fouling.

Formation and Characteristics of Carbonaceous Deposits from Heavy Hydrocarbon Coking Vapors

Deposition of carbonaceous material in the cyclone exit line is a chronic problem for fluid cokers and is a key process limitation to achieving longer run length. Extensive characterization studies were conducted for laboratory deposits from a bench-scale bitumen coker using modern analytical techniques, e.g., elemental analysis, X-ray fluorescence, thermogravimetric analysis, scanning electron microscopy, diffusive reflection infrared spectroscopy, and solid-state 13C nuclear magnetic resonance. Simulated distillation was also applied to solvent extracts of deposits. Results substantiate that on the laboratory scale physical condensation rather than chemical reaction was the primary reason for fluid coker cyclone exit line fouling. Entrained liquid droplets also contribute to the deposit formation. Although there are both polyaromatic and aliphatic structures in fresh laboratory deposits, the former dominate. High-temperature operation led to deposits an increased polyaromatic content. Industrial deposit...

A two stage Spouted Bed Process for Autothermal Pyrolysis or Retorting

Abstract A continuous autothermal two-stage pyrolysis/partial combustion process has been tested at the bench scale. Coal (or oil shale) up to 5 kg/h is fed to a spouted bed pyrolyzer in which the volatiles are driven off for tar recovery. Part of the resulting char is passed to a spouted bed partial combustor which produces the hot flue gas to provide heat and a spouting medium in the pyrolyzer. The two reactors are placed in a compact vertical configuration. The process is tested on two coals of different rank, and on oil shale. The effect of prime operating variables on yield are established and a number of operating modes demonstrated.