The Behavior of Free Lime in CFBC Ashes

2003 ◽  
Author(s):  
E. M. Bulewicz ◽  
K. Go´ra ◽  
E. J. Anthony
Keyword(s):  
Standard Method ◽  
Liquid Water ◽  
Hydration Process ◽  
Free Lime ◽  
Free Cao ◽  
Ash Disposal

Ash disposal and ash use are critical to FBC technology and in turn the reactions of FBC ash with water are key to both of these two issues. An effective ash reactivation technology would improve the economics for FBC firing of high-sulphur fuels. Similarly, controlled ash hydration before disposal is the standard method for conditioning FBC ashes when firing high-sulphur fuels with limestone addition. Ashes can be hydrated with liquid water or by steam under pressure and our earlier work suggested that when FBC ashes were hydrated by either method, the components derived from the coal and those from the sorbent can interact chemically. As a result, the amount of “free CaO” (defined as the proportion of CaO and Ca(OH)2, expressed as CaO) may change. Usually, “free CaO” increases after hydration, particularly under pressure. However, there is also evidence that some of the CaO, derived from excess limestone sorbent, enters into reaction with the ash components, possibly silica or silicates. Such processes must modify the exothermicity of the ashes with water and affect their subsequent behaviour. This implies that it is incorrect to assume, as has often been done, that the heat of the hydration process is directly proportional to the CaO content of the ash. Furthermore, the results presented here also strongly support the view that one must include these interactions when looking at FBC hydration.

THE INFLUENCE OF THE PREHEATING OF WOOD IN WATER ON THE RATE OF DELIGNIFICATION BY SULPHITE LIQUOR

1935 ◽  
Vol 13b (3) ◽  
pp. 149-155 ◽  
Author(s):  
A. J. Corey ◽  
O. Maass
Keyword(s):  
Standard Method ◽  
Liquid Water ◽  
Wood Chips ◽  
Tentative Explanation

The rate of delignification of wood chips has been measured and found to conform to the monomolecular relation, provided that the standard method of penetration developed in this laboratory is used (3). Pretreatment of the wood chips by heating in liquid water at 130 °C. decreases the rate of delignification by subsequent cooking in sulphite liquor, and the rate no longer conforms to the monomolecular relation. Preheating of the wood to 130 °C. in the absence of water does not influence the rate of subsequent delignification. The results indicate the advantage of reducing the time of cooking, and a tentative explanation has been offered regarding the mechanism involved.

Hydration of Partially Sulphated CFBC Ash With Saturated Steam

2003 ◽  
Author(s):  
Yinghai Wu ◽  
Edward J. Anthony ◽  
Lufei Jia
Keyword(s):  
Fly Ash ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Bottom Ash ◽  
Size Fraction ◽  
Hydration Process ◽  
Saturated Steam ◽  
Fluidized Bed Combustion ◽  
Free Lime ◽  
X Ray

The hydration of partially sulphated fluidized bed combustion (FBC) ash with saturated steam was carried out in the laboratory. The ash samples were obtained from a commercial-scale 165 MWe circulating fluidized bed combustor (CFBC) firing a petroleum coke and coal blend. Both bottom ash and fly ash were tested, and in addition the bottom ash was also separated into five size fractions and tested. These solid streams and the “as-received” fly ashes were hydrated by steam produced in a pressure bomb for different lengths of time at different saturated temperatures. Samples of the ashes were analyzed for free lime and calcium hydroxide content before and after the hydration process. Scanning electron microscopy (SEM) with an energy dispersive X-ray system (EDX) was employed to determine physical characteristics of the samples. X-ray diffractograms (XRD) were also used to determine the phase composition. These results show that after hydration treatment with saturated steam at elevated pressures, the unreacted CaO in the partially sulphated material can be quantitatively converted to Ca(OH)2. However, the free lime content is also observed to change throughout the hydration process, which indicates that the hydration of CaO is not the only reaction occurring in this system. It is also clear that for fines, i.e., fly ash and <75 μm size fraction bottom ash, the effectiveness of the hydration depends much more strongly on hydration time and temperature than for coarser ashes and it is also clear that the behaviour of each particle size fraction is different.

Percentage of Inadequate Phlebograms and Observer Agreement in Thromboprophylactic Multicenter Trials Using Standardized Methodology and Central Assessment

1996 ◽  
Vol 76 (06) ◽  
pp. 0893-0896 ◽  
Author(s):  
P Kälebo ◽  
S Ekman ◽  
S Lindbratt ◽  
B I Eriksson ◽  
U Pauli ◽  
...  
Keyword(s):  
Standard Method ◽  
Observer Agreement ◽  
Observer Variability ◽  
Intraobserver Agreement ◽  
Multicenter Trials ◽  
Kappa Value

SummaryThis study examines inadequacy rates for phlebography in two multicenter trials for the prevention of post-operative DVT and determines inter- and intra-observer variability in evaluating phlebograms. A total of 991 (I) and 385 (II) patients underwent bilateral phlebography in two studies of thromboprophylaxis. Phlebography was performed using a standard method designed to visualize and assess all deep veins. Each vein was scored as normal, DVT or inadequate by both local and central assessment. The study showed low inadequacy rates for phlebograms of 12.2% (121/991) and 6.5% (25/385). Inter-observer agreement (local vs. central assessment) was moderate in both studies (1:74.8%, Kappa-value 0.41; II: 82.6%, Kappa-value 0.51). Good intraobserver agreement (within the central assessment group) was observed (I: 88.8%, Kappa-value 0.75). This study demonstrates low inadequacy rates for phlebograms using a standardized methodology and superior intra-observer agreement compared to inter-observer agreement and supports the importance of central assessment of phlebograms in thromboprophylactic multicenter trials to reduce observer variability.

A Modified Thromboplastin Screening Test

1961 ◽  
Vol 06 (03) ◽  
pp. 492-497 ◽  
Author(s):  
Janet C. Macpherson ◽  
R. M Hardisty
Keyword(s):  
Standard Method ◽  
Comparative Studies ◽  
Screening Test ◽  
Incubation Mixture ◽  
Surface Contact ◽  
Modified Test ◽  
Effect Of Surface

SummaryA modification of the thromboplastin screening test of Hicks and Pitney is described, in which the effect of surface contact on the test plasma is controlled by the addition of a suspension of kaolin to the incubation mixture before recalcification.Comparative studies show the modified test to give more reproducible results than the standard method.

A Review on Utilization of Fly- Ash and Pond-Ash as a Partial Replacement of Cement in Concrete Mix Design

2018 ◽  
pp. 413-418
Author(s):  
Harshkumar Patel ◽  
Yogesh Patel
Keyword(s):  
Fly Ash ◽  
Electricity Generation ◽  
Power Plants ◽  
Renewable Energy Sources ◽  
Thermal Power ◽  
Strength Test ◽  
Partial Replacement ◽  
Pond Ash ◽  
Research Activities ◽  
Ash Disposal

Now-a-days energy planners are aiming to increase the use of renewable energy sources and nuclear to meet the electricity generation. But till now coal-based power plants are the major source of electricity generation. Disadvantages of coal-based thermal power plants is disposal problem of fly ash and pond ash. It was earlier considered as a total waste and environmental hazard thus its use was limited, but now its useful properties have been known as raw material for various application in construction field. Fly ash from the thermal plants is available in large quantities in fine and coarse form. Fine fly ash is used in construction industry in some amount and coarse fly ash is subsequently disposed over land in slurry forms. In India around 180 MT fly is produced and only around 45% of that is being utilized in different sectors. Balance fly ash is being disposed over land. It needs one acre of land for ash disposal to produce 1MW electricity from coal. Fly ash and pond ash utilization helps to reduce the consumption of natural resources. The fly ash became available in coal based thermal power station in the year 1930 in USA. For its gainful utilization, scientist started research activities and in the year 1937, R.E. Davis and his associates at university of California published research details on use of fly ash in cement concrete. This research had laid foundation for its specification, testing & usages. This study reports the potential use of pond-ash and fly-ash as cement in concrete mixes. In this present study of concrete produced using fly ash, pond ash and OPC 53 grade will be carried. An attempt will be made to investigate characteristics of OPC concrete with combined fly ash and pond ash mixed concrete for Compressive Strength test, Split Tensile Strength test, Flexural Strength test and Durability tests. This paper deals with the review of literature for fly-ash and pond-ash as partial replacement of cement in concrete.

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