Influence of the Ash Content

A novel ternary diagram for each coal was developed to uniformly assess the performance and potentials of all the gasification processes and the influence of the ash content shown in Chapter 7. An exergetic analysis also revealed the impact of the gas cooling methods. These results are presented in Chapter 8. 

Applying the boundary conditions from Table 5.11, the results are presented in Table 6.19. In line with Keller et al. [132], the best carbon conversion rate for hard coal (90%) was selected, yielding cold gas efficiencies of 80.2 for Pitt 8 and 77.4% for SAf coal, respectively. The oxygen and steam consumption for both cases are in the same order of magnitude, which indicates the limited influence of the ash content in fluid-bed systems. Due to the outlet temperature of 1000 °C, the methane concentration varies between 3.7 and 7.1vol% (dry) and elevated quantities of NHg and benzene can be expected in the raw gas. 

Table 3.14 shows the ash fusion behavior under reducing conditions and the corresponding ash composition. The influence of the iron content on IDT and ST can be clearly seen in the case of the Kentucky no. 9 and Illinois no. 5 coals. 

The normal levels of the major mineral constituents of cow s milk are listed in Table 5-1. These are average values there is a considerable natural variation in the levels of these constituents. A number of factors influence the variations in salt composition, such as feed, season, breed and individuality of the cow, stage of lactation, and udder infections. In all but the last case, the variations in individual mineral constituents do not affect the milk s osmotic pressure. The ash content of milk is relatively constant at about 0.7 percent. An important difference between milk and blood plasma is the rela-... 

Several studies have focused on the influence of wood type on CO2 gasification and steam gasification A general conclusion is that the ash content, composition and its catalytic properties explain the differences among the fuels. In particular, Hansen et al. refer to the potassium content of the ashes as being especially relevant. 

The amount of the tars in the fly ash from bark tested in the Vhmamo gasifier is in general higher than in fly ash from wood chips. It seems to be a relationship between the fixed carbon content of the fuel and the tars in the fly ash. Fuels with a high fixed carbon such as bark result in a higher amount of tars in fly ash than the fuels with low fixed carbon. However there is an indication that the fuel particle size have big influence on the tar content of the fly ash. The total amount of the unbumed carbon in the fly ash from both bark and wood chips in Vamamo plant is in the same range and at the same level as in the fly ash from combustion plants. 

As the ash content of different biomass could influence the gasification reactivity of biomass chars, a study has been conducted to determine the influence of heavy metals on the gasification process [6]-[7]. They show that the alkali metals increase the reactivity of wood char and that lead, copper and zinc, especially as chlorides, inhibited the gasification of the char (about 2.5 times slower that the char fromtmtreated wood). 

In the same way that the chemical composition of the mineral matter in coal influences the slagging potential, the chemical content of the ash will also affect the potential for fouling (in the cooler regions of the combustion plant). 

Purity The purity of activated carbon is essential for the performance of the final catalyst. Impurities of activated carbon originate from the raw material and the process conditions. Ash contents of up to 20% can be possible. Wood-based activated carbons have ash contents as low as 1 wt% [7]. The ash content can be lowered further by acid treatment of the activated carbon [8]. Typically, the ash consists of alkaline and alkahne earth metal oxides, silicates, and smaller amounts of other compounds (e.g., iron). The presence of the alkaline and alkaline earth metal oxides makes those carbons more basic in nature, so that some additional adjustments are necessary during catalyst manufacturing to meet the constant quality requirements. Since the supports are used in catalysts, the presence of catalytically active compounds that could have a potential influence on the performance of the final catalyst has to be considered as well. For the manufacture of catalysts, activated carbon based on wood, peat, nut shells, and coconut are commonly used. Due to a relatively high sulfur content in activated carbons derived from coal, those carbons are typically not used as catalyst support. 

The moisture content of the coal is a major variable affecting the performance of the ash monitor It alters the packing characteristics of the coal, and thereby, influences the bulk density of the sample Moisture also affects the handling characteristics of the coal Cammack and Balint ( 5) found that the compacted coal bed has a minimum density at 8% moisture and for moisture levels up to 7%, the maximum error in ash analysis was... 

The mineral matter content of coal varies considerably and may even be as high as 35% w/w of the coal. The composition of the mineral matter in the coal (or the composition of the mineral ash after combustion) is of importance for, as examples, the performance of design of postcombustion cleanup equipment, such as electrostatic precipitators and FGD units (Kelly and Spottiswood, 1982, 1989 Hjalmarsson, 1992). The alkali metals (sodium, potassium, and lithium) affect (decrease) the resistivity of the ash and can influence sulfur removal. 

As a rule activated carbons applied as catalyst carriers have to be very piu e. Chemical activated carbons are pure because of the choice of raw material and the production process. Steam activated carbons are mostly washed. In Table 5 the ash content and the Fe, Ca and Mg contents of the various carbon types are given. To show the influence of washing also an unwashed steam activated carbon with the same activation degree is given. The results show that washing decreases the mineral content. 

Although there are no special claims for the lactate content in buttermilk powder, a calibration for this component was still made (Table 20.10) because it may give information about (a) the original lactose content, (b) the ratio between lactose and protein, or (c) the amount of addition of neutralizing compounds for the lactic acid. The latter influences the ash content. 

Ash content of the coal affects the energy consumption because of physical heating and cooling or even melting of the ash material and is therefore linked to process efficiency. The ash content also directly influences the coal preparation (e.g., grinding) and transportation expenditures. 

There is no known method for accurately determining fruit juice content. For the determination of citrus juices in beverages it is shown by Stern that the percentage and alkalinity of the ash is of no value because of the influence of the alkalinity from sodium benzoate or sulphites added as preservatives and saccharin added in the presence of sodium bicarbonate. The phosphoric anhydride content is independent of these factors and the following table summarises the data for the range to be expected in natural juices. 

The ash content shows the amount of admixtures in carbon materials. For carbon materials, ash is oxides of sodium, potassium, calcium, and iron. For specialists in refractory materials, it is strange to tmite these oxides in one group and call it one word—ash. Still, if the ash content is within certain limits, it influences only the thermal and electrical conductivities. The ash content is determined according to DIN 51903 [51] and ISO 8005 [52]. 

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