Gases compositions of flue

Table 2. Composition of flue gases for the two modeled conditions...

Many different compositions of flue gases are encountered in practice. Depending on the combustion or melting process involved, the flue gases can be quite mild, or can be explosive and aggressive, while wide temperature differences ranging from 65°C to weU over 450°C can be encountered. 

The fact that the sensing of different gases can be controlled by the correct choice of catalytic metal and operating temperature opens the possibility to use arrays of these sensors together with pattern recognition techniques to provide detailed information about the composition of ambient gases. This has been tested in flue... 

Correct conclusion According to the technical literature, Gas testers are flue gas analyzers intended to determine the exhaust gas composition of oven gases.238 Such devices were standard equipment in crematoria. That the above mentioned order referred to such devices is clear from the fact that they were ordered by a heating technician from an oven construction firm. The letter in reply from the Topf corporation dated March 2, 1943, stating that one must first find out who marketed these devices, has been revealed on several occasions to be an absurdity 239... 

The composition of the biomass (C6H 20s) determines the flow rate of both the needed air and the flue gases and the composition of the last one. Considering an excess air flow rate of 15%, 4.86 Nm air/kg biomass is required, while the flow rate of the flue gases is 5.63 Nm flue gas/kg biomass. The total flow rates for a 2.5 tph combustor are then 12,150 Nm /hr of air and 14,100 Nm /hr of flue gases. 

In many cases, the performance of a combustion system can be quantified in terms of a few parameters, such as oxygen concentration and temperature of flue gases, pollutant emissions, steam production, and so on. However, these data may not be enough to describe the actual state of the combustion process. A clear example is the case of multiburner chambers, where global values do not represent necessarily the conditions at individual flames. Even for a single burner, bulk parameters (e.g., flue gas composition) can only afford a limited characterization of the flame. As it was pointed out in the introduction, a detailed description would require a vast amount of information in terms of the distributions in space (and maybe time) of many physicochemical variables. Imaging techniques are most valuable tools in this respect, since information on spatial patterns can be very helpful to describe, or even understand, important characteristics of a flame. 

Parameters for the analysis included the diameter and thermal conductivity of the granule, and the inlet flue gas temperature, velocity, and composition. Flue gas velocity and temperature profiles and the temperature distribution within the granule were determined from the simulations. In this analysis, the assumption is that flue gases only pass through a single granule. The effect of other particles on the flow and temperature of flue gases and the particle/particle Interaction are not considered. 

Figure 15. Average temperature ratio versus time at four inlet velocities of flue gases The effect of flue gas composition...

The composition and physical condition of flue gases present a challenging environment in which the adsorbents will need to operate. Water and oxygen will always be present in the flue gases, irrespective of the fuel combusted. As their removal prior to the capture process will involve a significant energy penalty, any solid sorbent for carbon capture will have to meet the performance requirements and be stable in the presence of these components. This leads to one key difference between amine solvent systems and solid adsorbent systems where water poses little problem in what is already an aqueous system. 

Because of the wide variation in composition and properties of brown coal (see Table 3), efficient combustion of these fuels caimot be accomphshed by a single system. The moisture content limits combustion efficiency because some chemical energy is required to convert Hquid water to steam in the flue gases. The steam then increases the dew point of the gases, requiring higher temperatures to avoid condensation in the stack. For fuels up to 25% moisture content, 80% efficiency can be achieved. As the moisture content increases to 60%, the efficiency decreases to 70% and efficiency continues to decline about another 1% for each additional 1% moisture to 70%. 

The failure took place in a large water-tube boiler used for generating steam in a chemical plant. The layout of the boiler is shown in Fig. 13.1. At the bottom of the boiler is a cylindrical pressure vessel - the mud drum - which contains water and sediments. At the top of the boiler is the steam drum, which contains water and steam. The two drums are connected by 200 tubes through which the water circulates. The tubes are heated from the outside by the flue gases from a coal-fired furnace. The water in the "hot" tubes moves upwards from the mud drum to the steam drum, and the water in the "cool" tubes moves downwards from the steam drum to the mud drum. A convection circuit is therefore set up where water circulates around the boiler and picks up heat in the process. The water tubes are 10 m long, have an outside diameter of 100 mm and are 5 mm thick in the wall. They are made from a steel of composition Fe-0.18% C, 0.45% Mn, 0.20% Si. The boiler operates with a working pressure of 50 bar and a water temperature of 264°C. 

The characterization of PIC (products of incomplete combustion) from the combustion of wood treated with pentachlorophenol (penta) is more widely documented in the open literature than creosote alone. However, both products are similar in chemical composition and likely result in comparable forms and concentrations of PIC. Literature reported studies on the combustion of these chemicals and wood treated by them, and the PIC generated are based upon optimal conditions. Optimal conditions are defined as those in which the fuel burns at the designed heat release rate with nominally 160% excess air and a low level (< 100 ppm) of carbon monoxide (CO) emissions in combustion (flue) gases. 

An ozone treatment (10 minutes at room temperature) of the HF-etched SiC surface before the metallization step was introduced as a very convenient processing step to produce Schottky diode gas sensors with an increased stability and reproducibility. The use of spectroscopic ellipsometry analysis and also photoelectron spectroscopy using synchrotron radiation showed that an oxide, 1-nm in thickness, was formed by the ozone exposure [74, 75]. The oxide was also found to be close to stochiometric SiO in composition. This thin oxide increased the stability of the SiC Schottky diodes considerably, without the need for any further interfacial layer such as Ta or TaSi which have been frequently used. Schottky diodes employing a porous Pt gate electrode and the ozone-produced interfacial layer have been successfully operated in both diesel exhausts and flue gases [76, 77]. 

The chemical composition of CCPs varies with coal origin and rank however, the major elemental constituents of all coal ash residues are O, Si, Al, Fe, and Ca, along with lesser amounts of Mg, S, and C. The relative abundance of constituents that typically make up more than 1 % of the total mass of fly ash and bottom ash are summarized in Table 4. These elements are found in the ash because of their lower volatility and the short time the particles actually remain in the furnace during combustion (Helmuth 1987). Both crystalline and non-crystalline compounds form on the surface of fly ash particles when elements react with oxygen in the flue gases, and through... 

Work is still in progress on determining the particle size distribution in the flue gases before and after the precipitator and in the stack. Also, studies on fly ash composition as a function of particle size are in progress. 

As discussed in Chapters 5 and 7, the use of lime to precipitate calcium arsenates is a common method for removing inorganic As(V) from water or flue gases. Calcium arsenates were also once extensively used in pesticides (Chapter 5). The compositions of some calcium arsenates, such as johnbaumite (Ca5(As04)3(0H) Table 2.5), resemble the very common phosphate mineral, apatite (Ca5(P04)3(F,Cl,0H)), where arsenate replaces phosphate. Some lead arsenates, such as mimetite (Pb5(As04)3Cl Table 2.5), also have crystalline structures that are related to apatite. Mimetite may occur in oxidized lead-rich hydrothermal deposits. 

Emissions from biomass-fueled boilers can be controlled by a variety of methods. The control systems needed depend mainly on the composition of the feedstock. First, good combustion control is essential to maximize combustion and to minimize emissions of unburned hydrocarbons and carbon monoxide. Efficient removal of particulate matter in the flue gases can be achieved by various combinations of cyclonic separation, electrostatic precipitation, agglomeration, and filtration. Removal of acid gas emissions can be achieved by flue gas scrubbing and treatment with lime. There are several approaches to the control of NO, emissions (Clearwater and Hill, 1991). Combustion control techniques include use of staged combustion, low excess... 

The influence of the maximum temperature in the combustor on the composition of the flue gases is shown on Figures 3 and 4, The temperature increase leads to better and faster combustion of the char and CO (Figure 3), It is clear that the temperature in the combustor cannot be too high to avoid ash melting and increase in the NOx formation. The concentration of NO is usually within 100 - 200 ppm limits (Figure 4) in reasonable agreement with experimental observations. 

Assuming different pyrolysis product distributions for almond shells according to the measurements of El Asri ct al. [5], Font et al. [12, 13], or Parodi et al. [14], different composition of the flue gases, in particular CO contents, have been predicted. It was found that the amount of char formed in the pyrolysis stage is of great importance. The fraction of fme particles that escape to the conical part of the reactor is of relevance for the CO production, but it doesn t affect the NO formation. The variation of the air splitting ratios between different blocks is of minor importance. 

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