Thermal Zones

Other thermal zones, which should be thermostatted separately from the column oven, include the injector and detector modules. These are generally insulted metal blocks fitted with cartridge heaters and controlled by sensors located in a feedback loop with the power supply. Detector blocks are usually maintained at a temperature selected to minimize detector contamination and to optimize the detector response to different sample types. The requirements for injectors may be different depending on their design, and may include provision for temperature programmed operation. 

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The importance of these concepts can be illustrated by the extent to which the pyrolysis reactions contribute to gas produdion. In a moving-bed gasifier (e.g., producer-gas gasifier), the particle is heated through several distinct thermal zones. At the initial heat-up zone, coal carbonization or devolatilization dominates. In the successively hotter zones, char devolatihzation, char gasification, and fixed carbon... 

In thermal building simulation, a thermal zone can be a part of a room, a room, or a combination of rooms defined as a part of the conditioned space, throughout which the internal temperature is assumed to have negligible spatial variations. The zone is enclosed by the surrounding walls (floor, ceiling, roof, wall elements) and windows. 

Building modelization is the process by which the program s user represents a building as a number of thermal zones, separated by walls. HVAC systems are connected to these zones. Abstraction is necessary for the definition of the zones and the buildup of walls, and those components available in the code which match the reality best must be selected. 

The identification of zones can be made in different degrees of detail, depending on the specific purpose of thermal building-dynamics simulation. In most cases a zone can include several rooms having the same thermal conditions. Sometimes it is necessary to split a very large room into two or more thermal zones in order to have more accurate results. 

HVAC system parameters include information for the sizing of components. First of all, the type of HVAC system must be specified, and the thermal zones served by the system must be identified. Afterward, information must be specified on the following items ... 

Single-zone systems deliver conditioned air to a single thermal zone. These systems are popular iu small buildings (fewer than 10,000 square feet) and in... 

A multiple-zone system must be able to deliver heating to a perimeter thermal zone in the winter while cooling an interior zone to offset internal... 

Position of column relative to thermal zone (very short distance)... 

In the thermal zone, above the catalyst bed, further conversion occurs by homogeneous gas-phase reactions. The main reactions in the thermal zone are homogeneous gas-phase... 

SMR (reaction 2.4) and shift (reaction 2.6) reactions. Reactions between N2 and hydrocarbon radicals leading to the formation of such by-products as NH3 and HCN can also take place in the thermal zone. By proper adjustment of 02/CH4 and H20/CH4 ratios, the partial combustion in the thermal zone provides the heat for the subsequent endothermic steam reforming reaction taking place in the catalytic zone [40]. Thus, simplistically, ATR of methane at temperature T can be represented as follows ... 

It is interesting to review a general pattern for oxidation of hydrocarbons in flames, as suggested very early by Fristrom and Westenberg [29], They suggested two essential thermal zones the primary zone, in which the initial hydrocarbons are attacked and reduced to products (CO, H2, H20) and radicals (H, O, OH), and the secondary zone, in which CO and H2 are completely oxidized. The intermediates are said to form in the primary zone. Initially, then,... 

The autothermal reformer consists of a thermal and a catalytic zone. The feed is injected into a burner and mixed intensively with steam and a substoichiometric amount of oxygen or air. In the combustion or thermal zone part of the feed reacts essentially according to the reaction... 

The reactor and preheater each divide naturally into three types of thermal zone. These are ... 

Reactor studies were done in the Catalyst Laboratory at the R D Center of Phillips Petroleum Company in Bartlesville, Oklahoma. More detailed descriptions of the hydroprocessing reactor system and experimental program are given elsewhere (ref, 14,15). The catalyst is laboratory-impregnated Ni-Mo on a commercial 0.156 cm diameter alumina extrudate support provided by Ketjen. The feeds are partially hydrotreated residua from Hondo, Oriente, and Cano Limon crude oils. Asphaltenes were precipitated with a 40 to 1 ratio of n-pentane to oil. Residual oil and hydrogen are pumped upflow through a thermal zone... 

Figure 14. Mechanically agitated thin-film evaporator, vertical design with cylindrical thermal zone. (Luwa Corporation.)...

The vast majority of these pollutant-forming pathways involve free radicals. It is generally assumed that these radicals are formed in the high-temperature flame zone of combustion systems. However, reactions occurring in the post-flame, thermal zone (Zone 3) and the gas-quench and surface-catalysis zones (Zones 4 and 5), may also form radicals responsible for pollutant formation. In some cases, the radicals may be stable and act as pollutants themselves. 

The attractive features of splitless injection techniques are that they allow the analysis of dilute samples without preconcentration (trace analysis) and the analysis of dirty samples, since the injector is easily dismantled for cleaning. Success with individual samples, however, depends on the selection of experimental variables of which the most important sample size, sample solvent, syringe position, sampling time, initial column temperature, injection temperature and carrier gas flow rate, often must be optimized by trial and error. These conditions, once established, are not necessarily transferable to another splitless injector of a different design. Also, the absolute accuracy of retention times in splitless injection is generally less than that found for split injection. For splitless injection the reproducibility of retention times depends not only on chromatographic interactions but also on the reproducibility of the sampling period and the evaporation time of the solvent in the column inlet, if solvent effects (section 3.5.6.2) are employed. The choice of solvent, volume injected and the constancy of thermal zones will all influence retention time precision beyond those for split injection. For quantitative analysis the precision of repeated sample injections is normally acceptable but the method is subject to numerous systematic errors that may... 

In Older to increase the speed of heat transfer during in situ combustion, water may be injected into the petroliferous bed simultaneously with the air. In comparison with the air, water possesses greater heat capacity [3]. Depending on the ratio of injected water to air, the so-called wet and superwet variants of in situ combustion can be distinguished. The two processes differ from each other with regard to the temperatures generated in the bed and the extent of thermal zones that develop. 

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