Pre-heating zone

The volume of the injection loops amounted to 20 pi the catalyst stream was set to 50 pi min In an electrothermal pre-heat zone the ethylene/comonomer mixture in toluene was brought close to reaction temperature before adding catalyst. The reaction was carried out at 175 °C and a pressure of 2.8 MPa. In several subsequent zones each of 16 cm length (volume 200 pi) along the reactor tubing, temperature was monitored by voltage pads. 

The fuel molecule breaks down in the pre-heat zone to give methoxy radicals... 

The temperature in the interior of the tube is measured by a moveable thermoelement. A pre-heat zone in the tube is left empty so that the hydrogen can attain the desired temperature before it reaches the catalyst. The course of the reduction can be recognized by the change in color of the catalyst or by the formation of water. If the reduced catalyst must be prevented from coming into contact with air, then, after cooling, the hydrogen is replaced by pure nitrogen or sulfur-free carbon dioxide it can then be emptied directly into liquid to be reduced or can be stored under an inert gas or inert liquid. 

Most of the volatile matter in the coal distilled shortly after firing and either burned in the pre-heating zone, or was emitted to atmosphere as dark smoke. 

The exhaust gas and lime discharge temperatures are generally monitored. The former has a safety role for the exhaust fan (if used) and also is an indication of any problems with heat transfer in the calcining and pre-heating zones. The lime discharge temperature should be monitored to protect rubber belt conveyors handling the lime it is also an indication of the efficiency of heat recovery in the cooling zone. 

Pure n-tetradecane (u-Cm) feed and hydrogen gas were fed by metering pump and gas mass flow controller, respectively, and mixed at the entrance to the reactor pre-heat zone. Upon leaving the reactor, the entire effluent stream was sufficiently heated, diluted with hydrogen and progressively reduced to atmospheric pressure so as to ensure complete vaporisation of all the hydrocarbon components prior to on-line gas chromatographic analysis. 

Figure 3.4. Schematic of a blast iron. Shown are 1 - incoming pre-heated air from the Cowper stove 2 - melting zone 3 - reduction zone of FeO 4 - reduction zone of Fe203 5 - pre-heating zone 6 - feed of iron ore, limestone, and coke 7 - exhaust gases 8 - column of ore, coke, and limestone 9 - removal of slag 10 - tapping of molten pig iron 11 - collection of waste gases. Image courtesy of Robert Blazek.

In the pre-heating zone (100-75 0°C), firmly bound water from the clay is lost. 

System Wave width Pre-heating zone Reaction zone Post-combustion zone... 

A polymerization front has a sharp temperature profile, (77) and profile measurements can provide much useful information. From Figure 4 it may appear that the chemical reaction is occurring in a zone about 0.5 cm in width. This is incorrect. If the chemical reaction has an infinitely high energy of activation, the chemical reaction will occur in an infinitely narrow region. In actuality, the 0.5 cm represents a pre-heat zone. The temperature below that at which significant chemical reaction occurs follows an exponential profile, which can be described with the following relationship in terms of... 

A heat balance for the blast furnace produced by Michard et al. (1967), shows tlrat nearly 80% of the heat generated in tire furnace is used to produce and melt the iron and slag. The gas which emerges from tire first zone is further used to pre-heat the ah injected in the tuyeres in large stoves. The process thus runs at a vety high efficiency, botlr from tire point of view of tire amount of metal and slag produced and from the heat generation and utilization. 

To reduce the chance of side reactions, such as the dimerization of the diamine to tUjtw -diaminodihexylamine in (3.17) and the degradation of adipic acid to Schiff bases in (3.16), the precondensation can be carried out either for 30-60 min below 250°C or very rapidly (seconds) at 250-290°C. In the (pre)polymerization step, a concentrated PA salt solution is pumped into a set of heating tubes. These tubes have several heating zones as their diameter gradually increases in size.5,6,28... 

This reactor comprises a single-channel reaction zone followed by a quenching (cooling) zone [72], Gases, pre-heated in a separate zone, are contacted in an T-junction and mixed in a short passage thereafter. Such mixed gases enter the above-mentioned reaction zone. 

In-pack pasteurisation normally demands very large and expensive tunnel pasteurisers which have several stages. Bottles are introduced into a pre-heating stage, typically around 40°C, to reduce thermal shock, and then into the pasteurisation zone, which will normally be at 70°C, for some 20 min. Following this are two hydro-cooling zones. The first of these reduces product temperature to around 40°C the second, to ambient temperature. Recovery of heat is essential to an economically viable operation. 

Axial temperature differences in isothermally operated laboratory reactors can be minimized by installing a sufficiently large number of independently controlled heating zones along the reactor, e.g., 3 or more in the case of a microreactor and at least 5 for a bench-scale reactor of 1 metre length, with pre- and post-reactor heating elements. A thick reactor wall will promote temperature equalization in axial direction. 

An important capability of Curie point pyrolysers should be that the sample does not suffer any modifications before the pyrolysis step itself. As previously indicated, the housing of the pyrolyser must be heated (commonly with electrical resistances) to avoid condensation or other modifications of the pyrolysate. However, because a waiting time is inherent between the moment of sample introduction in the pyrolyser and the start of the pyrolysis itself, the sample may be heated by radiation from the sample housing. Several Curie point pyrolysers [8b] have the capability to drop the ferromagnetic foil containing the sample from a cool zone into the induction area, which is pre-heated to avoid condensation. The pyrolysis takes place immediately after the sample is transferred into this induction area such that no uncontrolled preliminary sample decomposition takes place. 

Toshiba, in collaboration with Tokyo Electric Power Company, has developed a hybrid catalytic combustion. Here only a part of the fuel is converted heterogeneously on the catalyst. The system consists of a pre-combustion mixing zone, a low-temperature catalyst zone, and a gas-phase combustion zone. The fuel-air mixture is controlled to maintain the temperature of the catalyst below 800 C, because the catalyst is not stable above the temperature. More fuel is added downstream to attain the final combustion temperature. The function of the catalyst is to be a source of additional "pre-heat" to support the lean, homogeneous down-stream combustion. 

In the case of bituminous coal, the relatively inexpensive smalls grade was widely used. The coal was introduced to the kiln at the top of the calcining zone, either by hand-shovelling or by mechanical projection, into a space created by a narrowing of the shaft (see section 16.4.2 for details). After charging, the kiln was drawn to cover the bed of coal with pre-heated limestone. 

N.B. For the purposes of this model, additional excess air can be regarded as entering the calcining zone at ambient temperature as the heat in the lime entering the calcining zone is already insufficient to pre-heat the stoichiometric amount of air required for combustion to 900 °C.)... 

As the coal is crushed by the rolling action, the hot air dries it and blows the usable fine coal powder out to be used as fuel. The powdered coal from the pulverizer is directly blown to a burner in the boiler in which the powdered coal is mixed in the air suspension with additional pre-heated combustion air and forces it out of a nozzle similar in action to fuel being atomized by a fuel injector in modern cars. Under operating conditions, there is enough heat in the combustion zone to ignite all the incoming fuel. 

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