Temperature controls decomposition furnaces

Constant rate thermo gravimetry has been described [134—137] for kinetic studies at low pressure. The furnace temperature, controlled by a sensor in the balance or a pressure gauge, is increased at such a rate as to maintain either a constant rate of mass loss or a constant low pressure of volatile products in the continuously evacuated reaction vessel. Such non-isothermal measurements have been used with success for decomposition processes the rates of which are sensitive to the prevailing pressure of products, e.g. of carbonates and hydrates. 

Peripheral equipment further purifies, meters, and preheats the hydrocarbon feed, the nitrogen used for flushing, the air for catalyst regeneration, and the hydrogen for catalyst reduction. Two preheaters are used to preheat the feed to proper reaction temperature. The heaters are programed to minimize hydrocarbon decomposition before it enters the reaction zone of the reactor. An electrically heated aluminum-bronze block serves as a heat sink which provides adequate temperature control to the catalyst bed. A second flow reactor, heated by an electric furnace and located in series with the main reactor, is an isomerization reactor that produces an equilibrium mixture of n-butenes. 

A different heating protocol was used for the experiment with the Polaris instrument at ISIS (see Figure 3). Here a reference diffraction pattern was collected at room temperature while the furnace was initially evacuated, then the sample was heated rapidly up to a selected temperature (e.g., 1500,1550,1600,1700,andl800 °C) where it was held constant for an extended period during which a series of diffraction patterns, each of 15 minutes duration, were collected. The total time spent at each elevated temperature was manually controlled, based on the level of decomposition observed in the diffraction patterns as they were collected. At the end of each high temperature measurement the furnace was cooled to room temperature. 

The reliability and precision of all kinetic data collected depend sensitively on the constancy of the temperature within reactant sample and the reaction vessel that contains it. The control of the temperature of the reaction vessel by the furnace must include due allowance for the heat evolved or absorbed by the sample during the decomposition process (see below). Numerous designs of furnaces have been used. 

Step 3. The reaction is exothermal. After process/process energy saving for feed preheating, the excess energy is rejected to the cooling water. Because the only reason of the furnace is to ensure constant inlet reactor temperature the first control loop is inlet reactor temperature/fliel inflow. To prevent the thermal decomposition of the product, a second loop keeps constant outlet reactor temperature by manipulating the quench stream. 

This method measures the weight of a substance heated at a controlled rate as a function of time or temperature. To perform the test, a sample is hung from a balance and heated in the small furnace on the TGA unit according to a predetermined temperature program. As all materials ultimately decompose on heating, and the decomposition temperature is a characteristic property of each material, TGA is an excellent technique for the characterization and quality control of materials (Figs. 10-15 and 10-16). 

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